Synthesis of mono- and trinuclear palladium(II) complexes via oxidative addition of a bulky hexathioether containing a disulfide bond to palladium(0)

Article abstract of DOI:10.1016/j.jorganchem.2006.10.056

The oxidative addition reactions of a bulky hexathioether containing a disulfide bond, TbtS(o-phen)S(o-phen)SS(o-phen)S(o-phen)STbt (1) (Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, o-phen = o-phenylene), to a palladium(0) complex were studied. In t

Full text of DOI:10.1016/j.jorganchem.2006.10.056

Journal of Organometallic Chemistry 692 (2007) 2716–2728
www.elsevier.com/locate/jorganchem
Synthesis of mono- and trinuclear palladium(II) complexes via
oxidative addition of a bulky hexathioether containing a disulfide
bond to palladium(0)
*
Daisuke Shimizu, Nobuhiro Takeda, Norihiro Tokitoh
Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
Received 2 September 2006; received in revised form 27 October 2006; accepted 27 October 2006
Available online 7 November 2006
Abstract
The oxidative addition reactions of a bulky hexathioether containing a disulfide bond, TbtS(o-phen)S(o-phen)SS(o-phen)S(o-
phen)STbt (1) (Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, o-phen = o-phenylene), to a palladium(0) complex were studied. In
the reaction of 1 with 3 molar amounts of [Pd(PPh3)4], a trinuclear palladium(II) complex, [Pd3{S(o-phen)S}2{(o-phen)STbt}2(PPh3)2]
(2), was formed via three-step palladium insertion reaction including unusual C(aryl)–S bond cleavages. On the other hand, the reaction
of 1 with an equimolar amount of [Pd(PPh3)4] afforded mononuclear palladium(II) complex having a pseudo-octahedral structure,
[Pd{S(o-phen)S(o-phen)STbt}2] (3). The hexa-coordinated geometry for the palladium center in 3 was confirmed by the atoms in mol-
ecule (AIM) analysis, which revealed the presence of the bond critical points between the central Pd atom and the S atoms at the axial
positions. In contrast to the bulky system, the reaction of Ph-substituted hexathioether, PhS(o-phen)S(o-phen)SS(o-phen)S(o-phen)SPh
(4), with an equimolar amount of [Pd(PPh3)4] gave a palladium(II) complex having square-planar structure, [Pd{S(o-phen)S(o-
phen)SPh}2] (5). Theoretical calculations revealed that there is no remarkable difference among the energies of isomers of [Pd{S(o-
phen)SPh}2], 6a-syn, 6a-anti, 6b-syn, and 6b-anti. This result suggests that a reason for the preference of the trans-anti-conformation
in 3 is the steric repulsion between the bulky Tbt groups, and that of the cis-syn-conformations in 5 and 6 is the intermolecular
interactions.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Oxidative addition; Hexathioether; Octahedral structure; Tripalladium(II) complex; Bulky substituent
1. Introduction
one of the most explored systems due to two reasons.
One is the great interest in the investigation of the mecha-
nism for the S–S bond addition of diorganyl disulfides to
alkynes catalyzed by [Pd(PPh3)4], which is an efficient sin-
gle-step method for the formation of two C–S bonds in a
stereoselective manner [2]. Many mechanistic studies on
this reaction have been performed using various types of
disulfides and alkynes from the both aspects of experimen-
tal and theoretical studies [3,4]. The other reason is the pos-
sibility for the application to the synthesis of a variety of
palladium complexes having thiolato ligands by taking
advantage of the affinity of sulfur to palladium atoms [5].
For example, the reaction of disulfides (RS)2 with
[Pd(PPh3)4] initially yields a cis-bis(thiolato)palladium(II)
Cleavage of E–E bonds (E = S, Se, and Te) mediated by
transition metal complexes is one of the typical reactivities
of diorganyl dichalcogenides, and various bis(chalcogeno-
lato) mononuclear or chalcogenolato-bridged binuclear
complexes of transition metals have been synthesized so
far by the use of such oxidative additions of dichalcoge-
nides [1]. Particularly, reactions of diorganyl disulfides with
zero-valent palladium complexes, such as [Pd(PPh3)4], are
*
Corresponding author. Tel.: +81 774 38 3200; fax: +81 774 38 3209.
E-mail address: tokitoh@boc.kuicr.kyoto-u.ac.jp (N. Tokitoh).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.10.056

D. Shimizu et al. / Journal of Organometallic Chemistry 692 (2007) 2716–2728
2717
Chart 1.
complex cis-[Pd(SR)2(PPh3)2] via oxidative addition and
subsequently undergoes the dimerization along with the
dissociation of a PPh3 ligand to give cis and trans isomers
of sulfur-bridged binuclear complexes, cis- and trans-
[(RS)(Ph3P)Pd(l-SR)2Pd(SR)(PPh3)] [5b].
Scheme 1. Synthesis of bulky hexathioether 1.
Fig. 1 shows the ORTEP drawing of 1 and the selected
bond lengths, bond angles, and torsion angles are summa-
rized in Table 1.
In addition, the transition-metal-mediated activation of
a C–S bond has been extensively studied from the stand-
points of synthetic chemistry, petrochemical hydrodesulfu-
rization, and bioinorganic chemistry [6]. As far as C(sp2)–S
activation is concerned, a number of examples on thio-
phene derivatives have been studied and well established
[7]. On the contrary, there are relatively few reports on
an aryl C(sp2)–S bond activation [8].
Hexathioether 1 is made up of the interlinked sulfide
parts and the central disulfide moiety. In the crystal struc-
ture, hexathioether 1 has a conformation close to C2 sym-
metry. All the C–S bond lengths of diarylsulfide moieties of
˚
1 (1.772(4)–1.787(4) A) are within the range of C–S dis-
tances reported for diarylsulfides [14]. The lengths of the
C–S and S–S bonds of the diaryldisulfide moiety of 1
On the other hand, we have succeeded in the syntheses
of a variety of highly reactive low-coordinate species con-
taining main group metals by taking advantage of effective
steric protection groups, 2,4,6-tris[bis(trimethylsilyl)me-
thyl]phenyl (Tbt) and 2,6-bis[bis(trimethylsilyl) methyl]-4-
[tris(trimethylsilyl)methyl]phenyl (Bbt) groups [9]. We have
recently reported that the reaction of a bulky, o-phenylene
bridged hexathioether containing a disulfide bond, TbtS(o-
phen)S(o-phen)SS(o-phen)S(o-phen)STbt (1) (o-phen =
o-phenylene), with 3 molar amounts of [Pd(PPh3)4] affords
tetrakis(l-thiolato)tripalladium(II) complex 2 via the cleav-
age of the one S–S and the two C(aryl)–S bonds of 1 (see
Chart 1) [10]. As a general rule, an aryl C(sp2)–S bond
has been thought to be inactive against palladium(0) com-
plexes, and this is the first example of the cleavage of aryl
C(sp2)–S bond by a palladium(0) complex [11]. In this
paper, we describe the details of the reaction of 1 with
[Pd(PPh3)4], the studies to elucidate the mechanism for
the formation of 2, and the investigation on the pseudo-
hexa-coordinated geometry of monopalladium(II) complex
3 obtained by the reaction of 1 with an equimolar amount
of [Pd(PPh3)4].
˚
˚
(1.794(4) A for C(39)–S(3), 1.792(4) A for C(40)–S(4), and
˚
2.0364(15) A for S(3)–S(4)) are also close to those observed
in common diaryldisulfides (1.754–1.789 A for aryl C–S
bonds and 2.023–2.099 A for S–S bonds) [15].
˚
˚
Interestingly, almost linear alignment of the four inner
sulfur atoms (S2–S5) was observed. This alignment may
be explained in terms of the np(S)–r*(S–S)–np(S) four cen-
ter-six electron bond, which has been proposed by Nakani-
shi et al. based on the experimental and the theoretical
studies to explain the linear alignments of chalcogen atoms
in a bis[8-(arylthio)naphthyl]-1,10-disulfide system [16]. The
angles of S2–S3–S4 (163.5ꢁ) and S3–S4–S5 (162.2ꢁ) of 1 dif-
fer little from those observed in bis[8-(phenylthio)naph-
thyl]-1,10-disulfide (168.6 and 166.0ꢁ). The distances of
˚
˚
S2ꢀ ꢀ ꢀS3 (3.056 A) and S4ꢀ ꢀ ꢀS5 (3.054 A) of 1 are shorter
than the sum of the van der Waals radii of sulfur atoms
(3.70 A) [17], though the distances are relatively longer
than those observed in bis[8-(phenylthio)naphthyl]-1,10-
˚
˚
disulfide (2.988(2) A), probably due to the difference
between the 1,2-phenylene and 1,8-naphthylene systems.
Consequently, the linear alignment of the four sulfur atoms
observed in 1 might be interpreted in terms of the np(S)–
r*(S–S)–np(S) four center-six electron bond.
2. Results and discussion
2.1. Synthesis of bulky hexathioether 1
2.2. Reaction of 1 with [Pd(PPh3)4]
Coupling reaction of TbtSC6H4I [12] with an equimolar
amount of 1,2-benzenedithiol in the presence of Cu2O in
refluxing 2,4,6-trimethylpyridine [13] generated the corre-
sponding thiol intermediate. Oxidative coupling reaction
of the thiol intermediate gave disulfide 1 in good yield
(Scheme 1). Hexathioether 1 was characterized by NMR
and mass spectrometry together with elemental analysis,
and the molecular structure of 1 in the crystalline state
was definitively determined by X-ray structural analysis.
To a benzene solution of 1 was added 3 molar amounts
of [Pd(PPh3)4], and the resulting yellow solution was stir-
red at room temperature for 12 h. The crude product was
purified by GPC (gel permeation chromatography) to
afford trinuclear palladium(II) complex 2 as yellow crys-
tals in 71% yield (Scheme 2). Tripalladium(II) complex
2 was characterized by NMR and mass spectrometry
and elemental analysis, and its molecular structure in

