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

The electron-rich complex Ni­(PMe₃)₄ was utilized to react with perfluoropropene to obtain Ni­(CF₂CFCF₃)­(PMe₃)₃ (<b>1</b>). The selective C–F bond activation process of the π-coordinated perfluoropropene in <b>1</b> 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 (<b>2</b>), Br (<b>3</b>), I (<b>4</b>)). The structures of complexes <b>2</b> and <b>3</b> 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 (<b>7</b>), while only the addition products Ni­(CF₂CFHCF₃)­(CH₃COO)­(PMe₃) (<b>5</b>) and Ni­(CF₂CFHCF₃)­(CH₃SO₃)­(PMe₃) (<b>6</b>) were obtained with CH₃COOH and CH₃SO₃H. The transmetalation products Ni­(CF₃CCF₂)­Ph­(PMe₃)₂ (<b>8</b>), Ni­(CF₃CCF₂)­(<i>p</i>-MeOPh)­(PMe₃)₂ (<b>9</b>), and Ni­(CF₃CCF₂)­(CCPh)­(PMe₃)₂ (<b>10</b>) were obtained through the reactions of Ni­(CF₃CCF₂)­(PMe₃)₂Cl (<b>2</b>) with PhMgBr, (<i>p</i>-MeOPh)­MgBr, and PhCCLi. In contrast, the reaction of complex <b>2</b> with PhCH₂CH₂MgBr delivered complex <b>11</b>, Ni­(CF₃CHC–CH₂CH₂Ph)­(PMe₃)₂, via double C–F bond activation. All of the C­(sp²)–F bonds in complex <b>11</b> were activated and cleaved. The structures of complexes <b>5</b> and <b>7</b>–<b>11</b> were determined by X-ray single-crystal structure analysis. A reasonable mechanism was proposed and partially experimentally verified through operando IR and <i>in situ</i> ¹H NMR spectroscopy