Novel cyclopalladated imino-thiophenes: Synthesis and reactivity toward alkynes and carbon monoxide

Article abstract of DOI:10.1021/ic201158v

ortho-palladated complexes based on thiophene and benzothiophene ligands 1a and 1b have been synthesized by direct C-H activation under mild conditions. These species were fully characterized, including single-crystal X-ray diffraction analysis. The react

Full text of DOI:10.1021/ic201158v

ARTICLE
pubs.acs.org/IC
Novel Cyclopalladated Imino-thiophenes: Synthesis and Reactivity
Toward Alkynes and Carbon Monoxide
Luciano Cuesta,*,† Dune Prat,† Tatiana Soler,‡ Rafael Navarro,† and Esteban P. Urriolabeitia*,†
†Instituto de Síntesis Química y Catꢀalisis Homogꢀenea, CSIC-Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain
‡Servicios Tꢀecnicos de Investigaciꢀon, Facultad de Ciencias Fase II, Universidad de Alicante, 03690 San Vicente de Raspeig, Alicante,
Spain
S Supporting Information
b
ABSTRACT:
ortho-palladated complexes based on thiophene and benzothiophene ligands 1a and 1b have been synthesized by direct CꢀH
activation under mild conditions. These species were fully characterized, including single-crystal X-ray diffraction analysis. The
reactions of these novel complexes with internal alkynes afforded a variety of thieno[3,2-c]pyridinium salts substituted at the 6- and
7-positions. The thiophene-based complex 2a also reacts with carbon monoxide, in the presence of different alcohols, forming the
corresponding esters by tandem alkoxycarbonylations. This latter reaction can be exploited for the unexpected, but straightforward,
formation of the monomeric bis-cyclometallated complexes 6a and 6b from 2a or 2b, whose syntheses do not require the
employment of transmetallating agents. The structures of these monomeric palladacycles were also fully elucidated by means of
X-ray diffraction studies.
’ INTRODUCTION
process for the functionalization of heterocycles5 are scarce in
comparison with the vast number of examples dealing with the
cyclopalladation of arenes. In particular, to the best of our
knowledge, the reactivity of thiophene-based palladacycles to-
ward organic molecules has never been described, despite that
there seem to be a few examples of the synthesis and isolation of
this kind of complexes.6 Therefore, we have endeavored to
explore the synthesis and reactivity of this kind of complex and
report some of our results herein. Namely, we describe the
synthesis and characterization of novel thiophene- and ben-
zothiophene-based palladacycles, which were generated by direct
CꢀH activation under mild conditions employing imine units as
directing groups. Moreover, we developed a new and highly
efficient method, based on alkyne insertion, for synthesizing
thienopyridinium derivatives, species which have attracted tre-
mendous attention in the last years.7 Additionally, we have
studied the reactivity of these novel palladium complexes toward
Substituted thiophenes and benzothiophenes are relevant
molecular targets given their occurrence in a wide variety of
natural products and synthetic compounds with biological and
pharmaceutical activity.1 These species also attract the interest of
synthetic chemists because they are valuable building blocks for
the elaboration of organic materials,2 for example, novel con-
ducting polymers or devices with nonlinear optical properties. In
addition, a considerable variety of molecules containing the
thiophene or benzothiophene ring system are exploited by the
chemical industry as fragrances or insecticides,3 among other
applications. Therefore, methods for facile and versatile functio-
nalization of this class of heterocycles would be of great interest.
Between the transition metal-mediated transformations, cyclo-
palladation represents one of the most appealing options to
achieve this goal, because this synthetic strategy has been proved
to be an extremely useful and efficient approach for the functio-
nalization of organic substrates,4allowing for the selective incor-
poration of a large variety of functional groups in a plethora of
organic molecules. However, examples of the use of such a
Received: May 30, 2011
Published: August 02, 2011
r
2011 American Chemical Society
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Scheme 1. Synthesis of Thiophene-Based Palladacycles 2a
and 2b
carbon monoxide in alcoholic solvents. These reactions allow for
the production of valuable ester-substituted thiophene deriva-
tives and offer an unexpected, but straightforward, entry to mono-
meric bis-cyclometallated complexes, which, in contrast to all the
previous reported syntheses, does not require the employment of
strong bases or transmetallating agents.8
Figure 1. Top and side views of the complex 2b showing a partial atom-
labeling scheme. Displacement ellipsoids are scaled to the 50% prob-
ability level. Hydrogen atoms have been removed for clarity. Selected
bond distances (Å) and angles (deg) for 2b: Pd1ꢀC1 1.944(4),
Pd1ꢀN1 2.052(4), Pd1ꢀCl1 2.326(2), Pd1ꢀCl10 2.434(1),
C1ꢀPd1ꢀN1 80.2(2), C1ꢀPd1ꢀCl1 94.2(1), N1ꢀPd1ꢀCl10
97.4(1), Cl1ꢀPd1ꢀCl10 88.15(4).
’ RESULTS AND DISCUSSION
Synthesis and Characterization of ortho-Palladated Com-
plexes 2aꢀb. The reaction of Schiff bases 1a and 1b with 1 equiv
of Pd(OAc)2 at room temperature in acetic acid, followed by
treatment with lithium chloride in MeOH, afforded the corre-
sponding chloro-bridged complexes 2a and 2b in good yields
(see Scheme 1). Both ortho-metallated compounds were fully
characterized by means of NMR spectroscopy, mass spectro-
metry, and microanalysis.
the structure of 2a is shown in Figure S1 (see the Supporting
Information). The observed regioselectivity is predictable, since
it is well known that the reactivity of the R-position, adjacent to
the heteroatom, is considerable higher than the reactivity of the
β-position.10
The ortho-palladated complex containing the benzothiophene
moiety (2b) was characterized in the solid state by means of
X-ray diffraction studies. The crystal structure of the binuclear Pd
complex 2b is shown in Figure 1. As usually observed for dimeric
chloro-bridged palladacycles,4 each Pd center is coordinated to
the chloride bridge units, and to the respective N and C atoms of
the ortho-metallated ligand. The structure is almost planar
(Figure 1), the two metallic centers having a slightly distorted
square-planar geometry and a mutual transoid arrangement of
the two cyclopalladated moieties.
Reaction with Alkynes. Synthesis of Thienopyridinium
Derivatives. Among the heterocyclic systems containing thienyl
fragments, thienopyridines occupy unquestionably a special place.7
The considerable attention that they have received recently,
mainly motivated by their exceptionally broad spectrum of
biological activities,7a,b is clearly reflected in the huge number
of publications that have appeared recently, including patents.7a
Nevertheless, most of the reported synthetic approaches for the
production of these derivatives require complicated multistep
organic syntheses,7,11 which usually implicate low yields and often
suffer from low functional group tolerance. Therefore, the search
for alternative routes with improved yields and higher versatility
is a field of intense research nowadays. Considering that many
different types of palladacycles undergo alkyne insertion,13 we
envisioned that derivatives containing the thieno[3,2-c]pyridine
core, which remains as one of the isomeric structures more
challenging to synthesize,7,11,12 could be straightforwardly pro-
duced by alkyne insertion into complexes 2a and 2b, followed by
an intramolecular CꢀN bond coupling.
