Zwitterionic Ni(II) complexes bearing pyrazolyl-ether-imidazolium ligands: Synthesis, structural characterization and use in ethylene oligomerization

Article abstract of DOI:10.1039/c5nj01538c

A series of new tetracoordinated Ni(II) complexes of general formula NiCl₃(L) (Ni1, L = 1-(2-(2-methylimidazole-ethoxy)ethyl)-3,5-dimethylpyrazole; Ni2, L = 1-(2-(1,2-dimethylimizadole-ethoxy)ethyl)-pyrazole; Ni3, L = 1-(2-(1,2-dimethylimizadole-ethoxy)ethyl)-3,5-dimethyllpyrazole; Ni4, L = 1-(2-(2-n-butylimizadole-ethoxy)ethyl)-3,5-dimethylpyrazole) were prepared in high yields. All these complexes were characterized by elemental analysis, and X-ray crystallography was performed for Ni1, Ni2, and Ni3. In the solid state, these nickel complexes are monomeric with the pyrazolyl-ether-imidazolium acting as a monodentate ligand. The positive charge on the imidazolium unit is cancelled out by the negative charge that is provided by the third chloride ion linked to Ni(II), forming a zwitterionic structure. Upon activation with methylaluminoxane (MAO) or ethylaluminum sesquichloride (EASC), these complexes show moderate activity in ethylene oligomerization [TOF = 2100-29300 (mol C₂H₄)·(mol Ni^-1 h^-1)] with good selectivities for 1-butene (80.4-89.8 wt% of total products), which vary according to the ligand environment. Under biphasic conditions, the Ni3/[Bmim]·[AlCl₄]/toluene catalytic system proved to be active for ethylene oligomerization with a TOF of 10700 (mol C₂H₄)·(mol Ni^-1 h^-1) and highly selective towards production of 1-butene (90.9 wt%).

Full text of DOI:10.1039/c5nj01538c

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CASAGRANDE, J. Carpentier, T. Roisnel, A. H. Ulbrich and J. Milani, New J. Chem., 2015, DOI:
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New Journal of Chemistry
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DOI: 10.1039/C5NJ01538C
Graphical Contents entry
+
N
N
N
N
O
MAO, ethylene
+
o
Ni
30 C, 20 bar
Cl
Cl
Toluene or [Bmim][AlCl ]/toluene
Cl
4
2 4
H )
).(mol Ni-1. h-1
TOF = 2,100 - 29,300 (mol C
0.4-89.8 % yield for 1-butene
8
Nickel complexes bearing pyrazolyl-ether-imidazolium monodentate ligands have
been synthesized and their catalytic behavior in ethylene oligomerization has been
investigated in homogeneous and biphasic phase.

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ARTICLE
Zwitterionic Ni(II) Complexes Bearing Pyrazolyl-Ether-Imidazolium
Ligands: Synthesis, Structural Characterization and use in Ethylene
Oligomerization
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
b
c
DOI: 10.1039/x0xx00000x
Ana H. D. P. S. Ulbrich, Jorge L. S. Milani, Thierry Roisnel, Jean-François Carpentier, Osvaldo L.
Casagrande Jr.
a,*
www.rsc.org/
A series of new tetracoordinated Ni(II) complexes of general formula NiCl
ethoxy)ethyl)-3,5-dimethylpyrazole; Ni2, L = 1-(2-(1,2-dimethylimizadole-ethoxy)ethyl)-pyrazole; Ni3, L = 1-(2-(1,2-
dimethylimizadole-ethoxy)ethyl)-3,5-dimethyllpyrazole; Ni4, L= 1-(2-(2-n-butylimizadole-ethoxy)ethyl)-3,5-
3
(L) (Ni1, L = 1-(2-(2-methylimidazole-
dimethylpyrazole) were prepared in high yields. All these complexes were characterized by elemental analysis, and X-ray
crystallography was performed for Ni1, Ni2, and Ni3. In the solid state, these nickel complexes are monomeric with the
pyrazolyl-ether-imidazolium acting as a monodentate ligand. The positive charge on the imidazolium unit is cancelled out
by the negative charge that is provided by the third chloride ion linked to Ni(II), forming a zwitterionic structure. Upon
activation with methylaluminoxane (MAO) or ethylaluminum sesquichloride (EASC), these complexes show moderate
−1
−1
2 4
activity in ethylene oligomerization (TOF = 2,100-29,300 (mol C H )⋅(mol Ni h ] with good selectivities for 1-butene
(80.4−89.8 wt% of total products), which vary according to the ligand environment. Under biphasic conditions, the
4
Ni3/[Bmim]⋅[AlCl ]/toluene catalytic system proved to be active for ethylene oligomerization with TOF of 10,700 (mol
−
1
−1
C
2
H
4
)⋅(mol Ni h ) and highly selective towards production of 1-butene (90.9 wt%).
ligand promoting the formation of zwitterionic complexes that
feature formal charge separation between an anionic nickel
fragment and a positively charged imidazolium moiety within an
overall neutral molecular framework. Thus, Poli et al. showed that
Introduction
The oligomerization of ethylene is one of the most important zwitterionic Ni(II) complexes containing a monodentate phosphine–
1
industrial processes to obtain linear α-olefins (LAOs). These imidazolium ligand (A) were very active catalysts for the cross-
7
b,c
substrates have been extensively used for preparing detergents, coupling of aryl Grignard reagents with aryl chlorides.
Jin et al.
lubricants, plasticizers, and oil field chemicals or as monomers for described a catalytic system, based on pyridyl-imidazolium nickel(II)
2
copolymers, etc. Many efforts are still devoted to the development complex (B) capable to polymerize ethylene in presence of MAO
8
of highly selective ethylene oligomerization catalysts, and among producing high-density polyethylene.
classes of catalysts used for production of α-olefins, nickel
3
4
complexes containing bidentate and tridentate chelating ligands
are the most frequently studied. However, while several classes of
Ni(II) complexes bearing heterobi- and tridentate N-heterocyclic
n
N
+
+ N Me
N
Ph P
2
N
5
N
carbene ligands have been described in the literature, just a very
Ar
Br
Br
6
Ni
few examples have been used in ethylene oligomerization.
Ni
Br
Especially, Ni(II) compounds of general formula [NiX
3
L] (X = Br, Cl; L
Cl
Cl
=
functionalized-imidazolium ligand) have been restrictedly used in
Cl
7
8
A
B
Grignard cross-coupling, and ethylene polymerization reactions. In
this case, the functionalized-imidazolium acts as a monodentate
Chart 1. Examples of structurally characterized nickel complexes
7b-c,8
bearing functionalized-imidazolium ligands.
