A counterintuitive, yet efficient synthesis of bis(indenyl)zirconium dihalides

Article abstract of DOI:10.1016/S0022-328X(03)00124-4

The use of bisindenyl zirconium dimethyl in the synthesis of the corresponding dihalides is described. The synthesis of Ind₂ ZrCl₂ has been carried out, cleanly and quantitatively, by chlorination of Ind₂ZrMe₂ (2) with a variety of inorganic chlorides, including BCl₃, SCl₂ in either toluene or methylene chloride, and HCl in Et₂O. The latter method is the preferred one, since it produces methane as the only byproduct, and the formed Ind₂ZrCl₂ precipitates quantitatively from the Et₂O solvent: a simple filtration then gives the analytically pure product in quantitative yield. Ind₂ZrBr₂ and Ind₂ZrI₂ are obtained by reacting 2 with Br₂ and I₂, respectively. The 'inverse' synthesis of metallocene dichlorides by chlorination of their dimethyl 'derivatives' has advantages compared to the classic method: first, Ind₂ZrCl₂ is obtained in higher yield (90-96%); second, it is easier to purify (at the dimethyl stage) and is obtained free from LiCl. Five bisindenyl zirconium complexes with different sigma ligands have been investigated in solution propylene polymerizations: it is found that the σ-ligands have no relevant influence on the catalyst activity, nor on the polymer properties.

Full text of DOI:10.1016/S0022-328X(03)00124-4

Journal of Organometallic Chemistry 683 (2003) 2ꢀ10
/
www.elsevier.com/locate/jorganchem
A counterintuitive, yet efficient synthesis of bis(indenyl)zirconium
dihalides
Davide Balboni, Isabella Camurati, Antonio Cascio Ingurgio 1, Simona Guidotti,
Francesca Focante, Luigi Resconi *
Basell Polyolefins, Centro Ricerche G. Natta, 44100 Ferrara, Italy
Received 23 December 2002; received in revised form 14 February 2003; accepted 14 February 2003
Abstract
The use of bisindenyl zirconium dimethyl in the synthesis of the corresponding dihalides is described. The synthesis of Ind2ZrCl2
has been carried out, cleanly and quantitatively, by chlorination of Ind2ZrMe2 (2) with a variety of inorganic chlorides, including
BCl3, SCl2 in either toluene or methylene chloride, and HCl in Et2O. The latter method is the preferred one, since it produces
methane as the only byproduct, and the formed Ind2ZrCl2 precipitates quantitatively from the Et2O solvent: a simple filtration then
gives the analytically pure product in quantitative yield. Ind2ZrBr2 and Ind2ZrI2 are obtained by reacting 2 with Br2 and I2,
respectively. The ‘inverse’ synthesis of metallocene dichlorides by chlorination of their dimethyl ‘derivatives’ has advantages
compared to the classic method: first, Ind2ZrCl2 is obtained in higher yield (90ꢀ96%); second, it is easier to purify (at the dimethyl
/
stage) and is obtained free from LiCl. Five bisindenyl zirconium complexes with different sigma ligands have been investigated in
solution propylene polymerizations: it is found that the s-ligands have no relevant influence on the catalyst activity, nor on the
polymer properties.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Zirconium; Synthesis; Chlorination
1. Introduction
Using this synthetic method, Ind2MtMe2 (1, Mtꢂ
2, MtꢂZr, 3, MtꢂHf) are the simplest Group 4
metallocenes to make. Yields (typically 70ꢀ90%) depend
mostly on the purity of the starting reagents and on the
exact stoichiometry, and are similar for the three metals
(Table 1).
We describe here the efficient, ‘inverse’ synthesis of
bisindenyl zirconium dihalides from 2 and their evalua-
tion in propylene solution polymerization in comparison
with analogue complexes bearing different s-ligands.
/
Ti;
/
/
We recently described the ‘direct’ synthesis of Group
4 dimethylmetallocenes by means of the one-pot reac-
tion between the p-ligand, a twofold excess of MeLi, and
MtCl4 [1]. This simple synthetic method allows to obtain
the dimethyl metallocenes in a simple, rapid and
inexpensive way, leading to final yields and purities
which are in most cases higher than the ones obtainable
with the classic two-step route, that is first the synthesis
of the metallocene dichloride (two equivalents of the p-
/
ligandꢁtwo equivalents of MeLi, and then one equiva-
/
2. Results and discussion
lent of MtCl4) followed by its methylation with two
equivalents MeLi (Scheme 1) [2].
The availability of the dimethyl metallocene com-
plexes prompted us to test their conversion into the
corresponding dihalo complexes. This reaction has been
attempted before, by using PbCl2, and shown to be slow
and leading to partial decomposition [3]. Also in our
hands, the reaction of PbCl2 with Ind2ZrMe2 is very
slow, and leads to decomposition with partial formation
* Corresponding author. Tel.:
532468566.
ꢁ
/
39-532468368; fax:
ꢁ39-
/
E-mail address: luigi.resconi@basell.com (L. Resconi).
1
Present address: Pirelli Pneumatici S.p.A., Viale Sarca 222, 20126
Milano, Italy.
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00124-4

D. Balboni et al. / Journal of Organometallic Chemistry 683 (2003) 2ꢀ
/10
3
(two equivalents), which are sufficient to give 90ꢀ
/100%
conversion to Ind2ZrCl2. The reaction with HCl, carried
out in Et2O in which the dichloride is insoluble, is
quantitative and allows for a very simple product
separation: a simple filtration gives spectroscopically
and analytically pure Ind2ZrCl2. NEt3HCl did not prove
a good chlorinating agent.
Scheme 1.
One equivalent FeCl3 (Et2O, 40 8C, 2 h) gave a very
clean and almost quantitative conversion of Ind2ZrMe2
to the monochloro derivative Ind2ZrClMe.
Table 1
Synthesis of bis(indenyl)dimethyl metallocenes
Yield (%) a
CuBr gave mostly the monomethyl derivative in
combination with minor amounts of an as yet unidenti-
fied species. Ind2ZrBr2 and Ind2ZrI2 are obtained by
reacting 2 with Br2 and I2, respectively.
Entry No.
Complex
1
2
3
Ind2TiMe2
Ind2ZrMe2
Ind2HfMe2
79
85
74
The synthesis of Ind2ZrCl2 can be carried out quite
conveniently starting directly from indene and four
equivalents MeLi, without isolating the intermediate
a
From Ref. [1d]. Isolated yields based on the metal, all reactions at
room temperature, using titrated MeLi.
