Regiochemistry of the styrene insertion with CH2-bridged ansa-zirconocene-based catalysts

Article abstract of DOI:10.1021/ma034818r

Methylenebis(indenyl)zirconium dichloride substituted in C(3), activated by methylalumoxane, is able to give polystyrene and ethylene-styrene copolymers. In this study hydrooligomers, whose structure, determined by ¹³C NMR and GC-MS techniques, gives information about the regiochemistry and the stereochemistry of styrene insertion, have been purposefully prepared. The regiochemistry of the styrene insertion is related to the encumbrance of substituents in C(3). rac-[Methylene-(3-R-1-indenyl)₂]ZrCl₂ with R = H, CH₃, or CH₂CH₃ induces a prevailingly secondary styrene insertion into the zirconium-carbon bond. With increasing the substituent's steric hindrance (R = CH(CH₃)₂), regiochemistry inversion occurs and the primary insertion becomes prevailing. The analysis of ethylene-styrene copolymers obtained in the presence of the different catalysts allows confirming the correlation between regiochemistry and comonomers' reactivity. Besides, also the stereospecificity can be evaluated from the structure of the hydrotrimers, when the insertion is primary. Whereas the isospecificity in the absence of substituents (secondary insertion) and in the presence of the tert-butyl substituent (primary insertion) is well-known, a surprising syndiospecificity is observed when the indenyl ligand bears the isopropyl substituent in C(3).

Full text of DOI:10.1021/ma034818r

9340
Macromolecules 2003, 36, 9340-9345
Regiochemistry of the Styrene Insertion with CH2-Bridged
ansa-Zirconocene-Based Catalysts
Lor ella Izzo,* Ma r ia gr a zia Na p oli, a n d Leon e Oliva
Dipartimento di Chimica, Universita` di Salerno, I-84081 Baronissi (SA), Italy
Received J une 17, 2003; Revised Manuscript Received September 18, 2003
ABSTRACT: Methylenebis(indenyl)zirconium dichloride substituted in C(3), activated by methylalu-
moxane, is able to give polystyrene and ethylene-styrene copolymers. In this study hydrooligomers, whose
structure, determined by 13C NMR and GC-MS techniques, gives information about the regiochemistry
and the stereochemistry of styrene insertion, have been purposefully prepared. The regiochemistry of
the styrene insertion is related to the encumbrance of substituents in C(3). rac-[Methylene-
(3-R-1-indenyl)2]ZrCl2 with R ) H, CH3, or CH2CH3 induces a prevailingly secondary styrene insertion
into the zirconium-carbon bond. With increasing the substituent’s steric hindrance (R ) CH(CH3)2),
regiochemistry inversion occurs and the primary insertion becomes prevailing. The analysis of ethylene-
styrene copolymers obtained in the presence of the different catalysts allows confirming the correlation
between regiochemistry and comonomers’ reactivity. Besides, also the stereospecificity can be evaluated
from the structure of the hydrotrimers, when the insertion is primary. Whereas the isospecificity in the
absence of substituents (secondary insertion) and in the presence of the tert-butyl substituent (primary
insertion) is well-known, a surprising syndiospecificity is observed when the indenyl ligand bears the
isopropyl substituent in C(3).
In tr od u ction
(MAO) in the polymerization and copolymerization of
styrene.9 As a matter of fact, the polystyrene obtained
at different polymerization temperatures has isotactic
microstructure, and the chain ends arising from initia-
tion and termination steps indicate a prevailingly
primary insertion. The presence of 3-tert-butyl substit-
uents in indenyl ligands was invoked as responsible for
this unusual styrene regiochemistry. In the ethylene-
styrene copolymerization the formation of blockwise
structure instead of the alternating or “pseudorandom”
structure, generally obtained with ansa-zirconocene-
based catalysts, could be explained as consequence of
this regiochemistry.
