Coordination of new disulfide ligands to CuI and CuII: Does a CuIIμ-thiolate complex form?

• Synthesis of new ligands for possible formation of CuIIμ-thiolate complexes.
• The half-wave potentials of the synthesized CuI disulfide species were compared.
• New CuII complexes were analyzed by X-ray structure determination.

Interest in dinuclear CuIIμ-thiolate and CuI disulfide complexes is triggered by their similarity with the CuA site and the possibility to control this redox equilibrium. Three new disulfide ligands L1, L3 and L4 were synthesized and reacted with CuI salts to investigate whether thiolate or disulfide species would form. The nature of L1 precludes the formation of CuIIμ-thiolate species, resulting in the formation of [CuI2(L1)(CH3CN)](BF4)2 which was characterized via single crystal X-ray crystallography. Pyrazole-containing ligands L3 and L4 form CuI 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 CuII state. The half-wave potentials of the CuI complexes with L1 and L2 are less positive, indicating that in order to allow formation of both CuIIμ-thiolate and CuI disulfide species, a half-wave potential of roughly 0 V versus Ag/AgCl would be ideal. Furthermore, CuII 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.

Small ligand changes can have a large effect on whether a dinuclear CuIIμ-thiolate or a CuI disulfide complex is formed. Three new ligands were synthesized; it was found that all three form CuI disulfide complexes when reacted with CuI. The redox potentials of these complexes were compared and a series of new CuII disulfide complexes were synthesized.Figure optionsDownload as PowerPoint slide