Cyclometalated iridium(III)complexes with ligand effects on the catalytic C-H bond activation of toluene

Article abstract of DOI:10.1002/ejic.201601548

New cyclometalated iridium(IIcomplexes have been designed, prepared and applied as catalytic systems for the C-H bond activation (CHof toluene through a clean, highly efficient, and environmentally friendly process. The complexes have the general formula [(C^N)₂Ir(N^O)]. The C^N ligands are the monoanionic bidentate cyclometalating ligands 2-phenylpyridinato (ppy), 2-phenylbenzoxazolato (pbo), and 2-(3.5-difluorophenyl)-benzoxazolato (dfpbo). The (N^ligand is also a monoanionic bidentate cyclometalating ligand, namely picolinato (pic). The complexes [(ppy)₂Ir(pic)] (1), [(pbo)₂Ir(pic)] (2), and [(dfpbo)2-Ir(pic)] (3) were structurally characterized by¹H and¹³C NMR spectroscopy, FAB-MS, and X-ray crystallography. The activation energies for the catalytic CHA oxidation of toluene when using complexes 1-3 as catalysts are quite low, between 14.4 and 25.5 kcal mol^-1. The catalytic turnover frequencies (TOFare fairly high (up to 4.0 × 10³ mol_toluene mol_catalyst^-1 h^-1) with excellent reliability and the turnover number (TOcan reach 2.40 × 10⁴ mol_toluene mol_catalyst^-1 after 6 h of reaction time. A combination of catalytic tests, DFT calculations, X-ray absorption nearedge structure (XANEanalysis, and kinetic modeling was used to derive detailed insights into the characteristics of the catalysts and their effect on the reactions featured in the CHA oxidation of toluene.

Full text of DOI:10.1002/ejic.201601548

A Journal of
Accepted Article
Title: Cyclometalated Iridium(III) Complexes with Ligand Effect on
Catalytic Carbon-Hydrogen Bond Activation of Toluene in High-
Performance
Authors: Tsun-Ren Chen, Pei-Chun Liu, Hsiu-Pen Lee, Fang-Siou Wu,
and Kelvin H.-C. Chen
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201601548
Link to VoR: http://dx.doi.org/10.1002/ejic.201601548

10.1002/ejic.201601548
European Journal of Inorganic Chemistry
FULL PAPER
Cyclometalated Iridium(III) Complexes with Ligand Effect on
Catalytic Carbon-Hydrogen Bond Activation of Toluene in High-
Performance
Tsun-Ren Chen,*[a] Pei-Chun Liu,[a] Hsiu-Pen Lee,[a] Fang-Siou Wu[a] and Kelvin H.-C. Chen[a]
Abstract: New cyclometalated iridium (III) complexes are designed,
prepared and applied to a catalytic system for carbon-hydrogen
bond activation (CHA) of toluene using a clean, highly efficient and
reported complexes have an acceptable reactivity (the turnover
frequency (TOF) may be higher than 10), but a low reliability (the
turnover number (TON) may be less than 100), or some
complexes are active but not easily prepared and too unstable to
environmentally friendly process.
general formula (C^N)2Ir(N^O). The C^N ligands are monoanionic
bidentate cyclometalating ligands, including 2-phenylpyridinato (ppy), obtaining catalysts for
These complexes have the
be stored.
Therefore, our aim is to provide some ideas on
high-performance CHA. Those
a
2-phenylbenzoxazolato
(pbo)
and
2-(3.5-
catalysts should be stable and easy to prepare and their
characteristics able to be systematically tuned.
difluorophenyl)benzoxazolato (dfpbo), respectively; the (N^O) ligand
is also a monoanionic bidentate cyclometalating ligand, picolinato
(pic). Complexes (ppy)2Ir(pic) (1), (pbo)2Ir(pic) (2) and (dfpbo)2Ir(pic)
(3) are structurally characterized by 1H NMR, 13C NMR, FAB-MS and
X-ray crystallography. The activation energies needed for the
catalytic CHA oxidation of toluene when using complexes 1-3 as
catalysts are quite low, between 14.4 and 25.5 kcal mol-1. The
catalytic frequencies (TOF) are fairly high (up to 4.0×103 Moltoluene
In 1993, the Ir(III) complex CP*Ir(PMe3)(Me)(OTf) which was
prepared could undergo a mild and selective reaction with C-H
bonds in arenes and alkanes. This complex had a better
performance for CHA than that of low-valent iridium
complexes.35 Until now, the use of the Ir(III) complex for CHA
has rarely been reported.36,37 In other fields, Ir(III) complexes
with bidentate ligands, including carbon-nitrogen (C^N),
nitrogen-oxygen (N^O) and nitrogen-nitrogen (N^N), have been
widely applied to organic light-emitting diodes (OLEDs),38,39
biolabeling,40,41 dye-sensitized solar cells (DSCs)42,43 and the
photoreaction of water,44,45 in which most of the bidentate
ligands could be easily prepared and have a steady bond to a
metal center. Also, the character of the ligands was flexible and
could be modified. In general, the bidentate ligands C^N and
N^O are ionic, whereas the ligand N^N is neutral, which means
that ligands C^N and N^O could form a tighter bond to the
central metal than the ligand N^N. Moreover, since the bond
energy of metal-carbon is different from that of metal-oxygen,
the stability and activity of a complex composed of various
bidentate ligands could be finely and widely tuned.
-1
Molcatalyst h-1 ) with excellent reliability; the turnover number (TON)
can reach 2.40×104 Moltoluene Molcatalyst after 6 hours of processing
-1
time. A combination of catalytic tests, studies with density functional
theory (DFT), X-Ray absorption near edge structure (XANES) and
kinetic modeling is used to derive detailed insights into the
characteristics of the catalysts and their effect on the reactions
featured in the CHA oxidation of toluene.