The traditional Ziegler-Natta1 catalysts as well as
several more recent homogeneous catalysts promote
styrene polyinsertion to give stereoregular polymers.2,3
Some aspects of the styrene behavior are peculiar with
respect to that of olefinic monomers. Whereas styrene
insertion with δTiCl3/Al(13CH3)3 seems to follow the
general primary regiochemistry of 1-alkenes,4 experi-
mental evidence supports a secondary regiochemistry
of insertion (that is, the formation of the zirconium-
benzylydene bond) in the presence of most C2 and Cs
symmetry zirconocenes.5
Evidence of a secondary styrene regiochemistry has
also been reported by Rodewald and J ordan6 in the
study of the styrene monoinsertion with cationic zir-
conocene compounds. The same regiochemical behavior
was found in 1987 by Pellecchia et al.7 both by analyzing
chain end groups of a syndiotactic polystyrene (s-PS)
sample prepared with Ti(CH2C6H5)4/MAO/Al(13CH2CH3)3
and by isolating low molecular weight s-PS samples
where the presence of -CH(C6H5)CH3 and CH(C6H5)d
CH- end groups in equal amounts indicates the second-
ary insertion in both the initiation and termination
steps.8
Ethylene-styrene copolymers obtained with [(meth-
yl)(phenyl)methylene(1-cyclopentadienyl)(9-fluorenyl)]-
ZrCl2/MAO/Al(13CH3)3 showed the prevailing secondary
insertion of the aromatic monomer at least in the
initiation step.5a Moreover, a study on the microstruc-
ture of propene-ethylene-styrene copolymers, obtained
with C2 and Cs zirconocene-based catalysts, suggests the
secondary styrene insertion also in the propagation
steps.5b
In the present paper we report on the regiochemical
behavior of styrene in the presence of methylene-bridged
catalysts with different substituents in C(3) of the
indenyl ligands.
Moreover, ethylene-styrene copolymerizations were
performed in the presence of the same catalysts in order
to evaluate the possible correlation between regiochem-
istry and comonomers reactivity ratio.
Resu lts a n d Discu ssion
Ca ta lysts Syn th eses. The ansa-zirconocene com-
plexes rac-[methylene(3-R-1-indenyl)2]ZrCl2 (Chart 1)
were prepared as reported in the literature10 (R ) H,
CH(CH3)2, C(CH3)3) or following Scheme 1 in the case
of not previously described compounds (R ) CH3,
CH2CH3).
The indenyllithium salt was alkylated through reac-
tion with the suitable alkyl bromide. The reaction with
formalin (37% solution) and sodium ethoxide in dim-
ethylformamide yielded a solution from which the ligand
was purified through a chromatography column. Zir-
conocene dichlorides were prepared by reacting the
dilithiated ligand precursors with Me3SnCl and then
with ZrCl4 in toluene.10b,11 The complexes were purified
by crystallization from toluene. In the aromatic solvent
the racemic form is, in all the cases, less soluble than
the meso one.
In contrast with this picture, recently in our labora-
tory was observed the behavior of rac-[methylene(3-tert-
butyl-1-indenyl)2]ZrCl2 activated by methylalumoxane
* Corresponding author: Fax 39 089 965296; e-mail lizzo@
unisa.it.
10.1021/ma034818r CCC: $25.00 © 2003 American Chemical Society
Published on Web 11/07/2003

Macromolecules, Vol. 36, No. 25, 2003
CH2-Bridged ansa-Zirconocene-Based Catalysts 9341
Ch a r t 1
Sch em e 1
structures of hydrodimer and hydrotrimer account for
the styrene primary insertion into the zirconium-
hydrogen bond followed by secondary insertions into the
zirconium-carbon bond.
Spectra b and c are very similar but for the prevalence
of the 1,3,6-triphenylhexane trimer, so suggesting again
the secondary styrene insertion into the zirconium-
carbon bond. On the contrary, the intense signals at
22.66, 34.09, 39.66, and 40.14 ppm in spectra d and e
are assigned to 1,3-diphenylbutane and account possibly
for the primary styrene insertion into the zirconium-
hydrogen bond followed by further primary insertion
into the zirconium-carbon bond (Scheme 2). The cor-
responding trimer 1,3,5-triphenylhexane bearing two
asymmetric carbons is also detected in the spectrum.
In principle, the structure of 1,3-diphenylbutane could
also account for the secondary styrene insertion into the
zirconium-hydrogen bond followed by secondary inser-
tion into the zirconium-carbon bond. However, this
regiochemical hypothesis can be disregarded; in fact,
either with no or very large substituents in C(3) [i.e., R
) H, C(CH3)3] the styrene insertion into the zirconium-
hydrogen bond is primary. It seems reasonable to extend
to catalyst precursor 4 the regiochemical behavior of
styrene for the insertion into the zirconium-hydrogen
bond and consequently to infer the primary regiochem-
istry for the insertion into the zirconium-carbon bond.
