Communication Cite This: J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
pubs.acs.org/JACS
Unprecedented Reaction Mode of Phosphorus in Phosphinidene Rare-Earth Complexes: A Joint Experimental−Theoretical Study Haiwen Tian,† Jianquan Hong,† Kai Wang,† Iker del Rosal,§ Laurent Maron,*,§ Xigeng Zhou,*,†,‡ and Lixin Zhang*,† †
Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, People’s Republic of China ‡ State Key Laboratory of Organometallic Chemistry, Shanghai 200032, People’s Republic of China § LPCNO, CNRS, and INSA, Université Paul Sabatier, 135 Avenue de Rangueil, Toulouse 31077, France S Supporting Information *
Scheme 1. Reaction of 1a with Phenylacetylene
ABSTRACT: Reactions of trinuclear rare-earth metal complexes bearing functionalized phosphinidene ligand [L3Ln3(μ2-Me)2(μ3-Me)(μ3-η1:η2:η2-PC6H4-o)] (L = [PhC(NC6H4iPr2-2,6)2]−, Ln = Y (1a), Lu (1b)) with phenylacetylene, CO2, diisopropyl carbodiimide, isocyanide, or PhSSPh lead to the formation of a series of phosphorus-containing products. The reaction of 1 with CS2 yields two novel P-methyl-phosphindole-2,3-dithiolate dianion complexes, revealing an unusual tandem desulfurization/coupling/cyclization reaction mode of CS2. A possible reaction pathway was determined by density functional theory calculations. This emphasizes the key role of the reduction power of the formal P2− part of the phosphinidene in the C−S bond cleavage.
bonding modes of the phosphinidene ligands to rare-earth metals could lead to specific changes in reactivity.4b,j Recently, we synthesized [L3 Ln3 (μ 2-Me) 2 (μ3 -Me)(μ3 η1:η2:η2-PC6H4-o)] (Ln = Y(1a), Lu(1b)) by heating [LLn(μ2Me)]3(μ3-Me)(μ3-PPh) in toluene.4b The reactivity of complexes 1 with several unsaturated molecules, such as CO2, CS2, i PrNCNiPr, ArNC, and PhCCH, was investigated with special attention to the effect of the coordination mode and to the presence of the chelating aryl anion. In this Communication, a quite unique reactivity of the trinuclear rare-earth metal μ2bridged phosphinidene complexes is reported together with a mechanistic study at the DFT level on the CS2 activation reaction. Treatment of 1a with phenylacetylene gives only the μ3methyl-substituted complex 2a (Scheme 1), which significantly differs from phosphirene or phosphiran complexes obtained in reactions of transition metal analogues with alkynes.5 Complex 2a is isolated as a yellow crystalline solid in 92% yield. The 31P NMR spectrum of 2a shows a triplet of peaks at δ = 269.27 ppm, which is similar to the starting material, indicating that the phosphinidene group remained untouched and the P atom is still coordinated to two Y atoms. The molecular structure of 2a is further confirmed by X-ray crystal diffraction analysis (see Supporting Information (SI), Figure S26). Furthermore, monitoring the reaction by 1H NMR shows that the newly formed product 2a did not react with an excess of phenylacetylene at room temperature.
