10â100 μm has been used by Cui and coworkers in the MizorokiâHeck reaction but ...... polymer incarcerated (PI) method to form catalyst Pd-PI [74,75].
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5 Coupling Reactions Induced by Polymer-Supported Catalysts Babak Karimi, Sedigheh Abedi, and Asghar Zamani
5.1 Introduction
Carbon–carbon bond forming reactions, such as Heck, Suzuki–Miyaura, and Sonogashira couplings, have recently emerged as exceedingly important synthetic tools for the assembly of complex units, which are often versatile precursors in total synthesis of natural products [1], pharmaceuticals [2], functional materials [3], and conducting polymers [4]. These reactions are characteristically catalyzed by palladium and coupling of simple aryl iodides or bromides can be achieved with all forms of palladium. However, cross-coupling of aryl chlorides [5] that are generally less expensive and more easily available starting materials and heteroaryl substrates such as those found in drug molecules poses significant challenges and generally requires more sophisticated catalyst systems. Among the plethora of catalysts developed for this purpose, the use of spectator ligands that can modify the steric and electronic properties of Pd centers such as bulky electron-rich phosphanes [6] and N-heterocyclic carbenes (NHCs) [7] under homogeneous reaction conditions has shown outstanding success. In designing new improved catalytic systems, availability, cost, stability, tolerance to impurities, oxygen, moisture, and a wide range of reaction conditions, avoidance of toxic reagents and solvents, and ease of usage are often taken into consideration, in addition to intrinsic performance of the catalyst. Moreover, catalyst recycling (see Chapter 9) and the possibility of performing the reactions in greener solvents such as ionic liquids (ILs) [8a,b] (see Chapter 6) and water (see Chapter 7) are enormously important issues from both environmental and practical points of view. In this context, heterogeneous catalytic reactions are advantageous in comparison to the homogeneous ones because the former process allows the production and ready separation of desired products by using small quantities of catalyst in the absence of highly expensive nonrecyclable ligand systems. In addition, such catalyst systems may also be used in continuous-flow systems [9] or in flow-injection microreactors [10]. Another important issue in designing a heterogeneous catalyst system for practical and industrial applications is the nature of support. Although at first glance the support should provide a mean of easy and rapid recycling of the catalyst, in many instances their specific surface area, Palladium-Catalyzed Coupling Reactions: Practical Aspects and Future Developments, ad Molnar. First Edition. Edited by Arp # 2013 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2013 by Wiley-VCH Verlag GmbH & Co. KGaA.
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts hydrophobic–hydrophilic balance, and their functional groups could directly influence catalyst performance through synergistic pathways at the molecular level. In particular, the robust nature of the supports and their abilities in stabilizing reactive centers are crucial requirements for durable applications. The better and in-depth understanding of “true catalytic species,” particularly the catalyst evolution during the carbon–carbon coupling reactions and catalyst–support synergistic interactions, has grown increasingly in recent years and shall provide more accurate data for future advances in the rational design of sophisticated coupling catalysts. Although some reported systems are so close to these aims, it should be kept in mind that the actual active catalysts are very often soluble Pd species leaching into the reaction solution and then redepositing on the basic support. Thus, after a few runs, activity of the catalyst reduces gradually due to the loss of Pd species [11] (see Chapter 9). As a consequence, the development of novel welldefined recyclable systems by considering the above-mentioned requirements constitutes a major challenge in the mainstream of catalyst research context. It is also noteworthy that, while conventional homogeneous catalytic systems afford high reaction rate, high selectivity, and high yields, isolation of the catalyst from the products and high catalyst loading are often problematic in the homogeneous systems [12]. There are, in general, two different classes of materials applied as hosts to immobilize Pd species: Pd complexes or Pd nanoparticles (Pd NPs). One class is based on inorganic materials such as various kinds of silica and metal oxides, which are beyond the scope of this chapter. The second is organic polymers. Due to their unique properties, organic polymers are often used in depositing appropriate Pd species. Among many interesting properties, their hydrophobic nature and matched interactions with organic substrates diminish diffusing limitations that normally exist in systems based on inorganic supports. In addition, tunable hydrophilic– hydrophobic character of the polymer backbone has provided many opportunities to use water-soluble as well as organo-soluble Pd species in water without the need of special precautions. These properties render organic polymers to be attractive supports in catalysis. Wide ranges of water- and organo-soluble polymers as scaffolds for recoverable catalytic systems have been explored to overcome several shortcomings in the use of primary insoluble resins [13]. Moreover, in the case of polymer-supported catalytic systems, the loading level of Pd species is another challenging point and much research has been done to address this issue. The loading capacity of a polymer support basically depends on the number of anchoring sites per unit weight of the polymer, which can directly influence the level of metal loading. High loading capacities are advantageous to reduce the total expenditure for polymer supports and to make convenient amounts of material in medium- or largescale applications. Generally, solubility power decreases as loading capacity increases. Thus, to provide economic and manageable systems, it is critical to achieve a balance between polymer loading and its solubility power [2]. Nowadays, a range of polymers are available to choose from with loading capacities ranging from below 1 mmol g1 up to more than 20 mmol g1, and possessing different solvent compatibilities to attain the favorable requirements [14].
5.2 Polysaccharides
The primary basis of organizing this chapter is based on the structure of polymer backbones including natural polymeric materials (polysaccharides, such as starch, chitosan, alginate, and agarose) or synthetic unnatural polymers rather than on the types of Pd species (complexes or nanoparticles). Furthermore, it is also our aim to illustrate catalyst preparation techniques and highlight achievements in this area. In addition, because of the large number of publications about this topic, we focused predominantly on more recent works from 2005 until 2012 especially on common polymer supports applied in the most studied CC couplings such as Suzuki– Miyaura, Heck–Mizoroki, and Sonogashira coupling reactions.
5.2 Polysaccharides
Polysaccharides are carbohydrates containing as few as 10 or as many as several thousand sugar subunits linked together by glycosidic linkages [15]. Due to the advantages of polysaccharides, particularly starch and chitosan, such as ready availability, insolubility in most organic solvents, relatively high chemical stability, biocompatibility, and biodegradability, the use of these biopolymers as catalyst support has received increasing attention in recent years. Furthermore, the grafting method using appropriate trialkoxysilane reagents can also be used to functionalize polysaccharides for specific purposes. The chelating property and high sorption capacities of these polysaccharides have been efficiently used for immobilization of transition metals such as palladium ions and nanoparticles. These supported metal ions or nanoparticles have been then applied in several metal-catalyzed processes including CC coupling reactions. 5.2.1 Starch
Starch is polyglucose and is one of the most abundant natural polysaccharides. Major sources of this carbohydrate-based feedstock are flour, potatoes, rice, beans, corn, and peas. Hot water swells granular starch and allows its separation into two different polysaccharides: amylose (20%) composed of unbranched chains of Dglucose units, and amylopectin (80%) that is a branched polysaccharide. Both are soluble in hot water, but amylose is less soluble in cold water. Natural starch has a low surface area of only several m2 g1; therefore, it is necessary to be treated to enhance its surface area for the use as solid support and also solid phase in chromatography [16]. In 2005, Clark and coworkers described the modification of expanded starch with (3-aminopropyl)triethoxysilane and 2-acetylpyridine followed by complexation with Pd(OAc)2 to give catalyst 1. This material was a highly active catalyst in Suzuki (0.3 mol%, xylene, 140 C), Heck (0.1 mol%, xylene, 140 C), and Sonogashira (1 mol%, solvent-free conditions, 100 C) reactions of aryl iodides [17]. TEM image of the fresh catalyst showed a random dispersion of Pd nanoclusters with diameters of around 10 nm. Unfortunately, recycling
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O
expanded starch
Si
EtO
OAc AcO Pd N N OEt
1
Clark and coworkers have continued their studies on the application of novel mesoporous starch-stabilized Pd NPs in the Suzuki reactions of bromobenzene and Heck and Sonogashira reactions of iodobenzene under MW irradiations [18]. In contrast to 1, it was shown that starch-stabilized Pd NPs can be successfully reused up to four times under the described reaction conditions. It is believed that mesoporous starch plays a dual role, reducing Pd(OAc)2 to form Pd NPs and preventing the agglomeration of nanoparticles during preparation and CC coupling reactions. Although both EtOH and acetone can be used for the preparation of starch-stabilized Pd NPs, the authors found that acetone was better suited as the solvent for this purpose because it resulted in the generation of smaller Pd NPs, leading to the material with higher catalytic performances. Liu et al. prepared starch-supported Pd NPs of 5–7 nm in size. This catalyst (Pd-starch) was studied in the Suzuki coupling reaction of various types of aryl halides including activated (electron-poor) 4-chloronitrobenzene in DMF/water solvent mixture (Scheme 5.1) [19]. A recyclability study of this catalyst has also been successfully performed for three runs with iodobenzene. Unfavorable results in further recycling were attributed to the extensive aggregation of Pd NPs. R
R Pd-starch (0.1 mol%)
PhB(OH)2 +
NaOAc, DMF/H2O Ph
X R
X
t [h] T [ºC]
H MeO NH2 NO2
I Br Br Cl
0.5 80 1.5 80 80 3 120 20
Yield [%] 97 88 85 49
Scheme 5.1 Pd-starch-induced Suzuki coupling.
Khalafi-Nezhad and Panahi reported the preparation and characterization of immobilized Pd NPs (8 nm) on silica-supported starch (Pd-starch/SiO2) as a green, efficient, and renewable catalyst [20]. 1.2 mol% of this catalyst has been employed in the Heck and Sonogashira reactions of aryl bromides and chlorides in water at
5.2 Polysaccharides
R R' +
or
Pd-starch/SiO2 (1.2 mol%) K2CO3, H2O 100 ºC
Ph X Heck reaction R
X
R'
H H MeO MeO
Cl Br Cl Br
CO2Et Ph CO2Bu Br
Ar
R'
reflux, 2−12 h
reflux, 3−12 h
Ph
Ar
Sonogashira coupling Yield [%] 61 92 55 86
R
X
H H CN MeO
Cl Br Cl Br
Yield [%] 81 91 91 85
Scheme 5.2 Pd-starch/SiO2-induced Heck and Sonogashira reactions.
100 C (Scheme 5.2). It is interesting to note that in both CC coupling reactions this catalyst can be recycled in five runs without any loss of activity, while no data on the leaching and the catalyst evolution have been provided. 5.2.2 Chitosan
Chitin [poly(N-acetyl-D-glucosamine)], a naturally functionalized carbohydrate similar to cellulose, makes up the tough outer skeleton of several crustaceans, insects, and other arthropods and is also the structural material of fungi and shellfish waste [21]. However, it has been proven to be an unsuitable support, because of the difficulties concerning its manipulation. On the contrary, chitosan, the product of partial deacetylation of chitin (Figure 5.1), can be more readily manipulated and functionalized. For this reason, this amino sugar derivative has attracted chemists, particularly those studying heterogeneous catalysis [22]. A typical cross-linked chitosan modified with salicylaldehyde through Schiff base formation was synthesized and used for chelating palladium to give complex 2. The catalyst was then studied in the Heck coupling of electron-rich and electron-poor aryl iodides with acrylic acid and styrene with Pd loadings of 0.2 mol% carried out in air (yields of 93 to >97%) [23]. It was shown that catalytic activity and reusability of this supported Schiff base catalyst was decreased when cross-linked chitosan without
HO
OH
OH
O
O
O HO NHAc
O n NHAc
chitin Figure 5.1 Structures of chitin and chitosan.
OH
OH
O O HO
HO NH2
chitosan
O O n NH2
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts condensation with salicylaldehyde was used as a support. Surprisingly, no evidence of generation of Pd NPs and the leaching of the Pd species has been reported. OH OH
O
OH
O
O O
HO
O
HO
n
N Cl Pd O
N Cl Pd O
2
3
O O
HO
n
n
N Cl Pd N Cl 4
In a similar way, four different chitosan-supported palladium complexes modified with salicylaldehyde and 2-pyridinecarboxaldehyde were prepared by either coprecipitation or adsorption (complexes 3 and 4) [24]. These materials were then employed in microwave-assisted Suzuki reaction of 4-bromophenol and 40 -bromoacetophenone. Comparable activities were found under conduction heating condition. The catalysts were shown to exhibit high activity in microwave-assisted Heck and Sonogashira reactions of iodobenzene in DMF. It was also revealed that catalysts prepared by coprecipitation resulted in lower product yields in the reactions studied. Lee and coworkers have reported the immobilization of Pd NPs onto chitosan beads followed by cross-linking with diglycidyl ether PEG in order to increase its chemical and physical stability (catalyst Pd-chitosan/pol) [25]. Microwave-assisted Suzuki coupling of various aryl halides and boronic acids was performed using this efficient catalyst under aqueous conditions in the presence of TBAB (Scheme 5.3). The supported Pd NPs can be recycled in five reaction runs without loss of catalytic activity. R
R Pd-chitosan/pol (0.5 mol%)
PhB(OH)2 + X
K3PO4, TBAB H2O, MW, 150 ºC
R
X
t [h]
Yield [%]
MeO MeO Ac
I Br Cl
10 15 30
98 87 40
Ph
Scheme 5.3 Pd-chitosan/pol-induced Suzuki reaction.
Palladium complex supported on chitosan microsphere resin with a diameter of 10–100 mm has been used by Cui and coworkers in the Mizoroki–Heck reaction but unfortunately only iodoarenes and 4-bromonitrobenzene as an activated aryl bromide can be coupled with acrylic acid in NMP at 90 C [26]. This palladium catalyst system was recycled four times with slight decrease in catalytic activity.
5.2 Polysaccharides
Chitosan-supported Pd NPs were reacted with 2,4,6-trichlorotriazine followed by methoxy-PEG to generate catalyst 5 with nanoparticles of 15 nm in diameter [27]. Couplings of varied aryl bromides and iodides and 4 0 -chloroacetophenone as an activated chloroarene with phenylboronic acid afforded good yields in a sealed vessel at 150 C (Scheme 5.4). Recyclability study of 5 showed that this catalyst can be reused in six runs but high yields of the biaryl product upon further recycling can only be obtained in prolonged reactions. TEM studies have proved that size of Pd NPs has increased to 20–30 nm after the third catalytic cycle but no further increase in size of Pd NPs has been observed after the sixth cycle. Owing to grafting of PEG into the catalyst, no additional phase-transfer reagents such as TBAB were needed to improve the solubility of organic substrates in the aqueous phase. R
R
PEG O
5 (0.5 mol%)
PhB(OH)2 + X
NaOH, H2O 150 ºC
PdNP
Ph
N
MeO MeO Ac
X I Br Cl
H2C
t [h]
Yield [%]
3 5 3
O O
HO
95 77 55
Cl
N
O R
N
n
NH2 5
Scheme 5.4 Suzuki reaction catalyzed by 5.
Oxadiazoline and ketoimine palladium(II) complexes were immobilized onto chitosan giving catalyst systems 6 and 7, respectively [28]. Pombeiro and coworkers prepared and tested these catalysts in Suzuki–Miyaura cross-coupling of 4-bromoanisole and phenylboronic acid in water under microwave irradiation (Scheme 5.5). Notably, the use of TBAB as a phase-transfer agent was necessary to obtain high yields at lower temperature; however, the reaction proceeded well at elevated temperature (160 C) even in the absence of TBAB. Because of
OH
OH H2C
H2C
O O
HO
NH2 Cl Pd Cl N N Me Me 6
n
O O
HO
NH2 Cl Pd Cl N O
Me
N
O
Me Me 7
Cl
n
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts MeO
MeO 6 or 7
PhB(OH)2 +
K2CO3, TBAB, H2O MW, 15 min Br
Cat. (mol%)
TBAB
6 (0.106) 6 (0.106) 7 (0.075) 7 (0.075)
+ _
T [ºC]
Yield [%]
140 160 120 160
+ _
Ph
92 100 92 95
Scheme 5.5 Suzuki reaction catalyzed by 6 and 7.
agglomeration of Pd NPs, yields decreased continuously upon reuses in these systems. Recently, the use of nanofibers of cross-linked chitosan as a support material to immobilize Na2[PdCl4] was reported [29]. This catalyst was fabricated by electrospinning technique and employed in Heck cross-coupling of iodobenzene and butyl acrylate as a test reaction in DMF at 80 C. In the presence of Pd as low as 0.17 mol%, the recovered catalyst could be reused at least seven times without loss of activity. 5.2.3 Other Polysaccharides
Alginate, an anionic polysaccharide (Figure 5.2) found abundantly in the cell walls of brown seaweeds [30], was also used as support for Pd NPs of about 1 nm in size [31]. This system was studied in the Suzuki reaction of iodo- and bromoaromatics with phenylboronic acid in DMF. Recycling studies with 0.4 mol% catalyst gave decreasing yields, due to poisoning of the active surface sites and thus preventing their accessibility by reagents.
*
OHO
−O C 2
OH O CO2−
OHO
OH O
OH OH *
*
O
m
alginate
O OH
O O
O OH
n
*
agarose
Figure 5.2 Structures of alginate and agarose.
