Structure of Bis(trifluoromethyl)cuprate and Its Role in Trifluoromethylation Reactions

An equilibrium between [(SIMes)Cu-CF3] (1, SIMes = 1,3-dimesitylimidazolin-2-ylidene) and the cuprate salt [(SIMes)2Cu][(CF3)2Cu] (2) was observed. Synthetic methods to prepare and isolate 2 are reported. Trifluoromethylations using equilibrium mixtures of 1 and 2 occur readily for aryl iodides and even occur for aryl bromides at 90 °C. Kinetic data suggest the cuprate form does not play a significant role in trifluoromethylations using N-heterocyclic carbene complexes of copper.