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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.

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.

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.

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.

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.

Rotated geometry: The first example of a dinuclear iron(I)-iron(I) complex featuring a fully rotated geometry related to the active site of [Fe-Fe] hydrogenase is reported (see figure). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The one-electron oxidation of the diiron complex [Fe(2)(CO)(4)(κ(2)-dppe)(μ-pdt)] (1) (dppe = Ph(2)PCH(2)CH(2)PPh(2); pdt = S(CH(2))(3)S) has been investigated in the absence and in the presence of P(OMe)(3), by both electrochemical and theoretical methods, to shed light on the mechanism and the location of the oxidatively induced structure change. While cyclic voltammetric experiments did not allow to discriminate between a two-step (EC) and a concerted, quasi-reversible (QR) process, density functional theory (DFT) calculations favor the first option. When P(OMe)(3) is present, the one-electron oxidation produces singly and doubly substituted cations, [Fe(2)(CO)(4-n){P(OMe)(3)}(n)(κ(2)-dppe)(μ-pdt)](+) (n = 1: 2(+); n = 2: 3(+)) following mechanisms that were investigated in detail by DFT. Although the most stable isomer of 1(+) and 2(+) (and 3(+)) show a rotated Fe(dppe) center, binding of P(OMe)(3) occurs at the neighboring iron center of both 1(+) and 2(+). The neutral compound 3 was obtained by controlled-potential reduction of the corresponding cation, while 2 was quantitatively produced by reaction of 3 with CO. The CO dependent conversion of 3 into 2 as well as the 2(+) ↔ 3(+) interconversion were examined by DFT.

International audience; Six-membered heterocycles, 1,4-dithiane and 1,4-thioxane, were treated with [Fe2(CO)6(μ-pdt)] (pdt = propanedithiolate) in order to synthesise [2Fe3S] complexes with well positioned heteroatoms as potential base. Monosubstituted compounds of general formula [Fe2(CO)5L(μ-pdt)] (L = 1,4-dithiane, 1,4-thioxane) were mainly obtained and characterised by 1H NMR, IR, elemental analysis and X-ray diffraction studies. Electrochemical behaviour of these monosubstituted derivatives was investigated by cyclic voltammetry. An original tetranuclear cluster with a [4Fe8S] core was also isolated as a minor product and structurally characterised.

The doubly and quadruply bridged isomers [Mo2Cp 2Cl2(μ-SMe)2] (4) and [Mo2Cp 2(μ-Cl)2(μ-SMe)2] (3) have been obtained as side-products when the dicarbonyl precursor [Mo2Cp 2(CO)2(μ-SMe)3]Cl (1) is warmed in toluene solution, the main product being the tris-thiolato-bridged compound [Mo 2Cp2(μ-Cl)(μ-SMe)3] (2). Complex 4 is stable at room temperature but can be transformed into 3 at elevated temperatures. 3 and 4 have been crystallographically characterized, and both contain equivalent molybdenum centers. The Mo-Mo separations of 2.5909(11) and 2.4507(2) Å in 3(syn) and 4 are consistent with single and triple Mo-Mo bonds, respectively. © 2011 American Chemical Society.

A new dissymmetrically disubstituted diiron dithiolate species, [Fe(2)(CO)(4)(κ(2)-P(Ph)(2)N(Ph)(2))(μ-pdt)] (pdt = S(CH(2))(3)S), was prepared by using a flexible cyclic base-containing diphosphine, 1,3,5,7-tetraphenyl 1,5-diaza-3,7-diphosphacyclooctane (P(Ph)(2)N(Ph)(2) = {PhPCH(2)NPh}(2)). Preliminary investigations of proton and electron transfers on the diiron system have been done.

The purpose of the present study was to evaluate the use of a non-innocent ligand as a surrogate of the anchored [4Fe4S] cubane in a synthetic mimic of the [FeFe] hydrogenase active site. Reaction of 2,3-bis(diphenylphosphino) maleic anhydride (bma) with [Fe 2 (CO) 6 (µ-pdt)] (propanedithiolate, pdt = S(CH 2 ) 3 S) in the presence of Me 3 NO-2H 2 O afforded the monosubstituted derivative [Fe 2 (CO) 5 (Me 2 NCH 2 PPh 2 )(µ-pdt)] ( 1 ). This results from the decomposition of the bma ligand and the apparent C–H bond cleavage in the released trimethylamine. Reaction under photolytic conditions afforded [Fe 2 (CO) 4 (bma)(µ-pdt)] ( 2 ). Compounds 1 and 2 were characterized by IR, NMR and X-ray diffraction. Voltammetric study indicated that the primary reduction of 2 is centered on the bma ligand.

International audience; The substitution of PPh(3) for a carbonyl group at the {Fe(CO)(3)} moiety in [Fe(2)(CO)(4)(kappa(2)-phen)(mu-pdt)] results in the formation of the trisubstituted complex [Fe(2)(CO)(3)(PPh(3))(kappa(2)-phen)(mu-pdt)] (2). Unlike its tetracarbonyl precursor, the protonation of 2 at low temperature does not afford any apparent transient terminal hydride species. Hydride formation for [Fe(2)(CO)(3)(L)(kappa(2)-phen)(mu-pdt)] (L = PPh(3), CO) species is also studied by density functional theory calculations, which show that activation barriers to give terminal and bridging hydrides can be remarkably close for this class of organometallic compounds.