Quite recently, Cravotto and coworkers have developed the use of a polymeric b-cyclodextrin (b-CD) as an alternative support in Pd/Cu bimetallic catalyst system 8 in Sonogashira alkynylation of 4-iodoanisole (water, glycerol, or DMF, 70 C, triphenylphosphane) (Scheme 5.6) [32]. The idea of in situ polymerization of b-CD with diisocyanate under ultrasound has been employed to diminish the metal
5.2 Polysaccharides
MeO
8 (2 mol%) Ph3P (2 mol%)
Ph C CH +
Ph C C
OMe
Et3N, 70 ºC, 3 h I Solvent
Yield [%] 100 94 100
H2O glycerol DMF
Scheme 5.6 Sonogashira reaction catalyzed by 8.
leaching, providing a more reliable recycling process. Reusability of the catalyst in three runs showed slight decreases in activity.
n
O
O n
n
β O
H N
R
O
O O
H N
O Cu+ O
O O N H
R
8
N H
H N
Pd2+
O O
β O
O O n
H R N
N H
R N H
O
The natural linear polymer agarose is a polyagarobiose and can be found in cell walls of agarophyte red algae (Figure 5.2). Agarobiose, in turn, is a disaccharide formed from D-galactose and 3,6-anhydro-L-galactopyranose [33]. Firouzabadi et al. have reported the preparation and application of an efficient Pd catalyst consisting of agarose-stabilized Pd NPs (catalyst Pd-agarose) in the Suzuki coupling reaction [34]. It is noteworthy that, in addition to aryl iodides and bromides, electron-rich aryl chlorides and heteroaryl halides such as 3-bromothiophene and 3-bromopyridine have been found to be reactive in Suzuki coupling at a Pd loading as low as 0.52 mol % in water (Scheme 5.7).
Ar X + PhB(OH)2
Pd-agarose (0.00016 mol%) K2CO3, H2O, 80−100 ºC
Ar−X 4-bromoanisole 5-bromopyrimidine 3-bromothiophene 3-chlorotoluene
Yield [%] 80 85 84 78
Scheme 5.7 Pd-agarose-induced Suzuki coupling.
Ar Ph
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts This palladium catalyst system was successfully recycled five times with full conversion in every cycle.
5.3 Poly(ethylene glycol)
PEG as a cheap, easily accessible, and coordinating polymer appears to be a promising candidate for the use as either reaction medium or support in heterogenizing transition metal catalysts, particularly stabilizing metal nanoparticles. 5.3.1 Nonfunctionalized Poly(ethylene glycol)
A mixture of PEG-2000 with water has been evaluated in the Pd(OAc)2-catalyzed Suzuki coupling of aryl iodides and bromides with arylboronic acids under mild reaction conditions (50 C) without the use of phosphane ligands [35] (Scheme 5.8). In a three-run recycling experiment with 1 mol% Pd(OAc)2, the high initial yield significantly decreased after the third reaction run. The recycling of the catalyst mixture can be easily achieved by simple solidification at low temperatures. Electron-rich aryl bromides such as 4-bromoaniline, 4-bromoanisole, and 4-bromotoluene as well as hindered 2-substituted aryl bromides gave high yields of the corresponding coupling products (Scheme 5.8). Also, recyclability studies of this catalyst have been successfully performed for four runs and in the fourth cycle the yield dropped down to 89%. B(OH)2
X
Pd(OAc)2 (1 mol%)
+
Na2CO3 PEG-2000, H2O
R'
R
R
X
2-NH2 4-Me 2-Me 4-NO2
Br Br Br Cl
R'
T [ºC]
t [h]
H 4-CF3 4-MeO H
50 50 50 120
0.5 0.5 0.5 3
R
R'
Yield [%] 94 87 94 98
Scheme 5.8 Suzuki reaction catalyzed by Pd(OAc)2 in PEG-2000/H2O.
The same group continued their studies on the fluoride-free Hiyama crosscoupling reactions of aryltrimethoxysilanes with varied aryl and heteroaryl bromides in water using nearly identical reaction conditions [36] (Scheme 5.9). Satisfying results were observed with the use of both ArSi(OEt)3 and ArSi(OMe)3. It was revealed that the catalyst system (PEG/water/Pd) can be successfully recycled eight times with high efficiency. It is believed that PEG greatly influences the solubility of organic substrates in water, thus enhancing the reaction rate.
5.3 Poly(ethylene glycol)
Ar Br + PhSi(OMe)3
Pd(OAc)2 (1.8 mol%) NaOH, PEG-2000 H2O, 60 ºC, 2−24 h
Ar−X
Ar Ph
Yield [%]
4-bromoanisole 3-bromopyridine bromobenzene 2-bromotoluene
81 98 85 62
Scheme 5.9 Hiyama reaction catalyzed by Pd(OAc)2 in PEG-2000/H2O.
PEG-400 has also been considered as a solvent in CC couplings [37]. Homocoupling and cross-coupling reactions of aryl halides proceeded smoothly with Pd (OAc)2 in PEG-400 as solvent in the presence of K2CO3 [37a]. Notably, this system efficiently promotes the coupling of various types of heteroaryl bromides (Scheme 5.10) and was successfully reused in five runs with slight drop in efficiency. Ar X + Ar' X Ar−X
Pd(OAc)2 PEG-400, K2CO3
Ar'−X
4-bromoanisole 2-bromopyridine 3-bromothiophene 3-bromothiophene
Ar Ar'
Pd(OAc)2 T [mol%] [ºC]
t [h]
Yield [%]
130 120 120 120
28 8 7 10
85 91 95 92
4-bromoanisole 2-bromopyridine 3-bromothiophene 3-iodoanisole
5 2 2 5
Scheme 5.10 Homocoupling reaction catalyzed by Pd(OAc)2 in PEG-400.
The Sonogashira–Hagihara reaction proceeded smoothly with gelatin-supported Pd NPs (Pd-gelatin) in PEG-400 as solvent developed by Firouzabadi et al. [37b]. Notably, the immobilized catalyst showed high catalytic activity in the coupling of all types of aromatic halides including nonactivated chloroaromatics and halogen derivatives of heteroarenes (Scheme 5.11). In a recyclability study, this catalytic system was recovered and reused in three runs but satisfactory yields of the coupling products in further recycling required prolonged reactions. Ar X + Ph
Pd-gelatin (0.45 mol%) KOAc, PEG-400 100ºC, 2−24 h Ar−X 5-bromopyrimidine 3-bromothiophene bromobenzene 4-chlorotoluene
Yield [%] 75 75 74 60
Scheme 5.11 Pd-gelatin-induced Sonogashira reaction.
Ph
Ar
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts Table 5.1 C C couplings performed by using catalyst systems containing PEO.
Reaction
Substrates
Solvent/T ( C)
Suzuki Heck Sonogashira Suzuki Heck
I, Br I, activated Br I I, Br Br
H2O/rt DMA/80–120
— 3
Amphiphilic rod–coil PEO [40a] PS-co-PEO [40b]
H2O, MeOH/20–50 DMF/100
4 —
PS-co-PEO PEO-co-e-caprolactone
Runs Polymer
Reference
[40c] [40d]
Heck coupling of aryl iodides with a range of activated alkenes (acrylic acid, alkyl acrylates, acrylonitrile, styrene) also proceeded well in PEG-400 using 5 mol% of PdCl2 under microwave irradiation [38]. This air- and moisture-stable catalytic system was successfully recycled five times with a slight decrease in activity. Wang and coworkers performed Heck coupling of iodoarenes and activated bromoarenes in the mixed solvent toluene/ethanol (9 : 1) using as-synthesized Pd NPs in PEG-2000 [39]. PEG appeared to act as both reducing agent and stabilizer in this catalytic system, which leads to generation of Pd NPs with narrow pore size distribution. A reusability study of this system showed that it can be recycled in six successive runs but significant decreases in catalytic activity have been observed in further runs. Similarly, various types of poly(ethylene oxide) (PEO) such as amphiphilic rod–coil PEO [40a], block copolymer of PS and PEO [40b,c], and star-shaped block copolymer of PEO and poly(e-caprolactone) [40d] have been prepared and tested in various Pdcatalyzed CC coupling reactions (Table 5.1). 5.3.2 Functionalized Poly(ethylene glycol)
In this approach, the PEG chain is normally used in covalent anchoring of either monodentate or bidentate ligands. The modified PEGs are then reacted with different types of palladium salts to furnish the corresponding Pd-loaded PEG catalyst. PEG moieties help the catalyst and substrates to more easily penetrate into each other in green solvents such as water and poly(ethylene glycol) with different molecular weights. A wide range of research efforts have been focused on preparation of functionalized PEG as stabilizer of Pd species and their applications in CC bond formation. a,v-Bis(diphenylphosphano)poly(ethylene glycol) complex of PdII was also used in Heck and Sonogashira coupling reactions of iodobenzene [41]. Pd complex immobilized on PEG-modified dipyridyl ligand 9 was designed as a catalyst for the Suzuki reaction in either PEG-2000 or aqueous reaction medium at 110 C (Scheme 5.12) [42]. Notably, the catalyst exhibits outstanding activity in coupling reaction of sterically hindered 2-methoxyphenylboronic acid with aryl
5.3 Poly(ethylene glycol)
X
B(OH)2 +
+
R
R'
NaBPh4
Pd(OAc)2 (0.2−0.3 mol%) Pd(OAc)2 (0.5 mol%) 9 (0.2−0.3 mol%) 9 (0.5 mol%) PEG-2000, K2CO3 PEG-2000, NaOH, H2O 110 ºC, 15 −30 h 110 ºC, 2−15 h
R
Ph
R'
R X
R' H 2-MeO H
2-Me Br 4-OH Br 4-Ac Cl
Yield [%] 92 85 69
R' R
X
Yield [%]
2-Me Br 4-MeO Br 4-CHO Cl
90 85 67
Scheme 5.12 Suzuki reaction catalyzed by Pd(OAc)2/9 in PEG-2000.
bromides. Furthermore, coupling reaction of activated aryl chlorides gave satisfactory results as well. This catalyst system also provided relatively high and stable yields in six successive recycling experiments using 40 -bromoacetophenone and phenylboronic acid as coupling partners.
N O
PEG-2000
PEG-6000
O
N 9
10
Pd Cl
N OH
A PEG-anchored oxime carbapalladacycle complex 10 developed by Corma et al. and applied in various coupling reactions in PEG-6000 as solvent [43] provided medium to good yields in the coupling of various boronic acids with aryl bromides and chlorides. 40 -Bromoacetophenone and phenylacetylene were also coupled in the presence of 5 mol% of catalyst 10 to afford the corresponding coupling product in 99% yield. The catalyst was found to show a limited success in the Heck reaction of aryl bromides with styrene to provide low yields. In the Suzuki reaction, yields decrease continuously upon subsequent reuses because of decomposition of catalyst and parallel formation of 4–7 nm Pd NPs. However, reusability test of 10 in the Sonogashira reaction has proved its high recycling potential in this reaction. In their following study, Corma and coworkers applied a soluble phosphane ligand anchored to poly(ethylene glycol) (11) as a highly effective and reusable ligand for Pd-catalyzed Suzuki coupling of the sterically hindered substrates
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O P(Cy)2 OMe
11 B(OH)2
Cl +
Pd(OAc)2 (0.2 mol%) 11 (1.4 mol%) Cs2CO3, toluene 90 ºC, 24 h, N2 99%
Scheme 5.13 Suzuki reaction catalyzed by 11.
2-chloro-1,3-dimethylbenzene and 2-tolylboronic acid (Scheme 5.13) giving the corresponding trisubstituted biaryls [44]. Interestingly, the catalyst gave consistently higher yields than those obtained over polystyrene (PS)- or silica-based catalysts prepared for comparison. In the recycling study, in the coupling of 40 chloroacetophenone and 2-tolylboronic acid, it proved to be efficient to give nearly quantitative yield in the first run with progressively decreasing yields in subsequent reuses. The 31 P NMR studies of the reused anchored ligand revealed that the main reason for catalyst deactivation comes from oxidation of the phosphane to phosphane oxide. Bradley and coworkers have designed three types of Pd NPs encapsulated on the well-defined commercially available solid-phase resin PS-PEG (12–14) [45]. An interesting feature of this support available in a variety of sizes is its acceptable tolerance of a range of solvents. Hot filtration tests on catalysts 13 and 14 indicated that the reactions are catalyzed mainly by soluble Pd species. According to ICPOES analysis, however, only 0.09 ppm of palladium was detected in the hot filtrate from reaction mixture of cross-linked catalyst 12. It showed good activity toward the Suzuki coupling of various bromoarenes including sterically hindered 2substituted bromobenzenes with different arylboronic acids (Scheme 5.14). Chloroarenes, in turn, gave only very low yields of the corresponding coupling products (14–25%) under the same reaction conditions. Notably, no loss of efficiency was reported in six runs by using the recovered catalyst 12. The B(OH)2
Br
12 (10 mol%)
+
K2CO3, H2O 80 ºC, 4−16 h
R R' R
R'
Yield [%]
H 2-Me 72 2,4-diMeO H 63 MeO 91 4-MeO Scheme 5.14 Suzuki reaction catalyzed by 12.
R' R
5.4 Polystyrene
Heck reaction of aryl iodides with 0.08–0.6 mol% of 12 has also been performed (DMF, K2CO3, aerobic conditions, 115 C) [46]. O O
O
NH
HN
O NH
HN
PS-PEG
PS-PEG
12
13
PS-PEG
PPh2
14 Pd NP=
Pd NPs can also be entrapped inside the network of a poly(ethylene glycol)– polyurethane (PEG-PU) polymer film by the solution casting technique. The resulting catalyst gave good to high yields of biaryls in the coupling of iodo- and bromoarenes with phenylboronic acids (74–93%) [47]. Due to the compact film structure of the catalyst, it can be easily separated from the reaction products followed by simple washing. The yields in recycling studies with 4-iodonitrobenzene were high and no loss of activity was observed in 10 runs.
5.4 Polystyrene
Because of its ready availability, relative physical and chemical stability, and facile manipulation, PS is a versatile candidate in supporting homogeneous catalysts either in nonfunctionalized form or after functionalization with appropriate heteroatoms. 5.4.1 Nonfunctionalized Polystyrene
Supported Pd NPs (average size: 8 nm) embedded in PS were applied in various coupling reactions (Heck, Suzuki, and Sonogashira) of aryl iodides and activated aryl bromides [48]. Yields in the recycling study decreased considerably from 98 to 38% in just three successive reaction runs. The loss of activity was mainly related to the leaching of Pd species and to morphological changes during reaction. Liu, Yang, and coworkers have designed a catalyst comprising Pd NPs (average size: 5 nm) entrapped within PS hollow latex nanospheres [49]. The catalyst performance was then evaluated in the Heck reaction in DMF showing gradually decreasing activities in four successive runs. TEM studies indicated that Pd nanoparticles were attached mainly onto hollow latex nanospheres. Ohtaka et al. have developed PS-stabilized Pd NPs (average size: 2.3 nm, catalyst Pd-PS) by thermal decomposition of Pd(OAc)2 in the presence of PS (MW ¼ 6000). The resulting material was further treated with aqueous solution of K2CO3 and then subjected to hydrothermal treatment [50]. The catalyst showed high activity in the coupling of aryl bromides and activated aryl chlorides with 4-tolylboronic acid under aqueous conditions (Scheme 5.15).
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts B(OH)2
X
Pd-PS (1.5 mol%) +
Me
KOH, H2O, 80 ºC
R
R
Me R 2-Me 4-MeO 4-Ac
X
t [h]
Br Br Cl
1 1 12
Yield [%] 92 92 99
Scheme 5.15 Suzuki reaction catalyzed by Pd-PS.
I
PdO-PS (1.5 mol%)
+ R
Et3N, H2O, 80 ºC, 20h
OH R
Ph 4-MeC6H4 4-MeOC6H4 Hex
R O
Yield [%] 97 93 94 71
Scheme 5.16 PdO-PS-induced Sonogashira reaction.
Copper-free Sonogashira couplings of aryl iodides and alkynes proceeded smoothly using polystyrene-stabilized PdO nanoparticles (catalyst PdO-PS) in water in high yields (74–99%) [51]. The catalyst could be reused in both Suzuki and Sonogashira couplings without any significant decrease in catalytic activity in 10 and 5 successive reaction cycles, respectively. TEM images showed that any significant changes in the size of nanoparticles occurred after the fifth run in the Sonogashira reaction. Noteworthy, catalyst PdO-PS was able to catalyze the coupling of 2iodophenol and terminal alkynes providing benzo[b]furan derivatives in excellent yields as well (Scheme 5.16) [52]. 5.4.2 Functionalized Polystyrene 5.4.2.1 Polystyrene-Supported Ligands Containing Nitrogen An air- and moisture-stable Schiff base complex supported on Merrifield resin (catalyst 15) was prepared and used in the Suzuki coupling reaction of aryl and heteroaryl bromides with phenylboronic acid in medium yields in either batch or mini-continuous-flow reactor system (Scheme 5.17) [53]. Surprisingly, while the catalyst was completely inactive in the coupling reaction of heteroatomcontaining substrates such as 4-bromoaniline and 5-bromoisatin, it offered
5.4 Polystyrene
15 (0.5 mol%) Ar Br +
PhB(OH)2
Ar Ph
iPr2NEt DMF/H2O, 100 ºC
Ar−Br
Yield [%]
5-bromopyrimidine 2-bromothiophene 3-bromotoluene
85 82 42
Scheme 5.17 Suzuki reaction catalyzed by 15.
relatively high catalytic performances in the same reactions using heteroaryl substrates. N
N Pd
O Merrifield resin
R
PS N
O
Pd Cl
O
R = H, Me, Ph 15
Fe
16
A series of PS-supported cyclopalladated complexes 16 were synthesized and used in the Heck reaction of a limited range of aryl iodides and bromides [54]. High yields were found in a recycling study with iodobenzene and butyl acrylate using 16 (R ¼ Me) with necessary increases in reaction time. It was also found that among the investigated catalysts it gave the highest turnover frequency (TOF ¼ 12 600 h1) in the coupling of iodobenzene and butyl acrylate under the described reaction conditions. In 2010, Bakherad et al. used catalyst 17 with a PdII complex supported on PS resin functionalized with N,N-bis(naphthylideneimino)diethylenetriamine in the copperfree Sonogashira reaction of iodoarenes under aerobic conditions at room temperature (Scheme 5.18) [55]. Reproducibility tests illustrate that 17 can be reused for at least nine cycles. In a follow-up study, they prepared and used the recoverable PS-anchored palladium(0) 1-phenylpropane-1,2-dione-2-oxime thiosemicarbazone complex 18 in the copperand solvent-free Sonogashira-type reactions of terminal alkynes with acyl chlorides giving the corresponding ynones in good to excellent yields (Scheme 5.19) [56]. Cai and He have developed the synthesis of a relatively low-leaching polymersupported macrocyclic Schiff base Pd complex 19 [57]. This air- and moisture-stable catalyst was then applied in the Suzuki reactions of aryl bromides and phenylboronic acids in high yields at room temperature under aerobic conditions (Scheme 5.20). Catalyst 19 was also successfully used in the Sonogashira reaction of aryl iodides and activated aryl bromides with phenylacetylene in water [58]. After filtration and washing with water, methanol, and acetone followed by drying, it was reused in both
j157
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts PS N N
N Pd OO
17 I 17 (1 mol%)
+ R'
R'
Et3N, DMF rt, 3−4 h
R R 4-OMe 4-OMe 4-OMe 4-Ac
Ar 85−99%
R' Yield [%] Ph 92 Bu 92 TMS 85 Hex 93
Scheme 5.18 Sonogashira reaction catalyzed by 17.
