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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Study of Bis-Imidazol-2-Ylidines as Ligands for Transition Metal Catalyzed Coupling Reactions

Turnbull, Stanhope 17 December 2004 (has links)
Two bis-imidazol-2-ylidine N-heterocyclic carbenes have been employed as ancillary ligands in an attempt to illustrate their utility in the palladium-mediated preparation of aryl ethers from aryl halides. Ullman-type homo-coupling of the aryl halides persistently occurred instead of ether formation. One of the well known N-heterocyclic carbenes, IPr, was employed with the same results. A variety of reaction conditions and reagents were investigated including solvents, N-heterocyclic carbene species, palladium source, alkoxide base, palladium to ligand ratio and reaction time. Reactivity of the individual N-heterocyclic carbenes as ancillary ligands in the palladium-catalyzed amination reaction of aryl halides was investigated to determine functionality of the carbenes. Alternative procedures to prepare the key intermediates in the synthesis of the bisimidazol- 2-ylidines were developed. In this study the aryl imidazoles were prepared from the corresponding phenol and carbonyldiimidazole. Subsequent N-alkylation then furnished the Nheterocyclic carbenes in high yield. Novel unsymmetrical N-heterocyclic carbenes with aryl and benzylic side groups have been synthesized as models for the subsequent synthesis of unsymmetrical polymer-bound Nheterocyclic carbenes. The unsymmetrical ligands were employed in the palladium-catalyzed amination of aryl halides and in the Suzuki-Miyaura Reaction. Two Merrifield resin polymerbound N-heterocyclic carbene ligands were then synthesized and employed in the aryl amination and Suzuki-Miyaura Reactions. Both reactions were greatly accelerated by the implementation of microwave heating. The Merrifield resin polymer-bound palladium-ligand complexes have been recycled through several reactions without loss of activity.

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