Exploration Of Electron-rich Nickel Complexes In C(sp~2)-F Bond Activation And Functionalization Of Perfluoropropene

Fluorine chemistry has drawn more attentions of chemists now days, because of the widely application of the fluoro-compounds, especially the field of the methodology on the synthesis of fluorine-containing compounds. And some progress has been made in this field with the assistant of organometallic chemistry. Under the promotion of transition-metal complexes, selective C-F bond activation and funtionalization in perfluoro-compounds that are cheap and abundant have become a significant method to synthesize compounds containing fluorine atoms. Chemists have achieved great success on this method. However, the substrates in this sort of reaction are concentrated on perfluoro-aromatic compounds, and the transition-metals are mainly noble metals. There are also other limits such as unsatisfied selectivity and harsh reaction conditions.Researches on the C-F bond activation of perfluoroalkene are limited to tetrafluoroethene, but rare for perfluoropropene, because of the poor selectivity. Nickel as a fourth cycle VIII group element, compared with the noble transition metals in the same group, Pd, Pt, has obviously advantages, such as its low price and low toxicity. It has been widely used in organometallic chemistry, especially on the activation of the inert bonds such as C-Cl bond. Based on these facts, our research is concentrated on Ni(0) complex promoted selective C-F bond activation of perfluoropropene. Our strategy is utilizing Lewis acid to accelerate the C-F bond activation of perfluoropropene coordinated with Ni(0).Electron-rich complex Ni(PMe3)4was utilized to react with perfluoropropene to obtain Ni(CF2=CFCF3)(PMe3)3(1). The selective C-F bond activation process of the coordinated perfluoropropene was conducted under the promotion of proper Lewis acid (ZnCl2, LiBr, and LiI) under mild conditions, and the activated products were obtained as Ni(CF3C=CF2)(PMe3)2X (X=Cl (4), Br (2), â…  (3)). The structures of them were confirmed with X-ray single crystal diffraction, in which the activated position was at the geminal position of trifluoromethyl group. DFT calculation was used to explain the mechanism of the activation process. Conventionally, protonic acid could conduct facile addition with perfluoropropene coordinated transition metal complexes. The reactions of HCl, as a strong inorganic acid, and organic acid such as acetic acid (CH3COOH) and methanesulfonic acid(CH3SO3H) with complex1really obey the rule. However, surprisingly, CF3COOH as a protonic acid can also proceed similar activation reaction, and achieve Ni(CF3C=CF2)(CF3COO)(PMe3)2(8).To test the property of the activated product, Ni(CF3C=CF2)(PMe3)2Cl (2) was used to react with Grignard reagents (PhMgBr,(4-methoxyphenyl)magnesium bromide), and organolithium reagent ((phenylethynyl)lithium). The transmetallation products were achieved and the structures were well characterized and confirmed with X-ray single crystal diffraction studies. Astonishingly, when the similar reaction performed with phenethylmagnesium bromide, all the fluorine atoms connected with C=C were substituted by phenethyl group and hydrogen atom. A reasonable mechanism was proposed and verified with experiment. In order to deeply understand the mechanism and the kinetic characteristics of the reaction, in-situ IR was also performed.