Seven-membered Pd(II) complexes containing symmetric phosphorus ylides: Synthesis, characterization and high catalytic activity toward Suzuki cross-coupling reactions

Article abstract of DOI:10.1016/j.crci.2013.05.019

The reaction of 1,2-bis(diphenylphosphino)ethane (dppe) with various ketones in acetone produces the new phosphonium salts [RC(O)CH ₂PPh₂(CH₂)₂PPh₂CH ₂C(O)R]X₂ (R = 2-naphtyl, X

Full text of DOI:10.1016/j.crci.2013.05.019

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CRAS2C-3783; No. of Pages 10
C. R. Chimie xxx (2013) xxx–xxx
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´
Full paper/Memoire
Seven-membered Pd(II) complexes containing symmetric
phosphorus ylides: Synthesis, characterization and high
catalytic activity toward Suzuki cross-coupling reactions
a
a
Seyyed Javad Sabounchei a, , Mohammad Panahimehr , Mohsen Ahmadi ,
*
Fateme Akhlaghi a, Collete Boscovic b
a Faculty of Chemistry, Bu-Ali Sina University, Hamedan 65174, Iran
b School of Chemistry, University of Melbourne, Victoria 3010, Australia
A R T I C L E I N F O
A B S T R A C T
Article history:
The reaction of 1,2-bis(diphenylphosphino)ethane (dppe) with various ketones in acetone
produces the new phosphonium salts [RC(O)CH2PPh2(CH2)2PPh2CH2C(O)R]X2 (R = 2-
naphtyl, X = Br (1); R = 2,4-dichlorophenyl, X = Cl (2); R = 3-nitrophenyl, X = Br (3)). Further
Received 12 March 2013
Accepted after revision 30 May 2013
Available online xxx
treatment
with
a
base
gives
the
symmetrical
phosphorus
ylides,
RC(O)CH5PPh2(CH2)2PPh25CHC(O)R (R = 2-naphtyl (4), 2,4-dichlorophenyl (5), 3-nitro-
phenyl (6)). These ligands react with Pd(II) chloride to form C,C-chelated complexes with
the composition [RC(O)CH5PPh2(CH2)2PPh25CHC(O)R]PdCl2, where R = 2-naphtyl (7),
2,4-dichlorophenyl (8), 3-nitrophenyl (9). These compounds have been characterized by
elemental analysis and spectroscopic methods and consist of seven-membered rings
formed by the coordination of the ligands through the two ylidic carbon atoms to the metal
center. The structure of compound 5 has been characterized crystallographically. The
palladium complex 9 is employed in the Suzuki cross-coupling reaction between
phenylboronic acid and several aryl halides. It was found to be a competent catalyst for a
variety of substrates to afford the coupled products in high yields using DMF as a solvent.
The biaryl products were obtained under aerobic conditions in short reaction times with a
lower loading of the catalyst (0.001 mol%).
Keywords:
Seven-membered ring
Symmetric phosphorus ylides
Suzuki cross-coupling reaction
Low catalyst loading
X-ray crystal structure
´
ß 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
1. Introduction
coordination chemistry of carbonyl stabilized [12–14] and
bifunctionalized [2,15–18] ylides is an important research
Phosphorus ylides are reactive compounds, which take
part in many reactions of value in the synthesis of organic
products [1–4]. Resonance-stabilized phosphorous ylides,
particularly the keto ylides, are used as important ligands
in organometallic and coordination chemistry [5–9]. This
delocalization also makes these ligands weak nucleophiles,
but this does not reduce their interest as ligands. And it
was their weak donor ability that allowed us to prepare
new types of ylide complexes [9–11]. The reactivity and
field of our group. In recent years, this area was developed
while studying the organometallic chemistry of ketenyli-
denetriphenylphosphorane Ph3P5C5C5O towards Pt sub-
strates, obtaining complexes in which the ylide was
s-
bonded to the metal through the ylidic carbon atom
[19,20]. Phosphorus ylide complexes are versatile com-
pounds in catalytic reactions, such as the hydrogenation of
olefins [21], the cyclotrimerization [22] and polymeriza-
tion of acetylenes [23]. Phosphorus ylides of the type
Ph2P(CH2)nPPh2(CHC(O)R) (n = 1, or 2; R = Me, Ph or –OMe),
containing phosphine and keto-stabilized phosphorus
ylide moieties are also known, and their transition metal
complexes are mostly confined to palladium and, to a
*
Corresponding author.
E-mail address: jsabounchei@yahoo.co.uk (S.J. Sabounchei).
1631-0748/$ – see front matter ß 2013 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.crci.2013.05.019
Please cite this article in press as: Sabounchei SJ, et al. Seven-membered Pd(II) complexes containing symmetric
phosphorus ylides: Synthesis, characterization and high catalytic activity toward Suzuki cross-coupling reactions. C. R.
Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.05.019

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CRAS2C-3783; No. of Pages 10
2
S.J. Sabounchei et al. / C. R. Chimie xxx (2013) xxx–xxx
lesser extent, to platinum [24–26]. We have tried to
convert both phosphine moieties in 1,2–bisdiphenylpho-
sphinoethane into keto-stabilized ylides to facilitate the
coordination ability of the ylides. They coordinate to
palladium(II) to form chelate ylide complexes of the type
by the full-matrix least-squares method on F2 using the
SHELXTL-97 crystallographic package [36,37]. All non-
hydrogen atoms were refined anisotropically. Hydrogen
atoms were inserted at calculated positions using a riding
model, with isotropic displacement parameters.
PdCl2(Y) (Y = chelate ylide) with
a seven-membered
chelate ring [17]. However, the synthesis of cyclic bis-
ylides, and the study of their complexation to transition
metals, is a less documented field and very few examples
have been reported in the literature [27–29], in spite of
their practical importance [30,31]. Palladium catalysis is
ubiquitous in modern organic chemistry and a great
number of catalytic systems have been designed and fine-
tuned through careful ligand design and choice of
experimental conditions (solvent, temperature, catalyst
loading, etc.). The palladium-catalyzed Suzuki cross-
coupling of aryl halides with arylboronic acid is among
the most powerful C–C-bond-forming reactions available
to synthetic chemists [32]. Current technologies demand
new catalysts, which are inexpensive, readily accessible,
moisture- and air-stable and, most importantly, highly
effective under low catalyst loading [33]. Recently,
palladacycle complexes have attracted much attention
as exciting catalyst precursors to cross-coupling reactions
[32b–h,33c]. In conjunction with our previous work on the
synthesis and catalytic activity of palladacycle complexes
[34], herein, we report the synthesis, characterization and
application of a new Pd(II) complex as a catalyst in the
Suzuki cross-coupling reaction of various aryl halides
under aerobic and conventional heating conditions.
2.3. Sample preparation
2.3.1. Synthesis of diphosphonium salts
2.3.1.1. General procedure. A solution consisting of bis(di-
phenylphosphino)ethane (dppe) (0.32 g, 0.8 mmol) and
the related carbonyl compound (1.7 mmol) in acetone was
stirred at room temperature for 24 h. The resulting solution
was filtered off, and the precipitate obtained washed with
diethyl ether and dried.
2.3.1.2. Data
for
[C10H7C(O)CH2PPh2(CH2)2PPh2CH2-
C(O)C10H7]Br2 (1). Yield: 0.58 g, 81%. Mp 248–250 8C. Anal.
calcd. for C50H42Br2O2P2: C, 66.98; H, 4.72. Found: C, 66.89;
H, 4.70%. IR (KBr disk, cmÀ1 : 1658 (CO). 1H NMR (DMSO-
) n
d6)
8.02, 8.92 (m, 34H, Ph and 2-naphtyl). 31P NMR (DMSO-d6)
P: (ppm): 27.17 (s, PPh2). 13C NMR (DMSO-d6)
C: 23.43
dH: 3.74 (br, 4H, CH2); 6.02 (br, 4H, PCH2CO); 7.80, 7.95,
d
d
(br, CH2); 36.19 (br, PCH2CO); 119.38, 123.68, 124.80,
129.32, 139.44, 130.50, 131.70, 132.85, 133.63, 133.83,
134.76, 139.43 (Ph and 2-naphtyl); 193.25 (s, CO).
2.3.1.3. Data
for
[Cl2C6H3C(O)CH2PPh2(CH2)2PPh2CH2-
C(O)C6H3Cl2]Cl2 (2). Yield: 0.47 g, 69%. Mp 298–300 8C.
Anal. calcd. for C42H34Cl6O2P2: C, 59.67; H, 4.05. Found: C,
59.72; H, 4.01%. IR (KBr disk, cmÀ1 : 1684 (CO).1H NMR
) n
(CDCl3)
7.72, 8.02, 8.56, 8.75, 9.03 (m, 34 H, Ph). 31P NMR (CDCl3):
dP (ppm): 23.97 (s, PPh2). 13C NMR (CDCl3)
C: 21.36 (dd,
CH2, JPC = 64.58, JPC = 30.03); 38.09 (t, 2C, PCH2CO,
1JPC = 28.03 Hz); 116.29, 117.04, 117.9, 128.85, 130.72,
132.14, 133.33, 134.83,139.18, 139.29 (Ph); 191.79 (s, CO).
dH: 3.83 (br, 4H, CH2); 6.32 (br, 4H, PCH2CO); 7.66,
2. Experimental
d
2.1. Physical measurements and materials
1
2
All the reactions were carried out under an atmosphere
of dry nitrogen. Methanol was distilled over magnesium
powder and diethyl ether (Et2O) over a mixture of sodium
and benzophenone just before use. All the other solvents
were reagent-grade and used without further purification.
