Synthesis and catalytic applications of palladium N-heterocyclic carbene complexes as efficient pre-catalysts for Suzuki-Miyaura and Sonogashira coupling reactions

Article abstract of DOI:10.1039/c7nj00488e

A new palladium complex series with N-heterocyclic carbene (NHC), pyridine and phosphine ligands, PdCl₂(L)NHC (2a-c)(L = NHC), PdCl₂(L¹)NHC(3a-c)(L¹ = pyridine), PdCl₂(L²)NHC(4a-c)(L² = triphenylphosphine) was synthesised and fully characterized. The catalytic activities of these complexes were screened for the Sonogashira and Suzuki-Miyaura reactions between arylhalides and phenylacetylene, and phenylboronic acid, respectively. The results pointed out that the carbene/phosphine complexes 4a-c exhibited excellent catalytic activities as compared to 2a-c, 3a-c, and the well-known systems for the palladium-catalysed Sonogashira reaction. The reactivity of 4a-c in these preliminary Sonogashira coupling tests seems to be higher than that of previously reported catalytic systems based on Pd(NHC) moieties. These new palladium NHC complexes are among the first reported palladium catalysts that are efficient for catalysing the Sonogashira reaction from arylchloride substrates.

Full text of DOI:10.1039/c7nj00488e

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
rsc.li/njc

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Synthesis and catalytic applications of palladium N-heterocyclic
carbene complexes: As efficient pre-catalyst for Suzuki Miyaura
and Sonogashira coupling reactions
Received 00th January 20xx,
Accepted 00th January 20xx
a,b
a†
c
c
c
b
a
DOI: 10.1039/x0xx00000x
Lamia Boubakri, Sedat Yaşar, V. Dorcet, T. Roisnel, C.Bruneau, N. Hamdi, and İ. Ozdemir,
www.rsc.org/
A new palladium complex series with N-heterocyclic carbene (NHC), pyridine and phosphine ligands, (PdCl
2
(L)NHC (2a-
1
1
2
2
c)(L=NHC), (PdCl (L )NHC(3a-c)(L =pyridine), (PdCl (L )NHC(4a-c)(L =triphenylphosphine), were synthesised and fully
2
2
characterized. The catalytic activities of these complexes were screened for the Sonogashira and Suzuki-Miyaura reactions
between arylhalides and phenylacetylene, and phenylboronic acid, respectively. The results pointed out that
carbene/phosphine complexes, 4a-c exhibited excellent catalytic activities as compared to 2a-c, 3a-c, and the well-known
systems for palladium-catalysed Sonogashira reaction. The reactivity of 4a-c in these preliminary Sonogashira coupling
tests seems higher than that of previously reported catalytic systems based on Pd(NHC) moities. These new palladium NHC
complexes are among the first reported palladium catalysts that are efficient to catalyse the Sonogashira reaction from
arylchloride
substrates.
Introduction
catalyse system has unique advantages and disadvantages.
N-heterocyclic carbenes (NHCs) and phosphines have been among Homogeneous catalyze system is suffer from high cost, low
the most remarkable ligands for homogeneous catalysis with efficiency in separation of product and low recycling of catalyst.
1
transition metals towards medical applications and industry. The However, heterogeneous catalyze offer efficiently recycle and easy
use of different metal complexes have led to important innovation product separation in the reaction mixture with a decrease reaction
2
30c
30d
in homogeneous catalysis. With these developments, numerous rate or diffuse difficulty of reagents to catalyst. Homogeneous
3
4
5
6
7
8
9
10
metal-NHC derivatives including Ag, Co, Fe, Cu, Ni, Ru, Ir, Rh,
palladium-NHC complex catalyzed Suzuki-Miyaura cross-coupling
and Pd complexes have been prepared. Although there are reaction is one of the most powerfull and widely used reaction for
35
1
1
3
1
32
33
34
numerous metal-carbene complexes, the prominence of Pd-NHC the C-C bond formation. Nolan, Organ, Song, Mandal, Fu,
3
6
37
38
complexes is likely due to their catalytic efficiency and robustness Ying, Thiel and Lee have achieved significicant improvements
against air, moisture and high temperature. The basis of this in Suzuki-Miyaura reaction. In recent studies, Pd-NHC complexes
interest lies in the facile modulation of electronic and steric have revealed good activity in the difficult Suzuki coupling reaction
31-42
parameters reflected by a strong σ-donor and weak π-acceptor of arylchlorides under mild conditions.
ability and the ease of adjusting the steric effects of NHCs by The Sonogashira reaction is an another important cross-coupling
variation of nitrogen atom substituent. Complex bearing sterically reaction to produce valuable compounds by coupling terminal
4
3
bulky and electron-rich ligands exhibit enhanced catalytic activity in alkyne derivatives and arylhalides. Palladium complexes and
oxidative addition, and reductive elimination reactions that are key copper(I) salts still represent the most preferred catalysts
1
2-17
elemental steps of many catalytic reactions.
features have contributed to make them indispensable ligands for catalytic combinations based on phosphine-containing catalysts was
These unique combination for Sonogashira reaction. One limitation of the early
1
8-30
44,45
transition metals in homogeneous and heterogeneous catalysis.
The cross-coupling reactions were successfully performed under different applications.
homogeneous and heterogeneous catalyse conditions. This two still needed to achieve the Sonogashira coupling reaction with low
the sensitivity to air,
but modified protocols were developed for
Efficient, stable palladium catalysts are
4
6,47
3
0
4
8,49
catalyst loading under copper-free conditions.
In order to improve catalytic activity, we turned our attention to
new Pd(NHC)(L)Cl (L=NHC, pyridine, PPh ) palladium complexes and
2
3
investigated their catalytic performance as catalysts in Sonogashira
and Suzuki-Miyaura coupling reactions at low catalyst loading.
