Functionalized α-keto stabilized sulfonium ylides as highly active ligand precursors for palladium catalyzed Suzuki-Miyaura cross-couplings

Article abstract of DOI:10.1016/j.inoche.2014.07.027

Five α-keto stabilized sulfonium ylides as type (Me) ₂SCHC(O)C₆H₄-p-X (X = H, Br, NO₂, CH₃ and OCH₃) {L₁-L₅} were used as ligand precursors in the Suzuki-Miyaura cross-coupling reaction. The best catalytic performance was obtained by using a sulfonium ylide/Pd ratio of 2:1. The catalytic systems displayed high activities, which increased in the order R = NO₂ (L₃) < Br (L₂) < H (L₁) < CH₃ (L₄) < OCH₃ (L₅). The coupling reactions proceeded smoothly with 0.05 mol% PdCl₂ and 0.1 mol% L₅ in DMF at 130 °C between varieties of electronically activated, deactivated and neutral aryl halides and aryl boronic acids within short reaction times and without the need for exclusion of air which gave good to high yields of the corresponding products. All the studied ligands demonstrated very high activity in the Suzuki-Miyaura cross-coupling, which yielded turnover numbers up to 1940. Comparative studies showed that the performance of sulfonium ylide L₅ is significantly superior to that of related phosphine-free ligands.

Full text of DOI:10.1016/j.inoche.2014.07.027

Inorganic Chemistry Communications 47 (2014) 123–127
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Functionalized α-keto stabilized sulfonium ylides as highly active ligand
precursors for palladium catalyzed Suzuki–Miyaura cross-couplings
Seyyed Javad Sabounchei ⁎, Ali Hashemi
Faculty of Chemistry, Bu-Ali Sina University, Hamedan, 65174, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Five α-keto stabilized sulfonium ylides as type (Me) SCHC(O)C H -p-X (X = H, Br, NO , CH and OCH ) {L –L }
were used as ligand precursors in the Suzuki–Miyaura cross-coupling reaction. The best catalytic performance
was obtained by using a sulfonium ylide/Pd ratio of 2:1. The catalytic systems displayed high activities, which in-
2
6
4
2
3
3
1
5
Received 16 March 2014
Received in revised form 2 July 2014
Accepted 21 July 2014
creased in the order R = NO
2
3 2 1 3 4 3 5
(L ) b Br (L ) b H (L ) b CH (L ) b OCH (L ). The coupling reactions proceeded
Available online 22 July 2014
smoothly with 0.05 mol% PdCl
2
and 0.1 mol% L
5
in DMF at 130 °C between varieties of electronically activated,
deactivated and neutral aryl halides and aryl boronic acids within short reaction times and without the need
for exclusion of air which gave good to high yields of the corresponding products. All the studied ligands demon-
strated very high activity in the Suzuki–Miyaura cross-coupling, which yielded turnover numbers up to 1940.
Keywords:
Sulfonium ylide
Palladium catalyzed
Phosphine free
Comparative studies showed that the performance of sulfonium ylide L
5
is significantly superior to that of related
Suzuki–Miyaura reaction
phosphine-free ligands.
©
2014 Published by Elsevier B.V.
Palladium-catalyzed Suzuki cross-coupling reaction of aryl halides
with aryl boronic acids is a powerful method for the formation of C\C
bonds and generation of unsymmetrical biaryls [1–3]. Among the com-
mon protocols, aryl iodides and bromides have been found to be the
more reactive than aryl chlorides [4,5]. However, more economic aryl
chlorides have been partly employed in cross-coupling reactions [6,7].
On the other hand, wide varieties of aryl boronic acids with various sub-
stituents were used to the synthesis of a desired biphenyl product [8,9].
The traditional Suzuki reaction proceeds using a palladium complex
with a ligand (usually a phosphine) [10–12] and there has been much
recent attention attracted on employing new catalysts that are environ-
mentally benign and efficient [13]. Also, it is a well-known fact that in
Suzuki reactions, the activity of the catalyst depends on the nature of
the ligand structure attached to the Pd metal [14]. Bulky electron-rich
phosphine ligands are prominent in the palladium catalyzed Suzuki
cross-coupling reaction, resulting from their superior donor capability
and stabilization effects [15–17]. Though these catalysts exhibited ex-
cellent catalytic properties, most of them are sensitive to air and/or
moisture besides expensive and therefore require oxygen-free handling
to minimize ligand oxidation [18,19]. These drawbacks place a signifi-
cant limitation on their synthetic applications. In contrast, phosphine-
free ligands, containing N, O and S atoms, are typically inexpensive,
easily prepared and stable toward heat, moisture and air [20–24].
