Preparation of mononuclear, homodinuclear, and heterotrinuclear complexes by salicylaldiminato-functionalized imidazolium salt: Approach to multifunctional catalysts

Article abstract of DOI:10.1002/chem.201101557

A salicylaldiminato imidazolium salt that bears both a Schiff base and imidazolium salt moiety was used to synthesize heterometallic compounds that could serve as multifunctional catalysts in certain reactions. The successful preparation of seven mononuclear compounds with a variety of transition metals (Pd, Ir, Ru, Zn, Ni) illustrated the high versatility of this class of ligands, which is crucial for the design of catalysts. Synthesis of homodinuclear compounds and heterotrinuclear compounds provided practical methods to connect multiple metal fragments through these ligands. The heterotrinuclear complex (Ni/Ir) was employed as a catalyst in the reaction of dehalogenation/transfer hydrogenation of halo-acetophenones. The preliminary catalytic study showed that this heterometallic species is more active than a combination of the corresponding monometallic species.

Full text of DOI:10.1002/chem.201101557

FULL PAPER
DOI: 10.1002/chem.201101557
Preparation of Mononuclear, Homodinuclear, and Heterotrinuclear
Complexes by Salicylaldiminato-Functionalized Imidazolium Salt: Approach
to Multifunctional Catalysts
Rui Zhong, Ya-Nong Wang, Xu-Qing Guo, Zhen-Xia Chen, and Xiu-Feng Hou*[a]
Dedicated to Professor Zu-En Huang on the occasion of his 80th birthday
Abstract: A salicylaldiminato imidazo-
lium salt that bears both a Schiff base
and imidazolium salt moiety was used
to synthesize heterometallic com-
pounds that could serve as multifunc-
tional catalysts in certain reactions. The
successful preparation of seven mono-
nuclear compounds with a variety of
transition metals (Pd, Ir, Ru, Zn, Ni) il-
lustrated the high versatility of this
class of ligands, which is crucial for the
design of catalysts. Synthesis of homo-
dinuclear compounds and heterotrinu-
clear compounds provided practical
methods to connect multiple metal
fragments through these ligands. The
heterotrinuclear complex (Ni/Ir) was
employed as a catalyst in the reaction
of dehalogenation/transfer hydrogena-
tion of halo-acetophenones. The pre-
liminary catalytic study showed that
this heterometallic species is more
active than a combination of the corre-
sponding monometallic species.
Keywords: heterometallic
com-
plexes · nitrogen heterocyclic car-
benes · Schiff bases · tandem reac-
tions · transition metals
Introduction
ometallic complexes with biscarbene ligands have been de-
veloped,[5] and the triazolium biscarbene heterometallic
complexes have been successfully applied as multifunctional
catalysts in catalyzing certain tandem processes.[6] However,
homometallic and heterometallic complexes based on the
same coordination manner, such as NHC–metal coordina-
tion, could face limitations in catalyzing multiple reactions
that are fundamentally different in nature. Therefore, it is
necessary to develop new ligands with different coordination
manners to obtain more versatile catalysts for a wider range
of reactions.
With these in mind, we envisioned that ligands (1,
Scheme 1) that contained both a Schiff base and imidazoli-
um salt moiety (precursor for in situ generating NHC) could
be suitable candidates for the synthesis of multifunctional
catalysts. Thus, we decided to develop a practical methodol-
ogy to obtain heterometal complexes. Herein we describe
the synthesis of ligands 1a–c and their coordination with
transition metals to afford monometal, homodimetal and
heterotrimetal complexes of Ir, Ru, Pd, Ni, and Zn. We also
report the preliminary results of the catalytic activity of het-
erotrimetal complex 7b (Ni/Ir) in a tandem reaction.
The classical approach for catalyst design is to develop
highly selective catalysts for a single step in a specific reac-
tion. However, increasing demands for environmentally
benign and economical synthetic processes have necessitated
the development of one-pot multiple catalytic transforma-
tions to obtain desired products in the most efficient ways.[1]
Among the new approaches for organic transformations, de-
velopments of a single catalyst to mediate two or more reac-
tions in a single synthetic operation provide one solution to
achieve high catalytic efficiency and low environmental
impact.[2] The advantages of such catalysts are evident, as
the use of single multifunctional catalysts will save large
amounts of time, solvents, reagents, and reaction workups
during the preparations of both catalysts and the catalytic
processes.[3]
To prepare a catalyst for a multistep process, highly versa-
tile and stabile ligands are essential. N-Heterocyclic car-
benes (NHCs), ubiquitous ligands for homogeneous cata-
lysts, can bind to a wide range of metals with different oxi-
dation states, thereby affording transition-metal compounds
that are generally resistant to decomposition.[4] In the past
few years, a number of NHC-based homometallic and heter-
[a] R. Zhong, Y.-N. Wang, X.-Q. Guo, Dr. Z.-X. Chen, Dr. X.-F. Hou
Department of Chemistry, Fudan University
Shanghai 200433 (P.R. China)
Fax : (+86)21-6564-1740
E-mail: xfhou@fudan.edu.cn
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201101557.
Scheme 1. Salicylaldiminato imidazolium salt 1.
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Results and Discussion
Synthesis and characterization of ligands: Ligands (1a–c)
with both a Schiff base and imidazolium salt moiety were
prepared by using two different amines (mesitylamine and
2,6-diisopropylaniline) and two substituted imidazoles [1-
methylimidazole
and
2-(1-imidazolyl)pyrimidine]
(Scheme 2).[7] Compound 1a’, an anion-exchange product,
was obtained by using NH4PF6 as the anion-exchange re-
agent. All the ligands were characterized by NMR spectros-
copy, elemental analysis, and in the case of the ligand 1a’,
by X-ray diffraction studies.
The molecular structure of ligand 1a’ (Figure 1) shows
that the plane created by the phenolic aryl ring is roughly
perpendicular to the both imidazole and diisopropylphenyl
rings, as indicated by the dihedral angles (97.4 and 99.18, re-
spectively). This structure also suggests that the N,O-chelat-
ing moiety and the imidazole moiety could not coordinate
to the same metal ion due to the rigidity of the phenyl ring.
pentamethylcyclopentadiene), we also isolated
a minor
À
product 2a’, which could arise from intramolecular C H ac-
tivation. All four compounds were characterized by NMR
spectroscopy, elemental analysis, and in the case of the com-
plex 2a, by X-ray diffraction studies.
The 1H NMR spectra of 2a–c
showed the absence of the down-
field-shifted NCHN resonance,
thus indicating the deprotonation
of the acidic proton of 1a–c. The
13C{1H} NMR spectra provide
more direct evidence of the met-
alation, as seen by the signal at
d=156.20 and 156.68 ppm, as-
À
signed to the Ir Ccarbene of 2a and
2a’; d=173.84 ppm, assigned to
À
the Ru Ccarbene of 2b; and d=
À
156.78 ppm, assigned to the Pd
Scheme 2. Synthesis of ligands 1a–c.
Ccarbene of 2c. Furthermore, the
protons of the CH2 of benzyl
group of these two Ir complexes
2a and 2a’ are diastereotopic
and display signals at d=6.35
and 4.77 ppm (J=14.0 Hz) for 2a
and at d=4.85 and 4.67 ppm (J=
13.6 Hz) for 2a’, which are con-
sistent with the research of Peris
et al.[8a] Crystals of compound 2a
suitable for X-ray diffraction
were obtained by slow diffusion
of hexane into a concentrated so-
lution of 2a in CH2Cl2. The X-
Figure 1. X-ray structure of compound 1a’. Ellipsoids at the 30% probability level. Hydrogen atoms and sol-
ray structure of 2a can be re-
garded as a three-legged piano-
stool (Figure 2). Together with
the NHC moiety, two chloro
atoms and a Cp* ring complete
À
vent molecules have been omitted for clarity. Selected bond lengths [ꢁ] and angles [8]: N(1) C(12) 1.270(3),
À
À
À
À
N(3) C(2) 1.307(3), N(2) C(2) 1.316(3), N(3) C(2) 1.307(3), O(1) C(9) 1.336(3); N(2)-C(5)-C(6) 112.65(19),
C(12)-N(1)-C(13) 117.74(18), N(1)-C(12)-C(10) 122.8(2).
