Structural and dynamic features of bis[2-(2-furyl)indenyl]zirconium derivatives

Article abstract of DOI:10.1021/om0104518

Treatment of 2-indanone with 2-lithio-5-methylfuran, followed by hydrolysis, dehydration, deprotonation with n-butyllithium, and transmetalation, gave bis[2-(5-methyl-2-furyl)indenyl]-zirconium dichloride (6a). The dynamic 600 MHz ¹H NMR spectroscopic analysis in the temperature range between 253 and 128 K revealed the presence of two metallocene conformational isomers in a 60:40 ratio. It is likely that this observed feature just originates from freezing out the indenyl-furyl rotation. The corresponding activation barrier of 6a was determined at ΔG?_rot = 7.0 ± 0.4 kcal mol^-1 by a line shape analysis. A series of analogous 5-methyl-2-furyl- and 5-methyl-2-thienyl-substituted bis(indenyl)zirconium dibromides and dichlorides show analogous conformational behavior and almost identical rotational activation energies. In the bis[2-(5-methyl-2-furyl)indenyl]ZrR₂ series the metallocene rotational barrier can apparently be frozen on the 600 MHz ¹H NMR time scale for R = CH₂CMe₃ and R = CH₂Ph. The di(neopentyl)Zr complex 7b shows a metallocene rotational barrier of ΔG?_rot(Cp)(213 K) = 9.0 ± 0.3 kcal mol^-1, and for the di(benzyl)Zr complex 7c a ΔG?_rot(Cp) value of 11.4 ± 0.3 kcal mol^-1 was obtained at 243 K. In the cases of 7b and 7c only chiral rac-type metallocene conformers were found in solution within the limits of the accuracy of the ¹H NMR method. The complexes bis[2-(5-ethyl-2-furyl)indenyl]ZrCl₂ (8) and bis[2-(5-methyl-2-furyl)indenyl]Zr(neopentyl)₂ (7b) were characterized by X-ray crystal structure analyses. In the solid state both complexes exhibit chiral rac-like metallocene frameworks.

Full text of DOI:10.1021/om0104518

Organometallics 2001, 20, 5067-5075
5067
Str u ctu r a l a n d Dyn a m ic F ea tu r es of
Bis[2-(2-fu r yl)in d en yl]zir con iu m Der iva tives†
Thorsten Dreier, Klaus Bergander, Elina Wegelius,‡ Roland Fro¨hlich,‡ and
Gerhard Erker*
Organisch-Chemisches Institut der Universita¨t Mu¨nster, Corrensstrasse 40,
D-48149 Mu¨nster, Germany
Received May 29, 2001
Treatment of 2-indanone with 2-lithio-5-methylfuran, followed by hydrolysis, dehydration,
deprotonation with n-butyllithium, and transmetalation, gave bis[2-(5-methyl-2-furyl)indenyl]-
1
zirconium dichloride (6a ). The dynamic 600 MHz H NMR spectroscopic analysis in the
temperature range between 253 and 128 K revealed the presence of two metallocene
conformational isomers in a 60:40 ratio. It is likely that this observed feature just originates
from freezing out the indenyl-furyl rotation. The corresponding activation barrier of 6a
was determined at ∆Gqrot ) 7.0 ( 0.4 kcal mol-1 by a line shape analysis. A series of analogous
5-methyl-2-furyl- and 5-methyl-2-thienyl-substituted bis(indenyl)zirconium dibromides and
dichlorides show analogous conformational behavior and almost identical rotational activation
energies. In the bis[2-(5-methyl-2-furyl)indenyl]ZrR2 series the metallocene rotational barrier
can apparently be frozen on the 600 MHz 1H NMR time scale for R ) CH2CMe3 and
R ) CH2Ph. The di(neopentyl)Zr complex 7b shows a metallocene rotational barrier of
∆Gqrot(Cp)(213 K) ) 9.0 ( 0.3 kcal mol-1, and for the di(benzyl)Zr complex 7c a ∆Gqrot(Cp) value
of 11.4 ( 0.3 kcal mol-1 was obtained at 243 K. In the cases of 7b and 7c only chiral rac-
type metallocene conformers were found in solution within the limits of the accuracy of the
1H NMR method. The complexes bis[2-(5-ethyl-2-furyl)indenyl]ZrCl2 (8) and bis[2-(5-methyl-
2-furyl)indenyl]Zr(neopentyl)2 (7b) were characterized by X-ray crystal structure analyses.
In the solid state both complexes exhibit chiral rac-like metallocene frameworks.
In tr od u ction
time scale [e.g., (2-arylindenyl)2ZrCl2 systems] or only
degenerate enantiomerization of rac-conformers was
observed [e.g., (2-arylindenyl)2Zr(benzyl)2 examples].2,3
We have recently described a series of related (2-
hetarylindenyl)2zirconium and -hafnium complexes,
such as bis[2-(5-methyl-2-furyl)indenyl]zirconium dichlo-
ride (6a ).4,6 This shows a meso-like structure in the
Bis(2-arylindenyl)zirconium complexes (1) were shown
to feature two distinctly different conformational iso-
mers in the crystal that can be described as rac-1 and
meso-1 metallocene conformers (see Chart 1).1 Com-
plexes 1 give homogeneous Ziegler-Natta catalysts
when activated with methylalumoxane (MAO) that have
been used for the formation of high molecular weight
polypropylenes that exhibit elastomeric properties. The
conformational equilibration of the rac- and meso-bis-
(2-arylindenyl)zirconium frameworks during the polym-
erization process was suggested to be a decisive feature
for the production of the elastomeric polyolefins at such
catalysts.1,2
Unfortunately, the corresponding meso-bis(2-arylin-
denyl)zirconium conformational isomers have not been
detected so far to our knowledge in solution, potentially
because of an energy difference of g1.5 kcal mol-1
between the isomers.3 A variety of examples were
investigated by temperature-dependent NMR spectros-
copy, but either the conformational equilibration of
these systems was too fast to become frozen on the NMR
(2) Collette, J . W.; Tullock, C. W.; MacDonald, R. N.; Buck, W. H.;
Su, A. C. L.; Harrell, J . R.; Mu¨lhaupt, R.; Anderson, B. C. Macromol-
ecules 1989, 22, 3851-3866. Gauthier, W. J .; Collins, S. Macromol-
ecules 1995, 28, 3779-3786. Pietsch, M. A.; Rappe´, A. K. J . Am. Chem.
Soc. 1996, 118, 10908-10909. Bruce, M. D.; Coates, G. W.; Haupt-
mann, E.; Waymouth, R. M.; Ziller, J . W. J . Am. Chem. Soc. 1997,
119, 11174-11182. Maciejewski Petoff, J . L.; Bruce, M. D.; Waymouth,
R. M.; Masood, A.; Lal, T. K.; Quan, R. W.; Behrend, S. J . Organome-
tallics 1997, 16, 5909-5916. Kravchenko, R.; Masood, A.; Waymouth,
R. M.; Myers, C. L. J . Am. Chem. Soc. 1998, 120, 2039-2046. Hu, T.;
Kreichi, M. T.; Shah, C. D.; Myers, C. L.; Waymouth, R. M. Macro-
molecules 1998, 31, 6908-6916. Maciejewski Petoff, J . L.; Agoston, T.;
Lal, T. K.; Waymouth, R. M. J . Am. Chem. Soc. 1998, 120, 11316-
11322, and references therein. Tagge, C. D.; Kravchenko, R. L.; Lal,
T. K.; Waymouth, R. W. Organometallics 1999, 18, 380-388. Witte,
P.; Lal, T. K.; Waymouth, R. M. Organometallics 1999, 18, 4147-4155.
Maciejewski Petoff, J . L.; Myers, C. L.; Waymouth, R. M. Macromol-
ecules 1999, 32, 7984-7989. Lin, S.; Waymouth, R. M. Macromolecules
1999, 32, 8283-8290. Nele, M.; Collins, S.; Dias, M. L.; Pinto, J . C.;
Lin, S.; Waymouth, R. M. Macromolecules 2000, 33, 7249-7260. Lin,
S.; Tagge, C. D.; Waymouth, R. M.; Nele, M.; Collins, S.; Pinto, J . C.
J . Am. Chem. Soc. 2000, 122, 11275-11285.
† Dedicated to Professor Dieter Hoppe on the occasion of his 60th
birthday.
