Syntheses and Molecular Structures of Novel Ru(II) Complexes With Bidentate Benzimidazole Based Ligands and Their Catalytic Efficiency for Oxidation of Benzyl Alcohol

Abstract

Five bidentate ligands derived from quinoline-2-carboxylic acid, i.e. 2-(1H-benzimidazol-2-yl)quinoline (L1), 2-(1-benzyl-1H-benzimidazol-2-yl)quinoline (L2), 2-[1-(2,3,5,6-tetramethylbenzyl)-1H-benzimidazol-2-yl]quinoline (L3), 2-[1-(4-chlorobenzyl)-1H-benzimidazol-2-yl]quinoline (L4), and 2-[1-(4-methylbenzyl)-1H-benzimidazol-2-yl]quinoline (L5) were synthesized. Treatment of L1-5 with [RuCl<inf>2</inf>(p-cymene)]<inf>2</inf> and KPF<inf>6</inf> afforded six-coordinate piano-stool Ru(II) complexes, namely, [RuCl(L1)(p-cymene)]PF<inf>6</inf> (C1), [RuCl(L2)(p-cymene)]PF<inf>6</inf> (C2), [RuCl(L3)(p-cymene)]PF<inf>6</inf> (C3), [RuCl(L4)(p-cymene)]PF<inf>6</inf> (C4), and [RuCl(L5)(p-cymene)]PF<inf>6</inf> (C5). Synthesized compounds were characterized with different techniques such as 1H and 13C NMR, FT-IR, and UV-vis spectroscopy. The solid state structure of L1 and C3 was confirmed by single-crystal X-ray diffraction analysis. The single crystal structure of C3 verified coordination of L3 to the Ru(II) center. The Ru(II) center has a pseudo-octahedral three legged piano stool geometry. The complexes C1-5 were tested as catalysts for the catalytic oxidation of benzyl alcohol to benzaldehyde in the presence of periodic acid (H<inf>5</inf>IO<inf>6</inf>) (Substrate/Catalyst/Oxidant = 1/0.01/0.5). The best result was obtained with C2 (3 h→90%). © 2016 Elsevier B.V. All rights reserved.