Through GC-MS analysis, the relative abundance of
dimers and trimers produced by each catalytic system
has been calculated and reported in Table 1.
One can observe that in the presence of rac-[methyl-
ene(3-R-1-indenyl)2]ZrCl2 with R ) H, CH3, or CH2CH3
prevails secondary styrene insertion into the zirconium-
carbon bond. Increasing the substituent steric hindrance
(R ) CH(CH3)2), a regiochemistry inversion occurs and
the primary insertion is preferred with respect to the
secondary one.
The previously reported regiochemical behavior of
styrene in the case of system 5 (R ) C(CH3)3) was
attributed to the 3-tert-butyl substituents.9 The results
we report in the present paper confirm the hypothesis
that styrene regiochemistry is dependent on alkyl
substitutions on π ligands and fix the minimum steric
hindrance of substituents able to induce the primary
insertion and consequently the regiochemistry inver-
sion.
Styr en e Hyd r ooligom er iza tion . Aimed at clarify-
ing the regiochemistry of the styrene insertion, we have
carried out a series of polymerizations of styrene in the
presence of hydrogen (1 atm). The structure of hydro-
genated oligomers obtained with the different complexes
activated by MAO was analyzed by 13C NMR and GC-
MS techniques. This approach allows recognizing the
regiochemistry of both the monomer insertion into the
zirconium-hydrogen bond and the following insertions
into the zirconium-carbon bond. 13C NMR spectra of
hydrooligomers produced at 20 °C, with catalysts pre-
cursors 1-5 (spectra a-e), are shown in Figure 1. A very
similar hydrooligomeric composition is obtained at 60
°C.
Upon inspection of the aliphatic region of spectrum
a, the most intense peaks at 31.36 and 36.06 ppm are
due to carbon 2 and 1 of the 1,4-diphenylbutane,
whereas the less intense signals at 29.57, 34.01, 36.15,
36.86, 38.76, and 45.66 ppm can be attributed to 1,3,6-
triphenylhexane, in accordance with the literature
data.12 The GC-MS, with M+ ) 210 for the more
abundant compound and M+ ) 314 for the less abun-
dant one, are in agreement with this assignment. These
Data reported in Table 2 show the relative amount
of trimers and the ratio between the diastereoisomers

9342 Izzo et al.
Macromolecules, Vol. 36, No. 25, 2003
F igu r e 1. Aliphatic region of 13C NMR spectra and chemical shift assignments of styrene hydrooligomers obtained in the presence
of precursors 1-5 (spectra a-e) activated by MAO at 20 °C.
Ta ble 1. Rela tive Am ou n ts of Hyd r od im er a n d
Hyd r otr im er Obta in ed a t 20 °C a n d a t 1 a tm of Hyd r ogen
P r essu r e w ith th e Differ en t Ca ta lytic System s
Ta ble 2. Rela tive Am ou n ts of Ster eoch em ica l Isom er s of
Hyd r otr im er s Obta in ed a t 20 °C a n d a t 1 a tm of
Hyd r ogen P r essu r e w ith th e Differ en t Ca ta lytic System s
indenyl
substituents in
indenyl substituents
in C(3)
1,3,6-tphea
1,3,5-tphea
iso/syndio
C(3)
1,4-dphba 1,3-dphba 1,3,6-tpheb 1,3,5-tpheb
H
CH3
CH2CH3
CH(CH3)2
C(CH3)3
100
98.9
96.9
42.6
0.5
0
1.1
3.1
57.4
99.5
0
H
99.4
24
17.8
0.7
0
5.4
16
83.6
87.9
0.6
69.8
64.1
6.7
0
0.8
0.3
0.2
27
CH3
0.8
2.1
9.0
11.7
CH2CH3
CH(CH3)2
C(CH3)3
0.3
0.1
a
Triphenylhexane.
a
b
Diphenylbutane. Triphenylhexane.
isomers, that is, syndiotactic stereocontrol. This fact can
be justified by an asymmetric carbon induction on
stereocontrol because the symmetry features of the
catalysts cannot account for such a stereocontrol. By
further increasing the steric hindrance of C(3) substit-
uents on π ligands, with tert-butyl the catalyst site
control is restored and a diastereoisomers mixture
enriched in the (R,S + S,R) isomers is obtained.