Results and discussion
Materials and methods
Electronic Supplementary Information (ESI) available: X-ray crystallographic data and
Benzimidazole-based NHC palladium complexes PdCl
c)(L=NHC) and (PdCl (L1)(NHC)(3a-c)(L1= pyridine) were prepared in
very good yields (80-90%) in one step from PdCl and
2
(L)(NHC)(2a-
refinement parameters and CIF for the 3b and 4b. CCDC 1525626 and 1525627 See
DOI: 10.1039/x0xx00000x
2
2
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benzimidazolium salts in the presence of K CO as a base (Scheme The straight forward reaction of 1a-c with PdCl and K CO in THF
2
3
2
2
3
2 2
1). Importantly, the benzimidazolium halides 1a-c, the NHC afforded the bis(NHC)palladium complexes Pd(NHC) Cl (2a-c) in up
precursors, were easily obtained in 86-90% yield according to to 90% yield. PEPPSI complexes 3a-c (PEPPSI= pyridine-enhanced
reported methods, and their spectroscopic features were consistent precatalyst preparation, stabilisation, and initiation) were
50-52
with the literature data.
synthesized according to the method reported by Organ (Scheme
3
2
1
2
): the reaction of NHC precursors 1a-c with PdCl in pyridine at
Scheme 1 Synthesis pathway for palladium complexes 2a-4c
o
8
0 C in the presence of K
2
CO
3
afforded the palladium complexes 27.1, 27.4 and 26.5 ppm for 4a, 4b and 4c, respectively confirmed
3a-c in 80, 89 and 82% yield, respectively. The addition of 1 eq. of the substitutions of the pyridine by the triphenylphosphineligand.
PPh
3
to a solution of 3a-c in acetone afforded the PdCl (PPh )(NHC)
2
3
complexes 4a-c in 81-88 % yield in two steps. All these complexes Structural characterization of 3b and 4b
were purified by column chromatography on silica using Crystals of 3b and 4b suitable for X-ray crystallography were
1
dichloromethane as eluent, and characterized by H and C NMR, grown in a dichloromethane solution layered with diethyl
13
and HR-MS spectroscopy, elemental analysis, and X-ray single ether. The molecular structures of 3b and 4b were supported
crystal diffraction for complexes 3b and 4b. NCHN proton signals of by X-ray diffraction analysis. Details of data are given in the
1
1
a-c at low field disappeared in the H NMR spectra for 2a-c, and supporting information section. The ORTEP ellipsoid plot at
a-c, which indicated that the formation of the NHC complexes took 50% probability of the molecular structure of 3b and 4b are
3
place. Characteristic pyridine hydrogen signals disappeared in the shown in Figs. 1 and 2.
H NMR spectra of complexes 4a-c due to substitution of pyridine
1
1
3
1
by triphenylphosphine ligand. Also, in C { H} NMR, an important Suzuki-Miyaura cross-coupling reaction
down field shift of the NCN carbon from 1a-c to 2a-c was observed. To study the efficiency of the novel palladium-NHC complexes 2a,
1
3
1
Indeed, the C { H} N-C-N signals of 1a, 1b and 1c, which are 3a
respectively equal to 140.5, 137.9 and 141.4 ppm were shifted to 4-chloroacetophenone and phenylboronic acid were selected as
80.9, 181.0 and 181.5 ppm, respectively, in 2a, 2b and 2c. model substrates. The palladium complexes were associated with
and
4a
in
Suzuki-Miyaura
coupling
reactions,
1
1
3
1
ο
Similarly, the C { H} N-C-N signals of 3a-c were observed at 161.9, different bases and solvents at 80 C with reaction times limited to
61.3 and 163.7 ppm, respectively, whereas in the case of 4a-c, the 3 h in order to discriminate the most reactive catalysts and find the
corresponding signals appeared at 172.5, 171.5, and 173.8 ppm, efficient catalytic systems (Table 1).
1
3
1
respectively. Observation of the phosphorus atoms by P NMR at The catalytic systems exhibited different reactivity depending not
only on the palladium precursor but also on the nature of the base
2
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2 3
and the solvent. With K CO or t-BuOK as a base, DMF/water (1:1) difficult to active catalyst and led to low yield. The same behaviour
mixture was a good solvent for the Suzuki reaction in the presence was observed starting from chlorobenzene (Table 2, entry 9).
of the pyridine-containing palladium complex 3a (Table 1, entries 5,
6
), whereas much better activities were obtained in toluene with
complexes 2a and 4a using t-BuOK as a base (Table 1). The low
catalyst concentration causes to decrease the activity and the
amount of product increases with the extended reaction time(table
1
, entries 10-15). With the complex 4a, low yield were obtained in
the DMF/water mixture, which might be attributed to the low
solubility of 4a due to containing triphenylphosphine ligand.
These results reveal that the base/solvent combination selection for
this catalytic system was a key parameter and should be made
according to the structural diversity of the complexes. However, in
toluene, it was possible to reach high solubility and high conversion
whatever the catalyst precursor.
Fig. 2 The molecular structure of 4b showing the atom
numbering scheme. Selected bond lengths [Å]: Pd1-C1
=
=
1.984(2), Pd1-P1 = 2.2572(6), Pd1-Cl1 = 2.3418(6), Pd1-Cl2

2.3515(6), N1-C1 = 1.347(3). Selected bond angles [ ]: C1-
Pd1-P1= 92.95(7), C1-Pd1-Cl1= 175.86(6),P1-Pd1-Cl1=
6.79(2), C1-Pd1-Cl2= 87.93(7), P1-Pd1-Cl2= 177.27(2), Cl1-
Pd1-Cl2 =92.52(2),N2-C1-N1=108.17(18), N2-C1-Pd1=
23.85(16), N1-C1-Pd1= 127.96(17)
8
1
a
Fig. 1 The molecular structure of 3b showing the atom
numbering scheme. Selected bond lengths [Å]: Pd1-C7 =
Table 1. Condition optimization with 4-chloroacetophenone
1.9590(19), Pd1- N1 =2.1546(16), Pd1-Cl1 = 2.3005(5), Pd1-Cl2
=
bond angles [ ]: C7- Pd1- N1 = 177.34(7), C7-Pd1-Cl1 =
85.76(6), N1-Pd1-Cl1 = 92.77(5), N11-C7-N31 = 108.09(16),
N11-C7-Pd1 = 127.26(14),N31-C7-Pd1 = 124.56(14).
