Syntheses of polythioethers tethered with bulky aryl groups and their complexation with late-transition metals

Article abstract of DOI:10.1080/10426500590911421

New types of o-phenylene-bridged polythioethers tethered with extremely bulky aryl groups at their terminal sulfur atoms, such as TbtS(o-Phen)S(o-Phen) S(o-Phen)STbt (1) and TbtS(o-Phen)S(o-Phen)SS(o-Phen)S(o-Phen)STbt (2) (Tbt = 2,4,6-tris[bis(trimethyls

Full text of DOI:10.1080/10426500590911421

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Phosphorus, Sulfur, and Silicon
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Syntheses of Polythioethers
Tethered with Bulky Aryl
Groups and Their Complexation
with Late-Transition Metals
Norihiro Tokitoh a , Daisuke Shimizu a , Nobuhiro
Takeda a & Takahiro Sasamori a
a Institute for Chemical Research, Kyoto University ,
Gokasho, Kyoto, Japan
Published online: 16 Aug 2006.
To cite this article: Norihiro Tokitoh , Daisuke Shimizu , Nobuhiro Takeda & Takahiro
Sasamori (2005) Syntheses of Polythioethers Tethered with Bulky Aryl Groups and
Their Complexation with Late-Transition Metals, Phosphorus, Sulfur, and Silicon and
the Related Elements, 180:5-6, 1241-1245, DOI: 10.1080/10426500590911421
To link to this article: http://dx.doi.org/10.1080/10426500590911421
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Phosphorus, Sulfur, and Silicon, 180:1241–1245, 2005
Copyright © Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500590911421
Syntheses of Polythioethers Tethered with Bulky
Aryl Groups and Their Complexation with
Late-Transition Metals
Norihiro Tokitoh
Daisuke Shimizu
Nobuhiro Takeda
Takahiro Sasamori
Institute for Chemical Research, Kyoto University, Gokasho,
Kyoto, Japan
New types of o-phenylene-bridged polythioethers tethered with extremely bulky
aryl groups at their terminal sulfur atoms, such as TbtS(o-Phen)S(o-Phen)S(o-
Phen)STbt (1) and TbtS(o-Phen)S(o-Phen)SS(o-Phen)S(o-Phen)STbt (2) (Tbt =
2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, o-Phen = o-phenylene), were synthe-
sized and subjected to the complexation with several kinds of late-transition met-
als. In the case of polythioether 1, the reaction with RhCl3·3H2O in benzene/EtOH
resulted in the formation of a unique bimetallic complex, in which a part of ligand 1
is lost and the resulting sulfur atom is directly bound to the other Rh metal center.
Interestingly, similar treatment of 1 with IrCl3·3H2O afforded ethyl-coordinated
mononuclear Ir complex. Furthermore, 1 underwent complexation with Na2PdCl4
in EtOH to give the corresponding square planar dichloropalladium complex coor-
dinated with two inner sulfur atoms of 1, while the S6-ligand 2 reacted with excess
of Pd(PPh3)4 in benzene to afford a quite interesting trinuclear Pd complex via
multi-step metal insertion reactions.
Keywords Bimetallic complex; complexation; coordination; mononuclear complex; poly-
thioethers; transition metals
Received July 9, 2004; accepted October 5, 2004.
We thank Toshiko Hirano and Tomoko Terada of the Microanalytical Laboratory of
the Institute for Chemical Research of Kyoto University for the elemental analysis and
HRMS (high-resolution mass spetrometry) spectra. This work was partially supported by
Grants-in-Aid for Center of Excellence Research on Elements Science (No. 12CE2005),
Scientific Research on Priority Area (A) (No. 14078213), the 21st Century COE on Kyoto
University Alliance for Chemistry (Novel Organic Materials Creation & Transformation
Project), and Nanotechnology Support Project from the Ministry of Education, Culture,
Sports, Science, and Technology of Japan.
Address correspondence to Norihiro Tokitoh, Institute for Chemical Research, Ky-
oto University, Gokasho, Uji, Kyoto 611-0011, Japan. E-mail: tokitoh@boc.kuicr.kyoto-u.
ac.jp
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N. Tokitoh et al.
INTRODUCTION
Thiacrown ethers are well-known host compounds capable of complex-
ation with a variety of transition metals.1 Although their high ability at
metal recognition is achieved as a result of size selectivity, the rigidity
of the ring (crown) structure sometimes makes it difficult to coordi-
nate to a metal center as a three-dimensional multidentate ligand. On
the other hand, as an extension of our study on the sterically crowded
organosulfur compounds, we have recently prepared some new poly-
thioethers tethered with bulky aryl groups (1 and 2).2 We present here
the synthesis and structures of 1 and 2 together with their coordination
ability toward some late-transition metals.
RESULTS AND DISCUSSION
As a terminal protecting group, we introduced an extremely bulky aryl
group, that is, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt), which
has been successfully applied to the kinetic stabilization of a variety of
highly reactive species of heavier elements.3
Polythioether 1 was readily prepared by the treatment of o-ben-
zenedithiol with 2-I-C6H4STbt (A; 2 equivalents (eq.)) in the presence
of Cu2O (2 eq) and 2,4,6-trimethylpyridine in 80% yield (Scheme 1).4
SCHEME 1

