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Stable carbenes with spectator substituent Stable carbenes--neutral molecules in which a carbon atom is surrounded by only six electrons--are difficult to achieve. Usually an electron-active substituent is needed on either side of the carbene to stabilize it. A team led by Guy Bertrand of Paul Sabatier University in Toulouse, France, has synthesized stable singlet carbenes containing amino and aryl groups (shown) [Science, 292, 1901 (2001)]. The amino group, which has both -donor and -acceptor electronic character, ensures that the carbene center remains neutral. X-ray data indicate that the aryl group, which contains o-trifluoromethyl groups, does not interact with the carbene lone pair of electrons and serves as a spectator. These carbenes can be isolated at room temperature at close to quantitative yields. Because these carbenes don't require two strongly interacting substituents, the number and variety of such carbenes should increase, Bertrand and colleagues write, which will lead to new synthetic developments and applications. |
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