Acid-Promoted Selective Carbon–Fluorine Bond Activation and Functionalization of Hexafluoropropene by Nickel Complexes Supported with Phosphine Ligands
journal contributionposted on 09.12.2013, 00:00 by Wengang Xu, Hongjian Sun, Zichang Xiong, Xiaoyan Li
The electron-rich complex Ni(PMe3)4 was utilized to react with perfluoropropene to obtain Ni(CF2CFCF3)(PMe3)3 (1). The selective C–F bond activation process of the π-coordinated perfluoropropene in 1 was conducted with the promotion of Lewis acids (ZnCl2, LiBr, and LiI) under mild conditions to afford the products Ni(CF3CCF2)(PMe3)2X (X = Cl (2), Br (3), I (4)). The structures of complexes 2 and 3 determined by X-ray single-crystal diffraction confirmed that the C–F bond activation occurred at the geminal position of the trifluoromethyl group. Surprisingly, CF3COOH as a protonic acid could also carry out a similar activation reaction to give rise to Ni(CF3CCF2)(CF3COO)(PMe3)2 (7), while only the addition products Ni(CF2CFHCF3)(CH3COO)(PMe3) (5) and Ni(CF2CFHCF3)(CH3SO3)(PMe3) (6) were obtained with CH3COOH and CH3SO3H. The transmetalation products Ni(CF3CCF2)Ph(PMe3)2 (8), Ni(CF3CCF2)(p-MeOPh)(PMe3)2 (9), and Ni(CF3CCF2)(CCPh)(PMe3)2 (10) were obtained through the reactions of Ni(CF3CCF2)(PMe3)2Cl (2) with PhMgBr, (p-MeOPh)MgBr, and PhCCLi. In contrast, the reaction of complex 2 with PhCH2CH2MgBr delivered complex 11, Ni(CF3CHC–CH2CH2Ph)(PMe3)2, via double C–F bond activation. All of the C(sp2)–F bonds in complex 11 were activated and cleaved. The structures of complexes 5 and 7–11 were determined by X-ray single-crystal structure analysis. A reasonable mechanism was proposed and partially experimentally verified through operando IR and in situ 1H NMR spectroscopy.