Synthesis and structural characterization of Pd(II) and Cu(I) complexes containing dithiophosphorus ligand and their catalytic activities for Heck reaction

Article abstract of DOI:10.1016/j.poly.2016.09.002

2,4-Bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-disulfide (Lawesson's reagent) was made to react with benzylamine to produce [(PhCH₂NH)(p-C₆H₄OMe)PS₂]^?[PhCH₂NH₃]⁺in a very facile manner. From the abovementioned product, two new complexes {Pd[(PhCH₂NH)(p-C₆H₄OMe)PS₂]₂} (C1) and {Cu₂(PPh₃)₂[(PhCH₂NH)(p-C₆H₄OMe)PS₂]₂} (C2) were obtained in high yields whose molecular structures were ascertained by X-ray diffraction analysis, IR and NMR spectroscopy, and elemental analysis. The catalytic properties of both complexes were evaluated in the Heck reaction. High turnover numbers (TONs) and yields were observed for palladium catalyst and it was revealed that dicopper(I) complex by a distance of 2.84?? between metal ions, bearing triphenylphosphine and dithiophosphorus ligands, can catalyze the Heck reaction. This is the first report of Cu(I) complex as catalyst in the Heck reaction. Natural bonding orbital (NBO) analysis for C1 indicated that natural charge on Pd atom is ?0.07e and Pd atom has formed four sigma bonds with S atoms. Similarly, NBO analysis revealed no significant Cu?Cu interaction in dicopper complex C2.

Full text of DOI:10.1016/j.poly.2016.09.002

Accepted Manuscript
Synthesis and structural characterization of Pd(II) and Cu(I) complexes con-
taining dithiophosphorus ligand and their catalytic activities for Heck reaction
Khodayar Gholivand, Rasoul Salami, Kaveh Farshadfar, Raymond J. Butcher
PII:
S0277-5387(16)30422-3
DOI:
http://dx.doi.org/10.1016/j.poly.2016.09.002
POLY 12190
Reference:
Polyhedron
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Revised Date:
Accepted Date:
16 May 2016
29 August 2016
4 September 2016
Please cite this article as: K. Gholivand, R. Salami, K. Farshadfar, R.J. Butcher, Synthesis and structural
characterization of Pd(II) and Cu(I) complexes containing dithiophosphorus ligand and their catalytic activities for
Heck reaction, Polyhedron (2016), doi: http://dx.doi.org/10.1016/j.poly.2016.09.002
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Synthesis and structural characterization of Pd(II) and Cu(I) complexes
containing dithiophosphorus ligand and their catalytic activities for Heck
reaction
Khodayar Gholivanda,*, Rasoul Salamia, Kaveh Farshadfara, Raymond J. Butcherb
aDepartment of Chemistry, Faculty of Sciences, Tarbiat Modares University, Tehran, Iran
bDepartment of Chemistry, Howard University, Washington, D.C. 20059
* Corresponding author’s E-mail address: gholi_kh@modares.ac.ir
Tel.: +98 21 82883443; Fax: +98 218006544.
1

Abstract
2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-disulfide (Lawesson's reagent) was
made to react with benzylamine to produce [(PhCH2NH)(p-C6H4OMe)PS2]- [PhCH2NH3]+ in a
very facile manner. From the abovementioned product, two new complexes {Pd[(PhCH2NH)(p-
C6H4OMe)PS2]2} (C1) and {Cu2(PPh3)2[(PhCH2NH)(p-C6H4OMe)PS2]2} (C2) were obtained in
high yields whose molecular structures were ascertained by X-ray diffraction analysis, IR and
NMR spectroscopy, and elemental analysis. The catalytic properties of both complexes were
evaluated in the Heck reaction. High turnover numbers (TONs) and yields were observed for
palladium catalyst and It was revealed that dicopper(I) complex by a distance of 2.84 Å between
metal ions, bearing triphenylphosphine and dithiophosphorus ligands, can catalyze the Heck
reaction. This is the first report of Cu(I) complex as catalyst in the Heck reaction. Natural
bonding orbital (NBO) analysis for C1 indicated that natural charge on Pd atom is -0.07e and Pd
atom has formed four sigma bonds with S atoms. Similarly, NBO analysis revealed no
significant Cu…Cu interaction in dicopper complex C2.
Keywords: Copper, Palladium, Dithiophosphorus Ligand, NBO analyses, Heck Reaction,
2

