Sulfur-substituted tetrahedranes

Article abstract of DOI:10.1021/ja205361a

The stable sulfur-substituted tetrahedrane derivatives 2-4 were synthesized by the reaction of tris(trimethylsilyl)tetrahedranyllithium 1 with diphenyl disulfide, bis(4-nitrophenyl) disulfide, and bis(2,4-dinitrophenyl) disulfide, respectively, and characterized by both NMR spectroscopy and X-ray crystallography. Phenylsulfonyltetrahedrane 5 was prepared by the reaction of 2 and m-chloroperbenzoic acid. The UV-vis absorption spectra of 2-4 suggested an interaction of the σ orbital of the tetrahedrane core and the lone-pair electrons on the sulfur atom, whereas no interaction for 5 was found. Thermal reactions of 2 and 5 are also reported; 2 underwent fragmentation into two acetylene molecules, whereas 5 gave the corresponding cyclobutadiene.

Full text of DOI:10.1021/ja205361a

COMMUNICATION
pubs.acs.org/JACS
Sulfur-Substituted Tetrahedranes
Tatsumi Ochiai, Masaaki Nakamoto, Yusuke Inagaki, and Akira Sekiguchi*
Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan
S Supporting Information
b
A 1.5-fold excess of diphenyl disulfide was added at room
ABSTRACT: The stable sulfur-substituted tetrahedrane
derivatives 2À4 were synthesized by the reaction of tris-
(trimethylsilyl)tetrahedranyllithium 1 with diphenyl disul-
fide, bis(4-nitrophenyl) disulfide, and bis(2,4-dinitrophenyl)
disulfide, respectively, and characterized by both NMR spec-
troscopy and X-ray crystallography. Phenylsulfonyltetrahe-
drane 5 was prepared by the reaction of 2 and m-chlor-
operbenzoic acid. The UVÀvis absorption spectra of 2À4
suggested an interaction of the σ orbital of the tetrahedrane
core and the lone-pair electrons on the sulfur atom, whereas
no interaction for 5 was found. Thermal reactions of 2 and 5
are also reported; 2 underwent fragmentation into two acet-
ylene molecules, whereas 5 gave the corresponding cyclo-
butadiene.
temperature to a dark-brown solution of 1 in toluene. The re-
action occurred gradually, and the color of the reaction mixture
turned to pale-yellow. Tetrahedrane 2 was isolated by HPLC as
a colorless oil in 55% yield (Scheme 1).12 The introduction of
4-nitrophenylsulfanyl or 2,4-dinitrophenylsulfanyl groups into
the tetrahedrane core was also possible and allowed us to obtain
single crystals to perform crystallographic analyses (see below).
Thus, 1 was treated with bis(4-nitrophenyl) disulfide in THF to
give 4-nitrophenyl tetrahedranyl sulfide 3 as air-stable yellow
crystals in 52% isolated yield. Similarly, 4 was obtained by the
reaction of 1 with bis(2,4-dinitrophenyl) disulfide in THF, which
gave 4 as air-stable orange crystals in 30% yield. Interestingly, we
were able to oxidize the sulfide to the corresponding sulfone without
any oxidation of the tetrahedrane core or the SiÀC bonds in 2.
Thus, treatment of 2 with m-chloroperbenzoic acid (MCPBA) in
CH2Cl2 gave air-stable colorless crystals of phenylsulfonyltetra-
hedrane 5, which was isolated in 90% yield (Scheme 2).12
The 13C NMR signals of the tetrahedrane skeleton were ob-
served at 3.9 ppm (CÀSC6H5) and À15.0 ppm (CÀSiMe3) for
2, 2.2 ppm (CÀSC6H4NO2) and À15.1 ppm (CÀSiMe3) for 3,
2.2 ppm (CÀSC6H3(NO2)2) and À14.5 ppm (CÀSiMe3) for 4,
and 16.4 ppm (CÀS(O)2C6H5) and À10.7 ppm (CÀSiMe3)
for 5. Although an upfield shift of the skeletal C atoms is
typical for tetrahedranes, significant downfield shifts relative to
(Me3Si)4THD (À20.5 ppm)6 and 1 [À27.0 ppm (ring CÀLi)
and À22.0 ppm (ring C)]10 were observed for the sulfur-
substituted carbon atom: +24.4 ppm for 2, +22.7 ppm for 3,
+22.7 ppm for 4 and +36.9 ppm for 5 relative to (Me3Si)4THD.
