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Three hexacarbonyl diiron dithiolate complexes [Fe2(CO)6(μ-(SCH2)2X)] with different substituted bridgeheads (X=CH2, CEt2, CBn2 (Bn=CH2C6H5)), have been studied under the same experimental conditions by cyclic voltammetry in dichloromethane [NBu4][PF6] 0.2 M. DFT calculations were performed to rationalize the mechanism of reduction of these compounds. The three complexes undergo a two-electron transfer whose the mechanism depends on the bulkiness of the dithiolate bridge, which involves a different timing of the structural changes (Fe−S bond cleavage, inversion of conformation and CO bridging) vs redox steps. The introduction of a bulky group in the dithiolate linker has obviously an effect on normally ordered (as for propanedithiolate (pdt)) or inverted (pdtEt2, pdtBn2) reduction potentials. Et→Bn replacement is not theoretically predicted to alter the geometry and energy of the most stable mono-reduced and bi-reduced forms but such a replacement alters the kinetics of the electron transfer vs the structural changes.

International audience; A series of triiron clusters [Fe3(CO)5(2-dppe)(µ-pdtR2)(µ-pdt)] featuring different combination of dithiolate bridges have been prepared by using dinuclear and mononuclear precursors, [Fe2(CO)6(µ-xdt)] (xdt = pdt, pdtEt2, pdtBn2, adtBn) and [Fe(CO)2(2-dppe)(2-pdt)]. Novel triiron compounds, featuring sterically crowded dithiolate bridges (pdtEt2, pdtBn2), were spectroscopically and structurally characterized. Their protonation and redox behaviours are discussed. The effect of the dithiolate bridges on the electrochemical properties (oxidation and reduction) of the complexes [Fe3(CO)5(2-dppe)(µ-xdt)(µ-pdt)] has been examined by cyclic voltammetry and rationalized by DFT calculations. Studies of the protonation of these species and their proton reduction behaviour were considered.

The electrochemical reduction of complexes [Fe2 (CO)4 (κ2 -phen)(μ-xdt)] (phen=1,10-phenanthroline; xdt=pdt (1), adtiPr (2)) in MeCN-[Bu4 N][PF6 ] 0.2 m is described as a two-reduction process. DFT calculations show that 1 and its monoreduced form 1- display metal- and phenanthroline-centered frontier orbitals (LUMO and SOMO) indicating the non-innocence of the phenanthroline ligand. Two energetically close geometries were found for the doubly reduced species suggesting an intriguing influence of the phenanthroline ligand leading to the cleavage of a Fe-S bond as proposed generally for this type of complex or retaining the electron density and avoiding Fe-S cleavage. Extension of calculations to other complexes with edt, adtiPr bridge and even virtual species [Fe2 (CO)4 (κ2 -phen)(μ-adtR )] (R=CH(CF3 )2 , H) or [Fe2 (CO)4 (κ2 -phen)(μ-pdtR )] (R=CH(CF3 )2 , iPr) showed that the relative stability between both two-electron-reduced isomers depends on the nature of the bridge and the possibility to establish a remote anagostic interaction between the iron center {Fe(CO)3 } and the group carried by the bridged-head atom of the dithiolate group.

A series of dithiolate carbonyl diiron complexes with cyclic azadiphosphine, related to the active site of [FeFe]‐hydrogenases, has been prepared. Several combinations of diphosphines and dithiolate bridges have been examined in order to obtain information on the influence of electronic and steric effects of the group linked to the nitrogen atom of the phosphine (phenyl or benzyl) and the bridge‐head of the dithiolate (CH2, CEt2, CBn2). Products were spectroscopically and structurally characterized. Protonation experiments show that depending on the nature of the amine in the diphosphine, protonation processes are different. With NBn group, the process is arrested at N‐protonated species, while with NPh, the proton is transferred to the diiron site giving bridging‐hydride species. The effect of the bridge‐head group of the dithiolate is very slight on the electronic properties of compounds. Depending on the steric crowding of the bridge, different isomers related to the dibasal or basal‐apical position of the diphosphine, are observed in solution or in solid state. Electrochemical study was performed to examine the activity of these compounds in the presence of acid.

The electrochemical reduction of complexes [Fe

A novel complex featuring a mesoionic carbene [Fe2(CO)5(trz)(?-pdt)] (1) (trz = 1-phenyl-l,3-methyl,4-butyl-1,2,3-triazol-5-ylidene), was synthesized and spectroscopically and structurally characterized. The reductive behaviour of this compound in the presence and in the absence of acid (CH3CO2H) was examined by cyclic voltammetry (CV) that revealed the lack of efficient activity towards proton reduction.

International audience; Electrochemical oxidation of the complex [Fe2(CO)4(κ2‐dmpe)(µ‐adtBn)] (adtBn = (SCH2)2NCH2C6H5, dmpe = Me2PCH2CH2PMe2) (1) has been studied by cyclic voltammetry (CV) in acetonitrile and in dichloromethane in presence of various substrates L (L =MeCN, trimethylphosphite, isocyanide). The oxidized species, [1‐MeCN](PF6)2, [1‐(P(OMe)3)2](PF6)2 and [1‐(RNC)4](PF6)2 (R = tButyl, Xylyl), have been prepared and characterized by IR, NMR spectroscopies and, excepted [1‐MeCN](PF6)2, by X‐ray diffraction analysis. The crystallographic structures of the new FeIIFeII complexes reveal in any case that the association of one additional ligand (P(OMe)3 or RNC) occurs and, according to the nature of the substrates, further substitutions of one or three carbonyl groups, by P(OMe)3 or RNC, respectively, arise. Density functional theory (DFT) calculations have been performed for elucidating and discriminating, in each case, the mechanisms leading to the corresponding oxidized species. Moreover, the different degree of ligand substitution in the diiron core has been theoretically rationalized.

