Grafting reaction of organotin complexes on silica catalyzed by tungstic heteropolyacids

The grafting reaction of tetramethyltin on silica is catalyzed by H ₄SiW₁₂O₄₀ preliminary impregnated on the support. While the reaction proceeds at temperatures higher than 150°C on silica alone, the presence of the polyacid allows the grafting at room temperature. A study as a function of the polyacid coverage has shown that there is a direct correlation between the reaction rate and the number of highly acidic sites on the support, probing that there is a reaction of the tetraalkyltin with them (limiting step) followed by a migration of the grafted fragment on the silica surface. Not only monografted species (as observed on silica) but also multigrafted tin species are formed because of further reactions of the grafted fragments.