1. Introduction
Nowadays the Mizoroki-Heck or simply the Heck reaction, catalyzed by transition-metal
complexes, has become one of the most powerful and versatile tools in the formation of carbon-
carbon bonds which provides a basis for synthesizing a variety of important compounds used in
many areas such as pharmaceuticals, antioxidants, drug intermediates, UV absorbers and
industrial applications [1-4]. The catalytic performances of transition-metal complexes are
strongly dependent upon the nature of their ligands and the donor groups and thus, ligand design
is substantial to improvement of catalytic science. In this regard, the ancillary ligands play a key
role in the steric and electronic properties of the catalyst complexes. Moreover, the ligands are
determinative in the stability of the active species and catalyst lifetime [5,6].
In recent years, dithiophosphorus (DTP) derivatives come into focus owing to the potential
application as extraction agents for actinides from lanthanides via liquid/liquid extraction [7-11].
It has been shown that dithiophosphorus ligands are exceptional for this extraction as they are
classified as soft-donor species [7-14]. Furthermore, dithiophosphorus ligands can be
coordinated to the main group and transition metals, in particular, with soft metal centers such as
palladium(II) and copper(I) [15,16]. DTPs are common bidentate ligands that can create stable
complexes with soft acid type cations. Since in most homogeneous catalytic processes in C-C
bond coupling based on palladium, the formation of palladium aggregates is common under the
reaction conditions (which considerably reduces the catalytic activity), the use of stable
palladium(II) complexes as catalyst help achieve highest turnover numbers [17-19]. Some of
Pd(II) complexes with stabilizer chelating ligands showed very good catalytic activity in the
Heck reaction [17-21]. But mechanistic details and, particularly, the question of how these stable
complexes allow active species to be formed in catalytic cycle remain still unsolved.
Among transition-metal catalysts, palladium was mostly utilized for Heck coupling of aryl
halides with olefins. Despite this fact, there are few reports on the use of copper for this reaction
[22-26].However, there is a growing interest in using less expensive transition metal catalysts
due to the high price of palladium.
In the present paper, we prepared two novel complexes of Pd(II) and Cu(I) with
dithiophosphorus ligand (scheme 1) whose structural characterization and electronic properties
3

were studied by X-ray crystallography and NBO analyses. The catalytic activity of both
complexes in the Heck reaction was investigated.
3. Results and discussion
3.1. Spectral characterization
Ligand [PhCH2NH3] L was synthesized by reaction of two equivalent of benzylamine with one
equivalents of Lawesson's reagent in toluene, giving 94% yield. The ligand was used for
preparation of new complexes labeled with C1 (PdL2) and C2 (Cu2(PPh3)2L2), Scheme 1.
The infrared spectra of the C1 complex showed strong and medium-strong IR bands at 655 and
543cm-1 which are ascribed to ꢀasym (PS) and ꢀsym (PS), respectively. Similarly, two strong IR
bonds at 646 and 524 cm-1 were observed in the spectra of C2 complex for ꢀasym (PS) and ꢀsym
(PS), respectively. A number of studies suggest that the interval between the position of
symmetric and asymmetric P-S bonds (∆ꢀ) can be used to estimate the coordination mode of the
dithiophosphinate ligands [27-31]. Based on the literature [27-31], ∆ꢀ values larger than 95 cm-1
are observed when dithiophosphinate ligands are monodentate. We found ∆ꢀ value of 112 and
124 cm-1 for C1 and C2 complexes respectively, even though the X-ray data showed bidentate
chelating ligand for both complexes.
Cis and trans isomers are able to be formed regarding the nature of the chelating asymmetrical
ligands in C1. The solid state structure shows that the trans isomer is the only present one in
single crystals .The phosphorus atoms of cis and trans isomers are not chemically equivalent,
because the cis isomer has a dipole moment and no inversion center, while the trans isomer has
31
an inversion center and no dipole moment [32]. The P{1H} NMR spectrum for C1 reveals two
singlet peaks at 91.38 and 92.32 ppm by separation of about 1 ppm. It seems that these two peaks
are related to two isomers of cis and trans [32]. As the crystals are dissolved in the solvent, the
1
trans isomer quickly rearranges and also forms cis isomer. The H NMR spectrum of C1 for
OMe protons shows distinct peaks for each isomer: two singlet peaks at 3.80 and 3.83 ppm. The
protons of CH2 moiety and phenyl groups show multiplets with overlap of the peaks of the two
isomers. The 31P{1H} NMR spectra of C2 displays two doublet peak (PS2 and PPh3 moiety) with
a coupling constant (3jPP) at around 7 Hz.
4

