Controlled interaction of benzaldehyde thiosemicarbazones with palladium: Formation of bis-complexes with cis-geometry and organopalladium complexes, and their catalytic application in C-C and C-N coupling

Article abstract of DOI:10.1039/c3ra40829a

Reaction of a 1 : 1 mixture of 4-R-benzaldehyde thiosemicarbazone (R = OCH₃, CH₃, H, Cl and NO₂) and 2-picolinic acid with an equivalent quantity of Na₂[PdCl₄] in ethanolic medium, under relatively mild reflux, affords a group of complexes of type [Pd(NS-R)₂] as the major product and another family of complexes of type [{Pd(CNS-R)}_n] as the minor product (where NS-R and CNS-R denote the N,S- and C,N,S-coordinated thiosemicarbazone, respectively). The [{Pd(CNS-R)}_n] complexes are conveniently obtained in good yields from similar reactions carried out under prolonged reflux. The sulfur-bridge in the [{Pd(CNS-R)}_n] complexes undergoes facile cleavage upon their reaction with triphenylphosphine to yield complexes of type [Pd(CNS-R)(PPh ₃)]. Crystal structures of [Pd(NS-OCH₃)₂], [Pd(NS-CH₃)₂], [Pd(NS-Cl)₂], [Pd(CNS-CH ₃)(PPh₃)], [Pd(CNS-H)(PPh₃)] and [Pd(CNS-Cl)(PPh₃)] have been determined. In the [Pd(NS-R) ₂] complexes the thiosemicarbazones are coordinated to the metal center, via dissociation of the acidic proton, as monoanionic bidentate N,S-donors forming five-membered chelate rings, while in the [Pd(CNS-R)(PPh ₃)] complexes they are coordinated to palladium, via dissociation of the acidic proton and activation of an ortho C-H bond, as dianionic tridentate C,N,S-donors forming two adjacent five-membered chelate rings. The [Pd(NS-R)₂] and [Pd(CNS-R)(PPh₃)] complexes show characteristic ¹H NMR signals, and in dichloromethane solution they all display intense absorptions in the visible and ultraviolet regions. The [Pd(NS-R)₂] and [Pd(CNS-R)(PPh₃)] complexes have shown notable efficiency in catalyzing C-C and C-N coupling reactions. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3ra40829a

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Manuscript title:
Controlled interaction of benzaldehyde thiosemicarbazones with
palladium: Formation of bis-complexes with cis-geometry and
organopalladium complexes, and their catalytic application in C-C
and C-N coupling
Authors:
Jayita Dutta and Samaresh Bhattacharya*
Three types of thiosemicarbazone complexes of palladium have been synthesized, two of
which efficiently catalyze C-C and C-N coupling reactions.
[Pd(NS-OCH3)2]
[Pd(CNS-CH3)(PPh3)]

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Controlled interaction of benzaldehyde thiosemicarbazones with
palladium: Formation of bisꢀcomplexes with cisꢀgeometry and
organopalladium complexes, and their catalytic application in CꢀC
and CꢀN coupling†
Jayita Dutta and Samaresh Bhattacharya*
Department of Chemistry, Inorganic Chemistry Section,
Jadavpur University, Kolkata ꢀ 700 032, India.
Eꢀmail: samaresh_b@yahoo.com; Fax: 91ꢀ33ꢀ24146223
Abstract
Reaction of a 1:1 mixture of 4ꢀRꢀbenzaldehyde thiosemicarbazone (R = OCH3, CH3, H,
Cl and NO2) and 2ꢀpicolinic acid with an equivalent quantity of Na2[PdCl4] in ethanolic
medium, under relatively mild reflux, affords a group of complexes of type [Pd(NSꢀR)2]
as the major product and another family of complexes of type [{Pd(CNSꢀR)}n] as the
minor product (where NSꢀR and CNSꢀR denote the N,Sꢀ and C,N,Sꢀcoordinated
thiosemicarbazone respectively). The [{Pd(CNSꢀR)}n] complexes are conveniently
obtained in good yields from similar reactions carried out under prolonged reflux. The
sulfurꢀbridge in the [{Pd(CNSꢀR)}n] complexes undergoes facile cleavage upon their
reaction with triphenylphosphine to yield complexes of type [Pd(CNSꢀR)(PPh3)]. Crystal
structures of [Pd(NSꢀOCH3)2], [Pd(NSꢀCH3)2], [Pd(NSꢀCl)2], [Pd(CNSꢀCH3)(PPh3)],
[Pd(CNSꢀH)(PPh3)] and [Pd(CNSꢀCl)(PPh3)] have been determined. In the [Pd(NSꢀR)2]
complexes the thiosemicarbazones are coordinated to the metal center, via dissociation of
the acidic proton, as monoanionic bidentate N,Sꢀdonors forming fiveꢀmembered chelate
rings, while in the [Pd(CNSꢀR)(PPh3)] complexes they are coordinated to palladium, via
dissociation of the acidic proton and activation of an ortho CꢀH bond, as dianionic
tridentate C,N,Sꢀdonors forming two adjacent fiveꢀmembered chelate rings. The [Pd(NSꢀ
1
R)2] and [Pd(CNSꢀR)(PPh3)] complexes show characteristic H NMR signals, and in
dichloromethane solution they all display intense absorptions in the visible and ultraviolet
regions. The [Pd(NSꢀR)2] and [Pd(CNSꢀR)(PPh3)] complexes have shown notable
efficiency in catalyzing CꢀC and C–N coupling reactions.
† Electronic supplementary information (ESI) available: CCDC 906850 – 906852 and
CCDC 915182 – 915184 contain the supplementary crystallographic data for this paper.
Selected bond lengths (Å) and angles (°) for [Pd(NSꢀCH3)2], [Pd(NSꢀCl)2], [Pd(CNSꢀ
H)(PPh3)] and [Pd(CNSꢀCl)(PPh3)] (Table S1); effect of variation of reaction time for
[Pd(NSꢀH)2] catalyzed CꢀN coupling reactions (Table S2); crystallographic data for
[Pd(NSꢀCH3)2], [Pd(NSꢀCl)2], [Pd(CNSꢀH)(PPh3)] and [Pd(CNSꢀCl)(PPh3)] (Table S3);
and structures of [Pd(NSꢀCH3)2] (Fig. S1), [Pd(NSꢀCl)2] (Fig. S2), [Pd(CNSꢀH)(PPh3)]
(Fig. S3) and [Pd(CNSꢀCl)(PPh3)] (Fig. S4).

