The Caradonna lab has utilized the enzyme active site of TauD as a model for a synthetic, metal-based, oxidative catalyst. We have developed a series of small molecule, non-heme, manganese catalysts that are analogous to the previously synthesized iron complexes in our lab. These complexes, denoted MnII(N2Ox), where x = 1–3, were spectroscopically characterized, and their scope of utility explored. In addition to oxidizing methanol to formaldehyde, each catalyst in the series has exhibited the ability to epoxidize alkene substrates, including cyclooctene, cyclohexene, and cis-stilbene. After reaction condition optimization, the reactivity studies revealed certain trends in the reactivity of each catalyst, and the range of TONs was 10-120.
A heterogeneous catalyst system was also developed in which the iron catalyst was tethered onto a solid support. The iron catalyst, FeII(N2O1), where N2O1 is N-(2-(dimethylamino)ethyl)-N-methylglycine, is susceptible to dimerization and subsequent inactivation when it is in homogeneous solution. Thus, a homogeneous catalyst system was designed with a resin that contained a low concentration of amine functionalization, which was synthetically transformed into an azide-functionalized resin. An alkyne derivative of the N2O1 ligand scaffold was developed which could then be tethered onto the resin via CuAAC “click” chemistry, and low-loading levels of tethered catalyst were obtained.
Efforts towards modulating the N2O1 ligand were also explored. We sought to develop a synthetic methodology for facile ligand functionalization, which would provide greater accessibility to adding desired substituents. These substituents could aid in the solubility of the catalyst or provide ligand-directed asymmetric catalysis for prochiral substrates. The ligand was also modified electronically with electron-withdrawing and electron-donating substituents, in order to probe how the electronic structure of the catalyst affects its reactivity. Finally, efforts were made toward spectroscopically establishing the structure of the Fe(IV)-oxo intermediate with isotopically labeled reagents. The development of the manganese-based oxidative complexes and the optimization efforts towards the O2-activating iron-based complexes have exploited the utility of biomimetic, small molecule catalysis.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/47063 |
| Date | 06 October 2023 |
| Creators | McLernon, Bailey |
| Contributors | Caradonna, John P. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Rights | Attribution-NoDerivatives 4.0 International, http://creativecommons.org/licenses/by-nd/4.0/ |
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