Air-stable CpPd(NHC)Cl (NHC = N-heterocyclic carbene) complexes as highly active precatalysts for Kumada-Tamao-Corriu coupling of aryl and heteroaryl chlorides

Article abstract of DOI:10.1016/j.jorganchem.2010.10.009

A very straightforward one-pot method has been developed for preparation of air-stable CpPd(NHC)Cl complexes 1a-d. This new class of well-defined NHC-Pd complexes exhibits high catalytic activity in Kumada-Tamao-Corriu cross-coupling reaction involving various aryl and heteroaryl chlorides. Notably, the less sterically encumbered NHC ligand around Pd centre showed higher catalytic activity.

Full text of DOI:10.1016/j.jorganchem.2010.10.009

Journal of Organometallic Chemistry 696 (2011) 859e863
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Air-stable CpPd(NHC)Cl (NHC ¼ N-heterocyclic carbene) complexes as highly
active precatalysts for KumadaeTamaoeCorriu coupling of aryl and heteroaryl
chlorides
a
,
a
a
a
a
a,b,
*
*
Zhong Jin , Xiao-Peng Gu , Ling-Ling Qiu , Gui-Ping Wu , Hai-Bing Song , Jian-Xin Fang
a
Institute of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China
State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 September 2010
Received in revised form
A very straightforward one-pot method has been developed for preparation of air-stable CpPd(NHC)Cl
complexes 1aed. This new class of well-defined NHCePd complexes exhibits high catalytic activity in
KumadaeTamaoeCorriu cross-coupling reaction involving various aryl and heteroaryl chlorides. Notably,
the less sterically encumbered NHC ligand around Pd centre showed higher catalytic activity.
Ó 2010 Elsevier B.V. All rights reserved.
27 September 2010
Accepted 5 October 2010
Available online 13 October 2010
Keywords:
N-Heterocyclic carbine
Palladium
KumadaeTamaoeCorriu reaction
Cross-coupling
1. Introduction
complex. In contrast, well-defined NHCePd precatalysts [16], in
addition to the inherent merits of NHC ligands, consist of an accurate
Since the first free, stable N-heterocyclic carbene (NHC) was
isolated successfully in 1991 [1], research of this field has received
extensive interest from the chemistry community, especially when
their vast potential instead of the common tertiary phosphine
ligands in homogenous catalysis was disclosed in 1995 [2]. Over the
past twenty years, various types of N-heterocyclic carbenes have
been reported and their catalytic applications investigated inten-
sively [3e7]. Related to common tertiary phosphines, because of
their bulky substituents on the imidazole nitrogens, higher thermal
ratio (optimally 1:1) of the Pd/ligand that avoids the use of excess
costly ligand. Particularly, the NHCePd complexes with a ratio close
to 1 of the Pd/ligand generally exhibit enhanced reactivity associated
0
with formation of a highly active monoligated [Pd L] species [17].
Recently, we have synthesized a class of well-defined Cp-containing
NHCePd complexes, i.e. CpPd(NHC)Cl 1, which exhibit highly cata-
lytic activity in room temperature SuzukieMiyaura and Buch-
waldeHartwig cross-coupling reactions involving unactive aryl
chlorides as the substrates [18]. Additionally, they are found to be
extremely efficient catalysts in the deboronation homocoupling of
arylboronic acids at room temperature. As part of our ongoing
research, the catalytic potential associated with these well-defined
NHCePd complexes was examined further. We herein report the
application of these air-stable CpPd(NHC)Cl complexes as highly
active precatalysts for KumadaeTamaoeCorriu coupling of aryl and
heteroaryl chlorides.
stability and better
s-donating properties [8e10], which are in
favor of the oxidative-addition and reductive-elimination steps of
the cross-coupling catalytic cycle, N-heterocyclic carbenes have
proven to be an excellent alternative in numerous transition metal-
catalyzed cross-coupling reactions [11].
