Heck Heterocoupling within a Dendritic Nanoreactor

Abstract

Palladium nanoparticles (2−3 nm in diameter) have been prepared within covalently functionalized poly(propylene imine) (PPI) dendrimers, and the resulting composite materials are shown to be effective for Heck coupling reactions. Two novel concepts are demonstrated in this report. The first concept involves the incorporation of Pd 0 nanoparticles into PPI dendrimers covalently functionalized with perfluorinated polyether chains on their periphery. The second concept involves the first example of a carbon−carbon coupling reaction catalyzed by a dendrimer-templated nanomaterial, specifically, the catalytic heterocoupling between nonactivated aryl halides and n -butylacrylate mediated by the dendrimer-encapsulated catalysts. These reactions were carried out in a homogeneous fluorous/organic reaction phase at elevated temperature, and the catalyst was recovered by cooling to room temperature and concomitant phase separation. The catalyst was found to be catalytically active at a reaction temperature of only 90 °C in the absence of toxic phosphines, and it was 100% selective for the production of n -butyl- trans -formylcinnamate with unoptimized isolated yields up to 70%. The recovered catalysts retained a significant fraction of the original activity, comparable to coordination complex catalysts that use a similar catalyst recovery system.