Zirconium complexes of 9-phenyl-9-borataanthracene. Synthesis, structural characterization, and reactivity

Article abstract of DOI:10.1021/ja972651+

Lithium 9-phenyl-9-borataanthracene (3·Li(THF)(x), (x) = 2 or 3) is obtained quantitatively from the deprotonation of 9-phenyl-9,10-dihydro-9-borataanthracene (6) with LiTMP (TMP 2,2,6,6-tetramethylpiperidide) in THF. A comparison of the crystallographica

Full text of DOI:10.1021/ja972651+

J. Am. Chem. Soc. 1998, 120, 6037-6046
6037
Zirconium Complexes of 9-Phenyl-9-borataanthracene. Synthesis,
Structural Characterization, and Reactivity
Rip A. Lee, Rene J. Lachicotte, and Guillermo C. Bazan*,†
Contribution from the Department of Chemistry, UniVersity of Rochester, Rochester, New York 14627-0216
ReceiVed August 4, 1997. ReVised Manuscript ReceiVed April 23, 1998
Abstract: Lithium 9-phenyl-9-borataanthracene (3‚Li(THF)x, x ) 2 or 3) is obtained quantitatively from the
deprotonation of 9-phenyl-9,10-dihydro-9-borataanthracene (6) with LiTMP (TMP ) 2,2,6,6-tetramethylpiper-
idide) in THF. A comparison of the crystallographically determined structures of 6 and 3‚Li(TMEDA) (TMEDA
) N,N,N′,N′-tetramethylethylenediamine) highlights the effects of charge and delocalization on the heterocyclic
framework. The reaction of 3‚Li(THF)2 with Cp*ZrCl3 (Cp* ) C5Me5) and Cp*ZrMe2Cl affords the novel
complexes (AnB-Ph)Cp*ZrCl2 (4) (AnB-Ph ) 9-phenyl-9-borataanthracene) and (AnB-Ph)Cp*ZrMe2 (5),
respectively. The crystallographically determined molecular structure of 4 resembles a bent metallocene with
a tetrahedral disposition of ligands around zirconium. The borataanthracene ligand bends significantly (approx
16°) to avoid steric contacts with the Cp*ZrCl2 core. The angle of the exocyclic phenyl substituent relative
to the anthracene unit remains nearly invariant at 62° for 6, 3‚Li(TMEDA), and 4, suggesting that the steric
envelope around boron prevents an optimum orientation for orbital overlap between boron and the π-system
of the phenyl ring. Treatment of 5 with B(C6F5)3 gives [(AnB-Ph)Cp*ZrMe][MeB(C6F5)3] (7). Reaction of
4 with methylaluminoxane (MAO) and 1 atm of ethylene produces a mixture of low molecular weight 1-alkenes,
2-alkenes, and 2-alkyl-1-alkenes, whereas the reaction of 7 with ethylene gives low molecular weight
polyethylene. Reactions of 4/MAO and 7 with 1-tridecene were carried out to determine the fate of 1-alkenes
generated using 4/MAO/C2H4 and to delineate the role of the activator. The complex (C5H5B-Ph)Cp*ZrCl2
(8) is obtained by reaction of Cp*ZrCl3 with Li[C5H5B-Ph]. A comparison of the reactivity of 8/MAO/C2H4
against that of 4/MAO/C2H4 highlights, for the first time, the effect of sterics on the stability of catalysts
supported by boratacyclic ligands.
Introduction
of co-activators,4 and the requisite structural features for
stereoselective catalysis.5
Electron-deficient bent metallocenes of the general type
[Cp2MR]+[NCA]- (M ) Ti, Zr, or Hf; Cp ) η5-C5H5,
cyclopentadienyl; R ) alkyl or hydride; NCA ) noncoordi-
nating anion) constitute a major class of homogeneous olefin
polymerization catalysts. These systems have been the subject
of several reviews.1 Indeed, the wealth of information gleaned
from nearly two decades of research has led to a good
understanding of the mechanistic details involved in olefin
insertion chemistry,2 the nature of the active species,3 the role
Intense research efforts have centered on the design and
synthesis of sterically modified metallocenes of diverse archi-
tectures. In particular, the advent of ansa-metallocenes marked
an explosive growth of investigations into the stereospecific
polymerization of propylene.6,7 The structural correlation of
the catalyst with its reactivity, and with the resultant polymer
microstructure, has been the subject of much work,8 and
innovative strategies for the design of chiral metallocenes
continue to emerge in the literature.9 Collectively, the impor-
† Current address: Department of Chemistry, University of California,
Santa Barbara, CA 93106.
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R. J. Am. Chem. Soc. 1987, 109, 4111. (b) Horton, A. D.; Orpen, A. G.
Organometallics 1991, 10, 3910. (c) Yang, X.; Stern, C. L.; Marks, T. J. J.
Am. Chem. Soc. 1994, 116, 10015. (d) Bochmann, M. Angew. Chem., Int.
Ed. Engl. 1992, 31, 1181. (e) Bliemeister, J.; Hagendorf, W.; Harder, A.;
Heitmann, B.; Schimmel. I.; Schmedt, E.; Schnuchel, W.; Sinn, H.; Tikwe,
L.; von Thienen, N.; Urlass, K.; Winter, H.; Zarnacke, O. In Ziegler
Catalysts; Fink, G., Mu¨lhaupt, R., Brintzinger, H.-H., Eds.; Springer-
Verlag: Berlin, 1995. (f) Jia, L.; Yang, X.; Stern, C. L.; Marks, T. J.
Organometallics 1997, 16, 842.
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Angew. Chem., Int. Ed. Engl. 1985, 34, 507. (b) Ewen, J. A.; Jones, R. L.;
Razavi, A.; Ferrara, J. D. J. Am. Chem. Soc. 1988, 110, 6255. (c) Brintzinger,
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S0002-7863(97)02651-6 CCC: $15.00 © 1998 American Chemical Society
Published on Web 06/09/1998

6038 J. Am. Chem. Soc., Vol. 120, No. 24, 1998
Lee et al.
tance of metallocene catalysts is demonstrated by their rising
impact in the future direction of polyolefin technology.10
An alternative approach for catalyst design involves the
electronic modification of the metal center by preparing
metallocene-like complexes with ligands other than cyclopen-
tadienyl. One class of compounds includes the “constrained
geometry” metallocenes which contain, in addition to the
reduced steric volume, a less electron-donating amide function-
ality which enhances the electrophilicity of the metal.11 The
use of chelating bis-amides has also given rise to catalysts with
novel reactivities.12 The formal replacement of a monoanionic
Cp with dianionic π-donor ligands has also been exploited. Thus,
bent metallocenes containing “Cp-like” ligands such as dicar-
bollide,13 trimethylenemethane,14 and borollide15 have been
constructed, some of which display reactivities similar to those
of standard metallocenes.16
The use of boratabenzenes (C5H5B-L, L ) pendant group)
as ancillary ligands for early transition metals, though limited
thus far, is of growing interest.17 In particular, these ligands
have been used to construct precursors for homogeneous olefin
polymerization catalysts with structures and electronic properties
similar to those of standard group 4 metallocenes.18 It appears
that the electron density at the metal center can be controlled
by the orbital overlap between B and L. The rich chemistry of
boratabenzene metal complexes19 has spanned over two decades
since the landmark discovery of (C5H5B-Ph)CpCo in 1970.20
The elegant synthesis of uncomplexed Li[C5H5B-Ph],21 and
subsequently other alkali metal boratabenzenes,22 has provided
a more versatile strategy for the synthesis of new boratabenzene-
containing metal complexes. Further applications of this
heterocyclic ligand may be anticipated, especially as new
variations of the ligand framework continue to develop.23
As mentioned above, the salient feature of boratabenzene
ligands is their ability to tune the electron density at the metal
center and, hence, to modulate the reactivity of the metal
complex. Solutions of [C5H5B-N(iPr)2]2ZrCl2 (1) with methyl-
aluminoxane (MAO) polymerize ethylene to give high molecular
weight polyethylene (PE).18a In sharp contrast, solutions of
[C5H5B-Ph]2ZrCl2 (2) with MAO give 2-alkyl-1-alkenes under
similar reaction conditions. Differences in reactivities were
attributed to differences in the rates of â-hydrogen elimination
due to changing the exocyclic substituent.18b Strong π-donation
of the pendant dialkylamino group with boron24 results in the
coordination of boratabenzene to zirconium in an η5-pentadienyl
fashion. However, when the π-interaction is weaker, the
boratabenzene is best described as an η6-bound, aromatic ligand.
