The solution structures of the metallocenium homogeneous polymerization catalyst ion-pairs [Cp(2)ZrMe](+)[MeB(C(6)F(5))(3)](-) (1), [(1,2-Me(2)Cp)(2)ZrMe](+)[MeB(C(6)F(5))(3)](-) (2), [(Me(2)SiCp(2))ZrMe](+)[MeB(C(6)F(5))(3)](-) (3), [Me(2)C(Fluorenyl)(Cp)ZrMe](+)[FPBA](-) (FPBA = tris(2,2',2' '-nonafluorobiphenyl)fluoroaluminate) (4), [rac-Et(Indenyl)(2)ZrMe](+)[FPBA](-) (5), [(Me(5)Cp)(2)ThMe](+)[B(C(6)F(5))(4)](-) (6), [(Me(2)SiCp(2))Zr(Me)(THF)](+)[MeB(C(6)F(5))(3)](-) (7), [(Me(2)SiCp(2))Zr(Me)(PPh(3))](+)[MeB(C(6)F(5))(3)](-) (8), [(Me(2)SiCp(2))Zr(Me)(THF)](+)[B(C(6)F(5))(4)](-) (9), [(Me(2)Si(Me(4)Cp)(t-BuN)Zr(Me)(solvent)](+)[B(C(6)F(5))(4)](-) (solvent = benzene, toluene) (10), [(Cp(2)ZrMe)(2)(mu-Me)](+)[MePBB](-) (PBB = tris(2,2',2"-nonafluorobiphenyl)borane) (11), and [(Cp(2)Zr)(2)(mu-CH(2))(mu-Me)](+)[MePBB](-) (12), having the counteranion in the inner (1, 3, 4, 5, and 6) or outer (7, 8, 9, 10, 11, and 12) coordination sphere, have been investigated for the first time in solvents with low relative permittivity such as benzene or toluene by (1)H NOESY and (1)H,(19)F HOESY NMR spectroscopy. It is found that the average interionic solution structures of the inner sphere contact ion-pairs are similar to those in the solid state with the anion B-Me (1, 3) or Al-F (5) vectors oriented toward the free zirconium coordination site. The HOESY spectrum of complex 6 is in agreement with the reported solid-state structure. In contrast, in outer sphere contact ion-pairs 7, 8, 9, and 10, the anion is located far from the Zr-Me(+) moiety and much nearer to the Me(2)Si bridge than in 3. The interionic structure of 8 is concentration-dependent, and for concentrations greater than 2 mM, a loss of structural localization is observed. PGSE NMR measurements as a function of concentration (0.1-5.0 mM) indicate that the tendency to form aggregates of nuclearity higher than simple ion-pairs is dependent on whether the anion is in the inner or outer coordination sphere of the metallocenium cation. Complexes 2, 3, 4, 5, and 6 show no evidence of aggregation up to 5 mM (well above concentrations typically used in catalysis) or at the limit of saturated solutions (complexes 3 and 6), while concentration-dependent behavior is observed for complexes 7, 8, 10, and 11. These outer sphere ion-pairs begin to exhibit significant evidence for ion-quadruples in solutions having concentrations greater than 0.5 mM with the tendency to aggregate being a function of metal ligation and anion structure. Above 2 mM, compound 8 exists as higher aggregates that are probably responsible for the loss of interionic structural specificity.

The thermodynamic and structural characteristics of Al(C6F(5)3-derived vs B(C6F5)3-derived group 4 metallocenium ion pairs are quantified. Reaction of 1.0 equiv of B(C6F5)3 or 1.0 or 2.0 equiv of Al(C6F5)3 with rac-C2H4(eta5-Ind)2Zr(CH3)2 (rac-(EBI)Zr(CH3)2) yields rac-(EBI)Zr(CH3)(+)H3CB(C6)F5)(3)(-) (1a), rac-(EBI)Zr(CH3)+H3CAl(C6F5)(3)(-) (1b), and rac-(EBI)Zr2+[H3CAl(C6F5)3](-)(2) (1c), respectively. X-ray crystallographic analysis of 1b indicates the H3CAl(C6F5)(3)(-) anion coordinates to the metal center via a bridging methyl in a manner similar to B(C6F5)3-derived metallocenium ion pairs. However, the Zr-(CH3)(bridging) and Al-(CH3)(bridging) bond lengths of 1b (2.505(4) A and 2.026(4) A, respectively) indicate the methyl group is less completely abstracted in 1b than in typical B(C6F5)3-derived ion pairs. Ion pair formation enthalpies (DeltaH(ipf)) determined by isoperibol solution calorimetry in toluene from the neutral precursors are -21.9(6) kcal mol(-1) (1a), -14.0(15) kcal mol(-1) (1b), and -2.1(1) kcal mol(-1) (1b-->1c), indicating Al(C6F5)3 to have significantly less methide affinity than B(C6F5)3. Analogous experiments with Me2Si(eta5-Me4C5)(t-BuN)Ti(CH3)2 indicate a similar trend. Furthermore, kinetic parameters for ion pair epimerization by cocatalyst exchange (ce) and anion exchange (ae), determined by line-broadening in VT NMR spectra over the range 25-75 degrees C, are DeltaH++(ce) = 22(1) kcal mol(-1), DeltaS++(ce) = 8.2(4) eu, DeltaH++(ae) = 14(2) kcal mol(-1), and DeltaS++(ae) = -15(2) eu for 1a. Line broadening for 1b is not detectable until just below the temperature where decomposition becomes significant ( approximately 75-80 degrees C), but estimation of the activation parameters at 72 degrees C gives DeltaH++(ce) approximately 22 kcal mol(-1)and DeltaH++(ae) approximately 16 kcal mol(-1), consistent with the bridging methide being more strongly bound to the zirconocenium center than in 1a.

