Convenient and efficient Suzuki-Miyaura cross-coupling reactions catalyzed by palladium complexes containing N,N,O-tridentate ligands

Article abstract of DOI:10.1016/j.tet.2009.02.017

N,N,O-Tridentate ligands 1-9 were prepared from the condensation of amines with nine aromatic aldehydes or ketones. These ligands are thermally stable and neither air- nor moisture-sensitive. Combination of either 2-methoxy-6-[(pyridine-2-ylmethylimino)-m

Full text of DOI:10.1016/j.tet.2009.02.017

Tetrahedron 65 (2009) 2889–2897
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Convenient and efficient Suzuki–Miyaura cross-coupling reactions catalyzed
by palladium complexes containing N,N,O-tridentate ligands
*
Siddappa A. Patil, Chia-Ming Weng, Po-Cheng Huang, Fung-E Hong
Department of Chemistry, National Chung Hsing University, Taichung 40227, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
N,N,O-Tridentate ligands 1–9 were prepared from the condensation of amines with nine aromatic
aldehydes or ketones. These ligands are thermally stable and neither air- nor moisture-sensitive.
Combination of either 2-methoxy-6-[(pyridine-2-ylmethylimino)-methyl]-phenol, 1 or 2-(benzothiazol-
2-yl-hydrazonomethyl)-4,6-di-tert-butyl-phenol, 6 with Pd(OAc)2 furnished an excellent catalyst pre-
cursor for the Suzuki–Miyaura cross-coupling of various aryl bromides with arylboronic acids. The effects
of varying solvents, bases, and ligand/palladium ratios on the performance of the coupling reaction were
investigated. The molecular structures of both free ligand 1 and its palladium acetate complex 10 were
determined by single-crystal X-ray diffraction methods. The DFT studies revealed that the catalytic
performance of palladium complexes involving this type of a ligand may differ greatly upon a small
variation in its structure.
Received 14 October 2008
Received in revised form 23 January 2009
Accepted 6 February 2009
Available online 11 February 2009
Keywords:
N,N,O-Tridentate ligand
Suzuki–Miyaura cross-coupling reaction
Palladium complex
DFT methods
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
The object of this study was finding a versatile, robust, and easy-
to-prepare catalyst system suitable for a wide range of C–C bond-
The ligand assisted palladium-catalyzed cross-coupling re-
actions are probably among the most frequently employed methods
of carbon–carbon bond formation in organic synthesis. They have
been applied to the synthesis of many organic compounds, espe-
cially those of complex natural products, supramolecular chemistry,
and engineering materials such as conducting polymers, molecular
wires, and liquid crystals.1 The ligand choice is known to be crucial
to the success of a catalytic reaction.2 Therefore, tremendous efforts
have been dedicated to the search for more efficient and affordable
ligands. As a result, the design of novel ligands and transition metal
catalysts capable of carrying out desired transformations with both
high efficiency and high selectivity has become a fertile area of re-
search.3 Until now, phosphine-based ligands have remained to be
the most popular selection in the palladium-catalyzed cross-cou-
pling reactions.4,1b However, these ligands usually need to be han-
dled under inert atmosphere or dry conditions. In addition, they
sometimes suffer from significant P–C bond degradation at elevated
temperatures, which leads to palladium aggregation and eventually
affects the overall catalytic performance.5 Recent application of
phosphine-free ligands, such as N-heterocyclic carbenes, imines,
oxime palladacycles, and diazabutadienes to metal-catalyzed syn-
thetic transformations has opened new opportunities in catalysis.6
forming processes. Therefore, the initial step was the selection of
a potential catalyst class of ligands amenable to systematic struc-
tural and electronic variation. One of the appealing features of
imine ligands is that both their steric and electronic properties may
be tuned in a synthetically straightforward manner by variation of
the corresponding aldehyde/ketone precursors.7 The extraordinary
thermal stability, insensitivity to both oxygen and moisture as well
as ready availability and low cost of aromatic imines prompted us to
study their effectiveness as ligands in palladium-catalyzed C–C
bond-forming reactions and in Suzuki–Miyaura cross-coupling re-
action, in particular.
2. Results and discussion
2.1. Preparations of N,N,O-tridentate ligands 1–9 and 1-
chelated palladium complex 10
All the nine N,N,O-tridentate ligands, 1–9, were prepared from
the condensation of amines with corresponding aldehydes/ketones
in methanol/ethanol as solvent.8 They were characterized by
spectroscopic methods such as 1H, 13C NMR as well as mass spec-
trometry (Fig. 1). Furthermore, the structure of ligand 1 was also
verified by single-crystal X-ray diffraction method (Fig. 2).9
The preparation of 1-chelated palladium complex 10 was ach-
ieved via the reaction of ligand 1 with one molar equivalent of
Pd(OAc)2 in THF. The formation of this palladium complex was
confirmed by spectroscopic methods as well as single-crystal X-ray
* Corresponding author. Fax: þ886 4 22862547.
E-mail address: fehong@dragon.nchu.edu.tw (F. Hong).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.02.017

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S.A. Patil et al. / Tetrahedron 65 (2009) 2889–2897
OCH3
OH
(H3C)3C
C(CH3)3
OCH3
OH
(H3C)3C
C(CH3)3
OH
OH
H
N
H
N
H
N
H
N
N
N
HN
N
HN
N
O2N
H
2
4
3
1
OCH3
OH
OCH3
OH
(H3C)3C
C(CH3)3
OH
OH
OH
H
N
N
H
N
H3C
N
H
N
HN
HN
N
S
N
S
HN
HN
N
N
HN
N
S
S
S
8
9
6
7
5
Figure 1. Some selected N,N,O-tridentate ligands 1–9.
diffraction analysis.10 The ORTEP diagram of 10 is depicted in Fig-
ure 2. As revealed, it is indeed an N,N,O-chelated palladium com-
plex. The :N(1)–Pd(1)–N(2), :N(2)–Pd(1)–O(3), :O(3)–Pd(1)–
O(2) and :O(2)–Pd(1)–N(1) bond angles are 82.7(2)ꢀ, 96.49(18)ꢀ,
86.51(15)ꢀ, and 94.29(18)ꢀ, respectively. Thereby, the Pd(II) atom is
almost coplanar with all four coordinating atoms: N(1), N(2), O(3)
and O(2). The metal is in a square planar environment with four
coordinating sites comprised of an N,N,O-tridentate and an acetate
ligands. The acetate coordinates to the palladium atom in a mono-
dentate rather than bidentate mode.11 The N(1)–Pd(1), N(2)–Pd(1),
:O(3)–Pd(1), :O(2)–Pd(1) bond lengths are 1.932(5) Å, 2.005(5) Å,
2.038(4) Å, and 1.932(5) Å, respectively.
such as the kind of palladium salt or ligand employed, the presence/
absence of base, solvent, reaction temperature, etc.12 Furthermore,
the ligand/palladium salt ratio is also crucial since various bonding
modes are possible for different types of ligands. In this study, the
Suzuki coupling reactions were carried out in situ by employing the
synthesized N,N,O-ligands 1–9 in the presence of a palladium salt.
