Electronic and kinetic isotope effects on the electrooxidation of benzyl alcohols by a monoxo ruthenium (V) complex of tetramethylcyclam

The electrooxidation of substituted benzyl alcohols by trans-[Ruv(TMC)(O)(NCO)]2+(TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) was studied in acetonitrile by rotating disc voltammetry. The second order rate constant between RuVO and the benzyl alcohols increases in the presence of electron donating substituents and decreases in the presence of electron withdrawing groups. A linear Hammett plot with a slope of -2.0 was obtained. The large negative reaction constant is consistent with a build up of positive charge at the alcohol in the transition state. The primary kinetic isotope effect (kH/kD) in benzy] alcohol oxidation was determined to be 4.1. The results are consistent with a mechanism involving hydrogen atom abstraction by the oxo ligand on the ruthenium complex.