Melting points were measured on a SMP3 apparatus. IR
spectra were recorded on a Shimadzu 435-U-04 spectro-
photometer from KBr pellets. 1H, 13C and 31P NMR spectra
were recorded on 400 MHz Bruker and 90 MHz Jeol
spectrometer in DMSO-d6 or CDCl3 as the solvent at
25 8C. Chemical shifts (ppm) are reported according to
internal TMS and external 85% phosphoric acid. Coupling
constants are given in Hz. Elemental analyses for C, H and N
atoms were performed using a PerkinElmer 2400 series
analyzer.
2.3.1.4. Data for [O2NC6H4C(O)CH2PPh2(CH2)2PPh2CH2-
C(O)C6H4NO2]Br2 (3). Yield: 0.61 g, 85%. Mp 249–251 8C.
Anal. calcd. for C42H46Br2N2O6P2: C, 56.90; H, 4.09. Found:
C, 56.78; H, 4.12%. IR (KBr disk, cmÀ1
)
n
: 1682 (CO). 1H NMR
H = 3.8 (br, 4H, CH2); 6.58 (br, 4H, PCH2CO); 7.51,
(DMSO):
d
3
7.59, 7.67, 7.71, 7.80, 7.91, 8.07 (d, JPC = 5.58), 8.42 (d,
2JPC = 18.0), 8.52 (d, 2JPC = 16.5), 8.71 (m, 28 H, Ph). 31P NMR
(DMSO-d6):
C: 15.30 (t, CH2, 1JPC = 25.66); 33.56 (br, PCH2CO); 122.72,
d
P (ppm): 26.72 (s, PPh2). 13C NMR (DMSO-d6)
d
127.54, 128.67, 128.92, 129.21, 129.55, 132.65, 133.88,
134.63, 135.57, 146.66, 147.22; 190.1 (s, CO).
2.3.2. Synthesis of ligands
2.2. X-ray crystallography
2.3.2.1. General procedure. Phosphonium salts 1–3 were
further treated with sodium bis(trimethylsilyl)amide
(1.0 mL), leading to the elimination of HX (X = Cl, Br),
affording the free ligands 4–6 as the sole products.
The single-crystal X-ray diffraction data of suitable
crystals of 5 were collected with an Oxford Diffraction
single-crystal X-ray diffractometer using the mirror
˚
monochromated Mo Ka radiation (0.71073 A) at 130 K
2.3.2.2. Data
for
C10H7C(O)CH5PPh2(CH2)2PPh25CH-
(Table 3). Gaussian absorption corrections were carried out
using a multifaceted crystal model using CrysAlisPro [35].
Both structures were solved by direct methods and refined
C(O)C10H7 (4). Yield: 0.22 g, 60%. Mp 219–221 8C. Anal.
calcd. for C50H40O2P2: C, 81.73; H, 5.48. Found: C, 81.60; H,
Please cite this article in press as: Sabounchei SJ, et al. Seven-membered Pd(II) complexes containing symmetric
phosphorus ylides: Synthesis, characterization and high catalytic activity toward Suzuki cross-coupling reactions. C. R.
Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.05.019

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3
5.46%. IR (KBr disk, cmÀ1
3.40 (s, 4H, CH2); 4.36 (br, 2H, CH); 7.46, 8.02, 8.12, 7.80,
8.53 (m, 34 H, Ph and 2-naphtyl). 31P NMR (CDCl3)
P: 15.12
)
n
: 1517 (CO). 1H NMR (CDCl3) dH
:
1643 (CO).1H NMR (DMSO-d6)
d
H (ppm): 2.38 (br, 4H, CH2),
6.15 (br, 2H, CH), 7.46, 7.63, 7.92, 8.05, 8.22 (m, 24H, Ph).
d
31P NMR (DMSO-d6)
3JPP = 4.24 Hz, P2).
dP: 29.59 (br, P1), 32.76 (bd, PPh2,
(s, PPh2). 13C NMR (DMSO-d6)
dC:16.95 (br, CH2); 22.383 (t,
CH, 1JPC = 57.15 Hz); 116.02, 117.6, 119.94, 123.52, 130.07,
133.37, 134.86, 147.87 (Ph); 191.24 (s, CO).
2.4. General experimental procedure for Suzuki cross-
coupling reactions
2.3.2.3. Data for Cl2C6H3C(O)CH5PPh2(CH2)2PPh25CH-
C(O)C6H3Cl2 (5). Yield: 0.22 g, 57%. Mp 258–260 8C. Anal.
calcd. for C42H32Cl4O2P2: C, 65.30; H, 4.18. Found: C, 64.93;
A mixture of an aryl halide (0.75 mmol), phenyl boronic
acid (1 mmol), complex 9 (0.001 mol%), Cs2CO3 (1.5 mmol),
and DMF (2 mL) was heated to 110 8C for specified time.
