Cobalt(II) complexes bearing a bulky N-heterocyclic carbene for catalysis of Kumada-Tamao-Corriu cross-coupling reactions of aryl halides

Article abstract of DOI:10.1002/ejic.201200095

Cobalt(II) iodide, bromide, and chloride react with 1 equiv. of IPr [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene] to form a series of tetrahedral dimeric (30e) complexes of cobalt(II) in good yields. These were transformed into the monomeric forms in the presence of pyridine. These complexes were characterized by SQUID, XPS, UV/Vis spectroscopy, elemental analysis, and X-ray crystallography, and were found to have high catalytic activity for Kumada-Tamao-Corriu cross-coupling reactions of aryl halides. Copyright

Full text of DOI:10.1002/ejic.201200095

Job/Unit: I20095
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FULL PAPER
DOI: 10.1002/ejic.201200095
Cobalt(II) Complexes Bearing a Bulky N-Heterocyclic Carbene for Catalysis
of Kumada–Tamao–Corriu Cross-Coupling Reactions of Aryl Halides
[
a]
[a]
[a]
[a]
Kouki Matsubara,* Tsukasa Sueyasu, Mariko Esaki, Aya Kumamoto,
[a]
[a]
[a]
[a]
Shinya Nagao, Hitomi Yamamoto, Yuji Koga, Satoshi Kawata, and
Taisuke Matsumoto[
b]
Keywords: N-Heterocyclic carbene (NHC) ligands / Cobalt complexes / Antiferromagnetic interactions / Grignard cross-
coupling
Cobalt(II) iodide, bromide, and chloride react with 1 equiv. of
IPr [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene] to
form a series of tetrahedral dimeric (30e) complexes of co-
were characterized by SQUID, XPS, UV/Vis spectroscopy, el-
emental analysis, and X-ray crystallography, and were found
to have high catalytic activity for Kumada–Tamao–Corriu
balt(II) in good yields. These were transformed into the mo- cross-coupling reactions of aryl halides.
nomeric forms in the presence of pyridine. These complexes
Introduction
The N-heterocyclic carbene (NHC) is one of the most
versatile ligands bound to metal complexes, because of its
strong ability to act as a 2e donor and its variety of struc-
Cobalt-catalyzed organic transformations are now in-
creasingly more popular, because the first-row late-transi-
tion metals are expected to replace precious metals in the
catalysis of many organic reactions.[ Among the reactions,
cross coupling of halogenated substrates in the presence of
cobalt have been widely developed in recent years. Al-
though cobalt-catalyzed Grignard cross-coupling reactions
by the activation of alkyl halides have been known, aryl
halides, which are general substrates for the reactions in Ni
[5]
tures. Although several cobalt complexes bearing NHC
[6]
ligands have been reported, those having catalytic activi-
1]
ties in metal-catalyzed cross-coupling reactions are rare.
Chen et al. recently reported the first trivalent cobalt NHC
complexes as active catalysts for Kumada–Tamao–Corriu
[
2]
[3]
cross-coupling reactions. Deng. et al. reported divalent
and monovalent cobalt NHC complexes that are highly
active for oxidative homocoupling of aryl Grignard rea-
[
3]
and Pd chemistry, are rarely activated in the literatures.
[7]
gents. However, those bearing bulky NHC ligands, such
The cobalt species catalyzing these reactions are generally
formed in situ using easily available cobalt precursors, such
as cobalt halides, carbonyl, acetate, and acetylacetonate,
with appropriate ligands.[ To date there is little structural
evidence for either the initially generated metal complex or
the real active species, because the paramagnetic nature of
these compounds usually precludes NMR analysis. How-
ever, using structurally defined metal complexes and clearly
defining the reaction mechanism will open the gate to de-
velop highly active metal catalysts and new organic reaction
processes. These prompted us to prepare new cobalt com-
plexes that are easily accessible and can catalyze efficient
cross-coupling reactions of aryl halides.
as 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr)
have not been prepared for cross-coupling reactions, al-
though these ligands have been added as cocatalysts to the
cobalt precursors in several cross-coupling reactions of aryl
4]
[8]
and alkyl halides. Such a bulky ligand sometimes leads to
coordinatively unsaturated active species, which have been
[9]
observed in the chemistry of other metals.
Here we describe the synthesis and structures of a series
of new cobalt(II) complexes bearing bulky IPr ligands. We
also carried out catalytic cross-coupling reactions of aryl
and alkyl halides with arylmagnesium chloride. The dico-
balt(II) complexes are paramagnetic and not easy to handle
because of their extremely air-sensitive nature. To stabilize
them, the addition of pyridine was effective, successfully
forming monocobalt(II) pyridine complexes. These were
characterized by SQUID, XPS, UV/Vis spectroscopy, X-ray
crystallography, and elemental analysis. Interestingly, the
[
a] Department of Chemistry, Faculty of Science, Fukuoka
University,
8
-19-1 Nanakuma, Fukuoka 814-0180, Japan
Fax: +81-92-865-6030
E-mail: kmatsuba@fukuoka-u.ac.jp
[
b] Analytical Center, Institute for Materials Chemistry and complexes have little activity toward alkyl halides but are
Engineering, Kyushu University,
active for aryl halides at ambient temperature. This is the
first example of divalent cobalt NHC complexes that cata-
lyze cross-coupling reactions of aryl halides.
