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

An equilibrium between [(SIMes)Cu-CF<sub>3</sub>] (<b>1</b>, SIMes = 1,3-dimesitylimidazolin-2-ylidene) and the cuprate salt [(SIMes)<sub>2</sub>Cu][(CF<sub>3</sub>)<sub>2</sub>Cu] (<b>2</b>) was observed. Synthetic methods to prepare and isolate <b>2</b> are reported. Trifluoromethylations using equilibrium mixtures of <b>1</b> and <b>2</b> 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 <i>N</i>-heterocyclic carbene complexes of copper.