Rhodium(II) Porphyrins: Unusual Transition States and the Quest for Catalytic Turnover

ABSTRACT Rh(II) porphyrin complexes have been used to realize remarkable stoichiometric transformations, which include C─H activation in methane as well as C─H and O─H activation in methanol at room temperature. However, their catalytic application is often hindered by the formation of strong Rh─C and Rh─X bonds over the course of the catalytic cycle, in addition to a tendency to form dimeric species. In this Concept article, we highlight the unusual transition states and reaction steps observed with Rh(II) porphyrins, as well as the challenges associated with the regeneration of Rh(II) during catalytic cycles. We discuss how photochemistry, electrochemistry paired with spatial confinement, and remote metal–metal collaboration in solid matrices can be used to leverage the latent potential of Rh(II) porphyrin reactivity in catalysis.