Nickel(II) complexes with imino-imidazole chelating ligands bearing pendant donor groups (SR, OR, NR2, PR2) as precatalysts in ethylene oligomerization

Article abstract of DOI:10.1016/j.jorganchem.2012.07.044

New imino-imidazole ligands bearing a pendant donor function L were synthesized in excellent yields. The corresponding nickel(II) complexes [NiCl₂(imino-imidazole-L)]_n (L = (CH₂) ₂SMe (2a), (CH₂)₂OMe (2b), (CH ₂)₂NEt₂ (2c), (CH₂) ₂PPh₂ (2d), (C₆H₄)-p-OMe (2e), (CH₂)₃OMe (2f), (CH₂)₃CH₃ (2g); n = 1, 2) were prepared and characterized by FT-IR spectroscopy and elemental analysis. Furthermore, the coordination geometry around the metal center in the dinuclear complex 2a and the mononuclear complexes 2c and 2e was unambiguously established by single crystal X-ray diffraction. All complexes have been evaluated for the oligomerization of ethylene in the presence of EtAlCl₂ or MAO (methylaluminoxane) as cocatalyst, and mostly dimers and trimers were produced. Better activities were observed with EtAlCl ₂ as cocatalyst than with MAO.

Full text of DOI:10.1016/j.jorganchem.2012.07.044

Journal of Organometallic Chemistry 718 (2012) 31e37
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Nickel(II) complexes with imino-imidazole chelating ligands bearing pendant
donor groups (SR, OR, NR2, PR2) as precatalysts in ethylene oligomerization
,
a
a,
Adrien Boudier a, Pierre-Alain R. Breuil a , Lionel Magna , Hélène Olivier-Bourbigou
,
*
*
Pierre Braunstein b
a IFP Energies nouvelles, Rond point de l’échangeur de Solaize, 69360 Solaize, France
b Laboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS), Université de Strasbourg, 4 rue Blaise Pascal, F-67081 Strasbourg Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
New imino-imidazole ligands bearing a pendant donor function L were synthesized in excellent yields.
The corresponding nickel(II) complexes [NiCl2(imino-imidazole-L)]n (L ¼ (CH2)2SMe (2a), (CH2)2OMe
(2b), (CH2)2NEt2 (2c), (CH2)2PPh2 (2d), (C6H4)-p-OMe (2e), (CH2)3OMe (2f), (CH2)3CH3 (2g); n ¼ 1, 2) were
prepared and characterized by FT-IR spectroscopy and elemental analysis. Furthermore, the coordination
geometry around the metal center in the dinuclear complex 2a and the mononuclear complexes 2c and
2e was unambiguously established by single crystal X-ray diffraction. All complexes have been evaluated
for the oligomerization of ethylene in the presence of EtAlCl2 or MAO (methylaluminoxane) as cocatalyst,
and mostly dimers and trimers were produced. Better activities were observed with EtAlCl2 as cocatalyst
than with MAO.
Received 22 June 2012
Received in revised form
18 July 2012
Accepted 26 July 2012
Keywords:
Oligomerization
Ethylene
Nickel
Tridentate ligand
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
2. Results and discussion
The transition-metal catalyzed oligomerization of ethylene to
short chain -olefins has triggered considerable attention over
2.1. Synthesis and characterization of the ligands and Ni(II)
complexes
a
decades. Long after the discovery of the “nickel effect” by Wilke
et al. [1], renewed interest was generated by the work of Brookhart
and co-workers on the development of nickel-based complexes
Ligands 1ae1g were obtained in excellent yield (>95%) by
condensation reaction between 1-methyl-1H-imidazole-2-
carboxaldehyde and the corresponding amines. The volatility of
the different amino precursors, except the phosphino derivative,
allows easy purification. The ligands were characterized by 1H
NMR, 13C NMR and FT-IR spectroscopy. The nickel(II) complexes
(2ae2g) were then prepared by reaction of [NiCl2(DME)]
(DME ¼ dimethoxyethane) with a slight excess of the corre-
sponding ligand in CH2Cl2 (Scheme 1).
All complexes were obtained in high yields (w90%) and char-
acterized by FT-IR spectroscopy and elemental analysis. The coor-
dination of the ligand was confirmed by the shift of the absorption
band of the imino group (nC]N) to lower wavenumbers and its
weaker intensity in comparison to that for the free ligand
(1650e1641 cmꢀ1 for 1a and 2a, respectively; see Experimental
section). Elemental analyses confirmed the presence of one ligand
per metal center in each complex. X-ray diffraction studies on 2a, 2c
and 2e0 unambiguously established the coordination geometry
around the metal center (Scheme 2).
chelated by a-diimine ligands [2,3]. This resulted in the develop-
ment of a wide range of nickel precatalysts bearing P,P- [4e6], P,N-
[7e12], P,O- [13e19], N,N- [20e25] or N,O- [26e31] type bidentate
ligands. Understandably, tridentate ligands tend to be developed
with the advantage of offering an even wider diversity [32,33]. One
strategy consists in introducing an additional donor group on
bidentate ligands and this was successfully implemented for iron-
catalyzed [34e36] or titanium-catalyzed [37e41] oligomerization.
Herein, we report the straightforward synthesis of imino-imidazole
ligands bearing a pendant donor group. The corresponding nick-
el(II) complexes were prepared, characterized and evaluated for
ethylene oligomerization using EtAlCl2 or MAO as cocatalysts.
