Synthesis and properties of the first stable neutral germaaromatic compound, 2-{2,4,6-Tris-[bis(trimethylsilyl)methyl]phenyl}-2-germanaphthalene

Article abstract of DOI:10.1021/om020879m

The first stable neutral germaaromatic compound, 2-germanaphthalene 1a, was synthesized by taking advantage of an extremely bulky and efficient steric protection group, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt). The molecular structure and aromaticity of 1a were discussed on the basis of its NMR, UV-vis, and Raman spectra, X-ray crystallographic analysis, and theoretical calculations. All the ¹H and ¹³C NMR chemical shifts of the 2-germanaphthalene ring of 1a were in good agreement with the calculated values for 2-germanaphthalene and 2-phenyl-2-germanaphthalene. The patterns of UV-vis and Raman spectra of 1a were similar to those of naphthalene, although the shift to longer wavelength (in the UV-vis spectrum) and smaller wavenumber (in the Raman spectrum) resulting from the replacement of carbon with germanium were observed. X-ray crystallographic analysis of 1a revealed that the 2-germanaphthalene ring was almost planar and perpendicular to the benzene ring of the Tbt group. These experimental results indicate the delocalization of π-electrons in the 2-germanaphthalene ring of 1a. Theoretical calculations (NICS(1), Λ, and ASE_isom) also indicated the ring current effects and aromatic stabilization of 2-germanaphthalene. 2-Germanaphthalene 1a reacted as a Ge-C double-bond compound (germene) with water, t-BuLi, mesitonitrile oxide, 2,3-dimethyl-1,3-butadiene, and some elemental chalcogens to give the corresponding adducts.

Full text of DOI:10.1021/om020879m

Organometallics 2003, 22, 481-489
481
Syn th esis a n d P r op er ties of th e F ir st Sta ble Neu tr a l
Ger m a a r om a tic Com p ou n d , 2-{2,4,6-Tr is-
[bis-(tr im eth ylsilyl)m eth yl]p h en yl}-2-ger m a n a p h th a len e
Norio Nakata, Nobuhiro Takeda, and Norihiro Tokitoh*
Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, J apan
Received October 22, 2002
The first stable neutral germaaromatic compound, 2-germanaphthalene 1a , was synthe-
sized by taking advantage of an extremely bulky and efficient steric protection group, 2,4,6-
tris[bis(trimethylsilyl)methyl]phenyl (Tbt). The molecular structure and aromaticity of 1a
were discussed on the basis of its NMR, UV-vis, and Raman spectra, X-ray crystallographic
analysis, and theoretical calculations. All the 1H and 13C NMR chemical shifts of the
2-germanaphthalene ring of 1a were in good agreement with the calculated values for
2-germanaphthalene and 2-phenyl-2-germanaphthalene. The patterns of UV-vis and Raman
spectra of 1a were similar to those of naphthalene, although the shift to longer wavelength
(in the UV-vis spectrum) and smaller wavenumber (in the Raman spectrum) resulting from
the replacement of carbon with germanium were observed. X-ray crystallographic analysis
of 1a revealed that the 2-germanaphthalene ring was almost planar and perpendicular to
the benzene ring of the Tbt group. These experimental results indicate the delocalization of
π-electrons in the 2-germanaphthalene ring of 1a . Theoretical calculations (NICS(1), Λ, and
ASEisom) also indicated the ring current effects and aromatic stabilization of 2-germanaph-
thalene. 2-Germanaphthalene 1a reacted as a Ge-C double-bond compound (germene) with
water, t-BuLi, mesitonitrile oxide, 2,3-dimethyl-1,3-butadiene, and some elemental chalcogens
to give the corresponding adducts.
In tr od u ction
detection of 1,4-dialkylgermabenzenes in the gas phase
by VTPES (variable-temperature photoelectron spec-
troscopy) experiments.6 However, no isolation of a
neutral germaaromatic compound has been reported
yet, probably due to its high reactivity.
In recent years, there has been considerable interest
in the aromatic properties of germaaromatic com-
pounds,1 namely, Ge-containing [4n + 2]-π-electron ring
systems, since they are heavier congeners of aromatic
hydrocarbons2 which play very important roles in
organic chemistry. Although ionic germaaromatic com-
pounds, cyclotrigermenium cations3 and germole dian-
ions,4 have been successfully synthesized as stable
compounds and their aromatic character has been
demonstrated, the properties of neutral germaaromatic
compounds have been little known. Ma¨rkl et al. reported
the synthesis of 1,4-di-tert-butylgermabenzene,5 the
generation of which was confirmed only by the forma-
tion of its [2 + 2] dimer and the trapping reaction with
diene. Furthermore, they described the spectroscopic
Meanwhile, we have already succeeded in the syn-
thesis and isolation of kinetically stabilized silaben-
zene,7 2-silanaphthalene,8 and 9-silaanthracene,9 the
first examples of stable neutral silaaromatic compounds,
by taking advantage of an efficient steric protection
group, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt).
With these stable systems in hand, we have revealed
their molecular structures and reactivities and dis-
cussed the aromaticity of these silaaromatic compounds.
The successful results in the silaaromatic systems
naturally prompted us to extend this chemistry to the
much heavier metallaaromatic systems of group 14
elements, i.e., germaaromatics. In preliminary contribu-
tions, we have recently reported the synthesis and
structure of the first stable 2-germanaphthalene, 1a
(Chart 1), bearing a Tbt group on the germanium
(1) For reviews of germaaromatic compounds, see: (a) Barrau, J .;
Escudie´, J .; Satge´, J . Chem. Rev. 1990, 90, 283. (b) Lee, V. Y.;
Sekiguchi, A.; Ichinohe, M.; Fukaya, N. J . Organomet. Chem. 2000,
611, 228.
(2) Minkin, V. J .; Glukhovtsev, M. N.; Simkin, Y. B. Aromaticity
and Antiaromaticity; Electronic and Structural Aspects; Wiley: New
York, 1994.
(3) (a) Sekiguchi, A.; Tsukamoto, M.; Ichinohe, M. Science 1997, 275,
60. (b) Ichinohe, M.; Fukaya, N.; Sekiguchi, A. Chem. Lett. 1998, 1045.
(c) Sekiguchi, A.; Fukaya, N.; Ichinohe, M. Phosphorus, Sulfur Silicon
Relat. Elem. 1999, 59, 150. (d) Sekiguchi, A.; Fukaya, N.; Ichinohe,
M.; Ishida, Y. Eur. J . Inorg. Chem. 2000, 1155. (e) Sekiguchi, A.; Ishida,
Y.; Fukaya, N.; Ichinohe, M.; Takagi, N.; Nagase, S. J . Am. Chem. Soc.
2002, 124, 1158.
(4) (a) West, R.; Sohn, H.; Powell, D. R.; Mu¨ller, T.; Apeloig, Y.
Angew. Chem., Int. Ed. Engl. 1996, 35, 1002. (b) Choi, S.-B.; Boudjouk,
P.; Qin, K. Organometallics 2000, 19, 1806.
(6) Ma¨rkl, G.; Rudnick, D.; Schulz, R.; Schweig, A. Angew. Chem.,
Int. Ed. Engl. 1982, 21, 221.
(7) (a) Wakita, K.; Tokitoh, N.; Okazaki, R.; Nagase, S. Angew.
Chem., Int. Ed. 2000, 39, 634. (b) Wakita, K.; Tokitoh, N.; Okazaki,
R.; Takagi, N.; Nagase, S. J . Am. Chem. Soc. 2000, 122, 5648.
