Coordination of new disulfide ligands to Cu-I and Cu-II: Does a Cu-II mu-thiolate complex form?

摘要

Interest in dinuclear Cu-II mu-thiolate and Cu-I disulfide complexes is triggered by their similarity with the Cu-A site and the possibility to control this redox equilibrium. Three new disulfide ligands L1, L3 and L4 were synthesized and reacted with Cu-I salts to investigate whether thiolate or disulfide species would form. The nature of L1 precludes the formation of Cu-II mu-thiolate species, resulting in the formation of [Cu-2(I)(L1)(CH3CN)](BF4)(2) which was characterized via single crystal X-ray crystallography. Pyrazole-containing ligands L3 and L4 form Cu-I complexes that are stable in solution in air for hours with half-wave potentials of approximately +0.55 V versus Ag/AgCl, indicating high stability of the CuI state rather than the Cu-II state. The half-wave potentials of the Cu-I complexes with L1 and L2 are less positive, indicating that in order to allow formation of both Cu-II mu-thiolate and Cu-I disulfide species, a half-wave potential of roughly 0 V versus Ag/AgCl would be ideal. Furthermore, Cu-II crystal structures with L1, L2, L3 and L4 and different counterions were compared and analyzed. Pyrazolyl-containing ligands L3 and L4 form complexes that are very similar to the complexes with pyridyl-containing ligands L1 and L2. (C) 2015 Elsevier B.V. All rights reserved.