Ind2ZrMe2, in 90ꢀ96% isolated yield of a spectro-
scopically pure product.
The conventional synthesis of Ind2ZrCl2 (reaction of
the lithium salt of indene with ZrCl4) was performed for
comparison: Ind2ZrCl2 was obtained in very high purity
/
of Ind2ZrClMe, in several solvents (toluene, CH2Cl2,
ethers). The synthesis of Ind2ZrClMe from Ind2ZrCl2
and KFꢀAlMe3 in hot heptane with a yield of 71% has
/
been reported in a patent [4].
We have investigated other potential halogenating
agents, and the available results are collected in Table 2.
The chlorination of Ind2MtMe2 to Ind2MtCl2 was first
investigated with Me3SiCl and SiCl4. Me3SiCl gave no
reaction with Ind2ZrMe2 and Ind2HfMe2 (only trace
amounts of the monomethyl derivative was observed).
In the case of Ind2TiMe2, excess SiCl4 gave quantitative
(by 1H-NMR) conversion to Ind2TiClMe. Reacting
Ind2ZrMe2 with two equivalents CuCl, Ind2ZrClMe is
formed. Excess CuCl (five equivalents) is needed to
bring the reaction to complete conversion to Ind2ZrCl2.
More efficient chlorinating agents are BCl3 (one equiva-
lent in CH2Cl2), SCl2 (two equivalents) or HCl in Et2O
but in only 37% isolated yield in THF and 67% in Et2Oꢀ
/
pentane. The product has a low solubility even in
CH2Cl2, and requires a tedious procedure for removing
LiCl. The best literature result reported for the prepara-
tion of Ind2ZrCl2 gives a yield of 58% [5].
Although counterintuitive and requiring the sacrifice
of two equivalents MeLi, at least for the present case the
‘inverse’ synthesis of the metallocene dichloride by
chlorination of its dimethyl ‘derivative’ has some
distinct advantages: first, Ind2ZrCl2 is obtained in
higher yield (90ꢀ100%) compared to the classic method;
/
second, it is easier to purify and is obtained free from
LiCl, since LiCl can be efficiently removed by filtration
Table 2
Synthesis of metallocene dihalides
b
Starting complex
Halogenating agent (equivalents)
Solvent (halog. step)
Product
Yield a (%)
T
(8C)
50
Ind2TiMe2
Ind2ZrMe2
SiCl4 (2ꢁ
/
2)
Toluene
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
Et2O
Ind2TiClMe
Ind2ZrClMe
Ind2ZrClMe
Ind2ZrCl2
100 d
95 d
n.d.
90
23/23ꢀ
/
c
e
FeCl3 (1)
40
23
23
23
c
Ind2ZrMe2
Ind2ZrMe2
CuCl (2.3)
CuCl (5)
CuBr (5)
BCl3 (1)
e
e
Ind2ZrMe2
Ind2ZrMe2
Ind2ZrBrMeꢁ
/
?
n.d.
96
e
Ind2ZrCl2
Ind2ZrCl2
Ind2ZrCl2
0ꢀ
23
23
/23
c
Ind2ZrMe2
Ind2ZrMe2
BCl3 (1)
SCl2 (1.3)
96
c
100
n.d.
96
c
Ind2ZrMe2
Ind2ZrMe2
NEt3HCl (2ꢁ
HCl (2)
Br2 (2)
/3)
Ind2ZrClMeꢁ
/dec.
23ꢀ40
/
c
Ind2ZrCl2
Ind2ZrBr2
Ind2ZrI2
Ind2ZrI2
23
23
23
23
c
Ind2ZrMe2
Ind2ZrMe2
Ind2ZrMe2
CH2Cl2
Toluene
CH2Cl2
50
c
I2 (2)
I2 (2)
100
96
c
a
Isolated yields based on the metal.
b
c
T is the reaction temperature of the halogenation step.
Reaction carried out on isolated Ind2ZrMe2.
By 1H-NMR analysis.
d
e
Reaction carried out on the crude product between indene, MeLi, and ZrCl4, after filtration and drying.

4
D. Balboni et al. / Journal of Organometallic Chemistry 683 (2003) 2ꢀ10
/
Table 3
Chenical shifts (d, CD2Cl2, rt) of Ind2ZrX2 complexes
Xꢂ
/
CH3
Cl
Br
I
Cpꢀ
/
H(1,3)
H(2)
6.13
6.01
6.23
6.55
6.28
6.57
6.42
6.64
Cpꢀ
/
Scheme 2.
Aromatics
7.09ꢀ
/
7.19
7.50
7.28ꢀ
/
7.37
7.30ꢀ
/
7.38
7.70
7.30ꢀ
/
7.40
7.41ꢀ
/
7.60ꢀ
/
7.69
7.63ꢀ
/
7.66ꢀ
/
7.75
from the more soluble dimethyl complex, then the latter
is chlorinated with a reagent such as BCl3, SCl2 or HCl,
that give volatile byproducts (Scheme 2).
In Scheme 3, all reported yields for the synthesis of
Ind2ZrCl2 and Ind2ZrMe2, and their interconversion,
are compared (for details of each method, see Section 3).
The proton NMR resonances of the complexes are
listed in Table 3, showing the good correlation between
the polarizability of the s-ligand and the proton
chemical shifts.
The availability of a series of bisindenylzirconium
complexes carrying different sigma ligands prompted us
to study their use as MAO-activated complexes in
propylene polymerization, with the aim to verify
whether the change of the sigma ligands would induce
any changes in catalyst performance. Propylene poly-
merizations were carried out in toluene solution with the
five metallocenes Ind2ZrCl2, Ind2ZrMe2, Ind2ZrBr2,
Ind2ZrI2, Ind2Zr(OC6F5)2, [1d] with MAO as the
cocatalyst. The results are reported in Table 4. All
catalysts produce low molecular weight, atactic poly-
propylenes, as expected from a fluxional, achiral com-
plex [6]. End groups include a large predominance of
vinylidenes, formed via primary b-H elimination, and
only a minor contribution from 2-butenyl end groups
due to secondary b-H elimination [7]. Differences of
polymer average degree of polymerization, distribution
of end groups and tacticity, between the five catalysts,
are negligible.
