Syntheses and molecular structures of novel Ru(II) complexes with bidentate benzimidazole based ligands and their catalytic efficiency for oxidation of benzyl alcohol.

Five bidentate ligands derived from quinoline-2-carboxylic acid, i.e. 2-(1 H -benzimidazol-2-yl)quinoline ( L1 ), 2-(1-benzyl-1 H -benzimidazol-2-yl)quinoline ( L2 ), 2-[1-(2,3,5,6-tetramethylbenzyl)-1 H -benzimidazol-2-yl]quinoline ( L3 ), 2-[1-(4-chlorobenzyl)-1 H -benzimidazol-2-yl]quinoline ( L4 ), and 2-[1-(4-methylbenzyl)-1 H -benzimidazol-2-yl]quinoline ( L5 ) were synthesized. Treatment of L1-5 with [RuCl 2 ( p -cymene)] 2 and KPF 6 afforded six-coordinate piano-stool Ru(II) complexes, namely, [RuCl(L1)( p -cymene)]PF 6 ( C1 ), [RuCl(L2)( p -cymene)]PF 6 ( C2 ), [RuCl(L3)( p -cymene)]PF 6 ( C3 ), [RuCl(L4)( p -cymene)]PF 6 ( C4 ), and [RuCl(L5)( p -cymene)]PF 6 ( C5 ). Synthesized compounds were characterized with different techniques such as 1 H and 13 C 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 5 IO 6 ) (Substrate/Catalyst/Oxidant = 1/0.01/0.5). The best result was obtained with C2 (3 h→90%). [ABSTRACT FROM AUTHOR]