SYNTHESIS, STRUCTURE AND ELECTROCHEMICAL PROPERTIES OF COMPLEXES WITH A (MU-OXO)BIS-(MU-CARBOXYLATO)DIRUTHENIUM(III) CORE

Reaction of [Ru2O(O2CR)2(MeCN)4(PPh3)2](ClO4)2 (1) with 1,2-diaminoethane (en) in MeOH-H2O yielded a mixture of products, from which a purple diamagnetic and 1:2 electrolytic diruthenium(III) complex, [Ru2O(O2CR)2(en)2(PPh3)2](ClO4)2 (2), was isolated along with a trace by-product of [Ru2O(O2CR)2(en)2(PPh3)2](ClO4)(MeCONH) (3) (R = C6H4-p-X: X = H, a; OMe, b; Me, c). Complex 3b has been characterized by X-ray diffraction analysis. The structure shows the presence of a {Ru2(mu-O)(mu-O2CR)22+} core, with the metal centre bonded to an unidentate PPh3 and a bidentate chelating en terminal ligand. The Ru-Ru distance and the Ru-O-Ru angle in the core are 3.255(3) angstrom and 119.1(4)degrees. The amidate anion, formed presumably by nucleophilic attack of OH-on the MeCN ligand in complex 1, remains uncoordinated to the metal. In MeCN/0.1 M [NBun4]ClO4 complex 2 exhibits a nearly reversible Ru2III,III-Ru2III,IV couple near 0.9 V and an irreversible Ru2III,III-Ru2III,II process at -0.6 V (vs S.C.E.). The mechanistic aspects of the substitution and nucleophilic reactions in the formation of complexes 2 and 3 are discussed.