Ni(II) complexes bearing pyrrolide-imine ligands with pendant N-, O- and S-donor groups: Synthesis, structural characterization and use in ethylene oligomerization

Article abstract of DOI:10.1039/c5ra16782e

A series of new Ni(ii) complexes of general formula {L}NiCl [Ni1, L = 2-(C₄H₃N-2′-CHN)C₂H₄NHPh; Ni2, L = 5-tert-butyl-2-(C₄H₂N-2′-CHN)C₂H₄NHPh; Ni3, L = 2-(C₄H₃N-2′-CHN)C₂H₄OPh; Ni4, L = 2-(C₄H₃N-2′-CHN)C₆H₄-2′-OPh; Ni5, L = 2-(C₄H₃N-2′-CHN)C₆H₄-2′-SPh; Ni6, L = 2-(C₄H₃N-2′-CHN)CH₂C₆H₄-2′-OMe] were prepared and fully characterized. All nickel precatalysts, activated with methylaluminoxane (MAO), exhibited moderate to good activities for ethylene oligomerization [TOF = 6.1-71.3 × 10³ mol (C₂H₄) (mol (Ni)^-1 h^-1)] and producing high selectivities for 1-butene (68.3-94.0 wt%). The catalytic performance was substantially affected by the ligand environment regarding the pendant oxygen- and sulfur-donor groups, and the substituents on the pyrrolide group. Activation of nickel precatalyst Ni3 with ethylaluminum sesquichloride (Et₃Al₂Cl₃, EASC) instead of MAO produced a significantly more productive catalyst system than Ni2/MAO (TOF = 153:700 vs. 43:500 mol (C₂H₄) (mol (Ni)^-1 h^-1)); however, the 1-butene selectivity was drastically reduced, attaining only 53 wt% with a concomitant production of larger amounts of internal butenes (38 wt%). Under optimized conditions ([Ni] = 10 μmol, 30 °C, oligomerization time = 20 min, 20 bar ethylene, [Al]/[Ni] = 250), precatalyst Ni3 led to a TOF = 55:900 mol (C₂H₄) (mol (Ni)^-1 h^-1) and 82.8 wt% selectivity for 1-butene.

Full text of DOI:10.1039/c5ra16782e

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CASAGRANDE, A. Pinheiro, J. Carpentier, E. Kirillov, T. Roisnel and A. Virgili, RSC Adv., 2015, DOI:
10.1039/C5RA16782E.
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ARTICLE
Ni(II) Complexes Bearing Pyrrolide-Imine Ligands with Pendant O-
and S-donor Groups: Synthesis, Structural Characterization and
use in Ethylene Oligomerization
Received 00th January 20xx,
Accepted 00th January 20xx
A. C. Pinheiro,a A. H. Virgili,a T. Roisnel,b E. Kirillov,c J.-F Carpentier,c,* O. L. Casagrande Jr.a,*
DOI: 10.1039/x0xx00000x
A series of new Ni(II) complexes of general formula {L}NiCl [Ni1, L = 2-(C4H3N-2’-CH=N)C2H4NHPh; Ni2, L = 5-tert-butyl-2-
(C4H2N-2′-CH=N)C2H4NHPh; Ni3, L =2-(C4H3N-2’-CH=N)C2H4OPh; Ni4, L = 2-(C4H3N-2’-CH=N)C6H4-2’-OPh; Ni5, L = 2-(C4H3N-
www.rsc.org/
2’-CH=N)C6H4-2’-SPh; Ni6,
L =2-(C4H3N-2’-CH=N)CH2C6H4-2’-OMe] were prepared and fully characterized. All nickel
precatalysts, activated with methylaluminoxane (MAO), exhibited moderate to good activities for ethylene oligomerization
[TOF = 6.1−71.3 x 103 mol(C2H4)⋅(mol(Ni)−1 h−1)] with high selectivities for 1-butene produced (68.3–94.0 wt.%). The
catalytic performance was substantially affected by the ligand environment regarding the pendant oxygen- and sulfur-
donor groups, and the substituents on the pyrrolide group. Activation of nickel precatalyst Ni3 with ethylaluminum
sesquichloride (Et3Al2Cl3, EASC) instead of MAO produced a significantly more productive catalyst system than Ni2/MAO
(TOF = 153,700 vs. 43,500 mol(C2H4)⋅(mol(Ni)−1 h−1); however, the 1-butene selectivity was drastically reduced, attaining
only 53 wt.% with a concomitant production of larger amounts of internal butenes (38. wt.%). Under optimized conditions
([Ni] = 10 μmol, 30 °C, oligomerization time = 20 min, 20 bar ethylene, [Al]/[Ni] = 250), precatalyst Ni3 led to TOF = 55,900
mol( 2H4)⋅(mol(Ni)−1 h−1) and 82.8 wt.% selectivity for 1-butene.
precatalyst leading to selectivities in C4 olefins higher than 90%
when activated with ethylaluminum dichloride (EtAlCl2).9 Sun et al.
