Synthesis of [SSSS]-type bis(thiophenol) ligand based on a trans -cyclooctane-1,2-diyl(thio) platform and an unexpected reaction with platinum complexes to produce sulfide-bis(thiolato) PtII complex

Article abstract of DOI:10.1080/17415993.2013.781605

A new [SSSS]-type bis(thiophenol) ligand based on a trans-cyclooctane-1,2- diyl(thio) platform was prepared by the reaction of trans-cyclooctane-1,2- dithiol with 2 mol equiv. of 3,5-di-tert-butyl-2- (2-cyanoethylthio)benzyl bromide followed by deprotection. The reactions of the [SSSS]-type ligand with [Pt(nb)(PPh₃)₂] (nb=norbornene) or [PtCl ₂(PPh₃)₂] complexes produced unexpectedly a [sulfide-bis(thiolato)]-PPh₃ Pt^II complex accompanying loss of one of the 2-sulfanylbenzyl groups. The structure of the Pt^II complex was determined by X-ray crystallography. The physical property and formation mechanism for the Pt^II complex are discussed.

Full text of DOI:10.1080/17415993.2013.781605

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Synthesis of [SSSS]-type
bis(thiophenol) ligand based on a trans-
cyclooctane-1,2-diyl(thio) platform
and an unexpected reaction with
platinum complexes to produce sulfide-
bis(thiolato) PtII complex
Hiroki Mikamia, Eriko Toyodaa, Norio Nakataa & Akihiko Ishiia
a Department of Chemistry, Graduate School of Science and
Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku,
Saitama 338-8570, Japan
Published online: 19 Apr 2013.
To cite this article: Hiroki Mikami, Eriko Toyoda, Norio Nakata & Akihiko Ishii (2013) Synthesis of
[SSSS]-type bis(thiophenol) ligand based on a trans-cyclooctane-1,2-diyl(thio) platform and an
unexpected reaction with platinum complexes to produce sulfide-bis(thiolato) PtII complex, Journal
of Sulfur Chemistry, 34:6, 661-670, DOI: 10.1080/17415993.2013.781605
To link to this article: http://dx.doi.org/10.1080/17415993.2013.781605
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Journal of Sulfur Chemistry, 2013
Vol. 34, No. 6, 661–670, http://dx.doi.org/10.1080/17415993.2013.781605
Synthesis of [SSSS]-type bis(thiophenol) ligand based on a
trans-cyclooctane-1,2-diyl(thio) platform and an unexpected
reaction with platinum complexes to produce
sulfide-bis(thiolato) PtII complex
Hiroki Mikami, Eriko Toyoda, Norio Nakata and Akihiko Ishii*
Department of Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-
okubo, Sakura-ku, Saitama 338-8570, Japan
(Received 30 January 2013; final version received 27 February 2013)
A new [SSSS]-type bis(thiophenol) ligand based on a trans-cyclooctane-1,2-diyl(thio) platform was
prepared by the reaction of trans-cyclooctane-1,2-dithiol with 2 mol equiv. of 3,5-di-tert-butyl-2-
(2-cyanoethylthio)benzyl bromide followed by deprotection. The reactions of the [SSSS]-type ligand
with [Pt(nb)(PPh3)2] (nb = norbornene) or [PtCl2(PPh3)2] complexes produced unexpectedly a [sulfide-
bis(thiolato)]-PPh3 PtII complex accompanying loss of one of the 2-sulfanylbenzyl groups. The structure of
the PtII complex was determined by X-ray crystallography.The physical property and formation mechanism
for the PtII complex are discussed.
Keywords: tetradentate sulfur ligand; tridentate sulfur ligand; platinum; cyclooctane; 1,2-dithiol
1. Introduction
A number of transition-metal complexes bearing various types of sulfur ligands have been studied
so far from biological and industrial points of view (1), and the development of sulfur com-
pounds being employed as an auxiliary ligand in organic synthesis is of continuous and current
interest (2–5).
