Synthesis, structure and electrochemical properties of complexes with a (μ-oxo)bis-(μ-carboxylato)diruthenium(III) core

Abstract

Reaction of [Ru₂O(O₂CR)₂(MeCN)₄(PPh₃)₂](ClO₄)₂ (1) with 1,2-diaminoethane (em) 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(μ-O)(μ-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) Å and 119.1(4)°. 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 Ru₂^III,^III-Ru₂^III,^IV couple near 0.9 V and an irreversible Ru₂^III,^III-Ru₂^III,^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.