The reactions were monitored by thin-layer chromato-
graphy (TLC). The reaction mixture was then cooled to
room temperature. After completion of the reaction, the
mixture was diluted with n-hexane (15 mL) and water
(15 mL). The organic layer was washed with brine (15 mL),
dried over CaCl2. The solvent was evaporated and a crude
H, 4.24%. IR (KBr disk, cmÀ1 : 1582 (CO). 1H NMR (CDCl3)
) n
d
H: 3.31 (br, 4H, CH2); 4.45 (br, 2H, CH); 7.49, 7.55, 7.63,
7.72,8.17, 8.25 (m, 26 H, Ph). 31P NMR (CDCl3)
P: 13.50 (s,
PPh2). 13C NMR (CDCl3)
C: 18.14 (br, CH2); 25.01 (br, CH);
d
d
121.71, 125.88, 126.35, 127.53, 129.31, 131.63, 133.07,
134.28 (Ph); 185.11 (s, CO).
2.3.2.4. Data for O2NC6H4C(O)CH5PPh2(CH2)2PPh25CH-
C(O)C6H4NO2 (6). Yield: 0.25 g, 68%. Mp 203–205 8C. Anal.
calcd. for C42H44N2O6P2: C, 68.65; H, 6.04. Found: C, 68.61;
product was obtained, which was analyzed by 1H and 31
C
NMR. The liquid residues were purified by silica gel column
chromatography (n-hexane:EtOAc, 80:20), whereas the
solid ones were purified by re-crystallization from ethanol
and water.
H, 6.06%. IR (KBr disk, cmÀ1 : 1585 (CO). 1H NMR (CDCl3):
) n
2
d
H = 3.06 (bd, 4H, CH2, JPH = 3.20); 4.60 (t, 2H, CH,
2JPH = 11.21); 7.16, 7.24, 7.5, 7.62, 7.71, 8.24 (t,
3JPC = 7.83), 8.77 (m, 28 H, Ph). 31P NMR (CDCl3): dP
3. Results and discussion
(ppm): 15.49 (s, PPh2). 13C NMR (DMSO-d6)
dC: 17.34 (br,
CH2); 26.08 (br, CH); 120.80, 124.03, 125.47, 129.26,
129.32, 129.38, 129.50, 131.95, 132.01, 132.6, 133.25,
147.73 (Ph); 180.16 (s, CO).
3.1. Synthesis
Diphosphine Ph2P(CH2)2PPh2 reacts with 2 equiv of the
appropriate ketones, forming the corresponding phospho-
nium salts 1–3. Further treatment with sodium bis(tri-
methylsilyl)amide leads to two-fold elimination of HX
(X = Cl, Br), giving the free ligands 4–6. Reaction of these
ligands with Pd(II) chloride in 1:1 molar ratio form C,C-
chelated complexes [RC(O)CH5PPh2(CH2)2PPh25CH-
C(O)R]PdCl2, where R = 2-naphtyl (7), 2,4-dichlorophenyl
(8), 3-nitrophenyl (9) (Scheme 1). All complexes are
moderately soluble in dichloromethane and insoluble in
non-polar solvents, such as n-hexane.
2.3.3. Synthesis of the Pd(II) complexes
2.3.3.1. General procedure. To
a [PdCl2(COD)] (0.085 g,
0.3 mmol) dichloromethane solution (5 mL), a solution of
ylides 4–6 (0.3 mmol) (5 mL, CH2Cl2) was added dropwise.
The resulting solution was stirred for 2 h at room
temperature and then concentrated to ca. 2 mL in volume
and treated with cool n-hexane (ca. 15 mL) to afford the
products, which were collected and dried under vacuum.
2.3.3.2. Data
for
[C10H7C(O)CH5PPh2(CH2)2PPh25CH-
3.2. Spectroscopy
C(O)C10H7]PdCl2 (7). Yield: 0.17 g, 64%. Mp 212 8C dec.
Anal. calcd. for C50H40Cl2O2P2Pd: C, 65.83; H, 4.42. Found:
In the IR spectra of diphosphonium salts, a strong
stretching absorption due to carbonyl groups has been
observed, which confirms the formation of salts 1–3
symmetrically. IR data confirm the complete formation of
the phosphorus ylides with the vanishing of the phospho-
nium CO band between 1658 and 1684 cmÀ1 for dipho-
sphonium salts 1–3 and the appearance of a new strong CO
band relative to carbonyl stabilized ylides 4–6 at 1517 to
1585 cmÀ1 [17,20]. As we have noted earlier [38], the
coordination of the phosphorus ylides through carbon or
oxygen causes a significant increase or decrease, respec-
tively, in the carbonyl stretching frequency. Thus, the
infrared absorption bands observed for complexes 7–9
indicate that the coordination of the symmetric phosphorus
ylides with the palladium center occurs through the ylidic
carbon atoms. The two carbonyl groups of all complexes are
non-equivalent and discriminable in IR spectra (Table 1).
The 31P NMR spectra of all the compounds show all the
expected resonances for the proposed structures. The 31P
NMR spectra of phosphonium salts exhibit a singlet around
C, 65.71; H, 4.37%. IR (KBr disk, cmÀ1 : 1624 (CO). 1H NMR
) n
(CDCl3): dH = 3.42 (br, 4H, CH2); 5.25 (br, 2H, CH); 7.23,
7.27, 7.39, 7.57, 7.68, 7.79, 7.88, 8.30 (m, 34 H, Ph and 2-
naphtyl). 31P NMR (CDCl3) dP (ppm): 28.03 (d,
3
3JPP = 5.00 Hz, P1), 30.34 (d, JPP = 3.23 Hz, P2).
