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.