(8) (a) Tokitoh, N.; Wakita, K.; Okazaki, R.; Nagase, S.; Schleyer,
P. v. R.; J iao, H. J . Am. Chem. Soc. 1997, 119, 6951. (b) Wakita, K.;
Tokitoh, N.; Okazaki, R.; Nagase, S.; Schleyer, P. v. R.; J iao, H. J .
Am. Chem. Soc. 1999, 121, 11336. (c) Wakita, K.; Tokitoh, N.; Okazaki,
R. Bull. Chem. Soc. J pn. 2000, 73, 2157.
(9) Takeda, N.; Shinohara, A.; Tokitoh, N. Organometallics 2002,
21, 256.
(5) Ma¨rkl, G.; Rudnick, D. Tetrahedron Lett. 1980, 21, 1405.
10.1021/om020879m CCC: $25.00 © 2003 American Chemical Society
Publication on Web 12/31/2002

482 Organometallics, Vol. 22, No. 3, 2003
Nakata et al.
NPA (natural population analysis)16 charge distributions were
calculated at MP2/6-31G(d) levels. The diamagnetic suscepti-
bility exaltations (Λ) were calculated at CSGT-HF/6-31G(d)
levels. In the geometry optimization of 2-phenyl-2-germanaph-
thalene (1c), the phenyl group was fixed perpendicularly to
the 2-germanaphthalene ring (transition state).
Ch a r t 1
P r ep a r a tion of 2-{2,4,6-Tr is[bis(tr im eth ylsilyl)m eth yl]-
p h en yl}-1,2,3,4-tetr a h yd r o-2-ger m a n a p h th a len e (2). A
solution of o-(2-bromoethyl)benzyl bromide (1.98 g, 7.13 mmol)
in THF (70 mL) and a solution of TbtGeCl3 (6.71 g, 9.19 mmol)
in THF (70 mL) were simultaneously added dropwise to dried
magnesium (1.14 g, 46.94 mmol) and 100 mL of THF over 0.5
h, and the reaction mixture was stirred for 2 h at room
temperature. To the mixture was added LiAlH4 (0.37 g, 9.75
mmol) at 0 °C, and the resulting gray suspension was stirred
for 1 h. After slow addition of an aqueous solution of NaOH
(ca. 4 mL, 15% w/w) at 0 °C, the resulting white suspension
was filtered through Celite and rinsed with hexane (ca. 100
mL). The solvents were evaporated, and the residue was
purified by FCC (hexane) to give almost pure 2 (1.72 g, 33%)
atom,10 and the reactions of 1a with elemental sulfur
and selenium.11 In addition, a kinetically stabilized
germabenzene was also synthesized and its detailed
properties, especially its aromatic character, were re-
vealed.12 Here, we wish to describe the details of the
synthesis, structure, reactivity, and aromaticity of
2-germanaphthalene 1a kinetically stabilized by the Tbt
group, the first stable neutral germaaromatic com-
pound.
1
as a white powder. 2: mp 187-193 °C dec; H NMR (CDCl3)
δ 0.02-0.04 (s, 54H), 1.23-1.29 (m, 2H), 1.31 (s, 1H), 1.89 (s,
2H), 2.39-2.59 (m, 2H), 2.80-2.89 (m, 1H), 3.01-3.08 (m, 1H),
4.46 (br s, 1H), 6.29 (br s, 1H), 6.41 (br s, 1H), 7.10-7.18 (m,
4H); 13C NMR (CDCl3) δ 0.65 (q), 0.71 (q), 0.95 (q), 11.05 (t),
21.28 (t), 29.01 (d), 29.43 (d), 30.17 (d), 30.55 (t), 121.71 (d),
125.45 (d), 126.65 (d), 126.85 (d), 128.43 (d), 129.01 (d), 129.41
(s), 138.89 (s), 140.57 (s), 143.69 (s), 149.99 (s), 150.28 (s). Anal.
Calcd for C36H70GeSi6: C, 58.11; H, 9.48. Found: C, 58.05; H,
9.63.
Exp er im en ta l Section
Gen er a l P r oced u r e. All experiments were performed
under an argon atmosphere unless otherwise noted. All
solvents were dried by standard methods and freshly distilled
P r ep a r a tion of 2-{2,4,6-Tr is[bis(tr im eth ylsilyl)m eth yl]-
p h en yl}-1,2-d ih yd r o-2-ger m a n a p h th a len e (3). A mixture
of 2 (0.76 g, 1.02 mmol), N-bromosuccinimide (NBS; 4.43 g,
7.13 mmol), and a catalytic amount of benzoyl peroxide was
dissolved in benzene (25 mL), and the solution was refluxed
for 2 h. After removal of the solvent in vacuo and addition of
THF (20 mL), LiAlH4 (0.15 g, 3.98 mmol) was added to the
mixture at 0 °C. The gray suspension was stirred for 1 h, and
an aqueous solution of NaOH (ca. 0.5 mL, 15% w/w) was slowly
added to the mixture at 0 °C. The resulting white suspension
was filtered through Celite and rinsed with hexane (ca. 15 mL).
After evaporation of the solvents, the residue was purified by
FCC (hexane) to give an inseparable mixture of 3a and 3b
(ca. 1:1 ratio, which was determined by NMR). This mixture
was dissolved in THF (15 mL) and cooled to -78 °C, and then
t-BuLi (0.49 M in hexane/pentane, 2.3 mL, 1.13 mmol) was
added to it. After the solution was stirred for 30 min, an excess
amount of a saturated aqueous solution of NH4Cl was added.
The solvents were evaporated, and inorganic salts were
removed by SCC (hexane). Reprecipitation from CHCl3/CH3-
CN gave pure 3a (0.47 g, 62% from 2) as a white powder. 3a :
1
prior to use. H NMR (400 or 300 MHz), 13C NMR (100 or 75
MHz), and 77Se NMR (57 MHz) spectra were measured in
CDCl3 or C6D6 with a J EOL J NM AL-400 or J EOL J NM AL-
300 spectrometer at room temperature. High-resolution mass
spectral data were obtained on a J EOL J MS-700 spectrometer.
Flash column chromatography (FCC), short column chroma-
tography (SCC), and preparative thin-layer chromatography
(PTLC) were performed with Merck silica gel 60, Wakogel
C-200, and Merck Kieselgel 60 PF254, respectively. Prepara-
tive gel permeation liquid chromatography (GPLC) was per-
formed on an LC-908 or LC-918 (J apan Analytical Industry
Co., Ltd.) equipped with J AIGEL 1H and 2H columns (eluent
CHCl3). Electronic spectra were recorded on a J ASCO Ubest-
50 UV-vis spectrometer. Raman spectra were measured at
room temperature on a Raman spectrometer consisting of a
Spex 1877 Triplemate and an EG & G PARC 1421 intensified
photodiode array detector. An NEC GLG 108 He-Ne laser
(632.8 nm) was used for Raman excitation. All melting points
were determined on a Yanaco micro melting point apparatus
and are uncorrected. Elemental analyses were carried out at
the Microanalytical Laboratory of the Institute for Chemical
Research, Kyoto University. o-(2-Bromoethyl)benzyl bromide13
and trichloro{2,4,6-tris[bis(trimethylsilyl)methyl]phenyl}ger-
mane (TbtGeCl3)14 were prepared according to the reported
procedures.
