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Acceptorless amine dehydrogenation and transamination using Pd-doped layered double hydroxides

preprint
revised on 01.09.2018 and posted on 03.09.2018 by Diana Ainembabazi, Nan An, Jinesh Manayil, Karen Wilson, Adam Lee, Adelina Voutchkova-Kostal

The synthesis, characterization, and activity of Pd-doped layered double hydroxides (Pd-LDHs) for for acceptorless amine dehydrogenation is reported. These multifunctional catalysts comprise Brønsted basic and Lewis acidic surface sites that stabilize Pd species in 0, 2+, and 4+ oxidation states. Pd speciation and corresponding cataytic performance is a strong function of metal loading. Excellent activity is observed for the oxidative transamination of primary amines and acceptorless dehydrogenation of secondary amines to secondary imines using a low Pd loading (0.5 mol%), without the need for oxidants. N-heterocycles, such as indoline, 1,2,3,4-tetrahydroquinoline, and piperidine, are dehydrogenated to the corresponding aromatics with high yields. The relative yields of secondary imines are proportional to the calculated free energy of reaction, while yields for oxidative amination correlate with the electrophilicity of primary imine intermediates. Reversible amine dehydrogenation and imine hydrogenation determine the relative imine:amine selectivity. Poisoning tests evidence that Pd-LDHs operate heterogeneously, with negligible metal leaching; catalysts can be regenerated by acid dissolution and re-precipitation.


History

Email Address of Submitting Author

avoutchkova@gwu.edu

Institution

George Washington University

Country

USA

ORCID For Submitting Author

000-0002-7016-5244

Declaration of Conflict of Interest

n/a

Version Notes

prior to submission

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