(3) Schneider, N.; Schaper, F.; Schmidt, K.; Kirsten, R.; Geyer, A.;
Brintzinger, H. H. Organometallics 2000, 19, 3597-3604.
(4) Dreier, T.; Erker, G.; Fro¨hlich, R.; Wibbeling, B. Organometallics
2000, 19, 4095-4103.
(5) Dreier, T.; Fro¨hlich, R.; Erker, G. J . Organomet. Chem. 2001,
621, 197-206.
(6) Ewen, J . A.; J ones, R. L.; Elder, M. J .; Rheingold, A. L.; Liable-
Sands, L. M. J . Am. Chem. Soc. 1998, 120, 10786-10787.
* To whom correspondence should be addressed. Fax: +49 251
8336503. E-mail: erker@uni-muenster.de.
‡ Performed the X-ray crystal structure analyses.
(1) Waymouth, R. M.; Coates, G. W. Science 1995, 267, 217-219.
Hauptmann, E.; Waymouth, R. M.; Ziller, J . W. J . Am. Chem. Soc.
1995, 117, 11586-11587.
10.1021/om0104518 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 10/19/2001

5068 Organometallics, Vol. 20, No. 24, 2001
Dreier et al.
Ch a r t 1. Str u ctu r a lly Ch a r a cter ized Bis(2-a r yl)-
a n d Bis(2-h eta r yl)in d en ylzir con iu m Com p lexes
F igu r e 1. Dynamic 1H NMR spectra (600 MHz) of complex
6a in CDFCl2/CDF2Cl.
Sch em e 1
crystal, whereas its bis[2-(5-methyl-2-furyl)indenyl]zir-
conium dimethyl derivative (7a ) exhibits a rac-structure
in the solid state (see Chart 1). These furyl-substituted
systems also generate efficient Ziegler-Natta catalysts
for elastomeric polypropylene formation upon treatment
with MAO. We have now investigated the conforma-
tional features of a variety of substituted bis[2-(5-alkyl-
2-furyl)]- and bis[2-(5-alkyl-2-thienyl)indenyl]zirconium
systems by dynamic NMR spectroscopy and found that
here some dynamic features even at the stage of the
metallocene dihalides could be frozen out on the NMR
time scale under certain experimental conditions.7
Resu lts a n d Discu ssion
Bis[2-(5-a lk yl-2-fu r yl)in d en yl]zir con iu m Dih a -
lid es. The synthesis and X-ray crystal structure analy-
sis of bis[2-(5-methyl-2-furyl)]zirconium dichloride (6a )
was recently described by us.4 The synthesis starts by
the addition of 2-lithio-5-methylfuran to 2-indanone.8
Deprotonation of the resulting 2-(5-methyl-2-furyl)-
indene with n-butyllithium followed by treatment with
zirconium tetrachloride gave 6a . Complex 6a exhibits
temperature-dependent dynamic 1H NMR spectra (600
MHz) which could be brought to a static low-tempera-
ture limiting situation by using a mixture of CDFCl2
and CDF2Cl as the solvent9 (see Figure 1).
In such a situation the potential formation of a total
of six conformational diastereomers must be considered.
They shall be tagged by the letters A to F as depicted
in Scheme 2. There are three isomers (A, B, E) with
rac-like metallocene frameworks and three (C, D, F )
with meso-like skeletons. The latter will under experi-
mental conditions probably exhibit averaged Cs-sym-
metric core-frameworks; the rac-like isomers must be
considered to exhibit chiral C2-symmetric cores under
the experimental conditions.10 Thus, the three isomers
of each of the sets to a first approximation are distin-
guished by their relative orientations of the 5-methyl-
2-furyl substituents at their perimeter. As we have seen
from the many known structures, the furyl substituents
are arranged coplanar with the indenyl planes. At the
bent metallocene framework the furyl groups can then
be arranged with their oxygen atoms pointing toward
the front side or toward the narrow back side of the bent
metallocene wedge. Thus a simple metallocene rotation
interconverts, for example, the rac-front-side isomer A
(i.e., the isomer that exhibits the furyl oxygen atoms
both oriented toward the open front side of the bent
metallocene wedge) with the rac-back-side isomer B and
so forth.
1
At 253 K a simple H NMR spectrum of complex 6a
(7) For a related study see: Erker, G.; Aulbach, M.; Knickmeier,
M.; Wingbermu¨hle, D.; Kru¨ger, C.; Nolte, M.; Werner, S. J . Am. Chem.
Soc. 1993, 115, 4590-4601. Knickmeier, M.; Erker, G.; Fox, T. J . Am.
Chem. Soc. 1996, 118, 9623-9630.
(8) Paquette, L. A.; Bauer, W.; Sivik, M. R.; Bu¨hl, M.; Feigel, M.;
Schleyer, P. v. R. J . Am. Chem. Soc. 1990, 112, 8776-8789.
(9) Siegel, J . S.; Anet, F. A. J . Org. Chem. 1988, 53, 2629-2630.
(10) Piemontesi, F.; Camurati, I.; Resconi, L.; Balboni, D.; Sironi,
A.; Moret, M.; Zeigler, R.; Piccolrovazzi, N. Organometallics 1995, 14,
1256-1266. We thank a careful reviewer for several interesting and
helpful suggestions.
is monitored featuring a single sharp methyl resonance
at δ 2.48, the furyl 3-H and 4-H signals at δ 6.64 and
6.14, the indenyl 1-H/3-H resonance at δ 6.64, and the
indenyl arene 4-H/7-H and 5-H/6-H resonances at δ 7.24
and 7.10, respectively. The latter two signals have
broadened considerably at 173 K and have almost
disappeared in the baseline at 153 K. At this temper-
ature, the furyl 3-H signal has also become very broad

Bis[2-(2-furyl)indenyl]zirconium Derivatives
Organometallics, Vol. 20, No. 24, 2001 5069
Sch em e 2. Sch em a tic Rep r esen ta tion of P ossible
Rota m er ic Isom er Str u ctu r es of 6a
F igu r e 2. View of the molecular structure of complex 8
in the crystal, featuring a chiral (rac) metallocene confor-
mation. Selected bond lengths (Å), angles, and dihedral
angles (deg): Zr-C1 2.557(2), Zr-C2 2.548(2), Zr-C3
2.454(2), Zr-C3a 2.523(2), Zr-C7a 2.607(2), Zr-CCp 2.323,
Zr-Cl 2.4175(5), C1-C2 1.412(2), C1-C7a 1.417(2), C2-
C3 1.416(2), C2-C12 1.445(2), C3-C3a 1.431(2), C3a-C7a
1.424(2), C3a-C4 1.416(2), C4-C5 1.363(3), C5-C6 1.406-
(3), C6-C7 1.357(3), C7-C7a 1.416(2), O11-C12 1.369-
(2), O11-C15 1.371(2), C12-C13 1.344(3), C13-C14 1.427-
(3), C14-C15 1.334(2), C15-C21 1.481(3), C21-C22
1.512(3); CCp-Zr-CCp* 132.8, Cl-Zr-Cl* 97.44(3), C1-
C2-C3 108.5(2), C1-C2-C12 125.2(2), C12-C2-C3 126.3-
(2), C2-C3-C3a 107.4(2), C3-C3a-C7a 107.8(1), C3-
C3a-C4 132.8(2), C3a-C7a-C7 120.3(2), C3a-C7a-C1
107.8(2), C2-C12-O11 115.4(2), C12-O11-C15 106.9(3).
substituents that are arranged coplanar with their
adjacent Cp rings. The observed Gibbs activation energy
would then correspond to ∆Gqrot(Ar). In view of the
behavior of the related complexes 7b, 7c, and 10b (see
below), this is an attractive interpretation.
Bis[2-(5-ethyl-2-furyl)indenyl]ZrCl2 (8) was studied as
a second substituted furylindenyl zirconium dichloride
complex example in solution. In this case the topological
NMR situation is more complex: in all the systems
6-10 shown in Scheme 1 freezing of either the metal-
Cp rotation or the rotation about the Cp-furyl vector
(or both, of course) in the complex will result in
diastereotopic splitting of the -CH2- hydrogen atoms
of the furyl-attached ethyl groups. But aside from this
spectral complication a conformational behavior similar
to that observed in complex 6a is expected.