Introduction
Carbon-hydrogen bond activation (CHA), used to functionalize
saturated hydrocarbons to form a variety of organic compounds,
is an important process and widely applied in various fields.1-6
As to the hydrocarbons, the C-H bond is inert and has a fairly
strong bond energy, so a major challenge for CHA is how to
activate the bond and lower the energy needed. Much effort has
been dedicated to seeking out powerful candidates for CHA
catalysts. An early example of homogeneously metal-catalyzed
CHA is known as the Shilov system.7 Since Bergman, in 1984,
discovered that the products of the C-H oxidative addition
reaction of aromatic and aliphatic compounds could be isolated
by using d8-CP*Ir(PMe3) as the catalyst,8,9 the scope of
developing catalysts for CHA has been widened to include a
variety of complexes, for example, iridium,10-12 palladium,13-16
platinum,17-20 rhenium,21-24 rhodium25-29 and ruthenium.30-34
Although these studies reported certain achievements, some
issues still required further research. For example, some
Results and Discussion
Synthesis and Structure. Previously, we discovered that an
18+δ iridium dimer possessing a benzoxazole ligand can
spontaneously release metalloradicals, which promotes two
types of reactions: the carbon-hydrogen bond activation and a
rare but important carbon-carbon bond activation (CCA) for
ketones and aldehydes.46 We also discovered that the diiridium
bimetallic complexes having a benzoxazole ligand exhibit a
special type of oxidation-reduction reaction which directly splits
the carbonate into carbon monoxide and oxygen via a low-
energy pathway without the need of a sacrificial reagent.47 This
means that such complexes are active for various reaction
systems, including CHA. However, CHA was not a major type of
reaction in our previous report; moreover, metalloradicals are
quite unstable and hard to control. Therefore, we designed
[a]
Department of Applied Chemistry, National Pingtung University
No.4-18, Minsheng Rd., Pingtung County 90003, Taiwan
E-mail: trchen@mail.nptu.edu.tw
http://www.ac.nptu.edu.tw/bin/home.php
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10.1002/ejic.201601548
European Journal of Inorganic Chemistry
FULL PAPER
iridium complexes composed of an N^O and two C^N ligands,
which are six-coordinate complexes with a stable octahedral
geometry. In mild reaction conditions, for example, by heating
or irradiating with light, this kind of complex first releases the
N^O ligand to form a four-coordinate intermediate with the
vacant coordination sites required for oxidative addition, in which
the characteristic of the C^N ligand obviously affects the
property of the intermediate.
Scheme 1 shows the synthesis of the ligands and the iridium
complexes.
[(C^N)2Ir(N^O)], where C^N is a monoanionic cyclometalating
ligand, including 2-phenylpyridinato (ppy), 2-
phenylbenzoxazolato (pbo) and 3.5-difluorophenyl
Complexes 1-3 have
a
general formula
benzoxazolato (dfpbo), respectively; and N^O is the picolinato
group (pic), and also a monoanionic bidentate ligand. All the
iridium dimers and iridium complexes were purified and
identified by 1H NMR, 13C NMR, FAB-MS spectrometry and
elemental analyses; complexes 1-3 were characterized by a
single-crystal X-ray analysis.
N
N
IrCl3 / H2O
O
piclinic acid
N
Ir
O
N
Cl
Cl
Ir
N
N
Ir
N
Ethoxyethanol
Ethoxyethanol
NaHCO3
L 1
N
1
D 1
Figure 1. ORTEPdiag ram of (a) (ppy)2 Ir(pic) (1), (b) (pbo)2Ir(pic) (2), and (c)
(dfpbo)2 Ir(pic) (3). Thermal ellipsoids are draw at the 20% probability level.
The hydrogen atoms and solvent are omitted for clarity..
O
O
IrCl3 / H2O
2-aminophenol
PPA
R1
R1
OH
N
Ethoxyethanol
R1
L 2 and L 3
R1
O
O
O
R1
R1
R1
N
N
N
Cl
picolinic acid
O
O
R1
R1
R
R1
R1
Table 1. Selected Bond Distance (Å ) and Bond Angles for Complexes 1-3
Ir
Ir
Ir
R1
Ethoxyethanol
NaHCO3
N
Cl
complex
N
N
N
R1
R1
R1
1
2
3
O
O
O
2 and 3
parameter
Ir -N(1)
D 2 and D 3
2.042(4)
2.052(5)
2.141(4)
2.003(5)
2.012(5)
2.157(4)
175.67(18)
174.24(18)
171.69(19)
81.3(2)
2.043(2)
2.032(2)
R1 : H for L2, D2 and 2 ; F for L3, D3 and 3
Ir -N(2)
2.025(2)
2.043(2)
Scheme 1. Synthetic route of C^N ligands and complexes 1-3.
Ir -N(3)
2.120(2)
2.101(2)
Ir -C(A)a
2.015(3)
2.028(3)
Ir -C(B)b
2.009(3)
2.045(3)
The single-crystal structures of complexes 1-3 are represented
with ORTEP diagrams in Figure 1, where complex 1 belongs to
the monoclinic space group P 21 and complexes 2 and 3 belong
to the monoclinic space group P 21/c, respectively. Selected
bond distances and angles are listed in Table 1. The diversity of
the space groups for this series of complexes suggested that the
packing of these complexes was sensitive to the substituent of
the ligands.48
Ir –O(A)c
2.1461(17)
173.28(9)
171.83(10)
173.19(9)
79.88(10)
80.00(10)
2.129(2)
N(1)-Ir-N(2)
C(A)a -Ir-O(A)c
C(B)b -Ir-N(3)
N(1)-Ir-C(A)a
N(2)-Ir-C(B)b
176.87(10)
168.17(10)
174.56(11)
79.87(12)
79.84(11)
80.1(2)
a represented the atom label C(11) of complex 1, or C(13) of complex 2
and 3 on the x-ray crystal structures. b represented the atom label C(12)
of complex 1, or C(26) of complex 2 and 3. c represented the atom label
O(1) of complex 1, or O(3) of complex 2 and 3.