Overall, these features render the zirconium atom in 1 less
electrophilic than that in 2.
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Structural variations of the boratabenzene ligand may be
achieved by extending the framework around boron. In this
context, we became interested in the 9-phenyl-9-borataan-
thracene anion, first claimed by Jutzi,25 since its use as a ligand
in a metal complex has not been explored.26 The analogies
between this benzannulated derivative and phenylboratabenzene
should be similar to those between Cp and the sterically larger
Cp* (Cp* ) C5Me5) and fluorenyl analogues. The sterically
more protecting framework of borataanthracene should be useful
in stabilizing reactive and/or coordinatively unsaturated spe-
cies.27
The modified synthesis and the complete characterization of
lithium 9-phenyl-9-borataanthracene are described in the first
part of this paper.28 The use of this ligand as a boratabenzene
or Cp equivalent is shown by the synthesis of the novel
complexes (AnB-Ph)Cp*ZrX2 (AnB-Ph ) 9-phenyl-9-borataan-
(22) Herberich, G. E.; Becker, H. J.; Carsten, K.; Engelke, C.; Koch,
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J. E. J. Am. Chem. Soc. 1994, 116, 4459.
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U. Organometallics 1995, 14, 471. (c) Herberich, G. E.; Englert, U.;
Schmidt, M. U.; Standt, R. Organometallics 1996, 15, 2707. (d) Hoic, D.
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Organometallics 1996, 15, 387. (b) Ashe, A. J., III; Kampf, J. W.; Waas,
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(26) For related work with the 9-mesityl-9-borataanthracene anion, see:
(a) van Veen, R.; Bickelhaupt, F. J. Organomet. Chem. 1972, 43, C41. (b)
van Veen, R.; Bickelhaupt, F. J. Organomet. Chem. 1974, 74, 393. (c) van
Veen, R.; Bickelhaupt, F. J. Organomet. Chem. 1974, 77, 153. (d)
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Schenk, H.; Schagen, J. D. J. Am. Chem. Soc. 1980, 102, 5594. (e) Lapin,
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(27) For a lucid account of how sterics affects the stability of electrophilic
organometallic species, see: Piers, W. E.; Shapiro, P. J.; Bunel, E. E.;
Bercaw, J. E. Synth. Lett. 1990, 74.
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Zirconium Complexes of 9-Phenyl-9-borataanthracene
J. Am. Chem. Soc., Vol. 120, No. 24, 1998 6039
intra-ring B-C bond lengths in 6 (mean 1.555(3) Å) are shorter
than the exocyclic B-C bond (1.575(3) Å), and all three bonds
are slightly shorter than the average B-C bond length found
in Ph3B (1.577(6) Å).30 The pendant phenyl ring is not coplanar
with the anthracene unit but is skewed with a 62° torsion angle.
Presumably, this minimizes van der Waals repulsions between
the ortho hydrogens of the phenyl ring and those at the 1- and
8-positions of the borataanthracene ring system. Thus, optimum
overlap between the p orbital on B and the π electron system
of the phenyl ring does not occur.
The deprotonation of 6 to yield 3‚Li(THF)3 is readily achieved
using the bulky base, LiTMP (TMP ) 2,2,6,6-tetramethylpi-
peridide), in THF as shown in eq 2. The resulting tacky orange
Figure 1. ORTEP view of 6 showing the labeling scheme. Thermal
ellipsoids are shown at the 30% probability level.
thracene, X ) Cl (4), Me (5)). These metallocene mimics can
be activated toward olefin polymerization and isomerization,
and the resulting catalytic behavior is described. Finally, a
comparison of the reactivity of 4 with that of the non-
benzannulated complex, [C5H5B-Ph]Cp*ZrCl2 (8), is made to
evaluate the ligand steric effects in dictating catalyst selectivity
and stability.
solid was characterized by standard spectroscopic and elemental
analyses, and the results are consistent with its formulation. One
diagnostic feature in the H NMR (in C6D6) spectrum is the
1
sharp singlet located at 7.36 ppm due to the C-10 hydrogen. In
comparison, the C-10 methylene protons in 6 appear farther
upfield at 4.14 ppm. The deshielding of the C-10 carbon
observed in the 13C NMR spectrum (3‚Li(THF)3, 101.0 ppm;
6, 38.5 ppm) is also consistent with a change in hybridization
upon deprotonation. Insofar as the ring current effect is
evidence for aromaticity,31 it can be inferred from the spectro-
scopic data that there is delocalization of the π-electrons within
the borataanthracene moiety. Furthermore, the 11B NMR of
3‚Li(THF)3 shows a broad peak at 39.7 ppm ( 59.9 ppm for 6),
which is well within the range of values observed for other
boratabenzene anions.22,23
Results and Discussion
Ligand Synthesis. The synthesis of lithium 9-phenyl-9-
borataanthracene (3‚Li(THF)3) begins with the nearly quantita-
tive formation of 9-phenyl-9,10-dihydro-9-boraanthracene (6)
from the reaction of 9,9-dimethyl-9,10-dihydro-9-stannaan-
thracene29 with PhBCl2 (eq 1). The success of the transmeta-
In our hands, the deprotonation of 6 with t-BuLi/hexane/THF
to produce 3‚Li(THF)3.5, as reported in the literature,25 gave an
intractable, oily mixture of products. A pair of well-separated
multiplets which had been assigned previously to the C-10
1
hydrogen were consistently observed at 4.01 ppm in the H
NMR spectra of these mixtures. The higher quality of our
spectra shows that these signals display geminal coupling (J )
19 Hz) and correspond to two protons by integration. In
addition, the previously reported 11B NMR value of -10 ppm
has been questioned,32 since it suggests quaternization at boron
rather than deprotonation. We believe that the t-BuLi transfers
hydride to the boron atom, forming a borate species.33 Con-
sistent with this idea is the B-H coupling of J ) 69 Hz observed
in the 11B NMR spectra.
One THF solvate molecule can be removed from 3‚Li(THF)3
by repeated cycles of trituration in pentane and drying under
vacuum. This procedure affords 3‚Li(THF)2 as a yellow powder
which is more suitable for handling. The spectroscopic features
of both species are almost identical.
lation is highly dependent on the purity of the stannaanthracene.
It is best to isolate and purify the stannacycle by chromatography
using silica and 6:1 hexanes/CH2Cl2 as the eluent.
Single crystals of 6 suitable for X-ray diffraction studies were
obtained by recrystallization from diethyl ether. As shown in
Figure 1, the anthracene ring system is planar. The sums of all
angles at the ring fusions and at boron equal 360.0(2)°. The
(28) Our numbering scheme for the boraanthracene ring is shown below.
It is consistent with previous assignments but differs from that of dibenzo-
[b,e]borin in the following: Ring Systems Handbook; ACS Publications:
Columbus, OH, 1993. The carbon in the 5-position is referred to as C-5 in
the text. The atomic-numbering scheme used in the X-ray crystallographic
studies is arbitrary, and the numerals are enclosed in parentheses, i.e. C(5).
(30) Zettler, F.; Hausen, H. D.; Hess, H. J. J. Organomet. Chem. 1974,
72, 157.
(31) Lowry, T. H.; Richardson, K. S. Mechanism and Theory in Organic
Chemistry; Harper & Row: New York, 1987.
(32) Ander, I. In ComprehensiVe Heterocyclic Chemistry; Katritzky, A.
R., Rees, C. W., Eds.; Pergamon Press: Oxford, U.K., 1984; Vol. 1.
(33) Hydride transfer from t-BuLi to boron is a well-known process.
See: (a) No¨th, H.; Taeger, T. J. Organomet. Chem. 1977, 142, 281. (b)
Brown, H. C.; Kramer, G. W.; Hubbard, J. L.; Krishnamurthy, S. J.
Organomet. Chem. 1980, 188, 1.
(29) Jutzi, P. Chem. Ber. 1971, 104, 1455.

6040 J. Am. Chem. Soc., Vol. 120, No. 24, 1998
Lee et al.
