A new Pd(II) complex of a sulfur ylide; Synthesis, X-ray characterization, theoretical study and catalytic activity toward the Suzuki-Miyaura reaction

Article abstract of DOI:10.1016/j.poly.2016.05.046

The new sulfonium salt [SMe₂CH₂C(O)C₆H₄-m-OCH₃]Br (1) was synthesized from the reaction of dimethyl sulfide and 2-bromo-3′-methoxyacetophenone. Further treatment with NaOH 10% gave the α-keto stabilized sulfur ylide SMe₂C(H)C(O)C₆H₄-m-OCH₃ (2). This ligand was reacted with the dichloro(1,5-cyclooctadiene)palladium(II) complex, [PdCl₂(cod)], in a 2:1 ratio to give the new Cα-coordinated complexes cis- and trans-[PdCl₂(SMe₂C(H)C(O)C₆H₄-m-OCH₃)₂] (3a and 3b). Characterization of the obtained compounds was performed by elemental analysis, IR, ¹H, ¹³C NMR and mass spectroscopies. Since complexes 3a and 3b were insoluble in most organic solvents, we chose DMSO as a suitable solvent for the NMR spectroscopies. Crystallization of above solution led to the formation of single crystals. The X-ray analysis results revealed that complex 3a has undergone a ligand replacement reaction and the complex [PdCl₂(SMe₂C(H)C(O)C₆H₄-m-OCH₃)·DMSO] (4) was formed. This complex has two Cl atoms in cis positions, one sulfur ylide and one S-coordinated DMSO as ligands. The air/moisture stable complexes 3a and 3b were employed as efficient catalysts for the Suzuki-Miyaura cross-coupling reaction of several aryl halides. The coupled products of these reactions were obtained in good to excellent yields and purity, with short reaction times and low catalyst loading. Also a theoretical study on the structure and nature of the Pd-C bond in complex 4 is reported here at the BP86/def2-SVP level of theory.

Full text of DOI:10.1016/j.poly.2016.05.046

Accepted Manuscript
A new Pd(II) complex of a sulfur ylide; Synthesis, X-ray characterization, the-
oretical study and catalytic activity toward the Suzuki-Miyaura reaction
S.J. Sabounchei, A. Yousefi, M. Ahmadianpoor, A. Hashemi, M. Bayat, A.
Sedghi, F.A. Bagherjeri, R.W. Gable
PII:
S0277-5387(16)30199-1
DOI:
http://dx.doi.org/10.1016/j.poly.2016.05.046
POLY 12020
Reference:
Polyhedron
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Received Date:
Accepted Date:
16 March 2016
10 May 2016
Please cite this article as: S.J. Sabounchei, A. Yousefi, M. Ahmadianpoor, A. Hashemi, M. Bayat, A. Sedghi, F.A.
Bagherjeri, R.W. Gable, A new Pd(II) complex of a sulfur ylide; Synthesis, X-ray characterization, theoretical study
and catalytic activity toward the Suzuki-Miyaura reaction, Polyhedron (2016), doi: http://dx.doi.org/10.1016/j.poly.
2016.05.046
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A new Pd(II) complex of a sulfur ylide; Synthesis, X-ray characterization,
theoretical study and catalytic activity toward the Suzuki-Miyaura reaction
Sabounchei S.J.a*, Yousefi Aa, Ahmadianpoor Ma, Hashemi Aa, Bayat Ma, Sedghi Aa,
Bagherjeri F.A.b,Gable R.Wb.
aFaculty of Chemistry, Bu-Ali Sina University, Hamedan, 65174, Iran
b School of Chemistry, University of Melbourne, Victoria, 3010, Australia
*Corresponding author: jsabounchei@yahoo.co.uk (S.J. Sabounchei), Tel.: +98 8138272072; fax: +98
8138273231.
Abstract: The new sulfonium salt [SMe2CH2C(O)C6H4-m-OCH3]Br (1) was synthesized from
the reaction of dimethyl sulfide and 2-bromo-3'-methoxyacetophenone. Further treatment with
NaOH 10% gave the α-keto stabilized sulfur ylide SMe2C(H)C(O)C6H4-m-OCH3 (2). This ligand
was reacted with the dichloro(1,5-cyclooctadiene)palladium(II) complex, [PdCl2(cod)], in a 2:1
ratio to give the new Cα-coordinated complexes cis- and trans-[PdCl2(SMe2C(H)C(O)C6H4-m-
OCH3)2] (3a and 3b). Characterization of the obtained compounds was performed by elemental
1
13
analysis, IR, H, C NMR and mass spectroscopies. Since complexes 3a and 3b were insoluble
in most organic solvents, we chose DMSO as a suitable solvent for the NMR spectroscopies.
Crystallization of above solution led to the formation of single crystals. The X-ray analysis
results revealed that complex 3a has undergone a ligand replacement reaction and the complex
[PdCl2(SMe2C(H)C(O)C6H4-m-OCH3).DMSO] (4) was formed. This complex has two Cl atoms
in cis positions, one sulfur ylide and one S-coordinated DMSO as ligands. The air/moisture
stable complexes 3a and 3b were employed as efficient catalysts for the Suzuki-Miyaura cross-
coupling reaction of several aryl halides. The coupled products of these reactions were obtained
in good to excellent yields and purity, with short reaction times and low catalyst loading. Also a
1

theoretical study on thestructure and nature of the Pd–C bond in complex 4 is reported here at the
BP86/def2-SVP level of theory.
Keywords: Sulfur ylide, Palladium(II) complex, X-ray characterization, Suzuki-Miyaura
reaction, Theoretical study.
1. Introduction:
Sulfur ylides, R2S=C(Rʹ)(Rʺ), are an important class of compounds that have attracted
considerable interest because of their value for a variety of industrial, biological and chemical
synthetic uses [1-4]. The high stability and ambidentate character of these ylides makes them an
appropriate choice for organometallic synthesis [5-7]. The coordination behaviour of these
compounds towards several metal ions has been well studied and it was found that they can
coordinate through the carbanion or the enolate oxygen atom [8-10]. The Cα coordinated
complexes exhibit three canonical bonding modes, as depicted in Scheme 1: mononuclear,
binuclear and polymeric structures. Metal ions such as Pd(II) can interact with the methinic
carbon atom of the ylidic group and form a mononuclear structure [11]. If metal ions containing
bridging ligands, such as HgX2 (X = Cl, Br, I), react with sulfur ylides, a binuclear structure can
form with two halide bridging atoms [12]. Finally, polymeric structure complexes are observed
when the metal ions have polymerizing ligands. For example, AgNO3 interacts with the Cα atom
of these ylides and makes a structure with a metallic skeleton based on the polymeric nitrate
group [13]. Although, O-coordination modes of these compounds are possible, only a few
examples of these complexes are known [14].
2

