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UBC Theses and Dissertations

Yttrium amidate complexes for the catalytic synthesis of biodegradable polymers and amides Thomson, Jaclyn Alexa


Yttrium complexes are highly attractive systems for use in catalysis due to their high activity, low cost, and low toxicity. The highly modular amidate ligand set allows for easy variation of steric and electronic properties and, therefore, the reactive metal complex. This thesis explores the synthesis of yttrium amidate complexes and their use as catalysts in a variety of catalytic transformations. Mono-, bis-, and tris(amidate) complexes of yttrium are highly active initiators for the ring-opening polymerization of rac-lactide, yielding PLA with high molecular weight and narrow polydispersity. Termination of this polymerization is proposed to occur through formation of cyclic PLA with large ring sizes, once the monomer is consumed. Reaction of additional monomer is, therefore, not possible, and the polymerization is not living. The mechanical properties of the poly(ε-caprolactone) synthesized using tris(amidate) complexes of yttrium were determined to be consistent with those of commercially available polymer samples. Rheological testing of prepared poly(ε-caprolactone) suggested the possible formation of polymers with long-chain branching. However, the formation of long-chain branching in the poly(ε-caprolactone), synthesized with the tris(amidate) complex containing the naphthyl substituent, could not be confirmed or wholly refuted based on traditional chemical analyses. One yttrium tris(amidate) complex was also found to initiate the ring-opening polymerization of ε-caprolactone and rac-lactide to form diblock PCL/PLA copolymers. The mono-, bis-, and tris(amidate) complexes of yttrium are also highly active catalysts in the mild amidation of aldehydes with amines. The tris(amidate) complexes were most active, catalyzing the reaction in as little as 5 minutes. The best-performing catalyst can mediate the amidation of alkyl or aryl aldehydes, as well as aryl primary amines and alkyl or aryl secondary amines. This catalyst is also the first example of a rare-earth catalyst capable of tolerating pivalaldehyde in this transformation. The aforementioned class of complexes has been proven to be effective in a number of catalytic transformations. The modular synthesis of the amidate ligand, as well as the facile synthesis of yttrium amidate complexes, provide an easy means for altering the steric and electronic properties of the resulting complexes and, therefore, are ideal for further catalyst development.

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