Synthetic explorations towards sterically crowded 1,2,3-substituted bis(indenyl)zirconium(IV) dichlorides

Article abstract of DOI:10.1002/ejic.200400972

The systematic synthesis of 1,3-dialkyl-substituted 2-silylindenes and their suitability as zirconocene ligands is discussed. Unexpected reactivities rendered a number of substitution patterns unfeasible, especially for alkyl groups other than methyl in 2-(trimethylsilyl)indene derivatives, and essentially for all derivatives of 2-(dimethylsilyl)indene. The syntheses of rac/meso-bis[1-methyl-2-(trimethylsilyl)indenyljzirconium(IV) dichloride (12) and bis[1,3-dimethyl-2-(trimethylsilyl)indenyl]zirconium(IV) dichloride (13b) are de scribed. The solid-state structure of the latter displays strong deformations within the ligand framework and an unusually large C _PcentroidZr-C_Pcentroid angle. Both, 12/MAO and 13b/MAO, displayed ethene and ethene-co-1-hexene polymerization activity. Curiously, 13b/MAO shows an extraordinary monomer selectivity, which can be rationalized by means of DFT calculations on the active site. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).

Full text of DOI:10.1002/ejic.200400972

FULL PAPER
Synthetic Explorations Towards Sterically Crowded 1,2,3-Substituted
Bis(indenyl)zirconium(IV) Dichlorides
Andreas C. Möller,[a,b] Richard Blom,[a] Richard H. Heyn,*[a] Ole Swang,[a]
Carl-Henrik Görbitz,[c] and Tanja Seraidaris[d]
Keywords: Metallocenes / Ligand effects / Isomerization / Polymerization / Density functional calculations
The systematic synthesis of 1,3-dialkyl-substituted 2-silylin-
denes and their suitability as zirconocene ligands is dis-
cussed. Unexpected reactivities rendered a number of substi-
tution patterns unfeasible, especially for alkyl groups other
than methyl in 2-(trimethylsilyl)indene derivatives, and es-
sentially for all derivatives of 2-(dimethylsilyl)indene. The
syntheses of rac/meso-bis[1-methyl-2-(trimethylsilyl)inde-
nyl]zirconium(IV) dichloride (12) and bis[1,3-dimethyl-2-(tri-
methylsilyl)indenyl]zirconium(IV) dichloride (13b) are de-
scribed. The solid-state structure of the latter displays strong
deformations within the ligand framework and an unusually
large Cpcentroid-Zr–Cpcentroid angle. Both, 12/MAO and 13b/
MAO, displayed ethene and ethene-co-1-hexene polymer-
ization activity. Curiously, 13b/MAO shows an extraordinary
monomer selectivity, which can be rationalized by means of
DFT calculations on the active site.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
to present our results on a systematic study of 1,3-dialkyl-
2-silyl-trisubstituted indene ligands for the synthesis of zir-
conocene dichlorides.
Introduction
The field of metallocene-catalyzed olefin polymerization
has achieved significant improvements on polymer proper-
ties. The ligandϪtacticity relationship is well understood
and, apart from tailor-made stereocontrol, co-monomer in-
corporation and block length have been emphasized as keys
to innovative materials.[1] The detailed polymerization
mechanism with all its variations is complicated and the
choice of appropriate polymerization conditions to favor
one monomer over the other still requires vast and tedious
sets of experiments. An outline of the extensive efforts made
within this area can be found in the various review arti-
cles.[2]
Previous work from our laboratory addressed unbridged
zirconocene dichloride with silyl substituents in the 1 or
2 position.[3] Reports on trisubstituted indenyl ligands, i.e.
substituents in the 1, 2, and 3 positions, are still quite un-
common. It may be expected that steric congestion in such
complexes is significant and that overall polymerization ac-
tivity may be negatively influenced. In this study, we wish
Results and Discussion
Ligand Syntheses
The introduction of alkyl groups in the 1 and 3 position
of 2-silylindenes should be feasible in a straight forward
manner by simple double alkylation of indenyllithium salts.
Deprotonation of 2-(dimethylsilyl)indene (1a, 2-DMS-Ind)
and 2-(trimethylsilyl)indene (1b, 2-TMS-Ind) was achieved
by n-butyllithium in pentane at room temperature or
–90 °C, respectively. In spite of the nonpolar solvent, depro-
tonation at lower temperatures provided hydride substitu-
tion products for 1a, as observed by Kira et al.[4] Alterna-
tively deprotonation can be achieved with potassium hy-
dride at room temperature.
Methylation of the lithium salt of 1a with methyl iodide
at –40 °C in diethyl ether yielded exclusively 3-Me-2-DMS-
Ind (2a), while 1-Me-2-TMS-Ind (2b) was obtained likewise
from 2-TMS-Ind. Repetition of the deprotonationϪmethyl-
ation sequence afforded a 1:4 mixture of the 1,1-dimethyl
and 1,3-dimethyl isomers for both, 3a and 3b. Deproton-
ation and washing with pentane provided pure lithium salts
of the 1,3-dimethyl-2-silylindenes 3a and 3b (Scheme 1). 3a
exhibits diastereotopic methyl resonances of the silyl group
in a 1:1 ratio due to the presence of the chiral C(1) atom.
In order to determine whether bulkier alkyl substituents
could be placed in the 1,3 positions, studies on the introduc-
tion of the iPr group were conducted on 1b, as the TMS
[a] Department of Hydrocarbon Process Chemistry, SINTEF Ma-
terials and Chemistry,
P. O. Box 124, Blindern, 0314 Oslo, Norway
Richard.H.Heyn@sintef.no,
Fax: +47-22 06 73 50
[b] Department of Chemical Engineering, Norwegian University of
Science and Technology (NTNU),
7491 Trondheim, Norway
[c] Department of Chemistry, University of Oslo,
P. O. Box 1033 Blindern, 0315 Oslo, Norway
Fax: +47-22 85 54 41
[d] Department of Polymer Technology, Helsinki University of
Technology,
P. O. Box 6100, 02015 HUT, Finland
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DOI: 10.1002/ejic.200400972
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FULL PAPER
tection of 2-methylhexane (0.3 parts). Deprotonation of 4
with potassium hydride in refluxing THF failed to provide
a well-defined, insoluble potassium salt (K[5]). Due to the
solubility of these salts, washing with pentane was ac-
companied by a loss of material.
A compelling explanation for these solubilities can be de-
rived from a quenching experiment of Li[5] with methyl io-
dide in THF. GC/MS analysis of the reaction products re-
vealed ten major products, of which one could be identified
as 1-tBu-2-TMS-Ind. Apparently Li[5] equilibrates between
its indenyllithium and alkyllithium derivative, i.e. the lith-
ium migrates from the Cp moiety of the indenyl through
the iPr group resulting in a covalent lithium carbon bond.
Although satisfactory 1H and 13C NMR spectroscopic data
were obtained, K[5] appears to be an inhomogeneous, po-
orly described compound, partially soluble in hydro-
carbons. We suspect cation migration is still possible, de-
spite the significantly bigger potassium cation.
Scheme 1. General route towards 1,3-dialkyl-2-silylindenes. a)
nBuLi, pentane, room temperature; MeI, diethyl ether, –40 °C. a:
R = H, RЈ = Me. b: R = RЈ = Me. Yields are reported for the
purified lithium salts of 3a and 3b, whereas spectroscopic data were
obtained on the free ligands.
Introduction of a tBu group into 2-TMS-Ind may not
be expected to be easy. Even in the case of indenyllithium,
alkylation with tBu bromide or iodide succeeds only in
moderate yields.[5] Aiming for a possibly more demanding,
but still more efficient route, we investigated a literature
procedure for the synthesis of tBu groups from 6,6-dimeth-
yl(benzo)fulvenes.[6] 6,6-Dimethylbenzofulvene (6) is readily
available in a one-pot reaction from indene, pyrrolidine and
acetone in methanol,[7] and methyllithium is known to react
smoothly in a 1,4-addition in diethyl ether to 1-tBu-indenyl-
lithium in a 80% yield. Acidic work-up and distillation af-
forded 3-tert-butylindene (7) in a 58% yield. Application
of typical activators like TMEDA and BF3·Et2O does not
improve the yield, but running the reaction in pentane in
the presence of 10 wt.-% AlCl3 offers the advantage of
quantitative conversion, though acidic work-up is required
prior to further reactions.
moiety is less prone to substitution reactions in the presence
of lithium organyls. A brief summary of the results is given
in Scheme 2. Following the procedure for methylation, ex-
posure of the lithium salt of 1b to isopropyl iodide sufficed
to obtain the 1-iPr isomer 4 in good yield. The proton and
carbon NMR spectra of 4 reveal diastereotopic resonances
for the iPr methyl groups, and curiously the expected singlet
for the trimethylsilyl (TMS) moiety displays two resonance
maxima. We interpret these to arise from steric interaction
of the iPr and TMS groups. In addition, two different C(1)
resonances are found. Deprotonation of 4 with n-butyllith-
ium, however, leads to soluble lithium salts, which in a di-
rect second alkylation with isopropyl iodide without prior
isolation resulted in a mixture of four isomers, i.e. the
mono-alkylated 1 and 3 isomers (3:1 parts) and the dialkyl-
ated 1,3 and 1,1 isomers (2:0.1 parts). The slight excess of
n-butyllithium used in the reaction could be traced by de-
Scheme 2. Reactivity of 1-isopropyl-2-(trimethylsilyl)indene (4). a) nBuLi, pentane; b) potassium hydride, THF; c) 2-Iodopropane, diethyl
ether/THF (n.i. = not isolated); d) ZrCl4, THF, –40 °C; e) MeI, THF.
