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 Li-2[2] with (COD)PdMeCl and 4-(5-nonyl)-pyridine (py') generates the tetranuclear complex {(OPO-Li)PdMe(py')}(4)Li2Cl2 (3) in which four (phosphinesulfonate)PdMe(py') units are arranged around the periphery of a Li4S4O12 center dot Li2Cl2 cage. The Pd atoms in 3 are arranged in pairs with a Pd-Pd distance of 6.6 A within each pair. 3 is more resistant to disassembly to Pd-1 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 degrees C.