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) [Cu-3(btc),] (BTC=benzene-1,3,5-tricarboxylate). The crystalline material was characterized by X-ray diffraction, optical microscopy, SEM, X-ray photoelectron spectroscopy, N-2 sorption, thermogravimetry, and IR spectroscopy of adsorbed CO. CO adsorbs on a small number Of Cu2O impurities, and particularly on the free Cu-II coordination sites in the framework. [Cu-3(btC)(2)] is a highly selective Lewis acid catalyst for the isomerization of terpene derivatives, such as the rearrangement of a-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 [Cu-3(btC)(2)] are hard Lewis acids. Catalyst stability, re-usability, and heterogeneity are critically assessed.