(Butadiene)metallocene/B(C6F5)3 Pathway to Catalyst Systems for Stereoselective Methyl Methacrylate Polymerization: Evidence for an Anion Dependent Metallocene Catalyzed Polymerization Process

Article abstract of DOI:10.1021/ja035739y

The ansa-zirconocene dichlorides [Me₂Si(C₅H ₄)(3-R-C₅H₃)]ZrCl₂ 7a-e (R = H, CH₃, cyclohexyl, -CHMe₂, -CMe₃) were reacted with butadiene-magnesium to yield the respective (η ⁴-butadiene)metallocenes 17a-e. The chiral examples give a mixture of two s-cis and two s-trans diastereomers. The strong Lewis acid B(C ₆F₅)₃ adds selectively to a terminal butadiene carbon atom to yield the (butadiene)metallocene/B(C₆F ₅)₃ betaine complexes 18a-e. Initially, the formation of the Z-18 isomers is preferred. These consecutively rearrange to the thermodynamically favored isomers E-18. The dipolar systems 18 are active single component metallocene catalysts for the stereospecific polymerization of methyl methacrylate. With increasing steric bulk of the attached single alkyl substituent an increasingly isotactic poly(methyl methacrylate) is obtained. A similar trend is observed in the methyl methacrylate polymerization at the [Me₂Si(C₅H₄)(3-R-C₅H ₃)]ZrCH₃⁺ catalysts (9a-e) that were conventionally prepared by methyl abstraction from the corresponding ansa-zirconocene dimethyl complexes by treatment with B(C₆F ₅)₃. A comparison of the poly(methyl methacrylates) obtained at these two series of catalysts has revealed substantial differences in stereoselectivity that probably originate from an influence of the respective counteranions. An initial reactive intermediate of methyl methacrylate addition to the dipolar single component metallocene catalyst E-18a was experimentally observed and characterized by NMR spectroscopy at 253 K. The subsequently formed series of [PMMA-C₄H₆-B(C ₆F₅)₃]^- anion oligomers (at the catalyst 18c) was monitored (after quenching) and characterized by electrospray mass spectrometry.

Full text of DOI:10.1021/ja035739y

Published on Web 01/31/2004
(Butadiene)metallocene/B(C6F5)3 Pathway to Catalyst Systems
for Stereoselective Methyl Methacrylate Polymerization:
Evidence for an Anion Dependent Metallocene Catalyzed
Polymerization Process
Joachim W. Strauch, Jean-Luc Faure´, Ste´phane Bredeau, Cun Wang, Gerald Kehr,
Roland Fro¨hlich, Heinrich Luftmann, and Gerhard Erker*
Contribution from the Organisch-Chemisches Institut der UniVersita¨t Mu¨nster,
Corrensstrasse 40, D-48149 Mu¨nster, Germany
Received April 22, 2003; E-mail: erker@uni-muenster.de
Abstract: The ansa-zirconocene dichlorides [Me2Si(C5H4)(3-R-C5H3)]ZrCl2 7a-e (R ) H, CH3, cyclohexyl,
-CHMe2, -CMe3) were reacted with butadiene-magnesium to yield the respective (η4-butadiene)-
metallocenes 17a-e. The chiral examples give a mixture of two s-cis and two s-trans diastereomers. The
strong Lewis acid B(C6F5)3 adds selectively to a terminal butadiene carbon atom to yield the (butadiene)-
metallocene/B(C6F5)3 betaine complexes 18a-e. Initially, the formation of the Z-18 isomers is preferred.
These consecutively rearrange to the thermodynamically favored isomers E-18. The dipolar systems 18
are active single component metallocene catalysts for the stereospecific polymerization of methyl
methacrylate. With increasing steric bulk of the attached single alkyl substituent an increasingly isotactic
poly(methyl methacrylate) is obtained. A similar trend is observed in the methyl methacrylate polymerization
+
at the [Me2Si(C5H4)(3-R-C5H3)]ZrCH3 catalysts (9a-e) that were conventionally prepared by methyl
abstraction from the corresponding ansa-zirconocene dimethyl complexes by treatment with B(C6F5)3. A
comparison of the poly(methyl methacrylates) obtained at these two series of catalysts has revealed
substantial differences in stereoselectivity that probably originate from an influence of the respective
counteranions. An initial reactive intermediate of methyl methacrylate addition to the dipolar single component
metallocene catalyst E-18a was experimentally observed and characterized by NMR spectroscopy at 253
K. The subsequently formed series of [PMMA-C4H6-B(C6F5)3]- anion oligomers (at the catalyst 18c) was
monitored (after quenching) and characterized by electrospray mass spectrometry.
Introduction
related catalytic carbon-carbon coupling processes, it seems
likely that some of the more resistant problems will see
The advent of the group 4 metallocene catalysts has marked
the beginning of a remarkable advancement in ethylene and
R-olefin polymerization.1 Gaining detailed insight into their
functioning and the specific mechanistic features that govern
the remarkable reactivity/selectivity patterns of this and related
classes of catalysts has greatly contributed to the ongoing
development of the field.2-4 In view of the rapid progress that
can be followed in metal-catalyzed olefin polymerization and
interesting solutions appear in due time. One such area is the
involvement of functionalized alkenes in the polymerization
process.5 Yasuda et al.6,7 showed that metallocenes can play an
important role in the rapid and selective carbon-carbon coupling
of olefins bearing electron-withdrawing substituents. They
demonstrated that (Cp*2SmH)2 catalyzes the isospecific polym-
erization of methyl methacrylate. A reaction mechanism was
proposed that involved hydride addition to the â-position of
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10.1021/ja035739y CCC: $27.50 © 2004 American Chemical Society
J. AM. CHEM. SOC. 2004, 126, 2089-2104
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A R T I C L E S
Strauch et al.
Scheme 1
Scheme 2
the R,â-unsaturated carbonyl compound followed by enolate
addition to the coordinated monomer. The chain growth would
then take place by a series of repetitive enolate Michael additions
via an eight-membered transition state8 at the samarium center.
Collins et al. showed that methyl methacrylate (MMA) is
polymerized using alkylmetallocene cation Ziegler-Natta type
catalysts.9 In a series of papers they convincingly showed that
this polymerization reaction is taking place by a group transfer
type process that involves the active participation of a pair of
metallocene moieties.10 Isotactic poly(methyl methacrylate)
(PMMA) is formed at Brintzinger’s ansa-zirconocene [(ethyl-
ene)bis-indenyl]ZrCH3+, but the catalytic procedure developed
by Soga et al.11 requires the use of a large excess of a dialkylzinc
(ca. 1000 equiv was used).
Recently, independent studies by Ho¨cker et al.12-14 and
Gibson et al.15 have shown that chiral catalysts derived from
Green’s ansa-metallocene (1),16 which exhibit C1 molecular
symmetry, can effectively be used for making isotactic PMMA,
provided that a suitable activation procedure was used17 (see
Scheme 1).
ylzirconocene/B(C6F5)3 route.17,19 This was complemented by
preparing the corresponding butadiene complexes and adding
B(C6F5)3 to them.20 This led to active homogeneous single-
component catalysts, which produced isotactic PMMA under
suitable conditions. However, the obtained PMMA samples from
both series of catalysts, using the same backbone variations,
exhibited remarkable differences in detail. This may indicate
an active involvement of the respective anion in the isospecific
PMMA formation at these types of homogeneous metallocene
catalyst systems, which shall be discussed on the basis of the
experimental evidence presented in this article.
Results and Discussion
Preparation of the Catalyst Systems. The synthesis of the
dimethylsilanediyl bridged ansa-metallocenes was carried out
along the synthetic pathway described in the literature18,21 for
the corresponding dichlorozirconocenes. Dimethyldichlorosilane
was treated with one molar equivalent of the respective
[(C5H4R)Li] reagent to yield the silane derivatives 4. These were
isolated and then treated subsequently with 1 equiv of lithium
cyclopentadienide to yield 5 (as a mixture of isomers). This
order of the nucleophilic substitution reactions prevented the
formation of the unsubstituted [C5H4-SiMe2-C5H4] as a minor
side product and resulted in a clean product formation in good
yield. Deprotonation of both cyclopentadienyl ring systems in
5 was effected by treatment with n-butyllithium in ether at low
temperature. The resulting dilithiobis(cyclopentadienide) re-
agents 6 were isolated in good yield as air- and moisture-
sensitive compounds and adequately characterized (for details
see the Supporting Information). Transmetalation to zirconium
was carried out by treatment of 6 with [ZrCl4(thf)2] in toluene
(-78 °C to room temperature). The ansa-zirconocene dichloride
complexes 7a-e (see Scheme 2) were each isolated in ca. 60%
yield. They were then each treated with two molar equivalents
of methyllithium to yield the corresponding dimethyl ansa-
zirconocenes 8a-e.
A variety of alkyl-substituted dimethylsilanediyl bridged
homogeneous ansa-metallocene catalysts had previously been
used in stereoselective propene polymerization.18 We have taken
up this work and prepared a series of such complexes bearing
alkyl groups of increasing steric bulk at one of their ansa
connected Cp rings and used them for stereoselective MMA
polymerization after suitable catalyst activation. A series of
catalysts was activated by means of the conventional dimeth-
(8) Sustmann, R.; Sicking, W.; Bandermann, F.; Ferenz, M. Macromolecules
1999, 32, 4204-4213.
(9) Collins, S.; Ward, D. G. J. Am. Chem. Soc. 1992, 114, 5460-5462. Collins,
S.; Ward, D. G.; Suddaby, K. H. Macromolecules 1994, 27, 7222-7224.
Li, Y.; Ward, D. G.; Reddy, S. S.; Collins, S. Macromolecules 1997, 30,
1875-1883.
(10) Nguyen, H.; Jarvis, A. P.; Lesley, M. J. G.; Kelly, W. M.; Reddy, S. S.;
Taylor, N. J.; Collins, S. Macromolecules 2000, 33, 1508-1510.
(11) Soga, K.; Deng, H.; Yano, T., Shiono, T. Macromolecules 1994, 27, 7938-
7940. Deng, D.; Shiono, T.; Soga, K. Macromolecules 1995, 28, 3067-
3073. Deng, H.; Shiono, T.; Soga, K. Macromol. Chem. Phys. 1995, 196,
1971-1980. Deng, H.; Soga, K. Macromolecules 1996, 29, 1847-1848.
Shiono, T.; Saito, T.; Saegusa, N.; Hagihara, H.; Ikeda, T.; Deng, H.; Soga,
K. Macromol. Chem. Phys. 1998, 199, 1573-1579. Karanikolopoulos, G.;
Batis, Ch.; Pitsikalis, M.; Hadjichristidis, N. Macromolecules 2001, 34,
4697-4705.
(12) Frauenrath, H.; Keul, H.; Ho¨cker, H. Macromolecules 2001, 34, 14-19.
(13) Stuhldreier, T.; Keul, H.; Ho¨cker, H. Macromol. Rapid. Commun. 2000,
21, 1093-1098. Bandermann, F.; Ferenz, M.; Sustmann, R.; Sicking, W.
Macromol. Symp. 2000, 161, 127-134. Stuhldreier, T.; Keul, H.; Ho¨cker,
H.; Englert, U. Organometallics 2000, 19, 5231-5234.
(14) See also: Bolig, A. D.; Chen, E. Y.-X. J. Am. Chem. Soc. 2001, 123, 7943-
7944. Bolig, A. D.; Chen, E. Y.-X. J. Am. Chem. Soc. 2002, 124, 5612-
5613.
As expected, the chiral ansa-zirconocene dimethyl complex
8e (R ) tert-butyl) shows four separate methine 1H NMR signals
(at δ 6.74, 6.56, 5.58, 5.36; corresponding 13C NMR signals at
δ 122.2, 119.6, 114.4, 110.4) and three 1H NMR resonances of
the CH groups of the tert-butyl substituted Cp ring (at δ 6.67,
(15) Cameron, P. A.; Gibson, V. C.; Graham, A. J. Macromolecules 2000, 33,
4329-4334.
(16) Green, M. L. H.; Ishihara, N. J. Chem. Soc., Dalton Trans. 1994, 657-
(19) Massey, A. G.; Park, A. J.; Stone, F. G. A. Proc. Chem. Soc. 1963, 212.
Massey, A. G.; Park, A. J. J. Organomet. Chem. 1964, 2, 245-250.
Pohlmann, J. L.; Brinckmann, F. E. Z. Naturforsch. 1965, 20b, 5-11.
Massey, A. G.; Park, A. J. In Organometallic Syntheses; King, R. B., Eisch,
J. J., Eds.; Elsevier: New York, 1986; Vol. 3, pp 461-462.
(20) Temme, B.; Erker, G.; Karl, J.; Luftmann, H.; Fro¨hlich, R.; Kotila, S. Angew.
Chem. 1995, 107, 1867-1869; Angew. Chem., Int. Ed. Engl. 1995, 34,
1755-1757.
665.
(17) Bochmann, M.; Jaggar, A. J.; Nicholls, J. C. Angew. Chem. 1990, 102,
830-832; Angew. Chem., Int. Ed. Engl. 1990, 29, 780-782. Yang, X.;
Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1991, 113, 3623-3625. Chien,
J. C. W.; Tsai, W.-M.; Rausch, M. D. J. Am. Chem. Soc. 1991, 113, 8570-
8571.
(18) Mise, T.; Miya, S.; Yamazaki, H. Chem. Lett. 1989, 1853-1856. Antin˜olo,
A.; Lo´pez-Solera, I.; Otero, A.; Prashar, S.; Rodr´ıguez, A. M.; Villasen˜or,
E. Organometallics 2002, 21, 2460-2467.
(21) Schumann, H.; Glanz, M.; Rosenthal, E. C. E.; Hemling, H. Z. Anorg. Allg.
Chem. 1996, 622, 1865-1870.
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Metallocene Catalyzed Polymerization
A R T I C L E S
5.62, 5.32; 13C: 120.1, 111.9, 110.2). Complex 8e exhibits the
NMR signals of a pair of diastereotopic methyl groups at
zirconium (1H: δ 0.01, 0.00; 13C: δ 31.6, 28.2) in addition to
the tert-butyl NMR features [1H: δ 1.37; 13C: δ 33.4 (C(CH3)3),
31.3 (CH3)].
The two ansa-zirconocene dichlorides bearing the most bulky
substituents, the isopropyl and tert-butyl substituted systems 7d
and 7e, were characterized by X-ray diffraction. Single crystals
of 7d were obtained from toluene. The structure of 7d shows
the typical strained geometry of a silanediyl bridged ansa-
metallocene. The connection of the Cp rings by the SiMe2 group
(Si-C1 1.870(3) Å, Si-C6 1.867(3) Å) results in some
characteristic distortions of the complex framework. Conse-
quently, the Zr-C(ipso-Cp) bonds are rather short at 2.470(2)
Å (Zr-C6) and 2.484(2) Å (Zr-C1), whereas the distance
between the metal and the Cp carbon that bears the isopropyl
substituent is the longest Zr-C(Cp) bond found at d(Zr-C9):
2.592(2) Å. The bulky isopropyl group at C9 is effectively
shielding the Zr-Cl2 vector (dihedral angle θ Cl2-Zr‚‚‚C9-
C11 -19.9(2)°). In 7d the Zr-Cl1 (2.436(1) Å) and Zr-Cl2
(2.433(1) Å) bond lengths are in the typical range (angle Cl1-
Zr-Cl2 98.28(3)°).22 The endocyclic and exocyclic angles at
the bridging silicon atom are very different from each other
(C1-Si-C6 94.3(1)°, C14-Si-C15 114.8(1)°). The Cp-
(centroid)-Zr-Cp(centroid) angle in 7d amounts to 126.3°.
The tert-butyl substituted complex 7e was crystallized from
pentane. In the crystal we find a 72:28 mixture of the two
enantiomers. The Cp(centroid)-Zr-Cp(centroid) angles are
similar for both the major isomer (126.2°) and the minor isomer
(125.1°). The representative data of the major enantiomer will
be discussed. The overall structure is similar to that of 7d (see
above); however, the more bulky tert-butyl group seems to
further distort the ansa-metallocene framework. This is most
apparent for the Zr-C(Cp) distances. Again, the range of
observed Zr-C(Cp) bond lengths is rather large with Zr-C1
being the shortest at 2.449(19) Å. The longest Zr-C(Cp) bond
is between the metal center and carbon atom C9 (2.633(10) Å),
which bears the bulky tert-butyl group. It is ca. 0.04 Å longer
than the respective bond in 7d. The remaining structural features
of 7e are similar to those of 7d (see Figure 2). The tert-butyl
group in 7e is oriented such that it very effectively shields the
Zr-Cl2vectorfromtheoutside(θCl2-Zr‚‚‚C9-C11-25.5(15)°).
The structure of the isopropylidene bridged (Cp/indenyl)-
zirconium dimethyl complex 2 was characterized by X-ray
diffraction for comparison. Despite the presence of shorter
bridging bonds, some essential structural features of 2 closely
resemble those of 7e. Again the Zr-C(ipso-Cp) bonds at the
bridge are short (Zr-C19 2.456(2) Å, Zr-C23 2.463(3) Å).
The Zr-C13 bond length (2.642(2) Å) marks the top end of
the Zr-C(Cp) range in 2. Its position is equivalent to that of
the substituent-bearing C(Cp) atom in 7e, and these specific
Zr-C(Cp) bond lengths of the molecules 2 and 7e are almost
identical. The remaining structural features of complex 2 are
as expected (see Figure 3).
Figure 1. Molecular geometry of complex 7d. Selected bond lengths
(angstroms) and angles (deg): Zr-Cl1 2.436(1), Zr-Cl2 2.433(1), Zr-C1
2.484(2), Zr-C2 2.488(3), Zr-C3 2.556(3), Zr-C4 2.551(3), Zr-C5
2.472(2), Zr-C6 2.470(2), Zr-C7 2.467(2), Zr-C8 2.562(3), Zr-C9
2.592(2), Zr-C10 2.485(2), Si1-C1 1.870(3), Si1-C6 1.867(3), Si1-C14
1.849(3), Si1-C15 1.852(3), C9-C11 1.511(3), C11-C12 1.520(5), C11-
C13 1.519(4); Cl1-Zr-Cl2 98.28(3), C1-Si1-C6 94.3(1), C1-Si1-C14
113.4(1), C1-Si1-C15 110.6(1), C6-Si1-C14 110.8(1), C6-Si1-C15
111.3(1), C14-Si1-C15 114.8(1), C8-C9-C10 106.9(2), C8-C9-C11
127.4(3), C10-C9-C11 125.6(2), C9-C11-C12 112.1(3), C9-C11-C13
109.7(2), C12-C11-C13 111.4(3).
Figure 2. Molecular geometry of complex 7e. Selected bond lengths
(angstroms) and angles (deg) (major isomer): Zr-Cl1 2.424(4), Zr-Cl2
2.432(5), Zr-C1 2.476(11), Zr-C2 2.449(19), Zr-C3 2.534(13), Zr-C4
2.565(13), Zr-C5 2.494(16), Zr-C6 2.462(2), Zr-C7 2.460(11), Zr-C8
2.582(11), Zr-C9 2.633(10), Zr-C10 2.513(10), Si1-C1 1.868(11), Si1-
C6 1.859(12), Si1-C15 1.839(16), Si1-C16 1.851(16), C9-C11 1.533(16),
C11-C12 1.51(2), C11-C13 1.545(18), C11-C14 1.57(2); Cl1-Zr-Cl2
97.5(2), C1-Si1-C6 93.8(5), C1-Si1-C15 111.7(9), C1-Si1-C16
112.7(8), C6-Si1-C15 111.0(7), C6-Si1-C16 111.8(8), C15-Si1-C16
114.2(8), C8-C9-C10 106.5(11), C8-C9-C11 126.6(13), C10-C9-C11
126.2(15), C9-C11-C12 114.2(14), C9-C11-C13 110.2(13), C9-C11-
C14 104.7(12), C12-C11-C13 111.2(15), C12-C11-C14 109.7(13),
C13-C11-C14 106.5(15).
methyl ansa-zirconocene cation products (9a-e) but generated
them in situ for carrying out the methyl methacrylate polym-
erization experiments. For their spectroscopic identification we,
however, generated them in [D6]benzene. In each case we
observed a single set of NMR signals that probably originates
from a pair of ion pairs that rapidly equilibrates under the
conditions of our measurement.23 A typical example is the
isopropyl substituted product 9d that exhibits a total of seven
Cp-type methine 1H NMR resonances [δ 6.43, 6.30, 5.36, 4.82
1
We next activated the complexes 8a-e by removing one
methyl anion equivalent from zirconium by treatment with a
stoichiometric amount of the strong Lewis acid B(C6F5)3.17a,19
For this study we did not actually isolate the corresponding
(C5H4); δ 6.23, 5.38, 4.78 (C5H3)] in addition to the H NMR
(23) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1994, 116, 10015-
10031. Reviews: Kiplinger, J. L.; Richmond, T. G.; Osterberg, C. E. Chem.
ReV. 1994, 94, 373-431. Jia, L.; Yang, X.; Stern, C. L.; Marks, T. J.
Organometallics 1997, 16, 842-857. Beswick, C. L.; Marks, T. J. J. Am.
Chem. Soc. 2000, 122, 10358-10370. Chen, E. Y.-X.; Marks, T. J. Chem.
ReV. 2000, 100, 1391-1434.
(22) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D. G.;
Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1-S83.
9
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A R T I C L E S
Strauch et al.
Scheme 3
Scheme 4
Figure 3. Molecular geometry of complex 2. Selected bond lengths
(angstroms) and angles (deg): Zr-C1 2.263(3), Zr-C2 2.261(3), Zr-C23
2.463(3), Zr-C24 2.474(3), Zr-C25 2.558(3), Zr-C26 2.571(3), Zr-C27
2.494(3), Zr-C19 2.456(2), Zr-C11 2.487(2), Zr-C12 2.583(3), Zr-C13
2.642(2), Zr-C18 2.551(2), C20-C23 1.530(3), C20-C19 1.537(4), C20-
C21 1.536(3), C20-C22 1.536(4); C1-Zr-C2 102.8(1), C23-C20-C19
100.8(2), C23-C20-C21 111.6(2), C23-C20-C22 111.3(2), C19-C20-
C21 114.0(2), C19-C20-C22 111.5(2), C21-C20-C22 107.7(2).
Scheme 5
signals of a pair of methyl groups at silicon (δ 0.02, -0.21)
and a single Zr-CH3 signal of 3 H relative intensity at δ 0.29.
The isopropyl methyl groups are diastereotopic (a pair of
-
doublets at δ 0.90, 0.88). The corresponding [CH3B(C6F5)3
]
anion shows a broad methyl 1H NMR resonance at δ 0.50 (for
further details see the Experimental Section).
We had previously shown that N-pyrrolyl based borate anions
bind slightly stronger to zirconocene cations than the often used
[CH3B(C6F5)3]- system.24 We, therefore, treated the tert-butyl
substituted dimethyl ansa-zirconocene complex 8e with one
molar equivalent of the slightly less electron-deficient Lewis
acid (N-pyrrolyl)B(C6F5)2 (10).24 A methyl anion equivalent was
cleanly transferred from zirconium to boron to yield the product
11e. In this case the ion pair was persistent at room temperature,
giving rise to the observation of two isomers (anti-11e, syn-
11e) by NMR spectroscopy in a ratio of 3:1. The cation moieties
of each isomeric ion pair shows the characteristic set of seven
Cp methine (CH) 1H/13C NMR signals (for values see the
Experimental Section). Due to the chirality of the system and
the persistence of the ion pairs, we observed a set of four
pyrrolyl CH NMR resonances for each of the isomers [major
11e isomer: δ 7.40, 7.32, 5.91, 5.44 (1H), δ 140.3, 136.3, 103.8,
97.5 (13C); minor 11e isomer: δ 7.48, 7.46, 6.03, 5.92 (1H)].
cis-η4-butadiene)metallocene complex 15.27 To this B(C6F5)3
adds selectively to yield a single dipolar betaine complex isomer
(16) whose specific structure had been revealed by an X-ray
crystal structure analysis and confirmed by 1H/13C NMR
spectroscopy in solution (Scheme 4).27
In contrast, the dimethylsilanediyl bridged ansa-zirconocene-
dichloride (7a) forms a ca. 1:1 mixture of the (s-cis- and s-trans-
η4-butadiene)zirconocene (s-cis-17a, s-trans-17a) isomers28
when treated with “butadiene-magnesium”. These complexes
react with B(C6F5)3 (in a 1:1 stoichiometry) to yield a single
cisoid-substituted π-allyl betaine metallocene isomer (Z-18a)
under kinetic control that subsequently rearranges (at room
temperature) to yield the transoid π-allyl betaine metallocene
isomer (E-18a) under equilibrium conditions (see Scheme 5).
The complexes 16 and Z-18 both feature an internal Zr‚‚‚CH2-
ion pair interaction, whereas the systems E-18 are stabilized
by an intramolecular Zr‚‚‚F-C(Ar) coordination.29
A similar product mixture of the related ion pairs anti-13e
and syn-13e (4:1) was formed upon treatment of 8e with the
mild neutral Brønsted acid (2H-pyrrol)B(C6F5)3 (12).25 In this
case, protonation of the [Zr]Me2 unit occurs to liberate 1 equiv
of methane. Again the remaining pyrrolyl moiety at boron
coordinated to zirconium was shown to give a persistent pair
of stereoisomeric ion pairs. Each of these exhibits the charac-
teristic set of two pairs of diastereotopic pyrrolyl methine groups
that are monitored by NMR spectroscopy (see Scheme 3).
(26) Ramsden, H. E. U.S. Patent 3,388,179, 1968. Nakano, Y.; Natsukawa, K.;
Yasuda, H.; Tani, H. Tetrahedron Lett. 1972, 2833-2836. Fujita, K.;
Ohnuma, Y.; Yasuda, H.; Tani, H. J. Organomet. Chem. 1976, 113, 201-
213. Yasuda, H.; Nakano, Y.; Natsukawa, K.; Tani, H. Macromolecules
1978, 11, 586-592. See also: Datta, S.; Wreford, S. S.; Beatty, R. P.;
McNeese, T. J. J. Am. Chem. Soc. 1979, 101, 1053-1054. Wreford, S. S.;
Whitney, J. F. Inorg. Chem. 1981, 20, 3918-3924. Kai, Y.; Kanehisa, N.;
Miki, K.; Kasai, N.; Mashima, K.; Yasuda, H.;Nakamura, A. Chem. Lett.
1982, 1277-1280.
(27) Dahlmann, M.; Erker, G.; Fro¨hlich, R.; Meyer, O. Organometallics 2000,
19, 2956-2967.
(28) Dahlmann, M.; Erker, G.; Fro¨hlich, R.; Meyer, O. Organometallics 1999,
18, 4459-4461.
We had previously shown that the reference system 1 reacts
with the “butadiene-magnesium” reagent (14)26 to yield an (s-
(24) Kehr, G.; Fro¨hlich, R.; Wibbeling, B.; Erker, G. Chem. Eur. J. 2000, 6,
258-266.
(25) Kehr, G.; Roesmann, R.; Fro¨hlich, R.; Holst, C.; Erker, G. Eur. J. Inorg.
Chem. 2001, 535-538.
9
2092 J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004

