Synthetic methodology for preparation of dinitrosyl iron complexes.

After the first structural characterization of dinuclear dinitrosyl iron complex (DNIC) in 1958 and discovery of natural dinitrosyl iron unit (DNIU) [Fe(NO)2] in 1964-1965, continued investigations on natural and synthetic DNICs explored their ubiquitous functions as (1) a product for nitrosylation of non-heme Fe proteins and chelatable iron pool, (2) a biological vehicle for iron and nitric oxide, (3) a novel redox-active unit for stabilization and activation of small molecules, (4) an electrocatalyst for water splitting, and (5) a precursor for electrodeposition of Fe-containing hybrid material. From a synthetic chemistry perspective, herein, we summarize four synthetic methodologies for preparation of structure-characterized DNICs in the attempt to attract continued development of unexplored DNICs featuring novel functions. As collected from CCDC database, structure-characterized DNICs can be classified into (1) tetrahedral {Fe(NO)2}9 DNICs with C/N/P/O/S/Se/Cl/Br/I ligation modes, (2) five-/six-coordinate {Fe(NO)2}9 DNICs with N/O ligation modes, (3) tetrahedral {Fe(NO)2}10 DNICs with C/Sn/N/P/O/S/H ligation modes, (4) metallothiolate-bound {Fe(NO)2}9/{Fe(NO)2}10 DNICs, and (5) dinuclear {Fe(NO)2}9-{Fe(NO)2}9, {Fe(NO)2}9-{Fe(NO)2}10, and {Fe(NO)2}10-{Fe(NO)2}10 DNICs with thiolate/alkoxide/pyrazolate/CO bridging ligands. After buildup of the DNIU [Fe(NO)2] using NO, NO+, and NO2- as alternative sources of nitrosyl ligands, ligand substitution and modification reaction of DNICs, redox interconversion between {Fe(NO)2}9 and {Fe(NO)2}10 cores, and transformation between mononuclear and dinuclear DNICs establish the comprehensive pathways to bridge alternative types of DNICs in the chemical library of structure-characterized DNICs. This review on the synthetic methodology for preparation of DNICs will facilitate the incorporation of DNIU [Fe(NO)2] into (bio)materials for potential applications of DNICs in chemistry, catalysis, biology, and biomedicine.