Pd(II) and Pt(II) complexes of α-keto stabilized sulfur ylide: Synthesis, structural, theoretical and catalytic activity studies

Article abstract of DOI:10.1016/j.molstruc.2017.01.063

Reaction of dimethyl sulfide with 2, 3′-dibromoacetophenone led to formation of sulfonium salt [Me₂SCH₂C(O)C₆H₄-m-Br]Br (1). The resulted sulfonium salt was treated with NaOH and gave the α-keto stabilized sulfur ylide Me₂SC(H)C(O)C₆H₄-m-Br (2). This ligand was reacted with [MCl₂(cod)] (M?=?Pd, Pt; cod?=?1,5-cyclooctadiene) to form the new cis- and trans-[MCl₂(ylide)₂] (M?=?Pd (cis- and trans-3), Pt (cis- and trans-4)) complexes. Characterization of the obtained compounds was performed by elemental analysis, IR, ¹H and ¹³C NMR. Recrystallization of dichlorobis(ylide) palladium(II) and platinum(II) complexes from DMSO solution yielded the crystalline products, which X-ray diffraction data revealed that the both compounds were crystallized as cis-[MCl₂(ylide)(DMSO)] (M?=?Pd (5), Pt (6)) complexes. Also, a theoretical study on structure and nature of the M[sbnd]C bonding between the Y ligand (ylide) and [MCl₂·DMSO] fragments in [YMCl₂·DMSO] (M?=?Pd, Pt) complexes has been reported via NBO and energy-decomposition analysis (EDA). Furthermore, the palladium catalyzed Suzuki-Miyaura reaction of various aryl chlorides with arylboronic acids was performed. The results showed that the Pd(II) complexes cis- and trans-3 catalyzed efficiently coupling reactions at low catalyst loading and short reaction time.

Full text of DOI:10.1016/j.molstruc.2017.01.063

Accepted Manuscript
Pd(II) and Pt(II) complexes of α-keto stabilized sulfur ylide: Synthesis, structural,
theoretical and catalytic activity studies
Seyyed Javad Sabounchei, Ali Hashemi, Asieh Sedghi, Mehdi Bayat, Fateme
Akhlaghi Bagherjeri, Robert W. Gable
PII:
S0022-2860(17)30094-7
10.1016/j.molstruc.2017.01.063
MOLSTR 23368
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 23 May 2016
Revised Date: 1 December 2016
Accepted Date: 20 January 2017
Please cite this article as: S.J. Sabounchei, A. Hashemi, A. Sedghi, M. Bayat, F. Akhlaghi Bagherjeri,
R.W. Gable, Pd(II) and Pt(II) complexes of α-keto stabilized sulfur ylide: Synthesis, structural, theoretical
and catalytic activity studies, Journal of Molecular Structure (2017), doi: 10.1016/j.molstruc.2017.01.063.
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ACCEPTED MANUSCRIPT
Graphical abstract: pictogram

ACCEPTED MANUSCRIPT
Pd(II) and Pt(II) complexes of α-keto stabilized sulfur ylide: Synthesis,
structural, theoretical and catalytic activity studies
Seyyed Javad Sabounchei,a ,* Ali Hashemi,a Asieh Sedghi,a Mehdi Bayat,a Fateme Akhlaghi
Bagherjeri,b Robert W. Gableb
a Faculty of Chemistry, Bu-Ali Sina University, Hamedan,65174, Iran
b School of Chemistry, University of Melbourne, Victoria, 3010, Australia
ABSTRACT: Reaction of dimethyl sulfide with 2, 3ʹ-dibromoacetophenone led to formation of
sulfonium salt [Me2SCH2C(O)C6H4-m-Br]Br (1). The resulted sulfonium salt was treated with
NaOH and gave the α-keto stabilized sulfur ylide Me2SC(H)C(O)C6H4-m-Br (2). This ligand was
reacted with [MCl2(cod)] (M = Pd, Pt; cod = 1,5-cyclooctadiene) to form the new cis- and trans-
[MCl2(ylide)2] (M = Pd (cis- and trans-3), Pt (cis- and trans-4)) complexes. Characterization of
1
the obtained compounds was performed by elemental analysis, IR, H and 13C NMR.
Recrystallization of dichlorobis(ylide) palladium(II) and platinum(II) complexes from DMSO
solution yielded the crystalline products, which X-ray diffraction data revealed that the both
compounds were crystallized as cis-[MCl2(ylide)(DMSO)] (M = Pd (5), Pt (6)) complexes. Also,
a theoretical study on structure and nature of the M–C bonding between the Y ligand (ylide) and
[MCl2.DMSO] fragments in [YMCl2.DMSO] (M=Pd, Pt) complexes has been reported via NBO
and energy-decomposition analysis (EDA). Furthermore, the palladium catalyzed Suzuki-
Miyaura reaction of various aryl chlorides with arylboronic acids was performed. The results
* Corresponding author. Tel.: +98 8118272072; fax: +98 8118273231.
E-mail address: jsabounchei@yahoo.co.uk (S.J. Sabounchei).
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showed that the Pd(II) complexes cis- and trans-3 catalyzed efficiently coupling reactions at low
catalyst loading and short reaction time.
Keywords: Synthesis; Pd(II) and Pt(II) complexes; Sulfur ylide; X-ray characterization;
Theoretical study; Suzuki-Miyaura reaction.