In the last years, several classes of functionalized-imidazolium
ligands bearing kinetically inert coordination groups, such as
8
, 9
10
11
12
7, 13
pyridyl, bipyridyl, pyrazolyl, phenantroline, phosphine,
1
4
15
16
17
furan, phthalimido, thioether, and oxazolyl, have been
1
8
synthesized and used in coordination chemistry, homogeneous
and biphasic phase catalytic processes. In this latter case, the use of
This journal is © The Royal Society of Chemistry 2015
New J. Chem., 2015, 00, 1-3 | 1
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New Journal of Chemistry
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ARTICLE
functionalized-imidazolium ligands is especially suitable to avoid
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DOI: 10.1039/C5NJ01538C
NJC
1
9
catalyst leaching from the ionic liquid (IL) layer. Moreover, the
resulting ionic catalyst should be completely soluble in IL and would
allow the ethylene oligomerization to be carried out under standard
homogeneous conditions.
Over the past few years, pyrazolyl-based ligand metal
complexes have attracted attention as efficient catalysts for oligo-
2
0
and polymerization of ethylene. Our group has been interested in
exploring the potential applications of such pyrazolyl-based ligands
2
1
in the oligomerization catalysis field. Herein, we report the
synthesis and structural characterization of several new zwitterionic
Ni(II) complexes bearing pyrazolyl-ether-imidazolium ligands. Their
catalytic behavior for ethylene oligomerization upon activation with
MAO has been investigated. We discuss the performance of these
catalysts, evaluating the role of the ligand, and the experimental
parameters on the activity and selectivity towards the production of
PF6
Fig. 1 ORTEP drawing of L1 . Ellipsoids are drawn at the 30%
probability level. Selected bond distances (Å) and angles (deg):
N6−N7 = 1.3628(17), C9−O10 = 1.4300(15), O10−C11 = 1.4179(16),
1
-butene.
N13−C14
1.3773(19), C16−N17 = 1.3775(19), C15−C16 = 1.348(2), N17−C18 =
.4730(18). C11−O10−C9 = 112.70(10), N6−C8−C9 = 111.18(11),
N13−C12−C11= 111.88(11).
= 1.3291(18), C14−N17 = 1.3260(18), N13−C15 =
Results and discussion
1
Synthesis and Characterization of the Pyrazolyl-ether-imidazolium
ligands and Nickel Complexes
Cl
Cl
The pyrazolyl-ether-imidazolium ligands L1 -L4
were
prepared by reaction of 1-(2-(2-chloroethoxy)ethyl)-3,5-dimethyl-1-
pyrazole with the appropriate imidazole in moderate to good yields
(
60−95%) as shown in Scheme 1. The chloride counterion can be
exchanged for hexafluorophosphate using KPF in water to afford
the hexafluorophosphate salts L1 -L4 in good yields (typically
8−85%, Scheme 1). The identity of this class of ligands was
established by IR and NMR spectroscopy, elemental analysis, and by
6
PF6
PF6
6
PF6
PF6
an X-ray diffraction study for ligands L1 and L3
.
R2
R2
R1
100
0
C
R1
+
N
R3
Cl
N
Cl
+
N
N
R3
N
N
N
O
N
O
1
2 h
R4
R4
Cl
L1 -L4
Cl
R2
R
2
KPF
6
R3
R1
+
N
R3
R1
+
N
N
N
N
N
N
O
N
O
R4
Cl
H
2
O, r.t, 30 min
R4
PF
6
PF6
L1 : R ,R = Me;R3 = Me; R4 = H
PF6
1
2
Fig 2 ORTEP drawing of L3 . Ellipsoids are drawn at the 30%
probability level. Selected bond distances (Å) and angles (deg):
N6−N7 = 1.3695(17), C9−O10 = 1.4287(18), O10−C11 = 1.4262(18),
C14−N16 = 1.335(2), N13−C14 = 1.338(2), N13−C19 = 1.3759(19),
L2 : R ,R = H;R3 = Me; R4 = Me
PF6
1
2
L3 : R ,R = Me;R3 = Me; R4 = Me
PF6
1
2
L4 : R ,R = Me;R3 = Bu; R4 = H
PF6
1
2
N16−C18
= 1.379(2), C18−C19 = 1.345(2). C11−O10−C9 =
Scheme 1
1
13.58(12), N7−C8−C9 = 112.57(13), N13−C12−C11 = 110.86(13).
PF6
PF6
Single crystals of L1
and L3
suitable for an X-ray
diffraction analysis were obtained by recrystallization from
CH Cl /pentane solutions at room temperature. The molecular
geometry and atom-labeling scheme are shown in Figures 1 and 2.
Crystallographic data are summarized in Table S1.
2
2
The reaction of Ni(OAc) with the pyrazolyl-ether-imidazolium
salt was initially chosen in an attempt to prepare carbene-Ni(II)
complexes and to study the coordination behavior of pyrazolyl-
2
ether-functionalized NHC ligands. However, reacting Ni(OAc)
2
/LiCl
Cl
Cl
(
2 equiv) with L1 −L4 (1 equiv) in DMF at room temperature leads
to the corresponding pyrazole-coordinated nickel complexes (Ni1–
Ni4), which were isolated as blue solids in high yields (typically 81–
8
8%) (Scheme 2). Alternatively, Ni1−Ni4 can be obtained by
PF6
reaction of NiCl
temperature.
2
2 2
(dme)/LiCl (1 equiv) with L1−L4 in CH Cl at room
2
| New J. Chem., 2015, 00, 1-3
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NP lee wa s eJ od uo r nn oa tl aod fj uC s ht em ma ri sg it nr sy
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ARTICLE
R2
R2
C12−N13 = 1.472(2), N2−C8 = 1.463(2), O10−C11 = 1.429(2),
C9−O10 = 1.426(2), N13−C18 = 1.380(2), N1−N2 = 1.368(2),
N15−C17 = 1.365(2), C17−C18 = 1.344(2), C14−N15 =1.341(2),
N13−C14 = 1.320(2). N1−Ni1−Cl2 = 101,75(4). N1−Ni1−Cl3 =
114.34(4), N2−N1−Ni1 = 129.73(9), Cl2−Ni1−Cl1 = 115.19(2),
Cl1−Ni1−Cl3 = 102.99(2), Cl2−Ni1−Cl3 = 117.64(2).