The structure of complexes 2a and 2b was initially inferred
from the NMR data. The 1H NMR spectra in acetone-d6
solutions of 2a and 2b show clearly that one of the thiophene
ring protons is lost, and in the 13C{1H} NMR, there is a
significantly deshielded signal (170.4 ppm for 2a and 180.3
ppm for 2b), which is indicative of a carbon σ-bound to the
metallic center.6 Both facts strongly suggest that palladacycle-
type structures arising from the activation of a CꢀH bond of the
thiophene ring have been generated. For the compound contain-
ing the benzothiophene moiety, the NMR spectroscopic data are
only compatible with the formation of the species 2b depicted in
Scheme 1. However, the CꢀH activation process of the ligand 1a
could proceed, in principle, over the two nonequivalent CꢀH
bonds ortho to the imine (R and β to the sulfur atom), affording
two different metallacycles. The NMR data of 2a shows that it is
formed as a single isomer, and the regiochemistry displayed in
Scheme 1 for this palladacycle is assigned on the basis of the
coupling constant for the remaining two thienyl protons. The
observed value for the coupling constant 3JHH (5.2 Hz) indicates
that the position 2 (R to the sulfur atom) has been selectively
activated, since coupling constants in the range of 4.9ꢀ5.8 Hz
have been systematically reported for thienyl adjacent protons,9
4
and lower values (3.2ꢀ3.7 Hz) are expected for the JHH
coupling of two R-thienyl protons.9 The structure of 2a was also
studied by X-ray diffraction methods in the solid state, although
they provided data of modest quality not amenable for a
discussion of the distances and angles. An ORTEP drawing of
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Scheme 2. Synthesis of Thienopyridinium Derivatives by Alkyne Insertion
We initially directed our efforts toward the insertion of
3-hexyne. The alkyne was reacted with the cyclometallated
complex 2a in different solvents, temperatures, and conditions.
We found that keeping the reaction overnight at 80 °C in toluene
with an excess of the acetylene afforded, after removal of the
palladium black generated and purification over neutral alumina,
the respective N-phenylated thienopyridinium 3a as a chloride
salt (see Scheme 2) in good yield (71%). The derivative 3a was
characterized by NMR spectroscopy, mass spectrometry, and
of compounds were formed, probably due to multiple alkyne
insertions.
The cyclopalladated complex 2b also reacts cleanly with the
same alkynes described for 2a under identical reaction condi-
tions, affording in good yields (range of 64ꢀ73%) annelated
tricyclic systems based on thieno[3,2-c]pyridinium salts. Accord-
ingly with the results observed for 2a, the reaction with 2-hexyne
and 1-phenylpropyne yields mixtures of isomers (molar ratios:
4c/4d, 50/50; 4e/4f, 65/35). The formation of the species
4aꢀ4f in such a simple way is remarkable, due to the fact that
the synthesis and properties of polycyclic annelated thienopyr-
idines have been particularly extensively studied in the last years,
and there is an urgent demand for the development of synthetic
strategies amenable for generalization.7b It is also noteworthy
that, in the syntheses of 3aꢀ3f and 4aꢀ4f, only a single alkyne
insertion was observed instead of several successive insertions, as
it is typically found with palladacycles and usually causes the
formation of undesired carbocyclic systems instead of the
targeted heterocyclic products.13 Likewise observed for complex
2a, terminal and ester-substituted alkynes do not react satisfac-
torily. The finding that alkynes containing electron-withdrawing
groups do not form the targeted heterocycle could be an
indication that the mechanism for the heterocycle liberation
probably involves a CꢀN coupling by attack of the vinylic carbon
to the iminic nitrogen.
An interesting aspect of these reactions is that they could be
the base for the development of efficient methods for synthesiz-
ing different thieno[3,2-c]pyridines from readily available start-
ing materials, which might permit the introduction of a broad
range of groups on the pyridine ring.
Alkoxycarbonylations. Synthesis of Ester-Substituted Thio-
phenes and Monomeric bis-Cyclopalladated Complexes.
Treatment of palladacycles with carbon monoxide is a very
suitable synthetic method for the production of a myriad of
carbo- and heterocyclic organic compounds.4x,13a Prompted by
the results obtained with alkynes, we decided to attempt the
stoichometric insertion of carbon monoxide into the PdꢀC bond
of palladacycles 2a and 2b, aiming to synthesize heterocyclic
1
microanalysis. The most significant signal in the H NMR is a
singlet at 10.03 ppm, assigned to the initially iminic proton and
now belonging to the pyridinium ring. In both 1H NMR and 13
C
NMR spectra are observed the presence of two nonequivalent
ethyl groups, indicating that a single alkyne insertion has taken
place, irrespective of the amount of alkyne employed. With a
small increase of the reaction temperature (112 °C), the thio-
phene-based palladacycle 2a also reacts straightforwardly with
diphenylacetylene, affording, after the workup, the derivative 3b
in good yield. The complex 2a was also reacted with unsymme-
trical acetylenes, namely, the reaction with 2-hexyne in the same
conditions described for the synthesis of 3a was found to produce
a mixture of the corresponding isomers 3c/3d in a 50:50 ratio;
these species were isolated and characterized without separation.
In the same way, the reaction with 1-phenylpropyne produced a
mixture of the two expected regioisomers (3e/3f) in a molar ratio
of 60:40 (the identity of the major/minor compound was not
elucidated). In light of these results, we can conclude that the
insertion process does not display any steric or electronic
discrimination between the different alkyl chains tested (propyl
vs methyl) and shows reduced discrimination between phenyl
and methyl groups. The reaction with 1-hexyne or phenylacety-
lene did not produce the desired product, as usually encountered
when dealing with terminal alkynes.13 Attempts to perform the
synthesis of the respective thienopyridinium derivatives employ-
ing alkynes substituted with ester groups, for instance, DMAD
(DMAD = dimethyl acetylenedicarboxylate) or ethyl 3-phenyl
propynoate, were also unsuccessful. In this latter case, formation
of palladium black does not take place, and complicated mixtures
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Scheme 3. Synthesis of Ester-Substituted Thiophenes Generated by Alkoxycarbonylation and Formation of the Monomeric
bis-Cyclopalladated Complexes 6a and 6b
derivatives. Under all the conditions tested, the attempted car-
bonylation process does not take place, and usually a reduction
process prevails. However, when the reaction is carried out in
MeOH as the solvent, the corresponding alkoxylated product 5a
is formed (see Scheme 3), as a result of a tandem process in which
the alcohol probably intercepts the acyl-palladium intermediate.
The ester-substituted thiophene 5a is isolated by a chromato-
graphic column over silica gel with a yield of 63%, and its nature is
when longer reactions times were studied, we observed the
moderately slow, but continual, disappearance of the derivatives
5aꢀ5e, and their transformation into the interesting monomeric
bis-cyclopalladated complex 6a (see scheme 3). The alkyl chain
nature of the derivatives 5aꢀ5e seems to be somehow related to
the rate of the formation of complex 6a. For instance, the
derivative containing a methoxy group is totally consumed after
2 days, isolating the bis-cyclometallated complex 6a with a yield
of 61%, whereas compound 5d, which has an isopropoxy
substituent, only shows a 30% conversion after the same time.
The elucidation of the structure of the derivative 6a was
carried out by X-ray diffraction analysis, and confirmed by
NMR spectroscopy, mass spectrometry, and elemental analysis.