2.3099(5), C7-N11 = 1.346(2), C7-N31 = 1.352(2). Selected
o
b
Entry
Complex
2a
Base
Solvent
Yield(%)
1
2
3
4
5
6
7
8
t-BuOK
Toluene
88
K2CO
3
DMF/H O(1:1)
2
12
With the optimized reaction conditions, the reaction scope was
investigated with electron-rich and electron-deficient aryl chloride
and bromide substrates. As shown in Table 2, a very wide range of
substituents on the chloride and bromide substrates were tolerated
by the catalytic system. With all palladium precursors, bromides
substrates were efficiently coupled with phenylboronic acid with
high yields (Table 2, entry 2,4,6,8). As expected, the aryl bromides
substituted by an electron-withdrawing group (MeCO- or HCO –
entries 2 and 4) in para-position were more reactive than those
substituted by an electron-donating group (MeO- or Me – entries 6
and 8). Starting from aryl chlorides, only the electron-deficient p-
chloroacetophenone provided excellent yields (77-91%) and
formation of the sole coupling product with all palladium catalysts.
p-Chlorobenzaldehyde was also a good partner using 2a-c and 3a-c
as catalyst, but no reaction occurred in the presence of 4a-c (Table
t-BuOK DMF/H
t-BuOK Toluene
CO
t-BuOK DMF/H
2
O(1:1)
Trace
84
3a
4a
K
2
3
DMF/H
2
O(1:1)
O(1:1)
83
2
84
t-BuOK
Toluene
77
K2CO
3
DMF/H O(1:1)
2
Trace
nr
9
2
t-BuOK DMF/H O(1:1)
c
1
1
1
0
1
2
2a
3a
4a
2a
3a
4a
t-BuOK
t-BuOK
t-BuOK
t-BuOK
t-BuOK
t-BuOK
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
60
c
c
56
45
2
, entry 3). Starting from the electron-rich p-chloroanisole and
d
d
d
p-chlorotoluene, the reactions proved to be more difficult and
longer reactions time (12h) made possible the formation of the
coupling products in moderate yield in the presence of catalytic
amounts of 2a-c and 3a-c (Table 2, entries 5, 7). On the other hand
complexes 4a-c were not active in these Suzuki coupling reactions.
This may be due to the structure of the catalyst and the location of
1
1
3
98
4
98
15
93
a
Reaction conditions : Phenylboronic acid (0.75 mmol), aryl halide (0.5
mmol), catalyst (0.25 mol%), base (1 mmol), solvent (6 ml), 80 °C, 3h.
b
c
the triphenylphosphine ligand in the -cis position to the carbene GC yield against calibrated internal standart (undecane)
ligand. This can make the oxidative addition of the substrate mol%) catalyst (0.125 mol%), 80 °C, 8h. nr: No reaction.
.
catalyst (0.125
d
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were not poisoned by pyridinic substrates when heterocyclic halide
Finally, with the different types of palladium complexes featuring at substrates were used. Thus, complete yields were obtained starting
least one NHC, with an additional pyridine or phosphine ligands, we from 2,6-dibromopyridine in the presence of 0.25 mol% of catalysts
observed that palladium N-heterocyclic complexes (2a-c) and 2 and 3 with high diarylated product selectivity (Table 3, entry 1).
PEPPSI complexes (3a-c) were more active than the mixed With catalysts 4a-c, the efficiency and selectivity towards diarylated
phosphine/N-heterocyclic carbene palladium complexes (4a-c). products were much lower. Using 2-chloropyridine substrate even
Also, these lower catalyst performances of 4a-c might be attributed with longer reaction time, low yields were performed by all
3
to stronger σ-donor and π-acceptor properties of PPh ligand which catalysts (Table 3, entry 2).
located at –cis position to NHC. Moreover, the catalytic systems
a
Table 2. Suzuki coupling reaction with various aryl chlorides and bromides
b
Entry
Substrate
X
[catalyst]/ yield (%)
2
a
2b
2c
3a
3b
3c
4a
4b
4c
1
2
3
4
5
6
7
8
Cl
Br
Cl
88
94
89
95
95
94
95
96
98
94
94
96
84
93
80
88
86
91
90
92
89
95
89
95
77
91
nr
90
89
91
90
nr
nr
Br
Cl
97
96
97
d
d
d
d
d
d
d
d
d
12
65
56
72
68
71
39
93
11
85
14
86
Trace
80
Trace
72
Trace
85
c
Br
Cl
d
20
d
d
d
d
d
d
d
d
31
93
50
96
24
92
39
94
41
93
nr
nr
nr
c
Br
70
57
79
81
d
59
d
d
72
d
d
d
d
d
d
9
Cl
71
61
71
71
nr
nr
nr
a
b
Reaction conditions : Phenylboronic acid (0.75 mmol), aryl halide (0.5 mmol), catalyst (0.25 mol%), t-BuOK (1 mmol), toluene (6 ml), 80°C, 3h.
c
d
GC yield against calibrated internal standart (undecane). nr: no reaction. 6 h. 12h.
There is a lot of data in the literature for Suzuki coupling reactions increased electron richness of 2a, which facilitates the oxidative
catalysed by Pd(NHC)-derived complexes in a variety of different addition step. Also, in each series, complexes 2b and 2c on one
3
9-52
experimental conditions.
With respect to the related Organ’s hand, and complexes 3b and 3c on the other hand are more active
K (1.0 than the corresponding complexes 2a and 3a. This could be due to
system ((Pd-PEPPSI:2 mol%, chloroanisole (1 mmol), PhBF
3
o
32
mmol), 60 C, 24h, MeOH) in the Suzuki-Miyaura reaction, our the higher steric pressure imposed by two penta methyl-substituted
results show that complexes 2a-c and 3a-c exhibit modorate benzylic groups as compared to 3,5-dimethyl substituents on the
activity. When the catalytic activities of 2a-c and 3a-c were benzylic groups of 2a and 3a, which is known to facilitate the final
5
2-55
compared among themselves, complex 2a gave slightly better reductive elimination step.
results in each case with different substrates. This performance can considered, with respect to the related literature in the Suzuki-
be attributed to the Miyaura cross-coupling reaction, our catalyse system exhibit better
When the catalyst concentration is
3
4
35
36
38
activity than Mandal, Fu, Ying, Lee studies and worst activity
3
1
33
37
than Nolan, Song, , Thiel studies.
a
Table 3. Suzuki coupling reaction with 2,6-dibromopyridine and 2-chloropyridine
b
Entry
Substrate
[Cat.]/ (M/D) Yield ratio
2
a
2b
2c
3a
3b
3c
0/91
4a
4b
4c
1
29/54
10/81
13/75
0/90
0/92
19/10
14/23
15/19
4
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c
8
c
33
c
c
c
c
2
26
47
54
51
Trace
Trace
Trace
a
b
Reaction conditions : Phenylboronic acid (0.75 mmol), heteroaryl halide (0.5 mmol), catalyst (0.25 mol%), t-BuOK (1 mmol), toluene (6 ml), 80 °C, 6h. GC
c
yield against calibrated internal standart (undecane). 12h.