Sonogashira and Suzuki couplings in four and five runs, respectively, with slight decrease in catalytic activity. TEM studies demonstrated that the size of Pd NPs changed from 2–5 nm after the first use to 20–30 nm after the fifth reuse in the Suzuki reaction [57].
O PS
NHCNH
Ph N
N OH Pd0
18 O Cl
O 18 (1 mol%) Et3N, rt, 0.5 h
+ R'
R'
R
97−99% R 4-OMe 4-OMe 4-Me 4-OMe
R' Ph Bu Pr TMS
Yield [%] 98 98 98 98
Scheme 5.19 Acylation of terminal alkynes catalyzed by 18.
PS-bearing suitable functionalized heterocycles can also be a good candidate for immobilizing Pd species. Najera and coworkers have shown that di(2-pyridyl) methylamine–PdII complex anchored to a styrene–maleic anhydride copolymer
5.4 Polystyrene
Br
R
19 (0.1 mol%)
+ PhB(OH)2
Ar Ph
K2CO3, DMF/H2O rt, 20−30 min
R
Pd
O O
Yield [%] 98 90 97
4-OMe 2-OMe 4-Me
N
O
PS
N
19
Scheme 5.20 Suzuki reaction catalyzed by 19.
(catalyst 20) efficiently promotes coupling reactions of various types of substituted bromo- and iodobenzenes and heteroaryl bromides with alkynes in refluxing water (Scheme 5.21) [59]. Although this catalyst system was successfully reused in five runs in the Suzuki reaction, 2.4% Pd was detected by ICP-OES in the corresponding filtrate from the first reaction cycle. Catalytic activity of this system in the Suzuki reaction was relatively high and aryl bromides and chlorides were coupled with phenylboronic acid in high yields (68–99%) at 60 or 100 C in aqueous medium. The generation of Pd NPs in the recovered catalyst from the Suzuki reaction was confirmed. n
O
N
Ph O
N N Pd Cl Cl 20 Ar Br + Ph
20 (0.2 mol%) pyrrolidine, TBAB H2O, reflux
Ar−X
t [h]
4'-bromoacetophenone 2-bromothiophene 4-chlorobromobenzene
1.5 1 14
Ph
Ar
Yield [%] 99 92 99
Scheme 5.21 Sonogashira reaction catalyzed by 20.
Jones et al. have performed a comparative study by utilizing (2-methylthiomethylpyridine)–PdCl2 complex covalently anchored to organic polymer monolith (macroporous continuous copolymers of styrene derivatives and divinylbenzene) and Merrifield and Wang resins (21) under identical Heck and Suzuki coupling reactions in a capillary microreactor flow-through protocol [60]. This study shows that all three supported catalyst systems exhibit relatively similar trends in the
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts described coupling reactions and interestingly give higher yields in comparison with their homogeneous analogues.
polymer
S Cl Pd N Cl
O 21
PS-embedded phenanthroline–PdII complexes 22 and 23 were used in various types of palladium-mediated CC coupling reactions. While low yields were found in the coupling reactions catalyzed by 22 [61], catalyst 23 was shown to be effective for the Suzuki reaction of haloarenes including deactivated or sterically hindered 2substituted bromobenzenes, heterobromoarenes, and sterically hindered arylboronic acids (Scheme 5.22) [62]. Recycling experiments were conducted with catalyst 23, while a continuous microreactor flow system was employed in the case of catalyst 22. High initial yields decreased slightly in successive runs. Unfortunately, neither 22 nor 23 exhibited any significant catalytic activity in the coupling reactions of chloroarenes.
H N
monolith 22
Merrifield resin
N
O N
Cl Pd N Cl
23
N OAc Pd N OAc
The palladium nanoparticles stabilized by a water-soluble “click” poly(sodium sulfonate-triazolylmethyl)styrene (catalyst 24) developed by Astruc and coworkers displayed moderate activity in Suzuki–Miyaura coupling of iodobenzene with phenylboronic acid in water/ethanol (1 : 1) mixture at room temperature with a TON of 8200 [63]. Unfortunately, neither Pd leaching nor catalyst reproducibility was studied. B(OH)2 23 (0.5 mol%)
Ar Br + R
K2CO3, EtOH rt, 4 h
Ar−X
R
2-bromoanisole 2-bromoanisole 3-bromopyridine
H 2-MeO H
Ar R
Yield [%] 88 80 85
Scheme 5.22 Suzuki reaction catalyzed by 23.
The tetrazole–PdII complex 25 provides nearly quantitative yields in Suzuki– Miyaura coupling of aryl bromides [0.5 mol% of Pd, ethanol/H2O (1 : 1), room
5.4 Polystyrene
j161
temperature], but exhibits disappointing performance in the reaction of aryl chlorides even at 50 C [64]. The catalyst can be reused in three successive cycles; however, for further recycling it was necessary to increase the reaction time to ensure satisfactory product yields. n
AcO OAc N N Pd O N N
Pd NP N N N N N N
PS
SO3Na SO3Na 24
25
Pd complexes of a variety of nitrogen ligands such as palladated Kaiser oxime resin 26 [65], Pd complexes of dimethylaminomethyl-grafted PS 27 [66], PSanchored azo ligand palladacycle 28 [67], anthranilic Pd complex 29 [68], and PS functionalized with cyclohexyldiamine (30) [69] and diethanolamine (31) [70] have been designed and tested as recoverable catalysts in varied C C coupling reactions (Table 5.2).
Cl Pd
O N OH
PS
Pd(OPf)2
PS
N 27 Me2 (OPf = perfluorooctanesulfonate)
26
O
2
HO Pd N N
PS
NO2
28
PS NH Cl Pd O 2 O
29
H2N
PS
HN
Pd NP Pd NP 30
HO HO
P S
N O 31
5.4.2.2 Polystyrene-Supported Triphenylphosphane Pd microencapsulated in the non-cross-linked PS-supported triphenylphosphane prepared through copolymerization of 4-styryldiphenylphosphane and styrene did not show high catalytic activity in the Suzuki reaction and only aryl iodides and activated aryl bromides with arylboronic acids could be coupled by this catalytic system in 2-PrOH/H2O solvent mixture at 70 C [71]. However, Feng and
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts Table 5.2 C C coupling reactions performed by catalysts 26–31.
Reaction
Catalyst Substrates
Heck
26
I, Br
Sonogashira Sonogashira Suzuki Heck, Suzuki, Sonogashira Suzuki
27 28 29
I, Br, Cl I, Br I, Br, Cl I, Br, Cl
30
Br
Suzuki
31
Br, activated Cl
Solvent/T ( C)
Pd leaching TON Runs Reference
DMF or H2O/ 110–120 H2O/80/air H2O/70–80
þ
105
8
[65]
þ
— —
5 6
[66] [67]
DMF/70–90
—
5
[68]
Ethylene glycol/80 H2O/80
þ
436
3
[69]
—
3
[70]
coworkers have prepared new types of microcapsule-supported palladium catalysts based on cross-linked PS-containing phosphane ligand. The polymeric catalyst (0.4 mol%) was then evaluated in the Heck and Suzuki reactions [72,73]. Hindered 2-bromotoluene and 3-bromopyridine could be coupled with phenylboronic acid by 1 mol% of this catalyst in isopropyl alcohol at 80 C in 67 and 87% yields, respectively [73]. Kobayashi and coworkers have synthesized an amphiphilic cross-linked PSsupported triphenylphosphane with the use of styrene, 4-vinylbenzyl glycidyl ether, tetraethylene glycol mono-2-phenyl-2-propenylether, and 4-styryldiphenylphosphane (molar ratio ¼ 72 : 12 : 5 : 11) as monomers. The initial linear copolymer was shown to be capable of absorbing and stabilizing Pd NPs by treatment with Pd(PPh3)4 followed by cross-linking at 120 C and reducing with HSiCl3 through the polymer incarcerated (PI) method to form catalyst Pd-PI [74,75]. This catalyst displayed high activity in the coupling of sterically hindered bromoarenes and arylboronic acids (Scheme 5.23). Br
Ph Pd-PI (3 mol%) +
PhB(OH)2
K3PO4, toluene/H2O reflux, 4 h 85%
Scheme 5.23 Pd-PI-induced Suzuki reaction.
Notably, catalyst Pd-PI showed high and stable activity in recycling in five subsequent reaction cycles. Despite the relatively high Pd loading of 5 mol%, no leaching of Pd species was detected by using the hot filtration method under the optimized reaction conditions.
5.4 Polystyrene
j163
B(OH)2 32 (1−2 mol%)
+
R
K2CO3 H2O/toluene (99:1) 105 ºC
Br
R
R
Yield [%]
Selectivity [%]
90 77
3-Br 2-Br
96 99
Scheme 5.24 Suzuki reaction of dibromoarenes catalyzed by 32.
In 2005, Uozumi and Kikuchi described the use of the interesting amphiphilic PSPEG-stabilized PdII32 as a recoverable catalyst in the highly selective monoarylation of dibromoarenes with arylboronic acids in water (Scheme 5.24) [76]. Ph O PS
O
O n
O
N H
PS Cl
PPh2 Pd
O
O
O n
N H
n
N H
O
32
O
PPh2 Pd0 PPh2 Ph
33
Interestingly, hindered dibromoarenes and dibromopyridines were also monoarylated in high yields and selectivities (Scheme 5.25). Uozumi and coworkers continued their studies on the application of this catalyst in Sonogashira coupling of haloarenes but the catalyst gave satisfactory product yields only in the case of iodoarenes and activated bromoarenes [77]. It can easily be recovered and reused in four runs without significant loss of activity. A similar catalyst with Pd0 (33) was developed and applied in the alkylative cyclization of 1,6-enynes in water [78]. In a study by Becht and coworkers, effects of position of the methyl substituent in ditolylphosphanopolystyrene-supported palladium catalysts were compared. It was shown that bis(2-tolyl)phosphano catalyst 34 is superior in the Suzuki and
Br
Br
B(OH)2 N + Br
32 (1−2 mol%) K2CO3 H2O/toluene (99:1) 105 ºC
N
yield = 75% selectivity = 99%
Scheme 5.25 Suzuki reaction of dibromopyridines catalyzed by 32.
O
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts Sonogashira reactions, whereas the bis(3-tolyl)phosphano catalyst 35 displayed the highest catalytic performance in Heck coupling of aryl iodides [79]. These air- and moisture-stable catalysts can be recovered and reused four times in all studied coupling reactions with no significant decrease in yield. Pd0
PS
Pd0
PS
P
P
2
2
34
35
Similarly, various types of PS-supported phosphane ligands such as supported 2pyridyldiphenylphosphane 36 [80], PS-supported DPPF [bis(1,10 -diphenylphosphano)ferrocene] 37 [81], diphenylphosphane-functionalized Merrifield resin 38 [82], and PS-supported diphenylphosphanoethane 39 [83], as well as the soluble syndiotactic PS-supported triphenylphosphane (40) [84], have been prepared.
N PS
P
Fe
O
O PPh2
PS Merrifield resin Ph2P
36
Ph2P 39
37 Ph PS +P − Ph Cl
38
soluble syndiotactic PS PPh2
40
They were applied in different palladium-catalyzed coupling reactions in order to investigate the effects arising from the nature of the supported ligands in their catalytic performance. Illustrative is the use of PdCl2 supported on 38 (Scheme 5.26). It is very important to note, however, that despite excellent improvements in catalytic performances in some cases [82,83], these catalysts are not capable of performing the coupling reaction of chloroarenes. Br
S
Ac + Ph4BNa
PdCl2-38 (1 mol%) K2CO3, TBAB, H2O 120 ºC, 15 h
Ph
S
Ac
95%
Scheme 5.26 Suzuki reaction catalyzed by PdCl2-38.
Considering the inherent advantages of homogeneous catalysts such as better and well-defined efficiency and higher selectivity, as expected, catalyst 40 developed by Bae and coworkers displayed excellent catalytic activity in palladium-catalyzed Suzuki coupling reaction of bromoarenes (Scheme 5.27) as well as activated chloroarenes [84]. The catalyst could be simply recovered in quantitative yields by adding an appropriate quantity of a pure solvent such as methanol and filtrating of precipitated polymer through a short plug of celite.
5.5 Poly(norbornene)
R
j165
R Pd(OAc)2-40 (1 mol%)
PhB(OH)2 +
Cs2CO3, toluene 110 ºC, 1 h
Br
Ph
R = MeO 93% R = NMe2 82% Scheme 5.27 Suzuki reaction catalyzed by 40.
5.5 Poly(norbornene)
In 2005, Jones and coworkers immobilized SCS pincer PdII complex on soluble poly (norbornene) in five steps through a ring-opening metathesis polymerization (ROMP) approach (Scheme 5.28) [85]. The Heck reaction of iodobenzene with butyl acrylate with 41 gave the coupling product in a yield of 99% within 1 h (DMF, Et3N, 120 C). However, the results of poisoning tests with Hg0 and poly(4-vinylpyridine) (PVPy) showed that leaching of the complex occurred and the pincer complexes merely acted as precatalysts for soluble Pd species. SPh (CH2)11
NH
Grubb’s Ru catalyst
Pd Cl
O
CDCl3
50
(CH2)11
SPh
SPh
O NH
41
Scheme 5.28 Immobilized SCS pincer PdII complex on soluble poly(norbornene).
One year later, Weck and Sommer applied the same ROMP approach to prepare a poly(norbornene)-supported Pd catalyst but they utilized an N-heterocyclic carbene as the ligand instead of an SCS pincer [86]. The activity of all three poly(norbornene)supported Pd-NHC catalysts (42a–c) in the Suzuki–Miyaura, Sonogashira, and Heck coupling reactions was the same as their small monomer analogues. An important feature of this catalyst system is its excellent activity with chloroarenes including sterically hindered substrates (Scheme 5.29) and highly challenging 2-bromopyridines giving the corresponding coupling products in good to excellent yields.
PhB(OH)2 +
Cl
catalyst (1 mol%) Cs2CO3, dioxane 80 ºC, 130 min 42a 42b 42c
Scheme 5.29 Suzuki reaction catalyzed by 42.
90% 88% 81%
Pd Cl SPh
166
j 5 Coupling Reactions Induced by Polymer-Supported Catalysts *
*
y
x
O O(CH2)7CH3 x = 40, y = 10 Mes = 2,4,6-trimethylphenyl 42a L = OAc 42b L = dba 42c L = allyl Cl
O O (CH2)11 N PdL2 N Mes
Both poisoning and kinetic studies demonstrated that the stability of the polymersupported catalysts highly depends on the palladium precursor. Among the selected precursors, palladium acetate-based polymeric catalysts were the most stable ones. In their subsequent studies [87], Jones and Weck ruled out the contribution of the hypothetical PdII–PdIV cycle in the Heck catalytic cycle when pincer palladacyclic precatalysts are used. Moreover, it was shown that regardless of the structure of support and ligand, all of the described supported catalysts are indeed the source of generation of active soluble Pd0. In 2010, Reiser and coworkers prepared a nanomagnetic cobalt/carbon core– shell-based norbornene polymeric tag ligand through successive click/ROMP approach with norbornene units bearing triphenylphosphane moieties (catalyst 43) [88]. These hybrid magnetic nanoparticles were used for the Suzuki–Miyaura cross-coupling reaction of haloarenes with arylboronic acid in THF/water in the presence of Na2CO3 at 65 C. While high yields were obtained in the coupling of a few iodo- and bromoarenes (86–96%), the yield was much lower for chlorobenzene (38%). Because of the magnetic moment of Co/C nanoparticles, catalyst recycling can be easily achieved by employing an external magnetic field. Ph
Ph P
OAc
Pd
L
OAc
n
N N N
Carbon Cobalt
O
Co n
L
43
P Ph
OAc Pd
Ph
OAc
5.6 Polyacrylamide
5.6 Polyacrylamide
In 2006, Uozumi et al. introduced a microchannel reactor equipped with a palladium complex membrane, PA-TAP-Pd [poly(acrylamide)-triarylphosphane] 44 [89]. This innovative system can be constructed via self-assembling complexation of an ethyl acetate solution of PA-TAP and the aqueous solution of (NH4)2[PdCl4] in opposite direction through a Y-junction of the microchannels, which results in a two-phase parallel laminar flow with concomitant formation and precipitation of palladium polymer membrane at the interface between the two parallel flows. To this end, the solution of iodoarenes in EtOAc/2-PrOH and an aqueous solution of arylboronic acid with Na2CO3 were introduced into the membrane at 50 C with a constant flow. The Suzuki–Miyaura reaction under this condition was surprisingly completed within only 4 s. This catalyst was compared with two other similar devices containing palladium complex membrane of PVPy and cationic polyviologen. The coupling reaction of iodobenzene with 4-methoxyphenylboronic acid catalyzed by 44 afforded 99% yield in 4 s. In contrast, just 0 and 15% yield was obtained using the other described devices under similar reaction conditions. The catalytic performance might indeed be related to the ligand nature that is different in the three devices. Furthermore, the scope of this catalyst was expanded to the Suzuki coupling reaction of various aryl [89a], heteroaryl, and alkenyl halides [89b] with either arylboronic acids or sodium tetraarylborates. ICP-AES analysis indicated no Pd residue in the collected samples. Interestingly, allylic arylation of allylic esters with arylboron reagents under microflow conditions with this catalyst instantaneously afforded the corresponding coupling products [89c].