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Introduction
The chemistry of transition metal complexes of the thiosemicarbazone ligands has been
attracting significant current attention,1 largely because of their bioinorganic relevance. A
vast majority of the thiosemicarbazone complexes have found wide medicinal
applications due to their potentially beneficial biological (viz. antibacterial, antimalarial,
antiviral and antitumor) activities.2 Studies on the coordination chemistry of
thiosemicarbazone ligands of different types are therefore of considerable importance.
The present work has originated from our continued interest in the chemistry of
thiosemicarbazone complexes of selected transition metal ions, with particular reference
to variable binding mode of thiosemicarbazone ligands displayed in these complexes.3
Recently we have reported the synthesis and characterization of two groups of mixedꢀbis
complexes of palladium incorporating thiosemicarbazone and a N,Oꢀdonor ligand, viz.
the anion derived from quinolinꢀ8ꢀol or 1ꢀnitrosoꢀ2ꢀnaphthol via dissociation of the
phenolic proton.3b A group of five 4ꢀRꢀbenzaldehyde thiosemicarbazones (denoted in
general as HLꢀR) were utilized for this study, and in the mixedꢀbis complexes they were
found to bind to the metal center as monoꢀanionic N,Sꢀdonor, via release of the acidic
proton, forming stable fiveꢀmembered chelate ring (I).3b With respect to the structure of
R = OCH3, CH3,
Pd
R
H, Cl, NO2
H
N
S
N
NH2
N
H
NH2
S
H
N
R
HL-R
I
the uncoordinated HLꢀR ligand,3d,q the observed mode of binding (I) was quite interesting
as it involved a change in geometry around the preꢀexisting imine (C=N) bond. The
novelty of such mixedꢀbis complexes of palladium containing two different unsymmetric
bidentate ligands, which seems nonꢀexistent prior to our report,3b tempted us to
synthesize new mixedꢀbis complexes of palladium, utilizing Na2[PdCl4] as the source of
palladium, the same 4ꢀRꢀbenzaldehyde thiosemicarbazones (HLꢀR) as the principal

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ligand, and other anionic N,Oꢀdonor ancillary ligands. During our attempts to achieve
this target we have discovered that while 2ꢀpicolinic acid (denoted as Hpic) is used as the
N,Oꢀdonor ligand, the products obtained are not of the targeted mixedꢀbis type, i.e.
[Pd(LꢀR)(NꢀO)] type, but are actually a mixture of two types of complexes, viz. bisꢀ
thiosemicarbazone complex and oligomeric complex. More interestingly, these bisꢀ
chelated complexes are found to have cisꢀgeometry, which is rare for homoleptic bisꢀ
complexes of palladium,4 and the binding mode of the benzaldehyde thiosemicarbazones
in these complexes is also found to be rather uncommon (vide infra). Interesting
reactivity has been displayed also by the oligomeric complexes towards synthesis of
monomeric organopalladium complexes. Herein we report the chemistry of all these
palladium thiosemicarbazone complexes, with special reference to their formation,
structure and, efficiency in catalyzing CꢀC and CꢀN coupling reactions.

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Results and discussion
Syntheses and structures
As outlined in the introduction, this work was intended to synthesize a family of mixedꢀ
bis complexes of palladium containing two different anionic ligands provided, via
dissociation of the acidic proton, by a 4ꢀRꢀbenzaldehyde thiosemicarbazone (HLꢀR) and
2ꢀpicolinic acid. Accordingly, reactions of the chosen thiosemicarbazones and 2ꢀpicolinic
acid with Na2[PdCl4] have been carried out in ethanolic medium in the presence of
triethylamine, each of which has afforded an orange product in relatively low yield,
together with an insoluble species.5 Preliminary characterizations (C, H, N analyses,
NMR, IR) on these orange products indicate the absence of any picolinate ligand in them,
instead, all the characterization data are found to agree well with a bisꢀthiosemicarbazone
formulation. For an unambiguous characterization of these complexes, with regard to
their composition and stereochemistry, and coordination mode of the thiosemicarbazone
ligands in them, structure of a selected member of this family, viz. the one obtained from
the reaction with HLꢀOCH3, has been determined by Xꢀray crystallography. The structure
is shown in Fig. 1 and selected bond parameters are listed in Table 1. The structure shows
Fig. 1
that two thiosemicarbazone ligands are indeed coordinated to palladium as monoanionic
bidentate N,Sꢀdonor forming fiveꢀmembered chelate ring (II). Examination of the relative
R
H
Pd
N
S
H
N
NH2
II
disposition of the two coordinated thiosemicarbazone ligands shows that this complex
has a cisꢀgeometry, which is rare for the homoleptic bisꢀchelated palladium complexes.4
It is relevant to mention here that similar bisꢀthiosemicarbazone complexes of palladium,

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having the usual transꢀgeometry, have been synthesized by us by direct reaction of the 4ꢀ
Rꢀbenzaldehyde thiosemicarbazones (HLꢀR) with Na2[PdCl4].3d It is also interesting to
note that though in the present series of cisꢀbis complexes, as well as in the previously
reported transꢀbis complexes,3d 5ꢀmembered chelate rings (II and I, respectively) are
formed utilizing the same two donor atoms, they are not identical. In I, a change in
geometry, with respect to the uncoordinated HLꢀR ligand, around the preꢀexisting imine
(C=N) bond is observed, which moves the phenyl ring away from the metal center. In II,
no such drastic change in geometry is noticed, and the phenyl ring is found to remain on
the same side of the imine bond as it was in the uncoordinated ligand, which is rather
uncommon.3c In the uncoordinated ligand the phenyl ring shares almost the same plane
with the rest of the molecule, and keeping this stereochemistry intact five membered
chelate ring formation was predicted to be impossible due to steric problem between the
phenyl ring and the metal center.3q It is interesting to note that in chelate II the phenyl
ring is twisted significantly (through >20°) away from the plane containing the palladium
coordinated ꢀNꢀN=CꢀSꢀ fragment, presumably to get rid of the possible steric strain that
would develop without this twist. The observed twist of the two phenyl rings in the two
coordinated thiosemicarbazones is found to bring two ortho CꢀH bonds in close
proximity to the metal center (by ≥ 2.7 Å) along the axial side, and this closeness results
in an effective agostic interaction between the 16ꢀelectron distorted squareꢀplaner
palladium(II) and the CꢀH fragments. The PdꢀN and PdꢀS bond distances are all quite
normal, as observed in structurally characterized complexes of palladium containing
these bonds.6 The absence of any solvent of crystallization in the lattice of this crystal
indicates possible existence of nonꢀcovalent interactions between the individual complex
molecules. In order to check this, packing pattern in the lattice has been scrutinized,
which (Fig. 2) shows that intermolecular hydrogen bonding interactions of five types, viz.
Fig. 2
CꢀHꢀꢀꢀS, NꢀHꢀꢀꢀO, CꢀHꢀꢀꢀO, NꢀHꢀꢀꢀN and CꢀHꢀꢀꢀπ, are active in the lattice. Each
complex molecule is thus linked to six surrounding complex molecules through such
interactions involving different fragments on the two coordinated thiosemicarbazone
ligands. These hydrogenꢀbonding interactions, extended throughout the lattice, seem to
be responsible for holding the crystal together.

