Synthesis, characterization and catalytic activity of single site, Lewis acidic aluminosilicates

Abstract

A general synthetic strategy for the preparation of atomically dispersed, well-defined Lewis acidic aluminum sites in silicate matrices is described and illustrated. These amorphous matrices are composed of the spherosilicate cubes (Si8O20) linked together by combinations of aluminum and siloxane groups. The connectivity of the catalytically active aluminum centers to the surrounding silicate matrix can be varied by choice of aluminum precursor. “Extraframework” 3-connected Al⟵Py and Al⟵THF sites are obtained from the corresponding AlCl3·L complexes and 4-connected “framework” sites from Y[AlCl4] (Y = Lutidinium, [Bu4N]+). The aluminum sites in these porous silicates are characterized by gravimetry, IR and multinuclear SSNMR spectroscopies as well as ligand exchange reactions. Their catalytic activities as Lewis acids are investigated for the aminolysis of styrene oxide by aniline. These single site aluminosilicate catalysts exhibit activities that are comparable to or better than analogous, well-known zeolite and amorphous aluminosilicate materials. Their activities are dependent on the connectivity of aluminum to the surrounding silicate matrix as well as the length and flexibility of secondary linkers in the matrix.