Framework Catalysis

Shifting zwitterion reactivity

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Science  12 Jan 2018:
Vol. 359, Issue 6372, pp. 173-174
DOI: 10.1126/science.359.6372.173-g

Phosphines are often ligands for transition metal catalysts, but they can catalyze reactions at unsaturated carbon atoms by forming phosphonium zwitterions. For example, triphenylphosphine forms a zwitterion with methylvinylketone that acts as a nucleophile to convert n-alkyl aldehydes to β-hydroxy enones (the Morita-Baylis-Hillman reaction). Bauer et al. show that when the reaction is conducted in metal-organic framework compounds with linkers bearing amino groups, rather than in solution, the phosphonium zwitterion can act as an electrophile. The products—1- and 3-n-alkylesters of 2-alkyl-1,3-diols—form through the Aldol-Tishchenko reaction.

J. Am. Chem. Soc. 10.1021/jacs.7b10928 (2017).

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