Synthesis and characterization of monometal NHC com-
plexes: To explore the coordination properties of these li-
gands, monometal NHC complexes (2a–c) were prepared by
in situ transmetalation from the silver carbene complexes of
ligands 1a–c with different transition-metal complexes.[8] In
the reaction between ligand 1a and [{Cp*IrCl2}2] (Cp*=
the coordination sphere about the Ir center. The plane of
imidazole ring and the plane of phenol ring is perpendicular
À
with a dihedral angle of 93.88. The distances of Ir Ccarbene
À
À
(2.033 ꢁ), Ir Cl (2.414 and 2.426 ꢁ), and Ir Cp*
N
(1.790 ꢁ) are in the range of other analogous [Cp*Ir
ACHTUNGTRENNUNG(NHC)]
complexes.[8a,9]
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Imidazolium Salts
FULL PAPER
imidazolium salt moiety and
Pd
ACHTUNGTRENNUNG
Co
AHCTUNGTRENNUNG
to reflux in the presence of
NaOMe yielded unexpected
complex 4 (Scheme 3), which
had
a
pentacoordinated Co
center with the axial coordina-
tion site occupied by a free 1-
methylimidazole ligand, pro-
duced by the displacement of
the imidazole moiety in ligand
1a with MeOÀ. Reaction of 1a
with [{Cp*IrCl2}2] in THF in the
presence of KOtBu yielded
Figure 2. X-ray structure of compound 2a. Ellipsoids at the 30% probability level. Hydrogen atoms and sol-
À
vent molecules have been omitted for clarity. Selected bond lengths [ꢁ] and angles [8]: Ir(1) C(11) 2.032(7),
À
À
À
Ir(1) Cl(1) 2.426(2), Ir(1) Cl(2) 2.414(2), Ir(1) Cp*
R
Cl(2) 92.1(2), N(2)-C(15)-C(16) 112.2(6), C(22)-N(3)-C(23) 121.3(7), N(3)-C(22)-C(20) 122.2(7).
complex
5
(Scheme 3). The
structures of 4 and 5 were con-
Synthesis and characterization of monometal Schiff base
complexes: By the treatment of ligands 1a, 1a’, or 1c with
metal acetates, we isolated a series of monometal Schiff
base complexes (3a–c).[10] All of these complexes 3a–c were
firmed by elemental analysis and X-ray diffraction studies
(Figure 4) and in the case of 5 by NMR spectroscopy. The
formation of 4 and 5 revealed that ligand 1a with counteran-
ion ClÀ was not suitable for strong alkaline reaction condi-
À
tions because the C N bond
between the imidazole group
and the benzyl group was sus-
ceptible to nucleophilic attack.
Synthesis and characterization
of homodimetal complexes: To
further explore the reactivity of
these ligands towards metal
ions, we synthesized a series of
homodimetallic complexes by
reactions of ligand 1a’ with
[{Cp*IrCl2}2] or [{IrClACHTUNGTRENNUNG(cod)}2]
(cod=cyclooctadiene) in the
presence of base. Two air-stable
dinuclear complexes 6a and 6b
were synthesized, as shown in
Scheme 4.
1
The H NMR spectrum of 6a
shows the disappearance of the
resonances of the NCHN pro-
À
characterized by NMR spectroscopy, elemental analysis, and
tons and Ph OH protons, thus suggesting that double coor-
dination has occurred. The 13C NMR spectrum also confirms
this with two signals at d=180.62 and 165.97 ppm (IrI-O-C
in the case of complex 3b, by X-ray diffraction studies.
1
The H NMR spectra of compounds 3a–c show the reso-
I
À
C
nances of the NCHN protons and the disappearance of the
OH protons, thereby indicating that the coordination has oc-
curred in the Schiff base moiety. The X-ray structure of 3b
(Figure 3) shows an ideal square-planar geometry around
the Pd center, which is similar to other analogous Schiff
base Pd complexes.[10d,11] The plane of the phenolic aryl ring
is roughly perpendicular to the planes of both imidazole and
diisopropylphenyl rings (dihedral angle of 98.2 and 93.98, re-
spectively).
and Ir
carbene, respectively), similar to related iridium(I)
complexes.[12] Crystals of 6a suitable for X-ray diffraction
were obtained from slow evaporation of dichloromethane/
hexane (1:6) solution. Figure 5 shows the X-ray structure of
6a and the most representative distances and angles. The
structure reveals the expected square-planar arrangement of
the ligands at both IrI centers. The NHC plane lies close to
perpendicular to the Ircarbene coordination plane with a dihe-
dral angle of 80.08. The six-membered chelating ring Ir(1)-
O(1)-C(27)-C(22)-C(21)-N(3) is located in the same plane.
Unlike the reaction of ligand 1a’ with Pd
failed to obtain Schiff base Pd complex by the reaction of
ligand 1a and Pd(OAc)2 due to the possible reaction of the
ACHTUNGRTEN(NUNG OAc)2, we
À
À
À
The distances of Ir O, Ir N, and Ir Ccarbene are 2.009, 2.056,
and 2.019 ꢁ.
ACHTUNGTRENNUNG
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11043

X.-F. Hou et al.
1
The H NMR spectrum of 6b shows the two singlets from
which can be rationalized on the basis of steric repulsions
between the Cp* ring and the isopropyl group. This steric
hindrance may also lead to the loss of ClÀ from the iridium
two Cp* ligands (d=1.46 and 1.74 ppm). The orthometala-
tion could be observed by the benzyl methylene ( CH2
À
À
)
resonance at d=4.82 and 4.69 ppm (J=14.4 Hz). The
13C{1H} NMR spectrum confirms the double metalation,
with two signals at d=172.19 and 155.17 ppm (IrIII-O-C and
À
atom, but to form a more stable cationic compound with a
À
À
weak coordinating anion, such as PF6 . The Ir Ccarbene and
À
Ir Cphenyl distances are 2.02 and 2.06 ꢁ, respectively, similar
IrIII
C
carbene, respectively). The 31P NMR spectrum of 6b also
to other related [Cp*Ir
(NHC)] complexes. The Ircarbene Cl
(centroid) (1.828 ꢁ) distances lie
in the expected range for other known [Cp*Ir
À
À
exhibits a septet signal of d=À136.76 to À150.83 ppm. The
(2.41 ꢁ) and Ircarbene Cp*
A
X-ray structure of 6b (Figure 6) reveals that 6b is a cationic
ACHTUNGTRENUN(NG NHC)] com-
À
compound with a PF6 as anion. It also shows that one
plexes.[8a,9]
Cp*IrIII is coordinated by the NHC ligand through the car-
bene and phenyl fragment; the other Cp*IrIII is coordinated
by the O and N atoms of the salicylaldiminato fragment.
The structure also indicates that the orthometalation of the
phenyl ring of the imidazolylidene ligand has occurred, thus
leading to a chelate coordination of the ligand with a bite
The successful preparation of 6a and 6b reveals that
ligand 1a’ is more stable than ligand 1a in strong alkaline
conditions.
Synthesis and characterization of heterotrimetal complexes:
On the basis of the synthesis of monometal complexes, we
carried out the synthesis of heterometallic complexes. As
shown in Scheme 5, complexes 7a and 7b can be obtained
by transmetalation of 3a from
À
angle of 84.58. The Ir O distance of 1.966 ꢁ is shorter than
in previous reports by the groups of Suzuki[13] and Meng,[14]
the silver carbene derivative to
[{Ru
G
and
[{Cp*IrCl2}2] in good yield (57
and 54%).
Complexes 7a and 7b were
characterized by NMR spec-
troscopy, elemental analysis,
and in the case of 7a, by X-ray
diffraction
studies.
