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

Abstract

The synthesis and characterization of the a-mesityl NHC-complex (SIMes)CuMes (1) and the dicopper(I) oxalato complex (SIMes)Cu(C2O4) (2; SIMes = 1,3-dimesitylimidazolin-2-ylidene) are described. 1, a new example of a sigma-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 Xray crystallography, the cuprous ions are bridged by the oxalate in mu-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 CO2 in the temperature range 210-350 degrees C to finally give elemental copper in a controlled degradation process. (C) 2016 Elsevier B.V. All rights reserved.