International audience; Three different mononuclear copper(II) complexes 1-3 bearing ditopic macrocyclic ligands (L1 or L2) have been prepared. Both ligands include two coordinating cores, namely tris(methylpyridyl)amine (TPA) and pyridine-dicarboxamide (PydCA). Complexes 1-3 have been characterized in solid state, and in solution by UV-Vis and EPR spectroscopies, as well as by cyclic voltammetry. X-ray diffraction analyses of crystals of complexes 1 and 3 show that the Cu(II) ion is preferably coordinated in the TPA site. Moreover, the coordination sphere of the copper center fully depends on the Cu(II) salt used for the synthesis (CuCl2 for 1 and 2, Cu(OTf)2 for 3). Hence, the tetracoordinated bis-chloro complex 1 adopts a distorted square-planar geometry at solid state, whereas the pentacoordinated bis-aqua complex 3 displays an almost perfect square pyramidal conformation. Both complexes 1 and 3 react with H2O2 in acetonitrile, leading to the formation of copper(II)-hydroperoxo species according to the UV-Vis spectroscopic studies.

The electrochemical behavior of complexes [FeMo(CO) 5 (κ 2 -dppe)(μ-pdt)] (1) and [FeMo(CO) 4 (MeCN)( κ 2 -dppe)(μ-pdt)] (2), in the absence and in the presence of acid, has been investigated. The reduction of 1 follows at slow scan rates, in CH 2 Cl 2 -[NBu 4 ][PF 6 ] and acid-free media, an EC rev E mechanism that is supported by cyclic voltammetry (CV) experiments and digital CV simulations. In MeCN-[NBu 4 ][PF 6 ], the electrochemical reduction of 1 is the same as in dichloromethane and follows an ECE mechanism at slow scan rates, but with a positive shift of the redox potentials. In contrast, the oxidation of 1 is strongly solvent-dependent. In dichloromethane, the oxidation of 1 is reversible and involves a single electron, while in acetonitrile, it is irreversible at moderate and slow scan rates (v ≤ ca. 1 V s -1 ), and some chemical reversibility is apparent at higher scan rates (v = 10 V s -1 ). Density functional theory calculations revealed that the chemical step in the EC rev E mechanism corresponds to the dissociation of one PPh 2 end of the diphosphine ligand and the transfer of the semibridging CO to the Fe atom, similarly to the mechanism observed in the FeFe analogue complex. However, in the case of 1, the subsequent coordination of the phosphine ligand to the other metal is an unfavorable process.

Electrochemical oxidation of the complex [Fe

International audience; Advances in Bioorganometallic Chemistry examines the synthesis, structure and reactivity of bioorganometallics, their pharmaceutical applications, hydrogenase, vitamin B12-like systems, and metalloproteins. It is written by the top researchers in the field and compiled by editors Toshikazu Hirao and Toshiyuki Moriuchi. Developments in this new field of bioorganometallic chemistry, a hybrid between biology and organometallic chemistry, happen very quickly and this comprehensive reference offers the latest research and findings in the field. The book features a discussion of the synthesis, structure, and reactivity of bioorganometallics, and an examination of hydrogenase-like systems, which were designed to demonstrate catalytic activities and functional properties. Advances in Bioorganometallic Chemistry also includes a discussion of bioorganometallics as they relate to medicinal chemistry, specifically applications of metalloproteins, metalloenzymes, and applications in bioimaging. The book concludes with coverage of vitamin B12-like systems, including the latest developments in derivatives designed to perform bio-inspired catalytic reactions.Table of Contents1. Synthesis, structure and reactivity2. Hydrogenase3. Medicinal Chemistry and Metallodrugs4. Metalloproteins and metalloenzymes5. Vitamin B12

International audience; Electrochemical studies of [Fe2(CO)4(κ2-dmpe)(μ-dithiolate)] (dithiolate=adtBn, pdt) and density functional theory (DFT) calculations reveal the striking influence of an amine functionality in the dithiolate bridge on their oxidative properties. [Fe2(CO)4(κ2-dmpe)(μ-adtBn)] (1) undergoes two one-electron oxidation steps, with the first being partially reversible and the second irreversible. When the adtBn bridge is replaced with pdt, a shift of 60 mV towards more positive potentials is observed for the first oxidation whereas 290 mV separate the oxidation potentials of the two cations. Under CO, oxidation of azadithiolate compound 1 occurs according to an ECE process whereas an EC mechanism takes place for the propanedithiolate species 2. The dication species [1-CO]2+ resulting from the two-electron oxidation of 1 has been spectroscopically and structurally characterized. The molecular details underlying the reactivity of oxidized species have been explored by DFT calculations. The differences in the behaviors of 1 and 2 are mainly due to the presence, or not, of favored interactions between the dithiolate bridge and the diiron site depending on the redox states, FeIFeII or FeIIFeII, of the complexes.

International audience; The chemistry of tris(thiolato) bridged dimolybdenum compounds in low oxidation states (mostly III) is considered. Various synthetic routes lead to chalcogenide-bridged dinuclear complexes of group 6 metals (mainly Mo). Extensive chemistry of these derivatives is reviewed. Their reactivity towards various reagents such as alkynes, isonitriles, nitriles, propargylic alcohols, azides, hydrazines, carbon disulfide…, demonstrates their ability for activation of small unsaturated molecules through new C–X (X = C, N, O, S…) bonds formation or cleavage.