3. Experimental
3.1. General procedures and materials
All operations were performed under nitrogen by
using conventional Schlenk-line techniques. Solvents
were purified by degassing with N2 and passing over
activated (8 h, N2 purge, 300 8C) Al2O3, and stored
under nitrogen. MeLi (Acros), TiCl4, ZrCl4, FeCl3,
CuBr, PbCl2 and SiCl4 (Aldrich), HfCl4 (Roc-Ric,
99.99% Hf), CuCl (Carlo Erba, RPE-ACS, 95%), and
SCl2 (Riedel de Haen) were used as received. Technical
indene (Aldrich) was purified by passing over activated
Al2O3. All compounds were analyzed on an AC 200
Bruker spectrometer, by 1H-NMR (200.13 MHz,
CD2Cl2, referenced against the middle peak of residual
CHDCl2 at 5.35 ppm, or C6D6, referenced against the
peak of residual C6D5H at 7.15 ppm) and 13C-NMR
(50.323 MHz, Broad Band Decoupling, C6D6, refer-
enced to the central line of C6D6 at 128.00 ppm). All
NMR solvents were dried over P4O10 or CaH2 and
distilled before use. GC-MS analyses were carried out
on a HP 5890*series 2 gas-chromatograph and a HP
/
5970 mass spectrometer. All dimethyl metal complexes
were isolated by extraction with toluene at room
temperature, or by continuous extraction with refluxing
pentane in a modified Soxhlet apparatus equipped with
a glass filter. All reaction yields are based on the metal.
Caution: the solid residues after extraction of the
reaction mixture might be reactive towards water and
alcohols and must be carefully decomposed (e.g. with
EtOH) under nitrogen. The metal contents were deter-
mined by inductively coupled plasma on an ARL3580
From these results it is clear that, at least for solution
propylene polymerizations, the s-substituent does not
have a significant influence on the polymer molecular
weight, tacticity, or end group structure.
instrument. 1ꢀ/3 were prepared as previously described
[1d].
3.2. Ind2TiClMe
0.43 g of Ind2TiMe2 (1.4 mmol) were dissolved in 15
ml of toluene in a 50 ml Schlenk. 0.32 ml of SiCl4 (99%,
2.79 mmol) were added at room temperature and the
1
solution warmed up to 50 8C and stirred for 3 h. H-
NMR revealed the formation of a 70:30 mixture of
Ind2TiClMe and Ind2TiMe2. To bring the reaction to
completion, additional two equivalents of SiCl4 (0.32
Scheme 3.
ml) were added, and the redꢀorange solution stirred for
/

D. Balboni et al. / Journal of Organometallic Chemistry 683 (2003) 2ꢀ
/10
5
3 more hours at 50 8C, then dried, to give a quantitative
yield of Ind2TiClMe (spectroscopically pure by 1H-
NMR) as a brick red powder.
1H-NMR (C6D6, d, ppm): ꢃ
5.52 (t, CpꢀH(2), 2H, Jꢂ
or 3), 2H, Jꢂ0.88, 1.96, 3.33 Hz), 5.86 (ddd, Cpꢀ
1), 2H, Jꢂ0.88, 1.96, 3.33 Hz), 6.85ꢀ7.31 (m, Ar, 8H).
/
0.08 (s, Tiꢀ
3.33 Hz), 5.80 (ddd, Cpꢀ
H(3 or
/
CH3, 3H),
/
/
/H(1
/
/
/
/
3.3. Ind2ZrCl2, ‘classical’ synthesis in THF
Fourty milliliter of a 1.5 M solution of BuLi in Et2O
(60 mmol) were added dropwise to 7.0 ml of indene (60.0
mmol) in 20 ml of THF, cooled to ꢃ78 8C. At the end
/
of the addition, the solution was allowed to warm to
room temperature and stirred for 1 h, to give an orange
solution. Seven gram of ZrCl4 (30.0 mmol) were
dissolved in 30 ml of THF at ꢃ78 8C in a 100 ml flask
/
equipped with reflux condenser (exothermic reaction).
The mixture was allowed to reach room temperature
with stirring, then refluxed for 30 min, to give a clear,
brown solution. To this solution was added the THF
solution of indenyllithium at room temperature with
stirring, then the resulting suspension was stirred for 2 h.
The color turned yellow. The solvents were removed
under reduced pressure, the residue slurried in Et2O and
transferred into an extractor, washed with Et2O until
colorless, then extracted with CH2Cl2, the extract dried
and washed again with Et2O and then pentane, finally
dried to give 4.35 g of yellow, spectroscopically pure
(1H-NMR) Ind2ZrCl2. Isolated yield 36.9%.
3.4. Ind2ZrCl2, ‘classical’ synthesis in Et2Oꢀpentane
/
9.9 ml of a 1.6 M solution of MeLi in Et2O (15.8
mmol) were added dropwise to 1.97 g of technical
indene (93.3% by GC, 15.8 mmol) in 30 ml of Et2O. At
the end of the addition the mixture was stirred for 40
min at room temperature, then it was added at once to
1.84 g of ZrCl4 (7.9 mmol) slurried in 30 ml of pentane,
then the resulting suspension was stirred for 2 h. The
color turned yellow. The product in pentaneꢀEt2O was
/
transferred into an extractor, filtrated, the filtrate was
discarded, the residue dried and extracted at reflux with
80 ml of CH2Cl2 for 5 h. The extract was dried to give
2.08 g of lemon yellow Ind2ZrCl2, containing 4 mol.% of
Ind2ZrClMe (1H-NMR). Isolated yield 67%.
3.5. Ind2ZrMe2, ‘classical’ synthesis from Ind2ZrCl2
2.38 g (6.1 mmol) of purified Ind2ZrCl2 (purified by
multiple washing with Et2O followed by extraction with
CH2Cl2) were suspended in 60 ml of Et2O, cooled to ꢃ
/
78 8C, and 8 ml of a 1.6 M solution of MeLi in Et2O
(12.8 mmol) added dropwise in 10 min. At the end of the
addition, the mixture was allowed to warm to room
temperature and stirred for 4 h, to give a light brown

6
D. Balboni et al. / Journal of Organometallic Chemistry 683 (2003) 2ꢀ10
/
suspension. The suspension was evaporated under
reduced pressure to give a brown powder, that was
transferred into an extractor, and extracted with pen-
tane at reflux. The extract was brought to dryness under
reduced pressure, to give 1.63 g of white, powdery,
spectroscopically pure (1H-NMR) Ind2ZrMe2. Isolated
yield 76.4%.
reaction mixture was then heated at 40 8C for 3 h, but
1H-NMR analysis showed no reaction progress. Even
adding five equivalents of CuCl (0.64 g, 6.46 mmol) and
heating for 3 h no progress was observed by H-NMR
analysis.
