Synthesis, catalytic activity, and photophysical properties of 5,6-membered Pd and Pt SCS′-pincer complexes based on thiophosphorylated 3-amino(hydroxy)benzoic acid thioanilides

Article abstract of DOI:10.1039/c0dt01154a

Novel unsymmetrical SCS′-pincer ligands, 1-[PhNHC(S)]-3-[Ph ₂P(S)NH]-C₆H₄ (3) and 1-[PhNHC(S)]-3-[Ph ₂P(S)O]C₆H₄ (7), bearing a thiocarbamoyl moiety in combination with thiophosphorylamino- and thiophosphoryloxy-donating groups, respectively, were obtained via thiophosphorylation of 3-amino- and 3-hydroxy-benzoic acid (thio)anilides 1 and 6. Direct cyclometallation of the central benzene ring in the ligands 3 and 7 in reaction with (PhCN) ₂MCl₂ (M = Pd, Pt) as a metal precursor afforded κ³-SCS′-hybrid pincer complexes 8, 9 with 5- and 6-membered fused metallacycles in good to high yields (67-95%). The complexes 8 and 9 were characterized by multinuclear NMR (³¹P, ¹H, ¹³C) and IR spectroscopy as well as single-crystal X-ray crystallography. Palladium complexes 8a and 9a were shown to be active catalysts for the Suzuki-Miyaura cross-coupling reaction. In the solid state the ligands 3 and 7 as well as their Pt(ii) and Pd(ii) complexes 8 and 9 are luminescent at 300 K. The emission of the complexes has the different origin depending on the metal nature.

Full text of DOI:10.1039/c0dt01154a

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PAPER
Synthesis, catalytic activity, and photophysical properties of 5,6-membered Pd
and Pt SCS¢-pincer complexes based on thiophosphorylated
3-amino(hydroxy)benzoic acid thioanilides†
D. V. Aleksanyan,a V. A. Koz lov , a Y. V. Nelyubina,a K. A. Lyssenko,a L. N. Puntus,b E. I. Gutsul,a N. E. Shepel,a
A. A. Vasil’ev,c P. V. Pe t rov s k i i a and I. L. Odinets*a
Received 2nd September 2010, Accepted 16th November 2010
DOI: 10.1039/c0dt01154a
Novel unsymmetrical SCS¢-pincer ligands, 1-[PhNHC(S)]-3-[Ph2P(S)NH]-C6H4 (3) and
1-[PhNHC(S)]-3-[Ph2P(S)O]C6H4 (7), bearing a thiocarbamoyl moiety in combination with
thiophosphorylamino- and thiophosphoryloxy-donating groups, respectively, were obtained via
thiophosphorylation of 3-amino- and 3-hydroxy-benzoic acid (thio)anilides 1 and 6. Direct
cyclometallation of the central benzene ring in the ligands 3 and 7 in reaction with (PhCN)2MCl2 (M =
3
Pd, Pt) as a metal precursor afforded k -SCS¢-hybrid pincer complexes 8, 9 with 5- and 6-membered
fused metallacycles in good to high yields (67–95%). The complexes 8 and 9 were characterized by
multinuclear NMR (31P, 1H, 13C) and IR spectroscopy as well as single-crystal X-ray crystallography.
Palladium complexes 8a and 9a were shown to be active catalysts for the Suzuki–Miyaura
cross-coupling reaction. In the solid state the ligands 3 and 7 as well as their Pt(II) and Pd(II) complexes
8 and 9 are luminescent at 300 K. The emission of the complexes has the different origin depending on
the metal nature.
backbone bearing various substituents at the nitrogen atoms of
Introduction
thioamide units have been developed and investigated for photo-
Organometallic pincer complexes bearing a specific tridentate
and electroluminescence properties as well as catalytic activity.
scaffold primarily were in focus of mere fundamental research.
Thus, the metallacycles I based on isophthalic acid thioamides
However, since their successful introduction into homogeneous
were found to exhibit strong emission in the glassy frozen state as
catalysis in 1990s1 they got a second wind and now represent a
diverse and rapidly developing area.2,3 At present, a great variety
of PCP, NCN and SCS pincer complexes are known, but the
metallacycles of the latter type are still less studied compared
to the former ones. For the classical SCS pincer complexes one
may attribute those formed by bis(thioether) ligands, however,
of particular interest are non-classical SCS bisthiocarbamoyl
derivatives (Fig. 1). SCS and SNS palladium and platinum(II) pin-
cer complexes with benzene,4 pyrrole,5 pyridine,4g,6 and azulene7
well as in the solid state at room temperature.4c,e,f Their applica-
tion to light-emitting diodes and phosphorescence modulation
upon exposure to chemical stimuli or via introduction into a
poly(vinyl)pyrrolidone matrix are also described.4h,8,9 Moreover,
palladium complexes of types I and III appear to be rather
good catalysts for the Heck cross-coupling of 4-iodotoluene with
styrene.4d,g Incorporation of a few SNS palladacycles III into the
Negishi cross-coupling revealed their high efficiency providing
turnover numbers up to 6100000.6
Furthermore, SCS and SNS pincer complexes V–IX derived
from bis(thiophosphorylated) toluene,10 pyridine,11,12 indene,13 and
pyrrol,14 form the second family of non-classical SCS and SNS
pincer complexes with thione sulfur atoms described in the
literature (Fig. 2). Similar to their thioamide-based analogues,
complexes V possess photoluminescence properties in the glassy
frozen state (M = Pd, Pt) and in the solid state at room
temperature (M = Pt). At the same time, the related complexes
VI bearing a pyridine central unit (either neutral or quaternized)
practically did not show emission even in the frozen state. The data
concerning the catalytic performance of pincer complexes with
thiophosphoryl donating arms, to the best of our knowledge, are
restricted by the comparative investigation of palladium-catalyzed
aA. N. Nesmeyanov Institute of Organoelement Compounds, Russian
Academy of Sciences, 28 Vavilova Street, Moscow, 119991, Russia. E-mail:
odinets@ineos.ac.ru
bInstitute of Radioengineering and Electronics, Russian Academy of Sciences,
11-7 Mokhovaya str., Moscow, 125009, Russia
cN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of
Sciences, 47 Leninsky Prosp., 119991, Moscow, Russia
† Electronic supplementary information (ESI) available: Fragment of
packing in the molecule 3, the absorption spectra of ligands 3, 7 and their
Pd and Pt pincer complexes 8a,b, 9a,b, and the excitation and emission
spectra of complex 9b at 77 K, the luminescence spectra of ligands 3,7, and
complex 9a at 77 K, and the results of the B3LYP/6-311G** calculations.
CCDC reference numbers 791555–791558. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c0dt01154a
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Fig. 1 SCS and SNS thioamide-based palladium pincer complexes.
Fig. 3 5,5 and 5,6-membered hybrid thiocarbamoyl/thiophosphoryl
based metallacycles.
the ligand having two various coordinating arms of different
lengths, namely C S and P S, able to form 5- and 6-membered
fused metallacycles and compare their photophysical and catalytic
properties with those of their 5,5-membered analogues. Therefore,
in this paper we report the facile synthesis of the desired hybrid
pincer ligands as well as the intermediate 3-amino- and 3-
hydroxy-benzoic acid thioanilides as suitable precursors of such
ligands, and their 5,6-membered palladium and platinum pincer
complexes with coordinated thioamide and thiophosphoryloxy or
thiophosphorylamino groups. The effect of introduction of O- and
NH-bridges between the thiophosphoryl moiety and benzene
backbone on the catalytic performance in the Suzuki cross-
coupling and the photophysical properties of the metallacycles
is also discussed.
Fig. 2 SCS and SNS thiophosphoryl-based palladium pincer complexes.
electrophilic allylation of aldehydes with allylstannanes using Pd-
SCS catalyst V and the related SPS pincer complex with a central
4
l -phosphinine unit, which was less active.15 In light of the results
of DFT calculations, it was concluded that the reaction does not
1
involve the commonly proposed h -allyl palladium intermediates
but proceeds via a Lewis acid-related pathway.
Recently, we have elaborated a novel hybrid pincer system
possessing a thiocarbamoyl moiety along with thiophosphoryl
group directly bonded with the central benzene core. Reacting
with PdCl2(PhCN)2, these ligands readily undergo direct cy-
clopalladation to afford the corresponding SCS¢ palladium(II)
pincer complexes A in high yields (Fig. 3).16 As both their
symmetric prototypes, i.e. the above mentioned bisthiocarbamoyl
and bisthiophosphoryl palladium pincer complexes, palladacycles
A also exhibited luminescent properties in the glassy frozen state
and in the solid state at room temperature. However, in addition,
they were found to be active catalysts for the Suzuki cross-coupling
reaction.
