Synthesis and characterization of new Pd(II) non-symmetrical Pincer complexes derived from thioether functionalized iminophosphoranes. Evaluation of their catalytic activity in the Suzuki-Miyaura couplings

Article abstract of DOI:10.1016/j.jorganchem.2013.09.038

The iminophosphorane ligands (Ph₃PNC₆H₄SR) [R = CH₃ (1) and C₆H₅ (2)] were easily synthesized from triphenylphosphine and 2-(methylthio)aniline or 2-(phenylthio)aniline respectively by the Horner and Oediger variation of the Kirsanov reaction. The reactivity of both ligands was explored with [Na ₂PdCl₄] to afford the corresponding non-symmetric iminophosphorane pincer derivatives [PdCl{C₆H₄(Ph ₂PNC₆H₄SR-κ³-C,N,S)}] [R = CH₃ (3) and C₆H₅ (4)]. A careful monitoring of the reaction by ³¹P{¹H} NMR experiments revealed the N,S chelated species [PdCl₂{C₆H₄(Ph ₂PNC₆H₄SR-κ²-N,S)}] [R = CH₃ (5) and C₆H₅ (6)] to be stable intermediates through the formation of the pincer compounds. Thus, carrying out the reaction for the attaining of (4) at room temperature allowed the isolation and full characterization of the chelated complex [PdCl₂{C ₆H₄(Ph₂PNC₆H₄SPh-κ- N,S)}] (6). All above mentioned species were unequivocally characterized by single crystal X-ray diffraction experiments. In addition, the newly synthesized pincer complexes [PdCl{C₆H₄(Ph₂PNC ₆H₄SR-κ³-C,N,S)}] [R = CH₃ (3) and C₆H₅ (4)] were tested as catalyst, proven to be efficient in the Suzuki-Miyaura C-C cross coupling reactions of a series of para-substituted bromobenzenes.

Full text of DOI:10.1016/j.jorganchem.2013.09.038

Journal of Organometallic Chemistry 749 (2014) 287e295
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and characterization of new Pd(II) non-symmetrical Pincer
complexes derived from thioether functionalized iminophosphoranes.
Evaluation of their catalytic activity in the SuzukieMiyaura couplings
Sandra Ramírez-Rave a, Fabiola Estudiante-Negrete b, Rubén A. Toscano b,
,
Simón Hernández-Ortega b, David Morales-Morales b, Jean-Michel Grévy a
*
a Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Avenida Universidad # 1001, Colonia Chamilpa, CP 62209 Cuernavaca,
Morelos, Mexico
b Instituto de Química, Universidad Nacional Autónoma de México, Cd. Universitaria, Circuito Exterior, Coyoacán, 04510 México DF, Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
The iminophosphorane ligands (Ph3P]NC6H4SR) [R ¼ CH3 (1) and C6H5 (2)] were easily synthesized
from triphenylphosphine and 2-(methylthio)aniline or 2-(phenylthio)aniline respectively by the Horner
and Oediger variation of the Kirsanov reaction. The reactivity of both ligands was explored with
[Na2PdCl4] to afford the corresponding non-symmetric iminophosphorane pincer derivatives [PdCl
Received 10 May 2013
Received in revised form
24 September 2013
Accepted 25 September 2013
{C6H4(Ph2P]NC6H4SR-
k
3-C,N,S)}] [R ¼ CH3 (3) and C6H5 (4)]. A careful monitoring of the reaction by 31
P
{1H} NMR experiments revealed the N,S chelated species [PdCl2{C6H4(Ph2P]NC6H4SR-
k
2-N,S)}] [R ¼ CH3
Keywords:
(5) and C6H5 (6)] to be stable intermediates through the formation of the pincer compounds. Thus,
carrying out the reaction for the attaining of (4) at room temperature allowed the isolation and full
Pincer compounds
Palladium compounds
SuzukieMiyaura couplings
Catalysis
Crystal structures
Iminophosphoranes
characterization of the chelated complex [PdCl2{C6H4(Ph2P]NC6H4SPh-k-N,S)}] (6). All above mentioned
species were unequivocally characterized by single crystal X-ray diffraction experiments. In addition, the
newly synthesized pincer complexes [PdCl{C6H4(Ph2P]NC6H4SR-
were tested as catalyst, proven to be efficient in the SuzukieMiyaura CeC cross coupling reactions of a
series of para-substituted bromobenzenes.
k
3-C,N,S)}] [R ¼ CH3 (3) and C6H5 (4)]
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
activity when compared to their symmetric analogs [4], for
instance in SuzukieMiyaura cross-couplings.
Pincer complexes bearing a monoanionic tridentate backbone
constitute an exceptional class of organometallic compounds.
Mainly due to their extraordinary reactivities and high catalytic
activity in numerous chemical transformations. The vast majority
of pincer complexes reported so far include symmetrical ligands
(biphosphines, dithioethers, diamines etc.) and their structural
features as well as physical and chemical properties have been
amply reviewed [1,2]. However, in recent years there has been an
increasing interest in non-symmetric pincer compounds, particu-
larly those combining “hard” and “soft” donor atoms, in the search
of increasing activities and enhanced reactivities in potentially
relevant catalytic transformations [3]. Some of these compounds
have demonstrated hemilabile properties and high catalytic
On the other hand, the chemistry of iminophosphines has had a
steady growth and been the focus of considerable interest in the
last decade. In this sense, functionalized iminophosphines with
additional donor groups attached either to the imine or phosphine
backbones are of particular interest since they can be easily
modified to fine tune the chemical properties of their metal com-
plexes. The potential of functionalized iminophosphines in coor-
dination chemistry is now well established, and recent studies have
highlighted their utility as ligands in homogeneous catalysis [5]. In
addition, iminophosphines can undergo CeH bond activation [6].
