Abstract
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.