The aerobic oxidation of copper(I) to copper(II) was studied in the ionic liquid (IL) 1-n-butyl-3-methylimidazolium acetate [BMIm][OAc]. Temperatures above 100 °C promote the deprotonation of the C2 atom of the imidazolium ring and the dissolution of CuCl. 1H and 13C NMR spectra indicate the formation of the N-heterocyclic carbene (NHC) complex [NHC] CuICl under inert conditions. Upon aerobic oxidation, air-stable blue-green crystals of [BMIm]2[CuII2(OAc)4Cl2] precipitate in high yield and the NHC is recovered. X-ray diffraction on a single-crystal of the complex salt revealed a monoclinic structure with space group P21/n. The centrosymmetric dinuclear acetate complex [Cu2(OAc)4Cl2]2- has the paddle-wheel motif and is weakly paramagnetic.