DoM chemistry in the preparation of phosphine ligands for Pd-catalysed reactions
- Authors: Hughes, Tanya
- Date: 2010-04-01T05:32:33Z
- Subjects: Phosphine , Ligands , Phosphorus compounds synthesis , Metal catalysts
- Type: Thesis
- Identifier: uj:6741 , http://hdl.handle.net/10210/3149
- Description: M.Sc. , The objective of the project described in this dissertation was the preparation of a range of bulky electron-rich phosphine ligands making use of the directed ortho metallation (DoM) methodology developed in our labs. These ligands would then be employed in the Suzuki and Heck reactions of aryl bromides and aryl chlorides. A range of phosphinic amides were synthesised with various structural differences. These phosphinic amides all showed high activity in the DoM reaction when using TMSCl and MeI as electrophiles, by successfully incorporating TMS and Me groups in the ortho-positions of these phosphinic amide systems. A phosphonic amide was also synthesised and used in the DoM reaction, and also successfully incorporated TMS and Me in the ortho-position of this system. The success of these reactions was encouraging and provided a route to incorporate a phosphine on the ortho-position of these phosphinic amide and phosphonic amide systems by using a range of phosphine electrophiles Ar2PCl. The route was versatile and various electrophiles were used to prepare phosphine ligands with varying electronic and steric properties. These electrophiles were prepared from PCl3 and the corresponding Grignard reagent. Vaska-type complexes and phosphine selenium coupling constants were used to determine the electronic and stereo-electronic characteristics of the prepared ligands. The phosphine ligands prepared in this project making use of our DoM methodology were tested in the Suzuki cross-coupling reactions and Heck arylation reactions of aryl bromides and aryl chlorides and showed good reactivity with most of the substrates used. An advantage of the ligands prepared is that these ligands are oxidatively and hydrolytically stable
- Full Text:
- Authors: Hughes, Tanya
- Date: 2010-04-01T05:32:33Z
- Subjects: Phosphine , Ligands , Phosphorus compounds synthesis , Metal catalysts
- Type: Thesis
- Identifier: uj:6741 , http://hdl.handle.net/10210/3149
- Description: M.Sc. , The objective of the project described in this dissertation was the preparation of a range of bulky electron-rich phosphine ligands making use of the directed ortho metallation (DoM) methodology developed in our labs. These ligands would then be employed in the Suzuki and Heck reactions of aryl bromides and aryl chlorides. A range of phosphinic amides were synthesised with various structural differences. These phosphinic amides all showed high activity in the DoM reaction when using TMSCl and MeI as electrophiles, by successfully incorporating TMS and Me groups in the ortho-positions of these phosphinic amide systems. A phosphonic amide was also synthesised and used in the DoM reaction, and also successfully incorporated TMS and Me in the ortho-position of this system. The success of these reactions was encouraging and provided a route to incorporate a phosphine on the ortho-position of these phosphinic amide and phosphonic amide systems by using a range of phosphine electrophiles Ar2PCl. The route was versatile and various electrophiles were used to prepare phosphine ligands with varying electronic and steric properties. These electrophiles were prepared from PCl3 and the corresponding Grignard reagent. Vaska-type complexes and phosphine selenium coupling constants were used to determine the electronic and stereo-electronic characteristics of the prepared ligands. The phosphine ligands prepared in this project making use of our DoM methodology were tested in the Suzuki cross-coupling reactions and Heck arylation reactions of aryl bromides and aryl chlorides and showed good reactivity with most of the substrates used. An advantage of the ligands prepared is that these ligands are oxidatively and hydrolytically stable
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Ligand synthesis and Pd-catalysed C-C bond-forming reactions
- Authors: Hughes, Tanya
- Date: 2012-08-17
- Subjects: Ligands , Catalysis , Catalysts - Synthesis , Phosphine
- Type: Thesis
- Identifier: uj:2667 , http://hdl.handle.net/10210/6110
- Description: Ph.D. , The focus of this study was placed on developing stable recyclable catalyst systems that are both active and selective in Pd-catalysed reactions such as the Suzuki-Miyaura cross-coupling reaction, and the methoxycarbonylation reaction. The aim was therefore to prepare ligands with improved efficiencies as catalyst precursors, which are stable towards oxidation and/or hydrolysis, that are soluble in aqueous media and that can be recycled a number of times without significant loss in activity. This study initially focused on the preparation of functionalised phosphine ligands to be loaded onto the peripheries of different generations of PAMAM and PPI dendrimers. These functionalised ligands were then to be used in the Pd catalysed Suzuki-Miyaura cross-coupling of phenylboronic acid and aryl halides, as well as the Pd catalysed carbonylation of phenylacetylene. It was thought that loading of these ligands onto the dendrimers would result in a soluble support for subsequent catalyst systems to allow catalyst recycling. This would then potentially bridge the gap between heterogeneous and homogeneous catalysis. There has been a lot of progress made over the last decade or so in the preparation and use of dendritic phosphines and the positive effects seen are summarised in the first chapter. Water-soluble and thus environmentally friendly ligands have also gained widespread interest as these ligands offer economical and environmental advantages for many reactions. One of the aims of this study was therefore to prepare ligands that show greater solubility in aqueous solvents that can be successfully recycled and that show retention of activity upon reuse. Initially covalent loading of the prepared phosphine ligands onto the peripheries of the dendrimers were attempted. However based on all the problems experienced with the covalent bonding, as discussed in Chapter 2 of this document, a simple acid base titration allowed loading of the prepared phosphine ligands onto the peripheries of the dendrimers via electrostatic interactions, to afford a stable phosphine ligand-dendrimer salt. Electrostatic interactions contribute much more to the solubility enhancement of poorly soluble compounds, thus the formation of the non-covalent phosphine-dendrimer salts was expected to result in greater potential for catalysis in biphasic systems as well as catalyst recycling. Only low generation dendrimers were utilised as previous reports indicated that an increase of the dendrimer generation leads to observation of negative dendritic effects due to the increased bulk that inhibits the approach of the catalytic metal centre.