Eth ylen e-Styr en e Cop olym er iza tion s. Recently
we reported9 that the precursor 5 activated by MAO is
able to produce block ethylene-styrene copolymers such
structure probably being a consequence of the styrene
primary insertion. To relate the microstructure of
copolymers to the regiochemistry of styrene insertion,
a series of ethylene-styrene copolymerizations were
carried out in the presence of complexes 1-4 activated
by MAO, at different temperatures and comonomer feed.
of 1,3,5-triphenylhexane.
It is worth noting that increasing the steric hindrance
on metallocene ligands, the relative amount of 1,3,5-
triphenylhexane increases with respect to 1,3,6-triph-
enylhexane, according to the regiochemical trend.
In addition, from the stereochemical point of view, the
presence of 3-methyl substituents in C(3) of the indenyls
leads to a similar amount of (R,R + S,S) isomers (which
model an syndiotactic growing chain) and (R,S + S,R)
isomers (which model a isotactic growing chain) of 1,3,5-
triphenylhexane. The catalyst precursor is so aspecific
in the styrene polymerization according to the reported
behavior of C2-symmetric bridged 3-methylindenyl cata-
lysts in the propene polymerization.13
On the other hand with C2-metallocenes bearing ethyl
and isopropyl groups in carbon 3 prevail the (R,R + S,S)

Macromolecules, Vol. 36, No. 25, 2003
CH2-Bridged ansa-Zirconocene-Based Catalysts 9343
Ta ble 3. Rela tive Am ou n t of Tr ia d s a n d Aver a ge Len gth
of Meth ylen e Sequ en ces in th e Eth ylen e-Styr en ea
Cop olym er s Obta in ed w ith th e Differ en t Ca ta lyst
System s
Sch em e 2
indenyl substituents in C(3)
[SEE]/[SES]b
LhCH
2
H
CH3
CH2CH3
CH(CH3)2
C(CH3)3
0.14
0.22
0.31
0.92
n.d.
3.3
3.6
4.2
6.2
12
a
All the copolymerizations were carried out in the presence of
MAO as cocatalyst, in 20 mL of toluene, T ) 60 °C, t ) 1 h, [E]feed
/
b
[S]feed ) 9.0 × 10-2
.
Calculated according to ref 17.
be detected and consequently cannot be inferred the
formation of block copolymer. Probably the primary
insertion of styrene is not so prevalent on the secondary
one to induce an ethylene-styrene block copolymeriza-
tion. This is also evident from data reported in Table 2:
1,3-diphenylbutane is prevalent on 1,4-diphenylbutane,
but the two structural isomers of trimers are about in
the same amount, so indicating the scarce regioselec-
tively of the complex 4.
Finally, the copolymer obtained in the presence of
system 5 (R ) C(CH3)3) shows a strong increase of
average length of methylene sequences and from the 13
C
NMR spectrum as well as from GPC analysis is evi-
dently a blockwise structure.
Con clu sion s
Styrene hydrooligomers, produced in the presence of
differently substituted C2-symmetric ansa-zirconocenes
activated by MAO, are a representation of the monomer
initial insertion steps. In this work the structure of
hydrooligomers has been studied to understand how
substituent groups in C(3) of π ligands influence the
regiochemical behavior of styrene toward the metal-
carbon bond. Results show the styrene regiochemistry
changes from secondary to primary as increasing the
In the 13C NMR spectra of products obtained at 60
°C and with [E]feed/[S]feed ) 9.0 × 10-2, signals assigned
to atactic polystyrene sequences are present in addition
to the copolymeric one. Attemps to fractionate the
copolymerization products with boiling solvent failed,
despite a large polydispersity index (about 10) charac-
teristic of all the samples. So the contemporary presence
of ethylene-styrene copolymer and atactic polystyrene
cannot be disregarded.
bulk in C(3): H < CH3 < CH2CH3 < CH(CH3)2
<
C(CH3)3. In particular, the isopropyl group is the small-
est substituent capable to preferentially induce the
primary styrene insertion. This regiochemistry becomes
strongly prevalent in the presence of 3-tert-butyl-
substituted zirconocene catalyst.
