Synthesis of a neutral S-P-S pincer Pd(II) complex with the proligand PhP(C6H4-SH-2)2 [phPS2H2]. The X-ray crystal structure of [Pd(phPS2)(PPh3)]

Article abstract of DOI:10.1016/S0020-1693(02)01372-5

The reactivity of the hybrid phosphorus-sulfur proligand phPS₂H₂ with the trans-[Pd(Cl)₂(PPh₃)₂] precursor has been explored. By reacting trans-[Pd(Cl)₂(PPh₃)₂] with phPS₂H₂ in the presence of NEt₃ as base, the complex [Pd(phPS₂)(PPh₃)] was obtained. A single crystal X-ray structure determination for [Pd(phPS₂)(PPh₃)] shown the compound to be square planar with the ligand phPS₂ behaving as a S-P-S pincer ligand.

Full text of DOI:10.1016/S0020-1693(02)01372-5

Inorganica Chimica Acta 346 (2003) 256Á260
/
www.elsevier.com/locate/ica
Note
Synthesis of a neutral SÃ
/
PÃ
/
S pincer Pd(II) complex with the
SH-2)2 [phPS2H2]. The X-ray crystal structure
proligand PhP(C6H4Ã
/
of [Pd(phPS2)(PPh3)]ꢀ
Valente Go´mez-Ben´ıtez, Simo´n Herna´ndez-Ortega, David Morales-Morales *
Instituto de Qu´ımica, Universidad Nacional Auto´noma de Me´xico, Cd. Universitaria, Circuito Exterior, Coyoaca´n 04510 D.F., Mexico
Received 23 May 2002; accepted 27 September 2002
Abstract
The reactivity of the hybrid phosphorusÁ
By reacting trans-[Pd(Cl)2(PPh3)2] with phPS2H2 in the presence of NEt3 as base, the complex [Pd(phPS2)(PPh3)] was obtained. A
/sulfur proligand phPS2H2 with the trans-[Pd(Cl)2(PPh3)2] precursor has been explored.
single crystal X-ray structure determination for [Pd(phPS2)(PPh3)] shown the compound to be square planar with the ligand phPS2
behaving as a SÃ
/
PÃ
/
S pincer ligand.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Crystal structures; Palladium complexes; P,S-Proligands complexes; Pincer ligands complexes
1. Introduction
ing. Moreover, the presence of these ligands in the
coordination sphere of transition metal-complexes may
render interesting behaviours in solution as these ligands
can be capable of full or partial de-ligation (hemilability)
[7] being able to provide important extra coordination
sites for incoming substrates during a catalytic process
[8]. To date, most studies have focused on bidentate
The chemistry of metal complexes of both simple and
bulky thiolate ligands has been well documented [1].
Recently, attention has increasingly been paid to the
coordination chemistry of polydentate ligands incorpor-
ating both thiolate and tertiary phosphine donor
ligands, as their combination is likely to confer unusual
structures and reactivities on their metal complexes [2].
Some of these complexes have been used as models of
biologically active centres in metalloproteins such as
ferredoxins, nitrogenase, blue copper proteins and
metallothioneins [3] or as models for the design of
complexes with potential application as radiopharma-
ceuticals [4]. These complexes have shown an intriguing
variety of structures [5] or unusual oxidation states and
enhanced solubility [6], making these species excellent
candidates for further studies in reactivity. In the
specific case of compounds with elements of the Groups
ligands such as R2PCH2CH2SH [9] and R2P(C6H4Ã
2) [10], while the potentially tridentate proligands
RP(CH2CH2SH)2 and RP(C6H4ÃSH-2)2 have received
/SH-
/
much less attention [11]. Following our current interest
in the design and synthesis of new pincer complexes with
high thermal stability for potential application in
catalytic reactions we have turn our attention to the
potentially tridentated SÃ
as it may render analogous species to those obtained
P pincer type ligands
/
PÃ
/
S ligand PhP(C6H4Ã/SH-2)2
with the previously explored PÃ
/
CÃ
/
[12].
8Á10 these may be suitable species for catalytic screen-
/
2. Experimental
2.1. Materials and methods
ꢀ Bis(phenyl-2-thiol)phenylphosphine.
* Corresponding author. Tel.: 52-55-56224514; fax:
56162217.
E-mail address: damor@servidor.unam.mx (D. Morales-Morales).
ꢀ/
ꢀ/52-55-
Unless stated otherwise, all reactions were carried out
under an atmosphere of dinitrogen using conventional
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 3 7 2 - 5

