Synthesis, characterization and catalytic evaluation in the Heck coupling reactions of S-P-S pincer complexes of the type [Pd{PhP(C6H4-2-S)2}(PAr3)]

Article abstract of DOI:10.1016/j.ica.2006.10.029

A series of palladium complexes of the type [Pd(phPS₂)(PAr₃)] (phPS₂) = [PhP(C₆H₄-2-S)₂]^2- have been synthesized in good yields and their crystal structures determined. Heck coupling reactions were carried out using the [Pd(phPS₂)(PPh₃)] (1), [Pd(phPS₂){P(C₆H₄-4-Cl)₃}] (2), [Pd(phPS₂){P(C₆H₄-4-F)₃}] (3), [Pd(phPS₂){P(C₆H₄-4-CF₃) ₃}] (4), [Pd(phPS₂){P(C₆H₄-4-Me)₃}] (5) and [Pd(phPS₂){P(C₆H₄-4-OMe)₃}] (6) complexes as catalyst precursors in order to examine the potential effect of the para-substituted triarylphosphines in the reaction of bromobenzene and styrene.

Full text of DOI:10.1016/j.ica.2006.10.029

Inorganica Chimica Acta 360 (2007) 2128–2138
www.elsevier.com/locate/ica
Synthesis, characterization and catalytic evaluation in the
Heck coupling reactions of S–P–S pincer complexes of the
type [Pd{PhP(C6H4-2-S)2}(PAr3)]
´
´
´
´
´
Valente Gomez-Benıtez, Simon Hernandez-Ortega, Ruben A. Toscano,
*
David Morales-Morales
Instituto de Quı´mica, Universidad Nacional Auto´noma de Me´xico, Cd. Universitaria, Circuito Exterior, Coyoaca´n 04510 Me´xico DF, Mexico
Received 2 August 2006; received in revised form 18 October 2006; accepted 29 October 2006
Available online 9 November 2006
Abstract
A series of palladium complexes of the type [Pd(phPS2)(PAr3)] (phPS2) = [PhP(C6H4-2-S)2]2ꢀ have been synthesized in good yields and
their crystal structures determined. Heck coupling reactions were carried out using the [Pd(phPS2)(PPh3)] (1), [Pd(phPS2){P(C6H4-4-
Cl)3}] (2), [Pd(phPS2){P(C6H4-4-F)3}] (3), [Pd(phPS2){P(C6H4-4-CF3)3}] (4), [Pd(phPS2){P(C6H4-4-Me)3}] (5) and [Pd(phPS2){P(C6H4-
4-OMe)3}] (6) complexes as catalyst precursors in order to examine the potential effect of the para-substituted triarylphosphines in
the reaction of bromobenzene and styrene.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: S–P–S pincer complexes; Hemilability; Heck reaction; C–C coupling reactions; Triarylphosphines; Palladium complexes; Crystal structures;
Catalysis
1. Introduction
facts have led both inorganic and organic chemists
around the world to the search of cheap, easy to synthe-
size, highly active and stable catalysts. In this sense, in
recent years, several groups have been involved in the
design of ligands able to afford robust catalysts, capable
of withstand a variety of reaction conditions and oxidant
atmospheres, that would favor Heck couplings in an effi-
cient manner with cheap reagent grade starting materials.
From all the compounds employed so far, it seems that
polydentated ligands incorporating both thiolate and ter-
tiary phosphine donor ligands may offer an interesting
option to carry out this process [5]. Moreover, the pres-
ence of these ligands in the coordination sphere of transi-
tion metal complexes may render interesting behaviors in
solution as these ligands can be capable of full or partial
de-ligation (hemilability) [6], being able to provide impor-
tant extra coordination sites for incoming substrates dur-
ing a catalytic process [6]. Thus, given our continuous
interest in the design and synthesis of transition metal
complexes for potential application in industrial relevant
The importance that transition metal catalyzed reac-
tions have acquired in modern organic chemistry [1] has
been so vast that some transformations are simply uncon-
ceivable without the use of transition metal catalysts.
This, being particularly true in the case of cross-coupling
reactions [2]. Among them, palladium catalyzed C–C cou-
pling reactions have been recognized as power tools in
multiple organic transformations, from these the Heck
reaction has been denominated as an angular stone in
modern organic synthesis [3]. This reaction consists in
the coupling of a halo compound with a double bond.
The multiple applications of this reaction have been
clearly identified and efforts aimed to explore its potential
use at the industrial level [4] are a continuous research
topic both at the academic and industrial level. These
*
Corresponding author. Tel.: +52 55 56224514; fax: +52 55 56162217.
E-mail address: damor@servidor.unam.mx (D. Morales-Morales).
0020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.10.029

V. Go´mez-Benı´tez et al. / Inorganica Chimica Acta 360 (2007) 2128–2138
2129
catalytic transformations [7], we would like to report here
the use of the pincer type S–P–S proligand [phPS2H2] and
p-substituted triaryl phosphines as substituents for the fine
tuning of the electronics in the synthesis of a series of
Pd(II) complexes of the type [Pd(phPS2)(PAr3)]. The iden-
tification of the electronic effects of the different p-substi-
tuted triarylphosphines over the properties and reactivity
of these species in the palladium catalyzed Heck reaction
of bromobenzene with olefins will be discussed.
