Thermally Robust Heterobimetallic Palladium–Alkali Catalysts for Ethylene and Alkyl Acrylate Copolymerization

We report on the synthesis and characterization of a new family of palladium–alkali olefin polymerization catalysts using site-differentiated dinucleating platforms. Metal binding studies indicate that our palladium phosphine phosphonate polyethylene glycol (PEG) complexes form 1:1 adducts with alkali cations in solution, with relative affinities in the order Na + ≈ K + > Li + . We observed that these palladium–alkali complexes are more active for ethylene homopolymerization and ethylene/alkyl acrylate copolymerization in comparison to their monopalladium counterparts, although their effect on polymer branching and molecular weight is relatively modest. In some cases, the addition of external sodium salts to conventional palladium complexes (i.e., those that do not have pendant PEG chains) also led to remarkable catalyst enhancements, presumably also due to the formation of palladium–sodium species. The unique features of our heterobimetallic systems are that they display long catalyst lifetimes at 100 °C and can even operate at temperatures as high as 140 °C. Although we have shown that secondary cations clearly increase the electrophilicity of the metal catalyst, their precise role in these polymerization reactions is still under investigation.