The use of heterogeneous catalysts for homogenous reactions may not only enable the recyclability of the catalyst but can also lead to different catalytic reactivity and selectivity. In this study, Au40/SBA 15 was used as catalyst for styrene cyclopropanation with propargyl pivalate in toluene and PhICl2 as an oxidizer (1). The Au40 nanoparticles were encapsulated by G4 PAMAM dendrimer and loaded on a mesoporous silica support. When compared to the homogenous AuCl3 catalyst, the cyclopropanation rate of the heterogeneous catalyst is slower, however, a five fold increase was measured in the product diastereoselectivity (cis:trans ratio). The effect of the reaction medium was investigated and it was found that the usage of hydrophobic solvents, such as toluene, prevent the leaching of Au ions.In order to demonstrate the advantages of the heterogeneous catalyst, Au40/SBA 15 was used in a fixed bed flow reactor, a product yield of 90% was measured and the catalyst remained active for more than 5hr at room temperature before deactivation. PVP coated Au clusters at similar size (~2nm) showed low reactivity (5% product yield) in the flow system. Therefore, this unique system of Au clusters embedded in dendrimer can be used as catalyst for reactions that were previously catalyzed by homogeneous catalyst, with unique advantages of recyclability and selectivity.

Diastereoselective heterogeneous Au nanoparticle catalyst for homogeneous olefin cyclopropanation reaction in solution

243rd National Meeting (2012)

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