Synthesis, structural characterization, and photolysis of dibenzodehydro[16]annulenes containing E-E σ Bonds (E = Si and Ge)

Article abstract of DOI:10.1246/cl.2008.20

Dibenzodehydro[16]annulenes containing silicon-silicon and germanium-germanium σ bonds were newly prepared, and their structures were established by spectroscopic methods and X-ray diffraction analysis. On the photolysis, these sila- and germa-cycles evolve the corresponding divalent species, silylene and germylene, respectively, and in addition, the germanes led to the ring contraction to give a fourteen-membered germacycle. Copyright

Full text of DOI:10.1246/cl.2008.20

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Chemistry Letters Vol.37, No.1 (2008)
Synthesis, Structural Characterization, and Photolysis of Dibenzodehydro[16]annulenes
Containing E–E ꢀ Bonds (E = Si and Ge)
Kunio Mochida,ꢀ1 Junichi Ohto,1 Matsuri Masuda,1 Masato Nanjo,1 Hidekazu Arii,1 and Yasuhiro Nakadaira2
1Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588
2Department of Chemsitry, The University of Electro-Communication, Chofu, Tokyo 182-8585
(Received October 1, 2007; CL-071085; E-mail: kunio.mochida@gakushuin.ac.jp)
Dibenzodehydro[16]annulenes containing silicon–silicon
1,2-digermane (27.2 mmol) was added, and then, the mixture
was warmed to room temperature over a period of 10 h with stir-
ring. The reaction mixture was hydrolyzed, extracted with ether,
and then dried over sodium sulfate. Removal of the volatile com-
ponents in vacuo gave 2a as colorless solids in 3.0% isolated
yield. At the same time, considerable amounts of unidentified
cyclic and linear oligomers were also detected in the residue.
Li
and germanium–germanium ꢀ bonds were newly prepared, and
their structures were established by spectroscopic methods and
X-ray diffraction analysis. On the photolysis, these sila- and
germa-cycles evolve the corresponding divalent species, silylene
and germylene, respectively, and in addition, the germanes led to
the ring contraction to give a fourteen-membered germacycle.
BuLi
The electronic structure and properties of macrocyclic con-
jugated ꢁ-electron systems (annulenes) have been extensively
studied and have been the subject of current interest.1 New annu-
lenes containing the ꢀ bond of group 14-element catenates,
which is known to be as reactive as that of the corresponding
C=C ꢁ bond,2 are interesting research targets in view of annu-
lene, group 14-element chemistry, and new materials. While
the chemistry of ethynylene polysilanes has been studied by
Sakurai and co-workers,3–5 there have been few reports on ger-
manium analogs.5 We wish to report herein the syntheses and
their structures of 1,2,9,10-tetrametalladehydro[16]annulenes
(1,1,2,2,9,9,10,10-octaalkyl-1,2,9,10-tetrametalla-5,6,13,14-di-
benzocyclohexadeca-3,7,11,15-tetrayne (1: E = Si, R = Me; 2:
Et2O, -78 °C
r.t.
Li
R
E
R
R
R
E
E
ClR2EER2Cl
(1)
E
R
R
R R
1:(E = Si, R = Me), 8.8% yield; 2a:(E = Ge, R = Me), 3.0% yield;
2b:(E = Ge, R = iPr), 6.7% yield
The compound 2a6 was recrystallized from hexane and
characterized by spectroscopic methods coupled with X-ray
diffraction analysis.
Dibenzodehydro[1]annulenes, 17 and 2b,8 were prepared
similarly by the reaction of 1,2-(diethynyllithio)benzene with
1,1,2,2-tetramethyl-1,2-dichloro-1,2-disilane and 1,1,2,2-tetra-
isopropyl-1,2-dichloro-1,2-digermane in 9.0 and 7.0% isolated
yields, respectively. Figure 1 shows molecular structures of 1
and 2a determined by X-ray crystallography. Compounds, 1
and 2a, have chair-like geometries where the aromatic rings
adopt anti-configuration each other as shown.
i
E = Ge, R = Me: a, R = Pro: b). The photolysis of 1 and 2 led
to the ring contraction accompanied by the generation of diva-
lent species (silylenes and germylenes). The divalent species
formed were identified with appropriate trapping experiments
and laser flash photolysis.