1. Introduction
Sulfur ylides are a group of reactive compounds which have attracted considerable interest in
recent years [1-3]. This is not least because of their significant role in organic synthesis,
including Johnson-Corey-Chaykovsky reaction [4], which is due to the high stability and
ambidentate character as ligand can engage as an appropriate ligand for organometallic synthesis
[5-7]. The coordination chemistry of these compounds has been investigated extensively and it
was found that they can bond to a metal center through the carbanion or the enolate oxygen
(Scheme 1) [8-10]. From consideration of the Hard-Soft-Acid-Base principle (HSAB) [11], it can
be hypothesized that the title ligands tend to coordinate to soft metal ions via the soft ylidic
carbon as opposed to the hard carbonyl oxygen atom. The more observed Cα-coordination mode
corresponds to the transition metal complexes of Hg(II) [9], Cd(II) [10], Ag(I) [3] and Pd(II)
[12], while the O-coordination mode of these compounds is limited to a small number
of complexes with hard oxophilic metals such as tungsten [13].
Scheme 1 here
The palladium catalyzed Suzuki-Miyaura reaction is one of the most reliable methods for the
construction of Csp2-Csp2 bond [14-16]. Although this reaction originally catalyzed by palladium
complexes containing bulky phosphine ligands [17,18], but most of them are moisture/air
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sensitive and have environmental considerations. Application of more stable and cheaper
complexes containing sulfur or nitrogen ligands was developed to eliminate or reduce costs,
operational hazards and environmental pollution [19-21]. Very recently, our group reported the
synthesis of sulfur-containing palladium complexes and successful application as catalyst
precursors for the Mizoroki-Heck reaction [22]. Furthermore, attempts to use more economical
aryl chlorides which are less reactive than aryl bromides and iodides in C-C coupling reactions
showing a noteworthy growth [23-25]. Mostly electron-poor aryl chlorides, which are easier to
activate, have been used successfully in these reactions and non-activated aryl chlorides or even
deactivated aryl chlorides such as chloroanisoles were coupled by applying palladium complexes
in combination with phosphonium salts [26].
Notwithstanding this background, we choose the Pd(II) and Pt(II) complexes of sulfur ylides
as attractive candidates for the synthesis, X-ray characterization and theoretical studies.
Although, the complexation of sulfur ylides to various transition metals has been extensively
studied, however, application of the Pd(II) complexes of sulfur ylides in the Suzuki-Miyaura
reaction of less reactive aryl chlorides is the key advantage of this study.
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
[PdCl2(cod)] and [PtCl2(cod)] were prepared according to the published procedures [27]. Melting
points were measured on a SMP3 apparatus. IR spectra were recorded in the range of 4000–400
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cm-1 and on a Shimadzu 435-U-04 spectrophotometer from KBr pellets. NMR spectra (1H and
13C) were recorded on 500 MHz, 400 MHz and 250 MHz Bruker and 90 MHz Jeol spectrometers
in DMSO-d6 or CDCl3 as the solvent at 25 °C. Elemental analyses for Carbon, nitrogen,
hydrogen and sulfur atoms were determined by using a PerkinElmer 2400 series analyzer.
2.2. Synthesis of compounds
2.2.1. Synthesis of [Me2SCH2C(O)C6H4-m-Br]Br (1)
Dimethyl sulfide (0.28 mL, 3 mmol) was added to an acetone solution (5 mL) of ketone
BrCH2C(O)C6H4-m-Br (0.28 g, 1 mmol). The mixture was stirred for 15 h. The resulting solution
was filtered off, and the obtained precipitate 1 washed with acetone and dried. Yield 0.31 g,
95%. Anal. Calcd. for C10H12Br2OS (%): C, 35.32; H, 3.56; S, 9.43. Found: C, 35.44; H, 3.61; S,
1
9.32. Melting point: 197–199 °C. IR (KBr disk): ν(cm-1) 1682 (CO); 802 (C--S+). H NMR
(89.60 MHz, DMSO-d6) δH (ppm): 3.04 (s, 6H, S(CH3)2); 5.65 (s, H, CH); 7.38 (s, H, Ph); 7.58
(s, H, Ph); 7.67 (s, H, Ph); 7.94 (s, 1H, Ph); 8.17 (s, H, Ph). 13C NMR (62.90 MHz, DMSO-d6) δC
(ppm): 25.10 (s, S(CH3)2); 53.10 (s, CH2); 122.79 (s, Ph); 127.94 (s, Ph); 131.65 (s, Ph); 136.36
(s, Ph); 136.86 (s, Ph); 137.88 (s, Ph); 190.87 (s, CO).
2.2.2. Synthesis of Me2SCHC(O)C6H4-m-Br (2)
Treatment of compound 1 (0.31 g, 0.9 mmol) with H2O (0.5 mL) and aqueous NaOH 10%
solution (2 mL) led to elimination of HBr, affording the sulfur ylide 2. The mixture was stirred
for 30 min. Ligand 2 as orange oil was obtained by extraction of resulting solution with
chloroform, followed by washing with petroleum benzine. Yield 0.21 g, 84%. Anal. Calcd. for
C10H11BrOS (%):C, 46.35; H, 4.28; S, 12.37. Found: C, 46.40; H, 4.39; S, 12.17. IR (Nojul):
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ν(cm-1) 1577 (CO); 853 (C--S+). 1H NMR (89.60 MHz, CDCl3) δH (ppm): 2.98 (s, 6H, S(CH3)2);
4.65 (s, H, CH); 7.27 (s, H, Ph); 7.45 (s, H, Ph); 7.64 (s, H, Ph); 7.93 (s, 1H, Ph). 13C NMR
(22.53 MHz, CDCl3) δC (ppm): 28.08 (s, S(CH3)2); 54.97 (s, CH); 121.30 (s, Ph); 124.24 (s, Ph);
128.74 (s, Ph); 131.29 (s, Ph); 142.44 (s, Ph); 179.17 (s, CO).
