Dimerization and polymerization of ethylene catalyzed by nickel complexes bearing multidentate amino-functionalized indenyl ligands

Article abstract of DOI:10.1016/S1381-1169(02)00463-6

The combination of the neutral compound (η³:η ⁰-Ind(CH₂)₂NMe₂)Ni(PPh ₃)Cl (1) and methylaluminoxane (MAO) produces catalysts for the dimerization and the polymerization of ethylene. On the other hand, activation of the cationic complex (η³:η¹-Ind(CH ₂)₂NMe₂)Ni(PPh₃)][BPh₄] (2) by MAO or trimethylaluminum leads to a system which dimerizes ethylene with high turnover frequencies (2 × 10³ s^-1), but does not promote its polymerization. The effects of parameters such as ethylene pressure, reaction temperature and time, solvent type, and the type and amount of activator used have been studied in order to optimize the conditions for the formation of polyethylene. In addition, a number of reactions have been studied by NMR and GC-MS analysis in an effort to identify the catalytically active species. The results of these studies point to the involvement of cationic species in the dimerization of ethylene, whereas, the active catalyst for the polymerization of ethylene appears to be a non-cationic species.

Full text of DOI:10.1016/S1381-1169(02)00463-6

Journal of Molecular Catalysis A: Chemical 193 (2003) 51–58
Dimerization and polymerization of ethylene catalyzed by nickel
complexes bearing multidentate amino-functionalized
indenyl ligands
Laurent F. Grouxa,∗, Davit Zargariana,1, Leonardo C. Simonb, João B.P. Soaresb
a
Département de Chimie, Université de Montréal, Succursale Centre-Ville CP 6128, Montréal, Qué., Canada H3C 3J7
b
Department of Chemical Engineering, Institute for Polymer Research, University of Waterloo, Waterloo, Ont., Canada N2L 3G1
Received 22 May 2002; accepted 6 August 2002
Abstract
The combination of the neutral compound (η3:η0-Ind(CH2)2NMe2)Ni(PPh3)Cl (1) and methylaluminoxane (MAO) pro-
duces catalysts for the dimerization and the polymerization of ethylene. On the other hand, activation of the cationic complex
[(η3:η1-Ind(CH2)2NMe2)Ni(PPh3)][BPh4] (2) by MAO or trimethylaluminum leads to a system which dimerizes ethylene
with high turnover frequencies (2 × 103 s−1), but does not promote its polymerization. The effects of parameters such as
ethylene pressure, reaction temperature and time, solvent type, and the type and amount of activator used have been studied
in order to optimize the conditions for the formation of polyethylene. In addition, a number of reactions have been studied
by NMR and GC–MS analysis in an effort to identify the catalytically active species. The results of these studies point to the
involvement of cationic species in the dimerization of ethylene, whereas, the active catalyst for the polymerization of ethylene
appears to be a non-cationic species.
© 2002 Elsevier Science B.V. All rights reserved.
Keywords: Nickel; Indenyl; MAO; Polyethylene; Butene
1. Introduction
is anticipated that this characteristic will expand the
range of polyolefins accessible by catalysis. The key
element for an efficient system is the choice of the
ligand. For example, a family of bidentate ␣-diimine
ligands has been used in the development of highly
efficient Ni and Pd systems for the polymerization
of ethylene and propylene. These catalysts operate
through cationic intermediates formed by the action of
MAO-type activators [2,3]. On the other hand, recent
reports on the chemistry of nickel complexes contain-
ing salicylaldimine ligands have shown that neutral
intermediates could also be active and effective for
the polymerization of ethylene [4].
The recent success of late transition metal systems,
especially those of Group 10 metals, in the poly-
merization of ethylene has opened new vistas in the
development of the next generations of catalysts for
olefin polymerization [1]. Unlike the catalysts based
on early transition metals, late metal-based catalysts
tolerate polar functional groups in the monomers. It
∗
Corresponding author. Tel.: +1-514-343-6111x3939;
fax: +1-514-343-7586.
