Copper(II) complex of N,N´-bis-(benzimidazol-2-yl-methyl)-hexane-1,6-dicarboxamide ligand: synthesis, structure and catalytic oxidation of amines in ionic liquid

A new copper(II) complex, [Cu(L)NO₃]NO₃·2H₂O, has been synthesized with N, N'-bis-(benzimidazol-2-yl-methyl)-hexane-1,6-dicarboxamide as a ligand, L = GBSA (Ahuja and Mathur in Spectrochim Acta Part A 83:180–186, 2011). The single-crystal X-ray structure characterization confirms that copper(II) ion in the complex possesses a distorted penta-coordinate geometry with one of the nitrate anions bound to copper(II) as a monodentate ligand. The N₂O₂ equatorial plane of the copper(II) complex comprises of carbonyl oxygen atom (O1), nitrate oxygen atom (O3) and two benzimidazole nitrogen atom (N1,N4), while the axial position is occupied by oxygen atom (O2) of amide carbonyl. Low-temperature EPR study indicates distorted tetragonal geometry, while cathodic E_1/2 value indicates stabilization of copper in + 2 oxidation state in solution. TGA data demonstrated thermal decomposition pattern of the complex. The complex was studied as a catalyst for the oxidation of aromatic and aliphatic primary and secondary amines in ionic liquid, [BMIM][BF₄] as a solvent and TBHP as an external source of oxygen at 45–50 °C, affording good yields under mild conditions. Products formed were analyzed by GCMS.