*
* n
CONHCH2CH2N PA
P Pd P Cl2
PA L2Pd L= OAc or Cl
44
N
45
Another Pd-PA-based catalyst has been prepared by Mahdavi et al. (45) [90]. This supported catalyst performed the Heck reaction of various aryl iodides in dioxane at 100 C within 24 h. Although the scope of the method is rather limited and needs long reaction time even for highly active iodoarenes, the catalytic activity did not effectively diminish during six recycling runs. The capability of non-cross-linked poly(N-isopropylacrylamide) (PNIPAM) in immobilizing metal nanoparticles has been recognized since 1997 [91]. This polymer with inverse temperature-dependent solubility in water can be easily separated from the reaction mixture by adjusting the temperature. In 2008,
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts Zhang and coworkers employed PNIPAM to stabilize Pd NPs in the Suzuki reaction (catalyst 46) [92]. Due to the hydrophilic nature of PNIPAM at low temperature, hydrophobic aryl halides cannot diffuse into the hydrophilic environment of the polymer; as a result, no reaction takes place. In contrast, the polymer becomes hydrophobic at high temperature and the substrate can easily penetrate into the polymer shell, which results in high yields of coupled products under this condition. These results indicate that in this system the final results not only depend on the electronic nature and reactivity of aryl halides, but also significantly influenced by the hydrophobic–hydrophilic balance between substrates and the catalyst.
O
O NH
NH O O
CO2K
HN CO2K
O
O
O
n
Pd NP= 46
47
PNIPAM-co-PMA was used for immobilizing Pd NPs to furnish the final catalyst 47 [93]. Since PMA moieties induce hydrophilicity and increase ion binding property to the basic gel, catalyst samples with 0–2 mmol of PMA content have been prepared via the same protocol. The investigation of the optimum swelling ability in water, gel integrity, metal content, and homogeneous distribution of palladium nanoparticles without agglomeration indicated that the sample with a PNIPA:PMA ratio of 8.8 : 1.6 mmol gives the best catalyst. The Suzuki coupling of bromo- and iodobenzene with arylboronic acids including highly challenging pyridyl- and thienylboronic acid was successfully carried out in the presence of Na2CO3 as base in refluxing water at very low catalyst loading (0.001 mol%). In addition, the catalyst was recycled with small activity losses. Stark et al. have prepared a set of graphene-coated cobalt magnetic nanoparticle cores functionalized by covalent anchoring of amphiphilic PNIPAM [94]. The further transformation of the material with 3-aminopropyldiphenylphosphane followed by the treatment with a solution of Pd(dba)2 in THF/H2O (9 : 1) afforded the corresponding highly ferromagnetic thermoresponsive catalyst 48 (Scheme 5.30). Because of the amphiphilic character of the polymer branches, catalyst particles showed phase transfer upon temperature change and this property allowed easy recovery and reuse. Furthermore, the steric and electrostatic repulsion of the polymer branches ensures the stability of their dispersion in water for weeks. The Suzuki cross-coupling of iodobenzene and phenylboronic acid with 3 mol% of catalyst in 10 runs gave more than 91% conversion [K2CO3, toluene/H2O (2 : 1), 80 C] and led to a maximum Pd leaching of 1.3% in the product phase.
5.6 Polyacrylamide n
O O N
m
n
O O NH O O iPr N O
O
i) NH2(CH2)3PPh2 THF, 25 ºC, 16 h
O
ii) 25% NH3 (aq.) iii) Pd(dba)2
O
m
O O NH O iPr Ph2P L Pd L L 48
NH AIBN, tBuOH 80 ºC, 24 h Scheme 5.30 Graphene-coated cobalt magnetic nanoparticle cores functionalized by anchoring of PNIPAM.
A novel catalyst with Pd nanoparticles encaged in a nanoporous hydrophilic interpenetrating polymer network was developed by Dong and coworkers [95]. The Heck reactions of iodo- and bromobenzene were efficiently carried out in either DMF or water at 100 C in 10 h. The catalyst was separated by simple filtration and surprisingly could be recovered more than 20 and 13 times in DMF and water, respectively. Very recently, Tamami and Ghasemi immobilized Pd NPs into a modified crosslinked polyacrylamide containing phosphinite (49) [96]. The TEM analysis of catalyst 49 revealed the formation of stable and highly dispersed Pd NPs. The catalytic performance of 49 was studied in the Sonogashira reaction of varied aryl iodides (85–90%), aryl bromides (75–87%), and aryl chlorides (70–78%) as summarized in Scheme 5.31. 4.8% leaching of palladium was observed during the reaction of iodobenzene according to ICP analysis. The catalyst could be recycled in five runs without significant loss of activity.
CHCH2 O
R1
X + R2
NH OP
Ph Pd0
49
Ph
n
49 (0.5−1 mol%) K2CO3, TBAB NMP,100 ºC
X= Cl, Br, I R1= H, NO2, COMe, CH3, Cl, OMe R2= Ph, CH2OH Scheme 5.31 Sonogashira reaction catalyzed by 49.
R1
R2
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts 5.7 Polyaniline
Polyaniline (PANI) is a versatile conducting organic polymer that has been introduced as support for immobilizing Pd species [97]. However, catalytic applications are rather limited and there is much room for the development of novel supported catalyst systems based upon this interesting support. Diaconescu et al. exploited the advantages arising from the high surface area and porosity of PANI nanofibers to make metal-PANI nanocomposites [98]. The most important property of this catalyst is its extremely high activity in Suzuki coupling of activated, deactivated, and sterically hindered aryl chlorides, and even activated aryl fluorides. This is quite an achievement because very few examples for crosscoupling of fluoroarenes are known because of the strong CF bond. However, a mixture of products was obtained when substrates bearing two 2-substituents were reacted. The catalyst was reused in 10 runs and for activated aryl chloride the amount of Pd could be reduced to 105 mol%. Moreover, due to the high reducing capability of PANI, it was proved to be effective in Ullmann homocoupling and hydroxylation of highly deactivated aryl chlorides. This property makes Pd-PANI an interesting catalyst system to perform tandem Suzuki coupling/hydroxylation in one flask (Scheme 5.32). Cl
i) Pd-PANI (0.05 mol%), PhB(OH)2 NaOH, H2O, 100 ºC, 6 h
Cl
ii) KOH, H2O/1,4-dioxane (1:1) 100 ºC, 6 h
OH Ph
Scheme 5.32 Suzuki reaction catalyzed by Pd-PANI.
PANI has several amine and imine moieties; therefore, it can act not only as a support but also as a macro ligand, which facilitates the smooth oxidation of PdH to PdII under aerobic conditions. Likhar et al. have exploited these properties of PANI to stabilize Pd in the oxidative Heck reaction, which provides additional evidence to support this conclusion [99]. In this regard, coupling reaction of arylboronic acids with alkenes took place under base- and ligandfree conditions, in the presence of 5 mol% of catalyst 50 in CH3CN and air atmosphere (Scheme 5.33).
H N
N
N Cl Pd
H N
N 50
N
Cl
5.8 Poly(N-vinyl-2-pyrrolidone)
B(OH)2 50 (5 mol%)
+
R'
Ar
R'
MeCN, 80 ºC, 5 h, air
R R
R'
Ac H
CO2Bu Ph
Yield [%]
Selectivity [%]
90 77
96 99
Scheme 5.33 Suzuki reaction catalyzed by 50.
The catalyst was successfully recycled seven times with a small decrease in activity in the sixth run while no Pd leaching was detected in the filtrate using ICP-AES. Mallick and coworkers reported the synthesis of a novel Pd-PANI-Pd composite bearing nearly monodispersed Pd NPs (2–4 nm) well distributed over the in situ generated regular straight nanofibers of PANI with 20 mm length and 0.4–1.7 mm rectangular cross section [100]. Br
Ph + PhB(OH)2
Pd-PANI (0.02 mol%)
R
toluene, 80 ºC 8 h, air
R
R = MeO 90% R = NMe2 88% Scheme 5.34 Pd-PANI-induced Suzuki reaction.
Suzuki reactions of aryl iodides and bromides were performed with phenylboronic acid in the presence of 0.02 mol% of catalyst Pd-PANI to give biaryl products in high yields (Scheme 5.34). Chlorobenzene gave only a low yield of 37% even in the presence of higher catalyst loading (0.35 mol% of Pd), longer reaction time (16 h), and higher temperature (120 C). Recycling test of the catalyst has not been reported because of the nature of the catalyst and the small amounts of catalyst used made it difficult to be recovered and reused. The catalytic activity of Pd NPs/PANI prepared by the template approach [101,102] was also investigated for the oxidative coupling of 2,6-di-tert-butylphenol. In the presence of 5 mol% Pd, the coupling reaction afforded quantitative product yields in DMF in 24 h at 80 C under oxygen atmosphere [103].
5.8 Poly(N-vinyl-2-pyrrolidone)
An efficient, simple, practical, and economic catalyst system was developed by Wang and coworkers by depositing Pd NPs of 7 nm in size onto PVP (catalyst 51) [104]. The catalyst produced moderate to high yields (43–98%) in the coupling of varied iodoand bromoarenes including 2-bromopyridine (Scheme 5.35) with both aryl- and alkylacetylenes in ethanol at 80 C without any copper cocatalyst.
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N
Pd NP O 51 Ph
Br H +
Ph
51 (1 mol%) N
K2CO3, EtOH 80 ºC, 6 h
N 82%
Scheme 5.35 Sonogashira reaction catalyzed by 51.
The best result was obtained with a catalyst loading of 1 mol% Pd on PVP. The catalyst could be reused directly without any purification through addition of an organic solvent (Et2O) to extract the product with concomitant precipitation of the catalyst at the bottom of the flask. Evangelisti et al. used highly monodispersed Pd NPs in PVP with very small mean diameters (2.0 nm) for the Mizoroki–Heck reaction of iodobenzene and activated bromobenzenes with butyl acrylate in NMP [105]. The catalyst showed higher efficiency than commercially available catalysts such as Pd(OAc)2 and could be quantitatively recovered. Preparation of the catalyst was achieved by adding the solution of solvated Pd atoms in mesitylene/hex-1-ene, obtained by metal vapor synthesis (MVS) [106], to an ethanol solution of PVP. Iyer et al. have prepared palladium composite nanospheres using spinning disk processing as a facile one-step process and hydrogen gas as the reducing agent [107]. It was shown that the molar ratio of PVP to Pd, the disk spinning speed, and average molecular weight of PVP polymer significantly affected the size and distribution of the nanosphere composites, which in turn influenced the catalytic efficiency of the materials. The Mizoroki–Heck cross-coupling of aryl iodides and aryl bromides was then studied with 1 mol% Pd in DMF at 60 and 135 C, respectively, with varied results (Scheme 5.36). The reaction of electron-rich aryl bromides was not completed even after 24 h, giving poor yields of the coupled products (11–42%). The catalyst was reused five times in the reaction of iodobenzene and butyl acrylate.
Br +
CO2Me
Pd-PVP spheres (1 mol%) K2CO3, additive,DMF, 24 h
R R H H NMe2 MeO
Additive
Yield [%]
TBAB TBAC TBAC TBAC
Scheme 5.36 Heck reaction catalyzed by Pd-PVP.
25 76 42 25
Ar
CO2Me
5.9 Polypyrrole
H N + 7/2 PdCl2
3
25 ºC
H N
H N N H
H2O, NaCl Pd NP PPy
+ n
+ 7/2 Pd + 6 HCl
Cl−
PS 52
Figure 5.3 Synthesis of catalyst 52 with polypyrrole-Pd nanocomposite shell.
5.9 Polypyrrole
Polypyrrole (PPy) is another member of air-stable conducting organic polymers that in combination with appropriate noble metal nanoparticle systems produces electrically conductive composites exhibiting enhanced catalytic capability. Fujii et al. coated polystyrene seed particles with Pd-PPy nanocomposite shell (52) by chemical oxidative polymerization of pyrrole using PdCl2 as an oxidant in aqueous medium (Figure 5.3) [108]. The catalytic performance of the core–shell latex particles containing Pd NPs in the shell was then evaluated in the Suzuki and Heck cross-coupling reactions in water. The catalyst (0.03 mol% of Pd) was demonstrated to be stable against air and moisture, and it afforded high product yields (72–99%) in the Suzuki coupling of both activated and deactivated aryl bromides including hindered substrates such as 2,6-dimethylbromobenzene with phenylboronic acid and its derivatives (Scheme 5.37), whereas chloroarenes were not investigated [109]. Br
B(OH)2 +
52 (0.03 mol%) K2CO3 H2O, 80 ºC, 3 h 72%
Scheme 5.37 Suzuki reaction catalyzed by 52.
Moderate to good results (45–87%) were also observed for the Heck reaction of aryl iodides with activated olefins under the same reaction conditions, albeit at a higher catalyst loading of 1 mol% Pd. Recyclability of Pd-PPy/PS nanocomposites was examined in both the Suzuki and Heck couplings. The Suzuki reaction was repeated successfully five times without any leaching of the palladium. In the Heck coupling, however, about 3% of Pd leaching was detected after the fifth run. This nanocomposite was also used as an efficient catalyst for the aerobic oxidative homocoupling reaction of 4-carboxyphenylboronic acid (Scheme 5.38). Recycling of the catalyst was easily carried out by simple sedimentation of the particles [110].
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B(OH)2
Pd-PPy/PS O2, H2O
−O C 2
CO2− +
−O C 2
OH + 3 B(OH)3
Scheme 5.38 Aerobic oxidative homocoupling reaction of 4-carboxyphenylboronic acid catalyzed by Pd-PPy/PS.
5.10 Poly(4-vinylpyridine)
In 2006, Kirschning et al. immobilized an oxime-based palladacycle on poly(4vinylpyridine) resin (53, Figure 5.4) [111a]. This air-, temperature-, and moisture-insensitive precatalyst could effectively induce the Suzuki–Miyaura cross-coupling reaction of aryl bromides (1 mol% of Pd, K2CO3, toluene, 80 C). The robustness of the catalyst has been shown by recycling in 10 runs with slightly decreasing activity. Aryl chlorides bearing electronwithdrawing groups were coupled in water using K2CO3 as base in the presence of TBAB. Since the concentration of Pd in the solution was very low (1.1–2.1 ppb for four runs) and the filtrates were not catalytically active, they concluded that uncoordinated pyridyl sites present in the solid polymer efficiently scavenge the catalytically active soluble Pd species. Surprisingly, application of microwave could improve the catalytic activity of aryl chlorides and their coupling reaction was completed within 3 min compared to 16 h under thermal conditions. Two years later, the same group prepared three different precatalysts using (i) precipitation polymerization to make PVPy powder, (ii) a coating of the glass surface inside a megaporous glass rod that is part of a PASSflowTM [111b] flow microreactor, and (iii) megaporous glass Raschig rings coated with PVPy matrix [112]. All these catalyst systems not only exhibited high performance in the Suzuki coupling of aryl iodides as well as aryl bromides [DMF/H2O (10 : 1), CsF, 100 C], but also displayed excellent activity in the Heck reaction of aryl iodides and aryl bromides (DMF, Et3N, 110–150 C). The nature of catalytic species and the role of polymer support for scavenging and stabilizing the leached Pd species into the solution were indicated by providing some compelling evidence [113]. In particular, depositing Pd-PVPy
R N
N R .. Cl Pd Cl
R N
N R .. Cl Pd Cl
PVP N: Pd Cl 53
N
N OH
Cl 54
Figure 5.4 PVPy-supported Pd catalysts.
PVPy
N
CH2Cl2, rt, 20 h
PVP 55
5.11 Ionic Polymers
composite materials in an appropriate casing provides a continuous flow-through microreactor with a relatively high polymer surface area suitable for practical organic synthesis. In 2008, Kirschning and Mennecke immobilized the NHC-bearing Pd complex 54 on PVPy to furnish the corresponding supported precatalyst 55 (Figure 5.4) [114]. They used PASSflow microreactor with Raschig rings made of a megaporous glass and described the reactor in detail. The catalytic performance of 55 was investigated in the Suzuki–Miyaura reaction of aryl chlorides with varied substitution patterns in either a batch process (Scheme 5.39) or continuous-flow mode. As evidenced using several examples, catalyst 55 displayed inferior performance under continuous-flow mode in comparison with batch mode transformation. This observation has been ascribed to the strong convective flow in these systems, which results in significant removal of the Pd species from the polymeric surface inside the reactor; therefore, the Raschig rings have to be replaced by fresh rings after deactivation of the catalyst. Cl + PhB(OH)2
55 (0.1 mol%) K2CO3, KOtBu iPrOH, rt, 15 h
Ph 99%
Scheme 5.39 Suzuki reaction catalyzed by 55.
