Rearranging Nitriles

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Science  30 Mar 2007:
Vol. 315, Issue 5820, pp. 1768
DOI: 10.1126/science.315.5820.1768d

Although catalysis of alkene and alkyne metathesis has recently flourished, the analogous transformation of nitriles, which bear C-N triple bonds, has proven more challenging. This reaction is appealing in part because of the relative ease with which CN groups can be introduced to diverse organic molecules. However, the strength of metal nitride bonds can inhibit turnover. Geyer et al. have prepared a tungsten complex with trifluoromethyl-substituted alkoxy ligands that acts as an effective catalyst for the metathesis of aryl nitriles R-CN to the corresponding alkynes R-CC-R, with 3-hexyne serving as a N acceptor to yield propionitrile as a co-product; the reaction does not form N2 in the absence of an acceptor. Alkyne metathesis occurs more rapidly under the reaction conditions than nitrile alkyne crossmetathesis, and the authors note the conserved gas-phase thermodynamic preference for coupling the aryl partners and transferring N to the alkyl moiety. The catalyst tolerates halides, methyl ester, and vinyl groups, as well as thiophene substrates. — JSY

J. Am. Chem. Soc. 129, 10.1021/ja0693439 (2007).

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