Bioinspired manganese/picolinic acid catalyst system for organic oxidations
Abstract/Contents
- Abstract
- Transition metal-mediated oxidations of organic compounds are fundamental processes in biological systems. Metalloenzymes carry out these reactions with high selectivity and efficiency using earth-abundant transition metals and dioxygen or a reduced surrogate as the terminal oxidant. Motivated by these extraordinary reactions observed in metalloenzymes, synthetic "bioinspired" systems have been developed that are capable of similar reactivity in abiological contexts. One such segment of bioinspired oxidation systems focuses on non-heme Mn coordination complexes, which have demonstrated efficacy for challenging oxidation reactions such as catalytic alkene epoxidation and alkane C--H oxidation. A bioinspired, non-heme catalyst system comprised of a MnII salt, the ligand picolinic acid (2-PyCO2H), and peracetic acid (PAA) as an oxidant generates a remarkably general and powerful oxidant for O-atom transfer reactions to organic substrates. This catalyst system selectively transforms alkenes to their corresponding epoxides and is compatible with a wide range of alkene steric and electronic properties, including difficult electron-deficient substrates. Modifications to this system enable the epoxidation of traditionally incompatible basic nitrogen-containing alkenes and enhanced selectivity at cryogenic temperatures. Epoxidation using the Mn/2-PyCO2H system with PAA is exceptionally fast, reporting a record turnover frequency for a homogeneous epoxidation catalyst of 270 s-1. The reaction is mediated by an electrophilic Mn-based oxidant, with a transient MnIV species observable by complementary in situ high-resolution mass spectrometry (HRMS) and electron paramagnetic resonance (EPR) spectroscopy experiments. A combined experimental and computational approach suggests a novel redox-assisted Lewis acid mechanism mediated by a MnIV--peracetate complex, in which epoxidation proceeds in a stepwise fashion with a short-lived MnIII intermediate containing a substrate-centered radical. The same catalyst system is also capable of activating alkane C--H bonds to produce oxygenated products. The putative MnIV--peracetate complex is highly reactive for H-atom abstraction from substrates, with some selectivity according to homolytic C--H bond strengths. Experiments suggest a bifurcated reaction coordinate from the resultant organic radical in which radical dissociation (and subsequent reactions) is competitive with the desired oxygen rebound.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2017 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Moretti, Ross |
|---|---|
| Associated with | Stanford University, Department of Chemistry. |
| Primary advisor | Stack, T. (T. Daniel P.), 1959- |
| Thesis advisor | Stack, T. (T. Daniel P.), 1959- |
| Thesis advisor | Chidsey, Christopher E. D. (Christopher Elisha Dunn) |
| Thesis advisor | Du Bois, Justin |
| Advisor | Chidsey, Christopher E. D. (Christopher Elisha Dunn) |
| Advisor | Du Bois, Justin |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Ross Moretti. |
|---|---|
| Note | Submitted to the Department of Chemistry. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2017. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2017 by Ross Moretti
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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