* Corresponding authors.
E-mail addresses: pierre-alain.breuil@ifpen.fr (P.-A.R. Breuil), helene.olivier-
bourbigou@ifpen.fr (H. Olivier-Bourbigou).
Single crystals of 2a suitable for X-ray diffraction analysis were
grown by slow diffusion of diethyl ether into a methanol solution of
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.07.044

32
A. Boudier et al. / Journal of Organometallic Chemistry 718 (2012) 31e37
Scheme 1. Synthesis of ligands (1ae1g) and the corresponding nickel(II) precatalysts (2ae2g).
ꢀ
ꢀ
the complex. The molecular structure of complex 2a is shown in
Fig. 1 and selected bond distances and angles are listed in Table 1. In
the solid state, the complex adopts a dinuclear structure and the
N,N,S tridentate coordination mode of the ligand is established
2.211(4) A. The NieN distances are 2.030(4) A (Ni(1)eN(7)) and
ꢀ
2.068(4) A (Ni(1)eN(10)), respectively. Although the metal center
in complexes 2a and 2e0 adopts an octahedral coordination
geometry, there are slight differences in the interligand angles
between these structures. For example, the Cl(2)eNi(1)eCl(3) angle
is wider in complex 2e0 (95.78(6)ꢁ) than in 2a (93.01(3)ꢁ) and the
Cl(3)eNi(1)eO(20) angle of 169.58(10)ꢁ in 2e0 is smaller than the
Cl(3)(2)eNi(1)eCl(2) angle of 174.79(3)ꢁ in 2a.
ꢀ
(Ni(1)eS(4) ¼ 2.524(10) A). A terminal chloride ligand and two
bridging chlorides complete the metal coordination spheres. The
existence of a C2 axis passing through Cl(3) atoms results in the
planarity of the central Ni2Cl2 moiety. The NieNi separation of
ꢀ
3.586 A is too long to represent any significant direct interaction
and this is consistent with their d8 electronic configuration. The six-
coordinated metal centers adopt a distorted octahedral coordina-
tion geometry, as indicated by the values of the Cl(3)eNi(1)eN(10)
and S(4)eNi(1)eN(7) angles (97.53(8)ꢁ and 80.98(8)ꢁ) and by the
values of the Cl(3)eNi(1)eN(7) and Cl(3)(2)eNi(1)eCl(2) angles
(173.41(7)ꢁ and 174.79(3)ꢁ, respectively).
2.2. Ethylene oligomerization with the Ni-complexes 2ae2g
Nickel complexes 2ae2g were used as precatalysts for the
oligomerization of ethylene. Experiments were carried out at 5 or
10 bar and 45 ꢁC in n-heptane or in toluene. When activated by 15
equivalents of ethylaluminum dichloride (EtAlCl2) at 5 bar and
45 ꢁC, complex 2a presents an interesting activity
(1.63 ꢂ 106 gC2H4 (molNi h)ꢀ1) and compares favorably with
[NiCl2(DME)] used as reference (Table 2, entries 1 and 2). Due to the
lack of solubility of complexes 2ae2g, toluene was preferred to n-
heptane. This led to an increase of the activity
(3.14 ꢂ 106 gC2H4 (molNi h)ꢀ1) for 2a with no significant effect on the
reaction selectivity (Table 2, entry 3). A good stability of the pre-
catalyst 2a was observed over more than half an hour after acti-
vation in these solvents. As expected, adjusting the pressure to
10 bar of ethylene resulted in an increase of activity without
affecting the distribution of oligomers (Table 2, entry 4). Substitu-
tion of the thioether group in 2a by an ether as in 2b led to a slight
improvement of the activity (Table 2, entries 4 and 5) while
marginal effects on both activity and selectivity were observed
when an amino or a phosphino group was introduced, as in
complexes 2c and 2d, respectively (Table 2, entries 6 and 7). This
suggests that the functionalization introduced on the imino-
imidazole backbone has only a limited role, which was confirmed
to a certain degree by the use of complex 2g, which also presents
Single crystals of 2c were obtained by slow diffusion of diethyl
ether into an acetonitrile solution of the complex. The complex
adopts an overall distorted trigonal-bipyramidal geometry in which
the imino nitrogen atom N(7) and the chlorine atoms Cl(2) and
Cl(3) form the equatorial plane (Fig. 2). The nitrogen donor atoms of
the N,N,N tridentate ligand and the Ni center are almost coplanar.
Selected bond distances and angles are given in Table 1. The NieN
bond distance of the chelating pendant donor function is longer
ꢀ
(2.178(4) A) than NieN distances of either the imidazole ring
ꢀ
ꢀ
(2.105(4) A) or the imino group (2.038(4) A).
Crystals of 2e0, obtained by slow diffusion of diethyl ether into
a methanol solution of complex 2e, revealed that one molecule of
MeOH is bonded to the metal. This leads to a distorted octahedral
coordination geometry for the Ni center (Fig. 3), as evidenced by
a Cl(3)eNi(1)eN(7) angle of 89.56(11)ꢁ. The molecule of MeOH is
coordinated to the metal via a dative bond as established by the
presence of a H atom on the oxygen and by the Ni(1)eO(20)
ꢀ
distance (2.154(4) A) [23]. The pendant donor group occupies an
equatorial coordination site with a Ni(1)eO(18) bond length of
Scheme 2. Crystallographically characterized complexes 2a, 2c and 2e0.

