Synthesis of kinetically stabilized silaneselone and silanetellone

Article abstract of DOI:10.1246/cl.2002.34

Kinetically stabilized silaneselone [Tbt(Dip)Si=Se (4); Tbt=2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Dip=2,6-diisopropylphenyl] and silanetellone [Tbt(Dip)Si=Te] were synthesized by direct chalcogenation of Tbt(Dip)M: (M=Si, Ge) with elemental chalcogen. Deselenation of Tbt(Dip)SiSe₂ also gave 4. Metallanetellones [Tbt(Dip)M=Te; M=Si, Ge] were also synthesized by the reaction of Tbt(Dip)MLi₂ (M=Si, Ge) with TeCl₂, which is a new synthetic method for heavy ketones.

Full text of DOI:10.1246/cl.2002.34

34
Chemistry Letters 2002
Synthesis of Kinetically Stabilized Silaneselone and Silanetellone
Norihiro Tokitoh,ꢀ Tomonori Sadahiro,y Ken Hatano,yy Takayo Sasaki, Nobuhiro Takeda, and Renji Okazakiy
Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011
yDepartment of Chemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033
yyInstitute for Fundamental Chemistry of Organic Chemistry, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581
(Received October 26, 2001; CL-011058)
Kinetically stabilized silaneselone [Tbt(Dip)Si¼Se (4);
Tbt¼2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Dip¼2,6-diiso-
propylphenyl] and silanetellone [Tbt(Dip)Si¼Te] were synthesized
by direct chalcogenation of Tbt(Dip)M: (M¼Si, Ge) with ele-
mental chalcogen. Deselenation of Tbt(Dip)SiSe2 also gave 4.
Metallanetellones [Tbt(Dip)M¼Te; M¼Si, Ge] were also syn-
thesized by the reaction of Tbt(Dip)MLi2 (M¼Si, Ge) with TeCl2,
which is a new synthetic method for heavy ketones.
silaneselone 4 in a pure form.
Since ketones play very important roles in organic chemistry,
much interest has been focused on the chemistry of double-bond
compounds between heavier group 14 and group 16 elements (we
refer to this family of heavier congeners of ketones as ‘‘heavy
ketones’’).1 However, the chemistry of heavy ketones had been less
explored due to their extremely high reactivities. In recent years,
however, we have reported the syntheses of a variety of stable
examples of kinetically stabilized heavy ketones2{4 by taking
advantage of efficient steric protection group, Tbt.5 As for silicon-
containing heavy ketones, only a silanethione bearing Tbt and Tip
groups [Tbt(Tip)Si¼S (1); Tip¼2,4,6-triisopropylphenyl] was
isolated as a stable compound.2 Although some examples are
known for silaneselones stabilized by the intramolecular coordina-
tion of a nitrogen atom6 and transient silaneselones as reactive
intermediates,7 no coordination-free examples have been synthe-
sized yet for silaneselones and silanetellones so far. Here, we
present the synthesis of stable silaneselone and silanetellone by
taking advantage of kinetic stabilization afforded by the combina-
tion of Tbt and Dip groups.
Scheme 1.
On the other hand, the reaction of 2 with excess of elemental
selenium in C6D6 at 120 ꢁC for 19 h in a sealed tube resulted in
almost quantitative formation of diselenasilirane 59 having a novel
SiSe2 ring system (Scheme 1). The 29Si and 77Se NMR spectra of 5
showed signals at À44 and À174 ppm, respectively. The UV/vis
spectrum of 5 in THF showed an absorption maximum at 509 nm
most likely assignable to the n-ꢀꢀ absorption of the Se-Se moiety in
5. The considerable bathochromic shift observed for 5 should be of
interest as that for highly strained diselenasilirane skeleton in
comparison with those for 1,4-bis[tris(trimethylsilyl)methyl]te-
traselenadisilabicyclo[2.1.1]hexane [450 nm (" 60) in hexane]10
and typical diselenides [329 nm (" 1:1 Â 103) for diphenyl
diselenide in ethanol11].
Since 5 was considered to be a useful precursor of 4, desele-
nation of 5 was next examined with Ph3P in THF at room tem-
perature resulting in the change of the color from red to orange. The
29Si and 77Se NMR spectra (ꢁSi ¼ 174, ꢁSe ¼ 635; in C6D6) of the
resulting material are identical with those of 4 formed in the above-
mentioned direct selenation of 3. The electronic spectrum of the
reaction mixture in THF showedan absorptionmaximum at456 nm,
which was assignable to that for the n-ꢂꢀ transition of the Si¼Se
moiety. These results indicate that the formation of silaneselone 4
can also be performed by the deselenation method. Although the
formation of by-products was considerably suppressed in this
transformation, the isolation of 4 as pure crystals has not been
achieved yet even by this new method.