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10.1002/ejic.201601548
European Journal of Inorganic Chemistry
FULL PAPER
As Figure 1 shows, the three complexes adopted distorted
octahedral coordination geometry around the iridium, and the
two C^N ligands preferred a cis-C−C and a trans-N−N chelate
disposition. The bond lengths of the Ir− Cav bond for complexes
1-3 were 2.008(5), 2.012(3) and 2.037(3) Å, respectively, which
implied that the bidentate ligand C^N of 1 formed the strongest
σIr− C bond to the central metal, and that of 3 had the weakest
bond. Therefore, the C^N ligand of 1 should have a higher
trans-effect and so lengthen the bond distances between the
metal and N^O ligand. As can be seen in Table 2, the bond
lengths of Ir−N(pic) and Ir−O(pic) of complex 1 were 2.141(4)
and 2.157(4) (Å), respectively, and so longer than the bond
3
2
1
lengths of complex
2 (Ir−N(pic) = 2.120(2); Ir−O(pic) =
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
Voltage (V)
2.1461(17) Å ) or 3 (Ir−N(pic) = 2.101(2); Ir−O(pic) = 2.129(2) Å),
which implied that the structure of 1 was the most unstable and
the structure of 3 the most stable. The thermal gravimetric
analyses (TGA) (Figure 2) showed that complex 2 initially lost
the lattice solvent at 120℃ and completely released the N^O
ligand at 400℃, and complex 1 and 3 completely released the
N^O ligand at 360 and 414℃, respectively.
Figure 3. Cyclic voltammograms of complexes 1−3
As shown in Figure 3, complexes 1−3 were quite stable under
the oxidative and reductive reactions. The first oxidation
potentials (Eox1) of complexes 1−3 were 1.05, 1.23 and 1.49 V,
respectively. By the equation: HOMO (eV) = -{4.8 +[ (Eox1of
complex)-( Eox1of Fc/Fc+)]},50 we obtained the HOMO level of
complexes 1−3 of -5.37, -5.55 and -5.81 eV, respectively, which
showed the HOMO of complex 3 to be more stable than that of
complex 1 or 2.
100
1
2
3
90
80
70
60
50
Theoretical Calculations and X-Ray absorption near
edge structure spectra (XANES). computational study was
performed on the materials, including ligands, complexes,
reaction intermediates and adducts, to investigate the
characteristics of the molecules and their structural effect on the
CHA.
Theoretical calculations were performed using the
100
200
300
400
o
500
600
program package Gaussian 03 and employing Becke’s three-
parameter B3LYP for C, H, F, O and N and the LANL2DZ basis
set for the Ir element.51 Partial charges were calculated
according to the Mulliken, APT (atomic polar tensors) and NPA
(natural population).
temperature ( C )
Figure 2. Thermal gravimetric analyses (TGA) for complexes 1-3: samples
were heated up under nitrogen at a pressure of 1 atm with a heating rate of 10
oC min-1 and finished at 620 oC.
The highest occupied molecular orbital (HOMO) distribution of
the anions of the C^N ligand, including 2-phenylpyridinato (ppy-1),
2-phenylbenzoxazole
(pbo-1)
and
2-(3.5-
difluorophenyl)benzoxazole (dfpbo-1), are shown in Figure 4.
These anions resulted from removing the proton of the carbon
(denoted as C2) being a meta position to pyridyl or benzoxazole
group can be stabilized by the resonance of the aromatic
substituents. Also, since C2 is a γ-atom to the nitrogen of the
pyridyl or benzoxazole group, this kind of anion could chelate to
metal to form a stable five-membered ring. The HOMOs of the
anions were mainly composed of the atomic orbitals of carbons
C1, C2 and C3, and the negative charge was most localized on
the C2. The Mulliken atomic charges on C2 of ppy-1, pbo-1 and
dfpbo-1 were -0.3831, -0.3769 and -0.3340, respectively, which
implied that the ligand ppy provided the highest negative charge
to the central metal and that the dfpbo delivered the lowest
charge.
Electrochemical Properties. Cyclic voltammetry (CV) was
performed using a CHI voltammetric analyzer under a nitrogen
atmosphere. The supporting electrolyte of 0.1 M tetra(n-
-
butyl)ammonium
hexafluorophosphate
(Bu4N+·PF6 )
in
anhydrous dichloromethane (DCM) was used as the solvent, a
glassy-carbon rod as the working electrode, a platinum wire as
the counter electrode and an Ag/Ag+ electrode as the reference
electrode. The CV curves of complexes 1−3 had a reversible
route in the range of 1.0-1.6 V versus the ferrocene/ferrocenium
(Fc/Fc+) redox couple (Figure 3).49
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10.1002/ejic.201601548
European Journal of Inorganic Chemistry
FULL PAPER
(a) coordination of an oxygen to the intermediate Im;
(b) abstraction of a hydrogen atom from the C-H bond of
toluene;
(c) rebound of the newly formed OH group to the benzylic
radical to form benzyl alcohol;
C
C
C
1
C
C
4
1
4
4
C
1
C
3
..C
C
.. 2
.C. 2
C
C
2
3
3
(d) abstraction a hydrogen atom from the C-H bond of benzyl
alcohol;
(e) rebound of the newly formed OH group to the radical to
restore Im and give benzaldehyde hydrate;
(f) releasing of a water to form benzaldehyde.
(a)
(c)
(b)
N
N
N
N
CH2
Figure 4. Computational structure and the HOMO distribution of the anions of
(a) 2-phenylpyridine (ppy-1), (b) 2-phenylbenzoxazole (pbo-1), and (c) 2-(3.5-
difluorophenyl) benzoxazole (dfpbo-1)
C
C
R
C
C
R
C6H5CH3
H
Ir
Ir
+
O
O
O
O
b
O2
CH
CH
3
3
a
e
N
N
Because the partial negative charge on C2 of ppy-1 was higher
than that of pbo-1 or dfpbo-1, the partial positive charge on the
iridium atom of 1 should be lower than that of 2 or 3. The
calculation data showed the Mulliken atomic charge on the
iridium of 1 to be 0.91 lower than that of 2 (0.95) or 3 (1.04).
The computational results were verified by the normalized X-Ray
absorption near edge structure (XANES) spectra at the Ir L3-
edge for complexes 1-3 (Figure 5). Complex 3 (Figure 5c) had
the highest partial positive charge on the iridium atom, complex
2 (Figure 5b) the second highest and complex 1 (Figure 5a) the
lowest.52 It is to be noted that, in general, a complex with a
higher partial positive charge on metal would be a better
electrophile by attracting the substrates of electron donors, thus
being more active for oxidative addition.
