Ring Chain Isomerism: Ligands for Mediating Two-Electron Reactivity with First-Row Transition Metals Open Access

Abstract

The goal of this project is to generate ligands that can induce two-electron reactivity in first-row transition metals for catalysis. The primary focus of this research is to develop ligands capable of facilitating two-electron reactivity with first-row transition metals. These ligands, termed "electronically responsive ligands" (ERLs), are designed to undergo ring chain tautomerism (RCT) to stabilize Fe^II/IV cycles and disfavor Fe^II/III cycles. The core functionality in the approach to RCT in these ligands is to utilize an imino-pyridine and a pendant anionic nitrogen donor, specifically a sulfonimidate. The imino-pyridine will allow for stabilization of an Fe^II center; interconversion to the amido-pyridine, through intramolecular nucleophilic attack by the sulfonimidate, affects the stabilization of Fe^IV. Initially, the synthesis towards ERLs proved difficult due to the presence of multiple reactive sites in sulfonimides. Key intermediates obtained in the synthesis of the target ERLs exhibited the desired RCT in the absence of a coordinating metal. Unfortunately, the synthesis of these key intermediates was low-yielding. Furthermore, it was observed that sterics can bias RCT selectivity, with increased steric bulk disfavoring the ring form over the chain form. Taken together, these observations of ring chain tautomerism from our key intermediates support the idea that our ERL design could potentially be able to induce an Fe^II/IV cycle, particularly useful for catalysis with organic substrates.

Table of Contents

1. Introduction

1

1.1 Electronically Responsive Ligands

3

1.2 Design of ERLs for Fe^II/IV Stabilization

5 1.3 Goals of Project 7

2. Results and Discussion

8 2.1 o-Lithiation of Aryl Sulfonates ERL Synthesis Route 8 2.2 ERL Syntheses via Saccharin Derivatives 9

2.3 Syntheses and Metallation of Alternative Ligands

23

2.4 Preliminary Studies of Metal Complexes

27

3. Conclusion

32

4. Future Studies

36

5. Supporting Information

38

6. Appendix

66

6.1 Synthesis of Fe(14)2/Fe(14)3X

66

6.2 Synthesis of M(16)

67

6.3 O2 Uptake Studies on Fe(13)2

68

6.4 Revisiting the Synthesis of 12d

69

7. References

71

About this Master's Thesis

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School	Laney Graduate School
Department	Chemistry
Degree	MS
Submission	Master's Thesis
Language	English
Research Field	Chemistry, Organic Chemistry, Inorganic
Keyword	Ligands Ring Chain Isomerism 2-electron Reactivity
Committee Chair / Thesis Advisor	Scarborough, Christopher C, Emory University
Committee Members	McDonald, Frank, Emory University Blakey, Simon, Emory University

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