M
etal-promoted oxidative coupling between anionic ligands and reductive cleavage of chemical bonds have proven to crucial in organic synthesis. However, most rare-earth metals have no redox properties, reducing their use in bond formation and cleavage. Since the discovery of the first transition metal phosphinidene complexes in 1975,1 numerous studies have focused on the development of new phosphinidene complexes and their reactivity.2 Although phosphinidene (M = P) complexes are quite common in transition metal chemistry,3 analogous rare-earth complexes remain scarce due to their lower stability because of the orbital energy mismatch between the hard rare-earth metal (Sc, Y, and lanthanide metal) ions and the soft phosphorus atom.4 It is therefore a challenge to develop suitable synthetic strategies to access these complexes. To date, only very few examples of the reactivity of the binuclear rare-earth metal phosphinidene complexes have been reported.4c−j Chen’s and Kiplinger’s groups showed that these complexes can deliver the phosphinidene unit to ketones,4c,d whereas Mindiola’s group found that its Li-ate complex is active and can deliver the phosphinidene unit not only to ketones but also to phosphorus dichlorides and metal chlorides.4e In 2013, Chen’s group developed a four-coordinate bis-scandium-bridged phosphinidene complex that can initiate the homologation of CO.4g Recently, our group reported the synthesis and reactivity of a trinuclear rare-earth metal phosphinidene complex with a μ3-PPh bridge.4b All these results indicate that the variation of the © XXXX American Chemical Society
Received: October 18, 2017 Published: December 22, 2017 A
DOI: 10.1021/jacs.7b11032 J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
Communication
Journal of the American Chemical Society Scheme 2. Reactions of 1a with CO2, Carbodiimide, and ArNC
Scheme 3. Reaction of 1a with PhSSPh
The metal-mediated activation of heteroallenes is an area of growing interest.11,12 Apart from CO2, CS2 is also an important carbon source. CS2 is usually used as a model for CO2 and carbonyl sulfide (COS) because it is more reactive, often displays similar binding modes as the two other heteroallenes, and is easily handled as a liquid.13 Up to now, various binding modes of CS2 to one or more metal centers have been identified.14 Despite tremendous advances in insertions of CS2 into various metal− ligand bonds and CS2 as a source of thiocarbonyl,15 examples of fragmentation/recombination reactions of CS2 are rare.16 Unlike transition-metal and other rare-earth metal-bridged phosphinidene complexes,4b,g,j,17 the treatment of complexes 1 with 2 equiv of CS2 in toluene at room temperature affords the unusual tandem desulfurization/coupling/cyclization products 9a and 9b in excellent yields (Scheme 4). This one-pot sequence of
When compound 1a reacts with an excess of CO2, the insertion of CO2 molecule occurs into all Y−C and Y−P bonds yielding complex 3a (Scheme 2).6 The 31P NMR spectrum of 3a shows one doublet at δ = −14.68 ppm (J = 16.0 Hz), probably due to the weak coupling between the P atom and the C(Ar) atom.4g,7 In the same way, 1 equiv of diisopropylcarbodiimide (iPrNCNiPr) reacts with 1a to give L2Y2(μ2-Me)[(Me2CHN)2CPC6H4-o)] (4a) in 62% yield. In the 31P NMR spectrum of 4a, an irregular double peak is observed at δ = −1.17 (d, JYP = 22.7 Hz) due to the coupling between 31P and 89Y. The structures of complexes 3a and 4a are confirmed by X-ray diffraction (SI, Figures S27 and S28). In contrast to 1a, 1b is unreactive to PhCCH and iPrN CNiPr. Indeed, the 31P NMR monitoring indicates that only a small amount of new products was observed even heating at 120 °C for 10 days. This might be attributed to the increased steric bulk caused by the lanthanide contraction effect, which would prevent PhCCH and iPrNCNiPr from approaching the small Lu centers, as seen in other analogues.8 Complex 1a also reacts with 2-isocyano-1,3-dimethylbenzene to form the trinuclear complex 5a by the 1,1-insertion of one ArNC into the Y−P bond (Scheme 2). The bond parameters indicate that the resulting PCN moiety acts as both a bridging and side-on chelating group, in which the negative charge is delocalized over the PCN unit (SI, Figure S29). The long Y−P bond length (3.189 Å)4,9 and a singlet, without splitting due to coupling between 31P and 89Y, in the 31P NMR are in line with only weak interaction between the two atoms.10 The reaction of complex 1a with 2 equiv of PhSSPh yields complexes 6a and 7a. The formation of 6a involves a rare coupling of the phosphinidene dianion with one methyl ligand concomitant with ligand redistribution. The 31P and 1H NMR monitoring reveal that the chemoselectivity of the reaction of 1a with PhSSPh is independent of the amount of PhSSPh used. When 1 equiv of PhSSPh is used, only formation of 6a and 7a as well as some starting material 1a are observed. 6a and 7a do not further react even with an excess of PhSSPh. Complexes 6a and 7a were characterized by NMR spectroscopies, elemental analysis, and X-ray crystallography. 6a is a trinuclear structure with two μ2-SPh and two −P(Me)C6H42− dianion ligands, while 7a is a dinuclear structure containing four μ2-SPh ligands (Scheme 3). 31P NMR spectrum of 6a displays two singlets at δ = −36.60 and −47.98 ppm, which may be attributed to the different coordination environment of two P atoms. Recrystallizing 7a in THF gave LY(SPh)2(THF)2 (8a). However, with complex 1b, no reaction takes place under the same conditions.
