P,C-palladacycle complexes of triphenylphosphite: Synthesis, characterization and catalytic activity in the Suzuki cross-coupling reaction

Article abstract of DOI:10.1016/j.poly.2013.10.035

Five-membered P,C-palladacycles were synthesized through the reaction of the binuclear triphenylphosphite complex [Pd(μ-Cl)P(OPh)₂(OC ₆H₄)]₂ (1) with different monodentate ligands [L = triphenylphosphine (PPh₃), thiourea (tu), 2,4,6- trimethylpyridine (Me₃Py), pyridine (Py)] and bidentate ligands [N^N = 1,10-phenanthroline (Phen), 4-methyl-1,10-phenanthroline (MePhen)], giving mononuclear P,C-palladacycles [Pd(L)(Cl){P(OPh)₂(OC₆H ₄)}] [L = PPh₃ (2a), tu (2b), Me₃Py (2c)], [PyH]⁺[Pd(Cl)₂{P(OPh)₂(OC₆H ₄)}]^- (3d) and [Pd(N^N){P(OPh)₂(OC ₆H₄)}]⁺ NO₃^- [N^N = Phen (4a), MePhen (4b)]. The synthesized complexes were characterized by ¹H, ¹³C-{¹H} and ³¹P-{¹H} NMR spectroscopy, elemental analysis and FT-IR techniques. Structural details of complexes 2a, 2c and 3d were determined by X-ray crystallography, which showed these complexes crystallize in the triclinic (2a) and monoclinic (2c and 3d) crystalline systems. According to the structural data, the orthopalladated complex 3c has two different conformers (R,S) in the solid state, although it appeared as one isomer in the solution state, as confirmed by the NMR spectroscopy. Complex 2a, containing PPh₃, was evaluated as a homogeneous catalyst for a variety of substrates, affording coupled products in good to excellent yields, importantly at room temperature. Furthermore, the use of the lesser reactive aryl chloride as a substrate in the Suzuki reaction under mild conditions, has received much attention.

Full text of DOI:10.1016/j.poly.2013.10.035

Polyhedron 68 (2014) 249–257
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
P,C-palladacycle complexes of triphenylphosphite: Synthesis,
characterization and catalytic activity in the Suzuki cross-coupling
reaction
a
a
b
Kazem Karami a, , Shokouh Esfarjani , Sedigheh Abedanzadeh , Janusz Lipkowski
⇑
a Department of Chemistry, Isfahan University of Technology, Isfahan 84156/83111, Iran
b Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Five-membered P,C-palladacyclesweresynthesized through the reaction ofthe binucleartriphenylphosphite
complex [Pd( -Cl)P(OPh)2(OC6H4)]2 (1) with different monodentate ligands [L = triphenylphosphine (PPh3),
Received 22 September 2013
Accepted 30 October 2013
Available online 19 November 2013
l
thiourea (tu), 2,4,6-trimethylpyridine (Me3Py), pyridine (Py)] and bidentate ligands [N^N = 1,10-phenan-
throline (Phen), 4-methyl-1,10-phenanthroline (MePhen)], giving mononuclear P,C-palladacycles
[Pd(L)(Cl){P(OPh)2(OC6H4)}] [L = PPh3 (2a), tu (2b), Me3Py (2c)], [PyH]+[Pd(Cl)2{P(OPh)2(OC6H4)}]À (3d) and
[Pd(N^N){P(OPh)2(OC6H4)}]+ NO3 [N^N = Phen (4a), MePhen (4b)]. The synthesized complexes were
Keywords:
Palladacycle
Triphenylphosphite
Suzuki cross-coupling
À
characterized by 1H, 13C–{1H} and 31P–{1H} NMR spectroscopy, elemental analysis and FT-IR techniques.
Structural details of complexes 2a, 2c and 3d were determined by X-ray crystallography, which showed these
complexes crystallize in the triclinic (2a) and monoclinic (2c and 3d) crystalline systems. According to the
structural data, the orthopalladated complex3c has twodifferent conformers (R,S) in the solid state, although
it appeared as one isomer in the solution state, as confirmed by the NMR spectroscopy. Complex 2a, contain-
ing PPh3, was evaluated as a homogeneous catalyst for a variety of substrates, affording coupled products in
good to excellent yields, importantly at room temperature. Furthermore, the use of the lesser reactive aryl
chloride as a substrate in the Suzuki reaction under mild conditions, has received much attention.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
Our continuing interest in the synthesis of new palladacycles
[40–42] encouraged us to synthesize mononuclear orthopalladated
Organopalladium complexes have found many valuable uses in
different areas such as organic synthesis [1–4], homogeneous
catalysis [5–11], photochemistry [12–15], design of new
metallomesogenes [16–18], antitumor drugs [19,20], etc [21,22].