3.2. Crystal structure
An ORTEP view of one molecule of C1 with atom numbering scheme is given in Fig. 1, and
relevant bond distances and angles are presented in Table 1. The Pd(II) is coordinated in a
square–planar fashion with the four sulfur atoms from two chelating dithiophosphorus ligands,
resulting in the formation of the four-membered chelate rings. The sum of bond angles around
palladium is exactly 360°, indicating that the center atom and four sulfur atoms are located in the
same plane. The S1-Pd-S1A and S2-Pd-S2A angles are 180.00°, which shows no deviation from
linearity, while the S1-Pd-S2 (83.90(ꢁꢂ)°) and S1-Pd-S2A (96.09(ꢁꢂ)°) are not equal and
display deviation from the ideal value of 90°. The palladium-sulfur bond lengths of 2.3426(4)
and 2.3431(4) Å are within the normal Pd-S range of 2.2-2.5 Å [33, 34] and are close to those
found in phosphine sulfide palladium complexes [35-37]. Approximately, equal values of
phosphorus-sulfur bond lengths, 2.0336(6) and 2.0156(6) Å demonstrate that the negative charge
is delocalized throughout the S-P-S moiety. The P-N distance of 1.6282(15) Å in this complex is
shorter than the P-N single bond [38].
The interesting feature of this structure is a short intermolecular contact, Pd…H14-C14, between
palladium(II) centers with two H atoms of two adjacent molecules [fig. 2]. These contacts are
established with donor–acceptor distances of 3.324 Å. Wang et al. have shown that similar short
intermolecular contacts Pt…H-C (2.94-3.02 Å) exist in platinum(II) complexes [39]. Moreover,
the H14 atoms are positioned on both sides of the PdS4 plan and, consequently they are oriented
toward the dz2 orbital of palladium(II) center, with H14…Pd…H14 angle of 180.000°. These
short contacts with the Pd…H separation distance more than 2.2 Å provide a Pd…H-C
interaction which can be regarded as a 3 center-4 electron (3c-4e) interaction using the electron
pair in the dz2 orbital of the central atom [39-44], whereas many complexes of transition metal
showing well-known M…H-C interaction described as agostic interaction (3c-2e) with the
M…H separation distance in the range of 1.8-2.2 Å [39,45-47]. For Pd…H14-C14 contact,
Intermolecular binding energy, ∆E, was calculated at the M062X/LANL2DZ/6-311++G(d,p)
level to estimate the strength of this interaction. ∆E value of - 5.21 kcal mol-1 was obtained for
this contact, which is more than the strength of C-H…ꢃ interactions (2−4 kcal mol-1) and is
comparable with nonclassical intermolecular hydrogen bonds (5−9 kcal mol-1) [48,49].
5

The intermolecular nonclassical hydrogen bonds O1…H11-C11 (2.550 Å) and S2…H5-C5
(2.791 Å) link the molecules together in the solid state and generate a two-dimensional (2D)
framework [fig. 3]. The resulting 2D plans are further linked by S1…H1-N1 (2.56 Å), Pd…H-C
and C-H…ꢃ [fig. 2] to generate 3D supramolecular network.
As shown in Fig. 1, Complex C2 is a dicopper compound which each Cu(I) cation is
tetrahedrally coordinated by three sulfurs and one triphenylphosphine and the resultant dinuclear
structure contains two CuPS2 and one Cu2S2 rings. The L ligand acts as chelating ligand via its
two sulfur atoms in way that the one sulfur atom is bridged between two copper and the other
sulfur atom coordinates only to one copper. The Cu2S2 ring shows a particular geometry with
alternative long (2.6147(6) Å) and short (2.3085(6) Å) Cu-S distances due to the nature of the
orbitals and electrons of the bridging sulfur [50,51]. The Cu-P (Cu-P2, CuA-P2A) and Cu-
terminal S (Cu-S1, CuA-S1A) lengths are 2.2220(5) and 2.3857(6), respectively, which fall
within the range of copper(I) dithiocomplexes [52,53]. Regarding the fact that the sum of van der
Waals radii for two copper is ca. 2.8 Å [54], the observed Cu−Cu distance (2.8396(5) Å)
suggests the minor contribution of Cu ⋯Cu interaction. The bond angles around Cu(I) are in the
range of 84.050(16)°-127.633(19)° for the S1-Cu-S2 and P2-Cu-S2 angles, respectively. Each of
four-membered ring Cu2S2 and CuPS2 (sum of internal angles in the range of 359-360°) are flat.
The torsion angle between the two planes CuPS2 is 0.0° and each of these rings generates the
angle 73.359(17)° with Cu2S2, thus indicating that the CuPS2 planes are approximately
perpendicular to the Cu2S2 plane. The P-S distance for S in terminal position (P1-S1, P1A-S1A =
1.9914(7) Å) is slightly shorter than the P-S distance in bridging position (P1-S2, P1A-S2A =
2.0329(6) Å).
In this crystal structure, the sulfur atoms, as bifurcated acceptors, are involved in intermolecular
C-H…S1 nonclassical hydrogen bonds that lead to the formation of 2D framework [fig. 4]. In
these interactions, the C-H…S1 distances are 2.925 and 3.011 Å. The cooperation of
nonclassical hydrogen bonds with multiple weaker C-H…ꢃ and C-H…H-C interactions leads to
generation of 3D supramolecular network.
It is noteworthy, that no S···S intermolecular stacking, often found in dithiocomplexes, was
detected in the C1 and C2 complexes (probably because of the steric bulk of the ligands).
6