C
C
R
c
C
C
O
N
dissociation
O
Ir
Ir
recombination
N
N
R = picolinato
[Im]
N
N
N
R
R
OH
H
C
C
OH
C
C
HC
CH
d
Ir
O
H
O
+
Ir
H
O
C
+
HO
OH
CH
N
f
CH
3
CH
3
H2
O
Figure 6. A proposed catalytic cycle for the CHA oxidation of
benzylic compounds
In order to evaluate the reactivity and reliability of complexes 1-
3 for carbon-hydrogen bond activation, we applied them in
catalytic reaction systems to convert toluene to benzaldehyde
and to investigate the reaction rate, rate constant and activation
energy (Ea) for the CHA oxidation of toluene. The experimental
data are summarized in Table 2. As benzaldehyde was the only
detectable product under the reaction condition, the calibration
curve of the standard solutions containing toluene and
benzaldehyde was used to monitor the progress of the
reactions. The reaction solution was stirred well under air to
keep the concentration of oxygen constant.
(a)
(b)
(c)
complex 1
complex 2
complex 3
2.5
2.0
1.5
1.0
0.5
0.0
Table 2. Reaction rate, rate constants and activation energy for the CHA
oxidation of net toluene by using complexes 1-3 as catalysts
rate (μM s-1)
kg
h
M-1 s-1
Ea
C3c C4d
C1a
C2b
11200
11300
kcal/mol
Energy (eV)
T1e
T2f
0.009
0.080
0.014
0.115
0.007
0.011
0.338
1
2
3
25.5
23.1
14.4
Figure 5. Ir L3-edge XANES of crystalline (a) (■) [(pp)2IrIV(pic)] (1), (b) (●)
[(pbo)2IrIV(pic)] (2), and (c) (▲) [ (dfpbo)2IrIV(pic)] (3). A Si (111) double crystal
monochromator was employed for energy scanning. Fluorescence data were
obtained at room temperature using an Ar-filled ionization chamber detector,
each sample was scanned 3 times for averaging.
0.059
0.088
2.861
T
0.017
0.125
0.076
0.266
0.029
0.183
0.126
0.437
0.013
0.095
0.064
0.219
0.022
0.140
0.105
0.363
0.681
4.585
1
T2
T
3.246
1
11.189
T2
Performance on CHA for Toluene. All solutions of complexes 1-3
exhibited catalytic activity for the CHA oxidation of benzylic
compounds; A proposed catalytic cycle for the CHA process was
a 0.1mM of catalyst in net toluene ( [toluene] = 9.39 M), b 0.2mM of catalyst
c
in net toluene, 0.1mM of catalyst in a reaction solution consisted of 80%
d
of toluene and 20% of 1,2-dichlorobenzene (v/v) ( [toluene]=7.51M); 0.
2mM of catalyst in a reaction solution consisted of 80% of toluene and 20%
of 1,2-dichlorobenzene. e 333K of reaction temperature; f 353K of reaction
showed as Figure 6 via radical reaction that are selective for the
53-55
most highly substituted or benzylic CH bonds.
mechanism containing six steps:
The
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10.1002/ejic.201601548
European Journal of Inorganic Chemistry
FULL PAPER
g
temperature. rate constant(x10-6) h average of activation energy.
28
26
24
22
20
18
16
14
12
For the CHA oxidation of net toluene ( [toluene] = 9.39 M), the
reaction rates using 0.1m M of complexes 1-3 as catalysts at a
60℃ reaction temperature were 0.009, 0.017 and 0.076 μM s-1,
respectively, which showed complex 3 to be a most powerful
catalyst for CHA. At an 80℃ reaction temperature, the reaction
rates for complexes 1-3 were 0.080, 0.125 and 0.266 μM s-1. All
reaction rates showed an obvious increase, although the
reaction rate of complex 1 increased more sharply than that of
complex 2 or 3, which implied that the activation energy of the
reaction using complex 1 as catalyst was higher than that of
complex 2 or 3.
With 0.2 mM of catalyst for net toluene at a 60℃ reaction
temperature, the reaction rates of complexes 1-3 were 0.014,
0.029 and 0.126 μM s-1, respectively, which showed that the
catalytic reaction proceeded in an order of 0.67 with respect to
complexes 1-3 when the concentration of the complex ranged
between 0.1 and 0.2 mM. For the CHA oxidation of 80% (v/v)
toluene in dichlorobenzene ( [toluene] = 7.51M) with 0.1 mM of
catalyst at a 60℃ reaction temperature, the reaction rates of
complexes 1-3 were 0.007, 0.013 and 0.064 μM s-1, respectively,
which showed that the catalytic reaction was first order to
toluene.
25.5
23.1
14.4
1
2
3
Catalyst
Figure 7. Activation energy (EA, kcal/mol) for the CHA oxidation of net toluene
by using 0.1 mM of complexes 1-3 as catalysts at 100℃ of reaction
temperature
3.5
Cat.
3.0
1
The experimental data also showed that complex 1 had lower
rate constants (k333 = 0.34 x 10-6 M-1 s-1, k353 = 2.86 x 10-6 M-1 s-
1) with a higher activation energy (Ea = 25.5 kcal/mol), and that
complex 3 exhibited higher rate constants (k333 = 3.25 x 10-6 M-1
s-1, k353 = 11.19 x 10-6 M-1 s-1) with a lower activation energy (Ea
= 14.4 kcal/mol) (Figure 7). This result demonstrated that the
C^N ligand of complex 3 (dfpbo) better stabilized the transition
state in the CHA reaction. As we know that the dissociation
energy of the C-H bond in hydrocarbon is quite high (~105 kcal
mol–1), this was a robust chemical bond and could be hardly
cleaved. In most cases, some active reactants, such as
halogens or radical species, should be used to supply chemical
energy, and some stoichiometric amounts of sacrificial materials
should be supplied to the systems. It is of considerable
significance that by using cyclometalated iridium complexes as
catalysts, the activation energy needed was quite low (~ 20
kcal/mol), the reaction was exergonic and no sacrificial material
was needed.
2
3
10000
1000
100
2.5
2.0
1.5
1.0
0.5
0.0
60
70
80
reaction temp. ( C)
90
100
o
Figure 8. Reaction rate (μM/s) and the concentration of benzaldehyde
accumulated after 6 hours of reaction time (CP6, μM) for the CHA oxidation of
net toluene by using complexes 100 μM of complexes 1 (■), 2 (▲), and 3 (●)
as catalysts in various reaction temperature.