Thus, turning the neutral molecule into an anionic (or dianionic)
ligand increasing the number of possibilities for potential coordi-
nation. This chemical property has enabled iminophosphines, in
many cases, to easily provide cyclometallated complexes avoiding
the use of more complicated metallation methods such as trans-
metallation with lithium derivatives [7].
* Corresponding author. Tel.: þ52 77 73297997x6041.
E-mail addresses: damor@unam.mx (D. Morales-Morales), jeanmichelg@
gmail.com (J.-M. Grévy).
Urriolabeitia et al. reported in 2008 the straightforward palla-
dation via CeH activation of non-stabilized iminophosphines
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.09.038

288
S. Ramírez-Rave et al. / Journal of Organometallic Chemistry 749 (2014) 287e295
Ph3P]NeCH2eR (R ¼ CO2Me, CONMe2, CH2SMe, NC5H4-2) as a
consequence of their treatment with [Pd(OAc)2]. They observed
that the resulting anionic ligand often ended up just bonded as a
C,N-chelate to the Pd center. Moreover, these ligands exhibited a
preference for a tridentated coordination (C,N,Oe, C,N,Se or C,N,Ne
) leading to palladacycles remarkably stable towards the addition of
phosphine ligands. However, in comparison with the increasing
number of publications devoted to the chemistry of iminophos-
phines functionalized with ether, amine or phosphine moieties
(N w N, N w O, N w P) examples of iminophosphines functional-
ized with sulfur fragments are still scarce. To the best of our
knowledge, besides one compound reported by Urriolabeitia
(R ¼ CH2SMe), only two other examples of mixed iminophosphine-
thioether or -thiolate derivatives have been described. A titanium
phosphinimide with a pendant hemilabile thioether attached to the
phosphine reported by Stephan [8]. This compound was tested as
catalyst in the polymerization of ethylene exhibiting an increasing
stability at elevated reaction temperatures. The other example re-
ported by Auffrant [9], explored the coordination chemistry of the
iminophosphorane-thiolate anion [(PhNPPh2CH2SLi)THF] with
Pd(II) and Ru(II), these species were not further used in catalysis.
Until recently sulfur-containing ligands were neglected from
their use in catalysis due to the common belief that sulfur would
poison the complexes rendering the potential catalytic systems
inefficient. However, in the last decade this view has changed and
sulfur containing ligands and their complexes have had a renais-
sance and nowadays it is common to find reports including sulfur or
other chalcogen containing ligands and their complexes used suc-
cessfully in different potentially relevant catalytic transformations
[10]. Thus, in this opportunity we would like to report our findings
on the study of the coordination chemistry of iminophosphine li-
gands functionalized with sulfur-containing groups to Pd(II) start-
ing materials and the screening of the catalytic activity of these
complexes.
were desorbed from a nitrobenzyl alcohol (NOBA) matrix using
3 keV xenon atoms.
2.2. Synthesis of [Ph3P]NC6H4SCH3] (1)
To a solution of Ph3PBr2 (9.75 ꢀ 10ꢁ3 mol) in 25 ml of freshly
distilled benzene under N2 atmosphere at 0 ꢂC, a solution of
NH2C6H4SCH3 (1.18 ml, 9.75
ꢀ
10ꢁ3 mol) with Et3N
(19.75 ꢀ 10ꢁ3 mol) in 20 ml of benzene was added dropwise. The
addition was completed in 20 min. The resulting suspension was
taken to room temperature and further stirred for 4 h, and
additional 30 h at reflux temperature. Then the resulting sus-
pension was filtered through celite and the solvent was evapo-
rated to dryness, giving a yellowish powder. mp: 125 ꢂC. Yield
(3.35 g, 86%). MS-FABþ: 499 (35%) [M]þ. Anal. Calc. for
C
25H22N1P1S1 (399.49). C, 75.16; H, 5.55; N, 3.81. Found: C, 75.14,
H, 5.58, N, 3.79. IR (v, cmꢁ1): 1327 (vPN). 1H NMR (CDCl3):
d
2.323
(s, 3H, SCH3), 6.675 (dd, 1H3 SC6H4N), 6.940 (t, 1H4 SC6H4N),
7.737 (m, 1H5 SC6H4N), 6.125 (dd, 1H6 SC6H4N), 7.435 (m, 6Ho
PPh3), 7.361 (m, 6Hm PPh3), 7.706 (m, 3Hp). 13C{1H} NMR (CDCl3):
d
14.734 (Ci, SCH3), 136.900 (d, 3JPC ¼ 24.3, CieS, SC6H4N), 147.280
(CieN, SC6H4N), 126.743 (C3, SC6H4N), 132.010 (C4, SC6H4N),
129.447 (C5, SC6H4N), 129.352 (C6, SC6H4N), 131.250 (d, 1JPC ¼ 100,
Ci PPh3) 128.857 (d, 2JPC ¼ 10.6, Co PPh3), 136.808 (d, 3JPC ¼ 9.1, Cm
PPh3), 132.020 (d, JPC ¼ 3, Cp PPh3). 31P{1H} NMR (CDCl3):
4
d
¼ 2.80.
2.3. Synthesis of [Ph3P]NC6H4SPh] (2)
To a solution of Ph3PBr2 (9.75 ꢀ 10ꢁ3 mol) in 25 ml of freshly
distilled benzene under N2 atmosphere at 0 ꢂC, was added drop-
wise a solution of NH2C6H4SPh (1.96 g, 9.75 ꢀ 10ꢁ3 mol) with Et3N
(19.75 ꢀ 10ꢁ3 mol) in 20 ml of benzene. The addition was
completed in 20 min. The resulting suspension was taken to room
temperature and stirred for 4 h and additional 30 h at reflux tem-
perature. Then the resulting suspension was filtered through celite
and the solvent evaporated to dryness, giving a yellowish powder.
mp: 116 ꢂC. Yield (3.9 g, 85%). MS-FABþ: 462(25%) [M]þ. Anal. Calc.
for C30H24N1P1S1 (461.56 IR): C, 79.07; H, 5.42; N, 3.40. Found: C,
2. Experimental
2.1. Material and methods
Solvents were dried and distilled under nitrogen using standard
procedures [11] before use. [Na2PdCl4], PPh3, Br2, 2-(methylthio)
aniline and 2-(phenylthio)aniline were obtained commercially
from Aldrich Chem. Co and were used without further purification.