described the synthesis of nickel complexes bearing 2-
(benzimidazol-2-yl)-1,10-phenanthrolines; upon activation with
Introduction
diethylaluminum chloride (Et2AlCl), high catalytic activity of up to
The oligomerization of ethylene is one of the most important
industrial processes to obtain linear α-olefins (LAOs).1 LAOs are
extensively used for preparing detergents, lubricants, plasticizers,
and oil field chemicals or used as co-monomers, etc.2 Among classes
of catalysts used for the production of α-olefins, nickel complexes
containing P,P-,3 P,N-,4 P,O-,5 N,N-,6 or N,O-7 bidentate chelating
ligands are the most frequently studied. More recently, nickel
complexes bearing tridentate ligands have attracted much interest
owing to their good to excellent performance towards the
production of α-olefins.8 In this context, many different classes of
tridentate ligands bearing a variety of E-donor groups (E = N, O, P,
and S) have been explored and used to support nickel complexes
(Chart 1). In particular, Braunstein et al. reported the use of a
tridentate N,P,N-type ligand in the synthesis of the
pentacoordinated mononuclear nickel complex [NiCl2(NOPONMe2-
1
1.27 x 107 g⋅mol(Ni)− ⋅h−1 and high selectivity for 1-butene (90.5 wt.
%) could be achieved.10 More recently, Olivier-Bourbigou et al.
disclosed a new class of nickel complexes based on imino-imidazole
ligands bearing a pendant donor group that are able to oligomerize
ethylene in presence of EtAlCl2 or methylaluminoxane (MAO),
producing mostly dimers and trimers.11
In recent years our groups have been interested in exploring
the potential applications of tridentate ligands in the
oligomerization catalysis field.12 Thus, we have previously reported
on the use of nickel complexes based on tridentate nitrogen-,
oxygen- or sulfur-bridged bis(pyrazolyl) ligands as highly selective
and productive precatalysts for ethylene dimerization upon
activation with MAO.12a Replacement of a pyrazole group by a
pendant ether or thioether group on one side of the ether-
bis(pyrazolyl) ligand led to more active systems.12f
N,P,N)]
(NOPONMe2
=
bis(4,4-dimethyl-
2-
oxazolyldimethylmethoxy)phenylphosphine), which is an effective
a
Laboratory of Molecular Catalysis, Instituto de Química, Universidade Federal do
Rio Grande do Sul, Avenida Bento Gonçalves, 9500, RS, 90501-970 (Brazil). E-mail:
osvaldo.casagrande@ufrgs.br
Institut des Sciences Chimiques de Rennes, Centre de diffraction X, UMR 6226
b
CNRS-Université de Rennes 1, F-35042 Rennes Cedex, France
Institut des Sciences Chimiques de Rennes, Organometallics: Materials and
c
Catalysis Dept., UMR 6226 CNRS-Université de Rennes 1, F-35042 Rennes Cedex,
France. E-mail: jean-francois.carpentier@univ-rennes1.fr
† Electronic Supplementary Information (ESI) available: Crystallographic data for
Ni1
DOI: 10.1039/x0xx00000x
,
and typical GLC analyses of oligomerization mixtures. See
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ARTICLE
Ph
P
complexes are distorted from the ideal geometry in solution. Similar
results have been found for salicylaldiminato nickel(II) halide
complexes.13 The identity of Ni1-Ni6 was established on the basis of
elemental analysis and single-crystal X-ray diffraction studies for
Ni1.
H
O
O
N
N
O
O
N
N
N
Ni
N
Ni
Cl
Cl
Cl
Cl
Braunstein et al.9
Sun et al.10
N
1) NaH, THF, 0 °C to r.t
Z
R
N
N
H
Ni
Cl
2) NiCl2(dme)
N
R
Z
O
N
N
L1 L6
−
N
N
O
N
N
N
Ni
Ni
H
N
Cl
Cl
Cl
Cl
Ni4
Ni1
: R = H, Z =
: R = H, Z =
Ph
Ph
O
S
Carpentier et al.12a
Olivier-Bourbigou et al.11
H
N
Ni5: R = H, Z =
Ni6: R = H, Z =
Ni2: R = tBu, Z =
Ni3: R = H, Z =
O
O
N
N
O
Ni
O
Cl
Cl
Scheme 1
Casagrande et al.12f
Single crystals of Ni1 suitable for X-ray diffraction were grown
from a concentrated acetonitrile/ether solution (80:20) at room
temperature. In the solid state, this complex is monomeric with κ3
coordination of the monoanionic pyrrolide-imine-amine ligand onto
the nickel center. As shown in Figure 1, Ni1 adopts a distorted
square planar geometry around nickel(II). The N(1), N(7), N(10), and
Cl(1) atoms are nearly coplanar, with Cl and N(7) occupying the
trans positions (Cl(1)−Ni(1)−N(7) = 179.04(5)°, N(1) −Ni(1) −N(10):
168.77(6)°). The Ni(1)–N(1) and Ni(1)-N(7) bond distances
[1.8715(4) Å, 1.8585(14) Å, respectively] are close to the values
previously reported for Ni(II) complexes having pyrrole-imine
ligands.14
Chart 1. Examples of nickel complexes based on tridentate ligands
applied in ethylene oligomerization.