The activation energy needed for the CHA oxidation of toluene
was so low that the reaction could take place at room
temperature and that the reaction rate could increase rapidly
when the reaction temperature was raised. Figure 8 shows the
reaction progress for the CHA oxidation of net toluene using 0.1
mM of complexes 1-3 as catalysts at various reaction
temperatures. At 100℃, the catalytic rates of complexes 1-3
were in the range of 1.04 and 3.44 μM s-1; the catalytic
frequencies (TOF) were 37.72, 53.35 and 123.77 Moltoluene
Molcatalyst-1 h-1, respectively; the concentration of the product after
6 hours of reaction time was 22.63, 32.01 and 74.26 mM,
respectively; and the turnover number (TON6) 226, 320 and 743
-1
Moltoluene Molcatalyst
,
respectively.
The data showed the
performance of complexes 1-3 to be much better than that of
previously reported catalytic CHA reactions.56
To investigate the influence of the concentration of the catalysts
on the CHA oxidation of toluene, complexes 1-3 were loaded to
the reaction system in various concentrations between 1.0×101
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10.1002/ejic.201601548
European Journal of Inorganic Chemistry
FULL PAPER
and 1.0×10-5 mM at a 100℃ reaction temperature. The results
are summarized in Figure 10.
processing time. These complexes are quite stable and can be
stored in air at room temperature for a year without obvious
decomposing. A theoretical study involving density functional
theory (DFT) was used to explore the relations between the
structure and characteristics of the molecules. The experimental
data, including X-ray analysis and X-Ray absorption near edge
structure (XANES) for the single crystal of the complexes,
revealed that the characteristics of the complexes were
governed by the properties of the C^N ligand. . A new kind of
catalytic system was discovered for the CHA of benzylic
compounds, and it is a green process, not requiring a base,
halogen or other sacrificial materials.
Cat.
10000
1000
100
1000
100
10
1
2
3
1
10
0.1
Experimental Section
10
1
0.1
0.01
1E-3
1E-4
1E-5
Conc. of catalyst (mM)
Materials and methods. All solvents were of analytical reagent grade
and purified according to the standard procedure, 3,5-Difluorobenzoic
acid was purchased from Matrix, and IrCl3.nH2O was from Seedchem Co.
All other chemicals including 2-phenylprydine were purchased from
Acros and used as received. NMR spectra were measured on a Bruker
AVIIIHD-600 MHz or a Mercury 300 MHz NMR spectrometer. UV-vis
spectra were obtained from Hitachi U-3900 Spectrophotometer. Infrared
spectra were recorded on Agilent Technologies Model Cary 630 FTIR
instruments. X-ray Absorption Near-Edge spectroscopy (XANES) were
measured on a X-ray absorption measurements of national synchrotron
radiation research center (NSRRC, Taiwan). A Si (111) double crystal
monochromator was employed for energy scanning. Fluorescence data
were obtained at room temperature using an Ar-filled ionization chamber
Figure 9 Catalytic frequencies (TOF) and turnover in 6 hours of processing
time (TON6) for the CHA oxidation of net toluene at 100℃ of reaction
temperature by using complexes 1 (■), 2 (●), and 3 (▲) as catalysts in various
concentrations between 1.0×101 and 1.0×10-5m M.
As Figure 9 shows, the TOF of the CHA oxidation for 1.0×10-5m
M of complexes 1-3 was 5.6×102, 7.6×102 and 4.0×103 Moltoluene
Molcatalyst h-1, respectively, and the TON6 3.4×103, 4.5×103 and
-1
2.40×104 Moltoluene Molcatalyst-1, respectively. These results were
quite good, with the data also showing these complexes to be
very active for CHA with an excellent reliability under processing
conditions. Furthermore, when complexes 1-3 were applied to
the reaction system in higher concentrations, the catalytic rates
of the CHA oxidation for toluene increased, but those of the TON
decreased, as a result of the recombination of the intermediates
(Ims) of complexes 1-3 with the N^O ligand to regenerate the
complexes. However, the recombination rate could be lowered
by tuning the structures of the C^N and N^O ligands and a much
higher throughput achieved.
detector, each sample was scanned
3 times for averaging. A
thermogravimetric analysis (TGA) technique was employed to study the
thermal stability of the samples. The experiments were performed with a
Perkin-Elmer thermal gravimetric analyzer. The samples were heated up
under nitrogen at a pressure of 1 atm with a heating rate of 10 oC min-1
and finished at 620 oC. Mass spectra were taken with a Finnigan/Thermo
Quest MAT 95XL instrument with electron impact ionization for organic
compounds or fast atom bombardment for metal complexes.
As we know, the synthesis of benzaldehyde and its derivatives
by oxidation of the corresponding toluenes is an important
Synthetic procedures
industrial process in pharmaceutical drug synthesis.
The
Synthesis Procedure for Ligands and Iridium Complexes. Ligands
traditional technologies for the production of benzaldehyde are
carried out with a stoichometric quantity of metal oxide, mineral
acid and other chemicals. 57 The catalytic system discovered
here would provide a green and environmentally friendly process
for the production of benzaldehyde and its derivatives..
including
difluorophenyl)benzoxazole (dfpbo) (L3) were prepared by Philips’
condensation described on our previously reported procedure. The
cyclometalated Ir(III) chloro-bridged dimers having a general formula
(C^N)2Ir(μ-Cl2)Ir(C^N)2 (D1−D3) were synthesized by the method also
showed on our previous reports.58,59
2-phenylbenzoxazole
(L2),
and
2-(3.5-
Synthesis of bis[2-phenylpyridinato -N,C2’]iridium(III) (picolinato)
[Ir(pp)2(pic)] (1). A flask was charged with 0.2g (0.18 mmol) of D1,
0.05g (4 mmol) of picolinic acid, 0.07g (0.81 mmol) of sodium
bicarbonate, and 15 ml of ethoxyethanol . The solution was stirred under
N2 and warmed to 130 ℃. After 1.5 hr, the solution was cooled to room
temperature; the reaction mixture was purified by column
chromatography on silica gel with dichloromethane/n-hexane as eluent.
