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

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

Synthesis and Reactivity of N‑Heterocyclic PSiP Pincer Iron and Cobalt Complexes and Catalytic Application of Cobalt Hydride in Kumada Coupling Reactions

The new N-heterocyclic σ-silyl pincer ligand HSiMe­(NCH₂PPh₂)₂C₆H₄ (<b>1</b>) was designed. A series of tridentate silyl pincer Fe and Co complexes were prepared. Most of them were formed by chelate-assisted Si–H activation. The typical iron hydrido complex FeH­(PMe₃)₂(SiMe­(NCH₂PPh₂)₂C₆H₄) (<b>2</b>) was obtained by Si–H activation of compound <b>1</b> with Fe­(PMe₃)₄. The combination of compound <b>1</b> with CoMe­(PMe₃)₄ afforded the Co­(I) complex Co­(PMe₃)₂(SiMe­(NCH₂PPh₂)₂C₆H₄) (<b>3</b>). The Co­(III) complex CoHCl­(PMe₃)­(SiMe­(NCH₂PPh₂)₂C₆H₄) (<b>5</b>) was generated by the reaction of complex <b>1</b> with CoCl­(PMe₃)₃ or the combination of complex <b>3</b> with HCl. However, when complex <b>3</b> was treated with MeI, the Co­(II) complex CoI­(PMe₃)­(SiMe­(NCH₂PPh₂)₂C₆H₄) (<b>4</b>), rather than the Co­(III) complex, was isolated. The catalytic performance of complex <b>5</b> for Kumada coupling reactions was explored. With a catalyst loading of 5 mol %, complex <b>5</b> displayed efficient catalytic activity for Kumada cross-coupling reactions of aryl chlorides and aryl bromides with Grignard reagents. This catalytic reaction mechanism is proposed and partially experimentally verified

Synthesis and Reactivity of Silyl Iron, Cobalt, and Nickel Complexes Bearing a [PSiP]-Pincer Ligand via Si–H Bond Activation

The synthesis and characterization of a series of Ni, Co, and Fe complexes bearing a tridentate bis­(phosphino)­silyl ligand (κ³-(2-Ph₂PC₆H₄)₂SiMeH, [PSiP]-H, <b>1</b>) are reported. <b>1</b> reacted with Ni­(PMe₃)₄ to afford the mononuclear nickel(0) complex [η²(Si–H)-PSiP]­Ni­(PMe₃) (<b>2</b>). The halogeno nickel complexes [PSiP]­Ni­(X)­(PMe₃) (X = Cl (<b>3</b>)<b>,</b> Br (<b>4</b>), I (<b>5</b>)) were synthesized in the reactions of <b>2</b> with Me₃SiCl or MeHSiCl₂, EtBr, and MeI. Complex <b>2</b> underwent ligand substitution of PMe₃ by CO to give [η²(Si–H)-PSiP]­Ni­(CO) (<b>6</b>). Complex <b>3</b> reacted with NaOMe to deliver [PSiP]­Ni­(OMe)­(PMe₃) (<b>7</b>) through anionic ligand substitution, while the neutral ligand replacement of PMe₃ by CO in <b>3</b> afforded the rare hexacoordinate 20-electron nickel­(II) complex [PSiP]­Ni­(Cl)­(CO)₂ (<b>8</b>). Unexpectedly, reaction of <b>1</b> with NiMe₂(PMe₃)₃ produced the tetracoordinate nickel(0) complex [Me₂PSiP]₂Ni (<b>9</b>). The complex [Me₂PSiP]­Ni­(CO)₂ (<b>10</b>) was acquired from <b>9</b> after the substitution of one [PSiP] ligand by two carbonyl ligands. <b>1</b> reacted with Co­(PMe₃)₄ or CoCl­(PMe₃)₃ to afford the hydrido cobalt­(II) complex [PSiP]­CoH­(PMe₃) (<b>11</b>) or hydrido cobalt­(III) complex [PSiP]­Co­(H)­(Cl)­(PMe₃) (<b>13</b>). Complex <b>12</b>, [PSiP]­Co­(H)­(I)­(PMe₃), could be obtained from the reaction of MeI with <b>11</b> or <b>13</b>. Treatment of <b>13</b> with 1 equiv of MeLi or <i>n</i>-BuMgBr in THF resulted in the clean formation of cobalt­(I) complex [PSiP]­Co­(PMe₃)₂ (<b>14</b>) via reductive elimination. The simple anhydrous inorganic salt NiCl₂ or CoCl₂ could also react with <b>1</b> in the presence of PMe₃ to form the corresponding silyl complexes <b>3</b> and [PSiP]­Co­(Cl)­(PMe₃) (<b>15</b>) via Si–H bond cleavage. <b>1</b> reacted with Fe­(PMe₃)₄ to form the hexacoordinate octahedral hydrido iron­(II) complex [PSiP]­Fe­(H)­(PMe₃)₂ (<b>16</b>). The molecular structures of complexes <b>2</b>–<b>5</b>,<b> 10</b>,<b> 12</b>,<b> 13</b>,<b> 15</b>, and <b>16</b> were determined by X-ray single crystal diffraction. <b>16</b> has excellent catalytic reactivity for the reduction of aldehydes and ketones