The reaction mode of 4 was found to be almost similar to that of
other heavy ketones.1 Silaneselone 4 underwent 1,2-addition, C–O
insertion, [2 þ 3]cycloaddition, and [2 þ 2]cycloaddition as can be
seen in the reactions with ROH (R¼H, Me), cyclohexene oxide,
mesitonitrile oxide, and phenyl isocyanate, respectively (Scheme
2). Although theadducts 6-9 are stable inair and moisture and canbe
chromatographically purified, the [2 þ 2]adduct 10 is liable to be
gradually hydrolyzed to give 7 and phenyl isothiocyanate on
exposure to air. The mechanism for the hydrolysis of 10 is most
likely explained by initial attack of a water molecule to the silicon
atom, followed by the extrusion of phenyl isothiocyanate in
preference to phenyl isoselenocyanate.
The stable silanethione 1 was synthesized by the desulfuriza-
tion of the corresponding tetrathiasilolane, Tbt(Tip)SiS4.2 How-
ever, this type of synthetic method cannot be applied to the synthesis
of silaneselone, since the preparation of tetraselenasilolane
[Tbt(Tip)SiSe4] was unsuccessful due to its extreme instability.
Then, we have examined an alternative synthetic route to
silaneselone via direct selenation of a sterically hindered silylene.
When a C6D6 solutionof silanorcarane 2, which is known to givethe
corresponding silylene 3 by thermolysis,8 was heated in the
presence of equimolar amount of selenium at 100 ꢁC for 82 h in a
sealed tube, the resulting reddish orange solution showed peaks at
174 and 635 ppm in the 29Si and 77Se NMR spectra, respectively.
The characteristically down-fielded 29Si NMR chemical shift
strongly indicates the existence of the sp2 silicon center, i.e., the
formation of the stable silaneselone 4. Although 4 was a main
product in this reaction as judged by NMR, the reaction mixture
contained various by-products and it was difficult to isolate
As anextension of theabove-mentionedchemistry, synthesisof
a silanetellone was also examined by the thermolysis of 2 in the
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
35
This work was partially supported by Grants-in-Aid for Sci-
entific Research (Nos. 11166250, 12CE2005 and 13740353) from
Ministry of Education, Culture, Sports, Science, and Technology of
Japan. We thank Central Glass, Shin-Etsu Chemical, and Tosoh
Akzo Co., Ltds. for the generous gifts of tetrafluorosilane,
chlorosilanes, and alkyllithiums, respectively.
Dedicated to Prof. Teruaki Mukaiyama on the occasion of his
70th birthday.
Scheme 2.
References and Notes
presence of elemental tellurium. When the mixture of 2 and
elemental tellurium in C6D6 was heated in a sealed tube at 90 ꢁC for
5 days and then at 75 ꢁC for 25days, the color of the reaction mixture
turned dark green suggesting the formation of silanetellone 11a.
Although the UV/vis spectrum of the reaction mixture in THF
showed absorption maximum at 593 nm assignable to the n-ꢂꢀ
transition of a silanetellone, the 29Si NMR spectrum showed no
signal assignable to the sp2 silicon probably because of the low yield
of 11a.
1For recent reviews, see: a) N. Tokitoh and R. Okazaki, Adv. Organomet.
Chem., 47, 121 (2001). b) R. Okazaki and N. Tokitoh, Acc. Chem. Res.,
33, 625 (2000). c) N. Tokitoh, T. Matsumoto, and R. Okazaki, Bull.
´
Chem. Soc. Jpn., 72, 1665 (1999). d) J. Escudie and H. Ranaivonjatovo,
Adv. Organomet. Chem., 44, 113 (1999). e) N. Tokitoh and R. Okazaki,
in ‘‘The Chemistry of Organic Silicon Compounds, Vol. 2,’’ ed. by Z.
Rap-poport and Y. Apeloig, John Wiley & Sons Ltd., (1998), pp 1063-
1103. f) J. Barrau and G. Rima, Coord. Chem. Rev., 178-180, 593
(1998). g) K. M. Baines and W. G. Stibbs, Adv. Organomet. Chem., 39,
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2
3
a) H. Suzuki, N. Tokitoh, R. Okazaki, S. Nagase, and M. Goto, J. Am.
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Chem. Soc., 115, 8855 (1993). b) T. Matsumoto, N. Tokitoh, and R.
Okazaki, Angew. Chem., Int. Ed. Engl., 33, 2316 (1994). c) N. Tokitoh,
T. Matsumoto, and R. Okazaki, J. Am. Chem. Soc., 119, 2337 (1997). d)
T. Matsumoto, N. Tokitoh, and R. Okazaki, J. Am. Chem. Soc., 121,
8811 (1999).
In order to generate 11a more effectively, we developed an-
other useful synthetic method via the overcrowded diaryldili-
thiosilane 13a, which has recently been developed by us as a key
reagent in the synthesis of the first stable silacyclopropabenzene.12
Reaction of 13a, prepared by the exhaustive reduction of
dibromosilane 12a,12a with TeCl2 in THF at À78 ꢁC gave the
expected silanetellone 11a as a green solid (Equation 2). The 29Si
and 125Te NMR spectra of this reaction product in C6D6 showed
characteristic signals in low-field regions (ꢁSi ¼ 171, ꢁTe ¼ 731)
and the UV/vis spectrum (ꢃmax ¼ 593 nm in benzene) was almost
identical with that of the above-mentioned silanetellone formed by
the thermal reaction of 2 with elemental tellurium. It should be
noted that 11a is the first example of a stable silanetellone
spectroscopically identified. The n-ꢂꢀ transisions of silanethione 1
(396 nm in hexane), silaneselone 4 (456 nm in THF) and
silanetellone 11a (593 nm in benzene) are red-shifted in the order
of 1, 4, and 11a as in the case of other heavy ketones series.1b
4
5
M. Saito, N. Tokitoh, and R. Okazaki, J. Am. Chem. Soc., 119, 11124
(1997).