The reduction of the compound [Fe2(CO)4(κ2-dmpe){μ-(SCH2)2NBn}] [dmpe = 1,2-bis(dimethylphosphino)ethane], which is considered as an FeI-FeI model of the [2Fe]H subsite of [Fe-Fe]H2ases with a rotated conformation in the solid state, was investigated by cyclic voltammetry. Under reductive conditions, [Fe2(CO)4(κ2-dmpe){μ-(SCH2)2NBn}] undergoes electron-transfer-catalyzed isomerization to afford an isomer featuring a bridging diphosphine [Fe2(CO)4(μ-dmpe){μ-(SCH2)2NBn}]. Comparison of the crystallographic structures of the two isomers affords unique and direct experimental evidence that dissymmetrical coordination of the chelate ligand is required to promote the rotated conformation at one iron atom in this compound. DFT calculations were performed to rationalize this isomerization process and the slightly distorted structure of [Fe2(CO)4(μ-dmpe){μ-(SCH2)2NBn}]. The symmetrization of the coordination sphere results in the disruption of the agostic interaction that stabilized the rotated isomer.

International audience; Dimolybdenum thiolate-bridged complexes [Mo2Cp2(μ-SMe)2(μ-SCH2CH2E)] (E = O (2) or NH (4)) with a proton-dependent protecting device have been synthesized by reaction of [Mo2Cp2(μ-SMe)2(μ-Cl)2] (1) with SCH2CH2EH. The reactivity of the resultant quadruply bridged complexes with acid was investigated in the absence and in the presence of a potential ligand (N2, MeCN, RNC). While the protonation of complexes 2 and 4 under N2 in dichloromethane produced only the oxidized derivatives instead of the desired diazenido compound, ligand binding was observed in MeCN or in the presence of RNC (R = t-Bu, Xyl). Whereas acetonitrile loss from [Mo2Cp2(μ-SMe)2(μ-SCH2CH2OH)(MeCN)2]+ (8+) prevented the isolation and characterization of this species, the t-BuNC analogue (6+) could be characterized by an X-ray crystal structure. The electrochemistry of 2 and 2+ was investigated in CH2Cl2 and in MeCN, both in the absence and in the presence of acid. While the addition of HBF4·Et2O to a dichloromethane solution of 2 only produced 2+ (and presumably H2), 8+ was the major product of the protonation in MeCN.

The behavior of [Fe(2)(CO)(4)(κ(2)-PNP(R))(μ-pdt)] (PNP(R) =(Ph(2)PCH(2))(2)NR, R=Me (1), Ph (2); pdt=S(CH(2))(3)S) in the presence of acids is investigated experimentally and theoretically (using density functional theory) in order to determine the mechanisms of the proton reduction steps supported by these complexes, and to assess the role of the PNP(R) appended base in these processes for different redox states of the metal centers. The nature of the R substituent of the nitrogen base does not substantially affect the course of the protonation of the neutral complex by CF(3)SO(3)H or CH(3)SO(3)H; the cation with a bridging hydride ligand, 1 μH(+) (R=Me) or 2 μH(+) (R=Ph) is obtained rapidly. Only 1 μH(+) can be protonated at the nitrogen atom of the PNP chelate by HBF(4)·Et(2)O or CF(3)SO(3)H, which results in a positive shift of the proton reduction by approximately 0.15 V. The theoretical study demonstrates that in this process, dihydrogen can be released from a η(2)-H(2) species in the Fe(I)Fe(II) state. When R=Ph, the bridging hydride cation 2 μH(+) cannot be protonated at the amine function by HBF(4)·Et(2)O or CF(3)SO(3)H, and protonation at the N atom of the one-electron reduced analogue is also less favored than that of a S atom of the partially de-coordinated dithiolate bridge. In this situation, proton reduction occurs at the potential of the bridging hydride cation, 2 μH(+). The rate constants of the overall proton reduction processes are small for both complexes 1 and 2 (k(obs) ≈4-7 s(-1)) because of the slow intramolecular proton migration and H(2) release steps identified by the theoretical study.

The reactivity of [Fe2(CO)4(κ2-LL)(μ-pdt)]+ complexes (pdt = S(CH2)3S, propanedithiolate) with different substrates L′ (L′ = CO, MeCN, P(OMe)3) was investigated electrochemically in order to assess the influence of the chelating ligand κ2-LL (LL = IMe-CH2-IMe (1+), dppe (2+); IMe = 1-methylimidazol-2-ylidene). This latter ligand is effectively shown to affect the reactivity of the cations in different ways: when L′ = CO, the adduct [Fe2(CO)4(μ-CO)(κ2-dppe)(μ-pdt)]+ (2-CO+) was clearly observed by cyclic voltammetry, whereas [Fe2(CO)4(μ-CO)(κ2-IMe-CH2-IMe)(μ-pdt)]+ (1-CO+) was not detected, although DFT calculations show that the energies of the products and the activation barriers to their formation are similar. When L′ = MeCN, the adducts X-MeCN+ with X = 1, 2 are both observed, but the formation is easier when LL = dppe. Finally, the reaction of [Fe2(CO)4(κ2-IMe-CH2-IMe)(μ-pdt)]+ (1+) with P(OMe)3 produces the disubstituted dication [Fe2(CO)2{P(OMe)3}2(κ2-IMe-CH2-IMe)(μ-CO)(μ-pdt)]2+ (42+) via a disprop...