Scheme 1. The canonical bonding modes of Rʹ2SCHC(O)C6H4R to metal ions.
Over the past 30 years, palladium-catalyzed cross-coupling reactions have gained popularity,
especially as a suitable technique for the formation of carbon-carbon bonds [15,16] Specifically,
the Suzuki-Miyaura cross-coupling reaction of aryl halides with arylboronic acids has emerged
as the most important reaction and a reliable method for the construction of asymmetric biaryls
[17,18]. Recently, the application of some phosphorus and sulfur ylides in such cross-coupling
reactions by our group was reported [19-21]. Although palladium complexes of phosphorus
ylides show high efficiency and moisture/air stability, most of them are expensive and have
environmental considerations. The application of complexes containing sulfur or nitrogen as
phosphine free catalytic systems were developed recently to eliminate or reduce costs,
operational hazards and environmental pollution [22,23]. For example, Sindhuja et al. reported
the synthesis and application of palladium catalysts containing modified sulfur ligands which can
accelerate the coupling reactions of aryl bromides with phenylboronic acid [24]. It was found
that the release of Pd(0) species in such cross-coupling reactions depends on the nature of the
ligands around the palladium centre [25]. Organochalcogen ligands, such as sulfur ylides, show
3

rivalry with their respective phosphorus ylide analogues for releasing of Pd(0) species in the
Suzuki-Miyaura reaction [26]. The low catalyst loading and more environmentally safe reagent
than the other organometallic reagents make these ligands and their Pd(II) complexes ideal
catalysts for the Suzuki-Miyaura reaction [27,28].
The complexation of sulfur ylides to various transition metals has been extensively studied
[9,11-13], however the synthesis, X-ray characterization, theoretical study and also application
of a palladium complex of a sulfur ylide as a precursor in the Suzuki–Miyaura coupling reaction
are the key advantages of this study.
This paper includes the synthesis, spectroscopic and X-ray crystallographic characterization,
theoretical study and application of new palladium(II) complex of an α-keto stabilized sulfur
ylide in the Suzuki-Miyaura cross-coupling reaction.
2. Experimental
2.1. Physical measurements and materials:
All of the reactions were carried out under air. All the solvents and starting materials were
purchased from commercial sources and used without further purification. The starting material,
the dichloro(1,5-cyclooctadiene)palladium(II) complex [PdCl2(cod)], was prepared according to
the published procedures [29]. Melting points were measured on a SMP3 apparatus. IR spectra
were recorded in the range 4000-400 cm-1 on a Shimadzu 435-U-04 spectrophotometer from KBr
pellets. NMR spectra (1H and 13C) were recorded on 500 MHz and 250 MHz Bruker and 90 MHz
Jeol spectrometers in DMSO-d6 or CDCl3 as the solvent at 25 °C. Coupling constants are given
in Hz. Elemental analyses for carbon, nitrogen and hydrogen atoms were determined by using a
Perkin Elmer 2400 series analyzer.
4

2.2. Synthesis of the compounds
2.2.1. Synthesis of the sulfonium salt [Me2SCH2C(O)C6H4-m-OMe]Br (1): Dimethyl sulfide
(0.06 g, 1 mmol) was added to an acetonic solution (5 ml) of the ketone [BrCH2C(O)C6H4-m-
OMe] (0.22 g, 1 mmol). The mixture was stirred for 12 h. The resulting precipitate was filtered
off and the obtained salt 1 was washed with acetone and dried.
2.2.2. Data for [Me2SCH2C(O)C6H4-m-OMe]Br: Yield: 0.26 g, 0.93 mmol, 93%. Anal. Calc.
for C11H15O2SBr (%): C, 45.36; H, 5.15; S, 11.01. Found: C, 45.44; H, 5.01; S, 11.13. Melting
point: 132-134 °C. IR (KBr disk) ν(cm-1): 1676 (CO); 787 (C--S+). 1H NMR (DMSO-d6, ppm) δ:
2.97 (s, 6H, S(CH3)2); 3.84 (s, 3H, OCH3); 5.49 (s, 2H, CH2); 7.50 (Br, 4H, Ph). 13C NMR
(DMSO-d6, ppm) δ: 24.44 (s, S(CH3)2); 52.68 (s, CH2); 55.67 (s, OCH3); 113.18 (s, Ph); 119.19
(s, Ph); 121.06 (s, Ph); 130.28 (s, Ph); 135.31 (s, Ph); 159.58 (s, Ph); 191.33 (s, CO).
2.3.2. Synthesis of the sulfur ylide [Me2SCHC(O)C6H4-m-OMe] (2): Treatment of compound
1 (0.29 g, 1 mmol) with H2O (0.5 ml) and aqueous NaOH 10% solution (2 ml) led to elimination
of HBr, giving the sulfur ylide 2. The mixture was stirred for 30 min. Ligand 2 was obtained by
extraction of the resulting solution with chloroform, followed by precipitation with petroleum
benzine and dried.
2.2.4. Data for [Me2SCHC(O)C6H4-m-OMe]: Yield: 0.18 g, 0.86 mmol, 86%. Anal. Calc. for
C11H14O2S (%):C, 62.84; H, 6.66; S, 15.26. Found: C, 62.94; H, 6.7; S, 15.27. IR (KBr disk)
1
ν(cm-1): 1596 (CO); 847 (C--S+). H NMR (CDCl3, ppm) δ: 2.90 (s, 6H, S(CH3)2); 3.79 (s, 3H,
OCH3); 4.99 (s, 1H, CH); 6.89-7.23 (mm, 4H, Ph). 13C NMR (CDCl3, ppm) δ: 28.53 (s,
S(CH3)2); 52.79 (s, CH2); 55.24 (s, OCH3); 110.88 (s, Ph); 116.04 (s, Ph); 118.97 (s, Ph); 120.00
(s, Ph); 142.25 (s, Ph); 159.38 (s, Ph); 182.69 (s, CO).
5

