Abstract
N-methylamines, as an important class of chemicals, crucial building blocks, have been widely used in pharmaceutical companies and materials synthesis. Transition metal-catalyzed synthesis of N-methylamines, especially the heterogeneous catalyzed N-methylation of amines via different C1 sources has become the most promising methodology, due to the environmentally friendlier process and the recyclable and easily accessible catalysts. However, these reactions generally require activated toxic methyl iodide or dimethyl sulfoxide, and homogeneous catalysts or Raney nickel catalyst. The synthesis of amines still suffering from narrow scopes of amines, harsh reaction conditions, low selectivity of the desired products, and against the requirements of atomic economy and sustainable green environment. Herein, we developed a novel facile synthesis of nitrogen-doped graphene encapsulated Pd@NC nanocatalysts. The resulting heterogeneous catalyst was active for the synthesis of amines (more than 83 examples, yield up to 99%). The nitrogen-doped effect was unlike the previous report that poisoned the metal, it could increase the interaction with the active metal resulting in excellent stability. As far as we know, for the first time, the developed N-doped graphene encapsulated Pd@NC nanocatalyst showed excellent stability and activity of amines synthesis in the 20 times’ recycling test, industrially applicable flow reactor 2880 minutes’ test, and 99% purity of primary amine and tertiary amines product preparation test. Moreover, we have also shown the high atomic economy and environmentally friendlier tandem flow synthesis of N, N-dimethylamine products via the combination of reduction of nitrobenzene and N-methylation of amines, using the single one Pd@NC nanocatalyst with H2O as the only by-product. Upon our knowledge, this is a novel example of primary amine and tertiary amine synthesis methodology with the combined cascade reaction and flow process of nitrobenzene reduction and primary amines N-methylation with a single heterogeneous catalyst.
Effect of ring rize on photoisomerization properties of stiff stilbene macrocycles