In most cases the reactions were carried out with 1.0 mmol of 4-
bromo-benzaldehyde, 1.5-fold excess of phenylboronic acid, 2.0-
fold excess of a base in 1.0 mL solvent, and 1.0 mol % of Pd(OAc)2/L
(L¼1–9) (Scheme 1). K3PO4 was chosen as the base because pre-
viously it has shown a good performance in our related studies on
Suzuki reactions.
The impact of variation of solvent and temperature on the per-
formance of the coupling reaction was evaluated by employing
Pd(OAc)2/1 as the catalytic precursor (Table 1). Two of the most
commonly used solvents, THF and toluene, having been shown to
perform well in our previous studies, were chosen. The best yield
was observed with toluene at 85 ꢀC (Entry 8). As shown, high
temperature was required to reach reasonable reaction speed. By
contrast, the catalytic performance was not acceptable when
a more polar solvent THF was employed (Entries 1–3).
2.2. Application of Pd(OAc)2/L (L[1–9) in Suzuki reactions
A variety of diimines containing N,N,O-tridentate ligands, 1–9,
have been designed and prepared (Fig. 1). The combination of these
ligands with various palladium salts was expected to form excellent
catalytic systems for the Suzuki–Miyaura cross-coupling reactions.
The performance of a palladium-catalyzed Suzuki–Miyaura cross-
coupling reaction is known to be governed by a number of factors
Figure 2. ORTEP drawings of 1 and 10.

S.A. Patil et al. / Tetrahedron 65 (2009) 2889–2897
2891
_
1 mol % Pd(OAc)2/L, L=1 9
2 equiv. base, 1 mL solvent
O
H
O
H
Br
+
1.5 (HO)2B
Scheme 1. Suzuki–Miyaura cross-coupling reaction of 4-bromo-benzaldehyde with phenylboronic acid in the presence of Pd(OAc)2/L.
Table 1
Table 3
Suzuki–Miyaura coupling reactions using Pd(OAc)2/1 at various solvents and
Suzuki–Miyaura coupling reactions using various Pd(OAc)2/1 or Pd(OAc)2/6 ratiosa
temperaturesa
Entrya
Ligand
Ratio
Conv.b (%)
Entrya
Solvent
Temp (ꢀC)
Time (h)
Conv.b (%)
1
2
3
4
5
6
7
8
9
10
1
1
1
1
1
6
6
6
6
6
1.0/0.0
1.0/0.5
1.0/1.0
1.0/1.5
1.0/2.0
1.0/0.0
1.0/0.5
1.0/1.0
1.0/1.5
1.0/2.0
NR
1
2
3
4
5
6
THF
THF
THF
Toluene
Toluene
Toluene
25
25
25
25
25
25
1
2
4
1
2
4
NR
NR
1.2
3.1
3.2
3.9
100.0
100.0
57.4
NR
NR
100.0
100.0
NR
7
8
Toluene
Toluene
85
85
1
2
65.5
100.0
NR
a
Reaction conditions: 1.0 mmol of 4-bromo-benzaldehyde, 1.5 mmol of phenyl-
a
Reaction conditions: 1.0 mmol of 4-bromo-benzaldehyde, 1.5 mmol of phenyl-
boronic acid, Pd(OAc)2/1¼1:1 mol %, 2.0 mmol of K3PO4, 1 mL solvent.
boronic acid, Pd(OAc)2/1 (or 6)¼1:1 mol %, 2.0 mmol of K3PO4, 1 mL toluene, 85 ꢀC,
b
Average of two runs; measured by 1H NMR.
2 h.
b
Average of two runs; measured by 1H NMR.
Table 2
Nevertheless, the effect is more pronounced in the N,N,O-tridentate
ligand case compared with that of a phosphine ligand.
Suzuki–Miyaura coupling reactions using Pd(OAc)2/6 at various solvents and
temperaturesa
Entrya
Solvent
Temp (ꢀC)
Time (h)
Conv.b (%)
2.3. Effect of palladium salt on coupling reaction
1
2
3
4
5
6
THF
THF
THF
Toluene
Toluene
Toluene
25
25
25
25
25
25
2
4
24
2
4
24
11.9
12.7
21.4
61.6
63.9
68.4
To evaluate the effect of a palladium source, the coupling re-
action between 4-bromo-benzaldehyde and phenylboronic acid
was performed with a series of palladium compounds. The most
commonly used ones, such as Pd(OAc)2 and [(h
3-C3H5)ClPd]2 were
7
Toluene
85
2
100.0
found to be the most effective. Unexpectedly, (COD)PdCl2 combined
with ligand 1 led to mediocre conversion while that with ligand 6
yielded no conversion at all. The rest of palladium sources, namely
PdCl2 and PdCl2[MeCN]2, performed poorly as shown in Table 6.
a
Reaction conditions same as in the footnote of Table 1 except for the usage of 6 as
the ligand.
b
Average of two runs; measured by 1H NMR.
2.4. Effect of solvent on coupling reaction
Similar procedures for the Suzuki reactions were carried out for
the rest of N,N,O-ligands, 2–9. Among all the ligands involved, only
6 showed promising results (Table 2). Other ligands did not exhibit
competitive efficiencies. The catalytic performance of 6 was about
as good as that of ligand 1. Again, toluene was superior to THF as
a solvent.
