Sterically Controlled Self-Assembly of a Robust Multinuclear Palladium Catalyst for Ethylene Polymerization

The self-assembly and reactivity of a robust multinuclear Pd catalyst based on the sterically expanded phosphine- bis-arenesulfonate ligand PPh(2-SO₃^--4,5-(OMe)₂-Ph)₂ (OPO^2-, 2) are described. The reaction of Li₂[2] with (COD)PdMeCl and 4-(5-nonyl)-pyridine (py') generates the tetranuclear complex {(OPO-Li)PdMe(py')}₄Li₂Cl₂ (3) in which four (phosphine-sulfonate)PdMe(py') units are arranged around the periphery of a Li₄S₄O₁₂·Li₂Cl₂ cage. The Pd atoms in 3 are arranged in pairs with a Pd-Pd distance of 6.6 Å within each pair. 3 is more resistant to disassembly to Pd₁ species than previously studied {(OPO-Li)PdMe(py)}₄ compounds based on Li₄S₄O₁₂ cages. 3 is a single-site catalyst for the polymerization of ethylene to high-molecular weight polyethylene hexanes suspension at 80 °C.