Scheme 4. Reaction of Complexes 1 with CS2
transformations leading to the formations of two C−P bonds and one C−C bond, provides a straightforward method for the construction of 1-methyl-1H-phosphindole-2,3-dithiol rings. Reacting 10 equiv of CS2 for 3.5 days does not lead to any further reaction. The 31P NMR spectra of 9a and 9b display a singlet at δ = 3.2 and 5.2 ppm, respectively. The PMe unit shows a sharp singlet at 1.87 ppm for 9a and 1.90 ppm for 9b in 1H NMR spectrum in C6D6, respectively. As shown in Figure 1, 9a and 9b are isostructural, and have a trimetallic core with one bridging Pmethyl-phosphindole-2,3-dithiolate dianion ligand, which is coordinated to three metal ions in a μ-κ2:κ2-bonding mode through two sulfur atoms (Ln−S bond lengths ranging from 2.758(1) to 2.829(1) Å for yttrium and from 2.690(1) to 2.778(1) Å for lutetium). The 31P NMR monitoring results reveal the presence of two Pcontaining intermediates when the reaction of 1 with CS2 is carried out at −25 °C. Unfortunately, attempts to isolate these intermediates have not been successful. Therefore, possible reaction mechanisms were computed at the DFT level (B3PW91) in the yttrium case (Figure 2). The incoming CS2 undergoes an outer-sphere insertion onto the Y−P bond with an accessible enthalpy of activation (20.7 kcal/mol). This is different from the reactivity found for the phosphine complex4b where the CS2 is reacting in the inner sphere (this is computed to be higher in energy in this case, see SI). This yields product B B
DOI: 10.1021/jacs.7b11032 J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
Communication
Journal of the American Chemical Society
with the C−C bond of the μ 3 -phenyl of the former phosphinidene ligand (activation barrier of 11.2 kcal/mol). This cycloaddition leads to a bicyclic intermediate with the sixmember ring sharing a C−C bond with a phosphorus containing four-member ring (complex D). This intermediate is computed to be rather stable with respect to the entrance channel (−32.9 kcal/mol). However, it can react with another incoming CS2 molecule, in the same way as the first CS2 molecule reacted. The outer-sphere P−C coupling occurs with an activation barrier of 14.8 kcal/mol which is similar to the first insertion. This leads again to the formation of a formal P(IV) compound (complex F) with a pendant CS2 molecule, that is in equilibrium with complex D. The formal CS double bond of the pendant CS2 of F can undergo another [2+2] cycloaddition with the former PC double bond of the 4-member ring (barrier of 27.2 kcal/mol). This barrier is higher than the previous cycloaddition mainly because a C−S bond breaking is to occur at the same time to allow the addition; this forms an almost linear Y−S−Y moiety. This yields a rather unusual and unstable tricyclic intermediate with two 4-member rings sharing a P−C bond (complex G). The P− C−S−C four-member ring is disrupted (barrier of 31.9 kcal/ mol) to allow the thermodynamically favored complex H (−68.0 kcal/mol), yielding after two easy methyl migrations (barriers of 9.1 and 6.3 kcal/mol) the formation of the highly stable complex 9a. In summary, it is demonstrated that trinuclear Lu and Y complexes bearing the μ2-bridged phoshinidene ligand have a versatile reactivity toward unsaturated small molecules such as phenylacetylene, carbodiimide, carbon dioxide, isocyanide, PhSSPh and CS2. Depending on the nature of substrates, a series of derivatives involving ligand substitution, addition or oxidative coupling reactions are prepared. Reaction with CS2
Figure 1. Molecule structures of 9. Isopropyl groups on benzene rings and hydrogen atoms are omitted for clarity. Selected bond lengths (Å): 9a (Ln = Y): Y1−S1 2.758(2), Y−S2 (av.) 2.669(9), Y−S3(av.) 2.772(2), Y−S4(av.) 2.790(7), C2−S3 1.786(9), C3−P1 1.800(1), C4−C5 1.348(1), C4−S1 1.751(9), C4−P1 1.841(9), C5−C6 1.512(1), C5−S4 1.755(8). 9b (Ln = Lu): Lu1−S1 2.691(2), Lu−S2 (av.) 2.625(2), Lu−S3(av.) 2.730(2), Lu−S4(av.) 2.708(2), C2−S3 1.772(8), C3−P1 1.849(1), C4−C5 1.367(1), C4−S1 1.719(9), C4− P1 1.842(8), C5−C6 1.480(1), C5−S4 1.772(8).