A. Boudier et al. / Journal of Organometallic Chemistry 718 (2012) 31e37
33
Fig. 2. ORTEP view of the nickel(II) complex 2c. H atoms are omitted for clarity.
Ellipsoids are drawn at a 50% probability level.
significant than with EtAlCl2 as cocatalyst. The selectivity for dimers
was improved to 94% when complex 2c was used in combination
with 500 equivalents of MAO (Table 3, entry 4) and the selectivities
for a-olefins was higher than with EtAlCl2, up to 56% for 1-butene in
the C4 fraction (Table 3, entry 1). Similar or slightly higher activities
(from 0.93 ꢂ 106 to 1.15 ꢂ 106 gC2H4 (molNi h)ꢀ1) were observed
when the ligand bears an ether, an amino or a phosphino moiety, as
in 2b, 2c, and 2d, respectively, instead of a thioether group
(0.84 ꢂ 106 gC2H4 (molNi h)ꢀ1), as in 2a (Table 3, entries 1, 2, 4 and 6).
Increasing the molar ratio of MAO to nickel complexes 2b or 2c
from 500 to 1000 led to higher activities but to a decrease of the
selectivity in butenes (from 93% to 88% for 2b and from 94% to 88%
for 2c) and in 1-butene (from 40% to 32% for 2b and from 32% to 31%
for 2c) in the C4 fraction (Table 3, entries 2e5). Very low activity
was noticed when the molar ratio of activator to Ni was under 500.
Similarly to the observations made with EtAlCl2 as cocatalyst,
introduction of a rigid linker as in 2e resulted in a slight improve-
ment of the activity (Table 3, entries 2 and 7) while increasing the
length of the alkyl linker, as in complex 2f, led to a slight decrease of
activity (Table 3, entries 2 and 8). Surprisingly, a significantly
amount of higher olefins was produced with catalyst 2f (Table 3,
entry 8). As observed with EADC activation, complex 2g afforded
a comparable activity (Table 3, entry 9).
Fig. 1. ORTEP view of the nickel(II) complex 2a. H atoms are omitted for clarity.
Ellipsoids are drawn at a 50% probability level.
comparable performances (Table 2, entry 10). Interestingly, the
presence of an oxygen donor atom improved slightly the activity
(Table 2, entry 5). The best activity (12.03 ꢂ 106 gC2H4 (molNi h)ꢀ1
)
was obtained when a non flexible linker was introduced between
the imine and the functional group, as in complex 2e (Table 2, entry
8), which emphasizes the interest for a tridentate behavior of the
ligand. Lengthening the linker to three carbon atoms as in complex
2f has however a detrimental effect on the activity (Table 2, entry
9). For all the complexes, the selectivity for 1-butene was relatively
low (in a range 8e18%), probably due to the known isomerization
ability of nickel(II)/EtAlCl2 catalytic systems [20,42].
Precatalysts 2ae2g were then evaluated using methyl-
aluminoxane (MAO) as cocatalyst (Table 3). At 30 bar and 45 ꢁC, the
activities of complexes 2ae2g were approximately one order of
magnitude lower than with EtAlCl2 as activator. It should be noted
that under more dilute conditions than in Table 2 ([Ni] ¼ 0.2 mM vs
[Ni] ¼ 1 mM in Table 3), no significant production of oligomers was
observed, which led us to carry out the catalytic tests under more
concentrated conditions. Variations of selectivities were more
3. Conclusion
A series of nickel(II) complexes containing imino-imidazole
ligands with a pendant donor group have been synthesized and
Table 1
ꢁ
0
ꢀ
Selected bond distances (A) and angles ( ) for complexes 2a, 2c and 2e .
2a 2c
2e0
2.524(10) 2.178(4) 2.211(4)
Ni(1)eXa
Ni(1)eN(7)
Ni(1)eN(10)
C(6)eN(7)
N(7)eC(8)
Ni(1)eCl(3)
Ni(1)eCl(2)
Ni(1)eO(20)
N(7)eNi(1)eN(10)
XeNi(1)eN(7)a
XeNi(1)eN(10)a
Cl(3)eNi(1)eN(7)
Cl(3)eNi(1)eN(10)
Cl(2)eNi(1)eCl(3)
YeNi(1)eCl(2)b
Cl(3)(2)eNi(1)eCl(3)
2.056(2)
2.070(3)
1.454(4)
1.273(4)
2.382(8)
2.387(9)
2.038(4)
2.105(4)
1.446(5)
1.282(6)
2.312(12)
2.276(12)
2.030(4)
2.068(4)
1.419(6)
1.281(6)
2.373(15)
2.343(15)
2.154(4)
80.78(17)
75.88(15)
156.05(15)
89.56(11)
97.51(13)
95.78(6)
90.74(10)
e
e
e
79.84(10)
80.98(8)
160.69(8)
173.41(7)
97.53(8)
93.01(3)
174.79(3)
83.56(3)
77.99(14)
78.97(14)
151.76(14)
98.62(11)
102.49(11)
106.30(5)
e
e
a
X ¼ S(4) for 2a, X ¼ N(4) for 2c and X ¼ O(18) for 2e0.
Y ¼ Cl(3)(2) for 2a, Y ¼ O(20) for 2e0.
