Anodic Electrochemistry of Multiferrocenyl Phosphine and Phosphine Chalcogenide Complexes in Weakly Nucleophilic Electrolytes

The anodic electrochemistry of several compounds containing two or three ferrocenyl moieties linked by a phosphine or phosphine chalcogenide group has been studied in dichloromethane containing [NBu₄][TFAB], where TFAB is the tetrakis(perfluoroaryl)borate anion, [B(C₆F₅)₄]^-. In two cases, namely [CpFe(C₅H₄)]₃P (3) and [CpFe(C₅H₄)]₂PO(Ph) (6), the first one-electron-oxidation product is stable on the cyclic voltammetric (CV) time scale and subsequent oxidations at more positive potentials are also observed. The oxidations of [CpFe(C₅H₄)]₂PPh (2) and [CpFe(C₅H₄)]₃PSe (7) are not reversible, and their monocations undergo follow-up reactions that are first-order and second-order, respectively, in the neutral compound. The results are consistent with a model in which the initial oxidation always involves a largely ferrocenyl-based HOMO which, nevertheless, has significant phosphine or phosphine chalcogenide character, allowing radical-type reactions, including dimerizations, at the linking group. The traditional nonaqueous supporting electrolyte anions such as [PF₆]^- and [BF₄]^- are shown to be responsible for many of the earlier difficulties in interpreting the anodic electrochemistry of this oft-studied class of compounds.