Table 1. Selected Interatomic Distances (Å) and Bond Angles
(deg) for 6 and 3‚Li(TMEDA)
6
3‚Li(TMEDA)
A. Interatomic Distances (Å)
1.552(3)
B-C(1)
1.532(3)
1.549(3)
1.582(3)
1.444(3)
1.409(3)
1.409(3)
1.435(3)
1.448(3)
1.356(3)
1.409(3)
1.363(3)
1.431(3)
B-C(13)
1.549(3)
1.575(3)
1.408(2)
1.506(3)
1.506(3)
1.396(2)
1.404(2)
1.375(3)
B-C(14)
C(1)-C(6)
C(6)-C(7)
C(7)-C(8)
C(8)-C(9)
C(8)-C(13)
C(9)-C(10)
C(10)-C(11)
C(11)-C(12)
C(12)-C(13)
1.388(3)
1.376(3)
1.410(2)
B. Bond Angles (deg)
117.8(2)
C(1)-B-C(13)
C(1)-B-C(14)
C(13)-B-C(14)
B-C(1)-C(2)
B-C(1)-C(6)
C(2)-C(1)-C(6)
C(1)-C(6)-C(5)
C(1)-C(6)-C(7)
C(5)-C(6)-C(7)
C(6)-C(7)-C(8)
C(7)-C(8)-C(9)
C(7)-C(8)-C(13)
C(9)-C(8)-C(13)
B-C(13)-C(8)
115.9(2)
122.0(2)
122.1(2)
123.2(2)
119.7(2)
116.9(2)
118.5(2)
120.7(2)
120.8(2)
123.2(2)
120.9(2)
120.4(2)
118.7(2)
120.2(2)
123.4(2)
116.6(2)
120.8(2)
121.3(2)
122.7(2)
119.8(2)
Figure 2. ORTEP view of 3‚Li(TMEDA) showing the labeling scheme.
Thermal ellipsoids are shown at the 30% probability level.
117.6(2)
119.8(2)
121.9(2)
118.2(2)
118.4(2)
117.8(2)
122.4(2)
119.8(2)
119.6(2)
122.9(2)
117.4(2)
Yellow needles of 3‚Li(TMEDA) (TMEDA ) N,N,N′,N′-
tetramethylethylenediamine) precipitate within 10 min when a
solution of 3‚Li(THF)2 or 3‚Li(THF)3 in benzene is treated with
1 equiv of TMEDA (TMEDA ) N,N,N′,N′-tetramethylethyl-
enediamine) (eq 3). These crystals are marginally soluble in
1
benzene, and the H NMR spectrum of a saturated solution of
3‚Li(TMEDA) is similar to those of 3‚Li(THF)2 and 3‚Li(THF)3.
B-C(13)-C(12)
C(8)-C(13)-C(12)
torsion angle between the pendant phenyl ring and the borataan-
thracene unit remains invariant relative to 6, and this structural
feature further establishes that participation of the exocyclic
substituent in donating electron density to the boron atom is
minimal.
Coordination to Zirconium. The reaction of 3‚Li(THF)2
with Cp*ZrCl3 in toluene followed by extraction with CH2Cl2
affords (AnB-Ph)Cp*ZrCl2 (4) in 44% yield as bright orange
microcystals (eq 4). Recrystallization from CH2Cl2/pentane
The structure of 3‚Li(TMEDA), shown in Figure 2, was
determined by single-crystal X-ray diffraction. There are several
variations between the structures of 3‚Li(TMEDA) and 6 (see
Table 1). As expected on the basis of gained aromaticity, there
is a decrease in the C(6)-C(7) and C(7)-C(8) bond lengths
(from 1.506(3) to 1.409(3) Å), and the C(6)-C(7)-C(8) angle
increases from 118.4(2)° to 123.2(2)°. While the carbon-
carbon bond lengths of the central ring are comparable (mean
1.428(3) Å), those of the outer rings clearly exhibit single- and
double-bond character (in Å: C(8)-C(9) ) 1.435(3), C(9)-
C(10) ) 1.356(3), C(10)-C(11) ) 1.409(3), C(11)-C(12) )
1.363(3)). Thus, the borataanthracene anion can be described
as an aromatic boratabenzene flanked by two “diene” units. A
similar bonding description can be inferred from the structural
data of the 2-boratanaphthalene anion, where the boron-
containing ring is aromatic while the carbocyclic ring is diene-
like.34 The lithium atom in 3‚Li(TMEDA) is η6-bound, at least
in the solid state, and it lies above the central ring of
borataanthracene, being only marginally displaced from the
centroid of the ring toward C(7). The structures of [3-t-Bu-5-
MeC5H3BNMe2][Li(TMEDA)]23c and the Li[C5H5BH]2 anion23d
reveal a similar juxtaposition of the alkali metal atom. The
gave suitable crystals for a single-crystal X-ray diffraction study.
As seen in Figure 3, this novel compound resembles a bent
metallocene with a pseudotetrahedral ligand arrangement about
zirconium. The centroid-Zr-centroid angle is 138.4(2)°. An
examination of the structural parameters associated with 3‚Li-
(TMEDA) indicates that ligation to zirconium imposes distinct
structural changes. The three rings of the borataanthracene unit
are no longer coplanar in 4, and in fact, the outer rings are bowed
away from the Cp*ZrCl2 fragment and deviate from the mean
plane of the central heterocyclic ring by approximately 16°. The
net effect is to reduce friction between the borataanthracene and
the pentamethylcyclopentadienyl ligands.
(34) For the structure of the 2-boratanaphthalene anion, see: Paetzold,
P.; Finke, N.; Wennek, P.; Schmid, G.; Boese, R. Z. Naturforsch. 1986,
41b, 167. For a discussion of aromaticity in anthracene, see: (a) Schleyer,
P. v. R.; Maerker, C.; Dransfeld, A.; Jiao, H.; Hommes, N. J. R. v. E. J.
Am. Chem. Soc. 1996, 118, 6317. (b) Krygowski, R. M.; Cyranski, M.
Tetrahedron 1996, 52, 1713. (c) Schleyer, P. v. R.; Jiao, H. Pure Appl.
Chem. 1996, 68, 209.
Alkylation of 4 is complicated by boron’s susceptibility to
nucleophilic attack. This problem has been noted previously

Zirconium Complexes of 9-Phenyl-9-borataanthracene
J. Am. Chem. Soc., Vol. 120, No. 24, 1998 6041
resonances of the B(C6F5)3 fragment. All attempts to isolate
pure 7 were frustrated by its oily nature.
It is interesting to note that the two sides of the borataan-
thracene ligand in 7 (i.e., the two diene fragments) are equivalent
by 1H NMR spectroscopy. Two separate exchange mechanisms
have been identified for group 4 metallocenium ions generated
with B(C6F5)3: (1) ion-pair dissociation/reorganization, which
involves the site exchange of the Zr-Me group in the equatorial
plane of the metallocene, and (2) intermolecular Zr-Me/B-
Me exchange.4c Similar processes may be occurring with 7. In
the ion-pair dissociation/reorganization exchange, cleavage of
the weakly bound Zr‚‚‚MeB(C6F5)3 bridge results in the
formation of a solvent-caged or solvent separated ion-pair, B.
Upon recombination, the Zr-bound methyl group exchanges
sites, forming either A or C (eq 7). This process exchanges
Figure 3. ORTEP view of (AnB-Ph)Cp*ZrCl2 (4) showing the labeling
scheme. Thermal ellipsoids are shown at the 30% probability level.
Selected bond distances in Å: Zr-B, 2.882(2); Zr-Cl(1), 2.4260(4);
Zr-Cl(2), 2.4443(4); B-C(14), 1.579(2); Zr-C(1), 2.787(2); Zr-C(6),
2.676(2); Zr-C(7), 2.472(2); Zr-C(8), 2.697(2); Zr-C(13), 2.747(2).