Fig. 3. ORTEP view of the nickel(II) complex 2e0. H atoms are omitted for clarity
(except for MeOH). Ellipsoids are drawn at a 50% probability level.
b

34
A. Boudier et al. / Journal of Organometallic Chemistry 718 (2012) 31e37
ꢀ
Table 2
from SigmaeAldrich orEurisotop, freeze-pumped and stored over4 A
molecular sieves under argon. The 1H, 31P{1H}, and 13C{1H} NMR
spectra were recorded on a Bruker AC 300 MHz instrument at 293 K
unless otherwise stated. All chemical shifts are reported in ppm vs
SiMe4 and were determined with reference to residual solvent peaks
[43]. 31P NMR chemical shifts are reported in ppm relative to a 85%
H3PO4 solution inwater. All coupling constants are given in Hertz. Gas
chromatographic analyses were performed on an Agilent 6850 series
IIequipped withaflameionizationdetectorandusinganAgilentPona
Ethylene oligomerization with precatalysts 2ae2g using EtAlCl2 as cocatalyst.a
Entry Precatalyst
Time PC2H4 Activityb Selectivity (wt%)c
(min) (bar)
C4 (1 ꢀ C4)d C6 (1 ꢀ C6)d C6þ
1e
2e
3
4
5
6
7
8
9
[NiCl2(DME)] 85
5
5
5
10
10
10
10
10
10
10
n.d.f
1.63
3.14
9.56
11.08
9.79
9.87
12.03
8.98
9.90
e
e
e
e
1
2
1
1
2
1
1
e
2a
2a
2a
2b
2c
2d
2e
2f
75
40
15
15
15
15
15
15
15
79 (6)
83 (14)
84 (18)
86 (13)
86 (12)
87 (8)
83 (18)
86 (10)
83(18)
21 (2)
16 (2)
14 (2)
13 (3)
13 (2)
11 (1)
16 (3)
13 (2)
17(3)
column (50 m, 0.2 mm diameter, 0.5 mm film thickness). FT-IR spectra
were recorded in the region 4000e450 cmꢀ1 on a PerkineElmer
Spectrum one FT-IR spectrometer (ATR mode, ZnSe diamond).
Elemental analyses were performed by the Service Central d’Analyses
of the CNRS (Vernaison, France).
10
2g
a
Ni (20
m
mol), Al/Ni ¼ 15, toluene (100 mL), 45 ꢁC.
b
ꢂ 106 gC2H4 converted (molNi h)ꢀ1
.
c
Determined by GC.
4.2. Synthesis of the ligands (1ae1g)
d
Cn, wt% of hydrocarbons with n carbon atoms in oligomers, 1 ꢀ Cn, wt% of
terminal alkene in the Cn fraction.
e
4.2.1. Synthesis of N-((1-methyl-1H-imidazol-2-yl)methylene)-2-
(methylthio)ethanamine (1a)
Heptane was used instead of toluene.
Non determined.
f
2-(methylthio)ethanamine (0.46 mL, 4.89 mmol) was added to
a solution of 1-methyl-1H-imidazole-2-carbaldehyde (0.490 g,
4.45 mmol) in dichloromethane (15 mL) and the mixture was
stirred for 1 h at room temperature. Small amount of MgSO4 was
added to the yellow reaction mixture. The solution was then
filtered via canula. The solvent and the small excess of 2-(methyl-
thio)ethanamine were evaporated to afford the desired product as
fully characterized. Single crystal X-ray diffraction studies
confirmed the tridentate coordination mode of the ligand, whether
the complex crystallizes in a dinuclear form, as for 2a, or in
a mononuclear form, as for 2c and 2e0. Upon activation by EtAlCl2,
the precatalysts 2ae2g exhibit very high productivities toward
ethylene oligomerization leading to short chain olefins (C4eC6),
a pale yellow oil in 95% yield. 1H NMR (300 MHz, CD2Cl2):
d(ppm)
however with a low selectivity for
a-olefins. Higher selectivities
8.28 (m, 1H), 7.05 (d, 1H, J ¼ 1.0 Hz), 6.95 (s, 1H), 3.95 (s, 3H), 3.77
(td, 2H, J ¼ 6.8, J ¼ 1.3 Hz), 2.79 (t, 2H, J ¼ 6.8 Hz), 2.12 (s, 3H). 13C
in butenes and 1-butene are observed when the precatalysts were
activated with MAO. However in this case, the turnover frequencies
were generally lower by one order of magnitude. Regarding the
ether derivatives and irrespective of the cocatalyst used, the rigid
linker 1,2-phenylene was preferred over the flexible alkyl chains
containing two or three carbon atoms.
{1H} NMR (75 MHz, CD2Cl2):
d(ppm) 154.60, 143.50, 129.39, 125.24,
61.36, 35.52, 15.86. FT-IR (cmꢀ1): 2967m, 1650s (nC]N), 1518w,
1475m, 1437m, 1369w, 1287m, 1203w, 1174w, 1149w, 1067s, 919w,
748m, 707m, 691m, 500w, 468w.