Therefore, these advantages encourage us to use sulfonium ylide as
ideal alternatives to tertiary phosphines in transition-metal based ho-
as ligands, because the carbanion located at the Cα of the ylide or the
enolate oxygen is able to donate electron density to a transition metal
[25–28]. Furthermore, the rich coordination modes of these ylides in
bonding and use of these compounds in organic and organometallic
reactions can provide a variety of information [29]. Thus, using a combi-
nation of ligands with metal precursors, providing in-situ formation of
catalytic species, has seemed to be not only practical but also more effi-
cient than the isolated ligand–metal complexes. In some cases, this fact
arises from the low efficiency of complexation stages and/or aiming to
operational simplicity. The recent review published by Kumar and
coworkers shows a comparative study on organosulfur and related li-
gands in the Suzuki–Miyaura C\C coupling reaction [30]. During the
last review reported in 2013, there has been no report on using of sulfo-
nium ylides as ligand precursor in the Suzuki–Miyaura coupling reac-
tion. Therefore, investigation of catalytic activity of α-keto stabilized
sulfonium ylides can establish a new field in organosulfur and related li-
gands used in catalytic systems. In this communication, we attempted
to use sulfonium ylides that we recently developed [31,32] accompa-
nied by Pd precursors in the Suzuki–Miyaura cross-coupling reaction
(Scheme 1).
As shown in Scheme 2, all sulfonium ylides were synthesized as
described previously [31]. At first, 1 equiv. of 2-bromoacetophenone,
2-bromo-4′-bromoacetophenone, 2-bromo-4′-methylacetophenone,
2-bromo-4′-methoxyacetophenone and 2-bromo-4′-nitroacetophenone
was reacted with 3 equiv. of dimethyl sulfide in acetone to form the
respective sulfonium salts. Subsequent treatment with aqueous 10%
mogeneous catalysts. Sulfonium ylides R
2
S = C(R′)CO(R″) can behave
NaOH solution led to eliminate HBr, giving the L
The catalytic activity of L –L in Suzuki cross-coupling reactions was
then examined. Initially, we carried out a model reaction to optimizing
1 5
–L ligands.
⁎
Corresponding author.
E-mail address: jsabounchei@yahoo.co.uk (S.J. Sabounchei).
1
5
http://dx.doi.org/10.1016/j.inoche.2014.07.027
387-7003/© 2014 Published by Elsevier B.V.
1

124
S.J. Sabounchei, A. Hashemi / Inorganic Chemistry Communications 47 (2014) 123–127
PdCl2, Ln, Base, Solvent
R
X
(HO)2B
R'
R
R'
+
O
S
Ln
R"
Scheme 1. Suzuki–Miyaura cross-coupling reaction using sulfonium ylide ligands.
1 5
Scheme 2. Synthetic route of ligands L –L .
the reaction conditions. Reaction of phenyl boronic acid with 4-
bromobenzene was chosen as a model reaction. At the first stage of
optimization, we studied the catalyst loading effect on the reaction at
four different catalyst concentrations. As expected, various catalyst
loadings showed a significant effect on the performance of the catalyst
to the result obtained in entry 5 and indicates that excess amount of
PdCl cannot significantly increase catalyst performance. Therefore it
seems that the complex coordination is 1:2 palladium to ligand
(Table 1, entry 2).
In the next step, we investigated the influence of various bases on
the Suzuki–Miyaura cross-coupling reaction. The organic and inorganic
bases were investigated, as shown in Table 1. Addition of proper bases
has a remarkable accelerating effect on the reaction time. Thus, we in-
vestigated a series of reactions to screening influence of base on the cat-
2
2
systems. When the loading of PdCl was reduced to 0.005 mol% from
0
.05 mol%, the yield of the corresponding product (or biphenyl) was
decreased (Table 1, entries 3 (50%) and 2 (75%)). Also, excessive amount
of catalyst did not increase the yields significantly (Table 1, entry 4).
