Non-oxide sol-gel chemistry: Preparation from tris(dialkylamino)silazanes of a carbon-free, porous, silicon diimide gel

Article abstract of DOI:10.1002/(sici)1521-3773(19990712)38:13/14<2036::aid-anie2036>3.0.co;2-q

The acid-catalyzed ammonolysis of the hitherto unknown compound tris(dimethylamino)silylamine (1), which is prepared from SiCl₄ in high yield and purity, results in the preparation of a silicon diimide gel. The probable first step in this proce

Full text of DOI:10.1002/(sici)1521-3773(19990712)38:13/14<2036::aid-anie2036>3.0.co;2-q

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[
[
7] H. Schäfer, H. G. von Schnering, Angew. Chem. 1964, 76, 833.
8] a) S. J. Hibble, A. K. Cheetham, A. R. L. Bogle, H. R. Wakerley, D. E.
Cox, J. Am. Chem. Soc. 1988, 110, 3295 ± 3296; b) R. Dronskowski, A.
Simon, Angew. Chem. 1989, 101, 775 ± 777; Angew. Chem. Int. Ed.
Engl. 1989, 28, 758 ± 760; c) P. Gougeon, M. Potel, M. Sergent, Acta
Crystallogr. Sect. C 1990, 46, 1188 ± 1190; d) P. Gougeon, P. Gall, M.
Sergent, Acta Crystallogr. Sect. C 1991, 47, 421 ± 432; e) R. Dronskow-
ski, A. Simon, W. Mertin, Z. Anorg. Allg. Chem. 1991, 602, 49 ± 63; f) P.
Gall, P. Gougeon, Acta Crystallogr. Sect. C 1994, 50, 7 ± 9; g) P. Gall, P.
Gougeon, Acta Crystallogr. Sect. C 1994, 50, 1183 ± 1185; h) R.
Dronskowski, A. Simon, Acta Chem. Scand. 1991, 45, 850 ± 855; i) G. L.
Schimek, S. C. Chen, R. E. McCarley, Inorg. Chem. 1995, 34, 6130 ±
silica gel would be a gel of silicon diimide (Si(NH) ). A
2
putative imide/nitride pathway can be envisioned in which
dialkylamido compounds of silicon are subjected to ammo-
nolysis and condensation to an imide.
The reactions of Si(NR ) compounds, and of bimetallic
2
4
analogues, with ammonia have been reported to give amor-
[11±16]
phous powders
and, in OMCVD experiments, silicon
nitride films.[ However, silicon diimide gels have not been
reported from these or any other starting materials. We report
here the preparation of a silicon imide gel by acid-catalyzed
ammonolysis of the hitherto unreported tris(dimethylamino)-
silylamine [(CH ) N] SiNH , 1, which we have prepared from
17]
6140; j) G. L. Schimek, D. A. Nagaki, R. E. McCarley, Inorg. Chem.
1994, 33, 1259 ± 1265; k) E. Fais, H. Borrmann, H. Mattausch, A.
3
2
3
2
Simon, Z. Anorg. Allg. Chem. 1995, 621, 1178 ± 1184; l) R. Dron-
skowski, H. Mattausch, A. Simon, Z. Anorg. Allg. Chem. 1993, 619,
silicon tetrachloride in high yield and purity. The probable
first step in this process is the acid-catalyzed self-condensation
of 1 to the cyclic trimer [{(CH ) N} SiNH] (2), for which we
1397 ± 1408; m) G. L. Schimek, R. E. McCarley, J. Solid State Chem.
1994, 113, 345 ± 354.
3
2
2
3
[
9] a) C. C. Torardi, R. E. McCarley, J. Am. Chem. Soc. 1979 101, 3963;
b) R. E. McCarley, Polyhedron 1986, 5, 51 ± 61.
report the X-ray crystal structure. The acid-catalyzed ammo-
nolysis of 2, or the equivalent sequential self-condensation
and ammonolysis of 1, under mild conditions, yields a
semirigid translucent gel. On drying under mild conditions
in an ammonia atmosphere this non-oxide gel yields a high
surface area silicon diimide xerogel, the first example of a
porous non-oxide silicate gel.
[
10] D. Fenske, J. Ohmer, Angew. Chem. 1987, 99, 155; Angew. Chem. Int.
Ed. Engl. 1987, 26, 148.
[
11] a) C. A. Ghilardi, S. Midollini, L. Saccini, J. Chem. Soc. Chem.