4.2.2. Synthesis of 2-methoxy-N-((1-methyl-1H-imidazol-2-yl)
methylene)ethanamine (1b)
4. Experimental section
Ligand 1b was prepared according to the method described for
1a using 2-(methoxy)ethylamine (0.39 mL, 4.54 mmol) and 1-
methyl-1H-imidazole-2-carbaldehyde (0.455 g, 4.13 mmol) and
isolated as a pale yellow oil in 92% yield. 1H NMR (300 MHz,
4.1. General considerations
All manipulations were carried out using standard Schlenk tech-
niques under inert atmosphere. Toluene, THF, pentane and
dichloromethane were dried bya solvent purification system (SPS-M-
Braun). Dimethoxyethane (DME) was distilled over sodium/benzo-
phenone. Methanol and acetonitrile were degassed and dried over
CD2Cl2):
d(ppm) 8.26 (s, 1H), 7.04 (s, 1H), 6.94 (s, 1H), 3.95 (s, 3H),
3.75e3.68 (m, 2H), 3.67e3.60 (m, 2H), 3.33 (s, 3H). 13C{1H} NMR
(75 MHz, CD2Cl2): d(ppm) 154.96, 143.59, 129.32, 125.12, 72.53,
61.64, 58.86, 35.46. FT-IR (cmꢀ1): 2875m, 1650s (nC]N), 1518w,
1475m, 1437m, 1366w, 1287m, 1236w, 1191w, 1118s, 1026w, 955w,
919m, 802m, 757m, 708m, 690m, 558w, 473w.
ꢀ
molecularsieves(4A). Commercialstartingmaterialswerepurchased
from SigmaeAldrich and Alfa Aesar and used without further purifi-
cation. Deuterated solvents (CD2Cl2 and (CD3)2CO) were purchased
4.2.3. Synthesis of N,N-diethyl-N0-((1-methyl-1H-imidazol-2-yl)
methylene)ethane-1,2-diamine (1c)
Ligand 1c was obtained according to the method described for
1a using N,N-(diethyl)ethylenediamine (0.73 mL, 5.21 mmol) and
1-methyl-1H-imidazole-2-carbaldehyde (0.521 g, 4.73 mmol) and
isolated as a yellow oil in 94% yield. 1H NMR (300 MHz, CD2Cl2):
Table 3
Ethylene oligomerization with precatalysts 2ae2g using MAO as cocatalyst.a
Entry
Precatalyst
Al/Ni
Activityb
Selectivity (wt%)c
C4 (1 ꢀ C4)d
C6 (1 ꢀ C6)d
C6þ
1
2a
2b
2b
2c
2c
2d
2e
2f
500
500
1000
500
1000
500
500
0.84
0.93
2.44
1.15
2.21
1.01
1.04
0.90
0.93
91 (56)
93 (40)
88 (32)
94 (32)
88 (31)
89 (38)
88 (30)
80 (51)
86 (40)
5 (19)
4 (12)
9 (11)
4 (8)
9 (10)
7 (13)
8 (9)
4
3
3
2
3
4
4
13
4
d
(ppm) 8.25 (td, 1H, J ¼ 1.3, J ¼ 0.5 Hz), 7.04 (d, 1H, J ¼ 1.1 Hz), 6.94
2
(s, 1H), 3.95 (s, 3H), 3.64 (td, 2H, J ¼ 6.8, J ¼ 1.3 Hz), 2.72 (t, 2H,
3e
4
J ¼ 6.8 Hz), 2.56 (q, 4H, J ¼ 7.1 Hz), 1.00 (t, 6H, J ¼ 7.1 Hz). 13C{1H}
5e
6
NMR (75 MHz, CD2Cl2):
d(ppm) 154.16, 143.83, 129.23, 124.99,
60.70, 47.84, 35.44, 12.36. FT-IR (cmꢀ1): 2967m, 1650s (nC]N),
1518w, 1475m, 1437m, 1369w, 1287m, 1203w, 1174w, 1149w, 1067s,
919w, 748m, 707m, 691m, 500w, 468w.
7
8
9
500
500
7 (33)
10(11)
2g
a
Ni (20 m
mol), toluene (20 mL), ethylene pressure 30 bar, 45 ꢁC, 50 min.
4.2.4. Synthesis of 2-(diphenylphosphino)-N-((1-methyl-1H-imidazol-
2-yl)methylene) ethanamine (1d)
2-(Diphenylphosphino)ethanamine (0.707 g, 3.08 mmol) was
added to a solution of 1-methyl-1H-imidazole-2-carbaldehyde
b
c
ꢂ 106 gC2H4 converted (molNi h)ꢀ1
.
Determined by GC.
Wt% in the Cn fraction.
Reaction time: 30 min.
d
e

A. Boudier et al. / Journal of Organometallic Chemistry 718 (2012) 31e37
35
(0.339 g, 3.08 mmol) in dichloromethane (15 mL) and the reaction
mixture was stirred overnight at room temperature under inert
atmosphere. The solvent was evaporated under reduced pressure to
afford the desired product as a yellow oil in 95% yield. 1H NMR
and dried under vacuum. The desired product was obtained as
a yellow solid in 74% yield.
Anal. Calc. for C4H10Cl2NiO2: C, 21.87; H, 4.59; Ni, 26.71. Found:
C, 21.47; H, 4.73; Ni, 26.12.