2.2.3. Synthesis of cis- and trans-[PdCl2(Me2SCHC(O)C6H4-m-Br)2] (cis- and trans-3)
Dichloromethane solution of ylide 2 (0.21 g, 0.8 mmol, 5 mL) was added to a solution of
[PdCl2(cod)] (0.12 g, 0.4 mmol, 5 mL, CH2Cl2). The mixture was stirred for 2 h at room
temperature. The separated yellow solid was filtered and washed with diethyl ether and dried.
Yield 0.24 g, 85%. Anal. Calcd. for C20H20Br2Cl2O2PdS2 (%):C, 34.63; H, 2.91; S, 9.24. Found:
C, 34.71; H, 2.99; S, 9.11. Decomposition at: 181-193 ºC. IR (KBr disk): ν(cm-1) 1624 (CO); 798
(C--S+). Far-IR ν(cm-1): 256 (Pd-Cl) (cis isomer); 333 (Pd-Cl) (trans isomer). 1H NMR (250.13
MHz, DMSO-d6) δH (ppm): 2.59-2.81 (m, 6H, S(CH3)2) (trans isomer); 2.72-3.13 (m, 6H,
S(CH3)2) (cis isomer); 4.99 (s, 1H, CH) (trans, major diastereoisomer); 5.07 (s, 1H, CH) (trans,
minor diastereoisomer); 5.67-5.72 (m, 1H, CH) (cis isomer); 7.28-8.43 (m, 8H, Ph). 13C NMR
(62.90 MHz, DMSO-d6) δC (ppm): 26.46-27.43 (m, S(CH3)2) (trans isomer), 26.76-27.65 (m,
S(CH3)2) (cis isomer); 49.13 (s, SCH) (trans isomer), 49.78 (s, SCH) (cis isomer), 121.97-139.71
(m, Ph); 192.71-192.85 (m, CO) (trans isomer); 193.86 (m, CO) (cis isomer).
2.2.4. Synthesis of cis- and trans-[PtCl2(Me2SCHC(O)C6H4-m-Br)2] (cis- and trans-4)
Dichloromethane solution of ylide 2 (0.21 g, 0.8 mmol, 5 mL) was added to a solution of
[PtCl2(cod)] (0.15 g, 0.4 mmol, 5 mL, CH2Cl2). The mixture was stirred for 4 h at room
temperature. The separated pale yellow solid was filtered and washed with diethyl ether and
dried. Yield 0.23 g, 72%. Anal. Calcd. for C20H20Br2Cl2O2PtS2 (%):C, 30.63; H, 2.83; S, 8.18.
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Found: C, 30.71; H, 2.90; S, 8.12. Decomposition at: 190-198 ºC. IR (KBr disk): ν(cm-1) 1634
1
(CO); 796 (C--S+). H NMR (250.13 MHz, DMSO-d6) δH (ppm): 2.60-2.78 (m, 6H, S(CH3)2)
(trans isomer); 3.01-3.18 (m, 6H, S(CH3)2) (cis isomer); 5.70 (m, 1H, CH) (trans isomer); 5.90
2
(s, 1H, CH, JPt-H = 377.68 Hz) (cis isomer); 7.28-8.48 (m, 8H, Ph). 13C NMR (62.90 MHz,
DMSO-d6) δC (ppm): 25.68-26.68 (m, S(CH3)2) (trans isomer), 27.14-27.47 (m, S(CH3)2) (cis
isomer); 49.13 (s, SCH) (trans isomer), 47.12 (s, SCH) (cis isomer), 121.54-145.95 (m, Ph);
193.45-193.54 (m, CO) (trans isomer); 193.75- 193.87 (m, CO) (cis isomer).
2.2.5. Synthesis of cis-[PdCl2(Me2SCHC(O)C6H4-m-Br)(DMSO)] (5)
0.03 g (0.05 mmol) of complexes cis- and trans-3 was dissolved in DMSO (1 mL). The yellow
crystals were formed by the slow diffusion of methanol into the DMSO solution over two weeks.
The separated crystals were filtered and washed with diethyl ether and dried. Decomposition at:
1
181-193 ºC. IR (KBr disk): ν(cm-1) 1623 (CO); 1163 (SO). H NMR (250.13 MHz, DMSO-d6)
δH (ppm): 2.59-2.81 (m, 6H, S(CH3)2) (trans isomer); 2.72-3.13 (m, 6H, S(CH3)2) (cis isomer);
4.99 (s, 1H, CH) (trans, major diastereoisomer); 5.07 (s, 1H, CH) (trans, minor diastereoisomer);
13
5.67-5.72 (m, 1H, CH) (cis isomer); 7.28-8.43 (m, 8H, Ph). C NMR (62.90 MHz, DMSO-d6)
δC (ppm): 26.46-27.43 (m, S(CH3)2) (trans isomer), 26.76-27.65 (m, S(CH3)2) (cis isomer); 49.13
(s, SCH) (trans isomer), 49.78 (s, SCH) (cis isomer), 121.97-139.71 (m, Ph); 192.71-192.85 (m,
CO) (trans isomer); 193.86 (m, CO) (cis isomer).
2.2.6. Synthesis of cis-[PtCl2(Me2SCHC(O)C6H4-m-Br)(DMSO)] (6)
0.04 g (0.05 mmol) of complexes cis- and trans-4 was dissolved in DMSO (1 mL). The pale
yellow crystals were formed by the slow diffusion of methanol into the DMSO solution over two
weeks. The separated crystals were filtered and washed with diethyl ether and dried.
