Synthesis and properties of new Mo(II) complexes

Journal of Organometallic Chemistry 696 (2011) 2142e2152

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Synthesis and properties of new Mo(II) complexes with N-heterocyclic and ferrocenyl ligands Susana Quintal a,1, Serena Fedi b, Jacopo Barbetti b, Patrícia Pinto c, Vitor Félix d, Michael G.B. Drew e, Piero Zanello b, Maria José Calhorda a, * a

Departamento de Química e Bioquímica, CQB, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, Ed. C8, 1749-016 Lisboa, Portugal Dipartimento di Chimica dell’Università di Siena, Via A. De Gasperi 2, 53100 Siena, Italy c Instituto de Tecnologia Química e Biológica da Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal d Departamento de Química, CICECO and Secção Autónoma de Ciências da Saúde, Universidade de Aveiro, 3810-193 Aveiro, Portugal e Department of Chemistry, University of Reading, Whiteknights, Reading, RG6 6AD, UK b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 6 October 2010 Received in revised form 2 November 2010 Accepted 15 November 2010

New Mo(II) complexes with 2,20 -dipyridylamine (L1), [Mo(CH3CN)(h3-C3H5)(CO)2(L1)]OTf (C1a) and [{MoBr(h3-C3H5)(CO)2(L1)}2(4,40 -bipy)](PF6)2 (C1b), with {[bis(2-pyridyl)amino]carbonyl}ferrocene (L2), [MoBr(h3-C3H5)(CO)2(L2)] (C2), and with the new ligand N,N-bis(ferrocenecarbonyl)-2-aminopyridine (L3), [MoBr(h3-C3H5)(CO)2(L3)] (C3), were prepared and characterized by FTIR and 1H and 13C NMR spectroscopy. C1a, C1b, L3, and C2 were also structurally characterized by single crystal X-ray diffraction. The Mo(II) coordination sphere in all complexes features the facial arrangement of allyl and carbonyl ligands, with the axial isomer present in C1a and C2, and the equatorial in the binuclear C1b. In both C1a and C1b complexes, the L1 ligand is bonded to Mo(II) through the nitrogen atoms and the NH group is involved in hydrogen bonds. The X-ray single crystal structure of C2 shows that L2 is coordinated in a k2N,N-bidentate chelating fashion. Complex C3 was characterized as [MoBr(h3-C3H5)(CO)2(L3)] with L3 acting as a k2-N,O-bidentate ligand, based on the spectroscopic data, complemented by DFT calculations. The electrochemical behavior of the monoferrocenyl and diferrocenyl ligands L2 and L3 has been studied together with that of their Mo(II) complexes C2 and C3. As much as possible, the nature of the different redox changes has been confirmed by spectrophotometric measurements. The nature of the frontier orbitals, namely the localization of the HOMO in Mo for both in C2 and C3, was determined by DFT studies. ! 2010 Elsevier B.V. All rights reserved.

Keywords: Mo(II) complexes Ferrocenyl ligands Electrochemistry Spectroelectrochemistry X-ray crystal structures DFT calculations

1. Introduction Ferrocene derivatives have been widely studied and give rise to many applications in several fields, ranging from non-linear optical materials, electrochemical sensors, liquid crystals, catalysis and nanoparticles [1,2]. Ring functionalization can be easily achieved, affording new molecules whose properties can be tuned according to the required specifications. Amino acids and peptides have been introduced in order to bind biological targets [3]. Also, the cytotoxic activity displayed by the ferrocenium ion triggered the development of new ferrocenyl derivatives as anticancer agents [4]. Their

* Corresponding author. Tel.: þ351 217 500 196; fax: þ351 217 500 088. E-mail addresses: [email protected] (S. Quintal), [email protected] (V. Félix), [email protected] (P. Zanello), [email protected] (M.J. Calhorda). 1 Present address: Virginia Commonwealth University, Department of Chemistry, 1001 West Main Street, P.O. Box 842006, Richmond, VA 23284-2006, USA. 0022-328X/$ e see front matter ! 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2010.11.024

association to other molecules was also shown to enhance their activity [5]. Functionalized ferrocenes can be used as ligands in reactions with other metal fragments, opening a way into the synthesis of polymetallic species [6] with new structures and properties [7], such as in sensors [8], and even polymers [9]. In previous work we reported the coordination of ferrocenyl based nitrogen ligands, namely FcCO(NH2benzim), (FcCO)2(NHbenzim) [10], FcCO(im) and FcCO(benzim) [11] (benzim ¼ benzimidazole and im ¼ imidazole) to the Mo(II) fragment MoBr(h3-C3H5)(CO)2. The new bi- and tri- nuclear complexes thus obtained showed interesting redox properties, namely a switch in the nature of highest energy electron, which occupied a molybdenum level instead of an iron level. The association of Fe and Mo was also studied in order to improve cytotoxic activity relative to that of the isolated components [11]. In the present work, we explore structural alternatives of [MoBr(h3-C3H5)(CO)2(L-L)] and its cationic derivatives [Mo (h3C3H5)(CO)2(L-L)(NCMe)]þ, where L-L ¼ 2,20 -dipyridylamine ligand

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(L1), L2 ¼ {[bis(2-pyridyl)amino]carbonyl}ferrocene, and L3 ¼ N,Nbis(ferrocenecarbonyl)-2-aminopyridine (see Scheme 1). Besides the single crystal X-ray diffraction studies of L3 and three complexes, the electrochemical behavior of ligands L2 and L3, as well as their Mo(II) complexes C2 and C3 was investigated. We also performed DFT calculations to rationalize all the findings.

L L

Mo X

CO

X

CO

L

E

2. Results and discussion

L

L CO

L

2.1. Chemical studies. complexes of 2,20 -dipyridylamine (L1)

Mo

L

Y

CO

L

CO

L

L

OC

L

OC

Y

OC

Mo

OC

Mo X

CO

X

CO

L

Mo

Mo Y

CO OC

Mo

OC

L

L

L Mo Y

Y

E-E

A*

L

CO

E-A

CO

L CO

E*

A

L

The well known complex [Mo(h3-C3H5)Br(CO)2(NCMe)2] [12] reacts with L1 to afford a mononuclear complex [MoBr(h3-C3H5) (CO)2(L1)] (C1) [13], by substitution of the two nitrile ligands. This complex may undergo removal of the bromide, leading to the cationic complexes [Mo(CH3CN)(h3-C3H5)(CO)2(L1)]OTf (C1a) in the presence of CH3CN and TlOTf or [{Mo(h3-C3H5)(CO)2(L1)}2(4,40 bipy)](PF6)2 (C1b) in the presence of 4,40 -bipy and TlPF6. Crystals suitable for X-ray diffraction were obtained for both complexes (see below). For the mononuclear species, there are two low energy isomers, equatorial (E) and axial (A), as shown in Scheme 2. A third isomer is often observed in solution and can be assigned to the rotation of the allyl group (E*). The combination of the A and E isomers leads to three possibilities, E-E, E-A, and A-A (Scheme 2), as has been proposed earlier [14]. The crystal structure of C1a is built from an asymmetric unit composed of one [Mo(CH3CN)(h3-C3H5)(CO)2(L1)]þ cation, one CF3SO$ 3 (OTf) anion, and one CH3CN solvent molecule with half occupancy. The complex cation and the anion are hydrogen bonded through a NeH/O motif with N/O distance of 2.969(12) Å (H/O ¼ 2.15(5) Å) and an NeH/O angle of 168(5)% . A perspective view of this association is shown in Fig. 1. In the [Mo(CH3CN)(h3-C3H5)(CO)2(L1)]þ cation, the metal exhibits a pseudo-octahedral coordination environment with the allyl ligand and one nitrogen donor from the L1 chelating ligand occupying the axial positions. The remaining nitrogen donor of L1 together with two carbonyl ligands and one acetonitrile molecule positioned on the equatorial coordination plane complete the coordination sphere. This spatial disposition of the ligands in the molybdenum coordination sphere is consistent with the A isomer sketched in Scheme 2. Selected bond distances and angles are given in Table 1. The acetonitrile is linearly bonded to the metal center with MoeN distance of 2.238(7) Å and a MoeNeC angle of 171.9(6)% . It is interesting to notice that the equatorial isomer is the one found in the parent complex [MoBr(h3C3H5)(CO)2(L1)] (C1) [13]. Substitution of Br by NCMe leads to a change of isomer. The crystallization of binuclear complex C1b afforded a solid composed of ca. 50% powder and 50% of crystals. Several crystals were tested and all of them displayed poor defined and weak diffraction spots. However, the structure of C1b was unequivocally

CO

Mo

CO CO

Y Mo L

L

A-A

Scheme 2. Isomers of mono and binuclear complexes of Mo(h3-C3H5)(CO)2.