(300 MHz, CD2Cl2):
7.04 (d, 1H, J ¼ 1.0 Hz), 6.92 (s, 1H), 3.85 (s, 3H), 3.78e3.66 (m, 2H),
2.60e2.35 (m, 2H). 13C{1H} NMR (75 MHz, CD2Cl2):
(ppm) 153.95,
d(ppm) 8.27e8.19 (m, 1H), 7.51e7.29 (m, 10H),
4.3.2. Synthesis of NiCl2{N-((1-methyl-1H-imidazol-2-yl)
methylene)-2-(methylthio)ethanamine} (2a)
d
143.55, 139.14 (d, J ¼ 13.4 Hz), 133.11 (d, J ¼ 18.9 Hz), 129.35, 128.90
To a suspension of [NiCl2(DME)] (0.463 g, 1.48 mmol) in dichloro-
methane (15 mL) was added 1.05 equiv of ligand 1a (0.284 g,
1.55 mmol) in dichloromethane (10 mL). The reaction mixture was
stirred overnight at room temperature after which the solvent volume
was reduced to 10 mL. Diethyl ether (20 mL) was added to precipitate
a green solid which was washed with diethyl ether (3 ꢂ 20 mL) and
dried under vacuum. The complex was obtained as a green powder in
92% yield. FT-IR (cmꢀ1): 3133w, 2919m, 1641m (nC]N), 1542w, 1494s,
1425s,1362m,1290m,1217w,1179m,1090m,1029s, 952m, 847s, 817m,
735s, 710s, 665w, 569w, 477s, 470w. Anal. Calc. for C8H13Cl2N3NiS: C,
30.71; H, 4.19; N, 13.43. Found: C, 30.46; H, 3.91; N, 13.40.
(d, J ¼ 6.6 Hz), 128.77, 125.18, 59.08 (d, J ¼ 19.5 Hz), 35.47, 30.31 (d,
J ¼ 13.1 Hz). 31P{1H} NMR (121 MHz, CD2Cl2):
(ppm) ꢀ21.67. FT-IR
d
(cmꢀ1): 3051w, 1650s (nC]N), 1518w, 1478m, 1434s, 1412w, 1345w,
1287m, 1147w, 1025w, 919w, 739m, 697m, 631m, 534s.
4.2.5. Synthesis of 2-methoxy-N-((1-methyl-1H-imidazol-2-yl)
methylene)aniline (1e)
Ligand 1e was obtained according to the method described for 1a
using 2-(methoxy)aniline (0.39 mL, 3.49 mmol) and 1-methyl-1H-
imidazole-2-carbaldehyde (0.350 g, 3.18 mmol) and isolated as an
orange oil in 95% yield.1H NMR (300 MHz, (CD3)2CO):
d(ppm) 8.47 (d,
1H, J ¼ 0.5 Hz), 7.28 (s, 1H), 7.24e7.16 (m, 1H), 7.12 (d, 1H, J ¼ 1.0 Hz),
4.3.3. Synthesis of NiCl2{2-methoxy-N-((1-methyl-1H-imidazol-2-
yl)methylene)ethanamine} (2b)
7.08 (td, 2H, J ¼ 8.0, J ¼ 1.5 Hz), 7.02e6.94 (m,1H), 4.14 (s, 3H), 3.85 (s,
3H).13C{1H} NMR (75 MHz, (CD3)2CO):
d(ppm) 153.36,153.22,144.39,
Complex 2b was prepared according to the method described for
2a using [NiCl2(DME)] (0.304 g, 1.06 mmol) and ligand 1b (0.186 g,
1.12mmol)andobtainedasapalebluesolidin94%yield. FT-IR(cmꢀ1):
3128w, 2928w, 1625m (nC]N), 1542w, 1494s, 1450s, 1418s, 1354w,
1291m, 1243w, 1184m, 1115s, 1058m, 966s, 925w, 859w, 831w, 790s,
725s, 707m, 663m, 564w, 482s, 468m. Anal. Calc. for C8H13Cl2N3NiO:
C, 32.37; H, 4.41; N, 14.16. Found: C, 32.25; H, 4.51; N, 13.53.
142.02,130.52,127.64,126.78,121.86,121.37,113.07, 56.23,35.84. FT-IR
(cmꢀ1): 3102w, 2951w, 2835w, 1685w, 1626s (nC]N), 1585m, 1514m,
1439m, 1464m, 1430s, 1366w, 1288m, 1234s, 1178w, 1149w, 1115m,
1048w, 1025m, 965w, 919w, 869m, 816m, 745m, 687w, 631m, 536s.
4.2.6. Synthesis of 3-methoxy-N-((1-methyl-1H-imidazol-2-yl)
methylene)propan-1-amine (1f)
Ligand 1f was obtained according to the method described for 1a
using 2-(methoxy)propylamine (0.80 mL, 9.23 mmol) and 1-methyl-
1H-imidazole-2-carbaldehyde (0.924 g, 8.39 mmol). Compound 1f
was obtained as a yellowoil in 91% yield.1H NMR (300 MHz, CD2Cl2):
4.3.4. Synthesis of NiCl2{N,N-diethyl-N0-((1-methyl-1H-imidazol-2-
yl)methylene)ethane-1,2-diamine} (2c)
Complex 2c was obtained according to the method described for
2a using [NiCl2(DME)] (0.459 g, 1.36 mmol) and ligand 1c (0.279 g,
1.43 mmol) and isolated as an orange powder in 89% yield. FT-IR
d
(ppm) 8.27 (dd,1H, J ¼ 1.4, J ¼ 0.5 Hz), 7.03 (d,1H, J ¼ 1.1 Hz), 6.94 (s,
1H), 3.95 (s, 3H), 3.61 (td, 2H, J ¼ 6.8, J ¼ 1.3 Hz), 3.44 (t, 2H,
(cmꢀ1): 2924w, 160m
(nC]N), 1546w, 1486w, 1450m, 1424s,
J ¼ 6.4 Hz), 3.30 (s, 3H),1.90 (q, 2H, J ¼ 6.6 Hz).13C{1H} NMR (75 MHz,
1385w, 1346s, 1290w, 1229w, 1148w, 1087m, 1036w, 955m, 881w,
827s, 763s, 734m, 703m, 664m, 615w, 615w, 548m, 474w. Anal.