In a similar way, decreasing the tendency toward
secondary insertion decreases the alternating enchain-
ment of ethylene and styrene in copolymerization as
shown by the relative amount of SES and SEE se-
quences.
A surprising result arises from the stereochemical
analysis of the hydrooligomers containing couples of
asymmetric carbons. With the ethyl substituent in C(3)
and, even more, with the isopropyl substituent, a
syndiotactic-like stereocontrol, possibly induced by the
first asymmetric carbon, overcomes the isotactic-like
stereocontrol expected from the C2-symmetric catalytic
center. On the contrary, with the tert-butyl substituent
the site control is restored and the (R,S + S,R) hydrot-
rimers are obtained.
However, a close inspection of 13C NMR signals
belonging to the copolymeric structure can purchase
some information about the relative reactivity of eth-
ylene vs styrene.
As shown in Table 3 increasing the bulkiness in C(3)
(R ) H, CH3, CH2CH3) catalysts 1-3, which induce a
secondary styrene insertion, produces “pseudorandom”
copolymers with a slightly decreasing amount of alter-
nating styrene-ethylene-styrene (SES) sequences. At
the same time the average length of methylene se-
quences increases. The absence of stereoregularity of
copolymers obtained with precursors 2 and 3 (R ) CH3
and CH2CH3) is evident from 13C NMR spectra where
the Sââ is split into two signals.
Exp er im en ta l P a r t
In the same experimental conditions, [SEE]/[SES]17
and LhCH values of copolymer obtained in the presence
of precu2rsor 4 (R ) CH(CH3)2) indicate a decrease of
relative reactivity of styrene. Also, if precursor 4 is
scarcely prone to give styrene-ethylene alternating
sequences, the resonances of the junction carbons cannot
Ma ter ia ls a n d Gen er a l P r oced u r es. All operations were
performed under a nitrogen atmosphere by using Schlenk
techniques. Solvents were dried over metallic sodium or
LiAlH4.
Ethylene was purchased from Societa` Ossigeno Napoli and
used without further purification. Toluene (analytical grade

9344 Izzo et al.
Macromolecules, Vol. 36, No. 25, 2003
reagent, Carlo Erba Reagenti) was refluxed over metallic
sodium and distilled under a nitrogen atmosphere. Styrene
(99% GC, Aldrich) was stirred over CaH2 and distilled under
reduced pressure of nitrogen. Methylalumoxane (MAO), pro-
vided by Witco as 30 wt % solution in toluene, was dried before
use by removing in a vacuum the solvent. rac-[Methylene-
(3-R-1-indenyl)2]zirconium dichloride (R ) H, CH(CH3)2,
C(CH3)3) was synthesized according to the literature.10
Syn th esis of Bis(1-m eth yl-3-in d en yl)m eth a n e. 3.6 mL
of formalin (37% solution, 48.6 mmol) was added dropwise to
a mixture of methylindene14 (13 g, 97 mmol) and sodium
ethoxide (2.1 g, 31 mmol) in 140 mL of dimethylformamide.
The reaction mixture was stirred 18 h at room temperature,
then HCl 1 M (120 mL) was added, and the organic phase was
extracted with petroleum ether (3 × 100 mL). The organic
phases combined, anidrified with Na2SO4, were concentrated.
The yellow oil obtained was purified over a chromatography
column (eluent: petroleum ether) to yield 2.4 g of ligand
(yield: 18%).
then by washing with water until neutrality, and drying the
organic layer in a vacuum.
1,4-Diphenylbutane. 13C NMR (CDCl3): δ 31.36 (C2), 36.06
(C1), the aromatic C atoms resonated between 125.8 and 142.8.
MS: 210 (M+). Mp ) 49-52 °C.
1,3-Diphenylbutane. 13C NMR (CDCl3): δ 22.66 (C1), 34.09
(C4), 39.66 (C2), 40.14 (C3), the aromatic C atoms resonated
between 125.2 and 145.7. MS: 210 (M+). Bp ) 67-70 °C (0.01
Torr).
1,3,6-Triphenylhexane. 13C NMR (CDCl3): δ 29.57 (C2),
34.01 (C6), 36.15 (C1), 36.86 (C3), 38.76 (C5), 45.66 (C4), the
aromatic C atoms resonated between 126.2 and 145.6. MS: 314
(M+). Bp ) 109-116 °C (0.1 Torr).
