Flavins─one of nature's most ubiquitous organic cofactors─mediate proton and electron transfers in biological systems. Their heterocyclic (iso)alloxazine cores enable such reactivity through pronounce Show more
Flavins─one of nature's most ubiquitous organic cofactors─mediate proton and electron transfers in biological systems. Their heterocyclic (iso)alloxazine cores enable such reactivity through pronounced electro- and photochemical properties, as well as hydrogen bonding with surrounding residues. To harness these features in an organometallic context, we developed a redox-active, flavin-derived bidentate ligand (allLH) that engages both primary and secondary coordination spheres. Coordination with Fe(II) yields an octahedral complex, (allLH)2FeX2 (X = Cl, Br, OTf), stabilized by outer-sphere hydrogen bonds between the ligand and metal-bound (pseudo)halides. Upon deprotonation, allLH undergoes tautomerization to the isoalloxazine form (isoL), generating a hydrogen-bonded aqua complex, (isoL)2Fe(OH2)2. Furthermore, treatment of (allLH)2FeCl2 with cobaltocene triggers ligand tautomerization, affording [(allLH)(isoL)FeCl2][CoCp2] and highlighting the redox-responsive nature of the flavin scaffold. This work introduces a novel approach to repurpose flavin as a multifunctional ligand platform for constructing tunable coordination environments around transition metal centers, offering new opportunities in ligand design and bioinspired reactivity. Show less