Sonogashira coupling reaction
amount of the phosphine-containing complex 4b (Table 4).
CO , Cs CO , t-BuOK with DMF as solvent were suitable
bases to achieve the Sonogashira coupling at 100 C for 3 h
with yield higher than 62% (Table 4, entry 1-3). Protic solvents
such as water and ethanol or organic bases led to poor
conversions. By contrast and unexpectedly, the other
K
2
3
2
3
Several palladium–NHC complexes have been tested as catalysts for
o
56
Sonogashira coupling reaction, but these complexes have not
performed a satisfactory high reactivity except with reactive aryl
iodides under copper-free conditions. Copper salts are used as co-
catalyst in the Sonogashira reaction, although it makes the
Sonogashira process air sensitive and promotes Glaser-Hay coupling
palladium NHC complexes 2a
activity in the Sonogashira
p-bromoacetopheneone and phenylacetylene (Table 4, entry
3-15). A blank experiment revealed that in the absence of
,
2c and 3a did not show any
57
reaction involving
of the alkyne product. Despite this disadvantage, copper salts in
the presence of a base have been used extensively for the
formation of Cu-alkynyl species that transmetallate to palladium in
the catalytic cycle. In line with these observations, we tested our
new palladium NHC complexes as catalyst in the copper-free
Sonogashira coupling of aryl bromides and chlorides with terminal
1
palladium catalyst no reaction took place even in the presence
of CuI (2 mol%). We also investigated the effect of CuI as a co-
catalyst, and no positive contribution of CuI as co-catalyst was
observed in the Sonogashira reaction catalysed by 4b (Table 4,
entry 3, 10). In the presence of catalysts 4a and 4b, the
reaction times could be reduced to 1 h without deleterious
effects on the conversions (Table 4, entries 11, 12).
5
8
alkynes.
Table 4. Optimization of the solvent and base for the
Sonogashira coupling of p-bromoanisole with phenylacetylene
a
After optimisation, DMF was selected as solvent and t-
BuOK as base to evaluate the scope of the reaction with 1
mol% of palladium (NHC) complexes. Under these conditions,
mixed phosphine/N-heterocyclic carbene palladium complexes
4
a-c were found to efficiently convert activated and
b
Entry
Catalyst
4b
Base
CO
CO
Solvent
DMF
Yield (%)
unactivated aryl bromides and phenylacetylene into the
corresponding internal alkynes within one hour (Table 5,
entries 1-7). These results with catalysts 4a-c are among the
best results reported to date for Sonogashira reaction. With
these encouraging results in hands, we explored the catalysts
activities with more electron-donating or more sterically
demanding aryl bromide substrates. Good to excellent
conversions were obtained with the more electron-donating or
more sterically hindered methyl and methoxy-substituted aryl
bromide substrates under the selected reaction catalyzed by
1
2
3
4
5
6
7
8
K
2
3
62
80
91
53
51
0
4b
Cs
2
3
DMF
4b
t-BuOK
t-BuOK
t-BuOK
DMF
4b
DMF/H
2
O
4b
Toluene
4b
K
2
CO
CO
NEt
3
EtOH/H
EtOH/H
DMF
2
2
O
O
4b after 6h (Table 5, entries 8-14). Efficient double coupling
4b
Cs
2
3
20
trace
trace
59
91
81
0
was observed from 2,6-dibromopyridine in the presence of 4b
in 6h, indicating that the catalytic system was not poisoned by
pyridine substrates. As (pyridine)palladium complexes 3a-c are
not catalysts for the Sonogashira reaction, this result likely
shows that the phosphine ligand is not replaced by a pyridine
ligand during the catalytic cycle. When we explored the
reaction scope with aryl chloride, the situation was less
favourable than starting from aryl bromides (table 5, entry 16)
but the reaction could be efficiently achieved with the
activated 4-chloroacetophenone after prolonged reaction
time. In this case, complexes 4b and 4c performed convincing
activities after 24 h, which represents the best results shared
by all (NHC)Pd-based catalysts reported to date for the
Sonogashira reaction (Table 5, entries 17-21). As expected, in
4b
3
9
4b
Pyridine
t-BuOK
t-BuOK
t-BuOK
t-BuOK
t-BuOK
t-BuOK
DMSO
DMF
DMF
DMF
DMF
DMF
DMF
c
10
4b
d
1
1
2
4b
d
1
4a
1
3
2a
1
1
4
5
2c
0
3a
0
a
Reaction conditions : p-bromoanisole (0.6 mmol), phenylacetylene
o
1.2 mmol), catalyst (1 mol%), base (1.2 mmol), solvent (10 ml), 100 C,
(
3
b
h, under Argon, conversions were determined by GC. GC yield the presence of catalyst 4b, the more reactive iodoanisole
against calibrated internal standart (undecane) CuI (2 mol%) as co- provided a complete conversion within one hour (Table 5,
entry 22).
c
d
catalyst. 1 h.
In order to evaluate and compare the activities of our catalytic
5
9
systems, Biffis’s reaction conditions were initially selected for
the Sonogashira reaction. Preliminary results and optimization
were conducted starting from p-bromoanisole and a twofold
excess of phenylacetylene in the presence of a catalytic
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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DOI: 10.1039/C7NJ00488E
ARTICLE
Journal Name
from the palladium complex, which may be attributed to
excellent balance of strong σ-donation and π-acceptor
properties of NHC and PPh ligand, respectively, in complexes
Table 5. Sonogashira coupling of phenylacetylene with aryl halides
catalyzed by palladium complexes
a
3
4b-c. This superiority contributes positively to the activity of
these catalysts.
In summary, the reactivity of 4a-c in these preliminary
Sonogashira coupling tests seems higher than that of
previously reported catalytic systems based on Pd(NHC)
Entry
Ar-X
Catalyst
Time (h)
Yield
b
(
%)
56-59
moities.
Most importantly, these new (NHC) complexes
1
2
3
4a
4b
4b
0.25
0.25
1
55
are among the first reported palladium catalysts that are
efficient to catalyse the Sonogashira reaction from aryl
74
93
5
6-59
chloride substrates.
Further investigations in order to fine-
tune the characteristics of the ligands for Sonogashira reaction
with aryl chlorides are in progress.
