5-Methoxy-substituted zirconium bis-indenyl ansa -complexes: Synthesis, structure, and catalytic activity in the polymerization and copolymerization of alkenes

Article abstract of DOI:10.1021/om300160v

A number of 2-methyl-4-aryl-5-methoxy-6-alkylindenes and C ₂-symmetric Me₂Si-bridged ansa-zirconocenes based on them were synthesized. Zirconocenes were obtained by means of highly effective and scalable racemo-selective synthetic ap

Full text of DOI:10.1021/om300160v

Article
pubs.acs.org/Organometallics
5-Methoxy-Substituted Zirconium Bis-indenyl ansa-Complexes:
Synthesis, Structure, and Catalytic Activity in the Polymerization and
Copolymerization of Alkenes
Ilya E. Nifant’ev,*,†,‡ Pavel V. Ivchenko,† Vladimir V. Bagrov,† Andrei V. Churakov,§
and Pierluigi Mercandelli⊥
†Chemistry Department, M.V. Lomonosov Moscow State University, Moscow, Russia 119991
‡A.V. Topchiev Institute of Petrochemical Synthesis RAS, 29 Leninsky Prospect, Moscow, Russia 119991
§N.S. Kurnakov Institute of General and Inorganic Chemistry RAS, 31 Leninsky Prospect, Moscow, Russia 119991
⊥Dipartimento di Chimica Strutturale e Stereochimica Inorganica, Universita
I-20133 Milano, Italy
̀
degli Studi di Milano, Via Giacomo Venezian 21,
S
* Supporting Information
ABSTRACT: A number of 2-methyl-4-aryl-5-methoxy-6-
alkylindenes and C2-symmetric Me2Si-bridged ansa-zircono-
cenes based on them were synthesized. Zirconocenes were
obtained by means of highly effective and scalable racemo-
selective synthetic approach based on the use of a Zr tert-butyl
amide complex. The structure of μ-(bis-[η5-6-tert-butyl-5-
methoxy-2-methyl-4-tert-butylphenyl-1H-inden-1-yl]-
dimethylsilanediyl)dichlorozirconium(IV) (14) has been
established with X-ray analysis. The introduction of a methoxy
group into the indenyl fragment of zirconocene significantly
improved its catalytic performance (i.e., its activity, stereo-
selectivity, molecular mass potential, and thermal stability) in the polymerization and copolymerization of propylene in
comparison with the benchmark Spaleck-zirconocene. The role of the methoxy group is proposed to stabilize the cationic
catalytic intermediates, which was confirmed using DFT calculations.
number of publications have focused on quantum chemical
modeling of the formation and polymerization of alkylzircono-
cene cations, and these studies confirmed the desirability of
introducing electron-donating fragments for the design of
efficient polymerization catalysts.4
INTRODUCTION
■
Bis-indenyl ansa-zirconocenes are considered to be a promising
class of catalysts of the homo- and copolymerization of alkenes.
The large amount of experimental data accumulated during 25
years of research on isotactic polymerization of propylene with
metallocene catalysts has allowed for a number of general-
izations to be drawn that relate the structure of these
compounds to their catalytic properties. The most successful
ligand substitution pattern, which has led to higher activities,
higher molecular weights, and greater stereoselectivity, is based
on silicon-bridged 2-methyl-4-arylindenyl ligands and C2-
symmetry and has been developed by the Hoechst team.1 In
addition to structural factors, which determine the catalytic site
geometry (i.e., the length of the bridge and the presence of
alkyl substituents in position 2 and aryl substituents in position
4 of the indenyl fragment), the activity of the complex and the
properties of the resulting polymer are also affected by
electronic properties of η5-coordinated ligands.
Progress was made through the use of alkyl,2c,5 trialkylsilyl,6
and trialkylsiloxy groups in positions 27a−e or 4−67f and
through the use of dialkylsilanedioxy groups7f for indenyl
complexes. A series of indenyl8 and fluorenyl9 complexes with
dialkylamino substituents were also obtained. However, both
the activities of the catalysts and the molecular weight
characteristics of the synthesized polymers did not allow us
to consider these compounds even as prototypes of efficient
industrial catalysts. Meanwhile, a high activity was observed for
heteroanalogues of the indenyl complexes, the so-called
“heterocenes” that contain a η5-coordinated fragment fused to
an electron-excessive heterocycle (e.g., pyrrole or thiophene).10
The only commonly known commercialized group 4 metal-
locenes that contain electron-donating groups are the
perfluoroborate-activated constrained geometry Dow com-
The beneficial action of electron-donating η5-coordinated
ligands on the catalytic activity of zirconocenes has been
noted.2,3 The relationship between the presence of electron-
donating substituents and the ease of side reactions, particularly
polymer chain-transfer reactions, has also been discussed.3 A
Received: February 27, 2012
Published: July 12, 2012
© 2012 American Chemical Society
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Scheme 1
Scheme 2. General (a) and Practically Implemented (b) Approaches to Substituted Indenes 5
plexes that contain tertiary amine substituents in the indenyl
fragments.11
of MAO (Al/Zr ≈ 300); an increase in the Al/Zr ratio reduced
the activity.
The alkoxy group has also attracted researchers’ attention. In
the early 1990s, Piccolrovazzi12 (for sandwich complexes 1,
Scheme 1) and Collins and co-workers3 (for ansa-complex 2,
Scheme 1) mentioned the possibility of both positive
consequences (i.e., increasing concentration of catalytically
active species; enhancing the catalyst activity toward propylene
compared to ethylene) and negative consequences (i.e.,
weakening of the α-agostic interactions in the transition state,
thereby resulting in a decrease in stereoselectivity; facilitating
the chain transfer to aluminum) of the introduction of electron-
donating substituents into a zirconocene molecule. The first
polymerization experiments demonstrated that the introduction
of methoxy groups into the zirconocene molecule upon MAO
dichloride preactivation resulted in an almost complete loss of
catalytic activity; however, when the activation was performed
in the presence of the monomer and with low Al/Zr ratios, the
methoxy-substituted complexes exhibited moderate catalytic
activity.3 Complexes 3 with the −OCH2CH2O− group
(Scheme 1) synthesized in 2002 by Rieger and co-workers13
also showed moderate activity in the presence of small amounts
These results have been explained as being a consequence of
the reaction of alkoxy groups with MAO or other activating
agents, which results in inversion of the electronic effect of the
alkoxy group (π-donating → σ-withdrawing). A possible
interaction with MAO can be aggravated by ability of the
methoxy groups in complex 2 to form chelates to species such
as [Me2Al]+; similar processes have been detected in the
presence of chelating polyether ligands.14
We sought starting compounds within the class of 2-methyl-
4-arylindenyl ligands that would simplify their synthesis. One
class of candidates was the 2-alkyl anisoles. We hypothesized
that the alkoxy group could still be used as a structural fragment
of an effective zirconocene polymerization catalyst because its
interaction with the Lewis-acidic cocatalyst (methylaluminox-
ane or trimethylaluminum) could be hampered by the
placement of bulky groups adjacent to the alkoxy group.
