Reactions of Dibutylmagnesium with Modified Silica Gel Surfaces

The reaction products of dibutylmagnesium with modified silica gel surfaces have been studied as relevant olefin polymerization catalyst precursors. Reactions were carried out on thermally and/or chemically pretreated silica gel. The pretreatments effect changes in silica surface silanol type and concentration. A combination of methods including infrared spectroscopy, NMR spectroscopy, and elemental analysis were used to characterize the chemically modified surfaces. Dibutylmagnesium reacts with non-hydrogen-bonded silanols to give a bond to the surface with one surface silicon. One butyl group is retained on magnesium. Dibutylmagnesium reacts with two hydrogen-bonded silanols to give bonds to the surface with two surface silicons. Both butyl groups are lost in the reaction with non-hydrogen-bonded silanols. Dibutylmagnesium also reacts with surface siloxanes to give a singly bonded magnesium, analogous to the reaction with non-hydrogen-bonded silanols. The adjacent silicon in the siloxane is believed to react with the second butyl group to form a silicon−butyl surface species. A majority of surface-reacted magnesium on the thermally pretreated silica gels studied is a result of siloxane bond breaking.