SnO_x-Decorated Pt Catalysts for the Reductive N-Methylation of Quinoline with Methanol

Abstract

A direct and efficient synthesis of 2,3, is achieved through the one-pot reductive N-methylation of quinolines. The SnO x -decorated Pt/Al 2 O 3 (Pt-SnO x /Al 2 O 3 ) catalyst proves to be highly effective in the transformation from quinolines to MTHQs, using methanol as the exclusive source for hydrogen (H) and methyl (CH 3 ), without the addition of additional bases or additives. Mechanistic and kinetic studies reveal a tandem reaction pathway: (1) the dehydrogenation of methanol, (2) reduction of quinolines to 1,2,3,4-tetrahydroquinolines (THQs), and (3) Nmethylation of THQs to MTHQs, with the dehydrogenation of methanol identified as the ratedetermining step. Characterization and catalytic performance results demonstrate that SnO x modifies the morphology and electronic properties of Pt-based metal active sites, which dramatically facilitates the cleavage of O−H and less reactive C−H bonds in methanol, and maintains a delicate balance between methanol dehydrogenation and reductive N-methylation of quinolines, thus obtaining a high reactivity for the total transformation.