V. Go´mez-Ben´ıtez et al. / Inorganica Chimica Acta 346 (2003) 256Á
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257
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 H
NMR spectra were recorded on a JEOL GX300
spectrometer. Chemical shifts are reported in ppm
were greater than 2s(F2). Analysis of the data showed
negligible decay during data collection. The structure
was solved by Patterson method using SHELXS-97 [15]
program. The remaining atoms were located via a few
cycles of least-squares refinements and difference Four-
1
ier maps, using the space group Pc, with Zꢁ2.
/
down field of TMS using the solvent (CDCl3, dꢁ7.27)
/
Hydrogen atoms were input at calculated positions,
and allowed to ride on the atoms to which they are
as internal standard. 31P NMR spectra were recorded
with complete proton decoupling and are reported in
ppm using 85% H3PO4 as external standard. Elemental
attached. Thermal parameters were refined for hydrogen
˚
atoms on the phenyl groups using a Ueqꢁ1.2 A to
/
analyses were determined on a PerkinÁElmer 240.
/
precedent atom. The final cycle of refinement was
carried out on all non-zero data using SHELXL-97 [16]
and anisotropic thermal parameters for all non-hydro-
gen atoms. The details of the structure determination
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 nitrobenzyl alcohol (NOBA) matrix using 3 kev
xenon atoms. Mass measurements in FAB are per-
formed 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 (polyethylene glycol or cesium
iodide) reference ions. The PdCl2 was obtained from
Aldrich Chemical Co. and used without further purifi-
cation. The proligand phPS2H2 [13] and the starting
material trans-[Pd(Cl)2(PPh3)2] [14] were prepared ac-
cording to published procedures.
˚
are given in Table 1 and selected bond lengths (A) and
angles (8) in Table 2. The numbering of the atoms is
shown in Fig. 1 (ORTEP) [17].
Table 1
Summary of crystal structure data for complex [Pd(phPS2)(PPh3)] (1)
Empirical formula
Formula weight
Temperature (K)
C36H28P2PdS2
693.04
291(2)
0.71073
monoclinic
Pc
2.2. Synthesis of [Pd(phPS2)(PPh3)] (1)
˚
Wavelength (A)
To a solution of trans-[Pd(Cl)2(PPh3)2] (428 mg,
0.613 mmol) in CH2Cl2 (10 cm3) a solution (10 cm3)
of 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 filtrated and the volume
Crystal system
Space group
Unit cell dimensions
˚
a (A)
9.8375(5)
16.2918(9)
9.9065(5)
90
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
was then reduced in vacuum and the reddishÁ
residue recrystallized from a double layer solvent system
of CH2Cl2ÁMeOH. Yield 372 mg (87%).
/
brown
98.029(10)
90
3
˚
Volume (A )
Z
Dcalc (g cmꢂ3
1572.16(14)
2
1.464
/
)
2.3. Data collection and refinement for
[Pd(phPS2)(PPh3)] (1)
Absorption coefficient (mmꢂ1
F(000)
)
0.849
704
Crystal size (mm)
u Range for data collection
Index ranges
0.32ꢃ
2.09Á24.99
115h 5
115l 511
12 778
/
0.08ꢃ
/
0.07
195
/
A crystalline orange prism of [Pd(phPS2)(PPh3)],
ꢂ
ꢂ/
/
/
/11, ꢂ
/
/
k 519,
/
grown from a CH2Cl2ÁMeOH solvent system was glued
/
/
/
to a glass fiber. The X-ray intensity data were measured
at 291 K on a Bruker SMART APEX CCD-based X-ray
Reflections collected
Independent reflections
Absorption correction
Refinement method
5499 [Rint
none
ꢁ/0.0519]
diffractometer system equipped with a Mo-target X-ray
˚
full-matrix least-squares on F2
5499/2/370
tube (lꢁ0.71073 A). The detector was placed at a
/
Data/restraints/parameters
distance of 4.837 cm. from the crystal. A total of 1800
frames were collected with a scan width of 0.38 in v and
an exposure time of 10 s/frame. The frames were
integrated with the Bruker SAINT software package
using a narrow-frame integration algorithm. The inte-
gration of the data using a monoclinic unit cell yielded a
total of 12 778 reflections to a maximum 2u angle of
b
Final R indices [I ꢀ
/
2s(I)]
R1ꢁ
R1ꢁ
0.04(3)
0.895a
0.679 and ꢂ
/
0.0413, wR2ꢁ
/
0.0579
0.0608
b
R indices (all data)
Absolute structure parameter
Goodness-of-fit on F2
/0.0537, wR2ꢁ
/
ꢂ/
Largest difference peak and hole
ꢂ3
/0.550
˚
(e A
)
a
Sꢁ
/
[w(Fo)2ꢂ
total number of parameters.
R1ꢁ Fcj/jFoj, wR2ꢁ
jFoꢂ
[w((Fo)2ꢂ
/
(Fc)2)2/(nꢂ
/
p)]1/2 where nꢁ
/number of reflections
˚
50.008 (0.93 A resolution), of which 12 778 were
and pꢁ
/
b
/
/
/
/
(Fc)2)2/w(Fo)2]1/2
.
independent (Rint
ꢁ/5.19%, Rsig
ꢁ8.27%) and 4401
/

