Understanding the higher reactivity of B2cat2 versus B2pin2 in Copper(I)-catalyzed alkene diboration reactions

DFT calculations have been carried out to study the reactivity difference of B(2)cat(2) and B(2)pin(2) in the diboration reaction of alkenes catalyzed by carbene-ligated copper(I) complexes. The higher reactivity of B(2)cat(2), versus B(2)pin(2) in this reaction results largely from the enhanced electrophilicity/Lewis acidity of the former, which significantly lowers the barrier in the product-forming transmetalation step. Transmetalation reactions of B(2)cat(2) and B(2)pin(2) with (NHC)Cu-OMe have also been investigated, and the relative barriers are much closer than with analogous Cu-R systems.