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Okazaki, N. Tokitoh, and T. Matsumoto, in ‘‘Synthetic Methods of
Organometallic and Inorganic Chemistry,’’ ed. by W. A. Herrmann,
Thieme, New York (1996), Vol. 2, pp 260-269.
´
6
7
P. Arya, J. Boyer, F. Carre, R. Corriu, G. Lanneau, J. Lapasset, M.
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B. Neumann, and H.-G. Stammler, Organometallics, 15, 753 (1996). d)
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8
9
T. Sadahiro, Master Thesis, The University of Tokyo, Japan, 1998.
5: 1H NMR (C6D6, 500 MHz) ꢁ 0.19 (s, 18H), 0.20 (s, 18H), 0.29 (s,
18H), 1.21 (d, J ¼ 6:8 Hz, 6H), 1.32 (d, J ¼ 6:8 Hz, 6H), 1.51 (s, 1H),
2.89 (br s, 1H), 3.37 (br s, 1H), 3.97 (sept, J ¼ 6:8 Hz, 2H), 6.60 (s, 1H),
6.73 (s, 1H), 7.11 (d, J ¼ 7:8 Hz, 2H), 7.20 (t, J ¼ 7:8 Hz, 1H); 13C
NMR (C6D6, 68 MHz) ꢁ 1.2 (q), 2.0 (q), 2.1 (q), 23.1 (q), 27.6 (d), 27.9
(q), 28.0 (d), 31.3 (d), 36.6 (d), 122.7 (s), 124.4 (d  2), 129.7 (d), 131.1
(d), 136.5 (s), 146.3 (s), 153.6 (s), 154.0 (s), 154.3 (s); 29Si NMR (C6D6,
99 MHz) ꢁ À44:3, 2.3, 2.8, 3.3; 77Se NMR (C6D6, 51MHz) ꢁ À174.
The successful synthesis of 11a here described naturally
prompted us to apply this methodology to the synthesis of other
heavy ketones, and as an example we have examined the synthesis
of a stable germanetellone via the corresponding dilithiogermane
intermediate. Thus, dilithiogermane 13b,13 derived from dibromo-
germane 12b by the exhaustive reduction with lithium naphthale-
nide, was allowed to react with TeCl2 in THF at À60 ꢁC to give the
corresponding germanetellone 11b quantitatively (Equation 2).14
The 125Te NMR chemical shift (1194 ppm in C6D6) for 11b is
almost similar to that of Tbt(Tip)Ge¼Te (ꢁTe ¼ 1143 ppm in
C6D6), which was reported as the first example of a stable
diarylgermanetellone.3c
In summary, we have succeeded in the synthesis and spectro-
scopic characterization of kinetically stabilized silaneselone 4 and
silanetellone 11a. The isolation of the newly obtained heavy
ketones as crystals and their crystallographic analysis are currently
in progress.
10 H. Yoshida, Y. Kabe, and W. Ando, Organometallics, 10, 27 (1991).
11 J. G. Grasselli, ‘‘Atlas of Spectral Data and Physical Constants for
Organic Compounds,’’ CRS Press, Cleveland (1973).
12 a) N. Tokitoh, K. Hatano, T. Sadahiro, and R. Okazaki, Chem. Lett.,
1999, 931. b) K. Hatano, N. Tokitoh, N. Takagi, and S. Nagase, J. Am.
Chem. Soc., 122, 4829 (2000).
13 N. Tokitoh and K. Hatano, unpublished results.
14 11b: 1H NMR (C6D6, 400 MHz) ꢁ 0.14 (s, 18H), 0.19 (s, 18H), 0.24 (s,
18H), 1.28 (d, J ¼ 6:5 Hz, 6H), 1.36 (d, J ¼ 6:5 Hz, 6H), 1.48 (s, 1H),
3.48 (br s, 1H), 3.63 (sept, J ¼ 6:5 Hz, 2H), 3.87 (br s, 1H), 6.48 (br s,
1H), 6.64 br (s, 1H), 6.99 (d, J ¼ 7:8 Hz, 2H), 7.20 (t, J ¼ 7:8 Hz, 1H);
13C NMR (C6D6, 100 MHz) ꢁ 1.5 (q), 2.2 (q), 2.5 (q), 22.5 (q), 27.1 (q),
28.6 (d), 28.9 (d), 32.3 (d), 34.9 (d), 125.3 (d  2), 130.5 (d), 131.0 (d),
146.6 (s), 147.1 (s), 148.9 (s), 149.4 (s), 150.1 (s), 157.8 (s); 125Te NMR
(C6D6, 95 MHz) ꢁ 1194.