Ligand control of metal oxidation states. Synthesis, characterization and cyclic voltammetric studies of a group of ruthenium phenolates

Reaction of a series of phenolic ligands with different functional groups at the 2-position with [Ru(PPh(3))(3)Cl-2] affords stable complexes of ruthenium(II) and ruthenium (III); The ruthenium(II) complexes are diamagnetic and show intense absorption in the visible region due to MLCT transitions. In dichloromethane solution, the complexes show redox (ruthenium(II)-ruthenium(III)) behaviour, the potential of which varies with the electronic nature of the phenolic ligand. In two of these complexes, an irreversible ruthenium(III)-ruthenium(IV) oxidation was observed near 1.2 V (vs SCE). The ruthenium(III) complexes are one-electron paramagnetic showing rhombic ESR spectra at 77 K. Intense LMCT transitions were observed in the visible region together with low-intensity ligand-field transitions at lower energies. In acetonitrile solution the ruthenium(III) complexes show both ruthenium(III)-ruthenium(II) reduction and ruthenium(III)-ruthenium(IV) oxidation.