Recently, we prepared trans-cyclooctane-1,2-dithiol by the reaction of cis-cyclooctene with
(SCN)2 followed by the stepwise reduction with DIBAL and LiAlH4 (6). 1,ω-Dithiols are widely
*Corresponding author. Email: ishiiaki@chem.saitama-u.ac.jp
Dedicated to the memory of the late Professor Alessandro Degl’Innocenti
© 2013 Taylor & Francis

662 H. Mikami et al.
used in organic synthesis to prepare dithioacetals from aldehydes and ketones for umpolung
or protection (7). 1,2-Dithiols convert aldehydes to 1,3-dithiolanes that, unfortunately, easily
undergo cycloreversion when treated with a base. A solution for this serious problem is the
introduction of a silyl group at the 2-posion as reported by Capperucci and Degl’Innocenti
(8). On the other hand, we recently utilized trans-cyclooctane-1,2-dithiol in coordination chem-
istry by preparing a new [OSSO]-type bis(phenol) ligand 1 and showing that the zirconium
complex 2, upon activation with B(C6F5)3 or Ph3C[B(C6F5)4], performed highly active and
isospecific polymerization of 1-hexene (9–14). Furthermore, we reported the spontaneous O–
H and S–C bonds activation of 2-hydroxybenzyl sulfides with Pt0 complexes: The reaction of 1
with 3 mol equiv. of [Pt(C2H4)(PPh3)2] forms dithiolato PtII complex 3 and 1,2-oxaplatinacyle
4(Eq. (1)) (15).
(1)
In continuation to our studies on the coordination chemistry utilizing trans-cyclooctane-1,
2-dithiol, we report here the preparation of persulfurated tetradentate ligand, [SSSS]-
type ligand 5, for late-transition metals. Sellmann and Sutter (16) reported the synthe-
sis of a structurally related [SSSS]-type ligands 6a by the reaction of [Fe(benzene-1,2-
dithiolato)2(CO)2]2− with 1, 2-dibromoethane followed by decomplexation with hydrochloric
acid in THF (17). In a similar manner, 6b was also prepared. They synthesized iron (18–
23), ruthenium (24, 25), rhodium (26), and iron–nickel (27) complexes with 6 to employ
them as models for active sites of enzymes (17). Ligands 6 are different from 5 in the
manner of connection of the two inner sulfurs that are bonded directly to a thiophenol
group.

Journal of Sulfur Chemistry 663
2. Results and discussion
2.1. Synthesis and structure of [SSSS]-type ligand 5
Ligand 5 was synthesized as follows: 2,4-di-t-butylbenzenethiol (28) in ether was treated
with 2 equiv. of butyllithium and N, N, Nꢀ, Nꢀ-tetramethylethylenediamine (TMEDA) and then
paraformaldehyde to give 2-sulfanylbenzyl alcohol 7 in 62% yield. After the sulfanyl group in 7
was protected with a 2-cyanoethyl group (8, 99%) (29, 30), 8 was converted to benzyl bromide
9 by treatment with PBr3 in chloroform (71%) (Scheme 1).
Scheme 1. Synthesis of benzyl bromide 9. Reaction conditions: (a) BuLi (2 equiv.), TMEDA
(2 equiv.), Et2O, 0◦C, 7 h; (b) paraformaldehyde, rt, 15 h; (c) BrCH2CH2CN, K2CO3, THF, rt,
25 h; (d) PBr3, CHCl3, rt, 1.5 h.
The reaction of trans-cyclooctane-1,2-dithiol with benzyl bromide 9 was carried out in the
presence of triethylamine as the base in THF under reflux to give the protected [SSSS]-type
ligand 10 in high yield (Scheme 2). Incidentally, the reaction of trans-cyclooctane-1,2-dithiol
with the benzyl bromide derived from unprotected benzyl alcohol 7 gave a complex mixture, and
as a result protection of the sulfanyl group in 7 was required.
Deprotection of the 2-cycanoethyl groups in the protected [SSSS]-type ligand 10 was examined
using the standard method (29, 30) of CsOH to produce the desired [SSSS]-type ligand 5 in 31%
yield. Ligand 5 was also obtained with a yield of 48% by treatment of 10 with LiAlH4 in ether,
but the reproducibility of the yield was unsatisfactory.