For polydentate ligands such as 1–9, various bonding modes and
conformations are possible depending on the ligand to palladium
salt ratio. The Suzuki coupling reactions were carried out in situ by
employing ligands 1 and 6 in the presence of palladium acetate. As
shown in Table 3, excellent yields were obtained when the ratio of
Pd(OAc)2:L (L¼1 or 6) was close to 1:1 (Entries 2–3, 7–8). The yield
decreased rapidly when the ratio approached 1:2 (Entries 5, 10).
The fact that unsatisfactory results were detected in those entries
The solvent effect on the rate of the coupling reaction between
4-bromo-benzaldehyde and phenylboronic acid was probed using
a variety of solvents. As shown in Table 7, quantitative yields were
observed within 2 h with high-boiling solvents such as toluene,
DMF, DMSO, and 1,4-dioxane. On the contrary, unsatisfactory yields
were obtained with low-boiling solvents. In part, this may be due to
a better solubility of a palladium complex at higher temperatures.
Again, running the reaction at lower temperatures sharply de-
creases the catalytic performance in this system.
2.5. Effect of base on coupling reaction
The effect of a base on the catalytic performance of this system
was investigated by employing various bases (Table 8). The com-
monly used inexpensive bases such as K3PO4 and KOH were found
to be rather effective. However, using bases like K2CO3, Cs2CO3, and
KF led to low or zero conversion. No conversion was observed with
either NaOtBu or KOtBu.
can be explained by the formation of an exceedingly stable bis-L-
chelated palladium complex, 11, as shown in Scheme 2.6a The ro-
bust structure of 11 makes the reduction process, from Pd(II) to
Pd(0), rather difficult thus leading to a sharp decrease of the overall
catalytic performance.
The results of the Suzuki cross-coupling reactions between
phenylboronic acid and various substituted aryl bromides assisted
by ligands 1 and 6 are shown in Tables 4 and 5, respectively. The
catalytic performance varied from good to excellent for the sub-
strates with electron-withdrawing groups (Table 4, Entries 1–6;
Table 5, Entries 1–4). By contrast, it was unsatisfactory for the
substrates with electron-donating groups (Table 4, Entries 8–9;
Table 5, Entries 6–10). It is consistent with the general behavior
observed for the palladium-catalyzed Suzuki reactions.13
2.6. DFT studies on the geometries of compound 10
reduced species
As shown above, the catalytic performance of the Suzuki re-
actions employing ligands 1–9 differs significantly with a small
change in ligand structure. It is of interest to us to examine the
reasons behind the obvious differences in reactivities observed. The

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S.A. Patil et al. / Tetrahedron 65 (2009) 2889–2897
OCH3
OH
OCH3
OCH3
O
N
H
O
+ Pd(OAc)2
+ 1
OAc
N
Pd
O
Pd
N
H
N
H
N
H
N
N
N
1
10
11
H3CO
Scheme 2. The formation of 1-chelated palladium complexes 10 and 11.
catalytic cycle for the palladium-catalyzed Suzuki reaction is gen-
erally believed to begin with a Pd(0) species. Thereby, at first the
starting Pd(II) complex 10 must be reduced to an active Pd(0)
species. There are several possible routes for the reduction to
proceed.14 In the absence of a phosphine ligand, one and the most
probable reduction pathway involves the initial attack of the borate,
BPh(OH)ꢁ3 , on the Pd(II) metal center. The boronic acid PhB(OH)2 is
known to play a dual role in Suzuki reactions. In the first role, it acts
as the reducing agent via the formation of borate, BPh(OH)ꢁ3 , by
combining with base; in the second, it behaves as a reactant. The
mechanisms proposed for the reduction of Pd(II) of 10 to an active
Pd(0) species TS4 and the subsequent catalytic cycle are shown in
Scheme 3. The N,N-chelated Pd(0) intermediate, TS4, resulting from
the reduction via a series of sequential steps, might indeed be the
Table 4
Suzuki–Miyaura coupling reactions using Pd(OAc)2/1 and substituted
bromobenzenesa
Table 5
Entry
1
Aryl bromide
Product
Conv.b (%)
Yieldc (%)
95.6
Suzuki–Miyaura coupling reactions using Pd(OAc)2/6 and substituted
bromobenzenesa
NC
NC
Entry
Aryl bromide
Product
Conv.b (%) Yieldc (%)
d
Br
O
H
O
H
1
100
95.0
95.3
Br
2
3
4
5
6
d
98.3
95.0
95.0
94.5
90.8
NC
Br
NC
2
3
d
NC
Br
NC
O
O
NC
NC
Br
100
d
d
94.9
94.8
H3C
H3C
Br
F3C
F3C
O
O
Br
4
5
Br
100
H3C
H3C
F3C
F3C
O2N
O2N
O
O
100
d
Br
d
89.3
Br
Br
H
H
F3C
F3C
F3C
O2N
O2N
6
7
d
59.1
Br
F3C
Br
7
8
9
77.9
40.0
29.0
71.8
38.8
dd
5.0
dd
H3CO
Br H3CO
OCH3
OCH3
H3C
Br
H3C
Br
8
4.4
dd
dd
dd
OCH3
OCH3
H3CO
Br H3CO
9
Trace
Trace
HO
Br
HO
10
Br
H3C
Br
H3C
10
24.6
dd
dd
NH2
NH2
Br
11
Trace
dd
11
Trace
HO
Br
HO
NH2
NH2
a
a
Reaction conditions same as in the footnote of Table 1 except keeping the re-
action at 85 ꢀC for 2 h.
Reaction conditions same as in the footnote of Table 4 except for the usage of 6 as
the ligand.
b
b
Average of two runs; measured by 1H NMR.
Average of two runs; measured by 1H NMR.
Isolated yield.
c
c
Isolated yield.
Not isolated.
d
d
Not isolated.

S.A. Patil et al. / Tetrahedron 65 (2009) 2889–2897
2893
Table 6
Suzuki–Miyaura coupling reactions using various palladium salt/1 or 6a
Table 8
Suzuki–Miyaura coupling reactions using Pd(OAc)2/1 or 6 with various basesa
Entry
Ligand
Pd Source
Pd(OAc)2
Conv.b (%)
Entry
Ligand
Base
Conv.b (%)
1
2
3
4
5
6
7
8
9
10
1
1
1
1
1
6
6
6
6
6
100
100
55.7
NR
1
2
3
4
5
6
7
8
1
1
1
1
1
1
1
6
6
6
6
6
6
6
K3PO4
KOH
K2CO3
Cs2CO3
KF
100
100
23.8
19.1
NR
[(
h
3-C3H5)ClPd]2
(COD)PdCl2
PdCl2
PdCl2[MeCN]2
Pd(OAc)2
NR
100
100
NR
NR
NR
NaOtBu
KOtBu
K3PO4
KOH
K2CO3
KF
Cs2CO3
NaOtBu
KOtBu
NR
NR
[(
h
3-C3H5)ClPd]2
(COD)PdCl2
PdCl2
PdCl2[MeCN]2
100
100
89.1
60.2
NR
9
10
11
12
13
14
a
Reaction conditions same as in the footnote of Table 1 except using various
palladium salts.
