Control of symmetry in active cationic ansa-zirconocene species: Catalyst preparation, characterization and ethylene-norbornene copolymerization

Article abstract of DOI:10.1016/j.jorganchem.2004.08.013

New bis-hydrocarbyl complexes of methylene bridged ansa-metallocenes [H₂Me₂H₂)₂]ZrR₂ {R = Me (1), CH₂Ph (2), CH₂SiMe₃ (3), Ph (4)} have been prepared. They form catalytically active intermediates with borane or borate depending on solvent and Zr-R group. Specifically, [H₂C(Me₂C₅H₂)₂] Zr(CH₂Ph)₂ (2) produced an ion pair upon treatment with B(C₆F₅)₃ whereas [H₂ C(Me₂C₅H₂)₂]Zr(CH₂ SiMe₃)₂ (3) produced a zwitterionic species, identified by ¹H,¹³C, and ¹⁹F NMR spectroscopy. Copolymerization of ethylene and norbornene for the metallocene dichloride/MAO and bis-hydrocarbyl complex/borate systems was compared.

Full text of DOI:10.1016/j.jorganchem.2004.08.013

Journal of Organometallic Chemistry 689 (2004) 3402–3411
www.elsevier.com/locate/jorganchem
Control of symmetry in active cationic ansa-zirconocene
species: catalyst preparation, characterization and
ethylene–norbornene copolymerization
a,
a
a
a
Hyosun Lee *, Sung-Don Hong , Young-Whan Park , Boong-Goon Jeong
Dae-WooNamaHye Young Jung , Min Whan Jung , Kwang Ho Song
a
a
b
a
LG Chemical Ltd., Research Park, Munji-dong, Yuseong-gu, Daejon city 305-380, Republic of Korea
b
Department of Chemical and Biological Engineering, Korea University 1,5-ka, Anam-dong, Sungbuk-ku, Seoul 136-701, Republic of Korea
Received 25 June 2004; accepted 6 August 2004
Available online 11 September 2004
Abstract
New bis-hydrocarbyl complexes of methylene bridged ansa-metallocenes [H2C(C5Me2H2)2]ZrR2 {R = Me (1), CH2Ph (2),
CH2SiMe3 (3), Ph (4)} have been prepared. They form catalytically active intermediates with borane or borate depending on solvent
and Zr–R group. Specifically, [H2C(Me2C5H2)2]Zr(CH2Ph)2 (2) produced an ion pair upon treatment with B(C6F5)3 whereas
[H2C(Me2C5H2)2]Zr(CH2SiMe3)2 (3) produced a zwitterionic species, identified by 1H, 13C, and 19F NMR spectroscopy. Copolym-
erization of ethylene and norbornene for the metallocene dichloride/MAO and bis-hydrocarbyl complex/borate systems was
compared.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: ansa-Zirconocene; Bent metallocene; Borane; Borate; Copolymerization; Ethylene; Ion pair; Norbornene; Zwitterion
1. Introduction
create synthetic challenges. Alternative to preparing
non-MAO catalytic systems for olefin polymerization
is the ternary system, wherein an aluminum reagent is
used to give the metallocene ‘‘alkyl complex’’ in situ fol-
lowed by the use of a non-metallic cocatalyst such as
borane or borate [4,5].
To date, many reactions of hydrocarbyl metallocene
and Lewis acidic B(C6F5)3 or other borate salt such as
[Me2PhHN][B(C6F5)4] and [Ph3C][B(C6F5)4] have been
studied to elucidate the nature of the active metallocene
species [6]. Two species exist: the zwitterion and the ion
pair. For the ion-pair polymerization activity is gener-
ally higher [7]. The cocatalyst may change the environ-
mental sphere and reactivity [8]. In this paper, we
describe the synthesis and characterization of bis-hydro-
carbyl complexes of methylene bridged ansa-zirconoce-
nes. These complexes demonstrate different reactivity
towards cocatalysts; metallocene dihalide/MAO for
Many different group 4 metallocene hyrodrocarbyl
complexes have been previously synthesized, character-
ized and used industrially for a-olefin (co)polymeriza-
tion in combination with borane or borate cocatalysts
[1]. These catalytic precursors are attractive since they
bypass the use of a large amount of methylaluminoxane
(MAO), and production of polymer ash and metal con-
tent [2]. Borane and borate cocatalysts can be used in
equivalent amounts, but then hydrocarbyl derivatives
of the zirconocene are required [3]. In these reactions,
UV–Vis light, heat and solvent sensitivity of the species
*
Corresponding author. Tel: +82 42 866 2758; fax: +82 42 861
3647.
E-mail address: hyobone@lgchem.com (H. Lee).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.08.013

H. Lee et al. / Journal of Organometallic Chemistry 689 (2004) 3402–3411
3403
norbornene and ethylene copolymerization activities
have been compared.
ing on the extent of charge separation, there may be
either a zwitterion or a complete separation into an
ion pair from which changes in polymerization activity
arise [13]. Unlike B(C6F5)3, salt cocatalysts such as
[Me2PhHN][B(C6F5)4] and [Ph3C][B(C6F5)4] attack the
M–R group giving an active ionic species. Thus, reac-
tions with borates were favored entropically over bora-
nes as inferred from Scheme 2. So far, many reactions
of hydrocarbyl metallocenes with aryl boranes or borate
salt such as [Me2PhHN][B(C6F5)4] and [Ph3C][B(C6F5)4]
both inpolar and non-polar solvents have been studied
to elucidate the nature of the cationic metallocene active
species [14,15].
We have investigated the reactivity of hydrocarbyl
complexes with each cocatalyst in different solvent
and the stability of the active species. An equimolar
amount of hydrocarbyl complex and cocatalyst were
combined into solution and monitored by observation
of color change or oil formation and by NMR
spectroscopy.
2. Results and discussion
2.1. Preparation and characterization of complexes 1–4
The dichloride complex [H2C(C5Me2H2)2]ZrCl2 was
used to afford hydrocarbyl complexes 1 through 4 as
illustrated in Scheme 1 [9,10].
The chemical stability of each hydrocarbyl complex
of potential industrial importance was investigated.
Complexes 1 through 4 were stable at 80 ꢁC for one
day (toluene, benzene), whereas [H2C(C5Me2H2)2]ZrPh2
underwent reaction in toluene at 80 ꢁC to eliminate ben-
zene [11], but resisted decomposition in CH2Cl2.
