Synthesis, characterization, and reactivity of mixed nitrogen/sulfur non-heme iron complexes

Discerning structural and functional characteristics that are essential to the role of metal ions in metalloenzymes is a goal of this thesis. To tackle this problem, small-molecule analogs of non-heme iron active sites have been designed. These biomimetic complexes allow for atomic-level control over the metal ion geometry and ligand environment in a way that is often not possible when working directly with large biological systems. Superoxide reductase (SOR) and cysteine dioxygenase (CDO) are two metalloenzymes with non-heme iron active sites with a coordination environment comprised of nitrogen and sulfur donors. An overview of the structure and mechanism of these enzymes and the synthetic models of SOR is presented in chapter 1.;Synthetic methods have been pursued towards the ligand design of pyridine-containing macrocyclic and linear molecules. This class of ligands affords substantial variability in the ligand and the synthetic route. Five novel iron complexes have resulted from work with these pyridine-containing ligands and are presented in chapter 2 along with their synthesis are characterization.;In chapter 3, the rational tuning of the thiolate donor in model complexes of SOR of the form [FeII([15]aneN4)(SAr)] + is discussed. Comparison of the x-ray structures of these compounds is made. The stabilization of FeIII-OOR (R = tBu or cumenyl) species at low temperatures for all of the thiolate-ligated complexes is demonstrated. Spectroscopic characterization of these alkylperoxo complexes shows that they are low-spin iron(III) species with weak Fe-O and O-O bonds. DFT calculations on a simplified model for the FeIII-OOR complexes are also presented.;The alkylated ligand, Me4[15]aneN4, used to prepare another thiolate-ligated, (N4S)FeII complex as an accurate structural model of the reduced form of SOR is highlighted in chapter 4. At low temperatures, this complex produces the metastable alkylperoxo species [FeIII(Me4[15]aneN4)(SPh)(OOtBu)] + upon addition of alkylperoxide. Alkylation at nitrogen induces a spin state change for the alkylperoxo species from low-spin to high-spin iron(III). The nu(Fe--O) for this high-spin alkylperoxo species is lower than all other known high-spin alkylperoxo complexes lacking a thiolate ligand. A non-thiolate-ligated alkylperoxo complex was also generated, [Fe III(Me4[15]aneN4)(OTf)(OOtBu)+, and exhibits a strong upshift in nu(Fe--O).