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

Abstract

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)(CH 3CN)] +; 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)(CH 3CN)] + radical cations, which could also be generated by reversible oxidation of Mo(CO) 3(LL)(CH 3CN) in acetonitrile, can be irreversibly oxidized yielding [Mo(CO) 3(LL)(CH 3CN) 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)(CH 3CN) 3] 2+ species. Rate constants for the net disproportionation of [Mo(CO) 3(LL)(CH 3CN)] + and the carbonyl substitution reaction of [Mo(CO) 3(LL)(CH 3CN) 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)(CH 3CN)] +, [Mo(CO) 3(LL)(CH 3CN) 2] 2+ and [Mo(CO) 2(LL)(CH 3CN) 3] 2+ complexes.