R3
R1
+
N
R3
Ni(OAc)
2
/LiCl or NiCl
Cl , 20 h
2
(dme)/LiCl
R1
Cl
N
N
+
N
4
N
N
N
O
N
O
R4
X
DMF or CH
2
2
R
Ni
Cl
Cl
X = Cl, PF
6
Ni1: R ,R = Me;R3 = Me; R4 = H
1
2
Ni2: R ,R = H;R3 = Me; R4 = Me
1
2
Ni3: R ,R = Me;R3 = Me; R4 = Me
1
2
Ni4: R ,R = Me;R3 = Bu; R4 = H
1
2
Scheme 2
Single crystals of Ni1, Ni2 and Ni3 suitable for X-ray diffraction
were grown from a concentrated acetonitrile/ether solution (80:20)
at room temperature. In the solid state, these three complexes are
monomeric with a four-coordinated nickel center in a slightly
distorted tetrahedral geometry with the pyrazolyl-ether-
imidazolium acting as a monodentate ligand (Figures 3-5). Two
independent molecules were found in the asymmetric unit of Ni1,
but the two molecules are quite similar so that only the distances
and the angles for one of them are listed in Figure 3. The nickel
center is coordinated by the nitrogen atom of the pyrazolyl group
and by three chloride atoms. The positive charge on the
imidazolium unit is cancelled out by the negative charge that is
provided by the third chloride ion linked to Ni(II), forming a
zwitterionic structure. The Ni–N bond distance [2.0131(13) Å for
Ni1, 1.9968(16) Å for Ni2 and 2.0133(13) Å for Ni3] are close to the
values previously reported for Ni(II) complexes having pyrazole
2
1a-d,22
Fig. 4 ORTEP drawing of Ni2. Ellipsoids are drawn at the 50%
probability level. All hydrogen atoms are omitted for clarity.
Selected bond distances (Å) and angles (deg): Ni1−N1 = 2.0039(16),
Ni1−Cl1 = 2.2493(6), Ni1−Cl2 = 2.2665(6), Ni1−Cl3 = 2.2755(6),
C10−N11 = 1.470(3), N5−C6 = 1.463(3), C7−O8 = 1.422(2), O8−C9 =
ligands.
The average Ni–Clav bond distances are 2.2508 Å for
Ni1, 2.2605 Å for Ni2, and 2.2543 Å for Ni3. These values are
unexceptional and lie within the ranges found for other complexes
−
7,8
containing [Ni(L)X3] anions. The three Cl–Ni–Cl angles show a
significant deviation from their mean values, 112.8(1) °, with two
values greater than the ideal tetrahedral angle. In particular, for
Ni3, the Cl(1)–Ni–Cl(3) angle is significantly wider [122.49(4) °] than
the other two Cl–Ni–Cl angles. This could be attributed to the
1
1
1
.426(2), N11−C16 = 1.345(2), N11−C12 = 1.383(3), N14−C16 =
.342(3), N14−C15 = 1.463(3), C13−N14 = 1.389(3), C12−C13 =
.345(3), N1−N5 = 1.361(2). N1−Ni1−Cl1 = 108.77(5), N1−Ni1−Cl2 =
establishment of a hydrogen bonding interaction between the C(20) 103.47(5), Cl1−Ni1−Cl2 = 108.78(2), N1−Ni1−Cl3 = 104.66(5),
and C(6) hydrogen atoms and the chloride atoms Cl(1) and Cl(3), Cl1−Ni1−Cl3 = 120.82(2), Cl2−Ni1−Cl3 = 108.93(2).
respectively. In this case, the Cl(1)–H(20) and Cl(3)–H(6) distances
are 2.838 Å and 2.737 Å, which are shorter than the sum of the van
der Waals radii of H and Cl. The internal bond distances and angles
of the imidazolium ring are unexceptional and lie within the
2
3
expected range.
Fig. 5 ORTEP drawing of Ni3. Ellipsoids are drawn at the 50%
probability level. All hydrogen atoms are omitted for clarity.
Selected bond distances (Å) and angles (deg): Ni1−N4 = 2.0133(13),
Ni1−Cl1 = 2.2408(4), Ni1−Cl2 = 2.2537(5), Ni1−Cl3 = 2.2685(4),
C15−N16 = 1.461(2), N5−C11 = 1.459(2), C12−O13 = 1.4194(19),
Fig. 3 ORTEP drawing of Ni1. Ellipsoids are drawn at the 50% O13−C14 = 1.419(2), C21−C22 = 1.475(2), N16−C21 = 1.337(2),
probability level. All hydrogen atoms are omitted for clarity. N19−C21 = 1.330(2), C18−N19 = 1.392(2), N16−C17 = 1.392(2),
Selected bond distances (Å) and angles (deg): Ni1−Cl1 = 2.2438(5), C17−C18 = 1.329(3), N4−N5 = 1.3684(18). N4−Ni1−Cl1 = 100.90(4),
Ni1−Cl2 = 2.2398(5), Ni1−Cl3= 2.2687(4), Ni1−N1 = 2.013(1),
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N4−Ni1−Cl2 = 112.10(4), Cl1−Ni1− Cl2 = 111.659(18), N4−Ni1−Cl3 =
For all nickel complexes (Ni1−Ni4), the selectivity for butenes
and especially 1-butene were similar (80.4−89.8 wt%) indicating
that the variation of steric hindrance on the pyrazolyl group (H, Me)
had little influence on the product distribution. This observation is
in agreement with previous ethylene oligomerization results using
109.30(4), Cl1−Ni1−Cl3 = 122.493(18), Cl2−Ni1−Cl3 = 100.687(17)
Ethylene Oligomerization Studies
2
1a,21c,21e
MAO-activated nickel complexes bearing pyrazolyl ligands.
Nickel complexes Ni1−Ni4 were evaluated in ethylene
oligomerization at 30 °C, 20 bar constant ethylene pressure, and
In all cases, minimal amounts of hexenes (2.4−5.9 wt%) were
using methylaluminoxane (MAO) as cocatalyst. Table 1 summarizes detected with poor selectivity for 1-hexene (1.2−3.4 wt%).
the results of reactions carried out using 10 μmol of precatalyst in
The preliminary study was extended to investigate the effect
4
0 mL of a toluene. All experiments were at least duplicated,
of temperature, [Al]/[Ni] molar ratio, cocatalyst type, and solvent
on the catalytic performance of the Ni3/MAO (Table 1, entries 5−9).
Elevating the temperature from 30 °C to 50 °C led to a reduction in
yielding reproducible results within ±10%.
a
Table 1 Ethylene Oligomerization with Ni1−Ni4 catalytic systems.
−1
−1
2 4
activity [TOF = 1,820 (mol C H )⋅(mol Ni h )], suggesting that a
b
entry
cat
Olig.
g)
TOF
selectivity(wt%)
partial decomposition of the active catalytic species took place.
