Sulfurization of 4,5,6-triphospha[3]radialene

Article abstract of DOI:10.1080/10426507.2014.991828

Sulfurization reaction of a stable 4,5,6-triphospha[3]radialene led to the formation of the corresponding methylene(thioxo)phosphorane, which was isolated and characterized. The characteristic absorption maximum of the sulfurized compound in electronic sp

Full text of DOI:10.1080/10426507.2014.991828

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
Sulfurization of 4,5,6-Triphospha[3]Radialene
Hideaki Miyake, Takahiro Sasamori & Norihiro Tokitoh
To cite this article: Hideaki Miyake, Takahiro Sasamori & Norihiro Tokitoh (2015) Sulfurization
of 4,5,6-Triphospha[3]Radialene, Phosphorus, Sulfur, and Silicon and the Related Elements,
190:8, 1247-1250, DOI: 10.1080/10426507.2014.991828
To link to this article: http://dx.doi.org/10.1080/10426507.2014.991828
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Date: 30 September 2015, At: 01:58

Phosphorus, Sulfur, and Silicon, 190:1247–1250, 2015
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2014.991828
SULFURIZATION OF 4,5,6-TRIPHOSPHA[3]RADIALENE
Hideaki Miyake†, Takahiro Sasamori, and Norihiro Tokitoh
Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011,
Japan
GRAPHICAL ABSTRACT
Abstract Sulfurization reaction of a stable 4,5,6-triphospha[3]radialene led to the formation
of the corresponding methylene(thioxo)phosphorane, which was isolated and characterized.
The characteristic absorption maximum of the sulfurized compound in electronic spectrum
was shifted toward the longer wavelength region relative to that of the triphospha[3]radialene.
Desulfurization reaction of the sulfurized compound to 4,5,6-triphospha[3]radialene was also
demonstrated.
Keywords Low-coordinated phosphorus compound; sulfurization; radialene
INTRODUCTION
Radialenes are organic compounds of considerable chemical interest due to their
cyclic cross-π–conjugated system.1 We have recently reported the synthesis of the first
stable triphospha[3]radialene 1, where the three exo-carbon atoms of a [3]radialene skeleton
are replaced by phosphorus atoms.2 Compound 1 exhibits unique electronic properties due
to the cross-π–conjugation including three P C π bonds. From the viewpoint of further
functionalization of the triphospha[3]radialene for pursuit of its application with specific
functions, we are interested in the modification of the reactive P C moieties. Sulfurization
reaction of P=C bond compounds bearing bulky 2,4,6-(t-Bu)3C6H2 (Mes∗) group and their
Received 4 October 2014; accepted 20 November 2014.
†Present address: Graduate School of Science and Engineering, Yamaguchi University, 2-16-1 Tokiwadai,
Ube, Yamaguchi 755-8611, Japan
Address correspondence to Takahiro Sasamori and Norihiro Tokitoh, Institute for Chemical Research, Kyoto
University, Gokasho, Uji, Kyoto 611-0011, Japan. E-mail: tokitoh@boc.kuicr.kyoto-u.ac.jp
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H. MIYAKE ET AL.
Figure 1 (a) Sulfurization of 4,5,6-triphospha[3]radialene 1. Mes∗ = 2,4,6-(t-Bu)3C6H2. (b) Molecular structure
of 2 with thermal ellipsoids set at 50% probability. Selected bond lengths (Å): (a) P1–C1 = 1.656(3), P2–C2 =
1.651(3), P3–C3 = 1.657(3), C1–C2 = 1.437(4), C1–C3 = 1.437(4), C2–C3 = 1.431(4), P1–S1 = 1.9353(12),
P2–S2 = 1.9282(12), P3–S3 = 1.9266(12).
desulfurization reproducing the P=C bond reported so far3 naturally prompted us to examine
the sulfurization of the triphospha [3]radialene as a simple modification of P C bonds. We
report here the sulfurization of 1 to give the corresponding phosphine sulfide together with
the structure and properties of the sulfurized product.
RESULT AND DISCUSSION
The reaction of 1 with elemental sulfur (S8, 4.5 eq. as S) in the presence of triethy-
lamine at 80◦C for 3 h gave sulfurized compound 2 in 83% as a deep violet solid (Figure
1a). The reaction of 1 with elemental sulfur in the absence of triethyl-amine did not give
any sulfurized compound. The three phosphaalkene moieties of compound 1 were con-
verted to methylene(thioxo)phosphorane moieties by the sulfurization reaction. Compound
2 was fully characterized by NMR spectroscopy and elemental analysis, and its struc-
tural parameters were definitively determined by X-ray crystallographic analysis (Figure
1b). The central C3P3S3 core was revealed to be planar and almost C3 symmetric. The
bond lengths of 2 around the phosphorus atoms are almost the same as those of known
methylene(thioxo)phosphorane compounds.
The electronic spectrum of 2 in hexane showed a strong absorption at λmax = 593 nm
(ε = 3.17 × 104), which is longer than that of 1 at λmax = 526 nm (ε = 1.92 × 104) (Figure
2a), indicating the smaller HOMO-LUMO gap of 2 relative to 1. Cyclic voltammograms of
2 in THF at r.t. exhibited a reversible reduction couple at E1/2 = –1.38 V (vs FcH/FcH+),
showing its higher electron-accepting ability than that of 1 (E1/2 = –1.55 V vs FcH/FcH+)
1
(Figure 2b). The oxidation processes of 1 and 2 under these CV measurement conditions
were both irreversible (Epa = 1.13 V for 1, Epa = 0.83 V for 2), while the oxidation potential
of 2 would be lower than that of 1.
Desulfurization reaction of 2 with excess amount of tris(dimethylamino)-phosphine
(HMPT) in benzene at room temperature for 3 h gave 1 quantitatively. It can be concluded
that the electronic structure and properties should be facilely modified by the sulfurization
reaction, and the reproduction of the original triphospha[3]radialene would be also easily
achieved by the addition of HMPT. That is, sulfurization reaction should be ‘reversible’
functionalization toward triphospha[3]radialene.

