Ag2O cubes, octahedra, and rhombic dodecahedra have been synthesized to catalyze the coupling of aldehydes, amines, and alkynes, forming propargylamines. Rhombic dodecahedra exhibit the best catalytic activity. The interior and surface lattice variations should be factors in the activity differences. Despite the conversion of Ag2O crystals to Ag particles within 1 h of reaction, the in situ formed Ag particles were found to be catalytically active. In contrast, Ag cubes, which were pseudomorphically transformed from Ag2O cubes, gave very low product yields. X-ray photoelectron spectroscopy results indicate differences in their bonding environment. The Ag2O rhombic dodecahedra were used to synthesize a broad range of propargylamines. A reaction mechanism is proposed. It is envisioned that Ag2O polyhedra can be a superior choice to commercial Ag2O powder for other organic transformations.
Hsieh et al. (Wed,) studied this question.