An aryl group in position 4 of the indenyl ring may serve this
purpose. The alkoxy group must then be located in position 5,
whereas the remaining free neighboring positions should bear a
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Scheme 3
Scheme 4
bulky substituent. These considerations lead to general formula
4 (Scheme 1) of the target zirconocene.
reaction mixture; as a consequence, the yields of 8a and 8b did
not exceed 25%. Finally, performing the reaction with
methacrylic acid in Eaton’s reagent (P4O10 in MeSO3H)
allowed increasing the yields of the desired products to 40−
50% and substantially simplified the isolation procedure
compared to that of the products prepared using PPA and
especially SnCl4 (Scheme 2b).
RESULTS AND DISCUSSION
■
Preparation of Methoxy-Substituted Indanones and
Indenes. The synthesis of target compounds of type 4
assumed the development of a general synthetic approach to
methoxy-substituted indenes 5 and their precursors, the
corresponding indanones 6 (Scheme 2a). The sequence of
reactions we proposed also includes the arylation of
compounds 7, which can be obtained from previously
unpublished 6-alkyl-5-methoxyindanones 8 (Scheme 2a).
We supposed that the reaction of 2-alkylanisoles 9 with
methacrylic acid or methacryloyl chloride in various conditions
is the most convenient and fastest way to 8. Previously,
reactions of ring-unsubstituted ArOR with unsaturated acids in
The bromination of 8a and 8b by the method of Karlsson16
(in a two-phase system in the presence of aqueous AcONa) led
to 4-bromoindan-1-ones 7a and 7b in satisfactory yields. At this
stage, we separated bromoindanone 7b from small amount of
isomeric byproduct by recrystallization. The obtained bro-
moindanones were introduced into the Suzuki reaction with
phenylboronic or tert-butylphenylboronic acid. The resulting 4-
arylindanones 6 were reduced with LiAlH4 to form alcohols,
which were then dehydrated to indenes 5a−c (Scheme 2b).
Ligand and Zirconocene Synthesis. Lithium derivatives
of 5 were reacted with SiMe2Cl2 in ether in the presence of
catalytic amounts of CuCN. Bis-indenyl derivatives 10−12 with
a dimethylsilylene bridge were formed as isomer mixtures
(Scheme 3). The purity of the products (at least 90%) was
sufficient because they were used in the synthesis of ansa-
zirconocenes without purification.
PPA15 or with acid chlorides in the presence of AlCl3 were
13
used to prepare alkoxyindanones. When performing the
reactions of 2-tert-butylanisole 9a and 2-methylanisole 9b
with methacryloyl chloride in the presence of AlCl3, we found
that partial demethylation of the ester groups occurred during
the reaction in both cases, and, more importantly, almost
complete elimination of the tert-butyl substituent occurred in
the case of 9a. The replacement of AlCl3 by a softer Lewis acid,
SnCl4, permitted us to synthesize the target indanones 8a and
8b, in moderate yields (∼30%). Compound 8a was pure,
whereas indanone 8b contained an insignificant (<10% by
NMR) impurity of the isomer. The reaction with methacrylic
acid in PPA was accompanied by substantial tarring of the
Experimental difficulties were encountered during the
synthesis of the ansa-zirconocenes. For example, the reaction
of dilithium derivatives of 10−12 with ZrCl4(THF)2 in ether or
THF was accompanied by the formation of substantial amounts
of polymeric byproduct, which hampered isolation of the target
zirconocenes and the resolution of the diastereomers. Perform-
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ing the reaction between the dilithium derivatives of 10−12
and ZrCl4 in an inert nonpolar solvent (pentane) proved to be
more convenient.10a,17 This reaction resulted in the synthesis of
ansa-complexes 13−15 as mixtures of the rac- and meso-forms
(∼1:1 ratio) (Scheme 3). The racemic products were isolated
by recrystallization (in the case of 15, fractional crystallization
was used because of the lower solubility of the meso-form).
As far as the conventional approach to our target
zirconocenes gave us modest yields and required fractional
recrystallyzation, we applied an alternative procedure to prepare
these metallocenes. Recently we elaborated18 a new direct
racemo-selective approach to rac-ansa-zirconocenes, based on
the reaction of dilithium derivatives of bridged ligands with the
zirconium tert-buthylamide ZrCl3(THF)2NH-tert-Bu. We em-
ployed this approach to prepare complexes 13 and 14. We
found that dilithium derivatives of 10 and 11 react with
ZrCl3(THF)2NH-tert-Bu smoothly, and resulting amides 16
and 17 were formed with high rac-selectivity (only one isomer
by NMR monitoring). Subsequent treatment of the reaction
mixture with TMSCl allowed us to isolate zirconocenes 13 and
14 in yields of 55% and 61%, respectively, starting from indenes
5.
The synthetic procedure used is suitable for regenerating
indenes 5a and 5b to further increase the effective yield of the
zirconocenes. For this purpose, all remainders of the synthesis
of the complexes were combined, and after the solvents were
removed, they were hydrolyzed in an aqueous-ethanol alkaline
mixture for 16 h at ambient temperature. After the addition of
water, extraction with a diethyl ether−hexane mixture, and
vacuum distillation of the residue, 21 and 22 were isolated in
37% and 30% yields, respectively, based on starting amounts of
indenes 5. Thus, for the method based on Zr amide, the
irrecoverable loss of the ligand is less than 10%.
Molecular Structure of 14. The molecular structure of
racemic complex 14 is shown in Figure 1, and selected bond
lengths and angles are listed in Table 1. The coordination
environment of the Zr atom may be treated as a distorted
tetrahedron (assuming that η5-C5 rings occupy one coordina-
tion site). The Zr−C distances vary within a wide range of
2.446(5) to 2.641(5) Å. The high end of this range is typical for
indenyl zirconium complexes19 and reflects the tendency of Zr
atoms to form η3,η2 linkages with indenyl ligands. As expected,
the Zr−C(1) bond is the shortest because the C(1) and C(1A)
carbon atoms are linked by a small-scale −SiMe2− spacer. The
indenyl ligand is planar within 0.066(4) Å. The main geometric
parameters of molecule 14 are similar to the respective average
values for the closely related bis(indenyl)zirconocene di-
chlorides provided by the Cambridge Structural Database.20
Polymerization Results. The catalytic properties of
complex 13 were assessed for propylene homopolymerization
and ethylene−propylene copolymerization in solution at
relatively high temperatures (100 and 120 °C). Complex 181a
and its tert-butyl analogue 19,21a which was synthesized
previously, were used as reference compounds (Figure 2).
