Five-membered cyclopalladated complex containing bidentate phosphine ligands; Synthesis, characterization, and highly efficient Suzuki cross-coupling reactions

Article abstract of DOI:10.1080/00958972.2012.759216

A nonsymmetric phosphorus ylide and its palladium(II) complex have been synthesized as potential catalytically active compounds. The reaction of 1 equiv nonsymmetric phosphorus ylide, Ph₂PCH₂PPh ₂C(H)C(O)PhBr with [Pd(dppe)Cl₂], followed by treatment with 2 equiv AgOTf led to [(dppe)Pd(Ph₂PCH₂PPh ₂C(H)C(O)PhBr)](OSO₂CF₃)₂, which contains a five-membered P,P chelate ring on one side and a five-membered P,C chelate ring on the other side. The palladium complex was synthesized and investigated by fourier transform infrared spectroscopy (FT-IR), UV-visible, multinuclear (¹H, ³¹P and ¹⁹F) nuclear magnetic resonance (NMR), and electrospray ionisation-mass spectroscopic techniques. FT-IR and ³¹P NMR studies revealed that the phosphorus ylide is coordinated to palladium via the terminal phosphorus (P_c) of the ylide and methene group (CH). Suzuki reactions for varying aryl halides using the cyclopalladated complex as an efficient catalyst were performed. Various aryl halides were coupled with arylboronic acids in DMF, under air, in the presence of 0.001 mol% of the homogeneous catalyst to afford the corresponding cross-coupled products in good to excellent yields.

Full text of DOI:10.1080/00958972.2012.759216

This article was downloaded by: [University of Saskatchewan Library]
On: 27 September 2013, At: 00:11
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Coordination Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gcoo20
Five-membered cyclopalladated
complex containing bidentate
phosphine ligands; Synthesis,
characterization, and highly efficient
Suzuki cross-coupling reactions
SEYYED JAVAD SABOUNCHEI a , MOHSEN AHMADI a & ZAHRA NASRI b
a Faculty of Chemistry, Bu-Ali Sina University, Hamedan, Iran
b Department of Chemistry, University of Isfahan, Isfahan, Iran
Accepted author version posted online: 14 Dec 2012.Published
online: 29 Jan 2013.
To cite this article: SEYYED JAVAD SABOUNCHEI , MOHSEN AHMADI & ZAHRA NASRI (2013)
Five-membered cyclopalladated complex containing bidentate phosphine ligands; Synthesis,
characterization, and highly efficient Suzuki cross-coupling reactions, Journal of Coordination
Chemistry, 66:3, 411-423, DOI: 10.1080/00958972.2012.759216
To link to this article: http://dx.doi.org/10.1080/00958972.2012.759216
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Journal of Coordination Chemistry
Vol. 66, No. 3, 10 February 2013, 411–423
Five-membered cyclopalladated complex containing bidentate
phosphine ligands; Synthesis, characterization, and highly
efficient Suzuki cross-coupling reactions
SEYYED JAVAD SABOUNCHEI†*, MOHSEN AHMADI† and ZAHRA NASRI‡
†Faculty of Chemistry, Bu-Ali Sina University, Hamedan, Iran
‡Department of Chemistry, University of Isfahan, Isfahan, Iran
(Received 8 August 2012; in final form 26 October 2012)
A nonsymmetric phosphorus ylide and its palladium(II) complex have been synthesized as potential
catalytically active compounds. The reaction of
1 equiv nonsymmetric phosphorus ylide,
Ph2PCH2PPh2C(H)C(O)PhBr with [Pd(dppe)Cl2], followed by treatment with 2 equiv AgOTf led
to [(dppe)Pd(Ph2PCH2PPh2C(H)C(O)PhBr)](OSO2CF3)2, which contains a five-membered P,P che-
late ring on one side and a five-membered P,C chelate ring on the other side. The palladium com-
plex was synthesized and investigated by fourier transform infrared spectroscopy (FT-IR), UV–
visible, multinuclear (1H, 31P and 19F) nuclear magnetic resonance (NMR), and electrospray ionisa-
tion-mass spectroscopic techniques. FT-IR and 31P NMR studies revealed that the phosphorus ylide
is coordinated to palladium via the terminal phosphorus (Pc) of the ylide and methene group (CH).
Suzuki reactions for varying aryl halides using the cyclopalladated complex as an efficient catalyst
were performed. Various aryl halides were coupled with arylboronic acids in DMF, under air, in
the presence of 0.001 mol% of the homogeneous catalyst to afford the corresponding cross-coupled
products in good to excellent yields.
Keywords: Cyclopalladated complex; Bidentate phosphine ligands; Arylboronic acids; Nonsymmetric
phosphorus ylide; Suzuki cross-coupling reaction
1. Introduction
Palladium-catalyzed reactions, such as carbon–carbon bond formation, have attracted
considerable interest [1,2]. Specifically, the Suzuki cross-coupling reaction of aryl halides
with organoboron reagents is one of the most important and reliable methods for the con-
struction of biaryls, which are present in a wide range of natural products, pharmaceuticals,
agrochemicals, and functional polymer materials [3–10]. Like other types of palladium cat-
alyzed coupling reactions, the Suzuki coupling is highly dependent on the nature of the
ligand structure. Bulky, electron-rich phosphines are outstanding in the palladium-catalyzed
Suzuki cross-coupling reaction, resulting from their superior donor capability and stabiliza-
tion effects [11–14]. New palladacyclic complexes as active and air-stable catalytic candi-
dates have been employed in Suzuki reactions [15,16]. Cyclopalladated complexes are
important starting materials in organometallic chemistry [17,18], known for over 30 years
[19–25], and have applications in many areas, including organic synthesis, [26–29]
*Corresponding author. Email: sabounchei@basu.ac.ir
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online Ó 2013 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.759216

