Ruthenium(III) cyclometallates: Regioselective metallation of 1-pyrenyl in 1-pyrenaldehyde 4-R-benzoylhydrazones

Reactions of [Ru(PPh3)3Cl2] with 1-pyrenaldehyde 4-R-benzoylhydrazones (H2pnbhR, where R = H, Me, OMe, Cl and NO2) in presence of NaOAc afford ortho-metallated ruthenium(III) complexes of formula trans-[Ru(pnbhR)(PPh3)2Cl] (1–5). The complexes have been characterized by elemental analysis, magnetic susceptibility, spectroscopic (IR, UV–vis and EPR) and cyclic voltammetric measurements. Molecular structure of 2 (R = Me) determined by single crystal X-ray crystallography shows a distorted octahedral CNOClP2 coordination sphere around the trivalent metal centre assembled by the 1-pyrenyl ortho-C, azomethine-N and amidate-O donor pnbhMe2−, two mutually trans PPh3 and the chloride. Electronic spectra of 1–5 in dichloromethane display several strong bands within 555–276 nm due to ligand to metal charge transfer and ligand centred transitions. The complexes are one-electron paramagnetic (μeff = 1.90–1.99 μB) and display rhombic EPR spectra in frozen (130 K) dichloromethane–toluene (1:1). Cyclic voltammograms of the complexes in dimethylformamide display a ligand substituent sensitive metal centred one electron reduction couple in the E1/2 range −0.24 to −0.31 V (vs. Ag/AgCl).