The Suzuki–Miyaura cross-coupling of aryl halides with aryl boro-
nic acids is one of the most powerful methods for the preparation
of unsymmetrical biaryls [23–27]. Palladium derivatives poten-
tially have catalytic activities along with special advantages like
versatility, compatibility with most functional groups and rela-
tively low toxicity [28–34]. Furthermore, a great deal of interest
has been recently devoted to the synthesis of orthopalladated tri-
arylphosphite complexes which have extensive applications in
many organic reactions [35–38]. In these complexes, orthometalla-
tion of triarylphosphite to the Pd center occurred via C–H activa-
tion of the phenyl ring. In our previous work, the application of a
binuclear P,C-palladacycle of triphenylphosphite as a catalyst
precursor was investigated for the Heck and Suzuki reactions [39].
triphenylphosphite complexes with mono- and bidentate ligands.
Furthermore, due to the efficient characteristics of palladium com-
pounds containing phosphorous ligands [43,44], the catalytic
activity of the orthopalladated complex 2a, containing PPh3, was
evaluated in the Suzuki cross-coupling reaction, applying
representative range of aryl halides.
a
2. Experimental
2.1. General
Starting materials were purchased from the Merck, Sigma–Al-
drich or Alfa Aesar companies and solvents were used as commer-
cially available chemicals without any purification. The binuclear
palladacycle 1 was obtained using the procedure described earlier
[45]. 1H NMR (400.13 MHz), 13C–{1H} NMR (100.61 MHz) and
31P–{1H} NMR (161.97 MHz) spectra were recorded in CDCl3 and
DMSO-d6 solutions at room temperature on a 400 MHz Bruker
spectrometer. Chemical shifts (d) are reported relative to internal
TMS and external 85% phosphoric acid. FT-IR spectra were
⇑
Corresponding author. Tel.: +98 3113913239; fax: +98 3113912350.
E-mail address: karami@cc.iut.ac.ir (K. Karami).
recorded on a spectrophotometer (JASCO-680, Japan) in the
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.10.035

250
K. Karami et al. / Polyhedron 68 (2014) 249–257
spectral range 4000–400 cmÀ1 using the KBr pellet technique. Ele-
mental analysis was performed on Leco, CHNS-932 apparatus. Gas
chromatography was carried out with a Shimatzo GC 14-A gas chro-
matograph and was used for monitoring the progress of reactions.
over MgSO4. Afterwards, 0.071 mmol of the ligand [N^N = 1,10-
phenanthroline (4a) or 4-methyl-1,10-phenanthroline (4b)] was
added and the solution was stirred for 40 min, then the solvent
was evaporated to dryness and the residue treated with Et2O
(2 ml).
2.2. General synthesis procedure for cyclopalladated complexes 2a, 2b,
2c and 3d
À
2.3.1. [Pd(Phen){P(OPh)2(OC6H4)}]+NO3 (4a)
Yield: 23%. Anal. Calc. for C30H22N2O3PPd: C, 54.27; H, 3.20; N,
To a solution of complex 1 (0.1 mmol, 0.140 g) in CH2Cl2
(10 ml), 0.2 mmol of the desired nucleophile [triphenylphosphine
(2a), thiourea (2b), 2,4,6-trimethylpyridine (2c) or pyridine (3d)]
was added. The resulting mixture was stirred for 5 h at room
temperature. The solvent was removed the obtained product was
then recrystallized with CH2Cl2/n-hexane (1:3).
4.08. Found: C, 54.20; H, 3.50; N, 6.97%. IR (cmÀ1, KBr)
m: 1586 (aro-
matic C@C), 1625 (C@N), 3053 (aromatic C–H). 1H NMR (CDCl3,
3
4
ppm) d: 7.16 (dd, 1H, H6 phosphite, JHH = 8.0 Hz, JHP = 1.2 Hz),
Aromatic region {7.21-7.50}, 8.18 (bd, 1H, H8 Phen, JHH = 8.2 Hz),
3
8.19 (bd, 1H, H3 Phen, JHH = 8.2 Hz), 8.23 (s, 2H, H5,6 Phen), 8.93
3
(d, 1H, H7 Phen, JHH = 8.4 Hz), 8.94 (d, 1H, H4 Phen, JHH = 8.4 Hz),
9.11 (m, 2H, H2,9 Phen). 13C–{1H} NMR (CDCl3, ppm) d: Aromatic re-
gion {112.60, 120.86, 125.38, 126.68, 128.42, 129.25, 130.52},
3
3
2.2.1. [Pd(PPh3)(Cl){P(OPh)2(OC6H4)}] (2a)
2
Yield: 70%. Anal. Calc. for C36H29ClO3P2Pd: C, 60.60; H, 4.06.
