Synthesis, structure, and electrochemical characterization of a mixed-ligand diruthenium(III,II) complex with an unusual arrangement of the bridging ligands

A mixed-ligand metal-metal bonded diruthenium complex having the formula Ru-2(2,4,6-(CH3)(3)ap)(3)(O2CCH3)Cl where ap is the anilinopyridinate anion was synthesized from the reaction of Ru-2(O2CCH3)(4)Cl and H(2,4,6-(CH3)(3)ap), after which the isolated product was structurally, spectroscopically and electrochemically characterized. The crystal structure reveals an unusual arrangement of the bridging ligands around the dimetal unit where one ruthenium atom is coordinated to one anilino and two pyridyl nitrogen atoms while the other ruthenium atom is coordinated to one pyridyl and two anilino nitrogen atoms. To our knowledge, Ru-2(2,4,6-(CH3)(3)ap)(3)(O2CCH3)Cl is the only example of a mixed-ligand diruthenium complex of the type [Ru2L3(O2CCH3)](+), where L is an unsymmetrical anionic bridging ligand that has been structurally characterized with a (2,1) geometric conformation of the bridging ligands, all others being (3,0). The initial Ru-2(5+) compound in CH2Cl2 or CH3CN containing 0.1 M tetra-n-butyl-ammonium perchlorate (TBAP) undergoes up to four one-electron redox processes involving the dimetal unit. The Ru-2(5+/4+) and Ru-2(5+/6+) processes were characterized under N-2 using thin-layer UV-visible spectroelectrochemistry and this data is compared to UV-visible spectral changes obtained during similar electrode reactions for related diruthenium compounds having the formula Ru2L4Cl or Ru2L3(O2CCH3)Cl where L is an anionic bridging ligand. Ru-2(2,4,6-(CH3)(3)ap)(3)(O2CCH3)Cl was also examined by UV-visible and FTIR spectroelectrochemistry under a CO atmosphere and two singly reduced Ru-2(4+) species, [Ru-2(2,4,6-(CH3)(3)ap)(3)(O2CCH3)(CO)Cl](-) and Ru-2(2,4,6-(CH3)(3)ap)(3)(O2CCH3)(CO) were in situ generated for further characterization. The CO-bound complexes could be further reduced and exhibited additional reductions to their Ru-2(3+) and Ru-2(2+) oxidation states.