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Sterically Crowded 1,2,3-Substituted Bis(indenyl)zirconium(iv) Dichlorides
FULL PAPER
Introduction of a second tBu group by the same means
is more complicated (Scheme 3). Formation of the 1-tBu-
6,6-dimethylbenzofulvene (8) does not occur at room tem-
perature, but with an excess of pyrrolidine and refluxing
for several days, nearly quantitative conversion is achieved.
Addition of methyllithium to 8, provides 1,3-di-tBu-indene
(9), albeit in low yield. It may be reasoned that the tBu
group raises the energy of the exo double bond by its elec-
tron releasing character and thus inhibits nucleophilic at-
tack by methyllithium. Disappointingly, we had to find that
the synthesis of 2-TMS-6,6-dibenzofulvene starting from 1b
is not possible with the aforementioned procedure. Alterna-
tively we investigated the reaction of the lithium salt of 1b
with acetone and subsequent dehydration with phosphoric
acid or acid anhydrides. The first attempt, which employed
phosphoric acid, provided the benzofulvene. Reproduction
of this reaction was unsuccessful; we are not primarily in-
terested in ill-defined polymers, but could, however, en-
vision the obtained products to be useful for road building
purposes.
Scheme 4. Salt metathesis reaction of the potassium/lithium salts
with zirconium tetrachloride to form bis(indenyl)zirconocene di-
chlorides. a) ZrCl4, Et2O, 0 °C; b) ZrCl4, THF, –40 °C. When RЈЈЈ
= H, rac and meso isomers can be formed of which the latter one
is omitted for clarity.
meso diastereomers were assigned according to relative
chemical shifts, as published elsewhere.[3]
Reaction of 11a with zirconium tetrachloride in diethyl
ether at 0 °C provided a yellow oil upon filtration through
magnesium sulfate and subsequent solvent removal.
Crystallization from diethyl ether was only limitedly suc-
cessful, and we were not able to obtain an analytically pure
sample due to the low yield. NMR spectroscopic data sug-
gest, however, formation of bis[1,3-dimethyl-2-(dimethylsil-
yl)indenyl]zirconium(iv) dichloride (13a). Unreacted 11a
could easily be recovered in good yields. A change of sol-
vent from diethyl ether to THF did not improve the reac-
tion and only decomposition products could be obtained.
Metallation of 11b in diethyl ether succeeded with forma-
tion of a yellow precipitate. The solubility of bis[1,3-di-
methyl-2-(trimethylsilyl)indenyl]zirconium dichloride (13b)
in diethyl ether was too limited to allow work-up in this
solvent; toluene proved to be suitable. Orange or yellow
powders were obtained in a 44% yield upon recrystalli-
zation from diethyl ether solution at –40 °C, depending on
the crystallinity of the zirconocene. Single crystals grown
from diethyl ether solution are bright orange in color.
As it may be anticipated from the observation of inho-
megeneity of K[5], an orange oil was obtained as its reac-
tion product with zirconium tetrachloride (Scheme 2).
Crystallization was unsuccessful, though crystals would
form after a few weeks in the drybox. The ductility of the
crystals precluded further isolation.
Scheme 3. A selective synthesis of 1,3-di-tBu-indene (9). a) MeLi,
Et2O, 0 °C or MeLi, pentane, 5 mol-% AlCl3 / acidic work-up b)
Pyrrolidineex, acetoneex, MeOH, 48 h reflux; c) MeLi, Et2O, 6 h
reflux.
Zirconocene Syntheses
To facilitate introduction to the coordination sphere of
zirconium, 2b, 3a–b were all converted into their lithium
salts 10, 11a–b, respectively, by exposure to stoichiometric
amounts of a organyl lithium in pentane. The observed re-
activities mirrored those of the starting material 1a–b. The
syntheses of the zirconium complexes were subsequently at-
tempted by a salt metathesis reaction with zirconium tetra-
chloride, as illustrated in Scheme 4. For disubstituted li-
gands, rac and meso diastereomers may be obtained,
whereas trisubstituted ligands exclusively provide enantio-
mers.
Crystal Structure
An ORTEP[8] view of 13b is given in Figure 1; selected
bond lengths and angles are listed in Table 1. The coordina-
rac/meso-Bis[1-methyl-2-(trimethylsilyl)indenyl]zirconium- tion sphere of the zirconium atom can be described as a
(iv) dichloride (12) was obtained as a yellow powder in a distorted tetrahedron. The two indenyl and chloride ligands
respectable 55% yield. The rac and meso diastereomers are related by C2 symmetry. The dihedral angle φ, which is
1
were detected by H NMR at a 1:1 ratio, and isolation or defined as Si1–C3–C3*–Si1*, is measured to 165.7°, a ne-
enrichment by crystallization at –40 °C failed. The rac and arly perfect anti-periplanar conformation of the indenyl li-
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A. C. Möller, R. Blom, R. H. Heyn, O. Swang, C.-H. Görbitz, T. Seraidaris
FULL PAPER
gands. As a consequence, the 1,3-methyl groups on the pose a convex surface to the zirconium center. In transver-
frontside (C11, C11*) almost ideally intersect the Cl1–Zr1– sal direction, the frontside methyl groups are bent out of
Cl1* angle, which spans 92.8°. The dihedral angle C11–C4– the linear arrangement by 4.6°, whereas the sterically more
C4*–C11* is – with only 5.7° distortion – close to a perfect encumbered methyl groups on the backside are bent out by
syn-periplanar orientation of these methyl groups. In con- 12.2° – measured as C11–C4–Ct and C10–C2–Ct, respec-
trast, the methyl groups on the backside (C10, C10*) span tively. In longitudinal direction, the curvature climbs from
a dihedral angle (C10–C2–C2*–C10*) of –57.5° and mini- a modest 1.1° within the benzo moiety to 5.2° and 4.2° at
mize steric interaction by this strongly syn-clinal orienta- the transition from benzo to Cp moiety and within the Cp
tion.
ring, and finally reaches 19.3° for the transition Cp to silyl
moiety. Consequently, the distortion of the tetrahedral sym-
metry around the zirconium is stronger than usual; the Ct-
Zr1–Ct* angle ε measures 137.4°. To the best of our knowl-
edge, this is the largest value ever reported for unbridged
bis(indenyl)zirconium dichlorides. The largest values for ε
have been reported for rac-ferrocenyl-bis(1-indenyl)zirco-
nium dichloride, ferrocenyl-bis[2,3,4,5-tetramethyl-1-Cp]zir-
conium dichloride[9] and [(1,2,4-tri-(tBu)Cp)(1,2,3,4-tetra-
(iPr)Cp)]zirconium dichloride[10] with 129.7, 138.5 and
138.8°, respectively.
Polymerization Characteristics and DF Calculations
In order to establish a rough estimate on the properties
of 12 and 13b as polymerization catalyst precursors in eth-
ene homopolymerizations with MAO as cocatalyst, isobar
and isothermal experiments were run at two different cata-
lyst concentrations. Reference experiments were carried out
with bis(indenyl)zirconium dichloride/MAO (RefH) and
bis[2-(trimethylsilyl)indenyl]zirconium
dichloride/MAO
(RefTMS) at concentrations of c(Zr) = 1.0·10–7 mol/L and
c(Zr) = 1.0·10–6 mol/L at Al/Zr ratios of 10000 and 1000,
respectively. For 12/MAO and 13b/MAO, these conditions
were not sufficient for detectable polymerization activity.
Rather, 12/MAO and 13b/MAO required higher catalyst
and MAO concentrations in order to show sufficient ac-
tivity. A rough comparison of the catalyst’s activities and
the molecular weights obtained is given in Table 2.
The results for the homopolymerizations suggest a de-
crease in activity with increasing degree of substitution of
the catalysts’ ligand framework. We ascribe the significantly
lower activities for high catalyst concentrations of RefH/
MAO and RefTMS/MAO to diffusion control in the course
of polymerization. The high amount of polymer produced
increases the viscosity and hence reduces ethene up-take
and agitation of the reaction mixture. Considering the poly-
mer molecular masses, only 12/MAO displays a notably dif-
ferent value compared to the other catalysts. The higher
polydispersity index (PDI) obtained from 12/MAO may be
explained by the presence of the rac and meso isomer as
active sites. The PDI’s relative proximity to the value of
2 suggests their polymerization characteristics to be fairly
alike.
Figure 1. Refined crystallographic structure of bis[1,3-dimethyl-2-
(trimethylsilyl)indenyl]zirconium dichloride (13b). Hydrogen atoms
are omitted for clarity. Thermal ellipsoids are at the 50% prob-
ability level.
Table 1. Selected bond lengths [Å] and angles [°] for 13b.
Bond length/angle [Å / °]
13b
Zr1–Cl1
Zr1–Ct
2.4473(3)
2.263
Zr1–C1
Zr1–C2
Zr1–C3
Zr1–C4
Zr1–C5
Si1–C3
Cl1–Zr1–Cl1*
Ct–Zr1–Ct*
Ct–C3–Si1
Ct–C2–C10
Ct–C4–C11
2.6188(10)
2.5385(10)
2.5370(10)
2.5320(10)
2.6252(9)
1.8979(10)
92.843(13)
137.40
168.84
167.76
175.43
The comonomer response of the different catalysts can-
not be described by a simple consideration of steric conges-
tion. Whereas the unsubstituted RefH/MAO displays a pos-
The contribution of steric congestion is manifested in the itive comonomer response, RefTMS/MAO and 12/MAO
out-of-plane bend angles of the indenyl ligands, which ex- suffer from strong deactivation by 80 to 90% relative to the
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Sterically Crowded 1,2,3-Substituted Bis(indenyl)zirconium(iv) Dichlorides
FULL PAPER
Table 2. Polymerization activities of 12/MAO and 13b/MAO in ethene and ethene-co-1-hexene polymerizations. c(Zr) = 1.0·10–7 mol·L–1
and c(Zr) = 1.0·10–6 mol·L–1 at 30 °C in toluene; c(E) = 0.14 mol·L–1.
