Active Pd Catalyst for the Selective Synthesis of Methylated Amines with Methanol.

Selective -methylation of amines with methanol is an important reaction in the synthesis of high-value-added fine chemicals, including dyes, surfactants, pharmaceuticals, agrochemicals, and materials. However, -methylated amines possess higher reactivities and are prone to further transform into ,-dimethylated amines. Therefore, it is still a challenge to controllably regulate the selectivity of -methylation using heterogeneous catalysts without the use of base. Herein, we developed a series of Pd/Zn(Al)O catalysts with abundant basic sites, and the selectivity of -methylation was controlled by a heterogeneous Pd/Zn(Al)O catalyst with a Zn/Al ratio of 10 and a Pd loading of 0.4 wt % in the pressure of H. The experimental results showed that the appropriate basic properties of the catalyst were beneficial to form the desired -methylated amine. The low loading of Pd in the catalyst was highly dispersed on the support, providing sufficient active sites. These were attributed to the Zn vacancies formed by Al-doped Zn, which were beneficial to form the highly active and stable Pd sites. Furthermore, a series of amines and nitrobenzenes with different functional groups were well tolerated for the selective synthesis of -methylated amines in the absence of base.