4
5
4b
4a
1
1
48
92
Experimental
General considerations
All commercial chemicals were used as received. Unless stated
otherwise, all procedures were carried out under argon
atmosphere. All solvents were purified and dried by MBraun
SPS 800 solvent purification system. The melting points of the
complexes and NHC precursors were determined using Stuart
6
7
8
9
4a
4b
4a
4b
4c
1
1
6
6
6
92
93
69
90
88
1
13
automatic melting point apparatus (SMP-40). H, C NMR
6
3
spectra were recorded in CDCl or DMSO-d solutions operating
on a Bruker Advance II 300 and 400 MHz NMR spectrometer
and chemical shifts were reported relative to tetramethylsilane
1
13
10
11
12
for H, C NMR spectra as standard. Signals are quoted in parts
per million as δ downfield from tetramethyl silane (δ 0.00) as an
internal standard. Coupling constants (J values) are given in
hertz. NMR multiplicities are abbreviated as follows: s = singlet,
d = doublet, t = triplet, m = multiplet signal. All reactions were
monitored on a Shimadzu GC2010 Plus system by GC-FID with a
HP-5 column of 30 m length, 0.32 mm diameter and 0.25 μm
film thickness. Elemental analyses were performed by
ElementarVario EL III Carlo Erba 1108.
4a
4b
6
6
86
87
1
3
4
4b
6
89
1
,3-Bis-(3,5-dimethylbenzyl)-5,6-dimethylbenzimidazolium
bromide, 1a
1
4b
4b
6
6
91
80
o
1
o
m.p: 250.9 C.Yield: 86%. H NMR (300.1 MHz, CDCl
3
,25 C): δ=11.40
[
s, 1H, NCHN], 7.25[s, 2H, C H (CH ) -5,6], 6.96 [s, 4H,
6 2 3 2
CH
CH
CH
2
2
2
C
C
6
6
H
3
H
3
H
3
(CH
(CH
(CH
3
3
3
)
2
)
2
)
2
-3,5], 6.86[s, 2H, CH
-3,5], 2.26 [s, 6H, C
2
C
6
H
3
(CH
(CH
-3,5]. C NMR (75 MHz, CDCl ,25 C): δ=140.5, 138.0,
3
)
2
-3,5], 5.65 [s, 4H,
) -5,6], 2.19 [s, 12H,
3 2
c
1
5
6
H
2
1
3
o
C
6
3
1
1
36.4, 131.7, 129.7, 128.9, 124.6, 112.3, 50.1, 20.2,
9.7.Anal.Calcd.for C27 : C,69.97; H, 6.74; N, 6.04. Found: C,
1
6
7
4b
4b
6
24
66
H
31BrN
2
1
24
70.12; H, 6.88, N, 6.25.
18
4b
24
68
1
,3-Bis-(2,3,4,5,6-pentamethylbenzyl)-5,6-dimethylbenzimidazolium
chloride, 1b
1
9
0
4a
4b
24
24
9
o
1
o
m.p: 232.1 C. Yield: 90%. H NMR (300.1 MHz, D
2
O, 25 C): δ=not
2
55
observed due to substitued with doterium [s, 1H, NCHN], 7.60[s,
H, C (CH -5,6], 5.38 [s, 4H, CH (CH -2,3,4,5,6], 2.25 [s, 6H,
C H (CH ) -5,6], 1.89 [m, 30H, CH C (CH ) -2,3,4,5,6]. C NMR (75
2
6
H
2
3
)
2
2
C
6
3 5
)
1
3
2
1
2
4b
4b
24
1
61
89
6
2
3
2
2
6
3 5
o
MHz, D
9.6, 16.3, 15.9, 15.2.Anal.Calcd.for C33
N, 5.57. Found: C, 78.89; H, 8.79, N, 5.74.
2
O,25 C): δ=137.9, 133.9, 133.4, 130.6, 125.6, 112.7, 45.8,
1
H43ClN
2
: C, 78.77; H, 8.61;
2
a
Reaction conditions: aryl halide (0.6 mmol), phenylacetylene (1.2 mmol),
b
catalyst(1 mol%), t-BuOK (1.2 mmol), DMF (10 ml). GC yield against
calibrated internal standart (undecane)
1
,3-Bis-(2,3,4,5,6-pentamethylbenzyl)benzimidazolium chloride, 1c
c
2,6-dibromopyridine (0.6 mmol),
This known compound was synthesized according to literature
procedure and characterized by spectroscopic techniques. Results
are consistent with the literature.
phenylacetylene (2.4 mmol), t-BuOK (2.4 mmol), DMF (10 ml).
5
0
It is interesting to point out that the catalytic activity observed
with 4b-c appears to be due to facile reductive elimination
6
| J. Name., 2012, 00, 1-3
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NP lee wa s eJ od uo r nn oa tl aod fj uC s ht em ma ri sg it nr sy
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DOI: 10.1039/C7NJ00488E
Journal Name
ARTICLE
Preparation of the NHC-palladium complexes, (2a-c)
A Schlenk was charged with benzimidazole salts, 1a-c, (1 mmol),
125.4, 111.6, 53.2, 52.9, 52.6, 21.3, 20.3. Anal.Calcd.for
Cl Pd: C, 58.98; H, 5.11; N, 6.88. Found: C, 59.12; H, 5.26,
C
30
H
31
N
3
2
PdCl (0.5 mmol; 0.09g), K CO (0.6 g) and a stir bar under argon. N, 7.05.
2
2
3
Dry THF (25 ml) was then added as a solvent. The mixture was
heated under reflux for 24h. The reaction mixture was cooled at r.t Dichloro[1,3-bis-(2,3,4,5,6-pentamethylbenzyl)-5,6-
and the solvent was removed under vaccum. The residue was dimethylbenzimidazole-2-ylidene] pyridinepalladium(II), 3b
o
1
o
solved in DCM and purified by flash column, eluting with m.p: 262.4 C. Yield: 89%. H NMR (300.1 MHz, CDCl , 25 C): δ=8.87
3
DCM/hexane (8:2) until the product was completely recovered. [d, J=5.1 Hz, 2H, C H N], 7.77 [t, J=7.5 Hz, 1H,C H N], 7.34 [t, J=6.6
5
5
5 5
Solvents were removed under reduce pressure and the further Hz, 2H,C H N], 6.23 [s, 4H, CH C (CH ) -2,3,4,5,6], 6.15 [m, 2H,
5
5
2
6
3 5
purification was done using recrystallization (DCM-Hexane) or C H (CH ) -5,6], 2.34 and 2.25 [s, 30H,CH C (CH ) -2,3,4,5,6], 2.00
6
2
3
2
2
6
3 5
13
o
(DCM–ether) to get pure complexes for analysis and catalysis.