International audience; This review focuses on electron and proton transfers involving hexacarbonyl and substituted {2Fe2S} complexes inspired from the active site of the [FeFe]-hydrogenases ([FeFe]H2ases), and on different mechanisms by which the synthetic models catalyze the reduction of protons. Selected aspects of the mechanisms proposed for the biological process on the basis of DFT calculations are also briefly presented.

International audience; During the last decade, the structure of the subsite of [FeFe]H2ases (or Fe-only hydrogenases) has inspired organometallic chemists to find out whether it was possible to build synthetic molecules, based on sulfur, iron, carbon monoxide and cyanide or surrogates, having the same efficiency for hydrogen production/uptake as that of the enzyme. A short nonexhaustive overview of recent advances in this chemistry is presented

International audience; A few recent electrochemical studies of diiron models of the iron-only hydrogenases' active site are summarized. Emphasis is put on the reduction mechanisms of hexacarbonyl complexes and on the different mechanisms of proton reduction that may operate depending on the nature of the complex and the strength of the acid. An attempt is made to discuss the thermodynamic and kinetic limitations of proton reduction processes supported by these compounds.

International audience; Reductive coupling between isocyanide ligands attached to adjacent molybdenum atoms in the bis(aryl isocyanide) complex [Mo2Cp2(μ-SMe)3(xylNC)2](BF4) (1) was initiated by addition of the hydrosulfide anion (HS−) to 1 under reflux in tetrahydrofuran, affording, in nearly quantitative yields, the dimetallaimidoyl(amino)carbene derivative [Mo2Cp2(μ-SMe)3{μ-η1(C):η1(C)-C(NHxyl)C(Nxyl)}] (7), in which both isocyanide groups of 1 are now linked by a new C−C bond. When the previous reaction was conducted in the presence of a large excess of hydrosulfide (20 equiv), under similar experimental conditions, the dithiocarbonimidate compound [Mo2Cp2(μ-SMe)2(μ-S2CNxyl)] (8) was obtained in quantitative yields. This product results from subsequent thiolate exchange and substitution reactions to afford a quadruply sulfur bridged intermediate, followed by free isonitrile addition to sulfido S atoms. Treatment of the coupled isocyanide derivative 7 with HBF4 led exclusively to the formation of the starting complex 1 by reversible isocyanide ligand decoupling. The heating of a tetrahydrofuran solution of 1 with the base NaC≡CH gave, in high yields, the μ-alkylidyne and μ-acetylide product [Mo2Cp(μ-SMe)2{μ-(η5-C5H4)(xylN)CN(xyl)C}(μ-CCH)] (9), in which a deprotonated Cp and both isocyanide ligands of 1 are now linked by new C−C and C−N bonds, and in addition an acetylide has replaced a thiolate ligand of 5. Reaction of the μ-alkylidyne complex [Mo2Cp(μ-SMe)3{μ-(η5-C5H4)(xylN)CN(xyl)C}] (5) with NaC≡CH under reflux in tetrahydrofuran produced, in high yields, the μ-alkylidyne and bis(μ-acetylide) cationic compound [Mo2Cp(μ-SMe)2{μ-(η5-C5H4)(xylN)CN(xyl)C}(μ-CCH)2]Br (10), in which two xylNC ligands have replaced a thiolate group of 5. Further reactions of the bis(μ-isocyanide) complex 10 with NaOH (suspension), on the one hand, and HBF4, on the other hand, under reflux in tetrahydrofuran or at room temperature in dichloromethane, respectively, led to the formation in high yields of the known mixed μ-alkylidyne and μ-amino-oxycarbene species [Mo2Cp(μ-SMe)2{μ-(η5-C5H4)(xylN)CN(xyl)C}{μ-η1(O):η1(C)-OCNHxyl}] (12) and the new tetrakis(isocyanide) dicationic derivative [Mo2Cp2(μ-SMe)2(xylNC)4](BF4)2 (11), respectively. The latter complex results from successive protonation at one carbon atom of the cyclopentadienyl ligand linked with isocyanides of 10 and decoupling between deprotonated Cp and isocyanide ligands. The heating of a tetrahydrofuran solution of a mixture of the bis(alkyl isocyanide) complex [Mo2Cp2(μ-SMe)3(t-BuNC)2](BF4) (2) and NaSH proceeded exclusively through the dealkylation of one tert-butyl isocyanide ligand to afford the known product [Mo2Cp2(μ-SMe)3(t-BuNC)](CN)] (13). Similar reaction of the dicarbonyl derivative [Mo2Cp2(μ-SMe)3(CO)2]Cl (3) with NaSH proceeded through dealkylation of one thiolate group to yield the new neutral sulfido species [Mo2Cp2(μ-SMe)2(μ-S)(CO)2] (14). Further heating of 14 in dichloromethane led to the formation of the chloromethanethiolate derivative [Mo2Cp2(μ-SMe)2(μ-SCH2Cl)(CO)2]Cl (15). Treatment of the bis(nitrile) species [Mo2Cp2(μ-SMe)3(MeCN)2]BF4 (4) under reflux in tetrahydrofuran with NaSH afforded, in valuable yields, the thio-amidato derivative [Mo2Cp2(μ-SMe)3(μ-MeCSNH)] (18). All new complexes have been characterized by elemental analyses and spectroscopic methods, supplemented for 7−10, 11′, 14, and 15 by X-ray diffraction studies.