6
-1 Kasuga, Fukuoka, Japan
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201200095.
Eur. J. Inorg. Chem. 0000, 0–0
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K. Matsubara et al.
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Results and Discussion
Preparation of IPr-Cobalt(II) Complexes
Simple addition of IPr (1 equiv.) to cobalt(II) iodide
anhydrate in THF at room temperature under an inert at-
mosphere successfully afforded a dimeric IPr-cobalt(II)
complex, [Co(IPr)I] (μ-I) (1a). After recrystallization from
2
2
a toluene/hexane solution at –30 °C, complex 1a was ob-
tained in 48% yield as green crystals. Cobalt(II) bromide
and chloride also gave similar complexes, [Co(IPr)X]2-
(
(
μ-X) (1b: X = Br, 1c: X = Cl), as blue crystalline solids
Scheme 1). The isolated yields of 1b and 1c by recrystalli-
2
zation from toluene/hexane solutions were 46 and 31%,
respectively. It is of interest that these products were dimers
even when an excess amount of IPr was added to CoX2,
probably because steric hindrance derived from the bulky
IPr ligand prevented the second coordination of IPr. The
result is in contrast to the corresponding chemistry of
nickel, in which nickel complexes bearing two IPr ligands,
Scheme 1. Synthesis of dimeric cobalt(II) halides bearing bulky
NHC (1a–c) and monomeric complexes 2a–c.
[
NiX (IPr) ] (X = Cl and Br), have been prepared in good
2 2
[
9c]
yields. However, this is favorable for the construction of
an active catalyst, because many organometallic com-
pounds bearing only one bulky NHC ligand have high cata-
lytic activity in comparison to those bearing two NHC li-
[
9d,10]
gands.
We considered that the tetrahedral geometry of
cobalt(II), in contrast to the square-planer nickel(II) geom-
etry, made the simultaneous coordination of the two bulky
ligands difficult. In the chemistry of phosphane complexes,
the monomeric complexes of cobalt, [CoX (PCy ) ], have
2
3 2
Figure 1. The structures of the decomposed products 3b and 3c.
[
11]
been reported, but those bearing phosphanes with larger
cone angles are unknown. The crude products were sepa-
rated through Celite before recrystallization in toluene, in
order to remove the insoluble decomposition products
formed in the reaction. The chloride and bromide ana-
logues of the decomposition products were determined by
preliminary single-crystal X-ray diffraction studies as an-
ionic mononuclear cobalt(II) complexes with an imid-
azolium cation, 3b and 3c (see Supporting Information, and
Figure 1). The similar phosphorus analogues of 3 are well
known and have been widely studied.[ We considered that
these anionic complexes could be formed from the reaction
of 1b and 1c with contaminated proton sources in situ.
The complexes 1a–c were extremely unstable in air and
rapidly formed a red-brown solid. This could be a drawback
when these compounds are used as catalysts and should be
stabilized in order to be used as catalyst precursors. The
easy formation of the decomposed monomeric form 3
prompted us to add a 2e-donor ligand to stabilize 1a–c,
thus forming the monomeric complexes. When the com-
pounds were dissolved in pyridine or 1 equiv. of pyridine
was added, mononuclear pyridine complexes of cobalt(II),
Co(IPr)X (C H N) (2a: X = I, 2b: X = Br, 2c: X = Cl),
though we did not detect such species in the donor solvents,
such as THF, acetonitrile, and acetone.
Although elemental analysis of 1a–c is unsuccessful be-
cause of their air sensitivity, XPS spectra showed the distri-
bution of the elements existing at the bulk surface of the
crystals. In these complexes, the ratios of cobalt/halogen/
nitrogen were near 1:2:2 as shown in Table 1, suggesting
7
that the cobalt center is divalent (d ), and that only one IPr
ligand coordinates to a cobalt atom. The complexes 1a–c
12]
1
and 2a–c were found to be paramagnetic, and H NMR
spectra in the C D solutions showed several broadened sig-
6
6
nals over a wide range. The ESR spectra for 2a–c in toluene
at 77 K showed broad resonances as depicted in the Sup-
porting Information, presenting their paramagnetic charac-
[13]
ter in the toluene glass.
Table 1. Element (Co, N, X; X = Cl, Br, I) ratios in 1a–c measured
by XPS.