This remarkable deshielding could be attributed to the significant
electron-withdrawing effect of the phenylsulfanyl and phenylsul-
fonyl groups on the tetrahedrane skeleton.
The molecular structure of 3, as determined by X-ray crystal-
lographic analysis, is shown in Figure 1.12 The C1(tetrahedrane
skeleton)ÀS1 bond length is 1.7167(13) Å, which is significantly
shorter than the length of a typical C(sp3)ÀS single bond (1.82 Å).13
This shortening is attributed to the high s character of the carbon
atom of the tetrahedrane core.1 As a consequence of the difference
in the electronegativities of the elements (Pauling electronega-
tivities: Si, 1.90; S, 2.58),14 the tetrahedrane skeleton in 3 is not
symmetrical. Thus, the C(SC6H4NO2)ÀC(SiMe3) bond lengths
(C1ÀC2, C1ÀC3, C1ÀC4) in 3 range from 1.4792(19) to
1.4876(18) Å (av 1.482 Å), whereas the C(SiMe3)ÀC(SiMe3)
bond lengths (C2ÀC3, C2ÀC4 and C3ÀC4) range from
1.5041(19) to 1.5410(19) Å (av 1.518 Å). The CÀC bond
distances of the tetrahedrane core are similar to those previously
observed for tetrahedrane derivatives with electron-withdrawing
etrahedrane, cubane, and prismane are highly strained organic
T
molecules.1 Cubane and prismane were synthesized by Eaton
and Cole2 and Katz and Acton,3 respectively, but all attempts to
prepare the parent tetrahedrane have been unsuccessful because
of its high strain energy.1,4 In 1978, Maier and co-workers suc-
ceeded in synthesizing tetrakis(tert-butyl)tetrahedrane (tBu4THD)5
by photochemical isomerization of the corresponding cyclobu-
tadiene (tBu4CBD). In a similar manner, Maier and we succeeded in
synthesizing tetrakis(trimethylsilyl)tetrahedrane [(Me3Si)4THD]6,7a
by photochemical isomerization of the corresponding cyclobuta-
diene((Me3Si)4CBD).7,8 The four σ-donating trimethylsilyl groups
enhance the thermal stability of (Me3Si)4THD,6,9 which is stable
up to 300 °C. Furthermore, we demonstrated that (Me3Si)4THD
could be transformed into tris(trimethylsilyl)tetrahedranyllithium 1
by reaction with methyllithium.10 Since then, we have succeeded in
introducing a smaller group (e.g., H or Me) to the tetrahedrane
skeleton by reacting 1 with a variety of electrophiles.10 Recently, we
also reported the synthesis of perfluoroaryltetrahedranes, which ex-
hibit σÀπ conjugation between the strained tetrahedrane core and
the aromatic ring.11 Introduction of a heteroatom such as N, O, S, or
a halogen to the tetrahedrane core would be interesting because the
tetrahedrane σ framework has the potential to interact with the
nonbonding orbitals on the heteroatom; however, such heteroatom-
substituted tetrahedrane derivatives have remained elusive because
of the synthetic difficulty in preparing such molecules. Herein we
report the synthesis of the first stable sulfur-substituted tetrahedrane
derivatives 2À5, which were characterized by NMR spectroscopy
and X-ray diffraction. Evidence for the interaction of the σ orbital of
the tetrahedrane core and the lone-pair electrons on the sulfur
atom is also reported in this paper along with the unique thermal
reactions.