Catalyst
HDPE–XH = 0.0
c(Zr) [mol·L–1]
Activity/ [kg·molZr–1·molE–1·h–1]
Al/Zr
Mw [Kg·mol–1]
PDI
RefH
RefH
RefTMS
RefTMS
12
1.0·10–6
1.0·10–7
1.0·10–6
1.0·10–7
2.0·10–7
1.0·10–6
272000 3500
1560000 160000
327000 52000
817000 1400
165000 22000
135000 21000
1000
10000
1000
10000
10000
4000
770
820
625
785
450
790
2.7
2.0
2.6
2.6
3.5
2.6
13b
LLDPE–XH = 0.6
RefH
RefTMS
12
1.0·10–6
1.0·10–6
2.0·10–5
1.0·10–6
376000 14000
53,700 1700
15900 8800
176000
1000
1000
2000
2000
189
45
195
428
3.0
16
31[a]
2.2
13b
[a] Trimodal distribution observed, Mn = 6.2.
homopolymerization. In contrast, 13b/MAO displays vir-
tually no response to the comonomer and polymerises with
roughly the same rate as before.
The fairly low activity of 13b/MAO prompts the question
of whether or not the catalyst precursor is sufficiently acti-
vated by the MAO available during the polymerization. To
assess the dependence of 13b/MAO on the Al/Zr ratio, a
series of experiments was run at constant zirconium, ethene,
and 1-hexene concentrations, while varying the Al/Zr ratio
from approximately 1000 to 19000. The data obtained are
listed in Table 3. We suggest that the catalyst activity does
not strongly depend on the concentration of MAO or the
Al/Zr ratio, though the data point to a slight increase in
activity.
Scheme 5. Simplified representation of the active site with a poly-
mer chain (n-hexyl) attached: A1 with an ethene and A2 with a 1-
hexene ligand. For clarity, the 1,3-dimethyl-2-TMS-indenyl ligands
are abbreviated as “L” and charges are omitted.
Table 3. Polymerization activities of 13b in ethene-co-1-hexene po-
lymerizations as a function of the Al/Zr ratio. c(Zr) = 1.0·10–6
mol·L–1, c(E) = 0.14 mol·L–1, XH = 0.5 at 30 °C in toluene.
Activity
Al/Zr
[kg·molZr–1·molE–1·h–1
sible to calculate the Gibbs energy [Equation (1)] for the
enchainment of 1-hexene relative to ethene.
6000
18600
26100
45400
44000
33000
79100
950
1900
2800
5700
9500
14200
18900
ΔrG = –RTln(Keq)
(1)
xExH
Keq
=
(2)
XEXH
At 303.15 K with XE and XH = 0.5, and xE = 0.997 and
xH = 0.003, we obtain ΔrG = 11 kJ/mol and estimate the
Another issue of interest is the neutral to positive co- lower and upper limit to 10 and 14 kcal/mol, respectively.
monomer response of 13b/MAO, which does not fit into This value includes the reaction entropy, which could in ge-
the trend set by RefTMS/MAO and 12/MAO. A 13C NMR neral be obtained from an Arrhenius plot. A set of experi-
analysis of the copolymer obtained from 13b/MAO was ments was designed to investigate the dependence of the
conducted according to the signal assignments published by equilibrium constant Keq on the temperature, as suggested
Randall[11] and revealed a signal pattern typical for LLDPE by the van’t Hoff equation. The results summarized in
polymers. The comonomer content was determined to 0.3 Table 4 indicate that there is no detectable relation between
mol-% 1-hexene, which is essentially the detection limit. As- the polymerization temperature and catalyst activity or co-
suming that the statistical distribution of the comonomer monomer incorporation. The activity varies unsystemati-
in the polymer chain is proportional to the equilibrium con- cally, and the 1-hexene incorporation is constant. An exper-
stant Keq that would describe the population of the active imental estimate of the reaction entropy is therefore not
site models A1 and A2, as depicted in Scheme 5, it is pos- available.
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FULL PAPER
Table 4. Polymerization activities of 13b in ethene-co-1-hexene po- tution problems, which may arise for the DMS moiety, sub-
lymerizations as a function of the reaction temperature. The error
stituents larger than a methyl group are surprisingly prone
indicates the experimental standard deviation; c(Zr) = 1.0·10–6
to hydrogen shift reactions of the deprotonated ligands.
mol·L–1, c(E) = 0.14 mol·L–1, XH = 0.5 at Al/Zr = 4000 in toluene.
This side reaction affects the yield and applicability of the
Activity
Mw
indenyl salts significantly. Introduction of an alkyl moiety
without hydrogen shift capability like tBu was precluded by
steric strain in the synthesis of a suitable precursor. Further,
the DMS-substituted ligand would not afford the desired
zirconocene complex. As we have seen in earlier work, the
presence of hydrogen on the silyl groups in 2 position does
not seem to be favored for the zirconocene synthesis.[3]
In contrast, the syntheses of bis[1-methyl-2-TMS-inden-
yl]zirconium(iv) dichloride (12) and bis[1,3-dimethyl-2-
TMS-indenyl]zirconium(iv) dichloride (13b) were achieved
without undue difficulty, although the separation of the rac
and meso diastereomers of 12 failed. The (basic) polymer-
ization studies presented herein suggest that the activity in
ethene polymerizations decreases with an increasing degree
of substitution. In contrast to the very moderate activities,
the molecular weights are less effected and this may be ra-
tionalized by the reduction in available space at the active
site. Chain termination by chain transfer requires a β-agos-
tic structure and the association of a monomer unit. Chain
transfer to MAO requires an intimate interaction with the
very same. Both processes are likely to be suppressed by a
bulky ligand framework. This effect is even more pro-
nounced for 13b, which does not show the expected increase
in activity with increasing Al/Zr ratio. Such an effect is
often observed and poorly understood.
The virtual inertness of 13b towards 1-hexene as a mono-
mer is an interesting feature, which is to the best of our
knowledge unprecedented. The unsuccessful attempts to
find the transition state for this process support our idea
that the selectivity is governed by steric factors. Neverthe-
less an interesting agreement between experiment and
theory has been found: The calculated energy difference of
8 to 13 kJ/mol for the olefin complexes falls into the same
range as the Gibbs energy of 11 kJ/mol, as derived from
Boltzmann statistics on the 1-hexene incorporation into the
polymer chain. This may indicate that the insertion of the
monomer units may be controlled by a single activation
barrier, despite our inability to calculate any suitable transi-
tion state. Systems like 13b, employed in a catalyst mixture,
are industrially desirable as they show a monomer selectiv-
ity which could be used to produce long chain branches in
a copolymerization with 1-hexene. The catalyst activity is,
however, traded for this selectivity.
T/°C
PDI
xH
[kg·molZr–1·molE–1·h–1] [Kg·mol–1]
20
30
40
48
60
24400 3100
18900 1900
29600 2200
44400 1800
29800 2000
494
533
391
273
172
11
20
15
2.6
6.9
0.003
0.003
0.003
0.003
0.003
In order to validate the quality of our estimate of the
reaction Gibbs energy, we conducted DF calculations on an
active site of 13b which features a n-hexyl ligand and one
ethene or 1-hexene unit. For the ethene complex, a pro-
nounced α-agostic interaction of the polymer chain and the
zirconium center was found, stretching the C–H bond
length to 1.13 Å. The ethene ligand shows slight rehybrid-
ization through a HCH bond angle of 116.4° and is sym-
metrically coordinated at the typical Zr···C distances of
2.72 Å (C1) and 2.85 Å (C2). The 1-hexene complex dis-
plays evidence of steric strain already on visual inspection,
as the Z-side of the 1-hexene ligand is tilted away from the
zirconium center by a 16.5° deviation from the perfect or-
thogonal side-on coordination. This is due to intrusion of
the butyl substituent into the space occupied by the methyl
groups in the 1 and 3 positions of the indenyl ligands. Con-
sequently, the Zr-olefin distance is increased to 2.78 Å (C1)
and 3.32 Å (C2). An α-agostic interaction is not detectable,
and there is an insignificant lengthening of the ZrϪcarbon
bond to the polymer chain by 0.03 Å.
The relative energies of both olefin complexes, compared
to the energies of the uncoordinated olefins, is a measure
of their populations in the equilibrium during the polymer-
ization process (Scheme 5). Since both olefins were present
in equal amounts, stoichiometric corrections are not re-
quired. For the rac-like conformer of the active site the en-
ergy difference calculates to 8 kJ/mol, whereas the meso-like
conformer is somewhat less stable with 13 kJ/mol. A mean-
ingful comparison of product equilibria with stability of
starting materials usually requires the knowledge of acti-
vation enthaplies. All attempts to calculate the activation
enthalpies for the insertion process failed since the optimi-
zation of the transition state exclusively led to geometries
where the olefin ligands would rotate along the zirconiumϪ
olefin bond and result in non-planar geometries. Although
we have been able to calculate nonplanar transition states
for other systems, the calculations would not converge in
the case of A1 or A2. The polydispersity index of 2.2 for the
copolymerization suggests that only one active site needs to
be considered.
