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 [Fe2(CO)4(κ2-dppe)­(μ-pdt)] (1) (dppe = Ph2PCH2CH2PPh2; pdt = S­(CH2)3S) 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, [Fe2(CO)4–n{P­(OMe)3}n(κ2-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.