Metallocene Catalyzed Polymerization
A R T I C L E S
Scheme 6
(17, 17′) could be characterized from the respective isomer
mixtures by their very characteristic 1H/13C NMR features30 (see
Table 2).
Due to the C1 chirality of their ansa-metallocene backbones,
the B(C6F5)3 addition to the (butadiene)metallocene systems
17b-e could in principle give rise to the formation of a total
of eight ansa-zirconocene(butadiene)/B(C6F5)3 betaine complex
diastereoisomers, namely four inequivalent Z-18b-e isomers
and four inequivalent E-18b-e isomers. Fortunately, the systems
have turned out to show a considerable stereoselectivity. It seems
that in each case a single Z-18b-e isomer is formed which we
tentatively assign the structure shown in Scheme 7, in analogy
to the reference system 16 (see Scheme 4) that had been
characterized by X-ray diffraction.27 Under the conditions of
the preparative B(C6F5)3 addition, the kinetic products Z-18b-e
rapidly rearrange to their favored E-18b-e isomers,31 which
are the only products that remain after some time. Again, the
outcome of the rearrangement is quite stereoselective: in the
cases 18c-e we observe only a single isomer to be formed under
thermodynamic control to which we tentatively assign the
structures shown in Scheme 7. Only in the case of the methyl
substituted system 18b do we observe a second isomer (E-18′b)
under equilibrium conditions (E-18b:E-18′b ) 4:1). The transoid
E-18 isomers can readily be identified by their typical set of
Table 1. Ratios of (s-cis- and s-trans-Butadiene) ansa-Metallo-
cene Isomers 17/17′
a
b
compd
R
s-cis/s-trans
s-cis-17/17′
s-trans-17/17′
T (K)
17b
17c
17d
17e
CH3
C6H11
CHMe2
CMe3
95:5
98:2
97:3
99:1
4:1
4:1
3:1
1:1
5:1
c
5:1
c
268
228
248
253
a Ratios determined by 1H NMR integration in [D8]toluene. b Temperature
at which the s-cis-17/17′ ratio was determined. c Not determined.
1
E-π-allyl H NMR coupling constants (E-18a: 3J(1-Hsyn,2-H)
) 9.6 Hz, 3J(1-Hanti,2-H) ) 14.8 Hz, 3J(2-H;3-H) ) 16.2 Hz).
The E-18 and Z-18 complex series has easily been distinguished
The stereochemical situation becomes more complex when
a single alkyl substituent is present at the [Cp-SiMe2-Cp]-
type ligand framework. The reaction of the “butadiene-
magnesium” reagent (14) with the monoalkyl substituted ansa-
metallocene dichlorides (7b-e) now yields a set of four
diastereoisomeric (η4-butadiene)zirconocene complexes, namely
a pair of s-cis isomers and a pair of s-trans isomers (see Scheme
6). In each case all four complexes are actually found under
conditions where the rapid mutual interconversion of the s-cis
isomers is sufficiently slow to allow for their experimental
1
by the characteristically different 4-H/H′ H NMR chemical
shifts: the Z-18 series has the H2C-4 group connected to the
early metal center, which gives rise to a large shifting of the
4-H/H′ resonances to negative δ-values (∆δ between -3 and
-4 ppm relative to the E-18 isomers, see Table 3).
Methyl Methacrylate Polymerization. Polymerization ex-
periments were carried out with both series of cations (respec-
tively their ion pairs), namely the methylzirconocene cation
series 9a-e and the (butadiene)zirconocene/B(C6F5)3 series
18a-e. In addition, we used the previously reported system 3
(see Scheme 1)12,15 and its (butadiene)metallocene/B(C6F5)3
betaine analogue (16)27 as a reference for comparison.
1
observation by H/13C NMR spectroscopy. The attachment of
the alkyl substituent at one of the Cp rings has a profound
influence on the s-cis/s-trans isomer equilibrium state.30 In
contrast to the parent system (7a) the reaction of 7b-e with
“butadiene-magnesium” gave predominately the (s-cis-buta-
diene)zirconocene products (s-cis-17b-e, s-cis-17′b-e) and
only small amounts of their respective s-trans isomers (s-trans-
17b-e, s-trans-17′b-e; see Scheme 6 and Table 1). The (s-
cis-butadiene)zirconocene isomers are rapidly interconverting
on the NMR time scale around ambient temperature. For the
example of the tert-butyl substituted system (s-cis-17e / s-cis-
17′e), the activation barrier of this “ring-flip” isomerization was
The MMA polymerization reactions using the 9a-e catalysts
were carried out at 0 °C in dichloromethane solution. The
polymerization reactions were allowed to proceed for 1 h and
then quenched. The overall catalyst activities were determined
by the amount of monomer that had been converted during this
period of time. The resulting PMMA was isolated. Its stereo-
1
chemical composition was determined by H NMR spectros-
copy.32 The proton NMR spectrum shows an AX system at δ
2.19 and 1.48 (2JHH ) 15 Hz) of the CH2 group of the m diad
of the polymer backbone and a methyl ester resonance at δ 3.56
(3H). The remaining CH3 substituent at the quaternary center
shows a clean triad splitting under the conditions of this NMR
analysis (600 MHz, 298 K, [D]chloroform) and gives rise to
separate signals of the mm (δ 1.17), mr (δ 0.99), and rr (0.79)
triads. The relative intensities of these signals were used to
characterize the degree of isotacticity of the samples.
1
determined by dynamic H NMR spectroscopy following the
coalescence of their tert-butyl resonances (600 MHz, Tcoal
313 K, ∆Gq(Tcoal) ) 14.7 ( 0.3 kcal mol-1). Most of the isomers
)
(29) Karl, J.; Erker, G.; Fro¨hlich, R. J. Organomet. Chem. 1997, 535, 59-62.
Karl, J.; Erker, G.; Fro¨hlich, R.; J. Am. Chem. Soc. 1997, 119, 11165-
11173. Karl, J.; Dahlmann, M.; Erker, G.; Bergander, K. J. Am. Chem.
Soc. 1998, 120, 5643-5652. Dahlmann, M.; Erker, G.; Nissinen, M.;
Fro¨hlich, R. J. Am. Chem. Soc. 1999, 121, 2820-2828.
(30) Erker, G.; Wicher, J.; Engel, K.; Rosenfeldt, F.; Dietrich, W.; Kru¨ger, C.
J. Am. Chem. Soc. 1980, 102, 6344-6346. Erker, G.; Engel, K.; Kru¨ger,
C.; Chiang, A.-P. Chem. Ber. 1982, 115, 3311-3323. Yasuda, H.; Kajihara,
Y.; Mashima, K.; Nagasuna, K.; Lee, K.; Nakamura, A. Organometallics
1982, 1, 388-396. Kai, Y.; Kanehisa, N.; Miki, K.; Kasai, N.; Mashima,
K.; Nagasuna, K.; Yasuda, H.; Nakamura, A. J. Chem. Soc., Chem.
Commun. 1982, 191-192. Reviews: Erker, G.; Kru¨ger, C.; Mu¨ller, G. AdV.
Organomet. Chem. 1985, 24, 1-39. Yasuda, H.; Tatsumi, K.; Nakamura,
A. Acc. Chem. Res. 1985, 18, 120-126.
(31) Hoffmann, E. G.; Kallweit, R.; Schroth, G.; Seevogel, K.; Stempfle, W.;
Wilke, G. J. Organomet. Chem. 1975, 97, 183-202.
(32) Peat, I. R.; Reynolds, W. F. Tetrahedron Lett. 1972, 1359-1362. Ober, C.
K. J. Chem. Educ. 1989, 66, 645-647. McCord, E. F.; Anton, W. L.;
Wilczek, L.; Ittel, S. D.; Nelson, L. T. J.; Raffell, K. D.; Hansen, J. E.;
Berge, C. Macromol. Symp. 1994, 86, 47-64.
9
J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004 2093