Compounds 1 and 2 were obtained by the treatment of 1,2-
bis(2-lithioethynyl)benzene with the corresponding 1,2-dichlo-
rodisilane and 1,2-dichlorodigermanes, respectively (eq 1). Typ-
ically, to a solution of 1,2-diethynylbenzene (28.2 mmol) in
Et2O (40 mL) was added BuLi (27.6 mmol) in Et2O at ꢁ70 ꢂC
under argon. The reddish orange solution was stirred for addi-
tional 1 h. To the solution, 1,1,2,2-tetramethyl-1,2-dichloro-
The average bond distances of C(sp)–C(sp), Si–C(sp), and
˚
Si–Si of 1 are 1.23, 1.84, and 2.35 A, respectively. These bond
distances obtained are normal for cyclic organosilicon com-
pounds having ethynylene units.9 In sixteen-membered silacycle
1, the averages of C(sp)–Si–Si and C(sp)–C(sp)–Si bond angles
are 108.2 and 175.1ꢂ, respectively. On the other hand, in germa-
nium compound 2a, the average bond distances of C(sp)–C(sp),
˚
Ge–C(sp), and Ge–Ge are 1.21, 1.92, and 2.42 A, respectively.
The averages of C(sp)–Ge–Ge and C(sp)–C(sp)–Ge bond angles
are 106.3 and 171.3ꢂ, respectively.
These sixteen-membered ring compounds 1 and 2a show
UV maxima (ꢂmax) at 258 nm (": 8:0 ꢃ 104 Mꢁ1 cmꢁ1) and
254 nm (": 8:0 ꢃ 104 Mꢁ1 cmꢁ1), respectively.10 In comparison
with that of 3 (ꢂmax 241 nm, " ¼ 9:0 ꢃ 104 Mꢁ1 cmꢁ1), the large
bathochromic shift observed indicates appreciable electronic in-
teraction between these ethynylene units through the ꢀ (metal–
metal) bonds. Interestingly, the ꢀ (metal–metal) and the vertical
Figure 1. Molecular structures of 1 and 2a.
Copyright Ó 2008 The Chemical Society of Japan

Chemistry Letters Vol.37, No.1 (2008)
21
ꢁ (C=C) orbitals are well located for ꢀ–ꢁ conjugation albeit in
solids as shown in the figure. Theses results may be due to ꢀ
(metal–metal)–ꢁ (C–C) conjugation interaction in contrast with
that of 1,2-diethynylbenzene.
References and Notes
1
For recent reviews of annulene chemistry, see: a) R. Faust, Angew.
Chem., Int. Ed. 1998, 37, 2825. b) F. Diederich, L. Gobbi, Top
Curr. Chem. 1999, 201, 43. c) U. H. F. Bunz, Top. Curr. Chem.
1999, 201, 131. d) U. H. F. Bunz, Y. Rubin, Y. Tobe, Chem.
Soc. Rev. 1999, 28, 107. e) W. J. Youngs, C. A. Tessier, J. D.
Bradshaw, Chem. Rev. 1999, 99, 3153. f) F. Diederich, Chem.
Commun. 2001, 219. g) J. A. Marsden, G. J. Palmer, M. M. Haley,
Eur. J. Org. Chem. 2003, 2355.