135.00 (d, 1C, C1 coordinated C, JCP = 5.0 Hz), 141.30 (s, 2C, C–O
Found: C, 60.60; H, 4.30%. IR (cmÀ1, KBr)
m
: 1586 (aromatic C@C),
in free phenyls of phosphite), 151.59 (s, 1C, C2 phosphite).
3025 (aromatic C–H). 1H NMR (DMSO-d6, ppm) d: 6.87 (d, 3H, Hp
of PPh3, 3JHH = 8.0 Hz), 7.02 (dd, 1H, H5, 3JHH = 3.2 Hz, 3JHH = 7.2 Hz),
31P–{1H} NMR (CDCl3, ppm); 122.57 (s, 1P).
3
À
7.03 (d, 1H, H6, JHH = 3.2 Hz), Aromatic region {7.27–7.56}, 8.18
2.3.2. [Pd(MePhen){P(OPh)2(OC6H4)}]+NO3 (4b)
3
4
(dd, 1H, H3, JHH = 12.4 Hz, JHP = 7.0 Hz). 13C–{1H} NMR (DMSO-
d6, ppm) d: Aromatic region {119.77, 1119.83, 122.98, 123.06,
126.76, 130.22, 131.11, 133.98, 134.10, 134.47}, 136.94 (d, 1C, C1,
2JCP = 3.0 Hz), 142.53 (s, 2C, C–O in free phenyls of phosphite),
Yield: 51%. Anal. Calc. for C31H24N2O3PPd: C, 54.88; H, 3.43; N,
4.00. Found: C, 54.40; H, 3.98; N, 6.54%. IR (cmÀ1, KBr)
m: 1586 (aro-
matic C@C), 1625 (C@N), 2860 (aliphatic C–H), 3058 (aromatic
C–H). 1H NMR (CDCl3, ppm) d: 3.00 (s, 3H, Me), 7.16 (dd, 1H, H6
2
3
3
149.11 (d, 1C, C2, JCP = 5.9 Hz), 31P–{1H} NMR (DMSO-d6, ppm) d:
phosphite, JHH = 7.6 Hz, JHP = 1.2 Hz), Aromatic region {7.21–
3
17.92 (s, 1P, phosphine), 131.10 (s, 1P, phosphite) [45].
7.49}, 7.95 (d, 1H, H3 Phen, JHH = 8.0 Hz), 8.18 (dd, 1H, H8 Phen,
3JHH = 8.4 Hz, JHH = 8.40 Hz), 8.32 (q, 2H, H5 and H6 Phen,
3
2.2.2. [Pd(tu)(Cl){P(OPh)2(OC6H4)}] (2b)
3JHH = 8.8 Hz), 9.04 (m, 2H, H2 and H7 Phen), 9.11 (m, 1H, H9 Phen).
13C–{1H} NMR (CDCl3, ppm) d: 19.63 (s, 1C, Me), Aromatic region
{112.63, 120.85, 124.40, 125.34, 126.54, 126.81, 127.01, 128.44,
Yield: 51%. Anal. Calc. for C19H18ClN2O3SPPd: C, 43.27; H, 3.41;
N, 5.31; S, 6.47. Found: C, 41.13; H, 3.50; N, 6.03; S, 6.07%. IR
(cmÀ1, KBr)
m
: 687 (C@S), 1586 (aromatic C@C), 1617 (NH2-bend-
129.17, 130.49}, 135.04 (d, 1C, C1 phosphite, JCP = 4.0 Hz), 141.48
2
ing), 3173, 3283 (NH2-streching). 1H NMR (DMSO-d6, ppm) d: Aro-
matic region {6.80–7.21}, 7.28 (s, 4H, Hm), 7.43(s, 6H, Ho and Hp),
7.85 (s, 2H, NH2), 8.38 (s, 2H, NH2). 13C–{1H} NMR (DMSO-d6,
ppm) d: Aromatic region {110.82, 110.97, 120.91, 121.43, 124.87,
126.23, 127.40, 129.76, 130.12, 130.26}, 136.62 (d, 1C, C1,
2JCP = 6.0 Hz), 140.44 (s, 2C, C–O in free phenyls of phosphite),
144.09 (s, 1C, C2), 191.55 (s, 1C, C@S). 31P–{1H} NMR (DMSO-d6,
ppm) d: 129.48, 130.23 (s, 1P, R,S isomers).
(s, 2C, C–O in free phenyls of phosphite), 150.92 (s, 1C, C2 phos-
phite). 31P–{1H} NMR (CDCl3, ppm) d: 122.84 (s, 1P).