2.2.5. Synthesis of the Pd(II) complexes cis- and trans-[PdCl2(Me2SCHC(O)C6H4-m-OMe)2]
(3a and 3b): A dichloromethane solution of ylide 2 (0.21 g, 1 mmol, 5 ml) was added to a
dichloromethane solution of [PdCl2(cod)] (0.14 g, 0.5 mmol, 5 ml). The mixture was stirred for 4
h at room temperature. The yellow solid that formed was filtered, washed with diethyl ether and
dried.
2.2.6. Data for cis- and trans-[PdCl2(Me2SCHC(O)C6H4-m-OMe)2]: Yield: 0.27 g, 0.46
mmol, 92%. Anal. Calc. for C22H28O4Cl2S2Pd (%): C, 43.65; H, 4.68; S, 10.70. Found: C, 43.71;
H, 4.84; S, 10.74. Melting point: 198–201 ºC. Far-IR ν(cm-1): 255 (Pd-Cl) (cis isomer); 333 (Pd-
Cl) (trans isomer). IR (KBr disk) ν(cm-1): 1625 (CO); 843 (C--S+). 1H NMR (DMSO-d6, ppm) δ:
2.77-3.16 (cis and trans isomers, 12H, S(CH3)2); 3.84 (s, 3H, OCH3); 5.08-5.38 (trans isomer,
1H, CH); 5.66 (cis, major diastereoisomer, 1H, CH); 5.75 (cis, minor diastereoisomer, 1H, CH);
7.18-7.98 (cis and trans isomers, m, 8H, Ph). 13C NMR (DMSO-d6, ppm) δ: 26.42-27.74 (s,
S(CH3)2); 49.52, 49.86 (s, CH); 55.66, 55.91 (s, OCH3); 113.47 (s, Ph); 119.05 (s, Ph); 121.10 (s,
Ph); 129.39 (s, Ph); 138.60 (s, Ph); 159.38 (s, Ph); 194.21 (s, CO).
2.2.7. Synthesis of the Pd(II) complex [PdCl2(Me2SCHC(O)C6H4-m-OMe).DMSO] (4): 0.06
g (0.1 mmol) of the mononuclear complexes 3a and 3b were dissolved in DMSO (2 ml). Pale
yellow crystals were formed by the slow diffusion of methanol into the DMSO solution over two
weeks.
2.2.8. Data for [PdCl2(Me2SCHC(O)C6H4-m-OMe).DMSO]: Yield: 0.057 g, 0.12 mmol, 95%.
1
Decomposition: 170-175 ºC. IR (KBr disk) ν(cm-1): 1624 (CO); 1186 (SO); 833 (C--S+). H
NMR (DMSO-d6, ppm) δ: 2.77-3.16 (cis and trans isomers, 12H, S(CH3)2); 3.84 (s, 3H, OCH3);
5.08-5.38 (trans isomer, 1H, CH); 5.66 (cis, major diastereoisomer, 1H, CH); 5.75 (cis, minor
13
diastereoisomer, 1H, CH); 7.18-7.98 (cis and trans isomers, m, 8H, Ph). C NMR (DMSO-d6,
6

ppm) δ: 26.44-27.76 (s, S(CH3)2); 49.53, 49.88 (s, CH); 55.67, 55.93 (s, OCH3); 113.48 (s, Ph);
119.06 (s, Ph); 120.93 (s, Ph); 129.40 (s, Ph); 138.74 (s, Ph); 159.32 (s, Ph); 194.55 (s, CO).
2.3. X-ray crystallography:
A suitable crystal was selected and mounted on a SuperNova, Dual, Cu at zero, Atlas
diffractometer. The crystal was kept at 130.00(10) K during data collection. Using Olex2 [30],
the structure was solved with the ShelXT [31] structure solution program using direct methods
and refined with the ShelXL [32] refinement package using least squares minimization. All non-
hydrogen atoms were refined with anisotropic displacement parameters; H atoms were
constrained to geometrical estimates, with an isotropic displacement parameter of 1.5 times (Me)
or 1.2 times (other) that of the parent carbon atom.
2.4. Computational details (theoretical studies):
The geometry of the [Y.PdCl2.DMSO] complex (4) (Y: [SMe2C(H)C(O)C6H4-m-OCH3]) was
fully optimized at the BP86 [33,34] /def2-SVP [35] level of theory. It has been shown that BP86
is a suitable level for calculation of the M←L bonding situation in complexes such as these [36-
41]. All calculations were performed using the Gaussian 09 set of programs [42]. Natural bond
orbital (NBO) analyses [43] were also carried out with the internal model Gaussian 09. Bonding
analysis in terms of energy-decomposition were carried out at BP86/TZ2P(ZORA)//BP86/def2-
TZVPP with C1 symmetry. The basis sets for all elements are triple-ζ quality augmented by one
set of polarization functions (ADF basis set TZP(ZORA)) with the program package
ADF2009.01.
7

2.5. General experimental procedure for the Suzuki-Miyaura cross-coupling reactions: A
one-pot mixture of aryl halide (0.75 mmol), arylboronic acid (1 mmol), catalyst (0.005 mol%),
Cs2CO3 (1.5 mmol) and EtOH (2 ml) was heated to 78 °C for 4 h. The reactions progress was
monitored by thin layer chromatography (TLC). After completion of the reaction, the mixture
was cooled to room temperature and diluted with n-hexane (15 ml) and water (15 ml). The
resulting organic layer was twice washed with brine (15 ml) and dried over CaCl2, filtered and
purified by recrystallization or silica gel column chromatography (n-hexane:EtOAc, 80:20) and
analyzed by NMR spectroscopy (1H and 13C).
Characterization of the products of the Suzuki-Miyaura cross-coupling reactions:
1
Data for biphenyl: Melting point: 67-69 °C. H NMR (89.6 MHz, CDCl3, ppm) δ= 7.47-7.64
(m, 10H, biphenyl). 13C NMR (100.62 MHz, CDCl3, ppm) δ= 127.21-141.29 (m, biphenyl)
1
Data for 4-nitro biphenyl: Melting point: 112–113 °C. H NMR (89.6 MHz, CDCl3, ppm) δ:
7.26-8.34 (m, 9H, biphenyl). 13C NMR (250 MHz, CDCl3, ppm) δ: 124.10-146.97 (m, biphenyl).
1
Data for 4-methoxy biphenyl: Melting point: 90-91 °C. H NMR (89.6 MHz, CDCl3, ppm) δ:
13
3.86 (s, 3H, methyl), 6.93-7.50 (m, 10H, biphenyl). C NMR (250 MHz, CDCl3, ppm) δ: 55.41
(s, OCH3), 114.18-159.19 (m, biphenyl).
Data for 4-carboxaldehyde biphenyl
:
Melting point: 89-91 °C. 1H NMR (400.61 MHz, CDCl3,
13
ppm) δ: 7.40-7.86 (m, 9H, biphenyl), 9.98 (s, 1H, CHO). C NMR (100.62 MHz, CDCl3, ppm)
δ: 127.39-147.23 (m, biphenyl), 191.94 (s, CO).
8