NR
NR
b
Average of two runs; measured by 1H NMR.
a
Reaction conditions same as in the footnote of Table 1 except using various bases
in toluene.
catalytically active species that carries the catalytic cycle further.
The intermediate, TS5, is formed as a result of oxidative addition of
ArX to the Pd(0) intermediate, TS4. Subsequently, the trans-
metallation processes, from TS6 to TS8, take place by the attack of
borate, BPh(OH)ꢁ3 on TS6. Eventually, the reductive elimination
process brings about the desired coupling product and re-
generation of the catalytically active species TS4. Recently, some
theoretical investigations on the stability of low coordinated Pd(0)
based on DFT methods have been reported by Buchwald and
Norrby.15 The performance of a catalytic reaction is known to be
affected greatly by the structure of intermediate. At first glance, the
reactivity does not seems to be changed substantially upon varia-
tion of R substituent on the phenyl ring of TS4 since it is far away
from the inner coordination sphere of Pd(0) metal center. Never-
theless, a closer examination of the intermediate TS4 by DFT
methods shows otherwise.
b
Average of two runs; measured by 1H NMR.
Naturally, it leads to a sharp decrease in the overall reaction rate
and catalytic performance.
The optimized geometries of TS4a and TS4b also reveal that
the Pd(0) atom is stabilized by imine and pyridine nitrogen
atoms as well as the phenoxide oxygen. Unlike in 10, the Pd(0)
atom in TS4 is not coplanar with the imine and pyridine rings;
rather, it is located above the plane and leans toward the
phenoxide ring. The methyl group bends away from the phen-
oxide ring in TS4a thus reducing the steric hindrance. By con-
trast, the tBu group exhibits
a strong steric effect on the
phenoxide ring in TS4b. Interestingly, while the optimized
structure of TS4a shows an interaction between Pd(0) and the
ipso-carbon of the phenoxide ring; undoubtedly, there is a h2
-
As a versatile tool in the studies of reaction mechanism, the
density functional theory (DFT) at the B3LYP level has proven
repeatedly to be a reliable method in providing insightful in-
formation about the transition metal-mediated catalytic re-
actions.16 It has been employed in the current study to account for
the effect caused by a substituent on the phenyl ring of TS4. To
make the computations affordable, only the intermediates TS4a
and TS4b (a: R¼OMe; b: R¼tBu), derived from 10, were consid-
ered. The optimized structures of TS4a and TS4b from the cal-
culations carried out at B3LYP level of theory are shown in
Figure 3. A closer look at the conformation of the intermediate
TS4 provides some useful information concerning the effect
caused by the substituent on the phenyl ring. As shown from the
stereo view of TS4a and TS4b created by Gauss View, the bulky
tBu group in TS4b exerts a greater steric effect on the phenoxide
moiety than –OMe group does in TS4a, subsequently forcing the
phenoxide ring to get even closer to the Pd(0) metal center
(Fig. 3). Thereby, less space is available for the upcoming reaction
substrate, arylhalide, to attack the activated Pd(0) center of TS4b.
coordination to the Pd(0) through a double bond of the phen-
oxide ring in TS4b (Fig. 4). These results indeed show that the
catalytic performance of the palladium complex with this type of
N,N,O-ligand may indeed be significantly affected by a small
variation in structure of the ligand.
3. Conclusion
In summary, a series of versatile and inexpensive N,N,O-ligands
have been synthesized. It has been demonstrated that combina-
tions of Pd(OAc)2 with either 1 or 6 are efficient catalyst precursors
for Suzuki–Miyaura couplings of various aryl bromides with aryl-
boronic acid. The optimized conditions for this systems are found to
be the reaction in toluene with K3PO4 as a base at 85 ꢀC for 2 h.
Applications of this system to other catalytic transformations are
currently under investigation.
4. Experimental section
4.1. Materials and methods
Table 7
Suzuki–Miyaura coupling reactions using Pd(OAc)2/1 or 6 with various solventsa
All the chemicals and reagents used for the synthesis of these
imines were of highest purity or purified by the standard methods
of purification. 2-Aminomethylpyridine, 8-aminoquinoline, 2-
hydrazinopyridine, 2-hydrazinobenzothiazole, o-vanillin, 3,5-di-
tert-butyl-2-hydroxybenzaldehyde, 2-hydroxy-1-naphthaldehyde,
and 2-hydroxy-1-acetonaphthone were obtained from Aldrich and
were used without further purification. 1H and 13C NMR spectra
were recorded on a Varian Mercury-400 (400 MHz for 1H and
100 MHz for 13C) spectrometer with chemical shifts given in parts
per million from the internal TMS or center line of CHCl3. Mass
spectra were recorded on JEOL JMS-SX/SX 102A GC/MS/MS
spectrometer.
Entry
Ligand
Solvent
Temp (ꢀC)
Conv.b (%)
1
2
3
4
5
6
7
8
1
1
1
1
6
6
6
6
Toluene
DMF
DMSO
Dioxane
Toluene
DMF
85
85
85
85
85
85
85
85
100
100
100
100
100
100
25.9
17.9
DMSO
Dioxane
a
Reaction conditions same as in the footnote of Table 1 except using various
solvents.
b
Average of two runs; measured by 1H NMR.

