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Applications of Synthesis in Copolymer Upcycling, Reduction of CO₂, Ligand Non-Innocence, and New Weakly-Coordinating Anions


Bruening, Meaghan Ann (2024) Applications of Synthesis in Copolymer Upcycling, Reduction of CO₂, Ligand Non-Innocence, and New Weakly-Coordinating Anions. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/dm7p-vv68.


This dissertation focuses on a very diverse series of studies with synthetic applications to organometallic systems supported by a redox non-innocent ligand architecture, α,ω diene generation, ionomers for tuning performance of electrochemical CO2 reduction, and design of new weakly coordinating anions.

Chapter 2 discusses the reactivity of a 9,10-anthracenediyl bis(phenoxide) titanium complex, where the polyaromatic anthracene motif functions as a non-innocent ligand. This enables access to a reduced Ti complex which is competent for oxidative coupling of alkyne and nitrile substrates, and pyrimidines and substituted benzenes can be accessed catalytically. Additional reactivity with oximes and oxidative coupling of alkynes and CO2 is explored.

Chapter 3 reports a two-step method for generation of a distribution of α,ω-dienes from ethylene and butadiene. Copolymers are prepared with variable butadiene content, where 1,4-butadiene incorporation ensures the double bonds are in the polymer backbone. Subsequent ethenolysis of the copolymers produces α,ω-dienes in the C10-C20 range. The conditions can be modified to control product selectivity.

Chapter 4 presents a series of polystyrene-based ionomers to probe the impact of local [K+] in the Cu electrode microenvironment on CO2R performance (Part A). Partial current density towards C2+ products (|jC2+|) increases with [K+] in ionomer, up to 225 mA cm–2. When K+ is replaced with [Me4N]+, performance lowers to the level of bare Cu, highlighting the crucial role of K+ in improving C2+ product selectivity. Molecular dynamics simulations and partial pressure CO2 experiments support enhanced CO2 mass transport with the ionomers. An expanded series of ionomers is presented (Part B), where the incorporation of different neutral comonomers (vinyl biphenyl) and cross-linking monomers (biphenyl and terphenyl) dramatically boosts performance. Direct tends between K+ content and CO2R performance are not observed with the expanded series, highlighting the non-innocent role of the neutral monomer and polymer structure.

Chapter 5 presents a new, Si-based weakly-coordinating anion. A library of anions bearing a variety of R groups is prepared, enabling facile tuning of sterics and solubility. A range of cations employed in chemical reactivity is supported by these anions, including ether-free alkali cations, Ph3C+, and an ethylene/CO copolymerization catalyst [Pd(dppe)(NCMe)Me]+ (generated by salt metathesis or protonation of a metal-alkyl bond). Electrochemical studies on the [Bu4N]+ variant show an exceptionally wide stability window for the [MeSiF]- anion of 7.5 V in MeCN. The [C6F5SiF]- variant can be readily modified to access additional diverse and/or dianionic variants.

Chapter 6 discusses the electrochemical performance of a new class of magnesium electrolytes for next-generation batteries. [Mg(DME)3][MeSiF]2 demonstrates remarkable performance with good stability, moderate conditioning, high coulombic efficiency ( > 96%), and high current density ( ~100 mA cm-2). However, the sensitivity of the experiments requires careful study of many parameters including impact of MgR2 additives (identity and concentration), cycling protocol, synthetic route, and the Pt working electrode to understand how the electrochemical performance is impacted. While addition of MgMe2 improves electrochemical performance, it is not inherently required for reversible Mg deposition and stripping. Following an extensive investigation of the cyclic voltammetry (CV) performance of [Mg(DME)3][MeSiF]2, preliminary screening of additional [Mg(DME)3][RSiF]2 variants is discussed.

Appendix I discusses the characterization of ethylene/α-olefin copolymers generated from monometallic and bimetallic Zr catalysts. The decreased polar monomer incorporation for the bimetallic vs. monometallic catalysts is attributed to the steric clash of larger comonomers with the distal metal site in bimetallic catalysts.

Appendix II discusses the preparation of bulky anthracene phenoxide ligands for Ti and Ta.

Appendix III discusses the preparation of mixed aryl/hydride borates as electrolytes for next-generation Mg batteries.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:non-innocent ligands, carbon dioxide reduction, ionomers, weakly-coordinating anions, next-generation batteries, magnesium electrolytes
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Not set
Research Advisor(s):
  • Agapie, Theodor
Thesis Committee:
  • Peters, Jonas C. (chair)
  • Fu, Gregory C.
  • Gray, Harry B.
  • Agapie, Theodor
Defense Date:23 May 2024
Non-Caltech Author Email:meaghanbruening (AT)
Record Number:CaltechTHESIS:06032024-222310291
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Chapter 3 adapted for Chapter 4A adapted for Appendix A
Bruening, Meaghan Ann0000-0001-8132-9497
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:16489
Deposited By: Meaghan Bruening
Deposited On:06 Jun 2024 23:06
Last Modified:06 Jun 2024 23:06

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