Diverse stereocontrol effects induced by weakly coordinating anions.: Stereospecific olefin polymerization pathways at archetypal Cs- and C1-symmetric metallocenium catalysts using mono- and polynuclear halo-perfluoroarylmetalates as cocatalysts

Counteranion effects on propylene polymerization rates and stereoselectivities are compared using C-s-symmetric Me2C(CP)(Flu)ZrMe2 (1; CP = C(5)H(4)n(5)-cyclopentadienyl; Flu = C13H8,n(5) fluorenyl) and C-1-symmetric Me2Si(OHF)(CpR*)ZrMe2 (2; OHF = C13H16, n(5) -octahydrofluorenyl; CpR* = n(5) -3-(-)menthylcyclopentaclienyl) precatalysts activated with the mononuclear and polynuclear perfluoroarylborate, aluminate, and -gallate cocatalysts/activators B(C6F5)(3) (3), B(O-C6F5C6F4)(3) (4), AI(C6F5)(3) (5), Ph3C+-B(C6F5)(4)(6) Ph(3)C(+)FAI(O-C6F5C6F4)(3)- (7), Ga(C6F5)(3) (8), and recently reported mono- and polymetallic trityl perfluoroarylhalonnetalates Ph3C+FB(C6F5)(3)- (9), Ph3C+FB(O-C6F5C6F4)(3)- (10), (Ph3C+),F [Al(C6F5)(3)]y(x-) (x = 1, y= 1, 11; x= 1, y= 2, 12; x= 2, y= 3,13), Ph3C+(C6F5)(3)AlFAl(O-C6F5C6F4)(3)(-) (14), Ph3C+XAI(C6F5)(3)(-)(X = Cl, 15; X = Br, 16), and Ph3C+F[Ga(C6F5)(3)](2)(-) (17). Temperature, propylene concentration, and solvent polarity dependence are surveyed in polymerizations catalyzed by 1 activated with cocatalysts 3-16 and with a 1:2 ratio of Ph3CCl and 5, and with a 1:2 ratio of Ph3CBr and 5, and by 2 activated with 3, 6, 7, 12, and 14. Remarkable stereocontrol with high activities is observed for 1 + 12 and 1 + 14. Polypropylene samples produced using Ci-symmetric precatalyst 2 are subjected to microstructural analyses using stochastic models describing the relative contributions of enantiofacial misinsertion and backskip processes. A powerful technique is introduced for calculating interparametric correlation matrices for these nonlinear stochastic models. The collected results significantly extend what is known about ion-pairing effects in the case of Cs-symmetric precatalyst 1 and allow these findings to be applied to the case of Ci-symmetric precatalyst 2 as an agent of isospecific propylene polymerization.