Propylene polymerization was performed in cyclohexane
Figure 1. Molecular structure of 14. Displacement ellipsoids are
shown at the 50% probability level. Minor components of the
disordered tert-butyl groups are shown as dashed lines. Hydrogen
atoms are omitted for clarity.
Table 1. Selected Bond Lengths and Angles in 14
bond
bond length, Å
bond
bond angle, deg
b
Zr(1)−Cl(1)
Zr(1)−C(1)
Zr(1)−C(2)
Zr(1)−C(9)
Zr(1)−C(3)
Zr(1)−C(4)
2.4258(13)
2.446(5)
2.496(5)
2.544(5)
2.578(5)
2.641(5)
2.233
Cp−Zr(1)−Cp(A)
130.0
Cl(1)−Zr(1)−Cl(1A)
C(1)−Si(1)−C(26)
C(1)−Si(1)−C(26A)
C(1)−Si(1)−C(1A)
100.15(8)
114.3(3)
113.1(3)
95.6(3)
a
Zr(1)−Cp
Si(1)−C(26)
Si(1)−C(1)
1.852(6)
1.878(5)
a
b
Cp denotes the center of the η5-C5 ring. Symmetry operation: −x+2,
y, −z+1/2.
istics of the obtained polypropylene. The reference complex
(compound 18) exhibits fairly high activity at relatively high
temperatures; however, even at 100 °C, the molecular weight of
the polymer thus formed is at the boundary of the values that
are of commercial interest. An increase in temperature results in
an insignificant decrease in the activity accompanied by a
dramatic decrease in the Mw. When we began the synthesis of
complex 13, we hoped that the catalytic properties would be
somewhat enhanced; however, a more than 20-fold increase in
the activity and a 3-fold increase in the polymer molecular
weight, as observed in the experiment conducted at 100 °C,
were unexpected. At 120 °C, the activity of 13 also decreased
sharply, and the Mw of the polymer decreased more than 2-fold
but still remained within the acceptable range (Figure 2).
The increased molecular weight capability of 13 compared to
that of 18 is the most important feature of this new
metallocene. The results of the microstructural studies of the
obtained polymer structure are also noteworthy. Both metal-
locenes exhibit a clear-cut site stereocontrol typical of sterically
crowded bis-indenyl complexes. However, in the case of iPP
under 35
3 bar-g pressure. The catalyst was prepared
separately by the reaction of complex 13 or 18 with a solution
that contained MAO and triisobutylaluminum (TIBA) in a 2:1
(Al) molar ratio and with an overall Al/Zr ratio of 600.21b
Experimental details are presented in the Supporting
Information. Polymerization was performed for 30 min. Table
2 outlines the reaction conditions, the calculated catalyst
activity reduced to a standard dimension, and some character-
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polymer. Moreover, because of the decrease in the charge on Zr
in the alkylzirconocene cation formed from 13, the
coordination energy of the alkene molecule also decreases,
which leads to an increase in the stereoselectivity of the
monomer coordination and finally to the absence of mrrm
stereoerrors in the produced polypropylene.
Ethylene and propylene copolymerization experiments were
performed in cyclohexane under ∼30 bar-g pressure. The
catalyst was prepared using a MAO/TIBA mixture (2:1 molar
ratio) with an overall Al/Zr ratio of 800:1. In the reference
experiment, complex 19 was used, which is more active in
copolymerization than 18, along with an ethylene/propylene
mixture in a 70/30 ratio. Table 3 summarizes the reaction
Table 3. Results of Homogeneous Copolymerization of
Ethylene and Propylene (MAO, Ethylene and Propylene,
Cyclohexane, 100 °C, 30 atm)
a
ethylene/
propylene %
w/w
ethylene
content,
wt %
IV
activity,
kg/mmol h
(dL/
g)
no.
Tpol P, bar-g
19
100
100
100
33
31
36
70/30
70/30
17/83
30.5
236.3
219.5
67.2
66.4
11.3
1.88
2.46
2.78
13b
13c
a
Intrinsic viscosity.
conditions, the activity of the catalysts, and some characteristics
of the obtained copolymer. As evident from the results in the
table, complex 13 is almost an order of magnitude more active
than 19 at 100 °C, and the molecular weight (measured by
intrinsic viscosity) of the polymer formed with 13 is
significantly higher and lies in the region that is acceptable
for commercial production (Figure 2).
Influence of Ligand Substituents on Polymerization
Activity. The catalytic performance of formally 16-electron
complexes of general formula Me2Si(Cp′)2ZrMe2, where Cp′ is
a generically substituted cyclopentadienyl ligand, is strictly
related to the extent of the interactions between the cation and
the anion in the activated species. The cation is assumed to be
the 14-electron cation [Me2Si(Cp′)2ZrMe]+ generated from
the precatalyst by σ-ligand abstraction. Intuitively, if the Cp′
ligand is a good electron donor, it will stabilize the cation and
reduce the cation−anion electrostatic interactions by reducing
the positive charge on the metal. Steric factors also play a role
because they affect the accessibility of the metal center for the
reacting monomers.
To better understand the activity of the polymerization
catalysts considered in this work, we performed a computa-
tional study that compared the prototypical catalyst 18, which
contains the 2-methyl-4-phenylindenyl moiety, to complex 13,
which contains two additional substituents on the indenyl
moiety: a methoxy group in position 5 and a tert-butyl group in
position 6. Moreover, to understand the effect of the
substitution, we considered two additional species in which
only one of the two groups has been added (i.e., the 2-methyl-
Figure 2. Comparative catalytic activity of 13 in homogeneous
propylene polymerization and ethylene−propylene copolymerization.
produced with 15, the polymer did not contain any measurable
mrrm sequences, which indicates an extremely high enantioface
selectivity for primary insertion. However, the regioselectivity
of 13 is significantly lower than that of 18, as indicated by the
greater amount of the 2,1 and 3,1 insertion observed for 13;
this decreased regioselectivity results in a lower polypropylene
melting point.
The results of the polymer tests can be interpreted as
follows: the presence of an electron-donating fragment in the
indenyl ligand stabilizes the alkylzirconocene cation (which
increases the concentration of the catalytically active species)
and decreases the effective charge on the Zr atom. Most likely,
the latter factor decreases the probability of chain termination
through β-elimination (hydride transfer to Zr) via an agostic
transition state, which together entails a parallel increase in
both the activity and the molecular weight of the synthesized
Table 2. Results of Homogeneous Polymerization of Propylene (MAO, Propylene−Cyclohexane)
no.