The
1H NMR spectra of 7a and 7b
show the disappearance of the
resonances of the NCHN pro-
tons as the first indication that
metalation takes place. The
À
only one resonance due to N
CH3 of 7a and 7b, respectively,
reveals that the transmetalation
has occurred in two imidazoli-
um salt moieties of 3a to form
symmetrical structures of 7a
and 7b. The 13C{1H} NMR spec-
tra provide more direct evi-
dence of the metalation, as
seen by the signal at d=173.62
Figure 3. X-ray structure of compound 3b. Ellipsoids at the 30% probability level. Hydrogen atoms and part
À
of the isopropyl group have been omitted for clarity. Selected bond lengths [ꢁ] and angles [8]: Pd(1) O(1)
À
À
À
À
1.968(3), Pd(1) N(1) 2.017(3), N(1) C(12) 1.280(5), N(1) C(13) 1.461(4), O(1) C(9) 1.304(5); N(2)-C(5)-C(6)
110.4(3), C(12)-N(1)-C(13) 118.3(3), N(1)-C(12)-C(8) 127.2(3), O(1)-Pd(1)-N(1) 91.54(11) C(9)-O(1)-Pd(1)
127.3(2), C(12)-N(1)-Pd(1) 124.2(2).
À
À
and 155.95 ppm, assigned to the Ru Ccarbene of 7a and Ir
Ccarbene of 7b. The X-ray structure of 7a shows an ideal
square-planar geometry of the Ni center (Figure 7), with
À
both ligands including NHC Ru moiety trans to each other,
À
thereby suggesting that the two NHC Ru fragments are
symmetry related. This means the two imidazole rings are
essentially coplanar, with an anti configuration of the two
À
NHC Ru fragments along the Ru-Ni-Ru axis. The imida-
zole ring plane and the Ni coordination plane are roughly
À
perpendicular with a dihedral angle of 98.78. The Ru Ccarbene
À
distance is 2.125 ꢁ, similar to the distance in other cymene
Ru NHC complexes.[5e,15] The Ni O (1.810 ꢁ), and the Ni
N (1.930 ꢁ) distances are in the range of other analogous
Schiff base Ni complexes.[16]
À
À
Scheme 3. The generation of complexes 4 and 5 from ligand 1a.
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Imidazolium Salts
FULL PAPER
Figure 4. X-ray structure of compound 4 (left) and 5 (right). Ellipsoids at the 30% probability level. Hydrogen atoms and part of the isopropyl group
have been omitted for clarity.
Attempts to obtain other heterometallic complexes by
treating the monometal NHC complexes 2a or 2c with tran-
sition-metal acetates such as PdACHTNUTRGENN(UG OAc)2 and ZnACHTUGNTNER(NUGN OAc)2 failed
to afford heterotrimetal complexes, presumably due to the
high reactivity of the monometal NHC complexes.
Catalytic studies: With heterometallic complexes 7a and 7b
in hand, we decided to test their catalytic activity in reac-
tions that contained multiple organic transformations, which
require catalytic activities of different transition-metal cen-
ters. First we decided to study the dehalogenation/transfer
hydrogenation of halo-acetophenones in one pot catalyzed
by compound 7b, because the Ni center could catalyze the
dehalogenation process[17] and
Scheme 4. Synthesis of homodimetal complexes 6a,b.
the Ir center could catalyze
transfer-hydrogenation
reac-
tions.[18] The halo-acetophe-
nones were convenient starting
substrates, which have been
used in Pd/Ir catalytic systems
by Peris and co-workers.[6c] The
monometallic compounds 8[16a]
and 9[8a] were also used in this
catalytic process for compari-
son. Our preliminary results are
summarized in Table 1.
4-Iodoacetophenone
was
used to see the effect of a base
on the reaction in iPrOH
(Table 1, entry 1–3). All the
substrate of these three reac-
tions was completely converted
into the transfer-hydrogenation
Figure 5. X-ray structure of compound 6a. Ellipsoids at the 30% probability level. Hydrogen atoms and sol-
À
vent molecules have been omitted for clarity. Selected bond lengths [ꢁ] and angles [8]: Ir(1) O(1) 2.009(10),
À
À
À
À
À
Ir(1) N(3) 2.056(13), Ir(2) C(32) 2.019(18), Ir(2) Cl(1) 2.343(4), N(3) C(21) 1.305(16), O(1) C(27)
1.328(17); O(1)-Ir(1)-N(3) 91.1(4), C(27)-O(1)-Ir(1) 129.0(9), C(21)-N(3)-Ir(1) 124.0(10), C(32)-Ir(2)-Cl(1)
89.8(5), N(1)-C(28)-C(24) 111.4(13).
Chem. Eur. J. 2011, 17, 11041 – 11051
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11045

X.-F. Hou et al.
genation-transfer product B (89%). In view of this, 4-bro-
moacetophenone was used to carry out the comparative
study (entries 6–9). As expected, a higher conversion of
product C could be achieved by using a higher catalyst load-
ing of 7b (5 mol%) in 24 h (entry 6). By contrast, the com-
bination of complex 8 (5 mol%) and 9 (10 mol%) resulted
in an ineffective system (entry 7) with only 16% conversion
of C. Furthermore, complexes 8 and 9 were also used for
this catalytic process, respectively (entries 8 and 9); both re-
actions generated moderate amounts of product C. Given
that Ni/NHC complexes are effective in the transfer-hydro-
genation processes[19] and Cp*Ir/NHC is an effective catalyst
in the dehalogenation of aryl chlorides,[6c] the same reactions
might be catalyzed by the Ni complex 8 and Ir complex 9,
respectively. However, this preliminary result suggests that
the two metal fragments of the heterometallic complex 7b
may have some catalytic coop-
products B and C in various ratios. KOtBu was the best
base for the formation of prodcut C (entry 3). We then
tested the less-reactive substrates 4-bromoacetophenone and
4-chloroacetophenone in the presence of KOtBu for 24 h
(entry 4 and 5). A complete conversion of 4-bromoaceto-
phenone to B (31%) and C (66%) was obtained, whereas
the reaction of 4-chloroacetophenone produced only hydro-
erativity, which may lead to a
better catalytic performance of
7b than a combination of the
corresponding
monometallic
species in this tandem process.
Conclusion
In summary, four salicylaldimi-
nato-containing
imidazolium
salts 1a–c were synthesized effi-
ciently, from which we were
able to obtain ligands with dif-
ferent reactivity, structures, and
coordination modes. The syn-
thesis of mononuclear com-
pounds with a set of transition
metals (Pd, Ir, Ru, Zn, Ni) is
direct evidence of the high ver-
satility of this series of ligands,
which is critical for the design
of catalysts. Furthermore, the
effect of counteranions on the
stability and reactivity of the li-
gands was also observed,[20]
which allows us to choose suita-
ble ligands with certain counter-
anions according to different
reaction conditions. The suc-
cessful preparations of homodi-
nuclear metal complexes 6a,b
and heterotrinuclear metal
complexes 7a,b provided us
with easy access to complexes
that contained multiple metal
fragments, which may open the
possibility for a wide range of
homometallic and heterometal-
lic combinations. Finally, the
Figure 6. X-ray structure of compound 6b. Ellipsoids at the 30% probability level. Hydrogen atoms and sol-
À
vent molecules have been omitted for clarity. Selected bond lengths [ꢁ] and angles [8]: Ir(1) O(1) 1.966(3),
À
À
À
À
À
Ir(1) N(1) 2.036(4), Ir(2) C(27) 2.058(5), Ir(2) C(34) 2.017(5), Ir(2) Cl(1) 2.4084(12), O(1) C(29) 1.328(6),
À
N(1) C(23) 1.328(6); O(1)-Ir(1)-N(1) 89.34(15), C(34)-Ir(2)-C(27) 84.48(18), C(34)-Ir(2)-Cl(1) 90.04(14),
C(27)-Ir(2)-Cl(1) 87.19(13), N(2)-C(30)-C(26) 109.7(4).
Scheme 5. Synthesis of heterodimetal complexes 7a,b.