1 equiv. of the phosphino-dithiol phPS2H2 (200 mg,
0.613 mmol) and NEt3 (0.116 mg, 1.227 mmol) was added.
The solution was stirred for 24 h. Following the reaction
time the solution was filtered off and the volume reduced
in vacuum to obtain a reddish-brown residue that was
recrystallized from a double layer solvent system of
CH2Cl2/MeOH. Yield 372 mg (87%). Mp 253–256 ꢁC.
31
RMN P{1H} (121 MHz, CDCl3) d 85.33 (d, J2PP
¼
405:6 Hz, 1P), 22.76 (d, J2PP ¼ 405:6 Hz, 1P). MS–FAB+
[M]+ = 692 (53%), [M–PPh3]+ = 430 (25%), [M–
PdphPS2]+ = 263 (100%) m/z. Anal. Calc. for
C36H28P2PdS2 (Mw = 693.11): C, 62.38; H, 4.07. Found:
C, 61.13; H, 3.98%.
2. Experimental
2.1. Material and methods
Unless stated otherwise, all reactions were carried out
under an atmosphere of dinitrogen using conventional
Schlenk glassware, solvents were dried using established
procedures and distilled under dinitrogen immediately
prior to use. The IR spectra were recorded on a Nico-
let-Magna 750 FT-IR spectrometer as Nujol mulls. The
1H NMR spectra were recorded on a JEOL GX300 spec-
trometer. Chemical shifts are reported in ppm downfield
of TMS using the solvent (CDCl3, d 7.27) as the internal
standard. 31P NMR spectra were recorded with complete
proton decoupling and are reported in ppm using 85%
H3PO4 as the external standard. Elemental analyses were
determined on a Perkin Elmer 240. Positive-ion FAB
mass spectra were recorded on a JEOL JMS-SX102A
mass spectrometer operated at an accelerating voltage of
10 kV. The samples were desorbed from a nitrobenzyl
alcohol (NOBA) matrix using 3 keV xenon atoms. Mass
measurements in FAB are performed at a resolution of
3000 using magnetic field scans and the matrix ions as
the reference material or, alternatively, by electric field
scans with the sample peak bracketed by two (polyethyl-
ene glycol or cesium iodide) reference ions. The K2[PdCl4]
was obtained from Aldrich Chemical Co. and the phos-
phines P(C6H5)3, P(C6H4-4-Cl)3, P(C6H4-4-F)3, P(C6H4-
4-CF3)3, P(C6H4-4-Me)3 and P(C6H4-4-OMe)3 were pur-
chased from STREM Chemicals, Inc. All compounds
were used as received without further purification. The
proligand phPS2H2 [8] and the starting materials trans-
[PdCl2(PAr3)2] [9] were prepared according to published
procedures.
2.2.2. Synthesis of bis[(2-phenylthiolato)phenylphosphino-
S,S0,P]-tris(4-chlorophenyl)phosphine-palladium(II),
[Pd(phPS2){P(C6H4-4-Cl)3}] (2)
trans-[PdCl2{P(C6H4-4-Cl}3)2] (557 mg, 0.613 mmol).
Yield 432 mg (81%). Mp 240–242 ꢁC. RMN 31P{1H}
(121 MHz, CDCl3) d 86.04 (d, J2PP ¼ 408 Hz, 1P), 21.29
(d, J2PP ¼ 408 Hz, 1P). MS–FAB+ [M]+ = 795 (18%), [M–
P(C6H4-4-Cl)3]+ = 430 (16%), [M–PdphPS2]+ = 365 (8%)
m/z. Anal. Calc. for C36H25Cl3P2PdS2 (Mw = 796.44): C,
54.29; H, 3.16. Found: C, 53.21; H, 3.09%.
2.2.3. Synthesis of bis[(2-phenylthiolato)phenylphosphino-
S,S0,P]-tris(4-fluorophenyl)phosphine-palladium(II),
[Pd(phPS2){P(C6H4-4-F)3}] (3)
trans-[PdCl2{P(C6H4-4-F}3)2] (497 mg, 0.613 mmol).
Yield 417 mg (83%). Mp 242 ꢁC. RMN 31P{1H}
(121 MHz, CDCl3) d 85.74 (d, J2PP ¼ 408 Hz, 1P), 20.58
(d, J2PP ¼ 408 Hz, 1P). MS–FAB+ [M]+ = 746 (57%), [M–
P(C6H4-4-F)3]+ = 430 (34%), [M–PdphPS2]+ = 317 (44%)
m/z. Anal. Calc. for C36H25F3P2PdS2 (Mw = 747.08): C,
57.88; H, 3.37. Found: C, 56.70; H, 3.31%.
2.2.4. Synthesis of bis[(2-phenylthiolato)phenylphosphino-
S,S0,P]-tris(4-trifluoromethylphenyl)phosphine-
palladium(II), [Pd(phPS2){P(C6H4-4-CF3)3}] (4)
trans-[PdCl2{P(C6H4-4-CF3}3)2] (681 mg, 0.613 mmol).
Yield 494 mg (83%). Mp 230 ꢁC 31P{1H} (121 MHz,
CDCl3) d 86.78 (d, J2PP ¼ 403 Hz, 1P), 23.12 (d, J2PP
¼
403 Hz, 1P). MS–FAB+ [M]+ = 896 (37%), [M–
PdphPS2]+ = 466 (100%), [M–P(C6H4-4-CF3)3]+ = 430
(44%) m/z. Anal. Calc. for C39H25F9P2PdS2 (Mw = 897.1):
C, 52.21; H, 2.81. Found: C, 51.68; H, 2.78%.