NEt3 was dried with CaH2 and distilled under nitrogen atmosphere.
The ligand Ph3P]NC6H4SMe was prepared by a slight modification
of a literature procedure [12]. Mass measurements (FABþ) were
performed at a resolution of 3000 using magnetic field scans and
the matrix ions as the reference material or, alternatively, by elec-
tric field scans with the sample peak bracketed by two (poly-
ethylene glycol or cesium iodide) reference ions. NMR spectra were
acquired at ambient temperature with Varian Gemini 200 MHz and
Varian UnityInova 400 MHz instruments in CDCl3, which was used
as internal reference. 31P NMR spectra were recorded with com-
plete proton decoupling and are reported in ppm using 85% H3PO4
as external standard. Melting points are uncorrected and they were
measured in a Mel Temp II device using sealed capillaries. Infrared
spectra were recorded in KBr using a Bruker Vector 22 instrument.
Catalytic activity experiments were carried out in sealed Schlenk
tubes and a silicon oil bath. GC analyzes were carried out in an HP
5890A flame ionization detector (FID) and HP 5890 SERIES II with a
5971A mass selective detector gas chromatographs, and an HP-1
capillary column (25.0 m) from HewlettePackard. Elemental ana-
lyses were determined on a PerkineElmer 240. Positive-ion FAB
mass spectra were recorded on a JEOL JMS-SX102A mass spec-
trometer operated at an accelerating voltage of 10 kV. Samples
79.08; H, 5.43; N, 3.38. (v, cmꢁ1): 1330(vPN). NMR (CDCl3):
d
¼ 7.19
(dd, 1H3 SC6H4N), 6.973 (t, 1H4 SC6H4N), 7.235 (m, 1H5 SC6H4N),
6.780 (dd, 1H6 SC6H4N), 7.496 (m, 6Ho PPh3), 7.418 (m, 6Hm PPh3),
7.736 (m, 3Hp). 13C{1H} NMR (CDCl3):
d 164.563 (Ci, SPh), 136.726
(CieS, SC6H4N), 149.517 (CieN, SC6H4N), 126.466 (C3, SC6H4N),
130.110 (C4, SC6H4N), 130.988 (C5, SC6H4N), 126.861 (C6, SC6H4N),
1
2
131.200 (d, JPC ¼ 98.1, Ci PPh3) 131.881 (d, JPC ¼ 14.6, Co PPh3),
128.703 (d, 3JPC ¼ 11.8, Cm PPh3), 132.876 (d, 4JPC ¼ 8.8, Cp PPh3). 31
P
{1H} NMR (CDCl3):
d
¼ 0.29.
2.4. Synthesis of [PdCl{C6H4(Ph2P]NC6H4SMe-k-C,N,S)}] (3)
[Na2PdCl4] (0.015 g, 5 ꢀ 105 mol) was slowly added under N2
atmosphere to a mixture of 1 (0.02 g, 5 ꢀ 10ꢁ5 mol) and excess
Na3PO4 (0.0123 g, 7.5 ꢀ 10ꢁ5 mol) in 1,2-dichloroethane (20 ml).
The resulting reaction was refluxed for 1.5 h. After this time, the
solvent was removed under vacuum leading to the isolation of a
bright yellow powder. Mp (ꢂC): 152. Yield (0.022 g, 82%). IR (v,
cmꢁ1): 1269 (vPN). MS-FABþ: 541 (5%) [M]þ. Anal. Calc. for
C
25H21Cl1N1P1Pd1S1 (540.35): C, 55.67; H, 3.92; N, 2.59. Found: C,
55.68; H, 3.57; N, 2.55. 1H NMR (CDCl3):
d
¼ 2.830 (eSCH3), 6.873
(dd, 1H3 SC6H4N), 7.024 (t, 1H4 SC6H4N), 8.173 (d, 1H5 SC6H4N),
7.251 (dd, 1H6 SC6H4N), 7.865 (m, 4Ho PPh2), 7.567 (m, 4Hm PPh2),
7.658 (m, 2Hp PPh2). 13C{1H} NMR (CDCl3):
d 15.303 (eSCH3),
4
125.447 (d, JPC ¼ 26.8, CieS, SC6H4N), 152.855 (CieN, SC6H4N),
129.133 (C3, SC6H4N), 128.817 (C4, SC6H4N), 126.736 (C5, SC6H4N),

S. Ramírez-Rave et al. / Journal of Organometallic Chemistry 749 (2014) 287e295
289
Table 1
Crystal data and structure refinement for compound (1), (2), (3), (4) and (6).
(1)
(2)
(3)
(4)
(6)
Emp. formula
Formula mass
Crystal system
Space group
C31H28NPS
477.57
Monoclinic
P21/c
10.005(2)
26.972(6)
9.496(2)
94.538(3)
2554.4(9)
4
C36H30NPS
539.64
Monoclinic
P21/n
9.5436(13)
19.416(3)
15.812(2)
98.817(2)
2895.4(7)
4
C29H31ClNOPPdS
614.43
Monoclinic
P21/n
11.1834(9)
15.8514(13)
15.8230(13)
92.6880(10)
2801.9(4)
4
C30.25H23.50Cl1.50NPPdS
623.61
Monoclinic
P21/n
9.3538(8)
22.0993(19)
14.0577(12)
103.7770(10)
2822.3(4)
4
C30H24Cl2PdS
638.83
Monoclinic
P21/n
10.3189(10)
16.6942(16)
16.6933(15)
107.618(2)
2740.8(4)
4
ꢀ
a [A]
ꢀ
b [A]
ꢀ
c [A]
b
[ꢂ]
3
ꢀ
V [A ]
Z
Dc [Mg mꢁ3
]
1.242
0.209
1.238
0.193
1.457
0.912
1.468
0.950
1.548
1.027
m
[mmꢁ1
]
Refl. collected
18,373
18,823
22,890
23,026
29,863
Unique reflections
Data/restr./param.