1
mp 123-126 °C; H NMR (CDCl3) δ -0.06 (s, 18H), 0.05 (s,
36H), 1.31 (s, 1H), 2.07 (br s, 1H), 2.12 (br s, 1H), 2.55 (dd, J
) 15.5, 3.6 Hz, 1H), 2.70 (dd, J ) 15.5, 3.6 Hz, 1H), 4.96 (dd,
J ) 3.6, 3.6 Hz, 1H), 6.28 (br s, 1H), 6.40 (br s, 1H), 6.53 (d, J
) 12.8 Hz, 1H), 7.08-7.13 (m, 4H), 7.23 (d, J ) 12.8 Hz, 1H);
13C NMR (CDCl3) δ 0.36 (q), 0.62 (q), 0.71 (q), 0.95 (q), 18.22
Th eor etical Calcu lation s. The geometries of 2-germanaph-
thalenes were optimized by using the Gaussian 98 program
at B3LYP/6-31G(d) levels of density functional theory.15 The
GIAO-B3LYP and NICS calculations were carried out with
6-311G(3d) for Ge and 6-311G(d) for C and H. Mulliken and
(15) Calculations were carried out using the Gaussian 98 program:
Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M.
A.; Cheeseman, J . R.; Zakrzewski, V. G.; Montgomery, J . A., J r.;
Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.; Daniels,
A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J .; Barone, V.;
Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford,
S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma,
K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J . B.;
Cioslowski, J .; Ortiz, J . V.; Stefanov, B. B.; Liu, G.; Liashenko, A.;
Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J .; Keith,
T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.;
Challacombe, M.; Gill, P. M. W.; J ohnson, B. G.; Chen, W.; Wong, M.
W.; Andres, J . L.; Head-Gordon, M.; Replogle, E. S.; Pople, J . A.
Gaussian 98; Gaussian, Inc.: Pittsburgh, PA, 1998.
(10) Nakata, N.; Takeda, N.; Tokitoh, N. Organometallics 2001, 20,
5507.
(11) For the details of sulfurization and selenation of 1a , see:
Nakata, N.; Takeda, N.; Tokitoh, N. Chem. Lett. 2002, 818.
(12) Nakata, N.; Takeda, N.; Tokitoh, N. J . Am. Chem. Soc. 2002,
124, 6914.
(13) Fang, X.; Larson, D. L.; Portoghese, P. S. J . Med. Chem. 1997,
40, 3064.
(14) Matsumoto, T.; Tokitoh, N.; Okazaki, R.; Goto, M. Organome-
tallics 1995, 14, 1008.
(16) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88,
899.

The First Stable Neutral Germaaromatic Compound
Organometallics, Vol. 22, No. 3, 2003 483
(t), 28.92 (d), 29.23 (d), 30.23 (d), 121.71 (d), 125.94 (d), 126.60
(d), 127.50 (d), 128.15 (d), 128.35 (s), 131.16 (d), 132.08 (d),
135.14 (s), 135.24 (s), 143.92 (s), 144.21 (d), 150.41 (s), 150.59
(s). Anal. Calcd for C36H68GeSi6: C, 58.27; H, 9.24. Found: C,
58.16; H, 9.37.
and the solution was stirred for 30 min. After quenching with
a saturated aqueous solution of NH4Cl, the organic layer was
separated and the aqueous layer was extracted with hexane
several times. The combined organic layer was dried over
MgSO4, and the removal of the solvents in vacuo followed by
purification with PTLC (hexane) afforded 2-tert-butyl-2-{2,4,6-
tris[bis(trimethylsilyl)methyl]phenyl}-1,2-dihydro-2-germanaph-
thalene (6; 29.7 mg, 52%) as colorless crystals. 6: mp 223-
P r ep a r a tion of 2-Br om o-2-{2,4,6-tr is[bis(tr im eth ylsi-
lyl)m eth yl]p h en yl}-1,2-d ih yd r o-2-ger m a n a p h th a len e (4).
A mixture of 3a (0.37 g, 0.50 mmol), NBS (90 mg, 0.51 mmol),
and a catalytic amount of benzoyl peroxide was dissolved in
benzene (20 mL), and the mixture was refluxed for 2 h. The
solvent was evaporated, and hexane (10 mL) was added.
Filtration of the mixture followed by removal of the solvent in
vacuo afforded almost pure 4 (0.41 g, 99%) as a white powder.
4: mp 174-177 °C; 1H NMR (CDCl3, 300 MHz) δ -0.05 (s,
9H), 0.01 (s, 9H), 0.03 (s, 18H), 0.06 (s, 9H), 0.10 (s, 9H), 1.32
(s, 1H), 2.14 (br s, 1H), 2.17 (br s, 1H), 2.95 (d, J ) 15.2 Hz,
1H), 3.13 (d, J ) 15.2 Hz, 1H), 6.28 (br s, 1H), 6.41 (br s, 1H),
6.65 (d, J ) 12.8 Hz, 1H), 7.10-7.15 (m, 4H), 7.19 (d, J ) 12.8
Hz, 1H); 13C NMR (CDCl3, 74.8 MHz) δ 0.39 (q), 0.46 (q), 0.68
(q), 0.71 (q), 0.89 (q), 1.12 (q), 28.92 (d), 29.29 (d), 29.41 (t),
30.58 (d), 122.15 (d), 126.56 (d), 127.03 (d), 127.70 (s), 127.84
(d), 131.01 (d), 131.47 (d), 131.75 (d), 134.04 (s), 134.22 (s),
143.43 (d), 146.11 (s), 150.65 (s), 151.12 (s). Anal. Calcd for
1
225 °C; H NMR (CDCl3) δ 0.02 (s, 18H), 0.03 (s, 18H), 0.09
(s, 9H), 0.11 (s, 9H), 1.08 (s, 9H), 1.27 (s, 1H), 2.02 (br s, 1H),
2.09 (br s, 1H), 2.68 (d, J ) 15.3 Hz, 1H), 2.77 (d, J ) 15.3 Hz,
1H), 6.23 (br s, 1H), 6.35 (br s, 1H), 6.55 (d, J ) 13.2 Hz, 1H),
6.98-7.07 (m, 4H), 7.12 (d, J ) 13.2 Hz, 1H); 13C NMR (CDCl3,
74.8 MHz) δ 0.79 (q), 0.91 (q), 1.42 (q), 1.57 (q), 1.67 (q), 1.97
(q), 21.68 (t), 25.97 (s), 28.79 (d), 28.95 (d), 29.96 (d), 30.41
(q), 122.39 (d), 125.58 (d), 126.97 (d), 127.55 (d), 129.85 (s),
130.45 (d), 131.98 (d), 132.90 (d), 135.43 (s), 136.13 (s), 142.33
(d), 143.40 (s), 151.38 (s), 151.72 (s). Anal. Calcd for C40H76
GeSi6: C, 60.19; H, 9.60. Found: C, 60.25; H, 9.72.
-
Rea ction of 1a w ith Mesiton itr ile Oxid e. To a solution
of 1a (46.7 mg, 0.063 mmol) in THF (1 mL) was added
mesitonitrile oxide (34.6 mg, 0.215 mmol) at room tempera-
ture, and the solution was stirred for 10 h. After the solvent
was evaporated, purification of the residue by GPLC (CHCl3)
afforded 4,10b-dihydro-1-mesityl-4-{2,4,6-tris[bis(trimethylsilyl)-
methyl]phenyl}[2]benzogermino[1,2-d][1,2,5]oxazagermole (7;
C
36H67BrGeSi6: C, 52.67; H, 8.23. Found: C, 52.64; H, 8.47.
