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Tautomerizable Flavin Ligands for Constructing Primary and Secondary Coordination Spheres
Neetu Singh1, Haneul Im1, Seongyeon Kwon2
1Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea.
None:
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.
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