A direct and efficient synthesis of N-methyl-1,2,3,4-tetrahydroquinolines (MTHQs) is achieved through the one-pot reductive N-methylation of quinolines. The SnO_x-decorated Pt/Al₂O₃ (Pt-SnO_x/Al₂O₃) catalyst proves to be highly effective in the transformation from quinolines to MTHQs, using methanol as the exclusive source for hydrogen (H) and methyl (CH₃), 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) N-methylation of THQs to MTHQs, with the dehydrogenation of methanol identified as the rate-determining 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.

中文翻译：

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SnOx 修饰的 Pt 催化剂用于喹啉与甲醇的还原 N-甲基化

通过喹啉的一锅还原N-甲基化，实现了N-甲基-1,2,3,4-四氢喹啉(MTHQs)的直接高效合成。 SnO _x修饰的 Pt/Al ₂ O ₃ (Pt-SnO _x /Al ₂ O ₃ ) 催化剂被证明在喹啉向 MTHQ 的转化中非常有效，使用甲醇作为氢 (H) 和甲基 ( CH ₃ )，无需添加额外的碱或添加剂。机理和动力学研究揭示了串联反应途径：（1）甲醇脱氢，（2）喹啉还原为1,2,3,4-四氢喹啉（THQ），（3）THQ N-甲基化为MTHQ，甲醇脱氢被确定为速率决定步骤。表征和催化性能结果表明，SnO _x改变了 Pt 基金属活性位点的形貌和电子性质，极大地促进了甲醇中 O-H 和反应性较低的 C-H 键的裂解，并在甲醇脱氢之间保持了微妙的平衡和喹啉的还原性N-甲基化，从而获得总转化的高反应活性。