Syn th esis of 2-Ger m a n a p h th a len e 1a . In a glovebox
filled with argon, 4 (54.6 mg, 0.067 mmol) was dissolved in
THF (1 mL, dried over K mirror and distilled by trap-to-trap
method), and lithium diisopropylamide (LDA) (2.0 M in
heptane/THF/ethylbenzene, 41 µL, 0.082 mmol) was added to
the solution. The solvents were removed under reduced
pressure, and hexane (3.5 mL) was added to the residue. The
mixture was left for 10 h, and the generated precipitates were
removed by decantation. Removal of the solvent in vacuo
afforded almost pure 2-{2,4,6-tris[bis(trimethylsilyl)methyl]-
phenyl}-2-germanaphthalene (1a ; 49.1 mg, 98%). 1a : mp 143-
145 °C dec; 1H NMR (C6D6, 400 MHz) δ 0.13 (s, 36H), 0.20 (s,
18H), 1.52 (s, 1H), 2.38 (br s, 1H), 2.48 (br s, 1H), 6.64 (br s,
1H), 6.75 (br s, 1H), 7.03 (dd, J ) 6.8, 8.0 Hz, 1H), 7.20 (dd, J
) 6.8, 8.0 Hz, 1H), 7.60 (d, J ) 8.0 Hz, 1H), 7.65 (d, J ) 8.0
Hz, 1H), 7.85 (dd, J ) 12.1, 1.7 Hz, 1H), 8.24 (d, J ) 1.7 Hz,
1H), 8.55 (d, J ) 12.1 Hz, 1H); 13C NMR (C6D6, 100 MHz) δ
0.93 (q), 1.19 (q), 31.40 (d), 36.37 (d), 36.82 (d), 120.75 (d),
121.84 (d), 126.26 (d), 126.41 (d), 127.69 (d), 128.12 (s), 128.40
(d), 130.45 (d), 131.75 (s), 133.71 (d), 145.15 (s), 145.89 (d),
146.66 (s), 150.01 (s), 150.07 (s); UV-vis (hexane; λmax, nm (ꢀ,
M-1 cm-1)) 269 (2 × 104), 335 (1 × 104), 386 (2 × 103); HRMS
(FAB) found m/z 740.2983 ([M]+), calcd for C36H66GeSi6
740.2962. Although we tried the elemental analysis several
times, the results agreed not with the composition of 1a but
that of hydrolyzed product 5 due to the high moisture sensitiv-
ity of 1a .
1
35.9 mg, 86%) as a white powder. 7: mp 245-249 °C dec; H
NMR (CDCl3) δ -0.09 (s, 18H), 0.01 (s, 18H), 0.05 (s, 18H),
1.35 (s, 3H), 1.58 (s, 1H), 1.75 (br s, 1H), 1.77 (br s, 1H), 2.20
(s, 3H), 2.24 (s, 3H), 3.93 (s, 1H), 6.37 (br s, 1H), 6.48-6.52
(m, 2H), 6.55 (s, 2H), 6.83 (s, 1H), 6.91 (dd, J ) 6.9, 6.9 Hz,
1H), 7.11-7.21 (m, 2H), 7.39 (d, J ) 13.5 Hz, 1H); 13C NMR
(CDCl3) δ 0.23 (q), 0.65 (q), 0.67 (q), 1.01 (q), 18.65 (q), 19.74
(q), 21.02 (q), 30.06 (d×2), 30.65 (d), 41.59 (d), 121.87 (d),
126.78 (d), 126.80 (d), 127.40 (d), 127.55 (s), 127.69 (d), 127.84
(d), 127.98 (d), 129.21 (s), 130.13 (s), 132.39 (d), 134.28 (s),
135.09 (d), 135.33 (s), 137.54 (s), 138.31 (s), 146.07 (s), 146.55
(d), 150.04 (s), 150.26 (s), 160.08 (s). Anal. Calcd for C46H77
-
GeNOSi6: C, 61.31; H, 8.61; N, 1.55. Found: C, 61.39; H, 8.74;
N, 1.35.
Rea ction of 1a w ith 2,3-Dim eth yl-1,3-bu ta d ien e. In a
glovebox filled with argon, 1a (35.1 mg, 0.052 mmol) was
dissolved in C6D6 (0.5 mL) and the solution was put into a 5
mm i.d. NMR tube. After 2,3-dimethyl-1,3-butadiene (distilled
from CaH2 under Ar prior to use, 0.15 mL, 1.326 mmol) was
added to the solution, the NMR tube was evacuated and sealed.
Heating of the mixture at 80 °C for 2 h resulted in the
disappearance of the NMR signals for 1a . Then, the tube was
opened and the solvent was removed in vacuo. Purification of
the residue by GPLC (CHCl3) and PTLC (hexane) afforded
4b,5,8,8a-tetrahydro-6,7-dimethyl-8a-{2,4,6-tris[bis(trimethyl-
silyl)methyl]phenyl}-8a-germaphenanthrene (8; 25.0 mg, 58%)
as a white powder. 8: mp 142-144 °C; 1H NMR (CDCl3) δ
-0.10 (s, 9H), -0.07 (s, 9H), -0.05 (s, 9H), 0.01 (s, 27H), 1.26
(s, 1H), 1.45 (s, 3H), 1.64 (s, 3H), 1.86-1.96 (m, 4H), 2.33-
2.47 (m, 2H), 2.64-2.68 (m, 1H), 6.20 (d, J ) 13.2 Hz, 1H),
6.23 (br s, 1H), 6.35 (br s, 1H), 7.00-7.22 (m, 5H); 13C NMR
(CDCl3) δ 0.48 (q), 0.67 (q), 0.77 (q), 0.90 (q), 1.22 (q), 20.84
(q), 22.08 (q), 24.13 (t), 28.47 (d), 28.85 (d), 30.08 (d), 30.73
(d), 41.97 (t), 121.88 (d), 125.92 (d), 127.06 (d), 127.46 (s),
127.65 (d), 127.85 (s), 129.58 (d), 130.96 (s), 131.18 (d), 132.60
(d), 135.70 (s), 140.95 (s), 143.00 (d), 143.43 (s), 150.11 (s),
150.41 (s). Anal. Calcd for C42H76GeSi6: C, 61.36; H, 9.32.
Found: C, 61.00; H, 9.46.
Rea ction of 1a w ith Wa ter . To a solution of 1a (25.1 mg,
0.035 mmol) in THF (0.5 mL) was added water (0.5 mL) at
room temperature, and the solution was stirred for 30 min.
After the solvent was removed under reduced pressure,
purification by PTLC (CHCl3) afforded 2-hydroxy-2-{2,4,6-tris-
[bis(trimethylsilyl)methyl]phenyl}-1,2-dihydro-2-germanaph-
thalene (5) as a white powder (26.5 mg, 99%). 5: mp 165-
1
167 °C; H NMR (CDCl3, 300 MHz) δ -0.06 (s, 18H), 0.02-
0.07 (s, 36H), 1.24 (s, 1H), 1.30 (s, 1H), 2.18 (br s, 1H), 2.24
(br s, 1H), 2.67 (d, J ) 15.2 Hz, 1H), 2.79 (d, J ) 15.2 Hz, 1H),
6.26 (br s, 1H), 6.39 (br s, 1H), 6.54 (d, J ) 12.8 Hz, 1H), 7.08-
7.13 (m, 4H), 7.24 (d, J ) 12.8 Hz, 1H); 13C NMR (CDCl3, 74.8
MHz) δ 0.41 (q), 0.68 (q), 0.99 (q), 26.01 (t), 28.52 (d), 28.82
(d), 30.39 (d), 122.02 (d), 126.11 (d), 126.89 (d), 127.51 (d),
128.67 (s), 131.25 (d), 131.43 (d), 132.27 (d), 134.46 (s), 135.22
(s), 144.74 (d), 145.12 (s), 150.34 (s), 150.67 (s). Anal. Calcd
for C36H68GeOSi6: C, 57.04; H, 9.04. Found: C, 57.05; H, 9.25.