E-mail addresses: laurent.groux@umontreal.ca (L.F. Groux),
zargarian.davit@umnotreal.ca (D. Zargarian).
We have shown [5,6] that the complexes (Ind)(PR3)-
NiX (Ind: indenyl and its substituted derivatives; R:
1
Tel.: +1-514-343-2247; fax: +1-514-343-7586.
1381-1169/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S1381-1169(02)00463-6

52
L.F. Groux et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 51–58
Ph, Me or Cy, X: Cl, Me, CCPh) react with MAO
to generate both cationic and neutral intermediates
which convert ethylene to mostly butenes (>90%) as
well as some polyethylene (Mw ca. 5 × 105). On the
other hand, studies carried out on the polymerization
of styrene and norbornene have shown that an amino
alkyl substituent on the Ind ligand has a major in-
fluence on the course of the polymerization: poly-
mers with high weight average molecular weight (Mw)
were obtained with styrene, whereas, only oligomers
were formed with norbornene [7]. With these results
in mind, we set out to study the polymerization of
ethylene catalyzed by complexes bearing chelating
aminoindenyl ligands [8].
The present article reports the results of our in-
vestigation on the dimerization and polymerization
of ethylene catalyzed by the neutral complex (η3:η0-
Ind(CH2)2NMe2)Ni(PPh3)Cl (1) and the cationic
complex [(η3:η1-Ind(CH2)2NMe2)Ni(PPh3)][BPh4]
(2), Fig. 1. The effects of ethylene pressure, reac-
tion temperature, time, activator, and solvent on these
reactions have been studied. The results of NMR
studies on the reactivity of these complexes with the
activators MAO and AlMe3, both in the presence
and absence of ethylene, are also presented. GC–MS
Fig. 1.
analyses were performed on the resulting solutions in
order to track the reaction and decomposition prod-
ucts, thus providing clues on the reaction mechanism.
2. Results and discussion
2.1. Polymerization of ethylene with the neutral
complex 1
The outcome of the polymerization experiments
with the neutral pre-catalyst 1 are summarized in
Table 1. Most of these experiments resulted in the
predominant formation of butenes, but various quan-
tities of polyethylene (PE) representing ca. 1–4%
of the total mass of ethylene consumed were also
Table 1
Reactivitiesa of (η3:η0-Ind(CH2)2NMe2)Ni(PPh3)Cl (1) with ethylene
Run
AlMe3
(Eq.)
MAO
(Eq.)
Solvent
(300 ml)
P
(psi)
T
(◦C)
Total activity
(kg C2/(mol Ni h))
Activity
(kg PE/(mol Ni h))
Mn (×
PDI
(Mw/Mn)
10−5 g/mol)
1
2
3
–
–
–
50
200
1000
Toluene
Toluene
Toluene
75
75
75
40
40
40
84
2270
2350
0
0
90
–
–
1.1
–
–
2.3
4a
4b
4c
–
1000
Toluene
175
40
8400
4790
2920
144
360
695
2.6
2.5
5
6
7
8
9
10
11
12
13
14
15
–
–
2000
2000
1000
1000
–
Toluene
Toluene
Toluene
Toluene
Toluene
Hexanes
DCEb
175
175
175
175
270
175
175
175
175
175
175
60
80
60
40
40
40
40
60
80
40
40
8190
3980
460
5090
10950
8080
12970
11270
15330
1820
89
121
0
25
108
0
23
182
516
0
1.3
0.7
–
2.1
1.9
–
200
–
–
–
–
–
–
–
1000
1000
1000
1000
1000
100
–
1.7
0.3
C14–22
–
–
2.1
2.0
–
–
2.0
DCEb
DCEb
ClBzb
1000
ClBzb
19810
77
1.6
a Reaction time, 30 min except for runs 3 and 13 (60 min), and runs 4b (10 min) and 4c (4 min).
b DCE, dichloroethane; ClBz, chlorobenzene.