[s, 6H, C H (CH ) -5,6]. C NMR (75 MHz, CDCl , 25 C): δ=161.3,
6
2
3
2
3
1
51.1, 137.8, 135.6, 134.7, 133.6, 133.0, 131.2, 128.3, 124.2, 111.5,
Dibromodi-[1,3-bis-(3,5-dimethylbenzyl)-5,6-
50.9, 20.3, 17.5, 17.2, 16.9. Anal.Calcd.for C H Cl N Pd: C, 63.12;
3
8
47
2 3
dimethylbenzimidazole-2-ylidene]palladium(II), 2a
H, 6.55; N, 5.81. Found: C, 63.24; H, 6.67, N, 5.94.
o
1
o
m.p: 299.6 C. Yield: 85%. H NMR (300.1 MHz, CDCl
s, 4H, C (CH -5,6], 6.81[s, 8H, CH (CH
CH (CH -3,5], 5.76 [s, 8H, CH (CH -3,5], 2.20 [s, 12H, ylidene] pyridinepalladium(II), 3c
-5,6], 2.13 [s, 24H, CH -3,5]. C NMR (75 MHz, m.p: 332.5 C. Yield: 82%. H NMR (300.1 MHz, CDCl , 25 C): δ=8.84
3
, 25 C): δ=7.03
[
6
H
2
3
)
2
2
C
6
H
3
3 2
) -3,5], 6.73[s, 4H, Dichloro[1,3-bis-(2,3,4,5,6-pentamethylbenzyl)benzimidazole-2-
2
C
6
H
3
3
)
2
2
C
6
H
3
3 2
)
1
3
o
1
o
C
6
H
2
(CH
3
)
2
2
C
6
H
3
(CH
3 2
)
3
o
CDCl
25.4, 111.4, 52.2, 30.9, 21.1, 20.2. Anal.Calcd.for C50
7.76; H, 5.91; N, 6.32. Found: C, 67.88; H, 6.05, N, 6.52.
3
,25 C): δ=180.9, 137.9, 135.7, 133.4, 131.6, 129.1, 125.5, [d, J=4.8 Hz, 2H, C H N], 7.70 [t, J=7.5 Hz, 1H,C H N], 7.26 [t, J=7.5
5
5
5 5
1
6
H
52
N
4
Cl
2
Pd: C, Hz, 2H,C H N], 6.72 and 6.36 [dd, J= 3 Hz, 4H, C H ], 6.30 [s, 4H,
5
5
6 4
2 6 3 5 2 6 3 5
CH C (CH ) -2,3,4,5,6], 2.25, 2.24 and 2.16 [s, 30H,CH C (CH ) -
1
3
o
2
,3,4,5,6]. C NMR (75 MHz, CDCl , 25 C): δ=163.7, 151.1, 137.9,
3
Dichlorodi-[1,3-bis-(2,3,4,5,6-pentamethylbenzyl)-5,6-
dimethylbenzimidazole-2-ylidene]palladium(II), 2b
135.8, 135.0, 134.6, 133.0, 127.9, 124.3, 122.4, 111.2, 51.5, 17.5,
17.3, 16.9.Anal.Calcd.for C H Cl N Pd: C, 62.21; H, 6.24; N, 6.05.
3
6
43
2 3
o
1
o
m.p: 329.5 C. Yield: 90%. H NMR (300.1 MHz, CDCl
3
,, 25 C): δ=6.31 Found: C, 62.34; H, 6.38, N, 6.21.
[
s, 8H, CH C (CH ) -2,3,4,5,6], 6.06[s, 4H, C H (CH ) -5,6], 2.35 [s,
2
6
3
5
6
2
3 2
2
4H, CH
2
C
6
(CH ) -2,3,4,5,6], 2.19 [s, 12H, CH C (CH ) -2,3,4,5,6], Preparation of the NHC-palladium-triphenylphosphine complexes,
3 5 2 6 3 5
13
2.14 [s, 24H, CH C (CH ) -2,3,4,5,6], 1.83 [s, 12H, C H (CH ) -5,6]. C (4a-c)
2
6
3
5
6
2
3 2
o
NMR (75 MHz, CDCl
3
,25 C): δ=181.0, 135.3, 134.4, 133.6, 132.8, Under argon atmosphere, a Schlenk tube was charged with 3a
(2 mmol) and 30 mL of dry acetone. The reaction
130.5, 128.9, 112.0, 51.1, 20.3, 17.7, 17.1, 16.8.Anal.Calcd.for (1mmol), PPh
3
C
66
H
84Cl
2
N
4
Pd: C,71.48; H, 7.62; N, 5.04. Found: C, 71.48; H, 5.76, mixture was vigorous stirring for 1h at room temperature. All
volatiles were evaporated. Residue white solid was washed with
N, 5.30.
hexane (2x10 mL) and diethyl ether (2x10 mL).
Dichlorodi-[1,3-bis-(2,3,4,5,6-pentamethylbenzyl))benzimidazole-2-
ylidene] palladium(II), 2c
Dichloro[1,3-bis-(3,5-dimethylbenzyl)-5,6-dimethylbenzimidazole-2-
o
1
o
m.p: 320.6 C. Yield: 88%. H NMR (400.1 MHz, CDCl
[
3
, 25 C): δ=6.67 ylidene]triphenylphosphinepalladium(II), 4a
o
1
6
o
s, 4H, C H ], 6.39 [s, 8H, CH C (CH ) -2,3,4,5,6], 6.34 [s, 4H, C H ], m.p: 268.1 C. Yield: 81%. H NMR (300 MHz, DMSO-d , 25 C): δ=
6
4
2
6
3
5
6
4
2
.34 [s, 24H, CH
2
C
6
(CH
3
)
5
-2,3,4,5,6], 2.19 [s, 12H, CH
2
C
6
(CH
3
)
5
-
7.63-7.32 [m, 15H, PPh
3
2 6 3 3 2
], 7.21 [d, j=7.2 Hz, 4H, CH C H (CH ) -3,5],
13
2,3,4,5,6], 2.15 [s, 24H, CH C (CH ) -2,3,4,5,6]. C NMR (100 MHz, 6.89 [s, 2H, C H (CH ) -5,6], 6.68 [m, 2H, CH C H (CH ) -3,5], 6.08
2
6
3
5
6
2
3
2
2
6
3
3 2
o
CDCl
3
,25 C): δ=181.5, 134.5, 134.0, 133.3, 132.0, 128.0, 127.5, [m, 2H, CH
12H, CH
MHz, DMSO, 25 C): δ= 172.5, 137.3, 134.7, 134.4, 133.8, 131.1,
2
C
6
H
3
(CH
3
)
2
-3,5],5.0 [m, 2H, CH
2
C
(CH
6
H
3
(CH
3 2
) -3,5], 2.19 [s,
1
3
127.2, 121.0, 110.6, 50.4, 16.7, 16.1, 15.8.Anal.Calcd.for C62
H
76Cl
2
N
4
2
C
6
H
3
(CH -3,5], 2.08 [s, 6H, C
3
)
2
6
H
2
)
3
2
-5,6]. C NMR (75
o
Pd: C,71.26; H, 7.10; N, 5.19. Found: C, 71.34; H, 7.25, N, 5.34.