258
V. Go´mez-Ben´ıtez et al. / Inorganica Chimica Acta 346 (2003) 256Á260
/
Table 2
Selected bond lengths and angles for [Pd(phPS2)(PPh3)] (1)
agreement with a mutually trans configuration of the
phosphorus ligands. The coupling constant of JPÃP 405.6
Hz is also in agreement with a trans configuration for
the two phosphorus nuclei. Analysis by FAB-MS for 1
˚
Bond lengths (A)
Pd(1)Ã
Pd(1)Ã
Pd(1)Ã
Pd(1)Ã
/
P(1)
S(1)
S(2)
P(2)
2.2266(18)
2.2995(18)
2.3374(17)
2.3476(18)
exhibits the molecular ion at m/zꢁ692 with the appro-
/
/
/
priate isotope distribution [18]. An additional peak
corresponding to the lost of the fragment PPh3 is
/
Bond angles (8)
observed at m/zꢁ430.
/
P(1)Ã
P(1)Ã
S(1)Ã
P(1)Ã
S(1)Ã
S(2)Ã
/
Pd(1)Ã
Pd(1)Ã
Pd(1)Ã
Pd(1)Ã
Pd(1)Ã
Pd(1)Ã
/
S(1)
87.00(6)
84.13(6)
164.90(6)
177.73(8)
91.44(6)
97.04(6)
The reaction of the proligand phPS2H2 with trans-
[Pd(Cl)2(PPh3)2] it is likely to proceed in two steps
(Scheme 1), the first one which would involve the
addition of the proligand to the Pd metal center in a
bidentate manner with the concomitant elimination of
PPh3, further reaction would involve the addition of the
second S group to the metal to afford complex 1.
/
/S(2)
/
/S(2)
/
/
P(2)
P(2)
P(2)
/
/
/
/
3.2. X-ray crystal structure of [Pd(phPS2)(PPh3)] (1)
Crystals of complex 1 were obtained from a double
layer solvent system of CH2Cl2ÁMeOH as orange
/
prisms. The X-ray crystal structure analysis shows the
Pd center to be in a slightly distorted square planar
environment (Fig. 1). The coordination sphere of 1 is
constituted by the ligand phPS2 coordinated in a
tridentated SÃ
/
PÃ/S pincer like fashion and completed
by a PPh3 group located trans to the phosphorus atom
of the ligand phPS2. The main distortion from the
square planar geometry is caused by the rigidity of the
ligand and reflected in the angle S(1)Ã
164.90(6), a less pronounced distortion is observed in
the vector P(1)ÃPd(1)ÃP(2) with and angle value of
177.73(8). The PdÃS distances are slightly different
[Pd(1)ÃS(1)ꢁ2.2995(18) and Pd(1)ÃS(2)ꢁ2.3374(17)
A] and comparable to those found in other palladium
complexes like [Pd(Ph2PC6H4ÃS-2)2] [PdÃSꢁ2.308(2)
A] [19] and [Pd(Cl)(Ph2PC2H4S)(PPh3)] [PdÃSꢁ
/
Pd(1)Ã
/
S(2) to be
/
/
/
/
/
/
/
˚
/
/
/
˚
/
/
Fig. 1. An ORTEP representation of the structure of [Pd(phPS2)(PPh3)]
(1) at 50% of probability showing the atom labelling scheme.
˚
2.270(2) A] [20], the difference in bond distances can
be attributed to the strains imposed by the geometry of
the phPS2 ligand. A more marked difference is observed
3. Results and discussion
for the PdÃ
and Pd(1)ÃP(2)ꢁ
ences are the result of the constrains imposed by the SÃ
PÃS ligand. The Pd(1)ÃP(1) distance is shorter to those