Experimental Section
General: Unless otherwise indicated, all procedures were conducted
using Schlenk techniques under argon. All solvents were dried from
sodium with benzophenone or anthracene (diethyl ether, THF, and
toluene) or lithium aluminium hydride (pentane) and distilled prior
to use. Acetone (Merck) was dried with anhydrous magnesium sul-
fate for three days and distilled under argon. When used as a filter
Conclusions
The herein investigated syntheses of sterically demanding
1,2,3-substituted indenyl ligands on the basis of 2-silylin-
denes are unexpectedly difficult. Apart from hydride substi- agent, magnesium sulfate (Merck) was dried at 140 °C for at least
1764 © 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjic.org
Eur. J. Inorg. Chem. 2005, 1759–1769

Sterically Crowded 1,2,3-Substituted Bis(indenyl)zirconium(iv) Dichlorides
FULL PAPER
two days prior to use. Iodomethane (Fluka) was dried with calcium
hydride (Merck, used as received) and distilled under argon. 2-
Iodo-propane (Fluka) and methanol p.a. (Merck) were used as re-
ceived. Aluminum trichloride (resubl. grade, Aldrich Chemicals),
pyrrolidine (Fluka), magnesium turnings (Merck and Aldrich
Chemicals), n-butyllithium (Aldrich Chemicals or Merck), meth-
yllithium (Aldrich Chemicals), tert-butyllithium (Aldrich Chemi-
cals), boron trifluoride diethyl etherate (Aldrich Chemicals) and
zirconium tetrachloride (Strem, 99.95%+, sublimed grade) were
used as received. Column chromatography was conducted on silica
was stirred overnight with waterbath cooling to yield a white pre-
cipitate. By filtration with a cannula, washing with pentane
(2×20 mL) and drying under high vacuum a white powder (1.85 g,
10.3 mmol) was obtained. The 2-(dimethylsilyl)indenyllithium salt
was dissolved in 30 mL diethyl ether and placed in an addition
funnel mounted on a Schlenk flask charged with methyl iodide
(2.9 mL, 46.8 mmol) in diethyl ether (30 mL). Drop-wise addition
provided a yellow solution, which was stirred overnight prior to
acidic work-up (20 mL 0.1 mol/L hydrochloric acid) in diethyl
ether. Phase separation, washing of the organic layer with deion-
gel 60 (0.040–0.063 mm) provided by Merck. Methylalumoxane ized water followed by drying over magnesium sulfate and removal
(MAO) was purchased at Crompton Bergkamen, Germany, as a
10% toluene solution. Prior to use, the MAO solution was filtered
through a D4-frit and volatiles removed in vacuo yielding a white
solid. Polymerization grade ethene was provided by Borealis Sta-
thelle, Norway. 1-Hexene (Aldrich) was purified before copolymer-
ization by drying over potassium/benzophenone and subsequent
of solvent at 70 mbar/40 °C afforded a pale yellow liquid (1.56 g,
8.3 mmol, 71%). Impurities were not detectable by GC/MS analy-
sis. 1H NMR (300 MHz, [D6]benzene, 25 °C): δ = 0.19 [d, 3J =
5
3.9 Hz, 6 H, SiH(CH3)2], 2.15 [t, J = 2.1 Hz, 3 H, C(3)-Me], 3.14
[q, 5J = 2.4 Hz, 2 H, C(1)-H], 4.69 [hept, 3J = 3.9 Hz, 1 H,
SiH(CH3)2], 7.17–7.25 [m, 1 H, C(5)-H], 7.25–7.27 [m, 2 H, C(6,7)-
H], 7.32–7.37 [m, 1 H, C(4)-H] ppm. 13C{1H} NMR (75 MHz,
[D6]benzene, 25 °C): δ = –3.1 [2 C, SiH(CH3)2], 13.8 [1 C, C(3)-
Me], 42.6 (1 C, C-1), 119.7 (1 C, C-4), 124.0 (1 C, C-7), 125.6 (1
C, C-6), 126.8 (1 C, C-5), 137.2 (1 C, C-3), 147.1 (1 C, C-2), 147.9
(1 C, C-7a), 150.4 (1 C, C-3a) ppm. GC/MS (70 eV): m/z (%) = 188
(100) [M+], 173 (74) [M+ Ϫ CH3], 145 (41) [C9H9Si+], 128 (75)
[C10H8+], 115 (15) [C9H7+], 73 (10) [Si(CH3)3+], 59 (78) [SiH-
(CH3)2+].
1
distillation in an argon atmosphere. H- and 13C NMR spectra ac-
quired with a Varian Gemini 300 MHz instrument were referenced
to the residual solvent peaks. Low resolution MS was conducted
with a Hewlett–Packard 5973 MSD, coupled with a Hewlett–Pack-
ard 6890 GC unit. GC columns used were HP-5, I.D. 0.32 mm,
0.250 μm, 30 m and DB-17, I.D. 0.25 mm, 0.250 μm, 30 m, both
manufactured by J&W Scientific. GPC characterizations of the
HDPE samples were conducted with a Waters 150CVplus instru-
ment, operating with two HMW 6E and one HMW7, or three
HT6E styragel columns (Waters) at 140 °C with trichlorobenzene
as elution solvent and a dRI & viscosity detector. Alternatively,
weight and number average molecular weights and polydispersity
indices were measured at 140 °C with a Waters Alliance 2000 size
exclusion chromatography (SEC) instrument equipped with Waters
HT3, HT4, HT5 and HT6 columns. 1,2,4-Trichlorobenzene was
used as solvent at a flow rate of 1.0 cm3·min–1. The columns were
universally calibrated with narrow molecular weight polystyrene
standards. Well-characterized lithium salts which resulted in iso-
lable Zr complexes were not subjected to EA.
1-Methyl-2-(trimethylsilyl)indene (2b): The methylation of 1b was
conducted in a similar manner to 2a. To a Schlenk flask charged
with 2-(trimethylsilyl)indene (3.00 g, 15.0 mmol) dissolved in pen-
tane (40 mL) at room temperature, n-butyllithium (19.0 mL,
49.0 mmol) was added through a septum and stirred vigorously.
The reaction mixture was stirred overnight and warmed to room
temperature to yield a clear, yellow solution. Upon addition of di-
ethyl ether (2.0 mL) and stirring for another ten minutes, the for-
mation of copious precipitate was observed. Solvent volume re-
duction to approximately 60% and subsequent filtration through a
D4-frit provided a white solid, which was washed twice with pen-
tane (10 mL) and dried under vacuum for 1 h. A second Schlenk
flask equipped with an addition funnel and charged with methyl
iodide (3.0 mL, 48.5 mmol) in diethyl ether (20 mL) was cooled to
–40 °C. The lithium salt was dissolved in diethyl ether (30 mL),
transferred to the addition funnel of the second Schlenk flask and
dropwise added to the methyl iodide solution at –40 °C. After stir-
ring overnight, the reaction was quenched with hydrochloric acid
(20 mL, 0.1 mol/L). The organic layer was washed twice with water
(20 mL) and dried with magnesium sulfate. Removal of solvent af-
forded the product (2.45 g, 12.1 mmol, 81%) with a purity of 99%,
as determined by GC/MS. 1H NMR (300 MHz, [D6]benzene,
2-(Dimethylsilyl)indene (1a) and 2-(Trimethylsilyl)indene (1b): These
compounds were prepared according to a published literature pro-
cedure.[3]
2-(Dimethylsilyl)-3-methylindene (2a). Potassium Hydride Route:
Potassium hydride (432 mg, 10.8 mmol) was dissolved in THF
(40 mL) and cooled to –90 °C. 2-(Dimethylsilyl)indene (1.88 g,
10.8 mmol) dissolved in THF (8 mL) was injected into the cold
potassium hydride/THF suspension and the reaction mixture was
warmed to room temperature while being stirred overnight. Substi-
tution of THF by 20 mL diethyl ether and filtration through a can-
nula resulted in a clear, yellow-green solution of the 2-(dimethylsi-
lyl)indenylpotassium complex. In a second Schlenk flask equipped
3
25 °C): δ = 0.24 [s, 9 H, Si(CH3)3], 1.30 [d, J = 7.4 Hz, 3 H, C(1)-
3
5
5
CH3], 3.48 [dq, J = 7.4, J = 1.6 Hz, 1 H, C(1)-H], 6.90 [d, J =
1.6 Hz, 1 H, C(3)-H], 7.28–7.35 [m, 2 H, C(5,6)-H], 7.37–7.43 [m,
2 H, C(4,7)-H] ppm. 13C{1H} NMR (75 MHz, [D6]benzene, 25 °C):
δ = –0.2 [3 C, Si(CH3)3], 17.4 [1 C, C(1)-Me], 49.7 (1 C, C-1), 121.6
(1 C, C-4), 123.2 (1 C, C-7), 125.8 (1 C, C-6), 127.1 (1 C, C-5),
140.9 (1 C, C-3), 145.0 (1 C, C-2), 153.1 (1 C, C-7a), 154.8 (1 C,
C-3a) ppm. GC/MS (70 eV): m/z (%) = 202 (28) [M+], 187 (11) [M+
Ϫ CH3], 159 (5) [M+ Ϫ C3H7], 145 (6) [M+ Ϫ C4H9], 128 (14) [M+
Ϫ TMS], 115 (4) [C9H7+], 73 (100) [TMS+], 59 (7) [SiH(CH3)2+].
with
a pressurized addition funnel, methyl iodide (2.0 mL,
32.4 mmol) and diethyl ether (20 mL) were cooled to –40 °C before
the potassium complex was added dropwise under isothermal con-
ditions over a period of 30 minutes. The reaction was stirred over-
night and warmed to room temperature, to yield a copious white
precipitate. Filtration to remove insolubles and acidic quenching
was followed by extraction with water (2×20 mL). Drying over
magnesium sulfate and removal of solvent afforded the product
(1.29 g, 6.9 mmol, 64%) at 85% purity. The isomer distribution was
4% 3 isomer, 81% 1 isomer, 8% un- and 7% disubstituted.