During the past thirty years, particularly in recent ten years, Pd-
catalyzed cross-coupling reactions have experienced an unprece-
dent advance [12,13], notably the use of aryl chlorides as substrates
[
14]. Generally, to ensure the efficient coordination on the transition
2
. Results and discussion
metal centre, an excess, costly phosphine ligand [15] was necessary
in the procedure catalyzed by a tertiary phosphine ligand/Pd
2.1. Synthesis of CpPd(NHC)Cl complexes (1)
*
Corresponding authors. Institute of Elemento-Organic Chemistry, Nankai
The new complexes CpPd(NHC)Cl 1 were initially prepared by
treating the key intermediate NHCePdCl dimers at room temperature
2
University, Tianjin 300071, China. Tel.: þ86 22 2350 5330; fax: þ86 22 2350 3438.
E-mail addresses: zjin@nankai.edu.cn (Z. Jin), fjx@nankai.edu.cn (J.-X. Fang).
0
022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.10.009

860
Z. Jin et al. / Journal of Organometallic Chemistry 696 (2011) 859e863
with two equivalent, freshly prepared CpNa (CpNa ¼ sodium cyclo-
pentadienylide) in a solution of tetrahydrofuran (THF), and the desired
Cp-containing NHCePd complexes, CpPd(IMes)Cl 1a, CpPd(IPr)Cl 1b,
CpPd(SIMes)Cl 1c, and CpPd(SIPr)Cl 1d, were conveniently obtained in
almost quantitative yield [18]. The starting NHCePdCl
be readily prepared either from PdCl (PhCN) 2 through the direct
displacement of nitrile ligands with the free carbenes [19], or from [Pd
2
dimers could
2
2
3
(h
2
-allyl)Cl] dimer via a two-step sequence with high overall yields
[20]. Despite their simplicity and high yields of both routes, they
require multi-step reactions or the generation of the free carbene. As
a result, we focused our efforts to develop a simple, efficient synthetic
method which would avoid the use of a glovebox and therefore would
be more convenient for the synthetic workup.
As shown in Scheme 1, our efforts led us to a very expeditious
one-pot synthetic strategy for NHCePd complexes 1. A slight
modificationof Nolan’s method [19] was adoptedfor synthesis of the
Fig. 1. Molecular structure of compound 1a. All H atoms are omitted for clarity. The
final structure was obtained by refinement of a twin model in the unit cell. Selected
bond lengths (Å): Pd(1)eC(10) 1.977 (2), Pd(1)eCl(1) 2.3404 (8), Pd(1)eC(22) 2.390 (3),
Pd(1)eC(23) 2.428 (3), Pd(1)eC(24) 2.311 (2), Pd(1)eC(25) 2.287 (3), Pd(1)eC(26)
2.186 (3). Selected bond angle (ꢀ): C(10)ePd(1)eCl(1) 94.75 (7), C(10)ePd(1)eC(22)
key intermediate NHCePdCl
2
dimers. The corresponding imidazo-
115.98 (10), C(10)ePd(1)eC(23) 147.37 (9), C(10)ePd(1)eC(24) 159.79 (10), C(10)ePd
(1)eC(25) 124.49 (10), C(10)ePd(1)eC(26) 103.03 (10), N(1)eC(10)eN(2) 104.34 (18),
lium salts 3aed (for IMes and IPr, X ¼ Cl; for SIMes and SIPr, X ¼ BF
4
)
t
N(1)eC(10)ePd(1) 127.02 (16).
2 2
were mixed directly with Pd(PhCN) Cl 2 in the presence of KOBu in
THF at room temperature. The imidazolium salts were in situ
deprotonatedtogenerate the highly nucleophilic carbenes, followed
by subsequent displacement of the nitrile ligands in 2 to give the
that existing in compound 1b. It is noteworthy that the bond length
(
(
2.3404 Å) of PdeCl in compound 1a is obviously longer than that
2.3199 Å) in compound 1b. These structural characters might cause
requisite the NHCePdCl
air- and moisture-sensitive free carbenes and isolation of resulted
NHCePdCl dimers is not essential. Finally, after sequential reaction
2
dimers. The procedure avoids the use of
them different behavior in the catalytic procedures.
2
with two equivalent, freshly prepared CpNa (CpNa ¼ sodium
cyclopentadienylide) in a solution of tetrahydrofuran (THF), the
desired NHCePd complexes 1aed were obtained straightforward in
generally satisfied yield (80e90%). This one-pot synthetic procedure
for NHCePd complexes 1 obviates the use of a glovebox and
simplifies the workup.
