Development of iron-based compounds as effective catalysts for lactide polymerization and redox-regulated molecular tweezers

Takfa, Fatma (2024) Development of iron-based compounds as effective catalysts for lactide polymerization and redox-regulated molecular tweezers. Masters thesis, Memorial University of Newfoundland.

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Abstract

This Master’s thesis encompasses two distinct research projects in the field of organoiron chemistry. The first project focuses on addressing the global plastic waste problem through the synthesis of biodegradable polymers using non-toxic, abundant metals. Four iron complexes with tetradentate substituted-amino-bis(phenolato) ligands were prepared and characterized. These complexes were studied for their catalytic activities in the ring-opening polymerization (ROP) of rac-lactide under various conditions, including catalyst loading, temperature, co-catalysts, and initiators. The complexes demonstrated moderate to good activity for ROP of rac-lactide, with controlled and living polymerizations observed in the presence of propylene oxide. The resulting polymer products were characterized by gel permeation chromatographic, MALDI-TOF MS, and thermal analyses to evaluate their quality. Moreover, the kinetic behavior of the polymerization reactions catalyzed by the iron complexes was investigated. The experimetal results showed that the type of iron complex has potential in the production of polylactides. The second project involves the design and synthesis of a novel class of redoxactive molecular triads. These systems consist of two electron-donating dithiafulvene (DTF) groups connected to a central ferrocene (Fc) hinge unit via phenylene linkers. Three structural isomers of the (DTF)₂ – –Fc system were synthesized using Suzuki-Miyaura cross-coupling and phosphite-promoted olefination reactions. The compounds’ molecular and solid-state properties were investigated through X-ray single-crystal crystallography, while their electronic and electrochemical properties were examined using UV-Vis spectroscopy and cyclic voltammetry. The studies revealed multi-stage redox activities influenced by substitution patterns and steric factors. Density functional theory (DFT) and molecular dynamics (MD) simulations were carried out to provide further insights into the compounds’ conformational and electronic properties in various oxidation states. Notably, the para-substituted (DTF)₂ –Fc exhibited controllable conformational switching through redox reactions and supramolecular interactions with γ-cyclodextrin.

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