Taking into account the scarce literature data showing that
extension of the linkage between one of the two donor atoms
and central benzene ring could offer additional reactivity17
and enhance catalytic activity of pincer complexes,18 it seemed
reasonable to develop unsymmetrical pincer complexes B with
Results and discussion
Synthesis of the ligands
A convenient synthetic route for the desired unsymmetrical
SCS¢-pincer ligands evidently could be based on 3-amino and
3-hydroxybenzoic acid (thio)anilides as suitable key precur-
sors for further thiophosphorylation. In the case of thiocar-
bamoyl/thiophosphorylamino based pincer ligand 3 thiophos-
phorylation of 3-aminobenzamide 1 with Ph2P(S)Cl followed by
transformation of intermediate amide 2 into its sulfur counterpart
via thionation with Lawesson reagent was the method of choice
(Scheme 1). In turn, 3-aminobenzamide 1 was synthesized from
commercially available 3-nitrobenzoic acid according to the liter-
ature procedure comprising transformation to the corresponding
acid chloride followed by aminolysis and reduction of the nitro
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Scheme 1 Synthesis of thiocarbamoyl-thiophosphorylamino based pincer ligand 3.
Scheme 2 Synthesis of thiocarbamoyl-thiophosphoryloxy based pincer ligand 7.
group with SnCl2.19 Note that after water work-up amide 2 was
isolated as a stable hydrate.
To obtain the analogue of the pincer ligand 3 bearing a
thiophosphoryloxy group instead of the NH–P S moiety (ligand
7), thiophosphorylation with Ph2P(S)Cl of 3-hydroxybenzoic acid
6 as a key precursor was used. The desired substituted phenol 6 was
prepared by demethylation of 3-methoxybenzoic acid thioamide 5,
readily available via the reaction of the Grignard reagent prepared
from 3-bromoanisole with phenylisothiocyanate (Scheme 2).
The NMR (1H, 31P and 13C) and IR spectra of the ligands 3
and 7 unambiguously confirm the depicted structures. Thus, the
31P NMR spectra of 3 and 7 show singlet signals at ca. 53 and
84 ppm, respectively, which are typical for the phosphorus atoms
of thiophosphorylamino and thiophosphoryloxy groups. In the
1H NMR spectra of both ligands the singlet resonances of the
thioamide hydrogen atoms are observed at ca. 9 ppm along with
the signals of aromatic protons. In the corresponding spectra of
the ligand 3 the doublet signal of the NH-bridge proton adjacent
to the thiophosphoryl group appears at 5.20 ppm (2JPH = 6.6 Hz).
All the signals in the 13C NMR spectra of both ligands could
be unambiguously assigned to the certain carbon atoms. The
intensive bands at ca.1510 and 630–640 cm-1 in the IR spectra
of the ligands 3 and 7 are characteristic for the absorption of
C(S)NH and P S functionalities, respectively. The molecular
structure of the thioamide 3 was also confirmed by the single
crystal X-ray analysis (Fig. 4). According to these data, the
geometrical parameters of the molecule 3 are within the ranges
expected for thiophosphorylaminobenzene derivatives. The only
Fig. 4 The general view of 3 in representation of atoms by thermal
ellipsoids (p = 50%).
a “head-to-tail” and “back-to-back” manner (Fig. S1, ESI†). The
hydrogen bonds involving the H(2N) atom and the C S group
◦
˚
(N ◊ ◊ ◊ S 3.419(2) A, NHS 166(1) ) assemble these associates into
infinite tapes in such a way (“head-to-tail” and “face-to-face”)
that the substituents in the meta-positions of the benzene core
of the neighboring molecules are turned by 180◦ with respect to
each other (Fig. S1, ESI†). The additional stabilization of the
above tapes in the crystal of 3 is achieved owing to weaker C–
H ◊ ◊ ◊ S, C–H ◊ ◊ ◊ p and p ◊ ◊ ◊ p interactions; the smallest C ◊ ◊ ◊ S or
˚
C ◊ ◊ ◊ C distances are 3.697(2), 3.572(2) and 3.383(2) A, respectively.
The same types of intermolecular contacts, although the p ◊ ◊ ◊ p
interactions are now replaced by the H ◊ ◊ ◊ H ones, complete the
formation of the 3D-framework.
parameter worth mentioning is the mutual disposition of the P
S
and C S functionalities in 3. These groups deviate in opposite
directions from the benzene core with the torsion angle between
them being 100.4(1)◦, and the angles they form with the plane
of the core are 30.1(1) and 64.7(1)◦, respectively. In the crystal,
the acidic hydrogen atoms of the NH groups are involved in N–
H ◊ ◊ ◊ S hydrogen bonding of intermediate strength. In particular,
the H(1N) atom binds to the sulfur atom of the P S group
Synthesis of pincer complexes
The reaction of the ligands 3 and 7 with (PhCN)2PdCl2 readily
proceeded as cyclometallation of the central phenyl ring to afford
the corresponding SCS¢ pincer palladium(II) complexes 8a and
9a with 5 and 6-membered fused metallacycles in good to high
yields (79–95%, Scheme 3). By contrast, the related OCS ligand 2
◦
˚
(N ◊ ◊ ◊ S 3.382(2) A, N–H–S 151(1) ) leading to the formation of
the centrosymmetric dimers with the molecules of 3 organized in
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the case of palladium species) and reddish (in the case of platinum
ones) crystalline solids. All the metallacycles obtained are air and
moisture stable, as well as thermally stable up to ~150 ◦C (8a, 9a)
and 210 ◦C (8b, 9b).
The structures of 8 and 9 were unambiguously confirmed by
multinuclear NMR and IR spectroscopy as well as elemental
analysis data. Thus, the 31P NMR spectra of the complexes exhibit
an upfield shift relative to the signals of the corresponding free
ligands (Dd = 7.1–10.6 ppm) strongly indicating the coordination
either of NH–P S and O–P S groups. In the 31P NMR spectra
of platinum complexes 8b, 9b the typical platinum satellites are
Scheme 3 Cyclometallation of thiophosphoryl-thiocarbamoyl pincer
ligands.
