Molecular dicopper(I) oxalate stabilized by two N-heterocyclic carbenes: A potential precursor for copper deposition.

The synthesis and characterization of the σ -mesityl NHC-complex (SIMes)CuMes ( 1 ) and the dicopper(I) oxalato complex [(SIMes)Cu] 2 (C 2 O 4 ) ( 2 ; SIMes = 1,3-dimesitylimidazolin-2-ylidene) are described. 1 , a new example of a σ -organocopper complex bearing an imidazolin-2-ylidene ligand, is obtained from the stoichiometric reaction of mesitylcopper with SIMes. The single crystal X-ray structure determination of 1 reveals a linearly coordinated copper ion. Clean reaction of 1 with 0.5 equiv. of oxalic acid affords the dinuclear copper(I) oxalato complex 2 with concomitant elimination of mesitylene. As confirmed by X-ray crystallography, the cuprous ions are bridged by the oxalate in a μ -1,2,3,4 mode and are each coordinated by one NHC-capping ligand, thus both copper(I) exhibit trigonal coordination geometries, though with slight distortions. 2 represents the first example of a copper(I) oxalato complex stabilized by two N -heterocyclic carbene ligands. Whereas 1 is only moderately air-stable in the solid state, 2 resists to non-inert conditions at least for several days. The thermal decomposition behavior of 2 was investigated by thermal gravimetric analysis/differential scanning calorimetry coupled with mass spectrometry (TGA/DSC-MS) and revealed the elimination of HCN, CO and CO 2 in the temperature range 210–350 °C to finally give elemental copper in a controlled degradation process. [ABSTRACT FROM AUTHOR]