Copper(I)-catalyzed reaction of unsymmetrical alkyne with HB (pin): a density functional theory study

With the aid of density functional theory calculations, we have investigated the mechanism of copper(I)-catalyzed reaction between unsymmetrical alkyne 1-phenyl-1-butyne and HB(pin). The results of the density functional theory calculations show that the reaction mechanism involves syn-addition of catalyst ([NHC]CuH) (NHC = N-heterocyclic carbene) to 1-phenyl-1-butyne to form the alkenyl copper intermediates 2a and 5a, and then intermediates 2a and 5a react with HB(pin) to give intermediates 3 (3a, 3b) and 6 (6a, 6b), and finally elimination of catalyst completes the catalytic cycle and yields the alpha-product P-1 and beta-product P-2. We found that alpha-product should be more favored than beta-product. The calculated results are consistent with the experimental findings. The present paper may provide a useful guide for understanding other analogous copper-catalyzed hydroboration of unsymmetrical alkynes.