A unique thermal reaction of 9-anthryldiphosphene leading to the formation of a triphosphirane derivative

Article abstract of DOI:10.1080/10426500902719479

Heating of a 9-anthryldiphosphene kinetically stabilized by 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl substituent (denoted as Bbt) group, BbtP P(9-Anth) (9-Anth = 9-anthryl), with (n-Bu) ₃PTe afforded 1,2-bis(9-Ant

Full text of DOI:10.1080/10426500902719479

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Phosphorus, Sulfur, and Silicon
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A Unique Thermal Reaction
of 9-Anthryldiphosphene
Leading to the Formation of a
Triphosphirane Derivative
Norihiro Tokitoh a , Akihiro Tsurusaki a & Takahiro
Sasamori a
a Institute for Chemical Research, Kyoto University ,
Kyoto, Japan
Published online: 26 Mar 2009.
To cite this article: Norihiro Tokitoh , Akihiro Tsurusaki & Takahiro Sasamori (2009)
A Unique Thermal Reaction of 9-Anthryldiphosphene Leading to the Formation of a
Triphosphirane Derivative, Phosphorus, Sulfur, and Silicon and the Related Elements,
184:4, 979-986, DOI: 10.1080/10426500902719479
To link to this article: http://dx.doi.org/10.1080/10426500902719479
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Phosphorus, Sulfur, and Silicon, 184:979–986, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500902719479
A Unique Thermal Reaction of 9-Anthryldiphosphene
Leading to the Formation of a Triphosphirane Derivative
Norihiro Tokitoh, Akihiro Tsurusaki,
and Takahiro Sasamori
Institute for Chemical Research, Kyoto University, Kyoto, Japan
Heating of a 9-anthryldiphosphene kinetically stabilized by 2,6-bis[bis(trimethyl-
silyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl substituent (denoted as Bbt)
group, BbtP
P(9-Anth) (9-Anth = 9-anthryl), with (n-Bu)3P Te afforded 1,2-
bis(9-Anth)-3-Bbt-triphosphirane in moderate yield. The structural parameters and
physical properties of the isolated triphosphirane were determined by spectroscopic
and X-ray crystallographic analyses.
Keywords 9-Anthryldiphosphene; diphosphene; phosphine telluride; triphosphirane
INTRODUCTION
In recent years, there has been much interest in compounds with a
double bond containing heavier group 15 elements from the viewpoints
of their unusual chemical and physical properties.1 Up to now, several
examples of stable diphosphenes and diarsenes (RAs AsR) have
been synthesized by taking advantage of steric protection with bulky
substituents,1,2 following the isolation of the first stable diphosphene,
Mes*P PMes* (Mes* = 2,4,6-tri-t-butylphenyl), reported by Yoshifuji
et al.3 We have also succeeded in the synthesis and characteriza-
tion of the first stable distibenes (ArSb SbAr) and dibismuthenes
(ArBi BiAr) by taking advantage of efficient steric protection
Received 20 December 2007; received 31 January 2008.
Dedicated to Professor Marian Mikołajczyk from the CBMiM PAN in Ło´dz´, Poland,
on the occasion of his 70th birthday.
This work was partially supported by Grants-in-Aid for Creative Scientific Research
(No. 17GS0207), Science Research on Priority Areas (No. 19027024, “Synergy of Ele-
ments”), Young Scientist (B) (Nos. 18750030), and the Global COE Program (B09, “In-
tegrated Material Science”) from Ministry of Education, Culture, Sports, Science and
Technology, Japan. T.S. thanks for the financial support from Daiichi Pharmaceutical
Co., Ltd.
Address correspondence to Norihiro Tokitoh, Institute for Chemical Research, Kyoto
University, Gokasho, Uji, Kyoto 611-0011, Japan. E-mail: tokitoh@boc.kuicr.kyoto-u.ac.jp
979