The inset shows the bending of the borataanthracene ligand. The
remaining ligands about Zr have been omitted for clarity.
for 1 and 2, and is documented to be a function of the boron
substituent.18a We have obtained the yellow dimethyl derivative,
(AnB-Ph)Cp*ZrMe2 (5), in 70% yield by the reaction of
Cp*ZrMe2Cl with 3‚Li(THF)2 in toluene (eq 5).
the diastereotopic sides of the π-bound ligand(s). The two sides
of the borataanthracene ligand remain equivalent, even at
temperatures as low as -100 °C.35 We propose that 7 exists
as a discrete ion-pair structure such as B in eq 7. This is quite
conceivable, as the large borataanthracene and Cp* ligands
should promote cation/anion separation.36 Also, it has been
shown that the activation barrier for site exchange is lowered
and that the rate of dissociation is accelerated in solvents of
high dielectric constant.37 Note that the 1H NMR signal of MeB-
(C6F5)3 at 0.48 ppm in 7 is typical for compounds in which the
anion is free.38 Although the exact structural composition of 7
remains unclear, and in particular, the 11B signal of the
borataanthracene fragment appears surprisingly upfield, the
Following the protocol developed by Marks and co-workers
for group 4 metallocenes,4c the treatment of 5 with one
equivalent of the methide abstracting reagent, B(C6F5)3, in CD2-
Cl2 produces [(AnB-Ph)Cp*ZrMe][MeB(C6F5)3] (7 in eq 6)
cleanly and quantitatively by 1H and 13C NMR spectroscopies.
The pertinent spectroscopic features include (1) the low-field
shift of the Zr-Me resonance to 0.85 ppm, (2) a broad B-Me
peak at 0.48 ppm, and (3) two signals in the 11B NMR spectrum
at 4.8 ppm (AnB-Ph) and -12.9 ppm (B-Me). The 19F NMR
spectrum of 7 is unexceptional, displaying the expected three
(35) We have recently isolated and have obtained a crystal structure of
the analogous cationic complex [(C5H5B-Ph)Cp*ZrMe][MeB(C6F5)3]. The
kinetics of the site exchange process have been measured for this complex,
and we have obtained activation parameters which are comparable to those
observed for standard group 4 metallocenium ions. These results will be
disclosed in a future communication.
(36) Siedle, A. R.; Newmark, R. A. J. Organomet. Chem. 1995, 497,
119.
(37) Deck, P. A.; Marks, T. J. J. Am. Chem. Soc. 1995, 117, 6128.
(38) Guo, Z.; Swenson, D. C.; Guram, A. S.; Jordan, R. F. Organome-
tallics 1994, 13, 766.

6042 J. Am. Chem. Soc., Vol. 120, No. 24, 1998
Lee et al.
Since peak areas are proportional to the total ion count, with
heavier hydrocarbons yielding higher trace abundances, the GC/
MS data do not quantify the relative product ratio. However,
it is clear that there are two distributions corresponding to even-
carbon and odd-carbon olefin products. The most abundant
distribution in Figure 4 consists of an envelope of, in order of
increasing retention time, even-carbon 2-alkyl-1-alkenes (labeled
as c in Figure 4), 1-alkenes (labeled b), and 2-alkenes (labeled
a) in the range of C10 to C24. Each set of three olefins are
separated by 28 mass units, corresponding to an inserted
ethylene molecule. The components of the odd-carbon distribu-
tion (d and e in Figure 4) are also separated by 28 mass units.
The peaks of the two distributions are interspersed such that
the overall trace shows a progression of olefin products of
increasing mass (C10, C11, C12, etc.). For a series of reactions
using 4/1000 MAO/C2H4, the activities over a period of 30 min
lay in the range 1170-1200 kg/(mol of Zr‚h).
The product distribution from the 4/MAO/C2H4 reaction is
complicated because there is more than one reaction path which
the 1-alkenes follow after their formation and because of the
statistical nature of the propagation sequence. In addition, there
is also evidence for alkane formation. To clarify the fate of
1-alkenes formed by 4/MAO/C2H4, we chose to react 1-tridecene
directly.40
Figure 4. GC trace of the product from the reaction of 4/1000 MAO
with 1 atm of C2H4. Major distribution, even-carbon: (a) 2-alkenes,
(b) 1-alkenes, (c) 2-alkyl-1-alkenes. Minor distribution, odd-carbon:
(d) 2-alkenes, (e) 1-alkenes.
1
The H NMR spectrum of product mixture from the slow
addition of 1-tridecene to 4/MAO ([Zr] ) 9.9 × 10-4 M, [Al]
) 0.9 M) in toluene shows only two olefinic products,
2-tridecene (74%) and 2-methyl-1-tridecene (26%).41 Figure
5a shows the GC trace of this product mixture. The two peaks
are assigned to 2-tridecene (overlaps with tridecane, total 80%)
and 2-methyl-1-tridecene (20%). The product mixture is
different when neat 1-tridecene is injected rapidly into the
reaction solution. In addition to 2-tridecene and 2-methyl-1-
tridecene, 2-undecyl-1-pentadecene (tridecene dimer) is also
formed. Figure 5b shows the GC trace from the latter reaction
(2-tridecene and tridecane, 80%; 2-methyl-1-tridecene and
2-methyltridecane, 14%; 2-undecyl-1-pentadecene, 6%).
formation of 7 from B(C6F5)3 and 5 can be reversed by using
a suitable methyl source. Thus, when solutions of 7 are treated
with 2 equiv of Cp2ZrMe2, one obtains 5 as well as the expected
products from Cp2ZrMe2 and B(C6F5)3.39
Activation and Catalytic Activity Toward Olefins. The
electronic and structural similarities of 4 and 5 to group 4
metallocenes are obvious, and they suggest that these complexes
may serve as precatalysts for olefin polymerization. In this
section, we report on the activation of 4 and 5 and the reactivity
of the catalytic species toward ethylene and 1-alkenes. It is
also possible to study the reactivity of the well-defined species,
7. Finally, a comparison between catalysts containing the [AnB-
Ph]Cp* and [C5H5B-Ph]Cp* ligand sets highlights the role of
sterics in determining the stability of this class of compounds.
An exothermic, steady uptake of ethylene is observed when
1 atm of ethylene is introduced over a toluene solution of 4
and MAO ([Zr] ) 9.3 × 10-4 M, [Al] ) 0.9 M); however, no
polymer precipitates. Quenching the reaction and workup gives
Scheme 1 shows a plausible reaction sequence that accounts
for the fate of 1-tridecene. Insertion of the alkene into [Zr]-H
([Zr]-H ) [(AnB-Ph)Cp*Zr-H]+)42 gives alkyl species, A.
Since we know that the reaction with ethylene gives low
molecular weight oligomers, while keeping a high rate of
ethylene consumption, the rate of â-hydrogen elimination from
A is faster than those in typical metallocenes. When the
concentration of 1-tridecene is high, A can be trapped to give
the disubstituted alkyl, B. â-Hydrogen elimination from B gives
2-undecyl-1-pentadecene and regenerates [Zr]-H. The forma-
tion of 2-tridecene is the result of a 2,1-insertion of 1-tridecene
into [Zr]-H to give the secondary alkyl, C, followed by
â-hydrogen elimination. Once formed, 2-tridecene does not re-
enter the reaction cycle.
1
a waxy solid. The olefinic peaks in the H NMR spectrum of
the product reveals a composition of 47% 2-alkenes (5.39 ppm),
38% 1-alkenes (5.80 ppm (X), and 4.93 ppm (AB)), and 15%
2-alkyl-1-alkenes (4.66 ppm (s)) (eq 8).
The presence of 2-methyl-1-tridecene and tridecane in the
product mixture is best accommodated by invoking alkyl
exchange between Zr and the Al in MAO. Thus, [Zr]-R (where
R ) H or tridecyl) reacts with an Al-Me functionality to give
[Zr]-Me. Insertion of 1-tridecene into [Zr]-Me gives D,
affording 2-methyl-1-tridecene upon â-hydrogen elimination.
Tridecane is the hydrolysis product of Al-R when R ) tridecyl.
(39) Bochmann, M. B.; Lancaster, S. J. Angew. Chem., Int. Ed. Engl.
1994, 33, 1634.
(40) Reactions carried out using 1-hexene and 1-octene gave the same
type of products, but product isolation from the solvent was not practical.
(41) The 1H NMR and GC/MS data have been compared to those of an
authentic sample of 2-methyl-1-tridecene (see the Experimental Section).
GC/MS analysis proved useful in determining the exact
constitution of these olefins. Figure 4 shows the GC trace
obtained from the product mixture using 4/1000 MAO/C2H4.

Zirconium Complexes of 9-Phenyl-9-borataanthracene
J. Am. Chem. Soc., Vol. 120, No. 24, 1998 6043
Figure 5. GC traces of the products from the reactions of 1-tridecene with (a) 4/1000 MAO, [Al] ) 0.93 M, slow addition, (b) 4/1000 MAO, [Al]
) 0.93 M, rapid addition, (c) 1/1000 MAO, [Al] ) 3.1 M, and (d) 7.
