Synthesis and use of trans-dichlorido-tetrakis-(N-R-imidazole)nickel(II) complexes in Kumada-Tamao-Corriu cross-coupling reactions

Article abstract of DOI:10.1016/j.poly.2011.05.009

Two dichlorido-tetrakis-(N-R-imidazole)nickel(II) complexes (R = 2,6-diisopropylphenyl (1); methyl (2)) have been synthesised. A single crystal X-ray diffraction study was carried out for 1, which revealed a centrosymmetric complex with the nickel centre placed in an octahedral coordination environment. Both complexes showed high activities (TOFs up to 60200 mol(ArBr) mol(Ni) ^-1 h^-1) in Kumada-Tamao-Corriu cross-coupling of arylhalides with arylgrignards. No significant differences in activity were observed between the two complexes.

Full text of DOI:10.1016/j.poly.2011.05.009

Polyhedron 30 (2011) 2051–2054
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Polyhedron
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Synthesis and use of trans-dichlorido-tetrakis-(N-R-imidazole)nickel(II)
complexes in Kumada–Tamao–Corriu cross-coupling reactions
a,
b
Neslihan Sßahin a,c, Hani El Moll a, David Sémeril a, , Dominique Matt , Ismail Özdemir ,
⇑
⇑
_
Cemal Kaya c, Loïc Toupet d
a Université de Strasbourg, Laboratoire de Chimie Inorganique et Catalyse, UMR 7177 CNRS, 1 Rue Blaise Pascal, 67008 Strasbourg Cedex, France
b
_
Department of Chemistry, Faculty of Science and Art, Inönü University, Malatya, TR 44280, Turkey
c Department of Chemistry, Faculty of Science, Cumhuriyet University, Sivas, TR 58140, Turkey
d Institut de Physique, UMR 6251 CNRS, Université de Rennes 1, Campus de Beaulieu, 35042-Rennes Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Two dichlorido-tetrakis-(N-R-imidazole)nickel(II) complexes (R = 2,6-diisopropylphenyl (1); methyl (2))
have been synthesised. A single crystal X-ray diffraction study was carried out for 1, which revealed a
centrosymmetric complex with the nickel centre placed in an octahedral coordination environment. Both
complexes showed high activities (TOFs up to 60200 mol(ArBr) mol(Ni)ꢀ1 hꢀ1) in Kumada–Tamao–Corriu
cross-coupling of arylhalides with arylgrignards. No significant differences in activity were observed
between the two complexes.
Received 29 March 2011
Accepted 11 May 2011
Available online 18 May 2011
Keywords:
Imidazole ligands
Nickel
Ó 2011 Elsevier Ltd. All rights reserved.
Kumada–Tamao–Corriu
Cross-coupling
1. Introduction
2. Results and discussion
Imidazole ligands are of considerable interest in coordination
chemistry. These aromatic five-membered ring systems contain
two nitrogen atoms, a ‘‘pyridinic’’ one with an in-plane lone pair
allowing metal binding and a trigonal ‘‘pyrrole’’ nitrogen possess-
ing two electrons in an unhybridized orbital. Modification of the
substituent of this latter nitrogen atom provides a straightforward
way to modulate the steric and electronic properties of the flat pyr-
azole ligand. Metal ions that have been associated with imidazoles
for catalytic purposes include iron, [1,2] ruthenium, [3–7] rhodium,
[8] iridium, [8] nickel, [9] palladium [10–17] and copper [18–23]. A
rapid survey of the chemical literature revealed that imidazole-
based nickel complexes have, to the best of our knowledge, not
yet been assessed in Kumada–Tamao–Corriu (KTC) cross-coupling
reactions (Scheme 1), that is the coupling between a Grignard re-
agent and an arylhalide [24–26].
2.1. Synthesis and characterisation of nickel complexes 1 and 2
Complexes 1 and 2 were obtained in high yield from [NiCl2py4]
(py = pyridine) by treatment with the appropriate imidazole ligand
(Scheme 2). It is worth mentioning that complex 2 had previously
been synthesised by reacting hydrated nickel chloride with four
equivalents of N-methylimidazole in a mixture of ethanol and
2,2-dimethoxypropane [27]. Elemental analyses of the complexes
were in agreement with the presence of four imidazole ligands.
The mass spectrum of complex 1 revealed the presence of a strong
peak at m/z = 485.34 having the isotopic profile expected for the
dicationic species [1–2 Cl]2+. In keeping with the octahedral geom-
etry of the nickel(II) atom, complexes 1 and 2 exhibited paramag-
netic behaviour. We noted that no NMR signals corresponding to
hydrogen atoms of the imidazole ring could been seen in the range
0–12 ppm of the 1H NMR spectrum. On the other hand, those
belonging to the R substituents, which lie far from the nickel cen-
tre, appeared as broad signals.
In the present work we describe the synthesis of two dichlori-
do-tetrakis-(N-(R)-imidazole)nickel(II) (R = 2,6-diisopropyl-aryl;
R = Me) complexes, which differ essentially in steric bulk, and their
utilisation in KTC catalysis. The X-ray structure of one of the com-
plexes (R = 2,6-diisopropyl-aryl) is also reported.
2.2. X-ray diffraction studies of nickel complex 1
Single crystals of 1 suitable for X-ray diffraction study were ob-
tained by diffusion of hexane into a dichloromethane solution of
the complex (Fig. 1). The nickel atom of complex 1 assumes a
centrosymmetric, (nearly) octahedral geometry with two axially
⇑
Corresponding authors. Tel.: +33 368851719.
E-mail addresses: dsemeril@chimie.u-strasbg.fr (D. Sémeril), dmatt@chimie.
u-strasbg.fr (D. Matt).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.05.009

