1108 Bull. Chem. Soc. Jpn., 78, No. 6 (2005)
Tetrabromotetramethylcyclotetrasiloxane
Synthesis of cis-trans-cis-2,4,6,8-Tetraphenyl-2,4,6,8-tetra-
methylcyclotetrasiloxanes (1).
indicating the various structures of their Si–O skeleton. Fur-
thermore, a single peak was observed at ꢂ64:5 ppm in solid-
state 29Si NMR. This chemical shift is in good accordance with
those of laddersiloxanes (e.g., ꢂ65 to ꢂ67 ppm for tricyclic
laddersiloxanes, and ꢂ64 to ꢂ66 ppm for pentacyclic ladder-
siloxanes both with isopropyl groups6). These results indicate
that the structure of 4 is highly regulated, and thus the hydrol-
ysis–dehydration of tetrabromide proceeded in a stereospecific
manner.
Dichloro(methyl)phenylsilane
(200.3 g, 1.05 mol) was treated with water in THF. After refluxing
for 10 h, water and ether were added to the mixture, and the organ-
ic layer was separated. The aqueous phase was extracted three
times with ether. The combined organic phases were dried over
anhydrous MgSO4 and concentrated. cis-trans-cis Isomer 1
(16.4 g, 12%) was separated from the mixture by fractional crys-
tallization from methanol at ꢂ40 ꢁC for 7 d. Further recrystalliza-
tion was carried out in ether and methanol to give single crystals
ꢁ
1
of 1 (16.1 g, 11%). 1: colorless crystals, mp 95–98 C. H NMR
(CDCl3) ꢄ 0.29 (s, 3H), 7.35 (t, 1H, J ¼ 6:8 Hz), 7.40 (q, 2H, J ¼
6:8 Hz), 7.62 (d, 2H, J ¼ 6:8 Hz); 13C NMR (CDCl3) ꢄ ꢂ0:21,
127.73, 129.83, 133.34, 136.84; 29Si NMR (CDCl3) ꢄ ꢂ30:80
ppm. MS (70 eV) m=z (%) 544 (Mþ, 10), 529 (Mþ ꢂ Me, 100).
Dephenylchlorination of cis-trans-cis-Tetraphenyl-2,4,6,8-
tetramethylcyclotetrasiloxane (1). To a suspension of 1 (2.1
g, 4.0 mmol) and anhydrous aluminum chloride (1.4 g, 11 mmol)
in benzene (100 mL) was passed hydrogen chloride for 30 min
at room temperature. Then, argon gas was bubbled for 1 h. After
filtration of aluminum chloride and the removal of benzene, the
product was distilled at 70 ꢁC/0.5 mmHg with a bulb-to-bulb
distillation apparatus to give pure tetrachlorotetramethylcyclo-
tetrasiloxane (0.22 g, 15%). The result of the MS and NMR spec-
tra indicated that a mixture of isomer was obtained. Decomposi-
tion was observed during further purification, and no other identi-
fication was performed. 2,4,6,8-Tetrachloro-2,4,6,8-tetramethyl-
cyclotetrasiloxanes: 1H NMR (300 MHz, CDCl3) ꢄ 0.42 (s),
0.43 (s), 0.46 (s), 0.47 (s), 0.50 (s), 0.51 (s). MS (70 eV) m=z
(%) 363 (Mþ ꢂ Me, 100), 343 (Mþ ꢂ Cl, 20).
Summary
We performed the synthesis of functionalized tetramethylcy-
clotetrasiloxane. The first isomeric pure 2,4,6,8-tetrabromo-
2,4,6,8-tetramethylcyclotetrasiloxane was obtained in a facile
two-step reaction from chlorosilane. The reaction starting from
this potential precursor will be presented in due course.
Experimental
All of the reactions were carried out under an argon or dry ni-
trogen atmosphere, except when otherwise noted. The solvents
used in the reactions were purified and dried according to litera-
ture procedures. NMR spectra were obtained on a JEOL ꢁ-500
(1H, 500.00 MHz, 13C, 125.65 MHz, 29Si, 99.25 MHz) spectrom-
eter. Solid state MAS NMR was measured by a Bruker DMX-300
wide-bore spectrometer operating at 59.6 MHz. The spinning rate
was 3 kHz. EI mass spectrometry was performed with a JEOL
JMS-DX302. Infrared spectra were recorded on a SHIMADZU
FTIR-8700. Analytical HPLC was performed on a Jasco UV-
970 and 880-PU instrument with a Chemcosorb 4.6 mm ꢃ 500
mm 5-ODS-UH column.
Synthesis of cis-trans-cis-2,4,6,8-Tetrabromo-2,4,6,8-tetra-
methylcyclotetrasiloxanes (2). In the sublimation apparatus, 1
Preparation of Methylphenylcyclooligosiloxanes (General
Procedure). An aqueous KOH solution (2.0 equiv) was added
dropwise to MePhSiCl2 in THF for 30 min. After the mixture
ꢁ
(504 mg, 0.925 mmol) was placed and cooled to ꢂ30 C under
Ar. Bromine (778 mg, 4.86 mmol) was then added with vigorous
stirring. After 30 min, all volatiles were slowly pumped off (0.4
mmHg), resulting a light-yellow solid. Further purification by sub-
ꢁ
was heated to 80 C for 15 h, THF was removed. The resulting
mixture was extracted with ether three times. The combined or-
ganic phases were washed with water twice. The organic phase
was dried with anhydrous MgSO4 and concentrated. The residue
was separated by bulb-to-bulb distillation, and (MePhSiO)3,
(MePhSiO)4, and (MePhSiO)5 were obtained. The ratio of isomers
were determined by NMR spectra previously shown in the litera-
ture.13,16 Trimethyltriphenylcyclotrisiloxane (isomeric mixture):
1H NMR (CDCl3) ꢄ 0.36 (s), 0.42 (s), 0.50 (s), 7.15–7.60 (m);
13C NMR (CDCl3) ꢄ ꢂ0:43, ꢂ0:27, ꢂ0:07, 127.7, 127.8, 127.9,
130.0, 130.1, 130.2, 133.1, 133.2, 133.3, 135.8, 136.2, 136.6.