determined. The asymmetric unit is composed of one [{Mo anions, (h3-C3H5)(CO)2(L1)}2(4,40 -bipy)]2þ dication, two PF$ 6 and one water molecule with an occupancy factor of 0.5, leading to the molecular formula [{Mo(h3-C3H5)(CO)2(L1)}2(4,40 -bipy)] (PF6)2.0.5H2O. One PF$ 6 counter ion forms an NeH/F hydrogen bond to a {Mo(h3-C3H5)(CO)2(L1)}þ moiety with a N/F intermolecular distance of 3.14(2) Å (H/F ¼ 2.35 Å) and corresponding NeH/F angle of 152% . This structural feature is shown in Fig. 2 together with the overall structure of the binuclear cation. The second PF$ 6 counter ion is disordered over two octahedral positions, as described in the experimental section. As found for [Mo(CH3CN) (h3-C3H5)(CO)2(L1)]þ, each Mo(II) center of C1b displays a distorted pseudo-octahedral geometry, but with the centroid of the allyl ligand and the two nitrogen donors of L1 defining a triangular face of a fac octahedral coordination environment. Furthermore, it is also apparent from Fig. 2 that in both {Mo(h3-C3H5)(CO)2(L1)}þ entities, the allyl ligand is endo relative to the two equatorial carbonyl ligands, leading to formation of the E-E isomer. Indeed, the two {Mo(h3-C3H5)(CO)2(L1)}þ units are bridged by the nitrogen donors of the 4,40 -bipy ligand, which are precisely located in axial coordination positions, as drawn in Scheme 2. The two molybdenum centers are separated by a long distance of 11.716(7) Å consistent with the length of the 4,40 -bipy bridge. However, the two pyridine rings are almost planar with a dihedral angle of 2(1)% , which seems to indicate the existence of electronic communication between the two molybdenum centers through the 4,40 -bipy. A similar distance of 11.72(1) Å was found in the related [{Mo (h3C3H5)(CO)2(2,20 -bipy)}2(4,40 -bipy)]2þ complex [14], which displays 1' 1'

1'

c b

1'

d

O c d

c b

b

a

a

e

1'

d

N

1'

1'

C

N

1'

1'

Fe

1

N

c 1'

2 2

e d

Fe 1'

b

O

C 1

c 1'

a b

1'

1'

L1

2

a

Fe

e

N H

2

1

O

1

1

N N

2

N

C

2 d

e

a

e

N

1

1'

L2

L3

Scheme 1. 2,20 -dipyridylamine (L1), {[bis(2-pyridyl)amino]carbonyl}ferrocene (L2), and N,N-bis(ferrocenecarbonyl)-2-aminopyridine (L3) with the numbering scheme adopted.

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Fig. 1. View of [Mo(CH3CN)(h3-C3H5)(CO)2(L1)]OTf&0.5CH3CN (C1a) showing the labelling scheme adopted and the assembling of two ionic species assisted by a NeH/O hydrogen bond shown as a dotted line. A CH3CN solvent molecule with half occupancy is omitted.

a centrosymmetric crystallographic structure with the 4,40 -bipy bridging ligand planar. The MoeN distances to 4,40 -bipy of 2.294 (13) and 2.264(14) Å in C1b agree with the value of 2.29(1) Å found for that binuclear complex. The remaining distances and angles subtended at the molybdenum centers in C1b, also reported in Table 1, compare well with those found for C1a. In particular, the chelating NeMoeN angle for 2,20 -dipyridylamine in C1a is slightly Table 1 Selected bond lengths (Å) and angles (% ) for molybdenum complexes [Mo(CH3CN) (h3-C3H5)(CO)2(L1)]OTf&0.5CH3CN C1a and [{Mo(h3-C3H5)(CO)2(L1)}2(4,40 -bipy)]2þ C1b. C1a Bond lengths MoeC(100) MoeC(200) MoeN(100) Bond angles N(23)eMoeN(11) C(100)eMoeN(11) C(100)eMoeC(200) C(100)eMoeN(100) C(100)eMoeN(23) O(100)eC(100)eMo O(200)eC(200)eMo C1b Bond lengths Mo(1)eN(11) Mo(1)eN(51) Mo(1)eN(23) Mo(1)eC(100) Mo(1)eC(200) Mo(1)eallyl Bond angles N(11)eMo(1)eN(23) N(11)eMo(1)eN(51) N(23)eMo(1)eN(51) C(200)eMo(1)eC(100) C(100)eMo(1)eN(11) C(100)eMo(1)eN(23) C(100)eMo(1)eN(51) C(200)eMo(1)eN(51) C(200)eMo(1)eN(11) C(200)eMo(1)eN(23) O(100)eC(100)eMo(1) O(200)eC(200)eMo(1)

1.952(8) 1.965(6) 2.238(7)

MoeN(23) MoeN(11) Moeallyl

2.235(6) 2.295(4) 2.228(7)e 2.339(7)

77.7(2) 95.6(2) 77.5(3) 174.4(2) 91.4(3) 175.5(6) 175.5(8).

N(100)eMoeN(11) C(200)eMoeN(11) N(100)eMoeN(23) C(200)eMoeN(100) C(200)eMoeN(23) C(101)eN(100)eMo

83.5(2) 162.9(2) 83.0(2) 101.8(3) 86.7(2) 171.9(6)

2.214(14) 2.294(13) 2.280(16) 1.95(2) 1.851(18) 2.234(17)e 2.414(16)

Mo(2)eN(61) Mo(2)eN(43) Mo(2)eN(31) Mo(2)eC(300) Mo(2)eC(400) Mo(2)-allyl

2.264(14) 2.154(10) 2.301(17) 2.00(2) 1.881(19) 2.241(16)e 2.37(2)

84.2(6) 83.0(5) 84.9(5) 81.7(8) 98.8(6) 169.7(7) 85.7(6) 85.2(7) 168.1(7) 93.3(8) 172.7(15) 173.7(18)

N(43)eMo(1)eN(31) N(61)eMo(1)eN(31) N(43)eMo(1)eN(61) C(400)eMo(2)eC(300) C(300)eMo(2)eN(31) C(300)eMo(2)eN(43) C(400)eMo(2)eN(31) C(300)eMo(2)eN(61) C(400)eMo(2)eN(43) C(400)eMo(2)eN(61) O(300)eC(300)eMo(2) O(400)eC(400)eMo(2)

81.7(8) 85.6(5) 82.8(5) 81.1(8) 173.5(7) 97.8(7) 98.2(7) 87.8(7) 169.6(7) 86.9(7) 174(2) 173.9(18)

Fig. 2. Molecular structure of [{Mo(h3-C3H5)(CO)2(L1)}2(4,40 -bipy)]2þ (C1b) hydrogen bonded to one PF$ 6 counter ion.

more acute by 6% than that found in C1b. Furthermore, in C1a the 2,20 -dipyridylamine is twisted around the central NeH bond with a dihedral angle between the two pyridine rings of 47.4(3)% , while in the binuclear complex, the 2,20 -dipyridylamine ligands display less pronounced twisting, with dihedral angles of only 31.3(8) and 23.3(9)% . This is probably due to a steric effect derived from the presence of the 4,40 -bipy bridge in axial positions of the molybdenum coordination spheres. The FTIR spectra of complexes C1a and Clb show as most relevant features the two strong bands in the ranges1929e1953 and 1840e1871 cm$1 characteristic of the C^O stretching modes of ciscarbonyl groups, slightly shifted from the values for C1 (1929 and 1840 cm$1). The spectrum of complex C1a also shows two bands at 2311 and 2279 cm$1, assigned to the C^N stretching modes of the coordinated acetonitrile ligand, while another band at 2251 cm$1 can be assigned to n(C^N) of cocrystallized acetonitrile (see Experimental section). The 1H NMR spectrum of complex C1a at room temperature shows broad peaks, as seen in Fig. 3. At low temperatures the signals could be resolved and revealed the presence of three isomers, C1a-A, C1a-B and C1a-C in the 2:1:1 ratio, with C1a-B and C1a-C in chemical exchange. The NOESY spectrum does not allow us to group the dpa, allyl and CH3CN resonances for the isomers C1a-B and C1a-C.

S. Quintal et al. / Journal of Organometallic Chemistry 696 (2011) 2142e2152

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Fig. 3. 1H NMR stacked spectra of [Mo(CH3CN)(h3-C3H5)(CO)2(L1)]OTf (C1a) at several temperatures in CD2Cl2.

