The main objective of the research described in this dissertation was the preparation of a range of bulky and electron-rich phosphine ligands using the DoM methodology developed in our labs for this purpose. These ligands would be employed in the Suzuki cross-coupling reaction of deactivated aryl bromides and aryl chlorides. Initially, a range of phosphinic amides was synthesised and tested for DoM reactivity. TMSCl, MeI and O2 were successfully used as electrophiles, incorporating TMS, Me and OH groups in the ortho-position of these phosphinic amide systems. This development was encouraging and provided a route to incorporate a phosphine on the ortho-position of these phosphinic amide systems by using Ph2PCl and Cy2PCl as electrophiles to incorporate Ph2P and Cy2P, respectively. The route was versatile and a range of electrophiles was used to prepare phosphine ligands with varying electronic and steric properties. These electrophiles (of the R2PCl variety) were often specifically prepared from PCl3 and the corresponding Grignard reagent. Phosphine ligands synthesised in this research project using our DoM (directed ortho metallation) methodology were tested in Suzuki cross-coupling reactions of deactivated aryl bromides and some aryl chlorides and showed excellent reactivity, with the advantage that the ligands of this study are oxidatively and hydrolytically stable. Efforts were also made to modifying the phosphinic amide-functionalised phosphine ligands to generate their water-soluble derivatives. One way of achieving this was by the hydrolysis of the phosphinic amide moiety to the phosphinic acid analogue. Salts of these phosphinic acid derivatives have promising activities as water-soluble substrates. This route was successful only iii with less electron-rich systems providing an opening for more research in this regard. In an alternative synthetic route to polar water-soluble phosphines it was envisioned that phosphonate-derivatised phosphines would offer access to water-soluble phosphine ligands by using milder hydrolysis conditions. These phosphonate systems were also tested for DoM reactivity and showed promising reactivity. Phosphonates have not previously being employed as DoM groups, and this alone expands the application and potential scope of P-based DoM groups. / Prof. D.B.G. Williams
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:2601 |
| Date | 11 June 2008 |
| Creators | Mokhadinyana, Molise Stephen |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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