Zhang and coworkers developed a relatively simple strategy to facilitate catalyst recycling by immobilizing Pd NPs onto block copolymer micelles [115]. TEM images indicated raspberry-like colloid-supported Pd. The catalyst exhibited excellent performance in the Suzuki reaction of aryl iodides and bromides as well as activated aryl chlorides tested at 80–150 C in water and DMF/water mixture. The catalyst was recycled five times with a small activity decrease. Metal vapor synthesis was also used for depositing Pd NPs on cross-linked PVPy. The catalyst was applied in the Heck reaction in NMP at 100–175 C [116]. Aryl iodides and aryl bromides, especially the substrates bearing electron-withdrawing groups, reacted well. Although aryl chlorides converted in low yields, the observed catalytic activity for such less reactive substrates along with acceptable recyclability (five runs) underlines the importance of this catalytic system. A comprehensive XPS (X-ray photoelectron spectroscopy) analysis was also conducted to shed light on the nature of the Pd species. The major components in the pristine catalyst are metallic palladium (Pd0) particles, which are in electrostatic interaction with nitrogen atoms of the pyridine moieties in the support. This study also excluded the presence of any palladium oxides in the studied samples.
5.11 Ionic Polymers
In this part, two classes of polymer-supported Pd species are described based upon the type of their ligand, that is, N-heterocyclic carbenes and ionic liquid complexes.
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Homogeneous metal complexes of NHCs have attracted considerable attention in the past two decades. These are well known as a class of moisture-, temperature-, and air-stable catalysts with remarkable activity. Their high dissociation energy compared to those of phosphane ligands ensures much stronger binding between the NHC moiety and transition metals, which eventually leads to their higher chemical and thermal resistance against PdC bond cleavage. However, both ionic liquids and NHC ligands are very expensive. Therefore, there is continuing interest in immobilizing them onto appropriate supports. To achieve the advantages of polymers such as easy recovery of expensive transition metals and their anchored ligands and also to prevent the contamination of the final products with ligand residues, polymer-bonded NHCs have intensely been studied in recent years. Furthermore, due to high viscosity of ionic liquids under homogeneous conditions, the main part of the reaction proceeds in a thin layer of ILs denoted as a “diffusion layer.” Therefore, from both economic and practical points of view, it is very crucial to minimize the amount of ILs in a typical chemical transformation [117]. In 2005, Lee et al. designed the PS-supported NHC-Pd complex 57 through the copolymerization of ionic liquid monomer 56 [118]. The Suzuki reaction of varied activated and deactivated iodo- and bromoarenes led to the corresponding biaryl products within 1–6 h in excellent yields [1 mol% of 57, Na2CO3, DMF/H2O (1 : 1), 50 C]. The catalyst could be recycled successfully more than 10 times without any Pd leaching. It also showed high activity in the Heck reaction of iodoarenes in DMAc at 120 C [118b].
N N PF6− F6P Pd PF6
N + N
N N 56
57
Weberskirch and coworkers prepared a set of amphiphilic, water-soluble diblock copolymers based on 2-oxazoline derivatives with pendant NHC-Pd complexes 58 [119]. The most active catalyst (n ¼ 8, x ¼ 30.4, y ¼ 1.9, z ¼ 3.4) afforded good to excellent yields (81–97%) in the Heck coupling of iodobenzenes with styrene in the presence of various bases, giving the highest TOF of 2700 h1 (K2CO3, 110 C, water). An even better performance (TOF ¼ 5200 h1) was achieved in the Suzuki reaction of phenylboronic acid with a few iodo- and bromoarenes. It was proved that the polymer having longer spacer provided higher catalytic activity in the described reactions in neat water.
5.11 Ionic Polymers
H 3C N O CH3
O (CH2)n
O (CH2)n
x
N
N
N
z
H
N N Pd
I I
N N
y
58
stat.
Wang and coworkers conducted the preparation of 59 by esterification of 1-(2-hydroxyethyl)-3-methylimidazolium chloride with PEG-4000–succinic acid [120]. The Heck reaction of various aryl bromides with varied olefins furnished the coupled products in excellent yields (91–97%) with 0.5 mol% Pd(OAc)2 using 59 as solvent in the presence of K2CO3 at 140 C. With Cs2CO3 as base and higher loading of Pd(OAc)2 (5 mol%), activated aryl chlorides coupled as well at 160 C. The recycling experiment of the system was successfully achieved in six runs. However, due to the loss of the imidazoline groups upon the hydrolysis of succinic acid at relatively high reaction temperature, the product yield in the sixth run decreased to 88%. The accumulation of the inorganic salt in the 59 phase may be another reason for the reduction in activity. O O O O
N +
N Cl−
59
Lee and coworkers have developed the amphiphilic polymer NHC 60 for immobilizing Pd and used the resulting catalyst in the Suzuki coupling of iodo- and bromoarenes in neat water at 50 C [121]. It was also recycled in five consecutive runs exhibiting monotonous loss of activity in each run. O O
n
N
+ N Cl
−
O X = Cl or I
60
2
+ N
N
+ N
N
X−
61
Luo and coworkers reported the use of the polystyrene-supported NHC 61 as a ligand for Pd in Suzuki cross-coupling of aryl bromides [122] and arenesulfonyl chlorides [123] with arylboronic acids. The catalyst provided good to excellent yields
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts in most cases for aryl bromides by employing a Pd loading as low as 0.4 mol% in DMF/water (1 : 1) at room temperature [122]. In contrast, higher catalyst loadings (up to 2.5 mol%) and temperature (refluxing THF) were needed to obtain satisfactory result from arenesulfonyl chloride [123]. It was noted that in both protocols the catalyst showed high stability against air, water, and organic solvents and could be consistently reused in five reaction runs. Later, the same research group found that catalyst 61 (2 mol%) displays comparable catalytic performance in the Suzuki coupling of arenediazonium salts with arylboronic acids in yields of 60–96% [124]. Notably, highly selective monocoupling of even 4-iodobenzenediazonium tetrafluoroborate can be achieved in moderate yields, which in turn widen the scope of this catalyst system (Scheme 5.40). I
N2+ BF4− +
B(OH)2
61 (2 mol%) EtOH, rt, 12 h
I 65%
Scheme 5.40 Suzuki reaction of arenediazonium salts catalyzed by 61.
Luis, Garcia-Verdugo, and coworkers treated a polystyrene resin monolith bearing 1-methylimidazolium chloride with appropriate amounts of Pd(OAc)2 under either acidic or basic conditions to give supported palladium catalysts 62 and 63, respectively [125]. Both 62 and 63 (0.02 mol%) displayed excellent activity in the Heck reaction of iodobenzene with methyl acrylate in DMF affording consistently excellent yields in five and two reaction cycles (TONs of 30 000 and 11 000, respectively) within essentially the same reaction time. This suggests that 62 and 63 might indeed follow the same reaction pathway.
N PdX2 N 62
N Cl− + 0 N Pd
2
63
In this regard, the authors provided several experimental evidences confirming the notion that both catalyst systems are precatalyst for the formation of active soluble Pd species. They also correctly concluded that a “catch-and-release” mechanism operated under the described condition. Since monolithic materials could be used as part of a flow-through reaction system, a typical macroporous monolithic reactor was prepared and employed for the same transformation under near-critical EtOH and realized excellent performances within just 3–4 min. In another attempt, they have explored the use of supported N-methylimidazolium ligands 64–66 based on Merrifield resin for the Heck reaction of iodo- and
5.11 Ionic Polymers
bromoarenes [126]. The palladium complex derived from 64c provided a good TON value of 11 600 by employing even a very low catalyst/substrate ratio (0.005 mol% Pd). However, it exhibited poor performance in the third cycle at 90 C, which is possibly due to the precipitation of Pd species. In turn, polymers 65 and 66 generated more stable Pd pincer complexes upon the treatment with Pd(OAc)2 providing a clear improvement in the recycling of the catalyst up to five times even at higher temperature (130 C). All reactions were performed in DMF with Et3N as the base without the need of dry solvent or inert atmosphere. Cl− N N +
Cl−
X− N + N
N + N
a X- = BF4− b X- = CF3SO3− c X- = SbF6− 64
N +
N O
Cl− N
65
Cl− N N + 66
In 2007, the core–shell polymer-supported NHC-Pd catalyst 67 (1 mol%) was introduced for the Sonogashira reaction of aryl iodides and highly activated bromides with terminal alkynes in the absence of any Cu cocatalyst [DMF/H2O (3 : 1), Cs2CO3, or piperidine, 60 or 100 C] [127]. m
n
Ph
Ph
H2 C N N
PF6 Pd PF6
CH2 N N
67
Dyson and coworkers prepared an ionic polymer-based catalyst by mixing an acetonitrile solution of the water-insoluble ionic polymer 68 with ionic liquid 69 [128]. After evaporation of acetonitrile, an appropriate amount of 68 in 69 was allowed to react with PdCl2 at 80 C followed by the reduction of PdII to Pd NPs with NaBH4 at room temperature to give Pd-68/69. The catalyst furnished moderate to high yields in the Heck reaction (Scheme 5.41) and the Suzuki (46–97%) and Stille (35–100%) couplings of iodoarenes and activated bromoarenes. n
Tf2N− N + N 68
Tf2N− N + N
CN 69
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts O R
O Pd-68/69 (0.5 mol%)
X +
O Bu3N, 80 ºC, 1.5−4 h X = I, Br R = H, CN, NO2, OMe, COOH
R
O 49−99%
Scheme 5.41 Heck reaction catalyzed by Pd-68/69.
Poor performance was, however, found in the Stille reaction of bromobenzene and 4-chloronitrobenzene (6–10%) under identical reaction conditions. In 2009, Smith, Guijt, and coworkers used 1,10-phenanthroline and 1-methylimidazole to functionalize a CMS-DVB [poly(chloromethylstyrene-co-divinylbenzene)] monolith, followed by complexation with PdCl2(CH3CN)2 to afford the corresponding supported Pd catalysts 70 and 71 [129]. N CMS DVB
N
PdCl2L
HN
CMS DVB
N 70
PdCl2 N
71
Both catalysts displayed high activity in the Suzuki reaction of iodoarenes and activated bromoarenes (yields of 91–97%) and the Sonogashira coupling of 40 iodoacetophenone with phenylacetylene (95–96%) applying a flow-through microreactor technology. Furthermore, these catalysts were also quite active in performing the same reactions using a batch mode. However, they exhibited poor activity in the Suzuki coupling of nonactivated bromoarenes (28–53%) and even activated chloroarenes (9–13%). In 2010, Han et al. used the cross-linked poly(divinylbenzene) modified with 1aminoethyl-3-vinylimidazolium bromide to immobilize Pd NPs (72, 2.3 wt% Pd) (Figure 5.5) [130]. The catalyst applied for solvent-free Heck reaction (Scheme 5.42) was recycled easily four times with no significant loss of activity. Both hot filtration and ICP-AES analysis confirmed that active soluble Pd species are to some extent responsible for the observed catalysis. Polymer-supported NHC-Pd complex 73 [131] was prepared according to the protocol reported by Lee et al. [118a] and Smith and coworkers [129]. The catalyst
n
NH2·HBr Br− + N N
N+Br−
NH2
NH2NH2NH2NH2
N AIBN DVB
* n
n
PdCl2 NaBH4
copolymer 72
Figure 5.5 Preparation of Pd NPs stabilized by functional cross-linked poly(divinylbenzene).
5.11 Ionic Polymers
I
COOR2
72 (0.02 mol%) +
COOR2
R1
Et3N
R1
120 ºC, 1−6 h
93−97%
R1 = H, 4-MeO, 4-Me R2 = Me, Et, Bu Scheme 5.42 Heck reaction catalyzed by 72.
(1.5 mol%) was then successfully employed in the carbonylative Suzuki reaction of aryl and heteroaryl iodides with various arylboronic acids at 100 C under CO (100 psi) atmosphere giving moderate to high yields (31–95%) of the corresponding benzophenone derivatives. While no activity was observed in the hot filtration test, the catalyst performance declined after the third reaction. N N AcO
OAc Pd
73
A very similar ionic liquid polymer 74 was recently employed to support Pd by treatment with Pd(OAc)2. It is a readily recoverable catalyst for the carbonylative Sonogashira coupling reaction of aryl iodides with terminal alkynes and CO (6 MPa) in water at 130 C. It could be reused five times with a slight loss of activity [132]. OH
*
*
*
N+ I-
HO
N+ Cl-
N n
N *
m
*
* 74
75
Song and coworkers introduced a new functional ionic liquid copolymer 75 for immobilizing Pd NPs [133]. The idea was to use the stabilizing effect of the dihydroxy groups for metal nanoparticles, which was known from previous studies [134]. Excellent yields were obtained in the Suzuki coupling of iodo- and bromoarenes with 0.05 mol% Pd. This system gave 17% isolated yield for the reaction of chlorobenzene and phenylboronic acid with an increased catalyst loading (0.5 mol% Pd). The recycling test was successfully performed five times without significant activity drop. Polyisobutylene (PIB)-supported NHC-Pd complexes 76 and 77 have been prepared by Bergbreiter et al. [135]. While the preparation of the catalysts was accomplished through a relatively long multistep synthesis, they only displayed high activity in the Heck coupling of aryl iodides.
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iPr N
N
PdI2 N
iPr
PIB
N iPr
Pd
PIB
Cl
2
76
77
High yields could be attained in recycling of 76 in 10 runs (1 mol% of Pd, 75 C) and 6 runs (130 C), whereas catalyst 77 exhibited a sudden decrease in yield in the second run. This phenomenon was shown to be due to decomposition of 77 under the described reaction conditions. Polymeric ILs are often nonporous and insoluble in the reaction systems eventually causing mass-transfer limitations in the reaction mixture. To address this issue, Huang et al. prepared the porous ionic copolymer (PIC) 78 via radical copolymerization of 1-vinyl-3-(caboxymethyl)imidazolium bromide with divinylbenzene [136]. BET surface area and pore volume were calculated to be 397 m2 g1 and 0.29 cm3 g1, respectively. This material exhibited indistinct capillary condensation steps in N2 sorption measurements, implying irregular and broad pore size distribution in the microporous, mesoporous, and macroporous regions [137]. The Pd NPs-78 composite displayed excellent catalytic performance in the Suzuki coupling reaction of bromoarenes (0.001–0.01 mol% Pd, Na2CO3, TBAB, 100 C) and even chloroarenes (1 mol% Pd, Na2CO3, TBAB, 120 C) giving good to excellent yields of 95–99 and 85–96%, respectively (Scheme 5.43). This performance was attributed to the presence of both potential carbene and carboxylic groups, which resulted in the formation and stabilization of Pd NPs COO−
n
N
+
N * n
X +
B(OH)2
R
n
78
Pd-78 (0.001−1 mol%) Na2CO3 or NaOH, H2O
R 85−99%
R
X
t [h]
T [ºC]
2-CN 2-MeO 2-Naphthyl 2-HCO 4-MeO
Br Br Br Cl Cl
2 2 2 10 10
100 100 100 120 120
Scheme 5.43 Suzuki reaction catalyzed by Pd NPs-78.
Yield [%] 96 98 97 92 85
5.11 Ionic Polymers
(2–5 nm) and effectively prevented Pd NP agglomeration during the reaction. Indeed, TEM images of the catalyst after the fifth cycle in the reaction of 4bromoanisole with phenylboronic acid indicated that the mean particle diameter was the same as that of the pristine catalyst. Moreover, there was no detectable Pd species in the filtrate after the fifth run. 5.11.2 Polymers Containing Other Ionic Ligands
In 2005, Rothenberg et al. defined the polyelectrolyte shell as a perfect host and microreactor for catalysis. They showed that using a layer-by-layer self-assembly process to form hollow polyelectrolyte capsules, individual layers are replaced by palladium nanoclusters to make robust cell-type microcapsules [138]. Coupling reactions proceeded in the presence of 2 mol% of Pd cluster suspensions in the Sonogashira reaction between phenylacetylene and 4-iodotoluene at 110 C in DMF. Quantitative amount of 4-methyldiphenylacetylene was obtained after 15 min with 99% selectivity. They concluded that simple self-assembled polyelectrolyte shells are ideal to immobilize expensive catalysts and possibly can open a road to new cascade reactions. Li et al. used polymer-supported DABCO–palladium complex from simple inexpensive reagents and found it as an efficient and reusable catalytic system for the Suzuki–Miyaura cross-coupling reaction [139]. Merrifield resin was applied as the primary polymer support. In the presence of 0.25 mol% of the catalyst, a variety of aryl bromides were efficiently coupled with arylboronic acids in aqueous EtOH at room temperature under air. The reaction was rapid and the catalyst could be reused at least five times after recovery by simple filtration. In 2009, Basu et al. prepared polyionic Amberlite resin formate [140]. Good to excellent isolated yields were successfully achieved in the presence of the resulting Amberlite-supported Pd0 composite in the Heck (1 mol% Pd, Et3N, toluene, 90–100 C) and Sonogashira reactions (1 mol% Pd, Na 2CO3, DMF, 110–120 C) of varied iodoarenes as well as in Suzuki–Miyaura coupling of bromoarenes (1 mol% Pd, Et3N, MeCN, 80 C). Moreover, the catalyst was recovered easily with filtration and reused in five runs without any significant loss of activity. Ohtaka et al. stabilized Pd NPs by the polyion complex 79 [141]. The catalytic performance of the final catalyst was tested in the Suzuki and Heck couplings in water (1 mol% of Pd, KOH). A wide range of substrates could react in both reactions at 60 and 80 C, respectively. The ionic character and stability of the catalyst ensure facile redispersion of the catalyst in water by altering the pH of the solution. That is, it could easily be recovered by filtration after pH treatment and recycled at least twice without any loss of activity. However, in the fourth run a slight decrease in the yield was observed in both reactions. TEM did not indicate any change in the particle size of Pd NPs after the Suzuki reaction (2.4 0.6 nm), which has been attributed to the stabilizing effect of arylboronic acids. In contrast, the size of Pd NPs increased to 6.0 1.3 nm in the Heck reaction.