1
3.9. Ind2ZrCl2 from Ind2ZrMe2 and CuCl in CH2Cl2
3.6. Ind2ZrMe2, ‘direct’ synthesis in two-steps
A slurry of CuCl (0.20 g, 2.02 mmol) in 6 ml of
CH2Cl2 was added to a solution of Ind2ZrMe2 (0.69 g,
1.96 mmol) in 15 ml of CH2Cl2. After 40 min the
13.4 ml of a 1.4 M solution of MeLi in Et2O (18.7
mmol) were added dropwise to 2.36 g of technical
indene (92% by GC, 18.7 mmol) in 30 ml of Et2O. At the
end of the addition the mixture was stirred for 60 min at
room temperature, then it was added at once to 2.18 g of
ZrCl4 (9.35 mmol) slurried in 30 ml of pentane, then the
resulting suspension was stirred for 2 h. The color
turned yellow. Additional 13 ml of a 1.4 M solution of
MeLi in Et2O (18.2 mmol) were added dropwise and the
mixture stirred for 1 h. The product was dried in vacuo,
then slurried in 80 ml of pentane and transferred into the
extractor, then extracted at reflux for 5 h. The extract
was dried to give 2.49 g of light brown, spectroscopically
1
suspension turned from orange to black and H-NMR
analysis showed the presence of Ind2ZrClMe. A second
equivalent of CuCl (0.21 g, 2.12 mmol) was then added
with 4 ml of CH2Cl2. After 2 h stirring 1H-NMR
analysis showed the presence of a mixture of Ind2ZrCl2
and Ind2ZrClMe in the ratio 63/37. One additional
equivalent of CuCl (0.19 g, 1.92 mmol) was added to the
reaction mixture. Gas evolution was observed. After 18
h stirring at room temperature 1H-NMR analysis
showed the presence of Ind2ZrCl2 and some free indene.
3.10. Ind2ZrCl2 from Ind2ZrMe2 prepared in situ and
CuCl in CH2Cl2
1
pure (by H-NMR) Ind2ZrMe2 powder. Isolated yield
76%.
Heat stability test: an NMR tube containing this
Ind2ZrMe2 in C6D6 was kept at 70 8C in an oil bath and
monitored by 1H-NMR. After 4 h, the product is
perfectly stable, no decomposition products could be
observed. The same sample proved to be stable also at
room temperature for 72 h.
2.5 g of indene (92 wt.% by GC, 19.8 mmol) were
dissolved in 30 ml of Et2O in a 250 ml Schlenk tube. 24.8
ml of MeLi 1.6 M in Et2O (39.7 mmol) were added with
stirring at room temperature (exothermic reaction).
After stirring for 40 min, a yellowꢀorange solution
/
was obtained, to which was added a suspension of 2.3 g
of ZrCl4 (9.9 mmol) in 40 ml of pentane (exothermic
reaction, the mixture turned dark brown). The mixture
was stirred at room temperature for 2 h, then concen-
trated under reduced pressure to give a black powder,
which was slurried in 50 ml of CH2Cl2, and added of 4.9
g of CuCl (47 mmol). The resulting mixture was stirred
for 3 h at room temperature, then filtered and extracted
with the same CH2Cl2 for 4 h on a continuous extractor
(the product precipitated in part as a yellow solid during
extraction), the extract concentrated under reduced
pressure to give a dark brown powder, which was then
slurried in 50 ml of pentane, filtered, the filtrate
discarded, and the residue brought to dryness under
vacuum to give 3.5 g (90% yield based on Zr) of
spectroscopically pure Ind2ZrCl2.
3.7. Ind2ZrCl2 from Ind2ZrMe2 and CuCl in CH2Cl2
0.33 g of Ind2ZrMe2 (0.94 mmol) were charged in a 10
ml Schlenk tube, and dissolved in 4 ml of CD2Cl2. 0.485
g of CuCl (95%, 4.65 mmol) were added, and the
1
mixture stirred at room temperature for 6 h, when H-
NMR showed the reaction to be complete. Twenty
milliliter of CH2Cl2 were added and the mixture was
filtered over a G4 frit. The yellowꢀ/green solution was
brought to dryness to give 0.34 g of yellowꢀ
/
green
powder (yield 93%) whose 1H-NMR is identical to
that of a true sample of Ind2ZrCl2.
1H-NMR (CD2Cl2, d, ppm): 6.23 (d, H(1ꢀ
/
3), 4H, Jꢂ
3.32 Hz), 7.28ꢀ7.37 (m,
7.69 (m, Ar, 4H).
/
3.32 Hz), 6.55 (t, H(2), 2H, Jꢂ
/
/
Ar, 4H), 7.60ꢀ
/
3.11. Ind2ZrCl2 from Ind2ZrMe2 and BCl3 in CH2Cl2
3.8. Ind2ZrCl2 from Ind2ZrMe2 and CuCl in toluene
0.25 g of Ind2ZrMe2 (0.71 mmol) were dissolved in 10
ml of CH2Cl2 in a 25 ml Schlenk tube, and 0.71 ml of
BCl3 1 M in heptane (0.71 mmol) were added, a yellow
precipitate started to form, and the slurry was stirred at
room temperature for 1 h, when H-NMR showed the
conversion to Ind2ZrCl2 to be quantitative. The yellow
suspension was brought to dryness to give 0.27 g of
A slurry of CuCl (0.42 g, 4.24 mmol) in 15 ml of
toluene was added to a solution of Ind2ZrMe2 (0.71 g,
2.02 mmol) in 15 ml of toluene. The suspension turned
immediately from brown to black. After 24 h stirring,
1H-NMR analysis showed the presence of a mixture of
Ind2ZrCl2 and Ind2ZrClMe in the ratio 89/11. The
1

D. Balboni et al. / Journal of Organometallic Chemistry 683 (2003) 2ꢀ
/10
7
yellow, powdery, spectroscopically pure Ind2ZrCl2
was stirred at room temperature for 2 h, then concen-
trated under reduced pressure to remove about 30 ml of
solvent, the slurry was transferred into the extractor and
extracted at reflux for 3 h (bath temperature 95 8C): the
extracted slurry turned black, although 1H-NMR
showed the presence of pure Ind2ZrMe2 only.
