Electrochemistry and Infrared Spectroelectrochemistry of M_nSnPh_4−n(M = CpMo(CO)₃, Mn(CO)₅, CpFe(CO)₂; n = 1, 2)

The electrochemistry and infrared spectroelectrochemistry of the series M_nSnPh_4−n(M = CpMo(CO)₃, Mn(CO)₅ and CpFe(CO)₂; n = 1,2) and the corresponding homobinuclear compounds (M₂) were examined in CH₃CN/TBAH solutions (TBAH = tetra-n-butylammonium hexafluorophosphate). Cyclic voltammetric and double-potential step chroncoulometric data indicate that all of these compounds undergo net two-electron oxidations, with concomitant metal-tin or, in the case of the homobinuclear species, metal-metal bond rupture. The oxidation products for the triphenyltin adducts are the solvent adducts of the transition-metal cation and the triphenyltin cation. For Mn(CO)₅SnPh₃, the oxidation process is chemically reversible. Oxidation of the diphenyltin-bridged compounds results in cleavage of only one metal-tin bond, to give the metal cation and a base-stabilized stannylene cation. An ECE mechanism is proposed for the oxidation of these species. [Mn(CO)₅]₃SnPh undergoes metal-tin bond cleavage reactions. The reductions of the compounds in this series and the homobinuclear compounds were also studied. Almost all of the reductions were net two-electron processes, which, like the oxidations, resulted in metal-tin or metal-metal bond cleavage. The reduction products for the homobinuclear species were the monomeric metal anions. The triphenyltin adducts yielded the metal anions and either the triphenylstannate anion or the triphenyltin dimer species, Sn₂Ph₆, upon reduction, depending on the transition-metal moiety. The diphenyltin-bridged compounds were reduced to the transition-metal anions and an unreduced tin product, possibly an oligomerization product of diphenyltin. Infrared spectral data imply that this reduction proceeds via a terminal diphenylstannate anion adduct of the transition-metal moiety.