The First Stable Germabenzene
A R T I C L E S
13C NMR (CDCl3) δ 0.73 (q), 1.00 (q), 10.25 (t), 13.71 (q), 27.33 (t),
27.47 (d), 27.67 (d), 29.22 (t), 30.43 (d), 41.32 (t), 51.76 (q), 122.32
(d), 126.25 (d), 126.83 (s), 127.13 (d), 130.68 (d), 145.41 (s), 145.88
(d), 148.58 (d), 151.20 (s), 151.47 (s). Anal. Calcd for C46H98GeO2-
Si6Sn: C, 52.97; H, 9.47. Found: C, 52.85; H, 9.57.
The mixture was left for 10 h, and the generated precipitate was
removed by decantation. Removal of the solvent afforded almost pure
1-{2,4,6-tris[bis(trimethylsilyl)methyl]phenyl}-1-germabenzene (1a)
(40.7 mg, 98%). 1a: mp 118-122 °C (dec); H NMR (C6D6) δ 0.13
(s, 36H), 0.16 (s, 18H), 1.50 (s, 1H), 2.32 (br s, 1H), 2.40 (br s, 1H),
1
6.62 (br s, 1H), 6.72 (br s, 1H), 6.72 (tt, J ) 1.0, 8.4 Hz, 1H), 7.85
Preparation of 5-Iodopenta-1,4-dienyl(dimethoxy){2,4,6-tris[bis-
(trimethylsilyl)methyl]phenyl}germane (4). To a solution of 3 (731
mg, 0.70 mmol) in CH2Cl2 (10 mL) was added I2 (213 mg, 0.84 mmol)
at room temperature, and the mixture was stirred for 1 h. After the
reaction was quenched with a saturated aqueous solution of Na2S2O3,
the organic layer was separated, and the aqueous layer was extracted
with CH2Cl2 several times. The combined organic layer was dried over
MgSO4, and removal of the solvents followed by purification with
GPLC (CHCl3) afforded 4 (601 mg, 99%) as colorless crystals. 4: mp
(dd, J ) 1.0, 12.0 Hz, 2H), 8.06 (ddd, J ) 1.0, 8.4, 12.0 Hz, 2H); 13
C
NMR (C6D6) δ 0.66 (q), 0.82 (q), 31.06 (d), 36.02 (d), 36.33 (d), 114.56
(d), 121.72 (d), 126.30 (s), 128.28 (d), 132.32 (d), 140.96 (d), 146.49
(s), 149.98 (s×2); UV-vis (hexane) λmax 225 nm (ꢀ 5 × 103), 298 nm
(ꢀ 1 × 103), 322 nm (ꢀ 8 × 102), 326 nm (ꢀ 7 × 102). HRMS (FAB):
found m/z 691.2950 ([M + H]+), calcd for C32H65GeSi6 691.2884.
Crystal Data of 1a. Formula C32H64GeSi6, MW ) 689.96, ortho-
rhombic, space group Pna21, a ) 18.4873(10), b ) 10.9402(7), and c
) 20.2958(10) Å, V ) 4104.9(4) Å3, Z ) 4, Dcalcd ) 1.116 g cm-3, µ
) 0.940 mm-1; R1 (I > 2σ(I)) ) 0.022, wR2 (all data) ) 0.056, GOF
) 1.09 for 7962 reflections and 390 parameters. Colorless and prismatic
single crystals of 1a were grown by the slow evaporation of its hexane
solution in a glovebox filled with argon. The intensity data were
collected on a Rigaku/MSC Mercury CCD diffractometer with graphite-
monochromated MoKR radiation (λ ) 0.71071 Å) to 2θmax ) 55° at
103 K. The structure was solved by direct methods (SIR97)23 and
refined by full-matrix least-squares procedures on F2 for all reflections
(SHELX-97).24 Hydrogen atoms of the Tbt group were placed using
AFIX instructions, while all the other atoms were refined anisotropi-
cally.
