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

Abstract

Reaction of a series of phenolic ligands with different functional groups at the 2-position with [Ru(PPh₃)₃Cl₂] 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.