L.F. Groux et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 51–58
53
produced. The PE thus obtained has high molecular
weights and low polydispersity index (Mw ≈ 105;
Mw/Mn = 1.9–2.5), and is essentially linear with a
small number of ethyl branches exclusively.
products was calculated from the integration of signal
intensities.
Thus, reacting 1 with 2 equivalents of MAO forms
the Ni–Me analogue (η3:η0-Ind(CH2)2NMe2)Ni-
(PPh3)Me); this is evident from the characteristic
31P NMR signal for the Ni–Me derivative (47.8 ppm)
[9].3 The same Ni–Me species is also obtained when
1 is reacted with AlMe3 or MeLi. Experiments have
shown that this Ni–Me species does not react with
ethylene either on its own or when AlMe3 is used
as activator. On the other hand, MAO can activate
the Ni–Me bond toward ethylene polymerization. We
have proposed that the role of MAO is to weaken
the Ni–Me bond, thereby promoting the insertion of
ethylene.4
In order to determine the fate of the Ni–Me species,
we monitored its reaction with increasing amounts of
MAO. The 31P{1H} NMR spectra showed that the rel-
ative concentration of the Ni–Me species decreases as
the concentration of MAO increases, and a new species
(28.6 ppm) is formed in the presence of 7 equivalents
of MAO. The chemical shift of this new species is
very close to that of the cationic complex 2, but its
1H NMR spectrum reveals some differences. In fact,
this same compound is also obtained upon reacting 2
with MAO and leads to the dimerization of ethylene.
Increasing the quantity of MAO beyond 20 equiva-
lent leads to the formation of a number of uniden-
tified species (31P: 46.1, 44.7, 41.0, 36.9, 30.4, and
27.5 ppm) one of which might well be the species pro-
ducing polyethylene.
Runs 1–3 of Table 1 focused on the determination
of the optimum amount of activator. Examination of
the effect of pressure (runs 3, 4a and 9) led us to select
the conditions of run 4a (1000 equivalent of MAO,
300 ml toluene, 175 psi of ethylene, 40 ◦C for 30 min)
as the standard run to which all the others would be
compared. Next, we studied the effect of replacing
MAO by AlMe3 (runs 7 and 8), varying the reaction
time (runs 4a–c), and temperature (runs 4a, 5, 6 and
11–13), and finally the choice of solvent (polar and
non-polar, aromatic and aliphatic). The results of these
studies are described later.
2.1.1. Effect of activator
The dimerization of ethylene can be catalyzed by
complex 1 in the presence of only a few equivalents of
MAO or a large excess of AlMe3, whereas, only MAO
(in large excess) is an effective co-catalyst for the pro-
duction of PE (runs 4–6, 9, 11–13 and 15). It is not
clear why such a large excess of MAO is needed to ac-
tivate the pro-catalyst for the polymerization reaction,
but some of this excess is likely used to eliminate all
poisoning residues. This is illustrated by run 8 which
shows that if AlMe3, which does not activate the poly-
merization reaction, is first used to clean the solvent,
then a smaller amount of MAO can be used as activa-
tor (compare runs 2, 4, 7 and 8). A number of NMR
experiments were carried out in order to shed light
on the role of MAO in these reactions, as described
next.
These results indicate that the Ni–Me species, which
forms at the outset of the reaction between MAO
and 1, reacts further with MAO to produce a cationic
species that is structurally very similar to 2; the dimer-
ization reaction is likely catalyzed by this homologue
of 2. The reaction of 1 with large excess of MAO
also gives a number of unidentified species that show
31P NMR signals in a region associated with neutral
Ni–alkyl derivatives; we suspect that one or more of
2.1.2. NMR studies with complex 1
The reactions of compound 1 with various amounts
of MAO (2, 7, 14, 20, 30 and 100 equivalents; in the
absence of ethylene) were monitored by 31P and H
1
NMR spectroscopy (C6D6). Fig. 2 shows the conver-
sion of complex 1 into various species as a function
of MAO equivalents present in the reaction mixture.
