On the mechanisms of ethane dehydrogenation on silica-supported mononuclear Fe†

Abstract

With the increasing interest in developing catalytic materials based on atomically dispersed transition metals on heterogeneous supports, it is necessary to have an atomic-level understanding of the factors that impact their structural and electronic properties and, ultimately, their reactivity. In this contribution, we address and elucidate with electronic structure calculations open questions related to the ethane dehydrogenation mechanism on silica-supported mononuclear Fe(II) and Fe(III) sites. Contrary to prior hypotheses, we determine that the σ-metathesis on Fe(II) sites is an unlikely dehydrogenation mechanism. On tricoordinate and tetracoordinate Fe(II)@SiO₂, the reaction proceeds via heterolytic C–H bond activation and β-hydride elimination facilitated by spin-crossing. Atomically dispersed Fe(III) grafted on SiO₂ exhibits a more complex behavior as it seems to be undergoing autoreduction and we propose a new redox ethane dehydrogenation mechanism which, remarkably, is energetically competitive with the heterolytic C–H activation mechanism previously identified for other transition metals.