Therefore, with respect to the economic aspect, low catalyst loading of
alytic system. Among the tested bases, Cs
base for the coupled product with 90% yield (Table 1, entry 9), while
other bases, such as K CO , Na CO and NaOAc proved to be less active
and gave lower yields (Table 1, entries 2 (75%), 10 (62%) and 11 (55%)).
Use of organic base Et N gave inferior result and showed slow reaction
2 3
CO was the most effective
0
.05 mol% was chosen as the best concentration of catalyst (Table 1,
entry 2).
We then examined the effect of the ligand:metal (L:M) mole ratio on
2
3
2
3
yield of reaction. The L:M mole ratio shows a dramatic influence on the
3
Suzuki reaction. When L:M mole ratio was changed to 1:1 (both at
rates compared to inorganic bases (Table 1, entry 12 (40%)).
0
.05 mol%), the yield was lowered to 42% (Table 1, entry 5). At the 1:4
palladium to ligand ratio, the yield was not significantly changed
Table 1, entry 7 (76%)). Also when no ligand was used, the yield was
Finally, the model reaction was carried out in the presence of differ-
ent solvents and temperatures. It was found that the polarity of the sol-
vent had a considerable effect. For instance, a non-polar solvent like
toluene and n-hexane gave poor yields (Table 1, entries 14 (51%) and
15 (44%)), whereas polar solvents such as DMF and NMP were the
most productive solvents and were more efficient for the yield of biaryl
compounds up to 80% (Table 1, entries 9 and 13). Other polar aprotic
(
greatly decreased and trace amount of biphenyl was formed (Table 1,
entry 6). This result shows that in the absence of ligand, catalysis of
the reaction encounters with uphill. Finally, at the 2:1 palladium to li-
gand ratio, the yield decreased to 45% (Table 1, entry 8), that it is similar
Table 1
a
Optimization of reaction conditions.
Entry
PdCl
2
mol%
PdCl
2
:L
Base
Solvent
Temperature
Yieldb
TONc
156
1500
10,000
80
1
2
3
4
5
6
7
8
9
0.5
0.05
0.005
1.0
1:2
1:2
1:2
1:2
1:1
1:0
1:4
2:1
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
K
K
K
K
K
K
K
K
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
3
3
3
3
3
3
3
3
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
130
130
130
130
130
130
130
130
130
130
130
130
130
100
60
78
75
50
80
42
Trace
76
45
80
62
55
40
75
51
44
62
67
56
67
74
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
840
0
1520
900
1600
1240
1100
800
1500
1000
880
1240
1340
1120
1340
1480
Cs
Na
NaOAc
NEt
2
CO
3
10
11
12
13
14
15
16
17
18
19
20
2
CO
3
3
Cs
Cs
Cs
Cs
Cs
Cs
Cs
Cs
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
3
3
3
3
3
3
3
3
NMP
Toluene
n-Hexane
Methanol
60
100
60
80
100
2
H O
DMF
DMF
DMF
a
b
c
2 1
Reaction conditions: bromobenzene (2.0 mmol), phenylboronic acid (2.4 mmol), PdCl , L , base (4.0 mmol), solvent (3 ml) and 2 h.
Isolated yield based on aryl halide.
Mole of product per mole of catalyst.

S.J. Sabounchei, A. Hashemi / Inorganic Chemistry Communications 47 (2014) 123–127
125
Table 2
a
Evaluation of catalytic activity of the ligands in Suzuki cross-coupling reaction.
Entry
Ligand
None
R
PdCl
2
mol%
PdCl
2
:L
Yieldb
TONc
1
2
3
4
5
6
–
0.05
0.05
0.05
0.05
0.05
0.05
1:2
1:2
1:2
1:2
1:1
1:2
Trace
80
73
70
81
0
1600
1460
1400
1620
1780
L
L
L
L
L
1
2
3
4
5
\H
\Br
\NO
\CH
\OCH
2
3
3
89
a
2 n 2 3
Reaction conditions: bromobenzene (2.0 mmol), phenylboronic acid (2.4 mmol), PdCl , L , Cs CO (4.0 mmol), DMF (3 ml) and 2 h.