2.3.3.3. Data for [Cl2C6H3C(O)CH = PPh2(CH2)2PPh2 = CH-
C(O)C6H3Cl2]PdCl2 (8). Yield: 0.176 g, 62%. Mp 220 8C dec.
Anal. calcd. for C42H32Cl6O2P2Pd: C, 53.11; H, 3.39. Found:
C, 53.14; H, 3.38%. IR (KBr disk, cmÀ1
) n: 1625, 1655
(CO).1H NMR (DMSO-d6):
dH = 4.20 (s, 4H, CH2); 5.38 (s, 2H,
CH); 7.04, 7.039, 7.55, 8.29, 8.32, 8.92 (m, 26 H, Ph). 31P
3
NMR (DMSO-d6) dP (ppm): 26.10 (d, JPP = 4.85 Hz, P1),
3
32.04 (d, JPP = 6.16 Hz, P2).
2.3.3.4. Data for [O2NC6H4C(O)CH5PPh2(CH2)2PPh25CH-
C(O)C6H4NO2]PdCl2 (9). Yield: 0.324 g, 72%. Mp 245–
247 8C. Anal. Calc. for C42H34Cl2N2O6P2Pd: C, 55.92; H,
3.79. Found: C, 55.89; H, 3.76%. IR (KBr disk, cmÀ1
) n: 1611,
Please cite this article in press as: Sabounchei SJ, et al. Seven-membered Pd(II) complexes containing symmetric
phosphorus ylides: Synthesis, characterization and high catalytic activity toward Suzuki cross-coupling reactions. C. R.
Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.05.019

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Scheme 1. Synthetic route for the preparation of compounds 1–9.
Table 1
phosphonium salt, suggesting some electron density
IR data for compounds 1–9.
increase in the P–C bonds [17,39]. The 1H NMR spectra
show all the expected resonances of symmetric phos-
phorus ylides 4–6. Chemical shifts appear to be shifted
upfield with respect to the parent phosphonium salts,
indicating that synthesis of the ylides has occurred. The
room temperature 31P NMR spectra of complexes 7–9
exhibit two doublets around 28 and 32 ppm, which are
assigned to the P1 and P2 atoms, respectively. This
chemical shift is at a lower field than that observed for
the corresponding free ylide (around 15 ppm), indicating
that the coordination of the ylides has occurred. As
reported earlier [17,40], the downfield shift of the ylidic
phosphorus signifies the coordination of the ylidic moiety.
The coordination of the bis-ylides 4–6 to the palladium
center creates two stereogenic centers of the same
configuration, as indicated by the presence of two 31P
NMR signals (doublets with a coupling constant 3JP–P of 2–
7 Hz). In the 1H NMR spectra, the signals due to the
methinic protons for all the complexes are broad and
centered at 5–6 ppm. The 1H chemical shift values for the
complexes appear to be shifted downfield with respect to
the parent ylide, indicating also that the coordination of
the ylides has occurred [40,41]. Selected NMR chemical
shifts for compounds 1–9 are reported in Table 2.
Compound
n
(CO) cmÀ1
Reference
1
1658
1684
1682
1509
This work
This work
This work
[17]
2
3
PhC(O)CH5PPh2(CH2)2
PPh25CHC(O)Ph
4
1517
This work
This work
This work
[17]
5
1582
6
1585
[PhC(O)CH5PPh2(CH2)2
1632, 1679
PPh25CHC(O)Ph]PdCl2
7
8
9
1624, 1659
1625, 1655
1611, 1643
This work
This work
This work
23–27 ppm due to PPh2 groups, which indicates that the
two phosphorus atoms are equivalent. The 1H NMR spectra
show, in addition to the expected aromatic resonances,
two peaks centered around 4 and 6 ppm, which are
attributable to the P(CH2)2P and PCH2CO protons, respec-
tively. The 31P NMR spectrum of phosphorus ylides 4–6
shows a singlet around 15 ppm, which corresponds to the
PPh2 groups. The phosphonium atoms of these compounds
show upfield shifts compared to that of the parent
Table 2
Selected 1H and 31P NMR spectral data for compounds 1–9 [
d (ppm), J (Hz)].
Compound
d
PCH (2JP–H
)
d
PCH2CO (3JP–P
)
d
PCH (3JP–P
)
1a
2b
3a
4b
5b
6b
7b
8a
9a
–
–
–
27.17 (s)
–
–
–
23.97 (s)
26.72 (s)
4.36 (br)
4.45 (br)
–
–
–
–
–
–
15.12 (s)
13.50 (s)
15.49 (s)
4.60 (t, 11.21)
5.25 (br)
28.03 (5.00), 30.34 (3.23)
26.10 (4.85), 32.04 (6.16)
29.59 (br), 32.76 (4.24)
5.38 (s)
6.15 (br)
a
Record in DMSO-d6.
b
Record in CDCl3. br, broad; s, singlet.
