K.R. Pichaandi et al. / Journal of Organometallic Chemistry 696 (2011) 1957e1963
1959
9H) 1.16e1.29 (two doublets, 12H, J ¼ 1 Hz) 1.29e1.46 (m, 2H) 13C
144.9. 29Si{1H} NMR ( , C6D6) 3.9, 15.8. M.p. 123e135 ꢀC with
d
decomposition. Elemental analysis C20H42Br2Si2; observed (calcu-
lated): C, 47.33 (48.18) H, 8.11 (8.49).
{1H} NMR (
d
, CDCl3) 14.8, 18.9, 19.3, 21.9, 28.2 29Si{1H} NMR (
d
,
CDCl3) 41.2. IR (NaCl, cmꢁ1) 2946 (m), 2867 (s), 1465 (s), 1010 (s),
881(s), 815 (s). GCeMS(EI): m/z (relative abundance) 251(Mþ, 1),
207 (2), 194 (6), 165 (8), 131 (25), 101 (100), 75 (58), 39 (23)
Elemental analysis for C10H23BrSi; observed (calculated): C, 47.97
(47.80) H, 9.86 (9.23).
2.9. Synthesis of 3,30-bis(3-tert-butyl-1,1,2,2-tetramethyl-3-
silacyclopropane) 1c
Magnesium turnings (99.98%, 0.83 g, 31 mmol), 25 mL THF, and
a small amount of 1,2-dibromoethane (0.70 mL) were added to
a 100 mL Schlenk flask under argon and then stirred for 1 h in order
to activate the magnesium. Compound 3c (6.9 g), dissolved in 15 mL
of THF, was added to the magnesium slurry over a period of 4 h at
15 ꢀC, and then stirred at room temperature for an additional 5 h.
The mixture was stirred for an additional 10 min after the addition
of 25 mL of hexane, and the solids were allowed to settle. The clear
solution was decanted and filtered through a fritted Schlenk funnel.
The solvent was removed from the filtrate by applying vacuum to
give 1c as yellow color waxy substance. Analytically pure
compound was obtained by reverse phase HPLC using a binary
solvent system of methanol:THF in a ratio of 93:7. Yield 0.80 g
2.7. Synthesis of 1,2-di-tert-butyl-1,1,2,2-tetraisopropyldisilane (2c)
A degassed mixture of 6 (2.0 g, 7.8 mmol) and 22 mL of THF were
added to a 50 mL Schlenk flask loaded with KC8 (1.3 g, 9.7 mmol).
The mixture was initially stirred under argon at ꢁ30 ꢀC. The
temperature of the mixture was carefully brought to ꢁ10 ꢀC over
a 45 min period, and then to 25 ꢀC over a 1 h period. The resulting
slurry was then stirred for another 2 h and filtered through celite.
The filtrate was rotary evaporated to remove THF. Recrystallization
in hexane at ꢁ20 ꢀC gave colorless crystals of 2c. Yield 1.00 g (83%).
1H NMR (
d
, CDCl3) 1.04e1.32 (m, 42H) 1.33e1.47 (m, 4H) 13C{1H}
NMR (
d
, CDCl3) 15.0, 21.0, 22.1, 28.9, 32.0 29Si{1H} NMR (
d, CDCl3) 4.1.
GCeMS(EI) m/z (relative abundance) 285 (Mþ ꢁ tert-butyl, 2), 243
(23), 183 (13), 155 (15), 129 (15), 101 (100), 73 (60) Elemental
analysis C20H46Si2; observed (calculated): C, 70.06 (70.17) H, 13.44
(13.45). M.p. 185e192 ꢀC. This route is much more efficient than the
two step synthesis of hexa-tert-butyldisilane from tri-tert-butyl-
bromosilane previously reported by Wiberg [11] where the bro-
mosilane was reduced with potassium metal, followed by an
oxidation with the nitrosyl cation. A SieSi stretching vibration at
284.5 cmꢁ1 was observed in the Raman spectrum. This value lies
between the reported values for hexamethyldisilane (401 cmꢁ1) and
hexa-tert-butyldisilane (271 cmꢁ1) [11].
(23%). 1H NMR (
d, C6D6) 1.20e1.21 (s, 18H) 1.34e1.36 (d, 12H,
J ¼ 2 Hz) 1.36e1.37 (s, 6H) 1.41e1.43 (s, 6H). 13C{1H} NMR (
d
, C6D6)
20.6, 21.5, 23.4, 23.9, 24.2, 26.4, 28.2, 32.5. 29Si{1H} NMR (
d, C6D6)
ꢁ60.7. HRMS for C20H42Si2 (Mþ ion): observed (calculated)
338.28054 (338.28251). GCeMS(EI): m/z (relative abundance) 338
(Mþ, 4), 281 (17), 239 (2), 183 (2), 169 (7), 127 (19), 101 (100), 73
(55), 59 (49). Compound 9 was obtained as a byproduct in HPLC
separation of 1c. Characterization for 9. 1H NMR (
d, THF-d8)
1.16e1.17 (s, 9H), 1.17e1.18 (s, 9H), 1.12e1.14 (s, 6H), 1.25e1.26 (s,
6H), 2.01e2.03 (q, 3H), 5.46e5.51 (m, 1H), 5.76e5.81 (m, 1H) 13C
{1H} NMR (
d, THF-d8) 16.0, 16.2, 16.2, 21.5, 21.6, 22.2, 22.4, 22.6,
22.70, 27.1, 32.0, 32.3, 130.30,147.1 29Si{1H} NMR (
d
, C6D6) ꢁ5.6, 1.2.