The synthesis of bis[2-(5-ethyl-2-furyl)indenyl]ZrCl2
(8) was carried out as outlined in Scheme 1. 2-Ethylfu-
ran was deprotonated by treatment with n-butyllithium.
The resulting 2-lithio-5-ethylfuran reagent (3b) was
added to 2-indanone, hydrolyzed, and dehydrated to
yield 4b. Subsequent deprotonation by treatment with
n-BuLi followed by transmetalation gave complex 8
(35% isolated after crystallization from toluene at -30
°C). The obtained crystals were suitable for an X-ray
crystal structure analysis of 8. In the crystal complex 8
exhibits a single C2-symmetric rotational isomer. The
conformation of 8 in the solid state represents an
example of the rac-conformer type A (see Scheme 2).
The two symmetry-equivalent furyl substituents are
oriented coplanar with the indenyl ligand frameworks.
Their oxygen atoms point toward the open front side of
the bent metallocene wedge. Even the carbon atoms of
the furyl substituents are arranged in the overall lig-
and plane (see Figure 2). The bonding features of
the metallocene core are in a typical range (Cl1-Zr
2.417(5), Cl1-Zr-Cl1* 97.44(3)°, Cp(centroid)-Zr-
Cp(centroid) angle 132.8°).
and the furyl-methyl resonance shows considerable
broadening (see Figure 1). At 128 K decoalescence is
achieved. We observe an overlapping pattern of at least
14 resonances in the aromatic region (potentially cor-
responding to a total of 16 different protons) and a pair
of methyl resonances at δ 2.57 and 2.44 in a 60:40 ratio.
Since the methyl resonances are not found in an
equimolar ratio, we must conclude that two diastereo-
meric metallocene conformers are present in solution
1
and detected in the static H NMR spectrum at 128 K
(600 MHz) under these conditions. From the observed
behavior in the temperature range 173-153 K (and
additional evidence from other related molecules that
will be presented below) it is possible that in complex
6a the metallocene rotation is frozen out, coinciding with
or very narrowly followed by freezing the rotation
around the indenyl C2-furyl C2 vector. From a line
shape analysis11 of the furyl-CH3 1H NMR resonances
a Gibbs activation energy of ∆Gqrot(Cp) ≈ ∆Gqrot(Ar) ) 7.0
( 0.3 kcal mol-1 was calculated for the 6a (major) to
6a (minor) conformational equilibration. Alternatively,
this spectroscopic behavior could indicate that the
metal-indenyl rotation is still rapid at 128 K and that
we are freezing out the Cp-furyl rotation under our
experimental conditions. This would lead to the obser-
1
vation of two sets of H NMR spectra originating from
an (averaged) chiral C2-symmetric and achiral Cs-
symmetric arrangement of the planarly chiral furyl
(11) Kleier, D. A.; Binsch, G. DNMR 3; Indiana University, 1970.
Kleier, D. A.; Binsch, D. J . Magn. Reson. 1970, 3, 146-160. Marat, K.
XSIM; University of Manitoba, 1997. Green, M. L. H.; Wong, L.-L.;
Seela, A. Organometallics 1992, 11, 2660-2668, and references therein.
In CDFCl2/CDF2Cl solution complex 8 shows a tem-
1
perature-dependent H NMR behavior analogous to that

5070 Organometallics, Vol. 20, No. 24, 2001
Dreier et al.
Ta ble 1. Activa tion En er gies (∆Gqr ot) of th e
Obser ved Con for m a tion a l Equ ilibr a tion of th e
Bis[2-(5-a lk yl-2-h eta r yl)in d en yl]Zr X2 Com p lexes 6,
8, a n d 9 a s Deter m in ed fr om Th eir Dyn a m ic 1H
NMR Sp ectr a (600 MHz, in CDF Cl2/CDF 2Cl) by
Lin e Sh a p e An a lysis.
b
a
compd
X
subst
T (K)
δCH
ratio ∆Grot
3
6a
6b
8
9a
9b
Cl Me-furyl
Br Me-furyl
Cl Et-furyl
Cl Me-thienyl
Br Me-thienyl
143
143
143
133
138
2.41, 2.28
60:40
7.0
7.2
7.1
6.7
6.9
2.58, 2.42c 70:30
1.37, 1.27
2.60, 2.57
2.59, 2.56
60:40
44:56
50:50
a
b
(0.4 kcal mol-1
.
At 133 K. c At 128 K.
1
F igu r e 3. Dynamic H NMR spectra of complex 8. The
insets show the appearance of the signals of the diastere-
omeric methylene protons of the two diastereomers upon
decoupling by irradiation at their respective CH3 reso-
nances.
(2-hetarylindenyl) group 4 metal complexes requires the
presence of active Zr-C σ-bonds.12 Therefore, we in-
cluded investigation of the conformational behavior of
several examples of the respective dialkylmetallocene
systems in this study.
Dimethylbis[2-(5-methyl-2-furyl)indenyl]zirconium (7a)
was prepared by treatment of 6a with 2 molar equiv of
methyllithium, as recently described by us. The pres-
ence of the two σ-methyl ligands resulted in a marked
change of the dynamic behavior of the complex. The
system remained dynamic down to the lowest possible
temperature (128 K) in the CDFCl2/CDF2Cl Freon
solvent mixture.
previously observed for 6a (see above). At 253 K it shows
1
a single set of three H NMR signals originating from
the indenyl framework, two signals of the furyl protons,
and the quartet/triplet features of the furyl-CH2CH3
substituent (see Figure 3). All these signals rapidly get
broad upon lowering the temperature and decoalesce to
1
two sets of ligand signals in a ca. 65:35 ratio. The H
NMR spectrum at 128 K under static conditions shows
two broadened methyl signals at δ 1.37 and 1.27 and
two broad -CH2- multiplets at δ 2.88 and 2.73. The
methylene signals are both too broad to allow for the
Attaching bulky σ-neopentyl or σ-benzyl ligands at
zirconium has an opposite effect in these systems.2,3
The bis[2-(5-methyl-2-furyl)indenyl]di(neopentyl)zirconi-
um complex 7b was prepared by treatment of the
metallocene dichloride 6a with 2 equiv of neopentyl-
lithium. Complex 7b was isolated in 60% yield after
crystallization from pentane. Single crystals obtained
from pentane were suitable for an X-ray crystal struc-
ture analysis. Complex 7b also exhibits a chiral C2-
symmetric metallocene conformation in the solid state.
The observed specific rotamer represents an example
of the rac-type A conformer (as depicted in Scheme 2).
The furyl groups are arranged coplanar with the η5-
indenyl planes, and they have their oxygen atoms
oriented toward the front sector of the bent metallocene
wedge. The σ-neopentyl ligands are arranged C2-sym-
metrically at the front of the bent metallocene. Their
bulky tert-butyl groups are pointing away from the core
of the metallocene (dihedral angles C31*-Zr-C31-
C32 -66.7(7)°, Cp(centroid)-Zr-C31-C32 -178.5°,
Cp*(centroid)-Zr-C31-C32 42.3°). The Zr-C(31) bond
length is 2.256(3) Å, and the C31*-Zr-C31 angle of the
σ-ligands at zirconium amounts to 100.7(3)°.
The attachment of -CH2-R groups in the σ-ligand
plane of the bent metallocene unit has also resulted in
the introduction of a chirality sensor into the molecule.
Under static conditions a C2-symmetric metallocene
framework would render the pair of -CH2R σ-substit-
uents homotopic, but the pairs of the -CH2- hydrogens
at each individual -CH2-R group would be diastereo-
topic. In contrast, the two -CH2R groups at a substi-
tuted Cs-symmetric (meso) bis(indenyl)zirconium frame-
work would be expected to be diastereotopic, but with
the -CH2- hydrogens of each individual -CH2R σ-ligand
being enantiotopic.
1
required analysis of the spin pattern under static H
NMR conditions. Therefore, we have performed two
decoupling experiments (see insets in Figure 3). Irradia-
tion at the position of the methyl group of the major
isomer (δ 1.37) resulted in the observation of an AB
quartet of the adjacent methylene group, centered at δ
2
2.86 (δA ) 2.88, δB ) 2.84, J AB ≈ 16 Hz). This
experiment left the appearance of the CH2 signal of the
minor isomer unchanged, of course. However, irradia-
tion at the position of the CH3 resonance of the minor
isomer (δ 1.27) resulted in the observation of a narrow
2
AB quartet (δA ) 2.70, δB ) 2.68, J AB ≈ 16 Hz) of its
attached -CH2- group (see Figure 3). Thus, both
observed conformers of complex 8 exhibit diastereotopic
-CHAHB- moieties under static 1H NMR conditions at
low temperature, as expected. Again, it cannot be
decided which pair of rac- or meso-conformers from the
A to F set (see Scheme 2) is present in solution.