As a continuation of the work outlined above, we report here
the synthesis and structural characterization of a new family of
Ni(II) complexes bearing pyrrole-imine ligands with pendant O- and
S-donor groups and their catalytic behavior for ethylene
oligomerization upon activation with MAO and ethylaluminum
sesquichloride (Et3Al2Cl3, EASC). 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 1-butene.
Results and discussion
Synthesis and Characterization of Ni(II) Complexes Bearing
Pyrrolide-Imine Ligands with Pendant O- and S-donor Groups
The pyrrole-imino pro-ligands with pendant O- and S-donor
groups were readily synthesized by Schiff base condensations
between the corresponding primary amines and pyrrole-2-
carboxaldehyde in refluxing methanol. The identity of this class of
ligands was established by IR and NMR spectroscopy, elemental
analysis, and by an X-ray diffraction study for ligands L3, L4 and L5
(see Electronic Supplementary Information). Treatment of L1−L6
with 1.0 equiv. of NaH and then NiCl2(dme) yielded the
corresponding nickel complexes {L}NiCl (Ni1−Ni6), which were
isolated as brown solids in moderate to good yields (63−90 wt.%)
(Scheme 1). These nickel complexes show moderate solubility in
acetonitrile or THF at room temperature. The 1H NMR spectra of
these complexes featured very broad resonances and proved
uninformative. As complexes of Ni(II) with square-planar geometry
are expected to be diamagnetic, this observation implies that these
Fig. 1 ORTEP drawing of Ni1. Ellipsoids are drawn at the 50%
probability level. Selected bond distances (Å) and angles (deg):
Ni(1)−Cl(1)
= 2.1774(4), Ni(1)−N(1) = 1.8715(14), Ni(1)−N(7)=
1.8585(14), Ni(1)−N(10) = 1.9335(14). N(7)−Ni(1)−Cl(1) = 179,04(5).
N(1)−Ni(1)−N(10)
N(7)−Ni(1)−N(10)
=
=
168.77(6), N(7)−Ni(1)−N(1)
85.37(6), Cl(1)−Ni(1)−N(10)
=
=
83.74(6),
94.04(4),
N(1)−Ni(1)−Cl(1) = 96.81(4).
Ethylene Oligomerization Studies
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The performance of nickel precatalysts Ni1−Ni6 were
ARTICLE
Precatalyst Ni1, when activated with 250 equiv of MAO, was
explored in ethylene oligomerization using as cocatalyst found to give moderate activity [TOF = 11,600 mol (C2H4)⋅ mol
(Ni)−1⋅ h−1] along with good selectivity towards 1-butene (89 wt.%).
methylaluminoxane (MAO) containing 20 wt.% AlMe3, at 30 °C and
20 bar constant ethylene pressure. Table 1 summarizes the results
of reactions carried out using 10 μmol of precatalyst in 40 mL of
toluene. All experiments were at least duplicated, yielding
reproducible results within ±10%. When activated with MAO, all the
nickel complexes investigated were found to generate active
Increasing the steric hindrance on the pyrrolide unit, as in
precatalyst Ni2, caused an increase in activity by a factor of 2.50
suggesting that the tert-butyl substituent acts as a protecting group
of the active species, thereby increasing the catalytic
productivity.6b,15 Replacing the amine with an ether group as in
systems for the production of short-chain olefins in the C4−C6 range precatalyst Ni3 led to a much higher activity [TOF = 43,500 mol
(C2H4)⋅ mol (Ni)−1⋅h−1] as compared to the counterpart Ni1 [TOF =
with turnover frequencies (TOFs) varying from 6,100 to 71,300 mol
(C2H4)⋅ mol (Ni)−1⋅h−1. As shown in Table 1 (entries 1–6), the ligand
environment regarding the pendant oxygen- and sulfur-donor
groups, and the substituents on the pyrrolide group influenced the
catalytic performance of the nickel precatalysts on ethylene
oligomerization, as can be better visualized in Figure 2. It is should
be pointed out that, taking into account the lower donor ability of
the ether- and thio- groups as compared to the amine unit, we
cannot rule out that L3-L6 could act as bidentate and not tridentate
ligands. In the absence of structural data for Ni3-Ni6, we can only
speculate at this stage that the coordination of these pendant
oxygen- and sulfur-donor groups onto the nickel center could
stabilize the active catalytic species.
11,600 mol(C2H4) mol(Ni)−1⋅h−1]; however, a slight decreasing in 1-
butene selectivity was found using Ni3 [82.8 wt.% for Ni3 vs. 89.4
wt.% for Ni1].
80
70
60
50
40
30
20
10
0
100
80
60
40
20
0
Table 1. Ethylene Oligomerization with Ni1−Ni6 catalytic systems.a
entry cat
[Al]/[Ni] Olig.