Rea ction of 1a w ith t-Bu Li. To a solution of 1a (53.6 mg,
0.072 mmol) in hexane (0.5 mL) was added t-BuLi (0.49 N in
pentane/hexane, 0.15 mL, 0.074 mmol) at room temperature,
Rea ction of 1a w ith Elem en ta l Su lfu r . To a solution of
1a (53.1 mg, 0.072 mmol) in benzene (1.5 mL) was added
elemental sulfur (32.1 mg, 1.000 mmol as S atom) at room
temperature, and the solution was stirred for 48 h. After the
solvent was removed in vacuo, purification of the residue by
GPLC (CHCl3) and PTLC (hexane) afforded 4,10b-dihydro-4-
{2,4,6-tris[bis(trimethylsilyl)methyl]phenyl}[2]benzogermino-

484 Organometallics, Vol. 22, No. 3, 2003
Ta ble 1. Cr ysta llogr a p h ic Da ta for Com p ou n d s 1a , 6, 8, a n d 10
Nakata et al.
1a
6
8
10
formula
fw
cryst size (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C
36H66GeSi6
C
40H76GeSi6
C
42H76GeSi6
C
36H66GeSe3Si6
740.02
798.14
0.40 × 0.20 × 0.20
monoclinic
P21/n
12.276(7)
31.198(17)
12.720(7)
90
105.517(6)
90
4694(4)
4
822.16
976.90
0.40 × 0.40 × 0.35
triclinic
P1h
0.40 × 0.40 × 0.30
triclinic
P1h
0.40 × 0.20 × 0.15
triclinic
P1h
11.033(4)
12.112(5)
17.851(6)
72.423(15)
86.91(2)
75.064(9)
2196.6(14)
2
12.241(5)
13.024(6)
16.056(7)
106.988(6)
94.263(4)
96.959(5)
2414.0(19)
2
9.484(4)
12.021(4)
22.902(9)
75.562(16)
81.901(18)
68.746(13)
2352.8(15)
2
Z
Dcalcd (g cm-3
)
1.119
1.129
1.131
1.379
no. of indep rflns
no. of params
R1 (I > 2σ(I))
wR2 (all data)
goodness of fit
7709
479
0.053
0.138
8221
445
0.088
0.128
8319
462
0.038
0.081
6835
464
0.045
0.112
1.04
1.28
1.09
1.09
Sch em e 1
[2,1-d]-1,2,3,4-trithiagermole (9; 32.9 mg, 55%) as a pale yellow
powder. 9: mp 220-223 °C; 1H NMR (CDCl3) δ -0.10 (s, 9H),
-0.06 (s, 9H), 0.02 (s, 18H), 0.05 (s, 9H), 0.09 (s, 9H), 1.32 (s,
1H), 2.12 (br s, 2H), 4.44 (s, 1H), 6.32 (br s, 1H), 6.36 (d, J )
12.9 Hz, 1H), 6.44 (br s, 1H), 7.14 (d, J ) 12.9 Hz, 1H), 7.14-
7.32 (m, 4H); 13C NMR (CDCl3) δ 0.40 (q), 0.67 (q), 0.69 (q),
0.76 (q), 0.80 (q), 1.14 (q), 29.59 (d), 29.90 (d), 30.64 (d), 46.96
(d), 122.45 (d), 125.45 (s), 127.45 (s), 127.94 (d), 128.12 (d),
128.95 (d), 131.85 (d), 134.13 (d), 134.37 (d), 135.50 (s), 141.49
(d), 146.36 (s), 151.33 (s), 151.66 (s). Anal. Calcd for C36H66
GeS3Si6: C, 51.71; H, 7.96. Found: C, 51.63; H, 7.99.
-
Rea ction of 1a w ith Elem en ta l Selen iu m . To a solution
of 1a (48.9 mg, 0.066 mmol) in THF (2 mL) was added
elemental selenium (49.0 mg, 0.621 mmol as Se atom) at room
temperature, and the solution was stirred for 48 h. After the
solvent was removed in vacuo, purification of the residue by
GPLC (CHCl3) and PTLC (hexane) afforded 4,10b-dihydro-4-
{2,4,6-tris[bis(trimethylsilyl)methyl]phenyl}[2]benzogermino-
[2,1-d]-1,2,3,4-triselenagermole (10; 36.5 mg, 57%) as orange
by full-matrix least-squares procedures on F2 for all reflections
(SHELX-97).18 All hydrogen atoms were placed using AFIX
instructions, while all the other atoms were refined anisotro-
pically. The structures of the overlapped and disordered
2-germanaphthalene rings for 1a and trimethylsilyl groups in
para position of the Tbt group for 10 were restrained to be
identical with each other using the SAME and DELU instruc-
tions. The occupancies of each fragment for 1a and 10 were
refined with constraints that their sum is 1 (0.659(5):0.341(5)
for 1a and 0.775(7):0.225(7) for 10, respectively).
1
crystals. 10: mp 203-205 °C dec; H NMR (CDCl3) δ -0.11
(s, 9H), -0.07 (s, 9H), 0.01 (s, 18H), 0.09 (s, 9H), 0.12 (s, 9H),
1.30 (s, 1H), 2.22 (s, 2H), 5.06 (s, 1H), 6.30 (br s, 1H), 6.37 (d,
J ) 12.9 Hz, 1H), 6.42 (br s, 1H), 7.06 (d, J ) 12.9 Hz, 1H),
7.07-7.33 (m, 4H); 13C NMR (CDCl3) δ 0.54 (q), 0.72 (q), 0.95
(q), 1.31 (q), 29.49 (d), 29.75 (d), 30.64 (d), 44.12 (d), 122.58
(d), 124.38 (s), 127.61 (d), 127.65 (d), 127.84 (d), 131.56 (d),
131.71 (d), 133.65 (s), 133.70 (d), 137.16 (s), 139.97 (d), 146.04
(s), 151.34 (s), 151.61 (s); 77Se NMR (CDCl3) δ 296.0, 531.4,
716.9. Anal. Calcd for C36H66GeSe3Si6: C, 44.26; H, 6.81.
Found: C, 44.04; H, 6.82.
Resu lts a n d Discu ssion
Rea ction of 1a w ith cis-2,3-Dip h en ylth iir a n e. To a
solution of 1a (44.8 mg, 0.061 mmol) in THF (1 mL) was added
cis-2,3-diphenylthiirane (24.0 mg, 0.113 mmol) at room tem-
perature, and the solution was stirred for 5 h. After the solvent
was removed in vacuo, purification of the residue by GPLC
(CHCl3) and PTLC (hexane) afforded 9 (18.1 mg, 35%).
X-r a y Str u ctu r a l Deter m in a tion . Crystallographic data
for 1a , 6, 8, and 10 are collected in Table 1. Single crystals of
1a and 10 were grown by the slow evaporation of its saturated
solution in hexane at room temperature in a glovebox filled
with argon, while single crystals of 6 and 8 were grown by
the slow evaporation of their saturated solution in dichloro-
methane and acetonitrile, respectively, at room temperature.