980
N. Tokitoh et al.
groups: 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt) group and
2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl
(Bbt) group.4 Evidence has shown that such stable doubly bonded sys-
tems between heavier group 15 elements should be good precursors for
the corresponding heterocycles,5 especially in the case of chalcogena-
tion reactions.6 For example, sulfurization and selenization reactions
of kinetically stabilized diphosphenes such as Mes*P PMes*3 and
BbtP PBbt7 using elemental sulfur and selenium were reported to
give the corresponding thia- and selenadiphosphiranes as final stable
products, respectively, (Scheme 1),7,8 while sulfurization reactions of
BbtSb SbBbt and BbtBi BiBbt using elemental sulfur afforded the
corresponding four-, five-, and six-membered heterocycles containing
sulfur and pnictogen (Sb or Bi) atoms.6,9 We have reported that
the thermal tellurization reactions of BbtP PBbt with elemental
tellurium and (n-Bu)3P Te were unsuccessful and resulted in the
recovery of BbtP PBbt, in contrast to the case of the tellurization
reactions of the analogous distibene and dibismuthene, where the
treatment of BbtE EBbt (E = Sb, Bi) with (n-Bu)3P Te afforded the
corresponding telluradipnictiranes.10 The inertness of BbtP PBbt
toward the tellurization reagents mentioned above is likely due to the
extreme steric hindrance around the P P moiety.
Bbt
Bbt
S8 or Se
Me3Si
Me3Si
SiMe3
SiMe3
P
P
P
P
C6D6
120 °C
Ch
Ch= S, Se
Bbt
Bbt
Me3Si
SiMe3
R
Te or (n-Bu)3P=Te
Tbt: R = H
Bbt: R = SiMe3
no reaction
C6D6
SCHEME 1
However, we have recently reported the synthesis of the first sta-
ble 9-anthryldiphosphene 1a, TbtP P(9-Anth), bearing a less hindered
combination of steric protection groups—Tbt and 9-anthryl—at the
P P unit.11 Since 1a is expected to have enough space for reaction
with tellurization reagents, we have examined the reaction of 1a with
(n-Bu)3P Te with the expectation of obtaining the corresponding tellu-
radiphosphirane, which should be an interesting and important species
from the viewpoint of heteroatom chemistry.12 With a view to mak-
ing closer comparison of the reactivity toward tellurization reaction

Thermal Reaction of 9-Anthryldiphosphene
981
between BbtP PBbt (2) and the 9-anthryldiphosphene, we have at-
tempted the tellurization reaction of BbtP P(9-Anth) (1b), which has
a Bbt group at the phosphorus atom instead of the Tbt group of 1a.
RESULTS AND DISCUSSION
9-Anthryldiphosphene 1b was synthesized according to the reported
procedure as shown in Scheme 2.11,13 When a bright-red solution of
1b in THF was treated with an excess (10 equiv.) of (n-Bu)3P Te
at 80◦C (sealed tube) for 98 h, the solution turned deep red and a
yellow solid precipitated. The 31P NMR spectrum of the crude mix-
ture showed the formation of BbtP PBbt (2) and an unexpected prod-
uct, the triphosphirane 3, along with the recovery of (n-Bu)3P Te
as the expense of the starting material (Scheme 3). Filtration of
the reaction mixture afforded yellow precipitates, which were found
to be triphosphirane 3, in 68% yield. Alternatively, GPLC purifi-
cation of the concentrated filtrate afforded diphosphene 2 in 73%
yield. The 31P NMR spectrum of the crude mixture indicated almost
quantitative recovery of (n-Bu)3P Te, since no signal for other trib-
utylphosphine derivatives such as (n-Bu)3P or (n-Bu)3P O was ob-
served. Surprisingly, heating of 9-anthryldiphosphene 1b in the ab-
sence of (n-Bu)3P Te under the same conditions (in THF at 80◦C for 98
h) resulted in the almost quantitative recovery of 1b, but the formation
Ar
Cl
Cl
P
H
H
DBU
P
P
+
P
Ar
toluene
r.t.
1a: Ar = Tbt
1b: Ar = Bbt
SCHEME 2
Bbt
P
Bbt
Bbt
(n-Bu)3P=Te
1
+
2
P
P
P
P
2
THF
P
P
80 °C
9-Anth
Bbt
9-Anth
9-Anth
1b
3
68%
2
73%
9-Anth = 9-anthryl
SCHEME 3