However, upon elevating the temperature from 30 to 50 °C, the 1-
butene selectivity remained at the same level (84.4 wt%).
3
(
(x10 )
C4
C6
(α-C
4
)
6
(α-C )
1
2
3
4
Ni1
Ni2
Ni3
Ni4
Ni3
Ni3
Ni3
Ni3
Ni3
0.30
0.56
0.72
0.20
0.17
0.32
2.74
9.71
1.00
3.20
6.00
7.80
2.10
1.82
3.42
29.3
104.0
10.7
94.1
93)
94.6
85)
97.6
92)
95.3
84)
95.4
5.9
(59)
5.4
(27)
2.4
(50)
4.7
(30)
4.6
(41)
2.8
(51)
1.9
51
14.8
Increasing the [Al]/[Ni] molar ratio from 300 to 1,000
negatively affected the catalytic performance of nickel precatalyst.
Thus, with 1,000 equiv of MAO, a lower activity [TOF = 3,420 (mol
(
(
−1
−1
C H )⋅(mol Ni h ), entry 6] was observed. On the other hand, the
2
4
use of higher amounts of MAO had little impact on the selectivity
(
for α-C that remained in the same level (88.4 wt%) as compared to
4
that one obtained using 300 equiv of MAO. Quite interestingly,
activation of nickel precatalyst Ni3 with 50 equiv of ethylaluminum
(
d
5
sesquichloride (Et
3 2 3
Al Cl , EASC) instead of MAO produced a much
(88.5)
e
−1 −1
6
97.2
more active system [29,300 (mol C H )⋅(mol Ni h ], along with a
2 4
high, although lower selectivity for 1-butene (79.5 wt%). It is worth
noting that, even upon using a lower amount of EASC (50 equiv),
(
91)
f
8
98.1
81.1)
85.2
49.3)
95.7
Ni3 led to a much more active system than that based on NiCl {3,5-
(
(
2
g
7
dimethyl-1-(3-phenoxypropyl)-1H-pyrazole} [EASC = 100 equiv, TOF
−
1
−1
=
5500 (mol C H )·(mol Ni h ] under identical oligomerization
2 4
(11.9)
4.3
2
1g
h
conditions.
9
(
95)
(53)
a
Performing the oligomerization reaction in a more polar
solvent, such as dichloromethane, led to a much higher TOF
Reaction conditions: toluene = 40 mL, [Ni] = 10 ꢀmol,
oligomerization time = 20 min, P(ethylene) = 20 bar (kept constant),
−1
−1
[
2 4
104,000 (mol C H )⋅(mol Ni h ]. This high activity generated
T = 30 °C, MAO(Al)/[Ni] = 300. The results shown are representative
of at least duplicated experiments. Mol of ethylene converted
b
significant exothermicity, so that the reaction with Ni3/MAO
performed at an initial temperature of 30 °C (entry 7) rapidly rose
to 45−50 °C, despite the thermostating fluid around the reactor.
Although the catalyst activity was improved by approximately 13-
fold, the selectivity for 1-butene was drastically reduced, attaining
only 42 wt% with a concomitant production of larger amounts of
internal butenes (43.2 wt%) and hexenes (14.8 wt%). We assume
that, in polar solvents, dissociation of cationic active Ni-complex ion
pairs is made easier, which may favour chain transfer reactions and
−
1
−1
d
e
(
[
mol of Ni) ·h as determined by quantitative GLC. T = 50 °C.
f
g
Al]/[Ni] = 1,000. EASC as cocatalyst, [Al]/[Ni] = 50. CH
2
Cl
2
as
h
solvent.
oligomerization reaction performed in ionic liquid
[Bmim]⋅[AlCl4].
All the nickel complexes investigated have been found to
generate active systems for the production of short-chain olefins in
the C −C range. The oligomerization results showed that the
substituent at the C2 position of the imidazolium group influenced
the catalytic performance of the nickel catalysts on ethylene
oligomerization. Thus, the catalytic systems based on Ni1/Ni4 were
4
6
2
4
isomerization, accounting for the lower selectivity.
In order to investigate the catalytic behaviour of this nickel(II)
zwitterionic complex under biphasic conditions, we carried out an
oligomerization reaction using Ni3 in an organoaluminate ionic
liquid/toluene solvent system. Chloroaluminate 1-n-butyl-3-
found to give lower activities [TOF = 2,100−3,200 (mol C
Ni h )] as compared to the performance of Ni2/Ni3 [TOF =
2
H
4
)⋅(mol
−1
−1
−1
−1
6
,000−7,800 (mol C H )⋅(mol Ni h )]. This can be tentatively
2
4
methylimidazolium ionic liquid ([Bmim]⋅[AlCl ]) was chosen because
4
attributed to the reaction of acidic proton at the C2 position of the
imidazolium cation in Ni1/Ni4 with methylaluminoxane. Overall,
this class of catalysts showed lower activities than other classes of
nickel precatalysts bearing bi- and tridentate pyrazolyl ligands. We
surmise that this can be tentatively associated to the lower stability
of Ni1−Ni4 as a consequence of the monodentate coordination
mode of the pyrazolyl-ether-imidazolium ligands.
of it renown good dissolution abilities for metal complexes and its
25
convenient preparation. Thus, the ethylene oligomerization was
performed using a solution of the nickel precatalyst Ni3 dissolved in
[
4
Bmim]⋅[AlCl ] (3 mL), toluene (40 mL) and MAO (250 equiv) at 30 °C
and 20 bar constant ethylene pressure. Under these reaction
conditions, ethylene oligomerization proceeded with a TOF slightly
−
1
higher than in homogeneous phase [10,700 (mol C H )⋅(mol Ni
2
4
−1
h ), entry 9]
.
This activity is comparable to previously reported
4
| New J. Chem., 2015, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
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NP lee wa s eJ od uo r nn oa tl aod fj uC s ht em ma ri sg it nr sy
Page 6 of 10
View Article Online
DOI: 10.1039/C5NJ01538C
Journal Name
ARTICLE
biphasic oligomerization systems using nickel complexes; however, Synthesis of the pyrazolyl-ether-imidazolium ligands
]/toluene catalytic system showed a higher
the Ni3/[Bmim]⋅[AlCl
4
+
−
selectivity towards production of 1-butene (90.9 wt%) as compared [1-(2-(2-methylimidazole-ethoxy)ethyl)-3,5-dimethylpyrazole] Cl
Cl
to similar biphasic nickel-catalyzed ethylene oligomerization (21-83 (L1 )
2
5, 25a-c
wt%).
