Exploring the fundamentals of C-F bond activation on low-index metal surfaces

Per- and polyfluoroalkyl substances (PFAS) are fluorochemicals that are extremely persistent, widely distributed, and capable of bioaccumulation. These compounds cause a variety of health issues in humans and our feedstocks. The C–F bond in perfluoroalkyl substances (PFAS) has a high-energy cost associated with its breaking, which is the reason for their persistence. To effectively remove these toxins from our environment, it is necessary to develop new catalytic systems that are capable of breaking such a strong carbon-halogen bond.
In a 2022 publication (Jenness et al. Environ. Sci. Proc Imp. 24, 2085 (2022)), we demonstrated that the carborane anion ([HCB₁₁H₅F₆]⁻)/silylium (Et₃SiH/Et₃Si⁺) is an effective homogeneous catalyst for the degradation of PFAS. The degradation process involves a Et₃SiH/Et₃Si⁺ pair acting in tandem, with the carborane anion forcing unoccupied anti-bonding orbitals to be partially occupied, which weakens the C–F bond. This forced occupancy of unoccupied anti-bonding orbitals naturally calls to mind the Blyholder back-bonding chemistry, which has been demonstrated to activate super-strong chemical bonds with metal surfaces. While metal chemistry has been leveraged for the degradation of PFAS, to date no comprehensive study of PFAS on a variety of metal surfaces has occurred.
In this talk, we present the results from a recent study (Jenness and Shukla, Environ. Sci. Adv. 3, 383 (2024)) in which we explore how a set of 27 transition metal surfaces can activate the PFAS anti-bonding orbitals through the Blyholder back-bonding mechanism. We find that the degree of degradation is owed to the nature of the d-band of the metal surfaces and the location of the metal on the periodic table. Our results have allowed us to propose novel catalysts for the degradation of PFAS.