2.2. General procedure for the synthesis of complexes
[Pd(phPS2)(PAr3)]
2.2.5. Synthesis of bis[(2-phenylthiolato)phenylphosphino-
S,S0,P]-tris(4-methylphenyl)phosphine-palladium(II),
[Pd(phPS2){P(C6H4-4-Me)3}] (5)
trans-[PdCl2{P(C6H4-4-Me}3)2] (482 mg, 0.613 mmol).
Yield 446 mg (90%). Mp 221 ꢁC. RMN 31P{1H}
(121 MHz, CDCl3) d 84.89 (d, J2PP ¼ 408 Hz, 1P), 20.86
(d, J2PP ¼ 408 Hz, 1P). MS–FAB+ [M]+ = 734 (18%),
[M–P(C6H4-4-Me)3]+ = 430 (7%), [M–PdphPS2]+ = 305
(100%) m/z. Anal. Calc. for C39H34P2PdS2 (Mw =
735.18): C, 63.71; H, 4.66. Found: C, 62.58; H, 4.58%.
Complexes 1–6 were synthesized by using the same
experimental procedure. Thus, as a representative example,
the synthesis of [Pd(phPS2)(PPh3)] (1) is described [10].
2.2.1. Synthesis of bis[(2-phenylthiolato)phenylphosphino-
S,S0,P]-triphenylphosphine-palladium(II),
[Pd(phPS2)(PPh3)] (1)
To
a
solution of trans-[PdCl2(PPh3)2] (428 mg,
0.613 mmol) in CH2Cl2 (10 cm3) a solution (10 cm3) of

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V. Go´mez-Benı´tez et al. / Inorganica Chimica Acta 360 (2007) 2128–2138
2.2.6. Synthesis of bis[(2-phenylthiolato)phenylphosphino-
S,S0,P]-tris(4-methoxyphenyl)phosphine-palladium(II),
[Pd(phPS2){P(C6H4-4-OMe)3}] (6)
trans-[PdCl2{P(C6H4-4-OMe}3)2] (540 mg, 0.613 mmol).
Yield 367 mg (70%). Mp 218–220 ꢁC. RMN 31P{1H}
(121 MHz, CDCl3) d 84.59 (d, J2PP ¼ 419 Hz, 1P), 19.13 (d,
J2PP ¼ 419 Hz, 1P). MS–FAB+ [M]+ = 781 (15%), [M–P-
(C6H4-4-OMe)3]+ = 430 (4%), [M–PdphPS2]+ = 353 (27%)
m/z. Anal. Calc. for C39H34O3P2PdS2 (Mw = 783.18): C,
59.81; H, 4.38. Found: C, 60.41; H, 4.40%.
2.4. Data collection and refinement for [Pd(phPS2)-
{P(C6H4-4-Cl)3}] (2), [Pd(phPS2){P(C6H4-4-F)3}] (3),
[Pd(phPS2){P(C6H4-4-Me)3}] (5), [Pd(phPS2)-
{P(C6H4-4-OMe)3}] (6)
Crystalline orange-red prisms for 2, 3, 5 and 6 were
grown independently by a slow evaporation of CH2Cl2/
MeOH solvent systems, and mounted on glass fibers. In
all cases, the X-ray intensity data were measured at 293
or 291 K on a Bruker SMART APEX CCD-based
X-ray diffractometer system equipped with a Mo-target
˚
2.3. General procedure for the catalytic reactions
X-ray tube (k = 0.71073 A). The detector was placed at
a distance of 4.837 cm from the crystals in all cases. A
total of 1800 frames were collected with a scan width of
0.3 in x and an exposure time of 10 s/frame. The frames
were integrated with the Bruker SAINT software package
[11] using a narrow-frame integration algorithm. The inte-
gration of the data was done using a monoclinic unit cell
for 3 and 6, triclinic for 2 and orthorhombic for 5, to
yield a total of 40314, 6015, 27143 and 28099 reflections
for 2, 3, 5 and 6, respectively to a maximum 2h angle of
A DMF solution (5 mL) of 2.5 mmol of bromobenzene,
3.2 mmol of styrene, and the prescribed amount of catalyst
(4.33 · 10ꢀ3 mmol) was introduced into a Schlenk tube in
open air. The tube was charged with a magnetic stir bar
and an excess of Cs2CO3 (3.77 mmol) as base, sealed, and
fully immersed in a 160 ꢁC silicon oil bath. After the pre-
scribed reaction time (4 h), the mixture was cooled to room
temperature and the organic phase was analyzed by gas
chromatography (GC–MS) coupled to a selective mass
detector.