Scheme 1
Similarly, 2-methyltridecane results from transmetalation from
D to Al-Me, followed by hydrolysis of the resulting aluminum
alkyl.
Adding 1-tridecene to solutions of 4 and MAO at higher Al
concentrations results in a higher proportion of transmetalation
products. For example, when [Zr] ) 5.7 × 10-3 M and [Al]
) 3.1 M, the rapid injection of 1-tridecene produces 2-tridecene
(44%, 1H NMR spectroscopy), 2-methyl-1-tridecene and 2-meth-
yltridecane (42%), and 2-undecyl-1-pentadecene (14%) (Figure
5c).
carbons; δ 34.3, 27.3, 30.6, methylene carbons R, â, and γ to
the methine junction, respectively),43 indicates that the polymer
has a branched structure. The reaction of 1-tridecene and 7 in
CD2Cl2 was too fast to monitor by 1H NMR spectroscopy. The
spectrum shows that 2-tridecene and 2-undecyl-1-pentadecene
are formed in a 3:1 ratio. The GC trace of this product mixture
is shown in Figure 5d.
Synthesis of (C5H5B-Ph)Cp*ZrCl2 (8) and Reactivity of
8/MAO Toward Olefins. The reaction of [C5H5B-Ph]Li with
Cp*ZrCl3 in Et2O affords [C5H5B-Ph]Cp*ZrCl2 (8)44 as a bright
yellow solid (eq 9).
Reactivity of [(AnB-Ph)Cp*ZrMe][MeB(C6F5)3] (7). Pre-
cipitation of polyethylene is observed when one atmosphere of
ethylene is introduced above a solution of 7 ([Zr] ) 9.3 × 10-4
M). Standard workup gave soft, pliable material, corresponding
to an activity over a period of 30 min of 150 kg of PE/(mol of
Zr‚h). The melting point of this material determined by DSC
methods is 113 °C, with Mn ) 50 900 and Mw ) 108 000, as
determined by GPC, relative to polystyrene. This information,
coupled with 13C NMR analysis of the product (in 1,2,4-
trichlorobenzene/10% C6D6: δ 38.8, 37.1, 38.0, methine

6044 J. Am. Chem. Soc., Vol. 120, No. 24, 1998
Lee et al.
borataanthracene may not allow for optimum orbital overlap
between boron and its substitutent and that the effect of the
exocyclic substituent in modulating the electron density at the
metal will be less pronounced than that attained in boratabenzene
analogues. The severe bending of the outer rings away from
the [Cp*ZrCl2] core in 4 also reflects the spatial requirements
of the borataanthracene ligand.
The rate of monomer uptake by 4/MAO is among the highest
observed thus far at 1 atm by a catalyst supported with
boratacyclic ligands (in kg/(mol of Zr‚h): 4/MAO, 1170-1200
vs 1/MAO, 197; 2/MAO, 1144).45 However, poor selectivities
are observed in the reactions of 4/MAO and ethylene, as shown
in Figure 4. Since low molecular weight species are obtained,
the rate of â-hydrogen elimination from the growing chain must
be fast, and similar fast rates of â-hydrogen elimination have
been observed with catalysts derived from [C5H5B-R]2ZrCl2 and
MAO (R ) Ph,18b OEt46).
Reactions with 1-tridecene are useful in elucidating the fate
of the 1-alkenes which form in the ethylene reactions. Forma-
tion of 2-tridecene is favored under dilute conditions, and this
is likely a consequence of a 2,1-insertion/â-hydrogen elimination
sequence. Similar specificity for 2-alkenes results when 4/MAO
reacts with ethylene. Higher concentrations of 1-tridecene allow
for double insertion (A to B in Scheme 1), ultimately making
2-undecyl-1-pentadecene. Transmetalation reactions from [Zr]-
R to Al-Me functionalities in the MAO generate [Zr]-Me and
lead to the formation of 2-methyl-1-tridecene.
The observation of 7, together with its reactivity and its
relationship to the well-defined group 4 metallocene catalysts,
is an important step in confirming that the replacement of
cyclopentadienyl ligands with boratacyclic counterparts leads
to catalysts of similar overall structure. Also relevant in this
context is that the reaction of 7 toward 1-tridecene leads to a
similar product distribution as that with 1-tridecene and 4/MAO.
There are some notable differences between the two catalysts.
Ethylene is consumed at significantly higher rates with 4/MAO
(1170-1200 kg/(mol of Zr‚h) vs 150 kg/(mol Zr‚h) for 7), and
the average molecular weight of the resulting ethylene oligomers
is lower. In addition, the catalytic lifetime of 7 is shorter than
that of 4/MAO. These differences may be the result of different
counteranion properties and the more stringent conditions for
monomer purity required by 7.47 However, at this stage, it is
not possible to rule out exchange reactions between MAO and
the borataanthracene boron or the participation of byproducts
from the MAO activation which have catalytic activities of their
own.
The increased longevity of the catalytic species formed by
4/MAO, relative to 8/MAO, confirms our expectation that the
larger borataanthracene ligand more effectively stabilizes a
reactive metal center. This difference in size between the
boratacyclic ligands may also be used to account for the different
selectivities observed for 4/MAO and 8/MAO. Double insertion
of 1-tridecene to give the â-disubstituted alkyl (i.e., B in Scheme
1) appears to be more favored with 8/MAO, as would be
expected within a more open coordination environment. For
4/MAO, a consecutive insertion seems disfavored on steric
Figure 6. Rates of C2H4 uptake during ethylene polymerization
reactions using 4/MAO (9) and 8/MAO (O).
The reaction of 1 atm of ethylene with 8/1000 MAO ([Zr] )
8.9 × 10-4 M) gives polyethylene (Tm ) 128 °C by DSC, Mw
) 31 300, Mn ) 6290 by GPC). The 13C NMR (in 1,2,4-
trichlorobenzene/10% C6D6) spectrum of this sample displays
a single peak at 30.1 ppm, indicating that linear polyethylene
is formed. Multiple runs gave an average activity over a 30-
min period of 290 ( 5 kg of PE/(mol of Zr‚h). This activity is
considerably lower than that observed using 4/MAO. The slow
addition of 1-tridecene to 8/MAO gives a product containing
approximately 79% 2-undecyl-1-pentadecene, 11% 2-methyl-
1-tridecene, and only 2% 2-tridecene.
Relative Stability of Catalytic Species. To establish the
relative stabilities of the catalytic species, the rates of ethylene
consumption throughout the course of identical polymerization
reactions using 4/MAO and 8/MAO were measured.
A
comparison of the activities is illustrated in Figure 6 where the
relative activity is plotted against reaction time (see the
Experimental Section). The reaction using 4/MAO is character-
ized by a strong C2H4 uptake during the initial stages of the
reacton. This activity gradually levels off to about 42% of the
initial uptake. Lower ethylene uptake is observed for 8/MAO,
and the activity decreases sharply as the reaction proceeds. Note
that, after 60 min, ethylene consumption has nearly ceased for
8/MAO whereas the activity of 4/MAO is sustained. These
reaction profiles indicate that the active species derived from
4/MAO is more stable under these reaction conditions than that
derived from 8/MAO and suggest that the larger borataan-
thracene ligand confers significant steric stabilization.
Summary and Conclusion
We have shown that the borataanthracene framework can be
used as a ligand for zirconium. The solid-state molecular
structures of 6, 3‚Li(TMEDA), and 4 give good insight into
the effects of coordination and charge on the borataanthracene
heterocycle. In all cases, the angle between the pendant phenyl
ring and the inner core of the borataanthracene fragment remains
nearly invariant at 62°. In structurally characterized [4-t-
BuC5H4B-Ph]2ZrCl2,18b there is a nearly coplanar relationship
between the boratabenzene and the pendant phenyl rings.
Overall, this suggests that the steric environment around
(45) These activity values differ from previously reported values because
a new batch of MAO with improved properties is now commercially
available. Bazan, G. C.; Lee, R. A.; Rogers, J. S. Unpublished results.
(46) Rogers, J. S.; Bazan, G. C.; Sperry, C. K. J. Am. Chem. Soc. 1997,
119, 9305.