1,3-Dimethyl-2-(dimethylsilyl)indene (3a): The synthesis was carried
out in a fashion similar to 2a. 2-(Dimethylsilyl)-1-methylindene
(2.68 g, 14.3 mmol), n-butyllithium (8.8 mL, 14.1 mmol) and
n-Butyllithium Route: 2-(Dimethylsilyl)indene (2.04 g, 11.7 mmol) methyl iodide (3.5 mL, 57.2 mmol) were employed to obtain a yel-
and pentane (50 mL) were placed in a Schlenk flask. n-Butyllithium
(6.4 mL, 10.3 mmol) was slowly added via syringe. The solution
low liquid (2.65 g). Column chromatography with pentane on silica
provided a colorless liquid (1.61 g, 8.0 mmol, 57%), containing
Eur. J. Inorg. Chem. 2005, 1759–1769
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1765

A. C. Möller, R. Blom, R. H. Heyn, O. Swang, C.-H. Görbitz, T. Seraidaris
FULL PAPER
both the product (70%) and its 1,1 isomer (30%). No further puri-
128 (6) [C10H8+], 115 (5) [C9H7+], 73 (100) [C3H9Si+], 59 (7)
[C2H7Si+].
1
fication was attempted. H NMR (300 MHz, [D6]benzene, 25 °C):
3
3
δ = 0.24 [d, J = 3.9 Hz, 3 H, SiH(CH3)2], 0.25 [d, J = 3.9 Hz, 3
3
5
1-Isopropyl-2-(trimethylsilyl)indenyllithium/potassium (5): The prep-
aration of the lithium salt followed a literature procedure.[12] At
–90 °C 4 (4.44 g, 19.3 mmol) was reacted with n-butyllithium
(8.5 mL, 21.3 mmol) in pentane (30 mL). Stirring overnight and
warming to room temperature provided an orange solution. A pre-
cipitate could be obtained neither by addition of diethyl ether
(2 mL) nor by solvent removal. GC/MS analysis after quenching a
sample of the reaction with methyl iodide in THF displayed 10
major products, of which 7 could be identified by the fragmentation
pattern: (i) 1-Methyl-1-isopropyl-2-(trimethylsilyl)indene. GC/MS
(70 eV): m/z (%) = 244 (32) [M+], 229 (5) [M+ Ϫ CH3], 170 (40)
[M+ Ϫ TMS], 155 (17) [C12H11+], 141 (12) [C11H9+], 128 (7), 115
(6) [C9H7+], 73 (100) [C3H9Si+]; (ii) 1-isopropyl-2-(trimethylsilyl)
indene (4); (iii) 3-methyl-1-isopropyl-2-(trimethylsilyl)indene. GC/
MS (70 eV): m/z (%) = 244 (22) [M+], 229 (6) [M+ Ϫ CH3], 201
(12) [M+ Ϫ C3H7], 185 (6) [C12H14Si+], 170 (25) [M+ Ϫ C3H9Si],
155 (7) [C12H11+], 141 (6) [C11H9+], 128 (6), 73 (100) [C3H9Si+],
59 (8) [C2H7Si+]; (iv) 1,3-diisopropyl-2-(trimethylsilyl)indene; (v) 1-
methyl-3-isopropyl-2-(trimethylsilyl)indene. GC/MS (70 eV): m/z
(%) = 244 (36) [M+], 229 (8) [M+ Ϫ CH3], 170 (54) [M+ Ϫ TMS],
155 (14) [C12H11+], 141 (9) [C11H9+], 128 (7), 115 (5) [C9H7+], 73
(100) [C3H9Si+], 59 (7) [C2H7Si+]; (vi) 1,1-diisopropyl-2-(trimeth-
ylsilyl)indene. GC/MS (70 eV): m/z (%) = 272 (19) [M+], 257 (5)
[M+ Ϫ CH3], 198 (55) [M+ Ϫ TMS], 183 (18) [C14H15+], 169 (5)
[C13H13+], 155 (5) [C12H11+], 141 (5) [C11H9+], 73 (100) [C3H9Si+],
59 (7) [C2H7Si+]; (vii) 3-tert-butyl-2-(trimethylsilyl)indene. GC/MS
(70 eV): m/z (%) = 244 (25) [M+], 229 (69) [M+ Ϫ CH3], 214 (100)
[M+ Ϫ C2H6], 199 (43) [M+ Ϫ C3H9], 187 (5) [M+ Ϫ C4H9], 169
(5) [C13H14+], 155 (13) [C12H11+], 141 (6) [C11H9+], 128 (7), 115 (7)
[C9H7+], 73 (7) [C3H9Si+]. Attempted preparation of the potassium
salt: Potassium hydride (568 mg, 13.9 mmol) was added to a solu-
H, SiH(CH3)2], 1.21 [d, J = 7.5 Hz, 3 H, C(1)-CH3], 2.12 [d, J =
1.8 Hz, 3 H, C(3)-CH3], 3.36 [dq, 5Jd = 2.1, 3Jq = 7.5 Hz, 1 H,
C(1)-H], 4.68 [m, 3J = 3.9 Hz, 1 H, SiH(CH3)2], 7.17–7.24 [m, 2
H, C(5,6)-H], 7.24–7.31 [m, 2 H, C(4,7)-H] ppm. 13C{1H} NMR
(75 MHz, [D6]benzene, 25 °C): δ = –2.4 [2 C, SiH(CH3)3], 17.6 [1
C, C(1)-Me], 25.8 [1 C, C(3)-Me], 49.3 (1 C, C-1), 119.7 (1 C, C-
4), 122.9 (1 C, C-7), 126.0 (1 C, C-6), 127.0 (1 C, C-5), 143.5 (1 C,
C-3), 146.5 (1 C, C-2), 149.4 (1 C, C-7a), 152.7 (1 C, C-3a) ppm.
GC/MS (70 eV): m/z (%) = 202 (50) [M+], 187 (33) [M+ Ϫ CH3],
159 (19) [C10H11Si+], 142 (100) [C11H10+], 128 (42) [C10H8+], 115
(17) [C9H7+], 73 (25) [Si(CH3)3+], 59 (66) [SiH(CH3)2+].
1,3-Dimethyl-2-(trimethylsilyl)indene (3b): Prior to the addition of
n-butyllithium (15.0 mL, 37.5 mmol), 2b (2.45 g, 12.1 mmol) in
pentane (30 mL) was placed in a Schlenk flask and cooled to
–90 °C. The solution was stirred overnight and warmed to room
temperature, affording a suspension with a white precipitate after
addition of diethyl ether (1 mL). Reduction of the solvent volume
to approximately 60% was followed by a filtration through a D4-
frit and washing of the precipitate with pentane (3×10 mL). While
the white precipitate was dried in vacuo, a second Schlenk flask
was equipped with an addition funnel and methyl iodide (2.25 mL,
36.3 mmol) in diethyl ether (20 mL) and cooled to –40 °C. The lith-
ium salt was dissolved in diethyl ether (30 mL) and THF (10 mL),
transferred to the addition funnel and dropwise added to the solu-
tion at –40 °C. Stirring overnight and acidic work-up provided a
pale yellow crude product (2.21 g, 10.2 mmol). Its composition was
determined to be ca. 20% of the 1,1 and 80% the desired 1,3 iso-
mer. No further separation of the isomers was attempted. The spec-
troscopic data was derived from the hydrolysis of the pure 1,3-
dimethyl-2-(trimethylsilyl)indenyllithium. 1H NMR (300 MHz,
[D6]benzene, 25 °C): δ = 0.24 [s, 9 H, Si(CH3)3], 1.20 [d, 3J = tion of 4 (2.9 g, 12.6 mmol) in THF (40 mL) at –90 °C. Quantita-
5
7.4 Hz, 3 H, C(1)-CH3], 2.08 [d, J = 2.0 Hz, 3 H, C(3)-CH3], 3.48 tive reaction was not achieved before refluxing the suspension for
[qq, 5J = 2.0, 3J = 7.4 Hz, 1 H, C(1)-H], 7.19–7.25 [m, 2 H, C(5,6)-
H], 7.25–7.31 [m, 2 H, C(4,7)-H] ppm. 13C{1H} NMR (75 MHz,
[D6]benzene, 25 °C): δ = 0.9 [3 C, Si(CH3)3], 18.2 [1 C, C(1)-Me],
26.0 [1 C, C(3)-Me], 49.4 (1 C, C-1), 119.6 (1 C, C-4), 122.9 (1 C,
C-7), 125.9 (1 C, C-6), 127.0 (1 C, C-5), 146.0 (1 C, C-3), 146.8 (1
several days. Filtration with a cannula, solvent removal, washing
with pentane and drying in vacuo afforded a yellow-brown solid
(1.8 g, 6.7 mmol, 53%). 1H NMR (300 MHz, [D8]THF, 25 °C): δ =
3
0.46 [s, 9 H, Si(CH3)3], 1.68 [d, J = 9.0 Hz, 6 H, C(1Ј,3Ј)-H], 3.62
3
[hept, J = 9.0 Hz, 1 H, C(2Ј)-H], 6.16 [s, 1 H, C(3)-H], 6.47–6.59
C, C-2), 148.3 (1 C, C-7a), 152.8 (1 C, C-3a) ppm. GC/MS (70 eV): [m, 2 H, C(5,6)-H], 7.39 [m, 1 H, C(4)-H], 7.63–7.71 [m, 1 H, C(7)-
m/z (%) = 216 (29) [M+], 201 (12) [M+ Ϫ CH3], 141 (11) [M+ H] ppm. 13C{1H} NMR (75 MHz, [D8]THF, 25 °C): δ = 1.9 (3 C),
Ϫ
TMS], 128 (11) [M+ Ϫ Si(CH3)4], 115 (6) [C9H7+], 73 (100) [TMS+], 25.0 (2 C), 32.2, 99.8, 112.5, 112.8, 119.4, 119.8, 121.0, 123.1, 127.6,
59 (6) [SiH(CH3)2+].