where one of the two former Y−P bonds remains and the second one was replaced by two Y−S interactions. The latter activates a C−S bond that is broken with a barrier of 23.8 kcal/mol to allow the migration of a sulfur atom to the phosphorus (complex C). The formed product is formally a P(IV) one with a formed PC double bond. This bond easily achieves a [2+2] cycloaddition
Figure 2. Computed (DFT) enthalpy pathway at room temperature. C
DOI: 10.1021/jacs.7b11032 J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
Communication
Journal of the American Chemical Society
B. F.; Scott, J.; Andino, J. G.; Gao, X.; Mindiola, D. J.; et al. J. Am. Chem. Soc. 2010, 132, 3691. (f) Cui, P.; Chen, Y.; Borzov, M. V. Dalton Trans. 2010, 39, 6886. (g) Lv, Y.; Kefalidis, C. E.; Zhou, J.; Chen, Y.; et al. J. Am. Chem. Soc. 2013, 135, 14784. (h) Wang, W.; Lv, Y.; Gou, X.; Chen, Y. Chin. J. Chem. 2014, 32, 752. (i) O, W. W. N.; Kang, X.; Luo, Y.; Hou, Z. Organometallics 2014, 33, 1030. (j) Zhou, J.; Li, T.; Maron, L.; Chen, Y.; Leng, X. Organometallics 2015, 34, 470. (5) (a) Marinetti, A.; Mathey, F.; Fischer, J.; Mitschler, A. J. Am. Chem. Soc. 1982, 104, 4484. (b) Marinetti, A.; Mathey, F. Organometallics 1984, 3, 456. (c) Cowley, A. H. Acc. Chem. Res. 1997, 30, 445. (d) Alvarez, M. A.; Amor, I.; Ruiz, M. A.; et al. Inorg. Chem. 2007, 46, 6230. (e) Alvarez, M. A.; Amor, I.; García, M. E.; Ruiz, M. A.; et al. Organometallics 2012, 31, 2749. (f) Alvarez, M. A.; García, M. E.; Gonzalez, R.; Ruiz, M. A. Organometallics 2013, 32, 4601. (6) Hong, J.; Zhang, L.; Wang, K.; Zhang, Y.; Weng, L.; Zhou, X. Chem. - Eur. J. 2013, 19, 7865. (7) (a) Westerhausen, M.; Hartmann, M.; Schwarz, W. Inorg. Chim. Acta 1998, 269, 91. (b) Behrle, A.; Castro, L.; Maron, L.; Walensky, J. R. J. Am. Chem. Soc. 2015, 137, 14846. (8) Hong, J.; Zhang, L.; Yu, X.; Li, M.; Zhang, Z.; Zheng, P.; Nishiura, M.; Hou, Z.; Zhou, X. Chem. - Eur. J. 2011, 17, 2130. (9) Hitchcock, P. B.; Lappert, M. F.; MacKinnon, l. A. J. Chem. Soc., Chem. Commun. 1988, 1557. (10) (a) Fryzuk, M. D.; Haddad, T. S.; Rettig, S. J. Organometallics 1991, 10, 2026. (b) Krieck, S.; Gorls, H.; Westerhausen, M. Inorg. Chem. Commun. 2009, 12, 409. (11) (a) Mikkelsen, M.; Jørgensen, M.; Krebs, F. C. Energy Environ. Sci. 2010, 3, 43. (b) Riduan, S. N.; Zhang, Y. Dalton Trans. 