Hetero π Systems, 24
FULL PAPER
4000Ϫ400 cmϪ1, all spectra were recorded with 1 cmϪ1.resolution;
UV/Vis: Diode array spectrometer HP 8452A (Hewlett-Packard),
190-820 nm, resolution 2 nm.
1,1-Diethynyl-2,2,2-trimethyldisilane (16): 2,2,2-Trimethyldisilane-
1,1-diyl-1,1-bis(triflat) (15) was generated by reaction of 1.5 g of
1,1,1-trimethyl-2,2-diphenyldisilane (14) (5.8 mmol) with two
equivalents of trifluoromethanesulfonic acid (1.7 g) in 20 ml of pen-
tane at 0°C and stirring for 10 min at this temperature. Two equiva-
lents of ethynylmagnesium chloride in THF were added dropwise
at 0°C. After completion of the addition all volatiles including the
product were removed in vacuo. The solvents were largely removed
by distillation. The remaining solution (1 ml) contained about 25
Pulsed Flash Pyrolyses in Combination with Matrix Isolation:
Regulated by a pulsed magnetic valve, a gaseous mixture of the
precursor molecule and argon (1:1000) was expanded through a
corundum tube (inner diameter 1 mm, length of heated zone 10
mm, heated to ca. 1000°C by a tungsten resistance wire) directly
into the high vacuum of the cryostat. Experimental parameters:
duration of pulse 0.2 s, equivalent to ca. 1 ml/pulse of gas mixture
at 1000 mbar; pulse frequency 10 pulses/min.
% of 1,1-diethynyl-2,2,2-trimethyldisilane. For the matrix isolation
˜
studies it was purified by preparative GC. Ϫ IR (neat): ν ϭ 3283
cmϪ1 (CH), 2956 (CH), 2139 (SiH), 2036 (CC), 1249 (SiMe3). Ϫ
UV (cyclohexane): λmax (lg ε) ϭ 223 nm (3.00). Ϫ 1H NMR
(C6D6): δ ϭ 0.87 (s, 9 H, SiMe3), 3.15 (d, J ϭ 0.2 Hz, 2 H, acetyl-
enic H), 4.77 (m, J ϭ 0.2 Hz, 1 H, SiH). Ϫ 13C NMR (C6D6): δ ϭ
Ϫ1.54 (SiMe3), 81.24 (CϵCH), 98.97 (CϵCH) (s). Ϫ 29Si NMR
(C6D6): δ ϭ Ϫ79.40 (SiH), Ϫ15.80 (SiMe3). Ϫ MS (70 eV); m/z
(%): 152 (5) [Mϩ], 137 (19), 126 (5), 111 (11), 83 (21), 73 (100). Ϫ
HRMS calcd. for C7H12Si2 (Mϩ) 152.0478, found 152.0474.
General: All reactions were carried out under dry argon or nitro-
gen. Solvents were dried using standard techniques. All glassware
was thoroughly dried in an oven at 130°C prior to use. Ϫ NMR
spectra were recorded on Bruker AM-400 or AC-200 spec-
trometers. Ϫ IR spectra were recorded on a Bruker IFS 25 spec-
trometer. Ϫ Mass spectra were obtained on a Varian Mat 111 or
Varian Mat 311 A spectrometer. Ϫ A Carlo-Erba Fractovap 2900
gas chromatograph with a flame ionization detector and a 10 m ϫ
0.3 mm column coated with silicon phase OV 101 was used for
analytical gas chromatography. Preparative gas chromatography
was performed on a Carlo-Erba Fractovap 2450 using a thermal
conductivity detector and helium as the carrier gas (4 m ϫ 6 mm,
OV 101). Ϫ Trichlorosilane (17) and dichlorodiphenylsilane were
obtained from Fluka, 13C2H2 (99 atom-% 13C) from Cambridge
Isotope Laboratories. Chlorotriphenylsilane was synthesized by re-
action of dichlorodiphenylsilane and phenylmagnesium chloride.
Triethynylsilane (18) was prepared according to a literature pro-
cedure[9] by the reaction of three equivalents of sodium acetylide
and trichlorosilane in nitrobenzene and purified by preparative GC.
1,1-Diethynyl-3,4-dimethyl-1-silacyclopent-3-ene (19): A mixture
of 0.60 ml of crude diethynyldisilane 16 and 0.82 g (10 mmol) of
2,3-dimethylbutadiene was passed through an oven at 450°C. The
flow pyrolysis was performed in a quartz glass tube (length 33 cm,
length of heated zone 25 cm, diameter 15 mm), which was filled
with quartz glass Raschig rings. Nitrogen was used as the carrier
gas. The yellow pyrolysis product was trapped at 77 K and, after
the excess of 2,3-dimethylbutadiene was removed, 19 could be iso-
lated by preparative gas chromatography as a colorless liquid. Ϫ
˜
IR (neat): ν ϭ 3278 cmϪ1 (CH), 2912 (CH), 2041 (CC). Ϫ 1H
NMR (C6D6): δ ϭ 1.35 (s, 6 H, CH3), 1.51 (s, 4 H, CH2), 1.90 (s,
2 H, CH). Ϫ 13C NMR (C6D6): δ ϭ 18.77 (CH3), 25.47 (CH2),
84.47 (CϵCH), 96.00 (CϵCH), 127.25 (CϭC). Ϫ MS (70 eV); m/z
(%): 160 (100) [Mϩ], 145 (35), 134 (25), 119 (33), 105 (17), 93 (13).