Line shape analysis11 gave an observed activation
barrier of ∆Gq ) 7.1 ( 0.4 kcal mol-1 for the confor-
rot
mational equilibration of 8. Again, it is likely that only
the indenyl-furyl rotation became frozen on the 1H
NMR time scale under these conditions.
We have also investigated the temperature-dependent
dynamic 1H NMR of bis[2-(5-methyl-2-furyl)indenyl]-
ZrBr2 (6b) and the corresponding bis[2-(5-methyl-2-
thienyl)indenyl]ZrX2 complexes 9a (X ) Cl) and 9b
(X ) Br). They all showed an analogous conformational
behavior, each exhibiting the spectra of a diastereomeric
pair of rotational isomers below the coalescence tem-
perature. The activation energies ∆Gq in these cases
rot
were all very similar (ca. 7 kcal mol-1; see Table 1).
Beh a vior of th e Cor r esp on d in g Bis[2-(5-a lk yl-2-
fu r yl)in d en yl]zir con iu m Dia lk yl Com p lexes. The
catalytic polypropylene elastomer formation at the bis-
(12) Brintzinger, H.-H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew. Chem. 1995, 107, 1255-1283; Angew. Chem.,
Int. Ed. Engl. 1995, 34, 1143-1170, and references therein.

Bis[2-(2-furyl)indenyl]zirconium Derivatives
Organometallics, Vol. 20, No. 24, 2001 5071
F igu r e 5. Molecular structure of complex 7b. Selected
bond lengths (Å) and angles (deg): Zr-C1 2.588(2), Zr-
C2 2.556(2), Zr-C3 2.520(2), Zr-C3a 2.647(2), Zr-C7a
2.678(2), Zr-CCp 2.301, Zr-C31 2.256(3), C1-C2 1.412-
(3), C1-C7a 1.419(3), C2-C3 1.422(3), C2-C12 1.444(4),
C3-C3a 1.414(4), C3a-C7a 1.432(4), C3a-C4 1.428(4),
C4-C5 1.364(5), C5-C6 1.409(5), C6-C7 1.358(4), C7-
C7a 1.417(4), O11-C12 1.370(3), O11-C15 1.379(4), C12-
C13 1.352(4), C13-C14 1.419(5), C14-C15 1.334(5), C15-
C21 1.489(5); CCp-Zr-CCp* 128.5, C31-Zr-C31* 100.7(3),
C1-C2-C3 108.3(2), C1-C2-C12 125.4(2), C12-C2-C3
126.4(2), C2-C3-C3a 107.9(2), C3-C3a-C7a 107.8(2),
C3-C3a-C4 133.1(3), C3a-C7a-C7 120.0(2), C3a-
C7a-C1 107.8(2), C2-C12-O11 116.1(2), C12-O11-C15
106.5(3).
F igu r e 4. Experimental (600 MHz in CDFCl2/CDF2Cl)
and calculated 1H NMR spectra arising from the confor-
mational equilibration of 8 (only the signals of the (furyl)-
CH2CH3 groups are depicted).
Sch em e 3
F igu r e 6. Dynamic 1H NMR spectra of 7b (600 MHz,
CDFCl2/CDF2Cl).
pentyl ligands shows a -C(CH3)3 singlet at δ 0.80 and
a broad [Zr]-CH2- singlet at δ -1.33.
In reality, the dynamic features of complex 7b are
Lowering the temperature first results in a broaden-
ing of the three indenyl signals and eventually to their
decoalescence to give a total of six individual indenyl-H
resonances. At the same time the high-field [Zr]-CH2-
singlet splits into a (broadened) AX spin pair at δ -0.85
and -2.16. This behavior indicates freezing of the Zr-
indenyl rotation on the NMR time scale. The diaste-
reotopic splitting of the -CH2- hydrogens of the
-CH2-R “chirality sensor” indicates that complex 7b
in solution favors a chiral metallocene backbone con-
formation. At 173 K the metallocene rotation of 7b has
become frozen, but the indenyl-furyl σ-rotation is still
rapid under these conditions. From the dynamic NMR
spectra of the 253 K to 173 K transition a Gibbs
activation barrier of the metallocene rotation was
determined by the magnitude of three activation bar-
riers of conformational equilibration, namely, ∆Gq
,
rot(Cp)
the barrier of rotation about the metal-η5-indenyl
vector, ∆Gqrot(Ar), the barrier of rotation around the
connecting indenyl-furyl σ-bond, and ∆Gqrot(CH R), the
2
rotational barrier of the Zr-C σ-bond (see Scheme 3).
From the conformational NMR we assume that the
latter, ∆Grot(CH R), probably represents the lowest bar-
2
rier. It seems that freezing of the Zr-CH2R rotation was
not achieved in any of our experiments, even at the
lowest temperature reached (128 K) in the CDFCl2/
CDF2Cl Freon solvent. Rapid rotation around the Zr-
CH2R σ-bond, and thus rapid equilibration of the
possible σ-bond conformers in the whole temperature
range, will be assumed for our interpretation.
The 600 MHz 1H NMR spectrum of complex 7b at 253
K is very simple due to rapid equilibration of all
conformational processes. It shows three signals of the
indenyl hydrogens, two furyl-H resonances (see Figure
6), and a furyl-methyl group singlet. The pair of σ-neo-
determined at ∆Gq
) 9.0 ( 0.3 kcal mol-1 13
.
rot(Cp)
(13) Alternatively, this dynamic 1H NMR spectroscopic behavior
could be formally rationalized if rapid metal-indenyl rotation and
freezing out of the Zr-CH2R σ-ligand rotation would be assumed. We
regard this possible interpretation less likely in view of the observed
values of the activation energies.

5072 Organometallics, Vol. 20, No. 24, 2001
Dreier et al.
F igu r e 7. Experimental and calculated 600 MHz 1H NMR
spectra of the assumed 7b-A h 7b-E rotational intercon-
version (only the CH2CMe3 resonances are depicted).
Further lowering the temperature eventually results
in a broadening of the indenyl signals again and further
splitting, and decoalescence of the furyl signals (both
actually too much overlapping as to allow for a detailed
analysis). Also broadening and decoalescence of the
furyl-CH3 and further splitting of the [Zr]-CH2-R
resonances is observed; all spectral changes now indi-
cate the freezing of the indenyl-furyl σ-rotation. The
observed splitting of the [Zr]-CH2-R signals (see
Figure 6) indicates the occurrence of two rotameric
isomers in solution: one is C2-symmetric; it is charac-
terized by the appearance of a (broadened) AX system
at δ -1.05 and -2.11. This would be in accord with
either the conformer 7b-A or 7b-B (see Scheme 3). In
view of the results of the X-ray crystal structure analysis
(see Figure 5) we tentatively assign to it the structure
of 7b-A. The other isomer is of lower symmetry (C1), as
it has both -CH2-R groups differentiated and each split
into a (broadened) AX system. This would be consistent
with the rotameric structure of 7b-E to be assigned to
this isomer (see Scheme 3). Consequently this rotamer
exhibits a pair of furyl-CH3 resonances, whereas the
other isomer (7b-A) shows only a single furyl-CH3
signal. The two rotamers are found in a ca. 1:1 ratio in
this solvent at 133 K. From a line shape analysis the
∆Gqrot(Ar) ) 7.1 ( 0.4 kcal mol-1 value was obtained for
the activation energy of the indenyl furyl σ-rotation in
complex 7b, which is in the expected range for this
process.