A R T I C L E S
Strauch et al.
Table 2. NMR Spectroscopic Characterization of (s-cis- and s-trans-Butadiene) ansa-Zirconocene Isomers 17/17′: 1H/13C NMR Chemical
Shifts of η4-Butadiene Ligand Signalsa
compd
2-H
3-H
1-H
syn
4-H
syn
1-H
anti
4-H
anti
C2
C3
C1
C4
s-cis-17b
4.69
4.71
4.79
4.80
3.36
3.43
3.08, 2.61
3.16, 2.77
3.35
3.22
3.36
3.41
3.37
3.12
-0.76
-0.83
1.30, 1.23
1.33, 1.29
-0.73
-0.77
-0.78
-0.79
1.38, 1.23
1.43, 1.32
-0.72
-0.70
-1.50
-0.88
110.1
112.0
96.5, 95.0
112.3
112.7
49.5
50.6
60.5, 59.8
54.1
51.9
s-cis-17′b
s-trans-17b
s-trans-17′b
s-cis-17c
s-cis-17′c
s-cis-17d
s-cis-17′d
s-trans-17d
s-trans-17′d
s-cis-17e
2.89, 2.35b
2.90, 2.55
4.66
4.76
4.83
4.78
4.83
3.44
3.46
3.40
3.20
-1.45
-0.88
-1.45
-0.91
109.2
111.6
109.8
111.2
112.7
112.1
112.7
112.3
50.1
50.7
50.1
50.6
54.1
52.3
54.0
52.5
4.70
4.66
4.79
2.88, 2.55
3.30, 2.68
4.62
3.16, 2.61
3.24, 2.97
3.42
98.1, 97.9
61.2, 60.8
4.73
5.14
3.27
3.47
-0.86
-0.96
110.1
109.1
112.1
113.4
51.4
50.3
51.6
52.1
s-cis-17′e
4.67
3.25
a In [D8]toluene at the temperature given in Table 1, at 600 MHz (1H), 150.8 MHz (13C). b Relative assignment.
Scheme 7
(9c) to the isopropyl (9d) and tert-butyl substituted system (9d).
Although the latter are slightly less active than the system 3,
used as a reference, they seem to slightly exceed it with regard
to isotactic stereocontrol under the polymerization reaction
conditions that we have here applied. Figure 4 visualizes the
pronounced substituent effect of the catalysts 9 on the resulting
isotactic poly(methyl methacrylates) showing the change in
1
relative intensities of the H NMR triad signals of the angular
methyl substituent at the polymer chain.
The (butadiene)zirconocene/B(C6F5)3 betaine systems36 are
also active catalysts for methyl methacrylate polymerization.
Overall, the (butadiene)zirconocene derived catalysts seem to
be less active. This is hardly noticed with the generally very
active [(isopropylidene)Cp(indenyl)]Zr system, but becomes
very noteworthy with the less active series of the [(dimethyl-
silanediyl)(Cp)(CpR)]Zr systems. The catalysts 18 exhibit only
about half the activities as the more conventional catalyst
systems 9 (see Tables 4 and 5).35 There is a very pronounced
dependence of the stereochemistry of PMMA formation on the
method of catalyst formation. As expected, the unsubstituted
parent (butadiene)-ansa-zirconocene/B(C6F5)3 catalyst (18a)
shows no enantiomorphic site control on PMMA formation. A
partially syndiotactic PMMA has been obtained, which is typical
for this situation. The gradual turnover to isotactic poly(methyl
methacrylate) formation with increasing steric bulk of the alkyl
substituent at the ansa-metallocene backbone is also observed
for the systems 18b-e, but it is much less pronounced than
with their 9b-e analogues (see Tables 4 and 5). In each of the
respective catalyst pairs 18/9 the poly(methyl methacrylates)
derived from the (butadiene)metallocene/B(C6F5)3 betaine cata-
lyst systems show markedly lower isotacticities than those
obtained from the [(methyl)metallocene]+[MeB(C6F5)3]- cata-
lysts. The 1H NMR methyl triad signal sections of the respective
polymers shown in Figure 5 visualize this effect. However, the
(butadiene)metallocene/B(C6F5)5 method does not necessarily
lead to lower stereocontrol in general: the 16 derived PMMA
has turned out to be even slightly more isotactic than the PMMA
obtained at the conventional catalyst system 3 (see Figure 5,
Tables 4 and 5).
The complexes 9 are all rather active methyl methacrylate
polymerization catalysts, as can be seen from the data compiled
in Table 4. However, under the applied conditions they seem
to be slightly less active as compared to the “Gibson/Ho¨cker”
system (3).12,15 Ion pairing23,33 can have a strong adverse
effect: the strongly ion paired24,25 systems 11e and 13e (see
Scheme 3) are inactive under the analogous reaction conditions.
The bulk of the substituent attached at one of the Cp rings of
the systems 9 has a very profound influence on the features of
the polymerization reaction. Most profound (and expected) is
its control over the stereochemistry of the MMA polymerization
process. Polymerization of methyl methacrylate with the un-
substituted catalyst system 9a (R ) H) proceeds to yield a
markedly syndiotactic poly(methyl methacrylate) product, with
the stereochemical outcome probably being dominated by chain
end control.9,11,34 This is already turned over to the isotactic
regime upon attachment of the relatively small CH3 group to a
Cp ring at the catalyst backbone (9b, see Table 4).35 Conse-
quently, the isotacticity of the resulting PMMA is markedly
increased with increasing steric bulk of that single alkyl
substituent at the ligand backbone on going from cyclohexyl
(33) Mayr, H. Angew. Chem. 1990, 102, 1415-1428; Angew. Chem., Int. Ed.
Engl. 1990, 29, 1371-1384. Kochi, J. K.; Bockman, T. M. AdV. Organomet.
Chem. 1991, 33, 51-124. Eisch, J. J.; Caldwell, K. R.; Werner, S.; Kru¨ger,
C. Organometallics 1991, 10, 3417-3419. Luo, L.; Marks, T. J. Top. Catal.
1999, 7, 97-106.
(34) For syndiotactic PMMA formation by other catalytic processes, see, e.g.:
Reetz, M. T.; Knauf, T.; Minet, U.; Bingel, C. Angew. Chem. 1988, 100,
1422-1424; Angew. Chem., Int. Ed. Engl. 1988, 27, 1373-1374. Schlaad,
H.; Schmitt, B.; Mu¨ller, A. H. E. Angew. Chem. 1998, 110, 1497-1500;
Angew. Int. Ed. 1998, 37, 1389-1391. Davis, K. A.; Paik, H.-J.;
Matyjaszewski, K. Macromolecules 1999, 32, 1767-1776. Janeczek, H.;
Jedlinski, Z.; Bosek, I. Macromolecules 1999, 32, 4503-4507. Del Rio,
I.; Van Koten, G.; Lutz, M.; Spek, A. L. Organometallics 2000, 19, 361-
364. Chen, X.-P.; Qiu, K.-Y. J. Chem. Soc., Chem. Commun. 2000, 233-
234. Simon, P. F. W.; Mu¨ller, A. H. E. Macromolecules 2001, 34, 6206-
6213. Yamkimansky, A. V.; Mu¨ller, A. H. E. J. Am. Chem. Soc. 2001,
123, 4932-4937. Matsuo, Y.; Mashima, K.; Tani, K. Angew. Chem. 2001,
113, 986-988; Angew. Chem., Int. Ed. 2001, 40, 960-962. Jin, J.; Chen,
E. Y.-X. Organometallics 2002, 21, 13-15. Dove, A. P.; Gibson, V. C.;
Marshall, E. L.; White, A. J. P.; Williams, D. J. J. Chem. Soc., Chem.
Commun. 2002, 1208-1209; and references cited in these articles. Di
Maggio, R.; Fambri, L.; Cesconi, M.; Vaona, W. Macromolecules 2002,
35, 5342-5344.
(35) For some catalysts it has remained difficult to establish experimental
conditions that gave cleanly reproducible activities, molecular weights, and
dispersities. We assume that this is due to slow hydrolytic decomposition
of the very sensitive (probably living) catalyst systems, especially in the
case of the systems 18. Therefore, a larger compilation of such data,
including some from experiments that could not cleanly be reproduced under
our experimental conditions, is provided with the Supporting Information.
(36) Reviews: Erker, G. Acc. Chem. Res. 2001, 34, 309-317. Erker, G. J. Chem.
Soc., Chem. Commun. 2003, 1469-1476.
9
2094 J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004

Metallocene Catalyzed Polymerization
A R T I C L E S
Table 3. Comparison of 1H/13C NMR Features of the [B]-CH2-C3H4 Moiety of Complexes Z-18(b-e) and E-18(b-e)a
compd/R
1-H
syn
1-H
anti
2-H
3-H
4-H
4-H′
C1
C2
C3
C4b
Z-18b/CH3
E-18b/CH3
2.62
1.61
1.48
2.66
1.67
2.72
1.70
2.54
1.59
0.27
1.33
1.67
0.44
1.59
1.15
1.60
0.95
1.49
5.16
5.91
5.70
5.22
5.77
5.24
5.77
5.08
5.78
4.49
4.69
5.38
5.06
5.48
4.55
5.48
4.54
5.62
-0.43
2.50
2.51
-0.36
2.54
0.30
2.49
-0.39
2.66
-1.83
2.21
2.18
-1.79
2.22
-1.90
2.22
-1.74
2.44
55.0
53.5
51.4
55.2
51.0
55.2
51.3
55.8
51.1
131.4
132.5
129.1
127.2
131.3
128.5
127.1
133.9
132.2
117.9
120.5
114.4
112.3
120.4
110.1
110.5
110.6
124.2
25
27
27
25
27
25
29
24
27
E-18′bc/CH3
Z-18c/C6H11
E-18c/C6H11
Z-18d/CHMe2
E-18d/CHMe2
Z-18e/CMe3
E-18e/CMe3
a
1H (600 MHz) and 13C (150.8 MHz) NMR spectra recorded in [D8]toluene at 258 K (18b and 18e), 268 K (18c) or 298 K (18d). b Broad resonances.
c Second isomer.
Table 4. Selected Features of PMMA Formation with Methyl
Zirconocene Cation Catalysts 9a
(19a) in MMA polymerization at a group 4 metallocene
catalyst36 shows the typical NMR features of a Lewis acid
activated R,â-unsaturated carbonyl compound. A direct com-
parison between free MMA, which was present in stoichiometric
excess in the solution at 253 K (see Figure 7), revealed that the
1H NMR resonances of the coordinated MMA are generally
found at smaller δ values than the free MMA monomer [free/
coordinated MMA: δ 6.00, 5.07/5.29, 5.04 (dCH2), δ 1.70/
1.65 (CH3), δ 3.26/3.11 (OCH3)]. The 13C NMR carbonyl
resonance of 19a appears at δ 178.4, which is shifted by ∆δ )
8 ppm downfield from the corresponding value of the free MMA
molecule in the solution (δ 170.5), which is typical for a strong
group 4 metallocene cation coordination to a carbonyl func-
tionality.39 Likewise, the same effect is observed for the 13C
NMR chemical shift of the MMA Michael position in 19a (δ
131.8) vs δ 126.2 (free MMA). Warming the solution of 19a
above 253 K in the presence of excess methyl methacrylate
eventually results in PMMA formation without the observation
of further intermediates by NMR.
c
d,e
compd
R
convb
mm
mrc
rrc
M d
D
w
9a
9b
9c
9d
9e
3
11e
13e
H
CH3
C6H11
CHMe2
CMe3
f
g
g
42
47
36
37
53
94
0h
16
41
64
87
83
75
24
27
12
8
10
13
60
32
24
5
7
12
124 000
112 000
64 000
30 000
27 000
65 000
1.81
2.17
2.32
1.10
1.19
1.37
0h
a Polymerization reaction carried out in CH2Cl2 at 0 °C, 1 h; in most
cases averaged values from several independent experiments are given.
c
b Percent monomer conversion after 1 h. 1H NMR methyl triad intensities.
d Molecular weights and polydispersities of the PMMA polymers were
obtained by GPC relative to polystyrene standard. e Mw/Mn. f See Scheme
1. g See Scheme 3. h No polymer formation observed during 2 h.
We investigated the MMA polymerization reactions of the
isopropyl-substituted catalyst systems 9d and 18d in more detail.
In each case samples were taken from the polymerization
reaction mixtures at ca. 10 min intervals. After quenching, the
resulting PMMA samples were analyzed. In each series their
stereochemical composition was invariant with time, whereas
the molecular weights of the samples linearly increased with
increasing monomer conversion, which indicated living polym-
erization behavior at these catalyst systems. The low polydis-
persities of the obtained polymer samples (Mw/Mn ≈ 1.10) are
in support of this interpretation. The Mn vs percent conversion
graphs of a pair of representative examples are depicted in
Figure 6. Additional data are provided with the Supporting
Information.
It is possible that we here have observed an initial intermedi-
ate of the polymerization reaction. The carbon-carbon coupling
sequence would then probably be started by addition of the
[C3H4-CH2B(C6F5)3] moiety to the Michael position of the
conjugated carbonyl carbon of 19 to yield the zirconocene
enolate system (20).40 This could then sequentially coordinate
additional MMA to which enolate addition may occur to build
up the PMMA chain at the zirconium center. Eventually a series
of neutral oligomeric long chain zirconium-PMMA-enolate
complexes would be formed, each carrying a terminal [-CH2-
CHdCH-CH2-B(C6F5)3]- anionic moiety (21) (see Scheme
9). Hydrolysis of this mixture would then yield a series of
oligomeric [PMMA-CH2-CHdCH2-CH2-B(C6F5)3]- anions
(22). The formation of these anions is actually obserVed.
Treatment of the (butadiene)metallocene/B(C6F5)3 betaine cata-
lyst 18c (R ) cyclohexyl) with MMA for 20 min at 0 °C
followed by hydrolysis gave a typical oligomeric distribution
of the anions 22 which was analyzed by negative ion electro-
spray mass spectrometry (ES-MS). Under these conditions we
could monitor the appearance of the charged butadiene-
B(C6F5)3 terminated oligomeric products up to a 20-mer (see
Figure 8).36 A similar oligomeric anion mixture was obtained
analogously from MMA coupling at the reference catalyst
system 16. Details are given in the Supporting Information.
The Search for Intermediates
We have tried to get some direct experimental information
about reactive intermediates that might be involved in the
carbon-carbon coupling reaction of MMA at the ansa-zir-
conocene catalysts. For that purpose the (butadiene)zirconocene/
B(C6F5)3 betaine 18a (R ) H) was treated with a ca. 2-fold
excess of methyl methacrylate in [D8]toluene at low temperature
under direct NMR control.36,37 When the temperature was raised
from 195 to 253 K, a clean reaction was monitored. The Zr‚‚
‚F-C(Ar) coordination of 18a was cleaved,38 and 1 equiv of
methyl methacrylate was coordinated to the catalyst center. This
first example of an experimentally observed primary product
(37) For related studies with unfunctionalized alkenes and alkynes, see: Karl,
J.; Erker, G. Chem. Ber. 1997, 130, 1261-1267. Karl, J.; Erker, G. J. Mol.
Catal. A 1998, 128, 85-102.
(38) See, for a comparison: Dahlmann, M.; Fro¨hlich, R.; Erker, G. Eur. J. Inorg.
Chem. 2000, 1789-1793.
(39) Wonnemann, J.; Oberhoff, M.; Erker, G.; Fro¨hlich, R.; Bergander, K. Eur.
J. Inorg. Chem. 1999, 1111-1120.
(40) Spaether, W.; Klass, K.; Erker, G.; Zippel, F.; Fro¨hlich, R. Chem. Eur. J.
1998, 4, 1411-1417.
9
J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004 2095

