Ortho-metallated ruthenium(III) complexes with some acid hydrazide based Schiff bases

Ortho-metallated ruthenium(III) complexes with Schiff bases (H2L) derived from one mole equivalent each of benzaldehyde and acid hydrazides are described. Reactions of H2L with [Ru(PPh3)3Cl2] in presence of NEt3 (1:1:2 mole ratio) under aerobic conditions in methanol provide the complexes having the general formula trans-[Ru(L)(PPh3)2Cl] in 55–60% yields. The complexes have been characterized with the help of elemental analysis, magnetic susceptibility, electrochemical and various spectroscopic (infrared, electronic and EPR) measurements. The +3 oxidation state of the metal centre in these complexes is confirmed by their one-electron paramagnetic nature. Molecular structures of two representative complexes have been determined by X-ray crystallography. In each complex, the metal ion is in a distorted octahedral CNOClP2 coordination sphere. The dianionic C,N,O-donor ligand (L2−) together with the chloride form a CNOCl square-plane and the P-atoms of the two PPh3 molecules occupy the two axial sites. The electronic spectra of the complexes in dichloromethane solutions display several absorptions due to ligand-to-metal charge transfer and ligand centred transitions. In dichloromethane solutions, the complexes display a ruthenium(III) → ruthenium(IV) oxidation in the potential range 0.35–0.98 V (vs. Ag/AgCl). All the complexes in frozen (110 K) dichloromethane–toluene (1:1) solutions display rhombic EPR spectra.

Graphical abstractSynthesis, structure and properties of a series of cyclometallated ruthenium(III) complexes with acetic acid benzylidene-hydrazide and 4-R-benzoic acid benzylidene-hydrazides are described. The one-electron paramagnetic complexes show rhombic EPR spectra. All the complexes are electroactive and display ruthenium(III) → ruthenium(IV) oxidation.Figure optionsDownload full-size imageDownload as PowerPoint slide