Antagonistic Catalyst Turns Tandem Reaction

Chemists have succeeded in mimicking antagonistic acid and base catalytic functions observed in some enzymes by synthesizing a dual-purpose heterogeneous catalyst capable of carrying out one-pot tandem reactions (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201101449). Soluble homogeneous catalysts that combine chemically hostile functional groups have been made successfully, but synthesizing similar bifunctional solid catalysts “is no easy task,” saysGadi Rothenberg of the University of Amsterdam, who led the research team with colleague N. Raveendran Shiju. The trick, Rothenberg says, is to install the acid and base groups far enough apart so they don’t neutralize each other. To accomplish that, the researchers first grafted propylamine groups, –(CH₂)₃NH₂, onto mesoporous silica and then immobilized phosphotungstate groups, –(CH₂)₃NH₃[H₂PW₁₂O₄₀], on half of the amines. The team tested the catalyst by converting dimethoxymethylbenzene to trans-1-nitro-2-phenylethylene. The tandem reaction begins with an acid-catalyzed de­acetalization to form benzaldehyde, followed by a base-catalyzed Henry reaction with nitromethane to give the nitro product. The catalyst could be used for multiple types of reactions, Rothenberg adds, noting that it can be made primarily acidic, primarily basic, or equally acidic and basic by controlling the acid:base active-site ratio.