F igu r e 8. Experimental and calculated dynamic 600 MHz
1H NMR spectra (CH2Ph resonances) of 7c illustrating the
freezing of the metallocene rotation (∆Gqrot(Cp) ) 11.4 ( 0.3
kcal mol-1, in CD2Cl2, top), followed by freezing of the
indenyl-furyl σ-bond rotation (∆Gq
) 7.3 ( 0.4 kcal
rot(Ar)
mol-1, in CDFCl2/CDF2Cl, bottom)
Ta ble 2. Activa tion En er gies of [Zr ]-(η5-in d en yl)
Rota tion [∆Gqr ot(Cp )] a n d In d en yl-Heta r yl σ-Bon d
Rota tion [∆Gqr ot(Ar )] of th e Com p lexes 7 a n d 10a
∆Gq
∆Gq
rot(Cp)
(T)b
rot(Ar)
compd
hetaryl
σ-ligand
-CH2-CMe3 9.0 (213) 7.1 (143) 50:50
-CH2-Ph 11.4 (243) 7.3 (163) 45:55
12.0 (253)
(T)c
[A]:[E]
7b
7c
10b
Me-furyl
Me-furyl
Me-thienyl -CH2-Ph
d
d
a
For structures see Scheme 1; ∆Gq values determined from the
dynamic 600 MHz 1H NMR spectra (in CDFCl2/CDF2Cl) by line
shape analysis. (0.3 kcal mol-1
.
c (0.4 kcal mol-1, temp in K.
b
d
Not determined.
1H NMR resonance into a cleanly resolved AX system
at 213 K (see Figure 8) followed by a further splitting
of these signals into one broadened AX system of the
C2-symmetric 7c-A rotamer and a pair of AX systems
of the 7c-E isomer (one of these shows a fortuitous
double isochrony with one of the 7c-A resonances). The
7c ∆Gqrot(Ar) ) 7.3 ( 0.4 kcal mol-1 value, obtained from
the line shape analysis, is in the expected range.
Dibenzylbis[2-(5-methyl-2-thienyl)indenyl]zirconium
(10b) shows the same behavior. Here we have followed
the slowing of the metallocene rotational process and
determined its activation barrier (see Table 2). Dimeth-
ylbis[2-(5-methyl-2-thienyl)indenyl]zirconium (10a) again
is characterized by a much lower barrier of the Zr-
indenyl rotation, which could not be frozen out on the
The complex dibenzylbis[2-(5-methylfuryl)indenyl]-
zirconium (7c), prepared by the reaction of 6a with
benzylmagnesium chloride, shows an analogous dy-
namic behavior (see Figure 8). Freezing of the metal-
locene rotation seems to have an even higher barrier
(7c: ∆Gq
) 11.4 ( 0.3 kcal mol-1) than 7b. It
rot(Cp)
results in a splitting of the single -CH2Ph 600 MHz

Bis[2-(2-furyl)indenyl]zirconium Derivatives
Organometallics, Vol. 20, No. 24, 2001 5073
1H NMR 600 MHz time scale in the temperature range
investigated in this study.
question at present, but we must conclude that the
actual involvement of a meso-metallocene conformer
that is undergoing the proposed conformational “switch-
ing” process in elastomeric polypropylene formation
remains an unproven postulate,1 until a first example
of a 2-substituted meso-bis(indenyl) ZrX2 metallocene
rotamer has been found in solution and its equilibration
with the apparently ubiquitous rac-rotational conformer
has been demonstrated.
Con clu sion s
Our study has shown that the systems 6, 7a , 8, 9,
and 10a , which all have rather small σ-ligands of a high
local symmetry bonded to the zirconium center, exhibit
much lower conformational barriers than the systems
7b,c and 10b, which contain considerably more bulky
σ-neopentyl or σ-benzyl ligands. In the former case it is
likely that only the indenyl-furyl (or thienyl) rotation
Exp er im en ta l Section
1
was frozen out on the H NMR time scale at very low
Reactions were carried out under an argon atmosphere
using Schlenk-type glassware or in
a glovebox. Solvents
temperature and that the metal-indenyl rotation was
still rapid even at 128 K in the Freon solvent.
(including the deuterated solvents used for NMR spectroscopy)
were dried and distilled under argon prior to use. NMR spectra
were recorded on a Bruker AC 200 P NMR spectrometer (1H:
200 MHz, 13C: 50 MHz) at 300 K or a Varian Unity Plus NMR
spectrometer (1H: 600 MHz, 13C: 150 MHz) at 298 K. 2-(5-
Methyl-2-furyl)indenyllithium (5a ),4 2-(5-methyl-2-thienyl)-
indenyllithium (5c),4 neopentyllithium,19 bis[2-(5-methyl-2-
furyl)indenyl]zirconium dichloride (6a ),4 and bis[2-(5-methyl-
2-thienyl)indenyl]zirconium dichloride (9a )4 were prepared
according to literature procedures. Most of the compounds were
characterized by additional GCOSY, GHSQC, and GHMBC
NMR experiments;20 for details see the Supporting Informa-
tion.
In the systems 7b, 7c, and 10b we have probably
achieved a successive freezing of the metal-indenyl
rotation (i.e., the actual metallocene conformational
equilibration) followed by slowing the indenyl-furyl
rotation on the 1H NMR time scale. In the furyl systems
7b and 7c two conformational isomers were eventually
observed that both exhibit the characteristics expected
for the bent metallocenes containing chiral rac-type
frameworks. In no case could we secure the presence of
a meso-type conformer of these metallocene systems in
1
solution within the limits of the accuracy of the H NMR
2-(5-Eth yl-2-fu r yl)in d en e (4b). A solution of 2-ethylfuran
(3.96 g, 41.2 mmol) in diethyl ether (100 mL) was reacted at
room temperature with n-butyllithium (26.0 mL, 41.6 mmol,
1.60 M in n-hexane). After stirring overnight the reaction
mixture was cooled to -78 °C and solid 2-indanone (5.44 g,
41.2 mmol) was added by 0.50 g portions over a period of 4 h.
The solution was allowed to warm to -25 °C after stirring for
an additional 2 h and then hydrolyzed with 2 N HCl (75 mL).
After separation of the layers, drying over MgSO4, and column
chromatography (isohexane:diethyl ether, 4:1) 4.29 g (20.4
mmol, 50%) of the white product was obtained. Mp: 50 °C.
Anal. Calcd for C15H14O (210.3): C, 85.68; H, 6.71. Found: C,
85.37; H, 7.10. IR (KBr): ν˜ 3127 (w), 3061 (w), 3044 (w), 2968
(m), 2940 (w), 1690 (w), 1613 (vs), 1575 (s), 1514 (s), 1465 (s),
1394 (m), 1372 (m), 1218 (m), 1010 (vs), 916 (s), 801 (vs), 763
(vs), 719 (vs) cm-1. 1H NMR (dichloromethane-d2): δ 7.42 (ddd,
method, although in a few instances such rotational
isomers had previously been observed by X-ray diffrac-
tion in the solid state.1,2,4 This further indicates that
the meso-like conformers of the 2-(het)aryl-substituted
bis(indenyl)MR2 systems indeed must be regarded as
being markedly higher in energy as opposed to their
(ubiquitous) rac-like conformational isomers,3 at least
in solution. Whether this extends from the neutral
metallocene catalyst precursors to the cationic metal-
locene Ziegler-Natta catalysts16,17 that are actually
actively involved in the reported elastomeric polypro-
pylene formation18 must remain an experimentally open
(14) Benn, R.; Grondey, H.; Nolte, R.; Erker, G. Organometallics
1988, 7, 777-778. Erker, G.; Nolte, R.; Tainturier, G.; Rheingold, A.
Organometallics 1989, 8, 454-460. Erker, G.; Nolte, R.; Kru¨ger, C.;
Schlund, R.; Benn, R.; Grondey, H.; Mynott, R. J . Organomet. Chem.
1989, 364, 119-132. Benn, R.; Grondey, H.; Erker, G.; Aul, R.; Nolte,
R. Organometallics 1990, 9, 2493-2497, and references therein.
(15) Erker, G.; Mu¨hlenbernd, R.; Benn, A.; Rufin˜ska, A.; Tsay, Y.-
H.; Kru¨ger, C. Angew. Chem. 1985, 97, 336-337; Angew. Chem., Int.
Ed. Engl. 1985, 24, 321-323. Erker, G.; Mu¨hlenbernd, T.; Rufin˜ska,
A.; Benn, R. Chem. Ber. 1987, 120, 507-519.