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Imidazolium Salts
FULL PAPER
Experimental Section
General procedures: All manipulations were carried out under a nitrogen
atmosphere using standard Schlenk techniques unless otherwise stated.
Solvents were distilled under nitrogen from sodium benzophenone
(hexane, diethyl ether, THF, toluene) or calcium hydride (dichlorome-
thane), and methanol was distilled over Mg/I2. The starting materials 2-
(1-imidazolyl)pyrimidine,[21] [{RuCl (p-cymene)}2],[22] [{Pd(cod)Cl}2],[23]
2ACHTNUTRGENNUG HCATUNGTRENNGUN
[{Cp*IrCl2}2],[24] and complexes 8[10] and 9[8a] were synthesized according
to the literature procedures. Other chemical reagents were obtained from
commercial sources and used without further purification. NMR spectra
were recorded using Bruker spectrometers operating at 400 or 500 (1H),
162 (31P), and 100 or 125 MHz (13C), respectively. NMR spectra were re-
corded at room temperature in CDCl3 and [D6]DMSO, unless otherwise
stated. Elemental analysis was performed using an Elementar Vario EL
III analyzer. A gas chromatograph (HP-GC-6890 series)/mass spectrome-
ter (HP-MS-5974) was also used.
Synthesis of 1a–c: The corresponding amines (12.00 mmol) were added
dropwise to a solution of imidazolium salts (10.00 mmol) in methanol
(10 mL) with constant stirring at room temperature. The resulting solu-
tion was stirred at room temperature for 12–48 h. All volatiles were then
removed under high vacuum, and the residue was washed with ether (3ꢂ
5 mL) and dried under vacuum to afford corresponding ligands.
Compound 1a: Yellow solid, yield: 86%; 1H NMR (CDCl3, 500 MHz):
d=13.42 (s, 1H; OH), 10.58 (s, 1H; NCHN), 8.36 (s, 1H; imine H), 7.71
(d, J=2.0 Hz, 1H; Ph), 7.60 (d, J=8.0 Hz, 1H; Ph), 7.51 (s, 1H; CH, imi-
dazole), 7.49 (s, 1H; CH, imidazole), 7.18 (s, 3H; Ph), 7.04 (d, J=8.0 Hz,
Figure 7. X-ray structure of compound 7a. Ellipsoids at the 30% proba-
bility level. Hydrogen atoms, solvent molecules and parts of isopropyl
have been omitted for clarity. Selected bond lengths [ꢁ] and angles [8]:
À
À
À
Ru(1) C(12) 2.125(14), Ru(1) Cl(1) 2.412(4), Ru(1) Cl(2) 2.445(4),
À
À
À
À
Ni(1) O(1) 1.810(9), Ni(1) N(3) 1.930(12), O(1) C(19) 1.263(15), N(3)
C(22) 1.314(16); O(1)-Ni(1)-N(3) 93.3(4), C(12)-Ru(1)-Cl(1) 89.3(3),
C(12)-Ru(1)-Cl(2) 89.0(4), Cl(1)-Ru(1)-Cl(2) 85.65(14); C(22)-N(3)-Ni(1)
125.5(9), C(19)-O(1)-Ni(1) 130.8(9), N(2)-C(15)-C(16) 109.9(10).
À
À
1H; Ph), 5.60 (s, 2H; CH2 Ph), 4.05 (s, 3H; CH3-imidazole), 2.93 (sept,
2H; J=7.0 Hz, iPr CH), 1.16 ppm (d, 12H; J=7.00 Hz, iPr CH3);
13
À
C NMR (CDCl3, 125 MHz): d=166.02 (C=N), 162.04 (C OH), 145.51
(C N), 138.42 (Ph), 137.63(Ph), 133.87(Ph), 133.27 (Ph), 125.64 (Ph),
123.91 (Ph), 123.51 (CH imidazole), 123.19 (Ph), 121.79 (CH imidazole),
Table 1. Dehalogenation/transfer hydrogenation of halo-acetophenones
by 7b[a,b]
.
À
À
À
118.85 (Ph), 118.36 (Ph), 52.47 (CH2 Ph), 36.53 (N CH3), 28.03 (iPr
CH), 23.40 ppm (iPr CH3); elemental analysis calcd (%) for
C24H30N3ClO: C 69.97, H 7.34, N 10.20; found: C 70.09, H 7.41, N 10.17.
Compound 1a’: Yellow solid, yield: 91%; 1H NMR (CDCl3, 500 MHz):
d=13.52 (s, 1H; OH), 8.58 (s, 1H; NCHN), 8.31 (s, 1H; imine H), 7.52
(d, J=2.0 Hz, 1H; Ph), 7.41 (d, J=8.5 Hz, 1H; Ph), 7.21 (s, 2H; CH, imi-
À
À
dazole), 7.17 (s, 3H; Ph), 7.06 (d, J=8.5 Hz, 1H; Ph), 5.24(s, 2H; CH2
Ph), 3.86 (s, 3H; CH3-imidazole), 2.93 (sept, J=7.0 Hz, 2H; iPr CH),
1.15 ppm (d, J=7.00 Hz, 12H; iPr CH3); 13C NMR (CDCl3, 125 MHz):
Entry
Catalyst
X
Base
A
B
C
1
2
7b
7b
7b
7b
7b
7b
8+9
8
I
I
I
Br
Cl
Br
Br
Br
Br
K2CO3
K3PO4
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
0
0
0
0
0
6
9
8
7
>99
70
0
0
29
À
À
d=166.17 (C=N), 162.27 (C OH), 145.47 (C N), 138.56 (Ph), 135.99
(Ph), 133.71 (Ph), 133.43 (Ph), 125.70 (Ph), 123.61 (Ph), 123.25 (CH-imi-
dazole), 122.83 (Ph), 121.71 (CH-imidazole), 119.04 (Ph), 118.54 (Ph),
3
>99
66
0
4c
31
89
0
75
72
51
À
À
52.82 (CH2 Ph), 36.20 (N CH3), 28.07 (iPr CH), 23.43 ppm (iPr CH3);
elemental analysis calcd (%) for C24H30N3F6OP: C 55.28, H 5.80, N 8.06;
found: C 55.33, H 5.81, N 8.17.
5[c]
6[c,d]
7[c,e,f]
8[c,e]
9[c,f]
94
16
19
42
Compound 1b: Yield: 84%; 1H NMR (CDCl3, 500 MHz): d=13.55 (s,
1H; OH), 10.61 (s, 1H; NCHN), 8.39 (s, 1H; imine H), 7.74 (d, J=
2.0 Hz, 1H; Ph), 7.58 (d, J=2.0 Hz, 1H; CH, imidazole), 7.56 (d, J=
2.0 Hz, 1H; CH, imidazole), 7.55 (s, 1H; Ph), 7.48 (s, 1H; Ph), 7.01 (d,
9
[a] Reaction conditions: 4-haloacetophenone (0.25 mmol), base
(0.50 mmol), anisole as internal reference (0.25 mmol), catalyst (1 mol%)
and 2-propanol (3 mL), 808C, nitrogen atmosphere, 12 h. [b] Yields deter-
mined by gas chromatography. [c] Reaction for 24 h. [d] 5 mol% catalyst.
[e] 5 mol% 8. [f] 10 mol% 9.
À
À
J=8.5 Hz, 1H; Ph), 6.89 (s, 2H; Ph), 5.58 (s, 2H; CH2 Ph), 4.04 (s, 3H;
À
À
CH3-imidazole), 2.28 (s., 3H; Ph CH3), 2.13 ppm (s, 6H; Ph CH3);
13
À
C NMR (CDCl3, 125 MHz): d=166.09 (C=N), 162.05 (C OH), 144.94
(C N), 137.56 (Ph), 134.64 (Ph), 133.62 (Ph), 133.27 (Ph), 128.99 (Ph),
127.98 (Ph), 123.80 (CH imidazole), 123.45 (Ph), 121.86 (CH imidazole),
À
À
À
À
119.06 (Ph), 118.18 (Ph), 52.46 (CH2 Ph), 36.49 (N CH3), 20.67 (Ph
preliminary catalytic study of 7b in dehalogenation/transfer
hydrogenation of halo-acetophenones showed us the catalyst
with heterometallic species might improve its catalytic per-
formance due to possible catalytic cooperativity between
different metals, or at least it avoids any possible interfer-
ence between two different catalysts.