The isomer present in larger amounts should be the E one, as observed in the crystal structure (see above), the other two being assigned to the A and A* isomers (Scheme 2), as has been described in detail for complex C1 [13] and others [14,15]. The 1H NMR spectrum of the binuclear complex C1b, at room temperature, indicates the presence of only one isomer, since only one signal is observed for each set of allylic protons (Hmeso at 4.20, Hsyn at 2.95, and Hanti at 1.62 ppm). The isomer should be the E-E as observed in the crystal structure. 2.2. Chemical studies. Complexes with ferrocenyl ligands Both 2,20 -dipyridylamine (L1) and 2-aminopyridine react with FcCOCl (Fc ¼ (h5-C5H5)Fe(h5-C5H4)), in a 1:1 ratio, in the presence of NEt3 to give L2 ¼ {[bis(2-pyridyl)amino]carbonyl}ferrocene [16] and L3 ¼ N,N-bis(ferrocenecarbonyl)-2-aminopyridine, respectively. Crystals of both ferrocene derivatives of suitable quality for X-ray diffraction studies were grown from hexane diffusion into a CH2Cl2 solution of the compound. The structure of L2 has been reported [16]. The X-ray data of L3, namely the systematic absences, were consistent with monoclinic space groups Ic and I2/c (non-standard settings of Cc and C2/c, see experimental section) and consequently the structure solution was undertaken considering both spaces groups, but the structure refinement was only successful in centrosymmetric I2/c, ruling out the Ic possibility. On the other hand, in the I2/c space group, L3 has a 2-fold crystallographic axis running through the NamideeCpyridine bond axis, which is incompatible with the asymmetric structure of L3 (see Scheme 1). Therefore, in I2/c the L3 structure is necessarily disordered, with the nitrogen of the pyridine ring occupying the position of the carbon d (see Scheme 1) and vice-versa. In other words, the crystal is composed of two rotational conformers each with occupancies of 50% and related precisely by a 2-fold axis. The molecular structure of one of these conformers is presented in Fig. 4. The new L3 was also characterized by FTIR. A set of bands assigned to the ferrocenyl subunits was observed at 3083 (nCeH), 1449 (nCeC), 1105 (asymmetric ring breathing), 1004 (dCeH)∕∕, 835 (pCeH)t, 496 (dFe$Cp)a and 460 cm$1 (nFeeCp) [17]. Strong bands are also observed at 1655 and 1646 cm$1 assigned to the C]O stretching modes, and at 1585, 1569 (nC]N), 1438, 1428 (nC]C), 1313 (nCeN), assigned to the 2-aminopyridine fragment. No signals are observed for NH2 stretching. The 1H NMR spectrum of L3 shows the three signals of the 2-aminopyridine fragment (see Scheme 1 for numbering scheme) in the aromatic region at 8.56 (doublet, Ha), 7.73 (triplet, Hc) and 7.21 ppm (multiplet, Hb þ Hd). The signals of the ferrocenyl unit

Fig. 4. Molecular structure of one N,N-bis(ferrocenecarbonyl)-2-aminopyridine (L3) conformer found in the solid state.

appear as a singlet (H1 at 4.57 ppm) and as a multiplet (H10 and H2 at 4.37 ppm). Reaction of [MoBr(h3-C3H5)(CO)2(NCMe)2] with the ferrocenyl derivatives L2 and L3 gives the complexes [MoBr(h3-C3H5)(CO)2(L)] (C2, L ¼ L2, and C3, L ¼ L3), after substitution of the two acetonitrile ligands. A single crystal X-ray diffraction study confirmed the proposed formulation of complex C2, showing that the asymmetric unit is composed of a neutral [MoBr(h3-C3H5)(CO)2(L2)] complex and three water molecules, one with an occupancy factor of 0.25. In addition, the third molecule is disordered over two close positions with occupancies 0.25 and 0.75, respectively. The molecular structure of [MoBr(h3-C3H5)(CO)2(L2)], presented in Fig. 5, shows the metal atom to occupy a pseudo-octahedral coordination environment with two carbonyl ligands and a nitrogen donor from the 2,20 -dipyridylamine fragment of L2 defining a triangular face of a fac arrangement. The bromide, the allyl ligand and the remaining nitrogen donor of L2 define the other triangle, leading to the A axial isomer as found for C1. The two Cps rings in the ferrocenyl unit adopt an eclipsed conformation. The MoeN and MoeC distances and the corresponding angles, given in Table 2, are comparable to the equivalent ones found for complexes C1a and C1b (see Table 1). However, in C2, the steric bulk of the ferrocenyl unit leads to a more significant bending of L2 bis(2-pyridyl)amino fragment

Fig. 5. Molecular structure of [MoBr(h3-C3H5)(CO)2(L2)] (C2) with the labelling scheme adopted.

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Table 2 Selected bond distances (Å) and bond angles (% ) for [MoBr(h3-C3H5)(CO)2(L2)] (C2). Bond lengths MoeC(100) MoeC(200) MoeBr

1.945(6) 1.978(6) 2.6849(8)

MoeN(23) MoeN(11) Mo-allyl

2.253(4) 2.295(4) 2.224(6)e 2.346(6)

Bond angles N(23)eMoeN(11) C(100)eMoeN(11) C(100)eMoeC(200) C(100)eMoeBr C(100)eMoeN(23) O(200)eC(200)eMo

77.12(15) 98.1(2) 82.0(2) 169.16(17) 86.9(2) 176.5(6)

BreMoeN(11) C(200)eMoeN(11) BreMoeN(23) C(200)eMoeBr C(200)eMoeN(23) O(100)eC(100)eMo

83.82(11) 166.2(2) 83.08(11) 93.59(18) 89.1(2) 176.1(5)

around the NeC amide bond of 64.0(2)% than that observed for 2,20 dipyridylamine in C1a (47.4(3)% ) and C1b (31.3(8) and 23.3(9)% ). This comparison indicates that the ligands based on 2,20 -dipyridylamine have enough flexibility to rotate around the C(pyridine)eN(amide) bonds in order to minimize the steric interactions with other bulky ligands present in the metal coordination sphere or with other substituents, such as ferrocenyl derivatives. The FTIR spectrum of C2 displays two very strong bands at 1936 and 1846 cm$1, assigned to the two C^O stretching modes typical of cis-carbonyl groups. The nC]O stretching frequency is observed at 1691 cm$1, slightly higher than in the free L2 ligand (1673 cm$1), confirming that the carbonyl group does not coordinate to the metal center. The bands assigned to the ferrocenyl subunits appear at 3105 (nCeH), 1432 (nCeC), 1100 (asymmetric ring breathing), 1002 (dCeH)∕∕, 822 (pCeH)t, 494 (dFeeCp)a and 459 cm$1 (nFeeCp). In the FTIR spectrum of C3, the two very strong bands, assigned to the two C^O stretching modes of the carbonyl groups, are observed at 1934 and 1848 cm$1. Two nC]O stretching frequencies are observed at 1689 and 1600 cm$1. The frequency of the first band increases as in C2, indicating that the corresponding C]O group does not coordinate to the molybdenum. In contrast, the large shift to lower frequency (1600 cm$1) of the other band relative to the free C2 ligand suggests coordination of this C]O group to the metal. The bands assigned to the ferrocenyl subunits appear at 3102 (nCeH), 1437 (nCeC), 1096 (asymmetric ring breathing), 1002 (dCeH)∕∕, 819 (pCeH)t, 499 (dFe$Cp)a and 471 cm$1 (nFeeCp). The 1H NMR spectrum of C2 at room temperature shows very broad resonances that become well defined at lower temperatures (Fig. 6). At 223 K, eight resonances of the 2,20 -dipyridylamine ligand are observed at 9.09, 8.57 (Ha, Ha0 ), 7.93, 7.56 (Hc, Hc0 ), 7.85, 6.89

1

3

Fig. 6. H NMR spectra of [MoBr(h -C3H5)(CO)2(L2)] (C2) at several temperatures.

(Hd, Hd0 ) and 7.40, 7.27 ppm (Hb, Hb0 ), reflecting the non-equivalence of the two rings characteristic of the axial isomer (A, Scheme 2) as confirmed in the crystal structure (Fig. 5). For the same reason, all the ferrocenyl protons of the substituted Cp ring in C2 are nonequivalent (signals at 4.87, 4.39, 4.10 and 3.50 ppm). A singlet at 4.17 ppm is assigned to the ferrocenyl protons of the unsubstituted Cp ring. The allylic protons are also non-equivalent. The signals assigned to the Hmeso and one of the Hsyn overlap the signal of one Cp proton at 4.10 ppm; the second Hsyn is observed at 3.02 ppm, while two different doublets at 1.68 and 1.50 ppm correspond to the anti protons of the allyl ligand. These assignments are based on the COSY and HMQC spectra. At 233 K, new sets of resonances appear, owing probably to the presence of the isomer obtained by allyl rotation (A* in Scheme 2), since the formation of the equatorial isomer E is unlikely for steric reasons. In contrast to C2, the signals in the 1H NMR spectrum of C3 at room temperature are well resolved. The aromatic region shows one broad signal at 9.41, two triplets at 8.08 and 7.54, and one multiplet at 8.01 ppm assigned, respectively, to the Ha, Hc, Hb and Hd protons of the 2-aminopyridine fragment (see Scheme 1). These values are significantly deviated from those of the free L3, specially for Ha (8.56e9.41 ppm), indicating that the pyridine ring is coordinated to the metal. The non-equivalent ferrocenyl protons are observed upfield, between 4.90 and 3.86 ppm. The allyl protons are also non-equivalent, with two broad signals for Hsyn (4.54, 3.27 ppm) and two doublets for Hanti (1.65 and 1.55 ppm). The resonance assigned to Hmeso (4.38 ppm) overlaps with that of one ferrocenyl proton. These assignments are consistent with the COSY and HMQC spectra. The presence of two signals for C]O in the 13C NMR spectrum of C3 supports the coordination mode of L3 as a k2N,O-bidentate ligand, in agreement with the infrared spectrum. The isomer should be the axial one, as suggested by the non-equivalence of the allylic protons and supported by the size of the L3 ligand. 2.3. Electrochemistry The cyclic voltammetric responses of L2 and its Mo(II) complex C2 in dichloromethane solution are compared in Fig. 7.