A R T I C L E S
Strauch et al.
Figure 4. Visualization of the pronounced influence of the alkyl groups at the ligand backbone of the catalyst 9 on the isotacticities of the resulting
1
poly(methyl methacrylates) by the relative intensities of the H NMR methyl triad resonances.
Table 5. Characteristic Features of Polymerization Reactions of
wedge (23 in Scheme 10) might result in a situation where
Methyl Methacrylate with (Butadiene)Zirconocene/B(C6F5)3 Betaine
enolate attack could equally facilely take place from either
enantioface. In contrast to the stereoselective former reaction
pathway, the latter situation would probably result in no specific
stereocontrol by the chiral ansa-metallocenesand thus allow
the chiral chain end to govern the overall reaction outcome.
Which of the two situations is preferred will, however, not be
determined by the relative stabilities of any of the respective
rapidly equilibrating ground states (e.g., 23 / 24 in Scheme
10). The stereochemistry will only be determined by the energy
differences of the respective transition states of product forma-
tion, since this is a typical Curtin-Hammett situation.42 If we
name the equilibrium constant for 23 / 24 as Keq (regardless
of how equilibration is achieved) and the overall rate constants
of the selective/unselective product formation pathways as k1
and k2, then the selective PMMA formation in this typical
Curtin-Hammett situation is described by the rate expression
(1).
Catalysts 18a
c
d
compd
R
convb
mm
mrc
rrc
M d
D
w
18a
18b
18c
18d
18e
16
H
CH3
C6H11
CHMe2
CMe3
e
27
13
22
29
20
90
15
26
33
36
70
83
20
29
28
24
13
10
65
45
39
40
17
7
58 000
44 000
42 000
24 000
24 000
69 000
1.70
1.22
1.14
1.10
1.19
1.18
a In CH2Cl2 solution, 1 h, 0 °C; values given are in most cases averaged
c
from several independent experiments. b Percent conversion. 1H NMR
methyl triad intensities. d Molecular weights and polydispersities of the
PMMA polymers were obtained by GPC relative to polystyrene standard.
e See Scheme 4.
Conclusions
It is striking how different the stereochemical outcomes of
the polymerization reactions of methyl methacrylate at the
[(methyl)zirconocene]+[MeB(C6F5)3]- systems 9/3 and the
(butadiene)zirconocene/B(C6F5)3 betaine catalysts 18/16 are.35
V1 k1
V2 k2
)
Keq
(1)
Where may these pronounced differences come from? From
our observation of the intermediate 19 it is likely that methyl
methacrylate coordination to the chiral catalysts is also an
essential step in the respective sequence of the polymerization
reaction.41 It may be assumed that MMA coordination from the
side of the alkyl substituent creates a situation where the R,â-
unsaturated carbonyl compound is effectively shielded from one
enantioface (e.g., 24 in Scheme 10) which leads to preferential
enolate attack from the other face. Conversely, binding the
MMA molecule to the other lateral side of the bent metallocene
It appears that methyl methacrylate favors coordination from
the side where the stereocontrolling alkyl substituent R is
located, leaving the less sterically encumbered opposite lateral
sector of the metallocene to be occupied by the rather bulky
growing polymer chain. As expected, increasing steric bulk of
the attached alkyl substituent at the catalyst backbone leads to
a more pronounced differentiation of the carbon-carbon bond
(42) Curtin, D. Y. Rec. Chem. Prog. 1954, 15, 111-128. See also: Seeman, J.
I. Chem. ReV. 1983, 83, 83-134.
(41) Ho¨lscher, M.; Keul, H.; Ho¨cker, H. Chem. Eur. J. 2001, 7, 5419-5426.
9
2096 J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004

Metallocene Catalyzed Polymerization
A R T I C L E S
Figure 5. 1H NMR methyl triad signals of the poly(methyl methacrylates) obtained with (butadiene)zirconocene/B(C6F5)3 catalysts 18 [R ) CH3 (18b),
CHMe2 (18d), CMe3 (18e)] and 16.
active species, we must assume that the actual active species
(e.g., 23/24) are in fact also ion pairs and that the anions
involved here exert a pronounced influence on the respective
transition states of the product formation, similar to what has
been discussed for anion dependent R-olefin polymerization at
metallocene catalysts.43-47 Unless the polymerization reactions
of the catalyst systems 9 and 18, respectively, proceed by
(43) Mohammed, M.; Nele, M.; Al-Humydi, A.; Xin, S.; Stapleton, R. A.;
Collins, S. J. Am. Chem. Soc. 2003, 125, 7930-7941. Song, F.; Cannon,
R. D.; Bochmann, M. J. Am. Chem. Soc. 2003, 125, 7641-7653.
(44) Chien, J. C. W.; Wang, B. P. J. Polym. Sci., Part A 1990, 28, 15-38.
Beck, S.; Geyer, A.; Brintzinger, H.-H. J. Chem. Soc., Chem. Commun.
1999, 2477-2478. Beck, S.; Lieber, S.; Schaper, F.; Geyer, A.; Brintzinger,
H.-H. J. Am. Chem. Soc. 2001, 123, 1483-1489. Liu, Z.; Somsook, E.;
White, C. B.; Rosaaen, K. A.; Landis, C. R. J. Am. Chem. Soc. 2001, 123,
11193-11207. Schaper, F.; Geyer, A.; Brintzinger, H. H. Organometallics
2002, 21, 473-483.
(45) For potentially related anion dependent examples, see: Jia, L.; Yang, X.;
Figure 6. Mn vs % monomer conversion plots for MMA polymerization
Stern, C. L.; Marks, T. J. Organometallics 1997, 16, 842-857. Chen, Y.-
at the catalyst systems 9d (4, linear regression r ) 0.992), and 18d (0, r
) 0.998) at 0 °C in dichloromethane (Mn by GPC relative to polystyrene
standard).
X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1997, 119, 2582-2583.
Hagihara, H.; Shiono, T.; Ikeda, T. Macromol. Chem. Phys. 1998, 199,
2439-2444. Beck, S.; Brintzinger, H. H.; Suhm, J.; Mu¨lhaupt, R.
Macromol. Rapid. Commun. 1998, 19, 235-239. Chen, Y.-X. E.; Metz,
M. V.; Li, L.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1998, 120,
6287-6305. Beswick, C.; Marks, T. J. Organometallics 1999, 18, 2410-
2412. Busico, V.; Cipullo, R.; Kretschmer, W. P.; Talarico, G.; Vacatello,
M.; Van Axel Castelli, V. Angew. Chem. 2002, 114, 523-526; Angew.
Chem., Int. Ed. 2002, 41, 505-508. Abramo, G. P.; Li, L.; Marks, T. J. J.
Am. Chem. Soc. 2002, 124, 13966-13967. Volkis, V.; Nelkenbaum, E.;
Lisovskii, A.; Haason, G.; Semiat, R.; Kapon, M.; Botoshansky, M.; Eishen,
Y.; Eisen, M. S. J. Am. Chem. Soc. 2003, 125, 2179-2194 and references
therein.
forming transition states and, thus, to an increased enantiomor-
phic site control, which consequently leads to more isotactic
poly(methyl methacrylates).
So, why do the two different methods of catalyst formation
give rise to such different poly(methyl methacrylates)? It is
obvious that two different types of anions are involved. These
anions ([MeB(C6F5)3]- associated with the systems 9/3 and the
pendent oligomeric [PMMA-C4H6-B(C6F5)3]- anions at the
18/16 type catalysts that are formed during the initial stages of
the living polymerization reactions) probably have quite different
ion pairing properties.23,27 Since the anions cannot kinetically
control the actual polymerization process in the Curtin-
Hammett situation via their reversible equilibration with the
(46) For potentially related olefin concentration dependence effects, see, e.g.:
Busico, V.; Cipullo, R. J. Am. Chem. Soc. 1994, 116, 9329-9330. Resconi,
L.; Fait, A.; Piemontesi, F.; Colonnesi, M.; Rychlicki, H.; Zeigler, R.
Macromolecules 1995, 28, 6667-6676. Busico, V.; Brita, D.; Caporaso,
L.; Cipullo, R.; Vacatello M. Macromolecules 1997, 30, 3971-3977.
Busico, V.; Cipullo, R. J. Organomet. Chem. 1998, 558, 219-222. Song,
W.; Yu, Z.; Chien, J. C. W. J. Organomet. Chem. 1998, 558, 223-226.
Veghini, D.; Henling, L. M.; Burkhardt, T. J.; Bercaw, J. E. J. Am. Chem.
Soc. 1999, 121, 564-573. Kaminsky, W.; Winkelbach, H. Top. Catal. 1999,
7, 61-67. Resconi, L.; Camurati, I.; Sudmeijer, O. Top. Catal. 1999, 7,
145-163.
9
J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004 2097

A R T I C L E S
Strauch et al.
Figure 7. 1H NMR spectrum (600 MHz, 253 K) of a solution of the intermediate 19a obtained from the reaction of 18a with ca. 2-fold amount of methyl
methacrylate in [D8]toluene (the signals of free and coordinated MMA are marked, and [B] indicates the signals of the (butadiene)borate fragment).
Scheme 8
Scheme 9
Figure 8. Negative ion ES-MS of the oligomeric [PMMA-C4H6-
B(C6F5)3-] anion products [m/z ) 567 + n(100)] derived by treatment of
the catalyst 18c with MMA at 0 °C in CH2Cl2, followed by hydrolysis.
Scheme 10
catalyzed polymerization reactions,43,45 similar to what is well
established in the chemistry of reactive organic carbenium ion
different mechanisms,48 their observed anion dependent stereo-
chemical performance may add to the cumulating evidence for
the involvement of different types of ion pairs in metallocene
systems.49
Experimental Section
Reactions with organometallic compounds were carried out under
argon using Schlenk-type glassware or in a glovebox. Solvents were
dried and distilled under argon prior to use. For additional general
(47) Strauss, H.-S. Chem. ReV. 1993, 93, 927-942. For recent examples, see,
e.g.: LaPointe, R. E.; Roof, G. R.; Abboud, K. A.; Klosin, J. J. Am. Chem.
Soc. 2000, 122, 9560-9561. Vagedes, D.; Erker, G.; Fro¨hlich, R. J.
Organomet. Chem. 2002, 641, 148-155.
(48) Jin, J.; Mariott, W. R.; Chen, E. Y.-X. J. Polym. Sci., Part A: Polym.
Chem. 2003, 41, 3132-3142.
(49) Winstein, S.; Clippinger, E.; Fainberg, A. H.; Heck, R.; Robinson, G. C.
J. Am. Chem. Soc. 1956, 78, 328-335. Winstein, S.; Robinson, G. C. J.
Am. Chem. Soc. 1958, 80, 169-181.
9
2098 J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004

Metallocene Catalyzed Polymerization
A R T I C L E S
information including a list of spectrometers used for physical
characterization of the compounds, see ref 29. Lithium cyclopentadi-
enides,50 indenyllithium,51 (cis-2-buten-1,4-diyl)bis(tetrahydrofuran)-
magnesium [“butadiene-magnesium”] (14),26,52 tris(pentafluorophenyl)-
borane,19 bis(pentafluorophenyl)-N-pyrrolylborane (10),24 N-(2H-
pyrrolium)tris(pentafluorophenyl)borate (12),25 (3-alkylcyclopenta-
dienyl)chlorodimethylsilane21,53 (4), (3-alkylcyclopentadienyl)cyclo-
pentadienyldimethylsilane18,54 (5), dilithiobis(alkylcyclopentadienyl)-
dimethylsilane18 (6), [dimethylsilylenbis(cyclopentadienyl)]dichloro-
zirconium (7a),27,54 [dimethylsilylenbis(cyclopentadienyl)]dimethyl-
zirconium55 (8a), {[dimethylsilylenbis(cyclopentadienyl)]methylzirconium}
{methyltris(pentafluorophenyl)borate} (9a),13,43 [dimethylsilylenbis-
(cyclopentadienyl)](butadiene)zirconium (17a),27 [isopropyliden(cyclo-
pentadienyl)(1-indenyl)]dichlorozirconium (1),13,16,56 [isopropyliden-
(cyclopentadienyl)(1-indenyl)]dimethylzirconium (2),13,15 [isopropyliden-
(cyclopentadienyl)(1-indenyl)](butadiene)zirconium (15),27 betaine 16,27
NMR (599.9 MHz, [D6]benzene, 298 K): δ ) 6.87, 6.75, 5.58, 5.35
(each pt, each 1H, C5H4), 6.44, 5.54, 5.06 (each m, each 1H, MeC5H3),
2.21 (s, 3H, C5H3-CH3), 0.14, 0.12 (each s, each 3H, Si(CH3)2). 13C
{1H} NMR (150.8 MHz, [D6]benzene, 298 K): δ ) 138.9 (ipso-C of
MeC5H3), 128.2, 115.5, 114.0 (MeC5H3), 127.9, 127.1, 114.2, 113.0
(C5H4), 107.6 (ipso-C of MeC5H3Si), 107.5 (ipso-C of C5H4Si), 15.5
(C5H3-CH3), -5.6, -6.0 (Si(CH3)2).
(7c): Reaction of 6c (2.96 g, 10.3 mmol) with tetrachlorobis-
(tetrahydrofuran)zirconium (3.88 g, 10.3 mmol) in toluene (80 mL)
gave 2.59 g (58%, light orange solid) of 7c. mp 172 °C. Anal. Calcd
for C13H16SiZrCl2 (362.5): C 50.21, H 5.62; found C 49.33, H 6.02.
1H NMR (599.9 MHz, [D6]benzene, 298 K): δ ) 6.83, 6.81, 5.55,
5.47 (each pt, each 1H, C5H4), 6.69, 5.54, 5.30 (each pt, each 1H,
cyC5H3), 2.99 (m, 1H, CH of cy), 2.32, 1.89, 1.70, 1.67, 1.60, 1.43,
1.38, 1.32, 1.14, 1.06 (each m, each 1H, CH2 of cy), 0.18, 0.11 (each
s, each 3H, Si(CH3)2). 13C {1H} NMR (150.8 MHz, [D6]benzene, 298
K): δ ) 147.8 (ipso-C of cyC5H3), 128.9, 126.5, 114.2, 113.1 (C5H4),
126.6, 113.9, 112.8 (cyC5H3), 107.6 (ipso-C of cyC5H3Si), 107.3 (ipso-C
of C5H4Si), 38.6 (CH of cy), 35.9, 31.8, 26.9, 26.5, 26.4 (CH2 of cy),
-5.5, -6.0 (Si(CH3)2).
27
and betaine 18a were prepared according to procedures reported in
the literature.
X-ray Crystal Structure Determinations. Data sets were collected
with a Nonius KappaCCD diffractomer, equipped with a rotating anode
generator Nonius FR591. Programs used: data collection COLLECT
(Nonius B.V., 1998), data reduction Denzo-SMN (Otwinowski, Z.;
Minor, M. Methods Enzymol. 1997, 276, 307-326), absorption
correction SORTAV (Blessing, R. H. Acta Crystallogr. 1995, A51, 33-
37; Blessing, R. H. J. Appl. Crystallogr. 1997, 30, 421-426), structure
solution SHELXS-97 (Sheldrick, G. M. Acta Crystallogr. 1990, A46,
467-473), structure refinement SHELXL-97 (Sheldrick, G. M. Uni-
versita¨t Go¨ttingen, 1997), graphics DIAMOND (Brandenburg, K.
Universita¨t Bonn, 1997). For further details, see the Supporting
Information.
(7d): Reaction of 6d (1.00 g, 4.13 mmol) with tetrachlorobis-
(tetrahydrofuran)zirconium (1.56 g, 4.13 mmol) in toluene (50 mL)
gave 0.96 g (60%, light brown solid) of 7d. mp 162 °C. Anal. Calcd
for C15H20SiZrCl2 (390.5): C 46.13, H 5.16; found C 46.04, H 5.49.
1H NMR (599.9 MHz, [D6]benzene, 298 K): δ ) 6.83, 6.80, 5.54,
5.45 (each pt, each 1H, C5H4), 6.67, 5.53, 5.29 (each m, each 1H,
iPrC5H3), 3.29 (sept, 1H, 3JHH ) 6.9 Hz, iPr-CH), 1.32, 1.09 (each d,
i
each 3H,3JHH ) 6.9 Hz, Pr-CH3), 0.17, 0.09 (each s, each 3H,
Si(CH3)2). 13C {1H} NMR (150.8 MHz, [D6]benzene, 298 K): δ )
i
148.8 (ipso-C of PrC5H3), 128.8, 126.6, 114.3, 112.9 (C5H4), 126.4,
i
113.9, 113.1 (iPrC5H3), 107.7 (ipso-C of PrC5H3Si), 107.5 (ipso-C of
Generation of [Dimethylsilylen(3-alkylcylopentadienyl)(cyclo-
pentadienyl)]dichlorozirconium (7b-e). General Procedure. Di-
lithio(3-alkylcyclopentadienyl)(cyclopentadienyl)dimethylsilane (6b-
e) and tetrachlorobis(tetrahydrofuran)zirconium were mixed as solids
in a Schlenk flask. The flask was cooled to -78 °C and toluene was
added. The reaction mixture was allowed to warm to room temperature
and stirred overnight. Subsequently the volume of the reaction mixture
was reduced to one-third and stored at -20 °C. The obtained precipitate
was collected and dried in vacuo.
C5H4Si), 29.0 (iPr-CH), 24.8, 21.4 (iPr-CH3), -5.5, -6.0 (Si(CH3)2).
(7e): Reaction of 6e (2.50 g, 9.75 mmol) with tetrachlorobis-
(tetrahydrofuran)zirconium (3.68 g, 9.75 mmol) in toluene (70 mL)
gave 2.54 g (64%, light yellow solid) of 7e. mp 165 °C. Anal. Calcd
for C16H22SiZrCl2 (404.6): C 47.50, H 5.48; found C 47.22, H 5.82.
1H NMR (599.9 MHz, [D6]benzene, 298 K): δ ) 6.84, 6.65, 5.65,
5.45 (each pt, each 1H, C5H4), 6.82, 5.7, 5.54 (each m, each 1H,
tBuC5H3), 1.42 (s, 9H, tBu-CH3), 0.22, 0.09 (each s,each 3H, Si(CH3)2).
13C {1H} NMR (150.8 MHz, [D6]benzene, 298 K): δ ) 150.4 (ipso-C
(7b):27,28 Reaction of 6b (1.00 g, 4.67 mmol) with tetrachlorobis-
(tetrahydrofuran)zirconium (1.76 g, 4.67 mmol) in toluene (150 mL)
gave 1.12 g (66%, colorless solid) of 7b. mp 159 °C. Anal. Calcd for
t
of BuC5H3), 130.9, 124.9, 117.5, 111.4 (C5H4), 129.5, 113.8, 113.7
(tBuC5H3), 107.9 (ipso-C of tBuC5H3Si), 105.7 (ipso-C of C5H4Si), 33.7
(C(CH3)3), 30.9 (tBu-CH3), -4.5, -6.6 (Si(CH3)2).
1
C13H16SiZrCl2 (362.5): C 43.08, H 4.45; found C 42.72, H 4.84. H
Generation of [Dimethylsilylen(3-alkylcylopentadienyl)(cyclo-
pentadienyl)]dimethylzirconium (8b-e). General Procedure. A
solution of methyllithium in ether was added dropwise to a solution of
the dichlorozirconocene complex 7 in toluene or diethyl ether at -78
°C. After 30 min the reaction mixture was allowed to warm to room
temperature and stirred for a further 3 h. Subsequently the reaction
mixture was filtered and the residue was washed twice with 10 mL of
pentane. The product 8 was obtained as a solid after removing the
solvent from the filtrate in vacuo.
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Organometallics 1982, 1, 388-396. Dorf, U.; Engel, K.; Erker, G.
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(8b): Reaction of 7b (0.30 g, 0.83 mmol) in toluene (30 mL) with
methyllithium in ether (1.85 M, 0.89 mL, 1.66 mmol) gave 0.19 g (70%,
light yellow solid) of 8b. Anal. Calcd for C15H22SiZr (321.5): C 56.01,
1
H 6.89; found C 55.75, H 6.80. H NMR (599.9 MHz, [D6]benzene,
298 K): δ ) 6.74, 6.70, 5.49, 5.34 (each pt, each 1H, C5H4), 6.37,
5.39, 5.08 (each m, each 1H, MeC5H3), 2.16 (s, 3H, C5H3-CH3), 0.15,
0.14 (each s, each 3H, Si(CH3)2), -0.08, -0.16 (each s, each 3H,
Zr(CH3)2)). 13C {1H} NMR (150.8 MHz, [D6]benzene, 298 K): δ )
130.1 (ipso-C of MeC5H3), 121.4, 112.9, 112.6 (MeC5H3), 120.4, 120.3,
112.4, 112.0 (C5H4), 100.2 (ipso-C of MeC5H3Si), 100.1 (ipso-C of
C5H4Si), 32.7, 29.0 (Zr(CH3)2), 14.8 (C5H3-CH3), -5.3, -5.5 (Si(CH3)2).
(8c): Reaction of 7c (0.50 g, 1.16 mmol) in diethyl ether (20 mL)
with methyllithium in ether (1.90 M, 1.22 mL, 2.32 mmol) was carried
out as described above. After stirring for 2 h at room temperature the
(56) Stone, K. J.; Little, R. D. J. Org. Chem. 1984, 49, 1849-1853. Gauthier,
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3771-3778.
(57) “So eine Arbeit wird eigentlich nie fertig, Man muss sie fu¨r fertig erkla¨ren,
wenn man nach Zeit und Umsta¨nden das Mo¨glichste getan hat.” Goethe,
J. W. Italienischen Reise. March 16, 1787.
9
J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004 2099