2
bearing a carbamoyl moiety did not react with the same palladium
precursor proving again that double S,S-coordination is the
crucial factor for the cyclopalladation of SCS pincer ligands.4e,10
To accomplish the cyclopalladation very mild conditions (room
temperature, ambient atmosphere, acetonitrile, dichloromethane
or the mixture of the latter with MeOH (1 : 1) as a solvent)
can be used. Performing the reaction in acetonitrile, it takes a
few days to achieve about 95% yield of the complex 9a (isolated
product), while its nitrogen-bridged analogue 8a was obtained in
the comparable yield (93%) upon stirring the reaction mixture
for only several minutes. To the best of our knowledge, this is
the fastest procedure for pincer complex preparation. The rate
of cyclopalladation for the ligand 7 significantly increased using
CH2Cl2 as a solvent (24 h vs. 4 days) and, under these conditions,
the desired product was isolated in a yield of 82%. Interestingly,
when the reaction of (PhCN)2PdCl2 with thiophosphorylamino-
based ligand 3 was performed in CH2Cl2 solution, the 31P NMR
monitoring of the reaction course revealed no difference in the
ratio of reaction products obtained after 24 h and 4 days,
hence suggesting establishment of an equilibrium. Addition of
MeOH shifted the equilibrium position to the formation of the
corresponding pincer complex 8a which precipitated from this
mixed solvent. The positive effect of MeOH on the rate of
cyclometallation of hybrid SCS¢ pincer ligands was previously
noted for the thiophosphoryloxy-thiophosphorylbenzenes20 and
thiophosphoryloxybenzaldimines.21
observed with the coupling constant JPPt about 60 Hz. In the
1H NMR spectra, the intensities of aromatic proton signals are
reduced by 1H proving occurrence of cyclometallation, and the
signals of both thioamide and thiophosphorylamino NH protons
are strongly deshielded upon complexation (Dd = 3–4 ppm). In the
13C NMR spectra of palladium complexes 8a, 9a the signals of the
C2 atom, at which the metallation is occurred, are characterized
with the greatest downfield shift (almost 20 ppm) as well as with
3
an increase in JCP (in 1.5 times), although the resonances of the
other carbon atoms are also indicative of the complex formation
(see Experimental). In general, the patterns in the 13C spectra
of the platinum complexes 8b, 9b are similar to those of 8a, 9a,
however, the signals of the C2 atoms bound with the platinum are
not observed. A higher frequency shift of n(C–N) in the IR spectra
of the complexes 8, 9 comparing with that for the corresponding
ligand, serves as additional evidence for the coordination of the
sulfur atom of the thiocarbamoyl moiety. For example, the n((S)C–
N) band for 8a was observed at 1538 cm-1 instead of 1516 cm-1
for the corresponding ligand 3. A lower frequency shift of the
absorption bands corresponding to the valent vibrations of P
S
bonds (vs. those for the free ligands 3 and 7) indicate participation
of these groups in the coordination by metal ion.16
Furthermore, single-crystal X-ray diffraction analysis con-
firmed the structures of the palladium pincer complexes 8a, 9a
and that of the platinum complex 9b (Fig. 5–7). In general,
More severe conditions were required for direct cycloplatination
of the above NH- and O-bridged SCS¢-pincer ligands 3 and
7. Thus, the corresponding platinum(II) pincer complex 8b was
obtained in good yield (74%) from the reaction of ligand 3 with
(PhCN)2PtCl2 under refluxing in acetonitrile for 4 h. In the case
of thiophosphoryloxy-substituted ligand 7, a comparable yield
(67%) of the pincer complex 9b was achieved only upon heating
in benzonitrile solution (120 ◦C, 3 h). Moreover, we failed to
perform direct cycloplatination of 3-thiophosphorylbenzoic acid
thioamides, i.e. the ligands of the prototype A, using (PhCN)2PtCl2
as a metal precursor (the 31P NMR monitoring revealed formation
of several non-metallated Pt(II) complexes). Therefore, unlike the
cyclopalladation, the reaction of pincer ligands combining N–
C
S and P S coordination sites with (PhCN)2PtCl2 proved
to be rather sensitive to the ligand structure. Apparently, the
difference in reactivity of thiocarbamoyl-thiophosphoryl based
pincer ligands towards platinum(II) precursor may be explained by
the difference of the electron density of the lone pair of the P
sulfur atom decreasing in the series N–P(S)Ph2 > O–P(S)Ph2>
CAr–P(S)Ph2.
S
Fig. 5 The general view of 8a in representation of atoms by thermal
ellipsoids (p = 50%) illustrating the formation of the H-bond with the
molecule of DMSO. The bond lengths of the metallacycle (A) are:
˚
The complexes 8 and 9 spontaneously crystallized (except for
the complex 9b) from the reaction mixtures providing yellow (in
Pd(1)–Cl(1) 2.4004(5), Pd(1)–C(2) 2.0167(19), Pd(1)–S(1) 2.3409(5), and
Pd(1)–S(2) 2.2725(5).
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Pd(1)C(2)S(1)S(2) and Pd(1)Cl(1)S(1)S(2) planes, and deviations
of the chlorine atoms vary in relatively narrow ranges of 170.3(2)–
◦
◦
˚
173.5(2) , 6.9(2)–11.7(2) , and 0.29(1)–0.47(1) A, respectively.
Hence, the presence of the NH group in 8a and an oxygen atom
in 9a has little influence on the palladacyclic moiety, although
the disposition of phenyl rings is affected by the resulted crystal
packing effects.
The platinum pincer complex 9b was found to be isostructural
with the palladium one 9a, hence resulting in the similarity of
their geometrical parameters. Thus, the 5-membered rings of
the independent molecules 9b_B and 9b_B present an envelope
and a flattened envelope with the S(2) and C(1) atoms deviating
˚
by 0.19(1) and 0.11(1) A, respectively. The 6-membered rings
are characterized by a half-chair conformation (the S(1) and
˚
P(1) atoms deviate by 0.13 and -0.72 A in 9b_A, and -0.37
and 0.43 in 9b_B). The parameters describing the configuration
of the metal atom are as follows: the angle C(2)Pt(1)Cl(1)
170.8(2)–172.8(2)◦, the angle between the planes Pt(1)C(2)S(1)S(2)
and Pt(1)Cl(1)S(1)S(2) 9.3(2)–10.8(2)◦, and the deviation of the
Fig. 6 The general view of one independent molecule (A) of complex 9a
in representation of atoms by thermal ellipsoids (p = 50%) illustrating the
formation of the H-bond with the molecule of DMSO. The bond lengths
˚
of the metallacycle (A) in two independent molecules are: Pd(1)–Cl(1)
˚
chlorine atom 0.38(1)–0.44(1) A.
2.3773(8) and 2.3934(8), Pd(1)–C(2) 2.018(3) and 2.020(3), Pd(1)–S(1)
2.3519(8) and 2.3641(8), and Pd(1)–S(2) 2.2584(8) and 2.3934(8).
The peculiarities of the supramolecular binding in the com-
plexes X-rayed are also similar to each other. In the crystal of
9b, the molecules are held together with the molecules of the
solvent, namely dimethyl sulfoxide (DMSO), owing to the N(1)–
˚
H(1N) ◊ ◊ ◊ O(1S) hydrogen bonds (N ◊ ◊ ◊ O 2.781(6) and 2.846(6) A,
NHO 162(1) and 161(1)◦). The pairs thus formed are assembled
into the 3D-framework by weaker C–H ◊ ◊ ◊ Cl, C–H ◊ ◊ ◊ O, C–
H ◊ ◊ ◊ p and C–H ◊ ◊ ◊ S contacts. Similarly, both palladium pincer
complexes 8a, 9a also form crystallo-solvates with DMSO by
means of the N(1)–H(1N) ◊ ◊ ◊ O(1S) hydrogen bonds (for 8a:
◦
˚
N ◊ ◊ ◊ O 2.799(2) A, NHO 159(1) ; for 9a: N ◊ ◊ ◊ O 2.775(4) and
◦
˚
2.851(4) A, NHO 163(1) and 162(1) ). In 8a, the second proton
donor, which is the NH group, leads to the formation of addi-
˚
tional hydrogen bond N(2)–H(2N) ◊ ◊ ◊ Cl(1) (N ◊ ◊ ◊ Cl 3.2086(17) A,
NHCl 155(1)◦) accompanied by a certain elongation of the Pd–Cl
˚
bond (2.4004(5) A). At the same time, the Pd–Cl bonds in the two
independent molecules of the second complex 9a are shorter only
˚
˚
by 0.023 A (9a_A) and 0.007 A (9a_B). The difference in the latter
values is, apparently, caused by the variation of C–H ◊ ◊ ◊ Cl binding
in the crystal. In 9a, the chlorine atom of molecule A forms two
contacts with the phenyl groups of the second complex moiety
Fig. 7 The general view of one independent molecule (A) of the complex
9b in representation of atoms by thermal ellipsoids (p = 50%) illustrating the
formation of the H-bond with the molecule of DMSO. The bond lengths
˚
(Cl ◊ ◊ ◊ C 3.588(4)–3.618(4) A); while that of molecule B shows five
˚
of the metallacycle (A) in two independent molecules are: Pt(1)–Cl(1)
contacts, with its symmetry-related analogue A, the first complex
moiety, and the DMSO molecule (Cl ◊ ◊ ◊ C 3.574(3)–3.775(4) A).
In addition, one can expect that an intramolecular C(8A)–H ◊ ◊ ◊ Cl
contact (Cl ◊ ◊ ◊ C 4.121(4) A) also occurs in molecule B. In 8a, there
2.3821(12) and 2.3880(11), Pt(1)–C(2) 2.000(5) and 2.016(5), Pt(1)–S(1)
2.3380(12) and 2.3429(12), and Pt(1)–S(2) 2.2561(13) and 2.2510(13).
˚
˚
the main geometrical parameters of the palladacycle moiety in
the complex 8a and in two independent molecules of 9a (A
and B) are rather typical for the 5,6-membered SCS¢-pincer
complexes.16,17 The conformation of the 5-membered rings is an
are no other interactions involving the chlorine atom. The 3D-
framework formation in the crystal of 8a is completed by weaker
S ◊ ◊ ◊ H–C, p ◊ ◊ ◊ S(1S), and p ◊ ◊ ◊ H–C contacts with DMSO, C–
H ◊ ◊ ◊ p and p ◊ ◊ ◊ p interactions between complex species. In 9a, the
pincer moieties A and B are assembled with the DMSO molecules
by C–H ◊ ◊ ◊ O and p ◊ ◊ ◊ H–C and with each other by C–H ◊ ◊ ◊
p contacts; there are also C–H ◊ ◊ ◊ S and C–H ◊ ◊ ◊ p interactions
between the molecules of type A.
