Sustainable chemical manufacturing requires catalytic innovation to address polymer waste, CO₂ emissions, and fossil feedstock dependence. This thesis explores homogeneous pincer catalysts for polymer depolymerisation, sustainable polymer synthesis, and CO₂ utilisation. Chapters 2 and 3 investigate hydrogenative depolymerisation of polyurethanes and polyethylene terephthalate. Spectroscopic studies (HPIR, NMR) reveal inhibition mechanisms in manganese-catalysed ester and polyurethane hydrogenation (Chapter 2), while optimized ruthenium catalysis achieves record turnover numbers (>37,000) for PET upcycling to a pharmaceutical precursor (Chapter 3), the highest reported for homogeneous PET hydrogenation at the time of publication. Chapter 4 establishes isocyanate-free polyurea synthesis, avoiding toxic diisocyanates and phosgene. Exploiting simultaneous catalyst decarbonylation and dehydrogenation, diformamides self-couple to form polyureas or react with diols to produce polyurearethanes, generating hydrogen and CO (syngas) as by-products. Chapter 5 develops a novel reverse water-gas shift approach using sequential amine formylation and decarbonylation. This strategy converts CO₂ and H₂ to CO with 100% selectivity at 170 °C at significantly milder conditions than conventional RWGS (>600 °C), while eliminating toxic NMP solvent and stoichiometric additives typical of previous homogeneous systems. These studies demonstrate the versatility of pincer catalysts for various chemical transformations and how mechanistic understanding can further enable their performance in sustainable polymer synthesis and depolymerisation, and CO₂ valorisation.
James Luk (Thu,) studied this question.