Please cite this article in press as: Sabounchei SJ, et al. Seven-membered Pd(II) complexes containing symmetric
phosphorus ylides: Synthesis, characterization and high catalytic activity toward Suzuki cross-coupling reactions. C. R.
Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.05.019

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5
Table 3
Table 4
˚
Crystal data and refinement details for 5.
Selected bond lengths (A) and bond angles (8) for 5.
Compound 5
Compound 5
Empirical formula
Formula weight
Temperature (K)
C44H34Cl10O2P2
C(1)–P(1)
1.7218(19)
1.384(3)
1.267(2)
1.815(2)
1.522(4)
1.814(2)
1.384(3)
1.266(2)
1.7233(19)
1.525(4)
1011.15
130(10)
0.71073
Triclinic
C(1)–C(2)
C(2)–O(1)
C(9)–P(1)
˚
Wavelength (A)
Crystal system
Space group
C(9)–C(9)
C(30)–P(2)
C(22)–C(23)
C(23)–O(2)
C(22)–P(2)
C(30)–C(30)
¯
P1
˚
a (A)
11.4908(3)
˚
b (A)
15.0297(5)
˚
c (A)
16.0555(5)
˚
a
b
g
Z
().
106.327(3)
˚
()
110.245(3)
C(9)–P(1)–C(1)
114.08(9)
113.44(10)
108.55(9)
104.32(9)
110.02(9)
106.09(9)
113.58(9)
114.72(10)
108.22(10)
103.74(9)
110.56(10)
105.70(9)
˚
()
103.841(3)
C(10)–P(1)–C(1)
C(16)–P(1)–C(1)
C(9)–P(1)–C(10)
C(16)–P(1)–C(9)
C(10)–P(1)–C(16)
C(22)–P(2)–C(30)
C(22)–P(2)–C(31)
C(22)–P(2)–C(37)
C(30)–P(2)–C(31)
C(30)–P(2)–C(37)
C(31)–P(2)–C(37)
2
Absorption coefficient (mmÀ1
)
0.708
u
range for data collection (8)
2.92 to 30.11
–15 ꢀ h ꢀ 15
–19 ꢀ k ꢀ 21
–22 ꢀ l ꢀ 20
Index ranges
Reflections collected
24918
Independent reflections
Absorption correction
Max. and min. transmission
Refinement method
12040 [R(int) = 0.0317]
Gaussian
0.965 and 0.980
Full-matrix least-squares on F2
1.046
Goodness-of-fit on F2
Final R indices [I > 2
R indices (all data)
s
(I)]
R1 = 0.0446, wR2 = 0.1034
R1 = 0.0701, wR2 = 0.1230
0.59 and À0.52
for the two independent but chemically identical mole-
cules found in the unit cell of 5 are displayed in Table 4. The
crystal structure (Fig. 1) shows that in this molecule the
geometry around the phosphorus atoms is nearly tetra-
hedral, and that the O atoms are oriented cis with regard to
the adjacent P atom. The P(1)–C(1) (1.7218(19)) and C(1)–
C(2) (1.384(3)) bond lengths are shorter than the (P+–C
(sp3) (1.800)) and (C–C (sp3) (1.511)) normal values [42],
respectively. The crystals of this compound contain CHCl3
as the solvent.
À3
˚
Largest diff. peak and hole (eÁA
)
3.3. X-ray crystallography
Colorless crystals of 5 were obtained from a chloroform
solution by slow evaporation of the solvent. Relevant
parameters concerning data collection and refinement for
5 are given in Table 3. Selected bond distances and angles
This bond shortening is due to the ylidic resonance and
is halfway between the common values for single (P–
C = 1.80) and double (P = C = 1.66) bonds. The CO bond
lengths of 5 (1.267(2)) also are larger than the normal
value (1.210). This bond distance suggests an electron
delocalization in this molecule [17,42]. The P–C(H)
(1.7218(19)) and C(1)–C(2) (1.384(3)) bond lengths are
close to the corresponding distances P–C(H) (1.705(2)) and
˚
C–C (1.404(3) A) found in similar phosphorus ylides, such
as [Ph2PCH2PPh2C(H)C(O)Ph] [43]. The packing structure
of 5 has short contacts between the adjacent molecules. In
this case, the interaction between the O2 and H44 atoms of
˚
the chloroform as the solvent (1.988 A) have a great
importance in the formation of the packing structure
(Supplementary data, Fig. 1S). The packing also shows two
hydrogen bonds between oxygen and chlorine atoms
(Fig. 2).
3.4. Suzuki cross-coupling reactions of aryl halides
The palladacycle complex 9 as a catalyst was assessed
for its activity in the Suzuki cross-coupling reaction
initially by studying the coupling of 4-bromoacetophenone
with phenylboronic acid to form 4-phenylacetophenone as
the sole product. Various parameters including solvent,
base, and catalyst loading were screened to optimize the
reaction conditions. The proper combination of base and
Fig. 1. ORTEP view of the X-ray crystal structure of 5. H atoms are omitted
for clarity. Color available online.