1a
1b
1c
Formula
C
2.00
4.16
3.62 [I(3d )]
66.86
54
H
72
N
4
I
4
Co
2
54 72 4 4 2 54 72 4 4 2
C H N Br Co C H N Cl Co
[a]
Co(2p)
2.00
3.80
4.46 [Br(3d)]
2.00
4.16
4.38 [Cl(2p)]
2
5
5
[a]
N(1s)
X
were generated (Scheme 1). These complexes were isolated
in 59, 38, and 30% yields, respectively, by recrystallization
from a toluene/hexane solution at –30 °C. The result sug-
gests that the dimeric complexes 1a–c are able to form mo-
[a]
5
[a]
[b]
[b]
[b]
C(1s)
a] All data were standardized by Co(2p) = 2.00. [b] The ratio of
the carbon sometimes goes wrong, ascribed to the carbon film
50.36
67.26
[
nomeric cobalt species in the presence of donor ligands, al- where the samples were applied.
2
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Kumada–Tamao–Corriu Cross-Coupling Reactions of Aryl Halides
From the measurements of the magnetic susceptibilities –24.2 cm–1 and g = 2.59. The parameters for the other co-
–1
of 1a–c and 2a–c by SQUID in the solid state, the values balt(II) dimers 1a and 1b were J = –40.2 and –37.9 cm ,
of χT per one cobalt atom were 2.04–2.27 (1a–c) and 2.36– and g = 2.51 and 2.39, respectively. This characteristic mag-
–
1
–1
2
.79 cm Kmol (2a–c) at 300 K, showing that the spin netic behavior of the dicobalt(II) complexes 1a–c is attrib-
quantum numbers were all 3/2 (Table 2). The result indi- uted to antiferromagnetic interactions between the S = 3/2
cates that divalent cobalt takes on a tetrahedral geometry spins of the two intramolecular cobalt(II) atoms, which is
in all the complexes. The temperature dependence of χT generally observed in multinuclear paramagnetic sys-
[
14]
for dicobalt complexes 1a–c demonstrated that the value tems.
gradually decreased upon cooling until about 5 K, whereas
Electronic spectra of 1a–c in the toluene solutions
those for 2a–c did not decrease, as shown in Figure 2 for 1c (5.0ϫ10–4 molL ) (Figure 3, a) at ambient temperature
and 2c, for example. The magnetic behavior of 1c can be showed a series of bands from the d–d transition at 662,
analyzed in terms of the dipolar coupling approach for the 727, and 782 (1a), 600, 685, and 720 (sh) (1b), and 575,
–1
II
Co dimer. The expression for the magnetic susceptibility 659, and 700 nm (1c). The absorbance of each compound
II
for the Co dimer, derived from Heisenberg–Dirac–Van decreases in the order of 1aϾ1bϾ1c, which agrees with the
Vleck’s equation, is
order of the spectrochemical series of halogen anions. The
appearance of the separated three bands may be a result of
the spin-orbit coupling and the unsymmetrical structure in
these cobalt complexes. These spectra suggest that 1a–c
have the same tetrahedral d7 structures in solution.
Moreover, these bands did not broaden at room tempera-
ture, suggesting that any equilibrium reactions, such as the
formation of the monomer with solvent from the dimer,
could be ruled out in these complexes. Similar but signifi-
cantly different spectra were observed for 2a–c in the tolu-
ene solutions (Figure 3, b). The blueshift at about –70 to
2
2
χ = Ng β /kT{[14 + 5exp(6x) + exp(10x)]/[7 + 5exp(6x) +
exp(10x) + exp(12x)]}
3
with x = –J/kT, where N, β, and k are Avogadro’s number,
Bohr magneton, and Boltzmann constant, respectively.
[15]
Table 2. χT and μeff of 1a–c and 2a–c at 300 K.
1a
1b
1c
2a
2b
2c
3
–1
χT [cm Kmol ]/
2.04
2.06 2.27 2.79 2.45 2.36
4.06 4.27 4.72 4.43 4.35
Co[
a]
μ
S/Co
eff/Co
4.03
3/2
3/2
3/2
3/2
3/2
3/2
[
a] Each χDmol ϫ10–6 cm–1 mol–1 per one cobalt atom was calcu-
lated and compensated for.
Figure 2. χT vs. T plots for the compounds 1c (᭺) and 2c (᭛) as
representative examples. The obtained χT values of 1c were calcu-
lated as half values to represent one cobalt atom. The solid line is
a best-fit calculated line for a dicobalt(II) tetrahedral complex (S
=
3/2), where J = –24.2 cm–1 and g = 2.59. The compound 1c may
have a small amount of a monocobalt(II) species (ca. 5%) as a
contaminated decomposed product.
The above expression can be fitted to the magnetic
susceptibility of the dicobalt(II) species to allow the intrad-
imer exchange integral J to be evaluated. The best-fit pa-
rameters for 1c obtained from the agreement of the calcu-
Figure 3. UV/Vis spectra for compounds (a) 1a–c and (b) 2a–c in
toluene (0.50 mm) from 500 to 800 nm. Each arrow shows the low-
lated line with the observed one in Figure 2 were J = est of the three bands assigned as the d–d transition.