˚
50.00 (0.93 A resolution), of which 11920 (2), 5674 (3),
6038 (5) and 6157 (6) were independent. Analysis of the
Table 1
Summary of crystal structure data for [Pd(phPS2)(PAr3)] Ar = C6H4-4-Cl (2), C6H4-4-F (3), C6H4-4-Me (5), C6H4-4-OMe (6)
Compound
2
3
5
6
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C
36H25Cl3P2PdS2
C36H25F3P2PdS2
747.02
291(2)
monoclinic
P21/n
10.2551(14)
15.4527(18)
20.9365(15)
90
103.801(7)
90
3222.0(6)
4
C39H34P2PdS2
735.12
291(2)
orthorhombic
Pna21
21.0875(12)
10.2671(6)
15.9009(9)
90
90
90
3442.7(3)
4
1.418
C39H34O3P2PdS2
783.12
293(2)
monoclinic
P21/n
14.847(1)
12.829(1)
19.403(1)
90
109.392(1)
90
3486.1(4)
4
796.37
293(2)
triclinic
ꢀ
P1
˚
a (A)
13.288(1)
13.294(1)
19.817(1)
105.283(1)
93.742(1)
91.615(1)
3365.9(4)
4
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
Volume (A )
Z
Dcalc (g/cm3)
1.572
1.540
1.492
Absorption coefficient 1.035
(mmꢀ1
F(000)
0.848
0.780
0.782
)
1600
1504
1504
1600
Crystal size (mm)
h Range for data
collection (ꢁ)
0.39 · 0.224 · 0.054
1.66–25.07
0.40 · 0.28 · 0.20
1.66–25.00
0.26 · 0.20 · 0.04
1.93–24.99
0.484 · 0.168 · 0.056
1.94–25.02
Index ranges
ꢀ15 6 h 6 15, ꢀ15 6 k 6 15,
ꢀ22 6 l 6 23
0 6 h 6 12, 0 6 k 6 18,
ꢀ24 6 l 6 24
ꢀ25 6 h 6 25, ꢀ12 6 k 6 12,
ꢀ18 6 l 6 18
ꢀ17 6 h 6 17, ꢀ15 6 k 6 15,
ꢀ23 6 l 6 23
Reflections collected
Independent
40314
6015
27143
28099
11920 [Rint = 0.0771]
5674 [Rint = 0.0277]
6038 [Rint = 0.0661]
6157 [Rint = 0.0920]
reflections
Absorption correction analytical face indexed
none
5674/0/398
none
6038/1/400
analytical face indexed
6157/0/427
Data/restraints/
parameters
11920/0/793
Final R indices
[I > 2r(I)]
R indices (all data)
R1 = 0.0594, wR2 = 0.0682
R1 = 0.1145, wR2 = 0.0771
0.957
R1 = 0.0303,
wR2 = 0.0522
R1 = 0.0503,
wR2 = 0.0550
0.889
R1 = 0.0464, wR2 = 0.0909
R1 = 0.053, wR2 = 0.0940
1.004
R1 = 0.054, wR2 = 0.0608
R1 = 0.1025, wR2 = 0.0688
0.955
Goodness-on-fit-on
F2

V. Go´mez-Benı´tez et al. / Inorganica Chimica Acta 360 (2007) 2128–2138
2131
Table 2
˚
Selected bond lengths (A) and angles (ꢁ) for [Pd(phPS2){(P(C6H4-4-Cl)3)}] (2), [Pd(phPS2){(P(C6H4-4-F)3)}] (3), [Pd(phPS2){(P(C6H4-4-Me)3)}] (5),
[Pd(phPS2){(P(C6H4-4-OMe)3}] (6)
˚
Bond lengths (A)
P
P
P
P
Pd
P
Pd
P
Pd
P
Pd
P
S
S
S
S
S
S
S
S
F
Me
OMe
Cl
F
Me
MeO
Cl
F
Me
MeO
Cl
(3)
(5)
(6)
(2)
Pd(1)–P(1)
Pd(1)–S(2)
Pd(1)–S(1)
Pd(1)–P(2)
2.2286(15)
2.3085(16)
2.3106(16)
2.3443(15)
Pd(1)–P(1)
Pd(1)–S(2)
Pd(1)–S(1)
Pd(1)–P(2)
2.2274(9)
2.3110(10)
2.3370(10)
2.3598(9)
Pd(1)–P(1)
Pd(1)–S(2)
Pd(1)–S(1)
Pd(1)–P(2)
2.2254(14)
2.3041(14)
2.3342(16)
2.3690(14)
Pd(1)–P(1)
Pd(1)–S(1)
Pd(1)–S(2)
Pd(1)–P(2)
2.2225(14)
2.3171(13)
2.3190(14)
2.3660(13)
Bond angles (ꢁ)
P(1)–Pd(1)–S(2)
P(1)–Pd(1)–S(1)
S(2)–Pd(1)–S(1)
P(1)–Pd(1)–P(2)
S(2)–Pd(1)–P(2)
S(1)–Pd(1)–P(2)
86.68(6)
85.62(6)
161.80(6)
178.04(7)
94.49(6)
93.71(6)
P(1)–Pd(1)–S(2)
P(1)–Pd(1)–S(1)
S(2)–Pd(1)–S(1)
P(1)–Pd(1)–P(2)
S(2)–Pd(1)–P(2)
S(1)–Pd(1)–P(2)
86.30(4)
84.18(3)
165.21(4)
173.07(3)
92.19(4)
98.56(3)
P(1)–Pd(1)–S(2)
P(1)–Pd(1)–S(1)
S(2)–Pd(1)–S(1)
P(1)–Pd(1)–P(2)
S(2)–Pd(1)–P(2)
S(1)–Pd(1)–P(2)
86.19(5)
84.54(6)
162.03(7)
176.28(6)
94.64(5)
95.60(5)
P(1)–Pd(1)–S(1)
P(1)–Pd(1)–S(2)
S(1)–Pd(1)–S(2)
P(1)–Pd(1)–P(2)
S(1)–Pd(1)–P(2)
S(2)–Pd(1)–P(2)
85.51(5)
85.03(5)
164.37(5)
175.76(5)
98.71(5)
90.91(5)
Fig. 1. An ORTEP representation of the structure of [Pd(phPS2){P(C6H4-
4-Cl)3}] (2). Displacement ellipsoids are drawn at 50% probability level
showing the atom labeling scheme. Hydrogen atoms have been omitted for
clarity.