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S.A. Patil et al. / Tetrahedron 65 (2009) 2889–2897
R
O
R
R
OH
OH
HO
B
+ Ph
B
O
H
OH
OH
OH
+ Pd(OAc)2
O
OAc
(II)
N
Pd
Pd
H
N
H
N
H
N
OAc-
N
N
TS1
1
10
R
O
R
O
OH
B
- B(OH)3
OH
Pd
Pd
H
N
H
N
(II)
O
H
N
N
TS2
TS3
R
O
Ar
-
Ar-X
+
Pd(0)
N
H
N
TS4
R
R
O
O
Ar
(II)
X
Pd
Pd
Ar
H
N
H
N
(II)
a: R=OMe
b: R=tBu
N
N
TS8
TS5
OH
- B(OH)3
Ph
X-
B
OH
OH
R
O
R
OH
OH
OH
H
O
HO
B
Ar
Ar
O
(II)
N
O
(II)
B
Pd
Pd
H
H
N
H
N
N
TS7
TS6
Scheme 3. Proposed catalytic cycle for the Suzuki–Miyaura cross-coupling reaction catalyzed by palladium complex with ligand 1.
4.2. 2-Methoxy-6-[(pyridine-2-ylmethylimino)-methyl]-
phenol (1)
This ligand has been prepared by a literature reported method.8a
2-Aminomethylpyridine (1.03 g, 0.01 mol) dissolved in ethanol
(10 mL) was added to a stirred ethanol (10 mL) solution of o-van-
illin (1.52 g, 0.01 mol). The reaction mixture was stirred overnight
and then the solvent was removed under reduced pressure. The
resulted red residue was saturated with diethyl ether to get a red
solid, which was recrystallized from hot methanol to obtain yellow
crystals suitable for X-ray analysis. Yield: 1.60 g (66.04%). 1H NMR
(CDCl3, d/ppm): 13.75 (s, 1H, OH), 8.55–8.53 (m, 1H, Py), 8.52 (t,
J¼1.2 Hz, 1H, HC]N), 7.67–7.63 (m, 1H, Py), 7.36 (d, J¼7.6 Hz, 1H,
Py), 7.19–7.16 (m, 1H, Py), 6.94–6.90 (m, 2H, Ar), 6.82 (t, J¼7.8 Hz,
1H, Ar), 4.94 (s, 2H, CH2), 3.89 (s, 3H, OCH3). 13C NMR (CDCl3,
d/
ppm): 166.58, 157.59, 151.28, 149.00, 148.09, 136.53, 122.90, 122.00,
121.47, 118.34, 117.84, 114.01, 64.28, 55.75. HRMS: m/z¼242.1053
(Mþ). Anal. Calcd for 1: C, 69.41; H, 5.82; N, 11.56. Found: C, 69.50;
H, 5.90; N, 11.60.
Figure 3. Optimized geometries of TS4a and TS4b. The calculations were carried out at
B3LYP level of theory.

S.A. Patil et al. / Tetrahedron 65 (2009) 2889–2897
2895
Me
O
4.6. 2-(Benzothiazol-2-yl-hydrazonomethyl)-6-methoxy-
phenol (5)
Me
Me
Me
Compound 5 was prepared by stirring o-vanillin (0.761 g,
0.005 mol) and 2-hydrazinobenzothiazole (0.826 g, 0.005 mol) in
ethanol (25 mL) for 4–5 h at 80 ꢀC. The resulted colorless com-
pound was filtered, washed three times with ethanol, and finally
O
O
Pd(0)
Pd(0)
N
H
N
H
N
N
dried in vacuo. Yield: 1.40 g (93.53%). 1H NMR (DMSO-d6,
d/
TS4a
TS4b
ppm): 12.20 (s, 1H, NH), 8.43 (s, 1H, HC]N), 7.73 (d, J¼7.2 Hz,
1H, Bt), 7.35 (s, 1H, Bt), 7.28 (t, J¼7.6 Hz, 1H, Bt), 7.21 (d, J¼8 Hz,
1H, Bt), 7.08 (t, J¼7.4 Hz, 1H, Ar), 6.99 (t, J¼4.20 Hz, 1H, Ar), 6.84
Figure 4. Sketched figures for the optimized structures of TS4a and TS4b.
(t, J¼7.8 Hz, 1H, Ar), 3.81 (s, 3H, OCH3). 13C NMR (CDCl3,
d/ppm):
4.3. 2,4-Di-tert-butyl-6-(pyridine-2-yl-hydrazonomethyl)-
phenol (2)
166.48, 147.93, 146.25, 126.12, 121.70, 121.51, 120.01, 119.15,
113.11, 55.86. HRMS: m/z¼299.0731 (Mþ). Anal. Calcd for 5: C,
60.14; H, 4.38; N, 14.04; S, 10.71. Found: C, 57.72; H, 5.27; N,
14.23; S, 10.98.
3,5-Di-tert-butyl-2-hydroxybenzaldehyde (1.64 g, 0.007 mol)
was added to
a
solution of 2-hydrazinopyridine (0.76 g,
0.007 mol) in ethanol (15 mL). The reaction mixture was under
refluxing for 3–4 h and cooled down afterward. The light yellow
precipitate of the title compound, 2, was filtered and crystallized
from methanol and dried in vacuo. Yield: 2.12 g (93.05%). 1H NMR
4.7. 2-(Benzothiazol-2-yl-hydrazonomethyl)-4,6-di-tert-
butyl-phenol (6)
The imine ligand 6 was synthesized by the following procedures.
3,5-Di-tert-butyl-2-hydroxybenzaldehyde (1.172 g, 0.005 mol) dis-
solved in hot ethanol (20 mL) was added to 2-hydrazinobenzo-
thiazole (0.826 g, 0.005 mol) in ethanol (20 mL). The reaction
mixture was heated to reflux for 4 h. The light yellow product
obtained was filtered out and washed several times with ethanol
(CDCl3, d/ppm): 11.12 (s, 1H, NH), 8.18–8.16 (m, 1H, Py), 7.98 (s, 1H,
HC]N), 7.64–7.60 (m, 1H, Py), 7.34 (d, J¼2.0 Hz, 1H, Ar), 7.13 (d,
J¼8.4 Hz, 1H, Ar), 6.99 (d, J¼2.4 Hz, 1H, Py), 6.81–6.78 (m, 1H, Py),
1.47 (s, 9H, t-Bu), 1.31 (s, 9H, t-Bu). 13C NMR (CDCl3,
d/ppm):
156.33, 154.15, 147.08, 144.60, 140.99, 138.67, 136.34, 125.32,
124.68, 117.53, 115.81, 106.84, 35.07, 34.13, 31.50, 29.50. HRMS:
m/z¼225.2152 (Mþ). Anal. Calcd for 2: C, 73.81; H, 8.36; N, 12.91.