3
1
1
29.3, 128.5, 128.3, 125.8, 111.6, 54.9, 20.8, 19.7. P NMR (300
6
o
Preparation of the NHC-palladium-pyridine (PEPPSI) complexes, MHz, DMSO-d , 25 C): δ= 25.1 ppm. Anal.Calcd.for C H Cl N PPd:
4
5
45
2 2
(
3a-c)
In air, a pressure tube was charged with PdCl
NHC∙HCl (1.1mmol), K CO (700 mg, 5mmol) and 3 mL of pyridine. Dichloro[1,3-bis-(2,3,4,5,6-penthamethylbenzyl)-5,6-
The reaction mixture was heated with vigorous stirring for 7 h at dimethylbenzimidazole-2-ylidene]triphenylphosphinepalladium(II),
C, 65.74; H, 5.52; N, 3.41. Found: C, 65.82; H, 5.62;N, 3.64.
2
(180 mg, 1mmol),
2
3
o
80 Cthen cooled to room temperature and diluted with 4b
dichloromethane (DCM). A short silica column was used for The synthesis of 4b was performed following the same procedure
filtration. All volatiles were evaporated. Residue yellow solid was employed for the preparation of 4a, starting from 3b.
o
1
o
washed with hexane (2x10 mL) and diethyl ether (2x10 mL).
m.p: 295.1 C. Yield: 88%. H NMR (300 MHz, CDCl , 25 C): δ= 7.32
3
[
3 2 6 3 5
m, 15H, PPh ], 6.52 [d, j=14.4 Hz, 2H, CH C (CH ) -2,3,4,5,6], 5.40
Dichloro[1,3-bis-(3,5-dimethylbenzyl)-5,6-dimethylbenzimidazole-2- [s, 2H, C H (CH ) -5,6], 4.91 [d, j=14.4 Hz, 2H, CH C (CH ) -
6
2
3
2
2
6
3 5
ylidene]pyridinepalladium(II), 3a
2 6 3 5
2,3,4,5,6], 2.20 [s, 6H, CH C (CH ) -2,3,4,5,6], 2.11 [s, 12 H,
o
1
o
m.p: 226.8 C. Yield: 80%. H NMR (300.1 MHz, CDCl
m, 2H, C N], 7.65 [m, 1H,C N], 7.18 [m, 6H, C
N and CH (CH -3,5], 6.84 [m, 4H, CH
.00[m, 4H, CH (CH -3,5], 2.23 [s, 12H,CH
3
, 25 C): δ= 8.90 CH C (CH ) -2,3,4,5,6], 1.91 [s, 12 H, CH C (CH ) -2,3,4,5,6], 1.71 [s,
2
6
3
5
2
6
3 5
1
3
o
[
5
H
5
5
H
5
6
H
2
(CH
3
)
2
-5,6 and 6 H, C H (CH ) -5,6]. C NMR (75 MHz, CDCl , 25 C): δ= 171.5,
6
2
3
2
3
C
5
H
5
2
C
6
H
3
3
)
2
2
2
C
6
C
6
H
3
(CH
3
)
2
-3,5], 136.1, 134.6, 133.8, 132.9, 131.5, 128.6, 128.5, 127.2, 111.5, 51.3,
3
1
o
6
2
1
1
2
C
6
H
3
3
)
2
H
3
(CH
3
)
2
-3,5], 20.3, 17.3, 17.2, 16.8. P NMR (600 MHz, CDCl , 25 C): δ= 27.05
3
1
3
o
.12 [s, 6H, C H (CH ) -5,6]. C NMR (75 MHz, CDCl ,25 C): δ=161.9, ppm. Anal.Calcd.for C H Cl N PPd: C, 67.59; H, 6.34; N, 3.09.
52.6, 152.1, 151.3,138.3, 138.0, 137.9, 137.8, 135.3, 135.2, 135.1, Found: C, 67.71; H, 6.46,N, 3.24.
33.5, 133.3, 133.2, 132.3, 132.2, 132.1, 129.6, 125.8, 125.7, 125.6,
6
2
3
2
3
51 57
2 2
This journal is © The Royal Society of Chemistry 20xx
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DOI: 10.1039/C7NJ00488E
ARTICLE
Journal Name
Dichloro[1,3-bis-(2,3,4,5,6-penthamethylbenzyl)benzimidazole-2-
ylidene]triphenylphosphinepalladium(II), 4c
and S. P. Nolan, Organometallics, 2005, 24, 6301-6309. (b) J.
Ramirez, R. Corberan, M. Sanau, E. Peris and E. Fernandez,
Chem. Comm, 2005, 24, 3056-3058. (c) R. A. Haque, S. Y. Choo,
S. Budagumpi, A. A. A. Abdullah, M. B. K. Ahamed and A. M. S.
Abdul, Inorg. Chim. Acta, 2015, 433, 35-44.
The synthesis of 4c was performed following the same procedure
employed for the preparation of 4a, starting from 3c.
o
1
o
m.p: 297.5 C. Yield: 83%. H NMR (300 MHz, CDCl
3
, 25 C): δ= 7.98-
7
5
2
.32 [m, 15H, PPh
.78 [dd, j=3.3 Hz, 2H, C
,3,4,5,6], 2.20 [s, 6H, CH
(CH -2,3,4,5,6], 1.92 [s, 12 H, CH
NMR (75 MHz, CDCl , 25 C): δ= 173.8, 136.3, 135.2, 134.4, 133.1,
3
], 6.55 [m, 4H, C
], 5.01 [d, j=14.4 Hz, 2H, CH
(CH -2,3,4,5,6], 2.11 [s, 12 H,
6
H
4
and CH
2
C
6
(CH
3
)
5
-2,3,4,5,6],
4
5
(a) C. B. Hansen, R. F. Jordan and G. L. Hillhouse, Inorg.