MS (70 eV) m=z (%) 408 (Mþ, 20), 393 (Mþ ꢂ Me, 70). Tetra-
ꢁ
limation was carried out at 0.2 mmHg with a 75 C oil bath. The
product was collected in a glove box, and pure cis-trans-cis-tetra-
bromotetramethylcyclotetrasiloxane (2) (437 mg, 85%) was ob-
tained. cis-trans-cis-2,4,6,8-Tetrabromo-2,4,6,8-tetramethylcyclo-
tetrasiloxane (2): colorless solid, 1H NMR (C6D6) ꢄ 0.39 ppm;
13C NMR (C6D6) ꢄ 3.61 ppm; 29Si NMR (C6D6) ꢄ ꢂ44:01 ppm.
MS (70 eV) m=z (%) 556 (Mþ, 5), 541 (Mþ ꢂ Me, 100).
Synthesis of anti-1,3,7,9-Tetramethyl-5,5,11,11-tetraphenyl-
tricyclo[7.3.1.13,7]hexasiloxane (3). Tetrabromide 2 was gener-
ated from 1 (1.2 g, 2.2 mmol) with bromine (0.5 mL, 9.8 mmol) in
a similar manner. Then, 2 was dissolved in pyridine (20 mL), and
diphenylsilanediol (0.90 g, 4.2 mmol) in Et2O (30 mL) was added.
After 12 h, the solution was subjected to a work-up. The crystals
of anti-tricyclic laddersiloxane (3, 0.94 g, 65%) were obtained
when hexane and Et2O were added to the mixture. anti-1,3,7,9-
Tetramethyl-5,5,11,11-tetraphenyltricyclo[7.3.1.13,7]hexasiloxane
1
methyltetraphenylcyclotetrasiloxane (isomeric mixture): H NMR
(CDCl3) ꢄ 0.14 (s), 0.26 (s), 0.29 (s), 0.39 (s), 0.41 (s), 0.49 (s),
7.1–7.7 (m) ppm; 13C NMR (CDCl3) ꢄ ꢂ0:39, ꢂ0:34, ꢂ0:20,
ꢂ0:17, ꢂ0:08, ꢂ0:06, 127.52, 127.63, 127.68, 127.77, 127.80,
127.86, 127.88, 129.66, 129.78, 129.79, 129.88, 129.94, 133.12,
133.28, 133.35, 133.40, 133.44, 136.29, 136.46, 136.68, 136.84,
137.08, 137.23; 29Si NMR (CDCl3) ꢄ ꢂ21:04, ꢂ20:99, ꢂ20:96.
MS (70 eV) m=z (%) 544 (Mþ, 15), 529 (Mþ ꢂ Me, 100).
Pentamethylpentaphenylcyclopentasiloxane (isomeric mixture):
1H NMR (CDCl3) ꢄ 0.03 (s), 0.25 (s), 0.37 (s), 0.40 (s), 0.48
(s), 0.52 (s), 0.57 (s), 7.13–7.7 (m); 13C NMR (CDCl3) ꢄ ꢂ0:57,
ꢂ0:38, ꢂ0:34, ꢂ0:28, ꢂ0:16, ꢂ0:13, ꢂ0:07, 0.02, 0.04, 127.57,
127.61, 127.63, 127.69, 127.71, 127.74, 127.77, 129.47, 129.61,
129.64, 129.68, 129.72, 129.73, 129.76, 129.78, 133.22, 133.27,
133.33, 133.36, 133.41, 136.87, 137.05, 137.20, 137.35. MS (70
eV) m=z (%) 680 (Mþ, 20), 665 (Mþ ꢂ Me, 60).
ꢁ
1
(3): colorless crystals; mp 193–194 C. H NMR (CDCl3) ꢄ 0.18
(s, 12H), 7.31–7.69 (m, 20H); 13C NMR (CDCl3) ꢄ ꢂ4:24,
127.62, 127.91, 130.38, 130.46, 133.98, 134.27; 29Si NMR
(CDCl3) ꢄ ꢂ51:91, ꢂ34:71. MS (70 eV) m=z (%) 664 (Mþ, 5),
649 (Mþ ꢂ Me, 10), 597 (Mþ ꢂ Ph, 100). IR (KBr): 507, 596,
619, 721, 742, 775, 841, 926, 995, 1120, 1159, 1168, 1193,
1271, 1429, 1593, 1780, 1832, 1900, 1967, 2854, 3074 cmꢂ1
;
Found: C, 50.47; H, 5.00%. Calcd for C28H32O8Si6: C, 50.57;
H, 4.85%.
X-ray Crystallography. Intensity data were collected on a