1
(yield 97%). Its H-NMR is identical to that of a true
sample of Ind2ZrCl2.
3.12. Ind2ZrCl2 from Ind2ZrMe2 prepared in situ and
BCl3 in CH2Cl2
8.36 ml of BCl3 1 M in heptane (8.36 mmol) were
added. The mixture was stirred for 30 min at room
temperature, then brought to dryness under reduced
pressure, to give 2.55 g of a 1:1 mixture of Ind2ZrCl2 and
Ind2ZrClMe (1H-NMR), the solid was slurried in 20 ml
of heptane and additional 5.0 ml of BCl3 1 M in heptane
(5.0 mmol) were added, and the mixture stirred over-
night. At this point, H-NMR shows complete conver-
sion to the dichloride, but also a relevant amount of
decomposition to unidentified organic byproducts.
2.5 g of indene (92 wt.% by GC, 19.8 mmol) were
dissolved in 30 ml of Et2O in a 250 ml Schlenk tube. 24.8
ml of MeLi 1.6 M in Et2O (39.7 mmol) were added with
stirring at room temperature (exothermic reaction).
After stirring for 40 min, a yellowꢀorange solution
/
was obtained, to which was added a suspension of 2.3 g
of ZrCl4 (9.9 mmol) in 40 ml of pentane (exothermic
reaction, the mixture turned dark brown). The mixture
was stirred at room temperature for 2 h, then concen-
trated under reduced pressure to give a black powder,
which was slurried in 50 ml of CH2Cl2, cooled to 0 8C,
and added of 9.9 ml of BCl3 1 M in heptane (9.9 mmol).
During the addition, the mixture turned from dark grey
to dark green. This was allowed to warm to room
temperature and stirred for 30 min at room temperature
1
3.15. Ind2ZrCl2 from Ind2ZrMe2 and FeCl3 in CH2Cl2
380 mg of Ind2ZrMe2 (1.08 mmol) were dissolved in 5
ml of CH2Cl2 in a 10 ml Schlenk tube. 175 mg of
anhydrous FeCl3 (99.9%, 1.08 mmol) were added at
room temperature (immediate darkening to black), and
then the mixture is heated at 40 8C for 6 h. After 3 h 1H-
NMR showed the presence of a 98:2 mixture of
Ind2ZrClMe and residual Ind2ZrMe2, traces of the
dichloride, and free from decomposition products. After
another 3 h the dimethyl species was absent, while the
dichloride was increased to 30 mol.% of the total. Traces
of indene were also present. This method appears to be
the most selective towards Ind2ZrClMe.
1
(complete conversion to the dichloride observed by H-
NMR at this time), then filtered and extracted with the
same CH2Cl2 for 8 h on a continuous extractor (the
product precipitated in part as a yellow solid during
extraction), the extract concentrated under reduced
pressure to give a yellow powder, 3.74 g (96% yield
based on Zr) of spectroscopically pure Ind2ZrCl2.
Anal. Calc. for C18H14Cl2Zr: C, 55.09; H, 3.6; Cl,
18.07; Zr, 23.24. Found: C, 54.9; H, 3.5; Cl, 18.5.
3.13. Ind2ZrCl2 from Ind2ZrMe2 and BCl3 in hexane
3.16. Ind2ZrCl2 from Ind2ZrMe2 and NEt3HCl
0.172 g of Ind2ZrMe2 (0.49 mmol) were slurried in 5
ml of hexane in a 10 ml Schlenk tube, and 0.49 ml of
BCl3 1 M in heptane (0.49 mmol) were added at room
temperature, and the mixture stirred for 2 h, to give a
45:55 mixture of Ind2ZrCl2 and Ind2ZrClMe (1H-
NMR); additional 0.3 ml of BCl3 1 M in heptane (0.3
mmol) was added and stirred for additional 2 h. At this
point the reaction was complete and the product
Ind2ZrCl2 was found spectroscopically pure by 1H-
NMR.
157 mg of Ind2ZrMe2(0.45 mmol) were dissolved in 15
ml of CH2Cl2 in a 25 ml Schlenk tube. 125 mg of
NEt3HCl (98%, 0.9 mmol) were added at room tem-
perature and after 10 min stirring the salt was com-
pletely dissolved. After 30 min 1H-NMR showed the
presence of a 60:40 mixture of starting dimethyl and
Ind2ZrClMe, also containing some free indene. After 1 h
at 40 8C, only traces of the starting material were
observed, and the product was mainly Ind2ZrClMe
and indene (26 mol.%). Adding three equivalents excess
NEt3HCl and heating at 40 8C for 2 h only increased the
amount of indene.
3.14. Ind2ZrCl2 from Ind2ZrMe2 prepared in situ and
BCl3 in hexane
1H-NMR (CD2Cl2, d, ppm): ꢃ
6.1ꢀ6.3 (m, CpꢀH, 6H), 7.2ꢀ73 (m, Ar, 4H), 7.4ꢀ
(m, Ar, 4H).
/
0.59 (s, Zrꢀ
/
CH3, 3H),
7.6
/
/
/
/
24.0 ml of MeLi 1.4 M in Et2O (33.5 mmol) were
added with stirring at room temperature (slightly
exothermic reaction) to 2.08 g of indene (93.3 wt.% by
GC, 16.7 mmol) in 60 ml of hexane in a 250 ml Schlenk
3.17. Ind2ZrCl2 from Ind2ZrMe2 and HCl in Et2O
tube. After stirring for 1 h, a cloudy yellowꢀ
/
orange
300 mg of Ind2ZrMe2 (0.85 mmol) were dissolved in
20 ml of Et2O in a 50 ml Schlenk tube. 0.85 ml of a 2 M
solution of HCl in Et2O (1.71 mmol) were added at
room temperature. Gas evolution (CH4) was observed,
solution was obtained, to which was added 1.95 g of
ZrCl4 (8.36 mmol) as a solid (slightly exothermic
reaction, the mixture turned dark brown). The mixture

8
D. Balboni et al. / Journal of Organometallic Chemistry 683 (2003) 2ꢀ10
/
together with instantaneous formation of a yellow
precipitate. After 2 h stirring 1H-NMR showed the
presence of a 80:20 mixture of Ind2ZrCl2 and In-
d2ZrClMe, free from decomposition products. Stirring
for additional 5 h did not change the composition, while
adding additional 0.1 ml of HCl in Et2O (0.2 mmol)
brought the reaction to completion. Removing the
solvent under reduced pressure gave 320 mg of pure
Ind2ZrCl2, yield 96%. This experiment shows that the
reaction between Ind2ZrMe2 and HCl is fast and
quantitative, without decomposition. The lack of com-
plete conversion in the first addition indicates that the
concentration of HCl in Et2O is approximate.