(g)
TOFb
Selectivity (wt. %)
(x 103)
C4
(α-C4)
97.2
(92)
97.1
(83)
97.4
(85)
98.9
(84)
94.8
(72)
100
C6
(α-C6)
2.8
(42)
2.9
(43)
2.6
(30)
1.1
(30)
5.2
(22)
0.0
Ni1
Ni2
Ni3
Ni4
Ni5
Ni6
1
2
Ni1
Ni2
Ni3
Ni4
Ni5
Ni6
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
250
250
250
250
250
250
500
100
50
1.10
2.90
4.00
1.40
7.10
0.60
1.00
2.50
0.50
2.50
1.40
3.50
15.3
11.6
29.1
43.5
14.7
71.3
6.10
11.0
26.6
2.10
27.3
55.9
18.9
153.7
Fig. 2 Influence of the nature of nickel precatalyst on TOF and
selectivity for 1-butene (T = 30 °C, 20 bar, time = 20 min, [Al]/[Ni] =
250).
3
4
5
The productivity for ethylene oligomerization is also
substantially affected by the ligand framework. Hence, precatalyst
Ni3 that contains an ethylene bridge unit is ca. 3.0 times more
active than Ni4 that contains a more rigid phenyl moiety (compare
entries 3 and 4). This result possibly arises from the presence of a
electron-withdrawing group (phenyl unit) that decreases the Lewis
base of the ether unit (OPh), and thus destabilizing the Ni(II) active
species. On the other hand, the selectivity for butenes and
especially 1-butene were similar (ca. 83.0 wt.%), indicating that this
variation in the ligand structure had no influence on the product
distribution.
6
(94)
97.7
(90.0)
98.2
(90)
97.7
(91.0)
97.4
(85)
96.4
(86)
94.5
(79)
91.5
(58)
7
2.3
(52)
1.8
(44)
2.3
(71)
2.6
(33)
3.6
(49)
5.5
(29)
8.5
8
9
10c
11d
12e
13f
250
250
250
50
Replacement of the ether by a thioether donor group (Ni5)
led to a highly active oligomerization system (TOF = 71,300
mol(C2H4)⋅ mol(Ni)−1⋅h−1] associated to a good selectivity for 1-
butene production (68.3 wt.%). Under identical oligomerization
conditions (10 ꢀmol [Ni], 30 °C, 20 bar of ethylene, [Al]/[Ni] = 250,
time = 20 min) Ni5 is much more active than similar nickel
(17)
a
complexes such as NiCl2{bis[2-(3,5-dimethylpyrazolyl)ethyl)]ether}
Reaction conditions: toluene
=
40 mL, [Ni]
=
10 ꢀmol,
12a
[TOF
=
7,100 mol(C2H4)⋅ mol(Ni)−1⋅h−1
]
and NiCl2{1-(2-(2-
35,800
oligomerization time = 20 min, P(ethylene) = 20 bar (kept constant),
phenoxyethoxy)ethyl)-3,5-dimethyl-1H-pyrazole} [TOF
=
Tpol = 30 °C. The results shown are representative of at least
mol(C2H4)⋅ mol(Ni)−1⋅h−1].12f As suggested above we assume that this
higher productivity may arise from the softer and greater donor
ability of S (as compared to O-donor) leading to substantially
improved catalyst lifetimes. Similar results have been found for the
class of nickel precatalysts NiCl2(NZN) based on nitrogen-, oxygen-,
b
duplicated experiments.
Mol of ethylene converted (mol of
1
1
c
d
Ni)− ·h− as determined by quantitative GLC.
Oligomerization time = 5 min, Oligomerization time = 40 min.
T = 50 °C.
e
f
EASC as cocatalyst.
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ARTICLE
or sulfur bridged ligands, whereas the replacement of O-bridged
donor atom by S- promotes a much higher activity for NiCl2{bis[2-
The influence of the MAO loading on the catalyst behavior was
also studied. When activated with 50 equiv of MAO, precatalyst Ni3
gave a lower activity [TOF = 2,100 mol(C2H4)⋅ mol(Ni)−1 h−1, entry 9],
which was increased upon using 100 equiv [TOF = 26,600 mol(C2H4)⋅
mol(Ni)−1 h−1, entry 8] and even further with 250 equiv [TOF =
43,500 mol(C2H4)⋅ mol(Ni)−1⋅h−1, entry 3]. On the other hand, a
greater loading of MAO (500 equiv) led to lower activity (entry 7). In
(3,5-dimethylpyrazolyl)ethyl)]sulfide} [TOF
mol(Ni)−1⋅h−1
as compared
=
57,200 mol(C2H4)⋅
NiCl2{bis[2-(3,5-
]
to
dimethylpyrazolyl)ethyl)]ether}
mol(Ni)−1⋅h−1].12a
[TOF
=
7,100 mol(C2H4)⋅
When the length of the spacer between the central imine and
the ether donor group was increased by one carbon (compare
complexes Ni6 with Ni3 and Ni4), the productivity decreased all cases, the use of different MAO loading ([Al]/[Ni] = 50−500) had
substantially [TOF = 6,100 mol(C2H4)⋅ mol(Ni)−1⋅h−1]. In this case, we little impact on the selectivity for α-C4 that remained in the range of
surmise a more difficult coordination of the OMe group onto the
metal center to deliver a stable 6-membered-ring nickel complex.
