Ortho-ruthenation of 1-naphthalenyl in 1-naphthaldehyde 4-R-benzoylhydrazones: Ruthenium(III) CNO pincer complexes

Abstract

In methanol, reactions of [Ru(PPh3)3Cl2], 1-naphthaldehyde 4-R-benzoylhydrazones (H2nabhR, where R = H, Me, OMe, Cl and NO2) and NaOAc in 1:1:2 mol ratio provide ortho-metallated ruthenium(III) complexes of general formula trans-[Ru(nabhR)(PPh3)2Cl] (1-5) in 50-58% yields. Elemental analysis, magnetic susceptibility, spectroscopic (IR, UV-Vis and EPR) and cyclic voltammetric measurements were used to characterize the complexes. Single crystal X-ray structures of 1 (R = H), 2 (R = Me) and 5 (R = NO 2) show pincer like coordination mode of nabhR2-. The 1-naphthalenyl ortho-C, the azomethine-N and the amidate-O donor nabhR 2-, two mutually trans PPh3 and the chloride assemble a distorted octahedral trans-CNOClP2 coordination sphere around the trivalent metal centre. In the electronic spectra, dichloromethane solutions of 1-5 display multiple strong bands within 506-272 nm due to ligand to metal charge transfer and intraligand transitions. The room temperature (298 K) magnetic moments (μeff) of 1-5 are within 1.92-1.99 μB and they display rhombic EPR spectra in frozen (130 K) dichloromethane-toluene (1:1). Cyclic voltammetry with dimethylformamide solutions of the complexes reveals ligand substituent sensitive Ru(III) → Ru(II) reduction and Ru(III) → Ru(IV) oxidation in the potential ranges -0.27 to -0.36 V and 0.94-1.13 V (vs. Ag/AgCl), respectively. © 2013 Elsevier B.V. All rights reserved.