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Acid-Promoted Selective Carbon–Fluorine Bond Activation and Functionalization of Hexafluoropropene by Nickel Complexes Supported with Phosphine Ligands

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journal contribution
posted 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(CF2CFCF3)­(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(CF3CCF2)­(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(CF3CCF2)­(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(CF3CCF2)­Ph­(PMe3)2 (8), Ni­(CF3CCF2)­(p-MeOPh)­(PMe3)2 (9), and Ni­(CF3CCF2)­(CCPh)­(PMe3)2 (10) were obtained through the reactions of Ni­(CF3CCF2)­(PMe3)2Cl (2) with PhMgBr, (p-MeOPh)­MgBr, and PhCCLi. In contrast, the reaction of complex 2 with PhCH2CH2MgBr delivered complex 11, Ni­(CF3CHC–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 711 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.