2718
D. Shimizu et al. / Journal of Organometallic Chemistry 692 (2007) 2716–2728
Fig. 1. ORTEP drawing of 1 (50% probability) (left: front view, right: side view). Hydrogen atoms, trimethylsilyl groups, and solvent molecules are
omitted for clarity.
First, we examined the reaction of 1 with an equimolar
amount of [Pd(PPh3)4]. To a benzene solution of the bulky
hexathioether 1 was added an equimolar amount of
[Pd(PPh3)4] at room temperature. After stirring for 12 h
at this temperature, the solvent was removed under
reduced pressure. The residue was washed with acetonitrile
and purified by recrystallization from chloroform/acetoni-
trile to give a mononuclear palladium(II) complex 3 in 88%
yield as green crystals (Scheme 3). Monopalladium(II)
complex 3 was characterized by NMR and mass spectrom-
etry together with elemental analysis. The molecular struc-
ture of 3 in the crystalline state was definitively determined
by X-ray structural analysis (vide infra).
In this reaction, the oxidative addition of the central
disulfide bond of hexathioether 1 to the palladium(0) center
occurred selectively. Taking this result into consideration,
the formation of tripalladium(II) complex 2 by the reaction
of 1 with 3 molar amounts of [Pd(PPh3)4] can be explained
in terms of the initial oxidative addition of the central S–S
bond to the palladium(0), followed by the oxidative addi-
tion of the aryl C(sp2)–S bonds toward monopalladium(0)
species.
The reaction of 1 with 2 molar amounts of [Pd(PPh3)4] in
benzene at room temperature for 12 h resulted in the forma-
tion of trinuclear palladium(II) complex 2 (51%) and mon-
opalladium(II) complex 3 (24%) together with the recovery
of 1 (18%) (Scheme 3). Interestingly, no bimetallic product
was obtained in this reaction, suggesting that a bimetallic
species generated by the oxidative addition of the aryl C–S
bond of a monopalladium(II) intermediate to a palldium(0)
complex is immediately converted to a tripalladium(II)
species by the further palladium(0) insertion reaction.
Table 1
Selected bond lengths (A), angles (ꢁ), and torsion angles (ꢁ) of 1
˚
S1–C1
1.782(4)
1.787(4)
1.794(4)
1.792(4)
1.773(4)
1.784(4)
S1–C28
S2–C34
S3–S4
S5–C45
S6–C51
1.772(4)
1.781(4)
2.0364(15)
1.779(4)
1.774(4)
S2–C33
S3–C39
S4–C40
S5–C46
S6–C52
C28–S1–C1
C39–S3–S4
C46–S5–C45
106.39(18)
106.17(14)
103.9(2)
C34–S2–C33
C40–S4–S3
C51–S6–C52
103.88(19)
105.52(15)
104.95(19)
C1–S1–C28–C33
C34–C39–S3–S4
S3–S4–C40–C45
C46–C51–S6–C52
167.8(3)
ꢁ169.4(3)
ꢁ169.1(3)
169.2(3)
C28–C33–S2–C34
C39–S3–S4–C40
C40–C45–S5–C46
62.8(4)
ꢁ84.65(19)
ꢁ148.7(3)
the crystalline state was determined by X-ray structural
analysis [10].
The formation of trinuclear palladium(II) complex 2 is
most likely interpreted in terms of the three-step palladium
insertion reaction into the one S–S and the two C–S bonds
of hexathioether 1. Since the insertion of transition metals
toward S–S bonds is one of the typical reactions of disul-
fides, the S–S bond cleavage of hexathioether 1 is not so
surprising. As mentioned above, the aryl C(sp2)–S bond
cleavage mediated by a palldium(0) complex is unprece-
dented, albeit a number of studies on palladium complexes
coordinated with sulfur ligand having aryl C(sp2)–S bonds
have been reported so far. Therefore, the reaction mecha-
nism of the aryl C(sp2)–S bond cleavage is very interesting.
2.3. Mechanism for the formation of 2
To elucidate the mechanism for the formation of trinu-
clear palladium(II) complex 2, we studied the reactions of
hexathioether 1 with various amounts of [Pd(PPh3)4].
Scheme 3. Reactions of hexathioether
[Pd(PPh3)4].
1 with various amounts of
Scheme 2. Synthesis of trinuclear palladium(II) complex 2.