132.0 (1 C) ppm.
1-Isopropyl-2-(trimethylsilyl)indene (4): The synthesis was carried
out according to the procedure for 2b. 2-(Trimethylsilyl)indenyl-
lithium (870 mg, 4.5 mmol) and 2-iodopropane (0.5 mL, 5.0 mmol)
Attempted Synthesis of 1,3-Diisopropyl-2-(trimethylsilyl)indene: The
preparation was attempted by in situ derivatization of Li[5] without
prior isolation. Following the procedure for the preparation of 3b,
2-iodopropane (2.1 mL, 21 mmol) was used. After stirring for 6 h
and incomplete conversion according to GC/MS analysis, another
aliquot of iodopropane was added and reacted overnight. Acidic
work-up and GC/MS analysis of the crude product revealed the
presence of four components: 1- and 3-isopropyl-2-(trimethylsilyl)-
1
were reacted to provide a yellow oil (770 mg, 3.3 mmol, 74%). H
NMR (300 MHz, [D6]benzene, 25 °C): δ = 0.202 [s, 4.5 H, Si-
(CH3)3], 0.204 [s, 4.5 H, Si(CH3)3], 0.48 [d, 3J = 6.6 Hz, 3 H, C(1Ј)-
3
3
3
H], 1.21 [d, J = 7.4 Hz, 3 H, C(3Ј)-H], 2.40 [dqq, J = 3.0, J =
4
3
6.9 Hz, 1 H, C(2Ј)-H], 3.52 [dd, J = 2.4, J = 2.7 Hz, 1 H, C(1)-
H], 6.99 [d, 4J = 1.8 Hz, 1 H, C(3)-H], 7.11 [ddd, 4J = 1.2, 3J = indene, 1,1- and 1,3-diisopropyl-2-(trimethylsilyl)indene. To the
3
3
3
7.2, J = 7.2 Hz, 1 H, C(5)-H], 7.22 [ddm, J = 0.6, J = 7.2, J =
crude product dissolved in THF at –40 °C, potassium hydride
3
7.2 Hz, 1 H, C(6)-H], 7.30 [dm, J = 0.6, J = 7.5 Hz, 1 H, C(4)-H], (791 mg, 19.3 mmol) was added. Stirring overnight afforded a green
7.45 [d, J = 7.5 Hz, 1 H, C(7)-H] ppm. 13C{1H} NMR (75 MHz, solution. Solvent removal and extraction with diethyl ether pro-
3
[D6]benzene, 25 °C): δ = –0.2, –0.1 [3 C, Si(CH3)3], 16.4 (1 C, C- vided a light green precipitate and a dark green filtrate. Washing
1Ј), 22.9 (1 C, C-2Ј), 30.3 (1 C, C-3Ј), 61.3, 61.4 (1 C, C-1), 121.7 the light green precipitate with pentane led to partial dissolution of
(1 C, C-4), 124.9 (1 C, C-7), 125.4 (1 C, C-6), 127.3 (1 C, C-5), the precipitate. Drying in vacuo provided a light green, pyrophoric
142.3, 142.4 (1 C, C-3), 146.8 (1 C, C-2), 149.2 (1 C, C-7a), 152.9
powder (3.3 g). We could not isolate a pure fraction of the desired
(1 C, C-3a). GC/MS (70 eV): m/z (%) = 230 (23) [M+], 215 (4) [M+
product. GC/MS (70 eV): m/z (%) = 228 (24) [M+], 257 (7) [M+
Ϫ
Ϫ CH3], 172 (6) [C11H12Si+], 156 (16) [C12H12+], 141 (7) [C11H9+], CH3], 198 (66) [M+ Ϫ TMS], 183 [C14H15+], 169 (6) [C13H14+], 155
1766
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2005, 1759–1769

Sterically Crowded 1,2,3-Substituted Bis(indenyl)zirconium(iv) Dichlorides
FULL PAPER
(6) [C12H11+], 141 (6) [C11H9+], 73 (100) [C3H9Si+], 59 (7)
[C2H7Si+].
C(2)-H], 7.13–7.24 [m, 2 H, C(5,6)-H], 7.60 [mc, 1 H, C(4)-H], 7.72
[mc, 1 H, C(7)-H] ppm. 13C{1H} NMR (75 MHz, [D6]benzene,
25 °C): δ = 23.0 (1 C, C-1Ј), 24.9 (1 C, C-3Ј), 30.2 (3 C, tBu-C),
35.6 (1 C, tBu-C), 122.2 (1 C, C-2Ј), 122.7 (1 C, C-4), 124.4 (1 C,
C-7), 124.9 (1 C, C-6), 126.2 (1 C, C-5), 136.3 (1 C, C-2), 138.9 (1
C, C-7a), 139.9 (1 C, C-3a), 143.6 (1 C, C-1), 151.0 (1 C, C-3) ppm.
GC/MS (70 eV): m/z (%) = 212 (29) [M+], 197 (10) [M+ Ϫ CH3],
182 (5) [M+ Ϫ C2H6], 165 (15), 156 (100) [C12H12+], 141 (50)
[C11H9+], 128 (13) [C10H9+], 115 (17) [C9H7+], 57 (47) [C4H8+].
Attempted Synthesis of 1-Isopropylidene-2-(trimethylsilyl)indene: To
a Schlenk flask charged with dry acetone (0.1 mL, 1.4 mmol) and
BF3·Et2O (0.1 mL, 789 μmol) in diethyl ether (20 mL), 2-(trimeth-
ylsilyl)indenyllithium (100 mg, 824 μmol) was added. Formation of
a colorless suspension was achieved within one hour. The solvent
was replaced by a mixture of pentane and THF (20 mL, 3 mL),
prior to addition of orthophosphoric acid (6 mL, 85%). The or-
ganic layer turned yellow while stirring overnight. Acidic work-up,
washing with deionized water, drying over magnesium sulfate and
drying in vacuo provided a yellow oil (100 mg, 284 μmol, 34%).
1,3-Di-(tert-butyl)indene (9): The synthesis followed essentially the
synthesis of 7. To an agitated solution of 3-tert-butyl-1-(isopro-
pylidene)indene (4.89g, 23.1 mmol) in diethyl ether (30 mL), meth-
yllithium (16.5 mL, 26.4 mmol) was added dropwise at 0 °C. After
stirring for 2 h with warming to room temperature, GC/MS analy-
sis of the reaction mixture showed only traces of the product. Ad-
dition of more methyllithium (15.0 mL, 24 mmol) and refluxing the
reaction for 10 h provided a conversion of 25% (GC/MS). The re-
action was poured over a mixture of diluted hydrochloric acid, di-
ethyl ether and crushed ice (300 mL). Adjustment to pH 4 was
followed by stirring for 10 minutes and phase separation. The or-
ganic layer was washed with deionized water (2×100 mL) and
dried with magnesium sulfate prior to solvent evaporation. Column
chromatography at silica gel (420 g) afforded a colorless liquid
(0.652 g, 2.9 mmol, 12%). 1H NMR (300 MHz, [D6]benzene,
25 °C): δ = 0.94 [s, 9 H, C(1)-tBu], 1.34 [s, 9 H, C(3)-tBu], 3.08 [d,
Product: GC/MS (70 eV): m/z (%) = 228 (31) [M+], 213 (6) [M+
Ϫ
CH3], 197 (13) [M+ Ϫ C2H6], 155 (6) [C12H11+], 141 (7) [C11H9+],
128 (5), 115 (6) [C9H7+], 73 (100) [C3H9Si+]. Hydrated intermedi-
ate: GC/MS (70 eV): m/z (%) = 228 (6) [M+ Ϫ H2O], 201 (14)
[C13H17Si+], 187 (43) [C12H14Si+], 173 (12) [C11H12Si+], 157 (6)
[C10H8Si+], 145 (21) [C9H9Si+], 128 (11), 115 (12) [C9H7+], 73 (100)
[C3H9Si+], 58 (15) [C3H7O+].
6,6-Dimethylbenzofulvene (6): The synthesis followed a literature
procedure and does not require Schlenk technique.[7] By stirring
indene (5 mL, 42.9 mmol), acetone (3.8 mL, 51.8 mmol) and pyr-
rolidine (4.3 mL, 51.8 mmol) in methanol (50 mL) for two days and
subsequent distillation (0.05Torr), a yellow oil (4.94 g, 31.7 mmol,
1
74%) was obtained. H NMR (300 MHz, [D6]benzene, 25 °C): δ =
3
3J = 2.4 Hz, 1 H, C(1)-H], 6.16 [d, J = 2.1 Hz, 1 H, C(2)-H], 7.10
1.84 [s, 3 H, C(1Ј)-CH3], 1.97 [s, 3 H, C(3Ј)-CH3], 6.72 [s, 2 H,
C(2,3)-H], 7.17 [mc, 2 H, C(5,6)-H], 7.28 [mc, 1 H, C(4)-H], 7.64
[mc, 1 H, C(7)-H] ppm. 13C{1H} NMR (75 MHz, [D6]benzene,
25 °C): δ = 22.9 (1 C, C-1Ј), 24.8 (1 C, C-3Ј), 121.8 (1 C, C-4),
124.3 (1 C, C-7), 125.4 (1 C, C-6), 126.7 (1 C, C-5), 128.2 (1 C, C-
3), 129.2 (1 C, C-2), 136.8 (1 C, C-2Ј), 137.8 (1 C, C-1), 142.7 (1
C, C-7a), 145.0 (1 C, C-3a) ppm. GC/MS (70 eV): m/z (%) = 156
(93) [M+], 141 (100) [M+ Ϫ CH3], 128 (21) [C10H9+], 115 (36)
[C9H7+].
