Pd catalyzed Heck reaction with the catalytic system [Pd(Ph 2PC6H4-2-(CH2NMe2)) (SRF)2]: Examination of the electronic effects of fluorinated thiolates

Article abstract of DOI:10.1016/j.molcata.2005.02.007

A series of palladium thiolate complexes of the [Pd(Ph₂PC ₆H₄-2-(CH₂NMe₂))(SR _F)₂] type have been synthesized in good yields by metathetical reactions of [Pd(Ph₂PC₆H₄-2- (CH₂NMe₂))Cl₂] (1) with [Pb(SR _F)₂], (SR_F = S-C₆F₅, S-C₆F₄-4-H, S-C₆H₄-2-CF₃, S-C₆H₄-4-F, S-C₆H₄-2-F) and their crystal structures determined. Heck coupling reactions were carried out using [Pd(Ph₂PC₆H₄-2-(CH₂NMe ₂))(SR_F)₂], SR_F = S-C ₆F₅ (2), S-C₆F₄-4-H (3), S-C ₆H₄-2-CF₃ (4), S-C₆H₄-4-F (5), S-C₆H₄-2-F (6) complexes as catalysts in order to examine the effect of the thiolates in the reaction of bromobenzene and styrene. The results obtained indicate that the less electron-withdrawing substituents on the thiolate moiety may favor higher yields in the Pd catalyzed Heck reaction using [Pd(Ph₂PC₆H₄-2-(CH₂NMe ₂))(SR_F)₂] as catalysts.

Full text of DOI:10.1016/j.molcata.2005.02.007

Journal of Molecular Catalysis A: Chemical 233 (2005) 17–27
Pd catalyzed Heck reaction with the catalytic system
[Pd(Ph2PC6H4-2-(CH2NMe2))(SRF)2]
Examination of the electronic effects of fluorinated thiolates
a
b
c
a
´
´
´
´
´
Jaime G. Fierro-Arias , Rocıo Redon , Juventino J. Garcıa , Simon Hernandez-Ortega ,
a
a,∗
´
Ruben A. Toscano , David Morales-Morales
a
Instituto de Qu´ımica, Universidad Nacional Auto´noma de Me´xico, Cd. Universitaria, Circuito Exterior, Coyoaca´n, 04510 Me´xico D.F., Mexico
b
Centro de Ciencias Aplicadas y Desarrollo Tecnolo´gico (CCADET), Universidad Nacional Auto´noma de Me´xico, Cd. Universitaria, Circuito Exterior,
Coyoaca´n, 04510 Me´xico D.F., Mexico
c
Facultad de Qu´ımica, Universidad Nacional Auto´noma de Me´xico, Cd. Universitaria, Circuito Exterior, Coyoaca´n, 04510 Me´xico D.F., Mexico
Received 23 November 2004; received in revised form 29 January 2005; accepted 1 February 2005
Abstract
A series of palladium thiolate complexes of the [Pd(Ph2PC6H4-2-(CH2NMe2))(SRF)2] type have been synthesized in good yields by
metathetical reactions of [Pd(Ph2PC6H4-2-(CH2NMe2))Cl2] (1) with [Pb(SRF)2], (SRF = −SC6F5, −SC6F4-4-H, −SC6H4-2-CF3, −SC6H4-4-F,
−SC6H4-2-F) and their crystal structures determined. Heck coupling reactions were carried out using [Pd(Ph2PC6H4-2-(CH2NMe2))(SRF)2],
SRF = −SC6F5 (2), −SC6F4-4-H (3), −SC6H4-2-CF3 (4), −SC6H4-4-F (5), −SC6H4-2-F (6) complexes as catalysts in order to examine the effect
of the thiolates in the reaction of bromobenzene and styrene. The results obtained indicate that the less electron-withdrawing substituents on
the thiolate moiety may favor higher yields in the Pd catalyzed Heck reaction using [Pd(Ph2PC6H4-2-(CH2NMe2))(SRF)2] as catalysts.
© 2005 Elsevier B.V. All rights reserved.
Keywords: P–N ligand; Hemilability; Heck reaction; C–C coupling reactions; Fluorinated thiolate complexes; Palladium complexes; Crystal structures; Catalysis
1. Introduction
this reaction have also evolved to achieve a better understand-
ing of the factors affecting activity, selectivity and stability. In
this sense, in recent years, several groups have been involved
in the design of ligands able to afford robust catalysts, capa-
ble to withstand reaction conditions and oxidant atmosphere,
which favor Heck couplings in an efficient manner with cheap
reagent grade starting materials. From all the compounds
employed so far, it seems like hemilabile hybrid ligands may
offer an interesting option to carry out this process [4]. More-
over, the presence of these ligands in the coordination sphere
of transition metal complexes may render interesting behav-
iorsinsolutionastheseligandscanbecapableoffullorpartial
de-ligation (hemilability) [4], being able to provide impor-
tant extra coordination sites for incoming substrates during a
catalytic process [4]. In addition, platinum group metal com-
plexes containing thiolate ligands on its structure are rare [5],
due in part to the well known tendency of these complexes
Transition metal catalyzed reactions have acquired a fun-
damental roll in the modern organic chemistry [1]. Among
them, palladium catalyzed C–C coupling reactions have been
recognized as power tools in multiple organic transforma-
tions, from these the Heck reaction has been denominated as
angular stone in modern organic synthesis [2]. This reaction
consists in the coupling of a halo compound with a double
bond. The importance of this reaction has transcended its
potential applications in the laboratory, to become the main
interest to scale these processes to an industrial level [3]. In
the same way, the different catalysts employed to carry out
∗
Corresponding author. Tel.: +52 5556224514; fax: +52 5556162217.
