21907-59-5

The electroreduction of the halofluoromethanes CF3Br, CF 2Br2 and CF2BrCl has been studied in high-pressure stainless steel autoclaves at different cathodes [Pt, steel (V2A, V4A), glassy carbon (GC)] and in various solvent-supporting electrolyte systems (SSE), e.g. DMF/[Bu4N]Br, NMP/[Bu4N]BF4 etc.. The reduction potentials for CF3Br increase from Pt (-1.6 V) 2Br2 and CF2BrCl suggesting a reductive cleavage of C-X bonds as the first step. CF2Br2 and CF2BrCl show a two-step reduction in accord with the C-X bond energies (C-F > C-Cl > C-Br) and the Perfluoro-effect . The electrolysis of CF3Br in different SSE-systems with sacrificial zinc or cadmium anodes has been reinvestigated with our experimental set-up to elucidate the influence of the experimental conditions on the type and ratio of the products. The observed products CF 3MBr·2L and (CF3)2M·2L (M = Zn, Cd; L = DMF or AN) are the same as in the previous investigations, but are obtained in different ratios, as a rule caused by a parallel chemical corrosion of the respective anodes. By using aluminium as sacrificial anode no CF 3Al compounds are formed. The CF3 species generated by electroreduction of CF3Br react with the solvents via hydrogen abstraction and formation of CF3H. The current yield with respect to the dissolution of the Al anode reaches 120 % indicating a considerable chemical corrosion in addition to the anodic oxidation. This result enabled a one-pot trifluoromethylation reaction of NMP as organic carbonyl substrate and solvent with CF3Br and aluminium powder (ratio 3 : 2) at higher temperatures (> 70°C). The complete reaction of CF3Br to give CF3H and 1-methyl-2-trifluoromethyl-4,5-dihydropyrrol allowed the isolation of the latter by vacuum condensation and distillation in 45 % yield, rel. to the CF 3Br used. Gallium and indium were also applied as sacrificial anodes in combination with CF3Br as substrate. In both cases, anodic current yields of about 280 % indicated an extreme chemical corrosion together with cathodic metal depositions corresponding to the cathodic current yield. These deposits - in contrast to those of Zn and Cd - do not react with CF 3Br in Grignard-type conversions to CF3Ga and CF 3In compounds. So, the observed products (CF3) nMBr3-n·L (M = Ga, In; n 1-3; L = DMF, NMP) are obviously formed by chemical corrosion of the electro-activated anodes. Finally, electrochemical and chemical trifluoromethylations were successfully carried out, using R3SiCl (R = Me, Vi, Ph), Me3M′Cl (M′ = Ge, Sn) and aluminium anodes or Al-powder. The products were characterized either after isolation or in the product solutions by NMR-spectroscopic investigations.

Difluoromethylstannanes have been obtained by hydrogenation of (CF3)4Sn with the hydrides (CH3)3MH (M=Sn, Ge).The reaction is shown to proceed via attack of the hydride on the tin atom; transfer of fluoride from the CF3 group to the MMe3 group along with elimination of CF2 yields the unstable (CF3)3SnH.Difluorocarbene is inserted quantitatively into Sn-H bonds, thus forming both Me3SnCF2H and (CF3)3SnCF2H.The latter is subject to further formal replacements of CF3 by CF2H groups, finally yielding Sn(CF2H)4.For M=Sn, further methyl/trifluoromethyl exchanges lead to a variety of methyl-containing species, (CF3)n(CF2H)mSnMe4-n-m.For M=Ge, insertion of CF2 into the Ge-H bond is not observed; the lower reactivity of GeMe3H towards CF2 is demonstrated independently by its reaction with such CF2 sources as CF3SiF3 and CF2Br2/C2(NMe2)4; trimethylgermyltin derivatives, (CF3)n(CF2H)mSnGeMe3, are formed, with evolution of CF2H2.The compounds have been identified by their characteristic NMR spectra.Owing to Lewis acid/base interactions NMR chemical shifts and coupling constants are very sensitive to the choice of solvent.Linear correlations between the 2J(SnF) couplings of CF3 and CF2H groups and between 1J(SnC) and 2J(SnF) are found. Key words: Tin; Difluoromethyl; Group 14; Fluorine

The hydrogenation of (CF3)nGeX4-n (X = halogen, n = 1-3) with NaBH4 in an acidic medium has been investigated.Deuteration with NaBD4 and D3PO4 gave the partially deuterated species CF3GeHnD3-n and (CF3)2GeHnD2-n in reasonable isotopic purity.The )CF3)2GeHBr was isolated and converted into the halides (CF3)2GeHX (X = F, Cl, I) by treatment with AgX or HX.Insertion of CF2 into a Ge-H bond has been observed, and (CF3)(CF2H)GeH2 has been characterized.Direct alkylation of Ge-H bonds brought about by reaction with a mixture of RI and R'2Zn (R, R' = CH3, C2H5), and the methyl(trifluoromethyl)germanes CF3GeH2(CH3), CF3GeH(CH3) and (CF3)2GeH(CH3) were isolated.For R = CD3, R' = CH3 the product distribution can be accounted in terms of two competing mechanisms.