Commun. 1981, 47; b) D. Fenske, J. Ohmer, J. Hachgenei, Angew.
Chem. 1985, 97, 993; Angew. Chem. Int. Ed. Engl. 1985, 24, 993; c) M.
Hong, Z. Huang, H. Liu, J. Chem. Soc. Chem. Commun. 1990, 1210.
12] V. E. Fedorov, M. R. J. Elsegood, S. S. Yarovoi, Y. V. Mironov, Chem.
Commun. 1998, 1861 ± 1862.
[
[
Compound 1 was prepared in high yield from silicon
tetrachloride (Scheme 1) as a colorless liquid, and character-
13] A. C. T. North, D. C. Phillips, F. S. Mathews, Acta Crystallogr. Sect. A
1968, 24, 351 ± 359.
1
13
29
ized by elemental analysis, IR and H, C, and Si NMR
spectroscopies, and mass spectrometry. It can be distilled
[
[
14] G. M. Sheldrick, Acta Crystallogr. Sect. A 1990, 46 ,467 ± 473.
15] G. M. Sheldrick, SHELXL97, Universität Göttingen, 1997.
Non-Oxide Sol ± Gel Chemistry: Preparation
from Tris(dialkylamino)silazanes of a
Carbon-Free, Porous, Silicon Diimide Gel
Riccardo Rovai, Christian W. Lehmann, and
John S. Bradley*
Sol ± gel chemistry plays an important role in the prepara-
tion and processing of oxide materials, including microporous
Scheme 1. Synthesis of 1 and 2 as well as the translucent gel of the
composition Si(NH)2�n[N(CH ) ] .
3 2 n
[
1, 2]
oxides and dense ceramics.
There are few examples of non-
and the only reported sol ± gel
[
3±5]
oxide sol ± gel techniques,
under atmospheric pressure without detectable decomposi-
preparation in silicon ± nitrogen chemistry is the synthesis of a
Si/C/N solid by the reaction of methyltrichlorosilane with
bistrimethylsilylcarbodiimide to form a nonporous gel in
which the structural framework contains only SiNCNSi
tion. Compound 1 is the simplest member of the series
(R
N)
Si(NH
)
(4�n) (R ˆMe, n ˆ3), and is one of very few
2
n
2
[18]
examples of a tris(amido)silylamine yet reported. We have
also prepared tris(morpholino)silylamine as a crystalline solid
analogue to 1. Details of the synthesis and structure of this
compound will be published separately.
[
6, 7]
units.
We are attempting to apply the chemistry of silicon
amide compounds to the development of a ªchimie douceº
methodology for carbon-free SiM(NH)x gels (M ˆSi or
metal), to give a sol ± gel route to non-oxide ceramics and
provide an alternative, mild synthetic route to nitridosili-
When 1 is heated in the presence of excess ammonia under
autogenous pressure (100 bar) at 1108C, a white powder is
[
19]
obtained, which is shown by IR spectroscopy to be Si(NH) .
2
[
8±10]
2
�1
cates.
Such gels would be the azo analogues of silica-based
The material is of low surface area (<50 m g ), and is
presumably identical to the powder prepared by Union
Carbide workers by the acid-catalyzed ammonolysis of
amorphous oxide gels, and the nitridosilicate analogue to
[11]
[
*] Prof. Dr. J. S. Bradley
(Me N) Si.
2
4
However, when 1, either neat or in THF, is
Department of Chemistry
University of Hull
Cottingham Road, Hull, HU6 7RX (UK)
E-mail: J.S.Bradley@chem.hull.ac.uk
treated at 508C with a catalytic amount of trifluoromethane-
sulfonic acid, self-transamination occurs with loss of dimethyl-
amine to give predominantly the cyclic trimer 2 (80%
according to MS, 61% after recrystallization; Scheme 1).
Compound 2 has been previously described as a product of
the reaction of (Cl SiNH) (a by-product (3% yield) of the
Dipl.-Chem. R. Rovai, Dr. C. W. Lehmann
Max-Planck-Institut für Kohlenforschung
Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr (Germany)
2
3
2
036
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Angew. Chem. Int. Ed. 1999, 38, No. 13/14

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reaction of ammonia with silicon tetrachloride) with dime-
thylamine, but neither its structure nor reaction chemistry
gelation conditions, and of variation of the alkyl substituent in
the tris(dialkyamido)siliylamine starting material, are under
investigation.