Please cite this article in press as: Sabounchei SJ, et al. Seven-membered Pd(II) complexes containing symmetric
phosphorus ylides: Synthesis, characterization and high catalytic activity toward Suzuki cross-coupling reactions. C. R.
Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.05.019

G Model
CRAS2C-3783; No. of Pages 10
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S.J. Sabounchei et al. / C. R. Chimie xxx (2013) xxx–xxx
˚
˚
Fig. 2. View, along b, of the packing in compound 5. H–bonds: O1ÁÁÁCl1 (3.178 A) and O2ÁÁÁCl3 (3.212 A). Color available online.
Table 5
Optimization of base and solvent for the Suzuki cross-coupling reactiona.
Entry
Base
Solvent
Temperature (8C)
Time (min)
Yield (%)b
1
Cs2CO3
K2CO3
Na2CO3
NaOAc
NaF
DMF
110
110
110
110
110
110
110
110
65
90
180
210
480
480
480
180
210
480
480
480
480
91
87
82
72
57
42
73
72
68
65
51
25
2
DMF
3
DMF
4
DMF
5
DMF
6
Et3N
DMF
7
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Dioxane
NMP
8
9
Methanol
Toluene
THF
10
11
12
110
60
H2O
100
a
Reaction conditions: 4-bromoacetophenone (0.75 mmol), phenyl boronic acid (1 mmol), base (1.5 mmol), solvent (2 mL), catalyst (0.001 mol%), in the
Isolated yield.
air.
b
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phosphorus ylides: Synthesis, characterization and high catalytic activity toward Suzuki cross-coupling reactions. C. R.
Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.05.019

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7
solvent is extremely important; we have examined several
different bases and solvents for the Suzuki reaction (Table
5). Initially, many commonly available bases were used
with DMF as the solvent. Cs2CO3, K2CO3, and Na2CO3 as a
base, which produced higher yields in short reaction times
(Table 5, entries 1–3), respectively. The use of NaOAc, NaF,
and NEt3 as bases gave lower yields (Table 5, entries 4–6),
respectively. In the reaction, several commonly used
solvents were also tested (Table 5). Solvents, such as
THF and H2O were less effective (Table 5, entries 11–12) for
this reaction. Dioxane, NMP, methanol, and toluene were
moderately effective (Table 5, entries 7–10), respectively.
Table 6
Suzuki cross-coupling reaction of aryl halides with phenylboronic acid catalyzed by Pd complex 9a.
Entry
1
Aryl halides
Product
Reference
[44,45b]
Time (min)
120
Yield (%)b
82
Br
2
[45]
90
90
O
O
Br
H
H
3
4
5
[44b,46]
[44b,47]
[45b,48]
90
180
90
90
80
91
O2N
O2N
Br
Br
H3C
O
H3C
O
Br
H3C
S
H3C
S
6
7
[47]
[46]
150
150
84
86
Br
Br
I
8
[49,50]
[50]
90
90
86
80
77
9
H3C
I
H3C
10
[44a,50]
180
Cl
11
[32c,49]
180
82
O
O
C
H3C
H3C
a
Reaction conditions: aryl halide (0.75 mmol), phenylboronic acid (1 mmol), Cs2CO3 (1.5 mmol), DMF (2 mL), catalyst (0.001 mol%), in the air, 110 8C.
Isolated yield (yields were calculated against consumption of the aryl halides).
b
Please cite this article in press as: Sabounchei SJ, et al. Seven-membered Pd(II) complexes containing symmetric
phosphorus ylides: Synthesis, characterization and high catalytic activity toward Suzuki cross-coupling reactions. C. R.
Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.05.019

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After an optimization process, we found that our complex
could perform the coupling of 4-bromoacetophenone with
phenylboronic acid using a 0.001 mol% catalyst loading
with Cs2CO3 at 110 8C in good yield in a 90-minute
procedure when using technical-grade DMF as the solvent.
In order to gauge the further potential of 9 towards the
Suzuki coupling methodology, we chose various substi-
tuted aryl halides for the reaction with phenylboronic acid,
as shown in Table 6. Aryl bromides with various functional
groups efficiently reacted with phenyl boronic acid (Table
6, entries 1–11) using Cs2CO3 and 2 mL DMF at 110 8C in
the presence of palladium(II) catalyst to give Suzuki
products in high 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 sub-
stituents [51]. The reaction of electron-deficient aryl
bromides with phenylboronic acid afforded efficiently
the coupling products in more than 90% yield in short
reaction times (Table 6, entries 2–3, 5). The electron-poor,
4-bromobenzaldehyde and 4-bromoacetophenone, also
afforded high yields (Table 6, entry 2, 90% and entry 5, 91%).