reduced pressure to give a yellow powder which was
1
characterized by H-NMR as a mixture of Ind2ZrCl2
and Ind2ZrClMe in the ratio 93/7. The powder was then
treated with 25 ml of ether, 25 ml of toluene and 1 ml of
the HCl solution previously used (2.1 mmol). After 2 h
stirring the yellow suspension was evaporated to dryness
under reduced pressure to give 4.38 g of a yellow powder
(100% metal-based yield), which was characterized by
1H-NMR as spectroscopically pure Ind2ZrCl2.
3.20. Ind2ZrCl2 from Ind2ZrMe2 and PbCl2 in toluene
A slurry of 2.53 g of PbCl2 (9.10 mmol) in 15 ml of
toluene was added to a solution of Ind2ZrMe2 (1.25 g,
3.56 mmol) in 35 ml of toluene, in a 100 ml Schlenk
flask. The dark orange suspension obtained was stirred
3.18. Ind2ZrCl2 from in situ prepared Ind2ZrMe2 and
HCl in Et2Oꢀtoluene
/
38 h at room temperature and 10 h at 40ꢀ45 8C, during
/
A 1.66 M MeLi solution in Et2O (17.4 ml, 28.9 mmol)
was added over a period of about 5 min at room
temperature under nitrogen atmosphere to a solution of
indene (93.4% by GC-MS, 1.76 g, 14.2 mmol) in 20 ml of
Et2O in a 100 ml Schlenk flask. During the addition
exothermicity and gas evolution were observed. So the
which time formation of a black powder was observed.
The suspension was then filtered on a G4 frit and the
filtrate was evaporated to dryness under reduced
pressure to give 1.1 g of a dark yellow powder, which
was shown by 1H-NMR to contain a mixture of
Ind2ZrClMe and Ind2ZrCl2 in the ratio 90/10.
obtained yellowꢀ
/
orange solution was stirred for 30 min
0.63 g of this mixture were treated with 30 ml of
toluene and 1.2 g of PbCl2 (4.31 mmol). The suspension
obtained was stirred for 30 h at room temperature and
12 h at 40 8C. H-NMR analysis showed some progress
of the reaction to Ind2ZrCl2 but also decomposition of
the product to indene.
at room temperature and then was added to a slurry of
ZrCl4 (1.68 g, 7.21 mmol) in 40 ml of toluene in a 250 ml
Schlenk flask (exothermic reaction). The brown reaction
mixture was stirred for 80 min at room temperature and
then filtered on a G4 frit. Other 10 ml of toluene were
used to transfer completely the final suspension into the
frit. The dark brown filtrate was treated at room
temperature with a 1.87 M HCl solution in Et2O (7.7
ml, 14.4 mmol): during the addition exothermicity and
gas evolution were observed. The resulting lemon yellow
suspension was stirred for 60 min at room temperature,
evaporated to dryness under reduced pressure to give
2.57 g of a salmon colored powder as product. The latter
was then washed with 20 ml of Et2O to give 2.46 g of a
yellow powder (86.9% metal-based yield), which was
characterized by 1H-NMR as spectroscopically pure
Ind2ZrCl2.
1
3.21. Ind2ZrCl2 from Ind2ZrMe2 and PbCl2 in CH2Cl2
A solution of Ind2ZrMe2 (0.71 g, 2.02 mmol) in 10 ml
of CH2Cl2 was added to a suspension of PbCl2 (1.65 g,
5.93 mmol) in 10 ml of CH2Cl2, in a 100 ml Schlenk
flask. The brown suspension formed turned to black in 1
h. After 24 h stirring at room temperature, the suspen-
sion was filtered on a G4 frit and the filtrate evaporated
to dryness under reduced pressure to give 0.62 g of a
yellow powder, which was characterized by 1H-NMR as
a mixture of Ind2ZrClMe and Ind2ZrCl2 in the ratio 91/
9. This powder was then treated with 20 ml of CH2Cl2
and 1.68 g of PbCl2 (6.04 mmol), but after 24 h stirring
at room temperature no reaction progress was observed
Anal. Calc. for C18H14Cl2Zr: C, 55.09; H, 3.60; Cl,
18.07; Zr, 23.24. Found: C, 53.8; H, 3.8.
1H-NMR (CD2Cl2, d, ppm): 6.23 (d, 4H, Cpꢀ
/
H(1,3),
3.32 Hz); 7.28ꢀ
7.69 (m, 4H, Ar).
1
Jꢂ
/
3.32 Hz); 6.55 (t, 2H, Cpꢀ
/
H(2), Jꢂ
/
/
by H-NMR. The reaction mixture was then heated at
35 8C for 24 h, but decomposition of the product was
observed by H-NMR.
7.37 (m, 4H, Ar); 7.60ꢀ
/
1
3.19. Ind2ZrCl2 from Ind2ZrMe2 and HCl in iPr2Oꢀ
/
toluene
3.22. Ind2ZrCl2 from Ind2ZrMe2 and SCl2 in toluene
A 2.1 M solution of HCl in Et2O (titrated against
KOH, 12.2 ml, 25.6 mmol) was added to a solution of
Ind2ZrMe2 (3.92 g, 11.1 mmol) in 60 ml of toluene and
60 ml of diisopropylether, in a 250 ml Schlenk flask. The
yellow suspension obtained was stirred at room tem-
perature for 2 h and then evaporated to dryness under
A solution of SCl2 (0.17 g, 1.65 mmol) in 5 ml of
toluene was added to a suspension of Ind2ZrMe2 (0.50 g,
1.42 mmol) in 12 ml of toluene. During the addition
exothermicity was observed and the reaction mixture
turned immediately from brown to yellow. After 45 min
stirring at room temperature the reaction mixture was

D. Balboni et al. / Journal of Organometallic Chemistry 683 (2003) 2ꢀ
/10
9
evaporated to dryness under reduced pressure to give
0.51 g (91.4% metal-based yield) of a pale-yellow
3.26. Ind2ZrI2 from Ind2ZrMe2 and I2 in CD2Cl2
1
powder which was characterized by H-NMR as spec-
troscopically pure Ind2ZrCl2.
