University of Illinois Urbana-Champaign

Cobalt catalysts towards parahydrogen induced polarization

Muhammad, Safiyah Ruth

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MUHAMMAD-DISSERTATION-2021.pdf

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https://hdl.handle.net/2142/113152

Description

Title
Cobalt catalysts towards parahydrogen induced polarization
Author(s)
Muhammad, Safiyah Ruth
Issue Date
2021-07-09
Director of Research (if dissertation) or Advisor (if thesis)
Fout, Alison R
Doctoral Committee Chair(s)
Fout, Alison R
Committee Member(s)
  • Girolami, Gregory S
  • Olshansky, Lisa
  • Guironnet, Damien
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Date of Ingest
2022-01-12T22:35:05Z
Keyword(s)
  • Cobalt
  • Catalysis
  • Parahydrogen
  • PHIP
  • SABRE
  • PHIP-IE
Abstract
Magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) spectroscopy are two techniques that hold great importance to the fields of medicine and chemistry, respectively. Used daily by researchers and medical practitioners alike, these techniques provide critical diagnostic information for molecular structure determination and irregularities in the body’s internal structures which is often key in early detection of diseases. Despite the frequent use of these two techniques, both suffer from the same inherent sensitivity issue which often increases the time required to collect highly resolved data. To address these problems, several techniques have been developed, with one of them relying on the use of a spin isomer of hydrogen gas termed parahydrogen (p-H2). Parahydrogen has been used in conjunction with rhodium and iridium homogeneous catalysts in the field of Parahydrogen Induced Polarization (PHIP) to yield large signal enhancements over the standard signals traditionally achieved in MRI and NMR spectroscopy. This field has advanced to yield enhancements via both hydrogenative (incorporation of p-H2 into the substrate) and non-hydrogenative methods, however, expansion of the field beyond the use of standardized rhodium and iridium catalysts is limited. This work builds on the application of the established hydrogenation catalyst, (MesCCC)Co-py [MesCCC = bis(2,4,6-trimethylphenyl-benzimidazol-2-ylidene)phenyl), py = pyridine] , towards hyperpolarization of substrates via PHIP chemistry. In Chapter 2, the development of structural and electronic variants of the CCC ligand platform is discussed. The synthesis of a chiral ligand and a tolyl variant is achieved through modification of the established Buchwald-Hartwig coupling of the respective amine precursor with 2-bromoiodobenzene. Metalation of the variants is reported with varying degrees of success using cobalt, nickel, and zirconium metal sources. Additionally, the synthesis of an electron rich CCC ligand was explored via the installation of amine, methoxy, and tert¬-butyl moieties in the backbone of the ligand. Success was achieved in the synthesis and isolation of the (MesCCCtBu)CoCl2py complex. Characterization of that complex, as well as its derivatives, was done via NMR and IR spectroscopies as well as X-ray diffraction studies. The application of the (MesCCCtBu)Co(N2)PPh3 towards the semi-hydrogenation of alkynes is discussed and a comparison to the (MesCCC)Co(N2)PPh3 and (MesCCCCF3)Co(N2)PPh3 complexes is made. Interested in further probing these electronic variants’ impact on PHIP chemistry, Chapter 3 reports the use of the (MesCCCtBu)Co-py and (MesCCCCF3)Co-py complexes towards the hyperpolarization of ethyl propionate via ALTADENA (adiabatic longitudinal transfer after dissociation engenders net alignment). Additionally, the substrate scope of the (MesCCC)Co-py-catalyzed ATLADENA chemistry is expanded, with long-lived hyperpolarization being achieved in the parahydrogenation of alkynes. The impact of the ligands flanking group on catalysis was examined in the application of the (DippCCC)Co(N2) towards ALTADENA hyperpolarization. And finally, the application of rhodium and iridium derivatives of the CCC ligand towards hyperpolarization is described. In Chapter 4, the expansion beyond hydrogenative hyperpolarization with the (MesCCC)Co-py catalyst is discussed with the enhancement of structurally intact olefins. A variety of olefinic substrates bearing different functional group is tolerated for non-hydrogenative hyperpolarization of both 1H and 13C nuclei, both with and without the use of microtesla fields. Mechanistic studies to probe the route of hyperpolarization were conducted, leading to the attribution of the enhancement to a net-non-hydrogenative route termed PHIP-IE, PHIP via Insertion and Elimination. The application of the previously discussed catalysts to this chemistry and the influence of catalytic parameters were examined. Finally, Chapter 5 describes the development and synthesis of novel cobalt and copper complexes for application towards PHIP chemistry. The metalation of two bidentate ligands as well as a CCN ligand is explored with various metal salts, with the use of Co2(CO)8 proving the most successful. Lastly, synthesis of a (ArCCC)Cu, (Ar = Mes or Dipp), complex is investigated with three different metalations routes: direct metalation, zwitterion formation, and transmetalation from a zirconium complex.
Graduation Semester
2021-08
Type of Resource
Thesis
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http://hdl.handle.net/2142/113152
Copyright and License Information
Copyright 2021 Safiyah Muhammad

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