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.