˚
envelope with the S(2) atom deviating by 0.33(1) A (8a) and
˚
0.21(1) A (9a_B), or a flattened envelope, with the C(1) atom
˚
deviating by 0.12(1) A (9a_A). The 6-membered ring is in a half-
chair conformation with the deviation of the S(1) and P(1) atoms;
˚
the corresponding values are equal to -0.87(1) and 0.23(1) A (8a),
˚
˚
0.17(1) and -0.68(1) A (9a_A), -0.56(1) and 0.44(1) A (9a_B). In
all cases, the Pd(1) atom is characterized by a distorted square-
planar configuration with folding along the S(1) ◊ ◊ ◊ S(2) line. The
corresponding C(2)Pd(1)Cl(1) angles, dihedral angles between the
Catalytic studies
A combination of thermal stability and readily available multiple
structure modifications of pincer complexes, affording fine tuning
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120 ◦C over 5 h using K3PO4 as a base and Bu4NBr as an additive.
Table 1 summarizes the results obtained. For all complexes under
investigation the normal dependence on the electron withdrawing
properties of the substituent X at the aryl bromide was observed.
However, application of unsymmetrical complexes 8a and 9a
provided higher conversions over a shorter period of time (5 h
vs. 6 h) even at significantly reduced catalyst loadings (0.01
mol% vs. 3 mol%) comparing with complex A. Such increase of
catalytic properties may be attributed to the more labile nature of
desymmetrized structure so facilitating substrate interaction with
the metal center.
Table 1 Thiophosphoryl-thiocarbamoyl based palladacycle catalyzed
Suzuki–Miyaura cross-coupling
At the same time, no significant difference in catalytic activity
was observed between NH- and O-bridged 5,6-membered com-
plexes, hence the electronic properties of the sulfur atom of the
Catalyst
mol (%)
X
Yield (%)
P
S group play a supporting role in catalytic activity. Note that
8a
8a
8a
8a
8a
8a
9a
9a
9a
9a
9a
9a
Ab
Ab
1
–C(O)CH3
–C(O)CH3
–C(O)CH3
–C(O)CH3
–OCH3
100
100
65
12
93
further decreasing of a catalyst loading to 0.001 mol% resulted
in a conversion of a less than 18% even for the most active 4-
bromoacetophenone.
0.1
0.01
0.001
1
0.1
1
0.1
0.01
0.001
1
0.1
3
–OCH3
77/99a
100
100
100
18
Interestingly, in the absence of tetrabutylammonium bromide –
a salt known to stabilize palladium(0) nanoparticles,27 the yields in
the reaction catalyzed by complex A decreased by about ~15%.16
At the same time this onium salt slightly inhibited the reaction
catalyzed by 5,6-membered complexes 8a, 9a. For example, in the
reaction with 4-bromoanisole at the catalyst loading of 0.1 mol%
the conversion increased from 77% up to 99% for 8a and from
89% up to 99% for 9a, respectively (Table 1).
–C(O)CH3
–C(O)CH3
–C(O)CH3
–C(O)CH3
–OCH3
–OCH3
–C(O)CH3
–OCH3
80
89/99a
94
3
80
a Without Bu4NBr. b 6 h, data are taken from ref. 16.
The 31P NMR monitoring of the fate of the catalyst after the
catalytic cycle revealed that complexes A16 remained unchangeable
after the cross-coupling reaction (excluding the possible change of
the Cl anion for Br in the presence of Bu4NBr as a component
of reaction mixture) while complexes 8a, 9a underwent decom-
position, including the hydrolysis of P–O and P–NH bonds and
possible rupture of the Pd–C bonds.
In this context it should be mentioned that the discussion about
the role of the pincer systems in the catalysis of cross-coupling
reactions is still open. In some cases, a Pd(II)/Pd(IV) catalytic
cycle has been suggested, but to the best of our knowledge,
the detection and isolation of Pd(IV) intermediates have been
reported only in two works.28 On the other hand, a good number
of experimental observations suggest that pincer palladacycles
operate as mere depots of zerovalent palladium nanoparticles.29
These considerations are applicable to both symmetric and
unsymmetrical complexes.2e Therefore, complexes A may operate
via a Pd(II)/Pd(IV) mechanism while palladacycles 8a, 9a serve
merely as precatalysts of zero-valent palladium (a Pd(0)/Pd(II)
catalytic cycle). The decrease in the catalytic efficiency of 8a and
9a at lower concentration (0.001 mol%) is also in a good agreement
with this supposition. Basing on these results we may suppose that
pincer complexes operating via a Pd(0)/Pd(II) catalytic cycle or
according to competitive mechanisms are more active catalysts in
the cross-coupling reactions.
of their steric and electronic properties, have promoted numerous
investigations of the applicability of this type of metal complexes
to homogeneous catalysis. Up to now, the significant advances
in this area have been achieved both in terms of TON and TOF
values22 and recycling of catalytic precursors,23 as well as utilization
of water as an environmentally friendly medium.24 In addition,
desymmetrization of a pincer structure by altering the nature of
donor atoms, length of linkages between benzene backbone and
donor atoms or by other strategies, allowed to develop unsym-
metrical pincer metallacycles which were shown to exhibit high
catalytic activities in various chemical processes, sometimes even
exceeding those of the reported classical symmetric complexes.25
However, examples of direct comparison of the non-symmetric
species with their symmetric prototypes and examples pertinent
to estimation of the influence of any desymmetrizing structural
modification on the catalytic performance of the complexes, are
rather scarce. Therefore, the dependence of the catalytic activity
on the pincer complex structure still remains the subject of further
detailed investigations.
Since the catalytic activity of the aforesaid 5,5-membered
palladium complexes A based on 3-thiophosphorylbenzoic acid
thioamides, was estimated for the Suzuki–Miyaura cross-coupling,
being one of the most popular and thoroughly investigated
palladium catalyzed reaction,26 the study of complexes 8a and
9a as catalysts for this reaction allowed the direct estimation of
the desymmetrization on the catalytic activity of thiophosphoryl-
thiocarbamoyl based Pd(II)-pincer complexes. To draw the
structure–catalytic activity relationship correctly, all experiments
were performed under the same conditions: heating in DMF at
Comparison of the data on catalytic performance of 5,5-
membered and 5,6-membered pincer palladium complex with
thiophosphoryl-thiocarbamoyl based ligands, i.e., A and 8a,
9a, respectively, unambiguously demonstrate that, regardless of
the fact whether the hybrid complexes are real catalysts or
precatalysts, the higher asymmetry for a ligand serves as a factor of
higher catalytic activity of Pd-complexes in the Suzuki–Miyaura
cross-coupling. These data are in agreement with observation
1540 | Dalton Trans., 2011, 40, 1535–1546
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Table 2 Photophysical data for ligands 3, 7 and the corresponding pincer
complexes 8a, 8b, 9a and 9b
Compound
lmaxa/nm (e/M-1 cm-1)
lemb/nm
3
230 (41 067), 315 (9128), 415 (497)
240 (36 125), 320 (8762), 425 (387)
245 (75 375), 275d(27 137), 320 (6116),
385 (7109)
410c, 560
415, 565
415, 550
7
8a
9a
265 (15 917), 325 (7321), 370c (4642), 455
(6208), 540 (910)
420, 545
8b
9b
235 (38 594), 315c (5821), 380 (4846)
265 (17 987), 360 (5067), 445 (6984), 520
(928)
650
685
a Absorption maxima at room temperature; b Emission maximum of a
microcrystalline sample at 300 K; c Very weak band; d Shoulder peak.
Fig. 8 Luminescence spectra of 3 (a), 8a (b), 8b (c) (left) and 7 (a), 9a (b),
9b (c) (right) at 300 K.
of Yamamoto and co-workers of higher catalytic activity of
palladium(II) complexes of the unsymmetrical5,6-memberedPCP¢
bis(phosphinito) ligand compared to the related 5,5-membered
complexes of the symmetrical PCP bis(phosphinito) ligand in
allylic alkylation,18 despite the fact that in none of the experiments
did they observe ligand dissociation or ring-opening, and their
explanation of increased catalytic activity was based on a more
flexible complex structure due to the presence of a six-membered
metallacycle, leading to an increase in the P–M–P angle.