The yield of complex 1 was 0.1827 g (79%) as yellow crystals. H NMR
(300 MHz, CDCl3, 298 K; δ (ppm)): 8.77 (d, J=5.4Hz, 1H), 8.31 (d,
J=7.5Hz, 1H), 7.81−7.88 (m, 3H), 7.66−7.76 (m, 3H), 7.58 (t, J=8.1,
8.7Hz, 2H), 7.44 (d, J=5.4Hz, 1H), 7.31 (t, J=6.6, 6.3Hz, 1H), 7.11 (t,
J=6.6, 6.3Hz, 1H), 6.70−6.94 (m, 5H), 6.39 (d, J=7Hz, 1H), 6.17 (d,
J=7.5Hz, 1H). 13C NMR (75 MHz, CDCl3, 298 K; δ (ppm)): 169.4, 167.8,
152.4, 149.2, 144.1, 137.2, 132.7, 130.1, 129.7, 128.4, 124.5, 122.2,
Conclusions
In summary, three types of cyclometalated iridium (III) complex
composed of various cyclometalating ligand were synthesized
and fully characterized. All exhibited CHA activity for the
oxidation of toluene: the activation energy was very low,
between 14.4 and 25.5 kcal/mol; the turnover frequency was
quite high, in the range of 5.6×102 and 4.0×103 Moltoluene
-1
Molcatalyst h-1; and the turnover number was also high, between
3.3×104 and 2.4×104 Moltoluene Molcatalyst in the 6 hours of
-1
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10.1002/ejic.201601548
European Journal of Inorganic Chemistry
FULL PAPER
121.7, 121.2, 119.2, 118.6. Anal. Calcd for C28H20N3O2Ir (MW = 622.69):
C, 54.01; H, 3.24; N, 6.75. Found: C, 53.67; H, 3.29; N, 6.56 %. MS
(FAB; m/z): 623.1261
Theoretical Calculations. Theoretical calculations were performed with the
program package Gaussian 03 by using Becke’s three-parameter B3LYP
for C, H, F, and N, and the LANL2DZ basis set for the Ir element. Partial
charges were calculated according to the Mulliken, APT (atomic polar
tensors), and NPA (natural population analysis) approaches, respectively.
Synthesis of bis[2-phenylbenzoxazolato-N,C2’]iridium(III) (picolinato)
[Ir(pbo)2(pic)] (2). A flask was charged with 0.5g (0.4 mmol) of D2,
0.11g (0.89 mmol) of picolinic acid, 0.15g (1.79 mmol) of sodium
bicarbonate, and 15 ml of ethoxyethanol. The solution was stirred under
N2 and warmed to 130 ℃. After 2 hr, the solution was cooled to room
temperature, the reaction mixture was purified by column
chromatography on silica gel with dichloromethane/n-hexane as eluent.
The yield of complex 2 was 0.2953g (56%) as yellow crystals. 1H NMR
(300 MHz, CDCl3, 298 K; δ (ppm)): 8.26(d, J=7.8Hz, H), 7.89−8.00 (m,
3H), 7.59−7.74 (m, 4H), 7.33 (t, J=11.4, 7.8Hz H), 6.77−7.01 (m, 5H),
Acknowledgements
This work was supported by Ministry of Science and Technology
(Grant No. MOST 103-2113-M-153-001).We are grateful to Dr.
Jyh-Fu Lee from National Synchrotron Radiation Research
Center (NSRRC) for the X-ray absorption measurements.
6.68(d, J=7.5Hz, 1H), 6.46(d, J=7.8Hz, 1H), 5.64(d, J=8.1Hz, 1H). 13
C
NMR (75 MHz, CDCl3, 298 K; δ (ppm)): 178.5, 177.4, 173.5, 153.3, 150.3,
148.2, 146.7, 138.0, 134.4, 133.8, 132.4, 132.0, 130.0, 129.7, 127.9,
126.5, 126.2, 125.8, 122.1, 121.6, 117.8, 114.4, 112.2, 53.5. Anal.
Calcd for C32H20N3O4Ir·CH2Cl2 (MW = 787.68): C, 50.32; H, 2.82; N, 5.34.
Found: C, 49.94; H, 2.86; N, 5.41 %. MS (FAB; m/z): 702.1 (Calcd MW
of C32H20N3O4Ir is 702.74).
Keywords: Iridium complex • CHA •benzaldehyde •oxidative
addition•cyclometalated ligand
[1] Y. W. Chan and K. S. Chan, Organometallics, 2008, 27, 4625–4635.
[2] B. Z. Li, H. S. Fung, X. Song, and K. S. Chan, Organometallics,
2011, 30, 1984–1990.
Synthesis
of
bis[2-(3.5-difluorophenyl)benzoxazolato-
N,C2’]iridium(III) (picolinato) [Ir(dfpbo)2(pic)] (3). A flask was charged
with 3g (2.18 mmol) of D3, 0.59g (4.796 mmol) of picolinic acid, 0.8058g
(9.592 mmol) of sodium bicarbonate, and 50 ml of ethoxyethanol. The
solution was stirred under N2 and warmed to 110 ℃. After 24 hr, the
solution was cooled to room temperature; the reaction mixture was
purified by column chromatography on silica gel with dichloromethane/n-
hexane as eluent. The yield of complex 3 was 3.2125 g (95%) as yellow
[3] K. S. Chan, X. Z. Li, W. I. Dzik, and B. Bruin, J. Am. Chem. Soc.
2008, 130, 2051–2061.
[4] M. S. Eric and F. H. John, J. Am. Chem. Soc. 2010, 132, 17092-
17095.
[5] M. Wasa, K. M. Engle, D. W. Lin, E. J. Yoo and J.-Q. Yu, J. Am.
Chem. Soc. 2011, 133, 19598–19601.
[6] B. David, C. Eric, and E. Odile, Chem. Rev. 2010, 110, 749-823.
[7] A. E. Shilov and G. B. Shul’pin, Chem. Rev. 1997, 97, 2879-2932.
[8] R. G. Bergman, Science. 1984, 223, 902-908.