Preliminary examination of thermal and photochemical
properties of 1 and 2a revealed that both were stable on pro-
longed heating at 150 ꢂC, but silacycle 1 was labile on UV irra-
diation, and in fact the irradiation of 1 with 110-W medium-pres-
sure Hg arc lamp at room temperature for 30 min under argon in
cyclohexane (ca. 0.05 M) gave unidentified complex mixtures
(81% conversion yield), whereas in similar photolysis of 1 in
the presence of 2,3-dimethylbuta-1,3-diene, only a small amount
of 1,1,3,4-tetramethyl-1-silacyclopenta-3-ene11 was formed and
detected with GC and GC-MS spectra (>10% yield) along with
complex reaction mixture. So, the laser flash photolysis12 of 1
was attempted to clarify the mechanism of silylene generation,
but any clear transient signal was not observed around 420–
430 nm being assigned to that due to the silylene.13
On the other hand, similar irradiation of 2a in cyclohexane
with the Hg arc lamp underwent the ring contraction to give
fourteen-membered germacycle 314 (20% yield) together with
a small amount of unreacted 2a (85% conversion yield). The for-
mation of 3 is indicative of the generation of dimethylgermylene
during the photolysis. Actually, dimethylgermylene generated
was trapped with 2,3-dimethylbuta-1.3-diene, a germylene-trap-
ping reagent, to give 1,1,3,4-tetramethyl-1-germacyclopenta-
3-ene15 in low yields (ca. 30% yield). At the same time, the
germylene reacted with the dissolved oxygen to form 1,3,5-
trioxacyclohexatrigermane (ca. 10% yield)16 Accord with those
results obtained, laser flash photolysis of 2a in cyclohexane gave
a weak transient absorption around 420–430 nm and is reasona-
bly assigned to that of the germylene from the comparison of its
spectral characteristics reported.17
2
a) H. Sakurai, Kagaku no Ryouiki 1975, 29-1, 36. b) M. Kira, in
Synthesis and Application of Organosilicon Compound, ed. by
H. Sakurai, CMC, Tokyo, 1989, Chap. 2.
3
4
5
6
H. Sakurai, Y. Nakadaira, A. Hosomi, Y. Eriyama, C. Kabuto,
J. Am. Chem. Soc. 1983, 105, 3359.
H. Sakurai, S. Hoshi, A. Kamiya, A. Hosomi, C. Kabuto, Chem.
Lett. 1986, 1781.
H. Sakurai, Advances in Inorganic Chemistry, 2000, Vol. 50,
p. 359.
2a: mp 230 ꢂC; 1H NMR (C6D6) ꢃ 0.71 (s, 24H), 6.72–6.75 (m,
4H), 7.40–7.43 (m, 4H); DI-MS (m=z, %) 660 (Mþ), 645
(Mþ ꢁ Me). Crystal data for 2a: C28H32Ge4, Mr ¼ 658:90,
monoclinic, space group P21=c (#14), a ¼ 10:4100ð10Þ, b ¼
ꢄ ¼ 121:111ð6Þꢂ,
V ¼
˚
12:1290ð13Þ,
c ¼ 13:3280ð12Þ A,
3
1440:8ð2Þ A , T ¼ 120 K, Z ¼ 2, Dcalcd ¼ 1:519 g/cm3, R1 ¼
˚
0:0516 (I > 2:0ꢀðIÞ), wR2 ¼ 0:1589 (all data). Ref. 18.
7
8
9
1: mp 205–206 ꢂC; 1H NMR (C6D6) ꢃ 0.41 (s, 24H), 6.66–6.69 (m,
4H), 7.32–7.39 (m, 4H); 29Si NMR (C6D6) ꢃ ꢁ37:5(s); DI-MS
(m=z, %) 240 (Mþ), 225 (Mþ ꢁ Me). Crystal data for 1:
C
28H32Si4, Mr ¼ 240:9, monoclinic, space group C2=c (#15),
˚
a ¼ 18:5630ð14Þ, b ¼ 8:4760ð3Þ, c ¼ 20:6090ð13Þ A, ꢄ ¼
114:898ð3Þꢂ, V ¼ 2941:2ð3Þ A , T ¼ 200 K, Z ¼ 4, Dcalcd
¼
3
˚
1:086 Mg/m3, R1 ¼ 0:0416 (I > 2:0ꢀðIÞ), wR2 ¼ 0:1546 (all
data). ref 18.