A
reaction
vessel
was
charged
with
1-(2-(2-
chloroethoxy)ethyl)-3,5-dimethyl-1-pyrazole (1.23 g, 6.1 mmol), and
-methylimidazole (1.15 g, 14.0 mmol). The vessel was closed and
1
Conclusions
stirred overnight at 100 °C. The crude product was extracted with
toluene (3 x 10 mL) and the solvent was removed under vacuo to
afford a beige solid. Recrystallization from THF yielded a white solid
Zwitterionic nickel complexes bearing pyrazolyl-ether-
imidazolium ligands have been synthesized and structurally
characterized. Upon activation with MAO or EASC co-catalysts,
these Ni(II) complexes show moderate to high catalytic activity
for ethylene oligomerization with good selectivity for 1-
butene. The substituent at the C2 position of the imidazolium
group influenced the catalytic performance of the nickel
1
(
(
(
1.14 g, 65%). H NMR (300 MHz, 298 K, CDCl ): δ 2.19 (3H, s), 2.22
3
3
3H, s), 3.81 (4H, m), 4.05 (3H, s), 4.14 (2H, t, JHH = 5.2 Hz), 4.56
2H, t, J = 4.6 Hz), 5.80 (1H, s), 7.34 (1H, t, J = 1.8 Hz), 7.42 (1H,
3
3
HH
HH
3
13
1
t, JHH = 1.6 Hz), 10.30 (1H, s). C{ H} NMR (75 MHz, 298 K, CDCl
0.8 (Pz 5-CH ), 13.3 (Pz 3-CH ), 35.9 (Im 3-CH ), 47.9 (CH ), 49.4
CH ), 68.2 (O-CH ), 69.5 (O-CH ), 104.9 (Pz 4-C), 122.9 (Im 2-C),
22.9 (Im 3-C), 135.9 (Im 2-C), 139.9 (Pz 5-C), 147.4 (Pz 3-C). Anal.
O: C, 53.83; H, 7.43; N, 19.67%. Found: C,
3.24; H, 7.08; N, 19.31%.
3
):
1
(
1
3
3
3
2
precatalysts; lower activities were found using Ni1 and Ni4
,
2
2
2
suggesting a possible reaction between the acidic proton at
the C2 position of the imidazolium cation and
methylaluminoxane. Preliminary results using Ni3 under
biphasic conditions showed that this catalyst was able to
oligomerize ethylene with good activity and improved
selectivitys for 1-butene. Further studies are underway in our
laboratories to investigate the recyclability and reuse of this
catalytic system as well as the influence of oligomerization
parameters on the activity and selectivity towards production
of 1-butene.
calcd. for C13H21ClN
4
5
+
−
[
(
1-(2-(2-methylimidazole-ethoxy)ethyl)-3,5-dimethylpyrazole] PF
6
PF6
L1
)
Cl
To a solution of L1 (0.44 g, 1.5 mmol) in distilled water
20 mL) was added potassium hexafluorophosphate (0.33 g, 1.8
(
mmol). The resulting mixture was stirred for 30 min at room
temperature, and the resulting pale yellow solid extracted with
dichloromethane (3 x 10 mL). The solution was dried on MgSO
4
and
Experimental
the solvent removed in vacuo to yield a pale yellow solid (0.59 g,
8
5%). Recrystallization from
a
concentrated CH
2
Cl
2
/pentane
as white
General Procedures
PF6
solution (90:10) at room temperature afforded L1
crystals, some of which proved suitable for X-ray diffraction studies.
All manipulations involving air- and/or moisture-sensitive
compounds were carried out in an MBraun glovebox or under dry
argon using standard Schlenk techniques. Solvents were dried from
1
H NMR (300 MHz, 298 K, CDCl ): δ 2.19 (3H, s), 2.20 (3H, s), 3.72
3
3
3
(
2H, t, JHH = 4.6 Hz), 3.80 (2H, t, JHH = 5.2 Hz), 3.84 (3H, s), 4.12 (2H,
3
3
t, J = 5.3 Hz), 4.24 (2H, t, J = 4.5 Hz), 5.81 (1H, s), 7.17 (1H, t,
the appropriate drying agents under argon before use. Ni(OAc)
2
,
HH
HH
3
13
1
J
HH = 1.8 Hz), 7.19 (1H, s), 8.30 (1H, s). C{ H} NMR (75 MHz, 298 K,
NiCl (dme) bis-(2-chloroethyl)ether, 1-methylimidazole, 1-n-
2
CDCl ): 10.6 (Pz 5-CH ), 13.1 (Pz 3-CH ), 35.8 (Im 3-CH ), 47.6 (CH ),
butylimidazole, and 1,2-dimethylimidazole were purchased from
Sigma-Aldrich and used as received. Ethylene (White Martins Co.)
and argon were deoxygenated and dried through BTS columns
3
3
3
3
2
4
1
9.8 (CH
2
2 2
), 67.8 (O-CH ), 69.1 (O-CH ), 104.7 (Pz 4-C), 122.4 (Im 2-C),
22.8 (Im 3-C), 140.1 (Im 2-C), 140.1 (Pz 5-C), 147.2 (Pz 3-C). IR
−
1
(
neat, cm ): 3178 (m), 3161 (m), 3124 (w), 2958 (m), 29033 (m),
881 (w), 1614 (w), 1566 (m), 1552 (m), 1461 (m), 1431 (m), 1387
w), 1303 (w), 1172 (s), 1134 (s), 1066 (m), 840 (s), 752 (m), 646 (m),
(BASF) and activated molecular sieves prior to use. 1-(2-(2-
2
(
Chloroethoxy)ethyl)-3,5-dimethyl-1H-pyrazole was prepared by
2
6
following literature procedures. The ionic liquid [Bmim]⋅[AlCl4]
was obtained by reacting 1-n-butyl-3-methylimidazolium chloride
6
1
22 (m), 557 (s). Anal. calcd. for C13
20 6 4
H F N OP: C, 39.70; H, 5.13; N,
2
7
4.25%. Found: C, 39.46; H, 5.15; N, 14.01%. Mp: 76.2 °C
([Bmim]Cl) with aluminum chloride, as described in the literature.
MAO (AXION CA 1310, 10 wt.-% solution in toluene) was used as
received. EASC (Akzo Nobel) was used with the previous dilution
+
−
Cl
[
1-(2-(1,2-dimethylimizadole-ethoxy)ethyl)-pyrazole] Cl (L2 )
(
2.1 wt.% Al solution in toluene). Infrared spectra were performed
This ligand was prepared according to the method described
above for L1 using 1-(2-(2-chloroethoxy)ethyl)-3,5-dimethyl-1-
using neat products in KBr pellets on a FT-IR Bruker Alpha
Spectrometer. H and C{ H} NMR spectra were recorded at 25 °C
on a Varian Inova 300 spectrometer operating at 300 MHz.