Some of the resulting species could be identified by
comparison of their 31P chemical shifts to those of
known compounds2 and the relative ratio of these
3
1
The known (1-MeInd)(PPh3)Ni–Me has a 31P { H} δ =
47.7 ppm.
4
The complex (1-MeInd)(PPh3)Ni–Me on its own is also inac-
tive for the polymerization of ethylene, but can be activated with
MAO. A weakening of the nickel–methyl bond in this complex
by MAO has been proposed to explain the insertion of ethylene
and chain growth [5].
2
The species were identified by correlation to completely char-
acterized species [7–9].

54
L.F. Groux et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 51–58
Fig. 2. [Ni] = (Ind(CH2)2NMe2)Ni(PPh3). Reactivities of 1 with MAO in C6D6.
these species is involved in the polymerization reac-
tion, but no firm conclusion can be drawn at this point.
The consumption of ethylene falls to nearly zero after
15 min at 80 ◦C in toluene. (Fig. 3).
2.1.3. Effect of reaction time
2.1.5. Solvent effect
In order to get more information on the active
species producing polyethylene, three runs were con-
ducted under otherwise identical conditions, changing
only the reaction time (run 4a–c; 30, 10 and 4 min,
respectively). The polymerization activity per unit of
time increases drastically from run 4a to 4c, implying
that the active species is unstable and deactivates over
time. Thus, it appears that 65% of the PE is produced
during the first 4 min, 20% in the next 6 min and 15%
in the last 20 min. On the other hand, the consumption
of ethylene increases during the first 15 min (TOF
goes from 25 to 100 s−1) and then stays constant
over the last 15 min, during which the dimerization
reaction is predominant.
The total activity increases with the increasing
polarity of the solvent (chlorobenzene > dichlo-
roethane > toluene > hexanes), whereas, aromatic
solvents tend to favor the polymerization activity (runs
4a, 10, 11 and 15). Polymers with the highest num-
ber average molecular weight (Mn) were produced in
toluene with modest activity. On the other hand, poly-
mers of lower Mn or even oligomers were obtained in
dichloroethane (DCE). These observations are con-
sistent with the idea that the dimerization reaction is
catalyzed by cationic species that are expected to be
more stable in a polar medium.
2.2. Dimerization of ethylene with the cationic
complex 2
2.1.4. Effects of pressure and reaction temperature
The total activity increases with pressure, but no
significant increase has been observed on the forma-
tion of PE (runs 3, 4a and 9). Higher temperatures lead
to higher activities and shorter chain lengths (runs 4–6
and 11–13). The TOF curves for runs 4 and 6 show
that higher temperatures increase the reaction rate ini-
tially followed by a rapid deactivation of the catalyst.
The results of the attempted polymerization experi-
ments with the cationic complex 2 are summarized in
Table 2. Run 16 (40 ◦C) and run 17 (80 ◦C) were used
to test the ability of complex 2 to react with ethylene
without activator. The observed inertness of this com-
plex is in contrast to its reactivity in the polymeriza-
tion of norbornene and styrene at 80 ◦C [7]. As will

L.F. Groux et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 51–58
55
Fig. 3. Turnover frequencies plot for runs 4 and 6.
be discussed later, this implies a different mechanism
for the polymerization of ethylene. The outcomes of
runs 19–21 show that a rather large amount of MAO
is needed to induce the dimerization of ethylene; no
polymers were obtained.
A large excess of activator (either MAO or AlMe3)
is crucial for both removing the contaminants present
in the reaction medium and also for binding the chelat-
ing amino moiety in 2; this binding frees a coordina-
tion site on the nickel center for ethylene. The cationic
compound 2 in the presence of MAO (or AlMe3)
does not produce a Ni–Me species or catalyze the
polymerization of ethylene. It is remarkable that no
PPh3–MAO adduct is formed even in the presence of
a large excess of MAO (PPh3–AlMe3: δ −7.18 ppm
(31P {1H} in C6D6)); [10] evidently, the phosphine
is strongly bonded to the nickel center and does not
dissociate.