Chem, 2015, 54, 4603-4610. (b) J. Sun, C. Ou, C. Wang, M.
Uchiyama and L. Deng, Organometallics, 2015, 34, 1546-1551.
(a) J. M. S. Cardoso, R. Lopes and B. Royo, J. Org. Chem. 2015,
775, 173-177. (b) C. M. Manna, H. Z. Li, B. Kaplan and J. A. Byers,
Polyhedron, 2014, 84, 160-167.
G. Zhang, R. Lang, W. Wang, H. Lv, L. Zhao, C. Xia and F. F. Li,
Adv. Synth.Catal, 2015, 357, 917-922.
(a) S. Wang, F. Ren, Y. Qiu and M. Luo, J. Org. Chem, 2015,
6
H
4
2
C
6
(CH
3 5
) -
2
C
6
3 5
)
1
3
CH
2
C
6
3
)
5
2
C
6
(CH
3
)
5
-2,3,4,5,6].
C
o
3
3
1
128.7, 128.5, 126.9, 122.4, 111.3, 51.6, 17.3, 17.2, 16.9. P NMR
o
(600 MHz, CDCl
3
,
25 C): δ= 27.00 ppm. Anal.Calcd.for
6
7
C
49 2 2
H53Cl N PPd: C, 67.01; H, 6.08; N, 3.19. Found: C, 67.15; H,
6.19,N, 3.38.
7
88, 27-32. (b) H. Ohta, N. Miyoshi, Y. Sakata, Y. Okamoto, M.
General procedure for Suzuki-Miyaura Reaction
In air, 2a-e (1.0 mmol %), aryl chloride (1.0 mmol), phenylboronic
acid (1.5 mmol), K CO (2 mmol), and 3 mL of 1:1 mixture of
2 3
Hayashi and Y. Watanabe, Tetrahedron Lett., 2015, 56, 2910-
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2304.
water/DMF were added to a small round bottom flask and the
o
mixture was heated at 80 C for 3 h. The reaction mixture was
8
9
2
cooled to room temperature and extracted with Et O. Extract was
filtered through a pad of silica with copious washing of diethyl
ether. The purity of the compounds was checked by GC using
internal standart undecane). The yields are based on aryl chloride.
General Procedure for Sonogashira Cross-Coupling Reaction
Under argon atmosphere, palladium catalyst (1.0 mmol %), aryl
(a) C. Vicent, M. Viciano, E. Mas-Marza, M. Sanau and E. Peris,
Organometallics, 2006, 25, 3713-3720. (b) B. Raible, V. Gierz
and D. Kunz, Organometallics, 2015, 34, 2018-2027.
halide (1.0 mmol), phenylacetilene (1.5 mmol), K
2 3
CO (2 mmol), and
1
0 mL of DMF were added to a small round bottom flask and the
o
mixture was heated at 100 C for 3 h. The reaction mixture was 10 L. Palacios, A. DiGiuseppe, R. Castarlenas, F. J. Lahoz, J. J. Perez
cooled to room temperature and extracted with Et O. Extract was
and L. A. Oro, Dalton Trans, 2015, 44, 5777-5789.
filtered through a pad of silica with copious washing of diethyl 11 (a) T. E. Schmid, D. C. Jones, O. Songis, O. Diebolt, M. R. L.
2
ether. The purity of the compounds was checked by GC using
Furst, A. M. Z. Slavin and C. S. J. Cazin, Dalton Trans, 2013, 42,
7345-7353. (b) A. E. Wang, J. H. Xie, L. X. Wang and Q. L. Zhou,
Tetrahedron, 2005, 61, 259-266.
internal standart undecane). The yields are based on aryl halide
.
1
1
2 S. Çekirdek, S. Yaşar and İ. Özdemir, Appl. Organometal. Chem,
Conclusions
2
014, 28, 423-431.
3 A. F. Littke and G. C. Fu, Angew. Chem. Int. Ed, 2002, 41, 4176-
211.
In conclusion, we have synthesized a new series of benzimidazole-
based palladium NHC complexes. These palladium(II) complexes
have been employed as precatalysts in Suzuki-Miyaura and
Sonogashira cross-coupling reactions. Suzuki coupling reaction of
electronically poor aryl chlorides and all types of aryl bromides
were catalysed by 2a-c and 3a-c complexes in moderate to excellent
yields. For the Sonogashira coupling reaction, only complexes 4a-c
show productive catalytic activity, and most importantly they
display very interesting activities from aryl chlorides.
4
1
1
4 J. F. Hartwig, Synlett, 2006, 1283-1294.
5 E. A. B. Kantchev, J. O’Brien and M. G. Organ, Angew. Chem. Int.
Ed, 2007, 46, 2768-2813.
6 G. C. Fu, Acc. Chem. Res, 2008, 41, 1555-1564.
7 M. G. Organ, G. A. Chass, D. C. Fang, A. C. Hopkinson and C.
Valente, Synthesis, 2008, 2776-2797.
1
1
1
1
8 N. Marion and S. P. Nolan, Acc. Chem. Res, 2008, 41, 1440-1449.
9 E. Peris and R. H. Crabtree, Coord. Chem. Rev, 2004, 248, 2239-
In these coupling reactions, we believe that the bulky and electron-
donor NHC ligands associated with pyridine in complexes 3 and
triphenylphosphine in complexes 4 provide the synergetic steric
and electronic effects to confer the metal center the appropriate
properties to make the elemental steps of the catalytic cycles
optimum.
2
246.
2
2
0 W. A. Herrmann, K. Öfele, D. V. Preysing and K. S.Schneider, J.
Organomet. Chem, 2003, 687, 229-248.
1 F. E. Hahn and M. C. Jahnke, Angew. Chem. Int. Ed, 2008, 47,
3
122-3172.
Acknowledgements
This work was financially supported by İnönü University
Research Fund (BAP:2016-195)
2
2
2 F. Glorius, Springer Verlag, Berlin, Germany, 2007.
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74-883.
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5 G. D. Frey, J. Schutz, E. Herdtweck and W. A. Herrmann,
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