1
Decomposition at: 190-198 ºC. IR (KBr disk): ν(cm-1) 1633 (CO); 1130 (SO). H NMR (250.13
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MHz, DMSO-d6) δH (ppm): 2.60-2.78 (m, 6H, S(CH3)2) (trans isomer); 3.01-3.18 (m, 6H,
S(CH3)2) (cis isomer); 5.70 (m, 1H, CH) (trans isomer); 5.90 (s, 1H, CH, 2JPt-H = 377.68 Hz) (cis
isomer); 7.28-8.48 (m, 8H, Ph). 13C NMR (62.90 MHz, DMSO-d6) δC (ppm): 25.68-26.68 (m,
S(CH3)2) (trans isomer), 27.14-27.47 (m, S(CH3)2) (cis isomer); 49.13 (s, SCH) (trans isomer),
47.12 (s, SCH) (cis isomer), 121.54-145.95 (m, Ph); 193.45-193.54 (m, CO) (trans isomer);
193.75- 193.87 (m, CO) (cis isomer).
2.3. X-ray crystallography:
Suitable crystals of complexes 5 and 6 were 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 [28], the structure was solved with the ShelXT [29] structure solution program using
Direct Methods and refined with the ShelXL [30] refinement package using Least Squares
minimisation. All non-Hydrogen atoms were refined with anisotropic displacement parameters;
all H-atoms were constrained at geometrical estimates, with isotropic displacement parameters of
either 1.5 times (Me) or 1.2 times (other) the displacement parameters of the parent carbon atom.
2.4. Computational studies
All of these studies have been down at DFT level of theory using the exchange functional of
Becke and the correlation functional of Perdew (BP86) [31,32]. The geometries of
[YPdCl2DMSO] and [YPtCl2DMSO] complexes were optimized at BP86/def2-SVP [33] with C1
symmetry. All calculations were performed using the Gaussian 09 set of programs [34]. NBO
[35] analysis was performed using internal model GAUSSIAN 09, and it gives good information
about the nature of bonding. For bonding analyses in the terms of energy-decomposition
analysis, were carried out at BP86/TZ2P(ZORA)//BP86/def2-TZVPP with C1 symmetry. The
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basis sets for all elements have triple-ζ quality augmented by one set of polarization functions
(ADF basis set TZP(ZORA)) with the program package ADF2009.01.
2.5. General procedure for Suzuki-Miyaura reaction
A one-pot mixture of aryl chloride (0.5 mmol), arylboronic acid (0.75 mmol), catalyst (1 mol%),
Cs2CO3 (1 mmol) and DMF/H2O (2 mL, 1:1) was heated to 100 °C for 2 h. The reaction
progress was monitored by thin layer chromatography (TLC). After completion of the reaction,
the tube was cooled and the mixture was diluted with n-hexane (15 mL) and water (15 mL). The
resulting organic layer was washed with brine (15 mL) and dried over CaCl2. Purification was
done either by flash chromatography (n-hexane:EtOAc, 8:2) or by recrystallization and the final
product was then characterized by 1H and 13C NMR spectroscopies.
2.6. Characterization of the Suzuki-Miyaura coupling products
2.6.1. 4-Nitro-biphenyl (7a)
1
Melting point: 67-69 °C. H NMR (89.6 MHz, CDCl3) δH (ppm): 6.74-8.15 (m, 9H, biphenyl).
13C NMR (100.62 MHz, CDCl3) δC (ppm): 124.08-147.59 (m, biphenyl).
2.6.2. 4-Acetyl-biphenyl (7b)
Melting point: 105–108 °C. 1H NMR (89.6 MHz, CDCl3) δH (ppm): 3.40 (s, 3H, CH3), 7.46-8.21
(m, 9H, biphenyl). 13C NMR (100.62 MHz, CDCl3) δC (ppm): 26.75 (s, CH3), 127.11-145.63 (m,
biphenyl), 197.53 (s, CO).
2.6.3. Biphenyl (7c)
Melting point: 67-69 °C. 1H NMR (400.61 MHz, CDCl3) δH (ppm): 7.40-7.64 (m, 10H, phenyl).
13C NMR (100.62 MHz, CDCl3) δC (ppm): 127.21-141.29 (m, biphenyl).
2.6.4. 4-Methyl-biphenyl (7d)
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1
Melting point: 48-50 °C. H NMR (89.6 MHz, CDCl3) δH (ppm): 2.46 (s, 3H, CH3), 7.26-7.61
(m, 9H, phenyl). 13C NMR (100 MHz, CDCl3) δC (ppm): 21.08 (s, CH3), 126.94-141.11 (m,
biphenyl).
2.6.5. 4-Methoxy-biphenyl (7e)
Melting point: 90-92 °C. 1H NMR (400.61 MHz, CDCl3) δH (ppm): 3.78 (s, 3H, OCH3), 6.90-
7.49 (m, 9H, phenyl). 13C NMR (100.62 MHz, CDCl3) δC (ppm): 55.36 (s, OCH3), 114.20-
159.15 (m, biphenyl).
2.6.6. 4-Nitro-4ʹ-ethyl biphenyl (7f)
Melting point: 82-83 °C. 1H NMR (400 MHz, CDCl3) δH (ppm): 1.32 (t, 3H, CH3), 2.75 (q, 2H,
CH2), 7.28-8.32 (m, 8H, biphenyl). 13C NMR (100 MHz, CDCl3) δC (ppm): 15.50 (s, CH3), 28.60
(s, CH2), 124.11-147.61 (m, biphenyl).
2.6.7. 4-Acetyl-4ʹ-ethyl biphenyl (7g)
Melting point: 105–108 °C. 1H NMR (400.61 MHz, CDCl3) δH (ppm): 1.29 (t, 3H, CH3), 2.71 (s,
13
3H, CH3), 2.74 (q, 2H, CH2), 7.26-8.03 (m, 8H, biphenyl). C NMR (100.62 MHz, CDCl3) δC
(ppm): 15.52 (s, CH3), 26.64 (s, CH3), 28.55 (s, CH2), 126.90-154.74 (m, biphenyl), 197.76 (s,
CO).