E-mail address: damor@servidor.unam.mx (D. Morales-Morales).
1381-1169/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2005.02.007

18
J.G. Fierro-Arias et al. / Journal of Molecular Catalysis A: Chemical 233 (2005) 17–27
to polymerize [6], affording in most of the cases intractable
solidsuselessaspotentialcatalystsinhomogeneouscatalysis.
Usually, compounds containing sulfur on its structure have
been neglected as potential homogeneous catalysts due to the
extended belief of sulfur to be a catalyst poison. Thus, given
our continuous interest in the design and synthesis of active
and robust complexes for their employment as potential
catalysts in industrial relevant transformations [7], we would
like to report here the use of the P–N ligand [Ph2PC6H4-2-
(CH2NMe2)] as a stabilizing ligand and fluorinated thiolates
as substituents for the fine tuning of the electronics in the
synthesis of a series of palladium(II) complexes of the type
[Pd(Ph2PC6H4-2-(CH2NMe2))(SRF)2]. The identification
of the electronic effects of the different fluorinated thiolates
over the reactivity of these palladium complexes in the Heck
catalytic reaction of bromobenzene and styrene will be
discussed.
Scheme 2.
the magnetic inequivalence of these protons. The multiplicity
of the signals for the protons of the CH2 groups is due to
the coupling between the protons themselves and given the
closeness that one of the protons keeps at a given time with
the P atom one of the signals is shown as a quartet. The other
signals in the spectrum, may account for the presence of the
other species in solution.
Analysis by 31P NMR reveals a single peak, at lower field
(22.9 ppm) clearly indicating that P moiety of the ligand is
coordinated to the metal center. Analysis by MS-FAB+ spec-
trometry exhibits a peak corresponding to loss of a chloride
[M − Cl]+.
2. Results and discussion
The stoichiometric reaction of the lead salt of the cor-
responding thiolate [Pb(SRF)2] with complex (1) afforded
complexes 2–6 in good yields. All compounds were obtained
as analytically pure products from recrystallization of
CH2Cl2/MeOH solvent systems. Given the similarity in the
structures of these complexes, common features in their
P–N ligand [Ph2PC6H4-2-(CH2NMe2)], was conveni-
ently synthesized by direct ortho-lithiation of N,Nꢀ-dime-
thylbenzylamine with n-BuLi and further treatment of the
resulting ortho-lithiated species with diphenylchlorophos-
phine (PPh2Cl) (Scheme 1).
1
This compound exhibits signals in the H NMR spectra
1
spectroscopic properties were found. Analysis from the H
due to the presence of the aromatic protons at 6.89–7.32 ppm,
and two singlets at 3.62 and 2.08 ppm due the presence of the
CH2 and CH3 groups respectively. 31P NMR analysis re-
veal a single peak in the NMR spectra at −14.78 ppm, from
these analyses it was determined that the ligand had been
obtained with enough purity to be used without further pu-
rification. Thus, reaction of the P–N ligand (1 equiv.) with one
equivalent of the palladium starting material [Pd(COD)Cl2]
afforded complex [Pd(Ph2PC6H4-2-(CH2NMe2))Cl2] (1) as
a yellow microcrystalline powder in good yield. This com-
pound exhibited similar 1H NMR spectra as that of the free
ligand, with signals due to the presence of the aromatic
protons between 6.3 and 7.9 ppm. Signals corresponding to
the CH2 and CH3 groups were identified at 3.1–3.7 and
2.8 ppm respectively. It is noteworthy that both these sig-
nals are broad, this being probably due to a dynamic pro-
cess of the ligand once coordinated to the metal as shown in
Scheme 2.
NMR of the series of complexes reveals a similar behavior
as that observed for complex (1) with signals corresponding
to the aromatic rings between 6.6 and 8.2 ppm and those
corresponding to the methylene and methyl groups between
3.1 and 4.2 and about 2.87 ppm respectively, the fact that in
all cases the signals for the CH2 and CH3 groups are broad
once again indicate the presence of a dynamic equilibrium in
solution. The 31P{1H} NMR spectra of the compounds are
also very illustrative affording in all cases single resonances
indicative of the presence of a single specie; another impor-
tant feature in these spectra is that the signals observed are
sensitive to the electronic environment, as expected, due to
the number and position of the fluorine atoms in the aromatic
rings of the thiolates. Thus, in the case of [Pd(Ph2PC6H4-
2-(CH2NMe2))(SC6F5)2] (2) the signal is shifted to lower
field (δ = 20.88 ppm) and in the case of [Pd(Ph2PC6H4-2-
(CH2NMe2))(SC6H4-2-CF3)2] (4) the signal is displaced to
higher field (δ = 19.57 ppm); these two examples represent
the upper and lower limits in the series of complexes. This
behavior can be rationalized from the point of view of
electron-withdrawing capability, being higher in the case of
complex 2 due to the higher substitution of fluorine of the
aromatic ring, and therefore, with the larger value of Group
Electronegativity (Eg) [8], having the dishielding of the P
nuclei in the P–N moiety as ultimate consequence. Thus, the
trend observed for the δ 31P{1H} in the series of complexes
[Pd(Ph2PC6H4-2-(CH2NMe2))(SRF)2] is: −SC6H4-2-CF3
1
In fact, further analyses of the H NMR spectra at low
temperature (233 K) for complex 3 confirms this hypothesis,
showing clear and very well defined signals for the CH2 and
CH3 groups (Fig. 1), with two signals for the methylenic
protons and two more for the methyl groups, thus confirming
Scheme 1.