82.8−88.4 wt.%.
Activation of the nickel precatalyst Ni3 with 50 equiv of
The preliminary study was extended to investigate the effect
of temperature, [Al]/[Ni] molar ratio, cocatalyst type, and
oligomerization time on the catalytic performance of the more
promising system, i.e. Ni3/MAO (Table 1, entries 7−13). Elevating
the temperature from 30 °C to 50 °C led to a reduction in
productivity [TOF = 27,300 mol(C2H4)⋅ mol(Ni)−1⋅h−1], suggesting that
a partial decomposition of the active catalytic species took place.
However, it should be pointed out that even at higher temperature
(50 °C), the Ni3/MAO still operates with high activity and good
selectivity for 1-C4 production (82.8 wt.%) when compared to
similar nickel precatalysts bearing tridentate ligands.8
ethylaluminum sesquichloride (Et3Al2Cl3, EASC) instead of MAO
produced a significantly better catalyst system with TOF = 153,700
mol(C2H4)⋅ mol(Ni)−1⋅h−1. This high activity eventually generated
some exothermicity, so that the reaction with Ni3/EASC performed
at an initial temperature of 30 °°C (entry 14) rapidly rose to 40−45
°C. Although the catalyst activity was improved by approximately
75-fold (compare entry 9 vs 13), the 1-butene selectivity was
drastically reduced, dropping down to 58 wt.% with a concomitant
production of larger amounts of internal butenes (33.5 wt.%) and
hexenes (8.5 wt.%). The possibility of using small amounts of
cocatalyst is obviously the most interesting feature of this catalyst
system.
The catalyst selectivities and activities were monitored as a
function of time in the ethylene oligomerization reaction promoted
by the Ni3/MAO catalytic system (Figure 3). The oligomerization
activity progressively decreased when the reaction time was
prolonged from 5 to 20 min and finally to 40 min; this indicates that
the catalyst lifetime is relatively short. Furthermore, it is important
to note that Ni3 undergoes almost complete deactivation after 20
min. On the other hand, the reaction time causes a minimum
impact on the selectivity for 1-butene, varying from 82.9 wt.% (5
min) to 74.6 wt.% (40 min), indicating that a single species is
operative in this system. These results also indicate that
isomerization of butenes is a minor pathway in these reactions and
that the observed selectivities directly reflect the dimerization
abilities of the catalyst.
Conclusions
A
new set of tetracoordinate nickel complexes bearing
pyrrolide-imine ligands with pendant O- and S-donor groups were
synthesized and structurally characterized. Upon activation with
MAO or EASC co-catalysts, these Ni(II) complexes showed moderate
to high catalytic activity for ethylene oligomerization with good
selectivity towards 1-butene production. Variations of the ligand
structure demonstrated that
a dramatic change in catalytic
behavior can be obtained upon a subtle modification in the ligand
skeleton. For instance, with nickel complex chelated by L2, the
increase in activity suggested the beneficial role of the tert-butyl
group as sterically protecting group of the active species. On the
other hand, an expansion of the imino-ether arm by introduction of
one additional CH2 unit in the spacer, generating a likely more
flexible ligand L6, decreased substantially the activity of Ni6; this
can be tentatively associated to the formation of a less stable 6-
membered-ring nickel complex. Within the prepared series, the
most active nickel catalyst (Ni5) is the one with a more rigid ligand
bearing a soft donor-group (SPh). However, variation of the ligand
structure does not play a significant role in the selectivity for
butenes and especially 1-butene, attaining 72.0-94.0 wt.% of the
total amount of olefins formed in the oligomerization reactions. The
use of EASC instead of MAO afforded a highly active species;
however the 1-butene selectivity was drastically reduced.
60
55
50
45
40
35
30
25
20
15
100
80
60
40
20
0
0
5
10
15
20
25
30
35
40
45
Experimental
Reaction time (min)
General Procedures
Fig. 3 Monitoring of selectivities and activities as a function of time
in the ethylene oligomerization reaction promoted by the Ni3/MAO
system (T = 30 °°C, 20 bar of ethylene, [MAO]/[Ni] = 250).
All manipulations involving air- and/or water-sensitive
compounds were carried out in an MBraun glovebox or under dry
argon using standard Schlenk techniques. Solvents were dried from
the appropriate drying agents under argon before use. The ligands
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N=C-H), 149.87 (C, Ar-C). IR (KBr, cm−1) ν: 3215 (m), 3165 (w), 3053
(w), 2975 (w), 2906 (w), 2864 (w), 1615 (s), 1562 (s), 1551 (m), 1463
(m), 1438 (m), 1405 (s), 1339 (m), 1315 (m), 1302 (w), 1262 (m),
1242 (w), 1198 (s), 1131 (s), 1088 (s), 1058 (m), 1032 (s), 962 (w),
935 (w), 912 (w), 879 (s), 848 (m), 831 (m), 785 (m), 741 (s), 718
(m), 688 (s), 679 (m), 601 (s), 582 (m), 522 (m), 495 (m). Anal. Calcd.
for C17H14N2S: C, 73.35; H, 5.07; N, 10.06. Found: C, 73.05; H, 5.06;
N, 10.02.
