Formation of a Strong Heterogeneous Aluminum Lewis Acid on Silica

Al(OC(CF3)(3))(PhF) reacts with silanols present on partially dehydroxylated silica to form well-defined equivalent to SiOAl(OC(CF3)(3))(2)(O(Si equivalent to)(2)) (1). Al-27 NMR and DFT calculations with a small cluster model to approximate the silica surface show that the aluminum in 1 adopts a distorted trigonal bipyramidal coordination geometry by coordinating to a nearby siloxane bridge and a fluorine from the alkoxide. Fluoride ion affinity (FIA) calculations follow experimental trends and show that 1 is a stronger Lewis acid than B(C6F5)(3) and Al(OC(CF3)(3))(PhF) but is weaker than Al(OC(CF3)(3)) and (Pr3Si+)-Pr-i. Cp2Zr(CH3)(2) reacts with 1 to form [Cp2ZrCH3][equivalent to SiOAl(OC(CF3)(3))(2)(CH3)] (3) by methide abstraction. This reactivity pattern is similar to reactions of organometallics with the proposed strong Lewis acid sites present on Al2O3.

Automated summary

This study discovers an effective approach to prepare aluminum-silicon oxide catalysts with well-defined structures. Through experimental and theoretical calculations, it is demonstrated that the catalyst exhibits strong Lewis acidity and can react with organometallic compounds.