New organo-Lewis acids.: Tris (β-perfluoronaphthyl)borane (PNB) as a highly active cocatalyst for metallocene-mediated Ziegler-Natta α-olefin polymerization

Tris(beta-perfluoronaphthyl)borane (B(C10F7)(3), PNB) is synthesized from beta-perfluoronaphthyllithium and BCl3 to serve as a new strong organo-Lewis acid cocatalyst. PNB efficiently activates a variety of group 4 dimethyl complexes to form highly active homogeneous Ziegler-Natta olefin polymerization catalysts. Reaction of PNB with rac-Me2Si(Ind)(2)ZrMe2 and CGCMMe(2) (M = Zr, Ti; CGC = Me2Si(eta(5)-Me4C5)((BuN)-Bu-t)) (1:1 molar ratio) rapidly produces the base-free cationic complexes rac-Me2Si(Ind)(2)ZrMe+MePNB- (1) and CGCMMe(+)MePNB(-) (M = Zr, 2; Ti, 3), respectively. The mu-methyl dinuclear cationic complex [(CGCTiMe)(2)(mu-Me)]+MePNB- (4) is formed when a 2:1 CGCTiMe(2):PNB stoichiometry is employed. In the case of group 4 dimethyl zirconocenes, L2ZrMe2 (L = eta(5)-C5H5, Cp; eta(5)-1,2-Me2C5H3, Cp "), reaction in a 1:1 metallocene:PNB ratio affords cationic complexes L2ZrMe+MePNB- (L = Cp, 5; Cp ", 6), while the reaction with a 1:2 molar ratio affords dinuclear mu-methyl cationic complexes [(L2ZrMe)(2)(mu-Me)]+MePNB- (L = Cp, 7; Cp ", 8). In both reactions, mu-F dinuclear cationic complexes [(L2ZrMe)(2)(mu-F)]+MePNB- (L = Cp, 9; Cp ", 10) are formed as byproducts. (C6F5)(3)BNCCH3 and PNBNCCH3 were synthesized and characterized. Analysis of the PNBNCCH3 + B(C6F5)(3) <--(-->) (C6F5)(3)BNCCH3 + PNB equilibrium yields Delta H degrees = +0.7(2) kcal/mol and Delta S degrees = +4.3(5) eu, suggesting PNB has somewhat higher Lewis acidity and is sterically more encumbered than B(C6F5)(3). Solution v(CN) values for PNBNCCH3 and (C6F5)(3)BNCCH3 are 2365.3 and 2366.5 cm(-1), respectively, which indicate strong Lewis acidity. PBBNCCH3 cannot be detected in the reaction of (C6F5)(3)BNCCH3 with PBB [PBB = tris(2,2',2 "-perfluorobipheny)lborane] over prolonged periods at 60 degrees C. In ethylene polymerization, PNB-derived cationic complexes 5, 6, 7, and 8 have catalytic activities similar to the B(C6F5)(3)-derived analogues, while 2 and 3 have substantially higher activities. In propylene polymerization, catalyst 1 has higher activity than the B(C6F5)(3) analogue. In the case of ethylene and 1-hexene copolymerization, PNB-derived cationic complex 3 exhibits higher polymerization activity with similar 1-hexene incorporation versus the B(C6F5)(3)-derived cationic complex. In large-scale batch copolymerizations of ethylene and 1-octene mediated by CGCTiMe(2), the PNB-based catalytic systems exhibit approximately twice the activity of the B(C6F5)3-based systems.