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9n
Cl
+ NBu3 Cl− 79
5.12 Organometallic Polymers
Coordination polymers prepared from a reaction mixture composed of multidentate organic ligands and metal ions have received considerable attention in recent years because of their potential applications in various fields, particularly catalysis. In one of the important families of these polymers known as metal–organic gels and metalcontaining macromolecules, transition metal ions are essential parts of the polymer chain [142]. In 2006, Chen and Deng reported the preparation and characterization of crosslinked star-shaped oxime-palladacycle 80 as an efficient and renewable catalyst [143]. 0.01–2 mol% of this catalyst has been employed in the Suzuki reaction of various aryl bromides in EtOH/H2O mixture and aryl chlorides in DMF (Scheme 5.44). The catalyst system was successfully recycled and reused four times with slight decrease in activity. O
O
O
O
O
O
O O
O
80
2
Pd N OH Cl
Very recently, we have developed the catalytic application of main-chain NHCbased organometallic polymers (MCOPs) with stoichiometric amounts of PdII (81) as an innovative self-supported catalyst system. This catalyst system was previously B(OH)2
X + R'
R R
X
4-MeO Br 4-Ac Cl 2-CN Cl
R' H 4-MeO 4-MeO
80 K2CO3
80 [mol%] T [ºC] 0.01 2 2
100 110 110
Scheme 5.44 Suzuki reaction catalyzed by 80.
R
TBAB — 2 equiv 2 equiv
R' t [h] 8 24 24
Yield [%] 98 55 78
5.12 Organometallic Polymers
prepared by Bielawski and coworkers by treating bis(imidazolium) bromide with a stoichiometric amount of Pd(OAc)2 in DMSO at 110 C [140,142]. One of the interesting features of this catalyst system is that it does not need any support in the Suzuki cross-coupling of aryl halides with arylboronic acids [144]. Catalyst 81a (0.05 mol%) displayed excellent activity in the Suzuki–Miyaura reaction of varied arylboronic acids and aryl chlorides and even activated aryl fluorides reacted in water at 80 or 90 C (Scheme 5.45). It was successfully recycled in six successive runs without significant loss of activity and selectivity. X
Ph + PhB(OH)2
R X
R
81a KOH, H2O 60−90 ºC, 18−30 h
81a
TBAB
Br MeO 0.005 Cl MeO 0.05 F CHO 0.05
R
Yield [%]
— 85 0.5 equiv 85 0.5 equiv 51
Scheme 5.45 Suzuki reaction catalyzed by 81a.
In continuation of this research, the catalytic application of similar catalysts in the Suzuki cross-coupling and the influence of N-alkyl substituents in their catalytic performance have been studied for the first time. We discovered that the catalyst bearing the more lipophilic dodecyl group 81c displayed superior catalytic performance in comparison with both 81a and 81b.
Br Pd Br
R N
R N
N R
N R
Br Pd Br
R N
R N
N R
N R
R = benzyl R = hexyl R = dodecyl R = triethylene glycol
n
Br Pd Br
81a 81b 81c 81d
It is a highly efficient heterogeneous catalyst in the Suzuki–Miyaura reaction of deactivated and even hindered aryl chlorides with arylboronic acids at a low catalyst loading of 0.05 mol% under aqueous conditions (Scheme 5.46) [145]. This study also demonstrated that 81c exhibited better recycling properties and could be successfully recovered in several reaction runs without significant loss of activity and selectivity. Moreover, bright-field microscopy and dynamic light scattering (DLS) studies of the reaction mixture indicate the involvement of numerous polydisperse capsular
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts Me
B(OH)2
X
81c (0.1−0.3 mol%)
+
KOH, H2O, 80−90 ºC 20−30 h
Me
R
R CHO Et CHO
X Br Br Cl
R
Yield [%] 70 71 74
Scheme 5.46 Suzuki reaction catalyzed by 81c.
structures in the range of 500 nm. Based on these observations and additional experimental evidences concerning the nature of the actual actives species, it was concluded that these organometallic polymers could be a source of producing trace amounts of soluble Pd nanoparticles. Furthermore, the capsular structures of these polymers allow the encapsulation of nanoclusters in a hydrophobic region. It was proposed that the superior performance of 81c in comparison with 81a and 81b is presumably due to a collaboration between higher lipophilic character of capsular chambers of this catalyst and hydrophilic effect of water, which results in increased concentration of coupling partners in close proximity of Pd species. Water-soluble (nanocentipede-like) main-chain sample 81d with triethylene glycol legs was developed as a highly efficient catalyst in the Suzuki–Miyaura coupling including activated, deactivated, and hindered substrates in high yields in water at room temperature (Scheme 5.47) [146]. Furthermore, the catalyst shows high catalytic activity and excellent reproducibilities over at least 17 runs. Notably, the catalyst can be easily separated in pure form using a simple dialysis method without the need for traditional filtration technique. B(OH)2
X + R
81d (0.005−0.3 mol%) KOH, H2O, 10−30 h
R' R
X
4-MeO Br 4-MeO Cl Br 2-Et
R' H H 2-Me
T [ºC]
Yield [%]
rt rt 80
88 74 69
R
R'
Scheme 5.47 Suzuki reaction catalyzed by 81d.
Self-supported thiourea-palladium complexes 82 were designed by Chen and coworkers [147]. The polymeric catalyst 82 gave the Suzuki cross-coupling products of bromoarenes in moderate to good yields in neat water at 100 C under aerobic conditions and could be recovered by filtration and reused up to five times without significant activity loss. According to ICP analysis, less than 2 ppm of palladium was detected in each run.
5.12 Organometallic Polymers n
Cl2Pd S Ar N
Cl2Pd S
m
N
N
n
N Ar
Ar = mesityl, 2,5-ditBuC6H3 m = 0,1 82
Zhang and coworkers have designed an amorphous coordination polymeric network based on PdII [148]. This catalytic system has been shown to catalyze the Suzuki coupling of a few aryl iodides and bromides with arylboronic acids in good to excellent yields (84–99%). The catalyst showed relatively low recyclability as testified in five runs with gradually longer reaction times to obtain acceptable yields. Zhang and coworkers continued their studies on the PdII and FeIII coordination networked complex 83 based on 5-1H-benzo[d]imidazole-1,3-dicarboxylic acid [149]. Catalyst 83 has also been successfully employed in the Suzuki reaction of iodo- and bromoarenes (91–95%) including bromopyridines (yields of 56–95%, methanol, 60 C). As may be expected, this catalyst system gave much lower yields in the case of chloroarenes (6–46%). Pd II N
metal− organic gel
N H 83
Magnetite nanoparticle-supported coordination polymer nanofiber 84 was also designed by Zhang and coworkers [150]. The polymeric catalyst 84 gave the Suzuki cross-coupling products in moderate to good yields in methanol at 60 C using iodoarenes and activated bromoarenes and could be recovered by a permanent magnet and reused up to four times without significant loss of its catalytic activity. Cl N Pd N Cl
HN
O
Fe3O4
Fe3O4 N
N Cl Pd Cl N
N N
H N
O NH
Cl Pd N Cl
O
Fe3O4
N
84
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts FDU-type mesoporous phenolic resin
AlCl3
OH
OH
OH
CH3OCH2Cl
Cl Li, PPh2Cl
PPh2
Cl
PPh2
Pd2(dba)3
FDU-PPh2/Pd0 85
OH
Figure 5.6 The procedure for preparing FDU-supported diphenylphosphane-Pd catalyst.
5.13 Functionalized Porous Organic Polymers
CC coupling reactions have also been accomplished using Pd complexes and Pd NPs supported by functionalized porous organic polymers. These kinds of polymers are lipophilic analogues of inorganic mesoporous materials that have recently received great attention especially because of their high surface area (100– 400 m2 g1) and pore volume, as well as excellent hydrophobic properties. An example is the ordered mesoporous FDU (Fudan University)-type functionalized mesoporous phenolic resin 85 described by Zhao and coworkers (Figure 5.6). The mesoporous FDU-14 backbone with cubic structure (Ia3d) was synthesized using a nanocasting protocol according to a known procedure [151a]. Good to excellent performance was shown in the Heck reaction of iodoarenes and activated bromoarenes (80–96%, 90–110 C), whereas highly activated chloroarenes gave lower yields even at 130 C. Recycling was successfully achieved in eight consecutive reactions using iodobenzene [151b]. In 2010, Ogasawara and Kato demonstrated a new strategy based on polymerization-induced phase separation (PIPS) techniques to immobilize Pd NPs in microporous polymers [152]. A mixture of PAMAM as a ligand for stabilizing Pd NPs and excess amounts of EGDMA was employed for stabilizing Pd NPs. The catalyst performance (0.01 mol%) was investigated in aqueous Suzuki reaction of varied bromoarenes (Scheme 5.48) and the corresponding products were obtained in high yields (81–96%). Recycling performance of the catalyst in the reaction of 40 bromoacetophenone and phenylboronic acid in water at 80 C was examined with no significant change in activity in eight runs. The authors finally introduced the PIPS as a useful method not only for preparation of the microporous polymer supports but also for conversion of palladium ions to Pd NPs. Another good example is a functionalized ordered mesoporous polymer bearing 2,4,6-trialkoxy-1,3,5-triazine moieties. The catalyst was prepared via radical polymerization of 2,4,6-triallyloxy-1,3,5-triazine in the presence of C12H23SO3Naþ (sodium dodecyl sulfate), an anionic structure-directing agent, followed by treatment with a solution of Pd(OAc)2 in refluxing CH3COOH, to afford the
5.14 Miscellaneous Polymers
R1
Br
Pd-PAMAM/EGDMA (0.01 mol%)
+
R1
K2CO3, H2O, 80 ºC
R2
R2
B(OH)2 R1
R2 H H H H CH3O
Ac CN OH CH3O CH3O
t [h]
Yield [%]
4 4 4 8 8
96 83 86 82 81
Scheme 5.48 Pd-PAMAM/EGDMA-induced Suzuki reaction.
n
Pd(OAc)2
O (AcO)2Pd n
N O 86
X + R1
R2
N N
O
n
Pd(OAc)2
86 (0.02 g) K2CO3 R1 H2O/EtOH (1:1) 110−140 ºC, 6−24 h
R2
50–95%
R1 = H, 4-MeO, 4-Me, 4-NO2, 4-Ac, 4-CHO R2 = Ph, COOH X = I, Br, Cl Scheme 5.49 Heck reaction catalyzed by 86.
corresponding supported Pd catalyst 86. It was then elegantly applied in the Heck coupling (Scheme 5.49) as well as Sonogashira and Suzuki reactions of varied haloarenes including a few chloroarenes [153].
5.14 Miscellaneous Polymers
Infrequently, sulfur-containing polymers such as polythiophene [154] and poly(1,4phenylene sulfide) have been used as supports for immobilizing either Pd NPs or Pd complexes for coupling reactions. Recently, Mandal and coworkers reported the synthesis of ynones via the palladium-catalyzed coupling of terminal alkynes with acid chlorides, known as the acyl Sonogashira reaction, with Pd NPs embedded into
j189
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts NH·HCl N
R1
N
H2N NH2
NH2
SiMe3 87
in one pot
R2 H 87 (0.05 g)
O
Et3N, toluene 25 or 50 ºC, 12 h
R1
O R1
Cl
R1 = Ph, 4-MeOC6H4, 2-HSC6H4, naphthyl, cinnamyl, tBu R2 = Ph, biphenyl, 4-FC6H4, Bu, Hex, decyl
R2 15− 98%
Scheme 5.50 Acyl Sonogashira reaction catalyzed by 87.
poly(1,4-phenylene sulfide) matrix 87 [155]. Many pharmaceutically important heterocyclic precursors such as 4-substituted 2-aminopyrimidines were efficiently prepared with this catalyst system (Scheme 5.50). S S
S
S
S Pd NPs
S
S
S
S S
87
S n
Ley and coworkers made an attempt to improve a catalytic system containing polyurea with encapsulated palladium and sodium carbonate as base for the Suzuki reaction [156]. They substituted the inorganic base with a polymer-supported carbonate (Sigma-Aldrich product, nominal loading: 2.5–3.5 mmol g1) to simplify the workup process. Although polymer-supported carbonate has been reported to be a boronic acid scavenger [157], the reaction product was contaminated with residual boronic acid. Incubating the reaction mixture with N,N-diethanolaminomethylpolystyrene at room temperature, following evaporation of the reaction mixture to remove water, and redissolution in DMF was found to be a simple and effective method for removal of excess boronic acid. This Suzuki system promotes efficient coupling of a range of iodo- and bromoarenes with boronic acids with microwave heating, resulting in substantial rate acceleration relative to thermal conditions. In 2010, in a study reported by Chergui et al., the synthesis of the carbon nanotube-supported poly(glycidyl methacrylate) (PGM) through click chemistry and immobilization of Pd NPs (3 nm) onto this polymeric stabilizer has been described (Figure 5.7) [158]. Catalyst 88 was used in the Suzuki reaction of
5.14 Miscellaneous Polymers
H2 O C CO2H O C H Me 2 N C ( C )n C CO2Et N N Me Me Pd NP
H2 O C CO2H O C H Me 2 N C ( C )n C CO2Et N N Me Me 88
Figure 5.7 Pd NPs stabilized by carbon nanotube-supported PGM.
bromobenzene (DMF, 100 C) and successfully recycled four times but an activity drop in the fifth run was observed with no Pd leaching. A Pd–poly(1,8-diaminonaphthalene) nanocomposite was synthesized by polymerization of 1,8-diaminonaphthalene using palladium acetate as an oxidizing agent. The electrons liberated during the oxidative polymerization process reduced palladium(II) ions to form Pd nanoparticles stabilized within poly(1,8-diaminonaphthalene) [159]. The composite shows high activity for the Heck reaction of a series of iodo- and bromobenzene derivatives with alkenes (Et3N, DMF, 80 C). However, catalyst recyclability was not feasible due to the minute quantity of the material used for the reaction and the support solubility in organic solvent. This group developed another catalytic system for Suzuki reaction using the in situ polymerization and composite formation (IPCF) technique to produce simultaneously both the polymer and the nanoparticles [160]. This method ensures an intimate contact between the particles and the functionalized polymer. The catalyst prepared in this way (0.045–0.147 mol% of Pd) induced Suzuki reaction of both aryl and heteroaryl bromides with boronic acids with high TOF values and could be recycled up to three runs with minimum loss of activity. Oki and Neelgund used poly(lactic acid) (PLA)-grafted CNT with Pd NPs as a catalyst in the Heck reaction between aryl halides and butyl acrylate [161]. The activity of the nanocatalyst was affected by PLA and more significantly with CNT. Coupling of bromobenzene and methyl acrylate in the presence of Pd NPs-PLA without carbon nanotubes and Pd NPs-CNT without PLA needed, respectively, 15 and 11 h for completion. Coupling with Pd NPs-PLA/CNT, in turn, completed the reaction in 8 h under the same conditions. After reaction, the nanocatalyst was recovered, washed with deionized water and acetone, and dried (110 C, 2 h). When reused in three additional cycles, it gave methyl cinnamate in 2% lower yields. That is, the nanocatalyst has sufficient stability to be used in multiple cycles. Palladium(0) nanoclusters stabilized by poly(4-styrenesulfonic acid-co-maleic acid) were prepared by Metin et al. in 2011 [162]. The catalyst showed excellent activity in Suzuki–Miyaura cross-coupling of a series of aryl bromides and iodides with phenylboronic acid in water. The high TOFs obtained in Suzuki–Miyaura reactions of phenylboronic acid with 40 -bromoacetophenone (1980 h1) and
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts Table 5.3 C C coupling reactions performed by miscellaneous polymeric catalysts.
Coupling reaction
Runs Solvent/T ( C) Substrates
Polymer
Reference
Epoxy resin N,Ndiglycidyl-4glycidyloxyaniline Poly(2-aminophenol) Nafion–Teflon
[163a]
Suzuki, Heck
—
Dioxane/H2O, I NMP/90–120
Heck Heck, Sonogashira Heck, Suzuki
2 4
DMF/80 CH3CN/100
I, Br I
3
DMF, H2O/80–120
Heck
4
DMF
Suzuki
4
H2O/30–100
Suzuki
4
DMF/120
Suzuki, Sonogashira Suzuki
—
EtOH/80
I, Br, activated Cl Poly[styrene-co-2(acetoacetoxy)ethyl methacrylate-co-methyl acrylic acid] I, Br Poly(N-vinylimidazole-coN-vinylcaprolactam) I, Br, Cl Poly(vinylidene fluoride)g-poly(dimethylaminoethyl methacrylate) Br Phosphanylated polyethylene chips I, Br Poly(methylphenylsilane)
7
Propan-2ol/water
Br
Homocoupling Stille
4
Dioxane DMA
I, Br
[163b] [164] [165]
[166] [167]
[168] [169a]
Poly[(3-N-imidazolopropyl) [169b] methylsiloxane-codimethylsiloxane] PS-supported [170] triphenylarsine
4-iodobenzene (5940 h1) are the highest values ever reported for this reaction in water as sole solvent. In addition, different types of poly(2-aminophenol) composites or other aminophenol derivatives [163], Nafion–Teflon bimembrane [164], poly[styrene-co-2-(acetoacetoxy)ethyl methacrylate-co-methyl acrylic acid] [165], poly(N-vinylimidazole) or poly(N-vinylimidazole-co-N-vinylcaprolactam) [166], poly(methyl acrylates) [167], polyethylenes [168], polysiloxanes [169], and PS-supported triphenylarsine [170] have been applied to immobilize Pd species in CC bond formation. The results are briefly summarized in Table 5.3.