Fig. 7. Cyclic voltammetric responses recorded at a platinum electrode in CH2Cl2 solution of: (a) L2 (0.9 ' 10$3 mol dm$3); (b) C2 (0.7 ' 10$3 mol dm$3). [NBu4][PF6] (0.2 mol dm$3) supporting electrolyte. Scan rate: 0.02 Vs$1.

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The ferrocenyl ligand L2 undergoes an oxidation process having features of chemical reversibility in the cyclic voltammetric time scale (Fig. 7a), which consumes one electron per molecule in controlled potential coulometry (Ew ¼ þ0.7 V, vs. SCE). Analysis of the pertinent cyclic voltammetric responses with the scan rate progressively increasing from 0.02 Vs$1 to 2.0 Vs$1 confirms the occurrence of a simple diffusion controlled process. In fact: (i) the current function ipc ' v$1/2 substantially remains constant; (ii) the current ratio ipa/ipc is constantly equal to 1; (iii) the peak-to-peak separation does not depart significantly from the theoretical value of 57 mV expected for a reversible one-electron process [18]. Exhaustive one-electron oxidation to the corresponding monocation causes the original yellow solution to turn emerald green (thus confirming the ferrocene-centered nature of the oneelectron removal), and the resulting solution exhibits a cyclic voltammetric profile quite complementary to the original one, thus indicating that the monocation [L2]þ is stable also in the longer times of macroelectrolysis. C2 exhibits two sequential oxidations with features of chemical reversibility in the cyclic voltammetric time scale, Fig. 7b. Controlled potential coulometry in correspondence of the overall anodic processes (Ew ¼ þ0.9 V) consumes two electrons per molecule and the original yellow solution tends to turn green. The spectrophotometric trend recorded upon progressive oxidation of C2 is illustrated in Fig. 8. As is apparent in Fig. 8, the typical absorption of the ferrocenium ion only appears after the consumption of 1.5 electrons/molecule, thus suggesting that, in agreement with theoretical calculations (see below), the Mo(II)/Mo(III) process precedes the Fe(II)/Fe(III) oxidation. We underline that the occurrence of the sequence Mo (II)/Mo(III)-Fe(II)/Fe(III) or vice-versa arises in reality from delicate electronic equilibria, in that from a series of somewhat related ferrocenyl-tris(pyrazolyl)borato complexes all containing Mo (CO)2(h3-C3H5) fragments, we observed either the sequence Mo(II)/ Mo(III)-Fe(II)/Fe(III) or the inverted sequence Fe(II)/Fe(III)-Mo(II)/ Mo(III) [19]. In spite of the apparent chemical reversibility of the second anodic process in the short times spans of cyclic voltammetry, exhaustive two-electron oxidation leads to decomposition of the molecule, as ascertained by cyclic voltammetric tests on the resulting solution, which also accounts for the pertinent disappearance of the ferrocenium absorption. Table 3 compiles the electrochemical and spectroelectrochemical features of the ferrocenyl derivatives under study and their Mo (II) complexes.

Fig. 8. Spectroelectrochemical profiles recorded upon progressive oxidation of C2 (0.5 ' 10$3 mol dm$3) in CH2Cl2 solution. [NBu4][PF6] (0.2 mol dm$3) supporting electrolyte. (a) Original solution; (b) after 1 electron/molecule; (c) after 1.5 electrons/ molecule; (d) after 2 electrons/molecule.

It is noted that the oxidation potential of L2 is higher by about 0.2 V with respect to that of ferrocene, thus suggesting that the dipyridylamino-carbonyl fragment exerts a marked electronwithdrawing effect with respect to the Fe(II) center. Let us now pass to complexes L3 and C3. In L3, as illustrated in Fig. 9a, the diferrocenyl ligand exhibits in dichloromethane solution a single oxidation having features of chemical reversibility in the cyclic voltammetric time scale. As expected for the concomitant oxidation of the two ferrocenyl appendices, controlled potential coulometry (Ew ¼ þ0.8 V) consumes two electrons/molecule. Upon exhaustive oxidation the original orange solution (lmax ¼ 457 nm) tends progressively to turn brown, but maintaining the absorption at lmax ¼ 626 nm of the ferrocenium ion, see Figure S1 in Supplementary material. The final control by cyclic voltammetry shows that the electrogenerated dication [L3]2þ in reality undergoes a very slow decomposition, as proved by the appearance of a minor reduction process at about $0.1 V following the main reduction [L3]2þ/0, Fig. 9b, which probably is responsible for the non-green color of the final solution. The appearance of a single two-electron oxidation suggests that no interaction between the two ferrocenyl appendices is operative [18]. As illustrated in Fig. 10, the electrochemical behavior of C3 appears rather complex, in that it displays a sequence of oxidation

Table 3 Electrochemical and spectroelectrochemical features of complexes L2, C2, L3, C3 in CH2Cl2 solution. Complex

E% 0 (0/þ) (V, vs. SCE)

DEpa (mV)

E% 0 (þ/2þ) (V, vs. SCE)

DEpa (mV)

E% 0 (0/2þ) (V, vs. SCE)

DEpa (mV)

lmax (nm)

L2 [L2]þ L3 [L3]2þ C2 [C2]2þ e C3 Fe(C5H5)2 [Fe(C5H5)2]þ

þ0.58 e e e þ0.62 e e þ0.39 e

82 e e e 64 e e 74 e

e e e e þ0.81 e e e e

e e e e 110 e e e e

e e þ0.64 e e e þ0.66f,g e e

e e 99b e e e 70 e e

446 636 456 625c

a b c d e f g

Measured at 0.1 Vs$1. Concomitant two-electron oxidation. Coupled to very slow decomposition (see text). A very intense band at 374 nm obscures any eventual absorptions up to 430 nm (see Fig. 8). Short-lived dication (see text). further oxidation processes are also present (see text). Multielectron process.

d

625 350, 468 430 618

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From a qualitative viewpoint, also based on the results from theoretical calculations, the first main oxidation (E%0 ¼ þ0.66 V) is conceivably assigned to the concomitant oxidation of both the ferrocenyl and Mo(II) moieties, whereas the subsequent anodic steps in principle could be attributed to the bromide ligand. In fact, controlled potential coulometry in correspondence of the first oxidation(s) (Ew ¼ þ0.8 V) indicates the occurrence of a multielectron process (more than five electrons per molecule have been spent to carry out the exhaustive oxidation). In particular, after the consumption of about 2.5 electrons/molecule the original redeorange colour is maintained; the voltammetric profile still shows the main oxidation process, but the peaks at about þ0.85 V and þ0.95 V tend to disappear. The process is also accompanied by the disappearance of the cited irreversible reduction. Finally, after about five electrons/molecule, the solution turns grey (exhibiting the adsorption at lmax ¼ 628 nm typical of the oxidised form of L3; see Figure S1 in the Supplementary material) and displays a reversible reduction at þ0.64 V, which is coincident with the reduction process recorded after the two-electron oxidation of the free ligand L3. In conclusion, the exhaustive oxidation of C3 induces defragmentation of the Mo-center through a multielectron pathway, which could not be electrochemically identified in detail. 2.4. DFT calculations

Fig. 9. Cyclic voltammetric responses recorded at a platinum electrode in a CH2Cl2 solution of: (a) L3 (0.7 ' 10$3 mol dm$3); (b) after exhaustive two-electron oxidation. [NBu4][PF6] (0.2 mol dm$3) supporting electrolyte; scan rate 0.2 Vs$1.

processes not easily attributable. In addition, an irreversible reduction (not shown in the Figure) is present at $1.7 V. As deducible from Fig. 9b, the only evidence from the voltammetric profiles recorded at increasing scan rates is that the most anodic step (Ep ¼ þ1.25 V) arises from by-products originated at the first oxidation steps.

Fig. 10. Cyclic voltammetric responses recorded at a platinum electrode in a CH2Cl2 solution of C3 (0.5 ' 10$3 mol dm$3). [NBu4][PF6] (0.2 mol dm$3) supporting electrolyte. Scan rates: (a) 0.05 Vs$1; (b) 2.0 Vs$1.