412
S.J. Sabounchei et al.
material science, [30] biologically active compounds [31], and as building blocks in mac-
romolecular chemistry [32–34].
Our group has obtained cyclopalladated complex from the nonsymmetric phosphorus
ylide, Ph2PCH2PPh2C(H)C(O)PhBr with [Pd(dppe)(OTf)2], and the complex is an excel-
lent catalyst for Suzuki cross-coupling reactions. Coordination, organometallic chemistry,
and catalytic chemistry of stabilized phosphorus ylides with palladium(II) have been inves-
tigated extensively and their ambidenticity was explained in terms of a delicate balance
between electronic and steric factors [35–38]. In conjunction of our previous work on the
synthesis and structural characterization of dichlorocyclopalladated complexes, [19] herein
we report the application of a new cyclopalladated complex (scheme 1) in Suzuki cross-
coupling reactions of various aryl halides under relatively mild experimental conditions.
2. Results and discussion
2.1. Synthesis and characterization
The nonsymmetric phosphorus ylide and its Pd(II) complex were synthesized (synthetic
route, scheme 2) and its structure was elucidated using a variety of physico-chemical tech-
niques.
The proclivity of OTf to be replaced by nucleophiles is shown by the poorly coordi-
nated OTf in [Pd(dppe)(OTf)2] being exchanged with the phosphorus ylide. Fluorine
nuclear magnetic resonance (NMR) (measured in CDCl3) shows a weak peak for trifluoro-
methanesulfonate at 67.5 ppm in [Pd(dppe)(OTf)2]. 19F NMR spectroscopy at room tem-
perature reveals a single resonance due to OTf at À77.9 ppm in the final complex, which
indicates that trifluoromethanesulfonate is a counter ion [39–41].
Cat.
K2CO3
Ar
Ar'
Ar'
B(OH)2
Ar
Br +
DMF
130 oC
Cat.
Br
O
Ph2
P
, 2OTf(-)
CH
PPh2
Pd
P
Ph2P
Ph2
Scheme 1. Suzuki cross-coupling reactions of various aryl halides with arylboronic acid in catalytic amount of
Pd complex.

Cyclopalladated complex
413
Ph2
Ph2
P
Br
P
OTf
OTf
Cl
Cl
ii
i
K2PdCl4
AgOTf 1
+
dppe
+
Pd
Pd
P
P
O
d
Ph2
Ph2
Ph2
, 2OTf(-)
v
P
CH
c
b
PPh2
Pd
O
a
O
iii
iv
P
PPh2
Ph2P
Br
dppm
+
Ph2
Br
HC
PPh2
H2C
Br
Scheme 2. Synthetic route for preparation of Pd(II) complex. Reagents and conditions: (i) In ethanol, in the
presence of hydrochloric acid, using Celite and refluxing for 8 h. (ii) In dichloromethane, using aluminum foil to
prevent oxidation and Celite for filtering precipitate, 2 h at 25 °C. (iii) In chloroform, using dry nitrogen, 2 h at 25 °C.
(iv) In triethyl amine (0.5 mL) in toluene, 15 min at 25 °C. (v) In methanol, using dry nitrogen, 12 h at 25 °C. 1Silver
trifluoromethanesulfonate.
The IR spectrum of the phosphorus ylide and its complex showed a band at
ꢀ1500 cmÀ1 assigned to carbonyl. The ν(CO), which is sensitive to complexation, occurs
at 1600 cmÀ1 in the parent ylide [42,43]. Coordination of the ylide through carbon causes
an increase in the ν(CO), while, when O-coordination occurs, a lowering in the value of
ν(CO) would be expected [44]. The band at 850À900 cmÀ1 characteristic of the P–CH of
the phosphorus ylide and its complex are assigned to P–C vibration. Thus, the IR absorp-
tion bands for the complex at lower frequencies indicate that C-coordination has occurred
[45].
In the 31P {1H} NMR spectra of Ph2PCH2PPh2C(H)C(O)PhBr, the signal due to PCH
(Pd) and PCH2 (Pc) appears as two doublets at 11.4 and À30 ppm, respectively. The 31P
chemical shift of [Pd(dppe)Cl2] due to Pa and Pb is a singlet at 66.7 ppm. The 31P NMR
spectrum of the complex shows an interesting pattern of signals which allows the assign-
ment of the structure of this complex. The four P atoms in this complex are chemically
and magnetically nonequivalent (scheme 2); therefore, the 31P {1H} NMR spectrum exhib-
its four separate resonances. The upfield peak (δp = 55, m), (Δδ = À11.7 ppm) is assigned
to Pa of the bidentate dppe, directly attached to Pd trans to CH and thus, shielded. The
3JPbPa coupling constant of 20 Hz lies within the typical values for similar systems [46–
2
3
48]. The JPcPa and JPdPa coupling constants are 58.1 and 14 Hz, respectively [49]. The
upfield peak (δp = 55.1, ddd), (Δδ = À11.6 ppm) is assigned to Pb of dppe, directly attached
to Pd trans to PCH2 (Pc) and thus, shielded [this value is intermediate between the two
peaks at 50.1 and 60.1 (see Supplementary material). The extremely strong coupling with
Pb of dppe (2JPbPc = 355 Hz) can only be rationalized in the context of a trans arrangement
3
between Pb and Pc [47,48,50,51]. The JPbPd coupling constant is 12 Hz. Two downfield
peaks are assigned to two phosphorus of the chelate phosphorus ylide. The ylidic Pd of the
phosphorus ylide is not directly coordinated to the metal center, thus coupling with Pc is
weak (2JPdPc = 27 Hz) as expected [49]. Coupling with Pb (3JPdPb = 12) and Pa
(3JPdPa = 14 Hz) gives a downfield ddd (δp = 37.6, ddd), (Δδ = +26.2 ppm). The chemical
shifts for the two nonequivalent phorphorus of the ambidentate P,CH–ligand are assigned
on the basis of published NMR data for related complexes [19]. Finally, the downfield
peak (δp = 19.1, ddd), (Δδ ≈ +49.1 ppm) is assigned to PCH (Pc). The significant downfield
shift of the signal from that of the free ylide is in agreement with the C-bonding of the
ylide. The coordination via the phosphine moiety is also clearly evidenced from the strong
downfield shifts of the signal due to PPh2 when compared to that of the same signal in the
free ylide [45,50].

