Ru(II)–arene complexes with N-substituted 3,4-dihydroquinazoline ligands and catalytic activity for transfer hydrogenation reaction

In this study, N-coordinated 3,4-dihydroquinazoline ruthenium(II) complexes were synthesized by the cleavage reaction of [RuCl2(p-cymene)]2 with N-substituted 3,4-dihydroquinazolines. In addition, the X-ray crystal structure of 2,4,6-trimethylbenzyl substituted 3,4-dihydroquinazoline Ru(II) complex (1a) is reported. Furthermore, the resulting piano–stool complexes were evaluated as transfer hydrogenation catalysts for reduction of acetophenone in the presence of 2-propanol and KOH at 82 °C. All the complexes showed good to excellent performance after 1 h in the conversion of acetophenone to alcohol and the reaction rate was found to be sensitive to changes on the N-substituent. Additionally, the most active catalyst 1a was used in transfer hydrogenation of different ketones to investigate the effect of substituents on ketones.

Graphical abstractThe evaluation of N-coordinated 3,4-dihydroquinazoline ruthenium(II) complexes showed good to excellent performance in the conversion of acetophenone to alcohol after 1 h in the presence of 2-propanol and KOH at 82 °C. The reaction rate was sensitive to changes on the N-substituent: electron donating substituents on the N atom increased the yield. The most active catalyst, 2,4,6-trimethylbenzyl substituted complex 1a, was used in transfer hydrogenation of different ketones to investigate the effect of substituents on ketones. It was observed that electron-withdrawing groups in the para position of the acetophenone increased the yield.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Quinazoline–metal complexes are rarely found in the literature. ► 3,4-Dihydoquinazoline Ru(II) complexes were synthesized and used as homogenous catalyst. ► They showed good to excellent catalytic activity in transfer hydrogenation reaction of acetophenone and its derivatives.