DFT calculations [20] using the ADF program [21] were performed in order to propose a structure for complex C3 and to determine the nature of the frontier orbitals of L2, L3, C2, and C3, to complement the electrochemistry results. The geometries of L2, L3, and C2 were optimized from the crystal structure determinations, while for C3 the model was built from the MoBr(h3-C3H5)(CO)2 fragment and the ligand L3, assuming that it would bind the metal by the pyridine nitrogen and one O]C group, a structure consistent with the spectroscopic evidence (see above). The two O]C groups are equivalent in L3 and the preferred isomer should be the axial, as observed for C2, since the ligand is even bulkier. The DFT optimized structure of C3 is shown in Fig. 11. In this complex, the MoeC bonds to the allyl ligand vary from 2.215 to 2.359 Å, very close to the 2.224e2.346 Å range observed for the related C2. Also, the MoeBr distance 2.704 Å, as well as MoeC(O) 1.946, 1.950 and the MoeN 2.273 Å compare very well with those found for complex C2 and given in Table 2 above. The two C]O bonds are different, with the coordinated one longer

Fig. 11. DFT optimized structure of complex [MoBr(h3-C3H5)(CO)2(L3)] (C3), showing some relevant distances (Ǻ).

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(1.249 Å) than the free one (1.218 Å). On the other hand, the calculated nC^O frequencies are 1911 and 1840 cm$1, very close to the experimental values of 1934 and 1848 cm$1, while the two nC]O vibrational modes were calculated at 1672, 1569 cm$1, comparing well with the experimentally observed 1689 and 1600 cm$1 (all these frequency values were not corrected by any scaling factor). The optimized structures of L2, L3, and C2 were found to reproduce very closely the experimental ones. The HOMOs of both L2 and L3 are iron based d orbitals, the HOMO being slightly FeeCp bonding (see Figure S2 in Supplementary material). Since L3 contains two Cp rings, these high energy occupied orbitals are duplicated. The nature of the HOMO changes when these ferrocenyl derivatives bind to molybdenum and it becomes mostly located on molybdenum with some small bonding contribution of the two carbonyls and an antibonding contribution of the bromide. The HOMO of C3 also has a small contribution from iron. They are shown in Fig. 12 for C2 and C3. The next lower energy orbitals are localized on the iron d levels, being very similar to those found for the free ferrocenyl ligands. The LUMOs of the four species share a large contribution from the C]O(s) and Fe dz2, and the small amount remaining varies from molecule to molecule. These features of the HOMO and LUMO of the FeeMo complexes have been observed in related complexes [10]. These results support the electrochemistry experiments, suggesting that oxidation of C2 should occur at the molybdenum center, followed by oxidation of iron. In C3, the contribution of Mo and a small amount of Fe in the HOMO is in agreement with a more complicate behavior, though molybdenum should be involved in the first oxidation process. 3. Conclusions New Mo(II) complexes were obtained from reaction between [MoBr(h3-C3H5)(CO)2(NCMe)2] and with 2,20 -dipyridylamine (L1) or its ferrocenyl derivatives {[bis(2-pyridyl)amino]carbonyl}ferrocene (L2) and N,N-bis(ferrocenecarbonyl)-2-aminopyridine (L3), yielding [Mo(CH3CN)(h3-C3H5)(CO)2(L1)]OTf (C1a), [{MoBr(h3C3H5)(CO)2(L1)}2(4,40 -bipy)](PF6)2 (C1b), [MoBr(h3-C3H5)(CO)2(L2)] (C2), and [MoBr(h3-C3H5)(CO)2(L3)] (C3). The molybdenum complexes with L1 range from the neutral [MoBr(h3-C3H5)(CO)2(L1)] (C1) previously described as the equatorial isomer, to the cationic C1a (axial isomer) and the binuclear C1b, where two equatorial units were bridged by a 4,40 -bipy ligand that replaced the two bromines. The mixed FeeMo C2 contains the ferrocenyl unit as a bidentate nitrogen ligand occupying one equatorial and one axial position (axial isomer). In this complex, it is the bulk of the ligand that forces the appearance of the axial isomer. C3 could not be structurally characterized, but a combination of FTIR and 1H NMR spectroscopic data and DFT calculations led to

Fig. 12. HOMOs of the two complexes [MoBr(h3-C3H5)(CO)2(L)] (C2, L ¼ L2, left, and C3, L ¼ L3, right).

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a structure where L3 bound to the metal by a pyridine nitrogen and a C]O group, in a bidentate form, yielding the axial isomer. The redox capacity of the present complexes has been studied by electrochemistry and spectroelectrochemistry. The monoferrocenyl monocation [L2]þ proved to be stable, whereas its Mo(II) complex C2 is stable as Mo(III) monocation [C2]þ, but short-lived as Mo(III)Fe(III) dication [C2]2þ. As far as the diferrocenyl complex L3 is concerned, it undergoes a single two-electron oxidation generating the partially stable dication [L3]2þ. In turn, its Mo(II) complex C3 undergoes a multielectron oxidation, which by exhaustive oxidation releases the Mo-fragment generating the partially stable dication [L3]2þ. 4. Experimental 4.1. Syntheses All chemicals, including 2,20 -dipyridylamine (L1), were obtained from standard chemical suppliers. Solvents were dried using common procedures. All experimental manipulations were carried out under nitrogen atmosphere using Schlenk techniques. The ligand {[bis(2-pyridyl)amino]carbonyl}ferrocene (L2) [16], was prepared, as reported, by the coupling reaction between FcCOCl [Fc ¼ (h5-C5H5)Fe(h5-C5H4)] [22] and 2,20 -dipyridylamine in a 1:1 ratio, in dichloromethane and in presence of NEt3. Complexes [MoBr(h3-C3H5)(CO)2(NCMe)2] [12] and [MoBr(h3-C3H5)(CO)2(L1)] [13] were synthesized according to literature procedures. 4.2. Material and apparatus Infrared spectra were measured on a Mattson 7000 FT spectrometer. Samples were run as KBr pellets. 1H and 13C NMR spectra were recorded on a Bruker Avance-400 spectrometer using CD2Cl2, CDCl3 or acetone-d6 as solvent. Materials and apparatus for electrochemical measurements have been described elsewhere [23]. A Perkin Elmer Lambda 900 UVevis spectrophotometer was used for spectral measurements. Microanalyses (C, H, N, and S) were measured by elemental analysis service at ITQB or at University of Vigo, Spain. 4.2.1. [Mo(CH3CN)(h3-C3H5)(CO)2(L1)]OTf C1a A solution of [MoBr(h3-C3H5)(CO)2(L1)] (1 mmol, 0.444 g) and TlOTf (1 mmol, 0.353 g) in 20 ml of acetonitrile was stirred overnight. TlBr was filtered off and celite was added to the solution. After filtration, the solvent volume was reduced and diethyl ether was added. Orange crystals were isolated, washed with 3 ' 5 ml of diethyl ether, and dried under vacuum. A suitable crystal was selected for the X-ray diffraction study. Elemental analysis: calc. for C1a.0.5CH3CN (C19H18.5O5N4.5SF3Mo): C 39.70, H 3.24, N 10.96, S 5.58%; found: C 40.04, H 3.80, N 10.42, S 5.32%. IR (KBr pellets, cm$1): 3281 (m), 3135 (m), 3086 (m), 2936 (m), 2311 (w), 2279 (w), 2251 (w), 1953 (vs), 1871 (vs), 1631 (s), 1580 (m), 1649 (s), 1339 (m), 1285 (vs), 1246 (vs), 1168 (vs) 1029 (vs), 773 (m), 635 (s), 574 (m), 516 (m). 1H NMR (400 MHz, CD2Cl2, 233 K): Isomer A: d ¼ 9.67 (NH, s), 8.29 (d, He), 7.70 (m, Hc), 7.31 (d, Hb), 6.94 (t, Hd), 3.87 (m, Hmeso), 2.80 (d, Hsyn), 1.99 (s, CH3CN), 1.45 (d, Hanti) ppm. Isomer B and C (in chemical exchange): d ¼ 9.83 (NH0 /NH00 , s), 8.36 (d, He0 ), 7.89 (d, He00 ), 7.80 (t, Hc0 ), 7.70 (m, Hc00 ), 7.59 (d, Hb0 ), 7.42 (d, Hb00 ), 7.22 (t, Hd0 ), 7.08 (t, Hd00 ), 4.02 (m, Hmeso*/Hxmeso), 3.55 (br, Hsyn*), 2.80 (d, Hxsyn), 2.34 (s, CH3CNy), 2.23 (s, CH3CNz), 1.57 (d, Hxanti), 1.26 (d, H*anti) ppm. 13C NMR (100.6 MHz, CD2Cl2, 233 K): Isomer A: d ¼ 152.41 (Ca), 152.12 (Ce), 140.52 (Cc), 118.51 (Cd), 121.75 (CH3CN), 115.64 (Cb), 69.38 (Cmeso), 59.95 (Canti/syn), 2.42 (CH3CN) ppm. Isomer B and C: d ¼ 154.74 (Ca0 ), 152.75 (Ca00 ), 149.26 (Ce0 ), 147.08 (Ce00 ), 139.98 (Cc0 ), 139.80 (Cc00 ), 128.98 (CH3CNy), 123.95 (CH3CNz), 120.04 (Cd00 ), 119.33 (Cd0 ), 116.49 (Cb0 ), 115.07 (Cb00 ),