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In order to ensure that in all the five synthesized bisꢀcomplexes the
thiosemicarbazones are coordinated to palladium in the same fashion (II), structures of
two other complexes of this family, viz. those obtained from the reaction with HLꢀCH3
and HLꢀCl, have also been determined by Xꢀray crystallography. Both the structures (Fig.
S1 and Fig. S2, Table S1, ESI†) are found to be very similar, in every respect, to that of
the earlier complex. As all the five bisꢀcomplexes were obtained similarly and they show
similar properties (vide infra), the other two bisꢀcomplexes derived from HLꢀH and HLꢀ
NO2, are assumed to have similar structure as the other three structurally characterized
complexes. Based on the observed NSꢀmode of binding (II) of the thiosemicarbazone
ligands in these five bisꢀcomplexes, they will henceforth be abbreviated in general as
[Pd(NSꢀR)2].
After adequate characterization of the [Pd(NSꢀR)2] complexes, and being
particularly intrigued by their cis geometry and the agostic interactions prevailing in
them, we were interested to find out identity of the insoluble species, which was obtained
as a minor product from each of the synthetic reaction.5 It must be mentioned at this point
that during our attempts to optimize yields of the [Pd(NSꢀR)2] complexes, it has been
observed that with increase in the reflux time the yield of these insoluble species also
increases, and refluxing for about five hours is found to afford these insoluble species in
optimum yields. Microanalytical data on these complexes agree excellently with a
R
R
Pd
Pd
N
S
N
S
H
N
H
N
NH2
NH2
n
III
[{Pd(CNS-R)}n]
formulation where palladium(II) is coordinated by a doubly deꢀprotonated
thiosemicarbazone ligand in CNSꢀfashion, as shown in III. In this fragment, though

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dipositive charge on the metal center gets satisfied by the dianionic ligand, only three
coordination sites on palladium, out of required four, could be satisfied by a single
tridentate thiosemicarbazone. In order to fulfill the remaining coordination site on
palladium, this coordinatively unsaturated fragment III is believed to undergo
oligomerization through sulfurꢀbridge, affording the insoluble species,5 which is
abbreviated in general as [{Pd(CNSꢀR)}n] based on the speculated CNSꢀmode of binding
of the thiosemicarbazone ligands in them. Lack of solubility of these [{Pd(CNSꢀR)}n]
complexes vitiated their characterization in solution, and also their crystal growth
necessary for an unambiguous structure determination. However, in view of the observed
agostic interaction in the [Pd(NSꢀR)2] complexes between one ortho CꢀH of the NSꢀ
coordinated thiosemicarbazone and the palladium(II) center, this CNSꢀmode of binding
by the same ligands, leading to formation of the [{Pd(CNSꢀR)}n] complexes as byproduct
from the same reaction, seem plausible. It may be mentioned in this context that
formation of such oligomeric palladium thiosemicarbazone complexes, through sulfurꢀ
bridge, is well documented in the literature.3k,7
In order to explore the possibility of forming monomeric complexes by splitting
the sulfur bridge in the [{Pd(CNSꢀR)}n] complexes, their reaction has been carried out
with a monodentate ligand containing a soft donor atom, viz. triphenylphosphine. From
each of these reactions a yellow complex has been obtained in a decent yield.
Preliminary characterization (C, H, N analyses, NMR, IR) data on these yellow
complexes are indeed found to correspond well with the expected monomeric [Pd(CNSꢀ
R)(PPh3)] formulation. To authenticate the speculated CNSꢀmode of coordination of the
thiosemicarbazone ligand in these complexes, crystal structure of a selected member from
this group, viz. [Pd(CNSꢀCH3)(PPh3)], has been determined. The structure (Fig. 3) shows
Fig. 3
that the thiosemicarbazone is indeed coordinated to palladium as a tridentate CNSꢀdonor
forming two adjacent fiveꢀmembered chelate rings (III), and a triphenylphosphine has
taken up the remaining coordination site on the metal center. Palladium is thus nested in a
CNSP core, which is distorted significantly from ideal square planar geometry, as
manifested in the bond parameters around the metal center (Table 1). An examination of

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the packing pattern within the crystal lattice, to find out the nature of nonꢀcovalent
interactions in it, shows (Fig. 4) that three types of hydrogen bonding interactions, viz. Nꢀ
HꢀꢀꢀS, NꢀHꢀꢀꢀπ and CꢀHꢀꢀꢀπ, are active in this lattice, which link the individual complex
Fig. 4
molecules within the crystal. In order to ensure that in all the five [Pd(CNSꢀR)(PPh3)]
complexes the thiosemicarbazones are coordinated to palladium in the same CNSꢀfashion
(III), structures of two other complexes of this family, viz. [Pd(CNSꢀH)(PPh3)] and
[Pd(CNSꢀCl)(PPh3)], have also been determined by Xꢀray crystallography. Both the
structures (Fig. S3 and Fig. S4, Table S1, ESI†) are found to be very similar, in every
respect, to that of the [Pd(CNSꢀCH3)(PPh3)] complex. As all the five [Pd(CNSꢀR)(PPh3)]
complexes were obtained similarly and they show similar properties (vide infra), the
other two complexes of this family, viz. [Pd(CNSꢀOCH3)(PPh3)] and [Pd(CNSꢀ
NO2)(PPh3)], are assumed to have the same structure as the other three structurally
characterized complexes.
Formation of two types of complexes, viz. the bisꢀthiosemicarbazone complexes
having the uncommon cis geometry and the oligomeric complexes containing the CNSꢀ
coordinated thiosemicarbazone, from the same reaction has been quite intriguing.
Particularly mysterious is the role of picolinic acid in this reaction, as it is not present in
any form in the final products, but in its absence the reaction affords only the known bisꢀ
thiosemicarbazone complexes with usual transꢀgeometry. Though the exact mechanism
behind formation of the [Pd(NSꢀR)2] and [{Pd(CNSꢀR)}n] complexes is not clear to us,
some speculated steps, that seem logical, are presented in Scheme 1. In the initial step
Scheme 1
picolinic acid is believed to bind to palladium, via elimination of HCl and displacement
of few coordinated chlorides, to generate an intermediate A. Reaction of benzaldehyde
thiosemicarbazone with A seems to proceed via two different routes, both of which
involve loss of coordinated picolinate and chloride ions from A, which requires the
supply of two protons. When these two protons come from two interacting
thiosemicarbazones, the [Pd(NSꢀR)2] complexes with cisꢀgeometry are formed. However,