R1/wR2[I > 2s(I)]
Goodness of fit
T [K]
4636 [Rint ¼ 0.0959]
4636/0/309
0.0643/0.1059
1.020
5306 [Rint ¼ 0.0638]
5306/300/407
0.0469/0.0962
0.918
5132 [Rint ¼ 0.0495]
5132/141/363
0.0343/0.0671
0.898
5145 [Rint ¼ 0.1033]
5145/48/353
0.0388/0.0929
0.967
5023 [Rint ¼ 0.0425]
5023/0/325
0.0392/0.0956
1.066
173(2)
173(2)
298(2)
298(2)
173(2)
l
(Mo-Ka)
0.71073
0.71073
0.71073
0.71073
0.71073
136.113 (C6, SC6H4N), 125.822 (d, 1JPC ¼ 113.02, Ci PPh2), 132.996 (d,
2.7. SuzukieMiyaura couplings using complex (3) as catalyst
3
2JPC ¼ 10, Co PPh2), 129.484 (d, JPC ¼ 11.8, Cm PPh2), 133.566 (d,
1
4JPC ¼ 2.8, Cp PPh2), 141.937 (d, JPC ¼ 141.937, CieP, PC6H4Pd),
A DMF solution (5 ml) of 4.32 mmol of halobenzene, 4.75 mmol
of phenylboronic acid, and the prescribed amount of catalyst (1%
mol) was introduced into a Schlenk tube in the open air. The tube
was charged with a magnetic stir bar, an excess of base (Na3PO4,
9.5 mmol), sealed and then fully immersed in a 110 ꢂC silicon oil
bath. After the prescribed reaction time (5 h), the mixture was
cooled to room temperature and the organic phase analyzed by gas
chromatography (GCeMS) by duplicate.
156.927 (d,2JPC ¼ 31.9, CiePd, PC6H4Pd).31P{1H} NMR (CDCl3):
d
¼ 47.41.
2.5. Synthesis of [PdCl{C6H4(Ph2P]NC6H4SPh-k-C,N,S)}] (4)
[Na2PdCl4] (0.015 g, 5 ꢀ 105 mol) was slowly added under N2
atmosphere to a mixture of 2 (0.02 g, 5 ꢀ 10ꢁ5) and excess of
Na3PO4 (0.0123 g, 7.5 ꢀ 10ꢁ5 mol) in 1,2-dichloroethane (20 ml).
The resulting medium was refluxed for 1.5 h. After this reaction
time, the solvent was removed and a deep yellow þpowder was
obtained, mp: 150 ꢂC. Yield (0.021 g, 81%). MS-FAB : 603 (15%)
[M]þ. Anal. Calc. for C30H23Cl1N1P1Pd1S1 (602.42): C, 59.98; H, 3.95;
N, 2.33. Found: C, 60.01; H, 3.99; N, 2.30. IR (v, cmꢁ1): 1270 (vPN).
2.8. Data collection and refinement for compounds (1), (2), (3), (4)
and (6)
Crystals of the ligands (1) and (2) were grownbyslow evaporation
of saturated benzene solutions in a closed Schlenk flask. Crystals of
the pincer complexes (3) and (4), were obtained by slow diffusion of
PriOH over saturated solutions of the corresponding compound in
CH2Cl2 in closed vials and finally compound (6) was crystallized by
slowevaporation of a saturated solution in CH2Cl2 in a closed vial. The
X-ray intensity data were measured at 173(2) K for compounds (1)
and (2) and at 298 K for the complexes (3), (4) and (6) on a Bruker
NMR (CDCl3):
d
¼ 7.190 (dd, 1H3 SC6H4N), 7.269 (t, 1H4 SC6H4N),
8.270 (d, 1H5 SC6H4N), 7.370 (dd, 1H6 SC6H4N), 7.800 (m, 4Ho PPh2),
7.474 (m, 4Hm PPh2), 7.622 (m, 2Hp PPh2). 13C{1H} NMR (CDCl3):
4
d
125.365 (d, JPC ¼ 16.0, CieS, SC6H4N), 153.903 (CieN, SC6H4N),
134.775 (C3, SC6H4N), 128.817 (C4, SC6H4N), 136.606 (C5, SC6H4N),
131.070 (C6, SC6H4N), 128.457 (d, 1JPC ¼ 102.4, Ci PPh2), 132.892 (d,
2JPC ¼ 10.3, Co PPh2), 129.420 (d, JPC ¼ 11.7, Cm PPh2), 133.442 (d,
3
SMART APEX CCD-based three-circle X-ray diffractometer system
4JPC ¼ 2.6, Cp PPh2), 141.456 (d, 1JPC ¼ 143.2, CieP, PC6H4Pd), 167.935
ꢀ
using graphite mono-chromated Mo-K
a
(l
¼ 0.71073 A) radiation.
(s, CiePd, PC6H4Pd).31P{1H} NMR (CDCl3):
d
¼ 47.27.
-N,S)}] (6)
The detector was placed at a distance of 4.837 cm from the crystals in
all cases. The frames were integrated with the Bruker SAINTsoftware
package [13] using a narrow-frame integration algorithm. The
structures were solved by Patterson method using SHELXS-97 [14]
program. The details of the structure determinations are given in
Table 1. Geometric calculations were done using PLATON [15].