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69.38 (C*,xmeso), 63.19 (Cxanti/syn), 55.66 (C*anti/syn), 4.63 (CH3CNy), 3.98 (CH3CNz) ppm. 4.2.2. [{Mo(h3-C3H5)(CO)2(L1)}2(4,40 -bipy)](PF6)2 C1b [MoBr(h3-C3H5)(CO)2(L1)] (0.5 mmol, 0.222 g), TlPF6 (0.5 mmol, 0.175 g) and 4,40 -bipyridine (0.25 mmol, 0.391 g) in 40 ml of acetone were refluxed during 5 h. TlBr was filtered off in a celite bed. The volume of the filtrate was reduced and n-hexane was added. After 2 days an orange precipitate was isolated, washed with 3 ' 5 ml of n-hexane, and dried under vacuum. Diffusion of diethyl ether into an acetone solution of the compound gave crystals that were used for a single crystal X-ray diffraction study. Elemental analysis: calc. for C1.0.5H2O(C40H37O4.5N8P2F12Mo2): C 40.59, H 3.15, N 9.47%; found: C 42.71, H 3.65, N 9.47%. IR (KBr pellets, cm$1): 3381 (m), 3082 (w), 1940 (vs), 1850 (vs), 1632 (s), 1583 (s), 1474 (vs), 1412 (m), 1229 (m), 1164 (m) 1067 (m), 1010 (m), 842 (vs), 771 (s), 739 (m), 557 (vs). 1H NMR (400 MHz, acetone-d6, 295 K): d ¼ 8.98 (m, H2-bipy, 2H), 8.74 (m, H0 2-bipy, 2H), 8.28 (m, He, 4H), 8.05 (m, H3-bipy, 2H), 7.98 (m, Hc, 4H), 7.78 (m, H0 3-bipy, 2H), 7.36 (m, Hb, 4H), 7.11 (m, Hd, 4H), 4.20 (m, Hmeso, 2H), 2.95 (d, Hsyn, 4H), 1.62 (d, Hanti, 4H) ppm. 13C NMR (100.6 MHz, acetone-d6, 295 K): d ¼ 155.70 (C20 -bipy), 154.16 (Ce), 152.84 (C2-bipy), 152.52 (Ca), 144.56 (C4-bipy), 143.28 (Cc), 155.51 (C3-bipy), 123.21 (C30 -bipy), 121.13 (Cd), 117.92 (Cb), 71.49 (Cmeso), 60.85 (Canti/syn) ppm. 4.2.3. [MoBr(h3-C3H5)(CO)2(L2)] C2 A solution (10 ml) of L2 (0.5 mmol, 0.192 g) in CH2Cl2 was added to a yellow solution (CH2Cl2, 10 ml) of [MoBr(h3-C3H5)(CO)2(NCMe)2] (0.5 mmol, 0.177 g), under stirring and N2. The stirring was continued for 1 h and n-hexane was added. After a few days in the fridge, the yellow crystals were filtered off, washed with 3 ' 10 ml of n-hexane and dried under vacuum. A suitable crystal was selected for single crystal X-ray diffraction. Elemental analysis: calc. for C2.3H2O (C26H28O6N3BrMoFe): C 43.97, H 3.97, N 5.92%; found: C 43.53, H 3.33, N 5.62%. IR (KBr pellets, cm$1): 3105 (w), 3064 (w), 2985 (w), 1936 (vs), 1846 (vs), 1691 (s), 1600 (m), 1467 (s), 1443 (s), 1432 (m), 1376 (m), 1323 (m), 1274 (s),1151 (m), 1100 (m), 1002 (m), 822 (m), 783 (m), 763 (m), 738 (m), 494 (m), 459 (m). 1H NMR (400 MHz, CD2Cl2, 223 K): d ¼ 9.09 (d, Ha, 1H), 8.57 (d, Ha0 , 1H), 7.93 (t, Hc, 1H), 7.85 (d, Hd, 1H), 7.56 (t, Hc0 , 1H), 7.40 (t, Hb, 1H), 7.27 (t, Hb0 , 1H), 6.89 (d, Hd0 , 1H), 4.87 (br, H1, 1H), 4.39 (br, H1, 1H), 4.17 (s, H10, 5H), 4.10 (m, H2 þ Hsyn þ Hmeso, 3H), 3.50 (br, H2, 1H), 3.02 (br, Hsyn0 , 1H), 1.68 (d, Hanti0 , 1H), 1.50 (d, Hanti, 1H) ppm. 13C NMR (HMQC, CD2Cl2, 223 K): d ¼ 152.81 (Ca), 151.51 (Ca0 ), 138.92 (Cc0 ), 138.65 (Cc), 124.69 (Cd), 124.15 (Cd0 ), 123.74 (Cb0 ), 122.98 (Cb), 74.14 (Cmeso), 73.37 (C1), 70.31 (C10 ), 69.66 (C1), 69.41 (C2), 66.98 (C2), 61.96 (Canti/syn) 57.89 (Canti0 /syn0 ) ppm. 4.2.4. (FcCO)2(Npy) L3 2-aminopyridine (0.094 g, 1 mmol) and NEt3 (0.61 ml) were added to a red solution (CH2Cl2, 10 ml) of FcCOCl (0.248 g, 1 mmol) at 0 % C and under nitrogen and stirring. The mixture was stirred overnight. A saturated aqueous solution (20 ml) of NaHCO3 was added. The phases were separated and the organic phase was dried with anhydrous Na2SO4. After filtration, the solvent volume was reduced and n-hexane was added. Three days later, the mixture was filtered off and red crystals was isolated, washed with 3 ' 10 ml of n-hexane and dried under vacuum. A suitable crystal was selected for single crystal X-ray diffraction. IR (KBr pellets, cm$1): 3083 (w), 1688 (s), 1655 (vs), 1646 (vs), 1585 (s), 1569 (m), 1449 (s), 1438 (s), 1428 (s), 1372 (s), 1313 (s), 1254 (vs), 1105 (m), 1047 (m), 1004 (m), 835 (w), 819 (s), 767 (m), 749 (s), 530 (m), 496 (s), 481 (s), 460 (s). 1 H NMR (400 MHz, CDCl3, r.t.): d ¼ 8.56 (d, Ha, 1H), 7.73 (t, Hc, 1H), 7.21 (m, Hb/Hd, 2H), 4.57 (s, H1, 4H), 4.37 (m, H2/H10, 14H) ppm. 13C

NMR (100.6 MHz, CDCl3, r.t.): 174.99 (C]O), 154.19 (Ce), 149.23 (Ca), 137.86 (Cc), 122.19 (Cd), 121.99 (Cb), 71.37 (C1), 71.00 (C2), 70.54 (C10 ) ppm. 4.2.5. [MoBr(h3-C3H5)(CO)2(L3)] C3 A solution (10 ml) of L3 (0.3 mmol, 0.155 g) in CH2Cl2 was added, under stirring and N2, to a yellow solution (CH2Cl2, 10 ml) of [MoBr (h3-C3H5)(CO)2(NCMe)2] (0.3 mmol, 0.106 g). The stirring was continued for 1 h and n-hexane was added. After a few days in the fridge red crystals was formed. The crystals was filtered off, washed with 3 ' 10 ml of n-hexane and dried under vacuum. Elemental analysis: calc. for C3. 0.5CH2Cl2 (C32.5H26O4N2BrClMoFe2): C 46.94, H 3.15, N 3.37%; found: C 46.53, H 3.62, N 3.28%. IR (KBr pellets, cm$1): 3102 (w), 3085 (w), 2956 (w), 1934 (vs), 1848 (vs), 1689 (s), 1600 (vs), 1437 (m), 1264 (s), 1255 (s), 1150 (m), 1096 (m), 1028 (w), 1002 (w), 819 (s), 767 (s), 731 (w), 499 (m), 471 (m). 1H NMR (400 MHz, CDCl3, r.t.): d ¼ 9.41 (br, Ha, 1H), 8.08 (t, Hc, 1H), 8.01 (m, Hd, 1H), 7.54 (t, Hb, 1H), 4.90 (m, H1, 1H), 4.85 (m, H1, 1H), 4.73 (m, H1, 1H), 4.54 (br, Hsyn, 1H), 4.49 (m, H1, H2, 2H), 4.38 (m, H2 þ Hmeso, 2H), 4.28 (m, H2 þ H2, 2H), 4.26 (s, H10, 5H), 3.86 (s, H10, 5H), 3.27 (br, Hsyn0 , 1H), 1.65 (d, Hanti, 1H), 1.55 (d, Hanti0 , 1H) ppm. 13C NMR (100.6 MHz, CDCl3, r.t.): d ¼ 181.51 (C]O)c, 169.61(C]O), 154.08 (Ca), 147.54 (Ce), 138.94 (Cc), 123.49 (Cd), 123.36 (Cb), 75.92 (C1), 74.92 (Cmeso), 74.06 (C1), 71.81 (C10 ), 71.55 (C1), 71.31 (C2), 70.92 (C10 ), 70.54 (C2), 66.76 (Canti/syn), 56.84 (Canti0 /syn0 )ppm. 4.3. Crystal structure determinations X-ray diffraction data of C1a, C1b and L3 were collected at 293 K on a MARresearch image plate diffractomer and C2 at 150 K on a X-Calibur CCD both using graphite monochromatized Mo-Ka radiation (l ¼ 0.71073 Å) at Reading University. The crystals of the first three complexes were positioned at 70 mm from the Image Plate and 100 frames were measured with a counting time ranging between 2 and 10 m. Data analysis was carried out with the XDS program [24]. Data were corrected for empirical absorption effects with the DIFABS program [25]. A selected crystal of C2 was positioned at 50 mm from the CCD and 321 frames were collected with a counting time of 5 s. Data analysis was carried out with the Crystalis program [26]. Data were corrected for empirical absorption effects with the ABSPACK program [27]. The structures were solved by direct methods and subsequent difference Fourier syntheses and refined by full matrix least squares on F2 using the SHELX-97 system programs [28]. Anisotropic thermal parameters were used for all non-hydrogen atoms, apart the atoms with disorder or no-entire occupancies (from solvent molecules) in complexes C1a, C1b, and C2. The disordered atoms including the fluorine atoms of one PF$ 6 counter ion and the water molecule with occupation factor of 0.5 in C1b, acetonitrile solvent molecule with occupancy of 50% in C1, and two water molecules in C2 with occupancies of 25% (one of them the minor component of a disordered water) were refined with individual isotropic temperature factors. The major component of disordered water with occupancy of 75% was refined also with anisotropic thermal parameters. In addition, this disordered anion in C1b was refined considering two alternative positions with refined occupancies of x and 1$x, x being equal to 0.51(2). In all complexes the CeH and NeH hydrogen atoms were included in the structure refinement in calculated positions giving thermal parameters equivalent 1.2 times those of the atom to which were attached. The hydrogen atoms of the solvent water molecules were not localized from Fourier difference maps and consequently were not included in the structure refinement. The final R values together with pertinent crystallographic data are summarized in the Table 4. Molecular diagrams were drawn with PLATON [29].