Tpol, °C
P, bar-g
activity, kg/mmol h
mp
mmmm
mrrm
2,1
3,1
Mw, × 103
Mw/Mn
18
18
13
13
100
120
100
120
31.5
37
8.6
6.4
154.6
148.4
150.6
147.8
96.6
95.2
96.2
93.8
0.30
0.36
0
0.3
0.3
0.6
0.6
0.1
0.3
0.1
0.5
246
92
2.3
2.5
2.7
2.5
32
194
717
298
36
24.5
0
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Scheme 5
4-phenyl-5-methoxyindenyl derivative 20 and the 2-methyl-4-
phenyl-6-tert-butylindenyl derivative 21; Scheme 5).
is tucked into the ligand envelope.24 As previously observed,25
these parameters are highly sensitive to differences in the
number and type of ansa atoms, whereas the presence of
substituents on the ligand leads to only minor changes in the
local geometry around the metal atom. The values computed
for the four species are indeed similar. However, because of the
presence of bulky substituents that should reduce the
coordination gap aperture,26 the Zr atom accessibility for the
cation derived from complex 13 should be lower than that in
species 18. Because 13 outperforms 18 as a catalyst, electronic
effects must be the main factor at work.
The geometries of the precatalysts and the corresponding
cations were optimized at the B3LYP level of theory; the
Stuttgart−Dresden effective core potentials with the triple-ζ
basis set for Zr, and the 6-31G basis set for all the other atoms
were employed. Single-point energies were computed using the
same basis set for Zr, augmented with a set of f functions (α =
0.559522), and the 6-31G(d,p) basis set for all other atoms. All
the computations were performed with the Gaussian 09
software package.23 Table 4 presents some relevant geometric
Various physical, chemical, and computed quantities have
been proposed as a measure of the electron-donating capability
of the Cp′ ligand in attempts to quantify the substituent
electronic effect on the metal center.27 In this case, we used the
direct computation of the energy for the model reaction of
methyl removal from the precatalyst. The values reported in
Table 4 show that the introduction of either a methoxy group
at position 5 or a tert-butyl group at position 6 of the indenyl
moiety contributes, to a similar extent, to the stabilization of a
positive charge on the metal. Indeed, with respect to 18, the
formation of the cation is favored by 11 and 12 kJ/mol for the
substitution with OMe and with t-Bu, respectively. The
stabilization found for 13 with respect to 18 (17 kJ/mol)
shows that the effect of the substitution is not exactly additive,
probably as a consequence of the geometric distortions of the
indenyl moiety induced by steric interactions between the
substituents. These distortions lead to a partial lowering of the
donor capability of the ligand. Interestingly, the stabilization of
the cation can be attributed to the extended delocalization of
the HOMO of the charged species over the indenyl moiety. In
particular, complexes that contain a methoxy substituent clearly
show the involvement of a p orbital on the oxygen atom in the
π system of the indenyl ligand.
Computations therefore support the explanation of the
beneficial effect of the introduction of a methoxy substituent on
the catalyst activity via a direct stabilization of the cation
through the donation of the lone pair on the oxygen atom.28
We previously29 investigated the catalytic activity of complex
22 (Scheme 5), which contained the tert-butyl substituents in
position 6 of the indenyl moiety, at 100 °C and 30 bar in
propylene homo- and copolymerization reactions in which
MAO was used as an activator. In comparison with the Spaleck-
type complex 18, the tert-butyl-substituted analogue 22
demonstrated a 4-fold increase in the productivity in propylene
polymerization with satisfactory polymer Mw characteristics.
However, in the case of ethylene−propylene (1:10) copoly-
Table 4. Computed Geometric and Energetic Parameters for
Some Me2Si(Cp′)2ZrMe2 Complexes
a
Cp−Zr−
Cp (α)
[deg]
Cp/Cp
(β)
Zr−
Me
b
Zr−Cp
ΔE
Me2Si(Cp′)2ZrMe2
[deg]
[Å]
[Å]
[kJ/mol]
865
2-Me-4-Ph-indenyl
(18)
126.58
127.00
126.88
126.74
62.90
63.27
63.27
62.83
2.351
2.348
2.350
2.349
2.267
2.271
2.270
2.269
2-Me-4-Ph-5-OMe-
indenyl (20)
854
853
848
2-Me-4-Ph-6-t-Bu-
indenyl (21)
2-Me-4-Ph-5-OMe-
6-t-Bu-indenyl
(13)
a
Cp refers to the centroid of the cyclopentadienyl ring, while Cp refers
b
to the least-squares plane of the cyclopentadienyl ring. ΔE is the
energy for the model reaction Me2Si(Cp′)2ZrMe2 → [Me2Si-
(Cp′)2ZrMe]+ + Me−.
parameters computed for the four complexes and the energy
required for the process of methyl-group removal (i.e., the
energy for the model reaction Me2Si(Cp′)2ZrMe2 → [Me2Si-
(Cp′)2ZrMe]+ + Me−). The absolute energy values should be
considered with caution because they were computed without
taking into account the presence of the counterion and solvent.
However, the relative values can be safely used to compare one
complex to another if the systematic errors introduced by the
approximations are assumed to be similar for all of the species.
In these complexes, the metal atom is pseudotetrahedrally
coordinated by the two cyclopentadienyl groups of the bis-
indenyl moiety and by the two methyl ligands. As is typical for
bent metallocenes, the overall coordination environment is best
described by some parameters, as reported in Table 4, that can
be related to the accessibility of the Zr atom. In particular, the
smaller the angle between the least-squares planes of the two
cyclopentadienyl rings (the “bite angle” β) and the greater the
Cp−Zr−Cp angle α, the greater the extent to which the metal
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4-Bromo-6-tert-butyl-5-methoxy-2-methyl-1-indanone (7a).
Bromine (4.4 mL, 86 mmol) was added at 0 °C to a mixture of 8a (20
g, 86 mmol), NaOAc (20.4 g), and tetrabutylammonium bromide (0.5
g) in CH2Cl2 (50 mL) and H2O (150 mL). After 16 h 2.5 mL of Br2
and 12 g of NaOAc were added with stirring. After 6 h, the organic
phase was separated, washed with water, 10% aqueous Na2SO3, and
aqueous NaHCO3, dried over MgSO4, and evaporated. The residue
was used without purification. Anal. Calcd for C15H19BrO2: C, 57.89;
merization, despite the high activity of catalyst 22 compared to
that of 18 and 19, the molecular weight of the obtained
copolymer was lower than the industrial value. These results,
along with the very low synthetic accessibility of 22, favor the
methoxy-substituted bis(indenyl) complexes in the search for
promising catalysts of propylene homo- and copolymerization.