By analogy to previously reported studies, the
efficient dimerization of ethylene in the present sys-
tem points to a mechanism involving the insertion
of ethylene into a cationic Ni–H intermediate. The
insertion of a second molecule of ethylene into the
resulting Ni–ethyl bond, followed by ␤-H elimina-
tion would produce butene and regenerate the Ni–H
species [11,12]. The initial formation of the cationic
Ni–H species can occur by insertion of ethylene
into the Ni–Ind bond followed by ␤-H elimina-
tion to give the corresponding vinyl indene, 1,1- or
Table 2
Reactivitiesa of [(η3:η1-Ind(CH2)2NMe2)Ni(PPh3)][BPh4] (2) with
ethylene
Run
MAO
Solvent (300 ml)
Total activity
(kg butenesb/(mol Ni h))
16
17
18
19
20
21
22
23
24
25
26
0
0
25
Dichloroethane
Dichloroethane
Dichloroethane
Dichloroethane
Dichloroethane
Dichloroethane
Dichloroethane
Chlorobenzene
Toluene
0
0
0
400
51700
74800
76000
3000
54400
20000
20600
4900
1000
2000
2000c
1000
1000
1000
400c
=
1,3-(CH2 CH–Ind–CH2CH2NMe2). The involve-
ment of such mechanism has been supported by
the results of studies carried out on the analogous
complex (1-i-Pr-Ind)Ni(PPh3)OTf [13]. In contrast,
GC–MS analysis of the reaction mixtures using com-
plex 2 as catalyst failed to detect the postulated vinyl
indene intermediate in our studies (reaction of 2 plus
MAO and ethylene (1 atm)); as a result, the validity of
Hexanes
Hexanes
a 175 psi, 40 ◦C except for run 17 (80 ◦C); reaction time,
15–30 min.
b No solid isolated, only butenes are produced (13C NMR,
GC–MS analysis).
c AlMe3 instead of MAO.

56
L.F. Groux et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 51–58
the above proposed mechanism in the present system
cannot be confirmed.
by heating an electrical jacket and circulation of cool-
ing fluid through an internal coil. A four-blade im-
peller rotating at 800 rpm was used for stirring. Prior
to each reaction, the reactor was heated to 140 ◦C
and purged three times with nitrogen (10 bar), then
placed under vacuum for 30 min, and purged again
with nitrogen three more times. Using transfer nee-
dles, 295 ml of solvent and the co-catalyst were trans-
ferred in the reactor under a nitrogen flux. The stirring
was turned on, and the reactor was stabilized at the set
point temperature and fed with ethylene. The ethylene
flux was monitored using a mass flow sensor (Brooks
5860E) until diluent saturation was reached. When the
set-point temperature and ethylene saturation were at-
tained, 5 ml of a solution containing (2–10)×10−6 mol
of complex 1 or 2 was transferred into the reactor us-
ing a catalyst injection bomb. After the desired reac-
tion time had expired, 25 ml of ethanol was pumped
inside the reactor to quench the polymerization, and
then the reactor was vented. The liquid was poured
onto 500 ml of ethanol and kept there for 24 h to en-
sure complete precipitation. The polymer was filtered,
washed twice with ethanol, and dried under vacuum at
50 ◦C. The results are presented as shown in Tables 1
and 2.
3. Conclusion
The combination of the neutral nickel compound
(1) and MAO can convert ethylene to butenes and lin-
ear PE. The performance of the catalysts and the char-
acteristics of the resulting polymers were dependent
upon the reaction parameters. It was observed that po-
lar solvents favor the dimerization of ethylene versus
its polymerization. On the other hand, activation of
the cationic complex 2 by MAO or AlMe3 leads to a
system which only dimerizes ethylene with high ac-
tivity. This result implies that a promising system for
tandem production of linear low-density polyethylene
(LLDPE) could be developed using a mixture of com-
plex 2 and a selected catalyst for ␣-olefin polymeriza-
tion [14].