1
Data for 4-biphenyl carboxylic acid: Melting point: 223-226 °C. H NMR (89.6 MHz, CDCl3,
ppm) δ: 7.32-7.88 (m, phenyl, 9H), 11.04 (s, COOH, 1H). 13C NMR (100 MHz, CDCl3, ppm) δ:
124.37-144.81 (m, biphenyl), 163.39 (s, C=O).
Data for 1-phenyl naphthalene: Oil. 1H NMR (89.6 MHz, CCl3, ppm) δ: 7.23-7.49 (m, phenyl,
8H), 7.51-8.28 (m, phenyl, 4H). 13C NMR (100 MHz, CDCl3, ppm) δ: 125.34-140.70 (m,
aromatic).
1
Data for 2-phenyl thiophene: Melting point: 34-35 °C. H NMR (89.6 MHz, CDCl3, ppm) δ:
13
6.95-7.29 (m, phenyl, 5H), 7.29-7.55 (m, thiophene, 3H). C NMR (100 MHz, CDCl3, ppm) δ:
123.01-144.43 (s, aromatic).
1
Data for 4-nitro-4ʹ-ethyl biphenyl: Melting point: 82-83 °C. H NMR (89.6 MHz, CDCl3) δ:
1.34 (t, 3H, CH3), 2.73 (q, 2H, CH2), 7.26-8.34 (m, 8H, biphenyl). 13C NMR (250 MHz, CDCl3,
ppm) δ: 15.56 (s, CH3), 28.49 (s, CH2), 124.12-145.37 (m, biphenyl).
Data for 4-methoxy-4ʹ-ethyl biphenyl: Melting point: 73-75 °C. 1H NMR (89.6 MHz, CDCl3):
13
δ = 1.29 (t, 3H, CH3), 2.67 (q, 2H, CH2), 3.86 (s, 3H, OCH3), 6.92-7.46 (m, 8H, biphenyl). C
NMR (250 MHz, CDCl3, ppm) δ: 15.56 (s, CH3), 31.14 (s, CH2), 55.23 (s, OCH3), 114.03-
158.66 (m, biphenyl).
1
Data for 4-acetyl-4ʹ-ethyl biphenyl: Melting point: 105-108 °C. H NMR (400.61 MHz,
CDCl3, ppm) δ: 1.24 (t, 3H, CH3), 2.51 (s, 3H, CH3), 2.59 (q, 2H, CH2), 7.25-8.01 (m, 8H,
biphenyl). 13C NMR (100.62 MHz, CDCl3, ppm) δ: 15.52 (s, CH3), 26.64 (s, CH3), 28.55 (s,
CH2), 126.90-154.74 (m, biphenyl), 197.76 (s, CO).
Data for 4-ethyl-4ʹ-biphenyl carboxylic acid: Melting point: 195-197 °C. 1H NMR (89.6 MHz,
3
3
CDCl3, ppm) δ: 1.30 (t, CH3, J = 7.8 Hz, 3H), 2.68 (q, CH2, J = 6.5 Hz, 2H), 6.92-7.81 (m,
9

phenyl, 8H), 11.1 (s, COOH, 1H). 13C NMR (100 MHz, CDCl3, ppm) δ: 14.93 (s, CH3), 30.66 (s,
CH2), 127.78-141.62 (m, biphenyl), 169.34 (s, C=O).
1
Data for 1-(4-ethylphenyl) naphthalene: Oil. H NMR (89.6 MHz, CDCl3, ppm) δ: 1.45 (t,
3
3
13
CH3, J = 7.3 Hz, 3H), 2.83 (q, CH2, J = 7.6 Hz, 2H), 7.11–8.50 (m, phenyl, 11H). C NMR
(100 MHz, CDCl3, ppm) δ: 15.53 (s, CH3), 28.67 (s, CH2), 125.35-143.13 (s, aromatic).
Data for 2-(4ʹ-ethyl phenyl) thiophene: Melting point: 48-49 °C. 1H NMR (89.6 MHz, CDCl3,
ppm) δ: 1.16 (t, CH3, 3J = 7.2 Hz, 3H), 2.62 (q, CH2, 3J = 8.1 Hz, 2H), 6.91-7.80 (m, phenyl, H).
13C NMR (100 MHz, CDCl3, ppm) δ: 15.52 (s, CH3), 28.53 (s, CH2), 122.57-131.84 (m,
aromatic).
Data for 3-(4ʹ-ethyl phenyl) pyridine: Oil. 1H NMR (250 MHz, DMSO-d6) δ: 1.27 (t, CH3, 3
H), 2.69 (q, CH2, 2H), 7.29 (m, aromatic, 3H), 7.50 (d, aromatic, 2H), 7.84 (d, aromatic, 1H),
8.57 (d, aromatic, 1H), 8.85 (s, aromatic, 1H); 13C NMR (63 MHz, DMSO-d6) δ: 15.63 (s, CH3),
21.10 (s, CH3), 28.57 (s, CH2), 123.56-148.15 (s, aromatic).
The following compounds gave data consistent with those published, see Table 9: 4-methyl-
biphenyl (entry 2) [44], 4-acetylbiphenyl ( entry 6) [45], 4-ethyl-biphenyl (entry 11) [46], 4-
meyhyl-4ʹ-ethyl biphenyl (entry 12) [20], 4-carboxaldehyde-4ʹ-ethyl-biphenyl (entry 15) [20], 3-
phenyl pyridine (entry 10) [47].
3. Results and discussion
3.1. Synthesis
Dimethyl sulfide, SMe2, reacts with 2-bromo-3'-methoxyacetophenone in an equimolar ratio
forming the new sulfonium salt 1 in 93% yield. Further treatment of this salt with NaOH led to
10

elimination of HBr, giving the new sulfur ylide 2 in 86% yield. Reaction of this ligand with
[PdCl2(cod)] in a 2:1 ratio yielded the new mononuclear complexes 3a and 3b (Scheme 2).
Crystallization of these complexes from DMSO solution led to a ligand replacement reaction and
afforded the DMSO coordinated complex cis-[PdCl2(ylide).DMSO] (4). These complexes are
insoluble in most of organic solvents, such as chloroform, acetone and toluene. Therefore, we
chose DMSO as a suitable solvent for the NMR spectroscopies and crystallization.
Scheme 2: Synthesis of the Pd(II) complexes 3a/3b and 4.
3.2. Spectroscopy:
1
13
The structures were characterized successfully by H, C NMR and MS spectroscopies and
other conventional techniques, as well as IR spectroscopy and elemental analysis. Also, the
11