International audience; Reaction of the bis(nitrile) complex [Mo2Cp2(μ-SMe)3(NCMe)2](BF4) (1) with dimethylpropargylic alcohol, HCtriple bond; length of mdashCCMe2(OH), at room temperature in dichloromethane produced good yields of the μ-alkynol species [Mo2Cp2(μ-SMe)3{μ-CHCCMe2(OH)}](BF4) (2a) through replacement of the two acetonitrile ligands in 1 by the alkynol. The NMR spectra of 2a indicate a μ-η1:η1 coordination mode for the alkyne which is thereby incorporated into a dimetallacyclobutene ring like that found here by X-ray diffraction (XRD) analysis of the related complex [Mo2Cp2(μ-SMe)3(μ-η1:η1-CHCCO2Me)](BPh4) (2b). When 2a was stirred with Et3N at room temperature in dichloromethane, deprotonation gave high yields of the μ-3-hydroxyalkynyl derivative [Mo2Cp2(μ-SMe)3{μ-η1:η2-CCCMe2(OH)}] (3), together with small amounts of the already-known vinylacetylide [Mo2Cp2(μ-SMe)3{μ-η1:η2-CCC(Me)CH2}] (4) resulting from dehydration of 3. Treatment of 3 with 1 equiv. of HBF4 · OEt2 in diethyl ether at room temperature gave the 3-hydroxyvinylidene derivative [Mo2Cp2(μ-SMe)3{μ-η1:η2-CCHCMe2(OH)}](BF4) (5) as the major product, together with other minor products [Mo2Cp2(μ-SMe)3{μ-η1:η2-CCHC(Me)CH2}](BF4) (6), [Mo2Cp2(μ-SMe)3(μ-η1:η2-CCCMe2)](BF4) (7), [Mo2Cp2(μ-SMe)3(μ-η1:η2-CCH2)](BF4) (8), [Mo2Cp2(μ-SMe)3{μ-η1:η2-CCH(CHMe2)}](BF4) (9) and [Mo2Cp2(μ-SMe)3(μ-O)](BF4) (10). The vinylidene (6) and allenylidene (7) species resulted from dehydration of the 3-hydroxyvinylidene complex 5 whereas the vinylidene derivative 8 was formed by deketonisation of 5. When 3 reacted with a large excess of HBF4 · OEt2 in dichloromethane, the 3-isopropylvinylidene complex 9 was obtained nearly quantatively via a Hradical dot radical process. When left for several days CD2Cl2 solutions of 5 afforded mainly the vinylidene species 8 by deketonisation and the side-oxoproduct [Mo2Cp2(μ-SMe)3(μ-O)](BF4) (10) by hydrolysis or reaction with oxygen. Addition of nucleophiles (H−, OMe−, OH−, SMe−) to the allenylidene complex [Mo2Cp2(μ-SMe)3(μ-η1:η2-CCCPh2)](BF4) (11) resulted in the formation of the corresponding μ-acetylide derivatives [Mo2Cp2(μ-SMe)3(μ-η1:η2-CCCRPh2)] [R = H (12), OMe (16a), OH (17), SMe (16b)], which by further reaction with tetrafluoroboric acid afforded either the vinylidene species [Mo2Cp2(μ-SMe)3{μ-η1:η2-CCH(CRPh2)}](BF4) when R = H (13), or the starting complex 11 when R is a leaving group (OMe). Reaction of 13 with Na(BH4) gave the μ-alkylidyne complex [Mo2Cp2(μ-SMe)3(μ-η1-CCH2CPh2H)] (14) by nucleophilic attack of H− at the Cβ carbon atom of the vinylidene chain. Proton addition at Cα in 14 led to the formation of a μ-vinylidene compound 15 containing an agostic C–H bond. New complexes have been characterised by elemental analyses and spectroscopic methods, supplemented for 2b and 3 by X-ray diffraction studies.

Reactions of the di-iron complex [Fe 2 (μ-S) 2 (CO) 6 ] 2− with carboxy-functionalized dihalide derivatives (XCH 2 ) 2 R (X = Cl, R = NC 6 H 4 CH 2 CO 2 CH 3 ; X = Br, R = C 6 H 3 COOH, C 6 H 3 COON(COCH 2 ) 2 ) gave new functionalized dithiolate di-iron complexes [Fe 2 (μ-SRS)(CO) 6 ] (R = (CH 2 ) 2 NC 6 H 4 CH 2 CO 2 CH 3 ( 1 ), (CH 2 ) 2 C 6 H 3 COOH ( 2 ), (CH 2 ) 2 C 6 H 3 COON(COCH 2 ) 2 ( 3 )) in low yields. The azadithiolate complex 1 has been characterized by a single crystal X-ray diffraction analysis and studied by electrochemical methods.

The complexes [Fe2(CO)6{μ-SCH2N(R) CH2S}] (R = CH2CH2OCH3, 1a; R = iPr, 1b) and [Fe2(CO)6(μ-pdt)] 2 (pdt = S(CH2)3S) are structural analogues of the [2Fe] H subsite of [FeFe]H2ases. Electrochemical investigation of 1 and 2 in MeCN-[NBu4][PF6] under Ar and under CO has demonstrated that the reduction can be resolved into two one-electron transfer steps by using fast scan cyclic voltammetry. At slow scan rates the reduction of 1 tends towards a two-electron process owing to the fast disproportionation of the anion, while the two-electron reduction of 2 is clearly favoured in the presence of CO. Substitution of a CO ligand in 2 by a N-heterocyclic carbene results in the destabilisation of the anion. Thus, in MeCN-, thf- or CH 2Cl2-[NBu4][PF6], the electrochemical reduction of Fe2(CO)5LNHC(μ- pdt)] 3 (LNHC = 1,3-bis(methyl)-imidazol-2-ylidene, 3a; 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene, 3b) occurs in a single-step, two-electron process at moderate scan rates; under appropriate conditions this process can be separated into two one-electron steps. Density Functional Theory calculations successfully rationalize the effects of the S-to-S linkage on the electrochemistry of the complexes. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