Isolated yield based on aryl halide.
Mole of product per mole of catalyst.
b
c
solvents including methanol and water gave comparatively low yields
Table 1, entries 16 (62%) and 17 (67%)). Also, effect of temperature
of reactions by taking the model reaction in different ligands (see
Table 1).
(
on catalytic activity was investigated. Results showed that at a lower
temperature, the reaction was not completed and yield of product was
decreased (Table 1, entries 18 (56%), 19 (67%) and 20 (74%)). Best effi-
ciency was observed at reflux temperature (130 °C), so this tempera-
ture was chosen as the default reaction temperature.
1
Among the presented sulfonium ylides, ligand L has no any
electron-donating or electron-withdrawing substituent on benzene
ring and showed moderate efficiency and yielded the coupling product
at 80% (Table 2, entry 2). Substitution of electron withdrawing groups
such as \Br or \NO
2
in the benzene ring led to lower yields of 73%
After the optimization stage, we employed these reaction conditions
and 70% in L and L ligands (Table 2, entries 3 and 4). These results sug-
2
3
including Cs
2
CO
3
(1 mmol), 0.05 mol% of PdCl
2
, 0.1 mol% of ligand and 2
–L
gested that the decrease of the electron density on the donor atoms of
ligand plays an important role in the catalytic activity of ligands. On
ml DMF at reflux temperature to evaluate the catalytic activity of L
1
5
in the Suzuki cross-coupling reactions. To verify how the ligands would
3 3
the other hand, electron-donating groups such as \CH and \OCH , ac-
promote this coupling reaction most efficiently, we investigated a series
tivate the benzene ring and cause the increase in electron-donating
Table 3
a
Suzuki cross-coupling reaction of aryl halides with aryl boronic acids.
Entry
Ar–X
Ar′–B(OH)
2
Product (Ar–Ar′)
Yieldb
TONc
1
2
3
4
5
6
7
8
9
Ph–I
Ph–Br
Ph–Cl
p-Me–Ph–I
p-Me–Ph–Br
p-OHC–Ph–Br
p-OHC–Ph–Cl
p-CH
p-CH
Ph–B(OH)
Ph–B(OH)
Ph–B(OH)
Ph–B(OH)
Ph–B(OH)
Ph–B(OH)
Ph–B(OH)
Ph–B(OH)
Ph–B(OH)
Ph–B(OH)
Ph–B(OH)
Ph–B(OH)
Ph–B(OH)
p-Et–Ph–B(OH)
p-Et–Ph–B(OH)
p-Et–Ph–B(OH)
p-Et–Ph–B(OH)
p-Et–Ph–B(OH)
p-Et–Ph–B(OH)
p-Et–Ph–B(OH)
p-Et–Ph–B(OH)
p-Et–Ph–B(OH)
p-Et–Ph–B(OH)
p-Et–Ph–B(OH)
p-Et–Ph–B(OH)
p-Et–Ph–B(OH)
2
Ph–Ph
Ph–Ph
Ph–Ph
p-Me–Ph–Ph
p-Me–Ph–Ph
p-OHC–Ph–Ph
p-OHC–Ph–Ph
95
89
80
85
78
94
88
92
81
97
92
82
77
92
85
74
81
72
90
81
86
75
94
89
80
72
1900
1780
1600
1700
1560
1880
1760
1840
1620
1940
1840
1640
1540
1840
1700
1480
1620
1440
1800
1620
1720
1500
1880
1780
1600
1440
2
2
2
2
2
2
2
2
2
2
2
2
3
OC–Ph–Br
OC–Ph–Cl
N–Ph–Br
p-CH
p-CH
3
OC–Ph–Ph
OC–Ph–Ph
3
3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
p-O
2
2
p-O N–Ph–Ph
p-CH
p-CH
1-naphthyl–Br
Ph–I
Ph–Br
Ph–Cl
p-Me–Ph–I
p-Me–Ph–Br
p-OHC–Ph–Br
p-OHC–Ph–Cl
p-CH
p-CH
3
O–Ph–I
p-CH
p-CH
3
O–Ph–Ph
O–Ph–Ph
3
O–Ph–Br
3
10 7
C H –Ph
Ph–Ph–Et
Ph–Ph–Et
Ph–Ph–Et
p-Me–Ph–Ph–p-Et
p-Me–Ph–Ph–p-Et
p-OHC–Ph–Ph–p-Et
p-OHC–Ph–Ph–p-Et
2
2
2
2
2
2
2
2
2
2
2
2
2
3
OC–Ph–Br
OC–Ph–Cl
p-CH
p-CH
3
OC–Ph–Ph–p-Et
OC–Ph–Ph–p-Et
3
3
p-O
2
N–Ph–Br
2
p-O N–Ph–Ph–p-Et
p-CH
p-CH
1-naphthyl–Br
3
O–Ph–I
p-CH
p-CH
3
O–Ph–Ph–p-Et
O–Ph–Ph–p-Et
3
O–Ph–Br
3
C
10
7
H –Ph–p-Et
a
b
c
Reaction conditions: bromobenzene (2.0 mmol), phenylboronic acid (2.4 mmol), PdCl
Isolated yield based on aryl halide.
