Gold Particles Supported on Amino‐Functionalized Silica Catalyze Transfer Hydrogenation of N‐Heterocyclic Compounds

Abstract

AbstractIn this work we demonstrate that exceptionally small gold particles (d=0.6±0.2 nm) supported on amino‐functionalized mesoporous silicate SBA‐15 are highly active in transfer hydrogenation of structurally diverse unsaturated N‐heterocyclic compounds. The heterocyclic ring is reduced selectively. The gold particles aggregate to a diameter of 4–5 nm in the presence of formic acid/triethylamine (hydrogen donor) during the first catalytic run. In subsequent cycles the nanoparticles maintain their size, yielding a very stable catalytic system that was recycled more than five times. In contrast, analogous SBA catalysts featuring larger (∼5–35 nm) gold particles are not active. Excess formic acid also leads to the formation of formamide derivatives of the products of hydrogenation, which can be deformylated quantitatively. Fifteen structurally different substrates, including the scaffolds of quinoline, isoquinoline, quinoxaline, acridine, phenanthroline, quinazoline, and phenanthridine are hydrogenated and deformylated to give the amine products in >90% overall yield. Deuterium labeling experiments indicate that 1,2‐addition with subsequent disproportionation of the formed intermediate is the preferred reaction path over the 1,4‐addition one, suggesting the participation of a gold hydride species.magnified image