2.6.8. 4-Ethyl- biphenyl (7h)
Melting point: 82-83 °C. 1H NMR (89.6 MHz, CDCl3) δH (ppm): 1.39 (t, 3H, CH3), 2.78 (q, 2H,
CH2), 7.32-7.67 (m, 9H, biphenyl). 13C NMR (100 MHz, CDCl3) δC (ppm): 15.59 (s, CH3), 28.48
(s, CH2), 126.89-143.33 (m, biphenyl).
2.6.9. 4-Ethyl- 4ʹ-methyl biphenyl (7i)
Melting point: 90-91 °C. 1H NMR (400 MHz, CDCl3) δH (ppm): 1.32 (t, 3H, CH3), 2.44 (s, 3H,
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CH3), 2.74 (q, 2H, CH2), 7.27-7.57 (m, 8H, biphenyl). 13C NMR (100 MHz, CDCl3) δC (ppm):
15.64 (s, CH3), 21.12 (s, CH3), 28.54 (s, CH2), 126.88-143.01 (m, biphenyl).
2.6.10. 4-Methoxy- 4ʹ-ethyl biphenyl (7j)
Melting point: 73-75 °C. 1H NMR (89.6 MHz, CDCl3) δH (ppm): 1.29 (t, 3H, CH3), 2.67 (q, 2H,
CH2), 3.86 (s, 3H, OCH3), 6.93–7.46 (m, 8H, biphenyl). 13C NMR (250 MHz, CDCl3) δC (ppm):
15.56 (s, CH3), 31.15 (s, CH2), 55.23 (s, OCH3), 114.03-158.66 (m, biphenyl).
3. Results and discussion
3.1. Synthesis
As shown in Scheme 2, dimethyl sulfide reacts with the 2, 3ʹ-dibromoacetophenone in equimolar
ratios, forming the sulfonium salt 1 in 95% yields. The resulted salt was treated with NaOH 10%
to obtain the sulfur ylides 2 in 85% yields. Reaction of this ylide with [MCl2(cod)] (M = Pd and
Pt) in 2:1 ratio gives the new square-planar complexes cis- and trans-[MCl2(Me2SCHC(O)C6H4-
m-Br)2] (M = Pd, cis- and trans-3; M = Pt, cis- and trans-4). Recrystallization of these
complexes from DMSO solution leads to ligand replacement reaction, affording the DMSO
coordinated cis-[MCl2(ylide)(DMSO)] (M = Pd (5), Pt (6)) complexes. Because of the very low
solubility of these complexes in most of common solvents such as chloroform, acetone and
ethanol, we chose DMSO as a suitable solvent for the NMR spectroscopies and crystallization.
Scheme 2 here
3.2. Spectroscopy
1
The structures were characterized successfully by elemental analysis, IR, H and 13C NMR
spectroscopies. The CHNS elemental analysis of complexes 3 and 4 confirmed the complexation
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of sulfur ylide with MCl2 (M = Pd, Pt) in a 2:1 stoichiometry. Table 1 shows the brief summary
of the spectroscopic data.
Table 1 here
The ν(CO) in the IR spectrum of sulfur ylide 2 was observed as a sharp band around 1577 cm-
which shows lower frequency shift than the related sulfonium salt 1 (1682 cm-1). This
1
absorption band is sensitive to the coordination mode of ylide; that is coordination through the
carbanion shifts the ν(CO) to higher frequencies in complexes 3 and 4, while, if the
complexation occurred through oxygen atom, we expect decrease of ν(CO) [15]. Mid-IR
spectroscopy could not differentiate between geometric isomers (cis and trans) of these
complexes. However, the far IR spectrum of complexes cis- and trans-3 exhibit two Pd-Cl
stretching band around the 333 and 256 cm-1, indicating presence of both cis- and trans-
dichlorobis(sulfur ylide) structure in the solid state [36].
1H NMR spectrum of the sulfur ylide 2 exhibits the SCH signals at lower frequencies
compared to that of the sulfonium salt 1. This upfield shift is due to the presence of formal
negative charge on the methinic carbon, which increases the electron density in C-H bond. The
1
SCH signals in the H NMR spectra of complexes 3 and 4 are the best spectroscopic probe for
determining the coordination mode of ylide to metal center. These signals are appeared at higher
frequencies compared to the ylide 2, indicating that the Cα-coordination of ylide has occurred.
1H NMR spectroscopic studies was also confirmed the presence of both the cis and trans isomers
1
of complexes 3 and 4. H NMR spectra of these complexes show two sets of doublet peaks for
SMe2 and methine groups. The higher field pair of SMe2 and the methinic proton signals may be
assigned to the trans isomer [36]. Because these complexes have chiral centres at methinic
carbons, two diastereoisomers (RR/SS or RS/SR) are expected for each of them [3,13]. Also, it
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1
was concluded from the integrated intensities of the SMe2 signals in the H NMR spectrum of
complexes cis- and trans-3 that the ratio of the cis to trans isomer was about 2:1. The fact that
trans-PdCl2(ylide)2 is a major portion of isomers mixture would be mainly attributed to a smaller
1
steric repulsion between ylide ligands [36]. However, the signals of methine proton in the H
NMR spectrum of complexes cis- and trans-PtCl2(ylide)2 show similar intensities and implies
that both isomers have same proportion in the cis- and trans-4 complexes.