414
S.J. Sabounchei et al.
1
Regarding the H NMR spectrum of this complex, the phenyl protons of dppe and phos-
phorus ylide are observed in the aromatic region of the spectrum, between 6.9–7.7 ppm
1
[19]. According to published data, the H NMR spectrum of the Pd(II) complexes was
consistent with coordination of the phosphorus ylide to the metal through the CH and Pc.
1
In the H NMR spectrum, the signal due to the methynic proton of the complex is broad
[19]. Similar behavior was observed earlier for ylide complexes derived from PtCl2 [52].
Furthermore, the complex showed a multiplet at 4.82 ppm due to the methynic proton. The
1
expected lower shielding of the H nuclei for PC(H) upon complexation in the case of
C-coordination was observed in the corresponding spectra [53]. The complex showed
multiple peaks at 2.66–2.76 ppm due to CH2 of dppe. The CH2 protons in the complex of
the phosphorus ylide appear as a multiplet (m) δ = 4.63 ppm.
Positive ion electrospray-mass spectrum (ESI+-MS) of the palladium catalyst was
recorded as very dilute THF solution. The molecular ion was observed in the electrospray
ionisation (ESI) mass spectrum. The mass spectrum of the Pd complex was characterized
by the appearance of the fragment at m/z 1085.1 owing to the removal of two OTf groups
and one proton, thus the {[Complex]+ÀH} was formed. The peak at m/z 1235.06 is related
to the molecular ion which is formed by elimination of one OTf group to give [Com-
plex]+. Also, the peak at m/z 543.05 is related to the ion produced by the elimination of
two OTf groups and one radical hydrogen to give [Complex]•2+ (Supplementary material).
The above-mentioned data are in agreement with the calculated data (see Section 3).
The cyclopalladated complex has been found to be diamagnetic, indicating + 2 oxidation
state for palladium. Electronic spectra of the Pd complex were recorded in the solid state
and displayed three bands at 200–500 nm. The electronic spectrum of the phosphorus ylide
as a ligand showed spectral bands due to π→π⁄ and n→π⁄ transitions. On complexation,
these bands shift (see Supplementary material).
2.2. Suzuki cross-coupling reactions
Cyclopalladated complexes containing phosphorus ylides, which combines both good
donor strength and π-accepting capacity, always have high catalytic activity in Suzuki
cross-coupling reactions [38]. Therefore, we attempted to use our pd(II) complex as a cata-
lyst in the Suzuki reaction. The ability to use small amounts of catalyst and still achieve
high yields is a great concern in cross-coupling reactions due to the high cost of metals
and ligands.
Low catalyst loading tests were performed to determine the catalytic efficiency of the
catalyst in the presence of DMF and K2CO3. In order to optimize the reaction conditions
for the coupling reactions, different amounts of catalyst (mol%) were taken and the results
are summarized in table 1. Excellent yields were obtained from normal catalyst loads
down to a level of 0.1 and 0.01 mol%. A moderate yield (65%) was obtained even at cata-
lyst loading as low as 0.0005 mol%. Various catalyst concentrations were also tested and
0.001 mol% (table 1, entry 4) gave the best result. These are indications of an effective
catalytic system that merits more exploration.
To study the effects of different solvents in our catalytic system, we have chosen the
reaction between 4-bromobenzaldehyde with phenylboronic acid in the presence of various
solvents and K2CO3. In all instances, the solvent was used as obtained commercially
without further purification and the reactions were performed in air. After completion of
the reaction, the biphenyl was isolated from the reaction mixture. The results of the above

Cyclopalladated complex
415
Table 1. Effect of catalyst loading.a
Cat.
B(OH)2
+
OHC
OHC
Br
K2CO3, DMF
Entry
Catalyst (mol%)
Time (h)
Yieldb (%)
1
2
3
4
5
6
None
0.1
0.01
0.001
0.005
0.0005
10
0.5
0.5
0.5
0.5
5
–
100
100
99
99
65
aReaction conditions: 4-bromobenzaldehyde (0.75 mmol), phenyl boronic acid (1 mmol), K2CO3 (1.5 mmol), DMF
(2 mL).
bYield to the coupled product determined by GC based on aryl bromide.
reactions are summarized in table 2. A nonpolar solvent like toluene gave a moderate yield
(67%, entry 3), whereas polar solvents such as DMF or methanol were more efficient for
the yield of biaryl compounds to 99 and 73%, respectively (entries 2 and 4). A polar apro-
tic solvent (entry 1) gave a comparatively good yield. The lowest conversion (26%) was
obtained with THF as solvent. This could be due to the reflux temperature of the solvent.
In water, the reaction does not progress under reflux.
The effect of different mineral bases on this reaction was investigated by using the cou-
pling of 4-bromobenzaldehyde with phenylboronic acid as a test case. First, the reaction
was conducted without any base and no reaction was observed. In the presence of NaOAc
and NaF yields of 76 and 59%, respectively, were observed inorganic bases (table 2,
entries 8–11) which were much better than organic ones (table 2, entry 7); K2CO3 was the
best choice of base, and the yield of product could be increased to 99% (table 2, entry 2).
Under the optimized reaction conditions at hand, we have taken a series of aryl halide
and arylboronic acids and the yield of the coupled products are given in table 3. A general
Table 2. Optimization of base and solvent for Suzuki cross-coupling reaction.a
Cat.
Base, Solvent
+
OHC
OHC
Br
B(OH)2
Entry
Base
Solvent
Temp. (°C)
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Et3N
Na2CO3
Cs2CO3
NaOAc
NaF
Dioxane
DMF
Toluene
Methanol
THF
H2O
DMF
DMF
DMF
130
130
130
65
0.5
0.5
3
85
99
67
73
26
12
60
24
24
24
1
1
12
12
100
130
130
130
130
130
–
Trace
90
89
76
59
9
10
11
DMF
DMF
aReaction conditions: 4-bromobenzaldehyde (0.75 mmol), phenyl boronic acid (1 mmol), base (1.5 mmol), solvent
(2 mL), catalyst (0.001 mol%), 130 °C.
bGC yield.

