Half-sandwich para-cymene ruthenium(II) naphthylazophenolato complexes: Synthesis, molecular structure, light emission, redox behavior and catalytic oxidation properties

A series of conformationally rigid half-sandwich organoruthenium(II) complexes with the general formula [(η6-p-cymene)RuCl(L)] (where L = mono anionic 2-(naphthylazo)phenolato ligands) have been synthesized from the reaction of [{(η6-p-cymene)RuCl}2(μ-Cl)2] with a set of 2-(naphthylazo)phenolato O,N-donor ligands. All the ruthenium complexes were fully characterized by FT-IR, 1H NMR, and UV–Vis spectroscopy as well as elemental analysis. In dichloromethane solution all the metal complexes exhibits characteristic metal-to-ligand charge transfer bands (MLCT) and emission bands in the visible region. The molecular structure of one of the complexes [Ru(η6-p-cymene)(Cl)(L2)] (2) was determined by X-ray crystallography. Electrochemical data of all the ruthenium complexes show a two metal centered voltammetric responses with respect to Ag/AgCl at scan rate 100 mV s−1. Further, the complex (2) efficiently catalyzes the oxidation of a wide range of alcohols to their corresponding carbonyl compounds in the presence of N-methylmorpholine-N-oxide (NMO) up to 97%.

Graphical abstractFive half-sandwich organoruthenium(II) naphthylazo phenolate complexes have been synthesized and characterized. All the complexes show luminescent property in the visible region. Complex 2 was structurally characterized by X-ray crystallography and was used as an efficient catalyst for oxidation of a range of primary and secondary alcohols in the presence of NMO.Figure optionsDownload full-size imageDownload as PowerPoint slide