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in case both the protons are provided by a single thiosemicarbazone, the oligomeric
[{Pd(CNSꢀR)}n] complexes result. The sulfurꢀbridge in these oligomeric [{Pd(CNSꢀR)}n]
complexes undergo facile splitting upon reaction with triphenylphosphine to yield the
monomeric [Pd(CNSꢀR)(PPh3)] complexes. As already mentioned above, the role of
picolinic acid in the synthetic reaction, though not well understood, is absolutely crucial
in steering the course of the reaction in a definitive way. Evidence behind binding of
palladium by picolinic acid utilizing both pyridineꢀnitrogen and carboxylateꢀoxygen, as
shown in the intermediate A, comes from the fact that similar reactions carried out with
either pyridine or benzoic acid, instead of picolinic acid, neither afford the cisꢀ[Pd(NSꢀ
R)2] complexes, nor the oligomeric [{Pd(CNSꢀR)}n] complexes.
Spectral properties
1H NMR spectra of these complexes, recorded in CDCl3 solution, show all the expected
signals. For example, from the coordinated thiosemicarbazone, signals for the NH2
protons and the azomethine proton could be easily detected in all the complexes. In the
[Pd(NSꢀOCH3)2] and [Pd(NSꢀCH3)2] complexes, signals for the OCH3 and CH3 groups
have been observed at 3.85 ppm and 2.40 ppm respectively. In the four [Pd(NSꢀR)2] (R ≠
H) complexes, the expected two signals from the aryl rings of the coordinated
thiosemicarbazone have been clearly observed in the aromatic region. Out of the three
expected aryl proton signals in the [Pd(NSꢀH)2] complex, one doublet have been clearly
detected while two triplets could not be distinctly observed due to overlap problem. 1H
NMR spectra of [Pd(CNSꢀR)(PPh3)] complexes, also recorded in CDCl3 solution, show
broad signals for the phenyl protons of the PPh3 ligands within 7.4–7.9 ppm. The NH2
proton signal is observed within 4.8–5.1 ppm. In the [Pd(CNSꢀOCH3)(PPh3)] and
[Pd(CNSꢀCH3)(PPh3)] complexes, signals for the OCH3 and CH3 substituents are
observed respectively at 3.84 and 1.73 ppm. Most of the expected signals from the phenyl
ring of the coordinated thiosemicarbazone are clearly observed in the aromatic region.
The azomethine proton signal could not be detected in four [Pd(CNSꢀR)(PPh3)] (R =
OCH3, CH3, H and Cl) complexes, due to its overlap with the PPh3 signals. However, in
the [Pd(CNSꢀNO2)(PPh3)] complex the azomethine proton signal has been clearly
observed at 6.97 ppm.

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Infrared spectra of the [Pd(NSꢀR)2] complexes show many bands of varying
intensities within 2000 – 500 cmꢀ1. Assignment of each individual band to a specific
vibration has not been attempted. However, comparison of the spectrum of each [Pd(NSꢀ
R)2] complex with that of the corresponding uncoordinated thiosemicarbazone (HLꢀR)
ligand shows that the C=N stretch, observed near 1620 cmꢀ1 in HLꢀR, shifts to about 1600
cmꢀ1 on binding to palladium(II). Besides, a strong band displayed by all the complexes
within 1502 – 1522 cmꢀ1 is attributable to the C=N bond, which is formed due to
dissociation of the acidic proton and is in resonance with the negative charge on the
sulfur. The CꢀS stretch, which is observed around 865 cmꢀ1 in the free HLꢀR ligands,
appears within 808 – 835 cmꢀ1 in all the complexes indicating thiolate nature of the
coordinated sulfur. In the [Pd(NSꢀNO2)2] complex two prominent bands at 1356 and
1537 cmꢀ1, which are not found in the spectra of the other four complexes, are attributed
to the nitro group. Besides the appearance of three strong bands near 533, 693 and 746
cmꢀ1 due to the coordinated PPh3 ligands, infrared spectra of the [Pd(CNSꢀR)(PPh3)]
complexes are found to be qualitatively similar to those of the corresponding [Pd(NSꢀR)2]
complexes. Infrared spectra of the [{Pd(CNSꢀR)}n] complexes show many common
bands with the corresponding [Pd(NSꢀR)2] complexes. However, a sharp band is
displayed by each of the [{Pd(CNSꢀR)}n] complexes within 709 – 715 cmꢀ1, which is
absent in the corresponding [Pd(NSꢀR)2] complex, and hence it is attributed to the
1
bridging CꢀS fragment. The H NMR and infrared spectral data of palladium complexes
of all the three types are therefore consistent with their composition.
The [Pd(NSꢀR)2] and [Pd(CNSꢀR)(PPh3)] complexes are found to be readily
soluble in solvents like methanol, ethanol, acetone, acetonitrile, dichloromethane,
chloroform, etc., producing bright yellow solutions. Electronic spectra of all these
complexes have been recorded in dichloromethane solutions. Intense absorptions in both
visible and ultraviolet regions are displayed by these complexes (Table 2). The
absorptions in the ultraviolet region are assignable to transitions within the ligand
orbitals. In order to understand the origin of the absorptions in the visible region, DFT
calculations have been performed on all the five members of both [Pd(NSꢀR)2] and
[Pd(CNSꢀR)(PPh3)] complexes, and the results are found to be qualitatively similar for all
of them. Compositions of the highest occupied molecular orbital (HOMO) and the lowest

