Copper-NHC-Mediated Semihydrogenation and Hydroboration of Alkynes: Enhanced Catalytic Activity Using Ring-Expanded Carbenes

A series of two-coordinate copper tert-butoxide complexes bearing five-, six-, and seven-membered ring N-heterocyclic carbenes, prepared by protonolysis of (NHC)­CuMes with t BuOH, have been used as catalytic precursors in the semihydrogenation of alkynes with silanes/ t BuOH and the hydroboration of alkynes with HBPin. Both processes proceed with high regioselectivity and show enhancements with six- and seven-membered ring carbenes.