1,3,5-Triphenylhexane. 13C NMR (CDCl3): δ 21.38 (C1),
33.96 (C6), 37.51 (C2), 38.70 (C5), 43.26 (C3), the aromatic C
atoms resonated between 125.9 and 147.9. MS: 314 (M+). Bp
115-125 °C (0.01 Torr).
Example of Hydrooligomerization. In a 100 mL glass flask
were added, in a nitrogen atmosphere, 20 mL of toluene and
0.46 g (8.0 mmol) of MAO. The mixture was magnetically
stirred and thermostated at 20 °C, and then 2 mL of a 4 mM
toluene solution of rac-CH2[(3-CH3CH2-1-Ind)2]ZrCl2 (11 mg
in 6.0 mL of toluene) was added (Al/Zr in mol ) 1000). The
inert atmosphere was removed and replaced with hydrogen,
and then 10 mL of styrene was injected. The flask was fed
with hydrogen over the reaction time. The hydrooligomeriza-
tion was stopped after 2 h, adding acidified methanol. The
oligomers were recovered by treating the solution with acidi-
fied water, then by washing with water until neutrality, and
drying the organic layer in a vacuum (yield: 500 mg).
Eth ylen e-Styr en e Cop olym er iza tion s. Ethylene-sty-
rene copolymerizations were carried out in a 100 mL glass
flask charged under a nitrogen atmosphere sequentially with
styrene (10 mL) and MAO (11 mmol). The mixture was
magnetically stirred, and the glass flask was thermostated at
the desired temperature. The inert atmosphere was removed
and replaced with ethylene feed, and 3 mL of a 3.6 mM toluene
solution of the zirconocene compound was introduced (Al/Zr
in mol ) 1000). The flask was fed with an ethylene-argon
mixture over the polymerization time. The steadiness of
gaseous mixture composition was monitored via gas chroma-
tography. The reaction was stopped after 2 h, and the
copolymer was coagulated by pouring the reaction mixture into
acidified methanol, filtered, washed with additional methanol,
and dried in a vacuum.
1H NMR (CDCl3): δ 7.49-7.25 (m, 8H, C6H4); 6.28 (d, 2H,
C5 ring dCH); 3.81 (s, 2H, CH2); 3.08 (m, 2H, C5 ring, CH);
1.40 (s, 6H, CH3). MS: 272 (M+)
Syn th esis of Bis[3-m eth yl-3(tr im eth ylsta n n yl)in d en -
1yl]m eth a n e. To a solution of bis(1-CH3-3-indenyl)methane
(2.4 g, 8.8 mmol) in 45 mL of diethyl ether was added dropwise,
at -78 °C, 7 mL of nBuLi (2.5 M solution in hexane, 17.6
mmol). The mixture was stirred 1 h at -78 °C, and then it
was allowed to warm at room temperature and stirred for 18
h. Then the solution was treated at -40 °C with 3.5 g of
Me3SnCl (18 mmol) in 5 mL of diethyl ether and stirred
overnight. It was decanted and evaporated to obtain 3.9 g (6.5
mmol) of a yellow-orange oil (mixture of isomers)10b,11 (yield:
74%).
1H NMR (CDCl3): δ 7.47-7.17 (m, 8H, C6H4); 6.35 (s, 2H,
C5 ring CH); 1.85 (s, 2H, CH2 bridge); 1.58 (s, 6H, CH3); -0.11
(s, 18H, Sn(CH3)3).
Syn th esis of r a c-CH2[(3-CH3-1-In d )2]Zr Cl2. A solution of
3.9 g (6.5 mmol) of bis[3-methyl-3(trimethylstannyl)inden-1yl]-
methane in 10 mL of toluene was added dropwise to a
suspension of 1.5 g (6.5 mmol) of ZrCl4 in 22 mL of toluene.
The mixture was stirred 18 h at room temperature, then
stirred for 4 h at 100 °C, and finally cooled to 0 °C. 1.6 g (3.7
mmol) of a deep-red crystalline solid was filtered off and dried
in a vacuum (yield: 42% based on ligand).