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unoccupied molecular orbital (LUMO) are given in Table 3, and contour plots of these
molecular orbitals for one representative complex from each series, viz. [Pd(NSꢀOCH3)2]
and [Pd(CNSꢀCH3)(PPh3)], are shown in Fig. 5. For the [Pd(NSꢀR)2] complexes, both the
HOMO and LUMO have major (88 – 97%) contribution from the thiosemicarbazone
Fig. 5
ligand, and minor (3 – 12%) from the metal center. In the [Pd(CNSꢀCH3)(PPh3)]
complexes the HOMO has 88 – 91% thiosemicarbazone character and much less (9 –
12%) metal contribution, while the LUMO has 70 – 72% thiosemicarbazone character,
significant (26 – 30%) palladium contribution and relatively poor (0.3 – 2.0%)
contribution from the coordinated PPh3. Hence the lowest energy absorption in all these
complexes is assignable to a transition from a filled orbital to a vacant orbital, both of
which have dominant thiosemicarbazone character.
Catalytic activity
The fact, that palladium complexes are well known to serve as efficient catalysts in
bringing about C–C cross coupling reaction, has led us to explore such catalytic
properties in the present series of [Pd(NSꢀR)2] and [Pd(CNSꢀR)(PPh3)] complexes. These
palladium complexes were first tested as catalysts in the Suzuki type CꢀC cross coupling
reactions between arylhalides and phenylboronic acids to yield the biphenyl products
(Table 4). Initially the [Pd(NSꢀR)2] complexes were tried as catalyst for CꢀC coupling
between pꢀiodoacetophenone and phenylboronic acid, and they were found to
successfully catalyze the coupling reactions with 0.001 mol% catalyst loading, under
relatively mild experimental condition, and with comparable efficiency (entries 1–3).
When the amount of catalyst was reduced by ten times, the yield became significantly
lower (entry 4). With substituted boronic acids the coupling reactions turned out to be
relatively difficult, and the degree of difficulty was found to vary with the nature of
substituent. For example, the reaction with pꢀmethoxyboronic acid required longer time
to achieve same yield as that with unsubstituted boronic acid (entries 1 and 5). A sharp
decrease in yield was observed for a similar reaction with pꢀchloroboronic acid, even
with much higher catalyst loading (entry 6). With electronꢀwithdrawing substituents (viz.

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CHO and CN) in the arylbromides, longer time (relative to the COCH3 substituent) was
required to achieve full conversion (entries 7 and 8).
The observed ease of the Suzuki coupling reactions involving aryliodides, with
particular reference to the mild reaction conditions, low catalyst loading and high yields,
prompted us to examine similar coupling reactions with arylbromides. The targeted
reactions were found to proceed well using [Pd(NS–H)2] as the catalyst (entries 9–13).
However, compared to the corresponding aryliodides, longer time was needed for the
arylbromides to get similar yield. We also examined coupling of phenylboronic acids
with few arylchlorides, and as apprehended, the coupling reactions via C–Cl bond
activation were found to be quite difficult, as reflected in high catalyst loading and longer
reaction time (entries 14ꢀ17).
After witnessing the smooth Suzuki coupling reactions, via CꢀX (X = I, Br, Cl)
bond activation of arylhalides, catalyzed by the [Pd(NSꢀR)2] complexes, catalytic
potential of the corresponding organopalladium complexes, viz. [Pd(CNSꢀR)(PPh3)], was
also examined towards similar Suzuki coupling reactions. The [Pd(CNSꢀR)(PPh3)]
complexes too showed notable, and mutually comparable, catalytic efficiency (entries
18–34, Table 4). Here again, coupling reactions were found to be more and more difficult
on moving from aryliodide to arylbromide to arylchloride. Compared to any particular
[Pd(NSꢀR)2] complex, the corresponding [Pd(CNSꢀH)(PPh3)] complex was found to
display slightly better catalytic activity, manifested primarily in lesser reaction time
needed for achieving similar yield.
Inspired by the facile Suzuki coupling reactions catalyzed by palladium
complexes of both the types, we also investigated catalytic activity of these complexes
towards Buchwald type CꢀN coupling reactions between halobenzenes and primary, as
well as secondary, amines. At first CꢀN coupling was attempted using [Pd(NSꢀH)2] as the
catalyst, and the targeted products could be achieved under relatively mild experimental
condition in reasonably good yields (entries 1–15, Table 5). Coupling between
iodobenzene and primary aromatic amines proceeded smoothly with 0.01 mol% catalyst
loading, and XPhos as additive, to afford the products in high yield (entries 1ꢀ3).

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Catalytic efficiency of [Pd(NSꢀH)2] for CꢀN coupling reactions with the two chosen
secondary amines, viz. morpholine and piperidine, was also found to be similar (entries 4
and 5). Replacement of iodobenzene by bromobenzene was found to turn the coupling
slightly difficult, as manifested in ten times more catalyst loading needed to achieve
similar yield (entries 6–10). It is interesting to note that 24 h reaction time was necessary
for all the [Pd(NSꢀH)2] catalyzed CꢀN coupling reactions involving iodobenzene or
bromobenzene (entries 1–10). Several experiments have actually been carried out by
varying the time for these reactions, and it has been observed that reduction of reaction
time results in corresponding reduction in the yield of the product. The observed variation
of yield as a function of reaction time, for few of these reactions, is presented in Table S2
(ESI†). On moving to chlorobenzene from bromobenzene, the yield was observed to drop
sharply, even with 1 mol% catalyst loading (entries 11–15). When the same coupling
reactions were performed with the [Pd(CNSꢀH)(PPh3)] complex as catalyst, a similar
trend was observed as in the case of [Pd(NSꢀH)2] (entries 16–30). However, the
organopalladium [Pd(CNSꢀH)(PPh3)] complex was found to exhibit slightly better
catalytic efficiency than [Pd(NSꢀH)2], reflected in shorter reaction time or better yield.
The palladium thiosemicarbazone complexes of both types, viz. [Pd(NSꢀR)2] and
[Pd(CNSꢀR)(PPh3)], are thus found to be efficient catalysts for CꢀC and CꢀN coupling
reactions. It is interesting to note that for the Suzuki coupling reactions, which involved
relatively low catalyst loading and afforded the coupled product in reasonably high yield,
no additional ligand was necessary. This indicates that the organic ligands coordinated to
palladium in the native catalyst do not dissociate during in situ generation of
palladium(0) necessary for the catalysis, and they adequately stabilize the reduced metal
center. Another interesting aspect of this observed Suzuki reactions is that the catalysts
can not only activate CꢀI and CꢀBr bonds, but can also activate the rather difficult CꢀCl
bond and afford the coupled product in 100% yield. Catalysts that can activate CꢀCl bond
so efficiently are scarce in the literature.8 The catalytic efficiency of the present group of
[Pd(NSꢀR)2] complexes, having cisꢀgeometry, is found to be much better than the similar
group of bisꢀcomplexes having the usual transꢀgeometry.3d However, catalytic efficiency
of the [Pd(CNSꢀR)(PPh3)] complexes is found to be comparable with that of the reported
thiosemicarbazone complexes containing PPh3 as ancillary ligand.3d The observed