Polythioethers Tethered with Aryl Groups
1243
On the other hand, S6-ligand 2 was synthesized in 44% yield by the re-
action of o-benzenedithiol with equimolar amounts of thiol A and Cu2O
under similar conditions, followed by the oxidative coupling reactions
of the resulting thiol intermediate B with iodine (Scheme 1).
Both polythioethers 1 and 2 were isolated as stable, colorless crys-
tals, and their molecular structures were confirmed with 1H NMR,
3C NMR, and MS spectra. Crystallographic analysis of 1 and 2
showed that they have extended structures with some intramolec-
ular interactions among the sulfur atoms. In addition, it was ex-
pected that they might have enough flexibility for the complexation
toward transition metals with their sulfide moieties as a multidentate
ligand.
First, we have examined the complexation of polythioether 1 with
group 9 metal trichlorides. The reaction of 1 with RhCl3·3H2O in ben-
zene/EtOH under reflux for 24 h resulted in the formation of a unique
bimetallic complex 3 as a main product (56%), in which a part of ligand
1 is lost and the resulting sulfur atom is directly bound to the other Rh
metal center (Scheme 2). In this case, TbtSPh was isolated as a byprod-
uct in 71% yield, whereas similar treatment of 1 with IrCl3·3H2O af-
forded a mononuclear Ir complex 4 in 62% yield (Scheme 2). The molecu-
lar structures of the newly obtained complexes 3 and 4 were determined
by X-ray crystallographic analysis, which revealed the dirhodium core
structure for 3 bridged with two µ-sulfur ligands and the octahedral
Ir center for 4 coordinated with three sulfur and two chlorine atoms
together with an ethyl ligand. In the ball-and-stick model drawing of
complex 4 (Figure 1), one can see the unique coordination mode of ligand
1 toward the ethyl-substituted Ir center.
SCHEME 2
It is of great interest that the final products of the complexation of 1
with MCl3·3H2O (M = Rh, Ir) are drastically different from each other
although 1 was mixed with these metal trichlorides under similar reac-
tion conditions. The formation of such type of an ethyl-coordinated irid-
ium complex, trans-[IrCl(Et)L1]+, has previously been reported in the

1244
N. Tokitoh et al.
FIGURE 1 Molecular structure of 4.
reaction of a pyridine-containing tetraazamacrocycle, 3,7,11-trimethyl-
3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L1) with
IrCl3·3H2O in refluxing aqueous ethanolic solution.5 The formation of
dirhodium complex 3 together with TbtSPh in moderate yields strongly
implies the intermediacy of a mononuclear rhodium complex, which
may undergo some intramolecular C S activation.
Furthermore, polythioether 1 was found to undergo complexation
with Na2PdCl4 in refluxing EtOH for 1 h to give the correspond-
ing dichloropalladium complex 5 in an almost quantitative yield
(Scheme 3). The X-ray crystallographic analysis of 5 showed that the
dichloropalladium center was coordinated to the inner two sulfur atoms
of 1 with an almost square planar geometry, while the terminal sulfide
moieties (TbtS units) were oriented in the axial positions with weak
attractive interaction between the sulfur atoms and the Pd center.
Although the reaction product of S6-ligand 2 with Na2PdCl4 has
not been characterized yet because of the difficulty in its separa-
tion and purification, the reaction of 2 with 3 equivalent molar
amounts of Pd(PPh3)4 in benzene was examined at room temperature to

Polythioethers Tethered with Aryl Groups
1245
SCHEME 3
afford a quite interesting trinuclear Pd complex 6 in 58% isolated yield
(Scheme 3).
Further investigation of the formation mechanism of the newly ob-
tained complexes 3–6 and the complexation reactions of polythioether
ligands 1 and 2 with other transition metals are currently in progress.
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Soc., 109, 6181 (1987).
[2] D. Shimizu, N. Takeda, T. Sasamori, and N. Tokitoh, The 84th Annual Meeting of the
Chemical Society of Japan, 2F3-46, March 27, 2004 Nishinomiya, Japan.
[3] For recent accounts on the application of Tbt group, see N. Tokitoh, Acc. Chem. Res.,
37, 86–94 (2004); N. Tokitoh and R. Okazaki, Adv. Organomet. Chem., 47, 121 (2001);
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