Ruthenium(III) complexes with N-(acetyl)-N′-(5-R-salicylidene)hydrazines:: Syntheses, structures and properties

The reactions of 1 mol equiv. each of [Ru(PPh3)(3)Cl-2] and N-(acetyl)-N'-(5-R-salicylidene)hydrazines (H(2)ahsR, R = H, OCH3, Cl, Br and NO2) in alcoholic media afford simultaneously two types of complexes having the general formulae [Ru(HahsR)(PPh3)(2)Cl-2] and [Ru(ahsR)(PPh3)(2)Cl]. The complexes have been characterized by elemental analysis, magnetic, spectroscopic and electrochemical measurements. Molecular structures of [Ru(HahsH)(PPh3)(2)Cl-2] and [Ru(ahsH)(PPh3)(2)Cl] have been confirmed by X-ray crystallography. In both species, the PPh3 ligands are trans to each other. The bidentate HahsH(-) coordinates to the metal ion via the 0 atom of the deprotonated amide and the imine-N atom in [Ru(HahsH)(PPh3)(2)Cl-2]. In HahsH(-), the phenolic OH is involved in a strong intramolecular hydrogen bond with the uncoordinated amide N atom forming a seven-membered ring. In [Ru(ahsH)(PPh3)(2)Cl], the tridentate ahsH(2-) binds to the metal ion via the deprotonated amide 0, the imine N and the phenolate 0 atoms. In the electronic spectra, the green [Ru(HahsR)(PPh3)(2)Cl-2] and brown [Ru(ahsR)(PPh3)(2)Cl] complexes display several absorptions in the ranges 385-283 and 457-269 nm, respectively. Both complexes are low-spin and display rhombic EPR spectra in frozen solutions. Both types of complexes are redox active and display a quasi-reversible ruthenium(III) to ruthenium(II) reduction which is sensitive to the polar effect of the substituent on the chelating ligand. The reduction potentials are in the ranges -0.21 to -0.12 and -0.42 to -0.21 V (versus Ag/AgCl) for [Ru(HahsR)(PPh3)(2)Cl-2] and [Ru(ahsR)(PPh3)(2)Cl], respectively. (c) 2007 Elsevier Ltd. All rights reserved.