2.4. X-ray structure determinations
X-ray diffraction experiments were done at 100 K with the use
of an Agilent SuperNova single crystal diffractometer (Mo Ka radi-
ation). An analytical numeric absorption correction using a multi-
faceted crystal model based on expressions derived by R.C. Clark
and J.S. Reid was made [46]. The structures were solved by direct
methods using the SHELXS97 program and refined with the use of
SHELXL (Sheldrick 2008) program. Hydrogen atoms were added in
the calculated positions and were riding on their respective carbon
atoms during the refinement.
2.2.3. [Pd(Me3Py)(Cl){P(OPh)2(OC6H4)}] (2c)
Yield: 62%. Anal. Calc. for C26H25ClNO3PPd: C, 54.55; H, 4.37; N,
2.44. Found: C, 53.90; H, 4.50; N, 2.54%. IR (cmÀ1, KBr)
m: 1485 (C–
N), 1587 (C@C), 1622 (C@N), 2921 (aliphatic C–H), 3050 (aromatic
C–H). 1H NMR (CDCl3, ppm) d: 2.35 (s, 3H, Mep), 2.49 (s, 6H, Meo),
4
3
3
5.92 (ddd, 1H, H6, JHH = 1.2 Hz, JHP = 6.6 Hz, JHH = 9.9 Hz), 6.61
(td, 1H, H5, JHH = 7.2 Hz, JHH = 1.6 Hz), 6.94 (s, 2H, Hm of Me3Py),
Aromatic region {7.00–7.57}. 13C–{1H} NMR (CDCl3, ppm) d:
20.91 (s, 1C, MeP), 25.74 (s, 2C, Meo), Aromatic region {111.33,
111.54, 121.18, 122.54, 122.97, 123.87, 125.88, 127.04, 129.67}
2.5. General experimental procedure for the Suzuki cross-coupling
reaction
3
4
In this context complex 2a was used as a catalyst for the Suzuki
cross-coupling reaction. A 25 ml round-bottom flask was charged
with the appropriate aryl halide (0.50 mmol), phenylboronic acid
(0.55 mmol), base (1.00 mmol), and THF/H2O (6 ml of a 2:1 v/v
mixture). The catalyst (0.005 mmol) was then added to the solu-
tion and the mixture was stirred at room temperature for 1 h. Dif-
ferent aryl halides were employed in the Suzuki cross-coupling
reaction with phenylboronic acid and the coupling products are
listed in Table 4. Gas chromatographic (GC) analyses were per-
formed using an Agilent Technologies 6890 N chromatograph
equipped with a flame ionization detector (FID) and an HB-50+ col-
134.18 (d, 1C, C1, JCP = 4.0 Hz), 150.48 (s, 2C, C–O in free phenyls
2
of phosphite), 157.83 (s, 1C, C2), 31P–{1H} NMR (CDCl3, ppm) d:
134.78 (s, 1P).
2.2.4. [PyH]+[Pd(Cl)2{P(OPh)2(OC6H4)}]À (3d)
Yield: 50%. IR (cmÀ1, KBr)
m: 1585 (aromatic C@C), 1635 (C@N),
3058 (aromatic C–H). 1H NMR (CDCl3, ppm) d: Aromatic region
{6.80–7.50}. 31P–{1H} NMR (CDCl3, ppm) d: 130.11 (s, 1P).
2.3. General synthesis procedure for cyclopalladated complexes 4a and
4b
umn (length = 30 m, inner diameter = 320
lm, and film thick-
ness = 0.25 m). The temperature program for the GC analysis
l
Complex 1 (0.35 mmol, 0.030 g) was dissolved in THF (8 ml)
and treated with AgNO3 (0.071 mmol, 0.012 g). The resulting mix-
ture was stirred for 45 min at room temperature and then filtered
was from 70 to 200 °C at 20 °C/min, held at 200 °C for 0 min,
heated from 200 to 280 °C at 10 °C/min and held at 280 °C for
1 min. The inlet and detector temperatures were set at 260 and

K. Karami et al. / Polyhedron 68 (2014) 249–257
251
280 °C, respectively. Products were identified by comparison with
authentic samples.
found at 1485 cmÀ1, in comparison with 1465 cmÀ1 for the free li-
gand [46,47], indicating coordination to Pd. The vibrational fre-
quencies of C@N in 2c, 3d, 4a and 4b appeared at about
1625 cmÀ1. The FT-IR spectra of 2c and 4b show the typical bands
at 2921 and 2860 cmÀ1, respectively, related to their aliphatic C–H
groups.
