Room Temperature Preparation of Trifluoroethenylzinc Reagent by Metalation of the Readily Available Halocarbon HFC-134a and an Efficient, Economically Viable Synthesis of 1,2,2-Trifluorostyrenes

Trifluoroethenylzinc reagent [CF2CFZnX] was generated from the readily available halocarbon HFC-134a by an in situ metalation−transmetalation procedure at temperatures near to room temperature (15−20 °C). By systematic standardization of the metalation experiments by manipulation of solvent, cosolvent, temperature, zinc salt, and the base, the trifluoroethenylzinc reagent was produced in 73% yield at 20 °C in THF medium. The palladium-catalyzed cross-coupling reaction of the trifluoroethenylzinc reagent with various aryl iodides was carried out under mild reaction conditions to produce 1,2,2-trifluorostyrenes in 59−86% isolated yields. The stability of the intermediate trifluoroethenyllithium reagent was compared at different temperatures and solvent systems. Experimental evidence for the mono-anion from HFC-134a (CF3CHF-) was obtained by the trapping of the mono-anion with zinc halide in THF/TMEDA medium. The structure and complexation of both the mono- and bis-trifluoroethenylzinc reagents with TMEDA and other ligands are discussed.