164 mg of of Ind2ZrMe2 (0.46 mmol) were dissolved
in 2 ml of CD2Cl2 in a 10 ml Schlenk tube. 120 mg of I2
crystals (0.47 mmol) were added at room temperature.
The solution was warmed to 40 8C. After 5 min stirring
the I2 was fully solubilized, to give a bright orange
solution that was stirred for 6 h at 40 8C. 1H-NMR
analysis shows the presence of Ind2ZrMe2, Ind2ZrIMe
3.23. Ind2ZrCl2 from Ind2ZrMe2 and SCl2 in CH2Cl2
A solution of SCl2 (0.16 g, 1.55 mmol) in 10 ml of
CH2Cl2 was added to a suspension of Ind2ZrMe2 (0.55
g, 1.56 mmol) in 10 ml of CH2Cl2. During the addition
exothermicity was observed and the reaction mixture
turned clearer. After 3 h stirring at room temperature
the reaction mixture turned reddish and 1H-NMR
analysis showed a mixture of Ind2ZrCl2 and In-
d2ZrClMe in the ratio 61/39. Additional 0.055 g of
SCl2 (0.53 mmol) were added to the reaction mixture.
After 1 h stirring, the brown suspension was evaporated
to dryness under reduced pressure to give 0.61 g (100%
and Ind2ZrI2, in the ratio 6:67:27.
1
Ind2ZrIMe: H-NMR (CD2Cl2, d, ppm): ꢃ
/
1.47 (s, 3
3.52 Hz), 6.39 (m,
H(3,1)), 7.23ꢀ7.28
H, Zrꢀ
2H, Cpꢀ
(m, 4H, Ar), 7.64ꢀ
/
CH3), 6.09 (t, 2H, Cpꢀ
H(1,3)), 6.54 (m, 2H, Cpꢀ
7.69 (m, 4H, Ar).
/
H2, Jꢂ
/
/
/
/
/
Additional 60 mg of I2 were added, and the solution
stirred at room temperature for 72 h. 1H-NMR analysis
showed Â80% conversion to the target Ind2ZrI2.
/
1
Ind2ZrI2: H-NMR (CD2Cl2, d, ppm): 2.19 (CH3I,
cfr. CH3I in CDCl3ꢂ2.16 ppm); 6.42 (d, CpꢀH(1,3),
4H, Jꢂ3.33), 6.64 (t, CpꢀH(2), 2H, Jꢂ3.33), 7.30ꢀ
7.40 (m, Ar, 4H), 7.66ꢀ7.75 (m, Ar, 4H). An impurity
has H-NMR: 1.29 (s), ca. 6.6, ca. 6.8 (CpꢀH), 7.9 (m).
1
metal-based yield) of a clear brown powder. H-NMR
/
/
analysis showed the presence of Ind2ZrCl2 together with
a minor amount of unidentified impurities.
/
/
/
/
/
1
/
3.24. Reaction of Ind2ZrMe2 with CuBr
3.27. Ind2ZrI2 from Ind2ZrMe2 and I2 in toluene
A suspension of 0.40 g of CuBr (98%, 2.7 mmol) in 5
ml of CH2Cl2 was added to a solution of 0.46 g of
Ind2ZrMe2 (1.3 mmol) in 10 ml of CH2Cl2. The black
suspension obtained was stirred at room temperature for
4 h. After that time 1H-NMR analysis showed the
presence of Ind2ZrMeBr. The solution was then heated
at 40 8C for 4 h. 1H-NMR analysis showed the presence
of a mixture of Ind2ZrBr2 and Ind2ZrMeBr in a 1:1
ratio.
Crystals of I2 (0.70 g, 2.76 mmol) were added to a
suspension of Ind2ZrMe2 (0.48 g, 1.36 mmol) in 20 ml of
toluene. The orange suspension turned to dark purple in
a few minutes. After 30 min stirring at room tempera-
ture, the suspension was evaporated to dryness under
reduced pressure to give 0.83 g (100% yield) of an orange
1
powder, which was characterized by H-NMR as pure
Ind2ZrI2.
Ind2ZrMeBr was characterized by 1H-NMR (CD2Cl2,
1H-NMR (CD2Cl2, d, ppm): 6.42 (d, 4H, Cpꢀ
/
H(1,3),
3.33 Hz); 7.30ꢀ
7.75 (m, 4H, Ar).
d, ppm): ꢃ
CpꢀH(1,2,3); 7.21ꢀ
Ar).
/
0.93 (s, 3H, Zrꢀ
/
CH3), 6.20ꢀ
/
6.29 (m, 6H,
Jꢂ
/
3.33 Hz); 6.64 (t, 2H, Cpꢀ
/
H(2), Jꢂ
/
/
/
/
7.29 (m, 4H, Ar); 7.44ꢀ
/7.64 (m, 4H,
7.40 (m, 4H, Ar); 7.66ꢀ
/
3.28. Ind2ZrI2 from Ind2ZrMe2 and I2 in CH2Cl2
3.25. Ind2ZrBr2 from Ind2ZrMe2 and Br2
Crystals of I2 (0.72 g, 2.84 mmol) were added to a
suspension of Ind2ZrMe2 (0.50 g, 1.42 mmol) in 20 ml of
CH2Cl2. The orange suspension turned to dark purple in
few minutes. After 30 min stirring at room temperature,
the suspension was evaporated to dryness under reduced
pressure to give 0.79 g (96% yield) of an orange powder,
A solution of 0.59 g of Br2 (3.69 mmol) in 7 ml of
CH2Cl2 was added to a solution of 0.65 g of Ind2ZrMe2
(1.85 mmol) in 20 ml of CH2Cl2. The reaction was
exothermic, and gas evolution was observed. The light
brown suspension obtained was stirred at room tem-
perature for 18 h and then evaporated to dryness under
reduced pressure to give 1.11 g of a brick-red powder.
To remove the impurities, this powder was taken up in
30 ml of Et2O and filtered. No product dissolved in
Et2O. The residue was further purified by dissolving in
toluene and filtering. The filtrate was evaporated to
dryness under reduced pressure to give Ind2ZrBr2, pure
1
which was characterized by H-NMR as pure Ind2ZrI2.