2.2. Formation and identification of the zirconocene ion
pair
In general the zircononcene bis-hydrocarbyl complex
undergoes reaction with a cocatalyst to form a species
that exhibits some level of olefin polymerization activity
[12]. Specifically, the Lewis acidic B(C6F5)3 serves to ab-
stract a hydrocarbyl group (RÀ) to give an electron poor
metal center. The ability for borane to perform alkyl-
group abstraction depends on M–R bond strength and
the ability for RÀ to stabilize a negative charge. Depend-
2.2.1. The formation and characterization of an ion pair
with complex [H2C(C5Me2H2)2]ZrMe2 (1)
The complex [H2C(Me2C5H2)2]ZrMe2 underwent
reaction with [Me2PhHN][B(C6F5)4] and [Ph3C]-
[B(C6F5)4] immediately to give an oil precipitate not able
to be characterized by NMR spectroscopy. Also com-
bining [H2C(Me2C5H2)2]ZrMe2 with [Ph3C][B(C6F5)4]
in CH2Cl2 gave an immediate red color change to give
CH2Ph
Me
H
H
PhCH2MgCl
MeLi
Zr
Zr
THF
Ether
CH2Ph
Me
H
H
Cl
H
(2)
(1)
Zr
Cl
H
Ph
CH2SiMe3
H
H
PhLi
Zr
Me3SiCH2Li
Zr
THF
Ether
Ph
H
CH2SiMe3
H
(3)
(4)
Scheme 1. New methylene bridged bis-hydrocarbyl ansa-zirconocene complexes 1–4.
_
_
+
[H2C(Me2C5H2)2]ZrR2
Me2PhNHB(C6F5)4
{H2C(Me2C5H2)2ZrR} {RB(C6F5)4}
+
Me2PhN
PhCH3
+
+
+
[H2C(Me2C5H2)2]ZrR2
[H2C(Me2C5H2)2]ZrR2
{H2C(Me2C5H2)2ZrR} {RB(C6F5)4}
Ph3CB(C6F5)4
B(C6F5)3
+
+
Ph3CCH2Ph
+
_
+
{H2C(Me2C5H2)2ZrR} {RB(C6F5)3}
Scheme 2. Hydrocarbyl complexes with various cocatalysts.

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H. Lee et al. / Journal of Organometallic Chemistry 689 (2004) 3402–3411
1H NMR spectral peaks assigned to {[H2C(Me2C5H2)2]-
[Ph3C][B(C6F5)4] but then quickly decomposed. How-
ever, {[H2C(Me2C5H2)2]ZrPh}+{B(C6F5)4}À (4a) pro-
duced from the cocatalyst [Ph3C][B(C6F5)4] in toluene
was green and characterized from assignments made in
Zr(CH3)}+{B(C6F3)4}À (1a).
2.2.2. The formation and characterization of an ion pair
from complex [H2C(Me2C5H2)2]Zr(CH2Ph)2 (2)
The complex [H2C(Me2C5H2)2]Zr(CH2Ph)2 under-
went reaction with [Me2PhHN][B(C6F5)4], [Ph3C]-
[B(C6F5)4] and B(C6F5)3 immediately in toluene to give
1
the H NMR spectrum. In contrast, the complex 4 did
not react with B(C6F5)3, even in CH2Cl2. 1H NMR spec-
tral signals of identified species 2a–4a in each solvent are
listed in Section 4.
1
a soluble ion pair characterized by H NMR spectros-
copy as {[H2C(Me2C5H2)2]Zr(CH2Ph)}+{B(C6F5)4}À (2a).
However, the complex [H2C(Me2C5H2)2]- Zr(CH2Ph)2
underwent decomposition in the presence of [Ph3C]-
[B(C6F5)4] and B(C6F5).
2.2.5. Specific reactions of [H2C(Me2C5H2)2]Zr(CH3)2
(1), [H2C(Me2C5H2)2]Zr(CH2Ph)2 (2), and [H2C-
(Me2C5H2)2]Zr(CH2SiMe3)2 (3) with B(C6F3)3
Complexes 1, 2 and 3 showed distinctive reactivity
with B(C6F3)3 [16]. The ion pair {[H2C(Me2C5H2)2]-
Zr(CH3)}+{(CH3)B(C6F5)3}À (1b) was obtained clearly
in toluene, but became an immiscible oil in benzene.
When 3 was treated with B(C6F5)3 the species 3b was
2.2.3. The formation and characterization of an ion pair
from complex [H2C(Me2C5H2)2]Zr(CH2SiMe3)2 (3)
The
complex
[H2C(Me2C5H2)2]Zr(CH2SiMe3)2
1
formed; structural differences were observed by H, 13C
underwent reaction immediately with [Me2PhHN]-
[B(C6F5)4] in both toluene and CH2Cl2 to give a soluble
species identified by 1H NMR spectroscopy. {[H2-
C(Me2C5H2)2] Zr(CH2SiMe3)}+{B(C6F3)4}À (3a) after
treatment with [Me2PhHN][B(C6F5)4] was green in
CH2Cl2. The same species 3a was not produced from
the cocatalyst [Ph3C][B(C6F5)4] either in toluene or
CH2Cl2 even at elevated temperature, and gave a prod-
uct of decomposition with B(C6F5)3 in CH2Cl2.
NMR and 19F NMR spectroscopy. All complexes 1, 2
and 3 exhibited C2v molecular symmetry in solution, as
determined by NMR spectroscopy and were strictly
speaking ion pairs in which the anion is located outside
the metal coordination sphere [17] as in complexes 1, 2
and 3. It is proposed that the species {[H2C(Me2C5H2)2]-
Zr(CH2Ph)}+{(CH2Ph)B(C6F5)4}À (2b) exists as an ion
pair in toluene with one benzyl group bound to boron
1
in the anion, assigned by H NMR spectroscopy (Fig.
2). Thus, two hydrogens of the methylene bridge and
the four Cp methyls and hydrogens were chemically shift
2.2.4. The formation and characterization of an ion pair
from complex [H2C(Me2C5H2)2]ZrPh2 (4)
The complex [H2C(Me2C5H2)2]ZrPh2 immediately
underwent reaction with [Me2PhHN][B(C6F5)4] and
1
equivalent as reflected by the H NMR and 13C NMR
spectrum; these signals are consistent with the assignment
Fig. 1. 1H NMR of C2v symmetric complex 1 and Cs symmetric 1b.

