Synthesis, characterisation and electrochemical behaviour of rhodium(III) complexes containing 1,2-naphthoquinone-2-oxime and formation of imine complexes through N - O bond cleavage

The new rhodium(III) complexes [Rh(η2-nqo)L2Cl2] (1a-1d) and [Rh(η2-nqo)2LCl] (2b-2d) [1a, L = PPh3; 1b,2b, L = pyridine (py); 1c,2c, L = 4-phenylpyridine (ppy); 1d,2d, L = 4-acetylpyridine (apy)] have been prepared by treatment of the reaction mixture of RhCl3·3H2O and 1,2-naphthoquinone-2-oxime (nqo) in ethanol by P or N donor ligands. Cyclic voltammetric studies show that the new complexes display an irreversible metal-localised two-electron reduction from RhIIIto RhI, accompanied by the loss of the chloride ligands. The 1,2-naphthoquinone-2-imine (nqi) complexes [Rh(η2-nqo)(η2-nqi)Cl2]·L (3b-3d) (3b, L = py; 3c, L = ppy; 3d, L = apy), [Rh(η2-nqo)(η2-nqi)Cl2] (4) and [Rh(η2-nqo)2(nqi)Cl] (5) were obtained by deoxygenation of the oxime group in which N-O bond cleavage is observed. The molecular structures of 1a, 2b, 4 and 5 were established by single crystal X-ray analyses.