Probing the Mechanism for 2,4'-Dihydroxyacetophenone Dioxygenase Using Biomimetic Iron Complexes.

In this study, we report the synthesis and characterization of Fe(T1Et4iPrIP)(2-OH-AP)(OTf) (), Fe(T1Et4iPrIP)(2-O-AP) (), and Fe(T1Et4iPrIP)(DMF) () (T1Et4iPrIP = tris(1-ethyl-4-isopropyl-imidazolyl)phosphine; 2-OH-AP = 2-hydroxyacetophenone, and 2-O-AP = monodeprotonated 2-hydroxyacetophenone). Both and serve as model complexes for the enzyme-substrate adduct for the nonheme enzyme 2,4'-dihydroacetophenone (DHAP) dioxygenase or DAD, while serves as a model for the ferric form of DAD. Complexes - have been characterized by X-ray crystallography which reveals T1Et4iPrIP to bind iron in a tridentate fashion. Complex additionally contains a bidentate 2-OH-AP ligand and a monodentate triflate ligand yielding distorted octahedral geometry, while possesses a bidentate 2-O-AP ligand and exhibits distorted trigonal bipyramidal geometry (τ = 0.56). Complex displays distorted octahedral geometry with 3 DMF ligands completing the ligand set. The UV-vis spectrum of matches more closely to the DAD-substrate spectrum than , and therefore, it is believed that the substrate for DAD is bound in the protonated form. TD-DFT studies indicate that visible absorption bands for and are due to MLCT bands. Complexes and are capable of oxidizing the coordinated substrate mimics in a stoichiometric and catalytic fashion in the presence of O. Complex does not convert 2-OH-AP to products under the same catalytic conditions; however, it becomes anaerobically reduced in the presence of 2 equiv 2-OH-AP to .