structure of complex 4 was determined unequivocally by single crystal X-ray diffraction. Table 1
shows a brief summary of these spectroscopic data.
Table 1. Spectroscopic data for compounds
1-
3
and the starting ketone.
1H NMR; δ(SCH) ppm
4.45
IR; ν(CO) cm-1
13C NMR; δ(CO) ppm
Compound
1702
1676
1596
1630
192.16
Ketone
5.46
191.33
182.69
194.21
1
4.29
2
3a and 3b
5.08-5.88
The CHNS elemental analysis of the palladium complexes 3a and 3b indicates a 2:1
stoichiometry between the sulfur ylide and PdCl2. Also, the mononuclear structure of complexes
3a and 3b was confirmed by mass spectroscopy, with m/z values of 179.0, 210.0 and 598.0 for
the PdCl2 and ylide fragments and PdCl2(ylide)2 molecular ion, respectively.
In the far-IR spectra of complexes 3a and 3b, two Pd-Cl stretching bands were observed at
333 and 255 cm-1, which are in accord with both cis- and trans- dichlorobis(sulfur ylide)
structures in the solid state [11]. Also, the ν(CO) and in the mid-IR spectrum of sulfur ylide 2
was observed at around 1596 cm-1, occurring at a lower frequency than the related sulfonium salt
1 (1676 cm-1). This is due to the fact that the electron density on the C=O bond in the ylide is
somewhat removed. Moreover, the coordination of the ylide through the Cα atom (carbanion
mode) causes a significant increase in the ν(CO) frequencies of complexes 3a and 3b, as if the
coordination of the ylide occurred from an O atom, we would expect a decrease of the ν(CO)
frequency [14]. Furthermore, the ν(S=C) band of the ylide 2 is also sensitive to the coordination.
12

It was seen that coordination of the ylide 2 to the Pd(II) ion has caused a shift of ν(S=C) to lower
frequencies, which is consistent with some removal of electron density from the S–C bonds.
The 1H NMR spectrum of the sulfur ylide 2 shows an upfield shift in the SCH signal compared
to that of the sulfonium salt 1. This upfield shift is due to the presence of a formal negative
charge on the methinic carbon, which can increase the electron density in the C-H bond. Also,
the methinic signals of complexes 3a and 3b show a downfield shift compared to the ylide 2,
indicating that coordination of the ylide through the Cα atom has happened. The coexistence of
1
the cis and trans isomers is confirmed by the H NMR spectra. DMSO-d6 solutions of these
complexes displayed four signals for the SMe2 group and four signals for the methine group. The
higher field pair of SMe2 and the methinic proton signals may be assigned to the trans isomer
[48]. Since the methinic carbons are chiral, two (RR/SS or RS/SR) diastereoisomers are expected
for these complexes [11]. The presence of two such dynamic diastereoisomers was observed in
the 1H NMR spectrum of complexes 3a and 3b. The trans diastereoisomers exhibit the signals of
the methinic protons as one singlet and one doublet peak around 5.08-5.38 ppm, whereas, the cis
diastereoisomers exhibit two singlet peaks around 5.66-5.75 ppm.
In the 13C NMR spectrum of sulfur ylide 2, removal of the formal negative charge on the
sulfonium salt makes the methinic carbon atom deshielded. Thus, a downfield shift for the signal
of the SCH group and a decrease of the electron density in the S=C bond in the sulfur ylide was
expected. Contrariwise, coordination of the sulfur ylide through the Cα atom causes an upfield
shift in the 13C NMR signal of methinic group [11], from 52 ppm in ylide 2 to 49 ppm in
complexes 3a and 3b. This upfield shift of the SCH signal for these complexes is the most
important aspect of the 13C NMR spectra and this is due to the change in the hybridization of the
ylidic carbon atom from sp2 to sp3 [49]. Downfield shifts for the CO and OCH3 signals were also
13

observed for complex 3, indicating a much lower shielding of the carbon atoms of the CO and
OCH3 groups in this complex [11]. The presence of two nearby singlet peaks for SCH, OCH3
and four CH3 signals for two SMe2 groups in the 13C NMR spectra of complexes 3a and 3b
confirmed the diastereoisomerism of these complexes.
3.3. DMSO as ligand:
Evaluation through literature data on the coordination of dimethylsulfoxide (DMSO) to
relatively soft metal atoms showed that the coordination mode of this ligand is highly dependent
on both electronic and steric factors [50]. However, steric demands play a more significant role
in determining the coordination mode, rather than the moderate π-acceptor properties of S-
bonded DMSO [51]. Recently, the synthesis and characterization of a mononuclear Hg(II)
complex of a phosphorus ylide containing one DMSO molecule as a ligand was reported by our
group [51,52]. The O-coordination mode of DMSO was revealed by single crystal X-ray analysis
of the mononuclear complex [HgCl2.(P-ylide).DMSO], in which P-ylide is a bulky phosphorus
ylide of the type of Ph3PCHC(O)C6H4Cl. Although on the basis of the Hard-Soft-Acid-Base
principle [53], the S-bonding mode is preferred in the specific case of the Hg(II) soft metal ion,
the steric hindrance of a bulky ligand, like phosphorus ylides, may affect the coordination mode
of the DMSO ligand and induce the O-bonding mode.
Crystallization of DMSO solutions of complexes 3a and 3b led to formation of a yellow
single crystal of complex 4 and, as mentioned above, such a ligand replacement reaction was
expected. Also, the presence of non-bulky sulfur ylide ligands and the soft metal Pd(II) ion in
complexes 3a and 3b led to the preferential S-bonding coordination mode of the DMSO ligand
[54]. Although attempts to achieve suitable single crystals of complexes 3a and 3b were
unsuccessful, we obtained a single crystal of the new DMSO coordinated complex 4. This is
14

good confirmation of complex formation between the Pd(II) ion and the sulfur ylide. The
molecular structure of complex 4 is shown in Figure 1. Relevant parameters concerning data
collection and refinement are given in Table 2. Selected bond distances and angles for the unit
cell of complex 4 are displayed in Table 3.
Figure 1: The molecular structure of complex 4.
Table 2: Crystal data and refinement details for complex 4.
Compound
Compound
Empirical formula
C15H24Cl2O3PdS2
465.71
Formula weight
Temperature/K
130.00(10)
Orthorhombic
Pbca
Crystal system
Space group
a/Å
15.51248(13)
9.19756(8)
24.14916(16)
90
b/Å
c/Å
α/°
β/°
90
γ/°
90
Volume/Å3
3445.53(5)
8
Z
ρ calc./ g cm-3
µ/mm-1
F(000)
1.796
13.865
1872.0
15