(19.57 ppm) < −SC6H4-4-F
(20.35 ppm) < −SC6H4-2-

J.G. Fierro-Arias et al. / Journal of Molecular Catalysis A: Chemical 233 (2005) 17–27
19
Fig. 1. 1H NMR spectra for complex [Pd(Ph2PC6H4-2-(CH2NMe2))(SC6F4-4-H)2] (3) at 298 and 233 K.
(20.57 ppm) < −SC6F4-4-H
(20.97 ppm).
(20.88 ppm) < −SC6F5
ion of the fragment corresponding to the loss of one thiolate
ligand. Further loss of the other thiolate ligand and a methyl
fragment from the NMe2 moiety were also observed. Ele-
mental analyses for all the complexes are consistent with the
proposed formulations.
Crystals suitable for single crystal X-ray diffraction anal-
yses (Table 1) were obtained for complexes 1, 3 and 4 and
a rather unusual specie having a single thiolate in the coor-
dination sphere [Pd(Ph2PC6H4-2-(CH2NMe2))(Cl)(SC6H4-
2-F)] (7), this compound was obtained in minimum amount
as by-product of the reaction for the synthesis of complex
6. Once again these compounds share a number of common
structural features. The structures can be defined as slightly
F
On the other hand, the 19F{1H} NMR experiments of the
synthesized complexes reveal the fluorinated thiolates to be
present, with typical splitting patterns for the ligands −SC6F5
(2) and −SC6F4-4-H (3) and singlets for the cases −SC6H4-
2-CF3 (4), −SC6H4-4-F (5) and −SC6H4-2-F (6). These ob-
served patterns are in agreement with the proposed formula-
tions. In all cases the signals are duplicated, this being due to
the fact that the fluorines are not equivalent since one thiolate
has a phosphorus trans to it and the other one has the amino
group in the trans conformation. Additionally, analysis by
FAB+-mass spectrometry shows in all cases the molecular

20
J.G. Fierro-Arias et al. / Journal of Molecular Catalysis A: Chemical 233 (2005) 17–27
Table 1
Summary of crystal structure data for [Pd(P–N)(SRF)2] R = Cl (1), C6F4-4-H (3), C6H4-4-CF3 (4), (Cl)(C6H4-2-F) (7)
Compound
[Pd(P–N)(Cl)2] (1)
[Pd(P–N)(SC6F4-4-H)2] (3) [Pd(P–N)(SC6H4-2-CF3)2]
(4)
[Pd(P–N)(Cl)(SC6H4-2-
F)2] (7)
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C
21H22Cl2NPPd
C33
788.02
291(2)
Monoclinic
P21/c
H
24F8NPPdS2
C
35H30F6NPPdS2
C27H26ClFNPPdS
588.37
293(2)
Monoclinic
P21/c
496.67
293(2)
Orthorhombic
Pbca
780.09
291(2)
Monoclinic
P21/n
Crystal size (mm × mm × mm) 0.20 × 0.12 × 0.08
0.30 × 0.10 × 0.1
0.30 × 0.20 × 0.10
0.222 × 0.082 × 0.082
Unit cell dimensions
˚
a (A)
15.642(1)
14.820(1)
18.226(1)
90
11.3895(6)
16.4315(8)
17.9115(9)
90
11.8450(9)
9.1040(7)
31.280(2)
90
10.492(1)
18.149(1)
14.211(1)
90
˚
b (A)
˚
c (A)
˚
α (A)
˚
β (A)
90
90
4224.9(3)
8
106.809(1)
90
3208.9(3)
4
97.906(2)
90
3341.1(4)
4
107.005(2)
90
2587.7(3)
4
˚
γ (A)
3
˚
Volume (A )
Z
Density (g/cm3)
1.562
1.631
1.551
1.510
θ range for data collection (◦)
Reflections collected
Independent reflections
F(0 0 0)
2.20–25.00
32875
3722 [R(int) = 0.0622]
2000
1.87–25.00
25976
5654 [R(int) = 0.0645]
1576
1.77–25.00
26646
5879 [R(int) = 0.0635]
1576
1.87–32.59
35358
9363 [R(int) = 0.1017]
1192
Absorption correction
Goodness-of-fit on F2
R indices (all data)
Final R indices [I > 2σ(I)]
Face-indexed
1.027
R1 = 0.0485, wR2 = 0.0463
R1 = 0.0306, wR2 = 0.0447
None
0.965
None
0.956
Analytical: face-indexed
0.972
R1 = 0.2053, wR2 = 0.0780
R1 = 0.0569, wR2 = 0.0644
R1 = 0.0670, wR2 = 0.0618
R1 = 0.0424, wR2 = 0.0586
R1 = 0.0742, wR2 = 0.0856
R1 = 0.0.0460,
wR2 = 0.0777
5879/0/415
−14 ≤ k ≤ 14,
Data/restrains/parameters
Index ranges
3722/0/237
5654/0/417
−13 ≤ k ≤ 13,
9363/0/300
−15 ≤ k ≤ 115,
−18 ≤ k ≤ 18,
−17 ≤ h ≤ 17, −21 ≤ l ≤ 21 −19 ≤ h ≤ 19, −21 ≤ l ≤ 21
−10 ≤ h ≤ 10, −37 ≤ l ≤ 37 −27 ≤ h ≤ 27, −21 ≤ l ≤ 21
S = [w((Fo)2 − (Fc)2)2/(n − p)]1/2 where n = number of reflections and p = total number of parameters. R1 = |Fo − Fc|/|Fo|, wR2 = [w((Fo)2 − (Fc)2)2/
w(Fo)2].
