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

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Abstract

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 RuVO 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.

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