A R T I C L E S
Strauch et al.
1
1
diethyl ether solvent was changed for toluene (20 mL). The reaction
mixture was filtered, the obtained solid was washed with toluene (5
mL) twice, and the solvent from the filtrate was removed in vacuo.
The obtained crude product was stirred in pentane (20 mL) at -78 °C,
collected by filtration, and dried in vacuo to yield 0.30 g (67%, light
brown solid) of 8c. Anal. Calcd for C20H30SiZr (389.8): C 61.63, H
7.76; found C 61.33, H 7.98. 1H NMR (599.9 MHz, [D6]benzene, 298
K): δ ) 6.75, 6.71, 5.45, 5.44 (each pt, each 1H, C5H4), 6.59, 5.38,
5.28 (each pt, each 1H, cyC5H3), 2.71 (m, 1H, CH2 of cy), 2.12, 1.98,
1.72, 1.71, 1.63, 1.47, 1.38, 1.36, 1.31, 1.15 (each m, each 1H, CH2 of
cy), 0.19, 0.14 (each s, each 3H, Si(CH3)2), -0.03, 0.12 (each s, each
3H, Zr(CH3)2). 13C {1H} NMR (150.8 MHz, [D6]benzene, 298 K): δ
) 140.7 (ipso-C of cyC5H3), 121.3, 120.0, 112.8, 111.4 (C5H4), 118.8,
111.6, 110.9 (cyC5H3), 100.3 (ipso-C of cyC5H3Si), 99.7 (ipso-C of
C5H4Si), 38.5 (CH of cy), 36.4, 32.8, 27.0, 26.7, 26.5 (CH2 of cy),
32.1, 28.9 (Zr(CH3)2), -5.1, -5.7 (Si(CH3)2).
(C3, JCH ) 176 Hz), 104.2 (C3′, JCH ) 170 Hz), 100.0 (C1), 42.7
1
(Zr-CH3, JCH ) 123 Hz), 39.3 (C(CH3)2), 25.8 (C(CH3)2-anti), 24.6
(C(CH3)2-syn).
(3′) Minor Isomer: H NMR (599.9 MHz, [D2]dichloromethane,
1
253 K): δ ) 7.62 (m, 2H, 4-H, 7-H), 7.32 (m, 1H, 2-H), 6.81 (m, 1H,
C5H4), 6.73 (pt, 1H, 6-H), 6.48 (pt, 1H, 5-H), 5.87 (m, 1H, C5H4′),
5.80 (m, 2H, 3-H, C5H4′), 5.43 (m, 1H, C5H4′), 2.07 (s, 3H, C(CH3)2-
anti), 1.78 (s, 3H, C(CH3)2-syn), 0.66 (s, 3H, Zr-CH3). 13C {1H} NMR
(150.9 MHz, [D2]dichloromethane, 253 K): δ ) 128.4 (C3a), 126.8
(C6), 125.7, (C5), 124.8, 121.7 (C4, C7), 121.0 (C5H4′), 118.3 (7a),
116.8 (C1′), 114.9 (C3), 113.4 (C5H4′), 112.3 (C2), 108.5 (C5H4′), 104.0
(C5H4′), 99.4 (C1), 44.7 (Zr-CH3), 39.1 (C(CH3)2), 25.9 (C(CH3)2-
anti), 24.8 (C(CH3)2-syn).
In Situ Generation of {[Dimethylsilylen(3-alkylcyclopentadienyl)-
(cyclopentadienyl)]methylzirconium} {Methyltris(pentafluorophen-
yl)borate} (9b-e), {[Dimethylsilylen(3-tert-butylcyclopentadienyl)-
(cyclopentadienyl)]methylzirconium} {Methylbis(pentafluoro)phen-
yl]-N-pyrrolylborate} (anti/syn-11e), and {[Dimethylsilylen(3-tert-
butylcyclopentadienyl)(cyclopentadienyl)]methylzirconium} {Tris-
(pentafluorophenyl)-N-pyrrolylborate} (anti/syn-13e). General Pro-
cedure. Two separate solutions were prepared, one of [dimethylsilylen-
(3-alkylcyclopentadienyl)(cyclopentadienyl)]dimethylzirconium (8b-
d) in [D6]benzene (0.5 mL), and one of the borane in [D6]benzene (0.5
mL). Subsequently the borane solution was added dropwise to the
zirconocene solution. The obtained golden (8) or orange (11, 13)
reaction mixture was directly characterized by NMR experiments.
(9b) was generated by the reaction of 8b (20 mg, 62 µmol) with
tris(pentafluorophenyl)borane (32 mg, 63 µmol). 1H NMR (599.9 MHz,
[D6]benzene, 298 K): δ ) 6.44, 6.25, 5.37, 4.80 (each m, each 1H,
C5H4), 6.00, 5.31, 4.57 (each m, each 1H, MeC5H3), 1.85 (s, 3H, C5H3-
CH3), 0.90 (br s, 3H, (CH3)B(C6F5)3), 0.23 (s, 3H, Zr-CH3), 0.02,
-0.18 (each s, each 3H, Si(CH3)2). 13C {1H} NMR (150.8 MHz, [D6]-
(8d): Reaction of 7d (0.30 g, 0.77 mmol) in toluene (30 mL) with
methyllithium in ether (1.85 M, 0.83 mL, 1.54 mmol) gave 0.20 g (75%,
light yellow solid) of 8d. Anal. Calcd for C17H26SiZr (349.7): C 58.39,
1
H 7.49; found C 58.40, H 7.56. H NMR (599.9 MHz, [D6]benzene,
298 K): δ ) 6.74, 6.70, 5.44, 5.42 (each pt, each 1H, C5H4), 6.57,
5.36, 5.27 (each m, each 1H, iPrC5H3), 3.00 (sept, 1H, 3JHH ) 6.8 Hz,
iPr-CH), 1.28, 1.20 (each d, each 3H, 3JHH ) 6.8 Hz, iPr-CH3), 0.18,
0.12 (each s, each 3H, Si(CH3)2), -0.05, -0.13 (each s, each 3H,
Zr(CH3)2). 13C {1H} NMR (150.8 MHz, [D6]benzene, 298 K): δ )
i
141.7 (ipso-C of PrC5H3), 121.3, 120.0, 112.7, 111.5 (C5H4), 118.6,
i
111.7, 110.8 (iPrC5H3), 100.3 (ipso-C of PrC5H3Si), 99.8 (ipso-C of
C5H4Si), 32.1, 28.8 (Zr(CH3)2), 28.6 (iPr-CH), 25.3, 22.4 (iPr-CH3),
-5.1, -5.7 (Si(CH3)2).
(8e): Reaction of 7e (0.50 g, 1.24 mmol) in diethyl ether (20 mL)
with methyllithium in ether (1.83 M, 1.35 mL, 2.47 mmol) was carried
out as described above. After stirring for 2 h at room temperature the
solvent was changed to toluene (20 mL). The reaction mixture was
filtered, the obtained solid was washed with toluene (5 mL) twice, and
the solvent was removed from the combined filtrates in vacuo. The
obtained crude product was stirred in pentane (20 mL) at -78 °C,
collected by filtration, and dried in vacuo to yield 0.32 g (71%, light
yellow solid) of 8e. Anal. Calcd for C18H28SiZr (363.7): C 59.44, H
7.76; found C 60.10, H 7.65. 1H NMR (599.9 MHz, [D6]benzene, 298
K): δ ) 6.74, 6.56, 5.58, 5.36 (each pt, each 1H, C5H4), 6.67, 5.62,
1
benzene, 298 K): δ ) 149.2 (dm, JCF ) 245 Hz, o-B(C6F5)3), 138.3
1
1
(dm, JCF ) 235 Hz, p-B(C6F5)3), 137.4 (dm, JCF ) 245 Hz,
m-B(C6F5)3), 136.4 (ipso-C of MeC5H3), 128.2 (br, ipso-B(C6F5)3),
124.8, 121.9, 117.6, 111.5 (C5H4), 122.3, 118.2, 112.4 (MeC5H3), 105.1,
104.9 (ipso-C of MeC5H3Si and ipso-C of C5H4Si), 42.1 (Zr-CH3),
14.3 (C5H3-CH3), -5.9, -6.6 (Si(CH3)2). (Me-[B] was not observed).
(9c) was generated by the reaction of 8c (22 mg, 56 µmol) with
tris(pentafluorophenyl)borane (29 mg, 56 µmol). 1H NMR (599.9 MHz,
[D6]benzene, 298 K): δ ) 6.42, 6.34, 5.33, 4.90 (each pt, each 1H,
C5H4), 6.30, 5.40, 4.84 (each pt, each 1H, cy C5H3), 2.45 (m, 1H, CH
of cy), 1.68, 1.66, 1.57, 1.54, 1.48, 1.21, 1.18, 1.13, 0.98, 0.95 (each
m, each 1H, CH2 of cy), 0.54 (br, 3H, (CH3)B(C6F5)3), 0.32 (s, 3H,
Zr-CH3), 0.04, -0.19 (each s, each 3H, Si(CH3)2). 13C {1H} NMR
t
t
5.32 (each pt, each 1H, BuC5H3), 1.37 (s, 1H, Bu-CH3), 0.21, 0.12
(each s, each 3H, Si(CH3)2), 0.01, 0.00 (each s, each 3H, Zr(CH3)2).
13C {1H} NMR (150.8 MHz, [D6]benzene, 298 K): δ ) 145.1 (ipso-C
t
of BuC5H3), 122.2, 119.6, 114.4, 110.4 (C5H4), 120.1, 111.9, 110.2
(tBuC5H3), 100.5 (ipso-C of tBuC5H3Si), 98.6 (ipso-C of C5H4Si), 31.6,
28.2 (Zr(CH3)2), 33.4 (C(CH3)3), 31.3 (tBu-CH3), -4.3, -6.1 (Si(CH3)2).
In Situ Generation of {[Isopropyliden(cyclopentadienyl)-
(1-indenyl)]methylzirconium} {Methyltris(pentafluorophenyl)-
borate} (3). Two separate solutions were prepared, one of [isopropyl-
iden(cyclopentadienyl)(1-indenyl)]dimethylzirconium (2) (16 mg, 46
µmol) in [D2]dichloromethane (0.5 mL), and one of tris(pentafluo-
rophenyl)borane (24 mg, 46 µmol) in [D2]dichloromethane (0.5 mL).
Subsequently the borane solution was added dropwise to the zir-
conocene solution. The obtained reaction mixture was directly char-
acterized by NMR. A 4:1 mixture of the two regioisomeric ion pairs
was obtained.
1
(150.8 MHz, [D6]benzene, 298 K): δ ) 149.4 (dm, JCF ) 235 Hz,
1
1
o-B(C6F5)3), 139.0 (dm, JCF ) 245 Hz, p-B(C6F5)3), 137.9 (dm, JCF
) 245 Hz, m-B(C6F5)3), 146.8 (ipso-C of cyC5H3), 128.6 (ipso-
B(C6F5)3), 124.2, 122.6, 118.0, 110.8 (C5H4), 119.8, 116.4, 111.0
(cyC5H3), 105.3, 104.8 (ipso-C of cyC5H3Si and ipso-C of C5H4Si),
40.8 (Zr-CH3), 38.2 (CH of cy), 36.0, 31.6, 26.5, 26.0, 25.8 (CH2 of
cy), -5.6, -6.9 (Si(CH3)2). (Me-[B] was not observed.)
(9d) was generated by the reaction of 8d (20 mg, 57 µmol) with
tris(pentafluorophenyl)borane (29 mg, 57 µmol). 1H NMR (599.9 MHz,
[D6]benzene, 298 K): δ ) 6.43, 6.30, 5.36, 4.82 (each m, each 1H,
i
C5H4), 6.23, 5.38, 4.78 (each m, each 1H, PrC5H3), 2.66 (sept, 1H,
(3) Major Isomer: 1H NMR (599.9 MHz, [D2]dichloromethane, 253
K): δ ) 7.66 (m, 1H, 4-H), 7.52 (m, 1H, 7-H), 7.47 (m, 1H, 5-H),
7.10 (m, 1H, 6-H), 6.85 (m, 1H, 5′-H), 6.52 (pd, 1H, 3-H), 6.27 (pd,
1H, 2-H), 6.17, 5.81 (each m, each 1H, 3′ and 4′-H), 5.52 (m, 1H,
2′-H), 1.99 (s, 3H, C(CH3)2-syn), 1.89 (s, 3H, C(CH3)2-anti), -0.75 (s,
3H, Zr-CH3). 13C {1H} NMR (150.8 MHz, [D2]dichloromethane, 253
3JHH ) 7.2 Hz, iPr-CH), 0.90, 0.88 (each d, each 3H, 3JHH ) 7.2 Hz,
iPr-CH3), 0.50 (br s, 3H, (CH3)B(C6F5)3), 0.29 (s, 3H, Zr-CH3), 0.02,
-0.21 (each s, each 3H, Si(CH3)2). 13C {1H} NMR (150.8 MHz, [D6]-
1
benzene, 298 K): δ ) 148.7 (dm, JCF ) 240 Hz, o-B(C6F5)3), 148.2
i
1
(ipso-C of PrC5H3), 138.0 (dm, JCF ) 240 Hz, p-B(C6F5)3), 136.4
1
(dm, JCF ) 235 Hz, m-B(C6F5)3), 129.2 (br, ipso-B(C6F5)3), 124.9,
1
1
K): δ ) 129.5 (C3a), 127.5 (C5, JCH ) 163 Hz), 127.0 (C6, JCH
)
122.2, 117.6, 112.2 (C5H4), 119.3, 115.9, 111.4 (iPrC5H3), 105.3, 105.1
(ipso-C of iPrC5H3Si and ipso-C of C5H4Si), 42.1 (Zr-CH3), 28.5 (iPr-
CH), 24.8, 20.5 (iPr-CH3) -5.8, -6.8 (Si(CH3)2). (Me-[B] was not
observed.)
160 Hz), 126.4 (C4, 1JCH ) 163 Hz), 126.1 (C7, 1JCH ) 164 Hz), 119.8
1
1
(C5′, JCH ) 178 Hz and C7a), 115.8 (C1′), 115.3 (C4′, JCH ) 173
1
1
Hz), 113.2 (C2, JCH ) 168 Hz), 108.6 (C2′, JCH ) 173 Hz), 105.5
9
2100 J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004

