Multielectron Transfer Kinetics for Cis versus Trans Dioxorhenium(V) Species:Isoelectronic Modeling with Osmium(VI/V) and Control of Interfacial Reactivity by Rhenium(IV) Accessibility

摘要

Steady-state microelectrode voltammetry experiments show that the electrochemicalexchange kinetics for the two-electron, two-proton reduction of cis-(O)2(Rev(py)2(bpy)+ (py = pyridine, bpy = 2,2' bipyridine) at pH* = 6, exceed by more than a factor of 100 the kinetics for trans(0)2Rev(py)4+ reduction under identical conditions. Mechanistic studies indicate that both reactions proceed via rate-limiting Re(V yields IV) steps. Comparisons with isoelectronic (and nearly isostructural) osmium redox couples, reveal that the key intermediate state (Re(IV)) is far more accessible thermodynamically for the cis system than for the trans. Quantitative consideration of the thermodynamic accessibility difference shows that most or all of the two-electron reactivity difference (cis vs. trans) can be accounted for on this basis.