Dendrimer-Encapsulated Pd Nanoparticles as Fluorous Phase-Soluble Catalysts

TLDR: In this paper, the authors describe the application of dendrimer-encapsulated Pd nanoparticles to fluorous biphasic catalysis, and demonstrate that the resulting nanocomposites are preferentially soluble in fluorinated hydrocarbons.

Abstract: Here we describe the application of dendrimer-encapsulated Pd nanoparticles to fluorous biphasic catalysis. 1 Complexation of Pd/dendrimer composites with perfluorinated carboxylic acids renders the resulting nanocomposites preferentially soluble in fluorinated hydrocarbons. These new catalysts show high activity and selectivity for biphasic hydrogenation of alkenes and conjugated dienes. Moreover, the catalysts can easily be recovered and used for multiple reactions. Reactions in biphasic fluorous/organic systems were suggested by Horvath and Rabai in 1994 2 to facilitate recovery and recycling of soluble catalysts. The general approach to biphasic catalysis is illustrated in Scheme 1. 3 The system consists of organic and fluorous layers. The catalyst is selectively soluble in the fluorous phase, while the reactants are preferentially soluble in the organic solvent. Stirring, sonicating, and/or heating of the mixture leads to formation of a fine emulsion and partial homogenization (with some solvents, complete homogenization is obtained at elevated temperatures), and the catalytic reaction proceeds at the interface between the two liquids. When the reaction is over, the liquid phases are separated, the product is isolated from the organic phase, and the catalyst-containing fluorous layer is recycled. Such easy separation and recycling are particularly attractive in terms of “green chemistry”, and a number of fluorous phase-soluble catalysts have been reported in the literature, including some based on metal complexes. 4,5 Preparation of fluorous phase-soluble metal nanoparticles, however, has not previously been reported. Catalytic properties of metal nanoparticles have been explored since the pioneering studies of Rampino and Nord in the early 1940s. 6 Over the past decade research in this area intensified, 7