Spectroscopic and catalytic activity studies of VO(Saloph) complexes encapsulated in zeolite-Y and Al-MCM-41 molecular sieves

VO(Saloph) complexes, where Saloph = N,N'-o-phenylenebis(salicylide naminato), have been encapsulated in microporous zeolite NaY and mesoporous Al-MCM-41 molecular sieves by the "flexible ligand synthesis" method. Upon encapsulation the coordination of VO(Saloph) changes from a square pyramidal to an octahedral geometry. Encapsulation and the pore size have marked effects on the trans-stilbene and styrene epoxidation activities of VO(Saloph), with tert-butylhydroperoxide as oxidant. The encapsulated complexes are more active (by three to five times) than the "neat" complexes. The encapsulated complexes could easily be separated from the products and the catalysts can be reused. VO(Saloph) complexes encapsulated in Al-MCM-41 are relatively more active than the zeolite-Y-encapsulated complexes. The relaxed geometry of VO(Saloph) and easy access of the active site to the substrate molecules are perhaps responsible for the higher activity of VO(Saloph) encapsulated in Al-MCM-41.