1H NMR (CDCl3): δ 7.17-7.28 (m, 8 H, C6H4); 5.64 (s, 2 H,
C5 ring); 4.75 (s, 2H, CH2); 2.35 (s, 6H, CH3). Anal. Calcd for
The ethylene concentration in the liquid phase was calcu-
lated by using the Lewis and Luke’s equation conjoined with
the fugacity function chart of ethylene as reported in the
literature.15
C
21H18Cl2Zr: C, 58.32; H, 4.19. Found: C, 58.64; H, 4.55.
Syn t h esis of r a c-CH 2[(3-CH 3CH 2-1-In d )2]Zr Cl2. The
above-reported procedure was also employed for the synthesis
of rac-CH2[(3-CH3CH2-1-Ind)2]ZrCl2. The pure compound was
obtained by precipitation from toluene (yield: 20% based on
ligand).
Example of Copolymerization. In a 100 mL glass flask were
added, under a nitrogen atmosphere, 10 mL of styrene and
0.64 g of MAO (11 mmol), then the mixture was magnetically
stirred, and the glass flask was thermostated at 60 °C. The
inert atmosphere was removed and replaced with an ethylene-
argon feed (0.06 atm of ethylene partial pressure), and 3 mL
of a 3.6 mM toluene solution of rac-CH2[(3-CH3CH2-1-
Ind)2]ZrCl2 (10 mg in 6 mL of toluene) was introduced. The
steadiness of gaseous mixture composition was monitored via
gas chromatography. The reaction was stopped after 2 h, and
the copolymer was coagulated by pouring the reaction mixture
into acidified methanol, filtered, washed with additional
methanol, and dried in a vacuum (yield: 850 mg)
Bis(1-ethyl-3-indenyl)methane. 1H NMR (CDCl3): δ 7.47-
7.23 (m, 8 H, C6H4); 6.21 (d, 2 H, C5 ring, dCH); 3.75 (s, 2H,
CH2 bridge); 3.05 (m, 2H, C5 ring, CH); 1.55 (m, 4H, CH2); 0.91
(s, 6H, CH3). MS: 300 (M+).
Bis[3-ethyl-3(trimethylstannyl)inden-1yl]methane. 1H NMR
(CDCl3): δ 7.48-7.16 (m, 8 H, C6H4); 6.36 (s, 2 H, C5 ring,
CH); 2.25 (s, 2H, CH2 bridge); 1.56 (m, 4H, CH2); 0.87 (t, 6H,
CH3); -0.11 (s, 18H, Sn(CH3)3).
rac-CH2[(3-CH3CH2-1-Ind)2]ZrCl2. 1H NMR (CDCl3): δ 7.18-
7.48 (m, 8 H, C6H4); 5.67 (s, 2 H, C5 ring); 4.75 (s, 2H, CH2);
2.70 (m, 4H); 1.17 (t, 6H). Anal. Calcd for C23H22Cl2Zr: C,
59.98; H, 4.81. Found: C, 60.04; H, 4.99.
13C NMR An a lysis. The 13C NMR spectra of the hydrooli-
gomers were recorded on an AV 400 Bruker operating at 100
MHz in the Fourier mode at 293 K. The samples (5 mg) were
dissolved in 0.5 mL of CDCl3 into a tube with 5 mm o.d.
Tetramethylsilane (TMS) was used as internal chemical shift
reference. The assignment has been carried out through the
additivity rules16 and through comparison with the literature
data.12
Styr en e Hyd r ooligom er iza tion . Styrene hydrooligomer-
izations were carried out in a 100 mL glass flask charged under
a nitrogen atmosphere with toluene (20 mL) and MAO (8
mmol). The mixture, magnetically stirred, was thermostated
at 20 or 60 °C, and then 2 mL of a 4 mM toluene solution of
the catalyst was added (Al/Zr in mol ) 1000). The inert
atmosphere was removed and replaced with hydrogen, and
then 10 mL of styrene was injected. The flask was fed with
hydrogen over the reaction time. The hydrooligomerization was
stopped after 2 h, adding acidified methanol. The oligomers
were recovered by treating the solution with acidified water,
The 13C NMR spectra of copolymers were recorded in the
same way but dissolving 30 mg of sample in 0.5 mL of CDCl3.