D. Shimizu et al. / Journal of Organometallic Chemistry 692 (2007) 2716–2728
2719
The reaction of 1 with 4 molar amounts of [Pd(PPh3)4]
in benzene at room temperature for 12 h gave trinuclear
palladium(II) complex 2 in 96% yield (Scheme 3). In this
reaction, no tetrapalladium species could not be obtained,
although complex 2 still has unreacted thioether sites, Tbt–
S–C6H4 moieties.
To understand the formation mechanism of tripalla-
dium(II) complex 2 in more detail, we examined the step-
wise synthesis of 2 from the monopalladium(II) complex 3.
To a benzene suspension of 3 was added 2 molar
amounts of [Pd(PPh3)4], and the resulting mixture was stir-
red at room temperature for 62 h. After removal of the sol-
vent, the residue was washed with acetonitrile to recover
the starting material 3 quantitatively. This result indicates
that a palladium(0) complex does not react directly with
the aryl C–S bond of monopalladium(II) complex 3, that
is, tripalladium(II) complex 2 is not formed via monopalla-
dium(II) complex 3. Under the conditions for the forma-
tion of tripalladium(II) complex 2, a certain amount of
free PPh3 molecules dissociated from [Pd(PPh3)4] should
exist in the reaction mixture. To increase the concentration
of PPh3 in the reaction mixture, the reaction of 2 with 2
molar amounts of [Pd(PPh3)4] was examined in the pres-
ence of 10 molar amounts of PPh3 (Scheme 4).
Scheme 5. A plausible mechanism for the activation of 3.
When 10 molar amounts of PPh3 was added to a ben-
zene suspension of 3 and 2 molar amounts of [Pd(PPh3)4]
was added at room temperature, the resulting yellow sus-
pension gradually turned to a brown suspension. After stir-
ring for 62 h at this temperature, the reaction mixture was
filtered to recover 3 as green precipitates in 52% yield. The
organic filtrate was evaporated and the residue was purified
by GPC to afford trinuclear palladium(II) complex 2 in
28% yield. These results suggest that monopalladium(II)
intermediates having PPh3 ligand(s) are concerned in the
unusual C(aryl)–S cleavage. Additionally, considering that
the unusual C(aryl)–S cleavage by a palladium(0) complex
should requires a special electronic state around the
C(aryl)–S bond significantly different from those of usual
thioethers, 5- or 6-coordinated species, such as A or B
shown in Scheme 5, might be reactive intermediates of
the C(aryl)–S bond cleavage leading to the formation of 2.
2.4. X-ray structural analysis of mononuclear Pd(II)
complex 3
Fig. 2. ORTEP drawings of 3 (50% probability). Hydrogen atoms,
trimethylsilyl groups, and a solvent molecule were omitted for clarity.
Single crystals of 3 suitable for X-ray crystallographic
analysis were obtained by recrystallization from benzene/
acetonitrile. Fig. 2 shows the molecular structure of 3 in
the crystalline state and the selected bond lengths, angles,
and torsion angles are summarized in Table 2. The two
thiolato-S atoms and the two sulfide-S atoms are situated
with a slightly distorted trans-square planar coordination
geometry around the central palladium atom, and the
two sulfur atoms next to the Tbt groups exist at the axial
positions to construct a slightly distorted octahedral struc-
ture of 3. The two thiolato-S–Pd bond distances
*
˚
(2.307(3) A for S1–Pd1 and S1 –Pd1) are slightly longer
˚
than the two sulfide-S–Pd bond distances (2.270(3) A for
S2–Pd1 and S2*–Pd1). On the other hand, the distances
between the palladium and the two sulfur atoms at the
axial positions (Pd1ꢀ ꢀ ꢀS3 and Pd1ꢀ ꢀ ꢀS3* = 3.385(2) A) are
˚
Scheme 4. Reaction of 3 with [Pd(PPh3)4] in the presence of PPh3.
slightly shorter than the sum of the van der Waals radii

2720
D. Shimizu et al. / Journal of Organometallic Chemistry 692 (2007) 2716–2728
in general, a negative value of $2q indicates that the elec-
Table 2
˚
˚
Selected bond lengths (A), atomic distances (A), angles (ꢁ), and torsion
angles (ꢁ) of monopalladium(II) complex 3
tron density is locally concentrated, while a positive value
of $2q means that the electron density is locally depleted.
The positive value of $2qPdꢀ ꢀ ꢀS ð0:033 eaꢁ0 5Þ suggests that
the Pd1ꢀ ꢀ ꢀS3 and Pd1ꢀ ꢀ ꢀS3* interactions are dominantly
electrostatic in nature.
Pd1–S1
S1–C1
S2–C7
S3–C13
S1ꢀ ꢀ ꢀS2
S1–Pd1–S2
C1–S1–Pd1
C6–S2–C7
2.307(3)
1.759(10)
1.743(10)
1.782(8)
3.196(3)
Pd1–S2
S2–C6
S3–C12
Pd1ꢀ ꢀ ꢀS3
2.270(3)
1.784(10)
1.763(10)
3.385(2)
2.6. Synthesis of less bulky hexathioether 4
88.56(10)
102.2(4)
104.6(5)
S2–Pd1–S1*
C6–S2–Pd1
C12–S3–C13
91.44(10)
104.2(4)
103.8(4)
In order to investigate the effect of the bulky substituents
in the pseudo-6-coordination structure of 3, we synthesized
a phenyl analog of 1, PhS(o-phen)S(o-phen)SS(o-phen)S(o-
phen)SPh (4), and examined the reaction of 4 with an equi-
molar amount of [Pd(PPh3)4].
Pd1–S2–C7–C12
C7–C12–S3–C13
ꢁ54.8(8)
S1–Pd1–S2–C7
S3–Pd1–S1–C1
128.0(4)
54.6(3)
177.0(7)
˚
Ph-substituted hexathioether 4 was synthesized by the
method similar to that for 1, though in a relatively low
yield (Scheme 6). Hexathioether 4 was characterized by
NMR and mass spectrometry together with elemental anal-
ysis. The molecular structure of 4 in the crystalline states
was definitively determined by X-ray structural analysis.
Fig. 3 shows the ORTEP drawing of 4 and the selected
bond lengths, angles, and torsion angles are summarized
in Table 4.
of palladium and sulfur atoms (3.43 A) [18], suggesting
weak interactions between the palladium (Pd1) and the ter-
minal sulfur atoms (S3 and S3*) in the crystalline state.
Although some cationic species of 6-coordinate palla-
dium(II) complex have been synthesized using crown thio-
ether ligands [19], S- and N-donor macrocyclic ligands [20],
and tris(2,4,6-trimethoxyphenyl)phosphine ligands [21], the
neutral species are of great rarity [22].
The C–S bond lengths of the diarylsulfide moieties and
the C–S and S–S bond lengths of the diaryldisulfide moiety
of 4 are all close to those observed in common diarylsul-
fides [14] and diaryldisulfides [15], respectively. In contrast
to the almost C2 symmetrical conformation of bulky hexa-
thioether 1, Ph-substituted hexathioether 4 has no symmet-
rical conformation. This difference may be explained in
terms of the intermolecular interactions. In the crystalline
structure of 1, no remarkable intermolecular interactions
were observed probably due to the steric effect of the bulky
Tbt groups. On the other hand, there were some intermo-
lecular C–Hꢀ ꢀ ꢀp interactions in the crystalline structure of
4 (Fig. 4) [26]. Nevertheless, almost linear alignment of
the four inner sulfur atoms (S2–S5) is also observed as in
the case of 1, probably due to the existence of an np(S)–
r*(S–S)–np(S) four center-six electron bond (167.0ꢁ for
2.5. Atoms in molecule (AIM) analysis for the Pdꢀ ꢀ ꢀSax
interactions
To estimate the Pdꢀ ꢀ ꢀSax interactions (Pd1ꢀ ꢀ ꢀS3 and
Pd1ꢀ ꢀ ꢀS3*) of the palladium(II) complex 3, we examined
the topological analysis using Bader’s theory of atoms in
molecules (AIM) [23,24]. In the AIM analysis, chemical
bondings can be identified by the presence of a bond criti-
cal point (BCP), where the electron density becomes a min-
imum along the bond path.
For the Pdꢀ ꢀ ꢀSax interactions (Pd1ꢀ ꢀ ꢀS3 and Pd1ꢀ ꢀ ꢀS3*)
of 3, the BCPs could be located. The BCP properties of
the Pdꢀ ꢀ ꢀSax interactions are summarized in Table 3
together with those of Pd–Seq bonds. The electron density
(q) at a BCP correlates with the strength of an atomic inter-
action. The value of q obtained for the Pdꢀ ꢀ ꢀSax interac-
tions (qPdꢀ ꢀ ꢀS) is 0:013 eaꢁ0 3, which is smaller than those of
normal covalent bonds (e.g., qC–C ¼ 0:24 eaꢁ0 3) but larger
than those for the practical boundary of molecules
ðq ¼ 0:001 ea0ꢁ3Þ [25]. In addition, the qPdꢀ ꢀ ꢀS value is
approximately a seventh part of those for the Pd–Seq bonds
(0:091 eaꢁ0 3 for the Pd1–S1 and Pd1–S1* and 0:097 eaꢁ0 3 for
the Pd1–S2 and Pd1–S2*), and within the range of those for
neutral hydrogen bonds ðq ¼ 0:002–0:04 eaꢁ0 3Þ. The Lapla-
cian ($2) of q denotes the curvature of electron density in
the 3D-topologiccal space for two interacting atoms, and
˚
S2–S3–S4, 165.9ꢁ for S3–S4–S5, 3.096 A for S2ꢀ ꢀ ꢀS3, and
˚
3.043 A for S4ꢀ ꢀ ꢀS5).
Table 3
Estimated BCP properties of 3 by the AIM analysis
2
q ðeaꢁ0 3
Þ
r q ðeaꢁ0 5
Þ
Pd1ꢀ ꢀ ꢀS3, Pd1ꢀ ꢀ ꢀS3*
Pd1–S1, Pd1–S1*
Pd1–S2, Pd1–S2*
0.013
0.091
0.097
0.033
0.140
0.193
Scheme 6. Synthesis of Ph-substituted hexathioether 4.