2
.3. Catalytic activity of CpPd(NHC)Cl complexes (1) in
KumadaeTamaoeCorriu cross-coupling reaction
In recent years, due to their major drawback being functional
group tolerance, aryl halides coupling with Grignard reagents, i.e.
KumadaeTamaoeCorriu reaction, has suffered drastic challenge
from organoboron (SuzukieMiyaura reaction), organozinc (Negishi
reaction), organotin (Stille reaction), etc. in cross-coupling reac-
tions [12,13]. However, because of their easy preparation and high
stability, using Grignard reagents for synthesis of biaryl is still an
extremely efficient method in the absence of Grignard-sensitive
functionality [21e23].
2.2. X-ray crystal structure of CpPd(NHC)Cl complexes (1)
Suitable crystals for single-crystal diffraction analyses of com-
pounds 1a and 1b are obtained by slow diffusion of n-pentane into
ether solution (Figs. 1 and 2). Selected bond lengths and angles for
compound 1a and 1b were listed in the captions for figure, respec-
Firstly, by using PhMgBr and 4-chloroanisole as the coupling
substrates, catalytic potential of CpPd(NHC)Cl 1 in KumadaeTamaoe
Corriu cross-coupling reaction was examined intensively. As shown
in Table 1, with no catalyst, no coupling product was obtained in
5
tively. The crystal structure validated again the
h
coordination of
the Cp ring and the Cl atom around the Pd centre is opposite tothe Cp
ring. The bond length (1.977 Å) between carbene carbon and Pd
atom in compound 1a is parallel to that (1.975 Å) in compound 1b.
Due to the bulkiness of N-heterocyclic carbene ligands, the bond
lengths between five Carbon atoms in the Cp ring and the Pd centre
are not equal to each other, ranging from 2.186 Å to 2.428 Å in
compound 1a and from 2.200 Å to 2.459 Å in compound 1b,
respectively. In general, because of the less steric IMes ligand, the
distance of Pd to the Cp ring plane in compound 1a is shorter than
Pd(PhCN) Cl
2
2
NHC 1a NHC = IMes
1b
2
KOBu /THF CpNa/THF
t
NHC = IPr
c NHC = SIMes
Cl 1d NHC = SIPr
Pd
1
rt, 12 h
rt, 12 h
NHC HX
a-d
X = Cl or BF4
3
yield > 80 %
N
N
N
N
N
IMes
IPr
Fig. 2. Molecular structure of compound 1b. All H atoms are omitted for clarity.
Selected bond lengths (Å): Pd(1)eC(1) 1.975 (2), Pd(1)eCl(1) 2.3199 (8), Pd(1)eC(28)
N
N
N
2
.403 (2), Pd(1)eC(29) 2.200 (2), Pd(1)eC(30) 2.284 (2), Pd(1)eC(31) 2.308 (2), Pd(1)e
ꢀ
C(32) 2.459 (2). Selected bond angle ( ): C(1)ePd(1)eCl(1) 88.71 (6), C(1)ePd(1)eC
(28) 114.91 (8), C(1)ePd(1)eC(29) 106.88 (8), C(1)ePd(1)eC(30) 131.77 (9), C(1)ePd
SIMes
SIPr
(1)eC(31) 166.39 (9), C(1)ePd(1)eC(32) 143.77 (9), N(1)eC(1)eN(2) 104.75 (16), N(1)e
Scheme 1. One-pot synthesis of CpPd(NHC)Cl complexes 1.
C(1)ePd(1) 126.91 (14).

Z. Jin et al. / Journal of Organometallic Chemistry 696 (2011) 859e863
861
Table 1
Screen of reaction conditions.