In the solid state, ligands 3 and 7 exhibit green emission
with main maxima at 560 and 565 nm at ambient temperature,
respectively, which are assigned to fluorescent emission originating
from a ligand-centered p–p* transition (Fig. 8). The weaker
band centered at ~415 nm in the luminescence spectrum of 7
has a structure with vibronic progression ~1310 cm-1 attributed
to the stretching vibration of central aromatic ring with some
contribution of the C–O bond (according to B3LYP/6-311G**
calculation, see ESI†). The behavior of the luminescence spectra
of ligands 3 and 7 at 77 K is similar to that at 300 K (Fig. S5, ESI†).
It is worth noting that neither ligands 3, 7 nor their complexes
8, 9 exhibited light emission in solution (THF, CH3CN) at room
temperature, similarly to the related symmetrical pincer complexes
I and V formed by bis(thioamide)- and bis(thiophosphoryl)-based
complexes, respectively,8 or 5,5-membered unsymmetric prototype
A.16
Photophysical properties
The absorption spectra of ligands 3, 7 in THF at 293 K (Fig.
S2 and S3, respectively, see ESI†) display a very intense broad
band situated higher than 250 nm, assigned to a transition mainly
involving orbitals located on the thiophosphoryl groups, and less
intense bands at 315 and 320 nm (e = 9128 and 8762 M-1 cm-1 for 3
and 7, respectively) which correspond to transitions mainly located
on the aromatic rings (intraligand charge transfer transitions).
The weakest bands observed at 415 and 425 nm (e = 497 and
387 M-1 cm-1 for 3 and 7, respectively) in solutions of the ligands
are attributed to n–p* transitions in the thioamide group30,4f (Ta-
ble 2). The comparison of these absorption spectra with the corre-
sponding ones for the 3-diphenylthiophosphorylbenzthioamides,
i.e. the ligands in the above mentioned complexes A,16 does not
reveal significant changes. In particular the absorption spectrum
of 3-diphenylthiophosphorylbenzthioamide bearing the phenyl
group in the thioamide moiety, is quite similar to those for 3
and 7. The additional bands observed in the absorption spectra
for the palladium complexes 8a and 9a (Fig. S4, ESI†) in a region
of 370–460 nm are caused by the participation of the Pd center in
the corresponding electronic transitions. These bands are similar
to those of reported pincer palladium complexes, in which the
corresponding absorption bands have been tentatively assigned to
a spin allowed 4d(Pd) → p*(L) (metal-to-ligand charge transfer,
MLCT) transition.4e,16 The low-frequency absorption band of 8a
(385 nm) attributed to the MLCT state has a bathochromic shift
upon the comparison with that of 9a (370 nm) suggesting an
increase in the energy level of the p* orbital of the ligand passing
from the NH-bridged ligand 3 to the O-bridged one 7. A similar
tendency is observed for the corresponding platinum complexes
8b, 9b: the MLCT band of 8b (380 nm) shifts to 360 nm in 9b (Fig.
S2 and S3, ESI†).
The Pt(II) and Pd(II) complexes of ligands 3 and 7 (8 and 9,
respectively) are also luminescent at ambient temperature in the
solid state. The emission with maxima at ~650 and 685 nm with
decay lifetimes (t) of 3.8 and 9.2 ms were observed at 300 K for
microcrystalline platinum complexes 8b and 9b, respectively (Ta-
ble 2). Since the M ◊ ◊ ◊ M distance in the related complexes is 7.983
˚
and 7.032 A, respectively, and extended p-stacking interaction
is absent, an excimer contribution to the observed emission is
unlikely. We tentatively assigned that the emission occurs from
MLCT excited states similar to that for published palladium and
platinum complexes.4e,16 The excitation and emission spectra of
complex 9b at 77 K are shown in Fig. S6 (ESI†) as a representative
example; at this temperature emission decay lifetimes (t) of 12.7
and 20.2 ms were observed for 8b and 9b, respectively.
Generally room-temperature luminescence of mononuclear
Pd(II) complexes is very rare because of the presence of low-
lying metal-centered (MC) excited states which deactivate the
potentially luminescent metal-to-ligand charge transfer (MLCT)
and ligand-centered (LC) levels through thermally activated
surface-crossing processes. However a weak luminescence was
detected for microcrystalline palladium complexes 8a and 9a at
room temperature with emission decay lifetime t of 12.8 and
10.2 ms, respectively (t of 26.7 and 22.4 ms was observed at 77 K).
In the corresponding luminescence spectra of these complexes
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two emission bands are observed with maxima at 415, 550 nm and
420, 545 nm, respectively (Fig. 8). A relatively small red shift
of these bands in comparison with the luminescence data for
the corresponding ligands is typical upon ligand coordination.
Therefore the ligand-centered (LC) levels are involved to the
emission observed. Whereas the behavior of the luminescence
spectra of Pt(II) complexes at 77 K is the same, that for the Pd(II)
complexes is different. Indeed in the luminescence spectrum of
9a at 77 K only a broad band centered at 610 nm is observed
(Fig. S7, ESI†). This observation probably indicates that MLCT
levels are involved in the emission. The shift observed for the
MLCT transition to lower energies for the Pt(II) complexes in
comparison with Pd(II) ones is in line with published data.30,31
Hence, the presented data reveal that the origin of the observed
emission is different for Pd(II) and Pt(II) complexes in the solid
state at ambient temperature.
NMR spectra were registered using the JMODECHO mode; the
signals for the C atoms bearing odd and even numbers of protons
have opposite polarities. The numeration for carbon atoms of the
central benzene ring in the descriptions of the 13C spectral data
is in agreement with IUPAC nomenclature used for the ligand
3. The same principle of numbering was used for description
of the solid-state molecular structures characterized by X-ray
crystallography.
Column chromatography was carried out using Merck silica
gel 60 (230–400 mesh ASTM). Analytical TLCs were performed
with Merck silica gel 60 F254 plates. IR spectra were recorded
on a “Magna-IR750” Fourier spectrometer (Nicolet), resolution
2 cm-1, 128 scans. The assignment of absorption bands in the
IR spectra was made according to ref. 34. Melting points were
determined with MPA 120 EZ-Melt Automated Melting Point
Apparatus and were uncorrected.
The detectable emission at 300 K for all studied complexes
indicates that non-radiative decay pathways have been greatly
reduced in the new 5,6-membered complexes compared to the pre-
viously published 5,5-membered ones.16 The platinum complexes
emit quite brightly at room temperature whereas the photolumi-
nescence of the palladium complexes is scarcely detectable. The
photoemission observed is due to the different origin, namely
in the former the emission occurs from a MLCT exited state
while in the latter this can be assigned to a ligand-centered 3(p*p)
transition.
Syntheses
3-[(Diphenylthiophosphoryl)amino]-N-phenylbenzamide, 2.
A
solution of Ph2P(S)Cl (1.26 g, 5 mmol) in 5 mL of benzene was
slowly dropwise added to a stirred suspension of 3-amino-N-
phenylbenzamide (1.06 g, 5 mmol) and Et3N (0.5 g) in 20 mL
of C6H6. The resulting reaction mixture was stirred under reflux
for 5 h. After cooling to room temperature, it was washed with
water, dried over anhydrous Na2SO4, and evaporated to dryness.
The resulting residue was recrystallized from EtOAc to give 1.6 g of
2 as a white solid. Yield: 75%. Mp 120.5–122.6 ◦C (dec.) (EtOAc).
3
1
1
31P{ H} NMR (121.49 MHz, CDCl3): d 52.79 ppm. H NMR
Conclusions
2
(300.13 MHz, CDCl3): d 5.38 (d, 1H, NHP(S), JHP = 6.8 Hz),
To summarize the results presented, we have developed suitable
synthetic approaches to novel unsymmetrical SCS¢ pincer lig-
ands bearing the combination of a thiocarbamoyl coordination
arm along with thiophosphorylamino or thiophosphoryloxy
complexing moieties, based on thiophosphorylation of readily
available 3-amino- and 3-hydroxy-benzoic acid (thio)anilides as
key precursors. Reacting with (PhCN)2MCl2 (M = Pt, Pd), the
ligands obtained readily undergo direct cyclometallation at the C-
2 position of the central benzene core to afford hybrid palladium
7.10–7.22 (m, 3H, HAr), 7.31–7.40 (m, 4H, HAr), 7.45–7.58 (m, 8H,
HAr), 7.80 (s, 1H, NHC(S)), 7.97–8.04 (m, 4H, o-H in P(S)Ph2). IR
(KBr, n/cm-1): 513(m), 636(m), 691(s), 718(s), 753(m), 1104(m),
1297(m), 1321(s), 1438(s), 1466(m), 1499(m), 1529(s), 1587(s),
1597(s), 1654(m) (C O), 2853(w), 2925(w), 3055(w), 3258(m),
3356(m). Anal. Calc. for C25H21N2OPS·0.5H2O: C, 68.63; H, 5.07;
N, 6.40. Found: C, 68.54; H, 4.91; N, 6.14%.