The intensity data were collected on a Rigaku/MSC Mercury
CCD diffractometer with graphite-monochromated Mo KR
radiation (λ ) 0.710 71 Å) to 2θmax ) 50° at 93 K. The
structures were solved by direct methods (SIR97)17 and refined
Syn th esis of 2-Ger m a n a p h th a len e. Similarly to
the synthetic method of Tbt-substituted 2-silanaphtha-
lene, 2-bromo-1-hydro-2-germanaphthalene 4 was se-
lected as a precursor of 2-germanaphthalene 1a . At first,
1,2,3,4-tetrahydro-2-germanaphthalene 2 was synthe-
sized by the coupling reaction of o-(2-bromoethyl)benzyl
bromide with TbtGeCl3 using an excess amount of Mg
(Scheme 1). Bromination of 2 with an excess amount of
NBS followed by reduction with LiAlH4 gave an insepa-
rable mixture of the expected vinylgermane 3a and
overbrominated vinylgermane 3b. Treatment of the
mixture of vinylgermanes 3a and 3b with t-BuLi and
subsequent addition of saturated aqueous NH4Cl af-
forded the vinylgermane 3a as a pure compound.
(17) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R.
J . Appl. Crystallogr. 1999, 32, 115.
(18) Sheldrick, G. M. SHELX-97, Program for the Refinement of
Crystal Structures; University of Go¨ttingen: Go¨ttingen, Germany,
1997.

The First Stable Neutral Germaaromatic Compound
Organometallics, Vol. 22, No. 3, 2003 485
Sch em e 2
Ta ble 2. Obser ved a n d Ca lcu la ted 1H a n d 13C NMR
Ch em ica l Sh ifts (p p m ) for 2-Ger m a n a p h th a len esa
1a (R ) Tbt, obsdb) 1b (R ) H, calcdc) 1c (R ) Ph, calcdc,d
)
H1
H2
H3
H4
H5
H6
H7
C1
C2
C3
C4
C5
C6
C7
C8
C9
8.24
7.85
8.55
7.60
7.03
8.13
7.48
8.50
7.49
7.02
7.62
7.18
8.40
7.44
6.92
F igu r e 1. Calculated vibration modes with maximum
intensity: (a) 2-germanaphthalene; (b) naphthalene.
2-silanaphthalene (H2, 7.24 ppm; H3, 8.48 ppm) and
1,2-dihydro-2-silanaphthalene (H2, 6.27 ppm; H3, 7.30
ppm)8 and support the aromatic character of the 2-ger-
manaphthalene ring.
7.20
7.65
7.22
7.45
7.10
7.36
127.69
130.45
145.89
133.71
120.75
126.26
128.40
145.15
128.12
135.55
128.34
145.51
133.17
120.94
125.53
127.15
145.61
127.69
127.46
125.74
145.09
132.48
119.43
124.80
127.08
145.20
126.43
UV-Vis Sp ectr a . The UV-vis spectrum of 2-ger-
manaphthalene 1a in hexane showed three absorption
maxima (269 (ꢀ ) 2 × 104), 335 (ꢀ ) 1 × 104), and 386
nm (ꢀ ) 2 × 103 M-1 cm-1)) most likely assignable to
the E1, E2, and B bands, respectively. These values shift
to wavelength longer than those for naphthalene (221
(ꢀ ) 1.33 × 105), 286 (ꢀ ) 9.3 × 103), and 312 nm (ꢀ )
2.9 × 102 M-1 cm-1)),19 respectively. This propensity is
similar to that observed for 2-silanaphthalene (267 (ꢀ
) 2 × 104), 327 (ꢀ ) 7 × 103), and 387 nm (ꢀ ) 2 × 103
M-1 cm-1)).8 These results suggest that the 2-ger-
manaphthalene ring system has aromatic character as
well as in the cases of naphthalene and 2-silanaphtha-
lene.
a
b
See Chart 1. Measured in benzene-d6. c Calculated at the
GIAO-B3LYP/6-311G(d) (6-311G(3d) on Ge)//B3LYP/6-31G(d) level.
d
The phenyl group is fixed in such a way that it is perpendicular
to the 2-germanaphthalene.
Finally, careful bromination of 3a with NBS (1 equiv)
resulted in the quantitative formation of the corre-
sponding bromogermane 4, which is a suitable precursor
of 2-germanaphthalene 1a (Scheme 1).
Ra m a n Sp ectr a . The Raman spectrum of 1a showed
the most intense Raman signal at 1363 cm-1, which
corresponds to the most intense signals of 1382 and
1368 cm-1 for naphthalene and 2-silanaphthalene,8
respectively. This strongest vibrational frequency ob-
served for 1a is in good agreement with the theoretically
calculated value of the most intense line in 1b (1356
cm-1, computed at the B3LYP/6-31G(d) level and scaled
by 0.96).20 Furthermore, the calculated vibration modes
of 1b considerably resemble those of naphthalene and
2-silanaphthalene, suggesting the structural similarity
among naphthalene, 2-silanaphthalene, and 2-ger-
manaphthalene 1a (Figure 1).
Str u ctu r e. The molecular geometry of 1a was finally
determined by an X-ray crystallographic analysis (Fig-
ure 2). Crystal data for 1a are summarized in Table 1.
The structural analysis revealed the planarity of the
2-germanaphthalene ring and the trigonal-planar ge-
ometry around the germanium atom. In addition, the
benzene ring of the Tbt group is almost perpendicular
to the 2-germanaphthalene ring, and hence it is con-
sidered that there is very little conjugative interaction
between the two aromatic rings. The bond lengths of
the two Ge-C bonds in the 2-germanaphthalene ring
(1.803(5) and 1.859(5) Å) are between those of the
calculated Ge-C double (1.767 Å) and single bonds
(1.908-2.001 Å).21 In particular, the former Ge-C bond
length is close to the Ge-C double bond length of the
previously reported germene Mes2GedCR2 (1.803(4) Å;
2-Germanaphthalene 1a was synthesized by the de-
hydrobromination of bromogermane 4 with LDA in THF
at room temperature (Scheme 2).
Although 1a is highly moisture sensitive, it is ther-
mally very stable under an inert atmosphere either in
the solid state (at 100 °C for 30 min) or in solution
(benzene, at 100 °C for 1 h in a sealed tube), and neither
dimerization nor decomposition was observed.
1
NMR Sp ectr a . The H and 13C NMR signals of 1a
were assigned using 2D NMR techniques together with
the NOE and decoupling experiments. The assignments
1
of H and 13C NMR signals are listed in Table 2 along
with the calculated values for some model compounds:
i.e., 2-germanaphthalene (1b) and 2-phenyl-2-germanaph-
thalene (1c), where the observed values for 1a are in
good agreement with the calculated ones for 1b and 1c.
1
All the H NMR signals of the 2-germanaphthalene
ring protons (7.03-8.55 ppm) of 1a were observed in
the aromatic region, and the 13C NMR signals of the
2-germanaphthalene ring carbons (120.75-145.89 ppm)
were also located in the sp2 region. Thus, these results
clearly indicate the delocalized π-electronic system for
1a .
The aromatic character of Tbt-substituted 2-silanaph-
thalene 1a was discussed on the basis of the lower-field
shifts of its H2 and H3 protons as compared to those of
the 1,2-dihydro derivative 3a , as well as the case of
2-silanaphthalene.8 Approximately 1 ppm lower field
shifts were observed in 1a (H2, 7.85 ppm; H3, 8.55 ppm)
compared with 3a (H2, 6.53 ppm; H3, 7.23 ppm). These
shifts are similar to those between naphthalene (H2,
7.46 ppm; H3, 7.81 ppm) and 1,2-dihydronaphthalene
(H2, 5.82 ppm; H3, 6.33 ppm) and those between
(19) Silverstein, R. M.; Bassler, G. C.; Morril, T. C. In Spectrometric
Identification of Organic Compounds, 5th ed.; Wiley: New York, 1991.