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K. Matsubara et al.
FULL PAPER
–40 nm, from the lowest-energy absorbance in the spectra and these results strongly supported the above spectro-
of 1a–c indicated that a strong donation from pyridine sta- scopic results. All cobalt centers take on a tetrahedral ge-
bilizes the occupied d orbital of the unsaturated cobalt(II) ometry. Each of the distances between two cobalt atoms
in comparison with a 2e donation from the bridging halo- in 1a–c was over 3 Å, suggesting the absence of a direct
gen ligands in 1a–c. The results suggest that the coordina- interaction between the cobalt atoms. As shown in Table 3,
tion of pyridine dominantly stabilizes the cobalt complexes all cobalt–halogen bond lengths were in the range of single
also in solution by formation of 2a–c.
bond lengths, 2.574(1)–2.637 Å in 1a and 2a, representa-
Finally, the structures of all the complexes were con- tively. The distances between cobalt and carbene carbon in
firmed by single-crystal X-ray diffraction studies (Figure 4) all the complexes were in the range of single bond lengths
Figure 4. X-ray crystal structures of (a) 1a, (b) 1b, (c) 1c, (d) 2a, (e) 2b, and (f) 2c (50% probability of the thermal ellipsoids). Hydrogen
atoms and solvents are omitted for clarity. The half fragments of the molecules 1a–c are grown by a symmetric operation. Independent
two molecules of 2a and 1.5 molecules of toluene are included, and one molecule of toluene per one molecule, 2b or c, is included in the
lattice of the crystals.
4
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Kumada–Tamao–Corriu Cross-Coupling Reactions of Aryl Halides
and did not change depending upon the halogen atoms, studies of the cobalt-catalyzed coupling of alkyl bromides.[3]
.043(3) (2a), 2.057(3) (2b), 2.051(3) Å (2c). The cobalt– This could be a result of the electronic effect of the NHC
pyridine bond lengths in 2a–c are 2.066(3), 2.065(3), and ligand, which is a strong 2e donor.
.044(2) Å, respectively. Apparently, pyridine coordination
2
2
Table 4. Summary of reaction conditions of the various aryl (or
alkyl) halides with Grignard reagents mediated by Co–NHC com-
plexes.
excluded the formation of dimeric 1 to form the monomeric
complex 2.
Table 3. Representative bond lengths [Å] and angles [°] of 1a–c and
2a–c.
1a (X = I)
1b (X = Br) 1c (X = Cl)
Bond lengths [Å]
Co(1)–X(1)
Co(1)–X(1)Ј
Co(1)–X(2)
Co(1)–C(1)
2.631(1)
2.637(1)
2.574(1)
2.038(7)
2.4463(4)
2.4506(4)
2.3559(4)
2.027(2)
2.3144(4)
2.3245(4)
2.2238(4)
2.0298(13)
Bond Angles [°]
C(1)–Co(1)–X(1)
C(1)–Co(1)–X(2)
X(1)–Co(1)–X(2)
Co(1)–X(1)–Co(1)Ј
115.4(2)
109.8(2)
107.93(4)
80.87(4)
113.56(6)
111.07(5)
109.838(15) 112.649(18)
81.995(13) 84.759(14)
113.18(4)
109.78(4)
2a (X = I)
2b (X = Br) 2c (X = Cl)
Bond lengths [Å]
Co(1)–X(1)
Co(1)–X(2)
Co(1)–N(3)
Co(1)–C(1)
2.6012(6)
2.5869(7)
2.066(3)
2.043(3)
2.3888(7)
2.3866(7)
2.065(3)
2.057(3)
2.2532(8)
2.2414(8)
2.044(2)
2.051(3)
Bond angles [°]
[a] Isolated yields were determined by silica gel column chromatog-
C(1)–Co(1)–X(1)
C(1)–Co(1)–X(2)
C(1)–Co(1)–N(3)
N(3)–Co(1)–X(1)
N(3)–Co(1)–X(2)
118.7(1)
113.0(1)
115.4(1)
101.36(9)
104.44(9)
108.08(9)
115.42(9)
115.22(13)
102.79(9)
102.67(9)
106.69(8)
114.10(8)
116.76(10)
100.05(7)
103.17(7)
raphy.