Further development of new heterometallic catalysts and
their application in other tandem processes is currently un-
derway in our laboratory.
À
CH3), 18.35 ppm (Ph CH3); elemental analysis calcd (%) for
C21H24N3ClO: C 68.19, H 6.54, N 11.36; found: C 68.36, H 6.62, N 11.57.
Compound 1c: Yield: 76%; 1H NMR (CDCl3, 500 MHz): d=13.48 (s,
1H; OH), 11.33 (s, 1H; NCHN), 8.86 (d, J=5.0 Hz, 2H; pyrimidine)
8.36 (s, 1H; imine H), 7.95–7.92 (m, 2H; Ph and pyrimidine), 7.78 (d, J=
8.5 Hz, 1H; CH, imidazole), 7.51 (t, J=5.0 Hz, 1H; pyrimidine), 7.17 (s,
3H; Ph), 7.05 (d, J=8.5 Hz, 1H; CH, imidazole), 6.14 (s, 2H; CH2 Ph),
2.93 (sept, J=13.6 Hz, 2H; iPr CH), 1.16 ppm (d, J=7.00 Hz, 12H iPr
À
À
13
À
CH3); C NMR (CDCl3, 125 MHz): d=166.21 (C=N), 162.17 (C OH),
159.67 (pyrimidine), 152.26 (pyrimidine), 145.51 (C N), 138.40 (Ph),
À
Chem. Eur. J. 2011, 17, 11041 – 11051
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
11047

X.-F. Hou et al.
À
136.39 (NCN, imidazole), 134.45 (Ph), 134.06 (Ph), 125.62 (Ph), 123.97
(Ph), 123.50 (CH, imidazole), 123.17 (Ph), 122.08 (CH, imidazole), 118.93
imidine), 118.74 (Ph), 118.14 (Ph), 117.26 (CH imidazole), 52.79 (CH2
Ph), 28.07 (iPr CH), 23.44 ppm (iPr CH3); elemental analysis calcd (%)
for C27H29N5Cl2OPd: C 52.57, H 4.74, N 11.35; found: C 52.35, H 4.63, N
11.29.
À
À
(pyrimidine), 118.50 (Ph), 118.31 (Ph), 53.12 (CH2 Ph), 36.20 (N CH3),
28.05 (iPr CH), 23.40 ppm (iPr CH3); elemental analysis calcd (%) for
C27H30N5ClO: C 68.13, H 6.35, N 14.71; found: C 68.32, H 6.48, N 15.03.
Synthesis of 3a–c: Ligands 1a, 1a’, or 1c (0.5 mmol) were dissolved in
THF (20 mL), and the resulting solution was added dropwise at room
Synthesis of 2a–c: A suspension of the ligands 1a, 1b, or 1c (0.25 mmol)
and silver oxide (0.6 equiv, 0.15 mmol) in CH2Cl2 (8 mL) was stirred at
room temperature in the dark for 4–8 h. The mixture was then filtered to
temperature to metal acetate (0.24 mmol, Ni
ACHTUNGTRENNUG(OAc)2·4H2O, PdACHTUNGTRENNUNG(OAc)2, or
ZnAHCTUNGTR(ENNUNG OAc)2 in THF (10 mL)). The reaction mixture was stirred overnight
at room temperature. The resulting precipitate was filtered, washed with
THF (10 mLꢂ3), and vacuum-dried to give monometal Schiff base com-
pounds.
Compound 3a: Yield: 78%; 1H NMR ([D6]DMSO, 500 MHz): d=9.16
(s, 2H; NCHN), 7.84 (s, 2H; imine H), 7.68 (d, J=8.0 Hz, 4H; Ph), 7.35
(d, J=1.5 Hz, 2H; CH, imidazole), 7.28 (t, 2H; Ph), 7.17–7.16 (m, 4H;
Ph), 7.01 (dd, J=1.5 Hz, 2H; CH, imidazole), 5.43 (d, J=8.5 Hz, 2H;
a solution of metal precursors (0.12 mmol [{Cp*IrCl2}2] or [{RuCl
2ACHTUNGERTN(NUNG p-
cymene)}2], 0.23 mmol [{Pd(cod)Cl}2]) in dichloromethane (5 mL). After
AHCTUNGTRENNUNG
the mixture was stirred at room temperature for another 4 h, it was fil-
tered. Then the filtrate was concentrated and the residue was purified by
column chromatography or recrystallization. Compounds 2a and 2a’
were isolated in a ratio of 5:1 by column chromatography. Complexes 2b
and 2c were obtained in good yields upon recrystallization from dichloro-
methane/hexane.
Compound 2a: Orange solid, yield: 43%; 1H NMR (CDCl3, 400 MHz):
d=8.30 (s, 1H; imine H), 7.63 (d, J=2.0 Hz, 1H; Ph), 7.46 (d, J=2.0 Hz,
1H; CH, imidazole), 7.17 (s, 3H; Ph), 7.03 (d, J=8.4 Hz, 1H; CH, imida-
zole), 6.90 (d, J=1.6 Hz, 1H; Ph), 6.74 (d, J=1.6 Hz, 1H; Ph), 6.35 (d,
À
À
Ph), 5.14 (s, 4H; CH2 Ph), 4.08 (sept, 4H; J=6.5 Hz, iPr CH), 3.80 (s,
3H; CH3-imidazole), 1.38–1.19 ppm (dd, J=7 Hz, 24H; iPr CH3);
13C NMR ([D6]DMSO, 100 MHz): d=164.92 (C=N), 162.48 (C O),
144.87 (C N), 141.13 (Ph), 136.32 (Ph), 134.08 (Ph), 135.48 (Ph), 133.22
(Ph), 126.01 (Ph), 123.75 (CH imidazole), 122.56 (Ph), 122.06 (CH imida-
À
À
À
À
À
À
À
À
zole), 120.62 (Ph), 118.75 (Ph), 51.26 (CH2 Ph), 35.71 (N CH3), 28.42
(iPr CH), 23.94 (iPr CH3), 23.09 ppm (iPr CH3); elemental analysis calcd
(%) for C48H58N6O2Cl2Ni: C 65.47, H 6.64, N 9.54; found: C 65.51, H
6.71, N 9.57.
J=14.0 Hz, 1H; CH2 Ph), 4.77 (d, J=14.0 Hz, 1H; CH2 Ph), 3.99 (s,
3H; CH3-imidazole), 2.95 (sept, J=6.8 Hz, 2H; iPr CH), 1.66 (s, 15H;
CH3, Cp*), 1.16 ppm (d, J=6.8 Hz, 12H; iPr CH3); 13C NMR (CDCl3,
À
À
100 MHz): d=166.50 (C=N), 161.14 (C OH), 156.20 (Ccarbene Ir), 145.74
(C N), 138.46 (Ph), 134.01 (Ph), 133.17 (Ph), 126.92 (Ph), 125.45 (Ph),
123.40 (CH imidazole), 123.12 (Ph), 121.71 (CH imidazole), 121.43 (Ph),
118.68 (Ph), 117.38, 88.79 (C
Compound 3b: Yield: 86%; 1H NMR ([D6]DMSO, 400 MHz): d=9.05
(s, 2H; NCHN), 7.96 (s, 2H; imine H), 7.68 (s, 4H; Ph), 7.65 (s, 2H; Ph),
7.45 (d, J=1.6 Hz, 2H; CH, imidazole), 7.35(t, 2H; Ph), 7.24–7.25 (m,
4H; Ph), 7.15 (dd, J=1.6 Hz, 2H; CH, imidazole), 5.83 (d, J=8.5 Hz,
À
À
À
(CH3)5), 52.82 (CH2 Ph), 36.20 (N CH3),
5A(CH3)5); elemental analysis
28.01 (iPr CH), 23.43 (iPr CH3), 9.19 ppm (C CHTUNGTRENNUNG
calcd (%) for C34H44N3Cl2OIr: C 52.77, H 5.73, N 5.43; found: C 52.81, H
5.56, N 5.45.
