Acceptorless Amine Dehydrogenation and Transamination Using Pd-Doped Hydrotalcites

Abstract

The acceptorless dehydrogenation of acyclic secondary amines is a highly desirable but still elusive catalytic process. Here we report the synthesis, characterization, and activity of Pd-doped hydrotalcites (Pd-HTs) for acceptorless dehydrogenation of both primary and secondary amines (cyclic and acyclic). These multifunctional catalysts comprise Bronsted basic and Lewis acidic surface sites that stabilize Pd in 0, 2+, and 4+ oxidation states. Pd speciation and corresponding catalytic performance is a strong function of metal loading. High activity is observed for the dehydrogenation of secondary aliphatic amines to imines, and N-heterocycles, such as indoline, 1,2,3,4-tetrahydroquinoline, and piperidine, to aromatic compounds. Oxidative transamination of primary amines is achieved using low Pd loading (0.5 mol %), without the need for oxidants. The relative yields of secondary imines afforded are consistent with trends for calculated free energy of reaction, while yields for transamination products corre...