1
13
1
pyrazole (2.89 g, 16.0 mmol), and 1,2-dimethylimidazole (1.59 g,
Cl
1
1
(
4
=
(
6.0 mmol). L2 was obtained as a yellow oil (4.13 g, 92%). H NMR
4
Chemical shifts are reported in ppm vs. SiMe and were determined
300 MHz, 298 K, CDCl ): δ 2.60 (3H, s), 3.82 (4H, m), 3.92 (3H, s),
3
by reference to the residual solvent peaks. Elemental analyses were
performed by the Analytical Central Service of the Institute of
Chemistry-USP (Brazil) and is the average of two independent
determinations. Quantitative gas chromatographic analysis of
ethylene oligomerization products was performed on a Agilent
3
3
3
.26 (2H, t; JHH = 5.2 Hz), 4.45 (2H, t; JHH = 4.6 Hz), 6.22 (1H, t; JHH
3
3
2.1 Hz), 7.42 (1H, d; JHH = 2.1 Hz), 7.44 (1H, d; JHH = 1.5 Hz), 7,60
3
3
13
1
1H, d; JHH = 2.1 Hz), 7.67 (1H, d; JHH = 2.1 Hz). C{ H} NMR (75
MHz, 298 K, CDCl ): 10.2 (Im 2-CH ), 35.5 (Im 3-CH ), 48.5 (CH ),
3
3
3
2
5
1
1.3 (CH
2
2 2
), 690 (O-CH ), 69.2 (O-CH ), 105.3 (Pz 4-C), 121.7 (Im 2-C),
7
890A instrument equipped with a Petrocol HD capillary column
22.4 (Im 3-C), 129.7 (Im 2-C), 139.1 (Pz 5-C), 144.4 (Pz 2-C). Anal.
calcd. for C H ClN O: C, 52.27; H, 7.76; N, 18.75%. Found: C,
14 23 4
2.15; H, 7.54; N, 18.66%.
(methyl silicone, 100 m length, 0.25 mm i.d. and film thickness of
−
1
0
.5 μm) (36 °C for 15 min, then heating at 5 °C⋅min until 250 °C);
5
cyclohexane was used as internal standard.
This journal is © The Royal Society of Chemistry 20xx
New J. Chem., 2015, 00, 1-3 | 5
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New Journal of Chemistry
Page 7 of 10
ARTICLE
1-(2-(1,2-dimethylimizadole-ethoxy)ethyl)-pyrazole] PF
View Article Online
DOI: 10.1039/C5NJ01538C
NJC
+
−
PF6
[
6
(L2
)
This ligand was prepared according to the method described
above for L1 , using 1-(2-(2-chloroethoxy)ethyl)-3,5-dimethyl-1-
Cl
This ligand was prepared according to the method described pyrazole (1.62 g, 8.0 mmol) and 1-n-butyllimidazole (1.01 g, 8.0
PF6
Cl
Cl
1
6
above for L1 using L2 (3.70 g, 12.0 mmol), and KPF (2.70 g, 14.0 mmol). L4 was obtained as a yellow oil (2.48 g, 95%). H NMR (300
PF6
3
mmol). L2
was obtained as a white solid (3.10 g, 68%). MHz, 298 K, CDCl ): δ 0.97 (3H, t; J = 7.3 Hz), 1.39 (2H, m), 1.89
3 HH
3
Recrystallization from a concentrated CH
90:10) at room temperature afforded L2 as white crystals. H Hz), 4.29 (2H, t; J = 7.5 Hz), 4.60 (2H, t; J = 4.6 Hz), 5.80 (1H, s)
HH HH
3
NMR (300 MHz, 298 K, CD Cl ): δ 2.45 (3H, s), 3.70 (2H, t, JHH = 4.8 7.37-7.38 (2H, m), 10.37 (1H, s). C{ H} NMR (75 MHz, 298 K,
2
Cl
2
/pentane solution (2H, m), 2.20 (3H, s), 2.22 (3H, s), 3.82 (4H, m), 4.14 (2H, t; J = 5.1
HH
PF6
1
3
3
(
13
1
2 2
3
3
Hz), 3.73 (3H, s), 3.82 (2H, t, JHH = 5.1 Hz), 4.16 (2H, t, JHH = 4.8 Hz), CDCl ): 10.9 (Pz 5-CH ), 13.2 (Pz 3-CH ), 13.3 (CH CH ), 19.2 (CH ),
3
3
3
2
3
2
3
3
3
4
=
.23 (2H, t, JHH = 5.2 Hz), 6.22 (1H, t, JHH = 2.0 Hz), 7.09 (1H, d, JHH 31.9 (Im N-CH CH ), 47.9 (Im N-CH ), 49.2 (CH ), 49.5 (CH ), 68.9 (O-
2 2 2 2 2
3 3
2.2 Hz), 7.11 (1H, d, JHH = 2.2 Hz), 7.36 (1H, d, JHH = 2.2 Hz), 7.42 CH ), 69.4 (O-CH ), 104.8 (Pz 4-C), 121.0 (Im 2-C), 123.0 (Im 3-C),
2 2
3 13 1
(
1H, d, JHH = 1.3). C{ H} NMR (75 MHz, 298 K, CD
2
Cl
), 68.9 (O-CH
), 105.5 (Pz 4-C), 121.5 (Im 2-C), 122.4 (Im 3-C), 130.0 (Im 2-C), N, 17.01%.
2
): 9.7 (Im 2- 137.0 (Im 2-C), 139.4 (Pz 5-C), 147.2 (Pz 3-C). Anal. calcd. for
CH
CH
3
2
), 35.4 (Im 3-CH
3
), 48.8 (CH
2
), 51.7 (CH
2
2
), 69.8 (O- C H ClN O: C, 58.79; H, 8.33; N, 17.14%. Found: C, 58.35; H, 7.97;
1
6
27
4
−
1
1
1
6
3
7
39.3 (Pz 5-C), 145.0 (Pz 3-C). IR (neat, cm ), ν: 3157 (w), 3125 (w),
593 (w), 1542 (w), 1417(w), 1180(w), 1057 (m), 826 (s), 753 (m), [1-(2-(2-butylimizadole-ethoxy)ethyl)-3,5-dimethylpyrazole] Cl
69 (m), 649 (w), 614 (m), 556 (s). Anal. calcd. for C12H F N
19 6 4
OP: C, (L4 )
7.90; H, 5.04; N, 14.73%. Found: C, 37.74; H, 4.85; N, 14.53%. Mp:
+
−
PF6
This ligand was prepared according to the method described
7.7 °C.
