Unveiling the role of aniline as a Brønsted base in Rh-catalyzed C−H alkylation: Computational insights into amino-assisted outer-sphere CMD

C−H bond cleavage is a key step for the formation of new C−Rh bond in Rh-catalyzed alkylation of aniline derivatives. Due to the inherent basicity of aniline, there is ongoing debate regarding its ability to act as a Brønsted base to assist C−H bond cleavage in these type reactions. In this report, we present computational evidence supporting an amino-assisted outer-sphere concerted metalation-deprotonation (CMD) mechanism. Here, the aniline acts as a Brønsted base to facilitate C−H bond cleavage without any direct interaction between the Rh and the aniline. This amino-assisted outer-sphere CMD pathway is found to be lower in energy compared with the inner-sphere CMD and other base-assisted C−H bond cleavage pathways, providing new insights into the mechanism of Rh-catalyzed C−H functionalization of aniline derivatives. Geometric analysis was conducted to elucidate details of the C−H bond cleavage process. This mechanistic study of C−H bond cleavage in Rh-catalyzed oxidative C−H alkylation of aniline derivatives with allyl alcohols is an important case study of the involvement of amino-assisted outer-sphere CMD in Rh catalysis. We anticipate that the novel amino-assisted outer-sphere CMD mode may extend to other C−H bond functionalization processes and explain the unique effectiveness of aniline in many instances.