On the other hand, the coupling reaction of aryl halides
gave sufficient results, as indicated in the literature. The
reaction of 4-bromobiphenyl with phenylmagnesium chlor-
ide mediated by 1.5 mol-% of 1a (3.0 mol-% per Co) in
THF at room temperature for 19 h afforded p-terphenyl in
[8c]
9
2
0% yield after silica gel column chromatography (Entry
). 4-Bromoanisole gave 4-methoxybiphenyl in 84% yield
Catalytic Reactions Using IPr-Cobalt(II) Complexes
Catalytic reactions of aryl or alkyl halides with phenyl- (Entry 3), whereas 4-chloroanisole and 4-fluoroanisole gave
magnesium chloride in the presence of the cobalt complexes the cross-coupling product in moderate to low yields, 32
1a–c and 2a were conducted to form the cross-coupling and 4%, respectively, at room temperature after 21 h (En-
products in good to excellent yields as shown in Table 4. It tries 4 and 5). The results were comparable to previous re-
is notable that 1a has poor activity in the coupling reaction ports of cobalt(II)-catalyzed Kumada coupling reactions of
[
8c]
of n-octyl bromide, forming n-octylbenzene in low yield aryl halides. It is noteworthy that terphenyl was produced
16%) (Entry 1), although cobalt catalysts are known to be in a similar yield using the pyridine-coordinated complex
active for the cross-coupling reactions of alkyl halides with 2a as with 1a, showing that the existence of pyridine did
(
[
4]
Grignard reagents. The starting compound was recovered not disturb the reaction (Entry 6). Interestingly, the yields
dominantly from the other products. In contrast, a prelimi- of the product obviously depended on the halogen atoms
nary reaction of 1-bromooctane with phenylmagnesium coordinated in the complexes 2a, 2b, and 2c, with yields
chloride using a cobalt(II) iodide complex bearing 1,3- decreasing with the decreasing size of the halogen to 86, 81,
bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) gave 1- and 64%, respectively (Entries 6, 7, and 8). Although we
and 2-octenes dominantly for several minutes at room tem- could not define the origin of the behavior, we discussed
perature. These products can be formed by β elimination of some possibilities related to the halogen atoms bound to
octylcobalt species and cobalt-catalyzed isomerization of 1- cobalt, for example, (1) transmetallation with the Grignard
[
16]
0
alkene.
We supposed that the reductive elimination pro- reagent in the initial reaction to form a Co species, (2) a
I
III
cess of the alkyl aryl cobalt species might be very slow. In disproportionation process to form Co and Co species
the case of the cobalt complex bearing the IMes ligand, from the dimeric Co complexes with the movement of the
II
β elimination of the octylcobalt species overwhelmed the halogen atom. Since we cannot observe any decomposition
competing reductive elimination of the octyl(phenyl)cobalt products and color changes after leaving the solutions of
species forming n-octylbenzene, in contrast to the previous these complexes for several days, the latter hypothesis might
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K. Matsubara et al.
be unfavorable. However, because these halogen atoms (MBraun UniLab) unless otherwise noted. THF, toluene, hexane,
FULL PAPER
6
and [D ]benzene were distilled from benzophenone ketyl and stored
could be easily removed in the transmetallation process, we
considered that the initial activation process of the com-
plexes is important in forming the active cobalt species.
under a nitrogen atmosphere. Organic reagents used for coupling
reactions were distilled just before use. Other reagents were used as
received. N-Heterocyclic carbene (IPr) was prepared according to a
published method.[ Column chromatography of organic products
17]
was carried out using silica gel [Kanto Kagaku, silica gel 60N
Conclusions
1
(
spherical, neutral)]. The H NMR spectra were obtained with a
VARIAN Mercury Y plus 400 MHz spectrometer at room tem-
We have successfully prepared and structurally charac-
terized divalent cobalt complexes bearing a bulky NHC li-
gand IPr. In the absence of other smaller 2e-donor ligands,
these compounds took an unstable dimeric form, whereas
more stable monomeric complexes were obtained by the re-
perature. Chemical shifts (δ) were recorded in ppm from the solvent
–
1
signal. IR spectra were recorded in cm with a Perkin–Elmer Spec-
trum One spectrometer equipped with a universal diamond ATR.
The ESR spectra were obtained with a JEOL JES-RE1X ESR
2
spectrometer cooling the samples in liquid N . The g value was
action with pyridine. Such behavior made us believe that calibrated with a standard manganese maker. The spectra were re-
aryl halides may substitute the fourth position in the cobalt vised by deducing the spectrum for the empty tube cooled with the
atom enabling the cross-coupling reactions to proceed same glass bottle. The magnetic properties of the materials were
investigated using a Quantum Design MPMS-5S superconducting
smoothly. As expected, these cobalt complexes have an ac-
quantum interference device (SQUID) magnetometer. The elemen-
tivity toward a Kumada–Tamao–Corriu cross-coupling re-
tal analysis was carried out with a YANACO CHN Corder MT-5
action of aryl halides at room temperature. This is the first
AUTO-SAMPLER, using an aluminum pan, where the samples
example where well-defined divalent cobalt complexes are
were held in a glove box. The XPS measurements of the cobalt
complexes were conducted using a spectrometer (PHI 1800) with
used for the catalytic Grignard cross-coupling reaction of
aryl halides. Further investigations of the cross-coupling re-
α
Mg-K radiation. The X-ray source was operated at 14 kV and
actions of alkyl halides and the mechanistic studies are in
progress.
4
00 W. The instrument contained a hemispherical analyzer. The
samples for XPS analysis were prepared in a glove box and quickly
moved to the chamber of the XPS.