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S. Quintal et al. / Journal of Organometallic Chemistry 696 (2011) 2142e2152 Table 4 Pertinent crystallographic data for complexes C1a, C1b, L3, and C2. Compound

C1a

C1b

L3

C2

Empirical Mw Crystal System Space group a/[Å] b/[Å] c/[Å] b/[% ] V/[Å3] Z Dc [Mg m$3] m/[mm$1] Reflections collected Unique reflections, [Rint] Final R indices R1, wR2 [ I > 2s I] R1, wR2 (all data)

C19H18.50F3MoN4.50O5S 574.88 Monoclinic P21/c 11.24(3) 19.100(9) 12.54(2) 94.541(10) 2684(8) 4 1.423 0.621 11985 4462 [0.0988] 0.0635, 0.1681 [3550] 0.0816, 0.1779

C40H37F12Mo2N8O4.50P2 1183.60 Monoclinic P21/c 9.482(11) 15.511(16) 33.84(2) 92.485(10) 4973(8) 4 1.581 0.662 6644 4201 [0.0501] 0.0924, 0.2501 [2156] 0.1725, 0.2976

C27H22Fe2N2O2 518.17 Monoclinic I2/c 10.802(15) 10.480(14) 19.740(23) 95.99(1) 2222.5(7) 4 1.549 1.333 4388 1954, [0.0750] 0.0778, 0.1366 [1578] 0.0999, 0.1445

C26H27BrFeMoN3O5.25 697.21 Monoclinic P21/c 12.1692(10) 16.1180(13) 14.9071(8) 97.529(5) 2898.7(4) 4 1.598 2.351 16196 7645 [0.0270] 0.0631, 0.1981 [4896] 0.0999, 0.2137

4.4. DFT calculations Density Functional Theory calculations [20] were performed using the Amsterdam Density Functional program package (ADF) [21]. Gradient corrected geometry optimizations [30], without symmetry constraints, were performed using the Local Density Approximation of the correlation energy (Vosko-Wilk-Nusair) [31], and the Generalised Gradient Approximation (Becke’s exchange [32] and Perdew’s correlation functionals [33]). Relativistic effects were treated with the ZORA approximation [34]. The core orbitals were frozen for Mo, Br ([1-3]s, [2-3]p, 3d); Fe ([1-2]s, 2p); and C and N (1s). Triple z Slater-type orbitals (STO) were used to describe the valence shells C, N (2s, 2p), Br (4s, 4p, 3d), Mo (4d, 5s) and Fe (3d, 4s). A set of two polarization functions was added to C, N (single z, 3d, 4f), Br (single z, 4d, 5s), Mo (single z, 5p, 4f), and Fe (single z, 4p, 4f). Triple z Slater-type orbitals (STO) were used to describe the valence shells of H (1s) with two polarization functions (single z, 2s, 2p). The complexes were modeled from the crystal structures of L2, L3, and C2, while for C3 the model was built from the MoBr(h3C3H5)(CO)2 fragment and the ligand L3, assuming that it would bind the metal by the pyridine nitrogen and one O]C group. Other possible coordination modes did not lead to converged structures. Three-dimensional representations of the orbitals were obtained with Molekel [35], and structures with Chemcraft [36]. Acknowledgements S. Quintal thanks FCT for a post-doc fellowship (SFRH/BPD/ 11463/2002 and SFRD/BPD/27454/2006). The University of Reading and EPSRC are thanked for funds for the Image Plate and CCD diffractometers. P.Z. is indebted to Dr. Serena Losi for her helpful collaboration in electrochemical measurements. CIRCMSB is acknowledged for the support. MJC acknowledges FCT, POCI and FEDER (project PTDC/QUI/58925/2004) for financial support. Appendix A. Supplementary material CCDC-782781 (for C1a), -782782 (for C1b), -782783 (for L3) and -782784 (for C2), contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif. Supplementary data related to this article can be found online, at doi:10.1016/j.jorganchem.2010.11.024.

References [1] (a) A. Togni, T. Hayashi (Eds.), Ferrocenes, Homogeneous Catalysis, Organic Synthesis and Materials Science, VCH, Weinheim, 1995; (b) A. Togni, R.L. Halterman, Metallocenes. VCH, Weinheim, 1998. [2] (a) N.J. Long, Angew. Chem. Int. Ed. 34 (1995) 21e38; (b) I. Manners, Adv. Organomet. Chem. 37 (1995) 131e168; (c) I. Manners, Chem. Commun. (1999) 857e865; (d) Y. Zhu, O. Clot, M.O. Wolf, G.P.A. Yap, J. Am. Chem. Soc. 120 (1998) 1812e1821; (e) P.D. Beer, Acc. Chem. Res. 31 (1998) 71e80; (f) P.D. Beer, P.A. Gale, G.Z. Chen, J. Chem. Soc. Dalton Trans. (1999) 1897e1909; (g) R.V. Honeychuck, M.O. Okoroafor, L.H. Shen, C.H. Brubaker Jr., Organometallics 5 (1986) 482e490; (h) A.C. Templeton, W.P. Wuelfing, R.W. Murray, Acc. Chem. Res. 33 (2000) 27e36; (i) R.S. Ingram, M.J. Hostetler, R.W. Murray, J. Am. Chem. Soc. 119 (1997) 9175e9178. [3] (a) S.I. Kirin, D. Wissenbach, N. Metzler-Nolte, New J. Chem. 29 (2005) 1168e1173; (b) O. Brosh, T. Weyhermüller, N. Metzler-Nolte, Inorg. Chem. 38 (1999) 5308e5313; (c) X. Hatten, T. Weyhermüller, N. Metzler-Nolte, J. Organomet. Chem. 689 (2004) 4856e4867; (d) A. Hess, O. Brosh, T. Weyhermüller, N. Metzler-Nolte, J. Organom. Chem. 589 (1999) 75e84; (e) D.R. van Staveren, N. Metzler-Nolte, Chem. Rev. 104 (2004) 5931e5985; (f) S. Chowdhury, K.A. Mahmoud, G. Schatte, H.B. Kraatz, Org. Biomol. Chem. 3 (2005) 3018e3023; (g) F.E. Appoh, T.C. Sutherland, H.B. Kraatz, J. Organom. Chem. 689 (2004) 4669e4677; (h) M.A. Sierra, M. Rodríguez-Fernandéz, L. Casarrubios, M. Gómez-Gallego, C.P. Allen, M.J. Mancheño, Dalton Trans. (2009) 8399e8405. [4] (a) L.V. Popova, V.N. Babin, Y.A. Beleusov, Y.S. Nekrasov, A.E. Snegireva, N.P. Borodina, G.M. Shaposhnikova, O.B. Bychenko, P.M. Raevskii, M.N. Morozova, A.I. Ilyna, K.G. Shitkov, Appl. Organomet. Chem. 7 (1993) 85e94; (b) V.N. Babin, P.M. Raevskii, K.G. Snchitkov, L.V. Snegur, Y.S. Nekrasov, Mendeleev Chem. J. 39 (1995) 17; (c) H. Tamura, M. Miwa, Chem. Lett. (1997) 1177e1178; (d) D. Osella, M. Ferrali, P. Zanello, F. Laschi, M. Fontani, C. Nervi, G. Cavigliolo, Inorg. Chim. Acta 306 (2000) 42e48; (e) L.V. Snegur, A.A. Simenel, Y.S. Nekrasov, E.A. Morozova, Z.A. Starikova, S.M. Peregudova, Y.V. Kuzmenko, V.N. Babin, L.A. Ostrovskaya, N.V. Bluchterova, M.M. Fomina, J. Organomet. Chem. 689 (2004) 2473e2479; (f) M.D. Joksovi" c, V. Markovi" c, Z.D. Jurani" c, T. Stanojkovi" c, L.S. Jovanovi" c, cevi" c, I.S. Damljanovi" c, K.M. Szécsényi, N. Todorovi" c, S. Trifunovi" c, R.D. Vuki" J. Organomet. Chem. 694 (2009) 3935e3942; (g) Y.S. Xie, H.L. Zhao, H. Su, B.X. Zhao, J.T. Liu, J.K. Li, H.S. Lv, B.S. Wang, D.S. Shin, J.Y. Miao, Eur. J. Med. Chem. 45 (2010) 210e218. [5] (a) A. Vessières, S. Top, P. Pigeon, E. Hillard, L. Boubeker, D. Spera, G. Jaouen, J. Med. Chem. 48 (2005) 3937e3940; (b) J. Rajput, J.R. Moss, A.T. Hutton, D.T. Hendricks, C.E. Arendse, C. Imrie, J. Organomet. Chem. 689 (2004) 1553e1568; (c) S. Top, A. Vessières, G. Leclercq, J. Quivy, J. Tang, J. Vaisserman, M. Huché, G. Jaouen, Chem. Eur. J. 9 (2003) 5223e5236. [6] (a) F.E. Appoh, T.C. Sutherland, H.B. Kraatz, J. Organom. Chem. 690 (2005) 1209e1217; (b) O. Brosch, T. Weyhermüller, N. Metzler-Nolte, Eur. J. Inorg. Chem. (2000) 323e330.

