New magnesium oxide fluorides with hydroxy groups as catalysts for Michael additions

Abstract

Amorphous materials—magnesium oxide fluoride with hydroxy groups—of high surface area were prepared for the first time by a soft sol–gel method involving initial fluorination and subsequent hydrolysis of the fluorinated gel. Their structural properties were studied with XRD, FTIR, XPS, and ¹⁹F MAS NMR. The magnesium oxide fluorides with hydroxy groups were also tested as heterogeneous catalysts in Michael additions. The incorporation of F into the MgO network led to diverse fluorine coordinations and high surface areas. The introduction of F into the framework enables a tuning of the base properties of the materials and leads to varied catalytic activities and selectivities. A weaker basicity can be obtained by the bridging of isolated OH groups in the MgF₂ network with increasing fluorine content. The sample prepared with an F : Mg molar ratio of 1.6 exhibited a catalytic activity similar to that of calcined Mg–Al hydrotalcites and selectively produced Michael addition products in high yields.