2052
N. Sßahin et al. / Polyhedron 30 (2011) 2051–2054
Scheme 1. Kumada–Tamao–Corriu cross-coupling reaction.
Fig. 1. ORTEP drawing of complex 1. Displacement ellipsoids are drawn at the 50%
probability level. Selected bond lengths (Å) and angles (°): Ni(1)–Cl(1) 2.5380 (5),
Ni(1)–N(1) 2.109(2), Ni(1)–N(3) 2.091(2), N(1)–C(1) 1.313(3), N(1)–C(2) 1.379(4),
N(2)–C(1) 1.353(3), N(2)–C(3) 1.377(4), C(2)–C(3) 1.360(4); N(1)–Ni(1)–N(1) 180.0,
Cl(1)–Ni(1)–Cl(1) 180.0, N(3)–Ni(1)–N(1) 93.72(8) and N(1)–Ni(1)–Cl(1) 89.36(6).
was used (Table 1, entries 7 and 9). Repeating these tests with
complex 2 bearing the less encumbered methylimidazole ligand,
led to slightly lower conversions. For example, arylations of
2-bromotoluene with 2-tolylmagnesium chloride were achieved
in 85.7% and 84.5% yield using 0.01 mol% of complexes 1 and 2,
respectively (Table 1, entries 7 and 8).
Scheme 2. Synthesis of the nickel complexes 1 and 2.
The two nickel complexes were further assessed in the cross-
coupling of arylchlorides (Table 2). Using 1 mol% of 1 led to good
conversions after 1 h at 100 °C. Thus, 4- and 2-chlorotoluene were
converted in 45.2% and 44.1%, respectively, when 2-tolylmagne-
sium chloride was employed (Table 2, entries 4 and 9). Repeating
the runs with the same substrates at room temperature for 24 h,
led to conversions of 47.7% and 47.1%, respectively (Table 2, entries
5 and 10). As already observed with arylbromides, arylations car-
ried out with complex 2 gave conversions similar to those obtained
with complex 1. These observations suggest that the substituent of
the pyrrolic nitrogen is too far away from the catalytic center to ex-
ert any significant influence on the catalytic outcome.
located Cl atoms and four equatorial nitrogen atoms. Two trans-
disposed imidazole rings are orthogonal to the N4Ni plane. The
other two imidazole rings are both inclined by 16.3° with respect
to the equatorial plane, thereby minimising the steric interactions
between isopropryl groups of adjacent imidazole ligands. The eigth
NC(H) hydrogen atoms in alpha position to the coordinated N atom
are involved in hydrogen bonding with one of the two chlorido
atoms (CHꢁ ꢁ ꢁCl bond lengths lying in the range 2.588–2.788 Å).
The Ni–N (2.091(2) and 2.109(2) Å) and Ni–Cl (2.5380 (5) Å) bond
lengths are comparable to those found in the recently reported
complex dichlorido-tetrakis-(N-benzylimidazole)nickel(II) [28].
It is worth mentioning here that the isopropyl groups of para-
magnetic 1 appear as two distinct (broad) signals (intensity 1:1),
an observation which suggests the existence of a rotational barrier
about the Ni–N bonds.
3. Experimental
3.1. General considerations
2.3. Utilisation of complexes 1 and 2 in Kumada–Tamao–Corriu cross-
coupling
All reactions were performed in Schlenk-type flasks under dry
nitrogen. Solvents were dried by conventional methods and were
distilled immediately prior to use. Routine 1H was recorded with
FT Bruker AV-300 spectrometer. 1H NMR spectra were referenced
to residual protiated solvent (7.26 ppm for CDCl3). Chemical shifts
and coupling constants are reported in ppm and in Hz, respec-
tively. The catalytic solutions were analysed by using a Varian
3900 gas chromatograph equipped with a WCOT fused-silica col-
Complexes 1 and 2, which are both stable in air, were studied in
Kumada–Tamao–Corriu cross-coupling reactions. Reaction at
100 °C between 4-bromotoluene and phenylmagnesium bromide
using 0.1 mol% of complex 1 led after 3 h to a conversion of
82.9% (Table 1, entry 1). Employing 2-tolylmagnesium chloride in-
creased the reaction rate. For example, 4-bromotoluene was con-
verted in 95.8% after 1 h applying a catalyst loading of 0.01 mol%
umn (25 m ꢂ 0.25 mm, 0.25
lm film thickness). Elemental analy-
ses were performed by the Service de Microanalyse, Université
de Strasbourg. 1-(2,6-diisopropylphenyl)imidazole [29] and
[NiCl2(pyridine)4)] [30] were prepared according to a literature
procedure while 1-(methyl)imidazole was purchased from Sig-
ma–Aldrich. Single crystals of 1 suitable for diffraction study were
obtained by diffusion of hexane into a dichloromethane solution of
(Table 1, entry 3). Reducing the amount of complex
1 to
0.001 mol% resulted in a conversion of 60.2%, which corresponds
to a TOF of 60200 mol(ArBr) mol(Ni)ꢀ1 hꢀ1 (Table 1, entry 5). With
the more sterically hindered 2-bromotoluene, high conversions
were observed especially when 2-tolylmagnesium chloride reagent