[
20, 21]
have been reported.
The molecular structure of 2 was
determined by X-ray diffraction (Figure 1). The compound is
The xerogel produced by drying under reduced pressure,
which has a Brunauer± Emmett ± Teller (BET) surface area of
about 1000 m g , contains residual dimethylamino groups, as
2
�1
shown by the presence of n(CH) bands in the IR spectrum of
�
1
the dried material. A low-intensity shoulder (3475 cm ) on
�
1
the principal n(NH) band (3362 cm ) and a low-intensity
�
1
band at 1551 cm in the IR spectrum of the dried gels are
assigned to the n(NH ) and d(NH ) bands of SiNH groups.
2
2
2
The presence of these bands suggests that the condensation
reaction was not yet complete by the time rigid gel formation
was observed. Thermogravimetric analysis in combination
�
1
with mass spectrometry (TGA/MS; argon stream, 58Cmin ,
5 ± 9008C) of the gels shows only loss of dimethylamine and
2
ammonia, which are expected to be eliminated as the
condensation reaction goes to completion. Treatment of the
gel under flowing ammonia at 508C for 15 h removes all
dimethylamino groups. The IR spectrum of the resulting solid
shows only n(NH), n(NH ), d(NH ), and Si�N absorbances,
2
2
and thus identifies the resulting white amorphous solid
2
�1
(
surface area 500 m g ) as a porous, carbon-free silicon
diimide gel containing terminal NH groups.
2
The imide chemistry described here is a direct analogue to
the hydrolytic sol ± gel chemistry of tetraalkylorthosilicates
for the preparation of silica gels, and represents the first
example of ammonolytic sol ± gel synthesis of a porous silicon
diimide gel. The chemistry of 1 is ammenable to the synthesis
of other single-source molecular precursors for non-oxide
gels, and in future papers we will report on the preparation of
Si ± Al, Si ± B and Si ± Ti compounds and imide gels derived
from them.
Figure 1. Crystal structure of 2. Selected bond lengths [nm] and angles [8]:
Si1�N1 0.1717(2), Si1�N2 0.1716(2), Si1�N7 0.1722(1), Si1�N9 0.1723(2),
Si2�N3 0.1736(2), Si2�N4 0.1718(2), Si2�N7 0.1718(2), Si2�N8 0.1715(2),
Si3�N5 0.1730(2), Si3�N6 0.1713(2), Si3�N8 0.1717(2), Si3�N9 0.1710(2),
N7�H7 0.091(2), N8�H8 0.073(2), N9�H9 0.081(2); N9-Si1-N7 106.2(1),
N8-Si2-N7 105.3(1), N9-Si3-N8 107.1(1), Si2-N7-H7 113.6(13), Si1-N7-H7
113.1(13), Si2-N8-H8 116.3(19), Si3-N8-H8 112.8(19), Si1-N9-H9 116.4(16),
Si3-N9-H9 112.8(16).
made up of a six-membered Si N ring in which each of the
Experimental Section
3
3
three Si atoms is bound to two exocyclic nitrogen atoms of
dimethylamino groups and two endocyclic NH groups to
1
: Anhydrous dimethylamine (45.3 g, 1.86 mol) was allowed to react with
silicon tetrachloride (45 g, 0.27 mol) in diethyl ether (1.5 L) at �408C over
15 h. The resulting dimethylammonium chloride was removed by filtration
and washed with diethyl ether (2 Â200 mL). The combined solutions of
provide an SiN environment. The mean deviation of Si and N
4
atoms from a plane through the six-membered ring is 0.105 Š.
The sums of the interatomic angles at the three endocyclic
nitrogen atoms are 360.08 (N7), 360.18 (N8), and 359.98 (N9),
which reflect the essential planarity of these nitrogen atoms.
When the mixture obtained by acid-catalyzed self-conden-
sation of 1 in THF is exposed to ammonia, gelation occurs
with further loss of dimethylamine to give a semirigid,
dimensionally stable, translucent gel. The intermediacy of 2
in the ammonolysis of 1 is demonstrated by rapid gel
formation on exposure to ammonia of a solution of pure 2
in THF containing 1 mol% of trifluoromethanesulfonic acid.
It seems that four equivalents of ammonia are needed to cause
rapid gelation, instead of the three equivalents which the
stoichiometry of the ammonolysis reaction would require.