PF6
Cl
6
above for L1 using L4 (0.49 g, 1.5 mmol) and KPF (0.33 g, 1.8
PF6
1
[
1-(2-(1,2-dimethylimizadole-ethoxy)ethyl)-3,5-
mmol). L4 was obtained as a yellow oil (0.57g, 87%). H NMR (300
+
−
Cl
3
dimethylpyrazole] Cl (L3 )
MHz, 298 K, CDCl
2H, m), 2.18 (s, 3H), 2.20 (s, 3H), 3.72 (2H, J = 4.5 Hz), 3.80 (2H,
3
): δ 0.94 (3H, t; JHH = 7.3 Hz), 1.35 (2H, m), 1.82
3
(
HH
3
3
This ligand was prepared according to the method described t; JHH = 5.2 Hz), 4.11 (4H, m), 4.27 (2H, t; JHH = 4.6 Hz), 5.79 (1H, s)
1
3
1
above for L1 using 1-(2-(2-chloroethoxy)ethyl)-3,5-dimethyl-1- 7.21 (1H, s), 7.25 (1H, s), 8.38 (1H, s). C{ H} NMR (75 MHz, 298 K,
pyrazole (1.79 g, 8.9 mmol) and 1,2-dimethylimidazole (1.66 g, 17.0 CDCl ): 10.7 (Pz 5-CH ), 13.1 (Pz 3-CH ), 13.3 (CH CH ), 19.2 (CH ),
mmol). L3 was obtained as an orange oil (2.53 g, 95%). H NMR 31.6 (Im N-CH CH ), 47.9 (Im N-CH ), 49.5 (CH ), 49.5 (CH ), 68.3 (O-
), 69.5 (O-CH ), 104.9 (Pz 4-C), 121.6 (Im 2-C), 123.1 (Im 3-C),
.97 (3H, s), 4.07 (2H, t, JHH = 5.3 Hz), 4.48 (2H, t, JHH = 4.6 Hz), 135.1 (Im 2-C), 139.7 (Pz 5-C), 147.3 (Pz 3-C). IR (neat, cm ), ν: 3640
3
3
3
2
3
2
Cl
1
2
2
2
2
2
(
3
5
CDCl
CH
300 MHz, 298 K, CDCl
3
): δ 2.18 (6H, s), 2.68 (3H, s), 3.80 (4H, m), CH
2
2
3
3
-1
13
1
.78 (1H, s), 7.65 (1H, s), 7.67 (1H, s). C{ H} NMR (75 MHz, 298 K, (w), 3161 (w), 3117 (w), 2962 (w), 2932 (w), 2876 (w), 1563 (m),
): 10.0 (Pz 5-CH ), 10.8 (Im 2-CH ), 13.2 (Pz 3-CH ), 35.4 (Im 3- 1460 (m), 1421 (w), 1377 (w), 1302 (w), 1223 (w), 1163 (m), 1123
), 47.6 (CH ), 48.4 (CH ), 69.0 (O-CH ), 69.3 (O-CH ), 104.6 (Pz 4- (m), 1066 (w), 1027 (w), 825 (s), 749 (s), 642 (m), 554 (s). Anal.
C), 121.5 (Im 2-C), 122.3 (Im 3-C), 139.1 (Im 2-C), 144.1 (Pz 5-C), calcd. for C H F N OP: C, 44.04; H, 6.24; N, 12.84%. Found: C,
3
3
3
3
3
2
2
2
2
1
6 27 6 4
1
47.0 (Pz 3-C). Anal. calcd. for C14
H
23ClN
4
O: C, 52.27; H, 7.76; N, 43.70; H, 6.05; N, 12.78%.
Synthesis of the Zwitterionic Ni(II) Complexes
[L1][NiCl ] (Ni1)
This ligand was prepared according to the method described Method A: To a solution of Ni(OAc)
18.75%. Found: C, 52.15; H, 7.54; N, 18.66%.
[1-(2-(1,2-dimethylimizadole-ethoxy)ethyl)-3,5-
+
−
PF6
dimethyllpyrazole] PF
6
(L3
)
3
2
(0.11 g, 0.62 mmol) and LiCl
PF6
Cl
Cl
above for L1 using L3 (1.79 g, 6.0 mmol) and KPF
6
(1.32 g, 7.2 (0.054 g, 1.30 mmol) in DMF (4 mL) was added a solution of L1
was obtained as a white solid (2.83 g, 68%). (0.20 g, 0.71 mmol) in DMF (6 mL), and the resulting solution was
Recrystallization from a concentrated CH Cl
/pentane solution stirred for 20 h at room temperature. The solvent was removed
90:10) at room temperature afforded L3 as white crystals, some under vacuum, and the resulting blue solid residue was washed
PF6
mmol). L3
2
2
PF6
(
1
of which proved suitable for X-ray diffraction studies. H NMR (300 with Et
2
O (3 x 10 mL). Complex Ni1 was obtained as a blue solid
(dme) (0.10 g, 0.46
(5 mL) was added a
Cl (4 mL), and the
), 35.0 (Im 3- resulting solution was stirred for 20 h at room temperature. The
), 105.0 (Pz 4- solvent was removed under vacuum, and the resulting blue solid
C), 121.3 (Im 2-C), 122.0 (Im 3-C), 139.6 (Im 2-C), 144.6 (Pz 5-C), residue was washed with Et O (3 x 10 mL). Complex Ni1 was
blue solid (0.080 g, 40%). Anal. calcd. for
NiO: C, 37.68; H, 5.11; N, 13.52%. Found: C, 37.13; H,
.87; N, 13.31%.