5.15 Summary and Outlook
With ever-growing environmental and economic problems, increasing attention has been devoted toward the development of new improved recyclable catalyst systems for the palladium-catalyzed CC bond forming reactions. In this context, organic
Abbreviations
chemists have shown a growing interest of designing and employing a novel organic polymer-supported catalyst system in the form of either supported metal nanoparticles or metal complexes. However, despite the important advancements in this area, there are several limitations that still need to be addressed. It is very difficult to precisely predict what will be exactly held for this field in the future research. Nevertheless, as pointed out in this chapter, there are guidelines that would certainly help us to obtain relevant insight into systems wherein many of the current limitations of the heterogeneous catalysts can be minimized. In this regard, a few general remarks may be summarized as follows. i) Ever-growing mechanistic knowledge provides valuable information about the nature of active species and the cross-coupling reaction pathways. Such pieces of information, in turn, will result in numerous new opportunities of designing novel related catalyst systems with improved catalytic performances, including stability, selectivity, and lower metal leaching. ii) The use of more robust functional organic polymers, particularly new generation of porous functionalized polymeric materials, which has been somewhat less thoroughly studied, will likely attract much more attention to address the limitations of traditional simple cross-linked organic polymers. iii) There is no doubt that during the next few years the development of new improved protocols for the coupling reactions of nonactivated substrates such as alkenyl chlorides and aryl chlorides, which are industrially the most relevant haloarenes, using recyclable catalyst systems will continue to be one of the most challenging areas in both synthetic and industrial organic chemistry. As mentioned, despite significant successes having been achieved, particularly in the Suzuki reaction, the use of aryl chlorides in the Heck, Sonogashira, and Ullmann couplings is still not addressed properly. iv) The use of water as reaction medium will certainly contribute to the development of all CC bond forming reactions and in the years ahead it is expected to be rapidly growing (see Chapter 7). However, one of the major challenges in this area will likely be the discovery of new water-tolerant heterogeneous catalyst systems, which hopefully withstand progressive deactivation upon successive uses, undesirable metal leaching, and extensive support degradation. v) It is also not surprising to speculate that the development of new ecocompatible polymer-supported catalyst systems will also gain increasing importance and challenges in the coming years, where a deeper insight into the use of modified naturally occurring polymer systems will be directly involved. Abbreviations
b-CD AIBN tBuOK CMS-DVB CNT
b-cyclodextrin 2,20 -azobis(isobutyronitrile) potassium tert-butoxide poly(chloromethylstyrene-co-divinylbenzene) carbon nanotube
j193
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j 5 Coupling Reactions Induced by Polymer-Supported Catalysts DABCO DLS DMAc DMF DMSO DPPF EGDMA FDU ICP-AES ICP-OES IL IPCF MCOP MVS MW NHC NMP PAMAM PANI PASSflow Pd NP PEG PEG-PU PEO PGM PI PIB PIC PIPS PLA PMA PNIPAM PNIPAM-co-PMA PPy PS PVA PVP PVPy ROMP TBAB TBAC TGA TOF XPS
1,4-diazabicyclo[2.2.2]octane dynamic light scattering N,N-dimethylacetamide N,N-dimethylformamide dimethyl sulfoxide bis(1,10 -diphenylphosphano)ferrocene ethylene glycol dimethacrylate Fudan University inductively coupled plasma atomic emission spectroscopy inductively coupled plasma optical emission spectroscopy ionic liquid in situ polymerization and composite formation main-chain NHC-based organometallic polymer metal vapor synthesis microwave irradiation N-heterocyclic carbene N-methyl-2-pyrrolidone poly(amidoamine)-based dendrimer polyaniline polymer-assisted solution-phase synthesis in the flow-through mode Pd nanoparticle poly(ethylene glycol) poly(ethylene glycol)–polyurethane poly(ethylene oxide) poly(glycidyl methacrylate) polymer incarcerated polyisobutylene porous ionic copolymer polymerization-induced phase separation poly(lactic acid) potassium methacrylate poly(N-isopropylacrylamide) poly(N-isopropylacrylamide-co-potassium methacrylate) polypyrrole polystyrene poly(vinyl alcohol) poly(N-vinyl-2-pyrrolidone) poly(4-vinylpyridine) ring-opening metathesis polymerization tetrabutylammonium bromide tetrabutylammonium chloride thermogravimetric analysis turnover frequency X-ray photoelectron spectroscopy
References
References 1 (a) Miyaura, N. (2004) Metal-Catalyzed
2
3
4 5
6
7
8
9
10
11
Cross-Coupling Reactions, vol. 1 (eds A.de Meijere and F. Diederich), Wiley-VCH Verlag GmbH, Weinheim, pp. 41–109; (b) Corbet, J-.P. and Mignani, G. (2006) Chem. Rev., 106, 2651–2710. (a) Burello, E. and Rothenberg, G. (2003) Adv. Synth. Catal., 345, 1334–1340; (b) Pastre, J.C. and Correia, C.R.D. (2006) Org. Lett., 8, 1657–1660. (a) Kirsch, P. and Bremer, M. (2000) Angew. Chem., 112, 4384–4405; Angew. Chem., Int. Ed., 39, 4216–4235 (2000); (b) Kiryanov, A.A., Seed, A.J., and Sampson, P. (2001) Tetrahedron Lett., 42, 8797–8800; (c) Hird, M., Gray, G.W., and Toyne, K.J. (1991) Mol. Cryst. Liq. Cryst., 206, 221–237; (d) Sabat, M., and Johnson, C.R. (2000) Org. Lett., 2, 1089–1092. Farina, V. (2004) Adv. Synth. Catal., 346, 1553–1582. (a) Littke, A.F. and Fu, G.C. (2002) Angew. Chem., 114, 4350–4386; Angew. Chem., Int. Ed., 41, 4176–4211 (2002); (b) Bedford, R.B., Cazin, C.S.J., and Holder, D. (2004) Coord. Chem. Rev., 248, 2283–2321. Prim, D., Campagne, J.-M., Joseph, D., and Andrioletti, B. (2002) Tetrahedron, 58, 2041–2075. (a) Herrmann, W.A. (2002) Angew. Chem., 114, 1342–1363; Angew. Chem., Int. Ed., 41, 1290–1309 (2002); (b) Herrmann, € W.A., Olefe, K., Preysing, D.V., and Schneider, S.K. (2003) J. Organomet. Chem., 687, 229–248. (a) Liu, Y., Wang, S.-S., Liu, W., Wan, Q.-X., Wu, H.-H., and Gao, G.-H. (2009) Curr. Org. Chem., 13, 1322–1346; (b) Liu, S. and Xiao, J. (2007) J. Mol. Catal. A: Chem., 270, 1–43. Solodenko, W., Wen, H., Leue, S., Stuhlmann, F., Argirusi, G.S., Wen, H., Jas, G., Sch€ onfeld, H., Kunz, U., and Kirschning, A. (2004) Eur. J. Org. Chem., 3601–3610. Greenway, G.M., Haswell, S.J., Morgan, D.O., Skelton, V., and Styring, P. (2000) Sens. Actuators B, 63, 153–158. (2011) Chem. Rev., 111, (a) Molnar, A. (2011) Curr. 2251–2320; (b) Molnar, A. Org. Synth., 8, 172–186.
12 (a) Ertl, G., Kn€ ozinger, H., Sch€ uth, F., and
13 14 15 16
17
18
19 20 21
Weitkamp, J. (eds) (2008) Handbook of Heterogeneous Catalysis, 2nd edn, WileyVCH Verlag GmbH, Weinheim; (b) Ding, K. and Uozumi, Y. (2008) Handbook of Asymmetric Heterogeneous Catalysis, WileyVCH Verlag GmbH, Weinheim; (c) Cornils, B., Herrmann, W.A., Horvath, I.T., Leitner, W., Mecking, S., Olivier-Bourbigou, H., and Vogt, D. (eds) (2005) Multiphase Homogeneous Catalysis, Wiley-VCH Verlag GmbH, Weinheim; (d) Blaser, H.U. and Schmidt, E. (eds) (2004) Asymmetric Catalysis on Industrial Scale: Challenges, Approaches and Solutions, Wiley-VCH Verlag GmbH, Weinheim; (e) ColeHamilton, D.J. and Tooze, R.P. (eds) (2006) Catalyst Separation, Recovery and Recycling: Chemistry and Process Design, Springer, Berlin; (f) Gladysz, J.A. (2002) Chem. Rev., 102, 3215–3216; (g) Leadbeater, N.E. and Marco, M. (2002) Chem. Rev., 102, 3217–3273; (h) McNamara, C.A., Dixon, M.J., and Bradley, M. (2002) Chem. Rev., 102, 3275–3299; (i) Fan, Q.-H., Li, Y.-M., and Chan, A.S.C. (2002) Chem. Rev., 102, 3385–3466; (j) Karimi, B., Behzadnia, H., Farhangi, E., Jafari, E., and Zamani, A. (2010) Curr. Org. Synth., 7, 543–567. Janda, K.D., Dickerson, T.J., and Reed, N.N. (2002) Chem. Rev., 102, 3325–3344. Toy, P.H. and Lu, J. (2009) Chem. Rev., 109, 815–838. Carey, F.A. (2000) Chapter 25, in Organic Chemistry, 4th edn, McGraw-Hill, USA. Clark, J.H., Deswarte, F.E.I., Hardy, J.J.E., Hunt, A.J., Kerton, F.M., and Milkowski, K. (2004) PCT Patent Application PCT/ GB2004/003276. Gronnow, M.J., Luque, R., Macquarrie, D.J., and Clark, J.H. (2005) Green Chem., 7, 552–557. Budarin, V.L., Clark, J.H., Luque, R., Macquarrie, D.J., and White, R.J. (2008) Green Chem., 10, 382–387. Liu, S., Zhou, Q., and Jiang, H. (2010) Chin. J. Chem., 28, 589–593. Khalafi-Nezhad, A. and Panahi, F. (2011) Green Chem., 13, 2408–2415. Hirano, S., Elvers, B., Hawkins, S., Russey, W., and Schulz, G. (1993)
j195
196
j 5 Coupling Reactions Induced by Polymer-Supported Catalysts 22 23 24
25 26 27 28
29
30
31 32
33 34
35 36 37
38 39 40
Ullmann’s Encyclopedia of Industrial Chemistry, vol. A6, Wiley-VCH Verlag GmbH, Weinheim, pp. 231–232. Macquarrie, D.J. and Hardy, J.J.E. (2005) Ind. Eng. Chem. Res., 44, 8499–8520. Cui, Y., Zhang, L., and Li, Y. (2005) Polym. Adv. Technol., 16, 633–637. Leonhardt, S.E.S., Stolle, A., Ondruschka, B., Cravotto, G., De Leo, C., Jandt, K.D., and Keller, T.F. (2010) Appl. Catal. A: Gen., 379, 30–37. Yi, S.-S., Lee, D.-H., Sin, E., and Lee, Y.-S. (2007) Tetrahedron Lett., 48, 6771–6775. Zhang, H.-F., Zhang, L., and Cui, Y.-C. (2007) React. Funct. Polym., 67, 322–328. Sin, E., Yi, S.-S., and Lee, Y.-S. (2010) J. Mol. Catal. A: Chem., 315, 99–104. Lasri, J., Leod, T.C.O.M., and Pombeiro, A.J.L. (2011) Appl. Catal. A: Gen., 397, 94–102. Bradshaw, M., Zou, J., Byrne, L., Iyer, K. S., Stewart, S.G., and Raston, C.L. (2011) Chem. Commun., 47, 12292–12294. Law, D. (2009) Handbook of Pharmaceutical Excipients (eds R.C. Rowe, P.J. Shesky, and M.E. Quinn), Pharmaceutical Press, London, pp. 11–12. Primo, A., Liebel, M., and Quignard, F. (2009) Chem. Mater., 21, 621–627. Cintas, P., Cravotto, G., Gaudino, E.C., Orio, L., and Boffa, L. (2012) Catal. Sci. Technol., 2, 85–87. Araki, C. (1956) Bull. Chem. Soc. Jpn., 29, 543–544. Firouzabadi, H., Iranpoor, N., Gholinejad, M., and Kazemi, F. (2011) RSC Adv., 1, 1013–1019. Liu, L.-F., Zhang, Y.-H., and Wang, Y.-G. (2005) J. Org. Chem., 70, 6122–6215. Zhang, Y. and Shi, S. (2007) J. Org. Chem., 72, 5927–5930. (a) Wang, L., Zhang, Y., Liu, L., and Wang, Y. (2006) J. Org. Chem., 71, 1284–1287; (b) Firouzabadi, H., Iranpoor, N., and Ghaderi, A. (2011) Org. Biomol. Chem., 9, 865–871. Du, Z., Zhou, W., Bai, L., Wang, F., and Wang, J.-X. (2011) Synlett, 369–372. Luo, C., Zhang, Y., and Wang, Y. (2005) J. Mol. Catal. A: Chem., 229, 7–12. (a) Lee, M., Ryu, J.-H., Jang, C.-J., Yoo, Y.-S., and Lim, S.-G. (2005) J. Org. Chem., 70, 8956–8962; (b) Beletskaya, I.P.,
41
42 43 44 45
46
47
48 49
50
51
52
53 54
55
56 57
Kashin, A.N., Litvinov, A.E., Tyurin, V.S., Valetsky, P.M., and van Koten, G. (2006) Organometallics, 25, 154–158; (c) Beletskaya, I.P., Kashin, A.N., Khotina, I.A., and Khokhlov, A.R. (2008) Synlett, 1547–1552; (d) Meier, M.A.R., Filali, M., Gohy, J.-F., and Schubert, U.S. (2006) J. Mater. Chem., 163001–3006. Panda, A.G., Patil, Y.P., Tambade, P.J., and Bhanage, B.M. (2010) Ind. Eng. Chem. Res., 49, 8360–8364. Mai, W. and Gao, L. (2006) Synlett, 2553–2558. Corma, A., García, H., and Leyva, A. (2006) J. Catal., 240, 87–99. Leyva, A., García, H., and Corma, A. (2007) Tetrahedron, 63, 7097–7111. Cho, J.K., Najman, R., Dean, T.W., Ichihara, O., Muller, C., and Bradley, M. (2006) J. Am. Chem. Soc., 128, 6276–6277. Bradley, M., Najman, R., Cho, J.K., Coffey, A.F., and Davies, J.W. (2007) Chem. Commun., 5031–5033. Sher Shah, Md.S.A., Guin, D., and Manorama, S.V. (2010) Mater. Chem. Phys., 124, 664–669. Park, C.M., Kwon, M.S., and Park, J. (2006) Synthesis, 3790–3794. Miao, S., Zhang, C., Liu, Z., Han, B., Xie, Y., Ding, S., and Yang, Z. (2008) J. Phys. Chem. C, 112, 774–780. Ohtaka, A., Teratani, T., Fujii, R., Ikeshita, K., Shimomura, O., and Nomura, R. (2009) Chem. Commun., 7188–7190. Teratani, T., Ohtaka, A., Kawashima, T., Shimomura, O., and Nomura, R. (2010) Synlett, 2271–2274. Ohtaka, A., Teratani, T., Fujii, R., Ikeshita, K., Kawashima, T., Tatsumi, K., Shimomura, O., and Nomura, R. (2011) J. Org. Chem., 76, 4052–4060. Phan, N.T.S., Khan, J., and Styring, P. (2005) Tetrahedron, 61, 12065–12073. Liu, Y.-X., Ma, Z.-W., Jia, J., Wang, C.-C., Huang, M.-L., and Tao, J.-C. (2010) Appl. Organomet. Chem., 24, 646–649. Bakherad, M., Amin, A.H., Keivanloo, A., Bahramian, B., and Raeissi, M. (2010) Tetrahedron Lett., 51, 5653–5656. Bakherad, M., Keivanloo, A., Bahramian, B., and Jajarmi, S. (2011) Synlett, 311–314. He, Y. and Cai, C. (2011) Catal. Commun., 12, 678–683.
References 58 He, Y. and Cai, C. (2011) J. Organomet. 59 60
61
62 63
64 65 66 67
68
69
70 71 72
73
74 75 76 77
78
Chem., 696, 2689–2692. Gil-Molt o, J., Karlstr€om, S., and Najera, C. (2005) Tetrahedron, 61, 12168–12176. Jones, R.C., Canty, A.J., Deverell, J.A., Gardiner, M.G., Guijt, R.M., Rodemann, T., Smith, J.A., and Tolhurst, V.-A. (2009) Tetrahedron, 65, 7474–4481. G€ omanna, A., Deverell, J.A., Munting, K. F., Jones, R.C., Rodemann, T., Canty, A.J., Smith, J.A., and Guijt, R.M. (2009) Tetrahedron, 65, 1450–1454. Yang, J., Li, P., and Wang, L. (2011) Synthesis, 1295–1301. Ornelas, C., Diallo, A.K., Ruiz, J., and Astruc, D. (2009) Adv. Synth. Catal., 351, 2147–2154. He, Y. and Cai, C. (2010) Catal. Lett., 140, 153–159. Alacid, E. and Najera, C. (2006) Synlett, 2959–2964. Ye, Z.-W. and Yi, W.-B. (2008) J. Fluorine Chem., 129, 1124–1128. Islam, S.M., Mondal, P., Roy, A.S., Mondal, S., and Hossain, D. (2010) Tetrahedron Lett., 51, 2067–2070. Islam, M., Mondal, P., Tuhina, K., Roy, A. S., Mondal, S., and Hossain, D. (2010) J. Organomet. Chem., 695, 2284–2295. Borkowski, T., Trzeciak, A.M., Bukowski, W., Bukowska, A., Tylus, W., and Ke˛pi nski, L. (2010) Appl. Catal. A: Gen., 378, 83–89. He, Y., Wang, L., and Cai, C. (2011) J. Appl. Polym. Sci., 121, 286–291. He, H.S., Yan, J.J., Shen, R., Zhuo, S., and Toy, P.H. (2006) Synlett, 563–566. Liu, Y., Feng, X.J., Bao, D.C., Li a, K.X., and Bao, M. (2010) Chin. Chem. Lett., 21, 979–982. Liu, Y., Feng, X.J., Bao, D.C., Li, K.X., and Bao, M. (2010) J. Mol. Catal. A: Chem., 323, 16–22. Nishio, R., Sugiura, M., and Kobayashi, S. (2005) Org. Lett., 7, 4831–4834. Nishio, R., Sugiura, M., and Kobayashi, S. (2007) Chem. Asian J., 2, 983–995. Uozumi, Y. and Kikuchi, M. (2005) Synlett, 1775–1778. Suzuka, T., Okada, Y., Ooshiro, K., and Uozumi, Y. (2010) Tetrahedron, 66, 1064–1069. Nakai, Y., Kimura, T., and Uozumi, Y. (2006) Synlett, 3065–3068.