Fig. 2. An ORTEP representation of the structure of [Pd(phPS2){P(C6H4-
4-F)3}] (3). Displacement ellipsoids are drawn at 50% probability level
showing the atom labeling scheme. Hydrogen atoms have been omitted for
clarity.

2132
V. Go´mez-Benı´tez et al. / Inorganica Chimica Acta 360 (2007) 2128–2138
Fig. 3. An ORTEP representation of the structure of [Pd(phPS2){P(C6H4-
4-Me)3}] (5). Displacement ellipsoids are drawn at 50% probability level
showing the atom labeling scheme. Hydrogen atoms have been omitted for
clarity.
Fig. 4. An ORTEP representation of the structure of [Pd(phPS2){P(C6H4-
4-OMe)3}] (6). Displacement ellipsoids are drawn at 50% probability level
showing the atom labeling scheme. Hydrogen atoms have been omitted for
clarity.
data showed in all cases negligible decays during data col-
lections. The structures were solved by Patterson method
using SHELXS-97 [12] program. The remaining atoms were
located via a few cycles of least squares refinements and
difference Fourier maps, using the space group P21/n with
{P(C6H4-4-Me)3}] (5) and [Pd(phPS2){P(C6H4-4-OMe)3}]
(6) was carried out by reacting the corresponding palla-
dium starting materials trans-[PdCl2(PAr3)2] PAr3 =
P(C6H4-4-Cl)3, P(C6H4-4-F)3, P(C6H4-4-CF3)3, P(C6H4-4-
Me)3 and P(C6H4-4-OMe)3 with 1 equiv. of the sulfur
proligand phPS2H2 in the presence of triethylamine as base
(Scheme 1).
ꢀ
Z = 4 for 3 and 6, P1 with Z = 4 for 2 and Pna21 with
Z = 4 for 5. Hydrogen atoms were input at calculated
positions, and allowed to ride on the atoms to which they
are attached. Thermal parameters were refined for hydro-
˚
gen atoms on the phenyl groups using a Ueq = 1.2 A
Given the structural similarities between these com-
plexes they also share a number of common features. Thus,
in all cases the infrared spectrum does not result very infor-
to precedent atom in all cases. For all complexes, the
final cycle of refinement was carried out on all non-zero
data using SHELXL-97 and anisotropic thermal parameters
for all non-hydrogen atoms. The details of structure
determinations are given in Table 1 and selected bond
1
mative and analyses by H NMR techniques exhibit in all
cases signals corresponding to the presence of the phenyl
rings in the corresponding molecules and in the particular
case of complexes 5 and 6 signals due to the CH3 groups
in the phosphino ligands at d 2.34 and 3.80 ppm, respec-
tively, were also observed.
˚
lengths (A) and angles (ꢁ) are given in Table 2. The num-
bering of atoms is shown in Figs. 1–4, respectively
(ORTEP) [13].
The 31P{1H} NMR analysis results more interesting,
showing in all cases two doublets in the spectrum, one at
3. Results and discussion
ꢀ2
lower field due to the tridentated ligand phPS2 and the
As we have previously described for [Pd(phPS2)(PPh3)]
(1) [10], the synthesis of the analogous complexes
[Pd(phPS2){P(C6H4-4-Cl)3}] (2), [Pd(phPS2){P(C6H4-4-F)3}]
other at higher field due to the PAr3 ligands, respectively.
The multiplicity of these signals in all cases is in agreement
with a mutually trans conformation of the two phosphorus
ligands [14]. The coupling constant J2PP values being around
(3),
[Pd(phPS2){P(C6H4-4-CF3)3}]
(4),
[Pd(phPS2)-

V. Go´mez-Benı´tez et al. / Inorganica Chimica Acta 360 (2007) 2128–2138
2133
SH
Cl
PAr3
Cl
P
2 NEt3
Pd
+
P
Ar3P
Pd
P
S
S
PAr3
Ar
Ar
HS
Ar
H
F
Cl
CF3
(1)
(2)
(4)
(6)
Ar=
(3)
(5)
Me
OMe
Scheme 1. Synthesis of [Pd(phPS2)(PAr3)] Ar = C6H5 (1), C6H4-4-Cl (2), C6H4-4-F (3), C6H4-4-CF3 (4), C6H4-4-Me (5), C6H4-4-OMe (6) complexes.