3.3. Theoretical calculations
Full geometry optimization of dithiophosphorus ligand L, C1 and C2 complexes were performed
using DFT calculation with B3LYP functional and also, NBO analyses were carried out to gain
more insight about bonding and electronic aspects of the complexes. The obtained optimized
geometries of the compounds are shown in fig. 5 and some selected geometric parameters are
listed in Table 1. The optimized structure of C1 reproduces the square-planar coordination
surrounding the palladium center and its geometric parameters show good agreement with the X-
ray structure of C1. The comparison of the calculated P-S bond lengths in L and C1 reveal the
lengthening of the P-S bonds from free ligand L to C1 and C2 complexes. Cu…Cu distance in
the optimized C2 structure is larger by 0.896 Å than the corresponding one in solid state
structure. As can be seen in fig. 5, the optimized structure of C2 comprises an eight-membered
Cu2P2S4 ring in which two Cu are bridged by two S atoms of the L ligands. The minimum
calculated energy for C2 in the observed structure at the solid state is slightly higher compared to
the optimized one in gas phase (∆E= 8.74 kcal mol−1). However, this structure can be stabilized
(as observed in the X-ray structure) by intermolecular interactions with neighboring molecules,
which is a determinant factor in the solid state structure.
3.4. NBO analysis
Initially, it’s noteworthy that NBO analyses for C1 and C2 were performed on optimized
structures cut out from X-ray structures by freezing non-hydrogen atoms. Table 2 shows that in
C1 complex, the negative charges on sulfur atoms decrease by an average value about 0.34e
upon complexation, indicating the strong donor-acceptor interactions between the metal atom
and the sulfur atoms. But in C2 complex the negative charges on sulfur atoms increase by an
average value about 0.06e upon complexation, owing to the electrostatic field of Cu(I) ion [55].
The positive charge on phosphorus atom increases from L ligand to complexes. Meanwhile, no
significant ꢄ-bond contribution for P-S bonds was observed in any of the compounds within the
NBO
framework.
The
electron
configuration
of
palladium
in
C1
is
[core]5s0.374d9.195p0.496s0.015d0.01, indicating nearly full occupation of the 4d orbital by 9.19
electrons. The sum of core electrons (36e), valance electrons (9.56e on 5s and 4d) and Rydberg
electrons (0.51e on 5p, 6s and 5d) give 46.07 electrons in agreement with the calculated natural
charge of -0.07e at Pd atom. According to the NBO, the Pd atom forms four sigma bonds with S
7

atoms as a result of electron donation from the S lone pairs to the Pd orbitals in which σ(Pd − S)
bonds are strongly polarized toward sulfur atoms (ca.79% at S). Therefore, as a consequence of
electron density donation from S to Pd, the positive charge of Pd(II) was fully compensated. The
hybrid of σ(Pd − S) bonds on Pd atom is a mixture of s (24.35- 24.50%), p (50.00%) and d
(26.50-26.65 %) and also is a mixture of s (11.64-11.70%), p (88.15-88.21%) and d (0.15%) on S
atoms. The bonding orbital are occupied by about 1.82e for Pd-S bonds.
As follows from Table 2, the calculated charge distribution of +0.829 for Cu atoms in C2
complex is also consistent with the electron configuration of Cu, [core]4s0.403d9.744p0.025S0.01. In
bonding the L ligand and triphenylphosphine to Cu atoms, no σ-bond is found in the NBO
analysis, and the bonds of Cu with S or P can be described as predominant Coulomb-type
interactions [56]. According to the NBO, the amount of delocalization of electron density
between occupied Lewis-type orbitals, LP (S or P), and unoccupied non-Lewis orbitals,
LP*(Cu), corresponds to a stabilizing donor-acceptor interaction. The calculated second order
interaction energy (E2) between donor-acceptor orbitals can be used as a measure of interaction
strength. A strong donor−acceptor interaction by E2= 99.69 kcal mol-1 was found between P
atom of PPh3 and Cu atom. The other strong interaction was observed between terminal S atom
of L ligand and Cu atom by E2= 56.25 kcal mol-1. Two actually different energies of 28.27 and
67.02 kcal mol-1 were found for the interaction of bridge S atom with the two Cu atoms.
Similarly, within the NBO framework, no significant Cu…Cu interaction was observed at E2
higher than 3.1 kcalmol-1.
3.5. Catalytic Performance of the C1 and C2 complexes in the Heck Reaction
Initially, we evaluated the thermal stability of C1 after prolonged heating at 180 ℃ in N-
31
methylpyrrolidone (NMP) by P{1H} NMR spectrum. After three days, no decomposition and
no palladium black were observed for the compound. Catalytic studies of the complexes in Heck
reaction between bromobenzene and styrene have been performed to survey reaction parameters.
The screening results presented in Table 3 show that the polar aprotic solvent N-
methylpyrrolidinone (NMP) and N,N-dimethylformamide (DMF) obtain better results than other
solvents. The non-polar solvents such as toluene and dioxane gave comparatively similar yield
(entries 4,5) but below that of DMF and NMP. The polar protic solvent such as isopropanol gave
the lowest yields (entry 3). We then used DMF as the optimal solvent to find the best base. We
8