Table 2
a
Cross-coupling reaction of aryl and heteroaryl chlorides with Grignard reagents.a
b
CpPd(NHC)Cl
Entry
Grignard’s
reagent
Aryl/
heteroaryl
chloride
Biaryl product
Yield (%)
MgBr
Cl
OMe
OMe
solvent/additive
24 h
MgBr
Cl
ꢀ
b
Entry CpPd
Additive Catalyst
loading (mol%)
Solvent
T( C) Yield (%)
1
OMe
92
(
NHC)Cl
OMe
1
2
3
4
5
6
7
8
9
1
1
e
e
e
THF
THF
THF
THF
THF
THF
THF
THF
THF
RT
RT
RT
RT
RT
RT
50
RT
50
0
89
35
93
45
72
87
58
81
85
92
1a
1b
1c
1d
1c
1c
1c
1c
1c
1c
e
2
2
2
2
1
1
0.5
0.5
1
e
Cl
MgBr
MgBr
e
e
2
3
4
Me
86
96
82
Me
e
e
e
c
Cl
e
0
1
e
THFeDME 2:1 RT
THFeDME 2:1 RT
2 eq. LiCl
1
a
Reaction conditions: 4-chloroanisole (1 mmol), PhMgBr (1.5 mmol, 1 M in THF,
1
.5 mL), total volume of solvent 3 mL, Loading of CpPd(NHC)Cl 1 as indicated,
MeO
Me
reaction time 24 h.
MgBr
Me
OMe
Cl
b
Isolated yield based on the average of two runs.
Reaction time: 48 h.
c
a control experiment (Table 1, entry 1). Notably in the examined
Cl
Cl
coupling reaction, all four precatalysts 1aed were easily activated to
MgBr
Me
0
the required active (NHC)ePd species. With Grignard reagents
Me
5
6
85
added, the characteristic dark green of the solution of these com-
plexes faded gradually within several minutes at room temperature,
II
which suggested an easy transformation from the Pd precatalyst to
0
Pd catalyst. In both aspects, the saturated NHC ligands (SIMes and
SIPr) are more effective than the unsaturated ones (IMes and IPr),
92
which should attribute to their higher
s-donating properties [24].
MgBr
MgBr
Particularly, in regard to the new CpPd(NHC)Cl complexes 1, we
observed a distinct relationship between the steric bulk of substit-
uents on the imidazole nitrogens and their catalytic activities
(
(
Table 1, entries 2e5). For the less bulky IMes and SIMes ligand, CpPd
NHC)Cl 1a and 1c in 2 mol% catalytic loading could afford the cor-
N
7
8
N
N
Cl
Cl
87c
responding coupling product in 89 and 93%, respectively, over
a period of 24 h at room temperature. In sharp contrast, for the larger
sterically encumbered IPr and SIPr ligand, CpPd(NHC)Cl 1b and 1d
under the same conditions exhibited obviously less effective which
provided the yields of only 35 and 45%, respectively. The relation-
ships between the sterically constrained Pd centre and catalytic
activities we observed here are just opposite to the previous results
in the PEPPSI catalysts [25] and SuzukieMiyaura coupling reactions
MgBr
MgBr
MgBr
N
c
89
N
N
84c
[18], whereas the NHCePd catalysts with the larger sterically bulky
9
Cl
substituents on the imidazole nitrogens showed higher efficacy. We
ascribed the contrary to the existence of the Cp ring ligands. In
addition, obviously longer bond distance between the Cl atom and
Pd centre in the molecular structure of compound 1a should inter-
pret partially the situation.
N
10
Cl
N
Cl
79c,d
Given the stringent FDA requirements on the amount of Pd
present in pharmaceuticals, reducing the catalyst loading for this
reaction is quite important. When the loadings of 1c were decreased
to 1 mol% and 0.5 mol%, yields of the corresponding coupling
products also come down to 72 and 58%, respectively, over a period
of 24 h at room temperature (Table 1, entries 6 and 8). However, an
acceptableyield could be attained byelevating reaction temperature
with modestyand/or prolongingreaction time (Table 1, entries 7 and
MgBr
Me
Cl
1
1
1
2
N
Me
90c
N
N
9
). Notably, according to a modified Beller’s conditions [26], using
a mixed solvent of THFeDME (v:v 2:1) also led to a good yield with
mol% catalyst loading at room temperature (Table 1, entry 10).
82c
N
MgBr
Cl
1
Additionally, thepresenceofadditive LiClhas alsoapositive effecton
the coupling yield (Table 1, entry 11) [27].