1
In the H NMR spectrum of [SSSS]-type ligand 5, a set of protons for the 3,5-di-t-butyl-2-
sulfanylbenzyl groups and the methine protons of the cyclooctane ring were observed: δ 1.30 and
1.52 for t-butyl groups, δ 3.96 and 4.04 (Jgem = 12 Hz) for diastereotopic benzyl protons, δ 5.23
for sulfanyl protons, δ 7.15 and 7.38 for aromatic protons, and δ2.84 or methine protons. This
observation indicates that 5 has the same C2 symmetry on the NMR time scale in solution as
previously observed for [OSSO]-type ligand 1. This C2 symmetry was also reflected in the 13
C
NMR spectrum of 5, where 15 signals were observed, from which four signals at δ 26.0 (CH2),
26.5 (CH2), 31.2 (CH2), and 51.7 (CH) were assigned to carbons in the cyclooctane ring.
2.2. Reaction of [SSSS]-type ligand 5 with Pt complexes
The reaction of 5 with [Pt(nb)(PPh3)2] (nb = norbornene) in C6D6 at room temperature furnished
sulfide-bis(thiolato) PtII complex 11 in a low yield (21%) (Eq. (2)).We attempted, without success,

664 H. Mikami et al.
Scheme 2. Synthesis of [SSSS]-type ligand 5. Reaction conditions: (a) 9 (2.7 mol equiv.), Et3N,
THF, reflux, 15 h; (b) CsOH, MeOH, THF, rt, 3 h.
to observe the intermediates during formation of 11 by NMR spectroscopy to result.
(2)
On the other hand, the reaction of 5 with a PtII complex, [PtCl2(PPh3)2], in C6H6 at reflux
produced a small amount of colorless precipitates sparingly soluble in the solvent in addition to
11 (31%). The second product was identified as phosphonium salt 12 (3%) by NMR spectroscopy
and ESI-MS (Eq. (3)).1
(3)
In the 1H NMR spectrum of 11, two methine protons appeared at δ 3.06–3.18 and 3.23–3.35 ppm
as multiplets, and diastereotopic benzyl protons resonated at δ 4.11 and 4.81 ppm as a doublet
of doublets due to the geminal coupling (Jgem = 10 Hz) and the coupling with one 31P nucleus
(4JP−H = 6 Hz) accompanied by the satellites due to the 195Pt nucleus (3JPt−H = 54 Hz). In the 31
P
NMR spectrum, a singlet with satellites due to the 195Pt nucleus (1JPt−P = 3700 Hz) was observed

Journal of Sulfur Chemistry 665
Figure 1. ORTEP drawing of sulfide-bis(thiolato) PtII complex 11. Thermal ellipsoids are set at 50% probability.
Selected bond lengths (Å) and bond angles (◦) and torsion angles (◦): Pt1–S2 2.298(1), Pt1–S1 2.322(1), Pt1–S3
2.327(1), Pt1–P1 2.265(1), S2–C8 1.831(4), C8–C1 1.524(6), C1–S1 1.839(4), S2–C9 1.826(5), S3–C15 1.785(4);
S1–Pt1–S2 85.37(4), S2–Pt1–S3 91.56(4), S3–Pt1–P1 90.20(4), P1–Pt1–S1 92.91(4), S1–Pt1–S3 176.10(4); S2–Pt1–P1
178.03(4), Pt1–S2–C8 100.7(1), S2–C8–C1 103.5(3), C8–C1–S1 111.3(3), C1–S1–Pt1 104.0(1), S2–C9–C10 104.9(3),
C9–C10–C15 121.1(4), C10–C15–S3 119.1(3), C15–S3–Pt1 110.3(1); S2–C8–C1–S1 58.8(3), S2–Pt1–S1–C1–7.6(1),
C9–S2–Pt1–S3–33.0(1).
at δ 22.4 ppm. The structure of PtII complex 11 was finally determined by X-ray crystallography
as depicted in Figure 1. The sum of bond angles around the Pt1 atom is 360.04◦, and the geometry
aroundthePtatomisalmostplanar.Thefive-memberedring(Pt1–S1–C1–C8–S2)adoptsaslightly
distorted envelope form [S2–Pt1–S1–C1–7.6(1)◦] and the S1–Pt1–S2 bond angle is 85.37(4)◦ that
is smaller than the idealized 90◦ bond angle of square-planar tetracoordinated PtII complexes. The
S2–Pt1–S3 bond angle [91.56(4)◦] in the six-membered ring (Pt1–S2–C9–C10–C15–S3) is very
close to 90◦, and the ring strain appears to be small. The dihedral angle S2–C8–C1–S1 is 58.8(3)◦.
