Unusual Kinetics Induced by Ligands in Rhodium(III)-Catalyzed Dehydrogenative Olefination Reactions.

In this study, we investigate the effects of ligands on C-H activation during rhodium(III)-catalyzed C-H bond olefination reactions using well-defined [Cp X Rh III ] catalytic systems with three representative Cp X (Cp (η 5 -C 5 H 5 ), Cp CF3 (η 5 -C 5 Me 4 CF 3 ), and Cp* (η 5 -C 5 Me 5 )) ligands. Our results demonstrate that C-H activation as the rate-limiting step is significantly influenced by the steric properties of the Cp X ligands. Moreover, we observe a dramatic acceleration of the simple [CpRh III ]-catalyzed C-H olefination reaction with acid coproducts such as HOAc, implying an autocatalytic C-H activation process.