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) 2 phosphine. The (P,O)Ni-allyl + B(Ar f ) 4 - [Ar f = 3,5-(CF 3 ) 2 C 6 H 3 ] complexes 6a − c are active for polymerization of ethylene in the case of 6b (aryl = 2,4,6-(CH 3 ) 3 C 6 H 2 ) and for dimerization of ethylene to butenes in the case of 6a (aryl = C 6 H 5 ) and 6c (aryl = C 6 H 5, 2,4,6-(C 6 H 5 ) 3 C 6 H 2 ). 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(Ar f ) 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 -XC 6 H 4 ) 2 PCH 2 C(O)( p -YC 6 H 4 )]Pd(CH 3 )(C 2 H 4 ) + B(Ar f ) 4 - (X,Y = H, H; −OCH 3, H; −CF 3, H; H, −OCH 3; H, −CF 3 ) were measured. Values of Δ G ⧧ ranged from 18.2 to 20.3 kcal/mol and, relative to the unsubstituted system, decreased for X,Y = −CF 3 and increased for X,Y = −OCH 3 .