Composite Catalyst For Chiral Synthesis

With few exceptions, enantioselective reactions to make chiral molecules depend on solution-phase catalysts. Strategies for designing solid catalysts that control product chirality could lead to greater flexibility in preparing chiral compounds, as well as convenient methods for recycling the catalyst. Elad Gross, F. Dean Toste, Gabor A. Somorjai, and coworkers at the University of California, Berkeley, have come up with one strategy. Inspired by the chiral environment that surrounds the active site in many enzymes, the team embedded catalytic metal clusters in a film of chiral molecules. Specifically, they treated a porous silica material in a process that forms a self-assembled monolayer of a chiral compound such as proline on the pore walls and other silica surfaces. Then they incorporated gold nanoparticles in the monolayer by treating it with HAuCl₄ and then hydrogen. The researchers prepared a series of these supported monolayers and analyzed the cis and trans products of a cyclopropanation test reaction between styrene and propargyl pivalate. Initial tests show some of the catalysts yield chiral products with up to 51% enantiomeric excess (J. Am. Chem. Soc., DOI: 10.1021/ja310640b).