1
CONCLUSIONS
H, 6.15; O, 10.28; Br, 25.67. Found: C, 57.71; H, 6.24; O, 10.19. H
■
NMR (20 °C, CDCl3): δ 7.70 (s, 1H), 4.02 (s, 3H), 3.31 (q, J = 17.6,
7.9 Hz, 1H), 2.72 (m, 1H), 2.61 (dd, J = 17.6, 3.7 Hz, 1H), 1.41 (s,
9H), 1.32 (d, J = 7.5 Hz, 3H). 13C NMR (20 °C, CDCl3): δ 208.0,
162.7, 153.9, 145.4, 132.6, 121.4, 116.6, 61.6, 42.1, 36.0, 35.6, 30.5,
16.3.
In the present work, we have experimentally shown that the
introduction of a π-donating substituent, such as a methoxy
group, into the indenyl fragment of zirconocene might
dramatically affect its catalytic performance in the polymer-
ization and copolymerization of olefins. It is important that the
effect of the methoxy group is positive only if the oxygen atom
is not able to coordinate with the aluminoorganic cocatalyst, for
example, when bulky substituents are introduced into positions
ortho to the methoxy group.
4-Bromo-5-methoxy-2,6-dimethyl-1-indanone (7b). This
product was obtained using the same method as that used for 7a.
The residue was recrystallized from hexane. The yield was 24.7 g
(78.4%). Anal. Calcd for C12H13BrO2: C, 53.55; H, 4.87; O, 11.89.
1
Found: C, 53.44; H, 8.68; O, 5.49. H NMR (20 °C, CDCl3): δ 7.51
(s, 1H), 3.87 (s, 3H), 3.29 (dd, J = 17.6, 7.9 Hz, 1H), 2.72 (m, 1H),
2.59 (dd, J = 17.6, 3.8 Hz, 1H), 2.36 (s, 3H), 1.30 (d, J = 7.5 Hz, 3H).
13C NMR (20 °C, CDCl3): δ 207.8, 161.0, 153.2, 133.5, 133.1, 124.9,
The suggested role of the methoxy group is to stabilize the
cationic catalytic intermediates, and this role was confirmed by
our DFT calculations. The decreased effective charge of the Zr
atom might diminish the probability of chain release through β-
elimination and β-hydrogen transfer to monomer via agostic
transition states. These factors result in an increase in both the
productivity and the polymer molecular-mass growth.
Attractive catalytic properties as well as synthetic availability
of 13 and its analogues make this particular class of
zirconocenes very promising in the design of effective
zirconocene polymerization catalysts.
116.2, 60.1, 42.1, 35.9, 16.7, 16.2.
5-tert-Butyl-6-methoxy-2-methyl-7-phenyl-1H-indene (5a).
Pd(OAc)2 (0.2 g, 3 mol %) and PPh3 (0.47 g, 6 mol %) were
added to a well-stirred mixture of 7a (9.33 g, 30 mmol), phenylboronic
acid (5.1 g, 42 mmol), and K2CO3 (11.6 g, 83 mmol) in DME (115
mL)−H2O (38 mL). The resulting mixture was refluxed with stirring
for 5 h, cooled, poured into water, and extracted with CH2Cl2 (3 ×
100 mL). The combined organic phase was washed with aqueous
Na2CO3 and water, dried over MgSO4, evaporated, and purified by
extraction with hot hexane (3 × 100 mL). The residue obtained after
evaporation was used without purification.
EXPERIMENTAL SECTION
■
This compound was dissolved in Et2O (30 mL) and added
dropwise at 0 °C to LiAlH4 (0.57 g, 15 mmol) in Et2O (100 mL).
After 1 h of stirring, 5% HCl (50 mL) was added, and the organic
phase was separated, washed with aqueous Na2CO3, dried over
MgSO4, and evaporated. The residue was dissolved in benzene (150
mL), p-TSA (0.5 g) was added, and the resulting mixture was refluxed
for 10 min, cooled, washed with water, dried over MgSO4, evaporated,
and distilled in vacuo. The yield was 4.5 g (50%) of colorless, viscous
oil. Anal. Calcd for C21H24O: C, 86.26; H, 8.27; O, 5.47. Found: C,
86.10; H, 8.59; O, 5.31. 1H NMR (20 °C, CDCl3): δ 1.53 (s, 9H), 2.13
bs, 2.14 bs (3H), 3.20 bs, 3.37 bs (2H), 3.30 (s, 3H), 6.42 bs, 6.52 bs
(1H), 7.40−7.58 (m, 6H). 13C NMR (20 °C, CDCl3): δ 16.6, 16.8,
31.0, 31.1, 35.0, 35.1, 42.7, 43.0, 60.4, 60.6, 117.2, 120.9, 126.1, 126.6,
126.8, 126.9, 127.5, 128.2, 128.28, 128.32, 129.5, 130.1, 131.5, 137.8,
138.0, 138.4, 140.8, 140.9, 141.7, 144.4, 145.2, 146.6, 154.2, 156.1.
5-tert-Butyl-6-methoxy-2-methyl-7-tert-butylphenyl-1H-in-
dene (5b). This product was obtained using the same method as that
used for 5a. The yield of 6-tert-butyl-4-(4-tert-butylphenyl)-5-
methoxy-2-methyl-1-indanone was 60%. Anal. Calcd for C25H32O:
General Considerations. Some operations were performed under
argon using standard Schlenk techniques or under vacuum using
sealed glass “equipped-with-everything” systems. BuLi (1.6 or 2.5 M
solution in hexanes), methanesulfonic acid, methacrylic acid, and ZrCl4
were used as purchased (Merck). SiMe2Cl2 was refluxed over Al foil
and distilled prior to use. Pentane and hexanes were refluxed over Na
alloy for 8 h and finally distilled prior to use. CH2Cl2 (Merck) was
distilled over CaH2. Diethyl ether and toluene were refluxed over Na/
benzophenone and distilled prior to use. 1-tert-Butyl-2-methoxyben-
zene and 1-methoxy-2-methylbenzene were prepared in accordance
with a published procedure.30
Equipment. NMR spectra were recorded on Varian XR 300 and
XR 400 spectrometers. Elemental analysis was performed on a Perkin-
Elmer Series II CHNS/O analyzer 2400.