2152

S. Quintal et al. / Journal of Organometallic Chemistry 696 (2011) 2142e2152

[7] (a) K. Heinze, M. Beckmann, Eur. J. Inorg. Chem. (2004) 2974e2988; (b) K. Heinze, M. Beckmann, Eur. J. Inorg. Chem. (2005) 3450e3457; (c) V.P. Dyadchenko, N.M. Belov, D.A. Lemenovskii, M.Y. Antipin, K.A. Lyssenko, A.E. Bruce, M.R.M. Bruce, J. Organomet. Chem. 695 (2010) 304e309; (d) N. Sadhukhan, A. Sinha, R.K. Das, J.K. Bera, J. Organomet. Chem. 695 (2010) 67e73; (e) Z.H. Weng, Z.L. Chen, F.P. Liang, J. Coord. Chem. 62 (2009) 1801e1808. [8] (a) H. Shinohara, T. Kusaka, E. Yokota, R. Monden, M. Sisido, Sens. Actuators B. Chem. 65 (2000) 144e146; (b) C. Suksai, P. Leeladee, D. Jainuknan, T. Tuntulani, N. Muangsin, O. Chailapakul, P. Kongsaeree, C. Pakavatchai, Tetrahedron Lett. 46 (2005) 2765e2769; (c) A. Berduque, G. Herzog, Y.E. Watson, D.W.M. Arrigan, O. Reynes, G. Royal, E. Saint-Aman, Electroanalysis 17 (2005) 392e399; (d) H. Miyaji, G. Gasser, S.J. Green, Y. Molard, S.M. Strawbridge, J.H.R. Tucker, Chem. Comm. (2005) 5355e5357. [9] (a) C.Y. Cao, K.J. Wei, Inorg. Chem. Commun. 13 (2010) 19e21; (b) K.J. Wei, J. Ni, Y. Liu, Inorg. Chem. 49 (2010) 1834e1848. [10] P.N. Martinho, S. Quintal, P.J. Costa, S. Losi, V. Félix, M.C. Gimeno, A. Laguna, M.G.B. Drew, P. Zanello, M.J. Calhorda, Eur. J. Inorg. Chem. (2006) 4096e4103. [11] S. Quintal, J. Matos, I. Fonseca, V. Félix, M.G.B. Drew, N. Trindade, M. Meireles, M.J. Calhorda, Inorg. Chim. Acta 361 (2008) 1584e1596. [12] (a) H. tom Dieck, H. Friedel, J. Organomet. Chem. 14 (1968) 375; (b) R.G. Hayter, P1, J. Organomet. Chem. 13 (1967); (c) P.K. Baker, Adv. Organomet. Chem. 40 (1996) 45e115 (and references therein). [13] J.C. Alonso, P. Neves, C. Silva, A.A. Valente, P. Brandão, S. Quintal, M.J. Villa de Brito, P. Pinto, V. Félix, M.G.B. Drew, J. Pires, A.P. Carvalho, M.J. Calhorda, P. Ferreira, Eur. J. Inorg. Chem. (2008) 1147e1156. [14] P.J. Costa, M. Mora, M.J. Calhorda, V. Félix, P. Ferreira, M.G.B. Drew, H. Wadepohl, J. Organomet. Chem. 687 (2003) 57e68. [15] J.R. Ascenso, C.G. Azevedo, M.J. Calhorda, M.A.A.F.C.T. Carrondo, P. Costa, A.R. Dias, M.G.B. Drew, V. Félix, A.M. Galvão, C.C. Romão, J. Organomet. Chem. 632 (2001) 197e208.

[16] J.E. Aguado, O. Crespo, M.C. Gimeno, P.G. Jones, A. Laguna, Y. Nieto, Eur. J. Inorg. Chem. 19 (2008) 3031e3039. [17] L. Phillips, A.R. Lacey, M.K. Cooper, J. Chem. Soc. Dalton Trans. (1988) 1383e1391. [18] P. Zanello, Inorganic Electrochemistry. Theory, Practice and Application. RSC, U.K., 2003. [19] F. Fabrizi de Biani, F. Jäkle, M. Spiegler, M. Wagner, P. Zanello, Inorg.Chem. 36 (1997) 2103e2111. [20] R.G. Parr, W. Young, Density Functional Theory of Atoms and Molecules. Oxford University Press, New York, 1989. [21] (a) ADF2007, SCM, Theoretical Chemistry, Vrije Universiteit, Amsterdam, The Netherlands, http://www.scm.com; (b) G. Te Velde, F.M. Bickelhaupt, S.J.A. van Gisbergen, C.F. Guerra, E.J. Baerends, J.G. Snijders, T. Ziegler, J. Comput. Chem. 22 (2001) 931e967; (c) C.F. Guerra, J.G. Snijders, G. Te Velde, E.J. Baerends, Theor. Chem. Acc. 99 (1998) 391e403. [22] H.H. Lau, H. Hart, J. Org. Chem. 24 (1959) 280e281. [23] C. Cavazza, F. Fabrizi de Biani, T. Funaioli, P. Leoni, F. Marchetti, L. Marchetti, P. Zanello, Inorg.Chem. 48 (2009) 1385e1397. [24] W. Kabsch, J. Appl. Crystallorgr. 21 (1988) 916e932. [25] DIFABS N. Walker, D. Stuart, Acta Crystallogr. A 39 (1983) 158. [26] CrysAlis. Oxford Diffraction Ltd, Abingdon, U.K., 2006. [27] Abspack. Oxford Diffraction Ltd, Oxford, U.K., 2005. [28] G.M. Sheldrick, Acta Crystallogr. A 64 (2008) 112e122. [29] A.L. Spek, PLATON, A Multipurpose Crystallographic Tool. Utrecht University, Utrecht, The Netherlands, 2005. [30] (a) L. Versluis, T. Ziegler, J. Chem. Phys. 88 (1988) 322e328; (b) L. Fan, T. Ziegler, J. Chem. Phys. 95 (1991) 7401e7408. [31] S.H. Vosko, L. Wilk, M. Nusair, Can. J. Phys. 58 (1980) 1200e1211. [32] A.D. Becke, J. Chem. Phys. 88 (1987) 1053e1062. [33] (a) J.P. Perdew, Phys. Rev. B. 33 (1986) 8822e8824; (b) J.P. Perdew, Phys. Rev. B. 34 (1986) 7406. [34] E. van Lenthe, A. Ehlers, E.J. Baerends, J. Chem. Phys. 110 (1999) 8943e8953. [35] S. Portmann, H.P. Lüthi, Chimia 54 (2000) 766e770. [36] http:www.chemcraftprog.com/index.html.