Widespread interest in photoredox catalysis has simultaneously sparked the development of new photoactive metal complexes, particularly those comprised of earth abundant transition metals. However, most light-driven small molecule or organic functionalization reactions still rely on precious metal photosensitizers – either alone or in combination with a co-catalyst. We have developed a series of photoactive transition metal complexes (Mn → Zn) based on the N4-macrocyclic Mabiq ligand. The compounds can undergo light driven electron transfer processes and feature a uniquely wide range of photoaccessible redox states. Several of the M-Mabiq complexes also can undergo light induced homolysis, and coordinate substrates. This behavior underpins the ability of the Co-Mabiq compounds to photocatalyze styrene functionalization reactions in the absence of an added photosensitizer.
The Mabiq ligand also features a second metal binding site. The adjacent metal modulates the redox properties and enhances the photochemical properties of the central, N4-bound metal. Indeed, the bimetallic Cu/Fe-Mabiq complex acts as a self-sensitized catalyst for CO2 reduction. The bimetallic Mabiq complexes are thus highly promising scaffolds for challenging photocatalytic reactions.