Isolable, Copper(I) Dicarbonyl Complexes Supported by <i>N</i>‑Heterocyclic Carbenes

Cationic copper­(I) dicarbonyl complexes supported by N-heterocyclic carbene ligands, SIPr and IPr*, have been synthesized. [(SIPr)­Cu­(CO)2]­[SbF6] and [(IPr*)­Cu­(CO)2]­[SbF6] 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]­[SbF6] and [(IPr*)­Cu­(CO)2]­[SbF6] readily form the corresponding [(SIPr)­Cu­(CO)­(H2O)]­[SbF6] and [(IPr*)­Cu­(CO)­(H2O)]­[SbF6] 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(H2O)]­[SbF6] 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]­[SbF6].