Electrochemical and theoretical investigations of the reduction of Fe2 (CO) 5Lµ-SCH2XCH2S complexes related to FeFe hydrogenase

The complexes Fe2 (CO) 6μ-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 2FeH subsite of FeFeH2ases. Electrochemical investigation of 1 and 2 in MeCN–NBu4PF6 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 CH2Cl2–NBu4PF6, 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.