2-(C4H4N-2’-CH=N)C2H4(NH)Ph
(L1),
5-tert-Butyl-2-(C4H3N-2′-
CH=N)C2H4(NH)Ph (L2), and 2-(C4H4N-2′ꢀCH=N)C2H4OPh (L3) were
prepared by literature procedures. 16 5-tert-Butyl-1H-pyrrole-2-
carboxyaldehyde was prepared using the reported procedure.17
NiCl2(dme), pyrrole-2-carboxyaldehyde, 2-(phenylthio)aniline, 2-
phenoxyaniline, and 2-methoxybenzylamine were purchased from
Sigma-Aldrich and used as received. Ethylene (White Martins Co.)
and argon were deoxygenated and dried through BTS columns
(BASF) and activated molecular sieves prior to use. MAO (Witco,
5.21 wt.% Al solution in toluene) was used as received. EASC (Akzo
Nobel) was used with the previous dilution (2.1 wt.% Al solution in
toluene). Infrared spectra were performed on neat products using a
FT-IR Bruker Alpha Spectrometer operating in the ATR mode. 1H and
13C{1H} NMR spectra were recorded at 25 °C on a Varian Inova 300
spectrometer operating at 300 MHz. Chemical shifts are reported in
ppm vs. SiMe4 and were determined by reference to the residual
solvent peaks. Elemental analyses were performed by the Analytical
Central Service of the Institute of Chemistry-USP (Brazil) and are the
average of two independent determinations. Quantitative gas
chromatographic analysis of ethylene oligomerization products was
2-(C4H4N-2′-CH=N)CH2Ph-2-OMe (L6). This product was prepared as
described above for L4, starting from pyrrole-2-carboxyaldehyde
(0.250 g, 2.63 mmol) and 2-methoxybenzylamine (0.358 g, 2.63
mmol). L6 was recovered as pale brown needles (0.334 g, 60%). Mp:
62.2 °C. 1H NMR (300 MHz, CDCl3, 25 °C): δ 3.80 (s, 3H, CH3), 4.73 (s,
2
2H, CH2), 6.19 (t, 3J = 6.0 Hz, 1H, 4-pyrrole), 6.47 (d, J = 3.0 Hz, 1H,
3-pyrrole), 6.74 (s, 1H, 5-pyrrole), 6.87-6.92 (m, 2H, Ar-H), 7.21-7.24
(m, 2H, Ar-H), 8.14 (s, 1H, CH=N). 13C NMR (125 MHz, CDCl3, 25 °C):
δ 55.40 (CH3), 58.79 (CH2), 109.58 (CH, 4-pyrrole), 110.30 (CH, 3-
pyrrole), 114.37 (CH, Ar-C), 120.64 (CH,5-pyrrole), 122.00 (CH, Ar-C),
127.90 (C, Ar-C), 128.29 (CH, Ar-C), 129.41 (CH, Ar-C), 130.43 (C, 2-
performed on a Agilent 7890A instrument equipped with a Petrocol pyrrole), 153.04 (CH, N=C-H), 157.22 (C, Ar-C). IR (KBr, cm−1) ν: 3424
HD capillary column (methyl silicone, 100 m length, 0.25 mm i.d. (sh), 3170 (w), 3123 (w), 3063 (w), 2956 (w), 2832 (w), 1639 (s),
and film thickness of 0.5 μm) (36 °C for 15 min, then heating at 5 1601 (w), 1592 (w), 1490 (m), 1460 (m), 1441 (m), 1422 (m), 1353
°C⋅min−1 until 250 °C); cyclohexane was used as internal standard.
(m), 1315 (w), 1283 (m), 1244 (s), 1166 (w), 1136 (m), 1110 (m),
1031 (s), 975 (w), 879 (w), 837 (w), 757 (s), 739 (s), 606 (w), 581 (w).
Synthesis of the pyrrol-imine ligands with O- and S-donor groups
Anal. Calcd. for C13H14N2O: C, 72.87; H, 6.59; N, 13.07. Found: C,
72.81; H, 6.68; N, 13.20.