982
N. Tokitoh et al.
of only a trace amount of triphosphirane 3. This fact suggests that (n-
Bu)3P Te would work as a kind of catalyst in the thermal reaction of
1b leading to the formation of 2 and 3 under these conditions. Although
the reaction mechanism for the formation of 3 is unclear at present, the
corresponding telluradiphosphirane derivative, which would be highly
reactive, may be a key intermediate.
In the 31P NMR spectrum, triphosphirane 3 showed the signals of a
characteristic A2B-pattern in the high-field region at –93.1 ppm (dou-
blet) and –127.6 ppm (triplet) with the coupling constant of 1JPP = 188
1
Hz. Since the observed NMR spectral data (δP and JPP value) of 3
are similar to those of previously reported triphosphiranes,14 the bulky
combination of Bbt and 9-anthryl groups, should not electronically af-
fect the central triphosphirane skeleton.
In addition, the X-ray crystallographic analysis revealed the struc-
tural parameters of 3 as shown in Figure 1. The P–P bond lengths of
3 are 2.2144(14), 2.2136(13), and 2.2408(14) Å; these values are within
the range of typical P–P single bond lengths (ca. 2.2 Å)15 but are slightly
shorter than those of six-membered ring oligophosphanes [e.g., (PhP)6;
2.237(5) Å]16 probably due to the “banana-bonds” in three-membered
ring systems.17 The bulky Bbt group is oriented toward the opposite
side of the two 9-anthryl groups, which face each other with a distance
of ca. 3.2–4.3 Å.18 The bond length between the phosphorus atoms P(2)
and P(3), both of which are bonded to a 9-anthryl group, is longer than
those of P(1)–P(2) and P(1)–P(3), probably due to the steric repulsion
between the facing two 9-anthryl groups.
Theoretical calculations19 revealed that the structural parameters
for the parent triphosphirane 4 with the same configuration as that of
3 are almost similar to those experimentally observed for 3. Further-
more, in the theoretically optimized structure of 1,2-bis(9-anthryl)-3-
(2,6-dimethylphenyl)triphosphirane 5, which is a model compound of
3 having a 2,6-dimethylphenyl group instead of a Bbt group, the two
9-anthryl groups were found to step aside from each other and twist
around to avoid the steric repulsion as shown in Figure 2. Therefore,
the unique geometry of 3, where the two 9-anthryl groups are facing
parallel to each other, is most likely due to the packing force in the
crystalline state.
In summary, it was found that the thermal reaction of an-
thryldiphosphene 1b in the presence of (n-Bu)3P Te afforded the
triphosphirane 3 and the diphosphene 2. Furthermore, (n-Bu)3P Te
is necessary for the effective transformation of 1b, giving 2 and 3. Fur-
ther investigations on the properties of triphosphirane 3 are currently
in progress.

Thermal Reaction of 9-Anthryldiphosphene
983
FIGURE 1 Molecular structure of triphosphirane 3 in the crystal (displace-
ment ellipsoids are drawn at the 50% probability level). The hydrogen atoms
are omitted for clarity. Selected structural parameters: P(1)–P(2): 2.2144(14)
Å, P(1)–P(3): 2.2136(13) Å, P(2)–P(3): 2.2408(14) Å, P(2)–P(1)–P(3): 60.80(4)◦,
P(1)–P(2)–P(3): 59.58(4)◦, P(1)–P(3)–P(2): 59.62(4)◦.
EXPERIMENTAL
All experiments were performed under an argon atmosphere unless
otherwise noted. Solvents used for the reactions were purified by The
Ultimate Solvent System (Glass Contour Company).20 BbtP P(9-Anth)
was prepared according to the procedures similar to those for TbtP P(9-
Anth).11 1H NMR (300 MHz) spectra were measured in C6D6 with a
JEOL JNM AL-300 spectrometer using a signal due to C6D5H (7.15
ppm) as a reference. 31P NMR (121 MHz) spectra were measured in
C6D6 with a JEOL AL-300 spectrometer using a signal for 85% H3PO4
in water (0 ppm) as an external standard. High-resolution mass spec-
tral data were obtained with a JEOL JMS-700 spectrometer. Gel per-
meation liquid chromatography (GPLC) was performed with an LC-918