2.6. Synthesis of [PdCl2{C6H4(Ph2P]NC6H4SPh-
k
[Na2PdCl4] (0.013 g, 4.38 ꢀ 10ꢁ5 mol) was slowly added at 0 ꢂ
C
under N2 atmosphere to a solution of (2) (0.02 g, 4.38 ꢀ 10ꢁ5 mol)
in CH2Cl2 (20 ml). After 1 h of stirring the formation of a deep or-
ange turbidity was evident in the reaction media. The suspension
was filtered and a very insoluble oranþge powder was oþbtained. mp:
165 ꢂC. Yield (0.021 g, 84%). MS-FAB : 638 (13%) [M] . Anal. Calc.
for C30H23Cl2N1P1Pd1S1 (637.88): C, 56.49; H, 3.63; N, 2.20. Found:
C, 56.50; H, 3.65; N, 2.24. IR (v, cmꢁ1): 1267 (vPN). 1H NMR (CDCl3):
3. Results and discussion
Iminophosphines (1) and (2) were easily synthesized in high
yield by the classical HornereOediger method [16] from commer-
cially available amines in refluxing benzene (Scheme 1).
d
¼ 7.195 (dd, 1H3 SC6H4N), 7.207 (t, 1H4 SC6H4N), 7.754 (m, 1H5
SC6H4N), 7.372 (dd, 1H6 SC6H4N), 7.604 (m, 6Ho PPh3), 7.483 (m,
6Hm PPh3), 7.388 (m, 3Hp PPh3). 13C{1H} NMR (CDCl3):
d 123.426 (d,
4JPC ¼ 5.3, CieS, SC6H4N), 157.253 (CieN, SC6H4N), 133.117 (C3,
SC6H4N), 129.853 (C4, SC6H4N), 133.849 (C5, SC6H4N),128.960 (C6,
SC6H4N), 127.014 (d, 1JPC ¼ 96.6, Ci PPh3), 129.180 (d, JPC ¼ 8.8, Co
2
3
4
PPh3), 128.690 (d, JPC ¼ 13.2, Cm PPh3), 133.309 (d, JPC ¼ 2.6, Cp
PPh3). 31P{1H} NMR (CDCl3):
d
¼ 33.09.
Scheme 1. Synthesis of the ligands.

290
S. Ramírez-Rave et al. / Journal of Organometallic Chemistry 749 (2014) 287e295
Fig. 1. Molecular structure of (1) (H atoms are omitted for clarity; thermal ellipsoid set
ꢀ
at 50% probability). Selected bond lengths (A): P1eN1 1.571(2), S1eC2 1.770(3), S1eC7
1.798(3). Selected bond angles (ꢂ): C2eS1eC7 102.30(2), N1eP1eC8 115.66(1), N1e
P1eC14 116.60(1), N1eP1eC20 105.25(1), P1eN1eC1 128.98(2). Torsion angles (ꢂ):
C1eN1eP1eC20 172.28, C1eN1eP1eC8 70.32, C1eN1eP1eC14 54.51, C6eC1eN1eP1
16.43.
Fig. 2. Molecular structure of ligand (2) (H atoms are omitted for clarity; thermal
ellipsoid set at 50% probability). Selected bond lengths (A): P1eN1 1.569(19), S1eC2
ꢀ
1.773(2), S1eC7 1.775(2). Selected bond angles (ꢂ): C2eS1eC7 103.56(10), N1eP1eC13
103.57(10), N1eP1eC19 106.77(10), N1eP1eC25 105.83(10), P1eN1eC1 129.47(10).
Torsion angles (ꢂ): C1eN1eP1eC13 160.46, C1eN1eP1eC19 83.01, C1eN1eP1eC25
42.81, C6eC1eN1eP1 14.26.
Multinuclear NMR (31P{1H}, 1H and 13C{1H} NMR) and IR spec-
troscopy data confirmed the proposed structures for the ligands (1)
and (2). For both compounds the corresponding 31P{1H} NMR
The coplanarity of this phenyl ring bonded to P, the aniline ring
and the carbon on the sulfur atom originates from two different
intramolecular interactions (Fig. 3). The first interaction being a
contact between the proton at the ortho position of the phenyl ring
and the iminic nitrogen [C21eH21/N1 in (1) and C14eH14/N1 in
spectra, show unique signals at
d 2.80 and 0.30 ppm for (1) and (2)
respectively [17]. In the IR spectra the characteristic signals due to
the
n
(P]N) vibration [18] were observed at 1327 and 1346 cmꢁ1
for (1) and (2) respectively. The results obtained from the 1H and
13C{1H} NMR spectra were also in agreement with the proposed
formulations exhibiting the expected signals for the sulfur con-
ꢀ
(2) (2.57 A)]. This interaction is evident from the short H/N dis-
ꢀ
tances of 2.50 and 2.57 A for (1) and (2) respectively. But also from
taining functional groups, at
d
2.30 and 14.73 ppm for the 1H and
the smaller N1P1Cipso angle of 105.26(1)ꢂ in (1) and 106.49(1)ꢂ in
(2), when compared with the two other angles between the PeN
bond and the aromatic rings of the triphenylphosphine group.
These features are comparable with other triphenyl(phenylimino)
13C{1H} respectively in the case of ligand (1)eSCH3. While the
signal corresponding to the carbon SeCi in ligand (2)eSC6H5 can be
observed at d
164.6 ppm in the 13C NMR spectra. Both ligands in the
solid state are stable in the open atmosphere for months. However,
in solution they become unstable undergoing decomposition in
time on contact with ambient moisture.