3.29. Polymerization of propylene
The polymerizations were carried out in a 260 ml
Buchi glass reactor equipped with a mechanical stirrer, a
¨
thermocouple and monomer feeding line. The autoclave
was purged with N2, filled with 95 ml of toluene
containing 0.1 mmol AlEt3, warmed at 30 8C and
purged with propylene. The catalytic system was pre-
pared in 5 ml of toluene by mixing 6 mmol of the
1
by H-NMR. Yield 50%.
1H-NMR (CD2Cl2, d, ppm): 6.28 (d, 4H, Cpꢀ
/
H(1,3),
3.42 Hz); 7.30ꢀ
7.70 (m, 4H, Ar).
Jꢂ
/
3.42 Hz); 6.57 (t, 2H, Cpꢀ
/
H(2), Jꢂ
/
/
7.38 (m, 4H, Ar); 7.63ꢀ
/

10
D. Balboni et al. / Journal of Organometallic Chemistry 683 (2003) 2ꢀ10
/
metallocene and 3 mmol of MAO (Witco, 10% w/v
solution in toluene, used as received, AlMAO Zrꢂ500).
equivalents MeLi, yields the product in 90ꢀ100%
isolated yield and with a much easier purification
procedure.
/
ꢀ
/
/
This solution was introduced into the reactor after less
than 30 s stirring at room temperature, the reactor was
closed and the pressure raised to 4 bar g and kept
constant by feeding propylene. After 30 min, the
polymerization was stopped by degassing the reactor
and adding 1.5 ml of methanol. The solution was filtered
to remove the catalyst residues, and evaporated to
dryness. The low molecular weight, atactic PP produced
were dried overnight in a vacuum oven.
This procedure, for the bisindenylmetal halides,
appears to be more convenient than that recently
reported by Eisch et al. [8].
By reaction of Ind2ZrMe2 with one equivalent FeCl3,
the monochloro derivative Ind2ZrClMe is obtained
(98% conversion by 1H-NMR), while Ind2ZrBr2 and
Ind2ZrI2 are formed in good yields by reaction with Br2
and I2, respectively.
The availability of complexes with different sigma
ligands has prompted us to investigate the influence of
the latter on the polymerization performance of the
MAO-activated catalysts. We found that, in solution
propylene polymerizations, the s-ligands have no influ-
ence on polymer tacticity, molecular weights or end-
group structures. A possible influence of the s-ligands
on the rate and extent of catalyst activation would be a
further topic for study.
3.30. Polymer analysis
The 13C-NMR spectra were acquired at 120 8C on a
Bruker DPX-400 spectrometer, operating in the Fourier
transform mode at 100.61 MHz. The samples were
dissolved in C2D2Cl4 with a concentration of 8% w/v.
The spectra were acquired with a 908 pulse and 12 s of
delay between pulses. About 1500 transients were stored
for each spectrum. Proton spectra were acquired with a
458 pulse and 5 s of delay between pulses on the same
spectrometer at 120 8C. 256 transients were stored for
each spectrum. As references, the residual peak of
References
1
C2DHCl4 in the H spectra (5.95 ppm) and the peak
of the mmmm pentad in the 13C spectra (21.8 ppm) were
used.
[1] (a) L. Resconi, D. Balboni, G. Prini, Int. Pat. Appl. WO 99/36427
to Montell, 1999, (priority 14.1.98).;
(b) L. Resconi, D. Balboni, G. Baruzzi, C. Fiori, S. Guidotti,
Organometallics 19 (2000) 420;
(c) D. Balboni, G. Prini, M. Rinaldi, L. Resconi, Am. Chem. Soc.
Polym. Prepr. 41 (2000) 456;
4. Conclusions
(d) D. Balboni, I. Camurati, G. Prini, L. Resconi, S. Galli, P.L.
Mercandelli, A. Sironi, Inorg. Chem. 40 (2001) 6588.
[2] For the original synthesis of Ind2MtMe2: (a) E. Samuel, M.D.
Rausch, J. Am. Chem. Soc. 95 (1973) 6263;
(b) E. Samuel, H.G. Alt, D.C. Hrncir, M.D. Rausch, J. Organo-
met. Chem. 113 (1976) 331;
We have found that the ‘inverse’ synthesis of
Ind2ZrCl2 can be carried out, cleanly and quantitatively,
by chlorination of Ind2ZrMe2 with excess CuCl, one
equivalent BCl3, SCl2, or two equivalents HCl in Et2O.
The latter method is the preferred one, since it produces
methane as the only byproduct, and the formed
Ind2ZrCl2 precipitates quantitatively from the Et2O
solvent: a simple filtration then gives the analytically
pure product in quantitative yield.
(c ) A.R. Siedle, R.A. Newmark, J. Organomet. Chem. 497 (1995)
119;
(d) R.U.S. Lisowsky, Pat. 5,523,435 to Witco GmbH, 1996,
(priority 13.5.1994).
(e) T.J. Park, B.W. Woo, S.C. Yoon, S.C. Shim, J. Organomet.
Chem. 535 (1997) 29.
[3] G.A. Razuvaev, V.N. Latyaeva, L.I. Vyshinskaya, G.A. Vasil’eva,
V.I. Khruleva, L.I. Smirnova, Dokl. Akad. Nauk SSSR 231 (1976)
114.
Although counterintuitive, the synthesis of metallo-
cene dichlorides by chlorination of their dimethyl
‘derivatives’ has some manifest advantages: first,
Ind2ZrCl2 is obtained in higher yield compared to the
classic method; second, it is easier to purify (at the
dimethyl stage) and is obtained free from LiCl. In
summary, while the ‘classic’ route to Ind2ZrCl2 gives
[4] R.U.S. Lisowsky, Pat. 5,523,435 to Witco GmbH, 1996, (priority
13.5.1994).
[5] A.R. Siedle, R.A. Newmark, W.M. Lamanna, J.N. Schroepfer,
Polyhedron 9 (1990) 301.
[6] L. Resconi, L. Abis, G. Franciscono, Macromolecules 25 (1992)
6814.
37ꢀ67% yield of a low solubility product that requires a
/
[7] L. Resconi, I. Camurati, O. Sudmeijer, Top. Catal. 7 (1999) 145.
[8] J.J. Eisch, F.A. Owuor, P.O. Otieno, Organometallics 20 (2001)
4132.
tedious procedure for removing LiCl, the ‘inverse’
synthesis, although requiring the sacrifice of two