D. Shimizu et al. / Journal of Organometallic Chemistry 692 (2007) 2716–2728
2721
Fig. 3. ORTEP drawing of 4 (50% probability). Hydrogen atoms are omitted for clarity.
2.7. Reactions of Ph-substituted hexathioether 4 with an
equimolar amount of [Pd(PPh3)4]
Table 4
˚
Selected bond lengths (A), angles (ꢁ), and torsion angles (ꢁ) of hexathio-
ether 4
S1–C1
1.782(5)
1.767(5)
1.777(5)
1.775(5)
1.787(5)
1.777(5)
S1–C7
S2–C13
S3–S4
S5–C24
S6–C30
1.764(5)
1.778(5)
2.039(2)
1.773(5)
1.767(5)
The reaction of Ph-substituted hexathioether 4 with an
equimolar amount of [Pd(PPh3)4] was examined under con-
ditions similar to those for the synthesis of monopalla-
dium(II) (3). To a benzene solution of 4 was added an
S2–C12
S3–C18
S4–C19
S5–C25
S6–C31
C7–S1–C1
C18–S3–S4
C24–S5–C25
102.6(2)
104.84(17)
100.5(2)
C12–S2–C13
C19–S4–S3
C30–S6–C31
102.7(2)
104.39(17)
103.0(2)
C1–S1–C7–C12
S4–S3–C18–C13
S3–S4–C19–C24
C31–S6–C30–C25
ꢁ79.6(4)
ꢁ178.6(3)
ꢁ173.8(3)
ꢁ96.3(4)
C13–S2–C12–C7
C18–S3–S4–C19
C25–S5–C24–C19
170.6(4)
88.1(2)
78.5(4)
Fig. 4. Intermolecular interactions in the crystalline structure of 4.
Fig. 5. ORTEP drawings of 5 (top: the top view, bottom: the side view)
Scheme 7. Oxidative addition of hexathioether 4 to [Pd(PPh3)4].
(50% probability). Hydrogen atoms were omitted for clarity.

2722
D. Shimizu et al. / Journal of Organometallic Chemistry 692 (2007) 2716–2728
equimolar amount of [Pd(PPh3)4] at room temperature.
After stirring for 12 h at this temperature, the crude mix-
ture was purified by the recrystallization from benzene/ace-
tonitrile to give monopalladium(II) complex 5 as purple
crystals (Scheme 7).
Palladium(II) complex 5 was characterized by NMR
and mass spectrometry together with elemental analysis.
The molecular structure of 5 in the crystalline state was
definitively determined by X-ray structural analysis
(Fig. 5). Table 5 shows the selected bond lengths, angles,
and torsion angles of 5 together with those of [Pd{S(o-
phen)SPh}2] (6) (Chart 2), the synthesis and structure of
which has been already reported by us [27].
Chart 2.
˚
longer than the S3ꢀ ꢀ ꢀS4 distance (3.084 A) as well as, in
complex 6, the S2ꢀ ꢀ ꢀS4 distance is longer than the S1ꢀ ꢀ ꢀS3
distance. Furthermore, as in the case of complex 6, the
two benzene rings constructed by C7–C12 and C25–C30
are parallel to each other and the distance between these
˚
The structure of 5 resembles that of 6 rather than that of
3, i.e., the two thiolato-S atoms (S3 and S4) of 5 are in cis
position and the two C6H4SPh moieties are situated in cis
position to each other. Furthermore, the two terminal sul-
fur atoms are on almost the same plane as the central
PdS4 part, indicating no interactions between the palladium
and the terminal sulfur atoms. The central palladium atom
of 5 has a slightly distorted square planar coordination
geometry with the two thiolato-S atoms and the two sul-
planes is 3.77 A average, suggesting the existence of a weak
face-to-face p-stacking interaction [26,29].
2.8. Theoretical calculations
The palladium(II) complexes 3, 5, and 6 were synthe-
sized by the reactions of the corresponding hexa- or tetra-
thioethers 1, 4, and [PhS(o-phen)S]2, respectively, with an
equimolar amount of [Pd(PPh3)4]. Although their forma-
tions result from the simple insertion reactions of the palla-
dium(0) into the S–S bond, great differences were observed
among their crystalline structures, i.e., the bulky palla-
dium(II) complex 3 has the distorted octahedral structure
containing the trans-planar 4-coordination environment,
while the less bulky palladium(II) complexes 5 and 6 have
the slightly distorted cis-planar 4-coordination geometries,
respectively.
˚
fide-S atoms. The Pd1–S3 (2.2724(6) A) and Pd1–S4
˚
(2.2832(6) A) bond distances are shorter than the thiolato-
˚
S–Pd bond distances (2.307(3) A) observed in Tbt-analog
˚
3. By contrast, the Pd1–S2 (2.3192(6) A) and Pd1–S5
˚
(2.3330(6) A) bond distances are longer than the sulfide-
˚
S–Pd bond distances (2.270(3) A) observed in 3. In complex
5, the Pd1–S2 and Pd1–S5 bonds are slightly elongated due
to the steric repulsion of the two C6H4SPh moieties situated
in cis position to each other, whereby the Pd1–S3 and Pd1–
S4 bonds are shortened due to the trans-influence [28].
To clarify the reasons for the difference among the struc-
tures, the trans-conformation for 3 and the cis-conforma-
tion for 5 and 6, theoretical calculations were performed
˚
Indeed, the S2ꢀ ꢀ ꢀS5 distance (3.481 A) is comparatively
Table 5
˚
˚
Selected bond lengths (A), angles (ꢁ), atomic distances (A), and torsion angles (ꢁ) of monopalladium(II) complexes 5 and 6
Complex 5
Complex 6 [27]
Pd1–S2
Pd1–S4
S1–C1
S2–C12
S3–C18
S5–C24
S6–C30
Pd1ꢀ ꢀ ꢀS1
S2ꢀ ꢀ ꢀS5
2.3192(6)
2.2832(6)
1.786(2)
1.793(2)
1.757(2)
1.799(2)
1.782(2)
4.5962(8)
3.4810(8)
Pd1–S3
Pd1–S5
S1–C7
S2–C13
S4–C19
S5–C25
S6–C31
Pd1ꢀ ꢀ ꢀS6
S3ꢀ ꢀ ꢀS4
2.2724(6)
2.3330(6)
1.779(2)
1.783(2)
1.756(2)
1.797(2)
1.779(2)
5.2726(9)
3.0843(9)
Pd1–S1
Pd1–S2
Pd1–S3
Pd1–S4
S1–C1
S2–C6
S3–C7
S4–C12
S1ꢀ ꢀ ꢀS3
S2ꢀ ꢀ ꢀS4
2.2886(6)
2.3146(6)
2.2886(6)
2.3186(6)
1.758(2)
1.785(2)
1.759(3)
1.786(2)
3.1644(9)
3.4176(8)
S2–Pd1–S3
S3–Pd1–S4
Pd1–S2–C12
Pd1–S5–C24
Pd1–S3–C18
C7–S1–C1
88.80(2)
85.22(2)
108.15(6)
103.59(7)
104.75(7)
98.78(9)
S2–Pd1–S5
S4–Pd1–S5
Pd1–S2–C13
Pd1–S5–C25
Pd1–S4–C19
C30–S6–C31
96.874(19)
89.21(2)
104.30(7)
107.22(7)
104.41(7)
103.48(9)
S2–Pd1–S4
S1–Pd1–S3
S1–Pd1–S2
S3–Pd1–S4
Pd1–S2–C6
Pd1–S4–C12
95.06(2)
87.47(2)
88.72(2)
88.61(2)
104.63(8)
104.53(8)
C12–S2–Pd1–S3
C12–S2–C13–C18
C1–S1–C7–C8
106.16(7)
ꢁ112.24(17)
ꢁ112.71(17)
ꢁ172.88(7)
S4–Pd1–S5–C25
C19–C24–S5–C25
C29–C30–S6–C31
S3–Pd1–S4–C19
ꢁ108.03(7)
112.28(17)
16.64(18)
ꢁ178.18(7)
S1–Pd1–S2–C13
S3–Pd1–S4–C19
111.01(8)
ꢁ112.81(8)
C18–S3–Pd1–S4