3-[(Diphenylthiophosphoryl)amino]-N-phenylbenzenecarbothio-
amide, 3. A mixture of 2 (1.0 g, 2.3 mmol) and Lawesson
reagent (0.5 g, 1.2 mmol) was refluxed in toluene for 10 h.
After cooling to room temperature, the mixture was sequentially
washed with a saturated aqueous solution of Na2CO3 and water.
The organic layer was separated, dried over anhydrous Na2SO4,
and evaporated to dryness. The resulting residue was purified by
column chromatography (eluent hexane–acetone (3 : 1)) to give
0.65 g of 3 as a yellow solid. Yield: 63%. Mp 170.4–172.5 ◦C
3
and platinum pincer complexes with h -SCS¢ coordination in high
yields. The palladium complexes demonstrated higher catalytic
activity in Suzuki cross-coupling and stronger luminescent prop-
erties than their 5,5-membered analogues, proving the positive
effect of the desymmetrization on useful properties of pincer
complexes.
Experimental
(CHCl3–hexane (1 : 2)). 31P{ H} NMR (121.49 MHz, CDCl3):
1
1
All manipulations were carried out without taking precau-
tions to exclude air and moisture unless otherwise noted.
Benzene and THF were distilled over sodium/benzophenone
ketyl. Dichloromethane and acetonitrile were distilled from P2O5.
3-Nitro-N-phenylbenzamide,32 3-amino-N-phenylbenzamide 1,19
and Ph2P(S)Cl33 were obtained according to the literature proce-
dures. All other chemicals and solvents were used as purchased
without further purification.
NMR spectra were recorded on Bruker Avance-300 and Bruker
Avance-400 spectrometers and the chemical shifts (d) were in-
ternally referenced by the residual solvent signals relative to
tetramethylsilane (1H and13C) or externally to H3PO4 (31P). The13C
d 53.07 ppm. H NMR (300.13 MHz, CDCl3): d 5.20 (d, 1H,
NHP(S), 2JHP = 6.6 Hz), 7.07 (d, 1H, HAr, 3JHH = 8.0 Hz), 7.18 (t,
1H, HAr, 3JHH = 7.8 Hz), 7.27–7.58 (m, 11H, HAr), 7.75 (d, 2H, HAr,
3JHH = 7.5 Hz), 8.01 (dd, 4H, o-H in P(S)Ph2, JHH = 7.0, JHP
=
3
3
13.8 Hz), 9.02 (br s, 1H, NHC(S)). 13C{ H} NMR (100.61 MHz,
CDCl3–DMSO-d6): d 119.21, 119.29 (overlapped signals of C6 and
C2), 120.48 (d, C4, 3JCP = 5.1 Hz), 123.69 (s, o-C in NPh), 126.21
1
(s, p-C in NPh), 128.16 (s, C5), 128.38 (d, m-C in P(S)Ph2, 3JCP
13.2 Hz), 128.50 (s, m-C in NPh), 131.63 (d, o-C in P(S)Ph2, 2JCP
=
=
11.4 Hz), 131.80 (d, p-C in P(S)Ph2, 4JCP = 2.6 Hz), 133.78 (d, ipso-
C in P(S)Ph2, 1JCP = 103.8 Hz), 140.03 (s, ipso-C in NPh), 141.36
(s, C1), 144.26 (s, C3), 198.09 (s, C S). IR (KBr, n/cm-1): 510(w),
1542 | Dalton Trans., 2011, 40, 1535–1546
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633(m) (P S), 689(s), 709(s), 722(s), 882(w), 943(s), 1107(m),
1295(s), 1312(w), 1345(m), 1380(w), 1437(s), 1446(w), 1463(s),
1479(w), 1496(m), 1516(m) (C(S)NH), 1598(m), 3054(w), 3219(m),
3359(w), 3444(w). Anal. Calc. for C25H21N2PS2: C, 67.54; H, 4.76;
N, 6.30. Found: C, 67.61; H, 4.70; N, 6.05%.
1480(s), 1495(m), 1510(s) (C(S)NH), 1590(m), 2851(w), 2922(w),
3056(w), 3280(m). Anal. Calc. for C25H20NOPS2: C, 67.39; H, 4.52;
N, 3.14. Found: C, 67.09; H, 4.37; N, 3.11%.
{2-(Anilinothiocarbonyl)-6-[(diphenylthiophosphoryl)amino]-
phenyl}palladium chloride, 8a.
(a) Synthesis in CH3CN. A solution of PdCl2(PhCN)2 (23 mg,
0.06 mmol) in 1.5 mL of acetonitrile was slowly dropwise added
to a solution of 3 (27 mg, 0.06 mmol) in 1.5 mL of CH3CN. After
stirring for 5 min, the resulting yellow precipitate was collected by
filtration and washed with Et2O (8 mL) to give 33.0 mg of 8a. Yield:
3-Methoxy-N-phenylbenzenecarbothioamide, 5. A solution of
PhNCS (4.0 g, 0.030 mol) in 10 mL of THF was slowly dropwise
added to a solution of the Grignard reagent prepared from
magnesium (0.65 g, 0.027 mol) and 3-bromoanisole (5.3 g,
0.028 mol) in THF (30 mL) at 0–5 ◦C. The reaction mixture
was refluxed for 2 h and left overnight. Then the mixture was
treated with diluted hydrochloric acid (6 ml of conc. HCl/30 mL
of water) to pH = 0–1, diluted with Et2O, and washed with water.
The organic layer was separated, dried over anhydrous Na2SO4,
and evaporated to dryness. The resulting residue was crystallized
from hexane and recrystallized from benzene to give 4.1 g of 5 as a
yellow crystalline solid. Yield: 62%. Mp 93–94 ◦C (benzene) (lit:35
95–96 ◦C).
93%. Mp >185.9 ◦C (decomp.). 31P{ H} NMR (161.98 MHz,
1
DMSO-d6): d 45.96 ppm. 1H NMR (400.13 MHz, DMSO-d6): d
7.12 (t, 1H, HAr, JHH = 7.7 Hz), 7.22 (d, 1H, HAr, JHH = 7.3 Hz),
7.41–7.56 (m, 6H, HAr), 7.60–7.72 (m, 6H, HAr), 7.83 (dd, 4H,
3
3
o-H in P(S)Ph2, JHH = 7.1 Hz, JPH = 13.8 Hz), 8.85 (d, 1H,
NHP(S), JHP = 9.0 Hz), 11.90 (s, 1H, C(S)NH). 13C{ H} NMR
(100.61 MHz, DMSO-d6): d 118.98 (s, C6), 124.86 (s, p-C in NPh),
125.32 (s, C4), 125.88 (s, o-C in NPh), 128.24 (s, C5), 129.13 (s, m-C
in NPh), 128.92 (d, m-C in P(S)Ph2, 3JCP = 14.3 Hz), 130.05 (d, ipso-
2
1
C in P(S)Ph2, 1JCP = 100.1 Hz), 131.91 (d, o-C in P(S)Ph2, 2JCP
=
3-Hydroxy-N-phenylbenzenecarbothioamide, 6. A mixture of
5 (3.0 g, 0.012 mol) and pyridine hydrochloride (4.5 g, 0.040 mol)
11.4 Hz), 133.04 (d, p-C in P(S)Ph2, 4JCP = 2.6 Hz), 137.30 (s, ipso-C
in NPh), 141.21 (d, C2, 3JCP = 6.6 Hz), 143.90 (d, C1, 4JCP = 2.6 Hz),
149.75 (s, C3), 200.13 (s, C S). IR (KBr, n/cm-1): 514(m), 630(m)
(P S), 691(s), 715(s), 751(s), 992(m), 1005(m), 1017(m), 1046(s),
1106(m), 1112(m), 1278(m), 1395(m), 1435(s), 1447(s), 1493(m),
1538(m) (C(S)NH), 1577(m), 1592(m), 2922(w), 3024(w), 3054(w),
3139(m). Anal. Calc. for C25H20ClN2PPdS2·1.5DMSO: C, 47.86;
H, 4.16; N, 3.99. Found: C, 47.50; H, 3.70; N, 3.98%.