observed in [Pd(Ph2PC6H4Ã
[19] and [Pd(Cl)(Ph2PC2H4S)(PPh3)] [PdÃ
/
P bond distances [Pd(1)Ã
/
P(1)ꢁ
/
2.2266(18)
˚
3.1. Synthesis and characterisation of
/
/
2.3476(18) A] once again these differ-
[Pd(phPS2)(PPh3)] (1)
/
/
/
˚
The reaction of the palladium starting material trans-
[Pd(Cl)2(PPh3)2] with half equivalent of the sulphur
proligand phPS2H2 in the presence of triethylamine as
/
S-2)2] [PdÃ
/
Pꢁ
Pꢁ
P(2) is comparable to
that found in [Pd(Cl)(Ph2PC2H4S)(PPh3)] [PdÃPPh3ꢁ
2.343(2) A] [20]. The shorter distance in Pd(1)ÃP(1)
/2.291(1) A]
/
/
2.288(2)
˚
A] [20], while the distance Pd(1)Ã
/
base yields complex [Pd(phPS2)(PPh3)] (1) as redÁ
/
/
/
orange powder in good yield. The infrared and 1H
NMR spectra of 1 are not very informative since both
analysis only show absorptions and signals correspond-
ing to the presence of the phenyl rings in the molecule.
The 31P NMR analysis is more informative, showing a
couple of doublets in the spectrum, one at 85.33 ppm
corresponding the tridentated ligand phPS2 and the
other at 22.76 ppm which is assigned to the PPh3 present
in the molecule. The multiplicity of the signals is in
/
˚
reflects the strain exerted by both S moieties, bringing
the phosphorus atom closer to the metal center, this
bond robustness may suggest this specie to be suitable
for testing in catalytic reactions, were the tridentated
phPS2 ligand should behave as its bidentated counter-
part (Ph2PC6H4Ã
/
S-2), however the fact that the ligand
phPS2 contains an extra S arm may render in higher
activity without the lost of the hemilabile properties,

V. Go´mez-Ben´ıtez et al. / Inorganica Chimica Acta 346 (2003) 256Á
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259
Scheme 1. Proposed mechanism for the formation of complex [Pd(phPS2)(PPh3)] (1).
Coordination Chemistry, The Legacy of Joseph Chatt, Royal
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(d) H.-S. Lee, J.-Y. Bae, J. Ko, Y.S. Kang, H.S. Kim, S.O. Kang,
Chem. Lett. (2000) 602;
Supplementary data have been deposited at the
Cambridge Crystallographic Data Centre, CCDC No.
186027 for complex 1. Copies of this information are
available free of charge on request from The Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
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Acknowledgements
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V.G.-B. would like to thank CONACYT and DGA-
PA for financial support. We would like to thank Chem.
Eng. Luis Velasco Ibarra and M.Sc. Francisco Javier
Perez Flores for their invaluable help in the running of
the FAB-Mass Spectra. The support of this research
by CONACYT (37288-E) and DGAPA-UNAM
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