4. Experimental section
4.1. General Comments
All manipulations, except for the gel permeation
chromatography (GPC), were performed under an
inert atmosphere of N2 or argon using standard
Schlenk techniques and a dry box. The polymeriza-
tion experiments were carried out in oxygen free
solvents (dried using 3 Å molecular sieves). AlMe3
(2 M in toluene, Aldrich) and MAO (10 wt.% in
toluene, Aldrich) were used as received. Solid MAO,
obtained by evaporating the toluene solution to dry-
ness, was used in the NMR experiments. CP grade
ethylene and ultra high purity nitrogen (Praxair)
were purified by passing through 3 Å molecular
sieves and de-oxygenation catalyst beds. Synthe-
ses of (η3:η0-Ind(CH2)2NMe2)Ni(PPh3)Cl, 1, and
[(η3:η1-Ind(CH2)2NMe2)Ni(PPh3)][BPh4], 2, have
been reported previously [8].
4.3. Polymer characterization
The molecular weights (Mw) were determined by
GPC using a Waters 150CV system equipped with
three columns, differential viscometer, and refrac-
tive index detectors. The analyses were undertaken
using 1,2,4-trichlorobenzene as solvent (with 0.5 g/l
of Irganox 10/10 as antioxidant), at 140 ◦C, and Mw
calculated using a universal calibration curve built
with polystyrene standards. The results are reported
as shown in Tables 1 and 2.
The polymers formed in our studies were shown to
be linear PE with a small number of ethyl branches
on the basis of 13C {1H} NMR spectroscopy (Bruker
Avance 500 spectrometer, 125.75 MHz); the spec-
tra recorded at 120 ◦C in C2Cl4D2. For example,
the 13C {1H} NMR spectrum of the PE obtained
from run 14 shows the following signals (δ (integra-
tion, attribution [15,16])): 39.70 (1.0, brB2), 34.07
4.2. Polymerization of ethylene
δ
Ethylene polymerization was done using a 500 ml
autoclave engineering stainless steel reactor. The tem-
perature was controlled within 0.5 ◦C of the set point
(1.78, αB2), 30.48 (2.71, γ B2), 30.00 (53.68, B2),
27.32 (1.82, βB2), 26.74 (0.91, 2B2), 11.20 (1.20,
1B2) (Fig. 4). The branching is presumably due to

L.F. Groux et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 51–58
57
spectra were recorded on a Bruker AMXR400 spec-
trometer. The same procedure was repeated using 7,
14, 20, 30 and 100 equivalents of MAO. The result-
ing species were identified by their chemical shifts
where possible (31P {1H}): 30.7 ppm (1), 47.8 ppm
(η3:η0-Ind(CH2)2NMe2)Ni(PPh3)Me, 28.6 ppm (2),
unidentified species: 46.1, 44.7, 41.0, 36.9, 30.4,
27.5 ppm) and the ratios calculated from the integra-
tions. The results are presented as shown in Scheme 1
and Fig. 2.
Fig. 4.
the co-polymerization of ethylene and the 1-butene
formed in situ.
4.6. Reactivities of 1 with AlMe3
Compound 1 (13.0 mg, 0.024 mmol) and AlMe3
(0.12 ml of a 2 M solution in hexanes, 0.24 mmol,
10 equivalent) were mixed in C6D6. The 31P
{1H} spectrum was recorded after 15 min, show-
ing two phosphorus-containing species (47.2 and
47.0 ppm) characteristic of new Ni–Me complexes:
(η3:η0-Ind(CH2)2NMe2)Ni(PPh3)Me and (η3:η0-Ind-
(CH2)2NMe2AlMe3)Ni(PPh3)Me.