Found: C, 74.05; H, 8.75; N, 13.08.
and dried in vacuo. Yield: 1.52 g (79.67%). 1H NMR (CDCl3,
d/ppm):
10.97 (s,1H, NH), 8.32 (s,1H, HC]N), 7.57 (d, J¼8 Hz,1H, Bt), 7.38 (d,
J¼2.4 Hz, 1H, Bt), 7.33–7.28 (m, 2H, Bt), 7.15–7.11 (m, 1H, Ar), 7.00 (s,
1H, Ar), 1.50 (s, 9H, t-Bu), 1.28 (s, 9H, t-Bu). 13C NMR (CDCl3/DMSO-
4.4. 2,4-Di-tert-butyl-6-(quinolin-8-yliminomethyl)-
phenol (3)
d6, d/ppm): 165.67, 154.34, 152.04, 143.80, 140.23, 135.58, 125.61,
125.08, 124.86, 121.00, 116.98, 113.78, 34.42, 33.47, 30.88, 28.89.
HRMS: m/z¼381.1870 (Mþ). Anal. Calcd for 6: C, 69.26; H, 7.13; N,
11.01; S, 8.40. Found: C, 68.92; H, 7.46; N, 10.84; S, 8.66.
This ligand also has been prepared by a literature reported
method.8b To a stirred solution of 3,5-di-tert-butyl-2-hydroxy-
benzaldehyde (2.343 g, 0.01 mol) in methanol (30 mL) was added
8-aminoquinoline (1.442 g, 0.01 mol). Two drops of formic acid was
added to the reaction mixture. After refluxing for 1 h, the resulting
dark-brown colored precipitate was filtered out and was washed
with methanol to yield 3 as an orange powder and dried in vacuo.
4.8. 1-(Benzothiazol-2-yl-hydrazonomethyl)-naphthalen-
2-ol (7)
The preparation of compound 7 was carried out by refluxing
a solution of 2-hydroxy-1-naphthaldehyde (1.033 g, 0.006 mol) in
ethanol (15 mL) with a solution of 2-hydrazinobenzothiazole
(0.991 g, 0.006 mol) in ethanol (15 mL) for 4 h. The reaction mix-
ture was then allowed to cool down to room temperature over-
night. The resulted dark yellow colored compound was filtered and
washed with ethanol and dried in vacuo. Yield: 1.83 g (95.49%). 1H
Yield: 3.40 g (94.31%). 1H NMR (CDCl3,
d
/ppm): 8.99 (d, J¼4 Hz, 1H,
Qu), 8.91 (s, 1H, HC]N), 8.20 (d, J¼8.4 Hz, 1H, Qu), 7.70 (t, J¼4.4 Hz,
1H, Qu), 7.57 (t, J¼7.8 Hz, 1H, Qu), 7.48–7.44 (m, 4H, Ar and Qu), 1.50
(s, 9H, t-Bu), 1.33 (s, 9H, t-Bu). 13C NMR (CDCl3,
d/ppm): 166.28,
158.90, 150.08, 145.82, 142.08, 140.12, 136.93, 135.78, 128.99, 127.94,
126.84, 126.40, 125.58, 121.39, 119.26, 118.55, 35.04, 34.03, 31.40,
29.47. HRMS: m/z¼360.2196 (Mþ). Anal. Calcd for 3: C, 79.96; H,
7.83; N, 7.77. Found: C, 79.88; H, 7.72; N, 7.17.
NMR (DMSO-d6, d/ppm): 9.18 (s, 1H, NH), 8.63 (s, 1H, HC]N), 7.87
(t, J¼8.2 Hz, 3H, Ar and Bt), 7.75 (d, J¼7.2 Hz, 1H, Ar), 7.57 (t,
J¼7.2 Hz, 1H, Bt), 7.39 (t, J¼7.4 Hz, 1H, Bt), 7.29 (t, J¼7.4 Hz, 2H, Ar),
7.23 (d, J¼8.8 Hz, 1H, Ar), 7.09 (t, J¼8 Hz, 1H, Ar). 13C NMR (DMSO-
4.5. 2-Methoxy-6-(pyridine-2-yl-hydrazonomethyl)-
phenol (4)
d6, d/ppm): 165.92, 157.37, 132.28, 131.41, 128.82, 128.07, 127.67,
126.48, 123.51, 122.23, 122.12, 121.66, 118.47, 109.70. HRMS:
m/z¼319.0777 (Mþ). Anal. Calcd for 7: C, 67.69; H, 4.10; N, 13.16; S,
10.04. Found: C, 68.01; H, 4.19; N, 13.34; S, 10.14.
To a stirred solution of 2-hydrazinopyridine (0.764 g, 0.007 mol)
in ethanol (25 mL) was added drop-wise o-vanillin (1.065 g,
0.007 mol) in ethanol (25 mL). After the addition was completed,
the stirring was continued for 2 h at 70 ꢀC. The reaction mixture
was then allowed to cool to room temperature overnight. Then the
colorless precipitate of the title compound was filtered and washed
two times with ethanol and dried in vacuo. Yield: 1.60 g (93.96%).
4.9. 1-[1-(Benzothiazol-2-yl-hydrazono)-ethyl]-naphthalen-
2-ol (8)
The imine 8 was prepared by refluxing a mixture of 2-hydra-
zinobenzothiazole (0.991 g, 0.006 mol) and 2-hydroxy-1-aceto-
naphthone (1.117 g, 0.006 mol) in ethanol (30 mL) for 8–10 h. The
light yellow colored solution was concentrated to dryness on
a vacuum line. The colorless compound was washed three times
with hexane and crystallized with ether and dried on a vacuum
1H NMR (CDCl3,
7.93 (s, 1H, HC]N), 7.65–7.60 (m, 1H, Py), 7.08 (d, J¼8.4 Hz, 1H, Ar),
6.92–6.82 (m, 4H, Ar and Py), 3.93 (s, 3H, OCH3). 13C NMR (CDCl3,
d
/ppm): 10.78 (s, 1H, NH), 8.17 (t, J¼3.0 Hz, 1H, Py),
d/
ppm): 156.48, 147.94, 145.70, 138.98, 137.98, 120.80, 119.14, 119.09,
115.06, 112.27, 106.18, 55.83. HRMS: m/z¼243.1005 (Mþ). Anal.
