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.