International audience; The μ-alkylidyne complex [Mo2Cp2(μ-SMe)3(μ-CCH2Ph)] (1) reacts with HBF4 in acetonitrile to give the unstable bis-nitrile species [Mo2Cp2(μ-SMe)2(μ-CCH2Ph)](NCCH3)2](BF4) (2). Treatment with either borohydride or chloride converts 2 into [Mo2Cp2(μ-SMe)2(μ-CCH2Ph)(μ-κ1:κ1-BH4)] (3) or [Mo2Cp2(μ-SMe)2(μ-CCH2Ph)(μ-Cl)] (4), respectively. Clean evolution of 4 in non-degassed solvent affords the novel μ-thioalkylidene derivative [Mo2(O)(Cl)Cp2(μ-SMe)(μ-MeSCCH2Ph)](5).

International audience; Treatment of [Fe2(μ-pdt)(CO)6] [pdt = S(CH2)3S] with dppe (Ph2PCH2CH2PPh2) in refluxing toluene affords the asymmetric complex [Fe2(μ-pdt)(CO)4(dppe)] (1). Protonation of 1 with HBF4−Et2O in CH2Cl2 gives at room temperature the μ-hydrido derivative [Fe2(μ-pdt)(CO)4(dppe)(μ-H)](BF4) (2). Monitoring the reaction by 1H, 31P, and 13C NMR at low temperature reveals unambiguously that the process of the protonation of 1 implies terminal hydride intermediates.

International audience; The electrochemical reduction of isomeric complexes, [Mo2Cp2(μ-SMe)3(μ-η1:η1-HCCPh)]+ (1+) and [Mo2Cp2(μ-SMe)3(μ-η1:η2-C[double bond, length as m-dash]CHPh)]+ (3+), where the hydrocarbyl bridges in a η1:η1- or a η1:η2 mode, has been studied by cyclic voltammetry and controlled-potential electrolysis in thf–[NBu4][PF6] and CH2Cl2–[NBu4][PF6], in the absence and in the presence of acid. The binding mode of the CC fragment induces different electrochemical behaviour of the complexes in acid-free solutions since 1+ reduces in two diffusion-controlled one-electron steps while the first reduction of 3+ is characterized by slow electron transfer kinetics. Controlled-potential reduction of both 1+ and 3+ produces a mixture of the acetylide [Mo2Cp2(μ-SMe)3(μ-η1:η2-CCPh)] (2) and alkylidyne complexes [Mo2Cp2(μ-SMe)3(μ-η1-CCH2Ph)] (4). In the presence of acid, the electrochemical reduction of 1+ and of 3+ occurs according to ECE processes. The nature of the products formed by controlled-potential reduction of 1+ depends on the nature of the acid and of the solvent. The transient formation of a complex with a μ-alkenyl ligand, either [Mo2Cp2(μ-SMe)3(μ-η1:η2-CH[double bond, length as m-dash]CHPh)] (7) or an isomer, is suggested by the oxidative electrochemistry of 7 and by its reaction with acids. In thf–[NBu4][PF6] in the presence of an excess of acid (HBF4/Et2O) and of phenylacetylene, electrolysis of 1+ gives rise to catalytic reduction of phenylacetylene to styrene. However, unidentified reactions limit the efficiency of this process. The reduction of 3+ in acidic medium produces the alkyl complex [Mo2Cp2(μ-SMe)3(μ-CH2CH2Ph)] (6) through alkylidyne [Mo2Cp2(μ-SMe)3(μ-η1-CCH2Ph)] (4) and alkylidene [Mo2Cp2(μ-SMe)3(μ-η1-CHCH2Ph)]+ (5+) intermediates. Some ethylbenzene was formed after reduction of 5+ in the presence of acid. These results show an effect of the binding mode of the hydrocarbyl bridge on the mechanism and products of the reduction of the corresponding complexes.

International audience; Editing an encyclopedia has already been a formidable task in the not too distant past—it is an even more difficult task today. Thus it is not surprising to realize that an encyclopedia covering electrochemistry, an extremely diverse and multidisciplinary area of research and development, has not been published again after the “Encyclopedia of the Electrochemistry of the Elements” that has been finished decades ago by A.J. Bard—and this work actually covered only very selected and limited areas of the field. Thus the present volume, being a part of an eleven-book enterprise, attempts to be a building block of a work standing in the tradition of famous predecessors (e.g.. Encyclopédie by D. Diderot and J. d’Alembert 1751–1775).A certainly very challenging task is a complete overview of experimental methods including both traditional (classical) and nontraditional (e.g. spectroscopic or surface analytical) methods because of the extremely large number of methods in particular in the...

International audience; The bis(nitrile) complex [Mo2Cp2(μ-SMe)3(NCCH3)2](BF4) (1) reacts with HC⋮CCPh2(OH) to give the μ-alkyne product [Mo2Cp2(μ-SMe)3{HC⋮CCPh2(OH)}](BF4) (2). Sequential treatment with triethylamine and tetrafluoroboric acid converts 2 almost quantitatively, via the μ-alkynyl derivative 3, into [Mo2Cp2(μ-SMe)3(μ-η1:η2-CCCPh2)] (BF4) (4), the first example of a dinuclear μ-η1:η2-allenylidene species without carbonyl ligands.

