Kinetics of alkene oxidation by cationic trans-dioxoruthenium(VI) complexes. Effect of driving force on rate constants

Abstract

The kinetics of alkene oxidation by a series of isostructural trans-dioxoruthenium(VI) complexes with E°(Ru^VI–Ru^V) ranging from 0.23 to 0.7 V vs. saturated calomel electrode has been investigated in acetonitrile. The experimental rate law is rate =k₂[Ru^VI][alkene]. A linear free-energy relationship between log k₂ and E°(Ru^VI–Ru^V) for the oxidation of styrene and norbornene has been observed. Both steric and electronic effects of alkenes as well as the E° of the dioxoruthenium(VI) complexes affect the rate constants. For the oxidation of para-substituted styrenes, a linear Hammett plot of log k₂versusσ⁺ for the para substituents with a ρ value of –2.1 was found. A charge-transfer mechanism alone is insufficient to explain the experimental findings.