Crystal size/mm3
0.1138 × 0.07 × 0.03
CuKα (λ = 1.54184)
7.322 to 154.18
Radiation
2Θ range for data collection/°
Index ranges
-19 ≤ h ≤ 19, -11 ≤ k ≤ 10, -26 ≤ l ≤ 30
34284
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indexes [I>=2σ (I)]
Final R indexes [all data]
Largest diff. peak/hole / e Å-3
3632 [Rint = 0.0258, Rsigma = 0.0142]
3632/0/196
1.079
R1 = 0.0183, wR2 = 0.0500
R1 = 0.0198, wR2 = 0.0507
0.41/-0.53
Table 3: Selected bond lengths [Å] and bond angles [°] for complex 4.
Bond type
Bond Length/Å
Angle type
Angle/˚
Pd1 - Cl1
2.3272(4)
Cl1- Pd1 - Cl2
93.355(15)
Pd1 - Cl2
Pd1 - S2
Pd1 - C1
S1 - C1
2.3757(4)
2.2515(4)
2.0673(17)
1.7981(16)
1.8000(19)
1.791(2)
S2 - Pd1 - Cl1
S2 - Pd1 - Cl2
C1 - Pd1 - Cl1
C1 - Pd1 - Cl2
C1 - Pd1 - S2
C1 - S1 - C10
C11 - S1 - C1
O3 - S2 - Pd1
S1 – C1 - Pd1
C2 - C1 - Pd1
C2 - C1 - S1
175.983(15)
87.886(14)
89.01(5)
175.50(5)
90.01(5)
S1 - C10
S1 - C11
S2 - O3
S2 - C12
S2 - C13
O1 - C2
C1 – C2
101.36(8)
100.93(9)
118.12(6)
111.50(8)
110.36(11)
107.07(11)
1.4842(13)
1.7848(18)
1.7753(18)
1.225(2)
1.500(2)
The Pd atom is in a square planar environment, coordinated by one ylide ligand, two
chlorides and a DMSO molecule, [Y.PdCl2.DMSO]. The methoxy substituted aromatic ring is
oriented such that the methoxy group is trans to the ketone oxygen atom, the O2-C5...C2-O1
torsion angle being -164.8(2)°. There exist π-π interactions between the aromatic rings related by
16

(1-x, 1-y, 1-z), C5 is superimposed above C7’ and C6 lies above the center of the other aromatic
ring. There are a number of weak C-H…X intra- and inter-molecular interactions, the latter link
the molecules into a 3D network.
2.4. Computational details (theoretical studies):
A theoretical study on the structure and nature of the metal-ligand bond for complex 4 has
been reported at the BP86/def2-SVP level of theory. The X-ray crystal structure confirmed that
complex 4 exhibits a square planar structure in which two chloride atoms are in cis-like positions
(Figure 2).
Figure 2. Optimized structure of complex 4 at the BP86/SVP level of theory.
Thus further calculations, including the structure and nature of the C−Pd bond in complex 4,
were performed on the cis-like structure. The optimized structure of complex 4 at the BP86/def2-
SVP level of theory is shown in Figure 2 and trends for the variation of the corresponding bond
lengths and bond angles extracted from optimized geometry are given in Table 4. The calculated
bond lengths and bond angles of complex 4 are in good agreement with the X-ray experimental
values (Table 4).
17

Table 4. Selected bond lengths (Å) and bond angles (°) of complex 4 at the BP86/def2-SVP
level of theory.
Bond Lengths
Pd(1)-S(27)
Pd(1)-C(4)
Value/Å
Bond angles
Value/˚
2.38(2.25)a
2.08(2.06)
2.33(2.32)
2.39(2.37)
Cl(2)-Pd(1)-C(4)
Cl(1)-Pd(1)-S(27)
Cl(2)-Pd(1)-S(27)
C(1)-Pd(1)-S(27)
170.99(175.50)
177.77(175.98)
92.31(87.88)
102.58(90.01)
Pd(1)-Cl(2)
Pd(1)-Cl(3)
a The experimental values are given in parenthesis.
To studying the nature of the metal-ligand bond and/or possible interactions in this complex,
natural bond orbital (NBO) analysis was performed and used to estimate the delocalization of the
electron density between the occupied Lewis-type orbitals and the formally unoccupied non-
Lewis NBOs (antibonding or Rydberg), which corresponds to stabilizing the donor-acceptor
interaction [55]. The values of the WBI (Wiberg bond indices) and partial charges on the Pd, C
and Cl atoms involved in the bonding interactions between PdCl2.DMSO and Y of complex 4, as
well as the total charge of the ligand Y and [PdCl2.DMSO] fragment, were evaluated through
natural population analysis and the results are given in Table 5. The calculated partial charges on
both the Pd and C atoms of the Pd−C bond carry negative charges in the Pd−C bond, but the
results show that the q(C) is greater than q(Pd) and this may come from σ donation between the
C and Pd atoms of the Pd−C bond (Table 5). Also, the negative value of the total charge of the
[PdCl2.DMSO] fragment shows that there is a charge transfer of about 0.4 from the Y ligand to
the [PdCl2.DMSO] fragment in complex 4 and this data could confirm that the nature of the
Pd−C bond in this complex is more electrostatic.
18

Table 5. Wiberg bond indices (WBI) of the Pd−C and Pd-Cl bonds and natural charges of the Pd,
C and Cl atoms as well as the total charge of the Y ligand and the [PdCl2.DMSO] fragment.
0.50
Pd-C
0.68
WBIs
NPA
Pd-Cl(2)
0.61
Pd-Cl(3)
-0.018
-0.670
-0.289
-0.422
-0.413
0.413
Pd
C
Cl(2)
Cl(3)
[PdCl2.DMSO]
Y
Second-order perturbation theory analysis of the Fock matrix was carried out to evaluate
the donor-acceptor interactions on the basis of the NBO analysis. The values of the donor-
acceptor interactions in the compounds are given in Table 6. The important donor-acceptor
interactions in the case of the Pd–C bond were from σ(Pd–C) and the lone pair (LP) of the Cl
and S atoms as donors to σ* (Pd–C) and σ* (Pd–Cl) as acceptors (Table 6).
Table 6. The most important donor→ acceptor interactions concerning the Pd─C bond at the
BP86/def2-SVP level of theory.
Donor
Acceptor
Type
E2 (kcal/mol)
σ → σ*
σ → σ*
Lp → σ*
lp → σ*
19.44
4.02
Pd(1)−C (4)
Pd(1)−C(4)
Cl(3)
Pd(1)−Cl(2)
Pd(1)−C(4)
Pd(1)−C(4)
Pd(1)−C(4)
62.70
6.32
S(27)
19