The reaction of [Fe 3 (CO) 12 ] with diphenyl-2-pyridylphosphine (PPh 2 Py) in refluxing toluene for 1 h afforded three compounds, [Fe 2 (CO) 6 (μ-PPh 2 )(μ-κ 2 -C,N-C 5 H 4 N)] ( 1 ), [Fe(CO) 4 (κ 1 -P-PPh 2 Py)] ( 2 ), and [Fe(CO) 3 (κ 1 -P-PPh 2 Py) 2 ] ( 3 ) in 23%, 10% and 3.5% yields after work-up, respectively. The PPh 2 Py ligand acts as a terminal P-donor ligand in 2 and 3 , while in 1 it underwent a selective phosphorus–carbon(pyridyl) bond cleavage to afford phosphido- and pyridyl-bridged ligands. The complexes were characterized by elemental analysis, FAB-mass, FTIR, 1 H and 31 P–{ 1 H}NMR spectroscopies. Compounds 1 and 2 were also characterized by X-ray single crystal.

Reaction of the base-containing diphosphine (Ph2PCH2)2NCH3 with [Fe2(CO)6(μ-S2)] (1) yielded at room temperature the novel compound [Fe2(CO)4(μ-κ1:κ1-SPPh2){μ-κ2:κ2-SCH2N(Me)CH2PPh2}] (2) resulting from S−S and P−C bond cleavage concomitant with P−S and C−S bond formation. Experiments at low temperature allowed the isolation of an intermediate species, [Fe2(CO)5(μ-κ1:κ1-SPPh2){μ-κ2:κ1-SCH2N(Me)CH2PPh2}] (3), differing from 2 by the coordination mode of the PNS ligand and the presence of one additional carbonyl group. When the reaction was performed in the presence of an excess of tBuNC, an analogous compound of 3 was obtained. The X-ray analysis of this species, 4, revealed that an isocyanide replaced a carbonyl ligand in the axial position at one iron center.

International audience; Two hexacarbonyl diiron compounds featuring dithiolate bridges with strong electron-withdrawing groups (CO2Me, tetrachloro-biphenyl) were synthesized and structurally characterized. Electrochemical study of these compounds demonstrates that such electron-withdrawing groups have a pronounced effect on both the reduction potentials and the electron transfer process. The reduced forms of these compounds catalyze the reduction of protons in dichloromethane. However, the tetrachloro-biphenyl derivative is the only one able to work in the potential range of its primary reduction process. A catalytic reaction scheme is proposed.

International audience; Reactions of the trithiolato-bridged complex [Mo2Cp2(μ-SMe)3(MeCN)2](BF4) (1) with acyclic (e.g., Et2S) or cyclic (e.g., thiirane, thietane, tetrahydrothiophene, 1,4-dithiane, and 1,4-thioxane) thioethers and chalcogenophenes (benzothiophene, benzoselenophene, and dibenzothiophene) in dihaloalkanes led to either the thioether- and halide-bridged compounds [Mo2Cp2(μ-SMe)2(μ-SRR′)(μ-X)](BF4) (R = R′ = Et, X = Cl (3); RR′ = C4H8, X = Cl (10), X = Br (11) ; RR′ = C4H8O, X = Cl (14)), and dithioether- and chloro-bridged derivatives [Mo2Cp2(μ-SMe)2(μ-Cl){μ-κ1(S),κ1(S)-(SR′′x(CH2)nSR′′x}](BF4) (x = 1, R′′ = Me, n = 1 (4); x = 0, n = 4 (13)) or the μ-sulfido complex [Mo2Cp2(μ-SMe)3(μ-S)](BF4) (6) and the methyl 1,3-propylthiolate thioether-bridged compound [Mo2Cp2(μ-SMe)2{μ-κ2(S),κ2(S)-S(CH2)3SMe}](BF4) (8), according to the structural features of the organic sulfur reagents. Ring-opening reaction through the cleavage of C−S bonds occurred when small-ring thioethers (e.g., thiirane and thietane) are used as reagents, whereas facile C−X (X = Cl, Br) bond cleavage was observed for other sulfur molecules. Some reactions that were conducted in chlorocarbon solvents (e.g., CH2Cl2, (CH2)2Cl2) gave rise to the formation of the oxo-bridged complex [Mo2Cp2(μ-SMe)3(μ-O)](BF4) (7) as a byproduct with moderate yields. All new complexes have been characterized by elemental analyses and spectroscopic methods, supplemented for the tetraphenylborate or hexafluorophosphate salts of 4, 6−8, 10, and 13 by X-ray diffraction.

The electrochemical behaviour of the unsymmetrically disubstituted [Fe 2 (CO) 4 (κ 2 -dppe)(μ-pdt)(μ-H)] + ( 1μH + ) complex was studied by cyclic voltammetry (CV) in MeCN– and CH 2 Cl 2 –[NBu 4 ][PF 6 ] both in the absence and in the presence of acid (HBF 4 · Et 2 O or HOTs). In the absence of acid, 1μH + undergoes a reversible one-electron oxidation and two-successive one-electron reductions, the first of which is partially reversible. In contrast to symmetrical analogues, 1μH + does not regenerate its neutral precursor 1 upon reduction on the CV timescale. When acid is present, the reduction leads to catalytic proton reduction at a mild potential (ca. −1.3 V vs. Fc + /Fc) according to an original mechanism where 1μH + is the catalyst. A second proton reduction process at −1.5 V is also observed for both HBF 4 · Et 2 O and HOTs. The latter is proposed to be catalysed by the one-electron reduced form of the H-bridged complex, 1μH .