D. Shimizu et al. / Journal of Organometallic Chemistry 692 (2007) 2716–2728
2723
for two conformational isomers of bis[2-(phenylsulfa-
nyl)benzenethiolato]palladium(II) (cis-conformer: 6a and
trans-conformer: 6b). As shown in Chart 3, both of 6a
and 6b have two conformational possibilities, the syn-struc-
ture (two phenyl rings are on the same side of the
C6H4S2PdS2C6H4 plane) and the anti-structure (two phenyl
rings are on the opposite side of the C6H4S2PdS2C6H4
plane). Therefore, the energies of these four isomers, 6a-
syn, 6a-anti, 6b-syn, and 6b-anti, were calculated with
B3LYP/LANL2DZ(ECP) for Pd, 6-31G(2d) for S, and 6-
31G(d) for C and H level [30]. Their optimized structures
are shown in Fig. 6.
Contrary to the results of the X-ray structural analyses
of 5 and 6, the theoretical calculations revealed that the
6a-syn type structure has the highest energy among the four
isomers. However, there are little energy differences among
them, and the preference of complexes 5 and 6 for the 6a-
syn type structure in the crystalline state may be caused by
Fig. 7. Intermolecular interactions in the crystalline structure of 5.
the intermolecular C–Hꢀ ꢀ ꢀp interactions, which are
observed in the X-ray structural analyses (Fig. 7 and Ref.
[27]). On the other hand, no significant intermolecular
interactions were observed in the crystalline state of 3 prob-
ably due to the effect of the bulky Tbt groups, and the pref-
erence of complex 3 for the 6b-anti type structure may be
interpreted in terms of the effects of the steric repulsion
of the two Tbt groups.
3. Conclusion
We reported the oxidative addition of the bulky hexa-
thioether 1 to various amounts of [Pd(PPh3)4]. The reac-
tion of 1 with 3 molar amounts of [Pd(PPh3)4] afforded
tripalladium(II) complex 2 via three-step palladium(0)
insertion reactions including unusual aryl C–S bond cleav-
ages. Furthermore, the reaction of 1 with an equimolar
amount of [Pd(PPh3)4] afforded monopalladium(II) com-
plex 3. The conversion of 3 into 2 was achieved by the
reaction with [Pd(PPh3)4] in the presence of an excess
amount of PPh3, suggesting that the 5- or 6-coordinated
monopalladium (II) species having PPh3 ligand(s) are the
key intermediates for the unusual aryl C–S bond cleavage
by a palladium(0) complex. On the other hand, complex 3
has an interesting pseudo-octahedral structure in the crys-
talline state. AIM analysis supported the hexa-coordinated
geometry for the palladium center in 3. In contrast to the
bulky system, the reaction of Ph-substituted hexathioether
4 with an equimolar amount of [Pd(PPh3)4] generated
monopalladium(II) complex 5 having square-planar envi-
ronment around the Pd(II) atom. To clarify the factors
contributing to the structural differences between 3 and
5, theoretical calculations were performed for the cis-
and trans-isomers of [Pd{S(o-phen)SPh}2]. These calcula-
tions indicate that there is little difference among the
energies of 6a-syn, 6a-anti, 6b-syn, and 6b-anti. It is sug-
gested that a reason for the preference of the trans-anti-
conformation in 3 is steric repulsion between bulky Tbt
groups, and those of cis-syn-conformations in 5 and 6
are the intermolecular interactions.
Chart 3.
Fig. 6. Calculated structures for the four isomers, 6a-syn, 6a-anti, 6b-syn,
and 6b-anti.