416
S.J. Sabounchei et al.
Table 3. Suzuki cross-coupling reaction of aryl halides with aryl boronic acids catalyzed by Pd complex.a
Palladacycle catalyst
Ar′Β(ΟΗ)
Ar⎯Ar′
Ar⎯X
+
2
K2CO3. DMF
+
130°C
Entry
Ar-X
Ar-B(OH)2
Product (Ar-Ar′)
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
p-O2N-Ph-Br
p-O2N-Ph-Br
p-OHC-Ph-Br
p-OHC-Ph-Br
p-Me-Ph-Br
p-Me-Ph-Br
C10H7-Br
C10H7-Br
Ph-Br
Ph-Br
PhB(OH)2
p-Et-PhB(OH)2
PhB(OH)2
p-Et-PhB(OH)2
PhB(OH)2
p-Et-PhB(OH)2
PhB(OH)2
p-Et-PhB(OH)2
PhB(OH)2
p-Et-PhB(OH)2
PhB(OH)2
p-Et-PhB(OH)2
PhB(OH)2
p-Et-PhB(OH)2
PhB(OH)2
p-Et-PhB(OH)2
PhB(OH)2
p-Et-PhB(OH)2
PhB(OH)2
p-Et-PhB(OH)2
PhB(OH)2
p-Et-PhB(OH)2
PhB(OH)2
p-Et-PhB(OH)2
PhB(OH)2
p-Et-PhB(OH)2
PhB(OH)2
p-O2N-Ph-Ph
p-O2N-Ph-Ph-Et
p-OHC-Ph-Ph
P-OHC-Ph-Ph-Et
p-Me-Ph-Ph
p-Me-Ph-Ph-Et
C10H7-Ph
C10H7-Ph-Et
Ph-Ph
0.5
0.5
0.5
0.5
1.5
1.5
2
98
96
99
98
88
87
83
80
90
86
95
93
83
81
91
84
88
83
82
80
76
69
97
93
90
88
75
61
2
9
1.5
1.5
0.5
0.5
2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27c
28c
p-Et-Ph-ph
p-Br-Ph-CO2H
P-Br-Ph-CO2H
C4H3SBr
p-HO2C-Ph-Ph
p-HO2C-Ph-Ph-Et
C4H3S-Ph
C4H3S-Ph-Et
p-CH3OC-Ph- Ph
p-CH3OC-Ph- Ph-Et
Ph-Ph
p-Et-Ph-Ph
p-CH3OC-Ph- Ph
p-CH3OC-Ph- Ph-Et
p-Me-Ph-Ph
p-Me-Ph-Ph-Et
Ph-Ph
C4H3SBr
2
p-CH3OC-Ph-Br
P-CH3OC-Ph-Br
Ph-Cl
0.5
0.5
3
3
2
2
3
3
0.5
0.5
0.5
0.5
0.5
3
Ph-Cl
p-CH3OC-Ph-Cl
P-CH3OC-Ph-Cl
p-Me-Ph-Cl
p-Me-Ph-Cl
Ph-I
Ph-I
p-Me-Ph-I
p-Me-Ph-I
p-OHC-Ph-Br
p-Me-Ph-Cl
p-Et-Ph-Ph
p-Me-Ph-Ph
p-Me-Ph-Ph-Et
p-OHC-Ph-Ph
p-Me-Ph-Ph
PhB(OH)2
aReaction conditions: aryl halide (0.75 mmol), boronic acid (1 mmol), K2CO3 (1.5 mmol), DMF (2 mL), catalyst
(0.001 mol%), 130 °C.
bGC yields based on aryl halide.
cWith precursor complex [Pd(dppe)(OTf)2] as catalyst (0.001 mol%). See Ref. [70].
catalytic cycle for the cross-coupling reaction of organoboron reagents with aryl halides
involves oxidative-addition of the aryl halide, transmetalation, and reductive elimination
[3,4]. In a typical Suzuki cross-coupling reaction, the PdII species is reduced to Pd0 prior
to the oxidative addition step (see scheme 3).
Aryl bromides with various functional groups efficiently reacted with boronic acids
(table 3, entries 1–14) using K2CO3 and 2 mL DMF at reflux temperature in the pres-
ence of the palladium(II) catalyst to give Suzuki products in good to excellent yields. In
palladium-catalyzed carbon–carbon bond formation reactions, it is commonly believed
that better yields are achieved for aryl halides with electron-withdrawing rather than
electron-donating substituents [54]. Electron-deficient aryl bromides were transformed
efficiently to the coupling products in P 80% yield in short reaction times (table 3,
entries 1–4, 11–12, 15–16, and 19–20). The reaction of p-bromo-nitrobenzene with boro-
nic acid derivatives showed excellent yields (entries 1–2, 98-96%). In electron-rich or
deactivated p-bromotoluene, the yields are good in all the cases (entries 5–6, 88–87%).
The electron-poor 4-bromobenzaldehyde also afforded excellent yields (entries 3–4,

Cyclopalladated complex
417
99–98%). The electronically neutral bromobenzene (entries 9–10) produced a good
amount of the desired product when coupled with arylboronic acid. As expected, very
satisfactory results were obtained with the electron-deficient substrate of phenylboronic
acid (entries 1, 3, 11, 15, 19) and showed excellent yields. 2-Bromothiophene was an
efficient substrate (table 3, entries 13–14). Aryl chlorides were active for the Suzuki
reaction with good yields even for a prolonged time at 130 °C (entries 17–18). Electron-
deficient substrates such as 4-chloroacetophenone coupled with arylboronic acid yield the
coupling products (table 3, entries 19, 20). In electron-rich p-chlorotoluene, the yields are
moderate in all the cases (entries 21–22, 76–69%). Aryl iodides with arylboronic acids
for the Suzuki reaction gave good yields of the corresponding products under optimized
conditions (table 3, entries 23–26). The main drawback of the Pd-mediated Suzuki
cross-coupling reaction is that only aryl iodides and aryl bromides can be used effi-
ciently. Increasing the reaction rate of aryl chlorides allows us to overcome this problem
[55]. The stronger C–Cl bond is responsible for slower reaction rate of aryl halides,
because the oxidative addition step was rate determining in the cross-coupling catalytic
cycle. In all reactions of aryl halides, the color of the reaction mixture changed very fast
(ꢀ30 s) from light brown to black. Thus, it can be inferred that the reaction mechanism
starts with a pre-dissociation and/or reduction step [56]. In this state, the Pd(II) source is
converted into the more active and coordinatively unsaturated Pd(0) catalyst. This state
is followed by oxidative addition of the aryl halide which is often the rate-determining
step in C–C coupling catalytic cycles [57]. The catalytic cycle is completed by transmet-
allation, aryl group transfer from boron to palladium, and a final reduction–elimination
to release the biaryl product. A proposed mechanistic description of the Suzuki reaction
is presented in scheme 3. Initially, Pd(II) converts to Pd(0) [58], followed by oxidative
addition of aryl halide to Pd(0) to form the aryl palladium(II) intermediate 1. Then,
phenylboronic acid which is activated by K2CO3 reacts with intermediate 1. After the
transmetallation reaction, intermediate 2 is obtained. Finally, reductive elimination of 2
produces the desired coupling products.
[Pd(dppe)(OTf)2] can also be used as an active resource for producing Pd(0). We used
this complex as main catalyst under identical conditions. As can be seen in table 3, the
activity of [Pd(dppe)(OTf)2] with an ‘easy’ set of substrates (entry 27) and a ‘difficult’ set
of substrates (entry 28) was tested. When we use this complex as a catalyst in the Suzuki
reaction under the mentioned optimized conditions, moderate catalytic activity was
observed for the catalyst in both substrates.
Although several catalytic systems have been reported to support Suzuki C–C coupling
reactions, a homogeneous catalyst of this type is novel for its P donor dppe and P and CH
of the phosphorus ylide. The homogeneous nature of the catalysis was checked by the
classical mercury test [59]. Addition of a drop of mercury to the reaction mixture did not
affect the conversion of the reaction, which suggests that the catalysis is homogeneous in
nature, since heterogeneous catalysts would form an amalgam, thereby poisoning it.
The high efficiency of this catalyst at very low catalyst loading and short reaction time
make it valuable. Monomeric complexes are easier to reduce to the active Pd(0) species
compared with the dimeric Pd catalyst [60,63]. The comparison of data presented in table
4 shows the efficiency of this new catalyst towards the coupling reactions. Therefore, we
compared various homogeneous catalysts in the Suzuki reaction under the same conditions
(aryl halide, base and solvent) with the cyclopalladated complex used in this work. Low
catalyst loading, high reactivity with bromobenzene in short reaction time, and stability
toward air make it an ideal complex for Suzuki cross-coupling reactions.