Electrochemical investigations on a structural analogue of the [2Fe](H) subsite of [FeFe]H(2)ases, namely, [Fe(2)(CO)(6){micro-SCH(2)N(CH(2)CH(2)- OCH(3))CH(2)S}] (1), were conducted in MeCN/NBu(4)PF(6) in the presence of HBF(4)/Et(2)O or HOTs. Two different catalytic proton reduction processes operate, depending on the strength and the concentration of the acid used. The first process, which takes place around -1.2 V for both HBF(4)/Et(2)O and HOTs, is limited by the slow release of H(2) from the product of the {2 H(+)/2 e} pathway, 1-2H. The second catalytic process, which occurs at higher acid concentrations, takes place at different potentials depending on the acid present. We propose that this second mechanism is initiated by protonation of 1-2H when HBF(4)/Et(2)O is used, whereas the reduction of 1-2H is the initial step in the presence of the weaker acid HOTs. The potential of the second process, which occurs around -1.4 V (reduction potential of 1-3H(+)) or around -1.6 V (the reduction potential of 1-2H) is thus dependent on the strength of the available proton source.

International audience; Novel asymmetrically substituted azadithiolate compounds [Fe2(CO)4(κ2-dppe){μ-SCH2N(R)CH2S}] (R = iPr, 1a; CH2CH2OCH3, 1b; CH2C6H5, 1c) have been synthesized by treatment of [Fe2(CO)6(μ-adt)] [adt = SCH2N(R)CH2S, with R = iPr, CH2CH2OCH3, CH2C6H5] with dppe (dppe = Ph2PCH2CH2PPh2) in refluxing toluene in the presence of Me3NO. 1a−c have been characterized by single-crystal X-ray diffraction analyses. The electrochemical investigation of 1a−c and of [Fe2(CO)4(κ2-dppe)(μ-pdt)] (1d) [pdt = S(CH2)3S] in MeCN− and THF−[NBu4][PF6] has demonstrated that the electrochemical reduction of 1a−d gives rise to an Electron-transfer-catalyzed (ETC) isomerization to the symmetrical isomers 2a−d where the dppe ligand bridges the iron centers. Compounds 2a−d were characterized by IR and NMR spectroscopy, elemental analysis, and X-ray crystallography for 2a.

International audience; The reduction of the Fe(II)Fe(II) complex [Fe2(CO)2{P(OMe)3}2(κ2-IMe-CH2-IMe)(μ-CO)(μ-pdt)]2+ (2P2+; pdt = S(CH2)3S), which is a synthetic model of the H cluster of the [FeFe] hydrogenases in its inactive state, has been investigated electrochemically and theoretically (by density functional theory, DFT) in order to determine the mechanisms, intermediates, and products of the related processes. The electrochemical reduction of 2P2+ occurs according to an ECE-type reaction where the intervening chemical step is the loss of one P(OMe)3 ligand. This outcome, which is based on cyclic voltammetric experiments, is strongly supported by DFT calculations that provide additional information on the intermediates and the energetics of the reactions involved. The electrochemical reoxidation of the neutral product of the reduction follows an EEC process where the chemical step is the binding of P(OMe)3 to a dicationic intermediate. DFT calculations reveal that this intermediate has an unusual geometry wherein one of the two C–H bonds of a side methylene from the pdt group forms an agostic interaction with one Fe center. This interaction is crucial to stabilize the 32e− diferrous center and concomitantly to preserve Fe(II) from binding of weakly coordinating species. Nonetheless, it could be displaced by a relatively stronger electron donor such as H2, which could be relevant for the design of new oxidation catalysts.

International audience; This chapter focuses on models for the mixed‐valent Hox state as well as protonation reactions of Hred models and on some significant insights into proton reduction chemistry. Although numerous [FeFe] hydrogenase model complexes exist, synthetic access to iron‐chalcogenolato compounds is limited to substitution reactions and oxidative additions. During the past two decades, significant development in modeling the active site of [FeFe] hydrogenases allowed to reveal the fundamental modes of action at the molecular level.

Mixed μ-phosphido or μ-thiolato μ-halo-dimolybdenum(III) compounds [Mo 2 Cp 2 (μ-SMe) 2 (μ-X)(μ-Y)] (X = PPh 2 , Y = Cl ( 1 ); X = SCH 3 , Y = Br ( 3 ), I( 4 )) have been studied. Syntheses and X-ray structures of the new bromo and iodo analogues of [Mo 2 Cp 2 (μ-SMe) 3 (μ-Cl)] ( 2 ) are reported. While preparing 3 a side-product 5 was obtained and structurally characterised as the Mo 5 system [{Mo 2 Cp 2 Br(μ-O)(μ-SMe) 2 } 2 (μ-MoO 4 )], containing a {Mo IV –Mo IV –O–(Mo VI O 2 )–O–Mo IV –Mo IV } unit. The influence of the bridging groups on the structures and electrochemical behaviour of the complexes [Mo 2 Cp 2 (μ-SMe) 2 (μ-X)(μ-Y)] 1 – 4 has been investigated. In MeCN–[NBu 4 ][PF 6 ] the first oxidation of [Mo 2 Cp 2 (μ-SMe) 2 (μ-PPh 2 )(μ-Cl)] ( 1 ) is quasi-reversible, contrasting with the essentially irreversible first oxidation of the thiolate analogue [Mo 2 Cp 2 (μ-SMe) 3 (μ-Cl)] ( 2 ) under similar conditions. The effects of lowering the temperature or increasing the scan rate on the oxidation of 1 were examined: the initial quasi-reversible oxidation at first became irreversible but at still higher scan rates or lower temperatures the oxidation was again quasi-reversible. This suggests that the oxidation of 1 in MeCN is followed by reversible coordination of acetonitrile to afford the species [Mo 2 Cp 2 (μ-SMe) 2 (μ-PPh 2 )(Cl)(MeCN)] + ( 7 + ). Cyclic voltammetry of [Mo 2 Cp 2 (μ-SMe) 3 (μ-Y)](Y = Br ( 3 ) or I ( 4 )) showed two quasi-reversible diffusion-controlled oxidation steps in CH 2 Cl 2 –[NBu 4 ][PF 6 ] or thf–[NBu 4 ][PF 6 ]. In acetonitrile, the fast loss of the halide ligands results in the formation of [Mo 2 Cp 2 (μ-SMe) 3 (MeCN) 2 ] + species.

