Diverse Stereocontrol Effects Induced by Weakly Coordinating Anions. Stereospecific Olefin Polymerization Pathways at Archetypal C_s- and C_1- Symmetric Metallocenium Catalysts Using Mono- and Polynuclear Halo-perfluoroarylmetalates as Cocatalysts

摘要

Counteranion effects on propylene polymerization rates and stereoselectivities are compared using C_s-symmetric Me_2C(Cp)(Flu)ZrMe_2 (1; Cp = C_5H_4, η~5-cyclopentadienyl; Flu = C_(13)H_8, η~5-fluorenyl) and C_1-symmetric Me_2Si(OHF)(CpR~*)ZrMe_2 (2; OHF = C_(13)H_(16), η~5-octahydrofluorenyl; CpR~* = η~5-3-(-)-menthylcyclopentadienyl) precatalysts activated with the mononuclear and polynuclear perfluoroarylborate, -aluminate, and -gallate cocatalysts/activators B(C_6F_5)_3 (3), B(o-C_6F_5C_6F_4)_3 (4), AI(C_6F_5)_3 (5), Ph_3C~+B(C_6F_5)_4~-(6) Ph_3C~+FAI(o-C_6F_5C_6F_4)_3~- (7), Ga(C_6F_5)_3 (8), and recently reported mono- and polymetallic trityl perfluoroarylhalometalates Ph_3C~+FB(C_6F_5)_3~- (9), Ph_3C~+FB(o-C_6F_5C_6F_4)_3~- (10), (Ph_3C~+)_xF_x[Al(C_6F_5)_3]_y~(x-) (x = 1, y= 1,11; x= 1, y= 2,12; x= 2, y= 3,13), Ph_3C~+(C_6F_5AlFAl(o-C_6F_5C_6F_4)_3~- (14), Ph_3C~+XAl(C_6F_5)_3~-(X = Cl, 15; X = Br, 16), and Ph_3C~+F[Ga(C_6F_5)_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 Ph_3CCI and 5, and with a 1:2 ratio of Ph_3CBr 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 C_1-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 C_s-symmetric precatalyst 1 and allow these findings to be applied to the case of C_1-symmetric precatalyst 2 as an agent of isospecific propylene polymerization.