79 Schweizer, S., Becht, J.-M., and Le Drian,
80 81
82 83
84
85
86 87 88
89
90 91 92
93
94
95
C. (2007) Adv. Synth. Catal., 349, 1150–1158. Doherty, S., Knight, J.G., and Betham, M. (2006) Chem. Commun., 88–90. Yu, H.W., Tong, Q.S., Peng, Y.R., Jia, L., Shi, J.C., and Jin, Z.L. (2007) Chin. Chem. Lett., 18, 37–40. Bai, L. and Wang, J.-X. (2008) Adv. Synth. Catal., 350, 315–320. Bakherad, M., Keivanloo, A., Bahramian, B., and Mihanparast, S. (2009) Tetrahedron Lett., 50, 6418–6420. Shin, J., Bertoia, J., Czerwinski, K.R., and Bae, C. (2009) Green Chem., 11, 1576–1580. Yu, K., Sommer, W., Richardson, J.M., Weck, M., and Jones, C.W. (2005) Adv. Synth. Catal., 347, 161–171. Weck, M. and Sommer, W.J. (2006) Adv. Synth. Catal., 348, 2101–2113. Jones, C.W. and Weck, M. (2007) Inorg. Chem., 46, 1865–1875. Hanson, P.R., Reiser, O., Sch€atz, A., Long, T.R., Grass, R.N., and Stark, W.J. (2010) Adv. Funct. Mater., 20, 4323–4328. (a) Uozumi, Y., Yamada, Y.M.A., Beppu, T., Fukuyama, N., Ueno, M., and Kitamori, T. (2006) J. Am. Chem. Soc., 128, 15994–15995; (b) Yamada, Y.M.A., Watanabe, T., Torii, K., and Uozumi, Y. (2009) Chem. Commun., 5594–5596; (c) Uozumi, Y., Yamada, Y.M.A., Beppu, T., Fukuyama, N., Ueno, M., Kitamori, T., Watanabe, T., and Torii, K. (2010) Chem. Eur. J., 16, 11311–11319. Mahdavi, H., Zirakzadeh, A., and Amani, J. (2007) React. Funct. Polym., 67, 716–722. Chen, C.-W. and Akashi, M. (1997) Langmuir, 13, 6465–6472. Wang, Y., Wei, G., Zhang, M., Zhang, W., and Wen, F. (2008) J. Phys. Chem. C, 112, 10827–10832. Sivudu, K.S., Reddy, N.M., Prasad, M.N., Raju, K.M., Mohan, Y.M., Yadav, G.S., Sabitha, G., and Shailaja, D. (2008) J. Mol. Catal. A: Chem., 295, 10–17. Stark, W.J., Zeltner, M., Schatz, A., and Hefti, M.L. (2011) J. Mater. Chem., 21, 2991–2996. Zhan, K., You, H., Liu, W., Lu, J., Lu, P., and Dong, J. (2011) React. Funct. Polym., 71, 756–765.
j197
198
j 5 Coupling Reactions Induced by Polymer-Supported Catalysts 96 Tamami, B. and Ghasemi, F. (2011)
97 98
99
100
101 102 103 104 105
106
107
108
109
110
111
112
Collect. Czech. Chem. Commun., 76, 1967–1978. Kim, Y.M. and Yu, S. (2003) J. Am. Chem. Soc., 125, 1696–1697. Diaconescu, P.L., Gallon, B.J., Kojima, R.W., and Kaner, R.B. (2007) Angew. Chem., 119, 7389–7392; Angew. Chem., Int. Ed., 46, 7251–7254 (2007). Likhar, P.R., Roy, M., Roy, S., Subhas, M.S., Kantam, M.L., and Sreedhara, B. (2008) Adv. Synth. Catal., 350, 1968–1974. Islam, R.U., Witcomb, M.J., van der Lingen, E., Scurrell, M.S., Van Otterlo, W., and Mallick, K. (2011) J. Organomet. Chem., 696, 2206–2210. Amaya, T., Saio, D., and Hirao, T. (2008) Macromol. Symp., 270, 88–94. Amaya, T., Saio, D., and Hirao, T. (2007) Tetrahedron Lett., 48, 2729–2732. Hirao, T. and Amaya, T. (2011) Synlett, 435–448. Li, P., Wang, L., Pinhua, L., and Li, H. (2005) Tetrahedron, 61, 8633–8640. Evangelisti, C., Panziera, N., D’Alessio, A., Bertinetti, L., Botavina, M., and Vitulli, G. (2010) J. Catal., 272, 246–252. Klabunde, K.J. (1994) Free Atoms, Clusters and Nanoscale Particles, Academic Press, San Diego, CA. Iyer, K.S., Stewart, S.G., Zou, J., and Raston, C.L. (2011) New J. Chem., 35, 854–860. Fujii, S., Matsuzawa, S., Nakamura, Y., Ohtaka, A., and Teratani, T. (2010) Langmuir, 26, 6230–6239. Fujii, S., Ohtaka, A., Kono, Y., Teratani, T., Matsuzawa, S., Nakamura, Y., and Nomura, R. (2011) Catal. Lett., 141, 1097–1103. Fujii, S., Matsuzawa, S., Hamasaki, H., and Nakamura, Y. (2012) Langmuir, 28, 2436–2447. (a) Kirschning, A., Solodenko, W., Mennecke, K., Vogt, C., and Gruhl, S. (2006) Synthesis, 1873–1881; (b) Yamada, Y.M.A., Takeda, K., Takahashi, H., and Ikegami, S. (2003) J. Org. Chem., 68, 7733–7741. (a) Kunz, U., Kirschning, A., Altwicker, C., and Solodenko, W. (2003) J. Chromatogr. A, 1006, 241–249; (b) Kunz, U., Sch€onfeld, H., Solodenko, W., Jas, G.,
113
114 115
116
117
118
119
120 121
122 123
124 125
126
and Kirschning, A. (2005) Ind. Eng. Chem. Res., 44, 8458–8467; (c) Kunz, U., Kirschning, A., Wen, H.-L., Solodenko, W., Cecillia, R., Kappe, C.O., and Turek, T. (2005) Catal. Today, 105, 318–324. Kirschning, A., Mennecke, K., and Solodenko, W. (2008) Synthesis, 1589–1599. Kirschning, A. and Mennecke, K. (2008) Synthesis, 3267–3272. Jiang, X., Wei, G., Zhang, X., Zhang, W., Zheng, P., Wen, F., and Shi, L. (2007) J. Mol. Catal. A: Chem., 277, 102–106. Evangelisti, C., Panziera, N., Perticib, P., Vitulli, G., Salvadori, P., Battocchio, C., and Polzonetti, G. (2009) J. Catal., 262, 287–293. (a) Price, K.E., Mason, B.P., Bogdan, A.R., Broadwater, S.J., Steinbacher, J.L., and McQuade, D.T. (2006) J. Am. Chem. Soc., 128, 10376–10377; (b) Mu, X.-D., Meng, J.-Q., Li, Z.-C., and Kou, Y. (2005) J. Am. Chem. Soc., 127, 9694–9695; (c) Yan, N., Zhao, C., Luo, C., Dyson, P.J., Liu, H., and Kou, Y. (2006) J. Am. Chem. Soc., 128, 8714–8715. (a) Lee, Y.-S., Kim, J.-H., Kim, J.-W., and Shokouhimehr, M. (2005) J. Org. Chem., 70, 6714–6720; (b) Lee, Y.-S., Kim, J.-H., and Shokouhimehr, M. (2006) Synlett, 618–620. Sch€onfelder, D., Nuyken, O., and Weberskirch, R. (2005) J. Organomet. Chem., 690, 4648–4655. Wang, Y., Zhang, Y., Wang, L., and Xie, C. (2005) Synlett, 1861–1864. Lee, Y.-S., Kim, J.-H., Kim, J.-W., and Lee, D.-H. (2006) Tetrahedron Lett., 47, 4745– 4748. Kang, T., Feng, Q., and Luo, M. (2005) Synlett, 2305–2308. Luo, M., Zhang, S., Zeng, X., Wei, Z., Zhao, D., Kang, T., Zhang, W., and Yan, M. (2006) Synlett, 1891–1894. Luo, M., Qin, Y., and Wei, W. (2007) Synlett, 2410–2414. Luis, S.V., Karbass, N., Sans, V., GarciaVerdugo, E., and Burguete, M.I. (2006) Chem. Commun., 3095–3097. Karbass, N., Sans, V., Garcia-Verdugo, E., Burguete, M.I., Altava, B., Puzary, A., and Luis, S.V. (2006) Tetrahedron Lett., 47, 2311–2314.
References 127 Lee, Y.-S., Kim, J.-H., Lee, D.-H., and Jun,
128
129
130
131
132 133 134
135
136
137
138
139
B.-H. (2007) Tetrahedron Lett., 48, 7079–7084. Yang, X., Fei, Z., Zhao, D., Ang, W.H., Li, Y., and Dyson, P.J. (2008) Inorg. Chem., 47, 3292–3297. Guijt, R.M., Gomann, A., Deverell, J.A., Munting, K.F., Jones, R.C., Rodemann, T., Canty, A.J., and Smith, J.A. (2009) Tetrahedron, 65, 1450–1454. Han, B., Liu, G., Hou, M., Song, J., Jiang, T., Fan, H., and Zhang, Z. (2010) Green Chem., 12, 65–69. Qureshi, Z.S., Deshmukh, K.M., Tambade, P.J., and Bhanage, B.M. (2011) Synthesis, 243–250. Wang, Y., Liu, J., and Xia, C. (2011) Tetrahedron Lett., 52, 1587–1591. Wang, J., Song, G., and Peng, Y. (2011) Tetrahedron Lett., 52, 1477–1480. (a) Namboodiri, V.V. and Varma, R.S. (2001) Green Chem., 3, 146–148; (b) Kwong, F.Y., Klapars, A., and Buchwald, S.L. (2002) Org. Lett., 4, 581–584; (c) Cassez, A., Ponchel, A., Dr. Hapiot, F., and Monflier, E. (2006) Org. Lett., 8, 4823–4826; (d) Han, W., Liu, C., and Jin, Z.L. (2007) Org. Lett., 9, 4005–4007; (e) Cai, Y., Lu, Y., Liu, Y., He, M., and Wan, Q. (2008) Catal. Commun., 9, 1209–1213; (f) Cai, Y. and Liu, Y. (2009) Catal. Commun., 10, 1390–1393; (g) Yan, N., Xue, Y., Fei, Z., Li, Y., Kou, Y., and Dyson, P. (2009) Organometallics, 28, 937–939. Bergbreiter, D.E., Su, H.-L., Koizumi, H., and Tian, J. (2011) J. Organomet. Chem., 696, 1272–1279. Huang, J., Yu, Y., Hu, T., Chen, X., Xu, K., and Zhang, J. (2011) Chem. Commun., 47, 3592–3594. (a) Choi, M., Lee, D.-H., Na, K., Yu, B.-W., and Ryoo, R. (2009) Angew. Chem., 121, 3727–3730; Angew. Chem., Int. Ed., 48, 3673–3676 (2009); (b) Anderson, K.W., Buchwald, S.L., and Billingsley, K.L. (2006) Angew. Chem., 118, 3564–3568; Angew. Chem., Int. Ed., 45, 3484–3488 (2006). Rothenberg, G., Turkenburg, D.H., Antipov, A.A., Thathagar, M.B., Sukhorukov, G.B., and Eiser, E. (2005) Phys. Chem. Chem. Phys., 7, 2237–2240. Li, J.-H., Hu, X.-C., and Xie, Y.-X. (2006) Tetrahedron Lett., 47, 9239–9243.
140 Basu, B., Das, S., Das, P., Mandal, B.,
141
142
143 144 145 146 147
148
149
150
151
152 153
154
155
156
Banerjee, D., and Almqvist, F. (2009) Synthesis, 1137–1146. Ohtaka, A., Tamaki, Y., Igawa, Y., Egami, K., Shimomura, O., and Nomura, R. (2010) Tetrahedron, 66, 5642–5646. Williams, K.A., Boydston, A.J., and Bielawski, C.W. (2007) Chem. Soc. Rev., 36, 729–744. Liu, Q.-P., Chen, Y.-C., Wu, Y., Zhu, J., and Deng, J.-G. (2006) Synlett, 1503–1506. Karimi, B. and Fadavi Akhavan, P. (2009) Chem. Commun., 3750–3752. Karimi, B. and Fadavi Akhavan, P. (2011) Inorg. Chem., 50, 6063–6072. Karimi, B. and Fadavi Akhavan, P. (2011) Chem. Commun., 47, 7686–7688. Cen, W., Li, R., Huang, J., Wu, Y., Ding, L.-S., Shen, H., and Chen, Y.-C. (2006) Synthesis, 3058–3062. Wang, X., He, L., He, Y., Zhang, J., and Su, C.-Y. (2009) Inorg. Chim. Acta, 362, 3513–3518. Huang, J., He, L., Zhang, J., Chen, L., and Su, C.-Y. (2010) J. Mol. Catal. A: Chem., 317, 97–103. Liao, Y., He, L., Huang, J., Zhang, J., Zhuang, L., Shen, H., and Su, C.-Y. (2010) Appl. Mater. Interfaces, 2, 2333–2338. (a) Zhang, F., Meng, Y., Gu, D., Yan, Y., Yu, C., Tu, B., and Zhao, D. (2005) J. Am. Chem. Soc., 127, 13508–13509; (b) Wu, H., Wu, P., Yao, C., Li, H., and Liu, Y. (2009) Catal. Commun., 10, 1099–1102. Ogasawara, S. and Kato, S. (2010) J. Am. Chem. Soc., 132, 4608–4613. (a) Bhaumik, A., Modak, A., Mondal, J., and Sasidharan, M. (2011) Green Chem., 13, 1317–1331; (b) Bhaumik, A., Modak, A., and Mondal, J. (2011) J. Mol. Catal. A; Chem., 350, 40–48. (a) Bandini, M., Albano, V.G., Moorlag, C., Piccinelli, F., Pietrangelo, A., Tommasi, S., Umani-Ronchi, A., and Wolf, M.O. (2007) Organometallics, 26, 4373–4375; (b) Fujihara, H., Umeda, R., Awaji, H., and Nakahodo, T. (2008) J. Am. Chem. Soc., 130, 3240–3241. Santra, S., Dhara, K., Ranjan, P., Bera, P., Dash, J., and Mandal, S.K. (2011) Green Chem., 13, 3238–3247. Vickerstaffe, E., Villard, A.-L., Ladlow, M., and Ley, S.V. (2007) Synlett, 1251–1254.
j199
200
j 5 Coupling Reactions Induced by Polymer-Supported Catalysts 157 Lan, P., Berta, D., Porco, J.A., South, M.S.,
158
159
160
161 162
163
and Parlow, J.J. (2003) J. Org. Chem., 68, 9678–9686. Chergui, S.M., Ledebt, A., Mammeri, F., Herbst, F., Carbonnier, B., Romdhane, H.B., Delamar, M., and Chehimi, M.M. (2010) Langmuir, 26, 16115–16121. Islam, R.U., Witcomb, M.J., Scurrell, M.S., Van Otterlo, W., and Mallick, K. (2010) Catal. Commun., 12, 116–121. Islam, R.U., Witcomb, M.J., Scurrell, M.S., Van Otterlo, W., van der Lingen, E., and Mallick, K. (2011) Catal. Sci. Technol., 1, 308–315. Oki, A. and Neelgund, G.M. (2011) Appl. Catal. A: Gen., 399, 154–160. Metin, O., Durap, F., Aydemir, M., and Ozkara, S. (2011) J. Mol. Catal. A: Chem., 337, 39–44. (a) Arnold, U., Artner, J., Bautz, H., Fan, F., Habicht, W., Walter, O., and D€oring, M. (2008) J. Catal., 255, 180–189; (b) Mallick, K., Islam, R.U., Witcomb, M.J., Scurrell, M.S., van Otterlo, W., and
164 165 166
167 168
169
170
van der Lingen, E. (2011) Synth. Commun., 41, 3561–3572. Li, Y., Li, Z., Li, F., Wang, Q., and Tao, F. (2005) Tetrahedron Lett., 46, 6159–6162. Zheng, P. and Zhang, W. (2007) J. Catal., 250, 324–330. Beletskaya, I.P., Khokhlov, A.R., Tarasenko, E.A., and Tyurin, V.S. (2007) J. Organomet. Chem., 692, 4402–4406. Nandi, A.K., Samanta, S., and Layek, R.K. (2011) React. Funct. Polym., 71, 1045–1054. KoSc , F., Michalek, F., Rumi, L., Bannwarth, W., and Haag, R. (2005) Synthesis, 3362–3372. (a) Kobayashi, S., Oyamada, H., Akiyama, R., Hagio, H., and Naito, T. (2006) Chem. Commun., 4297–4299; (b) Borkowski, T., Zawartka, W., Pospiech, P., Mizerska, U., Trzeciak, A.M., Cypryk, M., and Tylus, W. (2011) J. Catal., 282, 270–277. (a) He, H.S., Zhang, C., Ng, C.K.-W., and Toy, P.H. (2005) Tetrahedron, 61, 12053– 12057; (b) Lau, K.C.W. and Chiu, P. (2007) Tetrahedron Lett., 48, 1813–1816.