Attempts at methylating cis -[Mo 2 Cp 2 (μ-SMe) 3 L 2 ](BF 4 ) [Cp = η 5 -C 5 H 5 ; L = CO ( 1a ) CNxyl ( 1b ), CNBu t ( 1c ), NCMe ( 1d )] with methyl triflate gave the corresponding thioether-bridged cations [Mo 2 Cp 2 (μ-SMe) 2 (μ-SMe 2 )L 2 ] 2+ ( 4 2+ ), except in the case of 1a which did not react at room temperature. The electronic properties of the ancillary ligands L thus have a crucial influence on the course of this reaction. The dimeric compounds [Mo 2 Cp 2 (μ-SMe) 3 (CNBu t )(CN)] ( 2 ) and [Mo 2 Cp 2 (μ-SMe) 3 {μ-η 1 -N C(CH 3 )CH 2 CN}] ( 3 ), which potentially offer the alternatives of S- or N-methylation, reacted with methylating agents to give mainly the S-methylated derivatives 5 and 7 . Only in the case of the nucleophilic reactant 2 was N-methylation also observed and isomer 6 was obtained as a minor product together with 5 . New complexes have been completely characterised by multinuclear NMR, IR and elemental analysis, supplemented for 5 by X-ray diffraction study at 100 K.

International audience; The design of the new FeMo heterobimetallic species [FeMo(CO)(5)(kappa(2)-dppe)(mu-pdt)] is reported. Mossbauer spectroscopy and density functional theory calculations give deep insight into the electronic and structural properties of this compound.

cited By 10; International audience; A series of chemical and electrochemical transformations of systems in which a Mo2Cp2(μ-SMe)3 core is bridged by a μ-C2HnR ligand (n = 0-4) are described in this paper. The reaction of the alkylidene complex [Mo2Cp2(μ-SMe) 3(μ-η1:η2-CHCH2Tol)] (BF4) (1) with LiBun at 0°C produces the μ-σ,π-vinyl complex [Mo2Cp2(μ-SMe) 3(μ-η1:η2-CH=CHTol] (2) in good yield. The molecular structure of 2 has been confirmed by X-ray analysis. Upon treatment with NaBEL4 1 is readily converted into the semibridging alkyl species [Mo2Cp2(μ-SMe)3(μ-CH 2CH2Tol)] (3), which is also formed by electrochemical reduction of 1 in acidic medium. NMR and X-ray diffraction studies of 3 are consistent with, but do not definitively establish, the presence of a η1 α-agostic interaction. Density functional theory has been used to confirm the presence of agostic interactions in both 1 and 3 and also to explore the exchange pathways for these hydrocarbyl dimolybdenum systems. Electrochemical transformation of the μ-alkylidene complex 1 gives 3 as the major product when acid is present and a mixture of 2 and 3 when acid is absent, production of 2 being favored by low initial concentrations of 1. Theoretical, spectroscopic, and diffraction data are used to explain the formation and structures of closely related [Mo2Cp 2(μ-SMe)3(μ-C2HnR] z- complexes (n = 0-4 and z = 0, 1), including 1-3. © 2005 American Chemical Society.

