Probing the Lewis Acidity and Catalytic Activity of the Metal–Organic Framework Cu3(btc)2 (BTC=Benzene‐1,3,5‐tricarboxylate)

An optimized procedure was designed for the preparation of the microporous metal-organic framework (MOF) Cu3(btc)2 (BTC=benzene-1,3,5-tricarboxylate). The crystalline material was characterized by X-ray diffraction, optical microscopy, SEM, X-ray photoelectron spectroscopy, N2 sorption, thermogravimetry, and IR spectroscopy of adsorbed CO. CO adsorbs on a small number of Cu2O impurities, and particularly on the free CuII coordination sites in the framework. Cu3(btc)2 is a highly selective Lewis acid catalyst for the isomerization of terpene derivatives, such as the rearrangement of alpha-pinene oxide to campholenic aldehyde and the cyclization of citronellal to isopulegol. By using the ethylene ketal of 2-bromopropiophenone as a test substrate, it was demonstrated that the active sites in Cu3(btc)2 are hard Lewis acids. Catalyst stability, re-usability, and heterogeneity are critically assessed.