Axial ligand substitution reactions of phosphine derivatives of ruthenium(II) and ruthenium(III) benzoquinone dioxime complexes

Abstract

Abstract The synthetic, spectral and kinetic studies of ruthenium(II) macrocyclic complexes, Ru(BQDH) 2 L 2 (where BQDH = benzoquinone dioximate), are reported. Axial ligands include nitrogen, phosphorus and sulphur donors. An oxidized species, Ru(BQDH)(BQD)(PPh 3 ) 2 , formed via one-electron oxidation followed by loss of a bridging hydrogen, was characterized as a ruthenium(III) complex. Kinetic and thermodynamic data of axial ligand substitution showed that the reaction mechanism is dissociative (D) and that the five-coordinate intermediate possesses little or no ability to discriminate between nucleophiles. The ruthenium(II) complexes were found to be more labile than the corresponding ruthenium(III) complexes. Trans -group and leaving-group effects are discussed. The BQDH ruthenium complexes differ from the DMGH analogues in that the former are much more labile, owing to the high delocalization of the conjugated π system of the BQDH. The ruthenium BQDH complexes were also found to be much more inert than the analogous iron complexes implying that the M → L π-back bonding is more important for ruthenium.