2724
D. Shimizu et al. / Journal of Organometallic Chemistry 692 (2007) 2716–2728
4. Experimental
4.1. General procedures
(s), 144.5 (s), 150.3 (s · 2); HRMS (FAB): found m/z
1598.5974 ([M]+), calcd. for C78H134S6Si12 1598.6041.
Anal. Calc. for C78H134S6Si12: C, 58.50; H, 8.43. Found:
C, 58.44; H, 8.52%.
All experiments were performed under an argon atmo-
sphere unless otherwise noted. All solvents were dried by
standard methods and fleshly distilled prior to use. 1H
NMR (300 MHz) and 13C NMR (75 MHz) spectra were
measured in CDCl3 with a JEOL JNM AL-300 spectrom-
eter using CHCl3 (7.25 ppm) and CDCl3 (77.0 ppm) as
4.3. Reaction of 1 with 3 molar amounts of [Pd(PPh3)4]
To a benzene solution (5 mL) of hexathioether 1
(20 mg, 12.5 lmol) was added 3 molar amounts of tetra-
kis(triphenylphosphine)palladium (43.3 mg, 37.5 lmol) at
room temperature. After the mixture was stirred for
12 h at the same temperature, the solvent was removed
under reduced pressure. The residual brown solid was
subjected to GPLC (CHCl3) followed by WCC (ben-
zene:hexane = 1:1) to give pure tripalladium complex 2
(21.4 mg, 8.8 lmol, 71%) as yellow crystals. 2: m.p.
182.7–183.7 ꢁC (decomp.). 1H NMR (300 MHz, CDCl3,
50 ꢁC): d ꢁ0.22 (s, 18H, SiMe3), ꢁ0.19 (s, 18H, SiMe3),
0.08 (s, 18H, SiMe3), 0.09 (s, 36H, SiMe3), 0.16 (s, 18H,
SiMe3), 1.38 (s, 2H, Tbt p-benzyl), 2.53 (s, 2H, Tbt o-ben-
1
internal standards for H NMR and 13C NMR, respec-
tively. High-resolution mass spectral data (HRMS) were
obtained on a JEOL JMS-700 spectrometer. Wet column
chromatography (WCC) was performed on Wakogel C-
200. Preparative gel permeation liquid chromatography
(GPLC) was performed on an LC-908, LC-918, or LC-
908-C60 (Japan Analytical Industry Co., Ltd.) equipped
with JAIGEL 1H and 2H columns (eluent: chloroform).
All melting points were determined on a Yanaco micro-
melting point apparatus and are uncorrected. Elemental
analyses were carried out at the Microanalytical Labora-
tory of the Institute for Chemical Research, Kyoto
University. 2-{2,4,6-Tris[bis(trimethylsilyl)methyl]phenyl-
thio} iodobenzenes (TbtSC6H4I) and 2-iodophenyl phenyl
sulfide (PhSC6H4I) were prepared according to the
reported procedure [12].
3
zyl), 3.30 (s, 2H, Tbt o-benzyl), 5.11 (d, J = 7.8 Hz, 2H),
5.80–5.94 (m, 4H), 5.97 (ddd, 3J = 7.8, ꢂ8.0 Hz,
4J = 1.5 Hz, 2H), 6.10–6.19 (m, 4H), 6.17–6.22 (m, 2H),
6.53 (ddd, 3J = 7.2, ꢂ8.0 Hz, 4J = 1.5 Hz, 2H), 6.58 (s,
2H), 6.66 (s, 2H), 7.09–7.26 (m, 18H), 7.44–7.91 (m,
12H); 13C NMR (75 MHz, CDCl3, 50 ꢁC): d 0.8 (q,
SiMe3), 0.9 (q, SiMe3), 1.5 (q, SiMe3), 2.0 (q, SiMe3),
26.4 (d, Tbt p-benzyl), 27.1 (d, Tbt o-benzyl), 30.8 (d,
Tbt o-benzyl), 122.0 (d), 122.5 (d), 122.6 (d), 123.8 (d),
124.6 (d), 125.5 (s), 128.1 (d), 128.3 (d), 130.3 (d), 131.7
(d), 134.4 (d · 2), 134.7 (s), 136.2 (d), 136.3 (d), 142.1
(s), 143.4 (s), 143.8 (s), 146.0 (s), 150.4 (s), 151.9 (s),
152.5 (s); 31P NMR (121 MHz, CDCl3, 50 ꢁC): d 28.1.
Anal. Calc. for C114H164P2Pd3S6Si12: C, 56.00; H, 6.76.
Found: C, 55.98; H, 6.83%.
4.2. Synthesis of bis[2-(2-{2,4,6-tris[bis(trimethylsilyl)
methyl]phenylsulfanyl}phenylsulfanyl)phenyl]disulfide (1)
To a suspension of 1,2-benzenedithiol (437 mg, 3.07
mmol) and Cu2O (293 mg, 2.05 mmol) in 2,4,6-trimethyl-
pyridine (30 mL) was added dropwise a solution of
TbtSC6H4I (1.61 g, 2.05 mmol) in 2,4,6-trimethylpyridine
(20 mL) at 170 ꢁC. The mixture was refluxed for 3 h under
argon to generate the corresponding thiol intermediate.
After stirring for further 12 h at room temperature in
the open air, the reaction mixture was passed through a
short column (SiO2, benzene) to remove inorganic salts.
After addition of benzene (200 mL), the mixture was
washed with a 0.2 M aqueous solution of HCl three times
(100 mL · 3). The organic layer was dried with MgSO4
and the solvents were removed under reduced pressure
to afford a light-yellow oil. The residue was subjected to
GPLC (CHCl3), and subsequently reprecipitated from
4.4. Reaction of 1 with an equimolar amount of
[Pd(PPh3)4]
To a benzene solution (5 mL) of hexathioether 1 (20 mg,
12.5 lmol) was added tetrakis(triphenylphosphine)palla-
dium (14.4 mg, 12.5 lmol) at room temperature. After
the mixture was stirred for 12 h at the same temperature,
the solvent was removed under reduced pressure. The res-
idue was subjected to GPLC (CHCl3) to give mononuclear
palladium complex 3 (18.7 mg, 11.0 lmol, 88%) as green
crystals. 3: m.p. 315.0–316.0 ꢁC (decomp.). 1H NMR
(300 MHz, CDCl3): d ꢁ0.26 (s, 18H, SiMe3), ꢁ0.24 (s,
18H, SiMe3), ꢁ0.11 (s, 18H, SiMe3), ꢁ0.01 (s, 18H, SiMe3),
0.04 (s, 36H, SiMe3), 1.35 (s, 2H, Tbt p-benzyl), 1.84 (s, 2H,
Tbt o-benzyl), 2.71 (s, 2H, Tbt o-benzyl), 6.30 (s, 2H), 6.44
(s, 2H), 6.54 (d, 3J = 8.0 Hz, 2H), 6.70 (dd, 3J = ꢂ7.3,
CHCl3/CH3CN to give hexathioether
1
(1.50 g,
0.93 mmol, 93%) as colorless crystals. 1: m.p. 188.0–
189.0 ꢁC. 1H NMR (300 MHz, CDCl3): d 0.03 (s, 72H,
SiMe3), 0.07 (s, 36H, SiMe3), 1.38 (s, 2H, Tbt p-benzyl),
2.66 (s, 4H, Tbt o-benzyl), 6.42 (s, 2H), 6.57 (s, 2H),
6.63–6.68 (m, 2H), 6.92–7.01 (m, 6H), 7.08–7.24 (m,
4H), 7.29 (dd, J = 1.4, 7.4 Hz, 2H), 7.56 (dd, J = 1.4,
8.0 Hz, 2H); 13C NMR (75 MHz, CDCl3): d 0.7 (q,
SiMe3), 0.9 (q, SiMe3), 26.5 (d · 2, Tbt o-benzyl), 30.6
(d, Tbt p-benzyl), 122.6 (d), 123.9 (s), 125.0 (d), 126.6
(d), 127.0 (d), 127.0 (d), 127.3 (d), 127.7 (d), 128.9 (d),
130.0 (d), 131.8 (s), 131.8 (s), 133.6 (d), 139.8 (s), 140.1
3
4J = 1.2 Hz, 2H), 6.73–6.80 (m, 4H), 6.84 (dd, J = ꢂ7.8,
4J = 1.2 Hz, 2H), 7.03 (dd, 3J = ꢂ7.3, 4J = 1.4 Hz, 2H),
7.17 (dd, 3J = ꢂ8.0, 4J = 1.4 Hz, 2H), 7.42 (d,
3J = 7.8 Hz, 2H); 13C NMR (100 MHz, CDCl3, 50 ꢁC): d
0.1 (q, SiMe3), 0.8 (q, SiMe3), 0.9 (q, SiMe3), 26.9 (d, Tbt

