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 (OPO2–, 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.