3
4
5
1H, 7-H, J ) 7.8 Hz, J ) 1.2 Hz, J ) 0.6 Hz), 7.35 (d, 1H,
3
3
3
4-H, J ) 7.2 Hz), 7.25 (dt, 1H, 5-H, J ) 7.8 Hz, J ) 7.2 Hz,
4J ) 1.2 Hz), 7.15 (dt, 1H, 6-H, J ) 7.8 Hz, J ) 7.2 Hz, J )
3
3
4
3
1.2 Hz), 7.00 (s, 1H, 3-H), 6.40 (d, 1H, 3-Hfuryl, J ) 3.0 Hz),
6.08 (dt, 1H, 4-Hfuryl,
3J ) 3.0 Hz, 4J ) 1.2 Hz), 3.70 (s, 2H,
1-H), 2.72 (dq, 2H, CH2, 3J ) 7.8 Hz, 4J ) 1.2 Hz), 1.29 (t, 3H,
CH3, 3J ) 7.8 Hz). 13C NMR (dichloromethane-d2): δ 158.5
(C, C-5furyl), 150.7 (C, C-2furyl), 145.7 (C, C-7a), 142.6 (C, C-3a),
137.0 (C, C-2), 127.0 (CH, C-5), 124.8 (CH, C-6), 124.0 (CH,
C-7), 123.9 (CH, C-3), 121.1 (CH, C-4), 108.3 (CH, C-3furyl),
106.5 (CH, C-4furyl), 38.4 (CH2, C-1), 21.9 (CH2), 12.4 (CH3).
(16) Early review: J ordan, R. F. Adv. Organomet. Chem. 1991, 32,
325-387.
(17) See also: Marks, T. J . Acc. Chem. Res. 1992, 25, 57. Aulbach,
M.; Ku¨ber, F. Chem. Unserer Zeit 1994, 28, 197. Bochmann, M. J .
Chem. Soc., Dalton Trans. 1996, 255-270, and references therein.
(18) Mallin, D. T.; Rausch, M. D.; Lin, Y.-G.; Dong, S.-H.; Chien, J .
C. W. J . Am. Chem. Soc. 1990, 112, 2030. Chien, J . C. W.; Llinas, G.
H.; Rausch, M. D.; Lin, Y.-G.; Winter, H. H.; Atwood, J . L.; Bott, S. G.
J . Am. Chem. Soc. 1991, 113, 8569. Llinas, G. H.; Dong, S.-H.; Mallin,
D. T.; Rausch, M. D.; Lin, Y.-G.; Winter, H. H.; Chien, J . C. W.
Macromolecules 1992, 25, 1242. Chien, J . C. W.; Llinas, G. H.; Rausch,
M. D.; Lin, Y.-G.; Winter, H. H.; Atwood, J . L.; Bott, S. G. J . Polym.
Sci., Part A 1992, 30, 2601. Gauthier, W. J .; Corrigan, J . F.; Taylor,
N. J .; Collins, S. Macromolecules 1995, 28, 3771-3778. Resconi, L.;
J ones, R. L.; Rheingold, A. L.; Yap, G. P. A. Organometallics 1996, 15,
998-1005. Sassmannshausen, J .; Bochmann, M.; Ro¨sch, J .; Lilge, D.
J . Organomet. Chem. 1997, 548, 23-28. Averbuj, C.; Tish, E.; Eisen,
M. S. J . Am. Chem. Soc. 1998, 120, 8640-8646. Bravakis, A. M.; Baily,
L. E.; Pigeon, M.; Collins, S. Macromolecules 1998, 31, 1000-1009.
Dietrich, U.; Hackmann, M.; Rieger, B.; Klinga, M.; Leskela¨, M. J . Am.
Chem. Soc. 1999, 121, 4348-4355. Kravchenko, R. L.; Sauer, B. B.;
McLean, R. S.; Keating, M. Y.; Cotts, P. M.; Kim, Y. H. Macromolecules
2000, 33, 11-13. Shmulinson, M.; Galan-Fereres, M.; Lisovskii, A.;
Nelkenbaum, E.; Semiat, R.; Eisen, M. S. Organometallics 2000, 19,
1208-1210.
2-(5-Eth yl-2-fu r yl)in d en yllith iu m (5b). Deprotonation of
2-(5-ethyl-2-furyl)indene (1.0 g, 4.75 mmol) dissolved in diethyl
ether (50 mL) with n-butyllithium (2.9 mL, 4.75 mmol, 1.6 M
in n-hexane) resulted in a dark red solution. After removal of
the solvent the residue was suspended in pentane overnight.
1
Filtration yielded 0.72 g (3.3 mmol, 70%) of a beige solid. H
NMR (benzene-d6/tetrahydrofuran-d8): δ 7.73 (m, 2H, 4-H,
7-H), 6.96 (m, 2H, 5-H, 6-H), 6.69 (s, 2H, 1-H, 3-H), 6.38 (d,
1H, 3-Hfuryl, ,
3J ) 3.2 Hz), 5.98 (dt, 1H, 4-Hfuryl 3J ) 3.2 Hz,
4J ) 0.8 Hz), 2.58 (dq, 2H, CH2, 3J ) 7.4 Hz, 4J ) 0.8 Hz),
3
1.16 (t, 3H, CH3, J ) 7.4 Hz).
(19) Schrock, R. R.; Fellmann, J . D. J . Am. Chem. Soc. 1978, 100,
3359-3370.
(20) Braun, S.; Kalinowski, H. O.; Berger, S. 150 and More Basic
NMR Experiments; VCH: Weinheim, 1998; and references therein.

5074 Organometallics, Vol. 20, No. 24, 2001
Dreier et al.
Bis[2-(5-eth yl-2-fu r yl)in den yl]zir con iu m Dich lor ide (8).
To a suspension of 2-(5-ethyl-2-furyl)indenyllithium (0.50 g,
2.31 mmol) in toluene was added at -78 °C solid ZrCl4 (0.27
g, 1.16 mmol). The reaction mixture was allowed to warm to
room temperature overnight, and the formed LiCl was filtered
off. The solution was concentrated and the product was
crystallized at -30 °C. The yellow crystals (0.22 g, 0.38 mmol,
35%) were suitable for an X-ray crystal structure analysis.
Mp: 129 °C. Anal. Calcd for C30H26Cl2O2Zr (580.7): C, 62.06;
H, 5.51. Found: C, 61.79; H, 4.88. IR (KBr): ν˜ 3086 (m), 3063
(w), 2972 (m), 2944 (w), 2904 (m), 1612 (w), 1561 (vs), 1437
(m), 1369 (m), 1352 (m), 1301 (m), 1210 (m), 1017 (vs), 966
(s), 842 (vs), 796 (vs), 750 (vs) cm-1. 1H NMR (dichloromethane-
d2): δ 7.27 (m, 4H, 4-H, 7-H), 7.12 (m, 4H, 5-H, 6-H), 6.57 (s,
7.28 (m, 4H, 4-H, 7-H), 7.12 (m, 4H, 5-H, 6-H), 6.68 (s, 4H,
1-H, 3-H), 6.49 (dd, 2H, 3-Hfuryl
,
3J ) 1.8 Hz, 5J ) 0.6 Hz),
3
4
6.17 (dq, 2H, 4-Hfuryl, J ) 1.8 Hz, J ) 1.2 Hz), 2.48 (dd, 6H,
CH3, 4J ) 1.2 Hz, 5J ) 0.6 Hz). 13C NMR (dichloromethane-
d2): δ 153.7 (C, C-5furyl), 147.3 (C, C-2furyl), 126.9 (CH, C-5, C-6),
126.5 (C, C-3a, C-7a), 125.5 (CH, C-4, C-7), 124.7 (C, C-2), 110.9
(CH, C-3furyl), 108.8 (CH, C-4furyl), 101.2 (CH, C-1, C-3), 14.0
(CH3). The rotational barrier (∆Gq
was determined by a line-shape analysis.