2.8. Synthesis of 1,2-di-tert-butyl 1,1,2,2-tetrakis(2-bromo-2-
GCeMS (EI): m/z (relative abundance) 340 (Mþ, 2), 283 (10), 241 (8),
propyl)disilane (3c)
171 (5), 127 (33), 101 (100), 73 (60), 59 (20).
Finely powdered N-bromosuccinimide (2.1 g, 12 mmol), AIBN
(0.40 g, 2.4 mmol), disilane 2c (0.50 g, 1.5 mmol) and 50 mL CCl4
were placed into a 100 mL Schlenk flask under nitrogen, stirred for
30 min, and then heated to 58e60 ꢀC. The mixture was then irra-
diated with a 75 W incandescent bulb. The solution became a light
yellow color and then to dark yellow after a few minutes. The
temperature of the solution was lowered to 55 ꢀC and maintained
at this temperature for 30 min. The solution was then cooled to 0 ꢀC,
stirred for an additional 30 min, and filtered through a fritted
Schlenk funnel to remove the precipitated succinimide. The solvent
was removed from the filtrate by vacuum and the filtrate was dried
to give 3c as a waxy substance. Recrystallization in hexane at
ꢁ30 ꢀC gave impure 3c. The impure solid was then separated by
HPLC using a CH3OH:THF eluent (93:7) to obtain analytically pure
2.10. Thermolysis of bis(silirane) 1c with bis(trimethylsilyl)
acetylene
Compound 1c (0.42 g, 1.2 mmol), bis(trimethylsilyl)acetylene
(1.5 g, 9.0 mmol) and 3.0 mL of toluene were placed in a pyrolysis
tube attached with a teflon stopcock. The solution was degassed
under high vacuum through five freeze-pump-thaw cycles. The
tube was then sealed with a torch and heated to 145e147 ꢀC for 16 h
in an oil bath. The tube was opened after cooling to room
temperature and the pyrolysate was transferred to a 10 mL Schlenk
flask. The solvent, as well as the excess trapping agent, were
removed by vacuum to give compound 11 as a brown color waxy
substance. Characterization for 11: 29Si{1H} NMR (
d
, C6D6) ꢁ40.5,
47.2 GCeMS(EI): m/z (relative abundance) 424 (Mþ, 2) 409 (5) 367
(22), 340 (5), 283 (100), 221 (22), 155 (16), 73 (67) HRMS for
C22H48Si4 (Mþ ion): calculated (observed) 424.28051 (424.28332).
Further purification of compound 11 by HPLC using a meth-
anol:THF solvent (85:15) resulted in the isolation of 12 as a color-
less waxy substance. Yield 0.20 g (36%) Characterization for 12: 1H
3c. Yield 0.35 g (37%). 1H NMR (
d, THF-d8) 1.58e1.67 (s, 18 H)
2.38e2.58 (d, 24H, J ¼ 15 Hz) 13C{1H} NMR (
d, THF-d8) 30.5, 34.3,
39.1 (b) 40.8 (b) 62.0 (b) 29Si{1H} NMR (
d, THF-d8) 29.0 Elemental
analysis C20H42Br4Si2; observed (calculated): C, 36.26 (36.49) H,
7.08 (6.43). M.p. 85e110 ꢀC with decomposition. Compounds 7 and
8 were the side products obtained during the HPLC separation.
NMR (
1.28e1.33 (s, 18H) 13C{1H} NMR (
29.3, 118.2 29Si{1H} NMR (
d
, C6D6) 0.3e0.4 (s, 18H), 0.89e0.95 (s, 6H), 1.13e1.17 (s, 6H),
Characterization for 7. 1H NMR (
d
, THF-d8) 1.37e1.38 (s, 9H)
1.4e1.42 (s, 9H) 2.18e2.22 (d, 12H, J ¼ 9 Hz) 4.35e4.54 (q, 2H)
7.37e7.45 (s, 1H). 13C{1H} NMR (
, C6D6) 16.9, 22.6, 22.6, 26.1, 26.1,
32.8, 33.1, 35.0, 36.9, 37.0, 37.2, 37.3, 58.2, 58.7, 131.1, 139.7. 29Si{1H}
NMR (
, C6D6) 3.2, 12.7. M.p. 102e115 ꢀC with decomposition
Elemental analysis C20H40Br4Si2; observed (calculated): C, 36.17
(36.60) H, 6.58 (6.14). Characterization for 8. 1H NMR (
, C6D6)
1.31e1.32 (s, 9H) 1.42e1.44 (s, 9H) 2.19e2.27 (m, 12H) 5.72e5.78
(m, 1H) 5.96e6.00 (m, 1H) 13C{1H} NMR (
, C6D6) 16.6, 22.6, 23.1,
25.3, 26.6, 27.6, 32.9, 33.2, 37.3, 37.6, 37.9, 38.1, 59.2, 59.3, 134.5,
d
, C6D6) 4.0, 19.5, 23.8, 25.2, 28.4,
d
, C6D6) ꢁ13.1, 8.73 GCeMS(EI): m/z
d
(relative abundance) 440 (Mþ, 2) 425 (7), 383 (5), 356 (19), 299
(100), 213 (7), 181 (7), 73 (33). HRMS for C22H48OSi4 (Mþ ion):
observed (calculated) 440.27816 (440.27823).
d
d
2.11. Computational details
d
All of the density functional calculations reported in this paper
used the GAUSSIAN03 [12] program system through the WebMo