The solid-state structure of 6a is shown in Figure 2a. The
structure reveals the formation of a monomeric complex, which
contains two independent cyclometallated thiophene-based imi-
nes 1a bound to the same palladium atom. The Pd atom lies in a
slightly distorted square-planar geometry, surrounded by two
iminic N atoms and two ortho-palladated C atoms in a mutual cis
arrangement. The formation of this cis conformation can be
attributed to the combination of the strong trans influence of the
carbanionic ligands and to the antisymbiotic effect,14 which
forces the molecule to adopt this particular arrangement.15 The
mutual cis disposition of the two C atoms of bis(ortho-palla-
dated) derivatives is a well-established fact, which has been
observed in most of the bis-cyclopalladated complexes charac-
terized up to now.16 As a consequence of this geometrical
situation, the phenyl rings are positioned in close proximity
and with a parallel disposition, displaying a considerable ar-
ylꢀaryl π-stacking interaction in the solid state. This situation
seems to being retained in solution, as judged by the significant
1
inferred from the IR, H and 13C NMR, mass spectrum, and
1
elemental analyses. For example, the H NMR of 5a in CDCl3
exhibits two doublets for the thiophene protons (7.89 and 7.52
ppm) and two singlets for the imine and methoxy groups (9.33
and 3.95 ppm, respectively), in addition to the phenyl reso-
nances. On the basis of the 13C NMR data, the formation of the
ester-functionalized thiophene is evident, because the signals
corresponding to the ester carbonyl group (162.6 ppm) and the
methoxy unit (52.7 ppm) are easily identified. The IR analysis
also indicates the presence of an ester moiety, because a charac-
teristic band is observed at 1709 cmꢀ1. Because the facile and
efficient preparation of functionalized thiophenes is of consider-
able interest for synthetic chemists, we decide to carry out the
carbonylation reaction in other alcoholic solvents, intending to
generate ester-substituted thiophenes with different alkyl chains.
Employing the adequate solvent and reaction time (15ꢀ45 min),
we succeeded in the synthesis of the species 5bꢀ5e, which have
incorporated ethyl, n-propyl, isopropyl, and n-butyl side chains in
the organic skeleton (see Scheme 3). All the species were
straightforwardly synthesized in optimal yields and were char-
acterized by conventional methods. The incorporation of the
1
respective alkoxy groups is at first inferred from the H NMR
spectra, where the characteristic multiplets of each alkyl chain are
observed, and confirmed by the analysis of the IR, 13C NMR and
mass spectra, and elemental analyses.
The reaction times described for the preparation of com-
pounds 5aꢀ5e are essential to achieve good yields, because,
1
mutual shielding displayed for the phenyl protons in the H
NMR spectrum, which resonate at 6.78ꢀ6.90 ppm.
When analogous alkoxycarbonylation reactions were attempted
for the cyclopalladated complex 2b with the same alcoholic
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Figure 2. Top views of the complexes 6a and 6b showing a partial atom-labeling scheme: (a) complex 6a and (b) complex 6b. Displacement ellipsoids
are scaled to the 50% probability level. Hydrogen atoms have been removed for clarity. Selected bond distances (Å) and angles (deg) for 6a: Pd1ꢀC1
1.974(2), Pd1ꢀC12 1.969(2), Pd1ꢀN1 2.150(2), Pd1ꢀN2 2.143(2), C1ꢀPd1ꢀN1 79.48 (8), C1ꢀPd1ꢀC12 97.11(9), C12ꢀPd1ꢀN2 79.51(8),
N2ꢀPd1ꢀN1 103.78(7). Selected bond distances (Å) and angles (deg) for 6b: Pd1ꢀC9 1.965(7), Pd1ꢀC24 1.975(7), Pd1ꢀN1 2.144(7), Pd1ꢀN2
2.137(5), C9ꢀPd1ꢀN1 78.3(3), C9ꢀPd1ꢀC24 99.2(3), C24ꢀPd1ꢀN2 79.1(3), N2ꢀPd1ꢀN1 103.4(2).
solvents tested for 2a, the corresponding ester-functionalized
benzothiophenes were not detected, observing in all the cases the
formation of the monomeric complex 6b, even when reaction
times as short as 5 min were employed. The structure of 6b was
studied by means of X-ray diffraction. The results, shown in
Figure 2b, indicate that 6b is a monomeric bis-cyclometallated
complex analogous to the derivative 6a. Accordingly, the palla-
dium center is located in a square-planar environment and bound
to the N iminic and C thienyl atoms of the ortho-metallated
benzothiophene ligands. The complex 6b also displays a cis
arrangement of the σ-coordinated C atoms, forcing the phenyl
rings to be in close parallel disposition.
Our proposed rationale for the formation of complexes 6a and
6b, admittedly a purely speculative one, is that they are formed
via decarboxylative processes by reaction of the respective ester-
substituted thiophenes with palladium (0) species formed in the
reaction mixture. It is well known that decarboxylation of esters
can be mediated or catalyzed by palladium (0) derivatives,17 and
the formation of metallic palladium in the reaction medium is
evident in all the reactions carried out. In the case of 6b,
apparently this decarboxylation reaction is so fast that the
ester-functionalized benzothiophene intermediates cannot be
detected. Aiming to gain some insight into the process of
formation of the bis(ortho-palladated) derivatives, we have
performed some experiments. It is clear that, at the beginning
of the reaction, when the concentration of 5 is still low, the main
species in the reaction mixture is the dinuclear complex 2a.
Therefore, and due to the fact that Pd(II) is also able to promote
the decarboxylation process,18we have reacted 5a with 2a in the
absence of CO. However, the mixture remains unaltered and 6a
was not observed even at the level of traces. On the other hand,
the formation of 6a from 2a in MeOH seems to be drastically
decelerated when Hg(0) is present in the solution. Because it is
well established that elemental mercury is an excellent scavenger
for Pd(0) heterogeneous species,19 this observation supports the
idea that decarboxylative processes initiated by palladium (0)
species are the source of the monomeric bis-cyclometallated
complexes.20
Complexes containing two cyclometallated ligands over the same
metal are attracting substantial attention, mainly because they
have been intensively exploited as models for CꢀX (X = C, N, O,
halogen) bond-forming reactions via oxidative coupling mediated
by palladacycles, providing notable mechanistic insights,21 but
also because they can display interesting photochemical and
photophysical properties.22However, the synthesis of this kind of
doubly metallated complexes is not simple, because, although the
first metallacycle might be formed quite easily, the second one
always involves a transmetallation process.8,16 This second metalla-
tion step usually implies the use of highly reactive organolithium
and magnesium derivatives, which display important drawbacks,
such as their low tolerance of functional groups or the existence
of side reactions. Other transmetallating agents have been tested
(mainly B, Sn, Si, Hg, and Au reagents).8 Unfortunately, they are
not as efficient as the organolithium and magnesium species, and
the most versatile ones (Sn- or Hg-based materials) are toxic
species. In principle, the CO-mediated reaction described in this
Article offers an unexplored synthetic route for the production of
this kind of complex, which displays obvious advantages over the
previous reported strategies.
’ CONCLUSION
In summary, this Article reports the synthesis by direct CꢀH
activation under mild conditions of ortho-palladated complexes
based on imino-thiophene and imino-benzothiophene ligands.
The reactivity studies carried out with these complexes revealed
that cyclopalladation has an enormous potential as a versatile and
efficient tool for the synthesis of new and interesting thiophene-
based structures. The reaction of internal alkynes with the
cyclometallated complexes provides an unexplored and efficient
tool for the metal-mediated synthesis of thieno[3,2-c]pyridinium
salts, a particularly important family of heterocyclic molecules.
Further studies of the scope of the reaction, and efforts to
perform this transformation in a catalytic way, are currently in
progress. Ester-substituted thiophenes are also accessible by
simple one-pot alkoxycarbonylations carried out by reaction of
the ortho-palladated complexes with CO in alcoholic solvents. In
addition, the latter reaction offers an unexpected, but simple and
We believe that the simple and straightforward synthesis of the
bis-cyclometallated complexes 6a an 6b is particularly interesting.
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ARTICLE
appealing, route for the production of a very special class of
organometallic complexes, namely, monomeric bis-cyclometal-
lated systems.