Received: June 9, 2011
Published: July 05, 2011
r
2011 American Chemical Society
11504
dx.doi.org/10.1021/ja205361a J. Am. Chem. Soc. 2011, 133, 11504–11507
|

Journal of the American Chemical Society
COMMUNICATION
Scheme 1. Syntheses of Sulfur-Substituted Tetrahedranes 2,
3, and 4 by the Reaction of Tetrahedranyllithium 1 with the
Corresponding Disulfides
Scheme 2. Synthesis of Sulfonyl-Substituted Tetrahedrane 5
by the Reaction of 2 with m-Chloroperbenzoic Acid
Figure 2. ORTEP drawing of 5 (30% thermal ellipsoids). Hydrogen
atoms have been omitted for clarity. Selected bond lengths (Å) and angles
(deg): C1ÀC2, 1.4792(19); C1ÀC3, 1.4932(19); C1ÀC4, 1.4739(19);
C2ÀC3, 1.5022(18); C3ÀC4, 1.5111(19); C4ÀC2, 1.5276(19); S1À
C1, 1.6973(14); S1ÀC14, 1.7650(15); C2ÀSi1, 1.8462(15); C3ÀSi2,
1.8361(14); C4ÀSi3, 1.8409(15). C2ÀC1ÀC3, 60.71(9); C3ÀC1À
C4, 61.23(9); C4ÀC1ÀC2, 62.30(9); C1ÀC2ÀC3, 60.11(9); C1À
C2ÀC4, 58.68(9); C1ÀC3ÀC4, 58.75(9); C1ÀC3ÀC2, 59.18(9);
C1ÀC4ÀC2, 59.02(9); C1ÀC4ÀC3, 60.02(9); C2ÀC3ÀC4, 60.92(9);
C3ÀC4ÀC2, 59.25(9); C4ÀC2ÀC3, 59.83(9);C1ÀS1ÀC14, 103.91 (7).
Figure 1. ORTEP drawing of 3 (30% thermal ellipsoids). Hydrogen
atoms have been omitted for clarity. Selected bond lengths (Å) and angles
(deg): C1ÀC2, 1.4792(19); C1ÀC3, 1.4876(18); C1ÀC4, 1.4794(18);
C2ÀC3, 1.5041(18); C3ÀC4, 1.5103(19); C4ÀC2, 1.5410(19); S1À
C1, 1.7167(13); S1ÀC14, 1.7591(14); C2ÀSi1, 1.8293(15); C3ÀSi2,
1.8301(14); C4ÀSi3, 1.8362(14). C2ÀC1ÀC4, 62.78(9); C3ÀC1À
C4, 61.20(9); C4ÀC1ÀC2, 62.78(9); C1ÀC2ÀC3, 59.81(9); C1À
C2ÀC4, 58.61(9); C1ÀC3ÀC4, 59.13(9); C1ÀC3ÀC2, 59.26(9);
C1ÀC4ÀC2, 58.60(9); C1ÀC4ÀC3, 59.67(9); C2ÀC3ÀC4, 61.49(9);
C3ÀC4ÀC2, 59.06(9); C4ÀC2ÀC3, 59.45(9); C1ÀS1ÀC14, 102.91(7).
Figure 3. UVÀvis spectra of 2, 3, 4, and 5 in hexane.
length in sulfone 5 [1.6973(14) Å] is shorter than those in sulfides 3
and 4 [1.7167(13) Å and 1.727(3) Å, respectively], as is typical
for sulfides and sulfones.13
The extended σÀπ conjugation in 2À4 is reflected in their elec-
tronic spectra. The absorption maxima in the UVÀvis spectra of 2,
groups, such as perfluorophenyltetrahedrane, in which the
C(C6F5)ÀC(SiMe3) bond lengths range from 1.475(2) to
1.504(2) Å (av 1.485 Å) and the C(SiMe3)ÀC(SiMe3) bond
lengths range from 1.504(2) to 1.524(2) Å (av 1.512 Å).11
We also carried out X-ray analyses of 4 (see the Supporting
Information) and 5 (Figure 2) and found that their tetrahedrane
core structures are quite similar to that of 3. The C1(tetrahe-
drane skeleton)ÀS1 bond length in 4 is 1.727(3) Å. In contrast,
the C1(tetrahedrane skeleton)ÀS1 bond length in 5 is 1.6973(14).