International audience; Reaction of the bis- isonitrile complex [Mo2Cp2(mu-SMe)(3)(xylNC)(2)](BF4) (2b) with NaOH (suspension) under reflux in tetrahydrofuran produced, in quantitative yields, the A-alkylidyne species [Mo2Cp(mu-SMe) (3){mu-(5-C5H4)(xylN)CN(xyl)C}] (4), in which a deprotonated Cp and both isonitrile ligands of 2b are now linked by new C-C and C-N bonds. Under prolonged reflux (72 h) in tetrahydrofuran 2b with either NaOH (suspension) or (Me4N) OH (in MeOH) in the presence of excess isonitrile RNC (R = xyl, Bu-t) was converted in high yields into the mixed (mu-alkylidyne)(mu-amino-oxycarbene) derivatives [Mo2Cp(mu-SMe)(2){mu-(eta(5)-C5H4)(xylN)CN(xyl)C}{mu-eta(1)(O),eta(1)(C)-OCNHR}] (R = xyl (5a1), R = Bu-t (5b2)) and [Mo2Cp(mu-SMe)(2){mu-(eta(C5H4)-C-5)(xylN)CN(xyl)C}{mu-eta(1)(O),eta(1)(C)-OCNMeR}] (R = xyl (6a)). All these products result from hydroxide-isonitrile coupling reactions. When the mixture of 2b, (Me4N) OH (excess), and ButNC (excess) in tetrahydrofuran was heated under reflux for a short time (2 h), complex 5b1 was formed in good yields. Compounds 5b1 and 5b2 are linkage isomers, which differ only in the mode of coordination of the mu-amino-oxycarbene ligand to the Mo1-Mo2 unit; 5b1 converts into 5b2 on prolonged heating. Reaction of the secondary amino-oxycarbene derivative 5a1 with a base (NaOH) and an alkylating agent R"4NBr (R" = Et, Bu-n) afforded the corresponding tertiary(amino)-oxycarbene complexes [Mo2Cp(mu-SMe)(2){mu-(eta(5)-C5H4)(xylN)CN(xyl)C}{mu-eta(1)(O),eta(1)(C)-OCNxylR"}] [R" = Et (6b), Bu-n (6c)]. On heating a tetrahydrofuran solution of the mu-alkylidyne compound 4 with NaOH (suspension) and an excess of either xylNC or (BuNC)-N-t, the mixed mu-alkylidyne and mu-amino-oxycarbene species 5a1 and 5b2 were obtained, demonstrating that 4 is an intermediate in the formation of 5a1 and 5b2 from 2b. Treatment of the mixed isonitrile-nitrile species [Mo2Cp2(mu-SMe)(3)(MeCN)(xylNC)](BF4) (3), containing a labile MeCN group, under reflux in tetrahydrofuran with NaOH (suspension) afforded quantitatively the mu-aminooxycarbene compound [Mo2Cp2(mu-SMe)(3){mu-eta(1)(O),eta(1)(C)-OCNHxyl}] (7). All new complexes have been characterized by elemental analyses and spectroscopic methods, supplemented for 5a1, 5b1, 5b2, 6a, 6b, and 7 by X-ray diffraction studies.

International audience; Reactions of the trinuclear iron cluster [Fe3Cp2(CO)3(μ-CO)(μ3-CO)(μ3-CF3C2CF3)] (1) with the bis(phosphino) ligands dppm and dppe give different results: dppe yields mainly the hexanuclear compound (2) in which two tri-iron cluster units are linked by the diphosphine, although a trinuclear derivative (3) with a chelating dppe ligand is also obtained as a minor product, whereas dppm displaces carbonyl to give complexes containing exclusively a single tri-iron unit, though the phosphine may be either dangling (4) or chelating (5). The complexes 2–5 have been characterised by elemental analyses and from their IR and NMR spectra, supplemented in the case of 2 by a single crystal X-ray diffraction analysis.

The electrochemical oxidation of [Mo2(cp)2(μ-SMe)3(μ-N2Ph)] and [Mo2(cp)2(μ-SMe)3(μ-N2HPh)]+ complexes where the diazo bridge adopts either an η1 or an η1:η1 coordination mode has been studied by cyclic voltammetry and controlled-potential electrolysis in THF– and CH2Cl2–[NBu4][PF6]. The electrochemical oxidation of [Mo2(cp)2(μ-SMe)3(μ-η1-N2Ph)] 1 and of [Mo2(cp)2(μ-SMe)3(μ-η1-N2HPh)]+1-H+++ triggers the isomerization of the diazo bridge to the η1:η1 mode found in 2+++ and 2-H2+2+2+ respectively. The electrochemical oxidation of [Mo2(cp)2(μ-SMe)3(μ-η1:η1-N2Ph)] 3 and of [Mo2(cp)2(μ-SMe)3(μ-η1:η1-HN2Ph)]+3-H+++ with a syn (“up–up”) arrangement of the Me substituents of the equatorial sulfur bridges is also followed by an isomerization to 2+++ and 2-H2+2+2+, respectively, with an anti (“up–down”) configuration of the equatorial Me groups. The rates of the isomerization 1++ → 2+++, 1-H2+2+2+ → 2-H2+2+2+, and 3-H2+2+ → 2-H2+2+2+ were studied by cyclic voltammetry at different scan rates and at different temperatures. The isomerization of the protonated complexes with either a hydrazido(2−) or a diazene bridge (respectively 1-H2+2+2+ and 3-H2+2+) is faster than that of the diazenido precursors (respectively 1++ and 3++). The diazenido complex 2+++ protonates readily, affording 2-H2+2+2+, while 2-H3+3+ undergoes proton loss.