(47) For the dependence of reactivity on counteranion properties in other
catalytic systems, see: (a) Chien, J. C. W.; Song, W.; Rausch, M. D. J.
Polym. Sci., Part A.: Polym. Chem. 1994, 32, 2387. (b) Siedle, A. R.;
Lamanna, W. M.; Newmark, R. A. Makromol. Chem., Macromol. Symp.
1993, 66, 215. (c) Reference 9b.
(42) It is assumed in these reactions that MAO alkylates the metal and
removes one ligand heterolytically to give a cationic zirconium species.
See refs 3 and 4.
(43) Randall, J. C.; Hsieh, E. T. Macromolecules 1982, 15, 1402.
(44) This compound has been synthesized independently by Ashe and
co-workers: Ashe, A. J., III. Private communication.

Zirconium Complexes of 9-Phenyl-9-borataanthracene
J. Am. Chem. Soc., Vol. 120, No. 24, 1998 6045
CH2O). 11B{1H} NMR (C6D6): δ 39.8. Anal. Calcd (C27H30BLiO2):
C, 80.22; H, 7.48. Found: C, 79.60; H, 7.33.
grounds, and most of the reaction is channeled to the 2-tridecene
product via 2,1-insertion.
[AnB-Ph]Li(TMEDA) (3‚Li(TMEDA)). A 50.0-mg (0.124-mmol)
sample of 3‚Li(THF)2 was dissolved in 1 mL of benzene. To this
solution was added 19.0 µL (0.126 mmol) of TMEDA. After stirring
for 10 min, the orange solution turned bright yellow, and microcrys-
talline material precipitated. Recrystallization was induced by warming
the solution to 60 °C and allowing it to cool gradually, whereupon
yellow crystals of 3‚Li(TMEDA) formed. The crystals were washed
with cold pentane and collected by filtration (35 mg, 75%). 1H NMR
(C6D6): δ 8.63 (d, 2H, J ) 8.1 Hz, H1, H8), 7.98 (d, 2H, J ) 6.8 Hz,
o-H), 7.80 (d, 2H, J ) 8.5 Hz, H4, H5), 7.59 (app t, 2H, J ) 7.6 Hz,
m-H), 7.44 (t, 1H, J ) 7.4 Hz, p-H), 7.36 (ddd, 2H, J ) 7.8, 6.8, 0.9
Hz, H3, H6), 7.29 (s, 1H, H10), 7.00 (ddd, 2H, J ) 7.9, 6.5, 1.4 Hz, H2,
H7), 1.00 (s, 12H), 0.96 (s, 4H). 13C{1H} NMR (C6D6): δ 139.0 (C4a,
These novel compounds are interesting as they show catalytic
potential. Further modifications of the borataanthracene ligand
(for instance, changing the substitutent on boron) or the synthesis
of bis(borataanthracene)zirconium complexes may lead to new
catalyst precursors which display improved product selectivities.
However, the preparation of the borataanthracene framework
remains, to date, synthetically demanding, and more practical
syntheses need to be developed before it can be adopted as a
ligand for routine use.
Experimental Section
General Methods. All manipulations were performed under an inert
atmosphere using standard glovebox and Schlenk techniques.48 Solvents
were degassed and distilled from the appropriate drying agents (Et2O,
THF, C6H6, toluene, and pentane from sodium-benzophenone; CH2-
Cl2 and CHCl3 from CaH2). Deuterated solvents obtained from
Cambridge Isotope Laboratories (all g99 atom % D) were treated
similarly. PhBCl2 (Alfa) and n-BuLi and [Ph3PCH3]Br (Aldrich) were
used as received. TMEDA, 1-hexene, 1-octene, 1-tridecene, and
2-tridecanone (Aldrich) were degassed and dried over molecular sieves
prior to use. Cp*ZrCl3,49 Cp*ZrMe2Cl,50 LiTMP,51 6,29 and [C5H5B-
Ph]Li21 were prepared according to literature procedures. B(C6F5)3 was
received as a gift from Exxon Chemicals and was sublimed prior to
use. MAO (9.6 wt % Al, d ) 0.88 g/mL) was purchased from Akzo
Chemicals Inc. Ethylene (Aldrich) was purified using an Oxiclear
disposable gas purifier (also available from Aldrich). 1H NMR (400
MHz), 13C NMR (100 MHz), and 11B NMR spectra (128 MHz) were
recorded on a Bruker AMX-400 spectrometer, while 19F NMR (473
MHz) spectra were recorded on a Varian INOVA-500 spectrometer.
Chemical shifts for 1H NMR and 13C NMR were referenced to internal
solvent resonances. Those for 11B NMR and 19F NMR were referenced
to external BF3‚OEt2 and R,R,R-trifluorotoluene, respectively. GC/
MS data were collected on a HP 5890 Series II gas chromatograph
coupled with a HP 5970 Series mass selective detector. Differential
scanning calorimetry measurements were performed on a TA Instru-
ments DSC 2920 Modulated DSC. Elemental analyses were performed
by Desert Analytics Laboratories, Tucson, AZ.
[AnB-Ph]Li(THF)3 (3‚Li(THF)3). To a solution containing 1.00
g (3.93 mmol) of 6 in 10 mL of THF at -35 °C was added 0.58 g (3.9
mmol) of LiTMP in 10 mL of THF. The reaction was stirred for 4 h.
Removal of volatiles under vacuum afforded 3‚Li(THF)3 as a tacky
orange solid (1.83 g, 97%). 1H NMR (C6D6): δ 8.64 (d, 2H, J ) 8.2
Hz, H1, H8), 8.03 (dd, 2H, J ) 7.9, 1.4 Hz, o-H), 7.84 (d, 2H, J ) 7.8
Hz, H4, H5), 7.60 (app t, 2H, J ) 7.8 Hz, m-H), 7.44 (tt, 1H, J ) 7.4,
1.4 Hz, p-H), 7.37 (ddd, 2H, J ) 7.9, 6.5, 1.6 Hz, H3, H6), 7.36 (s, 1H,
H10), 7.00 (ddd, 2H, J ) 7.9, 6.6, 1.3 Hz, H2, H7), 2.83 (m, 12H), 1.06
(m, 12H). 13C {1H} NMR (C6D6): δ 139.3 (C4a, C10a), 137.2 (C1, C8),
135.4 (C4, C5), 127.1 (p-C), 125.7 (C3, C6), 117.1 (C2, C7), 101.0 (C10),
67.5 (CH2CH2O), 25.2 (CH2CH2O), o-, m-C not observed. 11B{1H}
NMR (C6D6): δ 39.7. Anal. Calcd (C31H38BLiO3): C, 78.16; H, 8.04.
Found: C, 78.04; H, 7.79.
C10a), 137.3 (C1, C8), 135.5 (C4, C5), 127.6 (o-C), 127.5 (p-C), 127.2
(m-C), 125.8 (C3, C6), 117.5 (C2, C7), 101.1 (C10), 55.5 (CH2NMe2),
43.7 (CH2NMe2). 11B{1H} NMR (C6D6): δ 39.8. Anal. Calcd (C25-
H30BLiN2): C, 79.80; H, 8.04; N, 7.44. Found: C, 79.66; H, 7.80; N,
7.43.
(AnB-Ph)Cp*ZrCl2 (4). A solution of 100 mg (0.247 mmol) of
3‚Li(THF)2 in 10 mL of toluene was added to a rapidly stirred slurry
containing 82 mg (0.25 mmol) of Cp*ZrCl3 in 10 mL of toluene at
-35 °C. The reaction mixture was allowed to stir for 8 h. The solvent
was removed, and the residue was extracted with CH2Cl2. The extract
was filtered and reduced in volume. Recrystallization by vapor
diffusion of pentane into the CH2Cl2 extract afforded 4 as orange
microcrystals. A second crop of crystals could be obtained by
concentration of the mother liquor and vapor diffusion with additional
pentane (total yield, 60 mg, 44%). 1H NMR (CD2Cl2): δ 8.07 (d, 2H,
J ) 7.8 Hz, H1, H8), 7.68 (d, 2H, J ) 8.2 Hz, H4, H5), 7.68 (d (overlaps
with H4, H5), 2H, o-H), 7.54 (ddd, 2H, J ) 8.2, 6.8, 1.4 Hz, H3, H6),
7.47, (app t, 2H, J ) 7.8 Hz, m-H), 7.40 (m, 3H, H2, H7, p-H), 7.00 (s,
1H, H10), 1.90 (s, 15H). 13C{1H} NMR (CD2Cl2): δ 139.3 (C1, C8),
136.4 (C4a, C10a), 134.1 (C4, C5), 132.2 (C3, C6), 127.1 (o-C), 127.0
(p-C, 126.9 (m-C), 126.0 (C5Me5), 125.0 (C2, C7), 93.8 (C10), 12.5
(C5Me5). 11B{1H} NMR (CD2Cl2): δ 49.5. Anal. Calcd (C29H29BCl2-
Zr): C, 63.27; H, 5.31. Found: C, 63.13; H, 5.17.
