Isolable, copper(I) dicarbonyl complexes supported by N-heterocyclic carbenes

Cationic copper(I) dicarbonyl complexes supported by N-heterocyclic carbene ligands, SIPr and IPr*, have been synthesized. [(SIPr)Cu(CO)(2)][SbF(6)] and [(IPr*)Cu(CO)(2)][SbF(6)] have a trigonal planar, three-coordinate copper atom with an average Cu-CO distance of 1.915 Å and display C-O stretching frequencies higher than that of the free CO (2143 cm(-1)). The high CO stretching frequencies suggest that the Cu(I)-CO interaction in these cationic adducts is dominated by electrostatic and OC → Cu σ-donor components. [(SIPr)Cu(CO)(2)][SbF(6)] and [(IPr*)Cu(CO)(2)][SbF(6)] readily form the corresponding [(SIPr)Cu(CO)(H(2)O)][SbF(6)] and [(IPr*)Cu(CO)(H(2)O)][SbF(6)] with loss of a CO even with traces of water, but they can be converted back to the dicarbonyl adducts using excess CO. The synthesis and structure of [(IPr*)Cu(H(2)O)][SbF(6)] are also reported. It is a two-coordinate copper adduct with a Cu-O distance of 1.874(2) Å. It reacts with excess CO to form [(IPr*)Cu(CO)(2)][SbF(6)].