The differences observed, particularly in the 31P{1H}
NMR experiments, are complemented with the results ob-
tained from single crystal X-ray diffraction experiments. Al-
though we cannot make a complete comparison due to the
fact that we do not have the whole set of complexes crystallo-
graphically characterized, we can compare the two examples
(complexes 3 and 4) that represent extremes in the series.
Thus, the differences in changing the thiolates are very clear.
For instance, the Pd S bond lengths (Table 2) decrease as
the value of the Eg increases. This is most likely the result of
either steric hindrance or electrostatic repulsion phenomena.
We believe that we have an ideal system to evaluate
the importance of the fine tuning of the electronic effects
in the palladium catalyzed Heck reaction. Thus, catalytic
experiments were carried out employing [Pd(Ph2PC6H4-2-
(CH2NMe2))(SRF)2] complexes as catalysts. The reactions
of bromobenzene and styrene using N,N-dimethylformamide
(DMF) as solvent were carried out in the open air at different
reaction times, revealing that 2 h of reaction time would yield
enough product (stilbenes) to observe a clear trend to be able
to quantify the effects due to the variation of the Eg of the
thiolates. Given the fact that single substituted thiolates in
different positions of the aromatic ring were also employed,
some insights with respect to the sterics can also be obtained
Table 3.
distorted square planar in all cases, having the palladium cen-
ters with the P–N ligand coordinated in a bidentate manner
and completing the coordination sphere with the two thio-
lates adopting a cis conformation, one trans to one phospho-
rus and the other trans to the nitrogen of the P–N ligand.
The main distortion is due to the steric hindrance caused
by the phenyl rings in the P–N ligand. In all cases, the aro-
matic rings of the thiolates are not eclipsed as has been ob-
served in other cases due to ␲–␲ interactions [9]. Instead,
the aromatic rings are shifted, in an anti configuration. It is
probable that the fluorobenzene rings adopt this conforma-
tion due to steric hindrance or to have optimal packing in the
lattice.
In addition, analyses of the bond distances of the sub-
stituents trans to P and N in the series of complexes, reveal
that the more elongated distance is that corresponding to the
substituents trans to P. Therefore, one would expect the sub-
stitution of this ligand to proceed more easily than that of the
ligand trans to N (e.g. for complex 1 trans to P Pd(1)–Cl(1)
2. 3903 (9) > trans to N Pd(1)–Cl(2) 2.2786 (9)). In fact, the
trans influence of the phosphine is bigger than that of the
amino group (PR3 > R2N). However complex 6 is obtained
with the thiolate ligand trans to N, thus it seems that the rul-
ing factors in the substitution of the chlorides in complex 1,
are the kinetic and not thermodynamic ones.

J.G. Fierro-Arias et al. / Journal of Molecular Catalysis A: Chemical 233 (2005) 17–27
21
Table 2
◦
˚
Selected bond lengths (A) and angles ( ) for [Pd(P–N)(SRF)2], R = C6F4-4-H (3), C6H4-4-CF3 (4), C6H4-2-F (7)
[Pd(P–N)(Cl)2] (1)
[Pd(P–N)(SC6F4-4-H)2] (3)
[Pd(P–N)(SC6H4-2-CF3)2] (4)
[Pd(P–N)(Cl)(SC6H4-2-F)] (7)
˚
Bond length (A)
Pd(1)–N(1)
Pd(1)–P(2)
Pd(1)–Cl(2)
Pd(1)–Cl(1)
2.110(2)
Pd(1)–N(1)
Pd(1)–P(1)
Pd(1)–S(1)
Pd(1)–S(2)
2.174(3)
Pd(1)–N(1)
Pd(1)–P(1)
Pd(1)–S(1)
Pd(1)–S(2)
2.161(3)
Pd(1)–N(1)
Pd(1)–P(1)
Pd(1)–S(1)
Pd(1)–Cl(1)
2.166(3)
2.2240(9)
2.2786(9)
2.3903(9)
2.2618(11)
2.2851(11)
2.3659(11)
2.2634(11)
2.2983(11)
2.3830(11)
2.2232(12)
2.2935(12)
2.3803(12)
Bond angle (◦)
N(1)–Pd(1)–P(2)
N(1)–Pd(1)–Cl(2)
P(2)–Pd(1)–Cl(2)
N(1)–Pd(1)–Cl(1)
P(2)–Pd(1)–Cl(1)
Cl(2)–Pd(1)–Cl(1)
92.02(8)
173.13(8)
88.19(3)
91.26(8)
175.50(3)
88.93(4)
N(1)–Pd(1)–P(1)
N(1)–Pd(1)–S(1)
P(1)–Pd(1)–S(1)
N(1)–Pd(1)–S(2)
P(1)–Pd(1)–S(2)
S(1)–Pd(1)–S(2)
91.67(8)
174.06(8)
85.66(4)
88.05(8)
174.17(4)
95.15(4)
N(1)–Pd(1)–P(1)
N(1)–Pd(1)–S(1)
P(1)–Pd(1)–S(1)
N(1)–Pd(1)–S(2)
P(1)–Pd(1)–S(2)
S(1)–Pd(1)–S(2)
92.94(10)
170.13(10)
84.48(4)
88.35(10)
176.57(4)
94.77(4)
N(1)–Pd(1)–P(1)
N(1)–Pd(1)–S(1)
P(1)–Pd(1)–S(1)
N(1)–Pd(1)–Cl(1)
P(1)–Pd(1)–Cl(1)
S(1)–Pd(1)–Cl(1)
91.97(10)
173.05(12)
85.28(5)
90.95(10)
171.71(5)
92.65(5)
Table 3
Heck couplings of bromobenzene with [Pd(Ph2PC6H4-2-(CH2NMe2))(SRF)2], R = C6F5 (2), C6F4-4-H (3), C6H4-2-CF3 (4), C6H4-4-F (5), C6H4-2-F (6) as
