Ethylene Oligomerization and Polymerization by Palladium(II) Methyl Complexes Supported by Phosphines Bearing a Perchlorinated 10-Vertex closo-Carborane Anion Substituent

The synthesis and ethylene reactivity of the zwitterionic Pd methyl complexes (kappa(2)-P,Cl-PR2CB9Cl9)PdMe-(THF) (7, R = Pr-i; 8, R = Ph) and (kappa(2)-P,O-P(o-OMe-Ph)(2)CB9Cl9)PdMe(THF) (9), which contain the first phosphines appended with anionic 10-vertex perchlorinated closo-carboranes, are described. Complexes 7 and 8 oligomerize ethylene (23 degrees C, 2 atm) to a Schulz-Flory distribution of C-4-C-10 olefins with TOFs of ca. 8000 and 1800 t.o./h, respectively. 8 is ca. 4 times more active than the analogous (kappa(2)-P,F-ortho-PPh2C6H4BF3)PdMe(L) (L = pyridine or collidine) system reported by Jordan and Piers, which produces butenes. Complex 9 reacts with ethylene to yield polyethylene wax (M-n ca. 1000, D ca. 1.5) that is similar to commercial Fischer-Tropsch waxes. The activities of 7-9 are independent of ethylene pressure and the presence of B(C6F5)(3), suggesting that the catalyst resting state is the corresponding (PR2CB9Cl9)PdR(H2C=CH2) adduct. The molecular weights of the oligomer/polymer products are independent of ethylene pressure, which is consistent with an associative chain transfer mechanism. Reaction of 9 with ethylene generates the corresponding ethylene complex (kappa(2)-P,O-P(o-OMe-Ph)(2)CB9Cl9)PdMe(H2C=CH2), which inserts ethylene at -20 degrees C with a barrier (Delta G(insertion)(double dagger)) of 18.1 kcal/mol.