1,1,2-Trifluoroethenyl Zinc (Chloride, Bromide, Iodide)

Abstract

(1; X = Cl) [102526-37-4] C2F3ZnCl (MW 181.7) InChI = 1S/C2F3.ClH.Zn/c3-1-2(4)5;;/h;1H;/q;;+1/p-1 InChIKey = BAWRBXGQZOIZMJ-UHFFFAOYSA-M (2; X = Br) [105417-08-1] C2F3ZnBr (MW 226.3) InChI = 1S/C2F3.BrH.Zn/c3-1-2(4)5;;/h;1H;/q;;+1/p-1 InChIKey = HUIOAUQSDRXHEQ-UHFFFAOYSA-M (3; X = I) [105417-09-2] C2F3ZnI (MW 273.3) InChI = 1S/C2F3.HI.Zn/c3-1-2(4)5;;/h;1H;/q;;+1/p-1 InChIKey = DBNUOZDZZUMSJK-UHFFFAOYSA-M (perfluorovinyl building blocks that can participate in a range of Negishi-type cross-coupling reactions.1-5 Transmetallation of perfluorovinyl zinc bromide with copper6 or tin7 gives other useful fluorovinyl synthons that can be used in a range of coupling reactions) Physical Data: both CF2CFZnBr and CF2CFZnI exist in solution as an equilibrating mixture of mono- and bis-alkylated zinc compounds. The ratio of species in solution can be determined from 19F NMR analysis, and depends on both the vinyl halide starting material and the reaction solvent.8 Solubility: the chloride has been prepared in THF,9 while the bromide and iodides have been prepared in a variety of solvents including DMF, DMAc, THF, MeCN, and glymes.8 Analysis of Reagent Purity: 19F NMR (see Burton and co-workers).8 Preparative Method: CF2CFZnCl was first prepared in 1985 by Normant and co-workers by the lithiation of 1,1,2-trifluoroethenyl chloride with a range of butyllithiums in THF or Et2O at low temperature followed by transmetallation with ZnCl2 (eq 1). 9-11 The use of low temperature is necessary to prevent both the attack of the alkyllithium base on the starting material and the elimination of LiF from the product. Both side reactions occur at temperatures greater than −70 °C. An alternative preparation of the perfluorovinyllithium precursor has been recently reported beginning from the inexpensive and environmentally benign CF3CFH2 (Freon 134a). The two-step dehydrofluorination-hydrolithiation was carried out at low temperature.12-14 The necessity to use low temperatures was overcome by Burton and co-workers, who prepared the diisopropylamine complex of perfluorovinyl zinc chloride by reaction of CF3CFH2 with ZnCl2 in the presence of LDA at ambient temperature (eq 2).15 (1) (2) CF2CFZnBr and CF2CFZnI are also conveniently prepared by allowing 1,1,2-trifluoroethenyl bromide to react with acid-washed zinc metal at room temperature.8, 16, 17 The resulting mixture of mono- and bisalkylated zinc compounds was used without further purification (eq 3). (3) Handling, Storage, and Precautions: stock solutions of CF2CFZnBr and CF2CFZnI are reported to be stable for a period of several days at room temperature, or several weeks in the refrigerator. The reagents were readily hydrolyzed to CF2CFH.8