Compound 3a. A solution of the ortho-palladated complex 2a
(150 mg, 0.229 mmol) and 3-hexyne (0.260 mL, 2.29 mmol) in toluene
(15 mL) was heated during 12 h at 80 °C. After cooling the solution, the
solvent was removed under vacuum. The solid obtained was dissolved in
DCM (25 mL), filtered with Celite to remove black palladium, and the
solution was evaporated to a small volume (ca. 2 mL). Et2O (20 mL) was
then added, and the resulting precipitate was washed several times with
the same solvent. The product was purified by flash chromatography
over neutral alumina using DCM/MeOH (98/2) as the eluent and
isolated, after removal of the solvent, as a dark red solid. Yield: (98 mg,
’ EXPERIMENTAL SECTION
General Methods. Solvents were dried and distilled using standard
procedures before use. All reactions were carried out under an Ar
atmosphere (except in the carbonylations) using standard Schlenck
techniques. Flash column liquid chromatography was performed on
silica gel Kieselgel 60 (63ꢀ200 μm, 70ꢀ230 mesh) or on aluminum
oxide 90 neutral (50ꢀ200 μm). Elemental analyses were carried out on a
1
71%). MS (ESI+): 268.0 [M ꢀ Cl]+. H NMR (CDCl3): δ = 10.03
(s, 1H, pyridinium), 8.40 (d, 3JHH = 5.4, 1H, thiophene), 7.91 (d, 3JHH
=
5.4, 1H, thiophene), 7.66 (m, 5H, Ph), 3.12 (q, 3JHH = 7.6, 2H, CH2),
2.91 (q, 3JHH = 7.6, 2H, CH2), 1.47 (t, 3JHH = 7.6, 3H, CH3), 1.12 (t,
3JHH = 7.6, 3H, CH3). 13C{1H} NMR (CDCl3): δ = 156.4 (C), 146.3
(C), 143.1 (CH), 141.3 (C), 135.4 (C), 135.2 (C), 132.8 (CH), 131.4
(CH), 130.4 (CH), 127.2 (CH), 126.5 (CH), 25.8 (CH2), 23.3, (CH2),
1
PerkinElmer 2400-B microanalyser. H and 13C NMR spectra were
recorded in acetone-d6 or CDCl3 solutions at 25 °C on a Bruker AV300
or AV400 or Varian Gemini 300 spectrometers (δ in ppm, J in Hz) at a
1H operating frequency of 300.13 or 400.13 MHz. 1H and 13C spectra
were referenced using the solvent signal as an internal standard. The
infrared spectra (4000ꢀ380 cmꢀ1) were recorded on a PerkinElmer
Spectrum One spectrophotomer. ESI (ESI+) mass spectra were re-
corded using an Esquire 3000 ion-trap mass spectrometer (Bruker
Daltonic GmbH) equipped with a standard ESI/APCI source. Samples
were introduced by direct infusion with a syringe pump. Nitrogen served
as both the nebulizer gas and the dry gas. The imines 1a23 and 1b24 were
synthesized according to published methods. In the 1H NMR spectra of
compounds 5 measured in CDCl3, there is an overlapping of the CHCl3
and phenyl signals; therefore, the 1H NMR data of 5aꢀ5f are also given
in acetone-d6. In the latter solvent, the AB system of the thiophene
protons collapses to a singlet.
14.07 (CH3), 13.4 (CH3). Anal. Calcd for [C17H18ClNS] 2 CH2Cl2: C,
3
48.17; H, 4.68; N, 2.96; S, 6.77. Found: C, 47.92; H, 4.46; N, 3.11;
S, 6.79.
Compound 3b. A solution of the ortho-palladated complex 2a
(150 mg, 0.229 mmol) and diphenyl acetylene (409 mg, 2.29 mmol) was
refluxed in toluene (15 mL) for 12 h (112 °C). After cooling the
solution, the solvent was removed under vacuum, and the residue
generated was dissolved in DCM (25 mL). The solution was filtered
with Celite to remove black palladium, and evaporated to a small volume
(ca. 2 mL). Addition of Et2O (20 mL) caused the precipitation of a
yellow solid, which was washed several times with Et2O. The product
was purified by flash chromatography over neutral alumina using DCM/
MeOH (98/2) as the eluent and isolated as a yellow solid. Yield:
Complex 2a. Palladium acetate was added (540 mg, 2.40 mmol) to
a solution of 1a (450 mg, 2.40 mmol) in glacial acetic acid (15 mL). The
resulting solution was stirred overnight at room temperature, and the
solvent was removed under vacuum. The slurry obtained was dissolved
in methanol (25 mL) and an excess of lithium chloride (206 mg, 4.80
mmol) was added. The resulting solution was allowed to stir at room
temperature during 30 min and filtered through Celite to remove black
palladium. The solvent was evaporated under reduce pressure, and the
residue was redissolved in DCM (DCM = dichloromethane) and filtered
across a short plug of silica gel to remove the inorganic salts. The
resulting yellow solution was evaporated under vacuum to a small
volume and precipitated by addition of Et2O. The solid was washed
with Et2O (10 mL) and dried to afford 2a as a yellow solid. Crystals for
X-ray diffraction were grown by slow diffusion of Et2O into a saturated
solution of 2a in acetone. Yield: (541 mg, 69%). MS (ESI+): 620.8 [M ꢀ
Cl]+. 1H NMR (acetone-d6): δ = 7.99 (s, 1H, HCdN), 7.42ꢀ7.39 (m,
2H, Ph), 7.31ꢀ7.27 (m, 2H, Ph), 7.22ꢀ7.17 (m, 2H, 1H Ph + 1H
1
(130 mg, 71%). MS (ESI+): 364.1 [M ꢀ Cl]+. H NMR (CDCl3):
δ = 10.51 (s, 1H, pyridinium), 8.55 (d, 3JHH = 5.4, 1H, thiophene), 7.95
(d, 3JHH = 5.4, 1H, thiophene), 7.61 (m, 2H, Ph), 7.36ꢀ7.29 (m, 8 H,
Ph), 7.10ꢀ7.06 (m, 5H, Ph). 13C{1H} NMR (CDCl3): δ = 158.0 (C),
144.3 (CH), 144.1 (C), 142.9 (C), 136.6 (C), 136.0 (C), 135.2 (CH),
134.8 (C), 131.9 (CH), 131.2 (C), 130.8 (CH), 130.2 (CH), 130.1
(CH), 130.0 (CH), 129.7 (CH), 129.6 (CH), 128.7 (CH), 127.8 (CH),
127.5 (CH). Anal. Calcd for [C25H18ClNS]: C, 75.08; H, 4.54; N, 3.50;
S, 8.02. Found: C, 74.78; H, 4.61; N, 3.24; S, 7.76.
Compounds 3c/3d. 2-Hexyne (0.257 mL, 2.29 mmol) was added
to a solution of the ortho-palladated complex 2a (150 mg, 0.229 mmol)
in toluene (15 mL), and the mixture was heated during 12 h at 80 °C.
The solvent was removed under vacuum, and the residue obtained was
dissolved in DCM (25 mL) and filtered with Celite. The resulting
solution was evaporated to a small volume (ca. 2 mL), and the addition
of Et2O (20 mL) caused the precipitation of a dark red solid, which was
washed several times with Et2O. Finally, purification over neutral
alumina using DCM/MeOH (98/2) as the eluent afforded the regioi-
somers 3c/3d in a ratio of 50:50 (determined by 1H NMR integration,
assignation of the signals to the different isomers 3c/3d was not
3
thiophene), 7.03 (d, JHH = 5.2, 1H, thiophene). 13C{1H} NMR
(acetone-d6): δ = 170.4 (C), 168.9 (CH), 150.1 (C), 145.8 (C),
128.4 (CH), 126.5 (CH), 124.4 (CH), 124.3 (CH), 124.2 (CH). Anal.
Calcd for [C22H16Cl2N2Pd2S2]: C, 40.26; H, 2.46; N, 4.27; S, 9.77.
Found: C, 40.50; H, 2.79; N, 4.01; S, 9.43.