Calcd for 4: C, 64.19; H, 5.39; N, 17.27. Found: C, 64.44; H, 5.97; N,
17.36.
line. Yield: 1.82 g (91.06%). 1H NMR (CDCl3,
d/ppm): 7.67–7.62 (m,
2H, Bt), 7.53–7.50 (m, 2H, Ar), 7.46–7.42 (m, 2H, Bt), 7.30–7.26 (m,
1H, Ar), 7.16–7.12 (m, 1H, Ar), 6.75 (d, J¼8.8 Hz, 1H, Ar), 6.62 (d,

2896
S.A. Patil et al. / Tetrahedron 65 (2009) 2889–2897
J¼8.8 Hz, 1H, Ar), 2.38 (s, 3H, H3C]N). 13C NMR (DMSO-d6,
d
/
with the hybrid B3LYP-DFT method under C1 symmetry, in which
the Becke three parameter exchange functional18 and the Lee–
Yang–Parr correlation functional19 were used. The LANL2DZ in-
ppm): 152.75, 151.83, 132.67, 130.53, 130.04, 128.37, 128.12, 126.95,
126.65, 125.91, 123.97, 123.40, 122.92, 121.56, 121.29, 119.92,
118.70, 118.49. HRMS: m/z¼333.0935 (Mþ). Anal. Calcd for 8: C,
68.45; H, 4.53; N, 12.60; S, 9.62. Found: C, 68.47; H, 4.68; N, 12.68;
S, 9.74.
cluding the double-z basis sets for the valence and outermost core
orbitals combined with pseudopotential were used for Pd,20 and 6-
31G(d) basis sets for the other atoms.
4.10. 2-(Benzothiazol-2-yl-hydrazonomethyl)-6-methoxy-4-
nitro-phenol (9)
Acknowledgements
We are grateful to the National Science Council of the R.O.C.
(Grant NSC 95-2113-M-005-015-MY3) for financial support. The CPU
time that was used to complete this project was mostly provided by
the National Center for High-Performance Computing (NCHC).
The preparation of 9 was carried out by refluxing a solution of
0.005 mol of 3-methoxy-5-nitrosalicylaldehyde (0.985 g) in etha-
nol (10 mL) and with a solution of 0.005 mol of 2-hydrazino-
benzothiazole (0.826 g) in ethanol (10 mL) for 4–5 h. The reaction
mixture was then allowed to cool to room temperature at over-
night. The resulting dark yellow colored precipitate was filtered and
washed 2–3 times with hot ethanol and dried in vacuo. Yield: 1.68 g
Supplementary data
Tables for the Suzuki–Miyaura coupling reactions using
Pd(OAc)2/L (L¼2–5, 7–9) at various solvents and temperatures;
tables for the parameters of the optimized structures TS4a and
TS4b; X-ray crystallographic files (CIFs) for 1 and 10; ORTEP
drawings of 1 and 10 (Figs. S1 and S2). Crystallographic data for the
structural analysis have been deposited with the Cambridge Crys-
tallographic Data Center, CCDC nos. 683204 and 685915 for 1 and
10. Copies of this information may be obtained free of charge from
the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax:
þ44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk). Supplementary data associated with
this article can be found in the online version, at doi:10.1016/
j.tet.2009.02.017.
(97.65%). 1H NMR (DMSO-d6,
d/ppm): 8.47 (s, 1H, HC]N), 8.25 (d,
J¼2.8 Hz, 1H, Bt), 7.75 (d, J¼2.8 Hz, 3H, Ar and Bt), 7.30 (t, J¼7.6 Hz,
1H, Bt), 7.11 (t, J¼7.6 Hz, 1H, Bt). 13C NMR (DMSO-d6,
d/ppm):
166.94, 151.82, 148.00, 139.68, 126.11, 121.73, 120.00, 106.55, 56.41.
HRMS: m/z¼344.0577 (Mþ). Anal. Calcd for 9: C, 52.32; H, 3.51; N,
16.27; S, 9.31. Found: C, 52.41; H, 4.25; N, 16.42; S, 9.41.
4.11. General procedure for the palladium-catalyzed Suzuki
cross-coupling reactions
The five reactants, aryl bromide (1.0 mmol), boronic acid
(1.0 mmol), ligand L (L¼1–9) (1.0 mol %), Pd(OAc)2 (1.0 mol %), and
K3PO4 (3.0 mmol), were placed in an oven dried Schlenk flask. The
flask was evacuated and backfilled with nitrogen. To the mixture
then toluene/THF (1.0 mL) was added and stirred at required tem-
perature with designated hours. The mixture was then allowed to
cool to room temperature and quenched by adding ether (3.0 mL)
and water (2.0 mL). Ether layer is separated from water layer
through separatory funnel and dried with anhydrous magnesium
sulfate. The dried ether layer was concentrated in vacuo and puri-
fied by column chromatography using hexane and ethyl acetate as
eluting solvent.
References and notes
1. (a) Yin, L.; Liebscher, J. Chem. Rev. 2007, 107, 133; (b) Phan, N. T. S.; Van Der
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4.12. Preparation of Pd complex (10)
3. (a) Ojima, I. Catalytic Asymmetric Synthesis, 2nd ed.; Wiley-VCH: New York, NY,
2000; (b) Jacobsen, E. N.; Pfaltz, A.; Yamamoto, H. Comprehensive Asymmetric
Catalysis; Springer: Berlin, 1999; Vols. 1–3; (c) Metal-Catalyzed Cross-Coupling
Reactions; Diederich, F., Stang, P. J., Eds.; Wiley-VCH: Weinheim, 1998; (d) Tsuji, J.
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4. (a) Tang, W.; Zhang, X. Chem. Rev. 2003, 103, 3029; (b) Andersen, N. G.; Keay, B.
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Synthesis; John Wiley and Sons: New York, NY, 1994; (f) Parshall, G. W.; Ittel, S.
D. Homogeneous Catalysis, 2nd ed.; John Wiley and Sons: New York, NY, 1992;
Chapter 8.
