Preparation of Porous Polymers Based on the Building Blocks of Cyclophosphazene and Cage-like Silsesquioxane and Their Use as Basic Catalysts for Knoevenagel Reactions

Abstract

Phosphazene-containing porous materials are of a great interest due to their unique properties, caused by the synergetic presence of nitrogen and phosphorus atoms, and have found applications as adsorbents, basic catalysts, etc. On the other hand, cage-like silsesquioxanes are ideal building blocks for the preparation of covalently-linked porous materials. Here two new phosphazene-functionalized organosilsesquioxane cage-based porous polymers were synthesized successively by a Friedel-Crafts reaction of hexapyrrolylcyclotriphosphazene with octavinylsilsesquioxane in the presence of AlCl₃ and CF₃ SO₃ H as catalysts. The nature of acid catalysts barely influenced the character of pores due to the interaction of catalysts with basic nitrogen atoms of phosphazene units. The obtained polymers exhibited high efficiency as metal-free catalysts for the Knoevenagel reaction. This work opens new perspectives in the use of porous polymers based on cage-like organosiloxane compounds as basic catalysts for various reactions.

Keywords: Friedel-Crafts reaction; Knoevenagel reaction; PCSs; cage-like organosiloxanes; catalysis; phosphazenes; porous.