Electrochemical oxidation of Mo(CO)4(LL) and Mo(CO)3(LL)(CH3CN): Generation, infrared characterization, and reactivity of [Mo(CO)4(LL)] and [Mo(CO)3(LL)(CH3CN)] (LL = 2,2′-bipyridine, 1,10-phenanthroline and related ligands)

Mo(CO)₄(LL) complexes, where LL = polypyridyl ligands such as 2,2′-bipyridine and 1,10-phenanthroline, undergo quasi-reversible, one-electron oxidations in methylene chloride yielding the corresponding radical cations, Mo(CO)₄(LL)]⁺. These electrogenerated species undergo rapid ligand substitution in the presence of acetonitrile, yielding Mo(CO)₃(LL)(CH₃CN)]⁺; rate constants for these substitutions were measured using chronocoulometry and were found to be influenced by the steric and electronic properties of the polypyridyl ligands. Mo(CO)₃(LL)(CH₃CN)]⁺ radical cations, which could also be generated by reversible oxidation of Mo(CO)₃(LL)(CH₃CN) in acetonitrile, can be irreversibly oxidized yielding Mo(CO)₃(LL)(CH₃CN)₂]²⁺ after coordination by an additional acetonitrile. Infrared spectroelectrochemical experiments indicate the radical cations undergo ligand-induced net disproportionations that follow first-order kinetics in acetonitrile, ultimately yielding the corresponding Mo(CO)₄(LL) and Mo(CO)₂(LL)(CH₃CN)₃]²⁺ species. Rate constants for the net disproportionation of Mo(CO)₃(LL)(CH₃CN)]⁺ and the carbonyl substitution reaction of Mo(CO)₃(LL)(CH₃CN)₂]²⁺ were measured. Thin-layer bulk oxidation studies also provided infrared characterization data of Mo(CO)₄(ncp)]⁺ (ncp = neocuproine), Mo(CO)₃(LL)(CH₃CN)]⁺, Mo(CO)₃(LL)(CH₃CN)₂]²⁺ and Mo(CO)₂(LL)(CH₃CN)₃]²⁺ complexes.