H. Lee et al. / Journal of Organometallic Chemistry 689 (2004) 3402–3411
3405
Fig. 2. 1H NMR of C2v symmetric complexes 2 and 2b.
of C2v symmetry [18]. Also two distinct benzyl groups are
spectroscopically observed; one is present at the metal
center while the other is connected to the anion.
Zr(CH2SiMe3)}d+{(Me3SiCH2)B(C6F5)3}dÀ with partial
charges at zirconium and boron.
Only three resonances in each 19F NMR spectrum
were observed for 2b and 3b; these shifts were different
from those of free B(C6F5)3, indicating an interaction
between borane and an alkyl group. As shown in
Scheme 3, the ability to form metallocene ions with
B(C6F5)3 depends on the Zr–R group.
In contrast, {[H2C(Me2C5H2)2]Zr(CH3)}+{(CH3)B-
(C6F5)3}À (1b) and {[H2C(Me2C5H2)2]Zr(CH2SiMe3)}+
{(Me3SiCH2)B(C6F5)3}À (3b) exist as an ion pair, judg-
1
ing from the Cs molecular symmetric species in H and
13C NMR spectrum instead of C2v symmetry (Figs. 1
and 3). This would place a weak positive and a negative
charge at zirconium and boron, respectively. In this way
one methyl or (trimethylsilyl)methyl group is covalently
bonded to zirconium while another interacts with bor-
ane. The two Cp hydrogen and methyl groups in 1b
and 3b were inequivalent and the methylene bridge
hydrogens were diastereotopic. Additionally, there exist
two doublets for the [H2C] bridge resonances in 3b,
whereas the [H2C] signal in 1b is assignable as an AB
quartet (Fig. 3). In this way, both 1b and 3b can be con-
sidered as a contact ion pair with Cs molecular symme-
try. In addition, the spectrum of 3b shows that the
(trimethylsilyl)methyl group interacting with borane fea-
tures methyl groups in two different environments in the
1H NMR spectrum suggesting that one methyl group is
interacting closely with borane. In 3b there exists three
separate upfield carbon NMR signals associated with
{(Me3SiCH2)B(C6F5)3}À below ca. 10 ppm in the 13C
NMR spectrum, along with distinctive Cp methyl
signals, supporting Cs molecular symmetry. Thus, 3b
might be better represented as {[H2C(Me2C5H2)2]-
Reactions of 1–4 with the different cocatalysts in dif-
ferent solvent are summarized in Table 1.
2.3. Copolymerization of ethylene–norbornene using the
ion paired metallocene species
Since
methylene
bridged
ansa-zirconocenes
[H2C(Me2C5H2)2]ZrCl2 (5) were known for high copo-
lymerization activity with ethylene and norbornene, all
species here from 5 were tested for this copolymerization
activity with borane or borate. Unlike for MAO
systems, use of a scavenging agent such as triisobutylal-
uminum (TIBA) was required here in the polymer-
ization solution. Owing to the insolubility of
[Me2PhHN][B(C6F5)4] and B(C6F5)3 in toluene at room
temperature, the formation of the active species was car-
ried out under heating at 60 ꢁC. In contrast, cocatalyst
solubility was greater in CH2Cl2, and thus preactivation
could be carried out at room temperature. All identified
ionic species (2a, 3a and 2b) exhibited copolymerization
activity comparable to the 5/MAO system; the results of

3406
H. Lee et al. / Journal of Organometallic Chemistry 689 (2004) 3402–3411
Fig. 3. 1H NMR of C2v symmetric complex 3 and Cs symmetric 3b.
CH3
CH3
H
H
B(C6F5)3
+
Zr
Zr
(1b)
_
CH3
H
H
CH3B(C6F5)3
CH2Ph
CH2Ph
B(C6F5)3
_
H
H
+
Zr
Zr
[(PhCH )B(C F ) ]
CH2Ph
2
6 5 3
H
H
(2b)
CH2SiMe3
CH2SiMe3
CH2SiMe3
H
H
δ+
Zr
H
B(C6F5)3
δ -
Zr
CH2
Si
B(C6F5)3
H
CH3
H3C
(3b)
CH3
Scheme 3. Reactions of {[H2C(Me2 C5H2)2]ZrR2with B(C6F5)3}.
copolymerization of ethylene–norbornene are summa-
rized in Table 2. The active species {[H2C(Me2C5H2)2]
ZrPh}{B(C6F5)4} (4a) did not produce a copolymer.
Despite known catalysis for the CpTiPh2/MAO system
producing isotactic polypropylene and known nickel
(II) catalysis, we suggest that in this system the propagation

H. Lee et al. / Journal of Organometallic Chemistry 689 (2004) 3402–3411
3407
Table 1
Reactivity of hydrocarbyl complexes and cocatalysts in solvents (25 ꢁC)
Cocatalyst:
Solvent:
[Me PhHN][B(C6F5)4]
2
[Ph 3C][B(C6F5)4]
C7 D8
B(C 6F5)3
C7D8
C7D8
CD2Cl2
CD2Cl2
CD2Cl2
Catalyst
1
2
3
4
Oila
2a
Decomp.
2a
Oil
2a
N.R.b
4ac
1a
1b
2b
Decomp.
Decomp.
Decomp.
N.R.
Decomp.
N.R.
Decomp.
3a
4ac
3a
4ac
3b
N.R
a
Immediate reaction giving an immiscible oil not characterized by NMR spectroscopy.
No reaction at room temperature or elevated temperature.
The reaction formed an oil which quickly decomposed.
b
c
Table 2
Ethylene–norbornene copolymerization resultsa
Species
Catalyst
Cocatalyst
Yield(g)c
Activityd
Tg (ꢁC)
Mw
Mw/Mn
2a
2a
2ab
3a
3a
3ab
4a
2b
3b
5ce
2dg
a
2
2
2
3
3
3
4
2
3
5
2
[Me2PhHN][B(C6F5)4]
[Ph3C][B(C6F5)4]
[Me2PhHN][B(C6F5)4]
[Me2PhHN][B(C6F5)4]
[Ph3C][B(C6F5)4]
[Me2PhHN][B(C6F5)4]
[Me2PhHN][B(C6F5)4]
B(C6F5)3
34.7
26.2
26.8
30.4
26.4
26.3
19.9
16.2
23.1
20.0
–
239
229
233
234
230
–
102,000
123,000
N/A
1.6
1.6
N/A
1.6
1.6
–
127,000
117,000
–
f
–
f
–
18.1
–
–
–
–
13.7
–
222
–
139,000
–
1.6
–
f
–
B(C6F5)3
MAO
MAO
55.1
50.0
41.3
33.3
228
–
10,800
–
1.6
–
Polymerization conditions: zirconocene 4 lmol, TIBA 1 mL, toluene 150 mL (56 wt% norbornene), Tp = 70 ꢁC, Pp = 60 psi.
