Spectroscopic and Structural Assignment of the Absolute Stereochemistry in a Series of 1,2-Difluorovinyl Organometalloids. The First Crystallographic Characterization and Structural Series of Group 14 Fluorovinyl Compounds

Abstract

The group 14 trifluorovinyl compounds Ph(3)ECF=CF(2) (E = Ge, Sn, Pb) have been prepared in high yield by the low-temperature reaction of the triphenylelement halide with trifluorovinyllithium, generated from tetrafluoroethane (CF(3)CH(2)F, HFC-134a) and 2 equiv of n-butyllithium. The X-ray crystal structures of these materials have been obtained, so affording the first structural series for such species. Subsequent reaction of Ph(3)GeCF=CF(2) with LiAlH(4) and a range of organolithium reagents has led to preparation of the 1,2-difluorovinylgermanes Ph(3)GeCF=CFR (R = H, Me, n-Bu, t-Bu, Ph). Multinuclear NMR spectroscopic and X-ray crystallographic studies of these compounds have been undertaken and have shown unequivocally the exclusive trans-geometry of the 1,2-difluorovinyl moiety.

Ringing the Changes: A Remarkable Carbene‐Free Synthesis of Difluorocyclopropenes

“…NMR spectra were recorded as CDCl 3 3 ) was added, whilst maintaining the temperature at À10 8C. The mixture was then allowed to stir and attain ambient temperature overnight.…”

“…The mixture was then allowed to stir and attain ambient temperature overnight. Hexane (160 cm 3 ) was added to precipitate the inorganic salts, the settled mixture was then filtered through celite, and the filtrate was concentrated in vacuo. Purification on a silica column, eluting with 50:50 toluene/hexane, afforded 2 as a pale yellow solid (4.229 g, 85 %).…”

“…[2] In seeking to extend to these systems our recent work on the reactivity of organometallic fluorovinyl compounds, [3] we have discovered a remarkable transformation, which results in the facile formation of gemdifluorocyclopropenyls in good yields.…”

“…The trifluoropropynyls Ph 3 ECCCF 3 (1: E = C, 2: E = Si) are readily prepared by the reaction of Ph 3 EX (X = Cl, Br) with trifluoropropynyllithium (LiCCCF 3 ), derived from hydrofluorocarbon HFC-245fa (CF 3 CH 2 CF 2 H) as we have previously described, [2] and isolated as air-and moisturestable solids. These materials are characterized by singlet resonances at around d F = À50 ppm in the 19 F NMR spectra, and three quartet signals in the 13 C NMR spectra, (d C = 90-120 ppm), with infrared absorptions (CC stretch) at approximately 2200 cm À1 .…”

The synthesis and structural characterisation of an homologous series of group 14 1-chloro-2,2-difluorovinyl compounds

“…A variety of transition-metal trifluorovinyl derivatives have thus been investigated structurally, [7] and most recently our attention has turned to the study and derivatisation of main-group systems [8]. However, in contrast to the trifluorovinyls, there remain relatively few reports of 1-chloro-2,2-difluorovinyl containing organometallic species, [7b,9] and only three such materials, ClHg(CCl¼CF 2 ), [7b] [(Ph 3 P)Au(CCl¼CF 2 )]…”