François Y. Pétillon

New FeI–FeI Complex Featuring a Rotated Conformation Related to the [2 Fe]H Subsite of [Fe–Fe] Hydrogenase

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.

Dinuclear molybdenum thiolato-bridged compounds: syntheses, reactivities and electrochemical studies of site–substrate interactions

Abstract The synthesis, reactivity, structures and electrochemistry of dimolybdenum complexes jointly stabilized by cyclopentadienyl and bridging thiolate ligands are reviewed. The complexes involved are principally those of molybdenum(II) and molybdenum(III) and they contain from one to four thiolate bridges. It is shown that their reactivity can be controlled by varying the electronic and steric properties of the ancillary ligands and that they provide bimetallic sites for the activation and transformation of various substrates.

Electrochemical and Theoretical Investigations of the Role of the Appended Base on the Reduction of Protons by [Fe2(CO)4(κ2‐PNPR)(μ‐S(CH2)3S] (PNPR={Ph2PCH2}2NR, R=Me, Ph)

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.

Electrochemical Cleavage of NdN Bonds at a Mo2(μ-SMe)3 Site Relevant to the Biological Reduction of Dinitrogen at a Bimetallic Sulfur Centre

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.

Electrochemically-induced isomerization of {(η5-C5H5)Mo(CO)2(μ-SR)}2 (R Me, t-Bu, Ph) complexes. 1H NMR and electrochemical studies. Sythesis and X-ray crystal structure of {(η5-C5H5)Mo(CO)2(μ-S-t-Bu)}2(BF4)2

Abstract The first example of geometrical isomerization of thiolato-bridged dimolybdenum complexes induced by the transfer of two electrons at the same potential is reported. Variable temperature 1H NMR (R  Me, Ph) studies and an X-ray crystal structure determination for the dication (R  t-Bu) allowed the isomers to be identified. Comparisons of the cyclic voltammetry of the compounds {(η5-C5H5)MO(CO)2(μ-SR)}2 (R  Me, t-Bu, Ph) suggest that steric factors are responsible for the preferred trans geometry of the neutral complexes. The compound {(η5-C5H5)(CO)2 Mo(μ-S-t-Bu) 2 M o(CO)2 (η5-C5H5)}(BF4)2. CH3CN has been characterized by X-ray diffraction. The crystals are orthorhombic, space group P212121, with four molecules in a unit cell of dimensions a 10.598(3), b 13.489(3), c 21.801(3) A. The structure was refined to R = 0.60.

Non-innocent bma ligand in a dissymetrically disubstituted diiron dithiolate related to the active site of the [FeFe] hydrogenases.

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)(mu-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))(mu-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)(mu-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.

Reaction of BH4− with {Mo2Cp2(μ-SMe)n} species to give tetrahydroborato, hydrido or dimetallaborane compounds: control of product by ancillary ligands

The reaction of mono- or dichloro-dimolybdenum(III) complexes [Mo2Cp2(mu-SMe)2(mu-Cl)(mu-Y)] (Cp=eta5-C5H5; 1, Y=SMe; 2, Y=PPh2; 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 and 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 mu-azavinylidene derivative [Mo2Cp2(mu-SMe)2(mu-PPh2)(mu-N=CHMe)] (10) obtained from the insertion of acetonitrile into the Mo-H bond of 9. Reaction of NaBH4 with nitrile derivatives, [Mo2Cp2(mu-SMe)4-n(CH3CN)2n]n+(5, n=1; 6 n=2), afforded the tetrahydroborato compound 8, together with a mu-azavinylidene species [Mo2Cp2(mu-SMe)3(mu-N=CHMe)](14), when n=1, and the metallaborane complex 12, together with a mixed borohydrato-azavinylidene derivative [Mo2Cp2(mu-SMe)2(mu-BH4)(mu-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(mu-SMe)2(mu-X)(mu-Y)] (1, X/Y=Cl/SMe; 2, X/Y=Cl/PPh2; 4, X/Y=SMe/PPh2).

Oxidatively induced reactivity of [Fe2(CO)4(κ2-dppe)(μ-pdt)]: an electrochemical and theoretical study of the structure change and ligand binding processes.

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.

Unexpected coupling of Cp and two RNC ligands at a {Mo2(μ-SMe)3} nucleus

Reaction of the bis-isonitrile complex [Mo 2 -C p 2 (μ-SMe)3(t-BuNC) 2 ](BF 4 )(1) with n-BuLi (in hexane) produced the dealkylated derivative [Mo 2 C p 2 (μ-SMe) 3 -(t-BuNC)(CN)] (2) in quantitative yield. However, upon treatment with either NaOH (suspension) or (Me 4 N)OH (in MeOH), 1 was converted into a mixture of 2 and the μ-alkylidyne species [Mo 2 Cp(μ-SMe) 3 {μ-(η 5 -C 5 H 4 )(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.

Electrochemical deprotection of a substrate binding site in [Mo2(cp)2(µ-SMe)3(µ-Cl)](cp =η5-C5H5)via chloride-bridge opening. Kinetics of MeCN and ButNC binding at this site

The access to a co-ordination site in the quadruply bridged complex [Mo2(cp)2(µ-SMe)3(µ-Cl)](cp =η5-C5H5) has been found to be redox controlled. Electrochemical one-electron oxidation of the complex unlocks the chloride bridge but the radical cation retains the quadruply bridged geometry of the neutral parent as indicated by cyclic voltammetry and EPR spectroscopy. The chloride bridge opens up in the presence of a substrate (YZ = MeCN, ButNC, Me2C6H3NC or CO), leading to the formation of [Mo2(cp)2(µ-SMe)3Cl(YZ)]˙+ derivatives. The site is sensitive to the electronic properties of the substrate, and kinetic studies of the substrate-binding step demonstrated that ButNC reacts faster and is bound more tightly at [Mo2(cp)2(µ-SMe)3Cl]˙+ than is MeCN. The reduction of [Mo2(cp)2(µ-SMe)3Cl(YZ)]˙+ is reversible for YZ = CO and RNC (R = But or C6H3Me2) whereas MeCN is lost on reduction. In this case the fact that the chloride ligand is still present at the neighbouring molybdenum centre allows regeneration of the parent complex via bridge reclosure. The reactivity of [Mo2(cp)2(µ-SMe)3(µ-Cl)] in MeCN has also been investigated: instead of the bridge-opening process of the radical cation, the neutral parent loses the chloride bridge in MeCN; the resulting bis(acetonitrile) cation, [Mo2(cp)2(µ-SMe)3(MeCN)2]+, has been isolated and characterized.