In the 13C NMR spectrum of sulfur ylide 2, the signals of methinic carbon was shifted to
higher frequencies than those of sulfonium salt 1. Contrariwise, coordination of the sulfur ylide
through Cα, causes to an upfield shift of the signals due to the ylidic carbon atoms in complexes
13
3 and 4 [3]. This is the most important aspect of the C NMR spectra of these complexes and
attributed to the change in hybridization of the ylidic carbon atom upon coordination to metal
ions [37]. The 13C chemical shifts of the CO group for complexes 3 and 4 were found to be
around 190 ppm, compared with 180 ppm for the same carbon in the parent free ylide, indicating
13
a much lower shielding of the CO group in these complexes [3]. Also, the C NMR spectra of
complexes 3 and 4 displayed two sets of signals, which are in agreement with the mixture of two
geometric isomers. Such geometrical and optical isomerism led to observation of four CH3
signals due to the two SMe2 groups and two SCH signals due to the two methinic group in the
13C NMR spectra [36].
3.3. Crystallography
Yellow single crystals of complexes 5 and 6 were grown by vapour diffusion of methanol into
DMSO. The molecular structures of these complexes were shown in Fig. 1. Relevant parameters
concerning data collection, refinement and bond angles were given in Table 2. Selected bond
distances for the unit cells of 5 and 6 are displayed in Table 3.
12

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Fig. 1 here
Table 2 here
Table 3 here
The Pd and Pt atoms in complexes 5 and 6 are in a square planar environment, coordinated by
one ylide, two chlorides and a DMSO molecule. The bromo substituted aromatic ring is oriented
such that the bromine atom is trans to the ketone oxygen. There are number of weak inter- &
intra- molecular C-H…Cl, C-H…Br, C-H…O and C-H…S interactions. There is also a π…π
interaction between the aromatic rings of two adjacent molecules. These interactions link the
molecules into 3D network.
3.4. DMSO as ligand
Although DMSO is known as one of the best solvents for dissolving such compounds, but it can
behave as an ambidentate ligand and bind to a metal center either through the sulfur atom or
through the oxygen atom. Estimation of the coordination mode of DMSO is highly depends on
both electronic and steric factors [38]. Especially in the case of S-bonding, steric demands of
coordination have more contribution than the moderate π-acceptor properties [39]. For example,
our group reported the synthesis of Hg(II) complexes of type [HgCl2.(P-ylide).DMSO], in which
P-ylide was a bulky phosphine ligand (Ph3PCHC(O)C6H4Cl) [39, 40]. Despite the fact that
Hg(II) is a soft metal ion and S-bonding mode is preferred, but the steric hindrance of such bulky
ligands induce the O-bonding mode.
Based on the above mentioned rationale, such ligand-replacement reaction is expected for the
DMSO solution of complexes cis- and trans-3 and 4. Non-bulky sulfur ylide ligands and
relatively soft metal ions such as Pd(II) and Pt(II) lead to preferring of S-bonding coordination
mode of DMSO in complexes 5 and 6. Even though the attempts to achieve suitable single
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crystal of complexes cis- and trans-3 and 4 for X-ray characterization were unsuccessful, the
obtained new DMSO coordinated complexes 5 and 6 are good evidence for complex formation
between the Pd(II) or Pt(II) metal ions and the sulfur ylide 2.
3.5. Computational studies
A theoretical study on structures and nature of bond in [Y.PdCl2.DMSO] and [Y.PtCl2.DMSO]
(Y= ylide 2) complexes at the BP86/def2-SVP level of theory has been reported. It has been
shown that BP86 is suitable level for calculation of bonding situation between the M←L in such
as these complexes [40-55]. X-Ray crystal structures confirm that both of [YPdCl2.DMSO] and
[YPtCl2.DMSO] have square planar structures with two chlorine atom in cis position (see Fig. 2).
Thus, further studies including geometry optimization, NBO and EDA analysis were performed
on the Cis-like structure. The optimized structures of [YPdCl2.DMSO] and[YPtCl2.DMSO]
using BP86/def2-SVP level are shown in Fig 2 and also selected experimental and calculated
bond lengths, and bond angles for latter complexes are illustrated in Table 4. The calculated
bond lengths and bond angles of these complexes are in good agreement with the experimental
values.
Fig. 2 here
Table 4 here
In continuation the NBO analyses used for estimate the delocalization of electron density
between occupied Lewis-type orbitals and formally unoccupied non-Lewis NBOs (antibonding
or Rydberg), which corresponds to stabilizing donor-acceptor interaction [56].
The values of partial charges and WBI for Pd, Pt, C and Cl atoms involved in the bonding
interactions between [PdCl2DMSO] and [PtCl2DMSO] with Y fragment in [YMCl2DMSO] (M=
Pd, Pt) complexes as well as, the total charge of [MCl2.DMSO] (M= Pd, Pt) fragments were also
14

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evaluated through natural population analysis and are given in Table 5. The result showed that
the calculated partial charges on the C and M atoms in [YMCl2.DMSO] (M=Pd, Pt) complexes
are negative and positive. Thus, it can conclude that there is σ donation between the lone pair of
C atom for Y fragment and also empty orbital of M atoms from [MCl2DMSO] (M=Pd, Pt) in
M−C bond (see Table 5).
Table 5 here
Also the negative value of total charge of [MCl2.DMSO] (M=Pd, Pt) fragments show that
there are charge transfers about 0.4 from Y ligand to [MCl2.DMSO] (M=Pd, Pt) fragments in
[YMCl2.DMSO] complexes. These data could confirm the existence of a strong interaction
between the Y ligand and [MCl2.DMSO] (M=Pd, Pt) fragments in [YMCl2.DMSO] complexes.
In continuation, a second-order perturbation theory analysis of the Fock matrix was carried out to
evaluate the donor–acceptor interactions on the base of NBO analysis. The values of donor-
acceptor interactions for latter complexes are given in Table 6. The calculated data showed that
the important donor–acceptor interactions in the case of Pd–C bonds in [YPdCl2DMSO] complex
were concern to σ (Pd–C), σ (Pd–Cl) and LP of Cl atoms as donors and σ* (Pd–C), σ* (C–O),
as acceptors. Also in the case of Pt–C bonds in [YPtCl2DMSO] complex they concern to σ (Pt–
C), and LP of S atoms as donors and σ* (Pd–C), σ* (C–O), and LP* of Pt as acceptors (see
Table 6).