Metallocene Catalyzed Polymerization
A R T I C L E S
(9e) was generated by the reaction of 8e (21 mg, 58 µmol) with
tris(pentafluorophenyl)borane (30 mg, 58 µmol). 1H NMR (599.9 MHz,
[D6]benzene, 298 K): δ ) 6.40, 5.37, 5.27 (each pt, each 1H, tBuC5H3),
6.33, 6.29, 5.20, 5.07 (each d, each 1H, C5H4), 0.98 (s, 9H, tBu-CH3),
0.57 (br s, 3H, (CH3)B(C6F5)3), 0.46 (s, 3H, Zr-CH3), 0.03, -0.24
(each s, each 3H, Si(CH3)2). 13C {1H} NMR (150.8 MHz, [D6]benzene,
m-B(C6F5)3), 123.1, 121.4, 103.0, 101.6 (C5H4), 119.9, 113.1, 109.6
t
(tBuC5H3), 113.5, 113.2 (ipso-C of BuC5H3Si and ipso-C of C5H4Si),
102.7, 98.3 (â-pyrrole), 34.0 (Zr-CH3), 30.4 (C(CH3)3), 29.8 (tBu-
CH3), -5.7, -6.5 (Si(CH3)2).
Syntheses of the [Dimethylsilylen(3-alkylcylopentadienyl)(cyclo-
pentadienyl)](butadiene)zirconium Complexes (s-cis-17b-e/s-cis-
17′b-e, s-trans-17b-e/s-trans-17′b-e). General Procedure. The re-
spective dichlorozirconocene complex 7 and 1.1 mol equiv of the
butadiene-magnesium reagent were mixed as solids in a Schlenk flask.
The flask was cooled to -78 °C, and precooled toluene (20 mL) was
added slowly. During a time period of 6 h the reaction mixture was
allowed to warm to room temperature, and the system was stirred for
additional 6 h. After filtration and washing of the residue with toluene
(5 mL, twice), the volume of the filtrate was reduced to one-third.
Subsequently, the solution was stored at -20 °C. The product
precipitated as a powder, which was collected, washed with cold pentane
(5 mL), and dried in vacuo.
t
1
298 K): δ ) 151.4 (ipso-C of BuC5H3), 148.6 (dm, JCF ) 240 Hz,
1
1
o-B(C6F5)3), 137.6 (dm, JCF ) 250 Hz, p-B(C6F5)3), 136.4 (dm, JCF
) 245 Hz, m-B(C6F5)3), 128.3 (br, ipso-B(C6F5)3), 123.3, 123.2, 119.7,
109.7 (C5H4), 121.4, 115.9, 111.1 (tBuC5H3), 105.3, 103.6 (ipso-C of
tBuC5H3Si and ipso-C of C5H4Si), 42.1 (Zr-CH3), 33.6 (C(CH3)3), 30.5
(tBu-CH3), ∼21 (br, (CH3)B(C6F5)3), -4.9, -7.4 (Si(CH3)2).
(11e) was generated by reaction of 8e (20 mg, 55 µmol) with bis-
(pentafluorophenyl)-N-pyrrolylborane (23 mg, 55 µmol). Two isomers
were obtained: anti-11e:syn-11e ) 3:1.
1
anti-11e: H NMR (599.9 MHz, [D6]benzene, 298 K): δ ) 7.40,
7.32 (each d, each 1H, 3JHH ) 1.8 Hz, R-pyrrole), 6.29, 4.77 (each pt,
(17b):27,28 Reaction of 7b (500 mg, 1.40 mmol) with “butadiene-
magnesium” (326 mg, 1.46 mmol) gave 330 mg (68%, red-brown solid)
of 17b. s-cis:s-trans ) 95:5 (s-cis-17b:s-cis-17′b ) 4:1; s-trans-17b:
s-trans-17′b ) 5:1). Anal. Calcd for C17H22SiZr (345.7): C 59.07, H
6.42; found C 59.64, H 5.82.
t
each 1H, C5H4), 5.97, 5.10, 5.03 (each pt, each 1H, BuC5H3), 5.91,
5.44 (each d, each 1H, 3JHH ) 1.8 Hz, â-pyrrole), 4.95 (m, 2H, C5H4),
t
1.18 (br s, 3H, (CH3)B(NC4H4)(C6F5)2), 1.13 (s, 9H, Bu-CH3), 0.13
(s, 3H, Zr-CH3), 0.10, -0.15 (each s, each 3H, Si(CH3)2). 13C {1H}
NMR (150.8 MHz, [D6]benzene, 298 K): δ ) 150.1 (ipso-C of
1
tBuC5H3), 148.7 (dm, JCF ) 235 Hz, o-B(C6F5)3), 140.3, 136.3 (R-
1
s-cis-17b: H NMR (599.9 MHz, [D8]toluene, 268 K): δ ) 5.92
1
1
pyrrole), 137.7 (dm, JCF ) 250 Hz, p-B(C6F5)3), 137.4 (dm, JCF
)
(m, 1H, MeC5H3), 5.42 (m, 1H, MeC5H3), 5.19 (m, 1H, C5H4), 4.98
(m, 1H, C5H4), 4.91 (m, 2H, C5H4), 4.79 (q, 3JHH ) 11.8 Hz, 1H, 3-H),
235 Hz, m-B(C6F5)3), 129.0 (ipso-B(C6F5)3), 127.1, 124.1, 114.9, 109.0
(C5H4), 121.1, 112.6, 109.1 (tBuC5H3), 103.8, 97.5 (â-pyrrole), 102.7,
3
4.69 (q, JHH ) 11.8 Hz, 1H, 2-H), 4.21 (m, 1H, MeC5H3), 3.37 (m,
t
100.8 (ipso-C of BuC5H3Si and ipso-C of C5H4Si), 38.6 (Zr-CH3),
1H, 4syn-H), 3.36 (m, 1H, 1syn-H), 1.70 (s, 3H, C5H3-CH3), 0.42 (s,
32.6 (C(CH3)3), 30.9 (tBu-CH3), ∼11 (br, (CH3)B(NC4H4)(C6F5)2),
3
2
3H, 6-H), 0.29 (s, 3H, 5-H), -0.76 (dd, 1H, JHH ) 11.8 Hz, JHH
)
-
3
2
-5.3, -7.0 (Si(CH3)2).
9.2 Hz, 1anti-H), -1.50 (dd, 1H, JHH ) 11.8 Hz, JHH ) 8.4 Hz, 4anti
H). 13C {1H} NMR (150.8 MHz, [D8]toluene, 268 K): δ ) 142.8
(ipso-C of MeC5H3), 112.4 (C3), 110.1 (C2), 109.9 (C5H4), 109.0
(C5H4), 109.0 (MeC5H3), 103.2 (C5H4), 102.9 (ipso-C of MeC5H3Si),
101.2 (MeC5H3), 100.8 (C5H4), 99.9 (MeC5H3), 93.2 (ipso-C of C5H4Si),
54.1 (C4), 49.5 (C1), 14.7 (C5H3-CH3), -3.6 (C6), -6.5 (C5).
1
syn-11e: H NMR (599.9 MHz, [D6]benzene, 298 K): δ ) 7.48,
3
7.46 (each d, each 1H, JHH ) 1.8 Hz, R-pyrrole), 6.03, 5.92 (each d,
3
each 1H, JHH ) 1.8 Hz, â-pyrrole), 5.97, 5.13, 4.98, 4.85 (each m,
each 1H, C5H4), 5.94, 5.38, 5.07 (each pt, each 1H, tBuC5H3), 1.23 (br
t
s, 3H, (CH3)B(NC4H4)(C6F5)2), 0.98 (s, 9H, Bu-CH3), 0.31 (s, 3H,
Zr-CH3), 0.23, 0.16 (each s, each 3H, Si(CH3)2). 13C {1H} NMR (150.8
s-cis-17′b: H NMR (599.9 MHz, [D8]toluene, 268 K): δ ) 5.48
1
t
MHz, [D6]benzene, 298 K): δ ) 150.3 (ipso-C of BuC5H3), 148.7
(m, 1H, C5H4), 5.41 (m, 1H, MeC5H3), 5.22 (m, 1H, C5H4), 4.98 (m,
1H, MeC5H3), 4.80 (m, 1H, 3-H), 4.71 (m, 1H, 2-H), 4.56 (m, 1H,
C5H4), 4.25 (m, 1H, C5H4), 3.75 (m, 1H, MeC5H3), 3.43 (m, 1H, 1syn-
(dm, 1JCF ) 235 Hz, o-B(C6F5)3), 140.3, 136.3 (R-pyrrole), 137.7 (dm,
1
1JCF ) 250 Hz, p-B(C6F5)3), 137.3 (dm, JCF ) 235 Hz, m-B(C6F5)3),
129.0 (br, ipso-B(C6F5)3), 125.8, 121.1, 118.1, 112.5 (C5H4), 120.8,
112.7, 109.8 (tBuC5H3), 105.1, 104.7 (ipso-C of tBuC5H3Si and ipso-C
of C5H4Si), 101.8, 98.3 (â-pyrrole), 34.0 (Zr-CH3), 33.7 (C(CH3)3),
29.9 (tBu-CH3), ∼11 (br, (CH3)B(NC4H4)(C6F5)2), -5.9, -6.1
(Si(CH3)2).
H), 3.12 (m, 1H, 4syn-H), 1.26 (s, 3H, C5H3-CH3), 0.41 (s, 3H, 6-H),
0.28 (s, 3H, 5-H), -0.83 (m, 1H, 1anti-H), -0.88 (m, 1H, 4anti-H). 13C
{1H} NMR (150.8 MHz, [D8]toluene, 268 K): δ ) 130.0 (ipso-C of
MeC5H3), 112.7 (C3), 112.0 (C2), 111.2 (C5H4), 111.0 (C5H4), 109.2
(MeC5H3), 102.4 (ipso-C of MeC5H3Si), 97.3 (MeC5H3), 96.4 (MeC5H3),
95.5 (C5H4), 95 0 (C5H4), 94.0 (ipso-C of C5H4Si), 51.9 (C4), 50.6
(C1), 13.8 (C5H3-CH3), -4.8 (C6), -6.0 (C5).
(13e) was generated by reaction of 8e (20 mg, 55 µmol) with N-(2H-
pyrrolium) tris(pentafluorophenyl)borate (32 mg, 55 µmol). Two
isomers were formed: anti-13e:syn-13e ) 4:1.
1
s-trans-17b (Major s-trans Isomer): H NMR (599.9 MHz, [D8]-
1
toluene, 268 K): δ ) 5.97, 5.66, 5.62, 5.04, 4.89, 4.74, 4.48 (each m,
anti-13e: H NMR (599.9 MHz, [D6]benzene, 298 K): δ ) 7.21,
each 1H, MeC5H3, C5H4), 3.08 (dd, 1H, 3JHH ) 6.6 Hz, 2JHH ) 3.6 Hz,
7.18 (each br, each 1H, R-pyrrole), 6.55, 5.46, 5.28, 4.86 (each m,
3
3
t
H
syn), 2.89 (dt, 1H, JHH ) 15.6 Hz, JHH ) 6.6 Hz, Hmeso), 2.61 (dd,
each 1H, C5H4), 6.12, 5.31, 5.05 (each pt, each 1H, BuC5H3), 5.83,
1H, 3JHH ) 6.6 Hz, 2JHH ) 3.2 Hz, Hsyn), 2.35 (dt, 1H, 3JHH ) 15.6 Hz,
3
t
5.35 (each d, each 1H, JHH ) 1.8 Hz, â-pyrrole), 1.10 (s, 9H, Bu-
CH3), 0.23 (s, 3H, Zr-CH3), 0.21, -0.10 (each s, each 3H, Si(CH3)2).
13C {1H} NMR (150.8 MHz, [D6]benzene, 298 K): δ ) 155.4 (ipso-C
3JHH ) 6.6 Hz, Hmeso), 1.30 (dd, 1H, JHH ) 15.6 Hz, JHH ) 3.2 Hz,
3
2
H
anti), 1.23 (dd, 1H, 3JHH ) 15.6 Hz, 2JHH ) 3.6 Hz, Hanti), 1.48 (s, 3H,
t
1
1
C5H3-CH3), 0.31, 0.29 (each s, each 3H, Si(CH3)2).
of BuC5H3), 148.6 (dm, JCF ) 245 Hz, o-B(C6F5)3), 148.1 (dm, JCF
) 235 Hz, p-B(C6F5)3), 139.1, 136.9 (R-pyrrole), 137.6 (dm, JCF
s-trans-17′b: 1H NMR (599.9 MHz, [D8]toluene, 268 K): δ ) 3.16
1
)
3
2
3
(dd, 1H, JHH ) 7.2 Hz, JHH ) 4.2 Hz, Hsyn), 2.90 (dt, 1H, JHH
)
250 Hz, m-B(C6F5)3), 128.2 (ipso-B(C6F5)3), 125.9, 124.3, 115.8, 112.7
16.0 Hz, 3JHH ) 7.2 Hz, Hmeso), 2.77 (m, 1H, Hsyn), 2.55 (dt, 1H, 3JHH
) 16.0 Hz, 2JHH ) 7.2 Hz, Hmeso), 1.33, 1.29 (each m, each 1H, Hanti).
(Due to the low concentration of this isomer in the mixture, no further
resonances were identified.)
(C5H4), 120.5, 112.3, 111.4 (tBuC5H3), 105.5, 98.9 (â-pyrrole), 103.0,
t
101.6 (ipso-C of BuC5H3Si and ipso-C of C5H4Si), 41.3 (Zr-CH3),
32.7 (C(CH3)3), 30.7 (tBu-CH3), -5.6, -6.8 (Si(CH3)2).
1
syn-13e: H NMR (599.9 MHz, [D6]benzene, 298 K): δ ) 7.37,
(17c): Reaction of 7c (500 mg, 1.15 mmol) with “butadiene-
magnesium” (270 mg, 1.21 mmol) gave 304 mg (63%, red-brown solid)
of 17c. s-cis:s-trans > 98:2 (s-cis-17c:s-cis-17′c ) 4:1). Anal. Calcd
for C22H30SiZr (413.8): C 63.86, H 7.31; found C 64.57, H 6.85.
s-cis-17c: H NMR (599.9 MHz, [D8]toluene, 228 K): δ ) 6.02
(m, 1H, cyC5H3), 5.60 (m, 1H, cyC5H3), 5.28 (m, 1H, C5H4), 4.92 (m,
7.27 (each br, each 1H, R-pyrrole), 6.09, 5.81 (each m, each 1H,
t
â-pyrrole), 6.07, 5.47, 5.24 (each pt, each 1H, BuC5H3), 5.82, 5.71,
t
5.25, 5.22 (each m, each 1H, C5H4), 0.97 (s, 9H, Bu-CH3), 0.37 (s,
3H, Zr-CH3), 0.23, 0.15 (each s, each 3H, Si(CH3)2). 13C {1H} NMR
t
1
(150.8 MHz, [D6]benzene, 298 K): δ ) 151.6 (ipso-C of BuC5H3),
1
1
148.6 (dm, JCF ) 245 Hz, o-B(C6F5)3), 148.1 (dm, JCF ) 235 Hz,
1
p-B(C6F5)3), 140.9, 139.4 (R-pyrrole), 137.6 (dm, JCF ) 250 Hz,
2H, C5H4), 4.86 (m, 1H, C5H4), 4.76 (m, 1H, 3-H), 4.66 (m, 1H, 2-H),
9
J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004 2101

