Green design, synthesis, characterization, and application of a novel family of iron(III)-TAML peroxide activating homogeneous catalysts

Chapter 1. The driving forces, ethical and chemical, that have shaped TAML evolution since the early 1980s are described in a chronological fashion. The need for a clean environment sets the basis for the design. A brief introduction to FeIII-TAML oxidation catalysis is given. Studies of high valent transition metal salts and natural oxidation enzymes yielded key conceptual insights which led to TAML design for controlled oxidation catalysis. The manifestation of these ideas in the inorganic complexes produced by the Collins lab is also described, moving from the PAC complexes to today's TAMLs. Opportunities for continued TAML advancement are suggested.;Chapter 2. Macrocyclic synthetic chemistry presents unique challenges. Entropic forces must be considered when selecting reaction conditions. Likewise, enthalpic forces must be considered when designing the ligand. Synthetic techniques to overcome these issues are described. Rationale and design strategies for the parent ligand of the 2nd generation of H4TAMLs, referred to as H4D*, are given. Synthetic techniques and reaction conditions are described. Progress toward other promising ligand systems is also presented.;Chapter 3. Environmentally useful, small molecule mimics of the peroxidase enzymes must exhibit very high reactivity in water near neutral pH. Here we describe the design and structural and kinetic characterization of a second generation of FeIII-TAML activators (2) with unprecedented peroxidase-mimicking abilities. Iterative design has been used to remove the fluorine that led to the best performers in first-generation FeIII-TAMLs (1). The result is a superior catalyst (2e) that meets a green chemistry objective by being comprised exclusively of biochemically common elements. The rate constants for bleaching at pH 7, 9, and 11 of the model substrate, Orange II, shows that the new Fe III-TAML has the fastest reactivity at pH's closer to neutral of any TAML activator to date. Under appropriate conditions, the new catalyst can decolorize Orange II without loss of activity for at least 10 half-lives, attesting to its exceptional properties as an oxidizing enzyme mimic. Synthesis, characterization, behavior in aqueous solution, and the catalytic activity of the new D* family of the FeIII-TAML activators of peroxides designed for purification of water is also described. A comparative study of the oxidative decolorizing of the Orange II dye by H2O 2 catalyzed by the parent compound [ Fe&cubl0;OC 2&parl0;o,o'- N&parr0;C6H4N CO)2CMe2}(OH2)]- (2d) and its nitro (2e) and dichloro (2f) derivatives (per phenylene ring) indicated superior activity of catalysts 2d and 2e at pH 7.7, though the former (2d) is by ca. three orders of magnitude less stable than the nitro-substituted catalyst 2e in aqueous solutions buffered by phosphate. For that reason 2e was chosen for systematic studies in aqueous media. Evidence is presented that 2e is an octahedral species in water. Both axial aqueous ligands are deprotonated with pK a1 and pKa1' of 8.4 and 10.0 at 25°C, respectively, the former being the lowest for all FeIII-TAMLs previously reported. This is among the key reasons accounting for high catalytic activity of 2e in oxidations of organic matter by H2O 2 in neutral and slightly basic solutions. Therefore, compounds such as 2e consisting of just bioelements are valuable green oxidation catalysts for purifying environmental waters. Importantly, our studies revealed that the 2e catalyst does not display endocrine disrupting activity. X-ray structural data for 2e and 2f is reported.;Chapter 4. The ligand system of H4D* was observed to have issues of hydrolytic stability when chelating iron. To observe its electron donating properties, another metal with a precedent for acid stability was needed---cobalt. Other Co-TAMLs have been previously synthesized and characterized, providing benchmark data to compare this new H4D* ligand. Physico-chemical characterization in combination with density functional theory provide a thorough analysis of this new species in its CoIII and formally CoIV states. In addition, this work also clarifies an important bifurcation in the high-valent cobalt literature.;Chapter 5. Catalytic oxidation of polymers containing polybutadiene by peroxides and FeIII-TAML is described. This is an important direction for the application of Fe-TAML catalysts due to the massive volume of these commodities, and their macromolecular longevity in the environment. Reported here are reaction conditions, temporal degradation studies using polybutadiene and triblock poly(styrene-butadiene-styrene) as substrates, and functional group analysis by infra-red spectroscopy. Over the course of days, the polymers are cleaved into smaller segments with acid endgroups.;Chapter 6. Useful synthetic procedures are described for future Collins group chemists.