Syntheses of 1a–c
Experimental Section
1a: Anhydrous cobalt(II) iodide (93.6 mg, 0.30 mmol) was dis-
General: All experiments were carried out under an inert gas atmo-
sphere using standard Schlenk techniques and a glove box
solved in THF (5 mL), and IPr (121.0 mg, 0.31 mmol) was added.
The mixture was stirred for 2 h at room temperature. The solvent
Table 5. Crystallographic and measurement data for 1a–c, 2a–c.
1a
1b
1c
2a
2b
2c
Empirical formula
C
27
H
36CoI
701.34
0.10ϫ0.04ϫ0.03 0.40ϫ0.30ϫ0.20 0.30ϫ0.30ϫ0.30 0.12ϫ0.10ϫ0.10 0.25ϫ0.10ϫ0.10 0.20ϫ0.20ϫ0.20
2
N
2
C
607.34
27
H
36Br
2
CoN
2
C
518.44
27
H
36Cl
2
CoN
2
C
74.5
H
91.5Co
2
I
4
N
3
C
778.58
39
H
49Br
2
CoN
3
39 2 3
C H49Cl CoN
689.68
–1
M
r
[gmol ]
1696.50
Crystal size [mm]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
monoclinic
P2 /n
11.335(4)
18.139(6)
14.328(5)
monoclinic
P2 /n
12.4470(12)
14.2148(10)
16.613(2)
monoclinic
P2 /n
12.4859(3)
14.0711(3)
16.4752(4)
triclinic
P1
orthorhombic
P2
13.247(3)
15.981(3)
18.095(4)
monoclinic
C2/c
28.279(6)
13.829(3)
19.798(4)
¯
1
1
1
1 1 1
2 2
11.6186(17)
16.355(2)
20.458(3)
81.507(5)
82.493(5)
79.096(5)
3754.3(9)
2
α [°]
β [°]
98.189(2)
93.545(6)
94.9210(8)
103.711(4)
γ [°]
V [Å ]
3
2915.9(18)
4
2933.8(5)
4
2883.9(1)
4
3830.8(14)
4
7522(3)
8
Z
–3
ρcalcd. [gcm ]
1.597
123(1)
0.71070
2.723
1380
ω
1.375
201(1)
0.71070
3.333
1236
1.194
201(1)
0.71070
0.7959
1092
1.501
293(1)
0.71070
2.129
1693
1.350
123(1)
0.71070
2.570
1604
1.218
123(1)
0.71070
0.6279
2920
T [K]
λ (Mo-K
α
) [Å]
–
1
μcalcd. [mm ]
F(000)
Scan type
ω
ω
ω
ω
ω
2
θ
max [°]
55.0
6550
55.0
6632
55.0
6604
55.0
17104
55.0
8617
55.0
8411
Indep. reflections
(
R
int = 0.127)
(Rint = 0.0295)
5666
289
(Rint = 0.0323)
5639
(Rint = 0.0366)
15122
(Rint = 0.0480)
7745
407
(Rint = 0.1003)
7699
407
Used refl. [IϾ2σ(I)]
Variables
5988
291
289
785
2
Refinement method
full-matrix least-squares on F
GOF on F2
[
a]
1.202
1.071
1.045
1.093
1.048
1.055
[b]
R
R
1
1
/wR
/wR
ρ max [eÅ ]
2
[IϾ2σ(I)]
0.0816/0.2079
0.0888/0.2138
1.45
0.0304/0.0737
0.0385/0.0790
0.438
0.0303/0.0767
0.0370/0.0800
0.342
0.0450/0.0961
0.0535/0.1008
1.903
0.0422/0.0870
0.0495/0.0911
0.616
0.0791/0.2167
0.0838/0.2241
1.439
[c]
2
(all)
–3
a] GOF = [Σw(F 2
– F
2)2/(N – P)]1/2. [b] R(F) = Σ||F
| – |F
||/Σ|F
|. [c] wR(F
) = {Σ[w(F
2
– F
2)2]/Σ[w(F
) ]}1/2.
2 2
[
o
c
o
c
o
2
o
c
o
6
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Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: I20095
/KAP1
Date: 02-05-12 17:31:05
Pages: 9
Kumada–Tamao–Corriu Cross-Coupling Reactions of Aryl Halides
was removed under reduced pressure. The residual solid was dis-
solved in a small amount of toluene, filtered through Celite, and
added to a tube where n-hexane was slowly added to the solution.
Dark-green crystals were obtained (101 mg, 48%, based on half
of the molecular weight of 1a) from the solution at –30 °C. The
compounds were extremely air-sensitive and paramagnetic, only
showing broadened spectra in H NMR under an inert gas atmo-
sphere. So, we identified the compounds from UV/Vis, SQUID,
XPS, and X-ray crystallography.
parameters. All H atoms were located at ideal positions and were
included in the refinement, but were restricted to ride on the atom
to which they were bonded. The crystallographic and measurement
data for these compounds are listed in Table 5.