A R T I C L E S
Strauch et al.
3
3
2
4.02 (pt, 1H, cyC5H3), 3.44 (t, 1H, 3JHH ) 2JHH ) 9.6 Hz, 4syn-H), 3.35
(t, 1H, 3JHH ) 2JHH ) 9.6 Hz, 1syn-H), 3.21 (m, 1H, CH of cy), 1.80-
1.00 (10H, CH2 of cy), 0.48 (s, 3H, 6-H), 0.30 (s, 3H, 5-H), -0.73 (t,
11.9 Hz, JHH ) 6.4 Hz, Hmeso), 2.97 (dd, 1H, JHH ) 6.6 Hz, JHH
)
3
2
3.0 Hz, Hsyn), 2.68 (dpt, 1H, JHH ) 11.9 Hz, JHH ) 6.6 Hz, Hmeso),
1.43, 1.32 (each m, each 1H, Hanti).
(17e): reaction of 7e (500 mg, 1.24 mmol) with “butadiene-
magnesium” (292 mg, 1.31 mmol) gave 352 mg (73%, red-brown solid)
of 17e. s-cis:s-trans > 99:1 (s-cis-17e:s-cis-17′e ) 1:1). Anal. Calcd
for C20H28SiZr (387.8): C 61.95, H 7.28; found C 62.02, H 7.20.
2
3
2
1H, JHH ) 9.6 Hz, 1anti-H), -1.45 (dd, 1H, JHH ) 12.1 Hz, JHH
)
9.6 Hz, 4anti-H). 13C {1H} NMR (150.8 MHz, [D8]toluene, 228 K): δ
) 143.4 (ipso-C of cyC5H3), 112.7 (C3), 110.4 (C5H4), 109.2 (C2),
109.1 (C5H4), 105.2 (cyC5H3), 102.8 (cyC5H3), 102.0 (C5H4), 101.4
(ipso-C of cyC5H3Si), 99.8 (C5H4), 96.3 (cyC5H3), 95.4 (ipso-C of C5H4-
Si), 60.8 (CH of cy), 54.1 (C4), 50.1 (C1), 38.2, 36.7, 32.5, 26.9, 26.6
(CH2 of cy), -3.2 (C6), -6.7 (C5).
1
s-cis-17e: H NMR (599.9 MHz, [D8]toluene, 253 K): δ ) 5.99
t
t
(pt, 1H, BuC5H3), 5.65 (pt, 1H, BuC5H3), 5.31 (m, 1H, C5H4), 4.99
(m, 1H, C5H4), 4.89 (m, 1H, C5H4), 4.81 (dd, 1H, C5H4), 4.73 (q, 1H,
3JHH ) 13.1 Hz, 3-H), 4.62 (q, 1H, 3JHH ) 13.1 Hz, 2-H), 4.41 (pt, 1H,
tBuC5H3), 3.42 (dd, 1H, 3JHH ) 13.1, 2JHH ) 9.0 Hz, 1syn-H), 3.27 (dd,
1
s-cis-17′c: H NMR (599.9 MHz, [D8]toluene, 253 K): δ ) 6.07
(m, 1H, C5H4), 5.93 (m, 1H, C5H4), 5.69 (dd, 1H, C5H4), 5.53 (m, 1H,
cyC5H3), 5.16 (m, 1H, cyC5H3), 4.83 (m, 1H, 3-H), 4.70 (m, 1H, 2-H),
4.17 (m, 1H, C5H4), 4.08 (m, 1H, cyC5H3), 3.46 (m, 1H, 4syn-H), 3.22
(t, 1H, 3JHH ) 2JHH ) 9.2 Hz, 1syn-H), 2.61 (m, 1H, CH of cy), 1.80-
1H, 3JHH ) 13.1 Hz, 2JHH ) 9.0 Hz, 4syn-H), 1.09 (s, 9H, 3JHH ) tBu-
3
CH3), 0.44 (s, 3H, 6-H), 0.29 (s, 3H, 5-H), -0.72 (dd, 1H, JHH
)
13.1 Hz, 2JHH ) 9.0 Hz, 1anti-H), -0.86 (dd, 1H, 3JHH ) 13.1 Hz, 2JHH
) 9.0 Hz, 4anti-H). 13C {1H} NMR (150.8 MHz, [D8]toluene, 253 K):
δ ) 148.0 (ipso-C of tBuC5H3), 112.1 (C3), 110.9 (C5H4), 110.1 (C2),
108.9 (C5H4), 103.9 (tBuC5H3), 103.3 (tBuC5H3), 101.7 (C5H4), 101.1
1.00 (10H, CH2 of cy), 0.49 (6-H), 0.29 (5-H), -0.77 (dd, 1H, 3JHH
)
11.8 Hz, 2JHH ) 9.2 Hz, 1anti-H), -0.88 (dd, 1H, 3JHH ) 12.3 Hz, 2JHH
) 9.4 Hz, 4anti-H). 13C {1H} NMR (150.8 MHz, [D8]toluene, 253 K):
δ ) 137.6 (ipso-C of cyC5H3), 118.6 (C5H4), 112.1 (C3), 111.6 (C2),
108.6 (cyC5H3), 104.9 (C5H4), 104.5 (C5H4), 99.7 (ipso-C of cyC5H3-
Si), 99.1 (C5H4), 95.5 (cyC5H3), 94.5 (ipso-C of C5H4Si), 94.1 (cyC5H3),
61.1 (CH of cy), 52.3 (C4), 50.7 (C1), 37.7, 32.1, 26.7, 26.5, 26.4
(CH2 of cy), -3.0 (C6), -6.8 (C5).
(ipso-C of BuC5H3Si), 99.1 (C5H4), 97.3 (tBuC5H3), 95.3 (ipso-C of
C5H4Si), 51.6 (C4), 51.4 (C1), 32.6 (C(CH3)3), 32.1 (tBu-CH3), -3.1
(C6), -6.6 (C5).
s-cis-17′e: H NMR (599.9 MHz, [D8]toluene, 253 K): δ ) 6.19
(m, 1H, C5H4), 6.10 (m, 1H, C5H4), 5.72 (m, 1H, C5H4), 5.32 (pt, 1H,
tBuC5H3), 5.14 (q, 1H, JHH ) 13.0 Hz, 3-H), 4.90 (pt, 1H, BuC5H3),
t
1
3
t
s-trans-17c: Due to the low concentration of the trans isomers, only
1
t
3
the resonances of the butadiene fragments were clearly assigned. H
4.68 (pt, 1H, BuC5H3), 4.67 (q, 1H, JHH ) 13.0 Hz, 2-H), 4.00 (m,
NMR (599.9 MHz, [D8]toluene, 253 K): δ ) 3.26, 3.03, 2.85, 2.78.
(17d): Reaction of 7d (500 mg, 1.28 mmol) with “butadiene-
magnesium” (302 mg, 1.36 mmol) gave 304 mg (63%, red-brown solid)
of 17d. s-cis:s-trans ≈ 97:3 (s-cis-17d:s-cis-17′d ) 3:1; s-trans-17d:
s-trans-17′d ) 5:1). Anal. Calcd for C19H26SiZr (373.7): C 61.13, H
6.97; found C 61.50, H 7.08.
1H, C5H4), 3.47 (m, 1H, 4syn-H), 3.25 (m, 1H, 1syn-H), 0.96 (s, 9H,
t
3JHH ) Bu-CH3), 0.47 (s, 3H, 6-H), 0.28 (s, 3H, 5-H), -0.70 (dd,
3
2
3
1H, JHH ) 13.0 Hz, JHH ) 8.2 Hz, 1anti-H), -0.96 (ddd, 1H, JHH
)
13.0 Hz, JHH ) 7.8 Hz, 4anti-H). 13C {1H} NMR (150.8 MHz, [D8]-
toluene, 253 K): δ ) 135.2 (ipso-C of tBuC5H3), 117.6 (C5H4), 113.4
(C3), 110.7 (C5H4), 109.1 (C2), 109.0 (tBuC5H3), 106.1 (tBuC5H3), 102.8
(C5H4), 101.4 (C5H4), 99.9 (ipso-C of tBuC5H3Si), 98.8 (ipso-C of C5H4-
Si), 96.5 (tBuC5H3), 52.1 (C4), 50.3 (C1), 31.6 (C(CH3)3), 31.4 (tBu-
CH3), -2.2 (C6), -6.9 (C5).
2
1
s-cis-17d: H NMR (599.9 MHz, [D8]toluene, 248 K): δ ) 5.99
(m, 1H, iPrC5H3), 5.61 (m, 1H, iPrC5H3), 5.25 (m, 1H, C5H4), 4.92 (m,
3
2H, C5H4), 4.88 (m, 1H, C5H4), 4.78 (q, 1H, 3-H), 4.66 (q, JHH
)
i
Addition of Tris(pentafluorophenyl)borane to the (Butadiene)-
zirconocenes 17b-e. General Procedure for the Preparation of
Betaines 18b-e. Two separate solutions were prepared, one of
[dimethylsilylen(3-alkylcyclopentadienyl)(cyclopentadienyl)](butadiene)-
zirconium (17b-d) in toluene (5 mL), and one of the borane B(C6F5)3
in toluene (5 mL). At -78 °C the borane solution was added dropwise
to the (butadiene)zirconocene solution. Then the reaction mixture was
allowed to warm to room temperature. After stirring for further 2 h all
volatiles were removed in vacuo. The residue was suspended in pentane
(10 mL) and stirred for 30 min at -78 °C. Then the precipitate was
collected, washed with pentane (5 mL), and dried in vacuo.
(18b):27 Reaction of 17b (100 mg, 289 µmol) with tris(pentafluo-
rophenyl)borane (148 mg, 289 µmol) gave 196 mg (79%, light brown
solid) of 18b. Anal. Calcd for C35H22SiBF15Zr (857.6): C 50.18, H
2.96; found C 50.61, H 2.87.
(18c): Reaction of 17c (140 mg, 338 µmol) with tris(pentafluo-
rophenyl)borane (175 mg, 338 µmol) gave 258 mg (83%, light brown
solid) of 18c. Anal. Calcd for C40H30SiBF15Zr (925.7): C 51.90, H
3.27; found C 52.05, H 4.13.
(18d): Reaction of 17d (100 mg, 268 µmol) with tris(pentafluo-
rophenyl)borane (137 mg, 268 µmol) gave 165 mg (69%, light brown
solid) of 18d. Anal. Calcd for C37H26SiBF15Zr (885.7): C 49.02, H
2.96; found C 48.82, H 3.41.
10.9 Hz, 1H, 2-H), 4.10 (m, 1H, PrC5H3), 3.40 (m, 1H, 4syn-H), 3.36
3
i
(m, 1H, 1syn-H), 2.10 (sept, 1H, JHH ) 6.8 Hz, Pr-CH), 1.22, 0.90
(each d, each 3H, 3JHH ) 6.8 Hz, iPr-CH3), 0.43 (s, 3H, 6-H), 0.30 (s,
3
2
3H, 5-H), -0.78 (dd, 1H, JHH ) 12.3 Hz, JHH ) 8.8 Hz, 1anti-H),
-1.45 (dd, 1H, 3JHH ) 12.4 Hz, 2JHH ) 8.4 Hz, 4anti-H). 13C {1H} NMR
(150.8 MHz, [D8]toluene, 248 K): δ ) 143.1 (ipso-C of iPrC5H3), 112.7
(C3), 110.4 (C5H4), 109.8 (C2), 109.1 (C5H4), 105.9 (iPrC5H3), 102.7
(iPrC5H3), 102.3 (C5H4), 101.4 (ipso-C of PrC5H3Si), 100.1 (C5H4),
96.1 (iPrC5H3), 94.1 (ipso-C of C5H4Si), 54.0 (C4), 50.1 (C1), 28.3
i
i
(iPr-CH), 25.6, 22.1 (each Pr-CH3), -3.2 (C6), -6.6 (C5).
1
s-cis-17′d: H NMR (599.9 MHz, [D8]toluene, 248 K): δ ) 6.04
(m, 1H, C5H4), 5.89 (m, 1H, C5H4), 5.67 (m, 1H, C5H4), 5.28 (m, 1H,
iPrC5H3), 4.87 (m, 1H, iPrC5H3), 4.83 (m, 1H, 3-H), 4.79 (m, 1H, 2-H),
4.77 (m, 1H, iPrC5H3), 4.24 (m, 1H, C5H4), 3.41 (t, 1H, 2JHH ) 3JHH
)
11.2 Hz, 1syn-H), 3.20 (t, 1H, 2JHH ) 3JHH ) 9.6 Hz, 4syn-H), 1.87 (sept,
1H, 3JHH ) 6.8 Hz, iPr-CH), 1.02, 0.86 (each d, each 3H, 3JHH ) 6.8
i
Hz, Pr-CH3), 0.44 (s, 3H, 6-H), 0.29 (s, 3H, 5-H), -0.79 (m, 1H,
3
2
1
anti-H), -0.91 (dd, JHH ) 8.9 Hz, JHH ) 9.6 Hz,1H, 4anti-H). 13C
{1H} NMR (150.8 MHz, [D8]toluene, 248 K): δ ) 130.4 (ipso-C of
iPrC5H3), 118.5 (C5H4), 112.3 (C3), 111.5 (iPrC5H3), 111.2 (C2), 105.4
(iPrC5H3), 105.0 (C5H4), 104.5 (C5H4), 101.3 (ipso-C of PrC5H3Si),
i
99.0 (C5H4), 98.7 (iPrC5H3), 93.8 (ipso-C of C5H4Si), 52.5 (C4), 50.6
(C1), 28.2 (iPr-CH), 26.5, 21.9 (iPr-CH3), -3.1 (C6), -6.7 (C5).
Due to the low concentration of the trans isomers, only the
resonances of the butadiene derived ligand section are listed.
(18e): Reaction of 17e (100 mg, 258 µmol) with tris(pentafluo-
rophenyl)borane (132 mg, 258 µmol) gave 206 mg (88%, light yellow
solid) of 18e. Anal. Calcd for C38H28SiBF15Zr (899.7): C 50.73, H
3.14; found C 50.24, H 3.89.
In Situ Addition of Tris(pentafluorophenyl)borane to the (Buta-
diene)zirconocenes 17b-e. General Procedure for the Preparation
of Betaines 18b-e for NMR Experiments. Two separate solutions
were prepared, one of [dimethylsilylen(3-alkylcyclopentadienyl)(cy-
clopentadienyl)](butadiene)zirconium (17b-d) in [D8]toluene (0.8 mL),
1
s-trans-17d (Major Isomer): H NMR (599.9 MHz, [D8]toluene,
248 K): δ ) 3.16 (dd, 1H, 3JHH ) 7.0 Hz, 2JHH ) 4.0 Hz, Hsyn), 2.88
3
3
3
(dt, 1H, JHH ) 11.9 Hz, JHH ) 6.5 Hz, Hmeso), 2.61 (dd, 1H, JHH
)
6.5 Hz, 2JHH ) 3.7 Hz, Hsyn), 2.55 (dt, 1H, 3JHH ) 11.9 Hz, 3JHH ) 4.0
Hz, Hmeso), 1.38 (m, 1H, Hanti), 1.23 (m, 1H, Hanti).
s-trans-17d: 1H NMR (599.9 MHz, [D8]toluene, 248 K): δ ) 3.24
3
2
3
(dd, 1H, JHH ) 6.4 Hz, JHH ) 3.0 Hz, Hsyn), 3.30 (dt, 1H, JHH
)
9
2102 J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004

