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Baalbaki, Hassan

University of British Columbia

The transformation of CO₂ to value-added commodity chemicals presents an impactful strategy to obtain products that are less dependent on fossil fuels. Accordingly, numerous homogeneous catalysts have been developed to actively couple CO₂ with energetic organic compounds. Groups 12 and 13 metal based catalysts have received wide recognition due to their comparable activities with transition metals for CO₂ coupling reactions. Herein, a series of aluminum, gallium, indium, and zinc complexes have been designed and tested for CO₂ coupling with epoxides and silanes to generate valuable products such as cyclic carbonates, polycarbonates, and silyl formates. Group 13 metal halides have been developed for cyclic carbonate formation from CO₂ and epoxide. Simple InBr₃ Lewis acid with [n-Bu₄N]Br cocatalyst was found to be effective for this transformation at room temperature and at dilute CO₂ pressures. The InBr₃/[n-Bu₄N]Br catalytic system is tolerant toward different functional groups with high conversions and >96% selectivity for cyclic carbonate. A combination of in situ IR, NMR spectroscopy, and substrate labeling experiments enabled the proof of key catalytic steps and detection of reaction intermediates to elucidate the reaction mechanism. Understanding the mechanism of cyclic carbonate formation enabled the design of new group 13 metal complexes for CO₂ epoxide copolymerization to generate polycarbonate. Aluminum, gallium, and indium complexes supported by imino half-salen H[PNNiO] ligand with a pendent phosphine donor were described. In solution, the phosphine donor, is dissociated in the Al and Ga complexes while for the In complex it exhibits hemilabile behavior. The indium complex shows higher activity and selectivity than the Al or Ga analogues. IR spectroscopy experiments reveal that the initiation step is fastest in the indium complex. Zinc complexes, supported by reduced H[PNNO] ligand, were synthesized and characterized for CO₂ hydrosilylation reactions. The phosphine arm adopts two different configurations in solution and prevents aggregation. The monomeric zinc hydride complex is stable at elevated temperatures and reacts readily with CO₂ to afford a zinc formate species. The zinc hydride is active for CO₂ hydrosilylation and is selective for CO₂ reduction to the silyl formate at atmospheric CO₂ pressure.

Text

2024-07-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/82140

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/