Synthesis, structure and properties of di- and mononuclear ruthenium(III) complexes with N-(benzoyl)-N′-(salicylidene)hydrazine and its derivatives

The reactions of [Ru(PPh3)3Cl2], N-(benzoyl)-N′-(5-R-salicylidene)hydrazines (H2bhsR, R = H, OCH3, Cl, Br and NO2) and triethylamine (1:1:2 mole ratio) in methanol afford mononuclear ruthenium(III) complexes having the general formula trans-[Ru(bhsR)(PPh3)2Cl]. In the case of R = H, a dinuclear ruthenium(III) complex of formula [Ru2(μ-OCH3)2(bhsH)2(PPh3)2] has been isolated as a minor product. The complexes are characterized by elemental analysis, magnetic, spectroscopic and electrochemical measurements. The crystal structures of the dinuclear complex and two mononuclear complexes have been determined. In the dinuclear complex, each metal centre is in distorted octahedral NO4P coordination sphere constituted by the two bridging methoxide groups, one PPh3 molecule and the meridionally spanning phenolate-O, imine-N and amide-O donor bhsH2−. The terminal PPh3 ligands are trans to each other. In the mononuclear complexes, bhsR2− and the chlorine atom form an NO2Cl square-plane around the metal centre and the P-atoms of the two PPh3 molecules occupy the remaining two axial sites to complete a distorted octahedral NO2ClP2 coordination sphere. All the complexes display ligand-to-metal charge transfer bands in the visible region of the electronic spectra. The cryomagnetic measurements reveal the antiferromagnetic character of the diruthenium(III) complex. The low-spin mononuclear ruthenium(III) complexes as well as the diruthenium(III) complex display rhombic EPR spectra in frozen solutions. All the complexes are redox active in CH2Cl2 solutions. Two successive metal centred oxidations at 0.69 and 1.20 V (versus Ag/AgCl) are observed for the dinuclear complex. The mononuclear complexes display a metal centred reduction in the potential range −0.53 to −0.27 V. The trend in these potential values reflects the polar effect of the substituents on the salicylidene moiety of the tridentate ligand.