4
3
3
[ddd, J = 1.8, J = 7.5, J = 7.5 Hz, 1 H, C(5)-H], 7.21 [ddd, 4J =
3
3
3
1.2, J = 7.8, J = 7.8 Hz, 1 H, C(6)-H], 7.50 [d, J = 7.2 Hz, 1 H,
C(4)-H], 7.54 [d, J = 7.5 Hz, 1 H, C(7)-H] ppm. 13C{1H} NMR
3
(75 MHz, [D6]benzene, 25 °C): δ = 23.5 [1 C, C(1)-C(CH3)3], 29.0
[3 C, C(1)-C(CH3)3], 30.0 [3 C, C(3)-C(CH3)3], 32.6 [1 C, C(3)-
C(CH3)3], 59.2 (1 C, C-1), 122.8 (1 C, C-4), 124.4 (1 C, C-7), 125.7
(1 C, C-6), 126.6 (1 C, C-5), 130.4 (1 C, C-2), 145.1 (1 C, C-7a),
148.4 (1 C, C-3a), 153.4 (1 C, C-3) ppm. GC/MS (70 eV): m/z (%)
= 228 (41) [M+], 172 (43) [M+ Ϫ C4H8], 157 (59) [C12H13+], 141 (31)
[C11H9+], 128 (11) [C10H8+], 116 (37) [C9H8+], 57 (100) [C4H9+].
3-tert-Butylindene (7): Following a literature procedure,[6] the pro-
duct was obtained from reacting 6 (1.51 g, 9.7 mmol) with meth-
yllithium (6.9 mL, 9.7 mmol) at 0 °C in diethyl ether (30 mL).
Acidic work-up afforded a colorless liquid (740 mg, 4.3 mmol,
44%). As an alternative, the reaction may be run in pentane in the
presence of 10 wt.-% freshly resublimated AlCl3 at room tempera-
ture. Addition of methyllithium via syringe provided a white pre-
cipitate in quantitative yield within one hour. 1H NMR (300 MHz,
1-Methyl-2-(trimethylsilyl)indenyllithium (10): The deprotonation
was carried out in a similar fashion to 2b. The lithium salt could
be isolated as a white powder in quantitative yield.
1,3-Dimethyl-2-(dimethylsilyl)indenyllithium (11a): The deproton-
ation of the ligand precursors followed a literature procedure.[12]
The indene derivative (1.0 equiv.) and n-butyllithium (1.0 equiv.)
were placed in a Schlenk flask charged with pentane (30 mL). Stir-
ring at room temperature overnight provided little precipitate. Ad-
dition of 1 mL diethyl ether lead to the formation of appreciable
amounts of precipitate, but filtration via cannula turned out to be
difficult due to the formation of a viscous gel. Washing with pen-
tane (2×30 mL) and subsequent solvent removal under high-vac-
uum yielded a light yellow powder (1.07 g, 5.1 mmol, 64%).
C13H17LiSi (208.30): calcd. C 74.96, H 8.23; found C 74.40, H 8.16.
3
[D6]benzene, 25 °C): δ = 1.33 (s, 9 H, tBu), 3.02 [d, J = 2.1 Hz, 2
3
4
H, C(1)-H], 5.99 [t, J = 2.1 Hz, 1 H, C(2)-H], 7.12 [ddd, J = 1.8,
3J = 7.2, 3J = 7.2 Hz, 1 H, C(5)-H], 7.23 [dd, 3J = 7.8, 3J = 7.8 Hz,
1 H, C(6)-H], 7.32 [d, 3J = 7.5 Hz, 1 H, C(4)-H], 7.59 [d, 3J =
7.8 Hz, 1 H, C(7)-H] ppm. 13C{1H} NMR (75 MHz, [D6]benzene,
25 °C): δ = 29.9 (3 C, tBu), 33.6 (1 C, tBu), 37.7 (1 C, C-1), 122.8
(1 C, C-2), 124.67 (1 C, C-4), 124.72 (1 C, C-7), 126.35 (1 C, C-6),
126.40 (1 C, C-5), 144.6 (1 C, C-7a), 146.4 (1 C, C-7a), 154.0 (1 C,
C-3) ppm. GC/MS (70 eV): m/z (%) = 172 (78) [M+], 157 (77) [M+
Ϫ CH3], 142 (78) [M+ Ϫ C2H6], 128 (29) [C10H8+], 116 (82)
[C9H8+], 57 (100) [C4H9+].
3
1H NMR (300 MHz, [D8]THF, 25 °C): δ = 0.51 [d, J = 3.9 Hz, 6
3
H, SiH(CH3)2], 2.65 [s, 6 H, C(1,3)-Me], 4.94 [hept, J = 3.9 Hz, 1
H, SiH(CH3)2], 6.58 [mAAЈXXЈ, 2 H, C(5,6)-H], 7.38 [mAAЈXXЈ, 2 H,
3-tert-Butyl-1-(isopropylidene)indene (8). A Schlenk flask equipped
with a condenser was charged with 7 (1.54 g, 8.7 mmol), acetone
(1.5 mL, 20.5 mmol), pyrrolidine (1.7 mL, 20.5 mmol), and meth-
anol (30 mL) under air. Reflux of the reaction mixture for three
days and removal of all volatiles in vacuo provided a red-brown oil.
vacuum distillation provided a yellow liquid boiling at 80 °C0.05Torr
which would solidify at room temperature (1.05 g, 5.0 mmol, 58%).
1H NMR (300 MHz, [D6]benzene, 25 °C): δ = 1.39 (s, 9 H, tBu-H),
C(4,7)-H] ppm.
1,3-Dimethyl-2-(trimethylsilyl)indenyllithium (11b): The deproton-
ation was carried out in a similar fashion to 2b, but started at
–90 °C. Using an isomer mixture of 3b (2.21 g, 10.2 mmol, 78%
purity) and n-butyllithium (12.2 mL, 30.6 mmol) in pentane
(30 mL) provided a light green powder (1.58 g, 7.1 mmol, 89%) af-
ter filtration through a D4-frit, washing with pentane (2×10 mL)
1.92 [s, 3 H, C(1Ј)-CH3], 2.04 [s, 3 H, C(3Ј)-CH3], 6.60 [s, 1 H, and solvent removal under high vacuum.
Eur. J. Inorg. Chem. 2005, 1759–1769
www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1767

A. C. Möller, R. Blom, R. H. Heyn, O. Swang, C.-H. Görbitz, T. Seraidaris
FULL PAPER
rac/meso-Bis[1-methyl-2-(trimethylsilyl)indenyl]zirconium(IV
)
Di-
3.7 mmol) and zirconium tetrachloride (429 mg, 1.86 mmol), THF
(40 mL) was added at –40 °C. Stirring overnight afforded a yellow
solution. Solvent change from THF to diethyl ether led to the for-
mation of precipitate. Filtration via cannula and through magne-
sium sulfate on a D4 frit yielded a brown-yellow oil upon solvent
removal. Crystallization occurred after two months of storage in
the drybox, though the crystals were too ductile to be isolated.
No conclusive NMR spectroscopic data could be obtained for this
complex.
chloride (12): To a Schlenk flask equipped with a septum, charged
with 10 (714 mg, 3.4 mmol) and zirconium tetrachloride (396 mg,
1.7 mmol) and cooled to 0 °C, diethyl ether (30 mL) was added
via syringe. Stirring overnight afforded a suspension of a yellow
precipitate. Filtration trough a D4 frit with a layer of magnesium
sulfate (3 cm) and washing with diethyl ether until all yellow resi-
due in the Schlenk flask was dissolved, provided a clear, yellow
solution. Volume reduction to the formation of precipitate was fol-
lowed by crystallization at –40 °C. Subsequent crystallizations
failed to separate the rac and meso isomer, which were obtained in
a 1:1 ratio (528 mg, 941 μmol, 55%). C26H34Cl2Si2Zr (564.86):
calcd. C 55.29, H 6.07; found C 55.55, H 6.15. rac Isomer: 1H
NMR (300 MHz, [D6]benzene, 25 °C): δ = 0.32 [s, 18 H, Si-
(CH3)3], 2.29 [s, 6 H, C(1)-CH3], 5.62 [s, 2 H, C(3)-H], 6.84–6.94
[m, 4 H, C(5,6)-H], 7.48–7.56 [m, 2 H, C(4,7)-H] ppm. meso Isomer:
1H NMR (300 MHz, [D6]benzene, 25 °C): δ = 0.14 [s, 18 H,
Si(CH3)3], 2.52 [s, 6 H, C(1)-CH3], 5.07 [s, 2 H, C(3)-H], 6.94–7.00
[m, 4 H, C(5,6)-H], 7.10–7.15 [m, 2 H, C(4)-H], 7.25–7.30 [m, 2 H,
C(7)-H] ppm. rac and meso Isomer: 13C{1H} NMR (75 MHz, [D6]
benzene, 25 °C): δ = 0.7 [6 C, Si(CH3)3], 1.1 [6 C, Si(CH3)3], 14.1
[2 C, C(1)-CH3], 14.4 [2 C, C(1)-CH3], 106.8 (2 C, C-3), 109.8 (2
C, C-3), 124.7, 124.8, 125.0, 125.1, 125.2, 125.4, 125.6, 125.9, 126.3,
126.6, 127.6, 128.5, 132.3, 133.0, 135.3, 138.8 ppm.
