Mechanistic study on ligand-controlled cobalt-catalyzed regioselectivity-switchable hydroarylation of styrenes.

Density functional theory (DFT) calculations have been performed to study the mechanism of the recently reported Co-catalyzed ligand-controlled hydroarylation of styrenes as a means of preparing 1,1- or 1,2-diarylalkanes. The present study corroborates the previously proposed three-step mechanism, comprising C-H activation (C-H oxidative addition), styrene insertion, and reductive elimination. In the C-H activation and reductive elimination steps, our calculations suggest that styrene does not coordinate to the Co center. In the insertion step, styrene is inserted into the Co-H bond rather than the Co-C bond. Furthermore, the rate- and regiodetermining step is found to be C-C reductive elimination. It is significant that the regioselectivity observed experimentally has been successfully reproduced by our calculations. More importantly, in analyzing the origin of the ligand-controlled regioselectivity, we have found that the steric effects of different ligands mainly determine the observed regioselectivity. Both the shape (i.e., "umbrella-up" or "umbrella-down") and bulkiness of the ligand contribute to the steric effect.