Metallocene Catalyzed Polymerization
A R T I C L E S
2
2
and one of the borane B(C6F5)3 in [D8]toluene (0.4 mL). Subsequently
the borane solution was added dropwise to the (butadiene)zirconocene
solution. The Z-18 isomers were observed as kinetic products.
(18b): Reaction of 17b (20 mg, 57.9 µmol) with tris(pentafluo-
rophenyl)borane (29.6 mg, 57.9 µmol) gave 18b as a mixture of isomers
(E-18b:E-18′b ) 4:1).
2.54 (br d, 1H, JHH ) 17.4 Hz, 4′-H), 2.22 (dd, 1H, JHH ) 17.4 Hz,
3JHH ) 7.2 Hz, 4-H), 1.90-0.80 (10H, CH2 of cy), 1.67 (m, 1H, 1syn
-
H), 1.59 (m, 1H, 1anti-H), 0.21, -0.19 (each s, 3H, Si(CH3)2). 13C {1H}
1
NMR (150.8 MHz, [D8]toluene, 268 K): δ ) 148.5 (dm, JCF ) 250
Hz, o-B(C6F5)3), 139.3 (ipso-C of cyC5H3), 137.9 (dm, 1JCF ) 240 Hz,
p-B(C6F5)3), 137.2 (dm, 1JCF ) 240 Hz, m-B(C6F5)3), 131.3 (C2), 123.8,
121.3 (C5H4), 120.4 (C3), 118.0 (cyC5H3), 109.9 (C5H4), 107.3, 105.5
(cyC5H3), 102.8 (C5H4), 102.1 (ipso-C of cyC5H3Si), 100.4 (ipso-C of
C5H4Si), 58.4 (CH of cy), 51.0 (C1), 32.1, 25.8 (2×), 25.2, 23.6 (CH2
of cy), 27 (br, C4), -3.5, -4.3 (Si(CH3)2).
1
Z-18b: H NMR (599.9 MHz, [D8]toluene, 258 K): δ ) 5.82 (pt,
1H, MeC5H3), 5.38, 5.29 (each m, each 1H, C5H4), 5.16 (m, 1H, 2-H),
4.91 (m, 1H, C5H4), 4.74, 4.55 (each pt, each 1H, MeC5H3), 4.49 (t,
3
3
1H, JHH ) 11.8 Hz, 3-H), 4.23 (m, 1H, C5H4), 2.62 (t, 1H, JHH
)
(18d): Reaction of 17d (20 mg, 53.5 µmol) with tris(pentafluo-
rophenyl)borane (27.3 mg, 53.5 µmol) gave 18d.
13.4 Hz, 1syn-H), 1.53 (s, 3H, C5H3-CH3), 0.27 (m, 1H, 1anti-H), 0.11,
0.08 (each s, each 3H, Si(CH3)2), -0.43 (br, 1H, 4′-H), -1.83 (br, 1H,
4-H). 13C {1H} NMR (150.8 MHz, [D8]toluene, 258 K): δ ) 146.0
(dm, JCF ) 240 Hz, o-B(C6F5)3), 138.9 (dm, JCF ) 250 Hz,
p-B(C6F5)3), 137.6 (dm, 1JCF ) 250 Hz, m-B(C6F5)3), 136.6 (ipso-C of
MeC5H3), 131.4 (C2), 117.9 (C3), 117.6 (MeC5H3), 114.5 (C5H4), 114.1
(MeC5H3), 113.2 (C5H4), 112.5, 109.2 (C5H4), 103.2 (MeC5H3), 101.5
(ipso-C of MeC5H3Si), 99.6 (ipso-C of C5H4Si), 55.0 (C1), 25 (br, C4),
14.5 (C5H3-CH3), -5.8, -8.1 (Si(CH3)2).
1
Z-18d: H NMR (599.9 MHz, [D8]toluene, 298 K): δ ) 6.10 (m,
1
1
i
1H, C5H4), 5.99 (m, 1H, PrC5H3), 5.80 (m, 1H, C5H4), 5.51 (m, 1H,
iPrC5H3), 5.51 (m, 1H, C5H4), 5.24 (m, 1H, 2-H), 4.55 (m, 1H, 3-H),
4.23 (m, 1H, iPrC5H3), 4.16 (m, 1H, C5H4), 2.71 (t, 1H, 3JHH ) 9.0 Hz,
1
syn-H), 2.21 (sept, 1H, 3JHH ) 6.8 Hz, iPr-CH), 1.15 (m, 1H, 1anti-H),
3
i
0.94, 0.73 (each d, each 3H, JHH ) 6.8 Hz, Pr-CH3), 0.31, -0.08
(each s, each 3H, Si(CH3)2), -0.30 (br, 1H, 4′-H), -1.90 (br, 1H, 4-H).
13C {1H} NMR (150.8 MHz, [D8]toluene, 298 K): δ ) 149.4 (ipso-C
of PrC5H3), 145.1 (dm, JCF ) 240 Hz, o-B(C6F5)3), 138.8 (dm, JCF
) 250 Hz, p-B(C6F5)3), 137.6 (dm, 1JCF ) 240 Hz, m-B(C6F5)3), 128.5
(C2), 117.6 (C5H4), 116.3 (iPrC5H3), 113.6 (C5H4), 113.5 (iPrC5H3),
E-18b (Major E Isomer): 1H NMR (599.9 MHz, [D8]toluene, 258
K): δ ) 5.97 (m, 1H, C5H4), 5.91 (m, 1H, 2-H), 5.72 (m, 1H, C5H4),
5.58 (m, 1H, MeC5H3), 5.51 (m, 1H, C5H4), 5.17 (m, 1H, MeC5H3),
4.69 (m, 1H, 3-H), 4.35 (pt, 1H, MeC5H3), 4.23 (m, 1H, C5H4), 2.50
(br d, 1H, 3JHH ) 7.8 Hz, 4′-H), 2.21 (m, 1H, 4-H), 1.61 (dd, 3H, 3JHH
i
1
1
i
110.5 (C5H4), 110.1 (C3), 105.7 (ipso-C of PrC5H3Si), 105.4 (C5H4),
104.2 (iPrC5H3), 103.9 (ipso-C of C5H4Si), 55.2 (C1), 29.6 (iPr-CH),
25 (br, C4), 22.8, 22.1 (iPr-CH3), -6.3, -6.5 (Si(CH3)2).
3
) 7.6 Hz, JHH ) 4.8 Hz, 1syn-H), 1.57 (s, 3H, C5H3-CH3), 1.33 (dd,
3H, 3JHH ) 11.8 Hz, 2JHH ) 4.8 Hz, 1anti-H), 0.17, -0.26 (each s, each
3H, Si(CH3)2). 13C {1H} NMR (150.8 MHz, [D8]toluene, 258 K): δ )
1
E-18d: H NMR (599.9 MHz, [D8]toluene, 298 K): δ ) 6.04 (m,
1
1
i
148.5 (dm, JCF ) 250 Hz, o-B(C6F5)3), 138.0 (dm, JCF ) 240 Hz,
p-B(C6F5)3), 137.6 (dm, 1JCF ) 250 Hz, m-B(C6F5)3), 136.3 (ipso-C of
MeC5H3), 132.5 (C2), 123.5 (C5H4), 121.3 (MeC5H3), 120.5 (C3), 120.4
(C5H4), 107.7 (MeC5H3), 106.5 (C5H4), 106.0 (MeC5H3), 105.3 (C5H4),
104.0 (ipso-C of MeC5H3Si), 100.9 (ipso-C of C5H4Si), 53.5 (C1), 27
(br, C4), 14.5 (C5H3-CH3), -6.4, -8.1 (Si(CH3)2).
1H, C5H4), 5.85 (m, 1H, PrC5H3), 5.82 (m, 1H, C5H4), 5.77 (m, 1H,
2-H), 5.48 (m, 1H, C5H4), 5.48 (m, 1H, 3-H), 5.43 (m, 1H, PrC5H3),
i
i
2
4.57 (pt, 1H, PrC5H3), 4.54 (m, 1H, C5H4), 2.49 (t, 1H, JHH ) 18.6
Hz, 4′-H), 2.45 (sept, 1H, 3JHH ) 6.8 Hz, iPr-CH), 2.22 (dd, 1H, 2JHH
3
) 18.6 Hz, JHH ) 7.2 Hz, 4-H), 1.70 (m, 1H, 1syn-H), 1.60 (m, 1H,
3
i
1
anti-H), 1.12, 0.97 (each d, each 3H, JHH ) 6.8 Hz, Pr-CH3), 0.22,
-0.21 (each s, each 3H, Si(CH3)2). 13C {1H} NMR (150.8 MHz, [D8]-
E-18′b (Minor E Isomer): 1H NMR (599.9 MHz, [D8]toluene, 258
K): δ ) 6.01, 5.78 (each m, each 1H, C5H4), 5.70 (m, 1H, 2-H), 5.64
(m, 1H, MeC5H3), 5.51 (m, 1H, MeC5H3), 5.46 (m, 1H, C5H4), 5.38
(m, 1H, 3-H), 4.41 (m, 1H, C5H4), 3.89 (br s, 1H, MeC5H3), 2.51 (br
i
1
toluene, 298 K): δ ) 149.0 (ipso-C of PrC5H3), 148.5 (dm, JCF
240 Hz, o-B(C6F5)3), 137.8 (dm, JCF ) 250 Hz, p-B(C6F5)3), 137.4
)
1
1
(dm, JCF ) 240 Hz, m-B(C6F5)3), 127.1 (C2), 123.9, 122.9 (C5H4),
118.1 (iPrC5H3), 110.5 (C5H4), 110.5 (C3), 107.8 (iPrC5H3), 105.7
(C5H4), 105.1 (ipso-C of iPrC5H3Si), 103.4 (iPrC5H3), 101.0 (ipso-C of
C5H4Si), 51.3 (C1), 29 (br, C4), 28.0 (iPr-CH), 24.2, 22.1 (iPr-CH3),
-5.4, -7.4 (Si(CH3)2).
3
d, 1H, JHH ) 12.6 Hz, 4′-H), 2.18 (m, 1H, 4-H), 1.72 (s, 3H,
3
2
C5H3-CH3), 1.67 (dd, 1H, JHH ) 12.6 Hz, JHH ) 4.8 Hz, 1anti-H),
1.48 (dd, 1H, 3JHH ) 8.4 Hz, 2JHH ) 4.8 Hz, 1syn-H), 0.22, -0.23 (each
s, each 3H, Si(CH3)2). 13C {1H} NMR (150.8 MHz, [D8]toluene, 258
1
1
K): δ ) 148.5 (dm, JCF ) 250 Hz, o-B(C6F5)3), 138.0 (dm, JCF
)
(18e): Reaction of 17e (20 mg, 51.6 µmol) with tris(pentafluorophen-
yl)borane (26.4 mg, 51.6 µmol) gave 18e.
1
240 Hz, p-B(C6F5)3), 137.6 (dm, JCF ) 250 Hz, m-B(C6F5)3), 136.5
(ipso-C of MeC5H3), 129.1 (C2), 124.0 (C5H4), 121.9 (C5H4), 121.8
(MeC5H3), 114.4 (C3), 110.2 (C5H4), 109.1 (MeC5H3), 108.1 (MeC5H3),
105.8 (C5H4), 105.6 (ipso-C of MeC5H3Si), 101.9 (ipso-C of C5H4Si),
51.4 (C1), 27 (br, C4), 13.3 (C5H3-CH3), -6.4, -7.5 (Si(CH3)2).
(18c): Reaction of 17c (20 mg, 48.3 µmol) with tris(pentafluorophen-
yl)borane (24.7 mg, 48.3 µmol) gave 18c.
1
Z-18e: H NMR (599.9 MHz, [D8]toluene, 258 K): δ ) 5.95 (m,
t
1H, BuC5H3), 5.36 (m, 1H, C5H4), 5.31 (m, 1H, C5H4), 5.08 (m, 1H,
t
tBuC5H3), 5.08 (m, 1H, 2-H), 4.95 (m, 1H, BuC5H3), 4.86 (m, 1H,
C5H4), 4.54 (m, 1H, 3-H), 4.39 (m, 1H, C5H4), 2.54 (t, 1H, 3JHH ) 9.6
t
Hz, 1syn-H), 0.95 (m, 1H, 1anti-H), 0.83 (s, 9H, Bu-CH3), 0.14, 0.13
3
(each s, each 3H, Si(CH3)2), -0.39 (br d, 1H, JHH ) 10.8 Hz, 4′-H),
1
Z-18c: H NMR (599.9 MHz, [D8]toluene, 268 K): δ ) 5.90 (pt,
-1.74 (br, 1H, 4-H). 13C {1H} NMR (150.8 MHz, [D8]toluene, 258
t
1
1H, cyC5H3), 5.37, 5.31 (each m, each 1H, C5H4), 5.22 (m, 1H, 2-H),
5.06 (m, 1H, 3-H), 5.02 (pt, 1H, cyC5H3), 4.95 (m, 2H, cyC5H3, C5H4),
4.41 (m, 1H, C5H4), 3.24 (m, 1H, CH of cy), 2.66 (pt, 1H, 1syn-H),
1.90-0.80 (10H, CH2 of cy), 0.44 (m, 1H, 1anti-H), 0.33, -0.03 (each
K): δ ) 156.3 (ipso-C of BuC5H3), 145.1 (dm, JCF ) 240 Hz,
1
1
o-B(C6F5)3), 137.4 (dm, JCF ) 250 Hz, p-B(C6F5)3), 136.8 (dm, JCF
) 240 Hz, m-B(C6F5)3), 133.9 (C2), 115.2, 114.5, 112.0 (C5H4), 110.6
(C3), 110.0 (ipso-C of BuC5H3Si), 109.1, 108.1 (tBuC5H3), 108.1
t
s, each 3H, Si(CH3)2), -0.36 (br, 1H, 4′-H), -1.79 (br, 1H, 4-H). 13
C
(C5H4), 99.3 (ipso-C of C5H4Si), 98.3 (tBuC5H3), 55.8 (C1), 34.1 (tBu-
CH3), 33.4 (C(CH3)3), 24 (br, C4), -4.7, -7.8 (Si(CH3)2).
{1H} NMR (150.8 MHz, [D8]toluene, 268 K): δ ) 145.3 (dm, 1JCF
)
240 Hz, o-B(C6F5)3), 141.2 (ipso-C of cyC5H3), 137.2 (dm, 1JCF ) 250
1
E-18e: H NMR (599.9 MHz, [D8]toluene, 258 K): δ ) 6.06 (m,
1
1H, C5H4), 5.78 (ddd, 1H, 3JHH ) 16.2 Hz, 3JHH ) 14.8 Hz, 3JHH ) 9.6
Hz, p-B(C6F5)3), 136.8 (dm, JCF ) 240 Hz, m-B(C6F5)3), 127.2 (C2),
t
121.2 (C5H4), 119.3 (cyC5H3), 115.3 (C5H4), 112.3 (C3), 110.8
(cyC5H3), 109.0 (cyC5H3), 105.5, 103.9 (C5H4), 102.7 (ipso-C of
cyC5H3Si), 99.8 (ipso-C of C5H4Si), 58.3 (CH of cy), 55.2 (C1), 33.1,
27.8, 27.6, 24.9, 23.6 (CH2 of cy), 25 (br, C4), -5.1,-6.3 (Si(CH3)2).
Hz, 2-H), 5.73 (m, 1H, C5H4), 5.73 (m, 1H, BuC5H3), 5.62 (dd, 1H,
3JHH ) 16.2 Hz, 3JHH ) 8.4 Hz, 3-H), 5.45 (m, 1H, tBuC5H3), 5.38 (m,
1H, C5H4), 4.46 (m, 1H, BuC5H3), 4.36 (m, 1H, C5H4), 2.66 (d, 1H,
2JHH ) 18.0 Hz, 4′-H), 2.44 (dd, 1H, JHH ) 18.0 Hz, JHH ) 8.4 Hz,
4-H), 1.59 (d, 1H, JHH ) 9.6 Hz, 1syn-H), 1.49 (d, 1H, JHH ) 14.8
Hz, 1anti-H), 1.02 (s, 9H, 3JHH ) tBu-CH3), 0.16, -0.25 (each s, each
3H, Si(CH3)2). 13C {1H} NMR (150.8 MHz, [D8]toluene, 258 K): δ )
t
2
3
1
3
3
E-18c: H NMR (599.9 MHz, [D8]toluene, 268 K): δ ) 6.04 (m,
1H, C5H4), 5.82 (m, 1H, cyC5H3), 5.79 (m, 1H, C5H4), 5.77 (m, 1H,
2-H), 5.48 (m, 1H, 3-H), 5.46 (m, 1H, C5H4), 5.43 (m, 1H, cyC5H3),
4.52 (m, 1H, cyC5H3), 4.46 (m, 1H, C5H4), 3.12 (m, 1H, CH of cy),
t
1
153.2 (ipso-C of BuC5H3), 148.4 (dm, JCF ) 240 Hz, o-B(C6F5)3),
9
J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004 2103

A R T I C L E S
Strauch et al.
1
1
137.6 (dm, JCF ) 250 Hz, p-B(C6F5)3), 137.2 (dm, JCF ) 240 Hz,
m-B(C6F5)3), 132.2 (C2), 124.2 (C3), 124.2 (tBuC5H3), 122.6, 119.2,
109.7 (C5H4), 107.8 (tBuC5H3), 104.9 (C5H4), 103.2 (ipso-C of tBuC5H3-
Si), 100.9 (tBuC5H3), 99.6 (ipso-C of C5H4Si), 51.1 (C1), 30.5 (tBu-
CH3), 27 (br, C4), 29.9 (C(CH3)3), -5.9, -7.4 (Si(CH3)2).
Analysetechnik) at 35 °C. The polymer samples (20 mg) were dissolved
in THF (HPLC grade, 2-3 mL), and the solution was filtered before
the injection. The measured data were analyzed with WinGPC6 relative
to polystyrene standards. The stereochemical triad analyses were carried
out by H NMR (599.9 MHz) experiments at 25 °C, using PMMA
(50-60 mg) in CDCl3 solutions.57
1
Methyl Methacrylate Polymerization (PMMA). The polymeriza-
tion reactions were carried out in the dark at 0 °C in dichloromethane
(5 mL), which was dried with P2O5 or CaH2 and freshly condensed
prior to use. Also, directly before use, the MMA monomer was dried
by stirring it with calcium hydride for 2 h. Subsequently the MMA
was condensed in a flask, and 0.2 mL of triethylaluminum was added.
After agitation for 30 min the monomer (2 mL) was condensed directly
into the reaction flask. Injecting a solution of the respective freshly
prepared zirconocene/borane system in dichloromethane (1 mL) started
the polymerization reaction. After 1 h the reaction was quenched by
adding methanol (2 mL). Then all volatiles were removed in vacuo;
the obtained PMMA was dried and characterized by NMR. The
{[isopropyliden(cyclopentadienyl)(1-indenyl)]methylzirconium} {meth-
yltris(pentafluorophenyl)borate} system was used as a catalyst standard
for the MMA polymerization reactions. Molecular weights and poly-
dispersities of the PMMA polymers were obtained by GPC (Agilent
GPC equipped with a switchable UV detector (254 nm) and a refractive
index detector operating with a flow rate of 1 mL of THF (HPLC grade)
per minute) with two PSSVB columns (100 000 and 1000 Å; MZ
Acknowledgment. This work was in part supported by the
Fonds der Chemischen Industrie and the Deutsche Forschungs-
gemeinschaft, which is gratefully acknowledged. J.-L.F. thanks
the Alexander von Humboldt foundation for a stipend. R.F.
performed the X-ray crystal structure analyses, and H.L.
performed the mass spectrometry.
Supporting Information Available: Details of the X-ray
crystal structure analyses. Details of the syntheses of the ansa-
metallocene precursors. Additional spectroscopic features of the
metallocene systems. ES-MS of the anions formed by reaction
of MMA with the catalyst system 16. Additional data of the
polymerization experiments. This material is available free of
charge via the Internet at http://pubs.acs.org.
JA035739Y
9
2104 J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004