UBC Theses and Dissertations
Catalysis and ligand design : living ring opening polymerization of lactide with chiral dinuclear indium catalysts and template synthesis of functionalized carbenes on iron complexes Yu, Insun
A family of indium complexes were synthesized and their catalytic activity towards the ring opening polymerization of lactide to form poly(lactic acid), a biodegradable polymer, were assessed. Racemic and enantiopure mono- and bis-alkoxy-bridged complexes bearing bulky chiral diaminoaryloxy ligands were synthesized and characterized. The reaction of the bis-alkoxy-bridged complexes with water produced mono-hydroxy-alkoxy-bridged dinuclear indium complexes. Investigation of both the mono- and bis-alkoxy-bridged complexes confirmed dinuclear structures in solution and in the solid state. These dinuclear complexes were highly active catalysts for the ring-opening polymerization of lactide to form poly(lactic acid) at room temperature. A detailed mechanistic investigation showed that the selectivities obtained for the ROP of racemic LA with the mono- and bis-alkoxy-bridged complexes are different and, along with kinetics investigations, suggest a dinuclear propagating species for these complexes. Additionally, neutral and cationic alkyl indium complexes bearing a chiral diaminophenoxy ligand were synthesized and characterized. Investigation of the cationic complexes in solution by NMR spectroscopy showed the counter anions influenced the different chemical environments at the metal center in solution. The preliminary polymerization of methyl methacrylate with neutral dialkyl and cationic alkyl indium complexes produced poly(methyl methacrylate). This is the first demonstration of cationic indium complexes for catalytic reactivity not only in solution but also in neat monomer. Finally, a family of cyclic and acyclic Fischer-type carbenes were generated via nucleophilic attack at the carbon atom of a coordinated isocyande on a piano-stool iron(II) complex. All complexes were characterized by IR and NMR spectroscopy and, where possible, by single-crystal X-ray diffraction. In particular, rare donor-functionalized acyclic (phosphino)(amino)- and (silyl)(amino)carbenes were generated by a two-step template synthesis on the iron(II) complex. The methodology involves the initial formation of ylidene complexes followed by reduction of the resulting imine to yield the desired carbene complexes. The reversible conversion of an acyclic (sily)(amino)carbene complex to its ylidene precursor via slow deprotonation with hydride was demonstrated.
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