Group-13 catalysed protocols for utilisation of CO2 as a sustainable C1 source

BILLACURA, Maria Distressa Genita (2022). Group-13 catalysed protocols for utilisation of CO2 as a sustainable C1 source. Doctoral, Sheffield Hallam University.

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The research described in this thesis focuses on the preparation of group 13- containing compounds and their application as Lewis acid catalysts. This research is in the context of utilizing CO2 as a renewable C1 feedstock, through the atom-efficient conversion with epoxides/aziridines to form useful cyclic carbonates and cyclic oxazolidinones. Significant progress in the search for efficient catalysts for these conversions has been made over the years, with some highly active aluminium compounds being developed. However, potential gaps in this exploration exist, including the study of other metals from group 13 beyond aluminium that have been investigated in many other fields of chemistry. Notably, there are few reports of boron, indium and gallium-based compounds used as a catalyst for the cycloaddition of CO2 to epoxides. With aluminium being thoroughly explored this presents motivation for exploring the potential for use of these other group 13 elements. In this work, a series of trimethyl borate compounds with different parasubstitutions on the phenoxy moieties have been prepared. Further to this, boron, gallium and indium complexes containing aminotrisphenolate ligands have been prepared. All these complexes have been tested as potential catalysts for the synthesis of cyclic carbonates, and their reactivity investigated. Boron aminotrisphenolate complexes operate by hydrogen-bonding catalysis rather than the expected Lewis acid catalysis due to the incomplete coordination of the aminotrisphenol ligand to the boron. The resulting free phenol acts as a catalyst for the production of cyclic carbonates at relatively elevated catalyst loading. Meanwhile, the trimethyl borate compounds, with a trigonal planar geometry, provide Lewis acid-driven catalysis rather than via a hydrogen bonding interaction. The gallium aminotrisphenolate complex was used as a catalyst for oxazolidinone synthesis, demonstrating the gallium complex's versatile efficiency as a more powerful catalyst than the aluminium congener. The results show that the Ga complex converts aziridines into the corresponding oxazolidinones in high yields at relatively low catalyst loading. Indium complexes bearing aminotrisphenolate and halide ligands are competent catalyst for the cycloaddition of CO2 and epoxides to form cyclic carbonates, with evidence that a coordinated halide can also act as the nucleophile required for the ring-opening step of the mechanism, thus adding more future possibilities to this family of compounds. Finally, modified cellulose fibres, prepared through anchoring of an epoxide to the surface by the Fenton reaction, followed by cycloaddition of CO2 using gallium catalyst have been prepared. These fibres have shown a positive outcome in the search for materials with antibacterial properties. As a final note, the potential cycloaddition of CO2 to episulfide has been briefly studied. This reaction produces an intractable solid product for which it has been unable to fully confirm its structure.

Item Type: Thesis (Doctoral)
Thesis advisor - Bricklebank, Neil [0000-0002-1614-2260] (Affiliation: Sheffield Hallam University)
Thesis advisor - Whiteoak, Christopher [0000-0003-1501-5582] (Affiliation: Sheffield Hallam University)
Thesis advisor - Forbes, Sarah [0000-0002-8361-6390] (Affiliation: Sheffield Hallam University)
Additional Information: Director of studies: Prof. Neil Bricklebank / Supervisors: Dr. Christopher J. Whiteok and Dr. Sarah Forbes
Research Institute, Centre or Group - Does NOT include content added after October 2018: Sheffield Hallam Doctoral Theses
Identification Number:
Depositing User: Colin Knott
Date Deposited: 30 Jun 2023 15:43
Last Modified: 14 Mar 2024 09:19

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