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

The salts [NEt4][Ru(CN)(CO)(2)L(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)(2)L(o-O2C6Cl4)], react with the dimers [{Ru(CO)(2)L(mu-o-O2C6Cl4)}(2)] {L = PPh3 or P(OPh)(3)} to give [NEt4][(o-O2C6Cl4)L(OC)(2)Ru(mu-CN)Ru(CO)(2)L'(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)(2)Ru(mu-CN)Ru(CO)(2)L'(o-O2C6Cl4)] and [(o-O2C6Cl4)L(OC)(2)Ru(mu-CN) Ru(CO)(2)L'(o-O2C6Cl4)](+) which contain one and two semiquinone ligands respectively. Structural studies on the redox pair [(o-O2C6Cl4)(Ph3P)(OC)(2)Ru(mu-CN)Ru(CO)(2)(PPh3)(o-O2C6Cl4)](-) and [(o-O2C6Cl4)(Ph3P)(OC)(2)Ru(mu-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)(3)P}(OC)(2)Ru(mu-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)(2)Ru(mu-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)(2)L(o-O2C6Cl4).