1
possible). Yield: (94 mg, 68%). MS (ESI+): 268.0 [M ꢀ Cl]+. H
Complex 2b. The synthesis was carried out in an analogous way as
that described before for 2a, employing palladium acetate (470 mg,
2.10 mmol), imine 1b (500 mg, 2.10 mmol), and lithium chloride (180 mg,
4.20 mmol). Crystals suitable for X-ray diffraction were grown by slow
evaporation of a saturated solution of 2b in acetone. Yield: (594 mg,
75%). MS (ESI+): 723.3 [M ꢀ Cl]+. 1H NMR (acetone-d6): δ = 8.38
(s, 1H, HCdN), 7.93 (m, 1H, C6H4), 7.80 (m, 1H, C6H4), 7.49ꢀ7.46
(m, 2H, Ph), 7.35ꢀ7.30 (m, 2H, Ph), 7.27ꢀ7.23 (m, 2H, 1H Ph + 1H
C6H4), 7.20ꢀ7.14 (m, 1H, C6H4). 13C{1H} NMR (acetone-d6): δ =
180.3 (C), 166.9 (CH), 150.5 (C), 141.4 (C), 140.0 (C), 137.1 (C),
128.2 (CH), 126.6 (CH), 124.8 (CH), 124.7 (CH), 122.6 (CH), 122.2
(CH), 120.2 (CH). Anal. Calcd for [C30H20Cl2N2Pd2S2]: C, 47.64; H,
2.67; N, 3.70; S, 8.48. Found: C, 47.82; H, 2.79; N, 3.43; S, 8.11.
NMR (CDCl3): δ = 10.11 (s, 1H, pyridinium), 10.09 (s, 1H,
pyridinium0), 8.44 (d, 3JHH = 5.7, 1H, thiophene), 8.40 (d, 3JHH = 5.7,
1H, thiophene0), 7.93ꢀ7.92 (m, 2H, thiophene + thiophene0), 7.65
(m, 10H, Ph + Ph0), 3.09 (q, 3JHH = 8.1, 2H, CH2ꢀCH2ꢀCH3), 2.83
(q, 3JHH = 8.1, 2H, CH2 ꢀCH2ꢀCH3), 2.80 (s, 3H, Me), 2.53 (s, 3H,
0
0
Me), 1.84 (m, 2H, CH2ꢀCH2ꢀCH3), 1.51 (m, 2H, CH2ꢀCH2 ꢀ
CH3), 1.13 (t, 3JHH = 8.1, 3H, CH2ꢀCH2ꢀCH3), 0.82 (t, 3JHH = 8.1,
3H, CH2ꢀCH2ꢀCH3 ). 13C{1H} NMR (CDCl3): δ = 157.2 (C), 156.7
0
(C), 145.9 (C), 142.2 (CH), 142.0 (CH), 141.9 (C), 141.8 (C), 141.5
(C), 135.0 (C), 134.8 (C), 134.7 (C), 133.4 (CH), 133.1 (CH), 131.5
(CH), 131.4 (CH), 130.8 (CH), 130.5 (CH), 130.2 (C), 126.7 (CH),
126.6 (CH), 126.4 (CH), 126.2 (CH), 35.2 (CH2), 32.3 (CH2), 22.6,
(CH2), 21.9 (CH2), 18.2 (CH3), 17.9 (CH3), 14.6 (s, CH3), 14.3
8603
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Inorganic Chemistry
ARTICLE
(s, CH3). Anal. Calcd for [C17H18ClNS] CH2Cl2: C, 55.61; H, 5.19; N,
3.60; S, 8.25. Found: C, 55.27; H, 5.56; N, 3.43; S, 7.94.
(CH). Anal. Calcd for [C29H20ClNS]: C, 77.40; H, 4.48; N, 3.11; S,
7.13. Found: C, 77.27; H, 4.79; N, 2.87; S, 6.75.
3
Compounds 3e/3f. A mixture of the ortho-palladated complex 2a
(150 mg, 0.229 mmol) and 1-phenylpropyne (0.287 mL, 2.29 mmol) is
refluxed in toluene (15 mL) during 12 h. The solvent was removed
under vacuum; the residue obtained was dissolved in DCM (25 mL) and
filtered with Celite. Addition of Et2O (20 mL) caused the precipitation
of a dark red solid, which was washed several times with Et2O. The
product was purified by flash chromatography over neutral alumina
using DCM/MeOH (98/2) as the eluent and isolated as a mixture of the
regioisomers 3e/3f in a ratio of 60:40 (determined by 1H NMR
integration without elucidating the identity of the major/minor com-
pound, and assignation of the signals to the different isomers 3e/3f was
not possible). Yield: (108 mg, 70%). MS (ESI+): 302.0 [M ꢀ Cl]+. 1H
NMR (CDCl3): δ = 10.30 (s, 1H, pyridinium), 10.07 (s, 1H,
pyridinium0), 8.55 (d, 3JHH = 5.4, 1H, thiophene), 8.36 (d, 3JHH = 5.4,
Compounds 4c/4d. 2-Hexyne (0.224 mL, 2.00 mmol) was added
to a solution of the ortho-palladated complex 2b (150 mg, 0.200 mmol)
in toluene (15 mL), and the mixture was heated during 12 h at 80 °C.
The solvent was removed under vacuum. The residue was dissolved in
DCM (25 mL) and filtered over Celite. The solution was evaporated to a
small volume (ca. 2 mL), then addition of Et2O (20 mL) caused the
precipitation of a yellow solid, which was washed several times with
Et2O. Purification over neutral alumina using DCM/MeOH (98/2) as
the eluent afforded the regioisomers 4c/4d in a ratio of 50:50
(determined by 1H NMR integration; assignation of the signals to the
different isomers 4c/4d was not possible). Yield: (97 mg, 69%). MS (ESI
+): 318.1 [M ꢀ Cl]+. 1H NMR (CDCl3): δ = 10.54 (s, 1H, pyridinium),
0
10.49 (s, 1H, pyridinium0), 8.93ꢀ8.91 (m 2H, 1H C6H4 + 1H C6H4 ),
0
7.89ꢀ7.87 (m, 2H, 1H C6H4 + 1H C6H4 ), 7.70ꢀ7.60 (m, 14H, 4H
3
1H, thiophene0), 8.03 (d, JHH = 5.4, 1H, thiophene), 7.09ꢀ7.85
3
C6H4/C6H4 + 10 Ph/Ph0), 3.09 (q, JHH = 8.1, 2H, CH2ꢀCH2ꢀCH3),
0
(m, 2H, 1H thiophene0 + 1H Ph), 7.68ꢀ7.60, 7.54ꢀ7.51, 7.36ꢀ7.20
(m, 19 H, Ph + Ph0), 2.57 (s, 3H, Me), 2.41 (s, 3H, Me0). 13C{1H} NMR
(CDCl3): δ = 157.2 (C), 156.4 (C), 143.7 (C), 142.3 (CH), 142.2
(CH), 142.0 (C), 141.6 (C), 135.4 (C), 134.8 (s, C), 134.3 (s, C), 133.9
(CH), 133.6 (CH), 130.9 (CH), 130.6 (C), 130.5 (s, C), 130.4 (CH),
130.3 (CH), 130.0 (CH), 129.9 (CH), 129.8 (CH), 129.5 (CH), 129.3
(CH), 128.7 (CH), 128.6 (CH), 127.4 (CH), 126.2 (CH), 126.1 (CH),
3
0
2.91 (q, JHH = 8.4, 2H, CH2 ꢀCH2ꢀCH3), 2.87 (s, 3H, Me), 2.60
(s, 3H, Me0), 1.83 (m, 2H, CH2ꢀCH2ꢀCH3), 1.55 (m, 2H, CH2ꢀ
CH2 ꢀCH3), 1,14 (t, JHH = 7.2, 3H, CH2ꢀCH2ꢀCH3), 0.84 (t, 3JHH
=
3
0
7.2, 3H, CH2ꢀCH2ꢀCH3 ). 13C{1H} NMR (CDCl3): δ = 158.2 (C),
157.7 (C), 149.2 (C), 145.3 (C), 141.5 (C), 141.1 (C), 139.6 (CH),
139.4 (CH), 139.0 (C), 134.4 (C), 132.8 (C), 132.7 (C), 131.8 (C),
131.4 (C), 131.3 (CH), 131.2 (CH), 130.5 (CH), 130.2 (CH), 130.1
(CH), 130.0 (CH), 129.8 (C), 129.7 (C), 127.3 (CH), 127.2 (CH),
126.6 (CH), 126.4 (CH), 125.7 (CH), 125.6 (CH), 122.5 (2 CH), 35.3
(CH2), 32.7 (CH2), 22.5, (CH2), 21.7 (CH2), 18.4 (CH3), 18.3 (CH3),
0
125.8 (CH), 19.4 (CH3), 18.8 (CH3). Anal. Calcd for [C20H16ClNS]
1/2CH2Cl2: C, 64.74; H, 4.51; N, 3.68; S, 8.43. Found: C, 64.77; H, 4.91; N,
3.62; S, 8.17.