Preactivation of catalyst with cocatalyst in CH2Cl2 at room temperature for 2 min was conducted.
Yield is defined as the weight of copolymer obtained.
b
c
d
e
Activity in kg COC/mmol of Zrꢀh.
Polymerization conditions: zirconocene 4 lmol, Al/Zr = 2000, toluene 150 mL (56 w% norbornene), Tp = 70ꢁC, Pp = 60 psi, without
preactivation.
f
No polymerization occurred.
Polymerization conditions: zirconocene 4.5 lmol, Al/Zr = 2000, toluene 150 mL (56 wt% norbornene), Tp = 70ꢁC, Pp = 60 psi, without
g
preactivation.
step fails to proceed due to the presence of a Zr–Ph
group [20]. In addition, 2a from [Me2PhHN][B(C6F5)4]
in CH2Cl2 exhibited moderate copolymerization activ-
ity, while 3a from [Me2PhHN][B(C6F5)4] in CH2Cl2
shows no activity for copolymerization. Interestingly
{[H2C(Me2C5H2)2]Zr(CH2SiMe3)}d+{(Me3SiH2C)B(C6-
F5)3}dÀ (3b) did not form polymer, suggesting that the
zirconium center is too electron rich to conduct polym-
erization. For the active species of [H2C(Me2C5H2)2]
ZrMe2 with borane or borate, less than one gram of
copolymer was produced compared with the yields given
in Table 2. However, this complex is used in a ternary
system (1 with triisobutylaluminum and [Ph3C]-
[B(C6F5)4]), where the activity was 18 kg COC/mmol
of Zrꢀh. In this respect, cocatalyst decreases in the order
[Me2PhHN][B(C6F5)4] > [Ph3C][B(C6F5)4] > B(C6F5)3 when
considering a given hydrocarbyl. The nature of a given
hydrocarbyl group does affect the stability of the ionic
species and ultimately olefin polymerization activity
[21]. Catalytic use of MAO in copolymerization requires
a larger stochiometric amount than borate use does, but
the basic properties (such as Tg, Mw and PDI values) of
the resulting polymers were quite similar [19].
3. Conclusion
In summary, four bis-hydrocarbyl methylene bridged
ansa-metallocenes were synthesized and gave stable ion
pairs with cocatalysts [Me2PhHN][B(C6F5)4], [Ph3C]-
[B(C6F5)4] and B(C6F5)3. The activity of borane towards
these hydrocarbyl complexes is dependent on the Zr–R
group. The preactivated [H2C(C5Me2H2)2]Zr(CH2Ph)2/
[Me2PhHN][B(C6F5)4] system shows the highest activity
in norbornene/ethylene copolymerzation.
4. Experimental
4.1. General techniques and reagents
All manipulations were performed using a combina-
tion of glove box, high vacuum, and Schlenk techniques.
Solvents were purified and degassed by standard proce-
dures prior to use. All available reagents were purchased
commercially and used as received unless otherwise noted
in the experimental procedure. Elemental analyses were
performed using a Perkin–Elmer 2400 CHN Elemental

3408
H. Lee et al. / Journal of Organometallic Chemistry 689 (2004) 3402–3411
Analyzer. 1H NMR and 13C NMR spectra were recorded
on a Bruker Advance 400DRX spectrometer operating at
4.4. Dibenzyl {methylene-bis(2,5-dimethylcyclopentadie-
nyl)}zirconium (IV), [H2C(C5Me2H2)2]Zr(CH2Ph)2
(2)
1
399.9 MHz and 100.6 MHz, respectively. H NMR and
13C NMR spectral chemical shifts are reported in ppm rel-
ative to SiMe4 (d = 0) and were referenced internally, rel-
ative to the protio solvent impurity (d = 7.26 and d = 77.0
for CDCl3). All coupling constants are reported in hertz.
The glass transition temperature values (Tg) were meas-
ured using a TA instrument DSC2010. The sample was
first heated to 300 ꢁC, then cooled to 30 ꢁC (20 ꢁC/min),
and then reheated to 250 or 300 ꢁC (20 ꢁC/min). The data
reported here were taken from the second heating. The
average molecular weight (Mw) and distribution
(MWD) of E–N copolymers were measured by gel perme-
ation chromatography (GPC) using a Waters Millennium
instrument with three Waters chromatographic columns.
Chloroform was used as a solvent with a flow rate 1 mL/
min at 37 ꢁC. The polystyrene (PS) standards, with nar-
row molecular weight distribution, were used for the cal-
ibration of molecular weights versus retention time of the
column set.
PhCH2MgCl (1.90 mL, 0.370 mol, 2.0 M in THF
solution) was added slowly by a syringe to a solution
of [H2C(Me2C5H2)2]ZrCl2 (0.58 g, 0.161 mol) in THF
(50 mL) at room temperature. After stirring the yellow
reaction mixture at room temperature for 12 h, the vol-
atiles were removed in vacuo and the residue was ex-
tracted into pentane (450 mL). The solution was
concentrated to 10 mL and cooled to À78 ꢁC, giving
[H2C(Me2C5H2)2] Zr(CH2Ph)2 as yellow crystals iso-
lated by filtration (0.31 g, 66%). 1H NMR (C6D6,
d = 7.15): 1.58 {CH2(Me2C5H2)2, 12H, s}, 3.05
{CH2(Me2C5H2)2, 2H, s}, 2.06 {ZrCH2(C6H5), 4H, s},
5.87 {CH2 (Me2- C5H2)2, 4H, s}, 7.22 {ZrCH2(C6H5), t,
3
3
4H, JH–H = 8 Hz}, 6.94 {ZrCH2(C6H5), d, 4H, JH–
3
H = 8 Hz}, 6.91 {ZrCH2(C6H5), t, 2H, JH–H = 8 Hz}.