418
S.J. Sabounchei et al.
P
P
CH
P
Pd
P
Ar-Ar
CH
CH
Ar-X
P
(0)Pd
P
CH
Ar
Ar
Ar
(2)
(1)
P
P
Pd
Pd
X
P
P
ArB(OH)3K + KHCO3
ArB(OH)2+K2CO3+H2O
B(OH)
+ K2CO3
B(OH)4K + KHCO3
Scheme 3. Proposed mechanism for Suzuki cross coupling.
1
This method proved successful in most cases to give the product in > 99% purity. H
and 13C NMR data of the products indicated no Suzuki coupling by-products and NMR
spectra of the Suzuki products are given in Supplementary material.
3. Experimental
3.1. Materials and techniques
Aryl halides and arylboronic acids were purchased from Sigma-Aldrich. Technical grade
DMF was used for all catalytic reactions. GC analysis was performed on a Shimadzu 14B
gas chromatograph equipped with a flame ionization detector. Melting points were mea-
sured on a SMPI apparatus and are reported without correction. Elemental analyses for C,
H, and N were performed using a Perkin–Elmer 2400 series analyzer. Fourier transform IR
spectra were recorded on a Shimadzu 435-U-04 spectrophotometer from 400–4000 cmÀ1
and samples were prepared as KBr pellets. UV–vis spectra were recorded on a JASCO,

Cyclopalladated complex
419
V-670 Spectrophotometer, Japan, from 190–2700 nm. Mass spectra were recorded from a
JEOL JMS 700 B/ES spectrometer. 1H, 13C, 19F, and 31P NMR spectra were recorded
either on a 400 MHz Bruker or on a 90 MHz Jeol spectrometer using CDCl3 as a solvent
at 25 °C. Chemical shifts (δ) are reported relative to internal TMS (1H and 13C), internal
CFCl3 (19F), and external 85% phosphoric acid (31P). [Pd(dppe)Cl2] [69], [Pd(dppe)
(OTf)2] [70], and Ph2PCH2PPh2C(H)C(O)PhBr [19] were prepared by published proce-
dures (see Supplementary material).
3.2. General procedure for preparation of the palladium catalyst
To [Pd(dppe)(OTf)2] (0.4 g, 0.5 mmol) in methanol solution (10 mL), a solution of
(Ph2PCH2PPh2C(H)C(O)PhBr) (0.29 g, 0.5 mmol) (10 mL, CH3OH) was added dropwise.
The resulting solution was stirred for 12 h at room temperature and then concentrated to
2 mL and treated with diethylether (2 Â 10 mL) to give a final product. The product as a
white solid was collected and dried under vacuum (yield: 0.58 g, 84%). M.p. 225–227 °C.
1H NMR (CDCl3): δ (ppm) 6.91–7.77 (m, 44H, C6H5), 2.66 (m, 2H, CH2(dppe)), 2.76 (m,
2H, CH2(dppe)), 4.82 (br, 1H, CH(methine)), 4.63 (m, 2H, CH2(ylide)). 31P NMR
(CDCl3): δ (ppm) 55 (m, Pa), 55.1 (ddd, Pb, 2J(PbPc) = 355.1 Hz, 3J(PbPa) = 20 Hz, 3J
(PbPd) = 12 Hz), 19.15 (ddd, Pc, 2J(PcPb) = 355 Hz, 2J(PcPa) = 58.1 Hz, 2J(PcPd) = 27 Hz),
2
2
3
37.65 (ddd, Pd, J(PdPb) = 58 Hz, J(PdPc) = 20.1 Hz, J(PdPa) = 14 Hz). 19F NMR (CDCl3):
δ (ppm) À77.9 (s, CF3). Selected IR data (KBr, cmÀ1): ν = 997 (m, P–CH2), 820 (m, P–
CH), 1616 (s, C=O). UV–vis (λmax, nm): 241 (intra-ligand transition, phenyl group), 257
(intra-ligand transition, C=O), 300 (LMCT, s→d), 325 (MLCT). ESI-MS: m/z = 1235.06
((Calcd 1235.06), [(dppe)Pd(Ph2PCH2PPh2C(H)C(O)PhBr)]+), 1085.10 ((Calcd 1085.10),
[(dppe)Pd(Ph2PCH2PPh2C(H)C(O)PhBr)]+ minus a proton), 543.05 ((Calcd 543.05),
[(dppe)Pd(Ph2PCH2PPh2C(H)C(O)PhBr)]•2+ minus a radical hydrogen). Anal. Calcd for
C61H51BrF6O7P4PdS2: C, 52.92; H, 3.71. Found: C, 52.81; H, 3.65%.
3.3. General experimental procedure for Suzuki cross-coupling reactions
A mixture of an aryl halide (0.75 mmol), phenyl boronic acid (1 mmol), Pd complex
(0.001 mol%), K2CO3 (1.5 mmol), and DMF (2 mL) was heated to 130 °C for a specified
time. The reactions were monitored by thin-layer chromatography. The reaction mixture was
then cooled to room temperature. The combined organic extracts were washed with brine and
dried over CaCl2 and Na2SO4. The solvent was evaporated and a crude product was obtained,
analyzed by 1H and 31C NMR. A small aliquot of the reaction mixture was diluted in MeOH
for direct GC analysis. Yields were calculated against consumption of the aryl halides.
3.4. Characterization of the products of Suzuki cross-coupling reactions
3.4.1. 4-Nitro-4′-ethyl-biphenyl (entry 2, table 3). M.p. 82–83 °C. 1H NMR
3
(89.6 MHz, CDCl3): δ = 7.28–8.34 (m, phenyl, 8H), 2.70 (q, CH2, J = 7.5 Hz, 2H), 1.30
3
(t, CH3, J = 7.4 Hz, 3H). 13C NMR (100 MHz, CDCl3, ppm): δ = 147.5 (s, phenyl), 146.8
(s, phenyl), 138.7 (s, phenyl), 129.1 (s, phenyl), 128.8 (s, phenyl), 127.7 (s, phenyl), 127.3
(s, phenyl), 124.0 (s, phenyl), 32.4 (s, CH2), 14.6 (s, CH3).

