M.Sc. / There were two main objectives of the research presented m this dissertation. Firstly, the synthesis of bulky electron withdrawing phosphine-alkene ligands for classic ligand testing in the Suzuki cross-coupling reaction was performed. Previously, a range of electron deficient phosphine-alkenes was prepared from 2- ( diphenylphosphino )benzaldehyde, using both Wittig and Knoevenagel chemistry. These were tested for catalysis and gave high yields for the Suzuki reaction. In the present instance, 2-( di-otolylphosphino) benzaldehyde was synthesised making use of Grignard technology from acetyl protected 2-bromobenzaldehyde and chloro(di-o-tolyl)phosphine (itself prepared from PCh. And the appropriate o-tolyl Grignard reagent. This material served as a building block for the generation of P-alkene ligands which were synthesised making use of Wittig, Knoevenagel and transesterification chemistry. These o-tolyl analogues of the P-alkene ligands prepared in the previous study were used in ligand testing experiments in the Pd-catalysed Suzuki cross-coupling reaction. The results of the catalysis showed an enhanced activity with these ligands over the previous cases The second part of this dissertation involved determining the role (influence on activity) of the non coordinating counterion in the catalyst system in the methoxycarbonylation reaction. To this end discrete Pd complexes were synthesised and used directly in the methoxycarbonylation reaction. There have been a few reports on the role of the non-coordinating counterions of the catalyst systems in the methoxycarbonylation reaction. The catalyst is typically a palladium compound in the presence of a Bmnsted acid co-catalyst. Changes to the Bmnsted co-catalyst cause two variables to change, namely the acidity of the acid and the nature of the counterion that the acid provides. The work presented in this dissertation shows the results of only one variable being changed (that of the counterion) and as such allowed the specific role of the counterion in the outcome of the reaction to be determined. Previous work done in our laboratories made use of the Lewis acid Al(OTf)3 to co-catalyse the methoxycarbonylation reaction with rates and high yields being observed. In the present instance discrete Pd complexes were synthesised from Pd(OAc)2 using p-TsOH, MsOH and TfOH as the acids containing the weakly coordinating counterions. These Bnmsted acids have the ability to displace the OAc- anion from the Pd and as such formed the discrete L2PdX2complexes (L = PPh3; X = Mso-, p-Tso-, TfO} Synthesis of these discrete complexes was impeded by a lack of knowledge of the specific conditions under which to prepare the complexes and many avenues were pursued before successful isolation of these complexes was achieved. These discrete catalysts were used in the methoxycarbonylation reaction co-catalysed by Al(OT£)3. Here, the Al(OTt)3 forms the basis of a constant acid cocatalyst allowing only the counterion to be changed with the view to determining its role in these reactions. It was found that the counterion appears to play no role at all (Aco-, p-Tso-, Mso-, TfO-) in the outcomes of these reactions under the conditions employed. A comparative study is also detailed herewithin of the effects of both ex situ and in situ catalyst generation on the activity in the methoxycarbonylation reaction, which provides some insightful results.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:1718 |
| Date | 21 November 2011 |
| Creators | Bredenkamp, Tyler |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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