screened several inorganic and organic bases such as K2CO3, K3PO4, NaOH, Et3N and pyridine.
Accordingly, inorganic bases obtained higher yields than organic bases [table 3]. Of the three
inorganic bases, K2CO3 and K3PO4 gave the highest yields of the desired product for Catalyst C1
(entry 1) and Catalyst C2 (entry 6), respectively. A comparatively similar result was observed
using K2CO3 and K3PO4 as a base for C1 catalyst, but for C2 catalyst the reaction would be much
slower if K2CO3 was replaced with a stronger base K3PO4 (entries 1,6).
Furthermore, the optimizations of catalyst loading were performed in DMF as a reaction solvent
in the presence of K2CO3 for C1 catalyst and K3PO4 for C2 catalyst to determine the most
efficient of catalyst amount [table 4]. Increasing the amount of C1 from 0.00002 equivalent
(equiv.) in coupling of bromobenzene (PhBr) with styrene had no considerable impact on the
yield but caused to a decrease in turnover number (TON) certainly. When iodobenzene (PhI) was
used instead of PhBr, even C1 loading of 0.00001 equiv. (entry 9) gave 100% yield. Various
amounts of C2 were also examined and the best results were obtained in 0.03 and 0.10 equiv.
[table 4, entries 17, 14] for coupling of PhI and PhBr, respectively. As shown in table 4, C1
complex is a more robust catalyst compared to C2, but considering economy and toxicity, the use
of the C2 complex as the catalyst can be more attractive.
The time-yield plot of the coupling of the bromobenzene with styrene under copper catalyst
displays a sigmoidal-shaped curve with an induction period of 30 min and then reveals an
exponential increase in the yield of the reaction [fig. 6]. These observations suggest that the
copper complex acts as precursor to form catalytically active species. There have been few
reports of a similar activation step for palladium (II) complexes [57-60]. Furthermore, no
induction period is observed in the time-yield plot of palladium catalyst in the examined time
intervals and the catalyst should be immediately active at the beginning of the reaction. After 8 h,
none of the catalysts showed considerable increment in the yield.
Since NBO analysis revealed that four strong sigma bonds Pd-S for stable palladium complex
(C1) and that no induction period was observed in the time-yield plot of C1, it can be concluded
that C1 acts as a catalytically active species in catalytic cycle, probably, without being
dissociated Pd-S bonds. Moreover, it is worth noting that a number of Cu(I) complexes built in
our group were investigated for coupling aryl bromides with styrene, out of which only C2
complex was able to perform this coupling.
9

4. Conclusion
The new air and thermally stable complex of palladium(II) {Pd[(PhCH2NH)(p-C6H4OMe)PS2]2}
(C1) and the dicopper(I) complex {Cu2(PPh3)2[(PhCH2NH)(p-C6H4OMe)PS2]2} (C2) were
prepared in satisfactory yields and characterized using X-ray diffraction analysis, IR and NMR
spectroscopy, and elemental analysis. Based on NBO analysis and time-yield plot, we suggest
that the C1 complex probably acts as a catalytically active species, not as a precatalyst, in
catalytic cycle of the Heck reaction. Although copper complexes are often not active in the Heck
reaction, the present study suggests that the dicopper complex with the metal ions separated by
2.84 Å is an effective catalyst for the Heck reaction.
2. Experimental section
2.1. Materials and methods
All chemicals and solvents are commercially available, and used without further purification.
Drying of the solvents was done using standard methods. Melting points were obtained by an
electrothermal instrument. Elemental analyses were performed using a Heraeus CHN-O-RAPID
apparatus. Infrared spectra were recorded (400–4000 cm-1 region) on a Nicolet 510P
31
spectrophotometer using KBr disk. P{1H} NMR spectra were obtained on a Bruker Avance
DRX-500 spectrometer operating at 202 MHz with chemical shifts reported relative to a 85%
1
H3PO4 in D2O external standard solution. H NMR spectra were also obtained on a Bruker
Avance DRX-500 spectrometer with chemical shifts relative to the internal standard TMS. The
Heck coupling reactions were analyzed by HP Agilent 6890 gas chromatograph equipped with a
HP-5 capillary column and flame-ionization detector.
2.2. Preparation of [(OCH3C6H4)(phCH2NH)PS2]− [phCH2NH3]+ ([L] [phCH2NH3]+)
Titled compound was prepared using reported method [61]. To a suspension of Lawesson's
reagent (0.404 g, 1 mmol) in 10 mL dry toluene at room temperature, benzylamine (0.536 g, 5
mmol) was added and the mixture was stirred for 6h. The colorless precipitated solid was filtered
off and washed several times with dry toluene. The structure of ligand L is given in scheme 1.
Yield 94%, M.p. 164 °C. Anal. Calc. for C21H25N2OPS2 (416.45): C, 60.56; H, 6.00; N, 6.73.
Found: C, 60.60; H, 5.98; N, 6.76%. IR (KBr, cm-1): ν = 3321(m), 2925(br), 2853(br), 1587(s),
1491(s), 1451(m), 1395(w), 1290(w), 1249(s), 1180(w), 1103(m), 1056(m), 964(w), 817(br,),
10