1
100-103 °C; H NMR (CDCl3) δ 0.04 (s, 18H), 0.05 (s, 36H), 1.33
(s, 1H), 2.55 (br s, 1H), 2.57 (br s, 1H), 3.33 (dd, J ) 7.2, 7.2 Hz,
2H), 3.58 (s, 6H), 5.72 (d, J ) 12.9 Hz, 1H), 6.21-6.34 (m, 3H), 6.39
(br s, 1H), 6.50 (dt, J ) 7.2, 12.9 Hz, 1H); 13C NMR (CDCl3) δ 0.75
(q), 1.01 (q), 27.49 (d), 27.74 (d), 30.45 (d), 38.88 (t), 51.79 (q), 77.21
(d), 83.60 (d), 122.29 (d), 126.60 (s), 127.15 (d), 138.52 (d), 145.51
(s), 145.69 (d), 151.14 (s), 151.40 (s). Anal. Calcd for C34H71GeIO2-
Si6: C, 46.41; H, 8.13. Found: C, 46.61; H, 8.28.
Cyclization of 4. To a solution of 4 (788 mg, 0.90 mmol) in Et2O
(15 mL) was added t-BuLi (2.36 M in pentane, 0.85 mL, 2.01 mmol)
at -40 °C, and the solution was stirred for 2 h. After the solution was
warmed to room temperature and stirred for 12 h, the reaction was
stopped by the addition of 1 M HCl (10 mL). 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
solvent was removed to give the crude product as white solids,
containing 1-methoxy-1-{2,4,6-tris[bis(trimethylsilyl)methyl]phenyl}-
1-germacyclohexa-2,4-diene (5a) and the unreacted 4 in a molar ratio
of 5:1 (observed by 1H NMR). Purification using WCC (hexane/CHCl3
) 3:1) afforded 1-hydroxy-1-{2,4,6-tris[bis(trimethylsilyl)methyl]-
phenyl}-1-germacyclohexa-2,4-diene (6a) (311 mg, 49%) as a white
powder, which was formed by hydrolysis of methoxygermane 5a on
the SiO2, together with 4 (79 mg, 10%). 6a: mp 161-163 °C; 1H NMR
(CDCl3) δ 0.03 (s, 18H), 0.04 (s, 36H), 0.67 (s, 1H), 1.31 (s, 1H),
2.04-2.07 (m, 2H), 2.28 (br s, 2H), 5.90-5.97 (m, 1H), 6.08-6.15
(m, 1H), 6.26 (br s, 1H), 6.38 (br s, 1H), 6.47 (d, J ) 12.9 Hz, 1H),
6.70 (dd, J ) 6.3, 12.9 Hz, 1H); 13C NMR (CDCl3) δ 0.50 (q), 0.69
(q), 0.85 (q), 1.03 (q), 21.20 (t), 28.17 (d), 28.47 (d), 30.31 (d), 121.99
(d), 125.33 (d), 126.91 (d), 129.27 (s), 129.83 (d), 131.27 (d), 138.52
(d), 144.85 (s), 150.15 (s), 150.49 (s). Anal. Calcd for C32H66GeOSi6:
C, 54.29; H, 9.40. Found: C, 53.91; H, 9.46.
Reaction of 1a with Water. To a solution of 1a (24.5 mg, 0.036
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,
purification of the residue by PTLC (hexane/CHCl3 ) 3:1) afforded
6a (16.6 mg, 65%) and 1-hydroxy-1-{2,4,6-tris[bis(trimethylsilyl)-
methyl]phenyl}-1-germacyclohexa-2,5-diene (6b) (7.7 mg, 30%) as a
white powder. 6b: mp 166-170 °C; 1H NMR (CDCl3) δ 0.02 (s, 18H),
0.03 (s, 36H), 0.62 (s, 1H), 1.31 (s, 1H), 2.39 (br s, 2H), 2.89-3.17
(m, 2H), 6.26 (br s, 1H), 6.36 (ddd, J ) 2.0, 2.0, 14.1 Hz, 2H), 6.37
(br s, 1H), 6.70 (ddd, J ) 3.3, 3.3, 14.1 Hz, 2H); 13C NMR (CDCl3)