The bond length of S2(sulfide sulfur)–Pt1 [2.298(1) Å] is slightly shorter than those of S(thiolato
sulfur)–Pt1 [Pt1–S1 2.322(1) Å, Pt1–S3 2.327(1) Å].
Platinum complex 11 has a dianionic tridentate [SSS]-type ligand, which represents a rather
rare class of ligands in comparison with monodantate and bidentate sulfur ligands (31–34). A
structurally related NiII complex having a triphenylphosphine and a dianionic [SSS]-tridentate
ligand, [Ni(tpdt)(PPh3)] [tpdt = (−SCH2CH2)2S], has been reported (35). While the tpdt ligand
in [Ni(tpdt)(PPh3)] provides a 5-5 chelation system that is different from the unsymmetric 6-5
chelation system in 11, the central S(sulfide sulfur)-Ni bond [2.150(2) Å] is slightly shorter than
the terminal S(thiolato sulfur)-Ni bond lengths [2.180(2) and 2.168(2)Å], similar to that observed
in the case of 11.
A plausible mechanism for the formation of 11 is shown in Scheme 3. Ligand 5 can react
with [Pt(nb)(PPh3)2] or [PtCl2(PPh3)2] to give hydrido-thiolato PtII complex 13a by oxidative
addition of the sulfanyl group to the Pt0 center (36) or chloro-thiolato PtII complex 13b by
dehydrochlorination, respectively. Then, dissociation of a PPh3 and coordination of the sulfide
sulfur occur to form a six-membered sulfide-thiolato PtII complex 14a or 14b. Finally, elimination
of 15a or 15b by an intramolecular nucleophilic attack of X and coordination of the third sulfur
produces 11. Thiophenol 15a can further react with the remaining Pt0 or hydrido-PtII (13a)
complexes to form the unidentifiable byproducts. In the case of 15b, a portion of it was trapped
with dissociated PPh3 to give phosphonium salt 12.

666 H. Mikami et al.
Scheme 3. A plausible mechanism for the formation of 11.
3. Conclusion
[SSSS]-type bis(thiophenol) ligand 5 unexpectedly lost one 2-sulfanylbenzyl group in the reaction
with Pt0 and PtII complexes, and the remaining part coordinated to a PtII center as a dianionic
[SSS]-type tridentate ligand. This behavior is in stark contrast to that of [OSSO]-type bis(phenol)
ligand 1 which loses two 2-hydroxybenzyl groups, which can be attributed to the difference in the
reactivity of the SH and OH groups toward Pt complexes and in the difference between covalent
radii of sulfur and oxygen that influences the geometrical strain around the Pt atom. Further studies
on the reactivities of 1 and 5 toward transition metals are under investigation in our laboratory.
4. Experimental
4.1. General procedures
All melting points were determined on a Mel-Temp capillary tube apparatus and are uncorrected.
Solventsweredriedbystandardmethodsandfreshlydistilledpriortouse. Dehydrateddiethylether
and THF were purchased from Kanto Chemical Co., Inc., and used without further purification.
Column chromatography was performed with neutral silica gel (60 N, Kanto Chemical Co., Inc.).
Preparative gel permeation liquid chromatography was performed on an LC-918 (JapanAnalytical
1
Industry Co., Ltd.) equipped with JAIGEL 1H and 2H columns (eluent: CHCl3). H, 13C, and
1
31P NMR spectra were recorded on Bruker DRX-400 or AVANCE-400 (400 MHz for H and
100.7 MHzfor13C)orBrukerAVANCE-500(500 MHzfor1Hand202 MHzfor31P)spectrometers
using CDCl3 as the solvent at room temperature. IR spectra were recorded on a Perkin Elmer
System 2000 FT-IR spectrometer. X-ray crystallography was performed with a Bruker AXS
SMART diffractometer. LC–ESI–MS data were recorded by using a Hitachi NanoFrontier eLD.