2-(C4H4N-2′-CH=N)Ph-2-OPh (L4). To a stirred solution containing
pyrrole-2-carboxyaldehyde (0.250 g, 2.63 mmol) in ethanol (75 mL),
2-phenoxyaniline (0.560 g, 2.63 mmol) was added. The reaction
mixture was stirred for 72 h at 65 °C. The solvent was evaporated to
give a pale brown solid that was recrystallized from ethanol/ether
to give L4 as an off-white solid (0.413 g, 87%). Mp: 110.4 °C. 1H
NMR (300 MHz, CDCl3, 25 °C): δ 6.21 (dd, 2J = 2.6 and 3.6 Hz, 1H, H-
Synthesis of the Ni(II) Complexes
[Ni{2-(C4H3N-2-CH=N)C2H4(NH)Ph}Cl] (Ni1). To a solution of L1
(0.200 g, 0.94 mmol) in THF (5 mL) was added dropwise a
suspension of NaH (0.034 g, 0.94 mmol) in THF (5 mL) at 0 °C. The
resulting red solution was stirred for 4 h at room temperature and
then added dropwise to a solution of NiCl2(dme) (0.205 g, 0.94
2
pyrrole), 6.60 (dd, 2J = 1.3 and 3.6 Hz, 1H, H-py), 6.79 (d, J = 1.3 Hz,
1H, H-pyrrole), 6.90-7.27 (m, 9H, Ar-H), 8.23 (s, 1H, CH=N), 9.69 (br mmol) in THF (10 mL) at −78 °C. The reaction mixture was stirred
s, 1H, NH-pyrrole). 13C NMR (125 MHz, CDCl3, 25 °C): δ 110.38 (CH, overnight at room temperature and then volatiles were removed in
4-pyrrole), 116.68 (CH, 3-pyrrole), 117.89 (2CH, Ar-C), 120.98 (CH, vacuo. The brown crude solid was dissolved in toluene (15 mL),
5-pyrrole), 121.20 (CH, Ar-C), 122.56 (CH, Ar-C), 123.31 (CH, Ar-C), filtered by cannula and the resulting solution was concentrated (ca.
124.82 (CH, Ar-C), 126.25 (CH, Ar-C), 129.61 (2CH, Ar-C), 130.98 (C, 3 mL). Then, pentane (15 mL) was added to afford a pale brown
2-pyrrole), 144.04 (C, Ar-C), 149.21 (C, Ar-C), 150.88 (CH, N=C-H), solid which was washed with diethyl ether (2 × 10 mL) to give, after
1
158.27 (C, Ar-C). IR (KBr, cm−1) ν: 3238 (s), 3095 (w), 3063 (w), 2979 drying, Ni1 as a brown solid (0.210 g, 73%). IR (ATR, cm− ): ν 3048
(w), 2896 (w), 1687 (m), 1631 (s), 1594 (m), 1488 (s), 1455 (m), (w), 2954 (w), 2845 (w), 1626 (w), 1597 (w), 1576 (s), 1490 (m),
1418 (m), 1339 (w), 1319 (w), 1267 (w), 1237 (s), 1205 (m), 1184 1441 (m), 1387 (m), 1301 (s), 1246 (w), 1030 (s), 733 (s), 690 (s),
(w), 1159 (s), 1134 (m), 1090 (m), 1069 (w), 969 (w), 940 (w), 878 601 (m), 508 (m). Anal. Calcd. for C13H14ClNiN3: C, 50.96; H, 4.61; N,
(m), 845 (m), 795 (m), 751 (s), 693 (m), 603 (m), 490 (w), 460 (w). 13.71. Found: C, 51.27; H, 4.94; N, 13.60.
Anal. Calcd. for C17H14N2O: C, 77.84; H, 5.38; N, 10.68. Found: C,
[Ni{5-tert-butyl-2-(C4H2N-2-CH=N)C2H4(NH)Ph}Cl]
(Ni2).
This
77.26; H, 5.09; N, 10.69.
product was prepared as described above for Ni1, starting from L2
2-(C4H4N-2′-CH=N)CH2Ph-2-SPh (L5). This product was prepared as (0.183 g, 0.68 mmol), NaH (0.025 g, 0.68 mmol), and NiCl2(dme)
described above for L4, starting from pyrrole-2-carboxyaldehyde (0.150 g, 0.68 mmol) in THF (10 mL) to give Ni2 as a pale brown
1
solid (0.221 g, 90%). IR (ATR, cm− ): ν 3190 (w), 3102 (w), 2959 (w),
(0.250 g, 2.63 mmol) and 2-(phenylthio)aniline (0.529 g, 2.63
mmol). L5 was recovered as an off-white solid (0.219 g, 30%). Mp:
2899 (w), 1639 (m), 1593 (s), 1491 (m), 1441 (m), 1392 (m), 1341
(m), 1269 (m), 1231 (m), 1153 (w), 1093 (w), 1044 (s), 914 (m), 785
(m), 750 (s), 690 (s), 511 (m). Anal. Calcd. for C17H22ClNiN3: C, 56.32;
H, 6.12; N, 11.59. Found: C, 56.11; H, 5.87; N, 11.44.