Tetramethylsilane (TMS) was used as internal chemical shift
reference. The relative amount of triads in the ethylene-
styrene copolymers has been evaluated from the NMR spectra

Macromolecules, Vol. 36, No. 25, 2003
CH2-Bridged ansa-Zirconocene-Based Catalysts 9345
as reported in the literature.17 Likewise, the average length
of methylene sequences can be evaluated by means of the
following equation:
(3) For the isospecific styrene polymerization see e.g.: Capac-
chione, C.; Proto, A.; Ebeling, H.; Mulhaupt, R.; Moller, K.;
Spaniol, T. P.; Okuda, J . J . Am. Chem. Soc. 2003, 125, 4964
and references therein.
(4) Ammendola, P.; Tancredi, T.; Zambelli, A. Macromolecules
1986, 19, 2.
(5) (a) Oliva, L.; Caporaso, L.; Pellecchia, C.; Zambelli, A.
Macromolecules 1995, 28, 4665. (b) Caporaso, L.; Izzo, L.;
Oliva, L. Macromolecules 1999, 32, 7329.
LhCH
)
2
0.5(A25.4 + A27.8 + A29.9 + A35.0 + A37.0)/(A35.0 + A37.0
)
(6) Rodewald, S.; J ordan, R. F. J . Am. Chem. Soc. 1994, 116,
4491.
(7) Pellecchia, C.; Longo, P.; Grassi, A.; Ammendola, P.; Zambelli,
A. Makromol. Chem., Rapid Commun. 1987, 8, 277.
(8) Zambelli, A.; Longo, P.; Pellecchia, C.; Grassi, A. Macromol-
ecules 1987, 20, 2035.
(9) Caporaso, L.; Izzo, L.; Sisti, I.; Oliva, L. Macromolecules 2002,
35, 4866.
(10) (a) Resconi, L.; Balboni, D.; Baruzzi, G.; Fiori, C.; Giudotti,
S. Organometallics 2000, 19, 420. (b) Agarkov, A. Y.; Izmer,
V. V.; Riabov, A. N.; Kuz’mina, L. G.; Howard, J . A. K.;
Beletskaya, I. P.; Voskoboynikov, A. Z. J . Organomet. Chem.
2001, 619, 280.
GP C An a lysis. GPC of the copolymers was recorded on a
PSS SDV gel permeation chromatography with three polysty-
rene divinylbenzene gel columns (100, 104, 106 Å pore size), a
WGE refraction index detector using CHCl3 as eluent at 25
°C, a flow rate of 1 mL/min, and standard polystyrene samples
for calibration. The Mw values were in the range between 1.8
× 104 and 1.2 × 105; the polydispersity index was around 10
for all the samples.
GC-MS An a lysis. GC-MS measurements of the mixture of
hydrooligomers were recorded on a GC Trace 2000 SERIES
connected to a Finnigan Thermoquest GLQ Plus 2000 spec-
tometer operating with an ion trap detector.
(11) Nifant’ev, I. E.; Ivchenko, P. V. Organometallics 1997, 16,
713.
(12) Bergman, J .; Egestad, B. Tetrahedron 1986, 42, 763.
(13) Toto, M.; Cavallo, L.; Corradini, P.; Moscardi, G.; Resconi,
L.; Guerra, G. Macromolecules 1998, 31, 3431.
(14) Ready, T. E.; Chien, J . C. W.; Raush, M. D. J . Organomet.
Chem. 1996, 519, 21.
Ack n ow led gm en t. This research was financially
supported by PRIN 2002.
(15) Maxwell, J . B. Data Book on Hydrocarbons; Van Nostrand
Co.: New York, 1950; pp 45, 46, 52, 53.
Refer en ces a n d Notes
(16) Paul, E. G.; Grant, D. M. J . Am. Chem. Soc. 1963, 85, 1701.
(17) Oliva, L.; Longo, P.; Izzo, L.; Di Serio, M. Macromolecules
1997, 30, 5616.
(1) Natta, G.; Pino, P.; Corradini, P.; Danusso, F.; Mantica, E.;
Mozzanti, G.; Moraglio, G. J . Am. Chem. Soc. 1955, 77, 1708.
(2) (a) Po, R.; Cardi, N. Prog. Polym. Sci. 1996, 21, 47. (b)
Pellecchia, C.; Grassi, A. Top. Catal. 1999, 7, 125.
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