3. Result and discussion
3.1. Synthesis
In the 31P–{1H} NMR spectrum of 2a, two signals at 17.92 and
131.10 ppm are related to the P atoms of PPh3 and P(OPh)3, respec-
tively. Concerning the 1H NMR spectrum of 2b, two broad signals at
7.85 and 8.38 ppm are clearly attribiuted to the two NH2 groups of
the coordinated thiourea. The downfield shifting of the NH2 signals
when compared with the free ligand (7.06 ppm) [48] suggest Pd–S
bond formation. The NH2 protons are diastereotopic, resulting in
the formation of two separate signals in the 31P–{1H} NMR spec-
trum at 129.48 and 130.23 ppm. The 13C–1H} NMR spectrum of
complex 2b showed the typical signals of the quaternary carbon
in the thiourea at 191.55 ppm, which is shifted downfield when
compared with the free ligand (183.9 ppm). It is suggested that
the downfield shift is attributed to a lowering of the C@S bond or-
der due to the coordination to Pd. The 13C–{1H} NMR spectra of all
the synthesized complexes have the signal of C1 in P(OPh)3 at
about 135.00 ppm. The H6 aromatic proton of the palladacycle ring
in 2c (Scheme 1) is shifted to a lower frequency at 5.92 ppm be-
cause of the anisotropic shielding from the phenyl or pyridine ring
[49]. The 13C–{1H} NMR spectrum of 2c shows signals for the para
and ortho methyl groups at 20.91 and 25.74 ppm, respectively. It is
worth noting that the orthopalladated complex 2c has two differ-
ent conformers in the solid state, fully confirmed by X-ray crystal-
lography, but the multinuclear NMR spectra display the presence
of only one set of signals which indicate that complex 2c consists
of only one isomer in the solution state (Scheme 2). It is
Treatment of the chloro-bridged complex [Pd(l-Cl)P(OPh)2
(OC6H4)]2 (1) with two equivalents of monodentate ligand [triphen-
ylphosphine(PPh3), thiourea(tu), 2,4,6-trimethylpyridine (Me3Py)
or pyridine (Py)] in CH2Cl2 afforded the corresponding mononuclear
orthopalladated complexes 2a, 2b, 2c and 3d. Moreover, a solutionof
complex 1 in THF was reacted with AgNO3 in the dark. After filtera-
tion over MgSO4, an equimolar amount of the corresponding N^N
bidentate ligand [1,10-phenanthroline (Phen) or 4-methyl-1,10-
phenanthroline (MePhen)] was then added. The solution was stirred
for 40 minutes to produce cyclometallated complexes of the general
formula [Pd(N^N)(P^C)]+ (4a and 4b). For all the synthesized com-
pounds, the results of the elemental analysis are in the good agree-
ment with the calculated values.
3.2. Characterization
The IR spectra of the synthesized complexes show characteristic
bands for aromatic C@C and C–H at 1586 and 3050 cmÀ1, respec-
tively. In the IR spectrum of 2b, the m(C@S) band (that is sensitive
to complexation) appeared at 687 cmÀ1, whereas for the free thio-
urea, it should be at 725 cmÀ1 [46,47]. The complexation of thio-
urea is clearly confirmed by the appearance of additional
bands at 3173, 3283 (stretching) and 1617 cmÀ1 (bending). More-
over, the characteristic (C–N) band in the IR spectrum of 2b was
m(N–H)
m
Scheme 1. Representation of the cleavage reaction of the dimeric cyclopalladated complex 1 by mono- and bidentate ligands.

252
K. Karami et al. / Polyhedron 68 (2014) 249–257
Scheme 2. Conformational isomerism of complex 2c in the solid state versus the solution state.
significantly clear by the 31P–{1H} NMR spectrum which shows a
signal at 134.78 ppm.
solvents may be a reasonable explanation for this event. The H2
and H9 aromatic protons in the 1,10-phenanthroline ligand are
shifted downfield at 9.11 ppm because they are near the nitrogen
atoms. In the 31P–{1H} NMR spectra of complexes 4a and 4b one
signal was observed at about 122.60 ppm, corresponding to the P
atom of P(OPh)3. The methyl protons of 4-methyl-1,10-phenan-
throline are shown as a singlet at 3.00 ppm in the 1H NMR spec-
trum of complex 4b. The H2 and H9 aromatic protons in the
coordinated 4-methyl-1,10-phenanthroline are in the vicinity of
the nitrogen atoms, so their signals in the 1H NMR spectrum
appeared at higher frequencies, 9.04 and 9.11 ppm, respectively.
The 13C–{1H} NMR spectrum showed one signal at 19.63 ppm
related to the methyl carbon.