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efficiency is much better than that displayed by many such molecular palladium
complexes, including palladium acetate, under similar ligandꢀfree conditions.9 For the C–
N coupling reactions, in situ formation of palladium(0) is believed to take place with
simultaneous dissociation of the coordinated thiosemicarbazone ligand(s), and hence the
use of XPhos as a stabilizer of the reduced metal center was found to be essential for the
catalysis to proceed smoothly. In spite of the higher catalyst loading, compared to the C–
C couplings, the C–N coupling reactions are found to be very facile, which is relatively
less common.10 Between the two types of palladium complexes, viz. [Pd(NSꢀR)2] and
[Pd(CNSꢀR)(PPh3)], the latter are, in general, found to be better catalysts for both CꢀC
and CꢀN coupling reactions, and this may be attributed to the presence of PPh3 ligand in
the organopalladium complexes, which probably have supported the palladium(0) state,
generated in situ. The catalytic efficiency of the present group of complexes in C–N
coupling reactions is comparable to that of several other palladium complexes under
similar experimental conditions.11 The electronic nature of the substituents in the
thiosemicarbazone ligand seemed to have no predictable influence on the catalytic
activities of the complexes.
Conclusions
The present study shows that NSꢀcoordinated bisꢀthiosemicarbazone complexes of
palladium, [Pd(NSꢀR)2], with rather unusual cis geometry can be conveniently
synthesized via relatively simple reactions. The same reactions also afford a group of
interesting oligomeric organopalladium species of type [{Pd(CNSꢀR)}n] as byproduct,
which undergoes facile splitting upon interaction with triphenylphosphine to yield
monomeric [Pd(CNSꢀR)(PPh3)] complexes. The [Pd(NS–R)2], as well as the [Pd(CNS–
R)(PPh3)], complexes are found to be excellent catalysts for Suzuki type C–C coupling
and Buchwald type C–N coupling reactions.
Experimental
General procedures
Palladium chloride was obtained from Arora Matthey, Kolkata, India. Na2[PdCl4] was
prepared by following reported procedure.12 2ꢀPicolinic acid was purchased from

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Lancaster Synthesis, England. The paraꢀsubstituted benzaldehydes and thiosemicarbazide
were procured from EꢀMerck India Pvt. Ltd. Triphenylphosphine was purchased from
Spectrochem, Mumbai, India. The 4ꢀRꢀbenzaldehyde thiosemicarbazones were prepared
by reacting equimolar amounts of thiosemicarbazide and the respective paraꢀsubstituted
benzaldehyde in a hot 1:1 ethanolꢀwater mixture under stirring condition. All other
chemicals and solvents were reagent grade commercial materials and were used as
received. Microanalyses (C, H and N) were performed using a Heraeus Carlo Erba 1108
1
elemental analyzer. H NMR spectra were recorded in CDCl3 solution on a Bruker
Avance DPX 300 NMR spectrometer using TMS as the internal standard. IR spectra were
obtained on a Perkin Elmer Spectrum Two IR spectrometer with samples prepared as
KBr pellets. Electronic spectra were recorded on a JASCO Vꢀ570 spectrophotometer.
Molecular orbital calculations were carried out by density functional theory (DFT)
method using the Gaussian 03 (B3LYP/SDDꢀ6ꢀ31G) package.13 GCꢀMS analyses were
performed using a Perkin Elmer CLARUS 680 instrument.
Synthesis of the complexes
[Pd(NS-OCH3)2]. To a solution of 4ꢀmethoxybenzaldehyde thiosemicarbazone
(36 mg, 0.17 mmol) and 2ꢀpicolinic acid (21 mg, 0.17 mmol) in hot ethanol (30 mL)
triethylamine (34 mg, 0.34 mmol) was added followed by a solution of Na2[PdCl4] (50
mg, 0.17 mmol) in ethanol (10 mL). The mixture was heated at reflux for 20 min. On
cooling small amount of a brown solid was found to precipitate out, which was removed
by filtration.3 The solvent was then evaporated from the orange filtrate and the solid
mass, thus obtained, was subjected to purification by thinꢀlayer chromatography on a
silica plate. With 1:3 acetonitrileꢀbenzene as the eluant, an orange band separated, which
was extracted with acetonitrile. Upon evaporation of the acetonitrile extract [Pd(NSꢀ
OCH3)2] was obtained as a crystalline yellow solid. Yield: 30%. Anal. Calc. for
1
C18H20N6O2S2Pd: C 41.30; H 3.82; N 16.06. Found: C 41.72; H 3.91; N 16.02%. H
NMR (300 MHz, CDCl3):14 δ (ppm) = 3.85 (s, OCH3), 4.62 (s, NH2), 6.85 (d, J = 7.5 Hz,
2H), 7.13 (s, azomethine), 7.47 (d, J = 7.8 Hz, 2H). IR (wave number, cmꢀ1): 511, 686,
710, 835, 854, 1027, 1175, 1260, 1343, 1384, 1505, 1602.

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[Pd(NS-CH3)2]. This complex was synthesized by following almost the same
above procedure using HL-CH3 instead of HL-OCH3 and the refluxing was done only
for 10 min. Yield: 35%. Anal. Calc. for C18H20N6S2Pd: C 43.99; H 4.07; N 17.11. Found:
1
C 45.32; H 4.01; N 17.51%. H NMR (300 MHz, CDCl3): δ (ppm) = 2.40 (s, CH3), 4.83
(s, NH2), 7.15 (d, J = 7.8 Hz, 2H), 7.38 (s, azomethine), 7.54 (d, J = 7.8 Hz, 2H). IR
(wave number, cmꢀ1): 516, 696, 810, 875, 1019, 1181, 1290, 1302, 1384, 1522, 1606.
[Pd(NS-H)2]. This complex was synthesized by following almost the same above
procedure using HL-H as the ligand and the refluxing was done only for 5 min. Yield:
27%. Anal. Calc. for C16H16N6S2Pd: C 41.52; H 3.46; N 18.16. Found: C 41.66; H 3.59;
1
N 18.20%. H NMR (300 MHz, CDCl3): δ (ppm) = 5.59 (s, NH2), 7.42 (3H)*, 7.53 (s,
azomethine), 8.11 (d, J = 8.1 Hz, 2H). IR (wave number, cmꢀ1): 510, 692, 755, 692, 755,
808, 868, 940, 1219, 1305, 1384, 1446, 1518, 1607.
[Pd(NS-Cl)2]. This complex was synthesized similarly as above using HL-Cl as
the ligand and heating the reaction mixture until the temperature reached 60° C. Yield:
25%. Anal. Calc. for C16H14N6S2Cl2Pd: C 36.13; H 2.63; N 15.81. Found: C 36.47; H
1
2.62; N 15.83%. H NMR (300 MHz, CDCl3): δ (ppm) = 6.90 (s, NH2), 7.52 (d, J = 8.4
Hz, 2H), 7.60 (s, azomethine), 7.82 (d, J = 8.4 Hz, 2H). IR (wave number, cmꢀ1): 514,
816, 1012, 1089, 1316, 1384, 1403, 1483, 1507, 1598.
[Pd(NS-NO2)2]. This complex was synthesized by following the same procedure
followed for [Pd(NSꢀCl)2], using HL-NO2 instead of HL-Cl. Yield: 20%. Anal. Calc. for
1
C16H14N8O4S2Pd: C 34.76; H 2.53; N 20.27. Found: C 35.31; H 2.65; N 20.22%. H
NMR (300 MHz, CDCl3): δ (ppm) = 7.13 (s, NH2), 7.65 (d, J = 8.4 Hz, 2H), 8.26 (s,
azomethine), 8.41 (d, J = 8.5 Hz, 2H). IR (wave number, cmꢀ1): 519, 822, 1017, 1096,
1321, 1356, 1384, 1409, 1492, 1502, 1537, 1595.
[{Pd(CNS-R)}n] complexes. The [{Pd(CNSꢀR)}n] (R = OCH3, CH3, H, Cl, NO2)
complexes were prepared by following a general procedure. Specific details are given
below for a particular complex.