To better understand the nature of the Pd–C bonding between the Y ligand and the
[PdCl2.DMSO] fragment in complex 4, quantum chemical calculations in the terms of energy-
decomposition analysis at the BP86/TZ2P(ZORA)//BP86/def2-SVP level with C1 symmetry,
using the program package ADF2009.01, was carrying out. The ∆Eint value between the two
investigated fragments in complex 4 is about 73 kcal/mol (Table 7). The breakdown of the ∆Eint
values into Pauli repulsion ∆EPauli and two attractive components shows that roughly 62% comes
from the electrostatic attraction, ∆Eelstat, while ~32% comes from the orbital term, ∆Eorb, and the
remaining concern is from ∆Edispersion. Thus the values of ∆Eelstat show that the nature of the Pd–C
bonding in complex 4 is more electrostatic.
Table 7. EDA analysis (BP86/TZ2P(ZORA)//BP86/def2-SVP) of complex 4 with C1 symmetry.
∆Eint
-73.39
∆EPauli
∆Eelstat
∆Eorb
∆Edisp
190.42
-164.65(62.4%)
-85.64(32.5%)
-13.51(5.1%)
This data is in good agreement with the NBO analysis which shows about a 0.4 e charge
transfer from the Y ligand to the [PdCl2.DMSO] fragment (Table 6) and 0.5 WBI in the Pd–C
bonding (Table 6).
The covalent bonding between the [PdCl2.DMSO] fragment and the Y ligand in complex 4
becomes visible by calculated deformation densities (∆ρ). Figure 3 show the important
deformation densities and the associated energy values which provide about 90 % of the overall
orbital interactions for the complex 4. Visual inspection of Figure 3a, indicates ∆ρ1, which
shows the contribution to ∆Eorb and comes from the DMSO.Cl2Pd←Y σ donation. Figure 3b
displays the deformation density ∆ρ2 which comes from the Pd−Cl bond to Y ligand charge
20

transfer. Also Figures 3c-e display the deformation densities ∆ρ3, ∆ρ4 and ∆ρ5 which come
from the [PdCl2.DMSO] fragment to Y ligand π-back donation.
a
b
∆ρ1: ∆E= -60.33689
∆ρ2: ∆E= -5.36428
(kcal/mol)
(kcal/mol)
ν= 1.02431
ν= 0.24726
Counter =0.001
Counter =0.0003
c
d
∆ρ3: ∆E= -5.39094
∆ρ4: ∆E= -2.41387
(kcal/mol)
(kcal/mol)
ν= 0.21788
ν= 0.15397
Counter =0.0003
Counter =0.0003
e
∆ρ5: ∆E= -3.10553 (kcal/mol)
ν= 0.14754
Counter =0.0003
Figure 3. Deformation densities ∆ρ associated with the most important orbital interactions in complex 4. Note that
the colour in this Figure, denotes the charge flow, which is from the red to the blue region.
3.4. Suzuki-Miyaura cross-coupling reactions of aryl halides and boronic acid:
The catalytic performance of the palladium complexes 3a and 3b in the Suzuki-Miyaura
cross-coupling reaction was examined. Initially, we performed a model reaction to optimize the
reaction conditions, including the catalyst loading, base, solvent and temperature (Table 8).
Reaction of phenylboronic acid with bromobenzene in ethanol at 78 °C in the presence of
Cs2CO3 (1.5 mmol) was chosen as a model reaction. The reaction provided the coupled product
in 90% yield (Table 8, entry 1). Then, a series of experiments was performed to find optimum
conditions.
21

At the first stage of optimization, we studied the efficiency of the catalyst loading on the
reaction. As expected, varying the catalyst concentration has a considerable effect on the activity
of the catalyst. When the reaction was carried out with 0.001 mmol of catalyst, the reaction
proceeded very slowly and running the reaction in the absence of catalyst resulted in no
conversion (Table 8, entries 3 and 4). If the loading of the catalyst was increased to 0.005 mmol,
the yield of the coupled products for the reactions showed a rise (Table 8, entry 2). At a high
loading of the catalyst (> 0.05 mmol), the maximum efficiency was observed. Also, an excessive
amount of catalyst did not increase the yield dramatically (Table 8, entry 5). Therefore, due to an
economic aspect, a low catalyst loading of 0.005 mmol was chosen as the best concentration of
the catalyst.
The solvent optimization stage was done with several commonly used solvents. Polar aprotic
solvents such as DMF and NMP were tested and the results showed that the conversion for the
desired coupling product was good at reflux temperature (Table 8, entries 6 and 7, respectively).
Using of ethanol as a green solvent gave the highest yield for this reaction (Table 8, entry 2).
However, water required additional time for completing the coupling reaction (Table 8, entry 8).
Also, non-polar solvents such as toluene and hexane gave low conversions (Table 8 entries 9 and
10).
Next, we optimized the conditions to select the best base from the commonly used ones. A
base usually plays an important role in such cross-coupling reactions and has a striking
accelerating effect on the reaction time. Thus, we investigated a series of reactions to screen the
influence of the base on the catalytic system. Among the tested bases, Cs2CO3 and K2CO3 were
the most effective base for the reactions (Table 8, entries 2 and 12), while other bases, such as
Na2CO3 and NaOAc, proved to be less active (Table 8, entries 11 and 13). Using of the organic
22

bases NEt3 and pyridine instead of inorganic bases decreased the catalyst activity and lowered
the conversion (Table 8, entries 14 and 15).
Finally, we optimized the reaction temperature. The reaction at reflux gives the coupled
products with the highest yield. Decreasing the temperature led to an increased reaction time and
decreased yields (Table 8, entries 16, 17).
Table 8. Optimizations for the Suzuki-Miyaura cross-coupling reaction.
Catalyst
(HO)2B
Br
Solvent, Base
temperature.
Entry
1
Base
Cat. loading (mmol)
Solvent
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
NMP
Temp. (°C)
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
reflux
reflux
reflux
reflux
reflux
25
Yield (%)b
0.05
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Na2CO3
K2CO3
NaOAc
NEt3
90
88
35
-
2
0.005
0.001
-
3
4
5
0.1
93
82
79
61
70
75
69
80
54
40
40
51
78
6
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
7
DMF
8
H2O
9
Toluene
Hexane
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
10
11
12
13
14
15
16
17
Pyridine
Cs2CO3
Cs2CO3
50
23