Ϫ HRMS calcd. for C10H12Si (Mϩ) 160.0708, found 160.0669.
1,1,1-Trimethyl-2,2,2-triphenyldisilane (12): Triphenylsilyllithium
was generated by stirring of chlorotriphenylsilane with the stoichio-
metric amount of lithium granules in THF at room temperature
for six hours. The resulting solution was added slowly to an excess
of chlorotrimethylsilane in THF at 0°C. After aqueous workup di-
silane 12 was obtained in 82 % yield.
Adducts 20[10] and 21[5] were identified by comparison (GC/MS)
with authentic probes.
Bromo-2,2,2-trimethyl-1,1-diphenyldisilane (13): To 10 g of 1,1,1-
trimethyl-2,2,2-triphenyldisilane (12), 10 ml of HBr were condensed
at Ϫ196°C. In order to keep the reaction time as short as possible
the reaction flask was taken out of liquid N2 and immediately put
in a water bath of 45°C. After evaporation of the bulk of HBr the
formed benzene was removed in vacuo as fast as possible. The
crude bromo-2,2,2-trimethyl-1,1-diphenyldisilane (13) contained
about 15 % of 1,1-dibromo-2,2,2-trimethyl-1-phenyldisilane, as was
shown by analytical GC. The crude product was directly used for
the next step.
1,1-Bis(deuteroethynyl)-2,2,2-trimethyldisilane (27): Deutero-
ethynylmagnesium chloride was synthesized according to a pro-
cedure described earlier[5]. Reaction of this reagent with 0.5 equiva-
lents of triflate 15 in the same manner as in the case of unlabeled
16 (see above) yielded 1,1-bis(deuteroethynyl)-2,2,2-trimethyldi-
silane (27) which also was purified by preparative GC. Ϫ IR (gas):
˜
ν ϭ 2963 cmϪ1 (CH), 2590 (CD), 2151 (SiH), 1919 (CC), 1254
1
(SiMe3). Ϫ H NMR (C6D6): δ ϭ 0.88 (s, 9 H, SiMe3), 4.77 (s, 1
H, SiH). Ϫ 13C NMR (C6D6): δ ϭ Ϫ1.59 (SiMe3), 80.85 (CϵCD),
98.65 (CϵCD, J ϭ 36.2 Hz). Ϫ MS (70 eV); m/z (%): 157 (6) [Mϩ],
142 (36), 128 (32), 114 (29), 102 (3), 73 (100). Ϫ HRMS calcd. for
C7H10D2Si2 (Mϩ) 154.0603, found 154.0586.
1,1,1-Trimethyl-2,2-diphenyldisilane (14): The crude bromodisi-
lane 13 was dissolved in the double volume of diethylether and
added dropwise to a suspension of 0.38 g of LiAlH4 (10 mmol) in
25 ml of diethyl ether at 0°C. After stirring overnight aqueous
workup with 2 HCl yielded crude diphenyldisilane 14. Distillative
purification afforded 5.1 g of 1,1,1-trimethyl-2,2-diphenyldisilane
1,1-Diethynyl-2,2,2-trimethyldisilane-13C4 (29): About 200 ml of
gaseous 13C2H2 were frozen out at Ϫ196°C. At this temperature, a
solution of 18 mmol n-butylmagnesium chloride in THF was added
(14) (65 % referred to 12) as a colorless liquid of boiling point dropwise. By slow warming up to 0°C and stirring as soon as pos-
110°C/0.1 Torr, which slowly crystallized at room temperature. Ϫ sible, a maximum conversion of the acetylene could be achieved.
IR (neat): ν ϭ 3067 cmϪ1 (CH), 2952 (CH), 2092 (SiH), 1246 The reaction of this Grignard compound with triflate 15 was car-
(SiMe3). Ϫ UV (cyclohexane): λmax (lg ε) ϭ 230 nm (2.36), 261 ried out as described above and yielded after separation by pre-
˜
1
(2.41). Ϫ H NMR (C6D6): δ ϭ 0.01 (s, 9 H, SiMe3), 4.94 (s, 1 H, parative GC 45 µl of disilane 29 as a colorless liquid. Ϫ IR (gas):
˜
1
SiH), 6.26 (m, 10 H, aromatic H). Ϫ 13C NMR (C6D6): δ ϭ Ϫ1.36
ν ϭ 3321 cmϪ1 (CH), 2066 (CC), 2058 (SiH). Ϫ H NMR (C6D6):
(SiMe3), 118.89, 129.32, 134.30, 136.03. Ϫ 29Si NMR (C6D6): δ ϭ δ ϭ 1.05 (s, 9 H, SiMe3), 3.33 (dϫdϫm, 1J ϭ 173.8 Hz, 2J ϭ 147.3
Ϫ11.22 (SiH), 1.22 (SiMe3). Ϫ MS (70 eV); m/z (%): 256 (26) [Mϩ], Hz, 2 H, acetylenic H), 4.94 (m, 1 H, SiH). Ϫ 13C NMR (C6D6):
241 (11), 197 (36), 183 (61), 105 (74), 73 (100). Ϫ HRMS calcd. for
δ ϭ Ϫ1.54 (SiMe3), 81.45 (d, J ϭ 173.8 Hz, CϵCH), 99.09 (d, J ϭ
147.3 Hz, CϵCH). Ϫ MS (70 eV); m/z (%): 156 (10) [Mϩ], 141
C15H20Si2 (Mϩ) 256.1104, found 256.1106.
Eur. J. Org. Chem. 1998, 1285Ϫ1290
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