CCDC-863952 (for 1a), -863953 (for 1b), -863954 (for 1c), -863955
(for 2a), -863956 (for 2b), and -863957 (for 2c) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
1
1b: Blue crystals (56.5 mg, 46%, based on half of the molecular
Supporting Information (see footnote on the first page of this arti-
cle): ESR spectra for 2a–c and preliminary X-ray results for [Co(-
weight of 1b) were obtained from CoBr
2
(44.0 mg, 0.20 mmol) and
IPr (82.0 mg, 0.21 mmol).
–
+
3
IPr)X ] [HIPr] (X = Cl and Br).
1c: Blue crystals (39.3 mg, 38%, based on half of the molecular
weight of 1c) were obtained from CoCl
2
(25.1 mg, 0.20 mmol) and
IPr (82.0 mg, 0.21 mmol).
Acknowledgments
Syntheses of 2a–c
The authors are grateful to Dr. Shinya Kanekawa and Dr. Yusuke
Sunada (Institute for Materials Chemistry and Engineering, Kyu-
shu University) for kindly measuring the magnetic susceptibility
and to Dr. Kurisaki (Fukuoka University) for performing the XPS
measurements. This study was financially supported by the Japan
Society for the Promotion of Science (Grant-In-Aid for Scientific
Research, grant number 22550104).
2
a: Anhydrous cobalt(II) iodide (92.8 mg, 0.30 mmol) was dis-
solved in THF (1 mL). IPr (122 mg, 0.31 mmol) and pyridine
25.0 μL, 0.31 mmol) were then added. After another addition of
mL of THF, the solution was stirred for 2 h. The solvent was
(
1
removed under reduced pressure. The residual solid was dissolved
in a small amount of toluene, filtered through Celite, and added to
a tube where n-hexane was slowly added to the solution. Dark-
green crystals of 2a were obtained during cooling the tube to
–
30 °C (140 mg, 59%). The obtained compounds were identified
with UV/Vis, SQUID, EPR, and X-ray crystallography.
47CoI (including 0.75 molecules of toluene, C5.25 ):
calcd. C 52.66, H 5.58, N 4.95; found C 52.86, H 5.83, N 5.39.
[1] a) S. Chakraborty, H. Guan, Dalton Trans. 2010, 39, 7427–
7436; b) A. A. Kulkarni, O. Daugulis, Synthesis 2009, 24,
4
087–4109; c) G. Bauer, K. Kirchner, Angew. Chem. 2011, 123,
918; Angew. Chem. Int. Ed. 2011, 50, 5798–5800.
2] a) G. Cahiez, A. Moyeux, Chem. Rev. 2010, 110, 1435–1462;
b) C. Gosmini, J.-M. Bégouin, A. Moncomble, Chem. Com-
mun. 2008, 3221–3233.
C
37.25
H
2
N
3
H
6
5
[
2
(
(
b: Blue crystals (49.3 mg, 38%) were obtained from CoBr
44.0 mg, 0.20 mmol), IPr (82.0 mg, 0.21 mmol), and pyridine
17.0 μL, 0.21 mmol). C39 CoN (including toluene, C ):
2
[
[
3] Z. Xi, B. Liu, C. Lu, W. Chen, Dalton Trans. 2009, 7008–7014.
4] For recent examples of cross-coupling reactions using cobalt-
catalyst precursors, see: a) W. Zhou, J. W. Napoline, C. M.
Thomas, Eur. J. Inorg. Chem. 2011, 2029–2033; b) G. Cahiez,
C. Chaboche, C. Duplais, A. Moyeux, Org. Lett. 2009, 11, 277–
280; c) A. Moncomble, P. Le Floch, C. Gosmini, Chem. Eur. J.
H49Br
2
3
7 8
H
calcd. C 60.16, H 6.34, N 5.40; found C 59.08, H 6.55, N 6.04.
c: Blue crystals (34.9 mg, 30%) were obtained from CoCl
25.1 mg, 0.20 mmol), IPr (82.0 mg, 0.21 mmol), and pyridine
17.0 μL, 0.21 mmol). C39 CoN (including toluene, C ):
2
(
(
2
H49Cl
2
3
7 8
H
2009, 15, 4770–4774; d) M. Amatore, C. Gosmini, Angew.
calcd. C 67.92, H 7.16, N 6.09; found C 67.26, H 7.64, N 6.62.
Chem. 2008, 120, 2119; Angew. Chem. Int. Ed. 2008, 47, 2089–
2092; e) H. Hamaguchi, M. Uemura, H. Yasui, H. Yorimitsu,
K. Oshima, Chem. Lett. 2008, 37, 1178–1179; f) G. Cahiez, C.
Chaboche, C. Duplais, A. Giulliani, A. Moyeux, Adv. Synth.