420
S.J. Sabounchei et al.
Table 4. Comparison with other catalytic system.
Catalyst
K2CO3. DMF
Ph
Ph
Br PhB(OH)
Ph
+
2
Entry
[Pd] catalyst
mol%
Conditions
Yield (%)
Refs.
1
2
3
4
5
6
7
8
9
[Pd(S^O)2]
[Pd(N^O)2]
[PdCl2(Imidazole)2]
[Pd(C^N)(μ-Br)]2
[Pd(SC6F4–4-H)2(TMEDA)]
[Pd(C^N^N)Cl]
[PdCl2(HL)2]
[Pd(C^C)(PPh3)Cl]
[Pd(P^p)(C^p)]
0.01
0.001
0.001
0.001
0.1
1
0.1
0.001
0.001
100 °C, 1 h
100 °C, 6 h
120 °C, 12 h
130 °C, 3 h
110 °C, 12 h
80 °C, 5 h
100 °C, 1 h
75 °C, 1 h
130 °C, 1.5 h
73
88
97
92
43
96
100
46
90
[61]
[62]
[63]
[64]
[65]
[66]
[67]
[68]
This work
3.4.2. 4-Carboxaldehyde-4′-ethyl-biphenyl (entry 4, table 3). M.p. 81–82 °C. IR (KBr,
cmÀ1): ν = 3024, 2965, 2936, 1682 (C=O), 1605, 881, 835, 808. 1H NMR (89.6 MHz,
CDCl3, ppm): δ = 10.04 (s, CHO, 1H), 7.24–7.59 (m, phenyl, 8H), 2.68 (q, CH2,
3J = 7.9 Hz, 2H), 1.30 (t, CH3, 3J = 7.4 Hz, 3H). 13C NMR (100 MHz, CDCl3, ppm):
δ = 191.8 (s, C=O), 147.0 (s, phenyl), 144.7 (s, phenyl), 136.8 (s, phenyl), 134.8 (s, phe-
nyl), 130.1 (s, phenyl), 128.4 (s, phenyl), 127.3 (s, phenyl), 127.1 (s, phenyl).
1
3.4.3. 4-Methyl-4′-ethyl-biphenyl (entries 6 and 26, table 3). M.p. 59–61 °C. H NMR
3
(89.6 MHz, CDCl3, ppm): δ = 7.21–7.82 (m, phenyl, 8H), 2.71 (q, CH2, J = 7.9 Hz, 2H),
3
2.45 (s, CH3, 3H), 1.30 (t, CH3 (ethyl), J = 8.1 Hz, 3H). 13C NMR (100 MHz, CDCl3,
ppm): δ = 143.0 (s, phenyl), 138.4 (s, phenyl), 138.2 (s, phenyl), 136.6 (s, phenyl), 129.4
(s, phenyl), 128.2 (s, phenyl), 126.85 (s, phenyl), 126.80 (s, phenyl), 28.4 (s, CH2), 21.0
(s, CH3), 15.6 (s, CH3 (ethyl)).
3.4.4. 1-(4-Ethylphenyl)naphthalene (entry 8, table 3). 1H NMR (89.6 MHz, CDCl3,
ppm): δ = 7.11–8.50 (m, phenyl, 11H), 2.83 (q, CH2, 3J = 7.6 Hz, 2H), 1.45 (t, CH3,
3J = 7.3 Hz, 3H). 13C NMR (100 MHz, CDCl3, ppm): δ = 143.1 (s, phenyl), 140.2 (s, phe-
nyl), 137.9 (s, phenyl), 133.7 (s, phenyl), 131.6 (s, phenyl), 129.9 (s, phenyl), 128.2
(s, phenyl), 127.7 (s, phenyl), 127.3 (s, phenyl), 126.8 (s, phenyl), 126.0 (s, phenyl), 125.8
(s, phenyl), 125.6 (s, phenyl), 125.3 (s, phenyl), 28.6 (s, CH2), 15.5 (s, CH3).
3.4.5. 4′-Ethyl-biphenyl-4-carboxylic acid (entry 12, table 3). IR (KBr, cmÀ1):
ν = 3025, 3014, 2984, 1722 (C=O), 1604, 792, 765, 739. 1H NMR (89.6 MHz, CDCl3,
3
ppm): δ = 11.1 (s, COOH, 1H), 6.92–7.81 (m, phenyl, 8H), 2.68 (q, CH2, J = 6.5 Hz, 2H),
3
1.30 (t, CH3, J = 7.8 Hz, 3H). 13C NMR (100 MHz, CDCl3, ppm): δ = 169.3 (s, C=O),
141.6 (s, phenyl), 138.4 (s, phenyl), 135.8 (s, phenyl), 134.8 (s, phenyl), 130.1 (s, phenyl),
128.4 (s, phenyl), 127.8 (s, phenyl), 127.7 (s, phenyl), 30.6 (s, CH2), 14.9 (s, CH3).
3.4.6. 2-(4-Ethylphenyl)thiophene (entry 14, table 3). M.p. 48–49 °C. 1H NMR
3
(89.6 MHz, CDCl3, ppm): δ = 6.91–7.80 (m, phenyl, H), 2.62 (q, CH2, J = 8.1 Hz, 2H),
3
1.16 (t, CH3, J = 7.2 Hz, 3H). 13C NMR (100 MHz, CDCl3, ppm): δ = 131.8 (s, phenyl),