405 Hz, respectively (see Section 2). These values are also in
agreement with a trans conformation for the two phospho-
rus nuclei in all cases [14]. The 31P{1H} results are very diag-
nostic of the identity of the complexes, while the observed
variations in the chemical shift of the signals is a clear indic-
ative of the electronic effect of the different para-substituents
at the triarylphosphines. For instance, for complexes
[Pd(phPS2){P(C6H4-4-CF3)3}] (4) and [Pd(phPS2)ꢀ{2P(C6H4-
4-OMe)3}] (6) the phosphorus signals for phPS2 appear
at d = 86.78 and 84.59 ppm, respectively; these two exam-
ples representing the upper and lower limits in the series
of complexes. The results obtained can be rationalized in
terms of the higher electron-withdrawing capability of –
CF3 with respect to that of the –OMe substituent, being
higher in the case of complex 4 having the dishielding of
the P nuclei in the S–P–S moiety as the ultimate consꢀe2-
quence. Thus, the trend observed for the 31P{1H} phPS2
chemical shifts in the series of complexes [Pd(phPS2)(PAr3)]
goes: [Pd(phPS2){P(C6H4-4-OMe)3}] (6) (84.59 ppm) <
[Pd(phPS2){P(C6H4-4-Me)3}] (5) (84.89 ppm) < [Pd(phPS2)-
(PPh3)] (1) (85.33 ppm) < [Pd(phPS2){P(C6H4-4-F)3}] (3)
(85.74 ppm) < [Pd(phPS2){P(C6H4-4-Cl)3}] (2) (86.04 ppm) <
[Pd(phPS2){P(C6H4-4-CF3)3}] (4) (86.78 ppm). This linear
trend can be better observed in the following graphic where
the chemical shift values are plotted versus the Hammet
parameter for the phosphines employed (Graphic 1).
Another major common peak due to the loss of the corre-
sponding ligand PAr3 is also observed in all cases. For all
complexes, elemental analysis are in good agreement with
the proposed formulations.
The crystals suitable for single crystal X-ray diffraction
analysis were obtained for complexes [Pd(phPS2)(PPh3)]
(1) [10], [Pd(phPS2){P(C6H4-4-Cl)3}] (2), [Pd(phPS2)-
{P(C6H4-4-F)3}] (3), [Pd(phPS2){P(C6H4-4-Me)3}] (5) and
[Pd(phPS2){P(C6H4-4-OMe)3}] (6). Several attempts to
obtain suitable crystals of complex 4 were unfruitful. As
expected, these structures share a number of common
structural features, showing in all cases the palladium cen-
ters to be into slightly distorted square planar environ-
ments. The coordination spherꢀe2 for all complexes being
constituted for the ligand phPS2 coordinated in a triden-
tate S–P–S pincer like fashion and completed by the p-
substituted triarylphosphine (PAr3) located trans to the
phosphorus atom of the ligand phPS2ꢀ2. The main distor-
tion from the square planar geometry is caused in all cases
ꢀ2
by the rigidity of the phPS2 ligand and reflected in the
angles S(1)–Pd(1)–S(2) and in a less pronounced manner
in the vector P(1)–Pd(1)–P(2) (Table 2). The Pd–P(2) dis-
tances are slightly longer in the complexes having phos-
phines with electron-donating groups [–OMe (6)
˚
˚
2.3660(13) A, –Me (5) 2.3690(14) A] in comparison with
those observed in the complexes bearing PAr3 with elec-
˚
As expected from the structural similarity of the com-
plexes, analysis by FAB+–MS shows in all cases the molec-
ular ion with the appropriate isotope distribution [15].
tron-withdrawing groups [–Cl (2) 2.3443(15) A, –F (3)
˚
2.3598(9) A] (Table 2), this, due in part to the more pro-
nounced p-backbonding effect of the latter groups. The

2134
V. Go´mez-Benı´tez et al. / Inorganica Chimica Acta 360 (2007) 2128–2138
Chemical Shift [ph PS ]-2 ( ) vs Hammett parameter ( )
δ
σ
2
87
86.5
86
ph
R2 = 0.9841
85.5
85
84.5
84
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
Hammet Parameter (
)
σ
Graphic 1.
Pd–S distances are slightly different and comparable to
those found in other palladium complexes (Table 2).
The determination of the melting point of the different
[Pd(phPS2)(PAr3)] compounds suggest these complexes to
have a considerable stability to high temperatures, exhibit-
ing melting points within the range of 200 and 240 ꢁC with-
out any visible decomposition. Based on these observations
revealed that it is in fact Cs2CO3 with a 76% conversion
to stilbenes, a far better base than Na2CO3 with only
38% conversion and Et3N with a 43% conversion under
the same reaction conditions. With these results in hand
and under these optimized reaction conditions we pro-
ceeded to determine which compound of the series was
the best catalyst for the coupling of styrene and bromoben-
zene. The results obtained revealed that it is in fact complex
[Pd(phPS2)(PPh3)] (1) the more active catalyst precursor
(Table 3). However, from the results shown in Table 3 it
seems that apparently the para-substituted phosphines
have little or no effect in the process. These results lead
ꢀ2
and the fact that the phPS2 ligand may indeed behave as
a hemilabile ligand thus promoting the reactivity of these
complexes [16], we decided to examine the catalytic activity
of these species in the olefination of halobenzenes (Heck
reaction) by studying the C–C couplings between styrene
and iodo or bromobenzene (Scheme 2). The stability of
these SPS-Pd pincer complexes to air and moisture allowed
us to carry out the catalytic reactions in a completely aer-
obical environment using reagent grade substrates. Initial
screening of the reactions of styrene (3.2 mmol) with iodo
or bromobenzene (2.5 mmol) using complex 1 as catalyst
(4.33 · 10ꢀ3 mmol) in N,N0-dimethylformamide (DMF)
(3 mL) and Na2CO3 (3.77 mmol) as the base afforded in
both cases quantitative yields after 24 h reaction at
160 ꢁC. The initial choice of Na2CO3 is due to the fact that
it is a solid in the reaction mixture that remains in the solid
state having the sole effect of scavenging the acid formed
during the reaction without any further interference in
the catalytic process. Furthermore, from the economical
point of view this compound results the cheapest from a
series of potential bases employed to date for this process.