N. Sßahin et al. / Polyhedron 30 (2011) 2051–2054
2053
Table 1
Kumada–Tamao–Corriu cross-coupling of arylbromides using nickel complexes 1 and 2.
nickel complex
dioxane
+
Br
XMg
R
R
R'
R'
Entry
ArBr
ArMgX
Nickel complex (mol%)
Time (h)
Conversion (%)
Homocoupling (Ar0–Ar0 %)
1
2
3
4
5
1 (0.1)
2 (0.1)
1 (0.01)
2 (0.01)
1 (0.001)
3
3
1
1
1
82.9
73.1
95.8
91.7
60.2
10.8
13.6
1.8
2.1
4.0
Br
MgBr
MgCl
MgBr
6
7
1 (0.1)
1 (0.01)
5
1
51.6
85.7
15.6
2.8
Br
8
9
2 (0.01)
1 (0.001)
1
1
84.5
53.2
3.2
3.5
MgCl
Table 2
Kumada–Tamao–Curriu cross-coupling of arylchlorides using nickel complexes 1 and 2.
nickel complex
dioxane
T (°C)
+
Cl
XMg
R
R
R'
R'
Entry
ArCl
ArMgX
Nickel complex
Time (h)
Conversion (%)
Homocoupling (Ar0–Ar0 %)
1
2
3
4
5
6
1
2
1
1
1
2
100
100
25
100
25
1
1
24
1
24
24
26.2
26.0
14.4
45.2
47.8
49.2
17.3
15.5
16.2
6.6
6.8
5.5
Cl
MgBr
MgCl
MgBr
25
7
8
1
1
100
25
1
24
28.8
18.8
14.5
19.4
Cl
9
10
11
1
1
2
100
25
25
1
24
24
44.1
47.1
47.2
6.0
5.4
5.1
MgCl
the complex. Formula of the crystals: C30H40ClN4Ni0.5, Mr = 521.47,
3.2.1. Dichlorido-tetrakis-(N-(2,6-diisopropylphenyl)imidazole)-
nickel(II) (1)
ꢀ
triclinic, space group
P
a = 8.8698(1), b = 12.5988(3), c =
= 83.720(2)°, V =
) = 0.71073 Å,
13.6794(3) Å, = 75.208 (2), b = 75.189(1),
a
c
Yield: 0.152 g (73%). 1H RMN (300 MHz, CDCl3, in the range 0–
12 ppm): d = 8.08 (s br, 8H, arom. CH), 7.21 (t, 4H, arom. CH,
3J = 5.8 Hz), 3.29 (s br, 4H, CH(CH3)2), 1.41 (s br, 24H, CH(CH3)2),
1.20 (s br, 24H, CH(CH3)2). MS (ESI-TOF): m/z = 777.42
[MꢀC15H20N2ꢀCl]+, 549.27 [MꢀC30H40N4ꢀCl]+ and 485.34 [Mꢀ2
Cl]2+ (expected isotopic profile). Anal. Calc. for C60H80N8NiCl2: C,
69.10; H, 7.73; N, 10.74. Found: C, 69.03; H, 7.80; N, 10.72%.
1427.30(5) Å3, Z = 2, Dx = 1.213 mg mꢀ3
, k(MoKa
l
= 0.478 mmꢀ1, F(0 0 0) = 558, T = 130(2) K. The sample (0.28 ꢂ
0.26 ꢂ 0.20) was studied on an Oxford Diffraction Xcalibur Saphir
3 diffractometer with graphite monochromatized MoKa radiation.
The data collection (Crysalis, 2004) (2hmax = 27°, omega scan
frames via 0.7° omega rotation and 30 s per frame, range hkl: h,
ꢀ11, 11; k, ꢀ16,16; l, ꢀ17,17) gave 18929 reflections. The data
led to 5746 independent reflections from which 5049 with
3.2.2. Dichlorido-tetrakis-(N-methylimidazole)nickel(II) (2)
Yield: 0.071 g (78%). 1H RMN (300 MHz, CDCl3, in the range 0–
12 ppm): d = 4.06 (s br, 12H, CH3). Anal. Calc. for C16H24N8NiCl2: C,
41.96; H, 5.28; N, 24.46. Found: C, 42.05; H, 5.11; N, 24.37%.
I > 2.0r(I) were observed. The structure was solved with SIR-97,
[31] which revealed the non-hydrogen atoms of the molecule.
After anisotropic refinement many hydrogen atoms were found