In relation to the structures, monodentate nucleophiles (L) have
two possible positions to attack. Although PPh3 is a bulky group, it
is located in the cis position to the coordinated P atom of P(OPh)3
(A) in 2a and Me3Py is mutually trans to the P atom of P(OPh)3
(B) in 2c. Therefore, the electronic effects are determinant and con-
trol the site of the nucleophile with respect to the steric effects.
According to the HSAB effect, the soft P atom of PPh3 is trans to
the hard sp2 carbon in 2a. However, in 2c the hard N of Me3Py is
trans to the soft P atom of P(OPh)3.
The 31P–{1H} NMR spectra of complexes 2a, 2b, 2c and 3d show
a characteristic signal at about 130 ppm attributed to the P atom of
P(OPh)3. In 3d, our purpose was to reach an orthopalladated com-
plex in which the pyridine is coordinated to the palladium center
through the N atom. Concerning the FT-IR, NMR, CHN and espe-
cially crystallographic data, we fully characterized a 5-membered
palladacycle with two coordinated chloride anions in addition to
pyridinium as a counter ion. A trace of HCl in CH2Cl2 as the reaction
3.3. Crystal structures
To further clarify the coordination environment around the
Pd(II) center, molecular structures of 2a, 2c and 3d were deter-
mined by X-ray crystallography. Crystals were obtained by
Fig. 1. ORTEP view of the X-ray crystal structure of complex 2a. The disordered solvent molecule and all hydrogen atoms have been omitted for clarity.

K. Karami et al. / Polyhedron 68 (2014) 249–257
253
Fig. 2. ORTEP view of the X-ray crystal structure of complex 2c including two independent molecules. Hydrogen atoms have been omitted for clarity.
Fig. 3. ORTEP view of the X-ray crystal structure of complex 3d.
ꢀ
diffusion of n-hexane into a THF solution of complex 2a and CH2Cl2
solutions of complexes 2c and 3d. Figs. 1–3 show the ORTEP
diagrams of 2a, 2c and 3d. Crystallographic data and parameters
concerning data collection and structure solution and refinements
are summarized in Table 1 and some selected bond lengths (Å) and
angles (°) are collected in Table 2.
Palladacycles 2a, 2c and 3d crystallize in the triclinic P1, mono-
clinic P21 and monoclinic P21/n space groups, respectively. The
X-ray crystal data demonstrate that each palladium metal is
located in a distorted square-planar geometry surrounded by a
chelating triphenylphosphite-C,P moiety (C2 and P1), chloride
anion (Cl1) and phosphorus of PPh3 (P2) in 2a or nitrogen of Me3Py

254
K. Karami et al. / Polyhedron 68 (2014) 249–257
Table 1
Crystallographic data and structure refinement details for 2a, 2c and 3d.
Empirical formula
Formula weight
T (K)
Crystal system
Space group
Z
C39H37ClO4P2Pd, 2a
773.48
100(1)
C26H25ClNO3PPd, 2c
572.29
100(1)
monoclinic
P21
C23H20Cl2NO3PPd, 3d
566.67
100(1)
monoclinic
P21/n
triclinic
ꢀ
P1
2
4
4
a (Å)
b (Å)
c (Å)
10.4680(3)
13.5250(4)
14.5440(4)
103.187(2)
92.717(2)
111.543(3)
1845.12(9)
792
9.1490(2)
16.6420(5)
16.1460(4)
90.00
90.311(2)
90.00
2458.32(11)
1160
1.546
16.4210(8)
9.1650(5)
16.7780(7)
90.00
113.407(4)
90.00
2317.3(2)
1136
1.624
a
(°)
b (°)
c
(°)
V (Å3)
F000
Dcal (Mg/m3)
1.392
0.70
l
(mmÀ1
)
0.96
9.45
No. of measured reflections
No. of independent reflections
No. of parameters
23233
6266
493
0.036
0.104
25188
7033
596
0.042
0.108
27350
4357
279
0.036
0.098
0.066
R[F2 > 2
wR(F2)
Rint
r
(F2)]
0.027
0.064
S
0.83
0.94
1.04
Table 3
Optimization of the reaction conditions for the Suzuki reaction of bromobenzene with
phenyl boronic acid at room temperaturea.
Entry
Solvent
Base
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
THF/H2O (2:1)
THF/H2O (2:1)
THF/H2O (2:1)
THF/H2O (2:1)
MeOH
acetone
THF
toluene
THF/H2O (2:1)
THF/H2O (2:1)
K3PO4.3H2O
K2CO3
Na2CO3
KOH
KOH
KOH
KOH
KOH
KOH
KOH
1
1
1
1
1
1
1
1
33
64
65
94
54
10
32
27
68
85
2
0.5
10
a
Reaction conditions: bromobenzene (0.50 mmol), phenylboronic acid
(0.55 mmol), base (1.00 mmol), solvent (6 ml), [Pd(PPh3)(Cl){P(OPh)2(OC6H4)}]
(0.005 mmol).
b
Determined by GC.