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[{Pd(CNS-OCH3)}n]. To a solution of 4ꢀmethoxybenzaldehyde thiosemicarbazone
(36 mg, 0.17 mmol) and 2ꢀpicolinic acid (21 mg, 0.17 mmol) in hot ethanol (30 mL)
triethylamine (34 mg, 0.34 mmol) was added followed by a solution of Na2[PdCl4] (50
mg, 0.17 mmol) in ethanol (10 mL). The reaction mixture was heated at reflux for 5 h. A
brown precipitate settled down on cooling, which was collected by filtration, washed with
ethanol and dried in air to afford [{Pd(CNSꢀOCH3)}n] as a brown powder. Yield: 72%.
Anal. Calc. for (C9H9N3OSPd)n: C 34.46; H 2.87; N 13.40. Found: C 36.52; H 2.92; N
13.32%. IR (wave number, cmꢀ1): 690, 709, 752, 940, 1009, 1155, 1212, 1307, 1380,
1429, 1515, 1569, 1600.
[{Pd(CNS-CH3)}n]. Yield: 75%. Anal. Calc. for (C9H9N3SPd)n: C 36.31; H 3.03;
N 14.12. Found: C 36.37; H 3.09; N 14.08%. IR (wave number, cmꢀ1): 692, 711, 754,
942, 1011, 1157, 1213, 1308, 1383, 1432, 1517, 1571, 1601.
[{Pd(CNS-H)}n]. Yield: 78%. Anal. Calc. for (C8H7N3SPd)n: C 37.87; H 2.47; N
14.82. Found: C 37.92; H 2.54; N 14.75%. IR (wave number, cmꢀ1): 693, 713, 755, 942,
1014, 1158, 1216, 1310, 1385, 1433, 1519, 1572, 1601.
[{Pd(CNS-Cl)}n]. Yield: 82%. Anal. Calc. for (C8H6N3SClPd)n: C 30.19; H 1.88;
N 13.21. Found: C 30.27; H 1.96; N 13.28%. IR (wave number, cmꢀ1): 694, 715, 758,
943, 1019, 1160, 1217, 1313, 1389, 1436, 1521, 1575, 1603.
[{Pd(CNS-NO2)}n]. Yield: 80%. Anal. Calc. for (C8H6N4O2SPd)n: C 29.23; H
1.83; N 17.05. Found: C 29.29; H 1.92; N 16.97%. IR (wave number, cmꢀ1): 666, 689,
708, 747, 770, 835, 847, 894, 1059, 1107, 1145, 1291, 1370, 1409, 1489, 1512, 1605,
1621, 1675.
[Pd(CNS-R)(PPh3)] complexes. The [Pd(CNSꢀR)(PPh3)] (R = OCH3, CH3, H,
Cl, NO2) complexes were prepared by following a general procedure. Specific details are
given below for a particular complex.

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[Pd(CNS-OCH3)(PPh3)]. The polymeric [{Pd(CNSꢀOCH3)}n] species (100 mg,
0.32 mmol) and triphenylphosphine (100 mg, 0.32 mmol) were taken together in hot
ethanol (20 mL) and the solution was refluxed for 6 h to yield a clear yellow solution.
The solvent was evaporated and the solid mass, thus obtained, was subjected to
purification by thinꢀlayer chromatography on a silica plate. With 1:7 acetonitrileꢀbenzene
as the eluant, a major yellow band separated, which was extracted with acetonitrile. Upon
evaporation of the acetonitrile extract complex [Pd(CNSꢀOCH3)(PPh3)] was obtained as a
crystalline yellow solid. Yield: 65%. Anal. Calc. for C27H24N3OPSPd: C 56.25; H 4.16; N
7.29. Found: C 56.31; H 4.10; N 7.35%. 1H NMR (300 MHz, CDCl3): δ (ppm) = 3.84 (s,
OCH3), 4.79 (s, NH2), 5.84 (d, J = 3.0 Hz, 1H), 6.34 (d, J = 9.0 Hz, 1H), 7.05 (d, J = 7.9
Hz, 1H), 7.40ꢀ7.78 (PPh3+1H)*. IR (wave number, cmꢀ1): 511, 533, 576, 693, 746, 806,
832, 1027, 1097, 1172, 1255, 1308, 1436, 1461, 1504, 1601.
[Pd(CNS-CH3)(PPh3)]. Yield: 67%. Anal. Calc. for C27H24N3PSPd: C 57.86; H
1
4.29; N 7.50. Found: C 57.92; H 4.23; N 7.56%. H NMR (300 MHz, CDCl3): δ (ppm) =
1.73 (s, CH3), 4.87 (s, NH2), 5.99 (d, J = 3.2 Hz, 1H), 6.64 (d, J = 7.4 Hz, 1H), 6.99 (d, J
= 8.5 Hz, 1H), 7.40ꢀ7.70 (PPh3+1H)*. IR (wave number, cmꢀ1): 512, 533, 694, 746, 809,
998, 1028, 1097, 1158, 1183, 1304, 1435, 1481, 1582, 1602.
[Pd(CNS-H)(PPh3)]. Yield: 68%. Anal. Calc. for C26H22N3PSPd: C 57.15; H
1
4.03; N 7.69. Found: C 57.22; H 3.96; N 7.74%. H NMR (300 MHz, CDCl3): δ (ppm) =
4.92 (s, NH2), 6.24 (d, J = 7.3 Hz, 1H), 6.48 (t, J = 7.5 Hz, 1H), 6.84 (t, J = 7.5 Hz, 1H),
7.10 (d, J = 9.0 Hz, 1H), 7.37ꢀ7.74 (PPh3+1H)*. IR (wave number, cmꢀ1): 512, 533, 599,
693, 746, 849, 998, 1027, 1096, 1158, 1182, 1210, 1307, 1435, 1480, 1584, 1600.
[Pd(CNS-Cl)(PPh3)]. Yield: 62%. Anal. Calc. for C26H21N3PSClPd: C 53.75; H
1
3.62; N 7.24. Found: C 53.79; H 3.55; N 7.31%. H NMR (300 MHz, CDCl3): δ (ppm) =
4.93 (s, NH2), 6.07 (d, J = 4.5 Hz, 1H), 6.80 (d, J = 9.0 Hz, 1H), 7.0 (d, J = 9.0 Hz, 1H),
7.39ꢀ7.67 (PPh3+1H)*. IR (wave number, cmꢀ1): 512, 533, 693, 745, 808, 863, 998, 1027,
1098, 1158, 1184, 1304, 1436, 1481, 1565, 1584, 1603.