MHz, 298 K, CDCl ): δ 2.17 (3H, s), 2.18 (3H, s), 2.49 (3H, s), 3.70- (0.24 g, 88%). Method B: To a solution of NiCl
2
3
3
3
3
5
.78 (7H, m), 4.07 (2H, t, JHH = 5.1 Hz), 4.17 (2H, t, JHH = 4.4 Hz), mmol) and LiCl (0.019 g, 0.46 mmol) in CH
2
Cl
.78 (1H, s), 7.12 (1H, s), 7.13 (1H, s). C{ H} NMR (75 MHz, 298 K, solution of L1 (0.20 g, 0.51 mmol) in CH
): 9.3 (Pz 5-CH ), 10.9 (Im 2-CH ), 13.4 (Pz 3-CH
), 47.9 (CH ), 48.4 (CH ), 68.8 (O-CH ), 69.6 (O-CH
2
13
1
PF6
2
2
CDCl
CH
3
3
3
3
3
2
2
2
2
2
−
1
obtained as
a
1
(
1
47.5 (Pz 3-C). IR (neat, cm ), ν: 3152 (m), 2903 (w), 2876 (w), 1592
w), 1540 (w), 1517 (w), 1464 (w), 1420 (w), 1398 (w), 1354 (w),
332 (w), 1256 (w), 1180(w), 1123 (m), 1087 (m),1064 (w), 1041
C
4
13 3 4
H21Cl N
(
(
w), 997 (w), 947 (w), 915 (w), 828 (s), 753 (s), 717 (s), 667 (m), 649
m), 616 (m), 556 (s), 501 (m), 468 (w). Anal. calcd. for
[
L2][NiCl
3
] (Ni2)
C
14
H
22
F
6
N
4
OP: C, 41.28; H, 5.44; N, 13.76%. Found: C, 40.74; H, 5.91;
This compound was prepared according to the method
N, 13.42%. Mp: 91.8 °C.
described above for Ni1 using Ni(OAc)
2
(0.16 g, 0.90 mmol), LiCl
(0.076 g, 1.80 mmol) and L2 (0.27 g, 0.99 mmol). Complex Ni2 was
obtained as blue solid (0.27 g, 87%). Anal. calcd. for
C H Cl N NiO: C, 36.00; H, 4.78; N, 13.99%. Found: C, 35.77; H,
Cl
+
−
[1-(2-(2-butylimizadole-ethoxy)ethyl)-3,5-dimethylpyrazole] Cl
Cl
a
(L4 )
1
2
19
3 4
4
.23; N, 13.32%.
6
| New J. Chem., 2015, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
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NP lee wa s eJ od uo r nn oa tl aod fj uC s ht em ma ri sg it nr sy
Page 8 of 10
View Article Online
DOI: 10.1039/C5NJ01538C
Journal Name
L3][NiCl ] (Ni3)
ARTICLE
[
3
Notes and references
This compound was prepared according to the method
described above for Ni1 using Ni(OAc) (0.14 g, 0.79 mmol), LiCl
2
Cl
(
0.066 g, 1.58 mmol) and L3 (0.295 g, 0.99 mmol). Complex Ni3
was obtained as a blue solid (0.29 g, 87%). Anal. calcd. for
NiO: C, 39.25; H, 5.41; N, 13.08%. Found: C, 38.75; H,
.05; N, 12.89%.
14 3 4
C H23Cl N
5
[
L4][NiCl
3
] (Ni4)
This compound was prepared according to the method
described above for Ni1 using Ni(OAc)
2
(0.13 g, 0.73 mmol), LiCl
Cl
(0.062 g, 1.46 mmol), and L4 (0.26 g, 0.80 mmol). Complex Ni4 was
obtained as
a blue solid (0.27 g, 81%). Anal. calcd. for
C H Cl N NiO: C, 42.10; H, 5.96; N, 12.27%. Found: C, 42.01; H,
1
6
27
3 4
1
(a) S. Wang, W.-H. Sun, C. Redshaw, J. Organomet. Chem., 2014,
5.87; N, 12.08%.
7
51, 717. (b) M. Peuckert, W. Keim, Organometallics, 1983, 2,
94. (c) M. Peuckert; W. Keim, S. Storp, R.S. Weber, J. Mol.
5
General oligomerization procedure
Catal., 1983, 20, 115. (d) W. Keim, Angew. Chem. Int. Ed., 1990,
29, 235. (e) S.M. Pillai, M. Ravindranathan, S. Sivaram, Chem.
Rev., 1986, 86, 353. (f) J. Skupinska, Chem. Rev., 1991, 91, 613.
(a) D. Vogt, in: B. Cornils, W. A. Herrmann, (Eds.), In Applied
Homogeneous Catalysis with Organometallic Compounds,
Wiley-VCH, Inc. Weinheim, 2000, pp. 245–258. (b) P. W. N. N.
van Leeuwen, Homogeneous Catalysis, Kluwer Academic, Inc.
Dordrecht, 2004, pp. 175–190.
(a) J. N. L. Dennett, A. L. Gillon, K. Heslop, D. J. Hyett, J. S. Fleming,
C. E. Lloyd-Jones, A. G. Orpen, P. G. Pringle, D. F. Wass,
Organometallics, 2004, 23, 6077. (b) T. M. J. Anselment, S. I.
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and then cooled under vacuum for 30 min. A typical reaction was
performed by introducing toluene (30 mL) and the proper amount
of co-catalyst (MAO or EASC) into the reactor under an ethylene
atmosphere. After 20 min, the toluene catalyst solution (10 mL, [Ni]
2
3
=
10 μmol) was injected into the reactor under a stream of ethylene
and then the reactor was immediately pressurized. Ethylene was
continuously fed in order to maintain the desired ethylene
pressure. After 20 min, the reaction was stopped by cooling the
system to −60 °C and depressurizing. An exact amount of
cyclohexane was introduced (as an internal standard) and the
mixture was analyzed by quantitative GLC.
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X-ray Diffraction Analyses
PF6
PF6
Suitable single-crystals of L1 , L3 , Ni1, Ni2 and Ni3 were
mounted onto a glass fiber using the ‘‘oil-drop’’ method. Selected
bond lengths and angles are given in the Figure captions. Diffraction
data were collected at 150(2) K using an APEXII Bruker-AXS
diffractometer with graphite-monochromatized MoKα radiation (λ =
0.71073 Å). A combination of ω and φ scans was carried out to
obtain at least a unique data set. The crystal structures were solved
by direct methods, remaining atoms were located from difference
Fourier synthesis followed by full-matrix least-squares refinement
based on F2 (programs SIR97 and SHELXL-97) with the aid of the
WINGX program. All non-hydrogen atoms were refined with
anisotropic atomic displacement parameters. H atoms were finally
included in their calculated positions. Crystal data and details of
data collection and structure refinement can be obtained from the
Cambridge
www.ccdc.cam.ac.uk/data_request/cif (CCDC 1055620, 1055623,
055629, 1055632, and 1406895).
Crystallographic
Data
Centre
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Acknowledgements
This work was supported in part by the Petrobras S/A, CAPES,
French MESR, and CNRS. The authors are grateful to CAPES-
COFECUB for joined Action 804/14 and CAPES-CNRS for joined
action PICS05923.
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