Selective Meerwein–Ponndorf–Verley reduction of α,βα,β-unsaturated aldehydes over Zr-zeolite beta

Zr-zeolite beta with Si/Zr ratio of 75–200, as well as zeolite beta with both Zr (Si/Zr ratio of 100) and Al (Si/Al ratios of 100 and 25), were synthesized in a seeded synthesis using HF as the mineralizer. The Al-free Zr-zeolite beta was found to catalyse the MPV reduction of α,βα,β-unsaturated aldehydes to the corresponding alcohols with high selectivity. In the reduction of cinnamaldehyde to cinnamyl alcohol, TONs of 55–77 mol mol−1Zr h−1 were obtained with selectivity >98%>98%. Zr-zeolite beta maintained good activity and selectivity in the presence of water and benzoic acid. Reuse of the catalyst by washing with 2-propanol or recalcination led to recovery of activity. For the Al-containing Zr-zeolite beta, 27Al NMR spectra showed that Al was incorporated into the zeolitic framework. This is in agreement with pyridine adsorption studies in which Brønsted acidity was detected. However, the increased acidity decreased the selectivity in the MPV reduction of cinnamaldehyde as a significant amount of 1-cinnamyl 2-propyl ether was formed as a byproduct. Hence, Al-free Zr-zeolite beta is a useful chemoselective catalyst for the MPV reduction of α,βα,β-unsaturated aldehydes.