Selective Activation of Benzylic Carbon−Hydrogen Bonds of Toluenes with Rhodium(III) Porphyrin Methyl: Scope and Mechanism

Abstract

Toluenes underwent selective benzylic carbon−hydrogen bond activation (BnCHA) with rhodium(III) porphyrin methyl. The ortho-, meta-, and para-substituted toluenes yielded the corresponding rhodium porphyrin benzyls in high yields in solvent-free conditions as well as in benzene solvent. Mechanistically, Rh(ttp)Me likely undergoes a σ-bond metathesis pathway. The small value of the kinetic isotope effect (2.7) indicates a bent transition state. The negative slope (−1.1) of the linear free energy relationship Hammett plot supports that the benzylic carbon builds up a positive charge in the transition state.