2010, 39, 3347. (c) Tolman, W. B. Activation of small molecules; Wiley-VCH: Weinheim, Germany, 2006. (12) (a) Gibson, D. H. Chem. Rev. 1996, 96, 2063. (b) Yin, X.; Moss, J. R. Coord. Chem. Rev. 1999, 181, 27. (c) Benson, E. E.; Kubiak, C. P.; Sathrum, A. J.; Smieja, J. M. Chem. Soc. Rev. 2009, 38, 89. (d) Omae, I. Coord. Chem. Rev. 2012, 256, 1384. (13) (a) Mayer, R.; Gewald, K. Angew. Chem., Int. Ed. Engl. 1967, 6, 294. (b) Butler, I. S.; Fenster, A. E. J. Organomet. Chem. 1974, 66, 161. (c) Butler, R. N.; Wallace, L. M. J. Chem. Soc., Perkin Trans. 1 2000, 4335. (d) Mathur, P.; Tauqeer, M.; Lahiri, G. K.; et al. J. Cluster Sci. 2015, 26, 157. (e) Ang, M. T. C.; Phan, L.; Jessop, P. G.; et al. Eur. J. Org. Chem. 2015, 2015, 7334. (14) (a) Baird, M. C.; Wilkinson, G. J. Chem. Soc. A 1967, 865. (b) Baird, M. C.; Wilkinson, G. Chem. Commun. (London) 1966, 514. (c) Li, L.; Song, L.-C.; Wang, M.-M.; Song, H.-B.; Li, Q.-L. Organometallics 2011, 30, 4899. (d) Haack, P.; Limberg, C.; Tietz, T.; Metzinger, R. Chem. Commun. 2011, 47, 6374. (e) Mougel, V.; Maron, L.; Kefalidis, C. E.; Mazzanti, M.; et al. Angew. Chem., Int. Ed. 2012, 51, 12280. (f) Lam, O. P.; Heinemann, F. W.; Meyer, K. Angew. Chem., Int. Ed. 2011, 50, 5965. (15) (a) Manning, A. R.; Palmer, A. J.; McAdam, J.; Robinson, B. H.; Simpson, J. Chem. Commun. 1998, 1577. (b) Hong, J.; Li, Z.; Chen, Z.; Weng, L.; Zhou, X.; Zhang, L. Dalton Trans. 2016, 45, 6641. (c) Rungthanaphatsophon, P.; Barnes, C. L.; Walensky, J. R. Dalton Trans. 2016, 45, 14265. (d) Young, R. D.; Cavigliasso, G. E.; Stranger, R.; Hill, A. F. Angew. Chem., Int. Ed. 2013, 52, 3699. (e) Ghiassi, K. B.; Walters, D. T.; Aristov, M. M.; Olmstead, M. M.; Balch, A. L.; et al. Inorg. Chem. 2015, 54, 4565. (16) (a) Ballmann, J.; Yeo, A.; MacKay, B. A.; Patrick, B. O.; Fryzuk, M. D.; van Rijt, S. Chem. Commun. 2009, 46, 8794. (b) Jiang, X.-F.; Huang, H.; Chai, Y.-F.; Yu, S.-Y.; Lai, W.; Pan, Y.-J.; Delferro, M.; Marks, T. J.; Lohr, T. L. Nat. Chem. 2017, 9, 188. (17) (a) Leoni, P.; Chiaradonna, C.; Pasquali, M.; Marchetti, F. Inorg. Chem. 1999, 38, 253. (b) Albuerne, I. G.; Alvarez, M. A.; Amor, I.; García, M. E.; Ruiz, M. A.; García-Vivo, D. Inorg. Chem. 2016, 55, 10680.