catalyst
Entry
SRF
Eg
% Conversiona
30.22
1
3.07
2
3
2.92
2.48
52.35
66.86
4
5
2.48
2.48
43.28
40.82
Reaction conditions 50 mmol of halobenzene, 60 mmol of styrene, 60 mmol of base, 4.0 × 10−5 mmol of catalyst and 5 mL of DMF, 2 h at 120 ◦C.
a
Yields obtained by GC are based on bromobenzene.

22
J.G. Fierro-Arias et al. / Journal of Molecular Catalysis A: Chemical 233 (2005) 17–27
the mechanism involving these species may involve the par-
tial dissociation of the P–N ligand and thus acting, as ex-
pected, as a hemilabile ligand, and thus generating the neces-
sary coordination site for the incoming substrates to carry out
the catalysis, at this point it results logic to think that these
species may go through the accepted Pd(II)/Pd(0) mecha-
nism given the well known tendency of sterically hindered
thiolates to stabilize low coordination and oxidation states,
thus different thiolate ligands may confer to the active cat-
alytic species different stabilities or life times for the active
species, this accounting for the different yields obtained at
equal reaction times.
3. Experimental
Fig. 2. Group Electronegativity (Eg) vs. conversion (%).
3.1. Materials and methods
To better visualize the above-mentioned effects, graphics
Unless stated otherwise, all reactions were carried out un-
der 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 Nicolet-Magna 750 FT-IR
spectrometer as nujol mulls. The 1H NMR (300 MHz) spec-
tra were recorded on a JEOL GX300 spectrometer. Chemi-
cal shifts are reported in ppm down field of TMS using the
solvent (CDCl3, δ = 7.27) as an internal standard. 31P{1H}
NMR (121 MHz) and 19F{1H} spectra were recorded with
complete proton decoupling and are reported in ppm using
85% H3PO4 and C6F6 as external standards respectively. El-
emental 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. Samples were desorbed from a nitroben-
zyl 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 refer-
ence material or, alternatively, by electric field scans with the
sample peak bracketed by two (polyethylene glycol or cesium
iodide) reference ions. GC–MS quantitative analyses were
performed on a Varian Saturn 3 with a 30.0 m DB-5 capillary
column. Melting points were determined in a MEL-TEMP
capillary melting point apparatus and are reported without
correction.
of the yield of stilbenes versus Group Electronegativity (Eg)
(Fig. 2) were plotted. From this graphic, one can observe
that as the Group Electronegativity (Eg) increases the yield
of stilbenes decreases (solid line). However, from this figure
it is not clear whether the position of the substituent in the
aromatic ring of the thiolate plays an important role in the
production of stilbenes (dotted line). Thus, although we have
observed some variation in the catalytic performance of the
complexes, at least in the present case, it is not clear whether
sterics or electronics are important and this has to be investi-
gated further, probably by employing bigger substituents in
the aromatic ring of the thiolate. However, from the graphs
it seems that a palladium system containing the P–N ligand
and low electron-withdrawing substituents may lead to ex-
cellent catalysts for the high yield palladium catalyzed Heck
reaction.
In summary, we have reported an efficient synthetic
procedure for the synthesis of monomeric [Pd(Ph2PC6H4-
2-(CH2NMe2))(SRF)2] complexes. These compounds have
been evaluated in the palladium catalyzed Heck reaction
of bromobenzene and styrene. Preliminary catalytic exper-
iments indicate these complexes to be efficient catalyst in the
Heck reaction. Analysis of the electronic effects of the thi-
olates on the performance of the different complexes reveal
some variations, however, up to this point it remains unclear
whether electronics or sterics are important. This prelimi-
nary data indicate (for complexes 1, 2 and 3) that as the value
of Eg is increased, the total yield of stilbenes decreases, in-
dicating that low electron-withdrawing substituents may fa-
vor higher yields in the Pd catalyzed Heck reaction using
[Pd(Ph2PC6H4-2-(CH2NMe2))(SRF)2] as the catalytic sys-
tem. Efforts aimed to employ these compounds in metal me-
diated organic syntheses and other C–C coupling reactions
are currently under investigation.