3
Compound 4a. A mixture of the ortho-palladated complex 2b
(150 mg, 0.200 mmol) and 3-hexyne (0.227 mL, 2.00 mmol) was heated
in toluene (15 mL) at 80 °C during 12 h. The resulting solution was
evaporated under vacuum, and the residue obtained was dissolved in
DCM (25 mL). The black palladium formed was removed by filtration
with Celite, and the solution was concentrated to a small volume
(ca. 2 mL). Et2O (20 mL) was then added, and the obtained precipitate
was washed with the same solvent several times. The product was
purified by flash chromatography over neutral alumina using DCM/
MeOH (98/2) as the eluent and isolated, after removal of the solvent, as
a yellow solid. Yield: (102 mg, 72%). MS (ESI+): 318.1 [M ꢀ Cl]+. 1H
NMR (CDCl3): δ = 10.67 (s, 1H, pyridinium), 9.01 (m, 1H, C6H4),
7.91 (m, 1H, C6H4), 7.78ꢀ7.63 (m, 7H, 2H C6H4 + 5H Ph), 3.15 (q,
3JHH = 7.6, 2H, CH2), 2.97 (q, 3JHH = 7.6, 2H, CH2), 1.50 (t, 3JHH = 7.6,
3H, CH3), 1.16 (t, 3JHH = 7.6, 3H, CH3). 13C{1H} NMR (CDCl3): δ =
157.4 (C), 149.3 (C), 140.7 (C), 140.2 (CH), 138.7 (C), 134.8 (C),
132.5 (C), 131.7 (C), 131.8 (CH), 130.1 (CH), 130.0 (CH), 127.2
(CH), 126.4 (CH), 125.9 (CH), 122.3 (CH), 25.6, (CH2), 23.3 (CH2),
14.6 (CH3), 14.4 (CH3). Anal. Calcd for [C21H20ClNS] 1/2CH2Cl2:
C, 65.15; H, 5.34; N, 3.53; S, 8.09. Found: C, 65.07; H, 5.41; N, 3.62;
S, 8.32.
3
Compounds 4e/4f. 1-Phenylpropyne (0.250 mL, 2.00 mmol) was
added into a solution of complex 2b (150 mg, 0.200 mmol) in toluene
(15 mL), and the resulting mixture was refluxed for 12 h. The solvent
was removed under vacuum; the solid obtained was dissolved in DCM
(25 mL) and filtered over Celite. Addition of Et2O (20 mL) caused the
precipitation of a yellow solid, which was washed several times with
Et2O. Purification by means of flash chromatography over neutral
alumina using DCM/MeOH (98/2) as the eluent allowed for the
isolation of the regioisomers 3e/3f in a ratio of 65:35 (determined by
1H NMR integration without elucidating the identity of the major/
minor compound; assignation of the signals to the different isomers 4e/
4f was not possible). Yield: (99 mg, 64%). MS (ESI+): 352.1 [M ꢀ Cl]+.
1H NMR (CDCl3): δ = 10.74 (s, 1H, pyridinium)0, 10.49 (s, 1H,
pyridinium0), 9.06 (m, 1H, C6H4), 8.89 (m, 1H, C6H4 ), 8.00 (m, 1H,
0
C6H4), 7.92 (m, 1H, C6H4), 7.80 (m, 1H, C6H4 ), 7.72ꢀ7.56 (m, 13H,
1H C6H4 + 2H C6H4 + 10H Ph/Ph0), 7.33ꢀ7.28 (m, 10H, Ph/Ph0),
0
13.7 (CH3), 12.8 (CH3). Anal. Calcd for [C21H20ClNS] CH2Cl2: C,
3
60.21; H, 5.05; N, 3.19; S, 7.31. Found: C, 60.12; H, 4.88; N, 3.51; S, 7.61.
Compound 4b. Diphenylacetylene (357 mg, 2.00 mmol) was
added into a solution of complex 2b (150 mg, 0.200 mmol) in toluene
(15 mL), and the mixture was refluxed overnight (12 h). The solvent was
removed under vacuum, and the resulting solid was dissolved in DCM
(25 mL). The black palladium formed was removed by filtration with
Celite, and the solution was concentrated to a small volume (ca. 2 mL).
Addition of Et2O (20 mL) caused the precipitation of a yellow solid,
which was washed with additional Et2O (2 ꢁ 10 mL). The product was
isolated by flash chromatography over neutral alumina using DCM/
MeOH (98/2) as the eluent. Yield: (131 mg, 73%). MS (ESI+): 414.1
[M ꢀ Cl]+. 1H NMR (CDCl3): δ = 10.90 (s, 1H, pyridinium), 9.14 (m,
1H, C6H4), 7.94 (m, 1H, C6H4), 7.74ꢀ7.66 (m, 4H, 2H C6H4 + 2H
Ph), 7.45ꢀ7.38 (m, 8H, Ph), 7.19ꢀ7.08 (m, 5H, Ph). 13C{1H} NMR
(CDCl3): δ = 159.0 (C), 146.6 (C), 141.8 (C), 140.3 (CH), 140.2 (C),
135.2 (C), 133.9 (C), 132.6 (C), 132.4 (C), 130.9 (CH), 130.4 (C),
130.1 (CH), 130.2 (CH), 129.3 (CH), 129.2 (CH), 129.1 (CH), 128.9
(CH), 128.8 (CH), 127.8 (CH), 127.0 (2 CH), 125.6 (CH), 122.6
2.54 (s, 3H, Me), 2.46 (s, 3H, Me0). 13C{1H} NMR (CDCl3): δ = 158.9
(C), 158.1 (C), 147.3 (C), 146.3 (C), 142.0 (C), 141.6 (C), 140.0 (C),
139.7 (CH), 139.6 (CH), 139.5 (C), 135.0 (C), 134.6 (C), 132.9 (C),
132.6 (C), 132.5 (C), 131.9 (C), 131.2 (CH), 130.9 (2C), 130.5 (CH),
130.4 (CH), 130.3 (CH), 130.2 (CH), 130.1 (CH), 129.8 (CH), 129.5
(CH), 129.1 (CH), 128.9 (CH), 128.0 (CH), 127.5 (CH), 127.3 (CH),
127.2 (CH), 126.6 (CH), 126.2 (CH), 125.7 (CH), 124.2 (CH), 122.8
(CH), 122.6 (CH), 20.1 (CH3), 19.2 (CH3). Anal. Calcd for
[C24H18ClNS]: C, 74.31; H, 4.68; N, 3.61; S, 8.27. Found: C, 74.12;
H, 4.87; N, 3.40; S, 8.09.