13C NMR (C6D6, d = 128.0): 15.1 CH2(Me2C5H3)2,
4C, q, JC–H = 127 Hz, 20.7 {ZrC2(C6H5), 4C, t, JC–
1
1
1
H = 136 Hz}, 60.5 {C2(Me2C5H3)2, 1C, t, JC–H = 116
Hz}, 96.5 {ipso CH2(Me2C5H3)2, 2C, s}, 117.7
4.2. Representative gas tight NMR tube reaction
1
{CH2(Me2C5H3)2, 4C, d, JC–H = 171 Hz}, 120.4
1
{(Me2C5H3)2, 4C, s}, 121.1 {ZrCH2(C6H5), 4C, d, J
Deuterated toluene (1.0 mL) or CH2Cl2 (1.0 mL)
was added to the solid mixture of complex
[H2C(Me2C5H2)2]Zr(CH2Ph)2 (10 mg, 0.02 mmol) and
cocatalyst [Me2PhHN][B(C6F5)4] (17 mg, 0.02 mmol).
The formation of yellow {[H2C(Me2C5H2)2]Zr
(CH2Ph)}+{B(C6F5)4}À was instantaneous and quanti-
1
C–H = 151 Hz}, 125.9 {ZrCH2(C6H5), 2C, d, JC–
1
H = 161 Hz}, 128.8 {ZrCH2 (C6H5), 4C, d, JC–H = not
resolved}, 152.6 {ipso ZrCH2(C6H5), 2C, s}. CHN anal-
ysis calculated for C29H32Zr: C, 73.83; H, 6.84. Found:
C, 73.79; H, 6.94%.
1
tative as determined by H NMR spectroscopy.
4.5. Bis(trimethylsilylmethyl)
dimethylcyclopentadienyl)}zirconium
(Me2C5H2)2]Zr(CH2SiMe3)2 (3)
{methylene-bis(2,5-
(IV), [H2C-
4.3. Dimethyl {methylene-bis(2,5-dimethylcyclopentadie-
nyl)}zirconium (IV), [H2C(Me2C5H2)2]ZrMe2 (1)
MeLi (1.45 mL, 0.232 mmol, 1.6 M diethyl ether solu-
tion) was added slowly by syringe to [H2C
(Me2C5H2)2]ZrCl2 (0.35 g, 0.97 mol) in diethyl ether
(30 mL) (using THF did not work) at À78 ꢁC. After stir-
ring the yellow reaction mixture at room temperature
for 10 min, the volatiles were removed in vacuo and
the solid residue was extracted with pentane (150 mL).
The solution was concentrated to 10 mL and cooled to
À78 ꢁC, to give crystals of [H2C(Me2C5H2)2]ZrMe2
which were not isolated. The solvent was then removed
to give a yellow sticky product [H2C(Me2C5H2)2]ZrMe2
Me3SiCH2Li (1.0 M in pentane solution, 3.4 mL, 0.340
mol, 2.4 eq.) was added slowly by syringe to [H2C(Me2C5
H2)2]ZrCl2 (0.50 g, 0.139 mol) dissolved in THF (50 mL)
at room temperature. After stirring the yellow reaction
mixture at room temperature for 12 h, the volatiles were
removed in vacuo and the residue was extracted into pen-
tane (250 mL). The solution was concentrated to 10 mL
and cooled to À78 ꢁC, giving pale yellow crystals of
[H2C(Me2C5H2)2] Zr(CH2SiMe3)2 isolated by filtration
(0.16 g, 34%). 1H NMR (C6D6, d = 7.15): 1.80
{CH2(Me2C5H2)2, 12H, s}, 3.09 {CH2(Me2C5H2)2, 2H,
s}, 6.28 {ZrCH2(C6 H5)2, 4H, s}, À0.12 (ZrCH2SiMe3,
4H, s), 0.26 (ZrCH2SiMe3, 18H, s). 13C NMR (C6D6,
1
by the H NMR spectrum (0.31 g, 66%). This material
was used without further purification. 1H NMR
(C6D6, d = 7.15): 1.79 {CH2(Me2C5H2)2, 12H, s}, 3.11
{CH2(Me2C5H2)2, 2H, s}, 6.19 {CH2(Me2C5H2)2, 4H, s},
0.08 (ZrMe, 6H, s). 13C NMR (C6D6, d = 128.0): 28.5
{ZrMe2, 6C, t, 1JC–H = 115 Hz}, 15.5 {CH2(Me2C5H3)2,
4C, q, 1JC–H = 127 Hz}, 20.7 {C2(Me2C5H3)2, 1C, t, 1JC–
H = 132 Hz}, 98.1 ipso CH2(Me2C5H3)2, 2C, s, 116.6
1
d = 128.0): 3.6 {ZrCH2SiMe3 9C, t, JC–H = 118 Hz},
15.8 {CH2(Me2C5H3)2, 4C, q, JC–H = 127 Hz}, 20.5
1
1
{ZrC2SiMe3, 4C, t, JC–H = 132 Hz}, 41.4 {C2(Me2
1
C5H3)2, 1C, t, J C–H = 104 Hz}, 102.2 {ipso CH2 (Me2-
C5H3)2, 2C, s}, 115.4 {CH2(Me2C5H3)2, 4C, d,
1JC–H = 171 Hz}, 119.6 {(Me2C5H3)2, 4C, s}. CHN anal-
ysis calculated for C23H40Si2Zr: C, 59.54; H, 8.69. Found:
C, 58.73; H, 8.49%.
1
{CH2(Me2C5H3)2, 4C, d, JC–H = 161 Hz}, 119.8
{(Me2C5H3)2, 4C, s}.

H. Lee et al. / Journal of Organometallic Chemistry 689 (2004) 3402–3411
3409
4.6. Diphenyl {methylene-bis(2,5-dimethylcyclopentadie-
nyl)}zirconium (IV), [H2C(Me2C5H2)2]ZrPh2 (4)
{H2C(Me2C5H2) , 2H, s}, 6.35 {H2C(Me2C5H2)2, 4H,
2
s}, À0.08 (ZrCH2SiMe3 9H, s), 3.23 (ZrCH2SiMe3,
2H, s) or À0.08 (ZrCH2SiMe3, 2H, s).