δ 0.54 (q), 0.70 (q), 0.86 (q), 27.97 (d), 28.27 (d), 30.29 (d), 32.63 (t),
121.99 (d), 126.91 (d), 128.35 (s), 129.85 (d), 143.15 (d), 144.75 (s),
150.44 (s), 150.75 (s). Anal. Calcd for C32H66GeOSi6: C, 54.29; H,
9.40. Found: C, 54.22; H, 9.49.
Reaction of 1a with Methanol. To a solution of 1a (40.1 mg, 0.058
mmol) in THF (0.5 mL) was added MeOH (0.5 mL) at room
temperature, and the solution was stirred for 30 min. Removal of the
solvents afforded a 2:1 mixture of methoxygermanes 5a and 5b (as
1
judged by H NMR). Separation and purification of the mixture by
Chlorination of 6a. A mixture of 6a (209 mg, 0.30 mmol) and
excess PCl5 (601 mg, 2.88 mmol) in Et2O (20 mL) was refluxed for
3.5 h. After removal of the solvent, hexane was added to the residue,
and the mixture was filtered with Celite. Evaporation of the filtrate
under reduced pressure afforded almost pure 1-chloro-1-{2,4,6-tris-
[bis(trimethylsilyl)methyl]phenyl}-1-germacyclohexa-2,4-diene (7) (208
mg, 97%) as a white powder. 7: mp 174-176 °C; 1H NMR (C6D6) δ
0.14 (s, 18H), 0.20 (s, 18H), 0.23 (s, 18H), 1.45 (s, 1H), 2.37-2.59
(m, 2H), 2.44 (br s, 2H), 5.68-5.74 (m, 1H), 5.86-5.92 (m, 1H), 6.39
(dd, J ) 6.6, 12.9 Hz, 1H), 6.51 (br s, 1H), 6.63 (br s, 1H), 6.71 (d, J
) 12.9 Hz, 1H); 13C NMR (C6D6) δ 0.88 (q), 0.90 (q), 1.29 (q), 1.35
(q), 24.32 (t), 29.18 (d), 29.50 (d), 30.92 (d), 122.71 (d), 125.53 (d),
127.59 (d), 129.07 (d), 129.25 (s), 131.78 (d), 137.66 (d), 146.18 (s),
151.05 (s), 151.52 (s). Anal. Calcd for C32H65ClGeSi6: C, 52.91; H,
9.02. Found: C, 52.94; H, 9.07.
PTLC (hexane/CHCl3 ) 3:1) gave hydroxygermanes 6a (24.9 mg, 61%)
and 6b (12.0 mg, 29%). 5a: 1H NMR (CDCl3) δ -0.01 (s, 18H), 0.03
(s, 36H), 1.30 (s, 1H), 1.88-2.13 (m, 2H), 2.37 (br s, 2H), 3.40 (s,
3H), 5.91-5.97 (m, 1H), 6.11-6.18 (m, 1H), 6.25 (br s, 1H), 6.38 (br
s, 1H), 6.40 (d, J ) 13.5 Hz, 1H), 6.82 (dd, J ) 6.0, 13.5 Hz, 1H). 5b:
1H NMR (CDCl3) δ 0.01 (s, 18H), 0.03 (s, 36H), 1.29 (s, 1H), 2.47 (br
s, 2H), 2.99-3.16 (m, 2H), 3.33 (s, 3H), 6.22 (ddd, J ) 1.8, 1.8, 13.8
Hz, 2H), 6.25 (br s, 1H), 6.36 (br s, 1H), 6.78 (ddd, J ) 4.0, 4.0, 13.8
Hz, 2H).
Reaction of 1a with Mesitonitrile Oxide. To a solution of 1a (32.1
mg, 0.049 mmol) in THF (1 mL) was added mesitonitrile oxide (29.1
mg, 0.181 mmol) at room temperature, and the solution was stirred for
12 h. After the solvent was removed, purification of the residue by
GPLC (CHCl3) afforded 3-mesityl-7a-{2,4,6-tris[bis(trimethylsilyl)-
methyl]phenyl}-3a,7a-dihydro-1-oxa-2-aza-7a-germaindene (8) (35.9
1
Synthesis of Germabenzene 1a. In a glovebox filled with argon, 7
(43.8 mg, 0.060 mmol) was dissolved in THF (1 mL, dried over K
mirror and distilled by trap-to-trap method), and LDA (2.0 M in
heptane/THF/ethylbenzene, 33 µL, 0.066 mmol) was added to the
solution. After the solution was stirred for 1 h, the solvents were
removed under reduced pressure, and hexane was added to the residue.
mg, 86%) as a white powder. 8: mp 200-203 °C; H NMR (CDCl3)
(23) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovazzo, C.;
Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. SIR97:
a
new tool for crystal structure determination and refined, submitted, 1998.
(24) Sheldrick, G. M. SHELX-97, Program for the Refinement of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
9
J. AM. CHEM. SOC. VOL. 124, NO. 24, 2002 6919