Elemental analyses were carried out at the MolecularAnalysis and Life Science Center of Saitama
University.

Journal of Sulfur Chemistry 667
4.2. Synthesis of (3,5-di-tert-butyl-2-sulfanylphenyl)methanol (7)
A solution of TMEDA (2.2 ml, 14.8 mmol) and BuLi (9.5 ml, 1.55 M in hexane solution,
14.7 mmol) in ether (10 ml) was added to a solution of 2,4-di-tert-butylbenzenethiol (1.10 g,
4.95 mmol) in ether (10 ml) at 0◦C under argon. After stirring for 3 h at room temperature, a
suspension of paraformaldehyde (0.446 g, 14.8 mmol) in ether (10 ml) was added to the reaction
mixture at 0◦C, and the mixture was stirred for 15 h. Hydrochloric acid (2 M, 15 ml) was added and
the mixture was extracted with ether. The organic layer was dried over anhydrous sodium sulfate,
and the solvent was removed under reduced pressure to give a brown oil, which was purified by
silica-gel column chromatography (dichloromethane) to give 7 as a colorless solid (1.52 g, 62%).
7: Colorless crystals, mp 103–105◦C (dichloromethane–hexane). 1H NMR (400 MHz, CDCl3) δ
1.31 (s, 9H), 1.55 (s, 9H), 1.94 (t, J = 6 Hz, 1H, OH), 4.34 (s, 1H, SH), 4.81 (d, J = 6 Hz, 2H),
7.22 (d, J = 2 Hz, 1H), 7.45 (d, J = 2 Hz, 1H); 13C NMR (100.7 MHz, CDCl3) δ 30.3 (CH3),
31.3 (CH3), 34.7 (C), 36.9 (C), 66.9 (CH2), 124.2 (CH), 124.7 (CH), 126.9 (C), 139.9 (C), 148.6
(C), 149.4 (C); IR (KBr) ν˜ 3271 (OH), 2563 (SH) cm−1. Anal. Calcd for C15H24OS: C, 71.37; H,
9.58. Found: C, 71.34; H, 9.60.
4.3. Synthesis of 3-{[2,4-di-tert-butyl-6-(hydroxymethyl)phenyl]sulfanyl}propanenitrile (8)
A suspension of K2CO3 (138.9 mg, 1.00 mmol) in THF (2 ml) was added to a solution of
7 (211.2 mg, 0.84 mmol) in THF (6 ml) under argon, and then 3-bromopropionitrile (85 μl,
1.01 mmol) was added to the mixture. The reaction mixture was stirred for 25 h at room tem-
perature. Then, the reaction was quenched by addition of hydrochloric acid (2 M, 5 ml), and the
mixture was extracted with dichloromethane. The organic layer was dried over anhydrous sodium
sulfate, and the solvent was removed under reduced pressure to give almost pure 8 as yellow oil
(22.3 mg, 0.83 mmol, 99%). The analytical sample was obtained by purification of the yellow oil
with silica-gel column chromatography (dichloromethane) to give 8 as colorless oil. 8: Colorless
oil. 1H NMR (400 MHz, CDCl3) δ 1.32 (s, 9H), 1.56 (s, 9H), 2.26 (br s, 1H) 2.66 (t, J = 8 Hz,
2H), 3.00 (t, J = 8 Hz, 2H), 4.97 (s, 2H), 7.42 (d, J = 2 Hz, 1H), 7.47 (d, J = 2 Hz, 1H); 13C
NMR (100.7 MHz, CDCl3) δ 17.4 (CH2), 31.2 (CH3), 31.7 (CH3), 33.6 (CH2), 35.0 (C), 37.6 (C),
65.2 (CH2), 118.1 (C), 124.1 (CH), 124.9 (CH), 127.9 (C), 146.3 (C), 152.3 (C), 153.8 (C). Anal.