PhLi (1.8 M in cyclohexane/diethyl ether, 2.0 mL,
0.361 mol, 2.6 eq.) was added slowly by a syringe to a solu-
tion of [H2C(Me2C5H2)2]ZrCl2 (0.50 g, 0.139 mol) in
diethyl ether (30 mL) at room temperature. After stirring
this reaction mixture (yellow) for 12 h, the volatiles were
removed in vacuo and the residue was extracted into pen-
tane (250 mL). The solution was then concentrated to 10
mL and cooled to À78 ꢁC, giving [H2C(Me2C5H2)2]ZrPh2
as pale yellow crystals, isolated by filtration (0.09 g, 20%).
1H NMR (C6D6, d = 7.15): 1.89 {CH2(Me2C5H2)2, 12H,
s}, 3.27 {CH2(Me2C5H2)2, 12H, s}, 6.14 {ZrCH2(C6H5)2,
4H, s}, 7.64 {Zr(C6H5), d, 4H, 3JH–H = 8 Hz}, 7.18–7.11
{Zr(C6H5), m, 6H}. 13C NMR (C6D6, d = 128.0): 15.3
4.10. The ionic pair {[H2C(Me2C5H2)2]ZrPh)}+-
{B(C6F5)4}À (4a)
1H NMR (C7D8, d = 2.09): 1.91 {CH2(Me2C5H2)2,
12H, s}, 3.32 {H2C(Me2C5H2)2, 2H, s}, 6.11
{H2C(Me2C5H2) 2, 4H, s}, 7.59 {Zr(C6H5), 2H, d},
{Zr(C6H5), 1H, d}, 7.18 {Zr(C6H5), 2H, t}.
4.11. The ionic pair {[H2C(Me2C5H2)2]Zr(CH3)}+-
{(CH3)B(C6F5)3}À (1b)
1H NMR (C7D8, d = 2.09): 1.60 {H2C(Me2C5H2)2,
6H, s}, 1.32 {H2C(Me2C5H2)2, 6H, s}, 3.03
{H2C(Me2C5H2)2, 1H, s}, 2.95 {H2C(Me2C5H2)2, 1H,
s}, 5.86 {H2C(Me2C5H2)2, 4H, s}, 0.82 {(CH3)B(C6F5)3,
3H, s}, 0.38 (ZrCH3, 3H, s).
1
{CH2(Me2C5H3)2, 4C, q, JC–H = 128 Hz}, 68.3
1
{C2(Me2C5H3)2, 1C, t, JC–H = 129 Hz}, 97.2 {ipso
CH2(Me2C5H3)2, 2C, s}, 117.9 {CH2(Me2C5H3)2, 4C, d,
1JC–H = 171 Hz}, 121.1 {(Me2C5H3)2, 4C, s}, 126.1
1
{Zr(C6H5), 4C, d, JC–H = 161 Hz}, 127.5 {Zr(C6H5),
1
1
2C, d, J C–H = 151 Hz}, 136.0 {Zr(C6H5), 4C, d, JC–
H = 151}, 181.7 {ipso Zr(C6H5), 2C, s}. CHN analysis cal-
culated for C29H32Zr: C, 73.83.54; H, 6.84. Found: C,
73.79; H, 6.94%.
4.12. The ionic pair {[H2C(Me2C5H2)2]Zr(CH2Ph)}+-
{(PhCH2)B(C6F5)3}À (2b)
1H NMR (C6D6, d = 7.15): 1.27 {H2C(Me2C5H2)2,
12H, s}, 3.04 {H2C(Me2C5H2)2, 2H, s}, 2.10
{ZrCH2(C6H5), 2H, ABq}, 5.49 {H2C(Me2C5H2)2, 4H,
ABq}, 3.57 {(C6H5CH2)B(C6F5)3, 2H, s}, 7.30 {ZrCH2
(C6H5) or (C6 H5CH2)B(C6F5)3, 2H, m}, 7.04 {ZrCH2
(C6H5) or (C6 H5CH2)B(C6F5)3, 2H, m}, 6.88
{ZrCH2(C6H5) or (C6 H5CH2)B(C6F5)3, 3H, m}, 6.44
{ZrCH2(C6H5) or (C6 H5CH2)B(C6F5)3, 3H, m}. 13C
NMR (C6D6, d = 128.0): 14.2 {H2C(Me2C5H3)2, 4C},
22.7 {ZrC2(C6H5), 2C}, 20.5 {BC2(C6H5)}(C6F5), 2C},
53.6 {H2C(Me2C5H3)2, 1C,}, 98.3 {ipso CH2
(Me2C5H3)2, 2C}, 117.7, 129.3, 129.6, 103.4, 130.9,
131.8, 136.5, 137.0, 138.0, 138.9, 147.0, 147.5, 149.6,
150.1 {(Me2C5H3)2, 4C,4C; ZrCH2(C6H5), 2C, 2C, 1C,
1C; BCH2(C6H5)(C6F5), 2C, 2C, 1C, 1C; BCH2
(C6H5)(C6H5), 2C, 2C, 1C, 1C}. 19F NMR (C6D6, exter-
nal standard C6F6, d = À163): À129 {Me3SiCH2B
(C6F5), ortho, 6C}, À163 {Me3SiCH2B(C6F5), para,
3C}, À173 {Me3SiCH2B(C6F5), meta, 6C, br}.
4.7. The ionic pair {[H2C(Me2C5H2)2]Zr(CH3)}+-
{B(C6F5)4}À (1a)
1H NMR (CD2Cl2, d = 5.24): 2.13 {CH2(Me2C5H2)2,
12H, s}, 4.25 {CH2(Me2C5H2)2, 2H, s}, 6.19 {CH2-
(Me2C5H2)2, 4H, s}, À0.08 {ZrCH3, 3H, s}.
4.8. The ionic pair {[H2C(Me2C5H2)2]Zr(CH2Ph)}+-
{B(C6F5)4}À (2a)
1H NMR (C7D8, d = 2.09): 1.27 {CH2(Me2C5H2)2,
12H, s}, 3.12 {CH2(Me2C5H2)2, 2H, s}, 2.10
{ZrCH2(C6H5), 2H, s}, 5.52 {CH2(Me2C5H2)2, 4H, s},
6.89 {ZrCH2(C6 H5), t, 2H, 3JH–H = 8 Hz}.6.79 {ZrCH2-
(C6H5), 2H, 3 JH–H = 8 Hz}, 6.47 {ZrCH2(C6H5), t, 2H,
3JH–H = 8 Hz}. 1H NMR (CD2Cl2, d = 5.24): 3.29
{CH2(Me2C5H2)2, 12H, s}, 4.08 {CH2(Me2C5H2)2, 2H,
s}, 2.26 {ZrCH2(C6H5), 2H, s}, 6.36 {CH2(Me2C5H2)2,
3
4H, s}, 7.31 {ZrCH2(C6 H5), t, 2H, JH–H = 8 Hz},
3
4.13.