Mole of product per mole of catalyst.
2
(0.05 mol%), L
5
(0.1 mol%), Cs CO
2 3
(4.0 mmol), DMF (3 ml) and 2 h.

126
S.J. Sabounchei, A. Hashemi / Inorganic Chemistry Communications 47 (2014) 123–127
Table 4
Comparison with other catalytic systems.
Entry
Pd source
PdCl
Ligand
mol%
Condition
Yielda
TONb
Ref.
1
2
3
4
5
6
2
β-ketoamine
–
0.5
1.0
1.0
0.01
3
Na
2
CO
CO
3
, DMF, 60 °C, 6 h
67
24
69
12
94
56
67
74
80
134
24
69
1200
31
1120
1340
1480
1600
[24]
[33]
[34]
[35]
[9]
This work
Pd(OAc)
Pd(dba)
PdCl
Pd(OAc)
PdCl
2
Na
2
3
, PEG/DMF, 50 °C, 0.5 h
t
2
P,S-heterodonor
Benzimidazolium salt
1,4-Diaza-bicyclo-[2.2.2]octane
Sulfonium ylide
BuOK, DMF, 80 °C, 10 h
CO , DMF, 110 °C, 3 h
Na CO , DMF, 40 °C, 16 h
Cs CO , DMF, 60 °C, 2 h
0 °C
2
K
2
3
2
2
3
ꢀ
2
0.05
2
3
8
1
1
10 °C
30 °C
a
Isolated yield based on aryl halide.
Mole of product per mole of catalyst.
b
ability of both the carbanion and the enolate moieties of the ligand. The
systems have been reported to support Suzuki C\C coupling reactions,
phosphine free catalytic system of this sulfur ylide ligand is novel. A
comparison of catalytic efficiency among the most active in-situ Pd
complexes that catalyze the Suzuki cross coupling reaction under the
same conditions was also undertaken and presented in Table 4. Low cat-
alyst loading, high reactivity with bromobenzene in short reaction time
and stability toward air make it a superb complex for Suzuki cross-
coupling reactions.
conversion of the biphenyl product reached 81% and 89% for L
4
5
and L ,
respectively (Table 2, entries 5 and 6). Therefore, sulfonium ylide L
5
was chosen as proper ligand with high efficient activity toward the
Suzuki cross-coupling reaction.
Under optimized conditions, we examined the scope of the reaction
of phenyl boronic acid with various aryl halides bearing electron-
donating and electron-withdrawing groups in the presence of 0.05 mol%
of Pd catalyst to give Suzuki products in good to excellent yields. The results
are summarized in Table 3. Conversely, increasing electron density on the
aryl halides lowered the catalyst activity. That is, better yields are achieved
for aryl halides with electron-withdrawing rather than electron-
donating substituents. The electronic properties of aryl iodides did not
affect significantly the catalyst performance, so the reactions proceeded
very fast and resulted in excellent yields for both electron-deficient and
electron-rich aryl iodides (Table 3, entries 1 (95%), 11 (90%), 14 (92%)
and 24 (89%)). It was found that the cross-coupling reaction of aryl bo-
ronic acid with aryl bromides including electron-donating substituents
In summary, we have developed a novel protocol for Suzuki–
Miyaura cross-coupling reactions in a phosphine-free environment.
