Iron(iii) metal–organic frameworks as solid Lewis acids for the isomerization of α-pinene oxide

Abstract

A series of Fe³⁺-containing porous metal–organic frameworks (MOFs), including the commercial iron trimesate Basolite F-300 or Fe(BTC) (BTC: 1,3,5-benzenetricarboxylate) and the synthetic iron terephthalate MIL-88B (Fe₃O(BDC)₃X, X = Cl, OH, BDC = 1,4-benzenedicarboxylate), iron naphthalenedicarboxylate MIL-88C (Fe₃O(NDC)₃X, X = Cl, OH, NDC = 1,6-naphthalenedicarboxylate), iron trimesate MIL-100 (Fe₃O(BTC)₂X, X = Cl, OH) and iron azobenzenetetracarboxylate soc-MOF(Fe) or MIL-127 (Fe₆O₂(Tazb)₃X₂, X = Cl, OH, Tazb = 3,3′,5,5′-azobenzenetetracarboxylate; MIL stands for Materials from Institut Lavoisier), have been tested for the rearrangement of α-pinene oxide to camphonelal and isopinocamphone in the absence of solvent. Conversions of about 10% with 50% selectivity towards camphonelal were obtained. This catalytic performance has been compared with that of the copper trimesate Basolite C-300 or HKUST-1 of formula Cu₃(BTC)₂ and the aluminium terephthalate Basolite A-100 or MIL-53(Al) of formula Al(OH)(BDC) as well as with some homogeneous (ZnCl₂, Cu(NO₃)₂, Al(NO₃)₃) and heterogeneous (Fe³⁺-exchanged Y-zeolite) Lewis acids. Fe(BTC) also exhibits catalytic activity for the rearrangement of other epoxides (styrene, cyclohexene and norbornene oxides) under solventless conditions. Some partial deactivation of the Fe(BTC) with a slight degradation of the structure has nevertheless been observed.