The
ion
pair
{[H2C(Me2C5H2)2]Zr-
7.14 {ZrCH2(C6H5), d, 2H,
JH–H = 8 Hz}, 7.10
(CH2SiMe3)}d+{(Me3SiCH2)B(C6F5)4}dÀ (3b)
3
{ZrCH2(C6H5), t, 2H, JH–H = 8 Hz}.
1H NMR (C6D6, d = 7.15): 1.55 {H2C(Me2C5H2)2,
6H, s}, 1.36 {H2C(Me2C5H2)2, 6H, s}, 2.98
{H2C(Me2C5H2)2, 1H, brs}, 2.96 {H2C(Me2C5H2)2,
1H, brs}, 6.29 {H2C(Me2C5H2)2, 2H, s}, 6.01
{H2C(Me2C5H2)2, 2H, s}, À0.42 (ZrCH2SiMe3, 2H, s),
4.9. The ionic pair {[H2C(Me2C5H2)2]Zr(CH2-
SiMe3)}+ {B(C6F5)4}À (3a)
1H NMR (C7D8, d = 2.09): 1.31 {CH2(Me2C5H2)2,
12H, s}, 3.10 {H2C(Me2C5H2)2, 2H, s}, 5.50
0.47
{(Me3SiCH2)B(C6F5)4,
2H,
brs},
0.10
{H2C(Me2C5H ) , 4H, s}, À0.02 (ZrCH2SiMe3 9H, s),
2 2
(ZrCH2SiMe3 9H, s), À0.08 {(Me2MeSiCH2)B(C6F5)4,
6H, s}, 0.83 {(Me2MeSiCH2)B(C6F5)4, 3H, s}. 13C
NMR (C6D6, d = 128): À0.1 {BCH2SiMeMe22C}, 1.5
0.04 (ZrCH2SiMe3, 2H, s). 1H NMR (CD2Cl2,
d = 5.24): 2.12 {H2C(Me2 C5H2)2, 12H, s}, 4.05

3410
H. Lee et al. / Journal of Organometallic Chemistry 689 (2004) 3402–3411
[2] M. Yamaura et al., WO Pat. Appl. 20662, 1999.
[3] (a) For other hydrocarbyl group IV complexes see: V. Varga, J.
Hiller, R. Gyepes, M. Polek, P. Sedmera, U. Thewalt, K. Mach,
J. Organomet. Chem. 538 (1997) 63;
{ZrCH2SiMe33C}, 3.0 {BCH2SiMeMe2, 1C}, 7.2
{BC2SiMeMe2, 1C}, 15.2 {H2C(Me2C5H3)2, 2C}, 16.0
{H2C(Me2C5H3)2, 2C}, 20.9 {ZrC2SiMe3, 1C}, 58.3
{H2C(Me2C5H3)2, 1C}, 103.4 {ipso H2C(Me2C5H3)2,
2C}, 117.4, 122.4, 123.8, 124.6 {CH2(Me2C5H3)2, 2C},
136.3, 138.8, 141.0, 147.0, 147.5, 149.8 {Me3-
SiCH2B(C6H5), 1C}. 19F NMR (C6D6, external stand-
ard C6F6, d = À163 ): À133 {Me3SiCH2B(C6F5), ortho,
6C}, À159 {Me3SiCH2 B(C6F5), para, 3C, br}, À164
{Me3SiCH2B(C6F5), meta, 6C, br}.
´
(b) A. Cano, T. Cuenca, P. Gomez-Sal, B. Royo, P. Royo,
Organometallics 13 (1994) 1688;
´
(c) R. Gomez, T. Cuenca, P. Royo, Organometallics 10 (1991)
1505;
(d) S.J. Lancaster, O.B. Robinson, M. Bochmann, Organometal-
lics 14 (1995) 2456;
(e) J.J. Eisch, K.R. Caldwell, S. Werner, G.-X.C. Kruger,
¨
Organometallics 10 (1991) 3417.
[4] (a) J.J. Eisch, A.M. Piotrowski, S.K. Brownstein, E.J. Gabe, F.L.
Lee, J. Am. Chem. Soc. 107 (1985) 7219;
4.14. General procedure for ethylene–norbornene copo-
lymerization
(b) T. Shiomura, T. Asanuma, T. Sunaga, Macromol. Rapid
Commun. 18 (1997) 169;
(c) C. Go¨tz, A. Rau, G. Luft, Macromol. Symp. 178 (2002) 93.
[5] J.J. Eisch, S.I. Pombrik, G.-X. Zheng, Organometallics 12 (1993)
3856.
Ethylene-norbornene copolymerization was carried
out using a 500 mL jacketed stainless steel reactor,
equipped with a mechanical stirrer. All manipulations
were carried out in an inert atmosphere using a standard
Schlenk technique or a VAC dry-box. The norbornene
was dissolved in toluene to obtain 150 mL of a 56%
(by weight) solution. The solution was passed through
the purification column and injected into the reactor.
After the reactor temperature was stabilized, the
TIBA–toluene solution (1 mmol, triisobutylaluminum
1.0 M in toluene) 1 mL was injected into the reactor
and the reaction mixture was stirred for 15 min. The
TIBA–toluene solution used as a scavenger in the polym-
erization reactor. For catalyst preactivation, the catalyst
(4 · 10À6 mol/L) and same amount of cocatalyst
(4 · 10À6 mol/L) in 2 mL toluene or CH2Cl2 solution
was stirred for 15 min at 60 ꢁC. After the addition of
preactivated catalyst (4 · 10À6 mol/L), polymerization
began as a constant ethylene pressure 60 psi to the reac-
tor. The polymerization time was measured from the
start of reaction mixture stirring. After polymerization
occurred, the reactor was vented and the reaction mix-
ture was poured into acetone (2 L). The precipitated
white polymer was filtered, washed with acetone and
dried in a vacuum oven at 80 ꢁC.
[6] (a) M. Bochmann, J. Chem. Soc., Dalton Trans. (1996) 255;
(b) R.F. Jordan, C.S. Bajgur, R. Willett, B. Scott, J. Am. Chem.