However, further experiments reducing the reaction time to
only 4 hours, to better observe the effect of the base,
P
Pd
P
S
S
R
R
R
+
Base
Br
Scheme 2. Heck reaction using [Pd(phPS2)(PAr3)] Ar = C6H5 (1), C6H4-4-
Cl (2), C6H4-4-F (3), C6H4-4-CF3 (4), C6H4-4-Me (5), C6H4-4-OMe (6)
complexes as catalysts.

V. Go´mez-Benı´tez et al. / Inorganica Chimica Acta 360 (2007) 2128–2138
2135
Table 3
Heck couplings of bromobenzene with styrene using [Pd(phPS2)(PAr3)] Ar = C6H5 (1), C6H4-4-Cl (2), C6H4-4-F (3), C6H4-4-CF3 (4), C6H4-4-Me (5),
C6H4-4-OMe (6) as catalysts
P
Pd
P
S
S
R
R
Br
R
+
+
Cs2CO3
PAr3
Hammett parameter
gem-Stilbene
trans-Stilbene
Conversiona (%)
74.05
MeO
OMe
ꢀ0.27
9.83
64.22
P
OMe
Me
Me
ꢀ0.17
9.41
60.59
65.53
70.00
76.15
P
Me
H
H
0.00
10.62
P
H
F
F
0.06
8.25
57.24
65.49
P
F
Cl
Cl
0.23
10.82
64.14
74.96
P
Cl
F3C
CF3
0.54
9.40
61.30
70.70
P
CF3
Reaction conditions:2.5 mmol of halobenzene, 3.2 mmol of styrene, 3.77 mmol of base Cs2CO3, 4.33 · 10ꢀ3 mmol of catalyst and 3 ml of DMF, 4 h at 160 ꢁC.
a
Yields obtained by GC are based on bromobenzene and the average of two runs.
us to conclude that probably the initial step for the reaction
mechanism using these complexes may involve the de-liga-
tion of the phosphine PAr3 to generate the necessary coor-
dination site for the incoming substrates, which will later
be reduced to allow the oxidative addition of the haloge-
nated substrate over the Pd center.

2136
V. Go´mez-Benı´tez et al. / Inorganica Chimica Acta 360 (2007) 2128–2138
Table 4
Heck couplings of p-substituted bromobenzenes with styrene using [Pd(phPS2)(PPh3)] (1) as catalyst
P
Pd
P
S
S
Y
Y
+
+
Cs2CO3
Br
Y
Ar–Br
Hammett parameter (r)
ꢀ0.27
gem-Stilbene
trans-Stilbene
Conversiona (%)
32.49
2.55
29.94
Br
MeO
ꢀ0.17
2.62
7.66
1.74
6.05
33.88
65.53
46.31
84.54
36.50
76.15
49.86
100.0
Br
Me
H
0
Br
Br
0.23
0.42
Cl
Br
O
C
H
Reaction conditions: 2.5 mmol of halobenzene, 3.2 mmol of styrene, 3.77 mmol of base Cs2CO3, 4.33 · 10ꢀ3 mmol of catalyst and 3 ml of DMF, 4 h at
160 ꢁC.
a
Yields obtained by GC are based on halobenzene and the average of two runs.
Additionally, we decide to explore further the reactivity
of complex [Pd(phPS2)(PPh3)] (1) against a series of para-
substituted bromobenzenes, the results obtained from
these experiments show that electron-withdrawing groups
in the aromatic ring of the bromobenzenes favor the Pd
catalytic coupling with styrene, having conversions of up
to 99% for p-bromobenzaldehyde, these results can be
rationalized in terms of inductive effects, that in the case
of bromobenzenes bearing electron-donating groups, the
excess of electronic density would ultimately strengthen
the C–Br bond thus making its activation more difficult.
The reverse effect can be considered in the case of p-
bromobenzenes having electron-withdrawing substituents
(Table 4), although it is not clear why the point corre-
sponding to bromobenzene lays out of the trend. Experi-
ments aimed to clear this point are currently under
investigation in our research group.
Experiments using chlorobenzene resulted only in traces
of the products probably as a consequence of the quick and
clear decomposition of the complexes in the reaction mix-
ture to palladium black.
There has been a considerable debate in the literature
about the oxidation states of the species involved in
the catalytic cycle with Pd(IV)/Pd(II) and Pd(II)/Pd(0),

V. Go´mez-Benı´tez et al. / Inorganica Chimica Acta 360 (2007) 2128–2138
2137
(b) J.R. Dilworth, P. Arnold, D. Morales, Y.L. Wong, Y. Zheng,
The Chemistry and Applications of Complexes with Sulphur
Ligands, in: Modern Coordination Chemistry, The Legacy of
Joseph Chatt, Cambridge, UK, 2002, p. 217;
(c) M. Hiraoka, A. Nishikawa, T. Morimoto, K. Achiwa, Chem.
