Copper(I) β-Boroalkyls from Alkene Insertion:  Isolation and Rearrangement

The insertion of alkenes into an (NHC)copper(I) boryl affords isolable β-boroalkyl complexes in high yields; competition experiments using substituted styrenes show that electron-donating substituents slow the reaction. Although the insertion products are stable at ambient temperature, a β-hydride elimination/reinsertion sequence affords a rearranged α-boroalkyl complex on heating.