(
continued on next page)

862
Z. Jin et al. / Journal of Organometallic Chemistry 696 (2011) 859e863
Table 2 (continued )
Entry Grignard’s
attack to the Cp ligand leads to concerted formation of CpPh and
b
MgBrCl, or attack at palladium leads to a palladium complex CpPd
(NHC)Ph, which undergoes reductive-elimination to yield the
Aryl/
heteroaryl
chloride
Biaryl product
Yield (%)
reagent
0
desired [(NHC)Pd ] catalytic species. At this point, in view of
N
N
obviously different distances of the PdeCp and PdeCl bonds in
complexes 1a and 1b, the activation step by attack at the Pd centre
is preferred. Longer distance of the PdeCl bond in 1a appears to be
easier for nucleophilic substitution of Cl atom, while longer
distance of the PdeCp bond in 1b is more beneficial to direct
attack at the Cp ring. As a result, the distinct reactivity between
complexes 1a and 1b is probably caused by the different activation
pathways.
Cl
N
N
1
3
Cl
74c,d,e
MgBr
a
Reaction conditions: aryl or heteroaryl chloride (1 mmol), Grignard reagents
1.5 mmol), CpPd(SIMes)Cl 1c (1 mol%) unless indicated, anhydrous LiCl (2 mmol),
Solvent: THF 3 mL, rt, reaction time 24 h (reaction time not optimized).
(
b
Isolated yield on the average of two runs.
c
Solvent: THFeDME (v:v 2:1), total volume 3 mL, reaction time 36 h.
mmol Grignard reagents and 2 mol% 1c were used.
d
3
e
Reaction time 48 h.
3. Conclusion
In summary, we have achieved a new one-pot method for
preparation of air-stable CpPd(NHC)Cl complexes 1aed. This new
class of well-defined NHCePd complexes exhibit high catalytic
activity in KumadaeTamaoeCorriu cross-coupling reaction in-
volving a variety of aryl and heteroaryl chlorides. We found that
NHC ligand with the less sterically constrained substituents on the
imidazole nitrogens showed higher catalytic activity, which is just
opposite to the previous results in other catalytic systems
involving NHC ligands. The activity of this family of NHCePd
precatalysts in other cross-coupling reaction is currently under
investigation.
After identifying these optimal reaction conditions, we then
subjected the CpPd(NHC)Cl 1 into the KumadaeTamaoeCorriu
cross-coupling reaction involving a variety of aryl and heteroaryl
chlorides. As expected, in all cases various aryl and heteroaryl
chlorides coupled smoothly with different aryl Grignard reagents at
room temperature in high yields using 1c as the catalyst (Table 2).
As listed in Table 2, even with sterically hindered Grignard reagents
(
Table 2, entries 4e6, entries 11e13), the coupling reaction could
carry out smoothly to give good to excellent yields. It is noteworthy
that, in the presence of excess Grignard reagents, both Cl atoms in
the aryl or heteroaryl chloride substrate could be coupled under the
present conditions (Table 2, entries 10 and 13).
4. Experimental section
2.4. Mechanism consideration
4.1. General remarks
0
In all cases, leading to the active Pd species from well-defined
All reactions were carried out at Ar
2
atmosphere unless indi-
II
NHCePd complexes is the ultimate key in the cross-coupling
reactions. Generally, anion ligands surrounding the Pd metal centre
play a very crucial role to the activation step from Pd to Pd
species. For example, significant reactivity differences can be seen
when the allyl group in (NHC)Pd(allyl)Cl [28e30] was replaced by
the cinnamyl group [31,32]. It was supposed that as a ancillary
ligand, the steric demand cinnamyl group induced a more facile
activation step from Pd to Pd than the corresponding allyl group,
which lead to an increased concentration of active [(NHC)Pd ]
cated. Toluene, THF, DME(1,2-dimethoxyethane), 1,4-dioxane, and
xylene was dried and distilled over Ph CO/Na prior to use. All aryl
2
II
0
and heteroaryl chlorides were used as received from commercial
availability. Anhydrous LiCl was stored under argon in a desiccator.
All Grignard reagents were prepared from the corresponding aryl
bromides according to the literature methods and titrated using the
1
13
standard method prior to use. H and C nuclear magnetic reso-
nance (NMR) spectra were recorded on a Bruker 400 MHz spec-
II
0
0
3
trometer at ambient temperature in CDCl (Cambridge Isotope
catalytic species [31].
Laboratories, Inc). Melt points of compounds were recorded with
uncorrected thermometers. Flash column chromatography was
performed on silica gel 60 (230e400 mesh).
