Annulation of phenols with methylbutenol over MOFs: The role of catalyst structure and acid strength in producing 2,2-dimethylbenzopyran derivatives

• The catalytic performance of MOFs differing in structure was compared in annulation reaction of phenols with methylbutenol.
• Both nature of metal cation and structure of MOFs were found to determine their catalytic behavior.
• Intermediate Lewis acidity and perfect crystallinity make MIL-100(Fe) an efficient heterogeneous catalyst of annulation.

The catalytic behavior of metal–organic frameworks of different structures (Fe(BTC), MIL-100(Fe), MIL-100(Cr) and Cu3(BTC)2) was investigated in annulation reaction between 2-methyl-3-buten-2-ol and phenols differing in size (phenol, 2-naphthol). MIL-100(Fe) possessing intermediate Lewis acidity, perfect crystalline structure, and the highest SBET surface area showed the highest activity (TOF = 0.7 and 1.4 h−1 for phenol and 2-naphthol, respectively) and selectivities to target benzopyran (45% and 65% at 16% of phenol and 2-naphthol conversion, respectively). The increasing strength of Lewis acid centers for MIL-100(Cr) was found to result in the dramatically decreased activity of the catalyst, while negligible conversion of phenols was found over Fe(BTC), characterized by a less ordered framework.

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