À
À
2H; Ph), 5.15 (s, 4H; CH2 Ph), 3.80 (s, 6H; CH3-imidazole), 1.23–
1.13 ppm (dd, J=7.0 Hz, 24H; iPr CH3); 13C NMR ([D6]DMSO,
Compound 2a’: Orange solid, yield: 9%; 1H NMR (CDCl3, 400 MHz):
d=8.13 (s, 1H; imine H), 7.43 (s, 1H; Ph), 7.15 (s, 3H; CH, imidazole
and Ph), 6.95 (d, J=1.6 Hz, 1H; Ph), 6.91 (d, J=1.6 Hz, 1H; Ph), 6.88 (s,
À
À
125 MHz): d=164.89 (C=N), 163.96 (C O), 144.43 (C N), 141.94 (Ph),
136.80 (Ph), 135.66 (Ph), 135.48 (Ph), 127.20 (Ph), 124.26 (Ph), 123.05
(CH imidazole), 122.59 (Ph), 120.81 (CH imidazole), 120.72 (Ph), 119.71
À
À
(Ph), 51.74 (CH2 Ph), 36.20 (N CH3), 28.49 (iPr CH), 24.32 (iPr CH3),
23.31 ppm (iPr CH3); elemental analysis calcd (%) for
C48H58N6O2F12P2Pd: C 50.25, H 5.10, N 7.32; found: C 50.33, H 5.21, N
7.27.
Compound 3c: Yield: 67%; 1H NMR (CDCl3, 500 MHz): d=10.27 (s,
2H; NCHN), 9.04 (d, J=5.0 Hz, 4H; pyrimidine), 8.89 (d, J=3.5 Hz,
2H; imine H), 8.46 (s, 2H; Ph), 8.11 (s, 2H; Ph), 7.99 (m, 2H; Ph and
pyrimidine), 7.76 (t, J=5.0 Hz, 2H; pyrimidine), 7.46 (s, 2H; Ph), 7.43
(d, J=8.5 Hz, 2H; CH, imidazole), 7.20 (m, 6H; Ph), 6.70 (d, J=8.5 Hz,
À
À
À
1H; Ph), 4.85 (d, J=13.6 Hz, 1H; CH2 Ph), 4.67 (d, J=13.6 Hz, 1H;
À
CH2 Ph), 3.91 (s, 3H; CH3-imidazole), 3.01 (sept, 2H; J=6.8 Hz, iPr
CH), 1.73 (s, 15H; CH3, Cp*), 1.14 ppm (d, J=7.2 Hz, 12H; iPr CH3);
C NMR (CDCl3, 100 MHz): d=166.05 (C=N), 159.22 (C OH), 156.68
(Ccarbene Ir), 147.20 (C N), 139.06 (Ph), 130.74 (Ph), 129.81 (Ph), 126.43
(Ph), 124.67 (Ph), 123.00 (CH imidazole), 121.26 (Ph), 120.18 (CH imida-
13
À
À
À
À
zole), 113.85 (Ph), 112.08 (Ph), 90.61 (C
N
À
(N CH3), 27.93 (iPr CH), 23.55 (iPr CH3), 9.47 ppm (C
tal analysis calcd (%) for C34H43N3Cl2OIr: C 52.84, H 5.61, N 5.44;
found: C 52.90, H 5.66, N 5.48.
À
À
2H; CH, imidazole), 5.39 (s, 4H; CH2 Ph), 3.21 (br, 4H; iPr CH),
1.12 ppm (br, 24H iPr CH3); 13C NMR (CDCl3, 125 MHz): d=171.06
Compound 2b: Yield: 56%; 1H NMR (CDCl3, 500 MHz): d=13.38 (s,
1H; OH), 8.29 (s, 1H; imine H), 7.53 (d, J=2.0 Hz, 1H; CH, imidazole),
7.36 (d, J=2.5 Hz, 1H; Ph), 7.02 (d, J=8.0 Hz, 1H; CH, imidazole), 6.95
(d, J=2.0 Hz, 1H; Ph), 6.89 (s, 2H; Ph), 6.82 (d, J=2.0 Hz, 1H; Ph),
À
(C=N), 159.90 (C OH), 159.48 (pyrimidine), 153.61 (pyrimidine), 152.07
(C N), 140.82 (Ph), 136.86 (NCN, imidazole), 135.95 (Ph), 135.64 (Ph),
129.71 (Ph), 123.34 (Ph), 123.26 (CH, imidazole), 122.98 (Ph), 122.26
(CH, imidazole), 120.10 (pyrimidine), 119.49 (Ph), 116.94 (Ph), 52.18
(CH2 Ph), 27.58 (iPr CH), 23.11 ppm (iPr CH3); elemental analysis calcd
À
À
À
5.40 (s, 2H; CH2 Ph), 5.12 (d, J=6.0 Hz, 4H; cymene-C6H4), 4.03 (s,
3H; CH3-imidazole), 2.94 (sept, J=7.0 Hz, 2H; iPr CH), 2.28 (s, 3H;
À
(%) for C54H58N10O2Cl2Zn: C 63.87, H 5.76, N 13.79; found: C 64.03, H
5.91, N 13.68.
À
À
cymene-CH3), 2.14 (s, 6H; Ph CH3), 2.09 (s, 3H; Ph CH3), 1.26 ppm (d,
J=5.6 Hz, 6H; cymene-CHCH3); 13C NMR (CDCl3, 100 MHz): d=
À
À
À
173.84 ( Ccarbene Ru), 166.43 (C=N), 161.06 (C OH), 145.16 (C N),
134.62 (Ph), 134.50 (Ph), 133.26 (Ph), 132.68 (Ph), 128.96 (Ph), 127.03
(Ph), 123.88 (CH imidazole), 122.19 (Ph), 118.94 (CH imidazole), 117.29
Synthesis of 4: CoACTHNUGTRNEUNG(OAc)2·4H2O (0.12 mmol) and NaOH ( 0.25 mmol)
were added to a solution of ligand 1a (0.25 mmol) in MeOH (10 mL),
The reaction mixture was heated at reflux for 24 h under nitrogen atmos-
phere. After reaction, the solvent was evaporated. The residue was dis-
solved in dichloromethane (5 mL) and filtered. The filtrate was dried
under reduced pressure and the residue was washed with ether (3ꢂ5 mL)
and dried under vacuum to afford purple compound 4. Yield: 25%. Ele-
mental analysis calcd (%) for C46H58N4O4Co: C 69.94, H 7.40, N 7.09;
found: C 69.98, H 7.48, N 7.12.
À
À
(Ph), 108.55 (Ph), 99.20 (Ph), 53.92 (CH2 Ph), 39.67 (N CH3), 30.80 (iPr
À
À
À
CH), 22.60 (iPr CH3), 20.72 (Ph CH3), 18.70 (Ph CH3), 18.40 ppm (Ph
CH3); elemental analysis calcd (%) for C31H37N3Cl2ORu: C 58.21, H
5.83, N 6.57; found: C 58.15, H 5.78, N 6.63.
Compound 2c: Yield: 68%; 1H NMR (CDCl3, 500 MHz): d=9.69 (dd,
J=5.6 Hz, 1H; pyrimidine), 8.85 (dd, J=5.6 Hz, 1H; pyrimidine), 8.32 (s,
1H; imine H), 7.77 (d, J=8.5 Hz, 1H; CH, imidazole), 7.56 (m, 2H; Ph
and pyrimidine), 7.46 (t, J=5.2 Hz, 1H; pyrimidine), 7.18 (s, 3H; Ph),
7.07(s, 1H; Ph), 7.02 (d, J=8.5 Hz, 1H; CH, imidazole), 6.03(s, 2H;
Synthesis of 5: tBuOK (0.5 mmol) was added to
a solution of 1a
(0.4 mmol) in THF (10 mL). After stirring for 30 min, the mixture was
cannulated to a suspension of [{Cp*IrCl2}2] (0.2 mmol) in THF (10 mL).