6-tert-Butyl-5-methoxy-2-methyl-1-indanone (8a). A mixture
of 1-tert-butyl-2-methoxybenzene (32.8 g, 0.2 mol) and methacrylic
acid (21.5 g, 0.25 mol) was added at 60 °C to well-stirred Eaton
reagent (prepared from 55 g of P2O5 and 280 mL of methanesulfonic
acid). After 1 h of stirring the reaction mixture was cooled, poured into
ice water, and extracted with benzene (3 × 200 mL). The combined
organic layer was washed with water and aqueous NaHCO3, dried over
MgSO4, evaporated, and distilled at 145−150 °C at 0.7 Torr. The yield
was 20 g (43%, pale yellow, viscous oil). Anal. Calcd for C15H20O2: C,
77.55; H, 8.68; O, 13.77. Found: C, 77.44; H, 8.96; O, 13.60. 1H NMR
(20 °C, CDCl3): δ 7.69 (s, 1H), 6.88 (s, 1H), 3.93 (s, 3H), 3.31 (q, J =
7.8 Hz, 1H), 2.67 (m, 2H), 1.38 (s, 9H; 1.29 d, J = 7.3 Hz, 3H. 13C
NMR (20 °C, CDCl3): δ 208.2; 164.6; 154.4, 138.8, 128.7, 122.1,
107.8, 55.2, 42.1, 35.0, 34.6, 29.6, 16.6.
1
C, 86.16; H, 9.25; O, 4.59. Found: C, 86.10; H, 9.35; O, 4.55. H
NMR (20 °C, CDCl3): δ 7.76 (s, 1H), 7.50 (d, 2H), 7.35 (d, 2H), 3.29
(s, 3H), 3.17 (dd, 1H), 2.64 (m, 1H), 2.51(dd, 1H), 1.44 (s, 9H), 1,40
(s, 9H), 1.27 (d, 3H). The yield of 5b was 85% (colorless, crystalline
powder). 1H NMR (20 °C, CDCl3): δ 7.46 (d, J = 8.5 Hz, 2H; 7.42 (d,
J = 8.5 Hz, m, 2H), 7.23 (s, 1H), 6.46 (s, 1H), 3.23 (s, 3H), 3.17 (s,
2H), 2.08 (s, 3H), 1.46 (s, 9H), 1.40 (s, 9H). 13C NMR (20 °C,
CDCl3): δ 154.7, 150.0, 145.6, 142.1, 141.2, 141.1, 135.6, 131.9, 129.4,
127.2, 125.5, 117.3, 60.9, 43.1, 35.5, 34.9, 31.8, 31.3, 17.0.
7-(4-tert-Butylphenyl)-6-methoxy-2,5-dimethyl-1H-indene
(5c). This product was obtained using the same method as that used
for 5a. The yield was 77% (pale yellow, viscous oil, crystallized within
2 weeks). Anal. Calcd for C212H26O: C, 86.23; H, 8.55; O, 5.22. Found:
C, 86.10; H, 8.67; O, 5.23. H NMR (20 °C, CDCl3): δ 7.50 (d, J =
8.2 Hz, 2H), 7.44 (d, J = 8.2 Hz, 2H), 7.10 (s, 1H), 6.46 (s, 1H), 3.40
(s, 3H), 3.20 (s, 2H), 2.40 (s, 3H), 2.11 (s, 3H), 1.44 (s, 9H). 13C
NMR (20 °C, CDCl3): δ 152.7, 149.5, 145.7, 141.4, 141.3, 134.3,
5-Methoxy-2,6-dimethyl-1-indanone (8b). This product was
obtained using the same method as that used for 8a. The yield was
46% (pale yellow, viscous oil). Anal. Calcd for C12H14O2: C, 75.76; H,
7.42; O, 16.82. Found: C, 75.60; H, 7.59; O, 16.81; Zr, 13.8. 1H NMR
(20 °C, CDCl3): δ 7.51 (s, 1H), 6.81 (s, 1H), 3.91 (s, 3H), 3.31 (q, J =
8.0 Hz, 1H), 2.67 (m, 2H), 2.22 (s, 3H), 1.29 (d, J = 7.4 Hz, 3H). 13C
NMR (20 °C, CDCl3): δ 207.9, 163.7, 154.5, 128.7, 127.1, 125.3,
106.2, 55.5, 41.9, 34.9, 16.5, 16.3.
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Article
131.1, 129.0, 128.9, 126.5, 124.9, 120.8, 60.2, 42.7, 34.5, 31.4, 16.7,
16.5.
under reduced pressure (residual volume approximately 30 mL). The
yellow precipitate was filtered out, washed with pentane, and dried in
vacuo to yield 7.83 g (55%) of product 13. Pure (>98%) crystalline
product was obtained by recrystallization from pentane−CH2Cl2
(5:1). Anal. Calcd for C44H50Cl2O2SiZr: C, 65.97; H, 6.39; O, 3.94.
Bis(6-tert-butyl-5-methoxy-2-methyl-4-phenyl-1H-inden-1-
yl)dimethylsilane (10). A solution of 5a (1.63 g, 5.57 mmol) in Et2O
(25 mL) was cooled to −40 °C, and n-BuLi in hexane (1.6 M, 3.59
mL, 5.74 mmol) was added. The resulting mixture was allowed to
warm to room temperature and was then stirred for 3 h and cooled to
−60 °C; CuCN (15 mg, 0.17 mmol) was subsequently added. After 15
min, SiMe2Cl2 (0.34 mL, 2.84 mmol) in Et2O (5 mL) was added. The
resulting mixture was allowed to warm to room temperature and was
stirred for 16 h. H2O (5 mL) and benzene (100 mL) were added, and
the organic phase was separated, dried over MgSO4, passed through
silica gel, and evaporated. The residue was dried in vacuo (pale yellow
solid) and used without purification. Anal. Calcd for C44H521O2Si: C,
82.45; H, 8.18; O, 4.99. Found: C, 82.30; H, 8.26; O, 4.86. H NMR
(20 °C, CDCl3): δ 7.56−7.47 (group of m, 10H), 7.40 s, 7.38 s (2H;
CAr−H), 6.49 bs, 6.40 bs (2H, −CH), 3.63 s, 3.61 s (2H, >CH−),
3.27 (s, 6H, −OCH3), 2.17 bs, 2.02 bs (6H, −C-CH3), 1.48 s, 1.47 s
(18H, −C(CH3)3), −0.04 s, −0.12 s, −0.13 s (6H, Si-CH3). 1H NMR
(20 °C, C6D6): δ 7.50 (dd, J = 6.3, 3.0 Hz, 2H), 6.98 (dd, J = 6.3, 3.0
Hz, 2H), 6.54 (t, J = 3.3 Hz, 1H), 6.29 (d, J = 3.3 Hz, 2H), 4.41 (sept,
J = 6.0 Hz, 3H), 1.03 (d, J = 6.0 Hz, 18H).