Treatment of [Mo2(Cp)2(μ-SMe)3(MeCN)2]+ (1+) with NO3– or NO2– results in the conversion of one terminally bound acetonitrile ligand into an amidato bridge. The reaction produces [Mo2(Cp)2(μ-SMe)3{μ-η1,η1-OC(Me)NH}]0/+ (20/+) and involves the formation of an intermediate, which was detected by cyclic voltammetry but which could not be isolated, and which likely arises from the substitution of the NOx anion for one MeCN ligand. The electrochemical behaviour of 2+ was studied by cyclic voltammetry in THF and MeCN. The reduction of 2+ in the presence of acid (HBF4/H2O or HBF4/Et2O) in these solvents leads to the release of the amidate bridge. Controlled-potential electrolysis of 2+ in MeCN in the presence of acid produces 1+ quantitatively; the charge consumed (>1 F mol–1 of 1+) indicates that electrons are also used to reduce protons. This was confirmed by the formation of 2+ (in variable amounts depending on the conditions) on treating 2 with acid. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The reduction of [Mo2(Cp)2(µ-SMe)3(µ-O)]+ (1+) has been investigated by cyclic voltammetry and controlled-potential electrolysis in THF- and MeCN/NBu4PF6 without added acid or in the presence of various acids HX (HX: HTsO, CF3CO2H, HBF4). Reduction in the presence of acid follows an ECrevE mechanism in which the intermediate chemical step is an acid-base equilibrium between 1 and [Mo2(Cp)2(µ-SMe)3(µ-OH)]+ (2+). This electrochemical process is followed by protonation of the neutral µ-hydroxo complex 2 to afford different products which depend both on the solvent (THF or MeCN) and on the nature of the acid. Controlled-potential electrolysis of 1+ in the presence of HX (2 equiv.) leads to the generation of binding sites and finally gives products identical to those obtained from protonation of 2 by HX. The complex [Mo2(Cp)2(µ-SMe)3(µ-η1,η1-OCOCF3)] (3) which can be obtained either by protonation of 2 by CF3CO2H or by reduction of 1+ in the presence of CF3CO2H, has been characterized crystallographically. In the presence of HBF4 protonation of 1+ gives 22+. The reactivity of 2+ and of the complexes [Mo2(Cp)2(µ-SMe)3(H2O)(TsO)] (4) and [Mo2(cp)2(µ-SMe)3(H2O)L]+ (L = H2O or THF) (6+), all of which contain a terminal aqua ligand, has also been investigated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The reactions between alcohols ROH (R = Me, Et) and RR(OH)2 (RR = CH2−CH2) and the [perfluoro(sulfanyl)vinyl]diiron complex [{Fe(CO)3}2{µ-C(SMe)(CF3)CβCαF2}] (1) in THF at room temperature involve substitution at the Cα atom to give new (alkoxymethylene)thiaferracyclobutadiene compounds [{Fe(CO)3}2{µ-S(Me)C(CF3)CβCα(OR)2}] [R = Me (2a), Et (2b); RR = CH2CH2 (2c)]. Treatment of 1 with aniline and (methoxycarbonyl)hydrazine, bases of intermediate strength according to Pearson, produces α,β-substituted thiaferracyclopentadiene [{Fe(CO)3}2{µ-S(Me)C(CF3)Cβ(NHR)Cα(NHR)}] [R = Ph (5a), NHC(O)OMe (5b)] complexes. It is suggested that these compounds form through initial nucleophilic attack at Cα to give the zwitterionic intermediate [{Fe(CO)3}2{µ-S(Me)C(CF3)CC(NRH)2}] (f). Thermally induced C−F bond activation is a feature of these reactions. When 1 reacts with thioamides containing three “hard” competitive primary and secondary amine functions and one “soft” thione function, the nucleophile first attacks at Cα through a secondary amine and, in a second step, at Cβ through the thiol function to give α,β adducts [{Fe(CO)3}2{µ-S(Me)C(CF3)CβSC(=NR2)N(R1)Cα(Cβ−Cα)] [R1 = NH2, R2 = CH3 (6a); R1 = CH3, R2 = H (6b); R1 = R2 = CH3 (6c)] possessing novel iminothiazolidine systems fused to the five-membered metallacyclic ring. Treatment of 1 with acetylhydrazine, which has three “hard” nucleophilic functions, results in the formation of the compound [{Fe(CO)3}2{µ-S(Me)C(CF3)C(H)C(10)NNC(Me)O(C(10)−O)}] (7a), in which an oxadiazole function is fused to the thiaazaferracyclohexene ring. The position of the fluorine substituent on the CαCβCγ(CF3)S(Me) ring of ferracyclopentadiene complexes has been found to be the essential factor determining the specific activation of the C−F bond. A single fluoro substituent attached to the β-carbon atom of the chain can be activated by nucleophiles to give α,β adducts [{Fe(CO)3}2{µ-S(Me)C(CF3)Cβ(X)Cα(NRR′)}] [X = OR′′, R = R′ = R′′ = Me (3a); X = OR′′, R = R′′ = Me, R′′ = C(O)NMe2 (3b); X = SR′′ (4)]. In contrast, complexes in which a single fluorine atom is linked to the α-carbon atom do not undergo C−F bond cleavage reactions. X-ray structures of compounds 2a, 3b, 5a, 5b, 6a and 7a are reported.

The bis(nitrile) compound [Mo2Cp2(µ-SMe)3(MeCN)2](BF4) (1) (Cp = C5H5) reacted with substituted hydrazines RNHNH2 (R = Me, Ph) in acetonitrile at room temperature to give the stable diazene species [Mo2Cp2(µ-SMe)3(μ-η2-HN=NR)](BF4) [R= Me (2), Ph (3)]. Compounds 2 and 3 could be readily deprotonated with BuLi to produce neutral diazenido species [Mo2Cp2(µ-SMe)3(µ-η2-N=NR)] [R = Me (4), Ph (5)]. Photolysis of 4 in THF induced isomerization of the diazenide bridge, affording the complex [Mo2Cp2(µ-SMe)3(µ-η1-N=NMe)] (8). This species underwent protonation at the outer nitrogen atom (Nβ) to give the stable isodiazene/hydrazido(2−) complex [Mo2Cp2(µ-SMe)3(μ-η1-N=NHMe)](BF4) (9) which isomerised slowly back into 2 on warming. The molecular structure of the µ-η2-methyldiazenido complex 4 was established by an X-ray diffraction study.

