Copper hydrotris(3,5-diphenylpyrazolyl)borate dithiocarbamates: mimicking green copper proteins

Abstract

Three novel copper hydrotris(3,5-diphenylpyrazolyl)borate (Tp^Ph2) dithiocarbamate complexes, [Tp^Ph2Cu(dtc)] (dtc = S₂CNEt₂1, S₂CNBz₂2 and S₂CN(CH₂)₄3) have been prepared in a simple one pot reaction by sequential addition of KTp^Ph2 and Na(dtc) to CuCl₂·2H₂O. IR, UV-Vis and ESR spectroscopic studies suggest a mostly κ³ coordinated Tp^Ph2 ligand, bidentate dithiocarbamate ligands and therefore, a five coordinate copper centre. Unusually, a κ³ to κ² isomerisation of the Tp^Ph2 ligand is found in solution in 3 and to a lesser extent in 1. The X-ray crystal structures reveal geometries intermediate between trigonal bipyramidal and square pyramidal depending on the steric bulk of the dithiocarbamate ligand and a long Cu–N bond resulting in an asymmetrically bound Tp^Ph2 ligand. Electrochemical studies reveal quasi-reversible one-electron oxidation and reduction to Cu(I) with the reversibility and reduction potential strongly dependent on the dithiocarbamate. DFT calculations reveal a weakly antibonding Cu–S π* SOMO and a strongly antibonding Cu–S σ* LUMO consistent with the significant effect of the dithiocarbamate ligand on the electrochemical behaviour of these complexes.