Cyclopalladated complex
421
128.3 (s, phenyl), 128.2 (s, phenyl), 127.8 (s, phenyl), 126.8 (s, phenyl), 125.9 (s, phenyl),
124.2 (s, phenyl), 122.5 (s, phenyl), 28.5 (s, CH2), 15.5 (s, CH3).
3.4.7. 4-Acetyl-4′-ethyl-biphenyl (entries 16 and 20, table 3). IR (KBr, cmÀ1):
ν = 3060, 3019, 2976, 1655 (C=O), 1611, 815, 789, 751. 1H NMR (89.6 MHz, CDCl3, ppm):
3
δ = 7.25–8.01 (m, phenyl, 8H), 2.59 (q, CH2, J = 7.3 Hz, 2H), 2.51 (s, CH3, 3H), 1.24 (t,
CH3, 3J = 8.0 Hz, 3H). 13C NMR (100 MHz, CDCl3, ppm): δ = 190.8 (s, C=O), 140.9 (s, phe-
nyl), 138.4 (s, phenyl), 135.7 (s, phenyl), 133.7 (s, phenyl), 129.3 (s, phenyl), 128.3 (s, phe-
nyl), 127.8 (s, phenyl), 127.7 (s, phenyl), 33.4 (s, CH2), 30.3 (s, CH3), 15.9 (s, CH3).
The following compounds gave data consistent with those published: table 3:
4-Nitro-biphenyl (entry 3) [71,72], 4-phenylbenzaldehyde (entry 3) [73], 4-methyl-biphenyl
(entries 5, 25) [74], 1-phenylnaphthalene (entry 7) [71], biphenyl (entries 9, 17, 23) [38],
4-ethyl-biphenyl (entries 10, 18, 24) [75], 4-biphenylcarboxylic acid (entry 11) [76],
2-phenylthiophene (entry 13) [74], and 4-acetylbiphenyl (entries 15, 19) [60].
4. Conclusion
The present study describes the very efficient synthesis and characterization of a mononuclear
cyclopalladated complex. On the basis of the physicochemical and spectroscopic data, we
have proposed that ligands employed herein exhibit a chelate coordination behavior to the
metal center affording a five-membered chelate ring. The coordination ability of the phospho-
rus ylide and dppe has been proven in complexation with Pd(II). In this work, we used a pal-
ladium(II) complex as an efficient catalyst for the Suzuki reaction of various aryl halides.
This complex is a highly active and efficient catalyst for promoting the Suzuki cross-coupling
reaction of various aryl halides to produce the corresponding products in good to excellent
yields. With the catalyst loading of 0.001 mol%, the electron-rich substrate 4-bromobenzalde-
hyde couples with phenylboronic acid in high yield. The ease of preparation of the complex
(homogeneous catalyst), its high solubility in organic solvents, very low catalyst loading, and
stability toward air make it an ideal complex for the above transformations.
Supplementary material
For complete information please refer to supplementary data file.
Acknowledgment
This work was supported by Bu-Ali Sina University funds. We thank Mr. Zebarjadian for
recording NMR spectra. Our gratitude also goes to Miss. Behranj for all cooperation.
References
[1] F. Diederich de Meijer. Metal-Catalyzed Cross-Coupling Reactions , Vols. 1 and 2, 2nd Edn Edn, Wiley-
VCH, Weinheim (2004).
[2] S. Cacchi, G. Fabrizi. Chem. Rev., 105, 2873 (2005).

422
S.J. Sabounchei et al.
[3] N. Miyaura, A. Suzuki. Chem. Rev., 95, 2457 (1995).
[4] A. Suzuki. J. Organomet. Chem., 576, 147 (1999).
[5] A. Suzuki. Chem. Commun., 4759 (2005).
[6] A.F. Littke, G.C. Fu. Angew. Chem. Int. Ed., 41, 4176 (2002).
[7] N.T.S. Phan, M. Van Der Sluys, C.W. Jones. Adv. Synth. Catal., 348, 609 (2006).
[8] F. Alonso, I.P. Beletskaya, M. Yus. Tetrahedron, 64, 3047 (2008).
[9] V.F. Slagt, A.H.M. De Vries, J.G. De Vries, R.M. Kellogg. Org. Process Res. Dev., 14, 30 (2010).
[10] V. Polshettiwar, A. Decottignies, C. Len, A. Fihri. Chem. Sus. Chem, 3, 502 (2010).
[11] J. Hassan, M. Sévignon, C. Gozzi, E. Schulz, M. Lemaire. Acc. Chem. Res., 40, 676 (2007).
[12] R. Martin, S.L. Buchwald. Acc. Chem. Res., 41, 1461 (2008).
[13] G.C. Fu. Acc. Chem. Res., 41, 1555 (2008).
[14] G.A. Molander, B. Canturk. Angew. Chem. Int. Ed., 48, 9240 (2009).
[15] V. Farina. Adv. Synth. Catal., 346, 1553 (2004).
[16] J. Dupont, C.S. Consorti. J. Chem. Rev., 105, 2527 (2005).
[17] S.J. Sabounchei, H. Nemattalab, F. Akhlaghi, H.R. Khavasi. Polyhedron, 27, 3275 (2008).
[18] S.J. Sabounchei, F. Akhlaghi Bagherjeri, A. Dolatkhah, J. Lipkowski, M. Khalaj. J. Organomet. Chem., 696,
3521 (2011).
[19] S.J. Sabounchei, S. Samiee, D. Nematollahi, A. Naghipour, D. Morales-Morales. Inorg. Chim. Acta, 363,
3973 (2010).
[20] E.C. Alyea, G. Ferguson, J. Malito, B.L. Ruhl. Organometallics, 8, 1188 (1989).
[21] D.F. Brayton, T.M. Larkin, D.A. Vicic, O. Navarro. J. Organomet. Chem., 694, 3008 (2009).
[22] S. Mohanty, D. Suresh, M.S. Balakrishna, J.T. Mague. J. Organomet. Chem., 694, 2114 (2009).
[23] T. Mitsudo, W. Fischetti, R.F. Heck. J. Org. Chem., 49, 640 (1984).
[24] A.D. Tanase, G.D. Frey, E. Herdtweck, S.D. Hoffmann, W.A. Herrmann. J. Organomet. Chem., 692, 3316
(2007).
[25] (a) G. Aragay, J. Pons, J. García-Anton, X. Solans, M. Font-Bardia, J. Ros. J. Organomet. Chem., 693, 3396
(2008); (b) A.C. Cope, E.C. Friedrich. J. Am. Chem. Soc., 90, 909 (1968); (c) P. Braunstein, J. Dehand, M.
Pfeffer. Inorg. Nucl. Chem. Lett., 10, 521 (1974).
[26] R.B. Bedford, M. Betham, S.J. Coles, P.N. Horton, M.J. Lopez-Saez. Polyhedron, 25, 1003 (2006).
[27] R.B. Bedford, M. Betham, M.E. Blake, R.M. Frost, P.N. Horton, M.B. Hursthouse, R.M. López-Nicolás.
Dalton Trans, 2774 (2005).
[28] D.A. Albisson, R.B. Bedford, S.E. Lawrence, P.N. Scully. Chem. Commun., 2095, (1998).
[29] R.B. Bedford, M. Betham, J.P.H. Charmant, A.L. Weeks. Tetrahedron, 64, 6038 (2008).
[30] J. Buey, P. Espinet. J. Organomet. Chem., 507, 137 (1996).
[31] K.K. Lo, C. Chung, T.K. Lee, Lui, K.H. Tang, N. Zhu. Inorg. Chem., 42, 6886 (2003).
[32] C. Lopez, A. Caubet, S. Perez, X. Solans, M. Font-Bardía. J. Organomet. Chem., 681, 80 (2003).
[33] S. Perez, C. Lopez, A. Caubet, X. Solans, M. Font-Bardía, A. Roig, E. Molins. Organometallics, 25, 596
(2006).
[34] A. Moyano, M. Rosol, R.M. Moreno, C. Lopez, M.A. Maestro. Angew. Chem. Int. Ed., 44, 1865 (2005).
[35] U. Belluco, R.A. Michelin, M. Mozzon, R. Bertani, G. Facchin, L. Zanotto, L. Pandolfo. J. Organomet.
Chem., 557, 37 (1998).
[36] L.R. Falvello, S. Fernandez, R. Navarro, A. Rueda, E.P. Urriolabeitia. Inorg. Chem., 37, 6007 (1998).
[37] R. Navarro, E.P. Urriolabeitia. J. Chem. Soc., Dalton Trans, 4111 (1999).
[38] K. Karami, C. Rizzoli, M.M. Salah. J. Organomet. Chem., 696, 940 (2011).
[39] G. Annibale, P. Bergamini, V. Bertolasi, M. Cattabriga, V. Ferretti. Inorg. Chem. Commun., 3, 303 (2000).
[40] M. Agostinho, P. Braunstein. CR. Chim., 10, 666 (2007).
[41] M. Fuss, H.U. Siehl. Organometallics, 18, 758 (1999).
[42] S.J. Sabounchei, S. Samiee, S. Salehzadeha, Z.B. Nojini, E. Irran. J. Organomet. Chem., 695, 1441 (2010).
[43] S.J. Sabounchei, S. Samiee, S. Salehzadeha, M. Bayat, Z.B. Nojini, D. Morales-Morales. Inorg. Chim. Acta,
363, 1254 (2010).
[44] M. Kalyanasundari, K. Panchanatheswaran, W.T. Robinson, H. Wen. J. Organomet. Chem., 491, 103 (1995).
[45] M.M. Ebrahima, K. Panchanatheswaran, A. Neels, H. Stoeckli-Evans. J. Organomet. Chem., 694, 643
(2009).
[46] P. Braunstein, Y. Chauvin, J. Nahring, A. DeCian, J. Fischer, A. Tiripicchio, F. Ugozzoli. Organometallics,
15, 5551 (1996).
[47] L. Dahlenburg, K. Herbst, M. Kuhnlein. Z. Anorg. Allg. Chem., 623, 250 (1997).
[48] M. Lamac, I. Cisarova, P. Stepnicka. J. Organomet. Chem., 690, 428 (2005).
[49] S.M. Sbovata, A. Tassan, G. Facchin. Inorg. Chim. Acta, 361, 3177 (2008).
[50] A.M. Trzeciak, J.J. Ziolkowski, T. Lis, R. Choukroun. J. Organomet. Chem., 575, 87 (1999).
[51] P.S. Pregosin, R.W. Kunz. IR and NMR of Transition Metal Phosphine Complexes, Springer-Verlag, West
Berlin (1979).
[52] J.A. Teagle, J.L. Burmeister. Inorg. Chim. Acta, 118, 65 (1986).
[53] S.J. Sabounchei, M. Ahmadi Gharacheh, H.R. Khavasi. J. Coord. Chem., 63, 1165 (2010).