- Full Text:
- Authors: Hughes, Tanya
- Date: 2012-08-17
- Subjects: Ligands , Catalysis , Catalysts - Synthesis , Phosphine
- Type: Thesis
- Identifier: uj:2667 , http://hdl.handle.net/10210/6110
- Description: Ph.D. , The focus of this study was placed on developing stable recyclable catalyst systems that are both active and selective in Pd-catalysed reactions such as the Suzuki-Miyaura cross-coupling reaction, and the methoxycarbonylation reaction. The aim was therefore to prepare ligands with improved efficiencies as catalyst precursors, which are stable towards oxidation and/or hydrolysis, that are soluble in aqueous media and that can be recycled a number of times without significant loss in activity. This study initially focused on the preparation of functionalised phosphine ligands to be loaded onto the peripheries of different generations of PAMAM and PPI dendrimers. These functionalised ligands were then to be used in the Pd catalysed Suzuki-Miyaura cross-coupling of phenylboronic acid and aryl halides, as well as the Pd catalysed carbonylation of phenylacetylene. It was thought that loading of these ligands onto the dendrimers would result in a soluble support for subsequent catalyst systems to allow catalyst recycling. This would then potentially bridge the gap between heterogeneous and homogeneous catalysis. There has been a lot of progress made over the last decade or so in the preparation and use of dendritic phosphines and the positive effects seen are summarised in the first chapter. Water-soluble and thus environmentally friendly ligands have also gained widespread interest as these ligands offer economical and environmental advantages for many reactions. One of the aims of this study was therefore to prepare ligands that show greater solubility in aqueous solvents that can be successfully recycled and that show retention of activity upon reuse. Initially covalent loading of the prepared phosphine ligands onto the peripheries of the dendrimers were attempted. However based on all the problems experienced with the covalent bonding, as discussed in Chapter 2 of this document, a simple acid base titration allowed loading of the prepared phosphine ligands onto the peripheries of the dendrimers via electrostatic interactions, to afford a stable phosphine ligand-dendrimer salt. Electrostatic interactions contribute much more to the solubility enhancement of poorly soluble compounds, thus the formation of the non-covalent phosphine-dendrimer salts was expected to result in greater potential for catalysis in biphasic systems as well as catalyst recycling. Only low generation dendrimers were utilised as previous reports indicated that an increase of the dendrimer generation leads to observation of negative dendritic effects due to the increased bulk that inhibits the approach of the catalytic metal centre.
- Full Text:
N-Benzyl-P-(2-ethylphenyl)-P-phenylphosphinic amide
- Kinfe, Henok H., Hamese, Augustine, Hughes, Tanya, Omondi, Bernard
- Authors: Kinfe, Henok H. , Hamese, Augustine , Hughes, Tanya , Omondi, Bernard
- Date: 2011
- Subjects: X-ray crystallography , Crystallography , Phosphinamides
- Type: Article
- Identifier: uj:5941 , ISSN 1600-5368 , http://hdl.handle.net/10210/8136
- Description: Please refer to full text to view abstract
- Full Text:
- Authors: Kinfe, Henok H. , Hamese, Augustine , Hughes, Tanya , Omondi, Bernard
- Date: 2011
- Subjects: X-ray crystallography , Crystallography , Phosphinamides
- Type: Article
- Identifier: uj:5941 , ISSN 1600-5368 , http://hdl.handle.net/10210/8136
- Description: Please refer to full text to view abstract
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