Table 6 here
To better understand the nature of the M–C bonding between the Y ligand and
[MCl2.DMSO] fragments in [YMCl2.DMSO] (M=Pd, Pt) complexes, we carried out quantum
chemical calculations in the terms of energy-decomposition analysis at the
15

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BP86-D3/TZ2P(ZORA)//BP86/def2-SVP with C1 symmetry with the program package
ADF2009.01.
The ∆Eint between two investigated fragments in [YPdCl2DMSO] complex is about 73 kcal
mol-1 (see Table 7) and that for [YPtCl2DMSO] complex is about 85 kcal mol-1. The result shows
that the binding of Y fragment to [PdCl2DMSO] in [YPdCl2DMSO] complex is stronger than
that in [YPtCl2.DMSO] complex. The breakdown of the ꢀEint values into the Pauli repulsion
ꢀEPauli and the two attractive components shows that roughly 62-60% comes from the
electrostatic attraction ꢀEelstat while ~33% comes from the orbital term ꢀEorb and the remaining
concern to ꢀEdispersion for [YMCl2DMSO] (M=Pd, Pt) respectively. Also, the values of ∆Eelstat
showed that the percent of electrostatic nature of Pd–C bonding in [Y.PdCl2.DMSO] is slightly
more than [Y.PtCl2.DMSO]. The covalent bonding between the [MCl2.DMSO] fragment and Y
ligand in [Y.MCl2.DMSO] (M=Pd, Pt) complexes becomes visible by the calculated deformation
densities ꢀρ.
Table 7 here
Fig. 3 and Fig. 4 show the important deformation densities ꢀρ and the associated energy values
which provide about 90 % of the overall orbital interactions for the complex. Visual inspection
of Fig. (3a, c and 4a, c) indicates the ꢀρ1 and ꢀρ3, which show the main contribution to ꢀEorb
and comes from the [DMSOCl2M←Y] σ donation. Also Fig. (3b, d, e and 4b, d, e) display the
deformation density ꢀρ2, ꢀρ4, and ꢀρ5, which come from the [MCl2DMSO] (M=Pd, Pt) to Y
fragment π-back donation.
Fig. 3 here
Fig. 4 here
3.6. Catalytic activity
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Suzuki-Miyaura coupling reaction of varous aryl chlorides with arylboronic acids was then
examined by using the palladium complexes cis- and trans-3. As noted in literature, release of
Pd(0) as catalytic active species in C-C coupling reactions is highly depends on the nature of
ligands around the palladium center [57]. Although a wide variety of palladium(II) complexes
containing phosphorus ylide efficiently promote such coupling reactions, their sulfur ylide
analogues show rivalry for releasing of Pd(0) species in these reactions [58]. In order to
investigate the catalytic activity of the Pd(II) complexes cis- and trans-3, we carried out a model
reaction to optimize the reaction conditions including solvent, base, temperature and catalyst
loading (Table 8). As these catalysts are not sensitive to oxygen, the reactions were carried out in
the air atmosphere. Reaction of phenylboronoic acid with chlorobenzene in EtOH (2 mL) at
75°C in the presence of K3PO4 (1 mmol) and 1 mol% of complexes cis- and trans-3 was chosen
as model reaction. The reaction led to formation of coupled product in 38% yield (Table 8, entry
1). Then, a series of experiments was performed to find the optimum reaction conditions.
Table 8 here
At the first stage of optimization, we study the effect of base and solvent on the reaction.
Since the solubility and basicity of the base strongly depend on the solvent used, these two
parameters are closely connected. This optimization was done with several commonly used bases
and solvents, inclouding organic and inorganic bases and polar protic solvents to non-polar
aprotic solvents. The use of strong base Cs2CO3 led to increase in conversion (Table 8, entry 7);
However, the organic base NEt3 was ineffective and gave the coupled product in lower yield
(Table 8, entry 13). The higher solubility of catalyst in a dipolar aprotic solvent (DMF) rather
than a dipolar protic solvent (EtOH) resulted in higher yield of coupled product (Table 8, entries
2, 8 and 14). Addition of water to DMF in 1:1 (v/v) ratio leads to complete dissolution of the
17

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both of catalyst and base. Interestingly, the coupling reactions carried out in aqueous DMF gave
the the desired coupled product in highest yields (Table 8, entries 5, 11 and 17). Althogh the
reactions in EtOH/H2O gives more conversion in compared to the reactions in EtOH, but the
complexes cis- and trans-3 remains almost insoluble and causes low efficiencies (Table 8, entries
4, 10 and 16). Also, very poor catalytic activity for complex cis- and trans-3 was observed in the
toluene and water, due to low solubility of complexes cis- and trans-3 in these solvents (Table 8,
entries 3, 9, 15 and 6, 12, 18, respectively). These results indicates that solubility of both the
catalyst and base plays an important role in such catalytic systems.
Next, we investigate the effect of catalyst loading on the reaction. As expected, varying the
catalyst loading has a significant effect on the performance of catalyst. We choose the reaction
condition including DMF/H2O as solvent and Cs2CO3 as base (Table 8, entry 11) for more
investigation. When the loading of complexes cis- and trans-3 decreased to 0.2 mol%, the
coupling reaction will proceed slowly and even slower when the catalyst loading was 0.1 mol%
(Table 8, entries 20 and 21). Also, excessive amount of catalyst did not increase the yield
significantly (Table 8, entry 19). Therefore, with respect to the economic aspect, low catalyst
loading of 1 mol% was chosen as the best loading of catalyst.
