Expedient Synthetic Identification of a P-Stereogenic Ligand Motif for the Palladium-Catalyzed Preparation of Isotactic Polar Polypropylenes.

The iso-specific statistical copolymerization of unprotected polar monomers with propylene remains a grand challenge in the field of polymer chemistry. Current research is hampered because only a single natural-product-derived dimenthylphosphine-motif is known to allow for the preparation of moderately isotactic polypropylene copolymers. To overcome this structural limitation, we developed time-efficient synthetic methods that facilitate P-donor ligand development. The strength of these methods was demonstrated with preparation of twenty-five new P-stereogenic phosphine/sulfonate- and bisphosphine-monoxide-type palladium catalysts, which could typically be developed in parallel. A lead candidate was identified for iso-specific propylene polymerization. The best-performing catalysts utilizing the P-stereogenic donor motif achieved triad isotacticities of up to mm=0.75-the highest value within those reported for group 10 metal catalysts-for the homo- and copolymerization of propylene with unprotected polar monomers at an industrially relevant temperature of 50 °C.