Supported zirconium propoxide—a versatile heterogeneous catalyst for the Meerwein–Ponndorf–Verley reduction

Grafting of zirconium 1-propoxide on SBA-15 resulted in highly active catalysts for the MPV reduction. The activity increased with zirconium loading up to a monolayer coverage. In most cases, there were no side products other than the desired alcohol. Electron-donating groups adjacent to the carbonyl group in the substrate facilitate the reaction. The grafted zirconium catalysts did not lose their activity in the presence of moisture or on exposure to ambient atmosphere, making them easy to handle and reuse. No leaching of the grafted zirconium 1-propoxide into the reaction mixture was observed. The addition of pyridine and water to the reaction medium had only a small effect on its activity while benzoic acid led to severe deactivation. The deactivation is attributed to strong adsorption of benzoic acid at the Zr metal centres which could be reversed on removal of the poison. Aluminum 2-propoxide grafted on SBA-15 resulted in a less active catalyst than the zirconium catalysts. The good resistance to hydrolysis of the zirconium catalysts makes them superior to the aluminum 2-propoxide catalysts.