Metal complexes as catalysts for the synthesis of heterocycles

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Title: Metal complexes as catalysts for the synthesis of heterocycles
Author(s): Lal, Steven
Item Type: Thesis or dissertation
Abstract: Transition metal-based catalysts are undoubtedly one of the most powerful tools available to chemists. They mediate a plethora of reactions, and make numerous chemical processes viable while allowing cleaner/greener and safer routes. Most transformations require the use of ancillary ligands, and in practice, the actual catalytically active species might be formed either by the in situ combination of metal and ligand precursors, or directly from a pre- formed, well-defined organometallic complex. Pre-formed catalysts possess many advantages over in situ -generated systems. Not only are they usually better performing, but also allow strict control over the ligand/metal ratio. This is of importance since an increasing number of ligands are more expensive than common metal sources. More significantly, such control should be helpful to identify the actual catalyst, and hence, to better understand the reaction mechanism. This thesis describes the efforts in developing well-defined catalytic systems for the preparation and functionalisation of heterocycles, with a particular focus on 1,2,3- triazoles. The introductory Chapter outlines a brief overview of the chemistry of azides, including a discussion of the ligands and catalysts used for the 1,3-dipolar cycloaddition reaction of or ganic azides and alkynes. The synthesis, characterisation and X-ray crystal structures of novel copper(I) catalysts bearing phosphorus-based ligands is described in Chapter 2. These pre-formed catalysts have been screened in the copper(I)-catalysed azide-alkyne cycloaddition reaction. The scope and trends in reactivity are also described. The following Chapter provides an introduction to the ruthenium-catalysed azide-alkyne cycloaddition reaction and the efforts in developing water-soluble catalysts and substrates and testing them in this cycloaddition reaction. In Chapter 4, results of attempted metal-catalysed cycloadditions of azides and internal alkynes are presented. In addition, the development of two new catalytic systems for the preparation of 5-iodo-1,2,3-triazoles using pre-formed catalysts is discussed. Mechanistic studies for this transformation are also included. Chapter 5 includes our attempted functionalisation reactions of 5-iodo-1,2,3-triazoles. Furthermore, copper-catalysed direct arylation reactions of 1,2,3-triazoles are reviewed, and the results of the copper-catalysed direct arylation of 1,4-disubstituted-1,2,3-triazoles are included. The final Chapter contains experimental procedures and characterisation data of all compounds synthesised during this project.
Content Version: Open Access
Publication Date: Jun-2013
Date Awarded: Sep-2013
URI: http://hdl.handle.net/10044/1/39338
Advisor: Diez-Gonzalez, Silvia
Hii, Mimi
Sponsor/Funder: Imperial College London
Engineering and Physical Sciences Research Council
Department: Chemistry
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Chemistry PhD theses



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