Jean-François Capon

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.

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.

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.

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.

Synthesis of secondary allenylidene-molybdenum complexes with a ferrocenyl substituent from carbenium ions species stabilized by two organometallic moieties

The monoallenylidene complex [Cp2Mo2(CO)4{μ−σ:η2−CCC(Fc)(H)}] (5) and the diallenylidene complex [{Cp2Mo2(CO4(μ−σ:η2−CCC(H))}2Fc] (6) have been obtained from the corresponding monocarbenium ion [Cp2Mo2(CO)4{μ−η2:η3−HCCC(H)(Fc)}][BF4] and the dicarbenium ion [{Cp2Mo2(Co)4(μ−η2:η3−HCCC(H)}2Fc] [{BF4}2] (4) respectively, and their spectroscopic data are determined.

New synthesis of μ-allenylidene complexes from dimolybdenum carbenium ions crystal structure of [Mo(η5-C5H5)(CO)22(μ, η2-CCC6H10)]

Abstract A selective abstraction of the acetylenic proton of cationic allynyl complexes [MoCp(CO)22(μ-η2,η3-HCCCR1R2)][BF4](Cpη5-C5H5) by using the acetylide LiCCC(CH3)CH2 gives rise to allenylidene complexes [Cp2Mo2(CO)4(μ,η2-CCCR1R2)] R2 = C6H5 (6c). Compounds 3b and 4b exist as two isomers while for 6c the formation reaction is stereoselective. The crystal structure of [Cp2Mo2(CO)4(μ,η2-CCC6H10)] (1b) has been determined.

A diferrous dithiolate as a model of the elusive H(ox)(inact) state of the [FeFe] hydrogenases: an electrochemical and theoretical dissection of its redox chemistry.

The reduction of the Fe(II)Fe(II) complex [Fe2(CO)2{P(OMe)3}2(κ(2)-IMe-CH2-IMe)(μ-CO)(μ-pdt)](2+) (2P(2+); 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 2P(2+) 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.

Reaction of sodium amalgam with (μ-enyne)bis(dicarbonyl-η5-cyclopentadienylmolybdenum(I)) and (μ-η2,η3-allenyl)bis(dicarbonyl-η5-cyclopentadienylmolybdenum) tetrafluoroborate complexes. Crystal structure of [[{MO(η5-C5H5)(CO)22}2{μ-HCCCH(CH2CH3)}]2]

The behaviour of μ-enyne complexes [CP2MO2(CO)4(μ-HCCR)] [CP2MO2(CO)4  [Mo(η5-C5H5)(CO)2]2; R  C(CH3)CH2 (1); R  CHCHCH3 (2;) R  C6H9 (3)] and of the corresponding μ-η2,η3-allenyl [Cp2Mo2(CO)4(μ-η2,η3-HCCR′)][BF4] [R′  C(CH3)2 (4); R′  CHCH2CH3 (5); R′  C6H10 (6)] towards Na/Hg has been studied and compared with that of the vinylacetylene and protonated vinylacetylene species [Cp2Mo2(CO)4(μ-HCCCHCH2)] (11) and [Cp2Mo2(CO)4(μ-η2,η3 -HCCCHCH3)]-[BF4] (14), respectively. It appears that when the Cγ carbon atom of the μ-enyne bears a hydrogen atom (complexes 2 and 11), dimerization occurs leading to tetrametallic species [[{Cp2Mo2(CO)4}(μ-HCCCH2CHCH3)]2] (8) and [[{Cp2Mo2(CO)4}(μ-HCCCH2CH2)]2] (12). In the other cases, μ-σ,η3 allylic species such as [Cp2Mo2(CO)4 {μ-σ,η3-HC ⋯ CH ⋯ C(CH3)2}] (7) are formed. Reaction of Na/Hg with most of the μ-η2,η3 allenyl complexes regenerates the parent μ-enyne compounds. When the “C+” carbon atom bears a hydrogen atom, carbon-carbon coupling leading to a dimerization is favoured. The crystal structure of tetrametallic [[{Cp2Mo2(CO)4}{μ-HCCCH(CH2CH3)}]2] (10) obtained from 5 has been determined.

Reaction of sodium amalgam with carbenium ions species stabilised by two adjacent organometallic moieties

The ionic complexes [Cp2Mo2(CO)4{μ-η2:η3-HCCC(H)(Fc)}][BF4] (1) and [{Cp2Mo2(CO)4(μ-η2:η3-HCCC(H)}2Fc][{Bf4}2] (5) react with NaHg in toluene solution. The results are interpreted in terms of a radical mechanism involving intramolecullar intermolecular coupling reactions.

Phosphorus Functionalized Carbenes: Synthesis and Coordination Properties

Metal complexes with N-Heterocyclic carbene (NHC) ligands are widely used in organometallic chemistry.1 NHC are known to be good donor groups, and the incorporation of functionality is possible on the nitrogen atoms. We are interested in the synthesis of functionalized NHC with functionality offering a new coordination center or possessing hemilabile properties. In particular, the functionalization of NHC with phosphonate (A) leads us to develop original methods for their synthesis. The organometallics complexes, incorporating the functionalized NHC, has been synthesised following two pathways: 1—by using the silver carbene as intermediate2 2—by using the free carbene. According to the first method, several rhodium complexes have been synthesized and characterized. The use of these rhodium complexes (B) as precursor of active catalysts for C C coupling is still under investigation. Beside the chemistry of these rhodium complexes, we have designed models of hydrogenase3 possessing either a phosphite (complex C) or a carbene ligand (D). These complexes have been fully characterized including X-ray diffraction studies and electrochemistry methods. These results encourage us to study model of hydrogenase having functionalized NHC as ligand.