Homobinuclear cyanide-bridged linkage isomers containing the redox-active unit [(µ-XY)Ru(CO)2L(o-O2C6Cl4)] (XY = CN or NC)

Abstract

The salts [NEt₄][Ru(CN)(CO)₂L(o-O₂C₆Cl₄)] {L = PPh₃ or P(OPh)₃}, which undergo one-electron oxidation at the catecholate ligand to give neutral semiquinone complexes [Ru(CN)(CO)₂L(o-O₂C₆Cl₄)], react with the dimers [{Ru(CO)₂L(µ-o-O₂C₆Cl₄)}₂] {L = PPh₃ or P(OPh)₃} to give [NEt₄][(o-O₂C₆Cl₄)L(OC)₂Ru(µ-CN)Ru(CO)₂L′(o-O₂C₆Cl₄)] {L or L′ = PPh₃ or P(OPh)₃}. The cyanide-bridged binuclear anions are, in turn, reversibly oxidised to isolable neutral and cationic complexes [(o-O₂C₆Cl₄)L(OC)₂Ru(µ-CN)Ru(CO)₂L′(o-O₂C₆Cl₄)] and [(o-O₂C₆Cl₄)L(OC)₂Ru(µ-CN)Ru(CO)₂L′(o-O₂C₆Cl₄)]⁺ which contain one and two semiquinone ligands respectively. Structural studies on the redox pair [(o-O₂C₆Cl₄)(Ph₃P)(OC)₂Ru(µ-CN)Ru(CO)₂(PPh₃)(o-O₂C₆Cl₄)]⁻ and [(o-O₂C₆Cl₄)(Ph₃P)(OC)₂Ru(µ-CN)Ru(CO)₂(PPh₃)(o-O₂C₆Cl₄)] confirm that the C-bound Ru(CO)₂(o-O₂C₆Cl₄) fragment is oxidised first. Uniquely, [(o-O₂C₆Cl₄){(PhO)₃P}(OC)₂Ru(µ-CN)Ru(CO)₂(PPh₃)(o-O₂C₆Cl₄)]⁻ is oxidised first at the N-bound fragment, indicating that it is possible to control the site of electron transfer by tuning the co-ligands. Crystallisation of [(o-O₂C₆Cl₄)(Ph₃P)(OC)₂Ru(µ-CN)Ru(CO)₂{P(OPh)₃}(o-O₂C₆Cl₄)] resulted in the formation of an isomer in which the P(OPh)₃ ligand is cis to the cyanide bridge, contrasting with the trans arrangement of the X–Ru–L fragment in all other complexes of the type RuX(CO)₂L(o-O₂C₆Cl₄).