(20) For the scaling factor of 0.96, see: Bauschlicher, C. W., J r.;
Partridge, H. J . Chem. Phys. 1995, 103, 1788.
(21) Grev, R. S.; Schaefer, H. F., III. Organometallics 1992, 11, 3489.

486 Organometallics, Vol. 22, No. 3, 2003
Nakata et al.
Sch em e 3
Ta ble 3. Obser ved a n d Ca lcu la ted Bon d Len gth s
(Å) of 2-Ger m a n a p h th a len es
1a (R ) Tbt,
1b (R ) H,
1c (R ) Ph,
obsda)
calcdb)
calcdb)
C1-Ge1
Ge1-C2
C2-C3
C3-C9
C9-C4
C4-C5
C5-C6
C6-C7
C7-C8
C8-C1
C8-C9
1.803(5)
1.859(5)
1.368(7)
1.429(8)
1.416(8)
1.337(12)
1.391(15)
1.368(9)
1.413(8)
1.450(8)
1.430(7)
1.810
1.851
1.374
1.433
1.423
1.376
1.414
1.374
1.429
1.421
1.446
1.812
1.853
1.374
1.433
1.422
1.376
1.414
1.375
1.429
1.421
1.446
a
The major fragment; two overlapped fragments were re-
b
strained to have the same structure. Calculated at the B3LYP/
6-31G(d) level.
titative) and 6 (52%), respectively. In the reaction of 1a
with mesitonitrile oxide and 2,3-dimethyl-1,3-butadiene
(DMB), [2 + 3] and [2 + 4] cycloaddition reactions
proceeded to afford the corresponding cycloadducts 7
and 8 in 67 and 58% yields, respectively. All of these
reactions are similar to those of the previously reported
germenes whose reactivity has already been explored.1a,24
Moreover, reactions of 1a with excess sulfur and sele-
nium afforded the novel Ge-containing cyclic trisulfide
9 (55%) and triselenide 10 (57%), respectively, as stable
crystalline compounds.11
It has been reported that EdS and EdSe double
bonds (E ) Ge, Sn) react with an epoxide and an
episulfide to afford the corresponding five-membered-
ring products.25 Therefore, the reaction of styrene oxide
and cis-2,3-diphenylthiirane with 1a was examined in
the hope of obtaining the corresponding five-membered
heterocycles by the reactions of the GedC double-bond
F igu r e 2. ORTEP drawing of 2-germanaphthalene 1a
(major fragment, 30% probability).
CR2 ) fluorenylidene),22 which is stabilized by the
conjugation of the Ge-C double bond with the fluore-
nylidene moiety. The C-C bond lengths (1.337(12)-
1.450(8) Å) of the 2-germanaphthalene ring were found
to vary within almost the same range as reported for
naphthalene (1.378-1.426 Å).23 Furthermore, theoreti-
cal calculations for the model compounds 1b and 1c
were also performed for comparison (Table 3). The
experimentally obtained bond lengths for 1a are fairly
in good agreement with those theoretically calculated
for 1b and 1c.
Rea ctivity of 2-Ger m a n a p h th a len e. Despite the
high thermal stability of 2-germanaphthalene 1a , its
Ge-C double bond is quite reactive toward various
reagents, as shown in Scheme 3.
(24) For a review of the reactivity of germene, see: (a) Escudie´, J .;
Couret, C.; Ranaivonjatovo, H.; Satge´, J . Coord. Chem. Rev. 1994, 130,
427. (b) Escudie´, J .; Couret, C.; Ranaivonjatovo, H. Coord. Chem. Rev.
1998, 178-180, 565.
Thus, 2-germanaphthalene 1a reacted with water and
t-BuLi/H+ to give the corresponding adducts 5 (quan-
(25) For reviews on the reactivity of heavy ketones, see: (a) Tokitoh,
N.; Matsuhashi, Y.; Shibata, K.; Matsumoto, T.; Suzuki, H.; Saito, M.;
Manmaru, K.; Okazaki, R. Main Group Met. Chem. 1994, 17, 55. (b)
Tokitoh, N.; Matsumoto, T.; Okazaki, R. Bull. Chem. Soc. J pn. 1999,
71, 1665. (c) Okazaki, R.; Tokitoh, N. Acc. Chem. Res. 2000, 33, 625.
(22) Lazraq, M.; Escudie´, J .; Couret, C.; Satge´, J .; Draeger, M.;
Dammel, R. A. Angew. Chem., Int. Ed. Engl. 1988, 27, 828.
(23) Brock, C. P.; Dunits, J . D.; Hirshfeld, F. L. Acta Crystallogr.
1991, B47, 789.

The First Stable Neutral Germaaromatic Compound
Organometallics, Vol. 22, No. 3, 2003 487
F igu r e 3. ORTEP drawing of t-Bu adduct 6 (50% prob-
ability).
F igu r e 5. ORTEP drawing of selenium adduct 10 (major
fragment, 30% probability).
Ta ble 4. Selected Bon d Len gth s of 6, 8, a n d 10 (Å)
Compound 6
Ge1-C1
Ge1-C2
C2-C3
C3-C9
C9-C4
C4-C5
C5-C6
1.965(5)
1.957(5)
1.331(8)
1.458(8)
1.410(8)
1.370(9)
1.382(8)
C6-C7
1.381(7)
1.382(7)
1.513(6)
2.009(5)
1.541(7)
1.528(7)
1.525(7)
C7-C8
C8-C1
Ge1-C10
C10-C11
C10-C12
C10-C13
Compound 8
Ge1-C1
Ge1-C2
C2-C3
C3-C9
C9-C4
C4-C5
C5-C6
C6-C7
C7-C8
1.982(2)
1.937(2)
1.335(3)
1.471(4)
1.407(3)
1.382(4)
1.381(4)
1.387(3)
1.391(3)
C8-C9
1.414(3)
1.516(3)
1.559(3)
1.508(3)
1.334(3)
1.513(3)
1.508(3)
1.513(3)
1.984(2)
C8-C1
C1-C13
C13-C12
C12-C11
C12-C15
C11-C14
C11-C10
C10-Ge1
Compound 10
F igu r e 4. ORTEP drawing of DMB adduct 8 (50% prob-
ability).
Ge1-Se1
Se1-Se2
Se2-Se3
Se3-C1
Ge1-C1
Ge1-C2
C2-C3
2.4022(10)
2.3503(10)
2.3250(11)
1.984(4)
C9-C4
C4-C5
C5-C6
C6-C7
C7-C8
C8-C9
C8-C1
1.400(7)
1.378(8)
1.388(8)
1.387(7)
1.394(7)
1.421(6)
1.506(6)
Sch em e 4
1.979(5)
1.932(4)
1.336(7)
C3-C9
1.457(7)
2-Germanaphthalene 1a reacted with various re-
agents and afforded the corresponding adducts to the
double bond between the germanium atom and the
carbon atom at the 1-position of the 2-germanaphtha-
lene ring. These results agreed with the highly double
bond character of the Ge-C(1) bond indicated in the
X-ray crystallographic analysis of 1a . In addition, these
reactivities can be supported by the charge distribution
and molecular orbital theory. Figure 6 gives a drawing
of the calculated Mulliken and NPA (natural population
analysis)16 charge distributions and the LUMO and
HOMO of parent 2-germanaphthalene (1b). The charge
distributions of 2-germanaphthalene at the MP2/6-31G-
(d) level show greatly positive charge on the germanium
atom, and the LUMO of 2-germanaphthalene has large
coefficients on the germanium atom. The HOMO con-
tains a bonding π-orbital on the 1,2-positions of the
2-germanaphthalene ring with a large coefficient, while
the LUMO has an antibonding π-orbital on the same
moiety of 1a . However, the reaction of 1a with styrene
oxide did not occur even at 80 °C, and the reaction with
cis-2,3-diphenylthiirane afforded trisulfide 9 in 35%
yield. Thus, cis-2,3-diphenylthiirane served as a sulfur
source for 1a in this reaction (Scheme 4).
