Identifying Reactivity Differences of Two-Carbon-Atom-Based Legacy Refrigerants at Group 9 Metal Pincer Complexes

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.