Hydrogen transfer reaction to imines with 2-propanol catalyzed by ruthenium (II) complexes containing nitrogen-phosphorus (NPN) ligands. Experimental and computational studies

Abstract

This work reports the synthesis and characterization of ruthenium(II) complexes containing nitrogen -phosphorus -nitrogen (NPN) ligands, with L1 =N -(phenyl (pyridin-2-ylamino)phosphino)pyridin-2-amine and L2 = 4-methyl-N-((4-methylpyridin-2-ylamino)(phenyl)phosphino)pyridin-2-amine. The ruthenium complexes RuCl 2 PPh 3 (L1) ( 1 ) and RuCl 2 PPh 3 (L2) ( 2 ) show high activities in catalytic transfer hydrogenation of different substituted benzylideneanilines, with turnover frequencies up to 5882 h -1 and 5294 h -1 , respectively. The RuCl(CO)PPh 3 (L1) ( 3 ) and RuCl(CO)PPh 3 (L2) ( 4 ) complexes were non -active in the reaction studied. Theoretical calculations conducted for complex 4 showed that the carbonyl group promotes sigma-orbital interactions and backdonation phenomena from the metal centre to the pi* orbitals in the CO ligand, presenting a strong orbital contribution. This supports the hypothesis that complexes 3 and 4 are less reactive species and therefore present poor or null catalytic performance in the reaction studied.