[9] W. D. Jones and F. J. Feher, Acc. Chem. Res. 1989, 22, 91-100.
[10] L. Ilies, S. Asako and E. Nakamura, J. Am. Chem. Soc. 2011, 133,
7672–7675.
1
crystals. H NMR (300 MHz, CDCl3, 298 K; δ (ppm)): 8.27 (d, J=1.5Hz,1
H), 8.07−7.95 (m, 3H), 7.60 (t, J=8.7, 7.5Hz 2H), 7.56−7.49 (m, 1H),
7.45−7.30 (m, 5H), 6.99 (t, J=8.1, 8.1Hz 1H), 6.44−6.72 (m, 2H) , 5.53 (d,
J=8.1Hz, 1H). 13C NMR (75 MHz, CDCl3, 298 K; δ (ppm)): 173.7, 171.2,
168.1, 165.0, 153.0, 150.3, 149.9, 138.8, 138.5, 133.6, 128.3, 126.9,
126.0, 118.0, 114.6, 112.4, 111.6, 109.2, 107.6. Anal. Calcd for
C32H16N3O4F4Ir (MW = 775.07): C, 49.59; H, 2.08; N, 5.42. Found: C,
49.99; H, 2.58; N, 5.51 %. MS (FAB; m/z):775.0786
[11] J. Norinder, A. Matsumoto, N. Yoshikai and E. Nakamura, J. Am.
Chem. Soc. 2008, 130, 5858–5859.
[12] Y.-M. Lee, S. Hong, Y. Morimoto, W. Shin, S. Fukuzumi and W.
Nam, J. Am. Chem. Soc. 2010, 132, 10668–10670.
[13] B. Qian, S. Guo, J. Shao, Q. Zhu, L. Yang, C. Xia, and H. Huang, J.
Am. Chem. Soc. 2010, 132, 3650–3651.
Single Crystal X-ray Diffraction. All the crystals were obtained from a
mixed solution of dichloromethane and n-hexane. The diffraction data of
complexes 1-3 were collected on a Bruker SMART APEX CCD diffract
meter with graphite-monochromatized Mo Kα X-ray radiation (λ =
0.71073 Å) at 110 K. All the calculations for the structure determination
were carried out using SHELXS-97 package. The positions of the heavy
atoms, including the iridium atoms were located by the direct method.
The remaining atoms were found in a series of alternating difference
Fourier maps and least-square refinement. The crystallographic data for
all the structures reported here have been deposited in the Cambridge
Data Centre as supplementary publication numbers CCDC # 1491980,
953384 and 953385, respectively.
[14] R. Giri, Y. Lan, P. Liu, K. N. Houk and J.-Q. Yu, J. Am. Chem. Soc.
2012, 134, 14118–14126.
[15] B. Xiao, T.-J. Gong, Z.-J. Liu, J.-H. Liu, D.-F. Luo, J. Xu and L. Liu, J.
Am. Chem. Soc. 2011, 133, 9250–9253.
[16] Z. Chai and Rainey, T. J. J. Am. Chem. Soc. 2012, 134, 3615–3618.
[17] Y.-S. Lin, H. Misawa, J. Yamada and K. Matsumoto, J. Am. Chem.
Soc. 2001, 123, 569–575.
[18] A. F. Heyduk, J. A. Labinger and J. E. Bercaw, J. Am. Chem. Soc.
2003, 125, 6366–6367.
[19] A. F. Heyduk, T. G. Driver, J. A. Labinger and J. E. Bercaw, J. Am.
Chem. Soc. 2004, 126, 15034–15035.
[20] J. S. Owen, J. A. Labinger and J. E. Bercaw, J. Am. Chem. Soc.
2006, 128, 2005–2016.
Catalytic activity of catalysts. The reaction solution was stirred well under
air, and the reaction temperature was well controlled in a silicon oil bath
under constant temperature (±1℃). To evaluate the catalytic activity of
complexes 1-3, oxidation of toluene was done by the following procedure.
In round bottomed flasks, the toluene solution containing complexes 1-3
with various concentration between 1x10-8 and 1x10-2 M were prepared,
and the reaction temperature was gradually increased to 100 °C and kept
constant during the oxidation experiments. During the reactions, the
mixtures have been continually sampling, and the concentrations of
reactant and product were monitored with an instrument of the high
performance liquid chromatography (HPLC)..
[21] J. Oxgaard and W. A. Goddard, J. Am. Chem. Soc. 2004, 126, 442–
443.
[22] C. S. Yi, and S. Y. Yun, J. Am. Chem. Soc. 2005, 127, 17000–
17006.
[23] E. F. Flegeau, C. Bruneau and P. H. Dixneuf, J. Am. Chem. Soc.
2011, 133, 10161–10170.
[24] H. F. T. Klare, M. Oestreich, J.-I. Ito, H. Nishiyama, Y. Ohki and K.
Tatsumi, J. Am. Chem. Soc. 2011, 133, 3312–3315.
[25] A. M. Dreis and C. J. Douglas, J. Am. Chem. Soc. 2009, 131, 412–
413.
This article is protected by copyright. All rights reserved.

10.1002/ejic.201601548
European Journal of Inorganic Chemistry
FULL PAPER
[26] A. J. Vetter, R. D. Rieth, W. W. Brennessel and W. D. Jones, J. Am.
Chem. Soc. 2009, 131, 10742–10752.
[48] T.-R. Chen, J. Organomet. Chem. 2008, 693, 3117-3130.
[49] a) E. Rogers, D. S. Silvester, D. L. Poole, L. Aldous, C. Hardacre
and R. G. Compton, J. Phys. Chem. C, 2008, 112, 2729-2735; b) S.
M. Feldt, U. B. Cappel, E. M. J. Johansson, G. Boschloo and A.
Hagfeldt, J. Phys. Chem. C, 2010, 114, 10551-10558.
[27] M. E. Evans, C. L. Burke, S. Yaibuathes, E. Clot, O. Eisenstein and
W. D. Jones, J. Am. Chem. Soc. 2009, 131, 13464–13473
[28] T. K. Hyster and T. Rovis, J. Am. Chem. Soc. 2010, 132, 10565–
10569.
[50] W. Hong, B. Sun, H. Aziz, W.-T. Park, Y.-Y. Noh and Y. Li Chem.