with a Fourier Difference. The whole structure was refined with
SHELX-97 [32] by the full matrix least-square techniques (use of
F2; x, y, z, bij for C, N, Cl and Ni atoms, x, y, z in riding mode for H
3.3. General procedure for nickel-catalysed Kumada–Tamao–Corriu
cross-coupling reactions
atoms; 323 variables and 5049 observations with I > 2.0
r(I); calc
w = 1/[
r
2(Fo2) + (0.0691P)2 + 2.3509P] where P = (Fo2 + 2Fc2)/3 with
the resulting R1 = 0.0464, wR2 = 0.1305, Sw = 1.035,
D
q
< 1.469
A dioxane solution containing the nickel complex, arylhalide
(0.25 mmol), ArMgX (1.0 mmol, solution in THF), decane
(0.025 mL, internal reference) and an additional amount of dioxane
(so that the total reaction volume was 0.75 mL) were introduced
into a Schlenk tube. After each catalytic run, a small amount
(0.5 mL) of the solution was passed through a Millipore filter and
analyzed by GC. The NMR spectral data of the products formed,
4-methylbiphenyl [33], 2-methylbiphenyl [34], 2,20-dimethylbi-
phenyl [35], and 2,40-dimethylbiphenyl [36] were in agreement
with those reported in the literature.
eÅꢀ3).
3.2. General procedure for the preparation of nickel complexes 1 and 2
Imidazole (0.80 mmol) and [NiC12py4] (0.2 mmol) were dis-
solved in toluene (10 mL). The reaction mixture was refluxed for
20 h. After cooling to room temperature, the grey solution was fil-
tered. The solid recovered was recrystallized in CH2Cl2/hexane to
afford the desired product as blue–green crystals.

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N. Sßahin et al. / Polyhedron 30 (2011) 2051–2054
_
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29.
_
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We have prepared two octahedral dichlorido-tetrakis-(N-R-
imidazole)nickel(II) complexes (R = 2,6-diisopropylphenyl (1);
methyl (2)), having their four imidazole ligands located in the
equatorial plane. Both complexes turned out to be active in
Kumada–Tamao–Corriu cross-coupling of arylbromides, the ob-
served TOFs reaching 60200 mol(ArBr) mol(Ni)ꢀ1 hꢀ1. The com-
plexes were also efficient in the arylation of deactivated
arylchlorides at room temperature, provided 1 mol% of catalyst
was used. Further work is aimed at synthesising analogues of com-
plex 1 in which the imidazole substituent bears functional groups
able to sterically interact with the metal centre. The reported re-
sults constitute the first examples of KTC cross-coupling based
on Ni–imidazole complexes.
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Appendix A. Supplementary data
CCDC 758051 contains the supplementary crystallographic data
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