2-Methoxy-6-[(pyridine-2-ylmethylimino)-methyl]-phenol (0.1
21 g, 0.005 mol) and palladium acetate (0.112 g, 0.005 mol) were
placed in 100 mL round flask. The mixture was then allowed to
react in dried THF (10 mL) at room temperature for overnight. Re-
moval of the solvent in vacuum afforded complex as dark-brown
solid product. Yield: 0.192 g (94.51%). 1H NMR (CDCl3,
d/ppm): 8.13
(d, J¼5.6 Hz, 1H, Py), 8.06 (s, 1H, HC]N), 7.56 (t, J¼7.0 Hz, 1H, Py),
7.22 (d, J¼8.8 Hz, 1H, Py), 7.13 (t, J¼6.4 Hz, 1H, Py), 6.70 (d, J¼7.2 Hz,
2H, Ar), 6.33 (t, J¼7.6 Hz, 1H, Ar), 5.60 (s, 2H, CH2), 3.80 (s, 3H,
OCH3), 2.40 (s, 3H, CH3).
1H NMR (DMSO-d6,
d/ppm): 8.12–8.06 (m, 3H, HC]N and Py),
5. Louie, J.; Hartwig, J. F. Angew. Chem., Int. Ed. 1996, 35, 2359.
6. (a) Lai, Y.-C.; Chen, H.-Y.; Hung, W.-C.; Lin, C.-C.; Hong, F.-E. Tetrahedron 2005,
61, 9484; (b) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290; (c) Botella,
L.; Najera, C. Angew. Chem., Int. Ed. 2002, 41, 179; (d) Grasa, G. A.; Hillier, A. C.;
Nolan, S. P. Org. Lett. 2001, 3, 1077; (e) Herrmann, W. A.; Weskamp, T.; Bohm, V.
P. W. Adv. Organomet. Chem. 2001, 48, 1; (f) Jafapour, L.; Nolan, S. P. Adv. Or-
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7.71 (d, J¼8.0 Hz, 1H, Py), 7.53 (t, J¼6.8 Hz, 1H, Py), 7.05 (d, J¼8.4 Hz,
1H, Ar), 6.89 (d, J¼7.6 Hz, 1H), 6.52 (t, J¼7.8 Hz, 1H, Ar), 5.50 (s, 2H,
CH2), 3.67 (s, 3H, OCH3), 1.91 (s, 3H, CH3). 13C NMR (DMSO-d6,
d/
ppm): 167.47, 157.65, 151.50, 149.23, 148.01, 136.97, 123.23, 122.48,
122.02, 118.43, 117.81, 114.98, 63.29, 55.73. HRMS: m/z¼347.006
(MꢁOAcþ). Anal. Calcd for 10: C, 48.41; H, 4.54; N, 6.64. Found: C,
46.72; H, 5.82; N, 6.72.
4.13. Computational methods
7. (a) Mino, T.; Shirae, Y.; Saito, T.; Sakamoto, M.; Fujita, T. J. Org. Chem. 2006, 71,
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J. Organomet. Chem. 2003, 687, 269.
All calculations were carried out using the Gaussian 03 package,
in which the tight criterion (10ꢁ8 hartree) is the default for the SCF
convergence.17 The molecular geometries were fully optimized

S.A. Patil et al. / Tetrahedron 65 (2009) 2889–2897
2897
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Cheeseman, J. R.; Montgomery, J. A.; Vreven, T., Jr.; 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.;
Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Mo-
rokuma, 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.; Liu, G.; 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, J. A. Gaussian 03 Revision C.02; Gaussian:
Wallingford, CT, 2004.
9. Crystal data for 1: C14H15N2O2, Mw¼243.28, monoclinic, space group P21/c, a¼9.
0994(11) Å, b¼5.6642(7) Å, c¼24.308(3) Å,
b
¼92.628(2)ꢀ, V¼1251.5(3) Å3,
Dc¼1.291 Mg/m3, Z¼4,
m
¼0.088 mmꢁ1, 6688 data collected, 2453 unique data
[R(int)¼0.0217], R1¼0.0504, wR2¼0.1837, CCDC 683204.
10. Crystal data for 10: C16H16N2O4Pd$1.5H2O, Mw¼406.71, triclinic, space group P-1,
a¼7.4414(16) Å, b¼10.971(2) Å, c¼11.059(2) Å,
a
¼80.793(4)ꢀ,
b
¼74.361(4)ꢀ,
¼87.
g
814(4)ꢀ, V¼858.2(3) Å3, Dc¼1.678 Mg/m3, Z¼1,
m
¼1.112 mmꢁ1, 5009 data col-
lected, 3365 unique data [R(int)¼0.0260], R1¼0.0516, wR2¼0.1256, CCDC 685915.
11. Lee, J.-C.; Wang, M.-G.; Hong, F.-E. Eur. J. Inorg. Chem. 2005, 5011.
12. (a) Goldman, E. R.; Medintz, I. L.;Whitley, J. L.;Hayhurst, A.; Clapp, A. R.; Uyeda, H. T.;
Deschamps, J. R.; Lassman, M. E.; Mattoussi, H. J. Am. Chem. Soc. 2005, 127, 6744; (b)
Braga,A.A. C.; Morgon,N. H.;Ujaque,G.;Maseras, F. J. Am.Chem.Soc. 2005,127, 9298.
13. (a) Senn, H. M.; Ziegler, T. Organometallics 2004, 23, 2980; (b) Gooßen, L. J.;
Koley, D.; Hermann, H.; Thiel, W. Chem. Commun. 2004, 2141.
14. (a) Trzeciak, A. M.; Ciunik, Z.; Zio´lkowski, J. J. Organometallics 2002, 21, 132; (b)
Chemler, S. R.; Trauner, D.; Danishefsky, S. J. Angew. Chem., Int. Ed. 2001, 40,
4544; (c) Amatore, C.; Jutand, A. Acc. Chem. Res. 2000, 33, 314; (d) Amatore, C.;
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Carre, E.; Jutand, A.; M’Barki, M. A.; Meyer, G. Organometallics 1995, 14, 5605;
18. Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(e) Amatore, C.; Jutand, A.; M’Barki, M. A. Organometallics 1992, 11, 3009.
15. (a) Barder, T. E.; Buchwald, S. L. J. Am. Chem. Soc. 2007, 129, 12003; (b) Barder, T.
E.; Biscoe, M. R.; Buchwald, S. L. Organometallics 2007, 26, 2183; (c) Ahlquist, M.;
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20. (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299; (b) Dunning, T. H., Jr.; Hay,
P. J. Modern Theoretical Chemistry; Plenum: New York, NY, 1976.