ꢀꢀꢀꢁ
2ꢀ ꢀE. Weisheim et al.: Improved synthesis and crystal structure of the parent 1,3,5-trisilacyclohexane
Tetrahydrofuran was dried with potassium, hexane and
diethyl ether with LiAlH4. The solvents were distilled prior
to use. C6D6 was dried with Na/K alloy and condensed.
NMR measurements were performed on Bruker Avance III
500 and Bruker DRX 500 instruments. NMR spectra were
referenced to the residual signal of used protonated sol-
vents (1H, 13C) or external standards (29Si: TMS). GC/EI-MS
analyses were done using a Shimadzu GC-2010/GCMS-QP
2010S instrument (capillary column: Rtx®-200, Cross-
bond, trifluoropropylmethylpolysiloxane, 30 m, 25 mm,
0.25 μm). FT-IR spectra were recorded on a Bruker ALPHA
FT-IR spectrometer.
Fig. 1:ꢀMolecular structure of 1,3,5-trisilacyclohexane (1) in the
crystalline state. Displacement ellipsoids are shown at the 50%
probability level. Selected bond lengths (Å): Si(1)–C(1) 1.871(1),
Si(2)–C(1) 1.873(1), Si(2)–C(2) 1.873(1), Si(1)–H(1A) 1.39(3), Si(1)–
H(1B) 1.40(3), Si(2)–H(2A) 1.38(2), Si(2)–H(2B) 1.45(3); angles (deg):
C(1)–Si(1)–C(1′) 109.8(1), C(1)–Si(2)–C(2) 110.0(1), Si(1)–C(1)–Si(2)
113.5(1), Si(2)–C(2)–Si(2′) 112.4(1), C(2)–Si(2)–C(1)–Si(1) –54.9(1).
Symmetry code used for primed atoms: –x, y, z.
3.1 Synthesis of 1,1,3,3,5,5-Trisilacyclo-
hexane (1)
1,1,3,3,5,5-Hexamethoxy-1,3,5-trisilacyclohexane (8.56 g,
27.4 mmol), dissolved in diethyl ether (10 mL), was
dropped to a suspension of LiAlH4 (3.26 g, 85.9 mmol) in
diethyl ether (80 mL) in a Young-tap ampoule. Afterwards
the ampoule was cooled to –196 °C, evacuated, sealed and
heated at 45 °C for 4.5 d. Workup: All volatile constituents
of the reaction were condensed into another ampoule.
This was cooled to a temperature between –50 °C and
–45 °C and the diethyl ether was condensed off in dynamic
vacuum. The product remained as colourless, acicular
solid, with a melting point of 10 °C [lit. [8]: 10 °C]. Yield:
2.97 g (22.5 mmol, 82%). –1H NMR (500 MHz, C6D6, 298 K):
δ ꢀ=ꢀ 4.18 (quint, 3JH,H ꢀ=ꢀ 3.6 Hz, 6H, –CH2SiH2CH2–, 1JSi,H ꢀ=ꢀ 196
Hz), –0.35 (quint, 3JH,H ꢀ=ꢀ 3.6 Hz, 6H, –SiH2CH2SiH2–, 2JSi,H ꢀ=ꢀ
Table 1:ꢀComparison of structural parameters of experimental XRD
(mean values, individual values see caption to Fig. 1) and GED [11]
data of 1,3,5-trisilacyclohexane (1). Distances, r in Å, angles in deg.
Parameters
ꢁ
XRDꢁ
GED [12]
r(Si–C)
ꢂ
ꢂ
ꢂ
ꢂ
1.872ꢂ
112.9ꢂ
109.9ꢂ
107.5ꢂ
54.9ꢂ
1.872(1)
113.0(4)
110.7(14)
107.4a
∠(Si–CH2–Si)
∠(C–SiH2–C)
∠(H–Si–H)
ϕ(CH2–Si–CH2–Si)ꢂ
53.7(4)
aNot refined.
13
117 Hz). – C{1H} NMR (126 MHz, C6D6, 298 K): δ ꢀ=ꢀ –10.3
Si–C distances, in the solid state are as long as the in gas (s, –SiCH2Si–, 1JSi,C ꢀ=ꢀ 43 Hz). –29Si{1H} NMR (99 MHz, C6D6,
phase and an expansion of the C–Si–C angle compared to 298 K): δ ꢀ=ꢀ –34.3 (s, –CH2SiCH2–). –GC/EI-MS: m/z (%) ꢀ=ꢀ
+
+
Si–C–Si angle has been observed in the crystal structure. 130 (100) [M–H2] , 101 [M–SiH2] , retention time: 2.6 min.
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The same relation between the angles has also been found – FT-IR (gas phase) ν (cm ) ꢀ=ꢀ 2153 (Si–H, s), 2143 (Si–H, s).
in the gas phase structure.
The formal substitution of silicon by germanium
atoms leads to the known isostructurally crystallising 3.2 X-Ray diffraction experiments
compound 1,3,5-trigermacyclohexane [15]. The structure
1,3,5-trigermacyclohexane in the solid state has – like 1 – Single crystals of compound 1 suitable for X-ray diffrac-
a chair conformation and, expectedly, larger bond lengths tion measurement were obtained by in situ crystallisation
(Ge–C, mean: 1.951 Å). The angle Ge–C–Ge (mean: 112.0°) in a glass capillary on the goniometer of the diffractom-
and the angle C–Ge–C (mean: 109.8°) are comparable with eter. This was achieved by first establishing a solid-liquid
those of compound 1 (Table 1).
equilibrium at 288.2 K close to the melting point, then
melting all solid but a tiny crystal seed (using a thin
copper wire as external heat source) followed by chilling
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3 Experimental section
All manipulations were performed under dried argon with 10 K h to 265 K and 25 K h to the temperature of
or nitrogen using Schlenk and Stock techniques. measurement at 100 K. The measurement was carried out
very slowly with 3 K h until the whole capillary was filled
with a single crystalline specimen at 285 K, then chilling
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