Bis(6-tert-butyl-5-methoxy-2-methyl-4-tert-butylphenyl-1H-
inden-1-yl)dimethylsilane (11). This product was obtained using
the same method as that used for 10 and was used without
purification. Anal. Calcd for C52H68O2Si: C, 82.92; H, 9.10; O, 4.25.
Found: C, 82.78; H, 9.19; O, 4.20. 1H NMR (20 °C, CDCl3): δ 7.51−
7.38 (group of m, 10H), 6.54 bs, 6.52 bs (2H), 3.67 s, 3.64 s (2H),
3.26 (s, 6H), 2.18 bs, 2.10 bs (6H), 1.47 s, 1.46 s (36H), −0.12 bs,
−0.13 bs (6H).
1
Found: C, 65.44; H, 6.34; O, 3.88. H NMR (20 °C, CDCl3): δ 7.64
(broad, 4H), 7.54 (s, 2H), 7.45 (m, 4H), 7.35 (m, 2H) (CAr−H), 6.61
(s, 2H, H of C5 ring), 3.42 (s, 6H, −OCH3), 2.18 (s, 6H, C-CH3), 1.40
(s, 18H, −C(CH3)3), 1.31 (s, 6H, Si-CH3). 1H NMR (20 °C, C6D6): δ
7.50 (dd, J = 6.3, 3.0 Hz, 2H), 6.98 (dd, J = 6.3, 3.0 Hz, 2H), 6.54 (t, J
= 3.3 Hz, 1H), 6.29 (d, J = 3.3 Hz, 2H), 4.41 (hept, J = 6.0 Hz, 3H),
1.03 (d, J = 6.0 Hz, 18H). 13C NMR (20 °C, CDCl3): δ 160.0, 144.2,
136.9, 135.2, 133.6, 129.7, 128.5, 127.3, 126.9, 123.0, 121.05, 121.0,
81.7, 62.7, 35.8, 30.3, 18.4, 2.4.
For amide 16 (probe from the reaction mixture, dried in vacuo): 1H
NMR (20 °C, CDCl3): δ 7.73 (bs, 1H), 7.62 (m, 2H), 7.58−7.28
(group m, 9H) (CAr−H), 6.59 (s, 1H), 6.41 (s, 1H) (H of C5 ring),
3.40 (s, 3H), 3.30 (s, 3H) (−OCH3), 2.35 (s, 3H), 2.23 (s, 3H) (C5-
CH3), 1.44 (s, 18H, −C(CH3)3), 1.23 (s, 3H), 1.22 (s, 3H) (Si-CH3),
0.63 (s, 9H, N-C(CH3)3).
μ-(Bis-[η5-6-tert-butyl-5-methoxy-2-methyl-4-tert-butyl-
phenyl-1H-inden-1-yl]dimethylsilanediyl)dichlorozirconium-
(IV) (14). This product was obtained using the same method as that
used for 13. The yield for method A (11-Li2 + ZrCl4) was 29%,
whereas that for method B (11-Li2 + ZrCl3(THF)2NH-tert-Bu) was
61%. Anal. Calcd for C52H66Cl2O2SiZr: C, 68.39; H, 7.28; O, 3.50.
1
Found: C, 68.02; H, 7.39; O, 3.55. H NMR (20 °C, CDCl3): δ 7.65
(broad, 4H), 7.56 (s, 2H), 7.51 (m, 4H), 6.69 (s, 2H), 3.45 (s, 6H),
2.23 (s, 6H), 1.44 (s, 18H), 1.40 (s, 18H), 1.35 (s, 6H). 13C NMR (20
°C, CDCl3): δ 159.9, 159.0, 144.1, 135.0, 133.7, 133.6, 129.1, 127.0,
125.3, 123.0, 121.2, 120.7, 81.4, 62.5, 35.7, 34.5, 31.3, 30.2, 18.3, 2.3.
For amide 17 (probe from the reaction mixture, dried in vacuo): 1H
NMR (20 °C, CDCl3): δ 7.73 (bs, 1H), 7.58 (m, 2H), 7.55−7.28
(group m, 7H) (CAr-H), 6.64 (s, 1H), 6.44 (s, 1H) (H of C5 ring),
3.42 (s, 3H), 3.35 (s, 3H) (−OCH3), 2.37 (s, 3H), 2.25 (s, 3H) (C5-
CH3), 1.44 (bs, 18H), 1.38 (s, 9H), 1.37 (s, 9H) (−C(CH3)3), 1.25 (s,
3H), 1.24 (s, 3H) (Si-CH3), 0.64 (s, 9H, N-C(CH3)3).
Bis(6-(4-tert-butylphenyl)-5-methoxy-2,4-dimethyl-1H-
inden-1-yl)dimethylsilane (12). This product was obtained using
the same method as that used for 10 and was used without
purification. Anal. Calcd for C46H56O2Si: C, 82.58; H, 8.44; O, 4.78.
Found: C, 82.40; H, 8.60; O, 4.74. 1H NMR (20 °C, CDCl3): δ 7.62−
7.50 m, 7.31 s, 7.24 s (10H), 6.60 (bs, 2H), 3.77 s, 3.75 s (2H), 3.45 s,
3.44 s (6H), 2.43 s, 2.42 s, 2.26 s, 2.21 s (12H), 1.47 s, 1.43 s (18H),
−0.14 (s, 6H).
μ-(Bis[η5-4-(4-tert-butylphenyl)-5-methoxy-2,6-dimethyl-1H-
inden-1-yl]dimethylsilanediyl)dichlorozirconium(IV) (15). This
was obtained by the method used for 13, method A. The residue was
recrystallized from MeOCMe3: the solubility of the meso-form is lower
(red crystals). The filtrate was concentrated, and the resulting
precipitate was filtered off and recrystallized from pentane−CH2Cl2
(5:1), giving 5% of the rac-form (yellow, crystalline powder). Anal.
Calcd for C46H54Cl2O2SiZr: C, 66.64; H, 6.66; O, 3.86. Found: C,
μ-(Bis-[η5-6-tert-butyl-5-methoxy-2-methyl-4-phenyl-1H-
inden-1-yl]dimethylsilanediyl)dichlorozirconium(IV) (13).