2b: mp 225–226 ꢂC; 1H NMR (C6D6) ꢃ 1.42 (d, J ¼ 6:9 Hz, 24H),
1.44 (d, J ¼ 6:9 Hz, 24H), 1.74 (sep, 8H), 6.74–6.77 (m, 4H),
7.39–7.42 (m, 4H); DI-MS (m=z, %) 883 (Mþ), 840 (Mþ ꢁ Pr).
i
Me
Me
Crystal data for 2b: C44H64Ge4, Mr ¼ 883:31, triclinic, space
Ge
ꢀ
group P1 (#2), a ¼ 8:8790ð6Þ, b ¼ 10.3440(9), c ¼
h
ν
(λ=254 nm)
ꢂ
ꢂ
ꢂ
˚
(2)
:GeMe2
13:0790ð12Þ A, ꢅ ¼ 106:735 , ꢄ ¼ 98:573ð5Þ , ꢆ ¼ 98:585ð6Þ ,
2a
+
V ¼ 1113:83ð16Þ A , T ¼ 200 K, Z ¼ 1, Dcalcd ¼ 1:317 Mg/m3,
3
C6D12 , r.t., 30 min
˚
Ge
Me
R1 ¼ 0:0353 (I > 2:0ꢀðIÞ), wR2 ¼ 0:0911 (all data). ref 18.
K. Negishi, M. Unno, H. Matsumoto, Chem. Lett. 2004, 33, 430.
Me
3
10 Measured in cyclohexane.
11 Y. Nakadaira, Kagaku no Ryoiki, 1975, 29, 39.
12 Nanosecond transient absorption spectra measurements were per-
formed on degassed solutions of 1 and 2a (ca. 10ꢁ4 M) in cyclo-
hexane at 293 K using the fourth-harmonic pulse of Nd:YAG laser
as the exciting light source (ꢂ ¼ 266 nm). M. Wakasa, J. Phys.
Chem. B 2007, 111, 9434.
GeMe2
Me2
:GeMe2
(3)
Ge
O2
O
O
Me2Ge
GeMe2
13 H. Shizuka, H. Tanaka, K. Tonokura, K. Murata, H. Harutsuka,
J. Ohshita, M. Ishikawa, Chem. Phys. Lett. 1988, 143, 225.
O
In summary, we have newly prepared dibenzode-
1
14 3: mp 225–230 ꢂC; H NMR (CDCl3) ꢃ 0.70 (s, 12H), 7.21–7.24
hydro[16]annulenes 1 and 2 containing E–E ꢀ bonds (E = Si
and Ge). The electronic perturbation to the annulene due to the
ꢀ–ꢁ conjugation is not large but significant. The UV photolysis
of the silicon and germanium compounds led ineffectively to the
ring contraction with the formation of silylenes and germylenes,
respectively.
(m, 4H), 7.42–7.45 (m, 4H); DI-MS (m=z, %) 454 (Mþ), 439
(Mþ ꢁ Me).
15 M. Schriewer, W. P. Neumann, J. Am. Chem. Soc. 1983, 105,
897.
16 K. Mochida, S. Tokura, Bull. Chem. Soc. Jpn. 1992, 65, 1642.
17 K. Mochida, I. Yoneda, M. Wakasa, J. Organomet. Chem. 1990,
399, 53.
We thank Prof. M. Wakasa and Mr. M. Gohdo of Saitama
University for measuring laser flash photolysis of 1 and 2a.
18 Supporting Information is available electronically on the CSJ-
Journal Web site, http://www.csj.jp//journals/chem-lett/.
Published on the web (Advance View) November 27, 2007; doi:10.1246/cl.2008.20