Synthesis, characterization, and biomimetic studies of first-row transition metal complexes relating to bio-inorganic energy conversion, and crystallographic studies of molecular structure

Herein is presented the preparation and characterization of synthetic manganese and iron complexes that relate to energetic enzymes found in nature. The study of these complexes provides further insight into the mechanism by which nature captures and utilizes energy, thus assisting researchers in the synthesis of a robust catalyst that can provide mankind with a renewable source of energy.;N,N'-diphenylhydrazine (DPH) was reacted with Mn(NR2)2 (R=SiMe3) to form an orange four-coordinate tetranuclear "pinned butterfly" cluster with the formula Mn 4(mu3-N2Ph2)2(mu-N 2Ph2)(mu-NHPh)2(THF)4 (2) in a solution of tetrahydrafuran (THF) and pentane. In pyridine and pentane, a red pyridine ligated product with formula Mn4(mu3-N 2Ph2)2(mu-N2Ph2)(mu-NHPh) 2(py)4 (2a) was produced. The reaction proceeded using four molecules of DPH and four molecules of Mn[N(SiMe3) 2]2. The solution began as a clear MnII solution, turning black upon oxidation of the manganese, then turning orange as the manganese was reduced by an additional molecule of DPH to form a pink MN 2-(mu-NHPh)2(NR2)2(THF)2 (1b) intermediate, and finally forming crystals of 2 or 2a directly from solution in ∼90% yields. Products and reactants were stored at -40°C in a nitrogen glovebox due to air-sensitivity. 1b, 2, and 2a were identified using single crystal X-ray diffraction, and were characterized with FT-IR, UV-vis, and 1H NMR spectroscopy.;The mechanism by which 2 and 2a were formed was investigated using kinetic isotope effects, the substitution of a methyl in place of a hydrogen on the DPH reactant, kinetic measurements, kinetic competition experiments, hydrogen atom transfer (HAT) reagent substitution, and via the isolation and characterization of intermediates using X-ray diffraction, EPR, and freezing point depression. The data indicated a 1:1 ratio of Mn(NR 2)2 and DPH reacted to form a polymeric MnIII anilide chain. This black intermediate then underwent HAT with a molecule of aniline to produce 1b and the byproduct azobenzene. 1b reacts with two molecules of DPH and two molecules of Mn(NR 2)2 to produce the final product 2 or 2a.;2,5-bis(alpha-pyridyl)-pyrrolate (PDPH) was reacted with iron complexes due to its ability to act as a non-innocent ligand. A non-innocent ligand bonded to a dinuclear iron complex allows for stabilization of low oxidation state iron complexes that are useful for small molecule activation. Fe(Cl) 2 was reacted with PDPH to form a red, air-sensitive complex, Fe(PDP)Cl(THF) 2 as well as a more stable red complex, Fe(PDP)2. Further experiments resulted in the green, air-stable compounds [Fe(PDP)Cl]2 O and Fe(PDP)Cl2 being isolated. The use of reducing agents with these compounds resulted in the production of more Fe(PDP)2. Products were identified using single crystal X-ray diffractometry, and characterized using NMR, IR, Evan's Method, and elemental analysis.;Single crystal X-ray diffractometry was used to identify and examine all the iron and manganese complexes within this study, as well as two dozen structures unrelated to water oxidation and small molecule activation. These structures are briefly discussed as well as the fundamental principles of X-ray diffractometry. The ability to determine absolutely configuration, observe hydrogen bonds in solids, resolve disorder, solve for twins, eliminate disordered solvents from the refinement cycles, and the accuracy with which atom location can be determined are reviewed as they relate to the structures that were solved.