Catalysis^cubed

Abstract

In the first part of this work, porphyrin synthesis was optimised beyond the classical <em>Adler</em> protocol, which typically provides a simple Areaction but also suffers from low yields (~20%) due to incomplete precipitation and variable solubility. Key improvements included controlled dilution and cooling, solvent selection tailored to the respective compound and fluorescence-guided product monitoring. <br/> A major contribution of this thesis is the introduction of acid-base recrystallisation as a broadly applicable, sustainable purification method. Protonation precipitates porphyrins as stable salts, separating them from impurities, while subsequent controlled deprotonation yields highly pure neutral porphyrins. Combined with the modified synthesis, this method enabled isolated yield up to 70%, far exceeding conventional outcomes. The adoption of CHNS analysis as an analytical standard compensated for NMR limitation arising from poor solubility, providing a reliable assignment of identity and purity. The optimised workflow proved effective for different types of porphyrins, with synthetic limitation observed only for highly sterically hindered cases. <br/> The second part focused on assembling porphyrin-based supramolecular cubes and understanding how templates, cavity occupancy and isolation conditions affect their formation. Incorporation of a cobalt-porphyrin as a template significantly promoted cage formation, enabling a one-pot assembly of the "filled" cubic system. To preserve the fragile structures, conventional solvent-removal work-ups were replaced with direct filtration and subsequent collection. The cubes display notable tolerance towards water and air, simplifying their preparation and storage. DMF molecules remained trapped within the cavities and contributed to structural stability, though they introduce challenges in quantifying catalyst concentration. Characterisation relied primarily on ESI-MS due to solubility limitation and paramagnetic broadening in NMR spectra. <br/> The final part investigated cobalt-catalysed cyclopropanation reactions using the previously formed supramolecular catalysts. Systematic optimisation revealed enhanced turnover numbers for the encapsulated catalysis in comparison to the unencapsulated experiments. Substrate scope studies showed that electron-rich and electron-poor styrene derivatives delivered consistently higher yields and cis-selectivity when catalysed by the encapsulated systems compared to the free catalyst. Counterion from triflate to triflimide on the cube, drastically improved solubility, enabling mixed-solvent reactions and turnover numbers up to 360 at catalyst loading as low as 0.2 mol%.