With regard to the present catalytic system, there are two
possible pathways for nucleophilic attack by Grignard reagent
either at the Cp ring or at the palladium centre (Scheme 2). Direct
4.2. General procedure for synthesis of CpPd(NHC)Cl (1)
NHC
MgBrCl
PdII
Ph
In air, a 50-mL Schlenk flask was charged in turn with Pd
(
2 2
PhCN) Cl (950 mg, 2.5 mmol), IMes$HCl (850 mg, 2.5 mmol),
CpPh
Ar Cl
t
PhMgBr
KOBu (280 mg, 2.5 mmol). The flask was then caped with a rubber
septum and evacuated and backfilled with argon. This sequence
was repeated three times. THF (20 mL) was then injected through
the septum by syringe. The mixture was then stirred at room
temperature for 12 h. At that time, a sodium cyclopentadienylide
solution (5 mmol, 1 M in THF) (freshly prepared from sodium
dispersion in THF with freshly cracked cyclopentadiene) was
added by syringe at room temperature. Once sodium cyclo-
pentadienylide solution was added, the solution color became
green gradually from the original orange. The reaction mixture
was stirred overnight at room temperature. Finally, the resulting
mixture was directly subjected to flash column chromatography to
give the desired CpPd(NHC)Cl complexes 1aed as a green crystal.
Spectroscopic data for them are identical with literature [18].
NHC
PdII
activation step
NHC
PdII
Cl
Cl
NHC
Pd0
Ar
catalytic cycle
Ar'MgBr
PhMgBr
MgBrCl + CpPh
NHC
PdII
Ar Ar'
MgBrCl
Ar
Ar'
Scheme 2. Proposed activation pathways for complexes CpPd(NHC)Cl.

Z. Jin et al. / Journal of Organometallic Chemistry 696 (2011) 859e863
863
Table 3
Crystallographic data for compounds CpPd(NHC)Cl complexes 1a and 1b.
Acknowledgement
CpPd (IMes) Cl (1a) CpPd (IPr) Cl (1b)
29ClN Pd 41ClN Pd
Financial support for this work from the National Natural
Science Foundation of China (NNSFC) is gratefully acknowledged.
Chemical formula
C
26
H
2
C
32
H
2
Fw
511.36
P ꢁ 1
595.52
P2(1)/c
Space group
Cryst syst
a, Å
b, Å
c, Å
Appendix A. Supplementary material
Triclinic
Monoclinic
12.656(3)
14.680(3)
16.479(3)
90
103.84(3)
90
4
1.331
0.736
1240
1.88 to 25.02
19780
8.2190(16)
15.784(3)
19.374(4)
70.11(3)
85.26(3)
81.42(3)
4
1.454
0.924
1048
2.05 to 25.02
20362
CCDC 714852 and 714853 contain crystallographic information
for 1a and 1b. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
a
, deg
, deg
b
g
, deg
Z
ꢁ
ꢁ
3
D
calc., g cm
Appendix. Supplementary material
1
m
(Mo), mm
F(000)
range, deg
Detailed experimental procedures and spectroscopic data for all
coupling products (as supplementary data) can be found, in the
online version, at doi:10.1016/j.jorganchem.2010.10.009.
q
No. of reflns. collected
No. of unique reflns/Rint
No. of params/restraints
Final R indices
8193/0.0321
563/18
5236/0.0357
333/0
R
1
¼ 0.0282,
wR
¼ 0.0723
¼ 0.0333,
wR
R
1
¼ 0.0271,
wR
¼ 0.0670
¼ 0.0319,
wR
[
I > 2
s
(I)]
2
2
References
R indices (all indices)
R
1
R
1
2
¼ 0.0750
2
¼ 0.0701
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1.079
1.003
ꢁ
3
1.386 and ꢁ0.786
0.435 and ꢁ0.603
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reaction
In air, a vial equipped with a stir-bar was charged with NHCePd
complex 1 (1 mol%) and anhydrous LiCl (2 mmol), sealed with
a septum and evacuated and backfilled with argon. This sequence
was repeated three times. The aryl or heteroaryl chloride was
injected via syringe. Alternatively, if the aryl or heteroaryl chloride
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[12] A. de Meijere, F. Diederich, Metal-Catalyzed Cross-Coupling Reactions, Second
ed. Wiley, New York, 2004.