1
2
102.5 °C. H NMR (300 MHz, CDCl3, 25 °C): δ 6.30 (dd, J = 2.7 and
2
3.5 Hz, 1H, H-pyrrole), 6.67 (dd, J = 1.1 and 3.6 Hz, 1H, H-pyrrole),
6.96-7.07 (m, 4H, H-Ar + H-pyrrole), 7.16-7.22 (m, 1H, H-Ar), 7.30-
7.37 (m, 3H, H-Ar), 7.44-7.47 (m, 2H, H-Ar), 8.16 (s, 1H, CH=N), 9.55
(br s, 1H, NH-pyrrole). 13C NMR (125 MHz, CDCl3, 25 °C): δ 110.55
(CH, 4-pyrrole), 116.70 (CH, 3-pyrrole), 118.42 (CH, 5-pyrrole),
123.38 (CH, Ar-C), 125.88 (CH, Ar-C), 127.14 (CH, Ar-C), 127.84 (CH,
Ar-C), 128.93 (2CH, Ar-C), 129.37 (2CH, Ar-C), 130.93 (CH, Ar-C),
[Ni{2-(C4H3N-2-CH=N)C2H4OPh}Cl] (Ni3). This product was prepared
as described above for Ni1, starting from L3 (0.199 g, 0.93 mmol),
NaH (0.034 g, 0.93 mmol), and NiCl2(dme) (0.190 g, 0.93 mmol) in
THF (10 mL) to give Ni3 as a pale brown solid (0.193 g, 67%). IR
132.46 (C, 2-pyrrole), 133.46 (C, Ar-C), 134.19 (C, Ar-C), 149.77 (CH, (ATR, cm−1): ν 3011 (w), 2933 (w), 2924 (w), 2861 (w), 1586 (s),
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1487 (m), 1487 (m), 1443 (w), 1391 (m), 1312 (m), 1231 (s), 1198 of ω and φ scans was carried out to obtain at least a unique data
(w), 1172 (m), 1105 (w), 1079 (w), 1050 (m), 1034 (s), 1003 (w), 962 set. The crystal structures were solved by direct methods,
(w), 936 (w), 891 (w), 821 (w), 800 (w), 782 (w), 758 (s), 722 (s), 689 remaining atoms were located from difference Fourier synthesis
(w), 673 (m), 600 (m), 548 (w), 509 (m), 486 (w), 450 (s). Anal. followed by full-matrix least-squares refinement based on F2
Calcd. for C13H13ClNiN2O: C, 50.79; H, 4.26; N, 9.11. Found: C, 51.15; (programs SIR97 and SHELXL-97) with the aid of the WINGX
H, 4.46; N, 8.88.
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
[Ni{2-(C4H3N-2-CH=N)Ph-2-OPh}Cl] (Ni4). This product was
prepared as described above for Ni1, starting from L4 (0.299 g, 1.14
mmol), NaH (0.042 g, 1.14 mmol), and NiCl2(dme) (0.250 g, 1.14
mmol) in THF (10 mL) to give Ni4 as a pale brown solid (0.280 g,
69%). IR (ATR, cm−1): ν 3234 (w), 3065 (w), 2976 (w), 2899 (w), 1626
(s), 1573 (m), 1483 (s), 1452 (m), 1415 (s), 1332 (w), 1312 (w), 1268
(w), 1232 (s), 1182 (s), 1090 (s), 1036 (s), 968 (w), 874 (m), 835 (m),
795 (m), 746 (s), 690 (s), 601 (m), 490 (m). Anal. Calcd. for
C17H13ClNiN2O: C, 57.44; H, 3.69; N, 7.88. Found: C, 57.05; H, 3.44;
N, 7.66.
Crystallographic
Data
Centre
via
www.ccdc.cam.ac.uk/data_request/cif (CCDC 1407832).
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.
[Ni{2-(C4H3N-2-CH=N)CH2Ph-2-SPh}Cl] (Ni5). This product was
prepared as described above for Ni1, starting from L5 (0.326 g, 1.17
mmol), NaH (0.043 g, 1.17 mmol), and NiCl2(dme) (0.255 g, 1.17
mmol) in THF (10 mL) to give Ni5 as a pale brown solid (0.377 g,
87%). IR (ATR, cm−1): ν 3054 (w), 1590 (m), 1556 (s), 1497 (s), 1474
(m), 1463(m), 1437 (m), 1379 (m), 1291 (s), 1225 (w), 1185 (m),
1164 (w), 1074 (w), 1030 (s), 996 (w), 943 (w), 902 (m), 889 (w), 836
(w), 748 (s), 723 (m), 685 (m), 667 (w), 625 (w), 597 (m). Anal.
Calcd. for C17H13ClNiN2S: C, 54.96; H, 3.53; N, 7.54. Found: C, 54.81;
H, 3.94; N, 7.09.
Notes and references
[Ni{2-(C4H3N-2-CH=N)CH2Ph-2-OMe}Cl] (Ni6). This product was
prepared as described above for Ni1, starting from L6 (0.300 g, 1.40
mmol), NaH (0.051 g, 1.40 mmol), and NiCl2(dme) (0.307 g, 1.40
mmol) in THF (10 mL) to give Ni6 as a pale brown solid (0.271 g,
63%). IR (ATR, cm−1): ν 2999 (w), 2924 (w), 2835 (w), 1618 (w), 1600
(m), 1579 (s), 1490 (m), 1435 (m), 1378 (m), 1291 (m), 1241 (s),
1175 (w), 116 (m), 1026 (s), 805 (w), 730 (s), 601 (w). Anal. Calcd.
for C13H13ClNiN2O: C, 50.79; H, 4.26; N, 9.11. Found: C, 51.34; H,
4.96; N, 8.97.
1
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Ethylene oligomerization reactions were performed in a 100
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Graphical Contents Entry
Nickel complexes bearing pyrrolide-imine ligands with pendant O- and S-donor
groups have been synthesized and their catalytic behavior in ethylene
oligomerization has been investigated.