(b) Synthesis in CH2Cl2–MeOH mixed solvent. A solution of
PdCl2(PhCN)2 (47 mg, 0.123 mmol) in 3.5 mL of dichloromethane
was slowly dropwise added to a solution of 3 (55 mg, 0.123 mmol)
in 2.5 mL of CH2Cl2. The reaction mixture was left under ambient
conditions for 24 h, diluted with 1.5 mL of MeOH and left for
another 24 h. The resulting yellow precipitate was filtered off and
washed with diethyl ether (15 mL) to give 57 mg of 8a. Yield: 79%.
◦
was heated under stirring at 180–190 C (oil-bath) for 3 h. After
cooling toroom temperature, the reaction mixture was dilutedwith
chloroform, washed with water, dried over anhydrous Na2SO4,
and evaporated to dryness. The resulting residue was purified
by column chromatography (eluent CH2Cl2) to give 0.9 g of 6
as a white solid. Yield: 32%. Mp 149.3–150.8 ◦C. 1H NMR
(300.13 MHz, DMSO-d6): d 6.88–6.92 (m, 1H, HAr), 7.20–7.44
(m, 6H, HAr), 7.75–7.82 (m, 1H, HAr), 9.70 (s, 1H, NHC(S)), 11.66
(s, 1H, OH). IR (KBr, n/cm-1): 688(m), 710(w), 765(m), 789(w),
865(m), 1013(m), 1183(m), 1206(w), 1223(w), 1279(m), 1298(w),
1311(w), 1321(w), 1332(w), 1340(w), 1385(s), 1451(s), 1489(m),
1499(w), 1547(s), 1593(s), 1601(m), 3072(m), 3132(m), 3186(m),
3251(m). Anal. Calc. for C13H11NOS: C, 68.09; H, 4.84; N, 6.11.
Found: C, 68.04; H, 4.81; N, 5.99%.
{2-(Anilinothiocarbonyl)-6-[(diphenylthiophosphoryl)oxy]-
phenyl}palladium chloride, 9a.
Diphenylthiophosphonic acid O-[(3-anilinothiocarbonyl)phenyl]
ester, 7. A solution of Ph2P(S)Cl (1.0 g, 4 mmol) in 5 mL of
benzene was slowly dropwise added to a stirred mixture of 6 (0.9 g,
4 mmol) and Et3N (0.4 g) in 15 mL of C6H6. The stirred reaction
mixture was heated at 55–60 ◦C for 2.5 h and left for 3 days.
Then the reaction mixture was filtered and evaporated to dryness.
The resulting residue was purified by column chromatography
(eluent: hexane–CH2Cl2 (1 : 1)) to give 1.2 g◦ of 7 as a yellow
(a) Synthesis in CH3CN. A solution of PdCl2(PhCN)2 (64 mg,
0.166 mmol) in 3.5 mL of acetonitrile was slowly dropwise added
to a solution of 7 (74 mg, 0.166 mmol) in 4 mL of CH3CN. The
resulting reaction mixture was left under ambient conditions for
4 days to give a yellow precipitate. The product was filtered, washed
with ether (15 mL), and dried under vacuum to give 93 mg of
9a as a yellow powder. Yield: 95%. Mp >158.2 ◦C (decomp.).
1
crystalline solid. Yield: 69%. Mp 127.0–129.4 C. 31P{ H} NMR
1
1
(161.98 MHz, CDCl3): d 83.53 ppm. H NMR (400.13 MHz,
31P{ H} NMR (121.49 MHz, DMSO-d6): d 75.29 ppm. 1H NMR
CDCl3): d 7.14 (d, 1H, HAr, 3JHH = 7.2 Hz), 7.25–7.29 (m, 2H, HAr),
7.41–7.57 (m, 9H, HAr), 7.63 (d, 1H, HAr, 3JHH = 7.4 Hz), 7.73 (d,
2H, HAr, 3JHH = 7.4 Hz), 7.95–8.01 (m, 4H, o-H in P(S)Ph2), 8.92
(300.13 MHz, DMSO-d6): d 7.28 (t, 1H, 3JHH = 8.0 Hz), 7.43–7.73
(m, 13H, HAr), 8.03 (dd, 4H, o-H in P(S)Ph2, 3JHH = 7.1 Hz, 3JPH
=
1
13.9 Hz), 12.15 (s, 1H, C(S)NH). 13C{ H} NMR (100.61 MHz,
DMSO-d6): d 121.83 (s, C6), 125.85 (s, C4), 125.96 (s, o-C in
NPh), 126.13 (s, p-C in NPh), 128.38 (s, C5), 128.92 (d, ipso -C
1
(s, 1H, NHC(S)). 13C{ H} NMR (75.47 MHz, CDCl3): d 120.13
3
(d, C2, JCP = 4.9 Hz), 123.19 (s, C6), 123.45 (s, o-C in NPh),
3
1
3
124.11 (d, C4, JCP = 4.4 Hz), 126.83 (s, p-C in NPh), 128.49 (d,
in P(S)Ph2, JCP = 109.9 Hz), 129.42 (d, m-C in P(S)Ph2, JCP
13.7 Hz), 129.49 (s, m-C in NPh), 131.62 (d, o-C in P(S)Ph2, 2JCP
=
=
3
m-C in P(S)Ph2, JCP = 13.2 Hz), 128.83 (s, m-C in NPh), 129.37
(s, C5), 131.21 (d, o-C in P(S)Ph2, 2JCP = 11.5 Hz), 132.21 (d, p-C
12.2 Hz), 133.90 (d, p-C in P(S)Ph2, 4JCP = 1.9 Hz), 137.13 (s, ipso-
C in NPh), 139.78 (d, C2, 3JCP = 7.4 Hz), 149.98 (s, C1), 153.36 (d,
4
1
in P(S)Ph2, JCP = 2.7 Hz), 133.61 (d, ipso-C in P(S)Ph2, JCP
=
2
110.9 Hz), 138.64 (s, ipso-C in NPh), 144.03 (s, C1), 150.20 (d, C3,
2JCP = 8.8 Hz), 196.57 (s, C S). IR (KBr, n/cm-1): 512(m), 639(m)
(P S), 688(s), 702(m), 728(s), 744(m), 781(m), 835(w), 931(s),
1008(m), 1115(m), 1151(m), 1243(m), 1354(m), 1437(s), 1444(s),
C3, JCP = 9.3 Hz), 199.67 (s, C S). IR (KBr, n/cm-1): 513(m),
635(m) (P S), 692(s), 702(m), 720(s), 1018(m), 1027(m), 1037(s),
1110(s), 1117(m), 1175(m), 1197(m), 1268(m), 1415(m), 1438(s),
1535(s) (C(S)NH), 1579(w), 1591(m), 2895(w), 2945(w), 3030(w),
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Table 3 Crystal data and structure refinement parameters for 3, 8a, 9a, and 9b
3
8a
9a
9b
Empirical formula
Mr
T/K
C25H21N2PS2
444.53
100
C27H26ClN2OPPdS3
663.50
100
C27H25ClNO2PPdS3
664.48
100
Monoclinic
P21
4
13.7874(10)
9.6210(7)
21.4447(15)
—
107.1200(10)
—
2718.6(3)
1.623
10.97
C27H25ClNO2PPtS3
753.17
100
Monoclinic
P21
4
13.7922(9)
9.6927(6)
21.3471(13)
—
107.3340(10)
—
2724.2(3)
1.836
55.64
Crystal system
Space group
Z
Triclinic
Triclinic
¯
¯
P1
P1
2
2
˚
a/A
8.6678(14)
9.4087(15)
13.727(2)
77.734(3)
87.897(4)
87.815(4)
1092.6(3)
1.351
3.32
464
58
13017
8.5061(6)
9.2117(7)
17.5787(13)
101.584(2)
94.219(1)
90.813(1)
1345.09(17)
1.638
11.07
672
58
16148
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Dc/g cm-3
Linear absorption, m/cm-1
F(000)
2qmax
1344
58
28131
1472
56
30297
◦
/
Reflections measured
Independent reflections
5781
4762
271
0.0367
0.0922
1.004
7137
6011
327
0.0268
0.0551
1.004
14280
12724
654
0.0270
0.0457
1.000
13054
12337
654
0.0259
0.0577
1.010
Observed reflections [I > 2s(I)]
Parameters
R1
wR2
GOF
Drmax/min/e A
-3
˚
0.465/-0.346
0.788/-0.705
0.618/-0.539
1.339/-1.740
3104(w), 3145(w). Anal. Calc. for C25H19ClNOPPdS2: C, 51.29; H,
3.10; N, 2.39. Found: C, 51.29; H, 3.15; N, 2.48%.