13] E. Negishi, Handbook of Organopalladium Chemistry for Organic Synthesis.
Wiley, New York, 2002.
[14] A.F. Littke, G.C. Fu, Angew. Chem. Int. Ed. Engl. 41 (2002) 4176e4211.
15] According to newly prices of Strem Chemicals, Inc., most phosphine ligands
are even more expensive than precious metals except some simple phosphine
compounds.
[
[
(
1 mmol) was solid at room temperature, it was weighed out and
added to the vial in air following 1 addition. The Grignard reagent
1.5 mmol), prepared in THF, was added in one portion by syringe.
Additional THF was added to make the total volume of solvent to
mL. For heteroaryl chloride substrates, reaction solvent consists of
THFeDME (2:1 v:v). The reaction mixture was allowed to stir for
4 h at room temperature. The products were isolated and purified
by the general workup procedure.
[
(
[
3
[16] N. Marion, S.P. Nolan, Acc. Chem. Res. 41 (2008) 1440e1449.
17] U. Christmann, R. Vilar, Angew. Chem. Int. Ed. Engl. 44 (2005) 366e374.
18] Z. Jin, S.X. Guo, X.P. Gu, L.L. Qiu, H.B. Song, J.X. Fang, Adv. Synth. Catal. 351
[
[
2
(2009) 1575e1585.
[
[
[
[
19] M.S. Viciu, R.M. Kissling, E.D. Stevens, S.P. Nolan, Org. Lett. 4 (2002) 2229e2231.
20] D.R. Jensen, M.S. Sigman, Org. Lett. 5 (2003) 63e65.
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Int. Ed. Engl. 39 (2000) 1602e1604.
4.4. X-ray diffraction analysis
Suitablecrystalsof1aand1bforX-raydiffractionwereobtainedby
slow diffusion of n-pentane into ether solution. Crystallographic data
was collected on a Bruker SMART CCD area detector diffractometer
[23] Z. Xi, B. Liu, W. Chen, J. Org. Chem. 73 (2008) 3954e3957.
[
24] E.A.B. Kantchev, C.J. O’Brien, M.G. Organ, Angew. Chem. Int. Ed. Engl. 46 (2007)
768e2813.
2
[25] M.G. Organ, M. Abdel-Hadi, S. Avola, N. Hadei, J. Nasielski, C.J. O’Brien,
C. Valente, Chem. Eur. J. 13 (2007) 150e157.
with graphite-monochromated Mo Ka radiation (l0.71073 Å).
Diffraction measurements were made at room temperature. An
absorption correction by SADABS was applied to the intensity data.
The structures were solved by Patterson method. The remaining non-
hydrogen atoms were determined from the successive difference
Fourier syntheses. All non-hydrogen atoms were refined anisotropi-
cally except those mentioned otherwise. The hydrogen atoms were
generated geometrically and refined with isotropic thermal parame-
ters. The structures were refined on F2 by full-matrix least-squares
methods using the SHELXTL-97 program package [33]. The crystal
data and structural refinement details are listed in Table 3.
[26] A.C. Frisch, F. Rataboul, A. Zapf, M. Beller, J. Org. Chem. 687 (2003) 403e409.
[
[
[
[
27] M.G. Organ, S. Avola, I. Dubovyk, N. Hadei, E.A.B. Kantchev, C.J. O’Brien,
C. Valente, Chem. Eur. J. 12 (2006) 4749e4755.
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E.D. Stevens, L. Cavallo, S.P. Nolan, Organometallics 23 (2004) 1629e1635.
29] M.S. Viciu, R.F. Germaneau, O. Navarro, E.D. Stevens, L. Cavallo, S.P. Nolan,
Organometallics 21 (2002) 5470e5472.
30] M.S. Viciu, R.F. Germaneau, S.P. Nolan, Org. Lett. 4 (2002) 4053e4056.
[31] N. Marion, O. Navarro, J. Mei, E.D. Stevens, N.M. Scott, S.P. Nolan, J. Am. Chem.
Soc. 128 (2006) 4101e4111.
[
[
32] N. Marion, O. Navarro, J. Mei, S.P. Nolan, Chem. Eur. J. 12 (2006) 5142e5148.
33] G.M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal Structures.
University of Göttingen, Göttingen, Germany, 1997.