ꢂ
ꢀ
ꢀ
phosphoranes found in the literature [2.51(2) Ae2.67 A; 105 e
110ꢂ] [19,20]. The second intramolecular interaction is a 1,4-type
interaction found between the sulfur atom and the iminic nitro-
Crystals of (1) and (2) suitable for their analysis by single crystal
X-ray diffraction techniques were grown by slow diffusion of Et2O
over saturated solutions of the compounds in benzene in closed
Schlenk flasks under N2 atmosphere. Compound (1) crystallizes in
the monoclinic space group (P 21/c) (Fig. 1) while compound (2)
does it in the monoclinic space group (P 21/n) (Fig. 2). There is one
molecule of benzene in the asymmetric unit and four molecules in
the unit cell. The data collection and refinement parameters are
collected in Table 1.
ꢀ
ꢀ
gen. The S1/N1 distances in (1) (2.78 A) and (2) (2.76 A) are rather
short compared to similar compounds reported in the Cambridge
Structural Database [21]. Those interactions are observed in a large
number of organosulfur compounds and are believed to control the
conformation of small and large molecules [22].
The reaction of the iminophosphine ligands (1) or (2) with
[Na2PdCl4] (1:1 M ratio) in refluxing 1,2-dichoroethane (1.5 h) in
presence of excess of Na3PO4 afforded the corresponding
Compounds (1) and (2) are monomeric and show the P atom
into a slightly distorted tetrahedral environment, surrounded by
three C atoms and the iminic N atom. As expected the N atom is sp2
ꢀ
ꢀ
hybridized and the NeP distances,1.571(2) A for (1) and 1.569(19) A
for (2), fall in the usual range for aminophosphine compounds
ꢀ
ꢀ
(1.54 A to 1.64 A) [19]. The molecular geometries are similar for
both ligands. As can be seen from the values of the C6eC1eN1eP1
torsion angles [ꢁ16.4(5)ꢂ for (1) and ꢁ14.3(3)ꢂ for (2)], the aniline
ring is almost coplanar with the PeN bond. The values of torsion
angles C1eN1eP1eC14 [ꢁ54.4(3)ꢂ] in (1) and C1eN1eP1eC25
[42.81(2)ꢂ] in (2), indicate that one of the phenyl rings of the PPh3
group is only slightly twisted compared to the plane formed by the
PeN bond and the aniline ring.
Fig. 3. Schematic drawing of non-bonded interactions present in (1) and (2).

S. Ramírez-Rave et al. / Journal of Organometallic Chemistry 749 (2014) 287e295
291
R
S
[Na2PdCl4]
base
N
P
N
P
Pd
S
R
Cl
R= Me(1), Ph(2)
R= Me(3), Ph(4)
Scheme 2.
orthometallated complexes (3) and (4) in high yields (Scheme 2).
Both complexes were obtained as air- and moisture-stable yellow
solids that are soluble in chlorinated solvents and spectroscopic, as
well as analytical data, are consistent with the proposed structures.
The IR spectra of (3) and (4) show that the ligands are N-bonded,
since the position of the n(P]N) vibration has been shifted to lower
energy in comparison with the free ligand, e.g. 1269 cmꢁ1 for (3)
and 1252 cmꢁ1 for (4).
On the other hand, multinuclear NMR analysis of complexes
(3) and (4) confirms that orthopalladation reaction has occurred.
For both complexes, the 1H NMR shows signals due to the
presence of the PdC6H4 moiety in the aromatic region. In addi-
tion, for complex (3) a sharp signal due to the presence of the
Fig. 4. Molecular structure of (3) (H atoms are omitted for clarity; thermal ellipsoid set
at 50% probability). Selected bond lengths [A]: Pd1eCl1 2.310(1), Pd1eS1 2.349(1),
ꢀ
SCH3 group can be observed at
d 2.83 ppm. While in the case of
Pd1eN1 2.036(2), Pd1eC20 1.988(3), P1eN1 1.620(3). Selected bond angles [ꢂ]: Cl1e
Pd1eS1 92.38(3), Cl1ePd1eN1 177.50(8), Cl1ePd1eC20 94.69(1), S1ePd1eN1
85.25(8), S1ePd1eC20 172.89(1), N1ePd1eC20 87.67(1). Selected torsion angles [ꢂ]:
C1eN1eP1eC19e176.94, C1eN1eP1eC7 64.76, C1eN1eP1eC13e59.55, C3eC2eN1e
P1 11.06.
(4) the signals due to the SPh fragment overlap with those of the
other aromatic protons present in the molecule. The 13C{1H}
NMR exhibits signals for the expected functional groups and
further confirms the proposed structures for (3) and (4) by
showing the orthopalladated carbon atoms at
d
156.9
(2JPC ¼ 31.9) for (3) and at 167.9 ppm for (4) [23].
The molecular geometries are similar for both complexes and
due to their planarity they can be related to non-symmetrical
pincer complexes. As seen by the torsion angle values for C1e
C2eN1eP1 (3) and of C2eC1eN1eP1 (4), the aniline ring in the
Crystals of complexes (3) and (4) were obtained by slow diffu-
sion of PriOH in saturated solutions of both compounds in CH2Cl2.
Both structures evidence orthometallation and show the Pd atoms
into a slightly distorted square planar environments (Figs. 4 and 5
respectively). These results confirm unequivocally the previously
proposed structures based in the spectroscopic evidence and the
CeNeS tridentate ligand can be seen as a non-symmetric pincer
ligand.