1577(m), 1593(w), 2254(w), 2288(w), 2915(w), 3052(w), 3178(m),
3256(m). Anal. Calc. for C25H20ClN2PPtS2·CH3CN: C, 45.48; H,
2.97; N, 5.89. Found: C, 45.21; H, 2.93; N, 5.76%.
(b) Synthesis in CH2Cl2. A solution of PdCl2(PhCN)2 (58 mg,
0.151 mmol) in 2.5 mL of dichloromethane was slowly dropwise
added to a solution of the ligand 7 (67 mg, 0.151 mmol) in
3 mL of CH2Cl2. The resulting reaction mixture was left under
ambient conditions for 24 h to give a yellow precipitate. The solid
was collected by filtration, washed with diethyl ether (12 mL),
and dried in air to give 72 mg of 9a as a yellow powder.
Yield: 82%.
{2-(Anilinothiocarbonyl)-6-[(diphenylthiophosphoryl)oxy]phenyl}-
platinum chloride, 9b. A mixture of PtCl2(PhCN)2 (51 mg,
0.108 mmol) and the ligand 7 (48 mg, 0.108 mmol) in 9 mL of
benzonitrile was heated at 120 ◦C for 3 h. Addition of hexane
(15 mL) afforded precipitation of reddish crystals of the complex
9b. The desired product was collected by filtration, washed with
Et2O (15 mL), and dried in vacuo. Yield: 49 mg (67%). Mp
◦
1
>219.0 C (decomp.). 31P{ H} NMR (161.98 MHz, DMSO-d6): d
{2-(Anilinothiocarbonyl)-6-[(diphenylthiophosphoryl)amino]phe-
nyl}platinum chloride, 8b. A mixture of PtCl2(PhCN)2 (55 mg,
0.117 mmol) and the ligand 3 (52 mg, 0.117 mmol) in 15 mL
of acetonitrile was refluxed for 4 h to yield a reddish precipitate.
The product was collected by filtration, washed with diethyl ether
(15 mL), and dried in air. Half-evaporation of the acetonitrile
filtrate afforded additional precipitation of 8b. Yield: 62 mg (74%).
71.85 (2JPPt = 60.1 Hz) ppm. 1H NMR (400.13 MHz, DMSO-d6):
d 7.23 (t, 1H, JHH = 7.8 Hz), 7.43–7.47 (m, 2H, HAr), 7.50–7.58
3
(m, 4H, HAr), 7.62–7.67 (m, 5H, HAr), 7.71–7.75 (m, 2H, HAr), 8.02
(dd, 4H, o-H in P(S)Ph2, 3JHH = 7.1 Hz, 3JPH = 13.9 Hz), 11.97 (s,
1
1H, C(S)NH). 13C{ H} NMR (125.76 MHz, DMSO-d6): d 122.24
(s, C6), 124.34 (s, C5), 125.79 (s, o-C in NPh), 126.06 (d, C4, 3JCP
=
◦
1
Mp >218.0 C (decomp.). 31P{ H} NMR (121.49 MHz, DMSO-
5.7 Hz), 128.13 (d, ipso-C in P(S)Ph2, 1JCP = 107.5 Hz), 128.37 (s,
p-C in NPh), 129.30 (d, m-C in P(S)Ph2, 3JCP = 13.4 Hz), 129.32 (s,
m-C in NPh), 131.45 (d, o-C in P(S)Ph2, 2JCP = 11.5 Hz), 133.84 (s,
p-C in P(S)Ph2), 137.38 (s, ipso-C in NPh), 147.92 (s, C1), 153.67
d6): d 42.44 (2JPPt = 61.3 Hz) ppm. 1H NMR (300.13 MHz, DMSO-
d6): d 7.11 (t, 1H, JHH = 7.6 Hz), 7.21 (d, 1H, JHH = 7.7 Hz),
7.46–7.75 (m, 12H, HAr), 7.85 (dd, 4H, o-H in P(S)Ph2, JHH
3
3
3
=
3
2
2
7.1 Hz, JPH = 13.7 Hz), 8.89 (d, 1H, NHP(S), JHP = 9.4 Hz),
(d, C3, JCP = 9.6 Hz), 202.59 (s, C S), C2 was not observed.
11.76 (s, 1H, C(S)NH). 13C{ H} NMR (100.61 MHz, DMSO-d6):
1
IR (KBr, n/cm-1): 514(m), 630(m) (P S), 691(s), 718(s), 997(m),
1022(s), 1042(s), 1110(m), 1174(m), 1198(w), 1267(m), 1379(w),
1420(m), 1437(s), 1494(m), 1534(m) (C(S)NH), 1584(w), 2854(w),
2925(w), 3051(w), 3400(w). Anal Calc. for C25H19ClNOPPtS2: C,
44.49; H, 2.84; N, 2.08. Found: C, 44.44; H, 2.73; N, 2.20%.
d 119.78 (s, C6), 123.48 (s, C5), 125.97 (s, o-C in NPh), 126.24
3
(d, C4, JCP = 10.3 Hz), 128.24 (s, p-C in NPh), 129.21 (d, m-C
3
in P(S)Ph2, JCP = 13.1 Hz), 129.38 (s, m-C in NPh), 129.41 (d,
1
ipso-C in P(S)Ph2, JCP = 99.7 Hz), 132.05 (d, o-C in P(S)Ph2,
2JCP = 11.7 Hz), 133.27 (d, p-C in P(S)Ph2, 4JCP = 2.1 Hz), 137.76
4
(s, ipso-C in NPh), 143.47 (d, C1, JCP = 2.7 Hz), 147.49 (s, C3),
Catalytic experiments
203.72 (s, C S), C2 was not observed. IR (KBr, n/cm-1): 511(m),
627(m) (P S), 691(s), 715(s), 751(m), 1045(m), 1109(m), 1115(m),
1275(s), 1390(s), 1437(s), 1446(s), 1495(m), 1533(s) (C(S)NH),
In a typical experiment a solution of 0.25 mmol of aryl bromide,
0.375 mmol of PhB(OH)2, 2 mmol of K3PO4, 0.5 mmol of Bu4NBr,
1544 | Dalton Trans., 2011, 40, 1535–1546
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and the mentioned amount of the corresponding palladium
complex (used as titrated solutions in DMF) in 1 mL of DMF was
heated at 120 ◦C over 5 h. After cooling the reaction mixture was
immediately filtered, treated with water, extracted with benzene
and analyzed by GC.
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Luminescence measurements
The luminescence measurements (spectra and lifetimes) were
performed on a Fluorolog FL 3-22 spectrometer from Horiba-
Jobin-Yvon-Spex at 300 and 77 K. Phosphorescence lifetimes (t)
were measured on samples put into quartz capillaries; they are
averages of at least three independent measurements that were
achieved by monitoring the decay at the maxima of the emission
spectra. The single or bi-exponential decays were analyzed with
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R
the Originꢀ 7.0 program.
Crystal structure determination and data collection. Single
crystals suitable for X-ray experiments were obtained by recrystal-
lization of 3 from ethyl acetate or slow diffusion of methanol (8a)
or ethanol (9a and 9b) into DMSO solutions. The X-ray diffraction
experiments were carried out with a SMART APEX2 CCD
diffractometer, using graphite-monochromated Mo-Ka radiation
˚
(l = 0.71073 A, w-scans) at 100 K. The structures were solved
by direct methods and refined by the full-matrix least-squares
against F2 in anisotropic approximation for non-hydrogen atoms.
Hydrogen atoms of NH groups were found in difference Fourier
synthesis. The H(C) atom positions were calculated. All hydrogen
atoms were refined in isotropic approximation in riding model with
the Uiso(H) parameters equal to 1.2Ueq(Ci), and for methyl groups
equal to 1.5Ueq(Cii), where U(Ci) and U(Cii) are, respectively,
the equivalent thermal parameters of the carbon atoms to which
corresponding H atoms are bonded. Crystal data and structure
refinement parameters for 3, 8a, 9a and 9b are given in Table 3.
All calculations were performed using the SHELXTL software.36
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The authors are grateful to Russian Basic Research Foundation
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©