) 7.2 ( 0.3 kcal/mol)
133
K
Bis[2-(5-m et h yl-2-t h ien yl)in d en yl]zir con iu m Dib r o-
m id e (9b). Analogously as described above, 2-(5-methyl-2-
thienyl)indenyllithium (5c) (0.50 g, 2.29 mmol) was reacted
with ZrBr4 (0.47 g, 1.14 mmol) to yield 0.14 g (0.21 mmol, 19%)
of an orange-brown product. Mp: 133 °C. Anal. Calcd for
3
4H, 1-H, 3-H), 6.50 (d, 2H, 3-Hfuryl, J ) 3.0 Hz), 6.19 (dt, 2H,
C
28H22Br2O2Zr (641.5): C, 49.92; H, 3.92. Found: C, 50.37; H,
3
4
3
4-Hfuryl, J ) 3.0 Hz, J ) 1.2 Hz), 2.84 (dq, 4H, CH2, J ) 7.8
Hz, 4J ) 1.2 Hz), 1.39 (t, 6H, CH3, 3J ) 7.8 Hz). 13C NMR
(dichloromethane-d2): δ 159.3 (C, C-5furyl), 147.0 (C, C-2furyl),
126.7 (CH, C-5, C-6), 125.1 (C, C-3a, C-7a), 124.9 (CH, C-4,
C-7), 110.4 (CH, C-3furyl), 107.1 (CH, C-4furyl), 100.8 (CH, C-1,
C-3), 21.9 (CH2), 12.5 (CH3), the resonance of C-2 could not be
detected. The rotational barrier (∆Gq133 K ) 7.2 ( 0.4 kcal/mol)
was determined by a line-shape analysis.
3.77. IR (KBr): ν˜ 3114 (w), 3058 (w), 2927 (w), 2858 (w), 1618
(w), 1539 (w), 1510 (s), 1448 (m), 1380 (w), 1340 (w), 1227 (w),
1
1057 (w), 842 (vs), 819 (vs), 813 (vs), 751 (vs) cm-1. H NMR
(dichloromethane-d2): δ 7.22 (m, 4H, 4-H, 7-H), 7.12 (m, 4H,
5-H, 6-H), 7.05 (d, 2H, 3-Hthienyl
,
3J ) 3.6 Hz), 6.80 (dq, 2H,
4-Hthienyl
,
3J ) 3.6 Hz, 4J ) 1.2 Hz), 6.60 (s, 4H, 1-H, 3-H),
2.58 (d, 6H, CH3, 4J ) 1.2 Hz). 13C NMR (dichloromethane-
d2): δ 142.3 (C, C-5thienyl), 134.8 (C, C-2thienyl), 128.3 (C, C-2),
127.1 (CH, C-5, C-6), 126.9 (CH, C-3thienyl), 126.8 (CH, C-4
thienyl), 126.5 (C, C-3a, C-7a), 125.5 (CH, C-4, C-7), 103.6 (CH,
X-r ay Cr ystal Str u ctu r e An alysis of 8. Formula C30H26O2-
Cl2Zr, M ) 580.63, yellow crystal 0.20 × 0.15 × 0.05 mm, a )
23.052(1) Å, b ) 6.802(1) Å, c ) 18.587(1) Å, â ) 119.61(1)°,
V ) 2533.8(4) Å3, Fcalc ) 1.522 g cm-3, µ ) 6.71 cm-1, empirical
absorption correction via SORTAV (0.877 e T e 0.967), Z )
4, monoclinic, space group C2/c (No. 15), λ ) 0.71073 Å, T )
198 K, ω and æ scans, 4936 reflections collected ((h, (k, (l),
[(sin θ)/λ] ) 0.65 Å-1, 2882 independent (Rint ) 0.023) and 2565
observed reflections [I g 2 σ(I)], 160 refined parameters, R )
0.026, wR2 ) 0.063, max. residual electron density 0.28 (-0.33)
e Å-3, hydrogens calculated and refined as riding atoms.21
Bis[2-(5-m eth yl-2-fu r yl)in d en yl]zir con iu m Dich lor id e
C-1, C-3), 15.7 (CH3). The rotational barrier (∆Gq
) 6.9 (
133
K
0.3 kcal/mol) was determined by a line-shape analysis.
Bis[2-(5-m et h yl-2-fu r yl)in d en yl]d in eop en t ylzir con i-
u m (7b). Bis[2-(5-methyl-2-furyl)indenyl]zirconium dichloride
(6a ) (0.4 g, 0.72 mmol) was suspended in diethyl ether (40 mL)
and at -78 °C was added a solution of neopentyllithium (11.0
mL, 2.88 mmol, 0.26 M in isohexane). After stirring overnight
the solvent was removed in vacuo and pentane was added. The
formed LiCl was filtered off and the product was crystallized
at -30 °C. A second crystallization yielded 0.27 g (0.43 mmol,
60%) of an off-white solid. Mp: 142 °C (decomp). HRMS:
1
(6a ). H NMR (CDFCl2, CDF2Cl, 253 K): δ 7.24 (m, 4H, 4-H,
C
29H25O2Zr (M+ - CH2C(CH3)3; -CH2dC(CH3)2), requires
7-H), 7.10 (m, 4H, 5-H, 6-H), 6.64 (s, 4H, 1-H, 3-H), 6.45 (d,
3
3
2H, 3-Hfuryl, J ) 3.6 Hz), 6.14 (dq, 2H, 4-Hfuryl, J ) 3.6 Hz,
4J ) 1.2 Hz), 2.48 (s, 6H, CH3). 1H NMR (CDFCl2, CDF2Cl,
133 K): δ 7.30-6.14 (m, arom. CH), 2.57 (s, CH3), 2.44 (s,
495.09015, found m/z 495.08805. IR (KBr): ν˜ 3131 (w), 3058
(w), 2950 (vs), 2893 (s), 2870 (m), 1573 (s), 1448 (m), 1363 (s),
1233 (m), 1204 (m), 1097 (m), 1023 (vs), 944 (m), 836 (vs), 791
CH3*). The rotational barrier (∆Gq
was determined by a line-shape analysis.
) 7.0 ( 0.3 kcal/mol)
1
133
K
(vs), 745 (vs) cm-1. H NMR (dichloromethane-d2): δ 6.98 (m,
4H, 4-H, 7-H), 6.85 (m, 4H, 5-H, 6-H), 6.67 (s, 4H, 1-H, 3-H),
3
5
Bis[2-(5-m eth yl-2-th ien yl)in d en yl]zir con iu m Dich lo-
6.47 (dd, 2H, 3-Hfuryl, J ) 3.6 Hz, J ) 0.6 Hz), 6.20 (dq, 2H,
1
3
4
4
r id e (9a ). H NMR (CDFCl2, CDF2Cl, 253 K): δ 7.21 (m, 4H,
4-Hfuryl, J ) 3.6 Hz, J ) 1.2 Hz), 2.47 (d, 6H, CH3, J ) 1.2
Hz), 0.83 (s, 18H, C(CH3)3), -1.25 (s, 4H, CH2). 13C NMR
(dichloromethane-d2): δ 152.3 (C, C-5furyl), 148.4 (C, C-2furyl),
125.4 (C, C-3a, C-7a), 125.1 (CH, C-4, C-7), 124.3 (CH, C-5,
C-6), 119.3 (C, C-2), 108.5 (CH, C-3furyl), 108.2 (CH, C-4furyl),
95.2 (CH, C-1, C-3), 84.8 (CH2), 36.8 (C(CH3)3), 34.7 (C(CH3)3),
13.9 (CH3). The rotational barriers (∆Gqrot(Cp) ) 9.0 ( 0.3 kcal/
mol, ∆Gqrot(Ar) ) 7.1 ( 0.4 kcal/mol) were determined by a line-
shape analysis.
3
4-H, 7-H), 7.12 (m, 4H, 5-H, 6-H), 7.01 (d, 2H, 3-Hthienyl, J )
3.6 Hz), 6.79 (dq, 2H, 4-Hthienyl, 3J ) 3.6 Hz, 4J ) 0.6 Hz), 6.60
(s, 4H, 1-H, 3-H), 2.58 (d, 6H, CH3, 4J ) 0.6 Hz). 1H NMR
(CDFCl2, CDF2Cl, 133 K): δ 7.24-6.65 (m, arom. CH), 2.60
(s, CH3), 2.57 (s, CH3*). The rotational barrier (∆Gq
)
133
K
6.7 ( 0.3 kcal/mol) was determined by a line-shape analysis.
Bis[2-(5-m eth yl-2-fu r yl)in d en yl]zir con iu m Dibr om id e
(6b). To a stirred suspension of 2-(5-methyl-2-furyl)indenyl-
lithium (5a ) (0.50 g, 2.47 mmol) in 50 mL of toluene was added
at -78 °C a suspension of ZrBr4 (0.51 g, 1.24 mmol) in toluene.