984
N. Tokitoh et al.
FIGURE 2 (a) Optimized structure of the parent triphosphirane 4; selected
structural parameters: P(1)–P(2): 2.242 Å, P(1)–P(3): 2.242 Å, P(2)–P(3): 2.259
Å, P(2)–P(1)–P(3): 60.5◦, P(1)–P(2)–P(3): 59.7◦, P(1)–P(3)–P(2): 59.7◦. (b) Opti-
mized structure of triphosphirane 5; selected structural parameters: P(1)–P(2):
2.237 Å, P(1)–P(3): 2.277 Å, P(2)–P(3): 2.259 Å, P(2)–P(1)–P(3): 60.0◦, P(1)–
P(2)–P(3): 60.8◦, P(1)–P(3)–P(2): 59.1◦. (c) Experimentally observed structure
of 3. The substituents of the Bbt group are omitted for clarity.
(Japan Analytical Industry Co., Ltd.) equipped with JAIGEL 1H and
2H columns (eluent: toluene). The melting point was determined with
a Yanaco micro melting point apparatus and is uncorrected. Elemen-
tal analyses were carried out at the Microanalytical Laboratory of the
Institute for Chemical Research, Kyoto University.
Triphosphirane (3)
A THF suspension (0.6 mL) of BbtP P(9-Anth) (1b, 60.4 mg, 0.070
mmol) and (n-Bu)3P Te21 (231 mg, 0.70 mmol) was degassed and sealed
in an NMR tube. After heating of the mixture at 80◦C for 98 h, the bright
red color of the reaction mixture changed to deep red, and a yellow
powder precipitated. After the signals for 1b almost disappeared, the
yellow suspension was separated by filtration, and the yellow insoluble
materials were washed with hexane. The solvent of the mother liquid

Thermal Reaction of 9-Anthryldiphosphene
985
was removed under reduced pressure, and the residue was separated
by GPLC to afford BbtP PBbt (2, 16.7 mg, 0.013 mmol, 73%) as red
crystals. The yellow solid thus obtained was dissolved in toluene and
filtered through a glass filter to remove the inorganic salt. The filtrate
was evaporated under reduced pressure to afford triphosphirane 3 (25.7
1
mg, 0.024 mmol, 68 %) as yellow crystals. 3: mp 263◦C (decomp.). H
NMR (300 MHz, C6D6, 40◦C) δ = 0.39 (s, 36H), 0.43 (s, 27H), 4.07 (s,
3
2H), 6.82 (br s, 4H), 6.89 (pseudotriplet, JHH = 6.8 Hz, 4H), 7.07 (d,
3
4JPH = 2.5 Hz, 2H), 7.26 (d, JHH = 8.9 Hz, 4H), 7.46 (s, 2H), 9.11 (d,
3JHH = 8.5 Hz, 4H). 31P NMR (121 MHz, C6D6, r.t.) δ = −92.9, −127.4
(A2B spin pattern, 1JPP = 188 Hz). The signals observed in the 13C NMR
spectrum could not be assigned. Anal. Found: C, 64.15; H 8.00%. Calcd
for C58H85P3Si7 · H2O: C, 63.92; H, 8.05%. HRMS (FAB) m/z, found:
1071.4335 ([M+H]+), calcd for C58H86P3Si7 ([M+H]+): 1071.4327.
Single crystals of 3 suitable for X-ray diffraction were obtained by
slow recrystallization from THF/toluene at –40◦C. The intensity data
were collected on a Rigaku/MSC Mercury CCD diffractometer with
graphite monochromated MoKα radiation (λ = 0.71069 Å) at –170◦C
to 2θmax = 51◦. The structure was solved by direct methods (SHELXS-
9722) and refined by full-matrix least-squares procedures on F2 for all
reflections (SHELXL-9722). All hydrogen atoms were placed using AFIX
instructions. Crystal data for 3 (C58H85P3Si7): M = 1071.80, T = 103(2)
K, monoclinic, P21/n (no.14), a = 9.5518(3) Å, b = 27.2459(8) Å, c =
22.9089(8) Å, β = 94.2967(11)◦, V = 5945.2(3) Å3, Z = 4, Dcalc = 1.197
g cm–3, µ = 0.277 mm–1, 2θmax = 51.0, 52034 measured reflections,
11040 independent reflections [Rint = 0.1143], 634 refined parameters,
GOF = 1.036, R1 = 0.0558 and wR2 = 0.1019 [I >2σ(I)], R1 = 0.1195
and wR2 = 0.1158 [for all data], largest diff. peak and hole 0.710 and
–3
–0.410 e.Å
.
Crystallographic data (excluding structure factors) for the struc-
ture reported in this article have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no. CCDC
670466 for 3. Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax:
(+44)1223-336-033; E-mail: deposit@ccdc.cam.ac.uk.).
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