Soc. 108 (1986) 7410;
(c) G.G. Hlatky, H.W. Turner, R.R. Eckman, J. Am. Chem. Soc.
111 (1989) 2728;
(d) K.P. Bryliakov, E.P. Talsi, M. Bochmann, Organometallics
23 (2004) 149;
(e) M. Bochmann, S.J. Lancaster, M.B. Hursthouse, K.M.A.
Malik, Organometallics 13 (1994) 2235;
(f) L.H. Doerrer, M.L.H. Green, D. Ha¨ußinger, J. Saßmanns-
hausen, J. Chem. Soc., Dalton Trans. (1999) 2111C;
(g) D.J. Gillis, M.-J. Tudoret, M.C. Baird, J. Am. Chem. Soc. 120
(1993) 2543.
[7] (a) M.C. Sacchi, F. Forlini, S. Losio, I. Tritto, P. Locatelli,
Macromol. Symp. 193 (2003) 45;
(b) D. Coevoet, H. Cramail, A. Deffieux, Macromol. Chem. Phys.
200 (1999) 1208;
(c) J.J. Eisch, S.I. Pombrik, G.-X. Zheng, Makromol. Chem.
Macromol. Symp. 66 (1993) 109.
[8] (a) Y.-X. Chen, M.V. Metz, L. Li, C.L. Stern, T.J. Marks, J. Am.
Chem. Soc. 120 (1998) 6287;
(b) M.-C. Chen, J.A.S. Roberts, T.J. Marks, Organometallics 23
(2004) 932;
(c) T. Shiomura, T. Asanuma, N. Inoue, Macromol. Chem.
Rapid Commun. 18 (1997) 169;
(d) J.C.W. Chien, W. Song, M.D. Rausch, Macromolecules 26
(1993) 3239;
(e) J. Zhou, S.J. Lancaster, D.A. Walker, S. Beck, M. Thornton,
M. Bochmann, J. Am. Chem. Soc. 123 (2001) 223;
´
(f) J.W. Strauch, J.-L. Faure, S. Bredeau, C. Wang, G. Kehr, R.
Fro¨hlich, H. Luftmann, G. Erker, J. Am. Chem. Soc. 126 (2004)
2089.
Acknowledgments
[9] B.Y. Lee, Y.H. Kim, Y.C. Won, J.W. Han, I.S. Lee, W.H. Suh,
Y.K. Chung, K.H. Song, Organometallics 21 (2002) 1500.
[10] D. Balboni, I. Camurati, G. Prini, L. Resconi, S. Galli, P.
Mercandelli, A. Sironi, Inorg. Chem. 40 (2001) 6588.
[11] (a) H. Lee, P.J. Desrosiers, I. Guzei, A.L. Rheingold, G. Parkin,
J. Am. Chem. Soc. 120 (1998) 3255;
We are very grateful to LG Chemical Ltd. Research
Center and also to the Analytical lab for NMR spectro-
scopic and CHN analysis. Professor David G. Churchill
of KAIST (Taejeon, Republic of Korea) has been very
helpful in the written preparation of this manuscript.
(b) L.E. Schock, R.D. Sanner, J. Am. Chem. Soc. 110 (1988)
7701.
References
[12] (a) E.Y.-X. Chen, T.J. Marks, Chem. Rev. 100 (2000) 1391;
(b) R. Choukroun, F. Wolff, C. Lorber, B. Donnadieu, Organ-
ometallics 22 (2003) 2245.
[1] (a) R.F. Jordan, R.F. Lapointe, P.K. Bradley, N. Baenziger,
Organometallics 8 (1989) 2892;
[13] G. Lanza, I.L. Fragala, T.J. Marks, Organometallics 21 (2002)
5594.
[14] A.D. Horton, A.G. Orpen, Organometallics 10 (1991) 3910.
(b) T.J. Marks, Acc. Chem. Res. 25 (1992) 57;
(c) X. Yang, C.L. Stern, T.J. Marks, Organometallics 10 (1991)
840;
´
[15] (a) A. Cano, T. Cuenca, P. Gomez-Sal, B. Royo, P. Royo, J.
Organomet. Chem. 526 (1996) 227;
(d) R.F. Jordan, Adv. Organomet. Chem. 32 (1991) 325.

H. Lee et al. / Journal of Organometallic Chemistry 689 (2004) 3402–3411
3411
(b) A. Razavi, U. Thewalt, J. Organomet. Chem. 445 (1993) 111;
(c) E.P. Talsi, J.L. Eilertsen, M. Ystenes, E. Rytter, J. Organomet.
Chem. 677 (2003) 10;
[17] M. Bochmann, A.J. Jaggar, J.C. Nicholls, Angew. Chem., Int.
Ed. Engl. 29 (1990) 780.
[18] C. Pellecchia, A. Immirzi, D. Pappalardo, A. Peluso, Organome-
tallics 13 (1994) 3773.
[19] (a) See Ref. [10];
(d) M. Bochmann, S.J. Lancaster, Angew. Chem., Int. Ed. Engl.
33 (1994) 1634.
[16] (a) For the reaction of B(C6F5)3 with other metallocene com-
plexes, see: R. Choukroun, C. Lorber, C. lepetit, B. Donnadieu,
Organometallics 22 (2003) 1995;
(b) B.Y. Lee, Y.H. Kim, Y.C. Won, C.B. Shim, D.M. Shin, Y.K.
Chung, J. Organomet. Chem. 660 (2002) 161;
(c) H. Lasarov, K. Mo¨nkko¨nen, T.T. Pakkanen, Macromol.
Chem. Phys. 199 (1998) 1939.
(b) A.D. Horton, J.D. With, A.J. Van der Linden, H. Van de
Weg, Organometallics 15 (1996) 2672;
[20] (a) J.A. Ewen, J. Am. Chem. Soc. 106 (1984) 6355;
(b) , Additional references hereinS. Mecking, Angew. Chem., Int.
Ed. Engl. 40 (2001) 534.
(c) J. Cano, P. Go´mez-Sal, G. Heinz, G. Mart´ınez, R. Royo,
Inorg. Chim. Acta 345 (2003) 15;
(d) R. Choukroun, C. Lorber, B. Donnadieu, Organometallics 23
(2004) 1434.
[21] M. Bochmann, S.J. Lancaster, Organometallics 12 (1993)
633.