A Computational Study on the Reaction Mechanisms of Nickel-Catalyzed Diarylation of Alkenes

A density functional theory study on nickel-catalyzed diarylation of styrene (R1) with arylboron (R2) and aryl bromide (R3) is presented in this article, to unveil the plausible mechanism and the competition of the potential side reactions. The located reaction pathway involves the elementary steps of oxidative addition, migratory insertion, transmetalation, and reductive elimination. The total free-energy barrier is computed to be 27.3 kcal/mol, which should be consistent with the experimental temperature and reaction time reported. The Heck coupling reactions between R1 and R3 in the absence and presence of R2 are investigated at the same level of theory, respectively, and it is found that the presence of R2 could not only favor the formation of a eta(3)-benzyl-Ni complex leading to the desired diarylation but also disfavor the undesired beta-H elimination step as well. The Suzuki-Miyaura coupling pathway is also suppressed under the optimal conditions, because the migratory insertion of R1 takes place prior to the transmetalation of R2. However, addition of a strongly coordinating ligand could hinder the entry of R1 into the ligand field, which may retard the diarylation pathway and make the cross-coupling pathway dominant.