D. Shimizu et al. / Journal of Organometallic Chemistry 692 (2007) 2716–2728
2725
p-benzyl), 31.0 (d, Tbt o-benzyl), 122.1 (s), 122.5 (d), 122.6
(d), 126.3 (s), 127.7 (s), 128.0 (d), 128.4 (d), 128.9 (d), 129.0
(d), 129.6 (d), 131.0 (d), 135.7 (d), 144.3 (s), 145.0 (s), 150.8
(s), 152.8 (s); HRMS (FAB): found m/z 1706.5089 ([M]+),
calcd. for C78H134108PdS6Si12 1706.5080. Anal. Calc. for
C78H134PdS6Si12: C, 54.86; H, 7.91. Found: C, 54.59; H,
7.93%.
The organic layer was dried with MgSO4 and the sol-
vents were removed under reduced pressure to afford a
light-yellow oil. The residue was subjected to GPLC
(CHCl3) to give Ph-substituted hexathioether
4
(396.5 mg, 0.61 mmol, 58%) as colorless crystals. 4:
m.p. 93.6–94.6 ꢁC. 1H NMR (300 MHz, CDCl3): d
6.79–6.86 (m, 2H), 7.10–7.42 (m, 22H), 7.51–7.55 (m,
2H); 13C NMR (75 MHz, CDCl3): d 126.5 (d), 126.8
(d), 127.0 (d), 127.1 (d), 128.2 (d), 128.4 (d), 129.2 (d),
129.8 (d), 130.3 (s), 130.6 (d), 133.3 (d), 134.3 (s),
135.1 (s), 135.6 (d), 139.2 (s), 141.2 (s); HRMS (FAB):
found m/z 650.0366 ([M]+), calcd. for C36H26S6
650.0359. Anal. Calc. for C36H26S6: C, 66.42; H, 4.03.
Found: C, 66.47; H, 3.97%.
4.5. Reaction of 1 with 2 molar amounts of [Pd(PPh3)4]
To a benzene solution (5 mL) of hexathioether 1 (20 mg,
12.5 lmol) was added tetrakis(triphenylphosphine)palla-
dium (28.9 mg, 25.0 lmol) at room temperature. After
the mixture was stirred for 12 h at the same temperature,
the solvent was removed under reduced pressure. The res-
idue was subjected to GPLC (CHCl3) to give 2 (15.6 mg,
6.4 lmol, 51%) and 3 (5.1 mg, 3.0 lmol, 24%) together with
the starting material 1 (3.6 mg, 2.2 lmol, 18%).
4.9. Synthesis of bis{2-[2-(phenylthio)phenylsulfanyl]-
benzenethiolato}palladium (5)
To a benzene solution (15 mL) of Ph-substituted hexa-
thioether 4 (60 mg, 92.0 lmol) was added tetrakis(triphe-
nylphosphine)palladium (106.5 mg, 92.0 lmol) at room
temperature. After the mixture was stirred for 12 h at the
same temperature, the solvent was removed under reduced
pressure. The residual red-violet solid was purified by
recrystallization from chloroform/acetonitrile to give
mononuclear palladium complex 5 (69.7 mg, 92.0 lmol,
100%) as purple crystals. 5: m.p. 192.7–193.7 ꢁC (decomp.).
1H NMR (300 MHz, CDCl3): d 6.80 (ddd, 3J = 7.5,
4.6. Reaction of 1 with 4 molar amounts of [Pd(PPh3)4]
To a benzene solution (5 mL) of hexathioether 1 (20 mg,
12.5 lmol) was added tetrakis(triphenylphosphine)palla-
dium (57.8 mg, 50.0 lmol) at room temperature. After
the mixture was stirred for 12 h at the same temperature,
the solvent was removed under reduced pressure. The res-
idue was subjected to GPLC (CHCl3) to give 2 (29.3 mg,
12.0 lmol, 96%).
4
3
4
3J = 7.5, J = 1.2 Hz, 2H), 6.94 (dd, J = 7.5, J = 0.9 Hz,
3
3
4
4.7. Reaction of 3 with 2 molar amounts of [Pd(PPh3)4] in
the presence of an excess amount of PPh3
2H), 6.99 (ddd, J = 8.1, J = 7.5, J = 0.9 Hz, 2H), 7.05–
7.12 (m, 4H), 7.33–7.39 (m, 12H), 7.52 (dd, 3J = 8.1,
4J = 0.9 Hz, 2H), 7.71 (dd, 3J = ꢂ8.3, 4J = 1.2 Hz, 2H);
13C NMR (75 MHz, CDCl3): d 123.4 (d), 127.9 (d), 128.2
(d), 129.3 (d), 129.4 (d), 130.0 (d), 130.5 (d), 130.9 (d),
131.7 (s), 131.8 (d), 132.7 (d), 133.8 (s), 134.4 (s), 135.6
(d), 139.2 (s), 151.5 (s); HRMS (FAB): found m/z
756.9445 ([M]+), calcd. for C36H26106PdS6 756.9472. Anal.
Calc. for C36H26PdS6: C, 57.09; H, 3.46. Found: C, 57.08;
H, 3.48%.
To a benzene suspension (20 mL) of 3 (50.0 mg,
29.0 lmol) and 2 molar amounts of [Pd(PPh3)4] (67.7 mg,
58.0 lmol) was added 10 molar amounts of PPh3
(76.8 mg, 290 lmol) at room temperature. After stirring
for 62 h at this temperature, the brown suspension was fil-
tered through Celite. The filtrate was evaporated and the
residue was subjected to GPLC (CHCl3) to give 2
(18.1 mg, 8.0 lmol, 28%) together with the starting mate-
rial 3(26.3 mg, 15.1 lmol, 52%).
4.10. Synthesis of bis[2-(phenylsulfanyl)phenyl] disulfide
4.8. Synthesis of bis{2-[2-(phenylsulfanyl)phenylsulfanyl]-
phenyl}disulfide (4)
To
a
suspension of 1,2-benzenedithiol (697 mg,
4.90 mmol) and Cu2O (350 mg, 2.45 mmol) in 2,4,6-tri-
methylpyridine (20 mL) was added dropwise a solution
of iodobenzene (1.0 g, 4.90 mmol) in 2,4,6-trimethylpyri-
dine (10 mL) at 170 ꢁC. The mixture was refluxed for
3 h under argon to generate the corresponding thiol inter-
mediate, and stirred for further 12 h at room temperature
under the air. The reaction mixture was passed through a
short column (SiO2, benzene) to remove inorganic salts.
After addition of benzene (100 mL), the mixture was
washed with a 0.2 M aqueous solution of HCl three times
(50 mL · 3). The organic layer was dried with MgSO4 and
the solvents were removed under reduced pressure to
afford a light-yellow oil. The residue was subjected to
WCC (SiO2, hexane) to give bis[2-(phenylsulfanyl)phenyl]
To
a suspension of 1,2-benzenedithiol (299.2 mg,
2.10 mmol) and Cu2O (150.5 mg, 1.05 mmol) in 2,4,6-
trimethylpyridine (30 mL) was added dropwise a solution
of 2-iodophenyl phenyl sulfide (PhSC6H4I) (656.7 g,
2.10 mmol) in 2,4,6-trimethylpyridine (20 mL) at 170 ꢁC.
The mixture was refluxed for 3 h under argon to generate
the corresponding thiol intermediate. After stirring for
further 48 h at room temperature in the open air, the
reaction mixture was passed through a short column
(SiO2, benzene) to remove inorganic salts. After addition
of benzene (100 mL), the mixture was washed with a
0.2 M aqueous solution of HCl three times (50 mL · 3).