Catal. 2008, 350, 1484–1488; g) E. Shirakawa, T. Sato, Y. Im-
azaki, T. Kimura, T. Hayashi, Chem. Commun. 2007, 4513–
Kumada–Tamao–Corriu Cross-Coupling Reaction of Aryl Halide in
the Presence of the Cobalt Complex: In a typical example, 4-bromo-
biphenyl (233 mg, 1 mmol) and 1a (21.4 mg, 1.5 mol-%) were dis-
solved in THF (2 mL). After stirring for 5 min, a phenylmagnesium
chloride/THF solution (0.75 mL, 1.5 mmol) was added to the solu-
tion. After the appropriate reaction time, water (10 mL) was added.
The organic layer was extracted with dichloromethane and the sol-
vent was removed under reduced pressure. The residual product
was purified with silica gel column chromatography eluting with
hexane to give terphenyl (white solid; 207 mg, 90%).
4515.
[
[
5] For recent reviews of NHC complexes for catalysis, see: a) S.
Díez-González, N. Marion, S. P. Nolan, Chem. Rev. 2009, 109,
3
612–3676; b) H. Clavier, S. P. Nolan, Chem. Commun. 2010,
46, 841–861; c) R. Corberán, E. Mas-Marzá, E. Peris, Eur. J.
Inorg. Chem. 2009, 1700–1716; d) O. Schuster, L. Yang, H. G.
Raubenheimer, M. Albrecht, Chem. Rev. 2009, 109, 3445–3478;
e) F. E. Hahn, M. C. Jahnke, Angew. Chem. 2008, 120, 3166;
Angew. Chem. Int. Ed. 2008, 47, 3122–3172.
Single Crystal X-ray Diffraction Studies of 1a–c, 2a–c: Single crys-
tals of 1a–c and 2a–c for X-ray diffraction studies were grown at
–
1
30 °C from toluene/hexane solutions. The data for 1a and 2b–c at
23 K and 2a at 293 K were collected with a Rigaku Saturn CCD
6] a) C. L. Vélez, P. R. L. Markwick, R. L. Holland, A. G. DiPas-
quale, A. L. Rheingold, J. M. O’Connor, Organometallics 2010,
29, 6695–6702; b) E. Fooladi, B. Dalhus, M. Tilset, Dalton
Trans. 2004, 3909–3917; c) A. A. Danopoulos, J. A. Wright,
W. B. Motherwell, S. Ellwood, Organometallics 2004, 23, 4807–
diffractometer with confocal mirror, whereas that for 1b and 1c
were collected at 201 K with a Rigaku Mercury70 CCD dif-
fractometer and Rigaku R-AXIS RAPID imaging plate dif-
4
810; d) H. Van Rensburg, R. P. Tooze, D. F. Foster, A. M. Z.
fractometer, respectively, using graphite-monochromated Mo-K
α
Slawin, Inorg. Chem. 2004, 43, 2468–2470; e) X. Hu, K. Meyer,
J. Am. Chem. Soc. 2004, 126, 16322–16323; f) X. Hu, I. Castro-
Rodriguez, K. Meyer, J. Am. Chem. Soc. 2004, 126, 13464–
radiation (λ = 0.71070 Å). Data reductions of the measured reflec-
tions were carried out using the software package CrystalStructure.
The structures were solved by direct methods (see the Supporting
Information) and refined by a full-matrix least-squares fitting
1
3473; g) D. S. McGuinness, V. C. Gibson, J. W. Steed, Organo-
metallics 2004, 23, 6288–6292.
2
[18]
based on F using the program SHELXL97-2 PC version.
All
[7] Z. Mo, Y. Li, H. K. Lee, L. Deng, Organometallics 2011, 30,
non-hydrogen atoms were refined with anisotropic displacement
4687–4694.
Eur. J. Inorg. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
7

Job/Unit: I20095
/KAP1
Date: 02-05-12 17:31:05
Pages: 9
K. Matsubara et al.
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Received: January 31, 2012
Published Online: ᭿
8
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Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: I20095
/KAP1
Date: 02-05-12 17:31:05
Pages: 9
Kumada–Tamao–Corriu Cross-Coupling Reactions of Aryl Halides
Cobalt Catalysts
K. Matsubara,* T. Sueyasu, M. Esaki,
A. Kumamoto, S. Nagao, H. Yamamoto,
Y. Koga, S. Kawata,
T. Matsumoto ................................... 1–9
Cobalt(II) Complexes Bearing a Bulky N-
Heterocyclic Carbene for Catalysis of
Kumada–Tamao–Corriu Cross-Coupling
Reactions of Aryl Halides
A series of cobalt(II) dimeric tetrahedral
30e) complexes were obtained in good
yields and were transformed into the
monomeric forms with pyridine. These
complexes were characterized by SQUID,
XPS, UV/Vis spectroscopy, elemental
analysis, and X-ray crystallography, and
were found to have high catalytic activity
for Kumada–Tamao–Corriu cross-coupling
reactions of aryl halides.
(
Keywords: N-Heterocyclic carbene (NHC)
ligands / Cobalt complexes / Antiferromag-
netic interactions / Grignard cross-coupling
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9