Calcd for C18H27NOS: C, 70.77; H, 8.91; N, 4.59. Found: C, 70.63; H, 9.01; N, 4.51.
4.4. Synthesis of 3-{[2-(bromomethyl)-4,6-di-tert-butylphenyl]sulfanyl}propanenitrile (9)
A solution of PBr3 (90%, 8.6 μl, 0.08 mmol) in chloroform (3 ml) was added to a solution of
8 (67.3 mg, 0.25 mmol) in chloroform (3 ml) at room temperature under argon. The mixture
was stirred at room temperature for 1.5 h, and then the reaction was quenched with water. The
mixture was extracted with dichloromethane, and the organic layer was dried over anhydrous
sodium sulfate. After removal of the solvent, the resulting brown oil was purified by silica-
gel column chromatography (dichloromethane) to give 9 as yellow oil (64.4 mg, 0.18 mmol,
71%). The analytical sample was obtained by purifying the yellow oil with silica-gel column
chromatography (dichloromethane) to give 9 as a colorless powder. 9: Colorless powder, mp 68–
69◦C. 1H NMR (400 MHz, CDCl3) δ 1.32 (s, 9H), 1.56 (s, 9H), 2.70 (t, J = 8 Hz, 2H), 3.11 (t,
J = 8 Hz, 2H), 5.00 (s, 2H), 7.46–7.48 (m, 2H); 13C NMR (100.7 MHz, CDCl3) δ 17.4 (CH2),
31.1 (CH3), 31.7 (CH3), 33.0 (CH2), 34.2 (CH2), 34.9 (C), 37.8 (C), 117.9 (C), 125.1 (CH), 127.3
(CH), 129.0 (C), 143.7 (C), 152.4 (C), 154.2 (C). Anal. Calcd for C18H26BrNS: C, 58.69; H, 7.11;
N, 3.80. Found: C, 58.85; H, 7.17; N, 3.66.

668 H. Mikami et al.
4.5. Synthesis of trans-1,2-bis{[3,5-di-tert-butyl-2-{2-(cyanoethyl)sulfanyl}benzyl]sulfanyl}
cyclooctane (10)
A solution of 9 (293.2 mg, 0.80 mmol) inTHF (8 ml) was added to a solution of trans-cyclooctane-
1,2-dithiol (52.0 mg, 0.29 mmol) in THF (5 ml) at room temperature under argon, and then
triethylamine (0.12 ml, 0.86 mmol) was added to the reaction mixture. The mixture was heated
under reflux for 15 h, and the reaction was quenched by addition of hydrochloric acid (2 M, 5 ml).
The mixture was extracted with dichloromethane, and the organic layer was dried over anhydrous
sodium sulfate. After removal of the solvent, the residual yellow oil was purified by silica-gel
column chromatography (dichloromethane) to give 10 as yellow oil (184.4 mg, 0.25 mmol, 83%).
10: Yellow oil. 1H NMR (400 MHz, CDCl3) δ 1.27 (s, 20H), 1.53 (s, 20H), 1.77–1.83 (m, 4H),
2.08–2.14 (m, 4H), 2.61 (t, J = 8 Hz, 4H), 2.93–3.11 (m, 6H), 4.14 (d, J = 12 Hz, 2H), 4.28 (d,
J = 12 Hz, 2H), 7.37 (d, J = 2 Hz, 2H), 7.45 (d, J = 2 Hz, 2H); 13C NMR (100.7 MHz, CDCl3)
δ 17.4 (CH2), 26.0 (CH2), 29.7 (CH2), 30.5 (CH2), 31.2 (CH3), 31.7 (CH3), 33.4 (CH2), 34.9 (C),
36.1 (CH2), 37.7 (C), 51.1 (CH), 118.3 (C), 123.4 (CH), 126.4 (CH), 128.7 (C), 143.9 (C), 151.6
(C), 153.5 (C). HRMS (ESI, positive mode): Calcd. for C44H66N2NaS4: [M+Na]+ 773.40011.
Found: 773.40130.