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[Pd(CNS-NO2)(PPh3)]. Yield: 61%. Anal. Calc. for C26H21N4O2PSPd: C 52.80; H
1
3.55; N 9.48. Found: C 52.87; H 3.48; N 9.51%. H NMR (300 MHz, CDCl3): δ (ppm) =
5.13 (s, NH2), 6.61 (d, J = 9.0 Hz, 1H), 6.76 (d, J = 6.0 Hz, 1H), 6.97 (s, azomethine),
7.16 (d, J = 9.0 Hz, 1H), 7.42ꢀ7.89 (PPh3). IR (wave number, cmꢀ1): 511, 533, 693, 746,
839, 998, 1027, 1098, 1214, 1330, 1436, 1460, 1497, 1579.
Crystallography
Single crystals of [Pd(NSꢀOCH3)2], [Pd(NSꢀCH3)2], [Pd(NSꢀCl)2], [Pd(CNSꢀ
CH3)(PPh3)], [Pd(CNSꢀH)(PPh3)] and [Pd(CNSꢀCl)(PPh3)] were obtained by slow
evaporation of solvent from solutions of the respective complexes in acetonitrile.
Selected crystal data and data collection parameters for the [Pd(NSꢀOCH3)2] and
[Pd(CNSꢀCH3)(PPh3)] complexes are given in Table 6, and those for the other four
complexes are deposited as Table S3 (ESI†). Data on all the crystals were collected on a
Bruker SMART CCD diffractometer. Xꢀray data reduction, structure solution and
refinement were done using the SHELXSꢀ97 and SHELXLꢀ97 packages.15 The structures
were solved by the direct methods.
Application as catalysts. General procedure for Suzuki coupling reactions. In a
typical run, an ovenꢀdried 10 mL round bottom flask was charged with a known mole
percent of catalyst and NaOH (1.7 mmol), phenylboronic acid (1.2 mmol) and aryl halide
(1 mmol) with the appropriate solvents (4 mL). The flask was placed in a preheated oil
bath at required temp. After the specified time the flask was removed from the oil bath
and water (20 mL) added, followed by extraction with ether (4 × 10 mL). The combined
organic layers were washed with water (3 × 10 mL), dried over anhydrous Na2SO4, and
filtered. Solvent was removed under vacuum. The residue was dissolved in hexane and
analyzed by GCMS.
General procedure for C-N coupling reactions. In a typical run, an ovenꢀdried 10
mL round bottom flask was charged with a known mole percent of catalyst, NaOtBu (1.3
mmol), XPhos (0.1 mmol), amine (1.2 mmol) and aryl halide (1 mmol) with the
appropriate solvent(s) (4 mL). The flask was placed in a preheated oil bath at required
temp. After the specified time the flask was removed from the oil bath, water (20 mL)

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was added, and extraction with ether (4 × 10 mL) was done. The combined organic layers
were washed with water (3 × 10 mL), dried over anhydrous Na2SO4, and filtered. Solvent
was removed under vacuum. The residue was dissolved in acetonitrile and analyzed by
GCMS.
Acknowledgements
We thank the Referees for their constructive comments, which have been helpful in
preparing the revised manuscript. Financial assistance received from the Department of
Science and Technology, New Delhi [Grant No. SR/S1/ICꢀ29/2009 and SR/S1/RFICꢀ
01/2009] is gratefully acknowledged. Jayita Dutta thanks the Council of Scientific and
Industrial Research, New Delhi, for their fellowship [Grant No. 09/096(0702)/2011ꢀ
EMRꢀI].

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Chemical shifts are given in ppm and multiplicity of the signals along with the
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**********

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Table 1 Selected bond distances and bond angles for [Pd(NSꢀOCH3)2]
and [Pd(CNSꢀCH3)(PPh3)]
[Pd(NSꢀOCH3)2]
Bond distances (Å)
Pd1ꢀN1
Pd1ꢀS1
C8ꢀN1
N1ꢀN2
N2ꢀC9
C9ꢀS1
C9ꢀN3
2.066(4)
2.2784(17)
1.286(7)
1.405(5)
1.319(8)
1.741(6)
1.347(5)
Pd1ꢀN4
Pd1ꢀS2
C17ꢀN4
N4ꢀN5
2.063(4)
2.2613(17)
1.277(6)
1.415(6)
1.297(7)
1.742(6)
1.362(7)
N5ꢀC18
C18ꢀS2
C18ꢀN6
Bond angles (°)
N1ꢀPd1ꢀS2
N4ꢀPd1ꢀS1
168.59(11)
166.76(11)
N1ꢀPd1ꢀS1
N4ꢀPd1ꢀS2
81.85(12)
82.12(12)
[Pd(CNSꢀCH3)(PPh3)]
Bond distances (Å)
C8ꢀN1
Pd1ꢀC2
Pd1ꢀN1
Pd1ꢀS1
Pd1ꢀP1
2.051(3)
2.029(2)
1.276(5)
1.368(4)
1.294(5)
1.754(3)
1.357(5)
N1ꢀN2
2.3560(10)
2.2498(6)
N2ꢀC9
C9ꢀS1
C9ꢀN3
Bond angles (°)
N1ꢀPd1ꢀP1
C2ꢀPd1ꢀS1
176.76(9)
162.87(7)
N1ꢀPd1ꢀS1
N1ꢀPd1ꢀC2
81.36(9)
81.57(10)