(AnB-Ph)Cp*ZrMe2 (5). A mixture of 100 mg (0.247 mmol) of
3‚Li(THF)2 and 72 mg (0.25 mmol) of Cp*ZrMe2Cl was dissolved in
25 mL of cold (-35 °C) toluene. After stirring for 4 h, the solvent
was evaporated, and the crude product was extracted with pentane. The
extract was filtered, reduced in volume, and allowed to stand at -35
°C overnight, whereby 5 precipitated as yellow flakes (122 mg, 70%).
1H NMR (CD2Cl2): δ 8.07 (d, 2H, J ) 8.2 Hz, H1, H8), 7.71 (br, 2H,
3
o-H), 7.48 (m, 4H, H4, H5, m-H), 7.42 (tt, obscured, JHH ) 1.4 Hz,
p-H), 7.40 (ddd, 2H, J ) 8.2, 6.7, 1.5 Hz, H3, H6), 7.25 (ddd, 2H, J )
8.0, 6.8, 1.2 Hz, H2, H7), 6.61 (s, 1H, H10), 1.72 (s, 15H), -1.15 (s,
6H). 13C{1H} NMR (CD2Cl2): δ 138.6 (C1, C8), 136.0 (C4a, C10a),
134.9 (C4, C5), 130.9 (C3, C6), 127.7 (o-C), 127.4 (p-C), 127.2 (m-C),
123.0 (C2, C7), 119.2 (C5Me5), 93.4 (C10), 44.0 (ZrMe), 12.0 (C5Me5).
11B{1H} NMR (CD2Cl2): δ 46.2. Anal. Calcd (C31H35BZr): C, 73.06;
H, 6.71. Found: C, 72.79; H, 6.75.
[(AnB-Ph)Cp*ZrMe][MeB(C6F5)3] (7). A solution containing 49
mg (0.096 mmol) of B(C6F5)3 in 5 mL of CH2Cl2 was cooled to -35
°C. This was slowly added to a stirred solution containing 50 mg (0.098
mmol) of 5 in 5 mL of CH2Cl2 at -35 °C. The yellow solution turned
bright magenta then dark purple. 1H NMR (CD2Cl2): δ 8.11 (tt, 1H,
J ) 7.2, 1.2 Hz, p-H), 7.95 (d, 2H, J ) 8.1 Hz, H1, H8), 7.91 (d, 2H,
J ) 8.0 Hz, o-H), 7.86 (app t, 2H, J ) 7.1 Hz, m-H), 7.59 (ddd, 2H,
J ) 8.2, 7.1, 1.1 Hz, H3, H6), 7.40 (ddd, 2H, J ) 8.1, 7.1, 1.0 Hz, H2,
H7), 7.33 (d, 2H, J ) 8.2 Hz, H4, H5), 6.02 (s, 1H, H10), 1.43 (s, 15H,
Cp*), 0.85 (s, 3H, ZrMe), 0.48 (br s, 3H, BMe). 13C{1H} NMR (CD2-
[AnB-Ph]Li(THF)2 (3‚Li(THF)2). The 3‚Li(THF)3 prepared as
described above was repeatedly triturated with pentane and then filtered
until the orange color in the washings no longer persisted. Drying
under vacuum afforded a finely divided yellow powder. 1H NMR
(C6D6): δ 8.60 (d, 2H, J ) 8.0 Hz, H1, H8), 7.99 (d, 2H, J ) 6.8 Hz,
o-H), 7.81 (d, 2H, J ) 8.4 Hz, H4, H5), 7.60 (t, 2H, J ) 7.5 Hz, m-H),
7.44 (t, 1H, J ) 7.2 Hz, p-H), 7.37 (t, 2H, J ) 7.0 Hz, H3, H6), 7.29
(s, 1H, H10), 7.00 (t, 2H, J ) 7.2 Hz, H2, H7), 2.37 (m, 12H), 0.80 (m,
12H). 13C{1H} NMR (C6D6): δ 139.0 (C4a, C10a), 136.9 (C1, C8), 135.4
(C4, C5), 128.9 (br, C8a, C9a), 127.4 (o-C), 127.1 (p-C), 126.9 (m-C),
125.6 (C3, C6), 116.9 (C2, C7), 101.0 (C10), 67.6 (CH2CH2O), 25.0 (CH2-
1
Cl2, -70 °C): δ 155.4 (C4a, C10a), 147.2 (d, JCF ) 234 Hz), 138.6
1
(C1, C8), 136.6 (d, JCF ) 242 Hz), 136.3 (C4, C5), 135.8 (C3, C6),
1
(48) Burger, B. J.; Bercaw, J. E. In Experimental Organometallic
Chemistry; Wayda, A. L., Darensbourg, M. Y., Eds.; ACS Symposium
Series 353; American Chemical Society: Washington, DC, 1987.
(49) Wolczanski, P. T.; Bercaw, J. E. Organometallics 1982, 1, 793.
(50) Rodriguez, G. Ph.D. Thesis, University of Rochester, 1997.
(51) Olofson, R. A.; Dougherty, C. M. J. Am. Chem. Soc. 1973, 95, 581.
135.5 (d, JCF ) 244 Hz), 132.1 (C2, C7), 129.8 (o-C), 129.7 (p-C),
128.1 (m-C), 126.9 (C5Me5), 106.6 (C10), 16.6 (Zr-Me), 10.5 (C5Me5),
8.9 (B-Me). 11B{1H} NMR (CD2Cl2): δ 4.8 (AnB), -12.9 (B-Me).
19F NMR (CD2Cl2): δ 70.5 (d, J ) 19.8 Hz, o-F), 38.6 (t, J ) 20.3
Hz, p-F), 36.0 (t, J ) 21.8 Hz, m-F).

6046 J. Am. Chem. Soc., Vol. 120, No. 24, 1998
Lee et al.
[C5H5B-Ph]Cp*ZrCl2 (8). Approximately 10 mL of Et2O was
vacuum transferred into a flask containing 100 mg (0.625 mmol) of
[C5H5BPh]Li and 208 g (0.625 mmol) of Cp*ZrCl3 at -78 °C. The
pale yellow slurry was allowed to warm to room temperature and was
stirred overnight. The solvent was removed, and the residue was
extracted with toluene. The extract was filtered and reduced in volume,
and the addition of pentane caused the precipitation of a yellow solid.
This solid was washed with pentane and recrystallized from toluene/
pentane (1:2 v/v) (240 mg, 85%). 1H NMR (C6D6): δ 8.05 (d, 2H, J
) 6.8 Hz, o-H), 7.42 (t, 2H, J ) 7.4 Hz, m-H), 7.30 (t, 1H, J ) 7.3
Hz, p-H), 7.16 (m, 2H, CHCHCHB), 6.83 (d, 2H, J ) 9.2 Hz,
CHCHCHB), 5.69 (t, 1H, J ) 6.8 Hz, CHCHCHB), 1.68 (s, 15H).
13C{1H} NMR (C6D6): δ 142.9 (CHCHCHB), 134.0 (o-C), 129.3 (p-
C), 128.1 (m-C), 126.7 (br, CHCHCHB), 126.1 (C5Me5), 108.5
(CHCHCHB), 12.5 (C5Me5). 11B{1H} NMR (C6D6): δ 41.2. Anal.
Calcd (C21H25BCl2Zr): C, 56.00; H, 5.59. Found: C, 54.26; H, 5.60.