Calc. for C11H20Cl2N4Ni: C, 39.10; H, 5.97; N, 16.58. Found: C, 38.96;
H, 5.87; N, 16.28.
CD2Cl2): d(ppm) 153.85, 143.70, 129.21, 125.05, 70.64, 58.80, 58.66,
35.48, 31.37. FT-IR (cmꢀ1): 2925m, 2869m, 1649s (nC]N), 1517w,
1476m, 1437m, 1287m, 1184w, 1148w, 1118s, 1088m, 1020w, 962w,
809m, 755m, 707m, 508w, 481m.
4.3.5. Synthesis of NiCl2{2-(diphenylphosphino)-N-((1-methyl-1H-
imidazol-2-yl)methylene)ethanamine} (2d)
4.2.7. Synthesis of N-((1-methyl-1H-imidazol-2-yl)methylene)
butan-1-amine (1g)
Using the same procedure as for the synthesis of 1a, 1g was
obtained as a yellow oil in 95% yield using n-butylamine (0.48 mL,
4.89 mmol) and 1-methyl-1H-imidazole-2-carbaldehyde (0.490 g,
Complex 2d was obtained according to the method described
for 2a using [NiCl2(DME)] (0.180 g, 0.40 mmol) and ligand 1d
(0.136 g, 0.42 mmol) as a brown powder in 91% yield. FT-IR (cmꢀ1):
3051w, 1619w (nC]N), 1538w, 1487m, 1434s, 1347w, 1290w, 1174w,
1101m, 998w, 849w, 741s, 692s, 666s, 512m, 484m. Anal. Calc. for
C19H20Cl2N3NiP: C, 50.60; H, 4.47; N, 9.32. Found: C, 49.53; H, 4.71;
N, 9.40.
4.45 mmol). 1H NMR (300 MHz, CD2Cl2):
d
(ppm) 8.27 (d, J ¼ 6.2 Hz,
1H), 7.03 (s, 1H), 6.93 (s, 1H), 3.95 (s, 3H), 3.56 (td, J ¼ 6.8, 1.2 Hz,
2H), 1.64 (dq, J ¼ 12.2, 6.9 Hz, 2H), 1.50e1.32 (m, 2H), 0.94 (t,
J ¼ 7.3 Hz, 3H). 13C{1H} NMR (75 MHz, CD2Cl2):
d(ppm) 153.31 (s),
143.77 (s), 129.11 (s), 124.92 (s), 61.93 (s), 35.41 (s), 33.52 (s), 20.76
(s), 14.00 (s). FT-IR (cmꢀ1): 2930m, 1650s (nC]N), 1517w, 1476m,
1437s, 1413w, 1366w, 1287m, 1149w, 1026w, 972w, 919w, 859w,
748m, 708m, 628s, 528s, 468m.
4.3.6. Synthesis of NiCl2{2-methoxy-N-((1-methyl-1H-imidazol-2-
yl)methylene)aniline} (2e)
Complex 2e was prepared according to the method described
for 2a using [NiCl2(DME)] (0.530 g, 1.54 mmol) and ligand 1e
(0.347 g, 1.61 mmol) and isolated as a yellow powder in 95% yield.
FT-IR (cmꢀ1): 3084w, 2959w, 1602m (nC]N), 1540w, 1488s, 1439s,
1421s, 1370w, 1323m, 1297w, 1278w, 1248s, 1190m, 1169m, 1120m,
1089w, 1047w, 1017m, 968m, 938m, 823w, 806m, 755s, 728s,
698m, 667w, 607m, 587w, 479w. Anal. Calc. for C12H13Cl2N3NiO: C,
41.79; H, 3.80; N, 12.19. Found: C, 41.22; H, 3.80; N, 11.85.
4.3. Synthesis of the nickel complexes
4.3.1. Synthesis of [NiCl2(DME)]
In a 250 mL round bottom flask, NiCl2$6H2O (20.1 g, 84.5 mmol)
was heated to 130 ꢁC under vacuum for 1.5 h. The green solid
turned yellow. Triethyl orthoformate (27.7 g, 186.9 mmol) and
40 mL of freshly distilled dimethoxyethane (DME) were added. The
mixture was refluxed for 2.5 h. The resulting solid was filtered,
washed with DME (2 ꢂ 30 mL) and anhydrous pentane (3 ꢂ 40 mL)
4.3.7. Synthesis of NiCl2{3-methoxy-N-((1-methyl-1H-imidazol-2-
yl)methylene)propan-1-amine} (2f)
Complex 2f was obtained according to the method described for
2a using [NiCl2(DME)] (0.494 g, 1.59 mmol) and ligand 1f (0.302 g,

36
A. Boudier et al. / Journal of Organometallic Chemistry 718 (2012) 31e37
1.67 mmol) and isolated as a green powder in 95% yield. FT-IR
(cmꢀ1): 2949w, 2834w, 1629m (nC]N), 1542w, 1495m, 1448w,
1424m, 1374w, 1289m, 1213w, 1180w, 1118m, 1081s, 1044s, 976m,
960m, 931w, 848s, 766w, 746s, 710s, 665w, 623w, 492m, 481m,
463w. Anal. Calc. for C9H15Cl2N3NiO: C, 34.78; H, 4.86; N, 13.52.