a
Reaction conditions for the Suzuki-Miyaura cross-coupling reaction: bromobenzene (0.5 mmol),
phenylboronic acid (0.75 mmol), base (1.5 mmol), solvent (2 ml), catalyst, 4 h, in the air.
b Isolated yield.
According to the optimized reaction conditions (EtOH, Cs2CO3 and 0.005 mmol of catalyst at
reflux temperature) various types of functionalized aryl halides reacted with arylboronic acid and
were converted into the corresponding coupled products in high to excellent yields (Table 9).
A range of aryl halides bearing electron-withdrawing and electron-donating groups was
studied in the Suzuki-Miyaura reaction. It is well known that the type of aryl halide substituent is
important for catalytic activity. The reaction of aryl halides containing electron-withdrawing
substituents, such as -NO2, -CHO and -COCH3 groups, with phenylboronic acid gives the
required products in good to excellent yields (Table 9, entries 4-6). Conversely, the catalyst
activity is lowered by increasing the electron density on the aryl halides, e.g. using 4-
bromoanisole and 4-bromotoluene (Table 9, entries 2 and 3). Also among the aryl halides
reagents, aryl iodides and bromides were more reactive than aryl chlorides [56]. The small C–I
bond dissociation energy and easy oxidative addition to the Pd(0) species causes the aromatic
iodides to have a higher reactivity compared to other aryl halides in the coupling reactions. Aryl
chlorides are less reactive than the other aryl halides because of the large C–Cl bond dissociation
energy and they showed little or no activity in the coupling reactions. However, due to the
economical aspect of aryl chlorides and the challenge of activating the C–Cl bond, more
applications of aryl chlorides in cross-coupling reactions have resulted [57]. In this regard, both
electron neutral and electron rich 4-chlorobenzene and 4-chlorotoluene show relatively low
reactivity in coupling reactions compared with the analogous aryl bromides and aryl iodides
(Table 9, entries 1 (70%), 2 (69%)). However, 4-chlorobenzaldehyde is a bit more reactive than
24

the other aryl chlorides (Table 9, entry 5). The electronically neutral benzene halides produced a
good amount of the desired product when coupled with arylboronic acids (Table 9, entry 11).
Table 9: Suzuki-Miyaura cross-coupling reaction of aryl halides and arylboronic acids.
R
R
Cat. 3
(HO)2B
Ar
X
Ar
EtOH, Cs2CO3
78 °C
Entry
1
Ar
R
H
X
Product
Yield %
Cl
Br
I
70
88
93
PhX
Cl
Br
Br
I
69
84
81
90
2
3
4
5
p-Me-PhX
H
H
H
H
Me
p-OMe-PhX
p-NO2-PhX
p-C(O)H-PhX
MeO
Br
89
O2N
Cl
Br
O
74
84
HC
O
6
7
p-C(O)CH3-PhX
p-COOH-PhX
H
H
Br
84
H3CC
Cl
Br
Cl
Br
Cl
Br
76
86
73
81
71
84
8
9
1- naphthalene
2- thiophene
H
H
S
Cl
Br
67
79
10
11
3-pyridine
PhX
H
N
Cl
Br
I
68
84
94
p-Et
25

Cl
Br
67
83
12
p-Me-PhX
p-Et
p-Et
Me
MeO
O2N
Br
I
79
90
13
14
15
p-OMe-PhX
p-NO2-PhX
p-C(O)H-PhX
p-Et
p-Et
p-Et
Br
85
O
Cl
Br
70
83
HC
O
16
17
p-C(O)CH3-PhX
p-COOH-PhX
Br
83
H3CC
Cl
Br
Cl
Br
Cl
Br
Cl
Br
70
81
76
85
73
81
69
80
p-Et
p-Et
p-Et
p-Et
18
19
1- naphthalene
2- thiophene
3-pyridine
S
20
N
a
Reaction conditions for the Suzuki-Miyaura cross-coupling reaction: arylhalide (0.5 mmol), arylboronic acid (0.75
mmol), Cs2CO3 (1.5 mmol), ethanol (2 ml), catalyst (0.005 mmol), 4 h, in the air.
b Isolated yield.
To extend the scope of our work, we next investigated the cross-coupling of various electron
rich and deficient aryl halides with 4-ethyl-phenylboronic acid. As expected, electron-donating
substituents on the arylboronic acid have a decreasing effect on the yield of the reaction.
However, activated aryl halides, such as aryl iodides and aryl bromides containing electron-
withdrawing substituents, advance the reactions to give excellent yields (Table 9, entries 11-16).
26

4. Conclusion
In summary, the present study describes the synthesis and characterization of the new
sulfonium salt 1, sulfur ylide 2 and the new mononuclear palladium(II)-ylide complexes 3a, 3b
and 4. On the basis of the physico-chemical and spectroscopic data, we propose the C-
coordinated mode for these mononuclear complexes, which is further confirmed by the X-ray
crystal structures. X-ray analysis showed that the Pd atom is coordinated by one ylide ligand,
two chloride ions and a DMSO molecule. Also a theoretical study on the structure and nature of
the Pd–C bond in complex 4, investigated here at the BP86/def2-SVP level of theory, is reported.
The NBO analysis showed that a charge transfer about 0.4 occurred from the Y ligand to the
[PdCl2.DMSO] fragment in complex 4. This result proved that the electrostatic character of the
Pd−C bonding in this complex is greater than the covalent character. The EDA results also show
that the nature of the Pd–C bonding in complex 4 is more electrostatic and ETS-NOCV analyses
confirms that the main contribution to ∆Eorb in the Pd–C bonding in complex 4 comes from
DMSO.Cl2Pd←Y σ donation. The catalytic activity of complexes 3a and 3b toward the Suzuki-
Miyaura cross-coupling reaction between various aryl halides and arylboronic acids in EtOH as
the solvent at reflux temperature was investigated. The ease of preparation of the complexes, low
catalyst loading and stability toward air and moisture make these complexes ideal catalysts for
the Suzuki-Miyaura cross-coupling reaction.
Acknowledgements
Funding of our research from the Bu-Ali Sina University is gratefully acknowledged.
Supplementary material
Physical measurements and selected 13C and 1H NMR spectra of compounds can be found in the
online version. CCDC 1438733 contains the supplementary crystallographic data for the
27

complex 4. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif
or from the Cambridge Crystallographic Data Center, 12, Union Road, Cambridge CB2 1EZ,
UK. Tel.: +44 (0)1223 762911; or deposit@ccdc.cam.ac.uk.
5. Reference
[1] Clark, J. S.; Nitrogen, Oxygen and Sulfur Ylide Chemistry, in: A Practical Approach in
Chemistry, Oxford University Press, UK(2002).
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[12] Sabounchei, S. J.; Bagherjeri, F. A.; Boskovic, C.; Gable, R. W.; Karamian, R.; Asadbegy,
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