Yan Li

Year of Award

2023

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Chemistry

Other Degree Name/Area of Focus

Bioinorganic Chemistry

Department or School/College

Department of Chemistry and Biochemistry

Committee Chair

Dong Wang

Commitee Members

Bruce E. Bowler, Orion B. Berryman, Christopher P. Palmer, Stephen R. Sprang, Edward Rosenberg

Keywords

bio-inspired, bioinorganic, cobalt, high-valent, hydrocarbon, metal-oxo

Publisher

University of Montana

Abstract

The development of efficient and low-cost technologies that convert hydrocarbons, including methane, to liquid fuels through controlled functionalization of its inert C–H bond is a fundamental challenge. Also, the activation of carbon−hydrogen (C−H) bonds is the first step of functionalizing inert hydrocarbons. This transformation is a key step in many biological and synthetic processes. One representative example inspired by nature is the metalloenzyme called soluble methane monooxygenase (sMMO), a nonheme dinuclear iron-dependent enzyme that catalyzes the hydroxylation of the strong C–H bond of methane (bond dissociation energy BDE = 105 kcal/mol) using O2 as the oxidant. The catalytic cycle of sMMO has been extensively studied over decades, and features a highvalent bis-μ-oxo FeIV2(μ-O)2 “diamond core” intermediate called Q as the active oxidant for C–H bond activation. This research focuses on the study of an unprecedented highvalent CoIII,IV2(μ-O)2 complex supported by neutral tetradentate tris(2- pyridylmethyl)amine (TPA) ligand by one-electron oxidation of its CoIII2(μ-O)2 precursor. This new complex can activate C−H bonds 3−5 orders of magnitude faster than its iron and manganese counterparts, and represents the most reactive synthetic model for the sMMO enzymatic intermediate. This study expands the understanding of base metal complexes for C−H bond activation and serves as motivation to design C−H activation methods inspired by nature.

Chapter 1 provides the introduction of C-H bond hydroxylation mechanism and the biological background that initially inspired this project. In Chapter 2, we reported the characterization of cobalt diamond core complexes supported by TPA and related ligands. In Chapter 3, we studied the reactivity of those complexes. In Chapter 4, we discovered that the open core species provides an excellent strategy to achieve substrate specificity and to be applied in the deaminative C(sp3)-N bond activation. Chapter 5 describes a proposed monomer [Co(III)(TPA)(O2)]+ species and its nucleophilic reactivity. Chapter 6 lays out the overall conclusions and points out a few future directions as the prospective scope of the entire project.

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