The bite angles of the chelating moieties for complex (3) are
87.70(1)ꢂ (N1ePd1eC14) and 85.25(7)ꢂ (N1ePd1eS1) and the sum
of the bond angles around the Pd1 atom is 360.03(12)ꢂ. The
molecule deviates only slightly from planarity: for instance the
maximum deviations found in the best least-square planes defined
by (C20eC19eP1eN1ePd1) and (Pd1eN1eC2eC1eS1) are only
ꢀ
ꢀ
0.05 A and 0.01 A respectively. The dihedral angle between these
two planes in (3) is only 5.05ꢂ. In the case of (4), the bite angles for
the tridentate ligand [N1ePd1eC14 ¼ 87.40(1)ꢂ and N1ePd1e
S1 ¼ 84.34(8)ꢂ] and the sum of the angles around the Pd1
[360.05(13)ꢂ], are very similar to those found in (3). This molecule
also deviates only slightly from planarity, and the maximum de-
viations found in the planes defined by (Pd1eC14eC13eP1eN1)
ꢀ
ꢀ
and (Pd1eS1eC2eC1eN1) are of 0.004 A and 0.017 A. The dihedral
angle between the two planes is 5.09ꢂ.
The Pd1eCmetallated bond distance in both complexes
ꢀ
ꢀ
[1.99(3) A (3) and 1.99(4) A (4)] fall in the usual range for this
type of bond [24,7]. The Pd1eN1 bond distances in (3) and (4) are
ꢀ
identical and similar to other reported in the literature [2.03(2) A
Fig. 5. Molecular structure of (4) (H atoms are omitted for clarity; thermal ellipsoid set
ꢀ
ꢀ
at 50% probability). Selected bond lengths [A]: Pd1eCl1 2.316(1), Pd1eS1 2.377(1),
for (3) and 2.03(2) A for (4)]. The P1eN1 bond distances
Pd1eN1 2.031(1), Pd1eC20 1.998(3), P1eN1 1.622(3). Selected bond angles [ꢂ]: Cl1e
Pd1eS1 93.71(4), Cl1ePd1eN1 177.88(8), Cl1ePd1eC14 94.65(11), S1ePd1eN1
84.34(8), S1ePd1eC14 170.33(10), N1ePd1eC14 87.37. Selected torsion angles [ꢂ]: C1e
N1eP1eC13e175.21, C1eN1eP1eC25 66.49, C1eN1eP1eC19 57.83, C6eC1eN1eP1
5.21.
ꢀ
ꢀ
[1.62(3) A (3) and 1.62(3) A (4)] are equal even within the
experimental error, and fall in the expected range. Finally, the
Pd1eS1 [2.349(1) (3) and 2.377(1) A (4)] bond distances also lay
within the reported values [25].
ꢀ

292
S. Ramírez-Rave et al. / Journal of Organometallic Chemistry 749 (2014) 287e295
complexes remains more coplanar with the N]P bond than in the
free ligands, certainly because of the strained conformation. Like-
wise, the values of torsion angles C2eN1eP1eC19 (3) and C1eN1e
P1eC13 (4), indicate that phenyl ring D bonded to P is coplanar
with the P]N bond and the aniline ring A. This situation is
somewhat different when compared with the free ligands, where
ring D is slightly twisted from the plane of ring A and the P]N bond
(Figs. 1 and 2). For both complexes, the data collection and refine-
ment parameters are collected in Table 1.
The reactions for the attaining of the palladacycles, showed
some interesting changes in color as the reaction proceeded,
indicative of different species to be forming through the reaction.
Thus, in order to study these changes we performed the metallation
reactions at room temperature. Hence, the stoichiometric reaction
of [Na2PdCl4] with either ligand (1) or (2) in DCE in presence of a
base, first produced a deep orange solution with the formation of a
small amount of precipitate. As the reaction evolved and upon
further warming, the precipitate slowly dissolved and the reaction
mixture changed from the initial orangey color to yellow. Analysis
of the reaction mixture by 31P NMR at the initial stages of the re-
action afforded spectra that in both cases exhibited a signal at about
d
32 ppm [d 31.87 ppm for (1) and d 32.83 for (2)]. Signals that
completely disappeared upon warming the reaction mixtures up
Scheme 3.
(few hours of reflux). Analysis by 31P NMR at this point provided
NMR spectra that only showed single signals at about
d 47 ppm.
collected after 40 min (T ¼ 60 ꢂC). At this stage, the free ligand is no
Signals that are consistent with the sole presence of the pincer
complexes (3) and (4) already described (vide supra). In view of
these observations we decided to carry out VT-NMR experiments in
order to follow the formation of complex (4) (Fig. 6). Thus,
[Na2PdCl4], ligand (2), Na3PO4 and DCE where combined in an NMR
tube at room temperature. The 31P NMR spectrum collected a T ¼ 0
only shows, as expected, a signal due to the presence of the free
longer detectable and the only signal observed is that due to the
presence of the N,S chelated complex (6) at
time the reaction surpasses 60 ꢂC, a new signal is starting to show at
47.27 ppm indicating the clear formation of the pincer product
d 32.83 ppm. By the
d
and this transformation is completed only after 15 min (T ¼ 75 ꢂC).
These results are coherent with the formation of an intermediate
coordination N,S-chelated complex to finally produce the more
stable palladacyle product upon warming via electrophilic substi-
tution on a phenyl ring of the PPh3 ligand (Scheme 3) [6].
ligand at
d 1.87 ppm, with a minor signal at d 32.83 ppm corre-
sponding to the intermediate N,S chelated complex (6). After this
time the reaction was gradually warmed and a new spectrum was
Fig. 6. 31P{1H} VT-NMR experiments for the synthesis of complex (4).

S. Ramírez-Rave et al. / Journal of Organometallic Chemistry 749 (2014) 287e295
293
Table 2
SuzukieMiyaura couplings using complex (3) as catalyst precursor.