When a gel obtained in this manner in a cylindrical glass
mould was dried slowly over a period of several days under an
atmosphere of argon that was constantly replaced, it shrunk
from the walls of the mould but retained its cylindrical form
before cracking after about 50% linear shrinkage. We have as
yet made no attempt to optimize the drying procedure to
obtain fully dried monoliths, and the effect of changes in
[(CH
3
)
2
N]
3
SiCl in diethyl ether were cooled to �508C, and anhydrous
liquid ammonia (70 g, 4.0 mol) was added in two aliquots. After 15 h the
precipitated ammonium chloride was removed by filtration at room
temperature, and the filtrate concentrated under reduced pressure to
provide 1 as a colorless liquid (99.2% purity according to GC/MS). Yield
35.1 g (0.20 mol, 74% based on SiCl ); b.p. 1868C (760 torr); elemental
4
analysis calcd: C 40.9, H 11.4, N 31.8, Si 15.9; found: C 40.8, H 10.9, N 31.8,
1
Si 15.8; H NMR (300 MHz, C
6
D
6
): d ˆ2.3 (s, 18H, Si[N(CH
); C NMR (75 MHz, C
): d ˆ37.89 (s, Si[N(CH
NMR (79.5 MHz,
): d ˆ�21.73 (s, Si[N(CH
3
)
2
]
3
), 0.3 (brs,
13
29
2
H, SiNH
2
6
D
6
3
)
2
]
3
); Si
NMR
15
C
6
D
6
3
]
2
)
3
);
N
(60.8 MHz, C D , external CH NO ): d ˆ�376.1 (NH ), �375.4
6
6
3
2
2
(N(CH
3
)
2
); IR (liquid film): nÄ ˆ3475 (w), 3406 (w; 2 Ân(NH
2
)), 2972 (s),
)); MS (EI): m/z (%):
�
1
2
1
835 (s), 2788 (s; 3 Ân(CH
3
)), 1552 cm (m) (d(NH
2
‡
‡
76 (100) [M ], 132 (90) [M �N(CH
3 2
) ].
2
. To a sample of 1 (2.5 g, 14.2 mmol) was added trifluoromethanesulfonic
acid (12 mL, 0.142 mmol, 1 mol%) under argon, and the mixture heated to
008C, resulting in evolution of gaseous dimethylamine. After about 4 h the
1
mixture was cooled to room temperature where it solidified to a colorless
crystalline mass. Extraction into pentane (5 mL) and cooling to �808C
gave colorless crystalline 2. Yield 1.1 g (61%). Elemental analysis calcd: C
1
3
6.6, H 9.90, N 32.0, Si 21.3; found: C 36.9, H 9.86, N 32.0, Si 21.3; H NMR
(
300 MHz, C
6
D
6
): d ˆ2.43 (s, 12H, Si[N(CH
NMR (75 MHz,
): d ˆ�31.5 (s, Si[N(CH
3
)
2
]
3
), 0.0 (brs, 3H, SiNH);
13
29
C
C
6
D
6
): d ˆ36.61 (s, Si[N(CH
3
)
2
]
2
); Si NMR
(79.5 MHz, C
6
D
6
3
)
2
]; IR (KBr): nÄ ˆ3392 (m),
Angew. Chem. Int. Ed. 1999, 38, No. 13/14
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2037

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(
1
n(NH)), 2971 (s), 2865 (s, sh), 2855 (s, sh), 2834 (s), 2786 (s; 5 Ân(CH
3
‡
)),
[15] M. Jansen, H.-P. Baldus, O. Wagner (Bayer AG), EP-A 502399A2,
�
1
‡
171 (s), 987 cm (s); MS (EI): m/z (%): 393 (20) [M ], 349 (20) [M �
1992.
‡
N(CH
3
)
2
], 303 (100) [M �2N(CH
3
)
2
].
[16] N. Percheneck, H.-P. Baldus, J. Löffelholtz, M. Jansen (Bayer AG),
EP-A 623643, 1994.
Crystal structure analysis of 2: Crystals of 2 were grown from pentane at
[17] R. G. Gordon, D. M. Hoffman, U. Riax, Chem. Mater. 1990, 2, 480.
