Crystal structure of the [(1,3-dimesityl-1H-imidazol-3-ium-2-yl)methano-lato]copper(II) chloride dimer: insertion of formaldehyde into a copper-carbene bond.

The crystal structure of bis-[μ-(1,3-dimesityl-1H-imidazol-3-ium-2-yl)methano-lato-κ2O:O]bis-[di-chlorido-copper(II)], [Cu2Cl4(C22H26N2O)2], is reported. The complex is assumed to have formed via the insertion of formaldehyde into the copper-carbon bond in an N-heterocyclic carbene complex of copper(I) chloride. The structure of the binuclear mol-ecule possesses a crystallographic-ally centrosymmetric Cu2O2 central core with the O atoms bridging between the CuII atoms and thus Z' = 0.5. The copper centres are further ligated by two chloride ligands, resulting in the CuII atoms residing in a distorted square-planar environment. The Cu-O bond lengths are shorter than those previously reported in structures with the same central Cu2O2 motif. The complex displays C-H⋯Cl inter-actions involving the H atoms of the heterocycle backbone and the chloride ligands of a neighbouring mol-ecule.