Oxidatively Induced Reductive Elimination: Exploring the Scope and Catalyst Systems with Ir, Rh, and Ru Complexes

Abstract

Direct conversion of C-H bonds into C-C bonds is a promising alternative to the conventional cross-coupling reactions, thus giving rise to a wide range of efficient catalytic C-H functionalization reactions. Among the elementary stages in the catalytic C-C bond formation, reductive elimination constitutes a key step of the catalytic cycle, and, therefore, extensive studies have been made to facilitate this process. In this regard, oxidation on the metal center of a post-transmetalation intermediate would be an appealing approach. Herein, we have explored the substrate scope, catalyst systems, and oxidation tools to prove that the oxidatively induced reductive elimination (ORE) plays a critical role in the product-releasing C-C bond formation. Notably, we have demonstrated that ORE broadly operates with a series of half-sandwich d(6) Ir(III)-, Rh(III)-, and Ru(II)-aryl complexes. We have described that the metal center oxidation of the isolable post-transmetalation intermediates by means of chemical- or electro-oxidation can readily deliver the desired arylated products upon reductive elimination even at ambient temperature. Computational studies delineated the thermodynamics of the reductive elimination, where the activation barriers are shown to be significantly reduced upon increasing the oxidation states of the intermediates. We were also successful in corroborating this ORE in the corresponding Rh-methyl complex. In addition, catalytic conditions were optimized to incorporate this mechanistic understanding into the Ir-, Rh-, and Ru-catalyzed C-C bond formations under mild conditions.