Fig. 4. The crystal packing of complex 3d. Dotted lines represent the intermolecular
hydrogen bonding interactions.
Due to these steric constraints, the other two angles around the
Pd center are opened up and are significantly larger than 90°;
P1ÀPd1ÀP2 = 100.44(3)° and Cl1ÀPd1ÀC2 = 93.28(9)°. The angles
subtended by the cyclometallated P(OPh)3 ligand at the Pd(II) cen-
ter in 2c and 3d, are 81.48(17) and 80.40(9)°, respectively, for
C2ÀPd1ÀP1, indicating the distorted square-planar structures.
The Pd1-C2 bond distances of 2.067(3), 2.027(6) and 2.013(3) Å,
respectively for 2a, 2c and 3d are identical to those found in other
orthopalladated complexes [45].
(N1) in 2c or chloride anion (Cl2) in 3d, confirming the presence of
a five-membered palladacycle with a Pd-C2 bond. The angles
around each palladium center deviate from the ideal value due to
the small bite angle of the coordinated P(OPh)3. In complex 2a,
the C2ÀPd1ÀP1 bite angle is 80.00(9)°, while the opposite angle,
Cl1ÀPd1ÀP2, of 86.26(3)° deviates from the ideal value of 90°.
Table 2
Selected bond distances (Å) and angles (°) for 2a, 2c and 3d.
2a
2c
3d
Pd1—C2
Pd1—P1
Pd1—Cl1
Pd1—P2
C2—Pd1—P1
C2—Pd1—Cl1
P1—Pd1—Cl1
C2—Pd1—P2
P1—Pd1—P2
Cl1—Pd1—P2
2.067(3)
2.1686(8)
2.3473(8)
2.3737(8)
80.00(9)
93.28(9)
173.26(3)
177.61(8)
100.44(3)
86.26(3)
Pd1—C2
Pd1—N1
Pd1—P1
Pd1—Cl1
C2—Pd1—P1
C2—Pd1—N1
N1—Pd1—P1
C2—Pd1—Cl1
N1—Pd1—Cl1
P1—Pd1—Cl1
2.027(6)
2.115(5)
Pd1—C2
Pd1—P1
Pd1—Cl1
Pd1—Cl2
C2—Pd1—P1
C2—Pd1—Cl1
P1—Pd1—Cl1
C2—Pd1—Cl2
P1—Pd1—Cl2
Cl1—Pd1—Cl2
2.013(3)
2.1542(8)
2.3694(8)
2.4205(8)
80.40(9)
94.68(9)
174.61(3)
173.81(9)
94.05(3)
90.96(3)
2.1576(15)
2.3864(14)
81.48(17)
93.5(2)
172.77(13)
174.07(18)
91.88(13)
93.34(5)

K. Karami et al. / Polyhedron 68 (2014) 249–257
255
Table 4
Suzuki reaction of various aryl halides with phenylboronic acid using 0.005 mmol complex 2a.a
Entry
1
Ar-X
Product
Yield (%)b
94
2
80
3
96
4
72
5
100
6
83
7
76
(continued on next page)

256
K. Karami et al. / Polyhedron 68 (2014) 249–257
Table 4 (continued)
Entry
8
Ar-X
Product
Yield (%)b
80
9
83
10
70
11
66
12
73
a
Reaction conditions: Derivatives of aryl halides (0.5 mmol), phenylboronic acid (0.55 mmol), KOH (1 mmol), THF:H2O (2:1), (6 ml), Pd catalyst (0.005 mmol), r.t., 1 h.
Determined by GC.
b
According to Figs. 1 and 2, the P-donor incoming ligand PPh3 is
palladated aromatic ring more or less perpendicular to the hetero-
cycle of the auxiliary ligand; in the second structure, the angle be-
tween the planes formed by these two rings is smaller. So, these
two structures are a result of a slightly restricted rotation around
the single Pd–N bond due to the steric bulk of the auxiliary ligand.
Concerning the X-ray crystal structure of 3d, the pyridinum
molecule is located near the Pd(II) center as a counter ion. The
adjacent molecules are linked by an intermolecular hydrogen bond
between the coordinated chlorides and pyridinium cation (Fig. 4).
mutually trans to the orthometallated carbon of P(OPh)3 in 2a,
while in 2c, the N-donor incoming ligand Me3Py is located trans
to the P atom of P(OPh)3. The greater trans influence of the sp2 car-
bon (C2) in each of the crystal structures 2a, 2c and 3d leads to the
elongation of the mutually trans bond with respect to similar com-
plexes [50]. For instance, the Pd1ÀP2 bond distance (2.3737(8) Å)
is significantly longer than the Pd1ÀP1 bond (1.1686(8) Å) in 2a.
