Reaction Mechanism Study on Hydroboration and Dehydrogenative Borylation of Styrene Catalyzed by Co(II) Phosphinopyridonate Complex

Transition-metal-catalyzed borylation of styrene has been widely investigated. However, there are relatively few examples of the cobalt-catalyzed hydroboration and dehydrogenative borylation of styrene. In this study, a mechanistic investigation of divalent cobalt-catalyzed hydroboration and dehydrogenative borylation reactions of styrene with HBpin and HBcat was carried out by using density functional theory (DFT) methods. The reactivity difference between HBpin and HBcat toward styrene was analyzed to predict the different products. The calculated results indicate that the hydroboration reactivity of styrene with HBcat is superior to that of HBpin due to the phenyl–phenyl π-π stacking in the rate-determining step. In contrast, the dehydrogenative borylation product can be generated kinetically from HBpin owing to the very stable intermediate formed between HBcat and the Co catalyst as well as the high metathesis barrier following this intermediate.