4.4. Reactivities of 1 with MeLi
Compound 1 (13.0 mg, 0.024 mmol) and MeLi
(0.038 ml of a 1.5 M solution in Et2O, 0.029 mmol,
2.4 equivalent) were mixed in C6D6. The 31P {1H}
spectrum was recorded 15 min later, showing only
one phosphorus-containing species (47.8 ppm) char-
acteristic of (η3:η0-Ind(CH2)2NMe2)Ni(PPh3)Me.
The 1H NMR spectrum confirms the formation of this
species with the characteristic doublet at −0.67 ppm
(3JP-H = 5.5 Hz) due to the Ni–Me moiety [9].
4.7. Reactivities of 2 with MAO
Compound 1 (9.5 mg, 0.011 mmol) and MAO
(67 mg, 1.1 mmol assuming a Mw of 58, 100 equiv-
alents) were mixed in CDCl3. The 31P {1H} and
1H NMR spectra were recorded 30 min later. Only
one phosphorus-containing species was observed at
28.8 ppm.
4.5. Reactivities of 1 with MAO
Compound 1 (20.1 mg, 0.037 mmol) and MAO
(4.3 mg, 0.074 mmol assuming a Mw of 58) were
mixed in C6D6. After 30 min, 31P {1H} and 1H NMR
Scheme 1.

58
L.F. Groux et al. / Journal of Molecular Catalysis A: Chemical 193 (2003) 51–58
4.8. Reactivities of 2 with MAO in the presence of
ethylene (10 psi)
[2] L.K. Johnson, C.M. Killian, M. Brookhart, J. Am. Chem.
Soc. 117 (1995) 6414.
[3] L.K. Johnson, (DuPont) Int. Patent WO 96/23010 (1996).
[4] T.R. Younkin, E.F. Connor, J.L. Henderson, S.K. Friedrich,
R.H. Grubbs, D.A. Bansleben, Science 287 (2000) 460
(references therein).
[5] M.-A. Dubois, R. Wang, D. Zargarian, J. Tian, R.
Vollmerhaus, Z. Li, S. Collins, Organometallics 20 (2001)
663.
[6] R. Vollmerhaus, F. Bélanger-Gariépy, D. Zargarian, Organo-
metallics 16 (1997) 4762.
Compound 1 (12.0 mg, 0.0145 mmol) and MAO
(84 mg, 1.45 mmol assuming a Mw of 58, 100 equiva-
lent) were mixed in CDCl3 and the solution exposed
to 10 psi of ethylene for a period of 10 min. The
31P {1H}, 1H NMR and 13C {1H} spectra were
recorded on a Bruker AMXR400 spectrometer. One
major phosphorus-containing species is observed
at 28.8 ppm, whereas, traces of other phosphorus-
containing species are observed at 37.9, 36.1, 26.7 and
24.0 ppm. The major products obtained were butenes
(13C {1H}): Z-butene (12.5 and 124.7 ppm) and
E-butene (18.0 and 126.0 ppm) in a 1:2 ratio [17].5
[7] L.F. Groux, D. Zargarian, Organometallics 20 (2001)
3811.
[8] L.F. Groux, F. Bélanger-Gariépy, D. Zargarian, R.
Vollmerhaus, Organometallics 19 (2000) 1507.
[9] T.A. Huber, M. Bayrakadarian, S. Dion, I. Dubuc, F. Bélanger-
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Acknowledgements
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ural Sciences and Engineering Research Council of
Canada (NSERC), le fond FCAR of Que., and the
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5
The observation in the polymer of exclusively ethyl branches
implies a 1-butene/ethylene co-polymerization. On the other hand,
complexes such as (1-i-Pr-Ind)(PPh3)NiOTf, which is a precursor
to the cation [(1-i-Pr-Ind)(PPh3)Ni]+, isomerize 1-hexene to Z-
and E-2-hexene [13]. Therefore, it is reasonable to assume that
the initial product of the dimerization reaction is 1-butene, some
of which is co-polymerized to give the polymer obtained the
unreacted 1-butene is then isomerized to Z- and E-2-butene.