Pharm. Bull. 46 (1998) 704;
both being proposed at various times [3,17], however,
in this case given the type of species involved we
favor the Pd(0)/Pd(II) mechanism although the precise
mechanism of the catalytic reaction remains to be
elucidated.
(d) E. Hauptman, R. Shapiro, W. Marshall, Organometallics 17
(1998) 4976;
(e) E. Hauptman, P.J. Fagan, W. Marshall, Organometallics 18
(1999) 2061;
(f) H-S. Lee, J-Y. Bae, J. Ko, Y.S. Kang, H.S. Kim, S.O. Kang,
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(g) A.S. Abu-Surrah, K. Lappalainen, T. Repo, M. Klinga, M.
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In summary, we have reported a series of complexes of
the type [Pd(phPS2)(PAr3)]. These compounds have been
evaluated in the palladium catalyzed Heck reaction of
iodo, bromo and chlorobenzene with styrene. Preliminary
catalytic experiments indicate these complexes to be effi-
cient catalyst in the Heck reaction. Analysis of the elec-
tronic effects of the para-substituted triarylphosphines
on the performance of the different complexes reveal that
these ligands are easily displaced from the coordination
sphere of the complexes and have little or no effect in
the performance of the catalytic precursor, thus it is fair
to conclude that the series of [Pd(phPS2)(PAr3)] com-
plexes catalyze the Heck couplings of styrene and halo-
benzenes by a common intermediate. Efforts aimed to
employ these compounds in other metal mediated organic
syntheses and other cross-coupling reactions are currently
under investigation.
´
Gagne, J. Am. Chem. Soc. 122 (2000) 7905;
(i) J.R. Dilworth, D. Morales, Y. Zheng, J. Chem. Soc., Dalton
Trans. (2000) 3007;
(j) D. Morales-Morales, S. Rodr´ıguez-Morales, J.R. Dilworth, A.
Sousa-Pedrares, Y. Zheng, Inorg. Chim. Acta 332 (2002) 101;
´
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(k) D. Canseco-Gonzalez, V. Gomez-Benıtez, S. Hernandez-
Ortega, R.A. Toscano, D. Morales-Morales, J. Organomet. Chem.
679 (2003) 101;
´
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(l) D. Canseco-Gonzalez, V. Gomez-Benıtez, O. Baldovino-Pan-
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Chem. 689 (2004) 174;
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(m) G. Rıos-Moreno, R.A. Toscano, R. Redon, H. Nakano, Y.
Okuyama, D. Morales-Morales, Inorg. Chim. Acta. 358 (2005) 303.
[6] (a) C.S. Stone, D.D. Weinberger, C.A. Mirkin, Prog. Inorg. Chem.
48 (1999) 233;
4. Supplementary material
(b) P. Braunstein, F. Naud, Angew. Chem., Int. Ed. Engl. 40 (2001)
680.
CCDC 612748, 612749, 612750 and 612751 contain the
supplementary crystallographic data for 2, 3, 5 and 6. The
data can be obtained free of charge via htpp://www.
ccdc.cam.ac.uk/conts/retrieving.html, or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or
e-mail: deposit@ccdc.cam.ac.uk.
´
[7] (a) D. Morales-Morales, C. Grause, K. Kasaoka, R. Redon,
R.E. Cramer, C.M. Jensen, Inorg. Chim. Acta 300–302 (2000)
958;
´
(b) D. Morales-Morales, R. Redon, Z. Wang, D.W. Lee, C.
Yung, K. Magnuson, C.M. Jensen, Can. J. Chem. 79 (2001) 823;
´
(c) D. Morales-Morales, R. Redon, D.W. Lee, Z. Wang, C.M.
Jensen, Organometallics 20 (2001) 1144;
(d) D. Morales-Morales, R.E. Cramer, C.M. Jensen, J. Organo-
met. Chem. 654 (2002) 44;
(e) X. Gu, W. Chen, D. Morales-Morales, C.M. Jensen, J. Mol.
Catal. A. 189 (2002) 119;
Acknowledgements
V.G.-B. would like to thank CONACYT, DGEP and
DGAPA for financial support. We would like to thank
Chem. Eng. Luis Velasco Ibarra and M.Sc. Francisco Ja-
vier Perez Flores for their invaluable help in the running
of the FAB-Mass Spectra. The support of this research
by CONACYT (J41206-Q) and DGAPA-UNAM
(IN114605) is gratefully acknowledged.
´
(f) D. Morales-Morales, R. Redon, C. Yung, C.M. Jensen,
Inorg. Chim. Acta 357 (2004) 2953;
(g) O. Baldovino-Pantaleon, S. Hernandez-Ortega, D. Morales-
Morales, Inorg. Chem. Commun. 8 (2005) 955;
(h) O. Baldovino-Pantaleon, S. Hernandez-Ortega, D. Morales-
Morales, Adv. Synth. Catal. 348 (2006) 236;
(i) F.E. Hahn, M.C. Jahnke, V. Gomez-Benıtez, D. Morales-
Morales, T. Pape, Organometallics 24 (2005) 6458;
´
´
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(j) Z. Wang, S. Sugiarti, C.M. Morales, C.M. Jensen, D.
Morales-Morales, Inorg. Chim. Acta 359 (2006) 1923;
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