1
742(m), 696(m), 661(s, ꢀasym (PS)), 587(m), 545(s, ꢀsym (PS)). H NMR (500.13 MHz, DMSO-
3
d6): δ(ppm) = 3.21(br, 1H, NH(anion moiety )), 3.73(s, 3H, OCH3), 3.78(t, JPH = 8.9 Hz, 2H,
3
3
CH2(anion moiety)), 4.02(s, 2H, CH2(cation moiety)), 6.78(d, JHH = 4.3 Hz, 1H), 6.80(d, JHH
=
=
3
3
4.65 Hz, 1H), 7.12(t, JHH = 6.95 Hz, 1H), 7.19-7.24(m, 4H), 7.35-7.45(m, 5H), 7.90(dd, JHH
3
3
3
4.70 Hz, JHH = 6.74 Hz, 1H), 7.94(dd, JHH = 5.36 Hz, JHH = 6.18 Hz, 1H). 31P{1H}
NMR (202.46 MHz, DMSO-d6): δ(ppm) = 80.25 (s)
2.3. Preparation of C1 complex {Pd[(PhCH2NH)(p-C6H4OMe)PS2]2} (PdL2)
A solution of PdCl2 (0.086 g, 0.50 mmol) in acetonitrile (5 ml) was added drop-wise to a solution
of L (0.416 g, 1.00 mmol) in methanol (5 ml) and the mixture was stirred for 8h to obtain yellow
clear solution. Suitable crystals for X-ray analysis were obtained by slow evaporation of solvent
after 2 days. Yield 88%, M.p. 181 °C. Anal. Calc. for C28H30N2O2P2PdS4 (723.17): C, 46.50; H,
4.15; N, 3.87. Found: C, 46.51; H, 4.12; N, 3.88%. IR (KBr, cm-1): ν = 3235(vs), 3015(br),
2928(s), 1589(s), 1495(s), 1457(m), 1403(m), 1296(m), 1252(vs), 1178(m), 1107(vs), 1060(vs),
1
1022(m), 967(w), 870(m), 825(m), 746(m), 695(m), 655(s, ꢀasym (PS)), 543(s, ꢀsym (PS)). H
NMR (500.13 MHz, DMSO-d6): δ(ppm) = 3.33(br, overlapping with the solvent signal, NH),
3.80(s, 3H, OCH3), 3.83(s, 3H, OCH3) 4.15(m, 4H), 6.94(m, 2H), 7.13(m, 2H), 7.23(m, 2H),
31
7.31-7.42(m, 8H), 7.83.7.92(4H). P{1H}NMR (202.46 MHz, DMSO-d6): δ(ppm) = 91.37(s),
92.32(s).
2.4. Preparation of C2 complex {Cu2(PPh3)2[(PhCH2NH)(p-C6H4OMe)PS2]2} (Cu2(PPh3)2L2)
A solution of L (0.416 g, 1.00 mmol) in chloroform (12 mL) was added drop wise to stirred
solution of mixture copper(I) chloride (0.134 g, 1.00 mmol) and triphenylphosphine (PPh3)
(0.263 g, 1.00 mmol) in acetonitrile (6 ml). The mixture of reaction was filtered off to obtain a
colorless clear solution. Suitable single crystals of C2 were obtained by slow diffusion of diethyl
ether in the clear solution. Yield 76%, M.p. 233 °C (decompose). Anal. Calc. for
C64H60Cu2N2O2P4S4 (1268.45): C, 60.60; H, 4.77; N, 2.21. Found: C, 60.59; H, 4.78; N, 2.19%.
IR (KBr, cm-1): ν = 3321(m), 3050(br), 2905(br), 1588(m), 1487(m), 1433(m), 1383(m),
1287(w), 1251(m), 1174(m), 1097(s), 1055(m), 1024(m), 856(w), 802(m), 741(s), 692(s), 646(s,
1
ꢀasym (PS)), 614(m), 575(m), 524(s, ꢀsym (PS)). H NMR (500.13 MHz, DMSO-d6): δ(ppm) =
3
3.18(dd, 2JPH = 21.4 Hz, 3JHH = 7.2 Hz, 1H, NH), 3.68(s, 3H, OCH3), 4.09(d, JHH = 7.2 Hz, 2H,
11

3
CH2), 6.73(m, 2H), 7.03(t, JHH = 6.23 Hz, 1H), 7.16-7.43(m, overlapping with the solvent
31
3
signal), 7.73(m, 2H). P{1H}NMR (202.46 MHz, DMSO-d6): δ(ppm) = -1.69(d, JPP = 6.9 Hz,
PPh3), 75.65(d, 3JPP = 7 Hz, PS2).
2.5. Crystal structure determination
Crystals were selected under a microscope and mounted on a MiTeGen cryoloop using mineral
oil and transferred to a Bruker Quest diffractometer in a cold stream of nitrogen gas at -
173.15°C. Preliminary cell constants were obtained from a small set of frames and then a
complete hemisphere of data was collected. The Bruker diffractometer control program Apex 2
was used for the preliminary setup and data collection [62]. The collected data was processed
with the Bruker program Saint. A multi-scan type absorption correction was applied using
SADABS [63]. The structure was solved using the program Superflip [64] and refined using
Shelxl-2014. Files for publication and diagrams were prepared using Shelxtl [65]. Details of the
X-ray data collection parameters are given in Table 5.
2.6. Theoretical methods
All the DFT calculations reported here were carried out using Gaussian 03 package [66] in the
gas phase. The structure of the free ligand and the two complexes was fully optimized at the
B3LYP level [67]. The palladium atom was described by the LANL2DZ effective core potential
and basis set [68], but the standard basis set 6-311+G* was used for remaining atoms. All the
vibrational frequencies were real, indicating that the optimized structures to be minimal. Natural
bond orbital (NBO) analyses [69] were performed at the B3LYP/6-311+G** level for L and C2
and at the B3LYP/6-311+G**/LANL2DZ level for C1.
In order to calculate binding energy Pd…H in solid state, two selected fragment were cut out
from C1 X-ray structure and optimized by freezing of non-hydrogen atoms at the B3LYP/6-
311+G*/LANL2DZ level. The intermolecular Pd…H energy was evaluated at M062X/6-
311++G**/LANL2DZ level, according to the energy difference between the total energy of the
system and its fragments. Basis set superposition error (BSSE) in the interaction energy has been
removed by the counterpoise correction method of Boys and Bernardi [69].
2.7. General procedure for preparative Heck reactions
12

