Pd alkyl complexes that contain phosphine-bis(arenesulfonate) ligands (OPO), e.g. 1a-d, self-assemble into tetranuclear structures in which four (OPO)PdMe(py) units are arranged around the periphery of a cubic D4R Li4S4O12 cage. NMR and XRD data show that these "Pd4 cages" exist as single stereoisomers with SSRR configurations for the four P centers. The four Pd units are equivalent and are spatially separated into two pairs with a Pd−Pd distance of ca. 6 Å within each pair. The Pd−Me groups point toward the face of the py ring on the adjacent Pd center. Pd4 cages polymerize ethylene (E) to high-MW linear PE, and copolymerize E with vinyl fluoride (VF) to copolymers with 10x higher VF incorporation compared to mononuclear analogues. However, under polymerization conditions, the cages undergo partial dissociation to Pd1 species that generate low MW polymer, so broad MW distributions are observed. We have investigated new multinuclear systems to probe factors that influence the cage nuclearity, structure and stability and to generate robust cages. (OPO)PdMe(py) complex 2 self-assembles in the presence of LiCl to an expanded cage in which a Li2Cl2 layer is inserted between the “top” and “bottom” Li2S2O6 layers. 2 is much more stable toward dissociation to Pd1 species that 1 and functions as a single-site catalyst, producing HDPE with Mn = 800,000 and PDI = 2.3 at 80 oC. Self-assembled multinuclear catalysts based on Zn-phosphonate scaffolds, e.g. 3, will also be discussed.

Self-assembled multinuclear palladium catalysts for olefin polymerization

253rd National Meeting (2017)

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