Synthesis, spectroscopy and redox behaviors of 4,6-di-t-Bu-, 4-Me-6-t-Bu- and 4-t-Bu-2-nitrosophenolato copper(II) complexes; Characterization of radical species generated by PPh3.

The synthesis, spectroscopy (IR, UV-Vis, ESR), magnetic and thermal behaviors, as well electrochemistry and reactivity towards PPh3 of alkyl-substituted bis(2-nitrosophenolato)copper(II) complexes, CuLx2, where Lx = 4,6-di-t-Bu-2-nitrosophenolato (L1), 4-CH3-6-t-Bu-2-nitrosophenolato (L2), 4-t-Bu-2-nitrosophenolato (L3) mono-anion ligands, are presented. The solid-state and solution ESR spectra showed an axially symmetric g-tensors with gII > g 2.03 indicating that the unpaired electron is located in the dx2 - y2orbital. When CuLx2 complexes were treated with an excess of PPh3 in air or under vacuum in toluene (or other solutions) at 300K, as confirmed by UV-Vis and ESR examination, without formation of PPh3 adduct of the complexes, the immediately generation of semiquinone type radical species and reduction of Cu(II) to Cu(I) were observed. In the case of CuL(1)(2) the further conversion of the generated primary radical species to secondary bis(PPh3)2(phenoxazinolato)Cu(I) semiquinone type radical was detected. The cyclic voltammetry (CV) of CuLx2 exhibited two successive quasi-reversible ligand centered reductions and two irreversible metal and ligand centered oxidation processes. Electrochemical behaviors were interpreted in terms of the existence two-valence tautomeric nitroso and oximato isomers of CuLx2 in solution.