Finally, the reactions were carried out at different temperature. Decreasing the temperature of
the reactions has led to fall-off of the yields and increase of the reaction time to completion of
the reactions (Table 8, entry 23). Also, the reaction at 100 °C yielded the corresponding coupled
product in almost quantitative yield (Table 8, entry 22). Thus, the optimum condition obtained
for Suzuki-Miyaura coupling reaction consisting the DMF/H2O as solvent, Cs2CO3 as base, 1
mol% of complexes cis- and trans-3 as catalyst and reaction at reflux temperature (100 °C) for 2
h.
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Using the optimized reaction conditions, palladium complexes cis- and trans-3 were applied
to a range of aryl chlorides bearing electron-donating and electron-withdrawing substituents in
Suzuki-Miyaura reaction. Various functionalized aryl chlorides reacted with phenylboronic acid
and were converted into the corresponding coupled products in high to excellent yields (Table 9).
Conversely, increasing electron density on the aryl chlorides lowered the catalyst activity. That
is, excellent yields were achieved when phenylboronic acid reacted with aryl chlorides with
electron-withdrawing substituent such as -NO2 and -COCH3 (Table 9, entries 1 and 2).
Deactivated aryl chlorides 4-chlorotoluene and 4-chloroanisol gave lower yields indicating that
the reaction was sensitive to the electron density on the aryl chlorides (Table 9, entries 4 and 5).
The reaction of electronically neutral chlorobenzene with phenylboronic acid was also produced
good amounts of the product (Table 9, entry 3). It is noteworthy that the reactions of arylboronic
acid containing electron-donating substituent with aryl chlorides furnishes good amounts of
desired biaryls, albeit with reduced yields (Table 9, entries 6-10).
Table 9 here
Several studies on chemistry of palladium catalyzed coupling reactions indicate that the
palladium complexes may behave as a mere resource for producing Pd(0) nanoparticles. To
evaluate the homogeneous or heterogeneous nature of the active species, we carried out the
mercury drop test [59]. Addition of a drop of mercury to the reaction mixture at t=0 did not
affect the conversion of reaction, which suggests that amalgamation had not occurred and the
catalysis was homogeneous in nature.
As can be seen in Table 9, by using Pd(II) complexes of sulfur ylide ligand good amounts of
functionalized biaryl derivatives are yielded. The higher C–Cl bond dissociation energy
compared with C–Br and C–I bonds disfavors oxidative addition step in catalytic coupling
19

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reactions of less reactive aryl chlorides which makes this step becoming rate-determining step
[60]. However, more electron-rich and less bulky ligands facilitate the oxidative addition step
and counter wise, more bulky and less electron-rich ligands facilitate the reductive elimination
step [61, 62]. Therefore, sulfur ylides with low steric hindrance and suitable electron donating
properties can act as an ideal ligand for such coupling reactions, as well as their phosphorous
analogous or N-heterocyclic carbene (NHCs) ligands. Table 10 shows a comparison between the
efficiency of this catalytic system in Suzuki-Miyaura coupling reaction of aryl chlorides and
other catalytic systems. On the whole, the results of this comparison showed that the catalytic
activity of these Pd(II) complexes with sulfur ylide ligands are similar to or slightly better than
those of mono-and bidentate Pd(II) complexes of phosphine and NHCs ligands. From an
industrial view point, simple synthetic procedure, low catalyst loading and short reaction time
make these Pd(II) complexes one of the best choices for the Suzuki-Miyaura coupling reaction.
Table 10 here
4. Conclusion
In summary, the present study describes the synthesis and characterization of sulfonium salt 1,
sulfur ylide 2, and its new Pd(II) and Pt(II) complexes cis- and trans-3 and 4. On the basis of
physico-chemical and spectroscopic data, we propose C-coordination of ylide 2 to the metal ions,
which is further confirmed by the X-ray crystal structures. Density functional theory study has
been done on structures and nature of M-C bonding in [YMCl2DMSO] (M=Pd, Pt) complexes
via NBO and EDA analysis. The result of NBO analyses showed that there are charge transfers
about 0.4 from Y ligand to [MCl2.DMSO] (M=Pd, Pt) fragments in [YMCl2DMSO] complexes.
The EDA analyses confirm that the contribution of the electrostatic interactions (ꢀEelstat) and
ꢀEorb in C-M bond of the present complexes are about 60% and 33% respectively. Also the
20

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EDA-NOCV showed that the main contribution to ꢀEorb comes from the [DMSOCl2M←Y] σ
donation and [MCl2DMSO] (M=Pd, Pt) to Y fragment π-back donation. The catalytic activity of
complexes cis- and trans-3 toward Suzuki-Miyaura reaction between various aryl chlorides and
arylboronic acids in DMF/H2O at reflux temperature was investigated. Results showed that these
complexes act as efficient catalysts in Suzuki-Miyaura reaction for preparation of functionalized
biaryls.
Acknowledgements
The authors are grateful to the Bu-Ali Sina University for funding of our research and partial
support of this work.
Appendix A. Supplementary material
Materials, physical measurements and selected 13C and 1H NMR spectra of all compounds can be
found in the online version. Also, details of the refinement procedures for the crystal structures
are supplied. The deposition number of the studied complexes 5 and 6 are CCDC 1438730 and.
This data can be obtained free-of-charge via www.ccdc.cam.ac.uk/data_request/cif, by emailing
data request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax +44 1223 336033.
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ACCEPTED MANUSCRIPT
Scheme 1. Two coordination modes of Me2SCHC(O)C6H4R.
26

ACCEPTED MANUSCRIPT
Scheme 2: Synthesis of complexes 3-6.
27

ACCEPTED MANUSCRIPT
a
b
Fig. 1. ORTEP view of X-ray crystal structures of (a) 5 and (b) 6.
28