P
N
[Pd] =
Pd
S
OH
B
Me
Cl
Br
OH
1.0 mol % [Pd], Na3PO4, DMF
110oC, 5 h
+
R
R
p-Bromobenzene
% Conversiona
% Values of
conversion
NH2
55
NH2
OCH3
CH3
H
Br
Br
Br
Br
Br
Br
Br
Br
OCH3
CH3
H
60.5
65
Fig. 7. Molecular structure of (6) (H atoms are omitted for clarity; thermal ellipsoid set
ꢀ
at 30% probability). Selected bond lengths (A): Pd1eCl1 2.300(11), Pd1eCl2 2.296(12),
Pd1eS1 2.271(12), Pd1eN1 2.051(3), P1eN1 1.623(3). Selected bond angles (ꢂ): Cl1e
Pd1eCl1 91.73(4), Cl1ePd1eS1 90.41(4), Cl1ePd1eN1 173.61(9), S1ePd1eN1 83.32(9),
Cl2ePd1eS1174.45(4), Cl2ePd1eN1 94.63(9). Selected torsion angles (ꢂ): C1eN1eP1e
C13 36.10, C1eN1eP1eC25 150.33, C1eN1eP1eC19 85.75, C6eC1eN1eP1 28.05.
70
Cl
77
Cl
Performing the above mentioned reaction at room temperature
in the absence of base allowed us to isolate the intermediate
compound (6). Crystals of (6) suitable for their analysis by single
crystal X-ray diffraction techniques were obtained by slow evapo-
ration of a saturated CH2Cl2 solution of the crude product at room
temperature, thus confirming unequivocally the N,S-chelated na-
ture of the product (Fig. 7).
CHO
>99
93
CHO
COCH3
COCH3
CN
95
CN
From these results it can be observed that the Pd atom is located
into a slightly distorted square planar environment and completing
the coordination sphere two chloride atoms (Cl1 and Cl2) and the
iminophosphorane ligand coordinated in a bidentated manner
through the S1 and N1 atoms. The angles, 79.74ꢂ (S1ePdeN1) and
91.73ꢂ (Cl1ePdeCl2), clearly evidence the distortion around the
NO2
>99
NO2
Br
a
Yields obtained by GC are based on remaining bromobenzene and are the
average of two runs.
ꢀ
ꢀ
metal. Both PdeCl bond distances, 2.300(11) A and 2.296(12) A, lay
in the usual range for similar distances reported for this type of
compounds [24]. The Pd1eN1 bond distance of 2.051(3) A is also
The well known thermal stability of palladacylces and in
particular of pincer complexes both in solid state and in solution,
allowed us to start the catalytic experiments in the absence of an
inert atmosphere. And given the fact that these CeC couplings
depend of a series of parameters, initial experiments were focused
to determine the optimal conditions for these catalytic systems.
Thus, experiments were performed to evaluate the effect of the
reaction temperature, solvent, base and catalyst loading. Hence, we
first studied the reaction of bromobenzene and phenylboronic acid
using complexes (3) and (4) as catalysts. Based on previously re-
ported results [28] we set the reaction temperature at 110 ꢂC and
used DMF as preferred solvent, employing a 1% loading of catalyst
for 5 h. From these experiments it was observed that it is indeed
complex (3) the one that afforded the best conversions and using
complex (4) under analogous reaction conditions only provided
lower conversions when compared with those attained with (3).
From here all the following experiments were performed with
complex (3). Further, given the fundamental importance that the
proper selection of base plays in the SuzukieMiyaura couplings we
decided to explore the effect of different bases under the above
mentioned reaction conditions using (3) as catalyst. Thus, by using
Na2CO3 as base a 35% conversion was observed after 5 h. Replace-
ment of this base with Na3PO4 improved the conversion to 50%
ꢀ
comparable with other reported values in the literature [25], and is
only slightly longer than the distances found in the pincer com-
ꢀ
plexes (3) and (4) [2.036(2) and 2.031(1) A]. The P1eN1 bond dis-
ꢀ
tance of 1.623(3) A is comparable with the distances found in
ꢀ
complexes (3) and (4) [1.620(3) and 1.622(3) A] and is slightly
longer than the distances found in the free ligands (1) and (2)
ꢀ
[1.571(2) and 1.569(19) A]. Finally, as a result of the palladation
ꢀ
process the Pd1eS1 bond distance 2.271(12) A is smaller than those
ꢀ
observed in complexes (3) and (4) of 2.349(1) and 2.377(1) A
respectively. The data collection and refinement parameters for this
compound are collected in Table 1.
To the best of our knowledge Pd(II) pincer complexes including
the ligands reported in this work have not yet been employed in
catalysis. These compounds can be relevant and may exhibit
enhanced reactivity due to the presence of the thioether moieties
that in turn may confer hemilabile properties to these complexes.
Thus, the catalytic activity of the CeNeS pincer palladacycles was
explored in SuzukieMiyaura reactions. Hence, complexes (3) and
(4) were tested as catalysts in the SuzukieMiyaura CeC cross
couplings of different para-substituted bromobenzenes and phe-
nylboronic acid [26,27].

294
S. Ramírez-Rave et al. / Journal of Organometallic Chemistry 749 (2014) 287e295
Preliminary catalytic experiments of the new non-symmetric
-CHO
98
88
78
68
58
48
-NO2
pincer complexes were undertaken in SuzukieMiyaura CeC cross
coupling reactions. Showing the methyl substituted complex (3) to
be an efficient catalyst in this process. The fact that these catalytic
experiments were performed open to the air and no apparent
decomposition was observed provides and optimistic view to
further try this compound in other cross coupling reactions. Efforts
aimed to prove this are currently under progress in our
laboratories.
-COCH3
-CN
-Cl
Acknowledgments
-H
We gratefully acknowledged DGAPA-UNAM (IN201711-3) and
CONACYT for the financial support of this research (CB2009/134528
and CB2010/154732) and Ph. D. scholarships for S.R.-R. and F.E.-N.
-CH3
-OCH3
-NH2
Appendix A. Supplementary material
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
CCDC 937679e937683 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
Hammett Parameter (σ)
Fig. 8. % of conversion for the SuzukieMiyaura couplings catalyzed by (3) of different
p-substituted bromobenzenes versus Hammett parameter.
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