Synthesis, characterization, redox properties and reactivities of a group of phenolato complexes of ruthenium(III)

Abstract

Seven complexes of the type [Ru^III(PPh₃)₂(L)Cl₂] (where L = 8-quinolinolate, 4-methyl-2-(phenylazo) phenolate and salicylal-diminate anion) have been synthesized by the reaction of [Ru(PPh₃)₃Cl₂] with HL. These complexes are one-electron paramagnetic and show rhombic ESR spectra in 1¦1 dichloromethanetoluene at 77 K. In CH₂Cl₂ solution, these complexes show intense LMCT transitions in the visible region together with weak ligand-field transitions at lower energies. Each of these complexes shows a ruthenium(III)-ruthenium(II) reduction (-0.12 to -0.40 V vs SCE) and a ruthenium(III)-ruthenium(IV) oxidation (0.78-0.88 V vs SCE) in acetonitrile solution. The potentials of the ruthenium(III)-ruthenium(II) reduction vary linearly with the nature of substituent in L. The [Ru^III(PPh₃)₂(L)Cl₂] complexes react with bidentate chelating ligands (L′ = 8-quinolinolate anion, 2,2′-bipyridine, 1,10-phenanthroline) to afford complexes of type [Ru(PPh₃)₂(L)(L′)]ⁿ⁺These complexes are diamagnetic and show intense MLCT transitions in the visible region. The potential of the ruthenium(II)-ruthenium(III) couple in these complexes depend on the nature of both L and L′.