International audience; A novel reaction pathway to synthesize the linear trinuclear clusters [Fe3(CO)5(κ2-diphosphine)(μ-dithiolate)2] via the direct reaction of the dinuclear hexacarbonyl precursor [Fe2(CO)6(μ-dithiolate)] with the mononuclear species [Fe(CO)2(κ2-diphosphine)(κ2-dithiolate)] has been developed with diphosphine (dppe) and dithiolate (pdt = propanedithiolate) (1) or adtBn ({SCH2}2NBn = azadithiolate) (2). A crystallographic study was carried out on 2 and Mössbauer spectroscopy, and DFT calculations have been used to describe the electronic and structural properties of 1. The electrochemical properties of 1 in the absence and in the presence of a weak acid have been the subject of a preliminary investigation.

cited By 9; International audience; The bis(μ-thiolato)dicobalt complex [Co2Cp2(μ-SMe)2] (1) reacts with alkyne-cobalt complexes [Co2(CO)6(μ-F3CCCR)] (2) to give tri- and tetranuclear cobalt cluster compounds. When R=CF3 the main product is [Co2(CO)4(μ-CF3C2CF 3)μ-Co2Cp2(μ-SMe)2] (3) but the trinuclear cluster [Co3Cp(CO)4(μ-SMe)2(μ-CF 3C2CF3)] (4) is also obtained in low yield. When R=H the products are the isomeric clusters [Co3Cp(CO)4(μ-SMe)2(μ-CF 3C2H)] (5 and 6), [Co3Cp2(CO)3(μ-SMe)(μ-CF 3C2CH)] (7) and [CpCo(CO)2]. The solid state structures of 3, 4, 5 and 7 have been established by X-ray analysis. The 50 electron triangular cluster 4 has weak Co-Co bonds [2.573(1), 2.800(1), 2.838(1) Å]. The alkyne ligand bridges the shortest of these bonds in perpendicular fashion. 5 and 7 contain open chain tricobalt units [Co-Co 2.39-2.57 Å] more typical of 50 electron M3 species. In these complexes the alkyne is π-bonded to the central metal atom and σ-bonded to both terminal cobalt atoms. Variable temperature NMR indicates that 5, 6 and 7 each exist in solution as interconverting isomers which differ in the configuration at one sulphur atom. For 5 the activation parameters [ΔH‡=64 kJ mol-1 and ΔS‡=-85 J K-1 mol-1] were obtained spectroscopically. In the solid, molecules of 7 contain an asymmetrically bridging carbonyl [Co-C 1.833(4) and 2.050(3) Å] which is not detectable in the solution spectra. © 2001 Elsevier Science B.V.

The paramagnetic μ-amidato species [Mo2Cp2(μ-MeCONH)(μ-SMe)3]BF42a+ (Cp = η-C5H5) is formed exclusively when the compound [Mo2Cp2(MeCN)2(μ-SMe)3]BF41a in powder form is kept in air, whereas the same starting complex in solution gives a mixture of the μ-amidato species and the μ-oxo complex [Mo2Cp2(μ-O)(μ-SMe)3]BF43. The oxo complex is formed quantitatively on warming [Mo2Cp2(μ-Cl)(μ-SMe)3]BF4 in water. The reduction of 2a+ by NaBH4 in CH3CN affords the molecular product [Mo2Cp2(μ-MeCONH)(μ-SMe)3] 2a which has been characterised by X-ray analysis.

The reaction of the perfluorosulfanylvinyldiiron(I) complex [{Fe(CO)3}2{μ-C(SMe)(CF3)Cβ(CαF2)}] (1) with secondary mono- and diamines (L = Me2NH, (CH2)4NH, HN(CH2)4NH) in a 1:1 ratio in dichloromethane at room temperature led in a multistep reaction to the new monoaminocycloferrathiapentadiene compounds [{Fe(CO)3}2{μ-S(Me)C(CF3)CFCX}] (Χ = NMe2 (2), N(CH2)4 (3), N(CH2)4NH (4)) and [[{Fe(CO)3}2{μ-S(Me)C(CF3)CFC]2{μ-N(CH2)4N}] (5). However, when the reaction of 1 was conducted in THF with a large excess of amine, the diaminocycloferrathiabutene complexes [{Fe(CO)3}2{μ-S(Me)C(CF3)C(CX2)}] (X = NMe2 (6), N(CH2)4 (7)) and [{Fe(CO)3}2{μ-S(Me)C(CF3)C(CX)}] (X = MeN(CH2)2NMe (8), HN(CH2)2 NH (9)) were formed. It is suggested that these compounds form via initial nucleophilic attack at Cα to give the common zwitterionic intermediate [{Fe(CO)3}2{μ-S(Me)C(CF3)C(CFNX2)] (C). Thermally induced C−F bond activation is a feature of these reactions. Thermolysis of diaminocycloferrathiabutene compounds (6−9) in tetrahydrof...

International audience; [Mo2Cp2(μ-SMe)3(CH3CN) 2](BF4) (1) reacts with H[BF4] in acetonitrile at room temperature to give the tetrakis (acetonitrile) compound [Mo2Cp2(μ-SMe)2(CH3CN) 4](BF4)2 (3) through replacement of one SMe bridge by two terminal CH3CN ligands. In sharp contrast, the carbonyl analogue [Mo2Cp2(μ-SMe)3(CO)2]+ (2) fails to undergo a similar reaction. This suggests that the electronic properties of the ancillary ligands L in the [Mo2Cp2(μ-SMe)3L2]+ moiety govern the activation of a sulfur atom in protonation reactions. An X-ray diffraction study shows that 3 contains two CpMo(CH3CN)2 units bridged by two SMe groups and linked by a long Mo-Mo bond of 3.000(1) Å.

International audience; Studies of the protonation of [Fe2(CO)4(κ2-PNP)(μ-pdt)] (1; PNP = (Ph2PCH2)2NCH3) by HBF4·Et2O showed that the nature of the reaction product depends on whether the reaction is conducted in acetone or in dichloromethane. In acetone, an N-protonated form, 2, is isolated. Tautomerization of 2 in CH2Cl2 gives rise to a μ-hydride species 3. Variable-temperature NMR experiments have been performed to clarify the processes involved.