4,5,6-TRIPHOSPHA[3]RADIALENE
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Figure 2 (a) Electronic spectra in hexane of 2 (solid line) and 1 (broken line). (b), (c) Cyclic voltammograms
of 2 (solid line) and 1 (broken line) in the reductive region (b) and oxidative region (c). The measurements were
carried out in THF solution (0.1 mM) containing 0.1 M (n-Bu)4NPF6 as a supporting electrolyte with scan rates
of 50 mVs–1 at ambient temperature.
EXPERIMENTAL
To a mixture of 1 (87 mg, 0.10 mmol) and elemental sulfur (15 mg, 0.45 mmol as
S) in benzene (1 mL) was added triethylamine (0.14 mL, 1.0 mmol). After the reaction
at 80◦C for 3 h, the volatile materials were removed under reduced pressure. Hexane was
ꢀR
added to the residue, and then the mixture was filtered through Celite . After removal
of the solvent, the obtained residue was purified by column chromatography on silica gel
(hexane/CHCl3 = 5/1) to give compound 2 (80 mg, 83 μmol, 83%). 2: violet crystals,
m.p. 202◦C (decomp). 1H NMR (300 MHz, C6D6) δ 1.24 (s, 27H), 1.84 (s, 54H), 7.61 (s,
1
6H); 13C{ H} NMR (75 MHz, C6D6) δ 31.1 (CH3, s), 34.3 (CH3, s), 35.4 (C, s), 38.9 (C,
s), 122.9 (CH, dd, JPC = 5, 10 Hz), 154.4–154.5 (C, m), 156.0–156.2 (C, m); 31P NMR
(120 MHz, C6D6) δ 91.8 (s); Anal. Calcd for C57H87P3S3: C, 71.21; H, 9.12%. Found: C,
70.97; H, 9.19%.
ACKNOWLEDGMENTS
Two of the authors (NT and TS) are grateful and to Prof. R. Streubel and his group
members for their warm hospitality.
FUNDING
This work was partially supported by Grants-in-Aid for Scientific Research (B) (No.
22350017), Young Scientist (A) (No. 23685010), and Young Scientist (B) (No. 26810022)
from the Ministry of Education, Culture, Sports, Science, and Technology, Japan, and for
JSPS Fellows (23·3938) from the Japan Society for the Promotion of Science. Support
by the Joint Usage/Research Center (JURC) at ICR is also appreciated. The manuscript

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H. MIYAKE ET AL.
was written at Rheinische Friedrich-Whilhelms-Universita¨t Bonn during the tenure of a
Alexander von Humboldt Research Award (NT) and a Friedrich Wilhelm Bessel Research
Award (TS) for two of the authors (NT and TS), who are grateful to the Alexander von
Humboldt Stiftung for their generosity.
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2. Miyake, H.; Sasamori, T.; Tokitoh, N. Angew. Chem. Int. Ed. 2012, 51, 3458.
3. (a) Toyota, K.; Shimura, K.; Takahashi, H.; Yoshifuji, M. Chem. Lett. 1994, 1927. (b) Toyota,
K.; Takahashi, H.; Shimura, K.; Yoshifuji, M. Bull. Chem. Soc. Jpn. 1996, 69, 141. (c) Yoshifuji,
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