A Family of Diruthenium Compounds with Dianionic Tridentate Ligands of N-(2-Pyridyl)-2-oxy-5-R-benzylaminate (R = H, Me, Cl, Br, NO2): Isolation, Structure Determination, and Electrochemistry

The ligand substitution reaction of Ru2(O2CCH3)4Cl with 5-substituted N-(2-pyridyl)-2-oxy-5-R-benzylaminate (R = H, Me, Cl, Br, NO2) resulted in a family of anionic diruthenium species of [Ru2(O2CCH3)2(R-salpy)2]- that were isolated by using Na+- or K+-18-crown-6ether as the countercation: [A(18-crown-6)(S)x][Ru2(O2CCH3)2(R-salpy)2] (A = Na+, K+; S = solvent; R = H, 1; Me, 2; Cl, 3; Br, 4; NO2, 5). All compounds were structurally characterized by X-ray crystallography. The structural features of the anionic parts are very similar among the compounds: two acetate and two R-salpy2- ligands are, respectively, located around the Ru2 unit in a trans fashion, where the R-salpy2- ligand acts as a tridentate ligand having both bridging and chelating characters to form the M-M bridging/axialchelating mode. Compounds 1 and 5 with K+-18-crown-6-ether have one-dimensional chain structures, the K+-18-crown-6-ether interacting with phenolate oxygens of the [Ru2(O2CCH3)2(R-salpy)2]- unit to form a repeating unit, [···K···O-Ru-Ru-O···], whereas 2-4 are discrete. Cyclic voltammetry and differential pulse voltammetry revealed systematic redox activities based on the dimetal center and the substituted ligand, obeying the Hammett law with the reaction constants per substituent, (rho), for the redox processes being 127 mV for Ru25+/Ru24+, 185 mV for Ru26+/Ru25+, 92 mV for Ru27+/Ru26+, and 179 mV for R-salpy-/R-salpy2-. For 3, the singly oxidized and reduced species, Ru26+ and Ru24+, respectively, generated by bulk controlled-potential electrolyses were finally monitored by spectroscopy. The singly oxidized species can also be slowly generated by air oxidation.