We have introduced basic new α-keto stabilized sulfonium ylide ligand
5
used in Suzuki–Miyaura reactions. Results showed that L , with an
electron-donating structure, was most efficient and enabled the cou-
pling of various aryl halides with aryl boronic acid in good to excellent
yields. The ease of preparation of the ylidic ligand, its high solubility
in organic solvents, very low catalyst loading and stability toward air
and moisture make it an ideal catalytic system for the Suzuki cross-
coupling reaction.
such as the \CH
3
3
and \OCH group and electron withdrawing
substituents such as the \NO
2
and \CHO group was transformed effi-
ciently to the biaryl products. The reaction of electronically neutral
bromobenzene with boronic acid derivatives showed good yields
Appendix A. Supplementary material
Materials, physical measurements and selected 13C and 1H NMR
spectra of some compounds can be found in the online version, at
http://dx.doi.org/10.1016/j.inoche.2014.07.027.
(
Table 3, entries 2 (89%) and 15 (85%)). In electron rich or deactivated
p-bromotoluene and p-bromoanisole, the reaction gave yields around
0% and this indicated that the coupling was sensitive to the electron
8
density on the aryl halides due to the methyl and methoxy groups, re-
spectively (Table 3, entries 4 (85%), 12 (82%), 17 (81%) and 25 (89%)).
As expected, coupling reaction of the electron-poor or activated 4-
bromobenzaldehyde and 4-bromonitrobenzene with aryl boronic acids
leads to relatively excellent yields (Table 3, entries 6 (94%), 10 (97%),
References
[
[
[
1] A. Suzuki, Organoborates in new synthetic reactions, Acc. Chem. Res. 15 (1982)
78–184.
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4759–4763.
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reactions of primary alkyltrifluoroborates with aryl chlorides, J. Org. Chem. 74
1
1
9 (90%) and 23 (94%)). To extend the scope of our work, we
next investigated the coupling of various electron rich and defi-
cient aryl chloride substrates coupled to organoboron compounds.
While aryl bromides or iodides react readily, less expensive aryl
chlorides are inert and have slower reaction rate due to the
stronger C\Cl bond. Aryl chlorides with electron withdrawing
substituents (Table 3, entries 7, 9. 20 and 22) react more easily
than aryl chlorides with electron donating groups (Table 3, en-
tries 5 and 18). For instance, the \CHO substituted chloroben-
zene showed moderate reactivity with 88% and 81% yields
(2009) 3626–3631.
[4] Y. Harrak, M. Romero, P. Constans, M.D. Pujol, Preparation of diarylamines and
arylhydrazines using palladium catalysts, Lett. Org. Chem. 3 (2006) 29–34.
[
5] S. Zhang, X. Zeng, Z. Wei, D. Zhao, T. Kang, W. Zhang, M. Yan, M. Luo, Desulfitative
Suzuki cross-couplings of arylsulfonyl chlorides and boronic acids catalyzed by a re-
cyclable polymer-supported N-heterocyclic carbene-palladium complex catalyst,
Synlett 12 (2006) 1891–1894.
[
6] C. Song, Y. Ma, Q. Chai, C. Ma, W. Jiang, M.B. Andru, Palladium catalyzed Suzuki–
Miyaura coupling with aryl chlorides using a bulky phenanthryl N-heterocyclic
carbene ligand, Tetrahedron 61 (2005) 7438–7446.
(
3
Table 3, entries 7 and 20), while for the \CH substituted chlo-
robenzene yields reduce (Table 3, entries 5 (78%) and 18 (72%)).
Overall, the observed catalytic efficiency of these ligands in the
2
presence of PdCl was proven to be remarkably high and the Suzuki
corresponding products were obtained with reasonable yields in most
reactions. Also, results indicate that this catalytic system can be compa-
rable to those found in the literature for similar palladium (II)-catalyzed
Suzuki coupling reactions. Although several in-situ generated catalyst
[7] A. Furstner, A. Leitner, General and user-friendly method for Suzuki reactions with
aryl chlorides, Synlett 2 (2001) 290–292.
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