Chemistry

Catalyst Compatibility

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Science  01 Dec 2006:
Vol. 314, Issue 5804, pp. 1355
DOI: 10.1126/science.314.5804.1355d

The isolation and purification procedures that follow synthetic chemical reactions often produce substantial quantities of waste material. Research has thus increasingly focused on methods for carrying out multiple reaction steps in a single vessel. However, the mutual incompatibility of many catalysts, in particular Lewis acids and bases, presents a major challenge to this approach.

Poe et al. present an encapsulation technique that allows the mixing of a polymeric amine catalyst with a nickel-centered Lewis acid while avoiding the complexation reaction that would deactivate both. The poly(ethyleneimine) base is treated with a cross-linking agent in a methanol/cyclohexane emulsion, yielding a microcapsule morphology that conserves catalytic activity in the condensation reaction of benzaldehyde and nitromethane. Addition of a bis(diamino)nickel catalyst to the reaction mixture promotes a Michael addition of dimethyl malonate to the dehydrated product in ∼80% yield. Moreover, the compatibility of the two catalysts is a boon to selectivity as well as efficiency; the nickel complex staves off a side pathway that would lead to a double nitromethane adduct. — JSY

J. Am. Chem. Soc. 128, 10.1021/ja066476l (2006).

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