The thiolato-bridged binuclear molybdenum complexes [Mo 2 Cp 2 L 2 (μ-SMe) 2 (μ-L′)]Y (Cp = η 5 -C 5 H 5 ; L′ = SMe, L = Bu t NC ( 1a ), xylNC ( 1b ) or CO ( 3 ); L′ = PPh 2 , L = Bu t NC ( 16 ); Y = BF 4 , Cl) react with the anionic reagents NaBH 4 , NaBD 4 , LiR (R = Me, Bu n ), R′MgCl (R′ = Me, Pr i , Bu n or Ph). The products are unsubstituted ( 5 , 7 ) or substituted ( 8 – 12 ) η 4 -cyclopentadiene derivatives, [Mo 2 (η 5 -C 5 H 5 )(η 4 -C 5 H 5 R)L 2 (μ-SMe) 3 ] (L = xylNC, CO), or μ-formimidoyl dinuclear products, [Mo 2 Cp 2 L 2 (μ-SMe) 2 (μ-L′)(μ-CHNR)] (L′ = SMe, L = Bu t NC ( 4 ) or xylNC ( 6 ); L′ = PPh 2 , L = Bu t NC ( 17 )). Since the reduced dinuclear species [Mo 2 Cp 2 (CO) 2 (μ-SMe) 2 ] and the related oxo-compound [Mo 2 Cp 2 (CO)(O)(μ-SMe) 2 ] are sometimes isolated as minor products, the anionic reagent can play a secondary role as a reductant in these reactions in addition to its main role as a nucleophile. The electronic properties of the donor carbon atoms of the cyclopentadienyl rings and of the terminal ligands L, together with the nature of the anionic reagent, are the dominant factors controlling selective formation of 4 – 12 and 17 . Tetrafluoroboric acid reacts with the substituted cyclopentadiene derivatives 9 , 11 and 12 to form new functionalised cyclopentadienyl derivatives, [Mo 2 (η 5 -C 5 H 5 )(η 5 -C 5 H 4 R)(CO) 2 (μ-SMe) 3 ](BF 4 ) (R = Me ( 13) , Bu n ( 14 ) or Ph ( 15 )). New complexes have been characterised by spectroscopic and chemical methods, supplemented for 5 , 6 and 12 by X-ray diffraction studies at 100 K.

cited By 28; International audience; The reaction of mono- or dichloro-dimolybdenum(m) complexes [Mo 2Cp2(μ-SMe)2(μ-Cl)(μ-Y)] (Cp=η5-C5H5; 1, Y = SMe; 2, Y = PPh 2; 3, Y = Cl) with NaBH4, at room temperature gave in high yields tetrahydroborato (8), hydrido (9) or metallaborane (12) complexes depending on the ancillary ligands. The correct formulation of derivatives 8 and 12 has been unambigously determined by X-ray diffraction methods. That of the hydrido compound 9 has been established in solution by NMR analysis and confirmed by an X-ray study of the μ-azavinylidene derivative [Mo 2Cp2(μ-SMe)2(μ-PPh2)(μ-N= CHMe)] (10) obtained from the insertion of acetonitrile into the Mo-H bond of 9. Reaction of NaBH4, with nitrile derivatives, [Mo2Cp 2(μ-SMe)4-n(CH3CN)2n] n+ (5, n= 1; 6 =2), afforded the tetrahydroborato compound 8, together with a μ-azavinylidene species [Mo2Cp2(μ- SMe)3(μ-N=CHMe)] (14), when n= 1, and the metallaborane complex 12, together with a mixed borohydrato-azavinylidene derivative [Mo 2Cp2(μ-SMe)2(μ-BH4)(μ-N= CHMe)] (13), when n=2. The molecular structures of these complexes have been confirmed by X-ray analysis. Preparations of some of the starting complexes (3 and 4) are also described, as are the molecular structures of the precursors [Mo2Cp2(μ-SMe)2(μ-X)-(μ-Y)] (1, X/Y = Cl/SMe; 2, X/Y = Cl/PPh2; 4, X/Y = SMe/PPh2).

The bis(phosphido)-bridged complex [Fe 2 (μ-PPhH) 2 (CO) 6 ] (1) undergoes double deprotonation to give the phosphorus-centered dianionic derivative [Fe 2 (μ-PPh) 2 (CO) 6 ] 2 - (2) which in turn reacts with the tertiary base RN(CH 2 Cl) 2 to give [Fe 2 {(PPhCH 2 ) 2 NR}-(CO) 6 ] (3) in moderate yield. Treatment of 3 with HBF 4 .Et 2 O affords the N-protonated species [Fe 2 {(PPhCH 2 ) 2 NHR}(CO) 6 ] BF 4 (4). The structural changes to the heavy atom skeleton of 3 arising from protonation are slight, the most obvious being a ca. 0.03 A lengthening of the N-C bonds.