Commun. 2012,48, 8413-8415.
[29] H Mizuno, J. Takaya and N. Iwasawa, J. Am. Chem. Soc. 2011, 133,
1251–1253.
[51] DFT (B3LYP/LANL2DZ level) calculation: Frisch, M. J.; Trucks, G.
W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.;
Montgomery, J. A.; Vreven, Jr. T.; Kudin, K. N.; Burant, J. C.; Millam,
J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi,
M.; Scalmani, G.; Rega, N.; Petersson,G. A.; Nakatsuji, H.; Hada,
M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.;
Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox,
J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.;
Omperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.;
Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G.
A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.;
Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A.
D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul,
A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; G. Liu; Liashenko,
A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-
Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill,
P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople,
[30] H. Hata, H. Shinokubo and A. Osuka, J. Am. Chem. Soc. 2005, 127,
8264–8265.
[31] E. Ben-Ari, G. Leitus, L. J. W. Shimon and D. Milstein, J. Am. Chem.
Soc. 2006, 128, 15390–15391.
[32] D. L. Davies, S. M. A. Donald, O. Al-Duaij, S. A. Macgregor and M.
Pölleth, J. Am. Chem. Soc. 2006, 128, 4210–4211.
[33] M. Feller, A. Karton, G. Leitus, J. M. L. Martin and D. Milstein, J. Am.
Chem. Soc. 2006, 128, 12400–12401.
[34] M. T. Whited and R. H. Grubbs, J. Am. Chem. Soc. 2008, 130,
16476–16477.
[35] P. Burger and R. G. Bergman, J. Am. Chem. Soc., 1993, 115,
10462–10463.
[36] G. Bhalla, X. Y. Liu, J. Oxgaard, W. A. Goddard and R. A. Periana,
J. Am. Chem. Soc. 2005, 127, 11372–11389.
[37] S. R. Klei, T. D. Tilley and R. G. Bergman, J. Am. Chem. Soc. 2000
122, 1816–1817.
,
[38] X. Chu, M. Guan, L. Niu, Y. Zeng, Y. Li, Y. Zhang, Z. Zhu and B.
Wang, ACS Appl. Mater. Interfaces, 2014, 6, 19011–19016.
[39] D. Liu, H. Ren, L. Deng and T. Zhang, ACS Appl. Mater. Interfaces,
2013, 5, 4937–4944.
A. Gaussian 03, Revision B.04, Gaussian, Inc: Pittsburgh PA, 2003.
[52] Y. Dai, Y.-G. Wang, J. Geng, Y.-X. Peng and W. Huang Dalton
Trans. 2014, 43, 13883-13891.
[53] J, A, Labinger and J. E. Bercaw, Nature 2002, 417, 507-514
[54] V. Ritleng, C. Sirlin, and M. Pfeffer, Chem. Rev. 2002, 102, 1731-
1770
[40] Q. Zhao, M. Yu, L. Shi, S. Liu, C. Li, M. Shi, Z. Zhou, C. Huang and
F. Li Organometallics, 2010, 29, 1085–1091.
[41] Y. Wu, H. Jing, Z. Dong, Q. Zhao, H. Wu and F. Li, Inorg. Chem.,
2011, 50, 7412–7420.
[55] F. Li, K. K. Meier, M. A. Cranswick, M. Chakrabarti, K. M. V.
Heuvelen, E. Münck, and L. Q. Jr. J. Am. Chem. Soc., 2011, 133),
7256–7259
[42] M. Gennari, F. Légalité, L. Zhang, Y. Pellegrin, E. Blart, J. Fortage,
A. M. Brown, A. Deronzier, M.-N. Collomb, M. Boujtita, D.
Jacquemin, L. Hammarström and F. Odobel, J. Phys. Chem. Lett.,
2014, 5, 2254–2258.
[56] a) K. M. Steven, J. H. Y. Kenneth, H. E. Daniel, J. T. William, O.
Jonas, A. G. William and A. P. Roy, Organometallics 2009, 28,
5293-5304; b) W. Junmei and I. Enrique, J. Phys. Chem. B, 2004
,
[43] G. L. Schulz and S. Holdcroft, Chem. Mater., 2008
,
20, 5351–5355.
108, 4094-4103; c) E. Olga, D. A. S. Sebastian, R. Alisa, J. P. W.
Andrew and R. C. Mark, Organometallics, 2014, 33 ., 7027-7030.
[57] G. Eyal and A. Ibrahim, Synth. Commun. 1995, 25, 3149-3154;
Patent US613460; Patent US698355; Patent US780404.
[58] H.-P. Lee, Y.-F. Hsu, T.-R. Chen, J.-D. Chen, K. H.-C. Chen and J.-
C. Wang, Inorg. Chem. 2009, 48, 1263-1265.
[44] J.-G. Cai, Z.-T. Yu, Y.-J. Yuan, F. Li and Z.-G. Zou, ACS Catal.,
2014, 4, 1953–1963.
[45] S. M. Barrett, S. A. Slattery and A. J. M. Miller, ACS Catal., 2015, 5,
6320–6327.
[46] T.-R. Chen, H.-P. Lee, J.-D. Chen and K. H.-C. Chen, Dalton Trans.
2010, 39, 9458-9461.
[59] T.-R. Chen, H.-P. Lee and J.-D. Chen, Inorg. Chem. 2011, 50,
3645-3650.
[47] T.-R Chen, F. -S. Wu, H.-P. Lee and K. H.-C. Chen, J. Am. Chem.
Soc. 2016, 138, 3643–3646.
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Entry for the Table of Contents
FULL PAPER
Cyclometalated Iridium(III) Complexes
were designed and synthesized. All
of them exhibited excellent ability for
catalytic CHA oxidation of toluene by
a green process with a quite low
activation energy and pretty good
reliability.
CHA Functionalization
Tsun-Ren Chen*, Pei-Chun Liu, Hsiu-
Pen Lee, Fang-Siou Wu, and Kelvin H.-
C. Chen
Page No. – Page No.
Cyclometalated Iridium(III)
Complexes with Ligand Effect on
Catalytic Carbon-Hydrogen Bond
Activation of Toluene in High-
Performance
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