Selective Imine Synthesis by Acceptorless Dehydrogenative Coupling of Alcohols and Amines via Cooperative Catalysis of Basic‐Polyoxometalate‐Decorated Ag Nanoparticles on Al 2 O 3

Abstract Multi‐functional catalysts, polyoxometalate (POM)‐decorated silver nanoparticles (AgNPs) on Al 2 O 3 (POM‐Ag/Al 2 O 3 ), which work as Lewis base, oxidative dehydrogenation, and Lewis acid catalysts, have been developed. They were shown to be active for the acceptorless dehydrogenative coupling of alcohols and amines to selectively form imines, while suppressing undesired C═N hydrogenation. Notably, both molecular H 2 as reductive gas and imine as a readily reducible product are produced simultaneously. The POM‐Ag/Al 2 O 3 catalysts were easily synthesized by selective adsorption of basic polyoxoniobate [Nb 6 O 19 ] 8‐ on AgNPs, with loading controlled by the concentration of aqueous K 8 Nb 6 O 19 , without the passivation of Lewis acid sites on the Al 2 O 3 support. The desired imines were efficiently produced by tri‐functional catalysis of POM‐Ag/Al 2 O 3 through the following two‐step sequence: the acceptorless dehydrogenation of alcohols to form aldehydes and H 2 at the interface between AgNPs and basic [Nb 6 O 19 ] 8‐ , followed by the dehydrative condensation of amines and aldehydes on Lewis acid sites of Al 2 O 3 . The cationic AgNP surface stabilized key intermediates for proton abstraction by [Nb 6 O 19 ] 8‐ . Heteroassociation of hydrogen species occurred rapidly at the [Nb 6 O 19 ] 8‐ /Ag interface, effectively suppressing imine hydrogenation even under H 2 . This work highlights selective imine synthesis accompanied by H 2 evolution under completely acceptorless conditions using Ag‐based catalysts decorated by basic POMs.