cited By 9; International audience; Treatment of either the μ-alkyne complex [Mo2Cp 2(μ-SMe)3(μ-PhCCH)](BF4) (1) or the μ-vinylidene derivatives [Mo2Cp2(μ-SMe) 3(μ-η1:η2-(CCHR)](BF4) (2) (R=Ph, Tol, nPr, C(CH3)=CH2) with NaN3 in ethanol at room temperature readily afforded μ-tetrazolate carbene complexes [Mo2Cp2(μ-SMe)3)μ-η 1(C):η1(N)-N4CCR)] (R=Ph (4a), Tol (4b), nPr (4c), C(CH3)=CH2 (4d)). A mechanism which accounts for the formation of 4 by intramolecular 1,3-dipolar cycloaddition of metal-coordinated azide ligands to metal-coordinated nitriles is discussed. The structure of complex 4a has been determined by single X-ray diffraction analysis. © 2003 Elsevier Science B.V. All rights reserved.

cited By 21; International audience; Reaction of the bis-isonitrile complex [Mo2-Cp2(μ-SMe)3(t-BuNC)2] (BF4) (1) with n-BuLi (in hexane) produced the dealkylated derivative [Mo2Cp2(μ-SMe)3-(t-BuNC)(CN)] (2) in quantitative yield. However, upon treatment with either NaOH (suspension) or (Me4N)OH (in MeOH), 1 was converted into a mixture of 2 and the μ-alkylidyne species [Mo2Cp(μ-SMe)3μ-(η5-C5 H4)(t-BuN)-CN(t-Bu)C] (3), in which a deprotonated Cp and both isonitrile ligands of 1 are now linked by new carbon-carbon and carbon-nitrogen bonds.

The reduction of diazene complexes [Mo(2)Cp(2)(mu-SMe)(3)(mu-eta(2)-H-N=N-R)](+) (R=Ph (3 a); Me (3 b)) and of the hydrazido(2-) derivative [Mo(2)Cp(2)(mu-SMe)(3)[mu-eta(1)-N=N(Me)H]](+) (1 b) has been studied by cyclic voltammetry, controlled-potential electrolysis, and coulometry in THF. The electrochemical reduction of 3 a in the presence of acid leads to cleavage of the N=N bond and produces aniline and either the amido complex [Mo(2)Cp(2)(mu-SMe)(3)(mu-NH(2))] 4 or the ammine complex [Mo(2)Cp(2)(mu-SMe)(3)(NH(3))(X)] 5, depending on the initial concentration of acid (HX=HTsO or CF(3)CO(2)H). The N=N bond of the methyldiazene analogue 3 b is not cleaved under the same conditions. The ability of 3 a but not 3 b to undergo reductive cleavage of the N=N bond is attributed to electronic control of the strength of the Mo-N(R) bond by the R group. The electrochemical reduction of the methylhydrazido(2-) compound 1 b in the presence of HX also results in cleavage of the N=N bond, with formation of methylamine, 4 (or 5) and the methyldiazenido complex [Mo(2)Cp(2)(mu-SMe)(3)(mu-eta(1)-N=N-Me)]. Formation of the last of these complexes indicates that two mechanisms (N=N bond cleavage and possibly H(2) production) are operative. A pathway for the reduction of N(2) at a dinuclear site of FeMoco is proposed on the basis of these results.

cited By 7; International audience; A novel example of C-S bond cleavage in a dimolybdenum derivative leads to the formation of the quadruply bridged compound [Mo(IV)2Cp2(μ-O)(μ-S)(μ-SMe)2]. This μ-oxo species is formed by reaction of the chloro-bridged complex [Mo(III)2Cp2(μ-Cl)(μ-SMe)3] with PhCCLi and subsequent hydration at the dimolybdenum site. The Mo-Mo bond length of 2.4900(3)Å in [Mo2Cp2(μ-O)(μ-S)(μ-SMe)2] is unusually short. © 2001 Elsevier Science B.V.

cited By 7; International audience; 1-Phenyl-2,3,4,5-tetramethylphosphole reacts with [Mo(CO)6] to give the mono- and bis(phosphole) complexes [Mo(CO)5L] and cis- and trans-[Mo(CO)4L2], where L=C4Me4PPh (tmpPh). The new complexes have been characterised by spectroscopic methods, supplemented by single-crystal X-ray analyses in the case of the bis(phosphole) isomers. The isomeric bis-tmpPh complexes show little evidence of the overcrowding which is thought to lengthen bonds and distort the metal coordination in the corresponding bis-PPh3 and bis-PCy3 isomers. The structural basis for the greater stability of the trans isomers is briefly considered: the cis→trans isomerisation typically involves little change in the mean Mo-CO distance, whereas there is a marked shortening of the Mo-P bonds. © 2001 Elsevier Science B.V.

cited By 33; International audience; Reactions of the bis(nitrile) compound [Mo2Cp2 (MeCN)2(μ-SMe)3](BF4) (1) with terminal alkynes in a 1:1 ratio in dichloromethane at room temperature led to the alkyne adduct [Mo2Cp2(μ-SMe)3(RCCH)] (BF4) (2: R = Tol (2a), Ph (2b), CH3C=CH2 (2c), nPr (2d), CO2Me (2e), CF3 (2f)). Compounds 2a-d were readily deprotonated with Et3N to give neutral acetylide derivatives [Mo2Cp2(μ-η1:η2- C≡CR)(μ-SMe)3] (3). Protonation of 3 afforded exclusively the vinylidene complexes [Mo2Cp2(μ-η1: η2-C=CHR) (μ-SMe)3](BF3) (4). Reaction of 1 with an excess of terminal alkyne RCCH in dichloromethane gave either the six-membered metallacycle compounds [Mo2Cp2(μ- η2:η4-CR=CHCR=CHSMe)(μ-SMe)2] (BF4) (5) or the S-methylthiophenium derivatives [Mo2Cp2(μ-η2:η4- C4H2R2SMe)(μ-SMe)2] (BF4) (6), depending on the nature of the R groups. Further reactions of the alkyne adducts 2 with isocyanide and carbon disulfide led to the vinyl-thioether complexes [Mo2Cp2(μ- η1:η3-CR=CR′-SMe)-(μSMe)2 (RNC)](BF4) (7, 8) and to their CS2 adducts [Mo2Cp2(S2C-CR′=CRSMe)(μ- SMe)2]-(BF4) (9, 10), which arise from regioselective C-S coupling. A mechanism is proposed for the formation of the cyclic thiometalla compounds 5, 9, and 10 and of the thiophenium species 6 which assigns a key intermediate role to vinyl-thioether species. The molecular structures of 3a, 4b, and 7a have been established by X-ray diffraction studies.