This result shows that the C(tetrahedrane skeleton)ÀS bond
3, and 4 in hexane were observed at 273 nm (ε = 7300 cmÀ1 MÀ1
)
for 2, 324 nm (ε = 11 800 cmÀ1 MÀ1) for 3, and 362 nm (ε =
7900 cmÀ1 MÀ1) for 4 (Figure 3). The bathochromic shifts of 3
and 4 in comparison with 2 are attributed to the influence of the
nitro group on the phenyl ring, which lowers the π* level of the
phenyl group. However, the absorption maximum in the UVÀvis
spectrum of 5 in hexane was not observed in these regions, in-
dicating a larger HOMOÀLUMO gap than those in sulfides 2, 3,
and 4. This is probably due to the lack of conjugation between the
tetrahedrane σ unit and the phenylsulfonyl group in 5. The HOMOs
11505
dx.doi.org/10.1021/ja205361a |J. Am. Chem. Soc. 2011, 133, 11504–11507

Journal of the American Chemical Society
COMMUNICATION
derivative 11 to afford two acetylene molecules. Thus, it is quite
reasonable to assume that 5 isomerized to the corresponding
cyclobutadiene 8 because 5 has no lone pairs on the sulfur atom,
which means that the carbene intermediate cannot be stabilized.
’ ASSOCIATED CONTENT
S
Supporting Information. Experimental procedures and
b
Figure 4. HOMOs of (left) 2 and (right) 5 calculated at the B3LYP/
6-31G(d) level.
spectral data for 2, 3, 4, and 5; thermal reactions of 2 and 5; com-
putational results on 2 and 5; ORTEP drawing of 4; and crys-
tallographic data including atomic positional and thermal para-
meters for 3, 4, and 5 (CIF). This material is available free of charge
via the Internet at http://pubs.acs.org.
Scheme 3. Thermal Reaction of 2 To Give Bis(trimethylsilyl)-
acetylene (6) and Phenyl Trimethylsilylethynyl Sulfide (7) and
Thermal Reaction of 5 To Form (Phenylsulfonyl)tris(trimethyl-
silyl)cyclobutadiene (8)
’ AUTHOR INFORMATION
Corresponding Author
sekiguch@chem.tsukuba.ac.jp
’ ACKNOWLEDGMENT
This work was supported by Grants-in-Aid for Scientific Research
(19105001, 23108701, 23550042, 23655027) from the Ministry of
Education, Culture, Sports, Science, and Technology of Japan and
by a JSPS Research Fellowship for Young Scientists (Y.I.).
’ REFERENCES
(1) For reviews of tetrahedrane, see: (a) Maier, G. Angew. Chem., Int.
Ed. Engl. 1988, 27, 309. (b) Maier, G. Pure Appl. Chem. 1991, 63, 275.
(c) Lee, V. Ya.; Sekiguchi, A. In Strained Hydrocarbons; Dodziuk, H., Ed.;
Wiley-VCH: Weinheim, Germany, 2009; Chapter 2.
Chart 1. exo,exo-Bicyclo[1.1.0]butane-2,4-diyl 9, Cycloprop-
3-enemethylene 10, and Sulfur-Substituted Cycloprop-3-en-
emethylene Derivative 11
(2) Eaton, P. E.; Cole, T. W., Jr. J. Am. Chem. Soc. 1964, 86, 3157.
(3) Katz, T. J.; Acton, N. J. Am. Chem. Soc. 1973, 95, 2738.
(4) (a) Peterson, R. F., Jr.; Baker, R. T. K.; Wolfgang, R. L. Tetra-
hedron Lett. 1969, 10, 4749. (b) Shevlin, P. B.; Wolf, A. P. J. Am. Chem.
Soc. 1970, 92, 406. (c) Rodewald, L. B.; Lee, H. J. Am. Chem. Soc. 1973,
95, 623. (d) Maier, G.; Hoppe, M.; Lanz, K.; Reisenauer, H. P. Tetra-
hedron Lett. 1984, 25, 5645.
(5) (a) Maier, G.; Pfriem, S.; Sch€afer, U.; Matusch, R. Angew. Chem.,
Int. Ed. Engl. 1978, 17, 520. (b) Maier, G.; Pfriem, S.; Sch€afer, U.; Malsch,
K.-D.; Matusch, R. Chem. Ber. 1981, 141, 3965.
(6) Maier, G.; Neudert, J.; Wolf, O.; Pappusch, D.; Sekiguchi, A.;
Tanaka, M.; Matsuo, T. J. Am. Chem. Soc. 2002, 124, 13819.