The mixture was stirred at room temperature for an additional 24 h and
filtered. The filtrate was dried under high vacuum and the resulting solid
purified by recrystallization from THF/hexane (1:4) to give orange 5.
À
À
CH2 Ph), 2.94 (sept, J=4.8 Hz, 2H; iPr CH), 1.16 ppm (d, J=4.8 Hz,
12H; iPr CH3); 13C NMR (CDCl3, 125 MHz): d=166.16 (C=N), 161.66
À
À
(C OH), 160.47 (pyrimidine), 158.90 (pyrimidine), 156.78 (Pd Ccarbene),
153.17 (pyrimidine), 145.66 (C N), 138.44 (Ph), 133.76 (Ph), 132.75 (Ph),
125.61 (CH imidazole), 125.48 (Ph), 123.44 (Ph), 123.18 (Ph), 119.55 (pyr-
1
À
Yield: 46%. H NMR (CDCl3, 400 MHz): d=7.929 (s, 1H; NCHN), 7.15
(s, 1H; imidazole), 6.85 (s, 1H; imidazole), 3.70 (s, 3H; CH3-imidazole),
11048
www.chemeurj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 11041 – 11051

Imidazolium Salts
FULL PAPER
1.58 ppm (s, 15H; Cp*); 13C NMR (CDCl3, 100 MHz): d=139.06
(NCHN), 130.62 (CH imidazole), 121.44 (CH imidazole), 85.35 (C5-
6.4 Hz, 1H; iPr CH), 2.58 (sept, J=6.4 Hz, 1H; iPr CH), 1.74 (s, 15H;
Cp*), 1.46 (s, 15H; Cp*), 1.05 (d, J=6.4 Hz, 6H; iPr CH3), 0.90 ppm (d,
J=6.4 Hz, 6H; iPr CH3); 13C NMR (CDCl3, 100 MHz): d=172.19 (C-O-
À
G
G
À
À
Ir), 164.89 (C=N), 155.17 (Ccarbene Ir), 151.45 (C N), 140.88 (Ph), 140.77
(Ph), 134.70 (Ph), 131.80 (Ph), 128.61 (Ph), 127.47 (Ph), 125.23 (Ph),
123.88 (CH imidazole), 121.61 (CH imidazole), 120.84 (Ph), 109.64 (Ph),
(%) for C14H21N2Cl2Ir: C 35.00, H 4.41, N 5.83; found: C 35.23, H 4.57, N
5.90.
Synthesis of 6a: A solution of tBuOK in THF (1.0m, 0.26 mL) was added
dropwise to a stirred suspension of ligand 1a’ (0.25 mmol) in THF
(15 mL) at room temperature. After the mixture was stirred for 30 min,
À
À
92.30 (C
(iPr CH), 26.28 (iPr CH), 22.61 (iPr CH3), 22.69 (iPr CH3), 9.48 (C5-
(CH3)5), 9.30 ppm (C5A
5ACHTUNGTNER(NGU CH3)5, 92.11 (C5AHCTUNTGRNEN(GUN CH3)5, 56.47 (CH2 Ph), 36.91 (N CH3), 26.35
G
(CH3)5); 31P NMR (CDCl3, 202 MHz): d=À136.76
[{IrACHTUNGTRENNUNG(cod)Cl}2] (0.24 mmol) was added in one portion. The reaction mix-
to À150.83 ppm (sep); elemental analysis calcd (%) for
C44H57N3F6ClOPIr2: C 43.72, H 4.75, N 3.48; found: C 43.89, H 4.96, N
3.45.
ture was stirred for an additional 16 h. The solvent was evaporated, and
the residue was purified by flash chromatography on silica gel with
CH2Cl2 as eluent to afford 6a as an orange-red solid. Yield: 65%;
1H NMR (CDCl3, 400 MHz): d=8.16 (s, 1H; imine H), 7.53 (d, J=
8.8 Hz, 1H; imidazole), 7.24–7.21 (m, 4H; Ph), 7.22 (s, 3H; Ph), 7.12 (d,
J=8.8 Hz, 1H; imidazole), 6.76 (d, J=2.0 Hz, 1H; Ph), 6.59 (d, J=
Synthesis of 7a and 7b: A suspension of the compound 3a (0.1 mmol)
with silver oxide (0.13 mmol) in CH2Cl2 (25 mL) was stirred at room tem-
perature in the dark for 10 h. The mixture was then filtered to a solution
À
À
of [{RuCl2ACHTUNGTERNNU(G p-cymene)}2] (for compound 7a) or [{Cp*IrCl2}2] (for com-
2.0 Hz, 1H; Ph), 5.76 (d, J=14.4 Hz, 1H; CH2 Ph), 5.39 (d, J=14.4 Hz,
À
À
pound 7b) (0.1 mmol) in dichloromethane (10 mL). The mixture was
stirred at room temperature overnight and filtered. After concentration,
the resulting solid was washed by toluene (3ꢂ10 mL), and then purified
by recrystallization from dichloromethane/hexane (1:9, 10ꢂ3 mL) to give
the complexes 7a and 7b, respectively.
Compound 7a: Reddish-brown solid, yield: 57%; 1H NMR (CDCl3,
400 MHz): d=7.33 (s, 2H; imine H), 7.28 (s, 2H; Ph), 7.13–7.11 (m, 4H;
Ph), 6.96 (d, J=1.6 Hz, 2H; CH, imidazole), 6.90–6.97 (br, 4H; Ph), 6.79
(d, J=1.6 Hz, 2H; CH, imidazole), 5.55 (d, J=8.8 Hz, 2H; Ph), 5.30 (m,
1H; CH2 Ph), 4.60 (m, 2H; cod), 4.45 (m, 2H; cod), 3.96 (s, 3H; CH3-
imidazole), 3.33 (sept, J=6.8 Hz, 2H; iPr CH), 2.97 (m, 1H; cod),
2.93(m, 1H; cod), 2.68 (m, 2H; cod), 2.22–2.12 (m, 8H; cod), 1.74–1.59
(m, 8H; cod), 1.04 (d, J=6.8 Hz, 6H; iPr CH3), 1.01 ppm (d, J=6.8 Hz,
6H; iPr CH3); 13C NMR (CDCl3, 125 MHz): d=180.62 (Ccarbene Ir),
À
À
165.94 (C-O-Ir), 164.12 (C=N), 153.72 (C N), 145.76 (Ph), 140.98(Ph),
135.89 (Ph), 127.51 (Ph), 123.67 (Ph), 123.43 (Ph), 120.44 (Ph), 123.18
(CH imidazole), 122.08 (CH imidazole), 119.63 (Ph), 118.96 (Ph), 84.74
(d, cod), 70.09 (d, cod), 56.84 (d, cod), 53.47 (CH2 Ph), 51.67 (d, cod),
À
À
37.61 (N CH3), 33.72 (d, cod), 32.31
(d, cod), 29.79 (d, cod), 28.01 (iPr
À
À
8H; cymene-C6H4), 5.02 (s, 4H; CH2 Ph), 4.20 (sept, J=6.4 Hz, 4H;
iPr CH), 3.99 (s, 6H; CH3-imidazole), 2.90 (d, J=6.8 Hz, 2H; cymene-
CHCH3), 2.01 (s, 6H; cymene-CH3), 1.44 (d, J=6.8 Hz, 12H; cymene-
CHCH3), 1.22 ppm (d, J=6.8 Hz, 24H; iPr CH3); 13C NMR (CDCl3,
CH), 25.78 (d, cod), 22.49 ppm (iPr CH3); elemental analysis calcd (%)
for C40H52N3ClIr2: C 48.30, H 5.27, N 4.22; found: C 48.39, H 5.29, N
4.30.