The structures of 6, 8, and 10 were established by
X-ray crystallographic analysis (Figures 3-5). Crystal
data and selected bond lengths for 6, 8, and 10 are
summarized in Tables 1 and 4, respectively. The high
reactivity of 2-germanaphthalene 1a and the inspection
of the molecular structures of 6, 8, and 10 indicate that
the Tbt group affords enough reaction space around the
central Ge atom, despite its severe steric hindrance.

488 Organometallics, Vol. 22, No. 3, 2003
Nakata et al.
F igu r e 6. Charge distributions (top, Mulliken charges and NPA charges in parentheses) and molecular orbitals (bottom,
HOMO (left) and LUMO (right)) of the parent 2-germanaphthalene 1b.
Ch a r t 2. Ca lcu la ted Ar om a tic Sta biliza tion
En er gies (ASEisom in k ca l/m ol, B3LYP /
teraction at the 1,2-position with the molecular orbitals
6-311+G(d ,p )//Op t)
bond. These molecular orbitals indicate favorable in-
of 2,3-dimethyl-1,3-butadiene in the [2 + 4] cycloaddi-
tion. The high electrophilicity on the germanium atom
of 2-germanaphthalene can also be interpreted in terms
of the theoretical calculations.
Ar om a t icit y of 2-Ger m a n a p h t h a len e. As de-
scribed above, the spectral data and the structural
analysis of 2-germanaphthalene 1a strongly indicate its
aromaticity. On the other hand, we have already
revealed that 2-silanaphthalene has aromaticity as well
as naphthalene by theoretical calculations (nucleus-
independent chemical shifts (NICS)26 and aromatic
stabilization energy (ASE)).8b Similarly to the case of
2-silanaphthalene, the aromatic character of 2-ger-
manaphthalene was evaluated by computing the NICS-
(1) and ASEisom values. Moreover, the diamagnetic
susceptibility exaltation (Λ)27 of 2-germanaphthalene
was also calculated by the CSGT method.28 The NICS-
(1) value at 1 Å above the ring and Λ value of 2-ger-
manaphthalene 1b showed large negative values (NICS-
(1), -9.3 ppm for the C5Ge ring and -10.9 ppm for the
C6 ring, Λ, -27.9 ppm cgs), which were comparable to
that for naphthalene (NICS(1), -11.4 ppm; Λ, -30.4
thalene and 2-germanaphthalene based on the isomer-
ization reactions of methyl-substituted aromatic isomers
are summarized in Chart 2. The ASEisom value for
2-germanaphthalene was found to be almost the same
as that for naphthalene, suggesting that the aromatic
stabilization effect is very slightly reduced by the
replacement of the one ring carbon in naphthalene by
a germanium atom. These results indicate that the
2-germanaphthalene has ring current effects and is
stabilized by aromatization in the same manner as
naphthalene.
Meanwhile, 2-germanaphthalene is highly reactive,
in contrast to the ordinary aromatic hydrocarbons.
J udging from only this result, one can conclude 2-ger-
manaphthalene to be nonaromatic. However, molecules
with a Ge-C double bond are inherently much more
reactive than those with a C-C double bond. For
example, addition of water to a Ge-C double bond is
more exothermic than that to a C-C double bond by
about 40 kcal/mol.12 Therefore, the addition of water to
the Ge-C double bond of 2-germanaphthalene readily
proceeds, although 2-germanaphthalene has almost the
same aromatic stabilization effect as that of naphtha-
lene (ca. 45 kcal/mol). Thus, the high reactivity of
ppm cgs).29 In addition, the results of calculations for
8b,12,30
aromatic stabilization energies (ASEisom
)
of naph-
(26) Schleyer, P. v. R.; Maerker, C.; Dransfeld, A.; J iao, H.; Hommes,
N. J . R. v. E. J . Am. Chem. Soc. 1996, 118, 6317.
(27) Subramanian, G.; Schleyer, P. v. R.; J iao, H. Organometallics
1997, 16, 2362.
(28) (a) Keith, T. A.; Bader, R. F. W. Chem. Phys. Lett. 1993, 210,
223. (b) Keith, T. A.; Bader, R. F. W. Chem. Phys. Lett. 1992, 194, 1.
(29) The evaluation of Λ for 1b and naphthalene are described in
the Supporting Information.
(30) Havenith, R. W. A.; J iao, H.; J enneskens, L. W.; van Lenthe,
J . H.; Sarobe, M.; Schleyer, P. v. R.; Kataoka, M.; Necula, A.; Scott, L.
T. J . Am. Chem. Soc. 2002, 124, 2363.

The First Stable Neutral Germaaromatic Compound
Organometallics, Vol. 22, No. 3, 2003 489
2-germanaphthalene is not contradictory to its aroma-
ticity but is reasonably interpreted in terms of the
strong tendency to undergo an addition reaction across
the Ge-C double bond, which cannot be thoroughly
suppressed even by the aromatic stabilization of 2-ger-
manaphthalene.
ence of ring current effects and aromatic stabilization
in the 2-germanaphthalene ring. Thus, all the results
here obtained experimentally and theoretically indicate
the aromatic character of 2-germanaphthalene 1a .
Ack n ow led gm en t. This work was partially sup-
ported by a Grant-in-Aid for COE Research on Elements
Science (No. 12CE2005) and Grants-in-Aid for Scientific
Research (Nos. 14204064, 11304045, and 11166250)
from the Ministry of Education, Culture, Sports, Science
and Technology of J apan. We are grateful to Prof. Yukio
Furukawa, Waseda University, for the measurement of
FT-Raman spectra.
Con clu sion
We succeeded in the synthesis of 2-germanaphthalene
1a , the first example of a stable neutral aromatic
compound containing a germanium atom, by taking
advantage of a bulky Tbt group. A detailed analysis of
the spectral data (1H and 13C NMR, UV-vis, and
Raman spectra) and X-ray crystallographic analysis
revealed that 2-germanaphthalene 1a has a delocalized
10-π-electron ring system, as does naphthalene. 2-Ger-
manaphthalene 1a reacted with some reagents as a
Ge-C double-bond compound (germene) to give the
corresponding adducts to the double bond between the
germanium atom and the carbon atom at the 1-position
of the 2-germanaphthalene ring. Large negative NICS-
(1) values, diamagnetic susceptibility exaltation (Λ), and
theoretical energetic evaluations also indicate the exist-
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data with complete tables of bond lengths, bond angles, and
thermal and positional parameters for 1a , 6, 8, and 10, a table
of the observed Raman shifts for 1a and total electronic
energies and atomic coordinates for all molecules used in Chart
2, and a scheme and a table for evaluation of Λ for 1b and
naphthalene. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM020879M