Polymerization and Oligomerization of Ethylene by Cationic Nickel(II) and Palladium(II) Complexes Containing Bidentate Phenacyldiarylphosphine Ligands

A series of Ni(II) and Pd(II) catalysts have been synthesized from the P,O chelating ligands phenacyl(aryl)2phosphine. The (P,O)Ni-allyl+B(Arf)4 - [Arf = 3,5-(CF3)2C6H3] complexes 6a−c are active for polymerization of ethylene in the case of 6b (aryl = 2,4,6-(CH3)3C6H2) and for dimerization of ethylene to butenes in the case of 6a (aryl = C6H5) and 6c (aryl = C6H5, 2,4,6-(C6H5)3C6H2). These catalysts are characterized by their high initial activity but relatively short catalytic lifetime and poor thermal stability. The palladium analogues (P,O)PdMe(NCMe)+B(Arf)4 - are approximately an order of magnitude less active than the Ni analogues and generate butenes and hexenes. The barriers for migratory insertion in a series of methyl ethylene complexes [(p-XC6H4)2PCH2C(O)(p-YC6H4)]Pd(CH3)(C2H4)+B(Arf)4 - (X,Y = H, H; −OCH3, H; −CF3, H; H, −OCH3; H, −CF3) were measured. Values of ΔG ⧧ ranged from 18.2 to 20.3 kcal/mol and, relative to the unsubstituted system, decreased for X,Y = −CF3 and increased for X,Y = −OCH3.