Compound 5a. The ortho-palladated complex 2a (150 mg, 0.229
mmol) was dissolved in methanol (20 mL) and stirred under a CO
atmosphere (approximately 1 atm) during 10 min. The dark suspension
was filtered through a plug of Celite, and the yellow solution was
evaporated to dryness. The residue was dissolved in DCM and purified
by flash chromatography over silica gel employing DCM as the eluent.
The compound 5a was isolated as a yellow oil. Yield: (70 mg, 63%). MS
(ESI+): 245.9 [M + 1H]+. 1H NMR (CDCl3): δ = 9.3 (s, 1H, HCdN),
8604
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Inorganic Chemistry
ARTICLE
7.88 (d, 3JHH = 5.2, 1H, thiophene), 7.51 (d, 3JHH = 5.2, 1H, thiophene),
69.6 (CH), 21.4 (CH3). IR: ν = 1701 cmꢀ1 (CdO). Anal. Calcd for
[C15H15NO2S]: C, 65.91; H, 5.53; N, 5.12; S, 11.73. Found: C, 65.73;
H, 5.64; N, 4.94; S, 11.59.
1
7.41 (m, 2H, Ph), 7.28ꢀ7.26 (m, 3H, Ph), 3.95 (s, 3H, OCH3). H
NMR (acetone-d6): δ = 9.33 (s, 1H, HCdN), 7.86 (s, 2H, thiophene),
7.46 (m, 2H, Ph), 7.32ꢀ7.28 (m, 3H, Ph), 3.95 (s, 3H, OCH3). 13C{1H}
NMR (CDCl3): δ = 162.6 (C), 155.1 (CH), 152.0 (C), 144.9 (C), 133.2
(C), 130.7 (CH), 129.5 (CH), 128.4 (CH), 126.8 (CH), 121.4 (CH),
52.6 (CH3). IR: ν = 1709 cmꢀ1 (CdO). Anal. Calcd for
[C13H11NO2S]: C, 63.65; H, 4.52; N; 5.71, S 13.07. Found: C, 63.87;
H, 4.71; N, 5.61; S, 12.89.
Compound 5e. The ortho-palladated complex 2a (150 mg, 0.229
mmol) was dissolved in n-butanol (20 mL) and stirred under a CO
atmosphere (approximately 1 atm) during 45 min. The dark suspension
was filtered through a plug of Celite to remove the black palladium, and
the yellow solution was evaporated under vacuum. Compound 5e was
isolated as a yellow oil by means of flash chromatography over silica gel
with DCM as the eluent. Yield: (93 mg, 71%). MS (ESI+): 288.1 [M +
1]+. 1H NMR (CDCl3): δ = 9.33 (s, 1H, HCdN), 7.86 (d, 3JHH = 5.4,
1H, thiophene), 7.49 (d, 3JHH = 5.4, 1H, thiophene), 7.40 (m, 2H, Ph),
Compound 5b. The ortho-palladated complex 2a (150 mg, 0.229
mmol) was dissolved in ethanol (20 mL) and placed under a CO
atmosphere (approximately 1 atm). The reaction was stirred during
15 min, and the dark suspension was filtered through a plug of Celite.
The solvent was removed under vacuum, and the yellow residue was
purified by silica gel flash chromatography employing DCM as the
eluent. The compound 5b was isolated as a yellow oil. Yield: (74 mg,
3
7.29ꢀ7.26 (m, 3H, Ph), 4.35 (t, JHH = 6.6, 2H, OCH2ꢀCH2ꢀ
CH2ꢀCH3), 1.75 (m, 2H, OCH2ꢀCH2ꢀCH2ꢀCH3), 1.49 (m, 2H,
3
OCH2ꢀCH2ꢀCH2ꢀCH3), 0.98 (t, JHH = 7.5, 3H, OCH2ꢀCH2ꢀ
CH2ꢀCH3). 1H NMR (acetone-d6): δ = 9.32 (s, 1H, HCdN), 7.82 (m,
62%). MS (ESI+): 260.0 [M + 1H]+. H NMR (CDCl3): δ = 9.32
2H, thiophene), 7.44 (m, 2H, Ph), 7.31ꢀ7.26 (m, 3H, Ph), 4.36 (t, 3JHH
=
1
(s, 1H, HCdN), 7.85 (d, 3JHH = 5.2, 1H, thiophene), 7.48 (d, 3JHH = 5.2,
1H, thiophene), 7.40 (m, 2H, Ph), 7.27ꢀ7.25 (m, 3H, Ph), 4.40 (q, 3JHH
6.4, 2H, OCH2ꢀCH2ꢀCH2ꢀCH3), 1.76 (m, 2H, OCH2ꢀCH2ꢀ
3
CH2ꢀCH3), 1.47 (m, 2H, OCH2ꢀCH2ꢀCH2ꢀCH3), 0.97 (t, JHH
=
= 6.9, 2H, OCH2ꢀCH3), 1.40 (t, JHH = 6.9, 3H, OCH2ꢀCH3). H
7.3, 3H, OCH2ꢀCH2ꢀCH2ꢀCH3).13C{1H} NMR (acetone-d6):
δ = 161.6 (C), 154.5 (CH), 152.0 (C), 144.2 (C), 133.7 (C), 131.2
(CH), 129.2 (CH), 127.6 (CH), 126.4 (CH), 121.4 (CH), 65.1 (CH2),
30.5 (CH2), 19.0 (CH2), 13.1 (CH3). IR: ν = 1703 cmꢀ1 (CdO). Anal.
Calcd for [C16H17NO2S]: C, 66.87; H, 5.96; N, 4.87; S, 11.16. Found: C,
66.61; H, 6.02; N, 4.89; S, 11.19.
3
1
NMR (acetone-d6): δ = 9.32 (s, 1H, HCdN), 7.83 (s, 2H, thiophene),
3
7.42 (m, 2H, Ph), 7.28ꢀ7.26 (m, 3H, Ph), 4.39 (q, JHH = 7.2, 2H,
OCH2ꢀCH3), 1.38 (t, 3JHH = 7.2, 3H, OCH2ꢀCH3). 13C{1H} NMR
(CDCl3): δ = 162.5 (C), 155.3 (CH), 152.3 (C), 143.1 (C), 134.4 (C),
130.8 (CH), 129.4 (CH), 128.3 (CH), 127.6 (CH), 121.0 (CH), 61.9
(CH2), 14.1 (CH3). IR: ν = 1710 cmꢀ1 (CdO). Anal. Calcd for
[C14H13NO2S]: C, 64.84; H, 5.05; N, 5.40; S, 12.36. Found: C, 64.72;
H, 5.21; N, 5.26; S, 12.11.
Complex 6a. A solution of the ortho-palladated complex 2a
(150 mg, 0.229 mmol) in methanol (20 mL) was stirred under a CO
atmosphere (approximately 1 atm) during 2 days. The dark suspension
was filtered through a plug of Celite, and the orange-yellowish solution
was evaporated to dryness. The residue was dissolved in DCM and
purified by chromatography over silica gel. The first yellow band eluted
with DCM was collected and evaporated under vacuum, yielding
complex 6a as an orange-yellowish solid. Recrystallization from DCM/
pentane afforded crystals suitable for X-ray diffraction analysis. Yield:
(67 mg, 61%). MS (ESI+): 478.7 [M]+. 1H NMR (CDCl3): δ = 8.06 (s,
1H, HCdN), 7.30 (m, 2H, thiophene), 6.91ꢀ6.77 (m, 5H, Ph).
