Synthesis, Molecular Structures, and Reactivity of Mono- and Binuclear Neutral Copper(I) Carbenes

Mononuclear, neutral copper(I) carbenes [But2P(NSiMe3)2-κ2N]Cu=CPh2 and [But2P(NSiMe3)2-κ2N]CuC(p-NO2C6H4)2 (4a,b) as well as the binuclear μ-carbene copper complex {[But2P(NSiMe3)2-κ2N]Cu}2(μ-CPh2) (5) have been synthesized. The solid-state structures of 4b and 5 are reported. Carbene 4b is active in cyclopropanation of styrene. Reaction of 4b with (p-MeC6H4)CN2 afforded [But2P(NSiMe3)2-κ2N]CuC(p-MeC6H4)2, the corresponding mixed azine Ar2CNNCAr′2 and the carbene dimer Ar2CCAr′2, demonstrating an important pathway for carbene loss in cyclopropanation of olefins via reaction of the copper(I) carbene with nucleophilic diazo compounds. Complex 5 reacted with C2H4 or styrene to give 1:1 mixtures of the terminal carbene 4a and of the corresponding copper(I) olefin complexes, proving unambiguously that binuclear complexes like 5 are not relevant for copper-catalyzed cyclopropanation of olefins with diazo compounds. The electronic structure of 4b was investigated by means of DFT calculations.