DFT studies of alkene insertions into Cu-B bonds in copper(I) boryl complexes

DFT calculations have been carried out to study the insertion reactions of alkenes into the Cu-B bond in (NHC)Cu(boryl) complexes (NHC = N-heterocyclic carbene). The nature of the insertion reactions and the relevant regiochemistry have been examined along with beta-hydride eliminations, which are followed by reinsertion of the alkene into the Cu-H bond. Hyperconjugation (i.e., pi bonding) between the Cu-C sigma bond and the "empty" p(z) orbital on boron has been identified as the cause of the unexpectedly small Cu-C-B angle found experimentally by X-ray diffraction in alpha-borylalkyl Cu(I) complexes.