The resultant reaction mixture was allowed to warm to room
temperature and then filtered to separate the LiBr. Crystal-
lization at -30 °C yielded 0.29 g (0.45 mmol, 37%) of an orange
solid. Mp: 161 °C. Anal. Calcd for C28H22Br2O2Zr (641.5): C,
52.42; H, 3.46. Found: C, 52.01; H, 3.57. IR (KBr): ν˜ 3130
(w), 3013 (w), 2944 (w), 1619 (w), 1566 (vs), 1529 (m), 1433
(m), 1343 (m), 1200 (s), 1025 (s), 977 (m), 951 (m), 861 (s), 829
X-r a y Cr ysta l Str u ctu r e An a lysis of 7b. Formula C38
44O2Zr, M ) 623.95, yellow crystal 0.50 × 0.40 × 0.35 mm,
a ) 10.829(1) Å, b ) 17.669(1) Å, c ) 17.130(1) Å, â ) 101.12-
(1)°, V ) 3216.1(4) Å3, Fcalc ) 1.289 g cm-3, µ ) 3.73 cm-1
-
H
,
empirical absorption correction via SORTAV (0.835 e T e
0.881), Z ) 4, monoclinic, space group C2/c (No. 15), λ )
0.71073 Å, T ) 198 K, ω and æ scans, 9821 reflections collected
((h, (k, (l), [(sin θ)/λ] ) 0.65 Å-1, 3638 independent (Rint
)
0.029) and 3290 observed reflections [I g 2σ(I)], 221 refined
parameters, R ) 0.038, wR2 ) 0.088, max. residual electron
density 0.62 (-0.55) e Å-3, disorder in the tert-butyl group,
refined with split positions and geometrical restraints, hydro-
gens calculated and refined as riding atoms.21
Diben zylbis[2-(5-m eth yl-2-fu r yl)in den yl]zir con iu m (7c).
Bis[2-(5-methyl-2-furyl)indenyl]zirconium dichloride (6a ) (0.50
g, 0.91 mmol) was suspended in diethyl ether/tetrahydrofuran
(40 mL/20 mL), and a solution of benzylmagnesium chloride
(1.81 mL, 1.81 mmol, 1.00 M solution in diethyl ether) was
added. The suspension was stirred for 6 h at room tempera-
1
(s), 802 (vs), 744 (vs) cm-1. H NMR (dichloromethane-d2): δ
(21) Data sets were collected with a Nonius KappaCCD diffrac-
tometer, equipped with a rotating anode generator Nonius FR591.
Programs used: data collection COLLECT (Nonius B.V., 1998), data
reduction Denzo-SMN (Z. Otwinowski, W. Minor, Methods Enzymol.
1997, 276, 307-326), absorption correction SORTAV (R. H. Blessing,
Acta Crystallogr. 1995, A51, 33-37; R. H. Blessing, J . Appl. Crystal-
logr. 1997, 30, 421-426), structure solution SHELXS-97 (G. M.
Sheldrick, Acta Crystallogr. 1990, A46, 467-473), structure refinement
SHELXL-97 (G. M. Sheldrick, Universita¨t Go¨ttingen, 1997), graphics
DIAMOND (K. Brandenburg, Universita¨t Bonn, 1997).

Bis[2-(2-furyl)indenyl]zirconium Derivatives
Organometallics, Vol. 20, No. 24, 2001 5075
ture, and the solvent was removed in vacuo. Toluene (50 mL)
was added and then the reaction mixture was filtered.
Crystallization at -30 °C, filtration, and washing with toluene
(10 mL) and pentane yielded 0.20 g (0.30 mmol, 33%) of a
yellow solid. Mp: 65 °C. HRMS: C35H29O2Zr (M+ - CH2Ph),
requires 571.12146, found m/z 571.12288. IR (KBr): ν˜ 3120
(w), 3075 (w), 3023 (w), 2916 (w), 1595 (s), 1573 (s), 1488 (s),
1437 (m), 1374 (m), 1210 (vs), 1029 (s), 995 (vs), 965 (m), 859
(vs), 785 (s), 757 (vs), 706 (s) cm-1. 1H NMR (dichloromethane-
d2): δ 7.20 (t, 4H, m-H, 3J ) 8.4 Hz, 3J ) 7.2 Hz), 7.05 (m,
4H, 4-H, 7-H), 6.68 (t, 2H, p-H, 3J ) 7.2 Hz), 6.73 (d, 4H, o-H,
3J ) 8.4 Hz), 6.69 (m, 4H, 5-H, 6-H), 6.45 (d, 2H, 3-Hfuryl, 3J )
1488 (s), 1448 (m), 1369 (m), 1211 (m), 1017 (m), 989 (s), 881
(m), 836 (vs), 808 (s), 751 (vs), 700 (vs) cm-1 1H NMR
.
(dichloromethane-d2): δ 7.21 (t, 4H, m-H, 3J ) 7.8 Hz, 3J )
6.6 Hz), 7.05 (m, 4H, 4-H, 7-H), 6.99 (d, 2H, 3-Hthienyl, 3J ) 3.6
3
Hz), 6.88-6.86 (m, 4H, p-H, 4-Hthienyl), 6.79 (d, 4H, o-H, J )
6.6 Hz), 6.68 (m, 4H, 5-H, 6-H), 5.87 (bs, 4H, 1-H, 3-H), 2.63
(d, 6H, CH3, 4J ) 1.2 Hz), 0.24 (bs, 4H, CH2). 13C NMR
(dichloromethane-d2): δ 153.0 (C, ipso-C), 140.9 (C, C-5thienyl),
136.0 (C, C-2thienyl), 128.3 (CH, m-C), 126.7 (CH, C-4thienyl), 126.4
(CH, o-C), 126.0, (CH, C-4, C-7), 125.9 (C, C-3a, C-7a), 125.5
(C, C-2), 125.0 (CH, C-5, C-6), 124.8 (CH, C-3thienyl), 121.5 (CH,
p-C), 66.4 (CH2), 15.7 (CH3). C-1, C-3 was not detected. The
3
4
rotational barrier (∆Gq
determined by a line-shape analysis.
) 12.0 ( 0.3 kcal/mol) was
3.0 Hz), 6.24 (dq, 2H, 4-Hfuryl, J ) 3.0 Hz, J ) 1.2 Hz), 6.05
rot(Cp)
3
(s, 4H, 1-H, 3-H), 2.55 (d, 6H, CH3, J ) 1.2 Hz), 0.14 (bs, 4H,
CH2). 13C NMR (dichloromethane-d2): δ 153.6 (C, ipso-C), 152.9
(C, C-5furyl), 147.7 (C, C-2furyl), 128.2 (CH, m-C), 126.1 (CH, o-C),
125.9 (CH, C-4, C-7), 125.4 (C, C-3a, C-7a), 124.7 (CH, C-5,
C-6), 121.3 (CH, p-C), 121.2 (C, C-2), 108.9 (CH, C-3furyl), 108.5
(CH, C-4furyl), 66.9 (CH2), 13.9 (CH3). C-1, C-3 was not detected.
Ack n ow led gm en t . Financial support from the
Fonds der Chemischen Industrie and the Deutsche
Forschungsgemeinschaft is gratefully acknowledged.
E.W. thanks the Academy of Finland for financial
support.
The rotational barriers (∆Gq
) 11.4 ( 0.3 kcal/mol,
rot(Cp)
∆Gqrot(Ar) ) 7.3 ( 0.4 kcal/mol) were determined by a line-shape
analysis.
Dib e n zylb is[2-(5-m e t h yl-2-t h ie n yl)in d e n yl]zir con i-
u m (10b). Analogously as described above, bis[2-(5-methyl-
2-thienyl)indenyl]zirconium dichloride (9a ) (0.50 g, 0.86 mmol)
was reacted with a solution of benzylmagnesium chloride (1.72
mL, 1.72 mmol, 1.00 M in diethyl ether) to yield 0.34 g (0.48
mmol, 57%) of the yellow product. Mp: 107 °C. HRMS:
Su p p or tin g In for m a tion Ava ila ble: Detailed informa-
tion about the X-ray crystal structure analyses of the com-
1
plexes 7b and 8, series of the dynamic H NMR spectra, and
the line-shape analysis of the compounds 6a , 6b, 6c, 7b, 7c,
9a , 9b, and 10b. This material is available free of charge via
the Internet at http://pubs.acs.org.
C
35H29S290Zr (M+ - CH2Ph), requires 603.07581, found m/z
603.07424. IR (KBr): ν˜ 3052 (w), 3012 (m), 2916 (w), 1601 (s),
OM0104518