Stabilisation of copper(I) by an azoimine ligand: redox properties and reactions of bis(phenylazoacetaldoximato)bis(phenylacetaldoxime)dicopper(I)

Abstract

The high preference of phenylazoacetaldoxime, MeC(NOH)NNPh (HL), for copper(I) is rationalised in terms of electronic and steric factors. The complex [Cu₂(HL)₂(L)₂](1) undergoes a one-electron oxidation at ∼0.8 V vs. saturated calomel electrode to an unstable Cu^IICu^I species. Tertiary phosphines displace HL from (1) affording [CuL(PR₃)₂][R = Ph (2a) or C₆H₄Me-p(2b)]. (2a) reacts with HCl to form [{Cu(PPh₃)Cl}₄] and with HClO₄ to give the complex [Cu(HL)(PPh₃)₂(ClO₄)]. All complexes having the chelated CuL or Cu(HL) fragment are shown to have a characteristic low-energy metal-to-ligand charge-transfer transition (700–900 nm).