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

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 = NO2) show pincer like coordination mode of nabhR2−. The 1-naphthalenyl ortho-C, the azomethine-N and the amidate-O donor nabhR2−, 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.