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 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.