Anodic Reaction of Co(η5-C5H5)(CO)(PPh3): An Oxidatively Induced Ligand Exchange Involving a 17 e−/18 e− Redox Pair

Abstract

Unlike a number of other monocarbonyl-substituted complexes CoCp(CO)L (Cp = (η5-C5H5)), chemical oxidation of the L = triphenylphosphine derivative CoCp(CO)(PPh3), 1, is known to give, in the absence of added PPh3, the disubstituted phosphine complex [CoCp(PPh3)2]+ rather than the simple 17-electron radical cation 1+. Electrochemistry of 1 in CH2Cl2/[NBu4][B(C6F5)4] (E1/2(1/1+) = −0.38 V vs ferrocene) shows that the favored anodic products depend on the concentration of 1. At low concentrations (e.g., 10−4 M) and on the cyclic voltammetry time scale, the radical cation 1+ dominates, but at higher concentrations and longer reaction times, a quantitative mixture of CoCp(CO)2 and [CoCp(PPh3)2]+ is produced in an overall “half-electron” process. On the basis of cyclic voltammetry, chronoamperometry, bulk electrolysis, and IR spectroelectrochemistry, a “radical−substrate” mechanism is proposed involving the reaction of 1+ with 1 to give transient [Co2Cp2(CO)2(PPh3)2]+. This putative dimer radical cation interm...