Hexa-alkyldisilanes and Tetrakis(tri-alkylsilyl)silanes
silane, the product was distilled. In the case of hex-iso-propyldisilane,
the final product was a solid, which was filtered off, washed several
times with distilled water, dried and purified by sublimation.
above 385 °C, combined with low reactivity at lower tempera-
tures.[34] This means high dosages (200 Torr) and long expo-
sure times (minutes) are required, rendering the process inef-
ficient.
Pure [(C2H5)3Si]2 (1) was prepared by careful fractional distillation of
the dried organic layer obtained with chlorotriethylsilane as starting
material. The colorless liquid was proved (EA and MS) to be pure 1
(Table 1 and Table 2).
Silicon nitrides are of interest for passivation layers and
anti-reflection coatings for photovoltaics, whereas silicon car-
bide films may open up the possibility of compact high power
electronics. CVD of these materials requires rather high depo-
sition temperatures (ca. 500 and 800 °C, respectively),[35]
which currently limits the number of potential applications.
We have attempted the preparation of tetrakis(triethylsilyl)-
silane, tetrakis(tri-n-propylsilyl)silane, tetrakis(tri-iso-prop-
ylsilyl)silane, tetrakis(tri-n-butylsilyl)silane, and tetrakis(tri-
iso-butylsilyl)silane, using the procedure[1] reported for the
preparation of tetrakis(trimethylsilyl)silane. The resulting
products were proved by chemical analysis such as mass spec-
trometry (MS) and elemental analysis (EA) to be mainly hexa-
alkyldisilianes [(R3Si)2] mixed (except in the case of com-
pound 3) with other products such as (R2Si)4, (R3Si)4Si (as
minor phase in some cases) in addition to other un-identified
product(s). It appears that alkyl groups larger than methyl de-
stabilize the tetrakis(trialklysilyl)silane structure.
Table 1. Analytically determined and theoretically calculated
(printed in italics) composition (in wt%) for [(C2H5)3Si]2 (1),
(CH3CH2CH2)3Si]4Si (2), and [(iso-propyl)3Si]2 (3) complexes (ele-
mental analysis).
Complex
C
H
1
62.30
62.52
65.60
65.76
68.55
68.70
13.09
13.12
12.82
12.88
13.55
13.45
2
3
Table 2. Mass spectroscopic (MS) data for [(C2H5)3Si]2 (1).
Ions
m/z
obsd.
Relative intensity /%
a)
calcd
2 Experimental Section
+
+
C12H30Si2
C10H25Si2
230.1
201.1
173.1
145.0
115.1
87.0
230.19
201.15
173.17
145.14
115.09
87.12
54.44
40.28
29.6
20.46
100
C10H25Si+
C8H21Si+
C6H15Si+
2.1 Reactants and or Solvents
Chlorotriethylsilane (Aldrich, Wacker, Ն 99.0%), chlorotri-n-propyl-
disilane (VWR, Alfa Aesar, Ն 98%), Chlorotri-iso-propyldisilane
(VWR, Alfa Aesar, Ն 97%), Chlorotri-n-butylsilane (VWR, Alfa
Aesar, Ն 97%), Chlorotri-iso-butylsilane (Aldrich, Ն 99%), lithium
(Aldrich, granular, 99%), and silicone tetrachloride (Aldrich, 99%)
were used as reactants without further purification. THF (Merck,
Ն 99.9%) was refluxed over sodium and benzophenone for 1 d, dis-
tilled in an argon atmosphere and used directly after distillation.
+
C6H15
79.94
a) Calculated value according to the isotope with highest abundance.
Complex 2 was obtained from the reaction described above using
chloro-tri-n-propylsilane. After hydrolysis and separation of the aque-
ous layer, the organic layer was left to stand overnight, after which it
separated into three layers: a clear orange layer on the top, a thick
orange layer in the middle, and a thicker brighter orange layer on the
bottom. The last layer was dissolved in ether or hexane, filtered off
and the yellowish solution was left for slow evaporation at room temp.,
open to air. Afterwards, the yellowish solid was re-crystallized from
hot ethanol or alternatively it can be washed carefully with cold eth-
anol to obtain a white solid, which proved to be pure tetrakis(tri-n-
propylsilyl)silane (2), melting point (m.p.) = 262–267 °C. Single crys-
tals suitable for single-crystal X-ray structure determination were ob-
tained by re-crystallization of the white solid from a mixture of aceto-
nitrile and toluene at boiling point (Table 1 and Table 3).
2.2 Synthesis
All procedures until the hydrolysis were performed in a dry argon
atmosphere using a combination of glove box and Schlenk line. The
procedures were similar in all experiments and based on the reported
preparation of tetrakis(trimethylsilyl)silane:[1] In a glove box, Li
(0.96 mol, 50% excess), chlorotrialkylsilane (0.384 mol, 20% excess),
and THF (ca. 120 mL) were added to a round bottomed flask. SiCl4
(0.08 mol) and THF (70 mL) were added to a special funnel (which
can be sealed and used under inert atmosphere). This funnel was con-
nected to the reaction flask, closed and brought out from the glove
box. The system was joined to the Schlenk line and exposed to an
argon atmosphere. Ca. 8 mL of the mixture of SiCl4 and THF was
added to the reaction mixture of Li and chlorotrialkylsilane and stirred
for ca. 4 h. After that, the remaining SiCl4 in THF was added drop
wise to the reaction mixture at room temperature over ca. 4 h. The
reaction mixture was stirred at room temperature for ca. 30 h, after
which the system was transferred back to the glove box and filtered
through glass wool. The filtrate was brought out from the glove box
and added to a beaker containing HCl (ca. 180 mL, 15%) and some
ice and stirred well to allow hydrolysis. The organic layer was sepa-
rated from the aqueous layer, washed several times with distilled water,
and dried with anhydrous sodium sulfate. In the case of hexaethyldisil-
For R = iso-propyl, a quantitative amount of a solid precipitated di-
rectly on hydrolysis. The mixture was stirred well, filtered off, and
washed with distilled water several times, dried at 60 °C and sublimed
at 100 °C under vacuum. The white solid proved (EA and MS) to
be pure complex 3, m.p. 207–210 °C (yield ca. 50%) (Table 1 and
Table 4).
2.3 Elemental Analysis
Elemental analyses were performed by the standard combustion tech-
nique at Mikroanalytisches Labor Pascher (Germany) or Birmingham
ane, hexa-n-propyldisilane, hexa-n-butyldisilane and hexa-iso-butyldi- University (UK).
Z. Anorg. Allg. Chem. 2014, 2956–2961
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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