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

Article abstract of DOI:10.1016/j.jorganchem.2013.03.040

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 CNOClP ₂ coordination sphere around the trivalent metal centre assembled by the 1-pyrenyl ortho-C, azomethine-N and amidate-O donor pnbhMe^2-, 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 (μ_eff = 1.90-1.99 μ_B) 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 E _1/2 range -0.24 to -0.31 V (vs. Ag/AgCl).