Cyclopalladated complex
423
[54] N. Kataoka, Q. Shelby, J.P. Stambuli, J.F. Hartwig. J. Org. Chem., 67, 5553 (2002).
[55] (a) V.P.W. Böhm, C.W.K. Gstöttmayr, T. Weskamp, W.A. Herrmann. J. Organomet. Chem., 595, 186 (2000);
(b) C. Zhang, M.L. Trudell. Tetrahedron Lett., 41, 595 (2000); (c) A. Fürstner, A. Leitner. Synlett., 290
(2001).
[56] T. Rosner, J. Le Bars, A. Pfaltz, D.G. Blackmond. J. Am. Chem. Soc., 123, 1848 (2001).
[57] S.R. Chemler, D. Trauner, S.J. Danishefsky. Angew. Chem. Int. Ed., 40, 4544 (2001).
[58] I.P. Beletskaya, A.V. Cheprako. Chem. Rev., 100, 3009 (2000).
[59] (a) K. Inamoto, J. Kuroda, K. Hiroya, Y. Noda, M. Watanabe, T. Sakamoto. Organometallics, 25, 3095
(2006); (b) J.A. Widegren, R.G. Finke. J. Mol. Catal. A: Chem., 198, 317 (2003); (c) E. Peris, J.A. Loch, J.
Mata, R.H. Crabtree. Chem. Commun., 201 (2001).
[60] F. Yang, Y. Zhang, R. Zheng, J. Tang, M. He. J. Organomet. Chem., 651, 146 (2002).
[61] D.A. Safin, M.G. Babashkina, A. Klein. Catal. Lett., 129, 363 (2009).
[62] A. Kilic, D. Kilinc, E. Tas, I. Yilmaz, M. Durgun, I. Ozdemir, S. Yasar. J. Organomet. Chem., 695, 697
(2010).
[63] M. Trivedi, G. Singh, R. Nagarajan, N.P. Rath. Inorgan. Chim. Acta, 394, 107 (2013).
[64] A.R. Hajipour, K. Karami, A. Pirisedigh. Inorgan. Chim. Acta, 370, 531 (2011).
[65] M. Basauri-Molina, S. Hernández-Ortega, R.A. Toscano, J. Valdés-Martínez, D. Morales-Morales. Inorgan.
Chim. Acta, 363, 1222 (2010).
[66] F. Zeng, Z. Yu. J. Org. Chem., 71, 5274 (2006).
[67] D.A. Safin, M.G. Babashkina. Catal. Lett., 130, 679 (2009).
[68] K. Karami. J. Coord. Chem., 63, 3688 (2010).
[69] D.A. Slack, M.C. Baird. Inorg. Chim. Acta, 24, 277 (1977).
[70] S. Fallis, G.K. Anderson, N.P. Rath. Organometallics, 10, 3180 (1991).
[71] Z. Zhang, Z. Wang. J. Org. Chem., 71, 7485 (2006).
[72] J. Ma, X. Cui, B. Zhang, M. Song, Y. Wu. Tetrahedron, 63, 5529 (2007).
[73] J.-H. Li, Q.-M. Zhu, Y.-X. Xie. Tetrahedron, 62, 10888 (2006).
[74] L. Liang, P. Chien, M. Huang. Organometallics, 24, 353 (2005).
[75] B. Karimi, P. Fadavi Akhavan. Chem. Commun., 47, 7686 (2011).
[76] B. Mu, T. Li, C. Li, P. Liu, W. Shang, Y. Wu. Tetrahedron, 65, 2599 (2009).