4.6. Synthesis of trans-1,2-bis[(3,5-di-tert-butyl-2-sulfanylbenzyl)sulfanyl]cyclooctane (5)
4.6.1. With CsOH
A solution of CsOH•H2O (22.9 mg, 0.136 mmol) in MeOH (1 ml) was added to a solution
of 10 (38.8 mg, 0.052 mmol) in THF (2 ml) under argon. The mixture was stirred for 3 h at
room temperature, and hydrochloric acid (2 M, 1 ml) was added. The mixture was extracted
with dichloromethane, and the organic layer was washed with water and dried over anhydrous
sodium sulfate. The solvent was removed under reduced pressure, and the residue was subjected to
silica-gel column chromatography (dichloromethane/hexane 1/1) to give 5 as colorless crystals
(10.1 mg, 31%). 5: Colorless crystals, mp 133–135◦C (hexane). 1H NMR (400 MHz, CDCl3) δ
1.30 (s, 20H), 1.52 (s, 20H), 1.75–1.81 (m, 4H), 2.08–2.14 (m, 4H), 2.84 (br s, 2H), 3.96 (d,
J = 12 Hz, 2H), 4.04 (d, J = 12 Hz, 4H), 5.23 (s, 2H), 7.15 (s, 2H), 7.38 (s, 2H); 13C NMR
(100.7 MHz, CDCl3) δ 26.0 (CH2), 26.5 (CH2), 30.6 (CH3), 31.2 (CH2), 31.4 (CH3), 34.7 (C),
37.1 (C), 39.9 (CH2), 51.7 (CH), 123.7 (CH), 126.2 (CH), 127.9 (C), 136.8 (C), 148.2 (C), 149.9
(C). Anal. Calcd for C38H60S4: C, 70.75; H, 9.37. Found: C, 70.68; H, 9.46.
4.6.2. With LiAlH4
A suspension of LiAlH4 (3.8 mg, 0.10 mmol) in ether (2 ml) was added to a solution of 10 (8.3 mg,
0.01 mmol) in ether (1 ml) at 0 ◦C under argon.The mixture was stirred for 3 h at room temperature,
and the reaction was carefully quenched by addition of hydrochloric acid (2 M, 5 ml). The mixture
was extracted with ether, and the organic layer was dried over anhydrous sodium sulfate. After
removal of the solvent, the resulting yellow oil was purified by silica-gel column chromatography
(dichloromethane/hexane = 1/1) to give 5 as colorless crystals (3.4 mg, 48%).
4.7. Reaction of [SSSS]-type ligand 5 with [Pt(nb)(PPh3)2]
A solution of 5 (11.0 mg, 0.017 mmol) and [Pt(nb)(PPh3)2] (14.0 mg, 0.017 mmol) in C6D6
(0.5 ml) was made to stand at room temperature overnight.The solvent was removed under reduced
pressure. The residue was subjected to silica-gel column chromatography (dichloromethane), and

Journal of Sulfur Chemistry 669
the crude material was purified by recrystallization from a mixed solvent of dichloromethane and
hexanetogive 11asyellowcrystals(3.2 mg, 21%). 11:Yellowcrystals, mp160–163◦Cdecomp. 1H
NMR (400 MHz, CDCl3) δ 1.22 (s, 9H), 1.27 (s, 9H), 1.48–1.94 (m, 9H), 1.99–2.16 (m, 2H), 2.22–
3
2.33 (m, 1H), 3.06–3.18 (m, 1H), 3.23–3.35 (m, 1H), 4.11 (dd, J = 10, 6 Hz, JPt−H = 54 Hz,
3
1H), 4.81 (dd, J = 10, 6 Hz, JPt−H = 54 Hz, 1H), 7.05 (d, J = 2 Hz, 1H), 7.35 (d, J = 2 Hz,
1H), 7.35–7.45 (m, 10H), 7.65–7.74 (m, 5H); 13C NMR (100.7 MHz, CDCl3) δ 25.5 (CH2), 25.7
(CH2), 26.0 (CH2), 26.1 (CH2), 29.4 (CH2), 30.2 (CH3), 31.4 (CH3), 34.4(C), 35.9 (CH2), 37.2
(C), 40.1 (CH2), 45.3 (d, JP−C = 5 Hz, CH), 63.1 (CH), 124.1 (d, JP−C = 62 Hz, CH), 127.8 (d,
JP−C = 11 Hz, CH), 129.1 (d, JP−C = 58 Hz, C), 130.5 (CH), 130.6 (CH), 134.9 (d, JP−C = 11 Hz,
CH), 136.8 (C), 146.0 (C), 150.9 (C) (an aromatic quaternary carbon was not observed probably
because of broadening); 31P{1H} NMR (161 MHz, CDCl3) δ 22.4 (s, 1JPt−P = 3700 Hz). HRMS
(ESI, positive mode): Calcd. for C41H51NaPS3Pt: [M + Na]+ 888.2431. Found: 888.2429.