The Pd1ÀCl1 bond distances are elongated to (2.3864(14) Å) in
2c [24] and the Pd1ÀCl2 bond distance (2.4205(8) Å) is longer in
comparison with the Pd1ÀCl1 bond (2.3694(8) Å) in 3d. The
Pd1–N1 distance (2.115(5) Å) is similar to those found for related
orthopalladated complexes (2.0599(15) Å) [51].
3.4. Suzuki cross-coupling reactions of aryl halides
Concerning the efficient characteristics of palladium com-
pounds containing phosphorus ligands [43,44], the catalytic appli-
cability of Pd(II) complex 2a, containing PPh3, was evaluated for
The mononuclear complex 2c crystallizes with two indepen-
dent molecules in the asymmetric unit. One structure has the

K. Karami et al. / Polyhedron 68 (2014) 249–257
257
the Suzuki reaction. The cross-coupling of aryl halides with phenyl
Appendix A. Supplementary data
boronic acid was carried out according to the optimized conditions,
in the presence of 0.005 mmol catalyst at room temperature for 1 h
using THF/H2O (2:1) as the solvent (Table 3).
CCDC 921982, 921983 and 921984 contain the supplementary
crystallographic data for 2a, 2c and 3d, respectively. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk.
The coupling reactions were studied in the presence of various
bases (Table 3, entries 1-4), and KOH was found to be the most
effective base. Thus, the other substrates were examined using
KOH as the base (Table 3, entries 4–8). After optimization of the
base, different solvents, such as MeOH, acetone and toluene, were
tested in the Suzuki reaction for aryl bromides, which were not
effective (Table 3, entries 5, 6 and 8). Moreover, the conversion
of bromobenzene was low when THF was used as the solvent
(Table 3, entry 7). Finally, THF/H2O in a ratio of 2:1 was found to
be the best solvent condition for this reaction. The data (Table 3,
entries 9 and 10) clearly show that increasing the reaction time
did not lead to a higher conversion of bromobenzene, and changing
from 1 hour decreased the yield. All the cross-coupling reactions
were performed importantly at room temperature and yield the
data presented in Tables 3 and 4, which correspond to the average
values obtained in two or three identical catalytic experiments.
To demonstrate the versatility of the catalytic system, we inves-
tigated the reaction using a variety of aryl halides with phenyl
boronic acid under the optimized conditions. Table 4 summarizes
the results for the Suzuki reactions. Concerning Table 4, aryl ha-
lides with electron-withdrawing substituents in para positions re-
acted smoothly, but the efficiencies were lower for the substrates
with electron-donating groups (Table 4, entries 5, 9 and 12). Also
aryl halides with an ortho substituent were poor substrates due
to their sterically hindered conditions (Table 4, entry 8). In our cat-
alytic system, the more easily accessible and cheaper aryl chloride
also participated in these reactions (Table 4, entry 2).
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In this study we have successfully synthesized five-membered
P,C-orthopalladated complexes with different monodentate
ligands. The N^N bidentate ligands also reacted with the precursor
dimeric P,C-orthopalladated complex to yield new cationic ortho-
palladated complexes. These complexes were fully characterized
by NMR spectroscopy, elemental analysis and FT-IR techniques.
The identification of complexes 2a, 2c and 3d have also been con-
firmed by X-ray structure analysis. According to the crystallo-
graphic data, the orthopalladated complex 2c has two different
conformational isomers in the solid state, although it appeared as
one isomer in solution, as confirmed by NMR spectroscopy. The
X-ray structure of the orthopalladated complex 3d revealed that
the pyridine molecule is located near to the anionic complex as a
pyridinium counter ion. Due to the promising effects of palladium
compounds containing phosphorus ligands in C–C cross-coupling
reactions, complex 2a has been evaluated as an efficient catalyst
for the Suzuki cross-coupling reaction. Importantly, all of the reac-
tions were performed at room temperature and the corresponding
products were obtained in good to excellent yields. Also, in addi-
tion to diverse aryl bromides, the more easily accessible and
cheaper aryl chloride was employed under mild reaction condi-
tions. At present, further efforts to expand the catalytic applica-
tions of these palladacycles in other catalyzed reactions are in
progress in our group.
Acknowledgements
The authors acknowledge the Department of Chemistry, Isfahan
University of Technology (IUT) for financial supports. The Institute
of Physical Chemistry, Polish Academy of Sciences, is also acknowl-
edged for their kind support.
[51] K. Karami, C. Rizzoli, N. Rahimi, Transition Met. Chem. 36 (2011) 841.