Dinuclear and mononuclear oxorhenium(V) complexes chelated with the S,O bidentate thiourea ligand: Synthesis, crystal structure and catalytic activity

Abstract

N-(Diethylcarbamothioyl)-4-methylbenzamide ligand (HL) was prepared by subsequent reactions of p-toluoyl chloride with potassium thiocyanate and di-n-ethylamine, and used as a bidentate ligand for synthesis of mononuclear and dinuclear oxorhenium(V) complexes. The general procedure of mononuclear complexes involves the reaction of (n-Bu4)[ReOCl4] with the bidentate HL ligand in alcohol solution to generate complexes of the form cis-[ReVO(L-κ2S,O)2(D)] where D = -OMe, OEt or OiPr. The product isolated from the reaction was found to be dependent on the reaction conditions applied and solvents used in particular re-crystallization. The obtainment of dinuclear complex involves the reaction of (n-Bu4N)[ReOCl4] with the ligand in MeCN/H2O solution or the re-crystallization of mononuclear complexes in CH2Cl2/MeCN mixture. All complexes were characterized by 1H and 13C NMR, FTIR spectroscopy and single crystal X-ray diffraction studies. The ligand exchange chemistry of mononuclear complexes and their conversion to μ-oxo dimeric complexes based on solvent used to extend the coordination ability of the thiourea derivative ligand were also examined by 1H NMR spectroscopy. The obtained complexes furthermore tested for their ability to catalyze the oxidation of diphenyl sulfide. The effects of various factors, such as amounts of catalyst, oxidants and solvent have been also investigated. The dimeric complex cis-[(L-κ2S,O)2ReVOReV(L-κ2S,O)2], under the optimized reaction conditions displays good catalytic activity with high selectivity while all monomeric complexes lead to lower conversion with high selectivities.