PdCl2 was obtained commercially from Aldrich Chem.
Co. Compounds [Pd(COD)Cl2] [10], and [Pb(SRF)2] [11];
RF = C6F5, C6F4-4-H, C6H4-2-CF3, C6H4-4-F, C6H4-2-F
were synthesized according to the published procedures.
3.2. Synthesis of the ligand [Ph2PC6H4-2-(CH2NMe2)]
To a solution of C6H5CH2NMe2 (8.85 g, 0.07 mol) in
ether (100 mL), a hexane solution of n-BuLi (45 ml of a
2.0 M, 0.9 mol) was added dropwise under stirring, the re-
sulting orange solution was allowed to stand overnight at
room temperature, after which time orange crystals were de-
From the results obtained it is clear that the different thi-
olate ligands affect the activity of the complexes in their cat-
alytic performance, according to these results we believe that

J.G. Fierro-Arias et al. / Journal of Molecular Catalysis A: Chemical 233 (2005) 17–27
23
posited. The mixture was then cooled to −78 ◦C on a dry
ice/acetone bath and a solution of PPh2Cl (13.0 g, 0.06 mol)
in ether (100 mL) added dropwise. The mixture was then
allowed to reach room temperature and stirred for one ex-
tra hour. After this time, ethanol (5 mL) and water (100 mL)
were added to quench the reaction and the product extracted
with ether (3 × 30 mL) and dried over sodium sulfate. Evap-
oration of the solvent afford a viscous oil that crystallizes
with time. The product was analyzed by 31P NMR showing
the compound to be pure enough to be used without further
purification. Yield 40% m.p. 54–56 ◦C. 1H NMR (300 MHz,
CDCl3), δ 7.32–6.89 (m, Ph, 14H), 3.62 (s, CH2, 2H), 2.08
(s, CH3, 6H); 31P{1H} NMR (121 MHz, CDCl3), δ −14.78
(s, P). Elem. Anal. Calculated for [C21H22NP] Calc. %—C:
78.97, H: 6.94. Found %—C: 78.94, H: 6.96. MS-FAB+ [M+]
= 319 m/z.
added dropwise under stirring, the resulting red-brick so-
lution was allowed to stir overnight, after which time the
solution was filtered through a short plug of Celite® and
the solvent removed under vacuum. The residue was re-
crystallized from CH2Cl2–hexane, to afford 2 as a red
microcrystalline powder. Yield 85.4%. m.p. 217–218 ◦C.
1H NMR (300 MHz, CDCl3), δ 8.2–6.8 (m, Ph, 14H),
4.2–3.1 (br, s, CH2, 2H), 2.87 (br, s, CH3, 6H); 31P{1H}
NMR (121 MHz, CDCl3), δ 20.97 (s, P); 19F{1H} NMR
3
(282 MHz, CDCl3), δ −134.6 (dd, JFo-Fm = 22.01 Hz, o-F
trans to N), −135.6 (dd, 3JFo-Fm = 22.01 Hz, o-F trans to P),
3
−163.0 (t, JFm-Fp = 22.01 Hz, p-F trans to N), −164.5 (t,
3JFm-Fp = 22.01 Hz, p-F trans to P), −166.2 (m, 4JFo-Fp = 4.8,
4
m-F trans to N), −166.8 (m, JFo-Fp = 4.8, m-F trans to
P). Elem. Anal. Calculated for [C33H22F10NPPdS2] Calc.
%—C: 48.10, H: 2.69. Found %—C: 48.14, H: 2.68. MS-
FAB+ [M+] = 822 m/z.
3.3. Synthesis of [Pd(Ph2PC6H4-2-(CH2NMe2))Cl2] (1)
3.4.2. Synthesis of [Pd(Ph2PC6H4-2-(CH2NMe2))
(SC6F4-4-H)2] (2)
To a solution of [Pd(COD)(Cl)2] (153.6 mg, 0.47 mmol)
in CH2Cl2 (15 ml), a solution of the P–N ligand [Ph2PC6H4-
2-(CH2NMe2)] (150 mg, 0.47 mmol) in CH2Cl2 (15 mL) was
added dropwise under stirring, the resulting yellow solution
was allowed to stir overnight, after which time the solution
was filtered through a short plug of Celite® and the solvent
removed under vacuum. The residue was recrystallized from
CH2Cl2–pentane, to afford 1 as a yellow microcrystalline
powder. Yield 95%. m.p. 150–151 ◦C. 1H NMR (300 MHz,
CDCl3), δ 7.9–6.3 (m, Ph, 14H), 3.7–3.1 (br, s, CH2, 2H),
2.8 (br, s, CH3, 6H); 31P{1H} NMR (121 MHz, CDCl3), δ
22.9 (s, P). Elem. Anal. Calculated for [C21H22Cl2NPPd]
Calc. %—C: 50.78, H: 4.46. Found %—C: 51.00, H: 4.42.
MS-FAB+ [M+] = 497 m/z.
[Pd(Ph2PC6H4-2-(CH2NMe2))Cl2] (50.0 mg, 0.1 mmol)
in acetone (20 mL), a solution of [Pb(SC6F4-4-H)2]
(56.9 mg, 0.1 mmol) in acetone (20 mL). Yield 90.1%. m.p.