Pulsed field gradient spin-echo (PGSE) NMR and cryoscopic measurements have been performed on a series of homogeneous metallocene polymerization catalyst ion-pairs to determine if aggregation is a significant phenomenon under typical polymerization conditions. Cryoscopic measurements on [(Me5Cp)2ZrMe]+[MeB(C6F5)3]- (1), [rac-Et(Indenyl)2ZrMe]+[MeB(C6F5)3]- (2), [(1,2-Me2Cp)2ZrCHTMS2]+[MeB(C6F5)3]- (3), [Me2Si(Me4Cp)(t-BuN)TiMe]+[MeB(C6F5)3]- (4), [Me2Si(Me4Cp)(t-BuN)ZrMe]+[MeB(C6F5)3]- (5), and [Me2C(Fluorenyl)(Cp)ZrMe]+[MeB(C6F5)3]- (6) were carried out in benzene in the 10-18 millimolal concentration range. PGSE measurements, using (p-tolyl)4Si as an internal standard, were also performed on catalyst ion-pairs 1, 4, 6, [(Me5Cp)2ThMe]+[B(C6F5)4]- (7), [(Me2SiCp2)ZrMe]+[MeB(C6F5)3]- (8), and [Cp2ZrMe]+[MeB(C6F5)3]- (9) in the 0.8-10.0 millimolar range. All results are consistent with a 1:1 ion-pair structural model and show little evidence for ion-quadruples or higher-order aggregates.

A series of mononuclear and polynuclear trityl (perfluoroaryl)borate, -aluminate, and -gallate reagents, potential cocatalysts/activators for metallocene-mediated olefin polymerization, have been synthesized via fluoride abstraction from trityl fluoride (Ph3CF) by the organo Lewis acid reagents B(C6F5)3 (1), B(o-C6F5C6F4)3 (2), and Al(C6F5)3 (3), by derivatization of Ph3C+FAl(o-C6F5C6F4)3 - (4), and by reaction of trityl fluoride with in situ generated Ga(C6F5)3 (5). Reaction of trityl fluoride with the tris(perfluoroaryl)boranes 1 and 2 yields the trityl tris(perfluoroaryl)fluoroborates Ph3C+FB(C6F5)3 - (6) and Ph3C+FB(o-C6F5C6F4)3 - (7), respectively. The three trityl tris(perfluorophenyl)fluoroaluminates (Ph3C+) x F x [Al(C6F5)3] y x - (x = 1, y = 1, 8; x = 1, y = 2, 9; x = 2, y = 3, 10) can be isolated from the reaction of trityl fluoride with the tris(perfluoroaryl)alane 3 in the appropriate molar ratios. Reaction of the trityl tris(perfluoroaryl)fluoroaluminate 4 with 3 affords the asymmetric fluoro-bridged trityl bis[tris(perfluoroaryl)]aluminate Ph3C+(C6F5)3AlFAl(o-C6F5C6F4)3 - (11), while reaction of the trityl halides Ph3CCl and Ph3CBr with 3 gives the corresponding trityl tris(perfluorophenyl)haloaluminates Ph3C+XAl(C6F5)3 - (X = Cl, 12; X = Br, 13). The isolable, symmetric fluoro-bridged trityl bis[tris(perfluoroaryl)]gallate Ph3C+F[Ga(C6F5)3]2 - (14) is derived from a “one-pot” reaction of trityl fluoride with Ga(C6F5)3, generated in situ from 4 + Ga(CH3)3. Of these new species, compounds 7 and 10−14 were characterized by single-crystal X-ray diffraction. Trityl salts 6−13 react with the C s-symmetric metallocene precatalyst Me2C(Cp)(Flu)ZrMe2 (15:  Cp = C5H4; Flu = C13H8, fluorenyl) to form isolable ion-pair complexes or characterizable mixtures. Species 6 reacts with 15 to generate the known ion pair Me2C(Cp)(Flu)ZrMe+MeB(C6F5)3 - (16), and reaction of 7 with 15 gives the fluoro-bridged dimeric diastereomers [Me2C(Cp)(Flu)ZrMe]2(μ-F)+FB(o-C6F5C6F4)3 - (17). The trityl tris(perfluorophenyl)fluoroaluminates 8−10 all react with 15 to afford mixtures of Me2C(Cp)(Flu)ZrMe+FAl(C6F5)3 - (18) and diastereomeric [Me2C(Cp)(Flu)ZrMe]2(μ-Me)+(C6F5)3AlFAl(C6F5)3 - (19). Asymmetric species 11 cleanly affords the diastereomeric [Me2C(Cp)(Flu)ZrMe]2(μ-Me)+(C6F5)3AlFAl(o-C6F5C6F4)3 - (20) in reaction with the metallocene 15. Adducts of 12 and 13 with the metallocene 15 afford the decomposition products Me2C(Cp)(Flu)ZrCl(C6F5) (21) and [Me2C(Cp)(Flu)Zr(μ2-Br)]2 2+[Al(C6F5)4 -]2 (22), respectively. Complexes 17−22 were characterized by single-crystal X-ray diffraction.