Catalytically active palladium nanoparticles embedded in an organic-inorganic fluorinated hybrid material
Sandra Niembro, Alexandr Shafir,* and Adelina Vallribera*
Department of Chemistry, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Barcelona, Spain
E-mail:
[email protected]
Dedicated to Professor Benito Alcaide (Universidad Complutense de Madrid) on the occasion of his 60th anniversary
Abstract
Palladium nanoparticles were supported on a fluorous organic-inorganic hybrid material prepared by the sol-gel process without TEOS. Recycling studies on the Heck coupling reaction have shown that the catalyst can be readily recovered and reused.
Keywords: Palladium, nanoparticles, Heck, recycling, fluorous, sol-gel
Introduction
A large body of work has been dedicated to the use of palladium nanoparticles (PdNPs) as catalysts for the formation of C-C bonds.1,2 A major effort has been dedicated to supporting PdNPs on a variety of materials3 in order to facilitate the separation, recovery and reuse of expensive palladium catalysts. Our group in particular has contributed in this work with the preparation of nanosized metallic palladium particles embedded in silica and carbon aerogels.4
We have previously reported that heavily fluorinated star-shaped compounds (A, Figure 1) favor the formation of palladium nanoparticles (PdNPs-A) that were catalytically active in C-C bond forming processes.5 Although in principle heavily fluorinated compounds do not seem ideal stabilizers for nanoparticles, we demonstrated that some compounds can indeed be used with success as a protecting shield for nanoparticles. Furthermore, we demonstrated that PdNPs-A could be embedded within a fluorous silica gel matrix and that this material showed promise as a catalyst for the Heck reaction. However, subsequent analysis of the reaction mixture revealed some leaching of both the palladium and the fluorous stabilizer.6 Most recently, we prepared a more robust hybrid material PdNPs-B with the stabilizer linked covalently to the silica gel matrix.7 In this case, the matrix was prepared through sol-gel condensation between a