180–181 ◦C. 1H NMR (300 MHz, CDCl3), δ 8.1–6.6 (m,
Ph, 16H), 4.1–3.2 (br, s, CH2, 2H), 2.88 (br, s, CH3, 6H);
31P{1H} NMR (121 MHz, CDCl3), δ 20.88 (s, P); 19F{1H}
3
NMR (282 MHz, CDCl3), δ −135.0 (m, JFo-Fm = 25.0 Hz,
3
o-F trans to N), −136.0 (m, JFo-Fm = 25.0 Hz, o-F trans
3
to P), −143.4 (m, JFm-Fp = 25.0 Hz, m-F trans to N),
3
−143.9 (m, JFm-Fp = 25.0 Hz, o-F trans to P). Elem. Anal.
Calculated for [C33H24F8NPPdS2] Calc. %:—C: 50.29,
H: 3.07. Found %—C: 50.24, H: 3.08. MS-FAB+ [M+]
= 787 m/z.
3.4. General procedure for the synthesis of the
complexes [Pd(Ph2PC6H4-2-(CH2NMe2))(SRF)2]
3.4.3. Synthesis of [Pd(Ph2PC6H4-2-(CH2NMe2))
(SC6H4-2-CF3)2] (3)
All the complexes were obtained using the same experi-
mental procedure. As a representative example, the synthe-
sis of [Pd(Ph2PC6H4-2-(CH2NMe2))(SC6F5)2] is described
(Scheme 3).
[Pd(Ph2PC6H4-2-(CH2NMe2))Cl2] (50.0 mg, 0.1 mmol)
in acetone (10 mL), a solution of [Pb(SC6H4-2-CF3)2]
(56.1 mg, 0.1 mmol) in acetone (20 mL). Yield 82.2%. m.p.
203–204 ◦C. 1H NMR (300 MHz, CDCl3), δ 7.9–6.8 (m, Ph,
22H), 3.9–3.2(br, s, CH2, 2H), 2.87(br, s, CH3, 6H);31P{1H}
NMR (121 MHz, CDCl3), δ 19.57 (s, P); 19F{1H} NMR
(282 MHz, CDCl3), δ −61.99 (s, F trans to N), −63.11 (s, F
trans to P). Elem. Anal. Calculated for [C35H30F6NPPdS2]
Calc. %—C: 53.88, H: 3.88. Found %—C: 53.86, H: 3.86.
MS-FAB+ [M+] = 779 m/z.
3.4.1. Synthesis of [Pd(Ph2PC6H4-2-(CH2NMe2))
(SC6F5)2] (2)
To a solution of [Pd(Ph2PC6H4-2-(CH2NMe2))Cl2]
(50 mg, 0.1 mmol) in acetone (20 mL), a solution of
[Pb(SC6F5)2] (60.7 mg, 0.1 mmol) in acetone (20 mL) was
Scheme 3. Metathesis reactions for the synthesis of the complexes [Pd(Ph2PC6H4-2-(CH2NMe2))(SRF)2].

24
J.G. Fierro-Arias et al. / Journal of Molecular Catalysis A: Chemical 233 (2005) 17–27
3.4.4. Synthesis of
[Pd(Ph2PC6H4-2-(CH2NMe2))(SC6H4-4-F)2] (4)
[Pd(Ph2PC6H4-2-(CH2NMe2))Cl2] (50.0 mg, 0.1 mmol)
in acetone (10 mL), a solution of [Pb(SC6H4-4-F)2]
(46.1 mg, 0.1 mmol) in acetone (20 mL). Yield 30.2%.
m.p. 249–250 ◦C. H NMR (300 MHz, CDCl3), δ 7.9–6.6
1
(m, Ph, 22H), 3.9–3.8 (br, s, CH2, 2H), 3.2–2.6 (br, s,
CH3, 6H); 31P{1H} NMR (121 MHz, CDCl3), δ 20.97
(s, P); 19F{1H} NMR (282 MHz, CDCl3), δ −112.64 (s,
F trans to N), −118.98 (s, F trans to P). Elem. Anal.
Calculated for [C33H30F2NPPdS2] Calc. %—C: 58.28,
H: 4.45. Found %—C: 58.26, H: 4.46. MS-FAB+ [M+]
= 679 m/z.
Scheme 4. The palladium catalyzed Heck coupling reaction using
[Pd(Ph2PC6H4-2-(CH2NMe2))(SRF)2] as catalyst.
3.4.5. Synthesis of
3.5. General procedure for the catalytic reactions
[Pd(Ph2PC6H4-2-(CH2NMe2))(SC6H4-2-F)2] (5)
[Pd(Ph2PC6H4-2-(CH2NMe2))Cl2] (50.0 mg, 0.1 mmol)
in acetone (10 mL), a solution of [Pb(SC6H4-3-F)2]
(46.1 mg, 0.1 mmol) in acetone (20 mL). Yield 49.5%.
