NMR spectroscopic observation of a metal-free acetylide anion.
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 nonmetallic phosphazene base tBu-P4. In the presence of tBu-P4, the J coupling between the ethynyl carbon and hydrogen nuclei (1J(C,H)) 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.
Tanaka
Yoshiyuki
Y
Laboratory of Molecular Transformation, Graduate School of Pharmaceutical Sciences, Tohoku University, Aobayama, Aoba-ku, Sendai, Miyagi 980-8578, Japan. tanaka@mail.pharm.tohoku.ac.jp
Arakawa
Makoto
M
Yamaguchi
Yohei
Y
Hori
Chieko
C
Ueno
Masahiro
M
Tanaka
Takeyuki
T
Imahori
Tatsushi
T
Kondo
Yoshinori
Y
D000480:Alkynes / Q000737:chemistry; D000838:Anions / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry; D002412:Cations; D002621:Chemistry / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D008968:Molecular Conformation; D009942:Organometallic Compounds
D000480:Alkynes; D000838:Anions; D002412:Cations; D009942:Organometallic Compounds; D002244:Carbon