A reaction flask was charged with an appropriate amount of aryl halide (1.0 equiv.), styrene (1.2
equiv.), base (1.5 equiv.), dodecane as internal standard (40 mg), solvent (2 mL) and stirring bar.
The resulting mixture was heated to 100 °C for several minutes before the prescribed amount of
catalyst was added. After a specified period of time, the suspension was cooled to room
temperature, water was added, and the product was extracted with CH2Cl2 (three times). The
combined organic portions were dried over MgSO4, filtered, and evaporated under vacuum to
achieve the desired product which was then washed with hexane. The coupled products were
analyzed by a combination of GC analysis and NMR spectroscopy (comparison of NMR data
with those in the literature).
Acknowledgements
Financial
support
of
this
work
by
Tarbiat
Modares
University
is
gratefully acknowledged. We thank also the assistance of Dr. Matthias Zeller for
help in data collection and NSF Grant 1337296 for funds to obtain the
diffractometer.
Appendix A. Supplementary material
CCDC 1447974 and 1447975 contain the supplementary crystallographic information for C1 and
C2 complexes, respectively. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/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.
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15

Figure Captions
Fig. 1: ORTEP view of C1 (left) and C2 (right) (50% probability level) with atom-labeling
scheme (part of atom-labeling are omitted for clarity).
Fig. 2: Side view representation of C1, showing intermolecular S1…H1-N1 (2.56 Å), Pd…H-C
(3.324 Å) and C-H…π interactions (C8A-H8A…Cg: dH…C = 2.983 Å, dC…Cg = 3.921 Å, ꢅꢆ=
137.867°).
Fig. 3: 2D nonclassical hydrogen-bonded frameworks of C1, showing O1…H11-C11 (2.550 Å)
and S2…H5-C5 (2.791 Å).
Fig. 4: 2D nonclassical hydrogen-bonded frameworks of C2, showing S1…H25A-C25A (2.925
Å) and S1…H6A-C6A (3.011 Å).
Fig. 5: Optimized structures at B3LYP/6-311+G*/LANL2DZ level (Hydrogen atoms are omitted
for clarity).
Fig. 6: The time-yield curves for the coupling of PhBr with styrene at 100 ℃ in optimized
reaction conditions, catalyzed by C1 and C2 catalysts.
Scheme 1: Synthesis of C1 and C2 complexes.
16

Table 1: Selected geometrical parameters for C1 and C2 in solid state and in gas phase calculated
at B3LYP/6-311+G* (L and C2) and at B3LYP/LANL2DZ/6-311+G* (C1).
copmounds
C1
C2
L
X-ray
Calc.
X-ray
Calc.
Calc.
Bond lengths (Å)
P-S
2.0156(6)
2.0336(6)
1.6282(15)
2.3427(4)
2.3431(4)
2.048
2.053
1.681
2.423
2.424
1.9913(6)
2.0330(6)
1.6738(16)
2.3857(6)
2.041
2.060
1.689
2.338
2.429
2.019
2.025
1.688
P-N
M-Sta
b
M-Sb
2.3084(7)
2.6147(6)
2.2219(6)
2.8396(6)
M-P
M…M
2.222
3.736
Bond angles (°)
S-P-S
St-M-St
101.36(2)
83.905(14)
96.095(15)
103.05
82.97
97.02
112.79(3)
105.153(19)
113.26
105.14
100.63
Sb-M-Sb
84.052(17)
aSt: terminal S atom. bSb: bridge S atom
17

Table 2: Atomic Charge Distributions (e) and Natural Electron Configurations calculated for
selected atoms in L, C1 and C2.
atoms
L
C1
C2
M=
Pd, Cu
S
-0.07
+0.829
[core]5s0.374d9.195p0.496s0.015d0.01
-0.39
[core]4s0.403d9.744p0.025s0.01
-0.69a
-0.71
[core]3s1.843p4.843d0.015p0.01
-0.72
[core]3s1.793p4.583d0.01
-0.37
[core]3s1.813p4.853d0.014p0.01
-0.77b
[core]3s1.843p4.863d0.015p0.01
+1.26
[core]3s1.783p4.563d0.01
+1.36
[core]3s1.813p4.933d0.024p0.02
+1.36
P
[core]3s1.133p2.503d0.085p0.03
[core]3s1.113p2.423d0.084p0.02
[core]3s1.043p2.443d0.094p0.06
+0.75c
[core]3s1.263p2.874s0.013d0.034p0.0
7
N
-1.00
-0.98
-0.97
[core]2s1.442p4.533p0.014p0.01
[core]2s1.402p4.563p0.014p0.01
[core]2s1.382p4.573p0.01
aRelated to terminal S atom. bRelated to bridge S atom. cRelated to PPh3 moiety.
18

