Thermosensitive Hairy Particle-Supported 4-N,N-Dialkylaminopyridine Catalyst

摘要

4-N,N-Dialkylaminopyridines (DAAPs) are widely used as nucleophilic catalysts for many organic reactions, including acylation of sterically hindered alcohols and hydrolysis of activated esters. Polymer-supported DAAP catalysts have been a subject of intensive research for decades. The covalent attachment of a DAAP to a polymer allows facile recovery and reuse of the catalyst. Moreover, polymers create a distinct microenvironment for the supported DAAPs; the catalytic activity can be tuned by varying polymer structures. A variety of polymers have been employed for preparing polymer- supported DAAP catalysts. We have been interested in developing polymer brush-supported organocatalysts. This approach could potentially combine the advantages of both linear soluble polymer- (high activity) and crosslinked polymer-supported organocatalysts (recyclability). Unlike covalently immobilized small molecules that are completely fixed on the solid substrate, polymer brushes are a dynamic system possessing a certain degree of mobility. Therefore, if an organic catalyst is incorporated into the grafted polymer chains, this supported catalyst would resemble linear soluble polymer-supported catalysts, exhibiting a high catalytic activity. On the other hand, the substrate for polymer brushes can be silica particles, magnetic nanoparticles, etc., allowing facile recovery of the catalyst. Here, we described the synthesis of a thermosensitive polymer brush-supported DAAP on silica particles (Scheme 1) and compared its catalytic activity with the corresponding linear polymer-supported version in the hydrolysis of p-nitrophenyl acetate (NPA) in aqueous buffer solutions.