Method A (10-Li2 + ZrCl4): Compound 10 (1.66 g, 2.59 mmol)
was dissolved in Et2O (20 mL) and cooled to −40 °C, and n-BuLi (1.6
M in hexane, 3.4 mL, 5.44 mmol) was added. The reaction mixture
was allowed to warm to room temperature and was then stirred for 3 h
and evaporated. The resulting yellow powder was suspended in
pentane (50 mL) and cooled to −60 °C, and ZrCl4 (0.66 g, 2.85
mmol) was added. After 5 min, Et2O (0.3 mL) was added. The
resulting mixture was allowed to warm to room temperature and was
then stirred for an additional 16 h and filtered. The residue was
recrystallized from pentane−CH2Cl2 (5:1) to yield the racemic
product (0.23 g, 22%). Method B (10-Li2 + ZrCl3(THF)2NH-t-Bu): A
solution of n-BuLi in hexane (1.6 M, 11.9 mL, 19 mmol) was added to
a cooled (−20 °C) solution of tert-butylamine (2.0 mL, 19 mmol) and
THF (1.54 mL, 19 mmol) in toluene (20 mL). The mixture was
allowed to warm to room temperature and was then stirred for 2 h and
transferred to a dropping funnel. ZrCl4 × 2THF (7.11 g, 18.8 mmol)
was suspended in toluene (15 mL) and cooled to 0 °C, and lithium
tert-butyl amide was added within 10 min. This mixture was allowed to
warm to room temperature and was stirred for 2 h. A second solution
with the previously prepared 10 (12.0 g, 18.7 mmol) was dissolved in a
toluene (35 mL) and THF (3.1 mL, 38 mmol) solution and cooled to
−40 °C. n-BuLi (1.6 M in hexane, 23.8 mL, 38 mmol) was then added.
This second mixture was allowed to warm to room temperature and
was then stirred for 3 h and cooled to −20 °C. The mixture that
contained trichlorozirconium tert-butyl amide was added within 20
min. The resulting orange solution was stirred for 16 h, filtered, and
evaporated. The residue was dissolved in CH2Cl2 (50 mL), and the
resulting dark red solution was treated with chlorotrimethylsilane
(11.9 mL, 93 mmol). The mixture was stirred for 2 h; hexane (100
mL) was then added, and then most of the solvent was eliminated
1
66.31; H, 6.70; O, 3.78. rac-Form: H NMR (20 °C, CDCl3): δ 7.61
(d, J = 8.3 Hz, 4H), 7.46 (d, J = 8.3 Hz, 4H), 7.28 (s, 2H), 6.70 (s,
2H), 3.46 (s, 6H), 2.31 (s, 6H), 2.20 (s, 6H), 1.36 (s, 18H), 1.31 (s,
1
6H). meso-Form: H NMR (20 °C, CDCl3): δ 7.57 (d, J = 8.0 Hz,
4H), 7.45 (d, J = 8.0 Hz, 4H), 7.42 (s, 2H), 6.58 (s, 2H), 3.28 (s, 6H),
2.38 (s, 6H), 2.23 (s, 6H), 1.36 (s, 18H), 1.45 (s, 3H), 1.22 (s, 3H).
5-tert-Butyl-6-methoxy-2-methyl-7-phenyl-1H-indene (5a)
Recovery. Organic phases and precipitates obtained at all stages of
the preparation of 13 by method B were combined and evaporated
under reduced pressure. The residue was poured into the solution of
15 g of KOH in 50 mL of 1:1 EtOH−H2O with stirring. The mixture
was heated to reflux, allowed to warm to room temperature, and
stirred overnight. Then it was poured into water (100 mL) and
extracted by a 1:1 hexane−ether mixture (6 × 10 mL). The combined
organic phase was washed with water, dried over MgSO4, evaporated,
and distilled at 140−155 °C at 0.1 Torr. The yield was 4.0 g (37%).
ASSOCIATED CONTENT
■
S
* Supporting Information
Details of the crystal structure determination, atomic
coordinates, isotropic and anisotropic displacement parameters,
and bond lengths and angles for complex 14. Experimental
details for catalyst preparation, polymerization procedure, and
polymer analysis. The structure of 14 was deposited with
4969
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Article
(Basell) Appl. US2003/0148877 2003. (d) Fritze, C.; Resconi, L.;
Schulte, J.; Guidotti, S. (Basell) Appl. US2004171855, 2004.
(e) Nifant’ev, I. E.; Laishevtsev, I. P.; Ivchenko, P. V.; Kashulin, I.
A.; Guidotti, S.; Piemontesi, F.; Camurati, I.; Resconi, L.; Klusener, P.
A. A.; Rijsemus, J. J. H.; de Kloe, K. P.; Korndorffer, F. M. Macromol.
Chem. Phys. 2004, 205, 2275. (f) Resconi, L.; Guidotti, S.; Camurati, I.;
Frabetti, R.; Focante, F.; Nifant’ev, I. E.; Laishevtsev, I. P. Macromol.
Chem. Phys. 2005, 206, 1405. (g) De Rosa, C.; Auriemma, F.; Di
Capua, A.; Resconi, L.; Guidotti, S.; Camurati, I.; Nifant’ev, I. E.;
Laishevtsev, I. P. J. Am. Chem. Soc. 2004, 126, 17040.
Cambridge Crystallographic Database under the number
CCDC-868398. This material is available free of charge via
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: inif@org.chem.msu.ru.
■
Notes
The authors declare no competing financial interest.
(11) Klosin, J.; Kruper, W. J.; Nickias, P. N.; Patton, J. T.; Wilson, D.
R. (The Dow Chemical Company) Appl. WO98/06727, 1998.
(12) Piccolrovazzi, N.; Pino, P.; Consiglio, G.; Sironi, A.; Moret, M.
Organometallics 1990, 9, 3098.
ACKNOWLEDGMENTS
■
We thank Lyondell Basell for financial support and permission
to publish this work, the Basell research team at the G. Natta
Research Center in Ferrara for the polymerization experiments
and polymer characterization, and Dr. Isabella Camurati for the
13C NMR spectra of the polymers.
(13) Kukral, J.; Lehmus, P.; Klinga, M.; Leskela, M.; Rieger, B. Eur. J.
̈
Inorg. Chem. 2002, 1349.
(14) (a) Sangokoya, S. A.; Goodall, B. L.; Simeral, L. S. (Albemarle
Corp.) Appl. WO03/082879, 2003. (b) Luo, L.; Sangokoya, S. A.; Wu,
X.; Diefenbach, S. P.; Kneale, B. (Albemarle Corp.) Appl. US2009/
0062492, 2009.
(15) (a) Cedheim, L.; Eberson, L. Acta Chem. Scand. 1976, B30, 527.
(b) Kraft, P.; Eichenberger, W. Eur. J. Org. Chem. 2003, 3735.
(c) Tashmukhamedova, A. K.; Sarieva, G. M.; Levkovich, M. G.;
Kamaev, F. G. Chem. Nat. Compd. 1983, 19, 489. (d) Ramana, M. M.
V.; Potnis, P. V. Synth. Commun. 1995, 25, 1751. (e) London, G.;
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REFERENCES
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