The reaction of p-bromo nitrobenzene with phenylboronic
acid showed also high yields (Table 6, entry 3, 90%). In the
electron-rich or deactivated p-bromotoluene, the yields are
good (Table 6, entry 4, 80%). The electronically neutral
bromobenzene (Table 6, entry 1) produced good amounts of
the desired product. As expected, very satisfactory yields
were obtained with the 2-bromothiophene and the
1-bromonaphthalene of phenylboronic acid (Table 6, entry
6, 84% and entry 7, 86%). Next, we examined the reaction of
aryl iodides with phenylboronic acid for the Suzuki reaction.
And good yields of the corresponding products were
obtained under the optimized conditions (Table 6, entries
8–9). Trying to apply aryl chloride as an efficient substrate
was successful (Table 6, entries 10–11). Electron-deficient
substrates, such as 4-chloroacetophenone(Table 6, entry 11)
coupled with phenylboronic acid gave yields of the coupling
product in the order of 82%. The main drawback of the Pd-
mediated Suzuki cross-coupling reaction is that only aryl
iodides and aryl bromides can be used efficiently. Recent
progress with increasing the reaction rate of aryl chlorides
permitted to overcome this problem [52–54]. The stronger
C–Cl bond is, in fact, responsible for the slower reaction rate
of aryl halides because the oxidative addition step was
suggested to be the rate-determining step in cross-coupling
catalytic cycles [55].
The homogeneous nature of the catalysis was checked by
the classical mercurytest [56]. 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 fact that metallic Hg
does not kill the catalyst is a good point in favour of the fact
that no metallic Pd is being produced.
The catalytic activity of a seven-membered Pd complex
(A, 9) was higher than that of the five-membered Pd
complex (B) in all the reactions in our previous work [34].
Table 7
Comparison of the seven-membered (A)a and five-membered (B)b Pd complexes in the Suzuki cross-coupling reaction.
Entry
1
Ar–X
Complexes
Time (h)
Yield (%)c
Ph–Cl
A
B
A
B
A
B
A
B
A
B
A
B
3
12
2
77
76
82
80
86
82
80
83
91
87
82
80
2
3
4
5
6
Ph–Br
10
1.5
6
Ph–I
p-Me–Ph–Br
p-CH3CO–Ph–Br
p-CH3CO–Ph–Cl
2
4
1.5
4
3
6
a
Reaction conditions: aryl halide (0.75 mmol), phenylboronic acid (1 mmol), Cs2CO3 (1.5 mmol), DMF (2 mL), catalyst (0.001 mol%), 110 8C.
Reaction conditions: aryl halide (0.75 mmol), phenylboronic acid (1 mmol), K2CO3 (1.5 mmol), DMF (2 mL), catalyst (0.2 mol%), 130 8C [53].
Isolated yield.
b
c
Please cite this article in press as: Sabounchei SJ, et al. Seven-membered Pd(II) complexes containing symmetric
phosphorus ylides: Synthesis, characterization and high catalytic activity toward Suzuki cross-coupling reactions. C. R.
Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.05.019

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9
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26 (2007) 3491.
This may be due to the fact that Pd(II) in palladacycles with
five-membered rings is difficult to reduce to Pd(0). As it can
be seen in Table 7, some of the aryl halides with an
electron-withdrawing or an electron-donating substituent
have been tested, among which the seven-membered Pd
complex (A) has a higher efficiency as a catalyst in a shorter
reaction time. Although several catalytic systems have
been reported to support the Suzuki C–C coupling reaction,
a catalyst of this type is novel for its seven-membered ring
containing bisphosphine bis ylide as a ligand coordinated
through the CH methinic bond. The high efficiency of this
catalyst in low catalyst loading, under aerobic conditions
and short reaction times, makes it valuable.
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The present study describes the synthesis and char-
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derived from palladium chloride and new symmetric
phosphorus ylides. On the basis of the physicochemical
and spectroscopic data, we propose that ligands herein
exhibit a chelate C–C coordination behavior to the metal
center, affording a seven-membered chelate ring. We used
palladium(II) complexes as highly active and efficient
catalysts for promoting the Suzuki cross-coupling reaction
of various aryl halides to produce the corresponding
products in high yields. The easiness of preparation of the
complex, its high solubility in organic solvents, the low
catalyst loading, and the short reaction time needed under
aerobic conditions make it an ideal complex for the above
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Acknowledgements
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We are grateful to the Bu-Ali Sina University for a grant
and Mr Zebarjadian for recording the NMR spectra. Our
gratitude also goes to Ms Behranj for her cooperation.
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Supplementary data (CCDC 881004 contains the supple-
mentary crystallographic data for compound 5. These data
can be obtained free of charge via http://www.ccdc.cam.a-
c.uk/conts/retrieving.htmL or from the Cambridge Crystallo-
graphic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: +44 1223 336 033; or E mail: deposit@ccdc cam ac uk)
associated with this article can be found, in the online
version, at http://dx.doi.org/10.1016/j.crci.2013.05.019.
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Please cite this article in press as: Sabounchei SJ, et al. Seven-membered Pd(II) complexes containing symmetric
phosphorus ylides: Synthesis, characterization and high catalytic activity toward Suzuki cross-coupling reactions. C. R.
Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.05.019