A metal-free acetylide was observed by using NMR spectroscopy. Metal-free acetylides are closely related to reactive intermediates (carbanions) in solution; therefore, they have been regarded as unobservable species. However, we generated this highly reactive and unstable species through the deprotonation of phenylacetylene by using the strong nonmclallic phosphazene base tBu-P4. In the presence of tBu-P4, the J coupling between the ethynyl carbon and hydrogen nuclei (1JCH) of phenylacetylene disappeared: this indicates the deprotonation of the alkyne terminal. Furthermore, a large low-field shift (approximately 90 ppm) of the alkyne carbon resonance was observed. We concluded that we have observed a metal-free carbanion with a formal charge on an sp-hybridized carbon atom for the first time.
- Density functional calculations
- Metal-free acetylide anions
- Reactive intermediates
ASJC Scopus subject areas
- Organic Chemistry