(7) (a) Maier, G.; Neudert, J.; Wolf, O. Angew. Chem., Int. Ed. 2001,
40, 1674. (b) Sekiguchi, A.; Tanaka, M.; Matsuo, T.; Watanabe, H.
Angew. Chem., Int. Ed. 2001, 40, 1675.
of 2 and 5 calculated at the B3LYP/6-31G(d) level are shown in
Figure 4. This also shows that 5 does not exhibit σÀπ conjuga-
tion, whereas 2 shows conjugation between the σ orbital of the
tetrahedrane core and the lone-pair electrons on the sulfur atom
in 2. These results are in agreement with the UVÀvis absorption
spectra of 2 and 5.
We also carried out thermal reactions of 2 and 5. Tetrahe-
dranyl sulfide 2 decomposed into two acetylene molecules, bis-
(trimethylsilyl)acetylene (6) and phenyl trimethylsilylethynyl
sulfide (7), when a solution of 2 in benzene at 120 °C in a sealed
tube was heated (Scheme 3).15 In contrast, tetrahedranyl sulfone
5 isomerized to the corresponding cyclobutadiene 8 when a solu-
tion of 5 in benzene was heated at 80 °C (Scheme 3).15 Schreiner
and co-workers16 performed theoretical calculations on the iso-
merization of the parent tetrahedrane (C4H4), and they showed
that exo,exo-bicyclo[1.1.0]butane-2,4-diyl (9) is the intermediate
for isomerization of tetrahedrane to give cyclobutadiene, whereas
cycloprop-3-enemethylene (10) is the intermediate for breaking
tetrahedrane to give two acetylene molecules (Chart 1). From
consideration of this calculation, the thermal reaction of 2, which
undergoes fragmentation into two acetylene molecules, can
probably be explained by the fact that lone pairs on the sulfur
atom stabilize the carbene center17 of cycloprop-3-enemethylene
(8) For recent reviews of silyl-substituted cyclobutadienes, see: (a)
Matsuo, T.; Sekiguchi, A. Bull. Chem. Soc. Jpn. 2004, 77, 211. (b) Sekiguchi,
A.; Matsuo, T. Synlett 2006, 2683.
(9) (a) Dill, J. D.; Greenberg, A.; Liebman, J. F. J. Am. Chem. Soc.
1979, 101, 6814. (b) Clark, T.; Spitznagel, G. W.; Klose, R.; Schleyer,
P. v. R. J. Am. Chem. Soc. 1984, 106, 4412. (c) Cremer, D.; Kraka, E.
J. Am. Chem. Soc. 1985, 107, 3811.
(10) (a) Sekiguchi, A.; Tanaka, M. J. Am. Chem. Soc. 2003, 125, 12684.
(b) Tanaka, M.; Sekiguchi, A. Angew. Chem., Int. Ed. 2005, 44, 5821.
(11) Nakamoto, M.; Inagaki, Y.; Nishina, M.; Sekiguchi, A. J. Am.
Chem. Soc. 2009, 131, 3172.
(12) For experimental procedures, spectral data for 2À5, computa-
tional results for 2 and 5, and crystal data for 3À5, see the Supporting
Information.
(13) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1.
(14) Emsley, J. The Elements, 3rd ed.; Oxford University Press:
Oxford, U.K., 1998.
11506
dx.doi.org/10.1021/ja205361a |J. Am. Chem. Soc. 2011, 133, 11504–11507

Journal of the American Chemical Society
COMMUNICATION
(15) For the experimental procedures of the thermal reactions of 2
and 5, see the Supporting Information.
(16) Nemirowski, A.; Reisenauer, H. P.; Schreiner, P. R. Chem.—
Eur. J. 2006, 12, 7411.
(17) (a) Arduengo, A. J., III; Goerlich, J. R.; Marshall, W. J. Liebigs
Ann. 1997, 365. (b) Kassaee, M. Z.; Shakib, F. A.; Momeni, M. R.;
Ghambarian, M.; Musavi, S. M. Tetrahedron 2009, 65, 10093. (c) Kassaee,
M. Z.; Shakib, F. A.; Momeni, M. R.; Ghambarian, M.; Musavi, S. M. J. Org.
Chem. 2010, 75, 2539.
11507
dx.doi.org/10.1021/ja205361a |J. Am. Chem. Soc. 2011, 133, 11504–11507