Crystal Structure Determination: A yellow platelet with dimensions
0.85×0.33×0.10 mm was mounted on a glass fiber. Pertinent data
for the crystal and solution are collected in Table 5. Reflections
were measured with a Siemens SMART 1000 CCD-diffractometer
using Mo-Kα radiation. The data collections with SMART[13a] in-
cluded three sets of exposures with the detector set at 2θ = 26
and crystal-to-detector distance 50 mm. Data integration and cell
refinement was carried out by SAINT,[13b] while absorption correc-
tion was carried out by SADABS.[13c] SHELXTL[13d] was used for
structure solution by direct methods as well as for subsequent full-
matrix least-squares refinement on F2. All atoms except protons
were refined anisotropically.
CCDC-253467 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Attempted Synthesis of Bis[1,3-dimethyl-2-(dimethylsilyl)indenyl]zir-
conium(IV) Dichloride (13a): In a Schlenk flask, 11a (185 mg,
889 μmol) and zirconium tetrachloride (104 mg, 446 μmol) were re-
acted in diethyl ether (30 mL) at 0 °C. The initially brown-yellow
suspension turned green-yellow while stirring overnight. A clear
yellow solution was obtained by filtration through a layer of mag-
nesium sulfate on a D4 frit and washing of the reaction residue
with diethyl ether. Volume reduction to 10 mL and refrigeration
to –40 °C provided traces of precipitate. The obtained NMR spec-
troscopic data suggests the formation of the desired product, but
reliable analysis including elemental analysis was precluded by the
small amount of precipitate obtained. 1H NMR (300 MHz,
[D6]benzene, 25 °C): δ = 0.24 [d, 3J = 3.9 Hz, 12 H, SiH(CH3)2],
2.15 [s, 12 H, C(1,3)-CH3], 4.76 [hept, 3J = 4.2 Hz, 2 H, SiH-
(CH3)2], 6.80–7.00 [m, 4 H, C(5,6)-H], 7.15–25 [m, 4 H, C(4,7)-H]
ppm.
Table 5. Crystallographic data, collection and refinement parame-
ters for 13b.
Parameter
13b
Formula
Mass
System
Space group
a [Å]
C28H38Cl2Si2Zr
592.88
orthorhombic
Fdd2
18.2879(8)
38.1327(17)
8.0947(4)
5645.0(4)
8
b [Å]
c [Å]
V [Å3]
Z
Radiation
λ [Å]
T [°C]
Mo-Kα
0.71073
–168
Dcalcd. [g/mL]
μ (mm–1)
R(F0)
1.395
Bis[1,3-dimethyl-2-(trimethylsilyl)indenyl]zirconium(IV
)
Dichloride
0.679
(13b): A Schlenk flask with 11b (1.00 g, 3.4 mmol) and zirconium
tetrachloride (0.52 g, 1.69 mmol) was cooled to 0 °C before diethyl
ether (30 mL) was added dropwise. The suspension turned dark
yellow and formed a yellow precipitate while stirring overnight.
Filtration with a cannula and a D4-frit loaded with magnesium
sulfate (3 cm) afforded a dark yellow solution. Extraction of the
reaction residue and filter cake with diethyl ether and toluene, fol-
lowed by recrystallization from the respective solvent afforded four
crops of a yellow or orange solid (393 mg, 665 μmol, 44%). Single
crystals of X-ray quality were grown from a cold saturated diethyl
ether solution at –40 °C. C28H38Cl2Si2Zr (592.91): calcd. C 56.72,
1.91[a]
2
Rw(FO
)
4.75[b]
GOF
1.050
[a] Calculated on 5395 reflecions with I Ͼ 2σ(I). [b] Calculated on
all 5687 reflections.
General Polymerization Procedure: Polymerizations were carried
out in 100-mL glass reactors equipped with a cooling/heating man-
tle, an argon/vacuum connection, magnetic stirrer and a septum.
Prior to use, the reactors were evacuated at 90 °C for two hours
and flushed three times with argon. At 30 °C, the reactors were
charged with 50 mL aliquots of freshly distilled toluene, the appro-
priate amount of solid MAO and subsequently pressurized to a
preset pressure of ethene until no further ethene consumption
could be registered by the massflow controllers. Polymerization was
initiated by injection of the appropriate volume of a toluene solu-
tion of the catalyst precursor. Typically, the catalyst precursor solu-
tions had concentrations of 1.0·10–3 mol/L. The reaction was
stopped by addition of methanol (5 mL). Work-up of the polymers
included extraction of the toluene suspension with methanol/hydro-
chloric acid (9:1) to remove inorganic residues. Products were fil-
1
H 6.46; found C 56.75, H 6.48. H NMR (300 MHz, [D6]benzene,
25 °C): δ = 0.31 [s, 18 H, Si(CH3)3], 2.13 [s, 12 H, C(1,3)-CH3], 6.86
[mAAЈXXЈ, JA = 6.5, JX = 0.8, J = 8.7, JЈ = 1.0 Hz, 4 H, C(5,6)-H],
7.15–7.19 [m, 4 H, C(4,7)-H] ppm. 13C{1H} NMR (75 MHz,
[D6]benzene, 25 °C): δ = 2.0 [6 C, Si(CH3)3], 13.8 (4 C, 1,3-CH3),
121.0 (4 C, C-1,3), 124.0 (4 C, C-4,7), 124.8 (4 C, C-5,6), 127.7 (4
C, C-3a,7a), 139.9 (2 C, C-2) ppm.
Attempted Synthesis of rac/meso-Bis[1-isopropyl-2-(trimethylsilyl)in-
denyl]zirconium(IV) Dichloride (14): To a Schlenk flask charged
with 1-isopropyl-2-(trimethylsilyl)indenylpotassium (5) (1.00 g,
1768
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2005, 1759–1769

Sterically Crowded 1,2,3-Substituted Bis(indenyl)zirconium(iv) Dichlorides
FULL PAPER
[9] P. Scott, U. Rief, J. Diebold, H. H. Brintzinger, Organometallics
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[10] H. Sitzmann, P. Zhou, G. Wolmershauser, Chem. Ber. 1994,
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tered, washed with methanol and dried under high vacuum for two
days.
Computational Details: Hybrid DFT calculations were performed
with the Gaussian98 package.[14] The B3LYP functional with the
6-31G* basis set was employed for our purposes and proved to be
suitable.[15] For Zr, a modified version of the LANL2DZ ECP basis
was used.[16] In the original basis set, the 4d shell is described by
two contracted functions consisting of three and one primitive
Gaussians denoted (31), respectively. To increase flexibility in the
d shell we decontracted the set to three functions, consisting of 2,
1, and 1 primitive functions, respectively. For integration, ultrafine
grid was employed. All other settings remained default. Due to the
high demand for computation time of transition state searches,
these were conducted with the Gaussian03 package using the den-
sity fitting approximation with auxiliary basis sets as implemented
with a pure BP86 functional and a 6-31G* basis set.[17] All calcula-
tions were conducted with ultrafine integration grid, while all other
parameters remained default.
[11] J. C. Randall, JMS Rev. Macromol. Chem. Phys. 1989, C29(2 &
3), 201–317.
[12] J. S. Merola, R. T. Kacmarcik, Organometallics 1989, 8, 778–
784.
[13] a) Bruker AXS (1998). SAINT. Version 6.01 Integration Soft-
ware; b) Bruker AXS (1998). SMART. Version 5.054 Area-De-
tector Control. Bruker Analytical X-ray Instruments Inc.,
Madison, Wisconsin, USA; c) Bruker AXS (2000). SHELXTL
Version 6.10 Bruker Analytical X-ray Systems, Madison, Wis-
consin, USA; d) G. M. Sheldrick (1996), SADABS, Program
for Adsorption Correction, University of Göttingen, Germany.
[14] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
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Millam, A. D. Daniels, K. N. Kudin, M. C. Strain, O. Farkas,
J. Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C.
Pomelli, C. Adamo, S. Clifford, J. Ochterski, G. A. Petersson,
P. Y. Ayala, Q. Cui, K. Morokuma, P. Salvador, J. J. Dannen-
berg, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B.
Foresman, J. Cioslowski, J. V. Ortiz, A. G. Baboul, B. B. Ste-
fanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gom-
perts, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y.
Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B.
Johnson, W. Chen, M. W. Wong, J. L. Andres, C. Gonzalez, M.
Head-Gordon, E. S. Replogle, J. A. Pople, Gaussian 98, Re-
vision A.11, Gaussian, Inc., Pittsburgh PA, 2001.
Acknowledgments
We would like to thank Aud M. Bouzga for assistance with the
multi-nuclear NMR experiments. This research was generously
supported by the Research Council of Norway through a Dr.-Ing.
scholarship (to A. C. M., grant no. 145544/431). Heidi N. Brynte-
sen’s (Borealis Stathelle) generous effort of conducting GPC mea-
surements is very much appreciated.
[15] a) A. D. Becke, J. Chem. Phys. 1993, 98, 5648–5652; b) C. Lee,
W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785–789.
[16] P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 270–283.
[17] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T.
Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar,
J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P.
Hratchian, J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts,
R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pom-
elli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P.
Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich,
A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D.
Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui,
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Received: November 22, 2004
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