Ethylene Polymerization Reactions. The following description is
representative. A 7.03-g aliquot (25.0 mmol of Al) of MAO was
weighed into a 100-mL round-bottomed flask. With rapid stirring, a
14-mg sample (0.025 mmol, Zr/Al ratio ) 1/1000) of 4 dissolved in
5.0 mL of toluene was added to the MAO solution, followed by 15.0
mL of toluene as diluent. The flask was fitted with a Teflon inlet
adapter, and the entire assembly was weighed. The flask was immersed
in a 21 °C constant-temperature bath, and after evacuation for 15 s,
ethylene (1 atm) was introduced into the reaction vessel. After a
reaction time of 30 min, the flask was closed off from the ethylene
source, and the assembly was reweighed. The flask was then opened
to air, and the solution was quenched with distilled water. A 5-mL
attached to the vacuum line between the ethylene source and the vent.
For an uptake measurement, the ethylene source was closed, and the
time (to the nearest 1 s) required for the oil to rise up the length of the
flow tube (corresponding to a volume of 0.8 mL) was recorded.
Measurements were taken at 5-min intervals for a period of 1 h.
Measuring uptake times more precisely, especially at the intial stages
of the reaction where ethylene consumption is extremely fast, is difficult,
thereby introducing a margin of error in the measurement. The rates
of ethylene consumption in Figure 6 were normalized against the
maximum activity of the 4/MAO catalyst system.
Preparation of 2-Methyl-1-tridecene. A 16.7-mL aliquot of n-BuLi
(26.7 mmol, 1.6 M in hexanes) was added dropwise to a stirred solution
containing 9.50 g (26.6 mmol) of Ph3PCH3Br in 60 mL of THF at
-78 °C. After 30 min, the reaction was brought to 0 °C and was
allowed to stir at this temperature for an additional 1 h. A mixture
containing 5.28 g (26.6 mmol) of 2-tridecanone in 10 mL of THF was
slowly added to the flask, and the reaction was allowed to stir overnight,
during which time a white precipitate formed. The solution was filtered
through Celite, and the filter cake was washed with pentane. The
combined filtrate and washings were removed in vacuo to afford a
yellow residue. The residue was extracted with pentane, and crude
2-methyl-1-tridecene was isolated upon evaporation of pentane. Pure
product (5.02 g, 96%) was obtained by vacuum distillation (55 °C,
0.01 Torr). 1H NMR (CDCl3): δ 4.66 (s, 1H), 4.64 (s, 1H), 1.98 (t,
2H, J ) 7.6 Hz), 1.69 (s, 3H), 1.40 (br, 2H), 1.24 (s, 16H), 0.86 (t,
3H, J ) 6.8 Hz), -0.62 (s, 6H). 13C{1H} NMR (CDCl3): δ 146.2,
109.5, 37.9, 32.0, 29.8, 29.7, 29.6, 29.4, 29.4, 27.7, 22.4, 14.1. MS:
M+ 196, calcd for C14H28 196.4.
1
aliquot of the reaction mixture was drawn for H NMR and GC/MS
Structure Determination of 3‚Li(TMEDA), 4, and 6. X-ray
quality crystals of 3‚Li(TMEDA) were grown from a benzene solution
which was slowly cooled from 60 °C to room temperature. Crystals
of 4 were grown from methylene chloride vapor diffused with pentane
at -35 °C. Crystals of 6 were grown from diethyl ether at -35 °C.
Fragments of 3‚Li(TMEDA), 4, and 6 were cut and mounted on glass
fibers under Paratone-8277 and were placed on the X-ray diffractometer
in a cold nitrogen stream supplied by a Siemens LT-2A low-temperature
device. The X-ray intensity data were collected on a standard Siemens
SMART CCD area detector system equipped with a normal focus
molybdenum-target X-ray tube operated at 2.0 kW (50 kV, 40 mA)
for 3‚Li(TMEDA) and 4 and at 1.5 kW (50 kV, 30 mA) for 6. A total
of 1.3 hemispheres of data were collected using a narrow frame method
with scan widths of 0.3° in ω and exposure times of 10 s/frame for
3‚Li(TMEDA), 4, and 6. Frames were integrated to 0.75 Å for 3‚Li-
(TMEDA) and 6 and to 0.90 Å for 4 with the Siemens SAINT program
yielding a total of 7896 reflections for 3‚Li(TMEDA), 28 688 reflections
for 4, and 14 650 for 6. The unit cell parameters were based upon the
least-squares refinement of three-dimensional centroids of 2448 reflec-
tions, 5424 reflections, and 1849 reflections at -80, -90, and -50 °C
for 3‚Li(TMEDA), 4, and 6, respectively. The space groups were
assigned on the basis of sytematic absences and intensity statistics by
using the XPREP program (Siemens, SHELXTL 5.04). The structures
of 3‚Li(TMEDA) and 4 were solved by direct methods (SHELXTL
program, version 5.04) and were refined by full-matrix least-squares
on F2. The structure of 6 was solved using MITHRAL-88 (TEXSAN-
92). All non-hydrogen atoms for the structures were refined with
anisotropic thermal parameters, giving a data-to-parameter ratio of
>10:1 for both 3‚Li(TMEDA) and 4. H atoms were included in
idealized positions for the structures. Selected bond distances and
angles for 3‚Li(TMEDA) and 6 are provided in Table 1 in the text.
analyses. The remaining solution was stirred into 3 M NaOH until
the aluminum salts dissolved completely. The remaining polymer was
collected by vacuum filtration, washed with distilled water, and dried
under vacuum.
Reactions with 1-Alkenes. The procedure described using 1-tridecene
is representative. The catalyst solution was prepared as described for
the polymerization reactions. A 1.0-mL toluene solution containing
100 mg of 1-tridecene was added dropwise into the catalyst solution
over a period of 20 min. Alternatively, neat substrate was injected
rapidly into the catalyst solution. After a total reaction time of 30 min,
the reaction was quenched with water. The organic layer was separated
from the aqueous layer, and toluene was removed by rotary evaporation
to afford 87 mg of product.
Ethylene Polymerization with 7. A 15.0-mg (0.0293-mmol) sample
of B(C6F5)3 dissolved in 15.0 mL of toluene was added to 14.9 mg
(0.0292 mmol) of 5 in 15.0 mL of toluene at -35 °C. After the mixture
was stirred for 5 min, the flask was fitted with a Teflon inlet adapter
and the entire assembly was weighed. The flask was immersed in a
21 °C constant-temperature bath and partially evacuated for 15 s, and
ethylene (1 atm) was introduced into the reaction vessel. Following a
reaction time of 30 min, the flask was closed off from the ethylene
source and the assembly was reweighed. A 5-mL aliquot of the reaction
1
solution was drawn for H NMR and GC/MS analysis. The catalyst
was quenched by the addition of 5 mL of water, and the polymer was
isolated by removal of volatiles in vacuo.
Reaction of 7 with 1-Tridecene. A 10.0-mg (0.0195-mmol) sample
of B(C6F5)3 dissolved in 10.0 mL of toluene was added to 10.0 mg
(0.0196 mmol) of 5 in 11.0 mL of toluene at -35 °C. After stirring
for 5 min, 35.8 mg (0.196 mmol) of 1-tridecene was added dropwise
to the stirred solution. After 30 min, the reaction was quenched with
1 mL of water. The organic layer was separated off, and 32.0 mg of
the product was isolated by removal of toluene by rotary evaporation.
Measurement of Ethylene Consumption. Each catalyst solution
was freshly prepared prior to the activity measurement: (1) A solution
containing 9.0 mg of 4 in 5.0 mL of toluene was added dropwise with
stirring to 4.60 g of MAO. An additional 13.1 mL of toluene was
added to the catalyst solution as diluent. (2) In the same manner, a
toluene solution containing 7.4 mg of 8 and 4.60 g of MAO was
prepared in a separate reaction vessel ([Zr] ) 8.9 × 10-4 in each catalyst
solution).
Acknowledgment. G.C.B. is an Alfred Sloan Fellow and a
Henry and Camille Dreyfus Teacher Scholar. The authors are
grateful to these agencies for financial assistance and to the
anonymous reviewers for helpful suggestions. We are also
grateful to Thomas Mourey (Eastman Kodak Co.) for the GPC
data.
Supporting Information Available: Complete crystal-
lographic studies for complexes 3‚Li(TMEDA), 4, and 6 (34
pages, print/PDF). See any current masthead page for ordering
information and Web access instructions.
The reaction vessel was fitted with a Teflon inlet adapter. A specially
designed mineral oil bubbler equipped with a calibrated flow tube was
attached to the vent of the ethylene manifold. The reaction vessel was
JA972651+