A DMF solution (5 mL) of 50.0 mmol of bromobenzene,
60.0 mmol of styrene, and the prescribed amount of cata-
lyst was introduced into a Schlenk tube in the open air. The
tube was charged with a magnetic stir bar and an equimolar
amountofbase, sealed, andfullyimmersedina120 ◦Csilicon
oil bath. After the prescribed reaction time (2 h), the mixture
was cooled to room temperature and the organic phase was
analyzed by gas chromatography (GC/FID, GC–MS). A Var-
ian Saturn 3 with DB-5 capillary column (30.0 m) was used
for quantitative GC analysis (Scheme 4).
m.p. 240–241 ◦C. H NMR (300 MHz, CDCl3), δ 7.7–6.5
1
(m, Ph, 22H), 3.9–3.2 (br, s, CH2, 2H), 3.1–2.6 (br, s,
CH3, 6H); 31P{1H} NMR (121 MHz, CDCl3), δ 20.57
(s, P); 19F{1H} NMR (282 MHz, CDCl3), δ −103.5 (s,
F trans to N), −109.1 (s, F trans to P). Elem. Anal.
Calculated for [C33H30F2NPPdS2] Calc. %—C: 58.28, H:
4.45. Found %—C: 58.29, H: 4.50. MS-FAB+ [M+] =
679 m/z.
Fig. 3. An ORTEP representation of the structure of [Pd(Ph2PC6H4-2-(CH2NMe2))(Cl)2] (1) at 50% probability showing the atom labeling scheme.

J.G. Fierro-Arias et al. / Journal of Molecular Catalysis A: Chemical 233 (2005) 17–27
25
Fig. 4. An ORTEP representation of the structure of [Pd(Ph2PC6H4-2-(CH2NMe2))(SC6F4-4-H)2] (3) at 50% probability showing the atom labeling scheme.
Fig. 5. An ORTEP representation of the structure of [Pd(Ph2PC6H4-2-(CH2NMe2))(SC6H4-2-CF3)2] (4) at 50% probability showing the atom labeling scheme.

26
J.G. Fierro-Arias et al. / Journal of Molecular Catalysis A: Chemical 233 (2005) 17–27
Fig. 6. An ORTEP representation of the structure of [Pd(Ph2PC6H4-2-(CH2NMe2))(Cl)(SC6H4-2-F)] (7) at 50% probability showing the atom labeling scheme.
3.6. Data collection and refinement for
[Pd(Ph2PC6H4-2-(CH2NMe2))(Cl)2] (1),
[Pd(Ph2PC6H4-2-(CH2NMe2))(SC6F4-4-H)2] (3),
[Pd(Ph2PC6H4-2-(CH2NMe2))(SC6H4-2-CF3)2] (4),
[Pd(Ph2PC6H4-2-(CH2NMe2))(Cl)(SC6H4-2-F)] (7)
at calculated positions, and allowed to ride on the atoms to
which they are attached. Thermal parameters were refined for
hydrogen atoms on the phenyl groups using a Ueq = 1.2 A to
˚
precedent atom in all cases. For all complexes, the final cy-
cle of refinement was carried out on all non-zero data using
SHELXL-97 [13] and anisotropic thermal parameters for all
non-hydrogen atoms. The details of structure determinations
Crystalline red-orange prisms for 1, 3, 4 and 7 were grown
independently by slow evaporation of CH2Cl2/MeOH sol-
vent 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 sys-
˚
are given in Table 1 and selected bond lengths (A) and angles
(◦) are given in Table 2. Numbering of atoms is shown in
Figs. 3–6 respectively (ORTEP) [14].
˚
tem equipped with a Mo-target X-ray tube (λ = 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 col-
lected with a scan width of 0.3◦ in ω and an exposure time
of 10 s/frame. The frames were integrated with the Bruker
SAINT software package [12] using a narrow-frame inte-
gration algorithm. The integration of the data was done us-
ing a monoclinic unit cell in all cases, except for complex
1, where an orthorhombic cell was used to yield a total of
32875, 25976, 26646 and 35358 reflections for 1, 3, 4 and 7
respectively to a maximum 2θ angle of 50.00 (0.93 A reso-
lution), of which 3722 (1), 5654 (3), 5879 (4) and 9363 (7)
were independent. Analysis of the data showed in all cases
negligibledecaysduringdatacollections. Thestructureswere
solved by Patterson method using SHELXS-97 [13] program.
The remaining atoms were located via a few cycles of least
squares refinements and difference Fourier maps, using the
space group Pbca with Z = 8 for 1, P21/c with Z = 4 for 3 and
7 and P21/n with Z = 4 for 3. Hydrogen atoms were input
4. Supplementary material
Supplementary data for complexes 1, 3, 4 and 7
have been deposited at the Cambridge Crystallographic
Data Centre. Copies of this information are available
free of charge on request from The Director, CCDC,
12 Union Road, Cambridge, CB21EZ, UK (Fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk) quoting the deposition numbers
CCDC 256222 trough 256225.
◦
˚
Acknowledgements
JGF-A would like to thank CONACYT for financial sup-
port. We would like to thank Chem. Eng. Luis Velasco Ibarra,
´
´
M.Sc. Francisco Javier Perez Flores, QFB. Ma del Rocıo
˜
Patino and Ma. de las Nieves Zavala for their invaluable

J.G. Fierro-Arias et al. / Journal of Molecular Catalysis A: Chemical 233 (2005) 17–27
27
help in the running of the FAB+-Mass, IR and 19F{1H} spec-
tra respectively. The support of this research by CONACYT
(J41206-Q) is gratefully acknowledged.
(e) D. Morales-Morales, R.E. Cramer, C.M. Jensen, J. Organomet.
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A 189 (2002) 119;
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