À
À
125 MHz): d=173.62 (Ccarbene Ru), 163.83 (C=N), 163.29 (C OH),
Synthesis of 6b: A solution of nBuLi (1.6m, 0.31 mL, 0.5 mmol) in
À
145.38 (C N), 141.65 (Ph), 134.01 (Ph), 131.92 (Ph), 126.05 (Ph), 123.56
hexane was added dropwise to
a stirred solution of ligand 1a’
(Ph), 123.16 (Ph), 122.83 (CH imidazole), 122.79 (Ph), 122.50 (Ph),
121.43 (Ph), 118.75 (CH imidazole), 108.50 (Ph), 99.01 (Ph), 53.89 (CH2
Ph), 39.61 (N CH3), 30.70 (iPr CH), 29.62 (iPr CH), 28.80 (iPr CH),
24.33 (iPr CH3), 23.42 (iPr CH3), 18.60 ppm (Ph CH3); elemental analy-
(0.25 mmol) in THF (10 mL) at À788C. The mixture was slowly warmed
to room temperature and stirred for 3 h. Then the mixture was cannulat-
ed to a suspension of [{Cp*IrCl2}2] (0.24 mmol) in THF (10 mL) and
stirred overnight. After concentration the residue was purified by column
chromatography to afford 6b as a red solid. Yield: 28%; 1H NMR
(CDCl3, 400 MHz): d=8.35 (s, 1H; imine H), 7.97 (s, 1H; Ph), 7.36 (m,
3H; Ph and CH, imidazole), 7.07 (d, J=1.6 Hz, 1H; Ph), 7.01 (s, 1H;
À
À
À
sis calcd (%) for C68H84N6Cl4O2NiRu2: C 57.51, H 5.96, N 5.92; found: C
57.54, H 6.09, N 5.96.
Compound 7b: Yellow-green solid, yield: 54%; 1H NMR (CDCl3,
500 MHz): d=7.32 (s, 2H; imine H), 7.23–7.18 (br, 4H; Ph), 7.09 (br,
4H; Ph), 7.01 (s, 2H; Ph), 6.93 (d, J=9.0 Hz, 2H; Ph), 6.80 (d, J=
À
À
Ph), 6.91 (s, 1H; Ph), 4.82 (d, J=14.4 Hz, 1H; CH2 Ph), 4.69 (d, J=
À
À
14.4 Hz, 1H; CH2 Ph), 3.89 (s, 3H; CH3-imidazole), 2.96 (sept, J=
Table 2. X-ray crystallographic data for 1a’, 2a·CH2Cl2, 3b, and 4.
1a’
2a·CH2Cl2
3b
4
formula
Mr
crystal system
space group
a [ꢁ]
b [ꢁ]
c [ꢁ]
a [8]
b [8]
C24H30F6N3OP
521.48
monoclinic
P21/c
14.965(3)
9.7123(17)
19.323(3)
90
108.912(2)
90
2656.9(8)
4
0.166
1.304
1088
C35H46Cl4IrN3O
858.75
monoclinic
P21/c
16.556(2)
14.1137(17)
16.2376(19)
90
103.428(2)
90
3690.5(8)
4
3.938
1.546
1720
C48H58F12N6O2P2Pd
1147.34
monoclinic
P21/c
14.565(3)
10.0661(19)
18.573(4)
90
100.018(2)
90
2681.6(9)
4
C46H58CoN4O4
789.89
triclinic
¯
P1
12.2281(18)
12.8516(18)
16.912(4)
96.314(2)
107.595(2)
114.313(2)
2223.0(7)
2
g [8]
V [ꢁ3]
Z
m [mmÀ1
]
0.490
1.421
1176
0.430
1.180
842
1calcd [mgmÀ13
F [000]
]
T [K]
296(2)
296(2)
296(2)
293(2)
q range [8]
reflns collected/indep reflns
R(int)
2.23 to 25.00
12793/4680
0.0289
1.26 to 27.00
20756/7917
0.0580
1.42 to 25.50
13407/4982
0.0393
1.81 to 25.01
12026/7744
0.0176
data/restraints/params
GOF
4680/0/378
1.021
7917/22/394
1.016
4982/0/328
0.957
7744/0/515
1.025
R
wR2
(I>2s(I))
0.0503,
0.1244
0.0475
0.1123
0.0470
0.1215
0.0480
0.1396
Chem. Eur. J. 2011, 17, 11041 – 11051
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
11049

X.-F. Hou et al.
Table 3. X-ray crystallographic data for 5, 6a·CH2Cl2, 6b·CH2Cl2, and 7a·CH2Cl2.
5
6a·CH2Cl2
6b·CH2Cl2
7a·CH2Cl2
formula
Mr
crystal system
space group
a [ꢁ]
b [ꢁ]
c [ꢁ]
a [8]
b [8]
C14H21Cl2IrN2
480.43
monoclinic
P21/c
7.3275(7)
14.0818(13)
15.5413(15)
90
91.6740(10)
90
1602.9(3)
4
8.651
1.991
920
C40H52ClIr2N3O
1010.70
C45H59Cl3F6Ir2N3OP
1293.67
monoclinic
P21/c
15.7170(9)
15.4757(9)
20.1623(12)
90
103.8930(10)
90
4760.6(5)
4
C69H86Cl6N6NiO2Ru2
1504.99
triclinic
triclinic
¯
¯
P1
P1
8.274(3)
14.826(5)
17.521(6)
86.497(6)
86.139(5)
78.435(5)
2098.5(11)
2
14.447(7)
17.302(8)
17.543(8)
74.636(7)
65.689(7)
70.552(8)
3726(3)
2
g [8]
V [ꢁ3]
Z
m [mmÀ1
]
6.430
1.600
984
5.848
1.805
2528
0.910
1.341
1552
1calcd [mgmÀ13
F [000]
]
T [K]
296(2)
296(2)
296(2)
296(2)
q range [8]
reflns collected/indep reflns
R(int)
1.95 to 26.99
8922/3426
0.0267
1.40 to 25.00
12523/7278
0.0733
1.68 to 26.00
30532/9315
0.0195
1.60 to 25.10
18020/12633
0.0861
data/restraints/params
GOF
3426/0/178
1.118
7278/0/424
0.994
9315/3/550
1.012
12633/6/752
1.133
R
(I>2s(I))
0.0244
0.0545
0.0291
0.0905
wR2
0.0540
0.1289
0.1042
0.2130
1.5 Hz, 2H; CH, imidazole), 6.65 (d, J=1.5 Hz, 2H; CH, imidazole), 5.92
À
À
(d, J=14.0 Hz, 2H; CH2 Ph), 5.52 (d, J=8.5 Hz, 2H; Ph), 4.71 (d, J=
Acknowledgements
À
À
14.0 Hz, 2H; CH2 Ph), 4.22 (m, 4H; iPr CH), 3.94 (s, 6H; CH3-imida-
zole), 1.59 (s, 30H; CH3, Cp*), 1.43 (d, J=7.0 Hz, 12H; iPr CH3),
1.21 ppm (d, J=7 Hz, 12H; iPr CH3); 13C NMR (CDCl3, 125 MHz): d=
Financial support by the National Science Foundation of China (grant
nos. 20871032, 20971026), and by the Shanghai Leading Academic Disci-
pline Project (project no. B108) is gratefully acknowledged.
À
À
À
163.94 (C=N), 163.42 (C OH), 155.95 (Ccarbene Ir), 145.48 (C N), 141.74
(Ph), 134.64 (Ph), 132.70 (Ph), 128.19 (Ph), 126.00 (Ph), 123.00 (CH imi-
dazole), 123.12 (Ph), 121.59 (CH imidazole), 121.36 (Ph), 118.80 (Ph),
À
À
88.67 (C
(CH3)5), 53.58 (CH2 Ph), 38.60 (N CH3), 28.81 (iPr CH), 24.37
5A(CH3)5); elemental analysis
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 11041 – 11051

Imidazolium Salts
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Received: May 20, 2011
Published online: August 23, 2011
Chem. Eur. J. 2011, 17, 11041 – 11051
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
11051