leads to an unprecedented transformation of CS2, forming a cyclic 1-methyl-phosphindole-2,3-dithiolate dianion ligand through an unusual reaction mechanism mainly involving the phosphorus center. In particular, the reduction power of the formal P2− part of the phosphinidene ligand plays a crucial role in the CS bond cleavage of CS2. These results demonstrate that bonding and reactivity patterns of phosphinidene ligands in trinuclear rare-earth complexes can be tuned by introduction of a chelating anionic substituent.
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.7b11032. Crystallographic data, in CIF format, for 2a, 3a, 4a, 5a, 6a, 7a, 8a, 9a, and 9b (ZIP) Experimental, crystallographic, and computational details (PDF)
■
AUTHOR INFORMATION
Corresponding Authors
*
[email protected] *
[email protected] *
[email protected] ORCID
Laurent Maron: 0000-0003-2653-8557 Xigeng Zhou: 0000-0003-2948-9930 Lixin Zhang: 0000-0003-0423-0818 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (grant nos. 21672038, 21372047, and 21732007) and 973 program (2015CB856600). The authors acknowledge the HPCs CALcul en Midi-Pyrénées (CALMIPEOS grant 1415).
■
REFERENCES
(1) Huttner, G.; Mueller, H. D.; Frank, A.; Lorenz, H. Angew. Chem., Int. Ed. Engl. 1975, 14, 571. (2) Selected reviews on phosphinidene complexes: (a) Huttner, G.; Knoll, K. Angew. Chem., Int. Ed. Engl. 1987, 26, 743. (b) Lammertsma, K.; Vlaar, M. J. M. Eur. J. Org. Chem. 2002, 2002, 1127. (c) Lammertsma, K. Top. Curr. Chem. 2003, 229, 95. (d) Waterman, R. Dalton Trans. 2009, 18. (e) Aktas, H.; Slootweg, J. C.; Lammertsma, K. Angew. Chem., Int. Ed. 2010, 49, 2102. (f) Allen, D. W. Organophosphorus Chem. 2014, 43, 1. (g) García, M. E.; García-Vivó, D.; Ramos, A.; Ruiz, M. A. Coord. Chem. Rev. 2017, 330, 1. (3) Examples of transition metal phosphinidene complexes: (a) Cummins, C. C.; Schrock, R. R.; Davis, W. M. Angew. Chem., Int. Ed. Engl. 1993, 32, 756. (b) Bulo, R. E.; Trion, L.; Ehlers, A. W.; Lammertsma, K.; et al. Chem. - Eur. J. 2004, 10, 5332. (c) Adiraju, V. A. K.; Yousufuddin, M.; Rasika Dias, H. V. Dalton Trans. 2015, 44, 4449. (d) Alvarez, M. A.; García, M. E.; Ramos, A.; Ruiz, M. A.; Gonzalez, R. Organometallics 2010, 29, 1875. (e) Seidl, M.; Balazs, G.; Timoshkin, A. Y.; Scheer, M. Angew. Chem., Int. Ed. 2016, 55, 431. (4) Examples of rare-earth metal phosphinidene complexes: (a) Lv, Y.; Xu, X.; Chen, Y.; Leng, X.; Borzov, M. V. Angew. Chem., Int. Ed. 2011, 50, 11227. (b) Wang, K.; Luo, G.; Hong, J.; Zhou, X. G.; Weng, L.; Luo, Y.; Zhang, L. X. Angew. Chem., Int. Ed. 2014, 53, 1053. (c) Cui, P.; Chen, Y.; Xu, X.; Sun, J. Chem. Commun. 2008, 5547. (d) Masuda, J. D.; Jantunen, K. C.; Kiplinger, J. L.; et al. J. Am. Chem. Soc. 2008, 130, 2408. (e) Wicker, D
DOI: 10.1021/jacs.7b11032 J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
