Russell P. Hughes

We describe the first comparative data on metal-mediated C–H activation and functionalization reactions at two-carbon-atom legacy refrigerants and density functional theory (DFT) analyses on the resulting organometallic products. We reveal that, depending on the degree of fluorination in the refrigerant, C–H activation could lead either to stable M­(H)­R_f products or to a M­(fluoroolefin) complex. The first example of a metal-mediated dehydrofluorination of R-143a is described, resulting from a β-fluoride elimination reaction of a putative [Ir­(H)­(CH₂CF₃)] intermediate and the loss of hydrogen fluoride. This work also reports the first examples of metal-mediated activation of R-125 (CF₃–CF₂H) and R-134a (CF₃–CFH₂) where the direct C–H activation products can be observed spectroscopically and, in the case of R-125, structurally characterized. The stability of the [Ir­(H)­(R_f)] complexes is notable, given that the direct products of C–H activation of nonchelating alkanes at transition metals remains relatively rare. The clean formation of isolable [Ir­(H)­(R_f)] complexes is expected to facilitate studies of migratory insertion reactions in these species, which bodes well for efforts to repurpose high-global-warming-potential legacy refrigerants. Finally, DFT calculations provide insight into how the degree of fluorination affects CC bond lengths and energies of propellor-like rotations in the coordinated fluoroolefins, the relative free energies of fluoroolefin binding, and the role of observed CH···F contacts in the calculated structures.

We describe the first comparative data on metal-mediated C-H activation and functionalization reactions at two-carbon-atom legacy refrigerants and DFT analyses on the resulting organometallic products. We reveal that, depending on the degree of fluorination in the refrigerant, C-H activation could lead either to stable M(H)Rf products or to a M(fluoroolefin) complex. The first example of a metal-mediated dehydrofluorination of R-143a is described, resulting from a β-fluoride elimination reaction of a putative [Ir(H)(CH2CF3)] intermediate and the loss of hydrogen fluoride. This work also reports the first examples of metal-mediated activation of R-125 (CF3CF2H) and R-134a (CF3CFH2) where the direct C-H activation products can be observed spectroscopically and, in the case of R-125, structurally characterized. The stability of the [Ir(H)(Rf)] complexes is notable, given that the direct products of C-H activation of non-chelating alkanes at transition metals remains relatively rare. The clean formation of isolable [Ir(H)(Rf)] complexes is expected to facilitate studies of migratory insertion reactions in these species, which bodes well for efforts to repurpose high-global-warming-potential legacy refrigerants. Finally, DFT calculations provide insight into how the degree of fluorination affects C=C bond lengths and energies of propellor-like rotations in the coordinated fluoroolefins, the relative free energies of fluoroolefin binding, and the role of observed CH···F contacts in the calculated structures.

We report a new method for the regiodivergent dearomative (3 + 2) reaction between 3-substituted indoles and oxyallyl cations.

Supplementary Tables and Figures

Hydrofluoroolefins (HFOs) constitute the newest generation of fluorocarbon refrigerants and foam-blowing agents due to their reduced global warming potential vs their saturated analogues. To identify new synthetic routes to HFOs, we show that reactions of bulky Ni(0) phosphine and -NHC complexes with vinylidene difluoride (VF2) afford μ-fluoro-1,1,3-trifluorobut-3-enyl Ni complexes. Moreover, addition of triisopropylsilane allows for reductive elimination of the reduced product─2,4,4-trifluoro-1-butene─demonstrating the Ni-catalyzed hydrodefluorodimerization of VF2. Accompanying DFT calculations identify the T-shaped nickelacyclopentane intermediate that spontaneously undergoes selective intramolecular β-F (vs β-H) elimination.