2726
D. Shimizu et al. / Journal of Organometallic Chemistry 692 (2007) 2716–2728
disulfide (591 mg, 1.37 mmol, 56%) as colorless crystals;
mp. 119.5–120.5 ꢁC. 1H NMR (300 MHz, CDCl3): d
7.13–7.33 (m, 14H), 7.41 (dd, J = 1.5, ꢂ7.4 Hz, 2H),
7.50 (dd, J = 1.5, ꢂ7.8 Hz, 2H); 13C NMR (75 MHz,
CDCl3): d 93.1 (d), 93.2 (d), 93.6 (d), 95.8 (d), 95.9 (d),
96.0 (d), 98.2 (s), 101.6 (d), 102.4 (s), 107.0 (s); HRMS
(EI): found m/z 434.0297 ([M]+), calcd. for C24H18S4
434.0291.
found m/z 541.9348 ([M]+), calcd. for C24H18108PdS4
541.9360. Anal. Calc. for C24H18PdS4: C, 53.27; H, 3.35.
Found: C, 53.00; H, 3.55%.
4.12. Theoretical calculations
The geometries of model compounds 6a-syn, 6a-anti, 6b-
syn and 6b-anti were optimized by using the GAUSSIAN-98
program [31] with density functional theory at the
B3LYP level. The LANL2DZ basis sets for Pd were used
with effective core potential, and the 6-31G(2d) basis sets
for S and 6-31G(d) basis sets for C and H atoms were used,
respectively. The atoms in molecules (AIM) analysis was
performed by using the AIM-2000 package [32].
4.11. Synthesis of bis[2-(phenylsulfanyl)benzenethiolato]-
palladium (6)
To a benzene solution (5 mL) of bis[2-(phenylsulfa-
nyl)phenyl] disulfide (50 mg, 120 lmol) was added tetra-
kis(triphenylphosphine)palladium (133 mg, 120 lmol) at
room temperature. After the mixture was stirred for 12 h
at the same temperature, the solvent was removed under
reduced pressure. The residual red-violet solid was purified
by recrystallization from chloroform/acetonitrile to give
mononuclear palladium complex 6 (63.6 mg, 118 lmol,
98%) as red-purple crystals. 6: m.p. 252.8–253.8 ꢁC
(decomp.). 1H NMR (300 MHz, CDCl3): d 6.80 (dd,
3J = 7.4, 3J = ꢂ7.1 Hz, 2H), 6.99 (d, 3J = 7.4 Hz, 2H),
4.13. X-ray structural determination
The crystallographic data for 1 Æ 0.5CH2Cl2 Æ 0.5C6H14,
3 Æ 2CHCl3, 4, and 5 are summarized in Table 6. Single
crystals were grown at room temperature by the slow evap-
oration of the corresponding saturated solution in dichlo-
romethane/hexane for 1 Æ 0.5CH2Cl2 Æ 0.5C6H14, and
chloroform/acetonitrile for 3 Æ 2CHCl3, 4, and 5, respec-
tively. The intensity data were collected on a Rigaku/
MSC Mercury CCD diffractometer for 1 Æ 0.5CH2Cl2 Æ
0.5C6H14, 3 Æ 2CHCl3, and 5 and a Rigaku Saturn70
CCD system with VariMax Mo Optic for 4 with graph-
3
3
7.06 (dd, J = 8.2, J = ꢂ8.0 Hz, 2H), 7.10–7.23 (m, 6H),
7.23–7.31 (m, 2H), 7.36 (d, 3J = 7.1 Hz, 2H), 7.48 (d,
3J = 7.4 Hz, 2H); 13C NMR (75 MHz, CDCl3): d 123.5
(d), 129.7 (d), 129.9 (d), 130.0 (d), 130.6 (d), 131.0 (d),
132.4 (d), 133.9 (s), 134.3 (s), 152.3 (s); HRMS (FAB):
˚
ite-monochromated Mo Ka radiation (k = 0.71070 A for
Table 6
Crystal data and refinement details for 1 Æ 0.5CH2 Cl2 Æ 0.5C6H14, 3 Æ 2CHCl3, 4, and 5
Complex
1 Æ 0.5CH2Cl2 Æ 0.5C6H14
3 Æ 2CHCl3
4
5
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C
81.5H142ClS6Si12
C80H136Cl6PdS6Si12
1946.43
103(2)
Monoclinic
P21/c (No. 14)
16.1441(5)
12.4256(4)
25.6096(10)
90
96.3221(18)
90
5106.0(3)
2
1.266
0.640
C36H26S6
650.93
173(2)
Monoclinic
P21/c (No. 14)
16.037(6)
7.395(2)
26.842(10)
90
99.107(7)
90
3143.1(19)
4
1.376
0.461
C72H52Pd2S12
1514.66
103(2)
1686.84
103(2)
Triclinic
Triclinic
ꢀ
ꢀ
P1 ðNo:2Þ
P1 ðNo:2Þ
˚
a (A)
10.920(2)
20.424(5)
23.068(5)
71.290(7)
83.335(10)
83.675(11)
4825.5(18)
2
10.161(2)
11.417(2)
14.967(3)
110.149(3)
91.409(2)
105.895(2)
1554.0(5)
1
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dcalc (Mg mꢁ3
)
1.161
0.357
0.30 · 0.10 · 0.01
2.35–25.00
31210
1.618
1.027
0.40 · 0.30 · 0.20
2.71–25.00
10083
Absorption coefficient (mmꢁ1
Crystal size (mm)
)
0.20 · 0.03 · 0.03
2.17–25.50
29394
0.10 · 0.04 · 0.01
1.84–25.00
20363
h Range (ꢁ)
Number of reflections measured
Number of independent
reflections
16506
9021
5519
5332
Rint
0.0454
0.1162
0.0821
0.0127
Completeness (%)
Number of parameters
Goodness of fit
97.2
941
1.081
94.9
494
1.061
99.9
379
1.127
97.4
388
1.053
Final R indices [I > 2r(I)]
R1 = 0.0647,
wR2 = 0.1482
R1 = 0.0914,
wR2 = 0.1661
R1 = 0.0803,
wR2 = 0.1815
R1 = 0.1892,
wR2 = 0.2505
R1 = 0.0748,
wR2 = 0.1416
R1 = 0.1115,
wR2 = 0.1583
R1 = 0.0205,
wR2 = 0.0510
R1 = 0.0224,
wR2 = 0.0521
R indices (all data)

D. Shimizu et al. / Journal of Organometallic Chemistry 692 (2007) 2716–2728
2727
˚
´
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(SHELXS-97) and refined by full-matrix least-squares proce-
dures on F2 for all reflections (SHELX-97) [33]. All non-
hydrogen atoms were refined anisotropically. All hydrogen
atoms were placed using AFIX instructions.
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Acknowledgments
(c) M.D. Curtis, S.H. Druker, J. Am. Chem. Soc. 119 (1997) 1027;
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(e) G.E.D. Mullen, T.F. Fa¨ssler, M.J. Went, K. Howland, B. Stein,
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This work was partially supported by Grants-in-Aid for
Scientific Research [Nos. 12CE2005, 17GS0207, 14078213,
and 15750031] and the 21 COE Program on Kyoto Univer-
sity Alliance for Chemistry from the Ministry of Educa-
tion, Culture, Sports, Science and Technology, Japan. We
are grateful to Dr. Takahiro Sasamori, Institute for Chem-
ical Research, Kyoto University, for the valuable
discussions.
´
(f) C. Alvarez-Toledano, E. Delgado, B. Donnadieu, M.A. Gomez,
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Appendix A. Supplementary material
´
`
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Organometallics 22 (2003) 1585;
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[10] A part of this paper had been preliminary reported: D. Shimizu, N.
Takeda, N. Tokitoh, Chem. Commun. (2006) 177.
[11] Recently, phenyl C(sp2)–S bond cleavages using palladium nanopar-
ticles were reported: M.-K. Chung, M. Schlaf, J. Am. Chem. Soc. 126
(2004) 7386.
CCDC 285412, 619301, 619302 and 619303 contain the
supplementary crystallographic data for 1 Æ 0.5CH2Cl2 Æ
0.5C6H14, 3 Æ 2CHCl3, 4 and 5. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.
uk. Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/
j.jorganchem.2006.10.056.
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