X-ray crystallographic analysis:Yellow single crystals of 11 were grown by slow evaporation
of the saturated hexane–dichloromethane solution at –20◦C. The intensity data were collected
at 90 K employing graphite-monochromated Mo-Kα radiation (λ = 0.71073Å), and the struc-
tures were solved by direct methods and refined by full-matrix least-squares procedures on
F2 for all reflections (SHELX–97) (37): Crystallographic data: C41H51PPtS3 (866.06), yel-
low crystals, 0.29 × 0.20 × 0.15 mm3, 90 K, monoclinic, P21/c, a = 13.7792(6), b = 21.0969(9),
c = 14.1768(6) Å, β = 113.7800(10)◦, V = 3771.3(3)Å3, Z = 4, dcalc = 1.525 g cm−3, 7023
unique data, 421 parameters, R1 (I > 2σ(I)) = 0.0324, wR2 (all data) = 0.0781, GOF =
1.030: CCDC 922457 contains the supplementary crystallographic data of 11. These data
can be obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
4.8. Reaction of [SSSS]-type ligand 5 with [PtCl2(PPh3)2]
A solution of 5 (9.7 mg, 0.015 mmol) and [PtCl2(PPh3)2] (11.8 mg, 0.015 mmol) in benzene (2 ml)
was refluxed under argon for 7 h. After cooling to room temperature, the colorless precipitates
were collected by filtration to give phosphonium salt 12 (0.2 mg, 3%). The filtrate was evaporated
to dryness, and the residue was subjected to silica-gel column chromatography (dichloromethane)
to give 11 as yellow crystals (4.1 mg, 31%) and an unidentified material (see Note 1) (4.0 mg).
1
12: Colorless crystals. H NMR (500 MHz, CDCl3) δ 1.01 (s, 9H), 1.37 (s, 9H), 4.46 (s, 1H),
5.78 (d, 1JP−H = 14 Hz, 2H), 6.94 (t, J = 2 Hz, 1H), 7.34 (t, J = 2 Hz, 1H), 7.57–7.68 (m, 12H),
7.72–7.80 (m, 3H). 31P{1H} NMR (202 MHz, CDCl3) δ 25.4 (s). HRMS (ESI, positive mode)
Calcd. for C33H38PS: [M]+ 497.2426. Found: 497.2468.
Note
1. In this reaction, we isolated another platinum complex: 1H NMR (400 MHz, CDCl3) δ 1.18 (s, 18H), 1.25 (s, 18H),
4.13 (dd, J = 7, 6 Hz, JPt−H = 54 Hz, 2H), 7.09 (d, J = 2 Hz, 2H), 7.29 (d, J = 2 Hz, 2H), 7.35–7.47 (m, 9H),
7.72–7.82 (m, 6H); 13C NMR (100.7 MHz, CDCl3) δ 30.2 (CH3), 31.4 (CH3), 34.4 (C), 37.1 (C), 43.7 (CH2),
124.2 (d, JP−C = 55 Hz), 127.7 (d, JP−C = 11 Hz), 127.9 (d, C, JP−C = 59 Hz), 130.5 (CH), 130.6, (CH), 135.2,
(d, JP−C = 10 Hz), 136.6 (C), 146.3 (C) (an aromatic quaternary carbon was not observed probably because of
broadening); 31P NMR (162 MHz, CDCl3) δ 24.0 (s, JPt−P = 3686 Hz). We have not determined the structure but
will report it elsewhere in the future.
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