Found: C, 34.76; H, 4.99; N, 13.35.
atmosphere of ethylene before the toluene, the nickel precursor
and the cocatalyst were introduced. The total volume of solutions
introduced was 100 mL. The reactor was sealed and fed with
ethylene to the desired pressure. The reactor was heated at 45 ꢁC
and the magnetic stirring was set to 1000 rpm. During catalysis, the
pressure was maintained through a continuous feed of ethylene
from a bottle placed on a balance used to monitor the ethylene
uptake. At the end of the test, instantly after turning off the feed of
ethylene, aliquots of gaseous and liquid effluents were collected
and analyzed by GC. Stirring was then stopped and the reactor was
cooled down to 25 ꢁC. The gaseous effluents were quantified using
a flowmeter and collected in a 15 L polyethylene bottle filled with
water. The liquid effluents were weighed. The catalyst and the
cocatalyst were quenched by addition of 2 mL of a 10% H2SO4
solution in water. Aliquots of gaseous and liquid effluents were
analyzed by GC. The reactor was then washedꢀt2hree times with
xylene at 140 ꢁC and dried under vacuum (10 Torr) at 140 ꢁC
overnight. Finally, the reactor was cooled down to room tempera-
ture and filled with ethylene (30 bar).
4.3.8. Synthesis of NiCl2{N-((1-methyl-1H-imidazol-2-yl)
methylene)butan-1-amine} (2g)
Complex 2g was prepared according to the method described
for 2a using [NiCl2(DME)] (0.277 g, 0.94 mmol) and ligand 1g
(0.172 g, 1.04 mmol) and isolated as a pale blue powder in 95% yield.
FT-IR (cmꢀ1): 3111m, 2957m, 2866m, 1619m (nC]N), 1539w, 1372w,
1290m, 1184m, 1086w, 1043w, 960m, 849m, 793s, 707m, 666m,
559w, 465w. Anal. Calc. for C9H15Cl2N3Ni: C, 36.66; H, 5.13; N,14.25.
Found: C, 37.10; H, 5.41; N, 14.36.
4.4. X-ray crystal structure determination of 2a, 2c and 2e0
Diffraction data were collected on a Nonius KappaCCD diffrac-
4.5.2. Procedure for ethylene oligomerization using MAO as
cocatalyst
tometer with graphite monochromated Mo-K
a
radiation
ꢀ
(
l
¼ 0.71073 A). Data were collected using
J scans; the structure
Tests were run in six parallelized 100 mL reactors with ethylene
consumption monitoring and mechanical stirring. The reactors
were placed under an inert atmosphere of nitrogen before the
toluene, the nickel complex and the activator were added. The total
volume of solutions introduced was 25 mL. The ethylene pressure
was immediately increased to 30 bar and the temperature to 45 ꢁC.
The mechanical agitation was then set to 1000 rpm and the
ethylene uptake was measured. The test was stopped after 1 h or
after 25 g of ethylene was consumed. The autoclave was then
cooled to room temperature and depressurized. The liquid effluents
were weighed. The catalyst and the cocatalyst were quenched by
addition of 2 mL of a 10% H2SO4 solution in water. Aliquots of liquid
effluents were then analyzed by GC. The reactors were then washed
three times with xylene at 140 ꢁC and dried overnight in vacuum
(10ꢀ2 Torr) at 140 ꢁC. Finally, the reactor was cooled down to room
temperature and filled with ethylene (30 bar).
was solved by direct methods using the SIR97 software and the
refinement was by full-matrix least squares on F2. No absorption
correction was used.
Crystal data and structure refinement for compounds 2a, 2c, and
2e0.
2a
2b
2e0
Formula
C16H26C14N6Ni2S2
625.79
Monoclinic
C2/c
20.270(2)
6.9459(6)
19.414(3)
90
116.69(2)
90
2442.1(7)
1.702
C11H20Cl2N4Ni
337.92
Monoclinic
P21/n
7.065(1)
11.305(2)
18.417(3)
90
99.170(10)
90
1452.2(4)
1.546
C13H17Cl2N3NiO
376.91
Orthorhombic
Pbca
14.005(4)
12.137(3)
17.913(4)
90
Molecular weight
Crystal system
Space group
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
90
90
3
ꢀ
Cell volume (A )
Density
Z
3044.8(13)
1.644
8
Acknowledgment
4
4
F(000)
T (K)
1280
100
704
100
1552
150
We thank IFP Energies nouvelles for the permission to publish
these results and for their support. We are grateful to Erwann
Jeanneau (Université Claude Bernard - Lyon 1) for the crystal
structure determinations.
q
h
k
l
range (ꢁ)
3.5, 29.4
ꢀ27/27
ꢀ9/9
3.4, 29.5
ꢀ9/9
3.3, 29.2
ꢀ11/17
ꢀ16/16
ꢀ24/24
1.63
8163
2738
0.110
0.076
ꢀ15/14
ꢀ25/25
1.69
0/26
2.17
m
(mmꢀ1
)
References
Measd. reflections
Indep. reflections
Rint
17,288
3120
0.044
0.040
0.102
1.00
ꢀ1.14, 0.73
18,853
3683
0.067
0.059
0.204
1.04
ꢀ1.15, 1.24
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