Structural Modification of Functionalized Phosphine Sulfonate-Based Palladium(II) Olefin Polymerization Catalysts

The influence of phosphine sulfonate ligands bearing
a variety
of functionalities on the conformation of their derived Pd­(II) complexes
and their catalytic behavior in olefin polymerization reactions was
investigated. Analogous to the anisyl-derived 1a the
methyl thioether-substituted 8 as well as methoxylated
naphthalene-based compound 9 were successfully prepared.
NOESY NMR spectroscopy has been applied for the interpretation of
the complex configurations in solution and the correlation to the
corresponding molecular structures of 1a and 9. Ethene homopolymerization reactions were used for the determination
of reactivity trends and interpretation of effects originating from
the altered ligand substitution. Detailed analysis of the PE microstructure
shows that catalyst 9 acts as an efficient isomerization-type
catalyst during the formation of low molecular weight PE. Additionally
for compound 8 Pd–sulfur interactions with the
introduced methyl thioether functionalities are proposed, based on
NMR spectroscopic experiments. This catalyst promotes formation of
minimal amounts of high molecular weight PE. Comparison of 1a, 1b, 8, and 9 indicates that
the PE molecular weight is controlled by the protection of at least
one axial position of the palladium center, but no clear trends concerning
the catalyst activity could be observed.