International audience; Halogens I2, Br2, and Cl2 react with the neutral bridging sulfur site within the Mo2(SMe)2(S) core of the complex [Mo2(η5-C5 Me5)2(μ-S)(μ-SMe)2(CO)2](1) to give covalent halosulfide ligands. The stability of the halosulfide complexes decreases in the order iodine > bromine ≫ chlorine. The stable iodo derivative [Mo2(η5-C5 Me5)2(μ-SMe)2(μ-SI) (CO)2]I5 (2) is the first molydenum(III) compound containing an iodosulfide bridge to be crystallographically characterized.

International audience; The reaction of NaBH4 with the bis-nitrile compound [Mo2Cp2(μ-SMe)3(MeCN)2](BF4) 1 unexpectedly gives rise to the rare, stable μ-(η1-H)(η1-H) tetrahydroborato complex [Mo2Cp2(μ-SMe)3(μ-BH4)] 2, in addition to the expected azavinylidene product [Mo2Cp2(μ-SMe)3(μ-η1-NCHMe)] 3.

International audience; The electrochemical reduction of the imide complex [Mo2(cp)2(μ-SMe)3(μ-NH)]+ (1+) has been investigated in THF and MeCN electrolytes by cyclic voltammetry, controlled-potential electrolysis and coulometry. In the absence of free protons, the electrochemical reduction produces the amide derivative [Mo2(cp)2(μ-SMe)3(μ-NH2)] (2) after consumption of 1 F mol-1 of 1+. In THF in the presence of acid, the reduction of 1+ occurs through a two-electron process. The presence of acid also results in the shift of the equilibrium between 1+ and amide dication 22+ (MeCN electrolyte) or induces an isomerisation of the imide ligand (THF electrolyte). This allows the electrolysis to be conducted at a potential 600 mV less negative than the reduction potential of 1+. Controlled-potential electrolyses in the presence of acid (2 equiv HTsO) produce the ammine derivative. Ammonia is released from these compounds either by coordination of the solvent (MeCN electrolyte) or by the binding of chloride to the ammine-tosylate complex (electrolyses in THF in the presence of acid and chloride). The final products, isolated almost quantitatively (>95%), are [Mo2(Cp)2(μ-SMe)3(MeCN)2] + and [Mo2(cp)2(μ-SMe)3(μ-Cl)], respectively.

International audience; The electrochemical reduction of the phenyldiazene complex [Mo2(cp)2(μ-SMe)3(μ-η2-HNNPh)]+ in the presence of HX (X = TsO, CF3CO2) produces aniline and an ammino derivative. This may involve [Mo2(cp)2(μ-SMe)3(μ-NH)]+ as an intermediate since the imide complex also reduces to the ammino derivative in the presence of HX. These electrochemical steps complete a cycle whereby a phenyldiazenido ligand coordinated to the {Mo2(cp)2(μ-SMe)3+} core is cleaved to PhNH2 and NH3 by successive proton- and electron-transfer steps.

International audience; Removal of a proton from one of the two coordinated acetonitrile ligands in [Mo2Cp2(μ-SMe)3(CH3CN)2](BF4) (1) initiates its intramolecular condensation with the second of the acetonitrile ligands attached to the bimetallic [Mo2Cp2(μ-SMe)3] core, thereby giving rise to the novel μ- η1-azavinylidene complex (Mo2Cp2(μ-SMe)3[μ-η1-N=C(CH3)-CH2CN]) (2). Complex 2 has been characterized by NMR and X-ray methods.

International audience; Iron complexes with the _Fe2(cp)2(μ-SMe)2_ core have been synthesized and their electrochemistry investigated. Electrochemical reduction of the acetonitrile-substituted complexes cis-[Fe2(cp)2(μ-SMe)2(MeCN2) 2]2+ and cis-[Fe2(cp)2(μ-SMe)2(CO)(MeCN)] 2+ labilizes the MeCN ligand(s) and generates vacant sites at which CO and isocyanide substrates can bind. The mechanism of the electrochemical reduction of both complexes has been investigated in the presence of these substrates. A single-crystal X-ray analysis established that cis-[Fe2(cp)2-(μ-SMe)2(CO)(MeCN)][BF 4]2 contains an unusual dication in which different ligands (CO, MeCN) occupy corresponding sites in the co-ordination polyhedra of the two iron centres of the Fe2(μ-S)2 ring. Aspects of the reactivity and electrochemistry of complexes with Fe2(μ-SMe)2 and Mo2(μ-SR)2 cores are compared.

International audience; Rearrangements and protonation reactions of phenyldiazo ligands bound to the bimetallic center, {Mo2Cp2(μ-SMe)3}, are reported