13C{1H} NMR (CDCl3): δ = 168.4 (C), 167.1 (CH), 149.1 (C),
147.7 (C), 128.3 (CH), 127.5 (CH), 125.8 (CH), 125.3 (CH), 121.4
(CH). Anal. Calcd for [C22H16N2PdS2]: C, 55.17; H, 3.37; N, 5.85; S,
13.39. Found: C, 55.41; H, 3.24; N, 5.92; S, 13.44.
Complex 6b. Complex 2b (150 mg, 0.200 mmol) was dissolved in
methanol (20 mL), and the solution was stirred under a CO atmosphere
(approximately 1 atm) during 15 min. The dark suspension was filtered
through a plug of Celite to remove black palladium, and the orange
solution was evaporated under vacuum. Complex 6b was isolated as an
orange solid by means of chromatography over silica gel employing
DCM as the eluent. Recrystallization from DCM/pentane afforded
crystals suitable for X-ray diffraction analysis. Yield: (89 mg, 77%). MS
(ESI+): 341.3 [M ꢀ 1L, (L = C15H10NS)]+. 1H NMR (CDCl3):
δ = 8.36 (s, 1H, HCdN), 7.92 (m, 1H, C6H4), 7.78 (m, 1H, C6H4),
7.34 (m, 1H, C6H4), 7.28 (m, 1H, C6H4), 6.96ꢀ6.86 (m, 5H, Ph).
13C{1H} NMR (CDCl3): δ = 177.5 (C), 165.7 (CH), 149.5 (C), 143.8
(C), 141.9 (C), 137.2 (C), 128.7 (CH), 126.1 (CH), 124.9 (CH), 122.8
(CH), 122.5 (CH), 121.8 (CH), 119.2 (CH). Anal. Calcd for
[C30H20N2PdS2]: C, 62.23; H, 3.48; N, 4.84; S, 11.08. Found: C, 61.94;
H, 3.42; N, 4.93; S, 11.21.
Compound 5c. Complex 2a (150 mg, 0.229 mmol) was dissolved
in n-propanol (20 mL) and stirred under a CO atmosphere (appro-
ximately 1 atm) during 30 min. The dark suspension formed was filtered
through a plug of Celite, and the yellow solution was evaporated under
vacuum. The resulting residue was purified by silica gel flash chroma-
tography employing DCM as the eluent, affording 5c as a yellow oil.
Yield: (88 mg, 70%). MS (ESI+): 274.0 [M + 1H]+. 1H NMR (CDCl3):
3
δ = 9.32 (s, 1H, HCdN), 7.85 (d, JHH = 5.3, 1H, thiophene), 7.48
(d, 3JHH = 5.3, 1H, thiophene), 7.40 (m, 2H, Ph), 7.27ꢀ7.25 (m, 3H,
Ph), 4.30 (q, 3JHH = 6.6, 2H, OCH2ꢀCH2ꢀCH3), 1.81 (m, 2H, OCH2ꢀ
3
1
CH2ꢀCH3), 1.03 (t, JHH = 7.5, 3H, OCH2ꢀCH2ꢀCH3). H NMR
(acetone-d6): δ = 9.31 (s, 1H, HCdN), 7.83 (s, 2H, thiophene), 7.43
3
(m, 2H, Ph), 7.28ꢀ7.25 (m, 3H, Ph), 4.30 (q, JHH = 6.6, 2H,
OCH2ꢀCH2ꢀCH3), 1.80 (m, 2H, OCH2ꢀCH2ꢀCH3), 1.01 (t, 3JHH
=
7.5, 3H, OCH2ꢀCH2ꢀCH3). 13C{1H} NMR (acetone-d6): δ = 162.4
(C), 155.3 (CH), 152.9 (C), 145.1 (C), 134.5 (C), 132.1 (CH), 130.1
(CH), 128.5 (CH), 127.3 (CH), 121.8 (CH), 67.6 (CH2), 22.7 (CH2),
10.7 (CH3). IR: ν = 1701 cmꢀ1 (CdO). Anal. Calcd for [C15H15NO2S]:
C, 65.91; H, 5.53; N, 5.12; S, 11.73. Found: C, 65.87; H, 5.51; N, 5.06;
S, 11.71.
Compound 5d. A solution of the ortho-palladated complex 2a
(150 mg, 0.229 mmol) in iso-propanol (20 mL) was placed under a CO
atmosphere (approximately 1 atm), and the mixture was stirred 45 min.
The black palladium formed was removed by filtration with Celite, and
the yellow solution was evaporated under vacuum. The residue was
purified by silica gel flash chromatography with DCM as the eluent.
Compound 5d was isolated as a yellow oily material. Yield: (90 mg,
1
72%). MS (ESI+): 274.1 [M + 1H]+. H NMR (CDCl3): δ = 9.33
(s, 1H, HCdN), 7.85 (d, 3JHH = 5.2, 1H, thiophene), 7.47 (d, 3JHH = 5.2,
1H, thiophene), 7.40 (m, 2H, Ph), 7.27ꢀ7.25 (m, 3H, Ph), 5.24 (sep,
3JHH = 6.3, 1H, CH(CH3)2), 1.39 (d, 3JHH = 6.3, 6H, CH(CH3)2). 1H
NMR (acetone-d6): δ = 9.32 (s, 1H, HCdN), 7.82 (s, 2H, thiophene),
7.43 (m, 2H, Ph), 7.28ꢀ7.25 (m, 3H, Ph), 5.23 (sep, 3JHH = 6.2, 1H,
Xꢀray Crystallography. X-ray data collection was performed on
an Oxford Diffraction Xcalibur2 diffractometer using graphite-mono-
cromated MoꢀKR radiation (λ = 0.71073 Å). A single crystal was
mounted in each case at the end of a quartz fiber in a random orientation,
covered with perfluorinated oil and placed under a cold stream of N2 gas.
In all cases, a hemisphere of data was collected based on ω-scan or ϕ-scan
runs. The diffraction frames were integrated using the program CrysAlis
RED,25 and the integrated intensities were corrected for absorption with
3
CH(CH3)2), 1.39 (d, JHH = 6.2, 6H, CH(CH3)2). 13C{1H} NMR
(acetone-d6): δ = 161.2 (C), 154.8 (CH), 152.3 (C), 144.3 (C), 134.2
(C), 132.1 (CH), 131.4 (CH), 129.5 (CH), 127.9 (CH), 121.2 (CH),
8605
dx.doi.org/10.1021/ic201158v |Inorg. Chem. 2011, 50, 8598–8607

Inorganic Chemistry
ARTICLE
SADABS.26 The structures were solved and developed by Patterson and
Fourier methods.27 All non-hydrogen atoms were refined with aniso-
tropic displacement parameters. The hydrogen atoms were placed at
idealized positions and treated as riding atoms. Each H atom was
assigned an isotropic displacement parameter equal to 1.2 times the
equivalent isotropic displacement parameter of its parent atom. The
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2
structures were refined to Fo , and all reflections were used in the least-
squares calculations.28
’ ASSOCIATED CONTENT
S
Supporting Information. CIF files of complexes 2b, 6a,
b
and 6b, and Figure S1. This material is available free of charge via
the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: esteban@unizar.es (E.P.U.). Fax: (+0034)976761187
(L.C.).
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’ ACKNOWLEDGMENT
Funding by the Ministerio de Ciencia e Innovaciꢀon (MICINN)
(Spain, Project CTQ2008-01784) and Gobierno de Aragꢀon
(Spain, group E97 and Project PI071/09) is gratefully acknowl-
edged. L.C. thanks Consejo Superior de Investigaciones Cientí-
ficas (Spain) for a Juan de la Cierva contract.
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