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

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 d6 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.