Table 3: Solvent and base effects on the Heck coupling of PhBr with styrene.a
catalyst
Br
solvent, base
100 oCb, 8h
Yield (%)c (isolayed yield (%))d
Entry
solvent
DMF
NMP
isopropanol
toluene
dioxane
DMF
DMF
DMF
DMF
NMP
base
C1
68 (61)
63
8
33
39
61
21
13
6
C2
24
24
8
13
11
44 (38)
16
trace
trace
41
1
2
3
4
5
6
7
8
9
10
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K3PO4
NaOH
Et3N
pyridine
K3PO4
55
aReaction conditions: 1.0 equiv. of PhBr, 1.2 equiv. of styrene, 1.5 equiv. of base, 10-5 equiv. of catalyst C1 or 0.02
equiv. of catalyst C2, 2 mL of solvent. bBath temperature. cDetermined by GC, based on PhBr (dodecane as an
internal standard); average of two runs. dIsolated yield ; average of two runs.
19

a
Table 4: Effect of catalyst loading
catalyst
X
solvent, base
100 oC, 8h
Entry
X
Catalyst (equiv)
Yield (%)b
TON
1
2
3
4
5
6
7
8
Br
Br
Br
Br
Br
Br
I
C1 (0.000010)
C1 (0.000015)
C1 (0.000018)
C1 (0.000020)
C1 (0.000022)
C1 (0.000030)
C1 (0.000005)
C1 (0.000008)
C1 (0.000010)
C2 (0.02)
C2 (0.04)
C2 (0.08)
C2 (0.10)
C2 (0.12)
C2 (0.020)
C2 (0.030)
C2 (0.040)
68
86
91
94
93
96
73
95
100
44
61
72
83
84
71
96
98
68000
57330
50550
47000
42270
32000
146000
118750
100000
22
15
9
8
7
36
32
25
I
I
9
11
12
13
14
15
16
17
18
Br
Br
Br
Br
Br
I
I
I
aReaction conditions: 1.0 equiv. of PhX, 1.2 equiv. of styrene, 1.5 equiv. of K2CO3 for C1 or K3PO4 for C2, 2 ml of
DMF. bDetermined by GC, based on PhX (dodecane as an internal standard); average of two runs.
20

Table 5. Crystallographic data for compounds C1 and C2.
Compound
C1
C2
Empirical formula
Formula weight
C28H30N2O2P2PdS4
723.12
C32H60Cu2N2O2P4S4
1268.34
Temperature (K)
Wavelength (Å)
Crystal system, space group
a (Å)
b (Å)
c (Å)
100(2)
100(2)
0.71073 Å
Monoclinic, P21/c
11.0212(5)
16.2526(7)
8.5432(4)
0.71073 Å
Monoclinic, P21/n
13.631(2)
10.5473(15)
20.374(3)
α/°
90
90
β/°
101.168(2)
90
1501.31(12)
2, 1.600
1.033
736.0
0.260 × 0.120 × 0.100
4.524 to 66.438
-13 ≤ h ≤ 16
-25 ≤ k ≤ 23
-12 ≤ l ≤ 13
14026
95.531(2)
90
2915.6(7)
2, 1.445
1.029
1312.0
0.350 × 0.240 × 0.200
4.016 to 61.088
-19 ≤ h ≤ 19
-15 ≤ k ≤ 14
-28 ≤ l ≤ 29
34056
γ/°
V (Å3)
Z, Calculated density (g.cm-3)
Absorption coefficient (mm-1)
F(000)
Crystal size (mm3)
θ range for data collection (°)
Index ranges
Reflections collected
Independent reflections
5396 [Rint = 0.0249, Rsigma
0.0362]
=
8871 [Rint = 0.0326, Rsigma
0.0306]
=
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices
5396/12/187
1.040
R1 = 0.0321, wR2 = 0.0635
R1 = 0.0488, wR2 = 0.0691
0.93/-0.44
8871/0/357
1.047
R1 = 0.0374, wR2 = 0.0969
R1 = 0.0479, wR2 = 0.1018
1.08/-0.38
R indices (all data)
Largest diff. peak and hole (e.Å-3)
21

Fig. 1
22

Fig. 2
23

Fig. 3
24

Fig. 4
25

C2
C1
L
Fig. 5
26

Fig. 6
27

MeO
S
S
NH
S
S
P
P
Pd
HN
OMe
(C1 = PdL2)
l
MeO
C
d
P
S
S
S
Toluene
S
S
P
MeO
P
P
OMe
H3NCH2C6H5
C
u
HN
C6H5CH2NH2
C
S
l
3
([L] [PhCH2NH3] )
Ph3P
S
S
NH
MeO
P
Cu
Cu
S
P
OMe
HN
S
PPh3
(C2 = Cu2(PPh3)2L2)
Scheme 1
28

Graphical abstract
Synthesis and structural characterization of Pd(II) and Cu(I) complexes containing
dithiophosphorus ligand and their catalytic activities for Heck reaction
Khodayar Gholivanda*, Rasoul Salamia, Kaveh Farshadfara, Raymond J. Butcherb
29