A PNP pincer manganese complex was applied as catalyst for transfer hydrogenation of quinolines with ammonia borane as hydrogen source. 1,2,3,4-Tetrahydroquinolines were obtained under mild conditions with good to excellent yields. 1,2-Dihydroquinolines were detected by ¹H NMR in the progress and isotopic labelling experiments were performed to determine the destination of ammonia-borane hydrogen atoms.

Abstract

Herein, an efficient methodology for the homogeneous manganese-catalysed transfer hydrogenation of N-heterocycles by using ammonia-borane as a hydrogen source under mild reaction conditions is reported. Good to excellent isolated yields are achieved by applying a PNP manganese pincer complex. In the reaction, 1,2-dihydroquinoline is detected as intermediate by NMR spectra analysis and deuterium labelling experiment. The catalytic reaction likely proceeded by an outer-sphere pathway based on the bifunctional pincer complex.