�
408C, crystal dimensions 0.63 Â0.24 Â0.11 mm; l ˆ0.71073 Š; crystallo-
Å
[18] A referee has pointed out to us the previous preparation of
tris(trimethylsilylamido)silylamine: K. A. Andrianov, M. M. Ilꢁin,
V. N. Talanov, I. I. Zhuraskovskaya, Bull. Acad. Sci. USSR Div. Chem.
Sci. 1976, 25, 2432.
graphic data at 100 K: triclinic, space group P1 (no. 2); a ˆ832.83(17), b ˆ
1
1
0
069.0(2), c ˆ1408.3(3) pm; a ˆ69.62(3), b ˆ74.95(3), g ˆ69.41(3)8; Vˆ
3
�3
.0867(4) nm ; Z ˆ2;
1
calcd ˆ1.203 Mgm
;
F(000) ˆ432; m(MoKa) ˆ
�
1
.234 mm . Data were collected on a Bruker AXS SMART-CCD-System
[
[
19] J. Desmaison, D. Giraud, M. Billy, Rev. Chim. Miner. 1972, 9, 417.
20] U. Wannagat, P. Schmidt, M. Schulze, Angew. Chem. 1967, 79, 409;
Angew. Chem. Int. Ed. Engl. 1967, 6, 446.
with w scans. Of 13602 reflections collected (4.248 < 2q > 55.048), 4891
were independent (Rint ˆ0.0622). The structure was solved by direct
[
2
2
]
2
m
e
t
h
o
d
s
(
S
H
E
L
X
S
-
9
7
)
a
n
d
r
e
f
i
n
e
d
b
y
f
u
l
l
-
m
a
t
r
i
x
l
e
a
s
t
s
q
u
a
r
e
s
o
n
F
[21] U. Wannagat, M. Schulze, Inorg. Nucl. Chem. Lett. 1969, 5, 789.
using 241 parameters (R(F) ꢀ4s(F) ˆ0.0470, wR2 ˆ0.1328); max./min.
�
3
[22] a) G. M. Sheldrick, SHELXS-97, Program for the solution of crystal
residual electron density 0.728/ �0.571 eŠ
. Hydrogen atoms were
structures, Universität Göttingen, 1997; b) G. M. Sheldrick, SHELXL-
located from the difference Fourier map, all methyl hydrogen atoms were
constrained to idealized positions, and imido hydrogen atoms were refined
freely. Crystallographic data (excluding structure factors) for the structure
reported in this paper have been deposited with the Cambridge Crystallo-
graphic Data Centre as supplementary publication no. CCDC-112321.
Copies of the data can be obtained free of charge on application to CCDC,
9
7, Program for structure refinement, Universität Göttingen, 1997.
1
2 Union Road, Cambridge CB21EZ, UK (fax: (‡44)1223-336-033;
e-mail: deposit@ccdc.cam.ac.uk).
Silicon imide gel preparation by ammonolysis of 1 and 2: To a solution of 1
Solid Xenon: A Medium for Unusual
Photoreactions**
(
2.5 g, 14.2 mmol) in dry THF (100 mL) in a 250-mL round-bottomed glass
flask was added trifluoromethanesulfonic acid (12 mL, 0.14 mmol,
mol%). On warming to 508C evolution of gaseous dimethylamine was
observed. After 18 h analysis by IR and MS showed complete conversion of
into 2 (ca. 80%) and other unidentified by-products (ca. 20%). A
1
Günther Maier* and Christian Lautz
1
As is shown in this communication, a molecule isolated in a
xenon matrix at 10 K can react upon irradiation depending on
the conditions by four, in principle different mechanisms
solution of ammonia (42 mmol) in dry THF (40 mL) was added, and the
mixture was left quiescent at 508C for 18 h, at which point a slight
opalescence was observed. Addition of further ammonia (14 mmol)
resulted in rapid gelation to give, after several minutes, a translucent rigid
gel filling the original volume of the reaction mixture. Evaporation of the
solvent and dimethylamine in a stream of argon followed by drying under
reduced pressure at 508C for 10 h yielded a translucent white solid. IR
(Scheme 1). Of course, as in any other transparent medium a
(
2
9
KBr): nÄ ˆ3475 (w, sh; (n(NH
2
)), 3362 (m; n(NH)), 2973 (m), 2863 (m, sh),
857 (m, sh), 2835 (m), 2787 (m; n(CH )), 1551 (w; d(NH )), 1181 (s),
3
2
�
1
85 cm (s).
Received: December 17, 1998 [Z12793IE]
German version: Angew. Chem. 1999, 111, 2073 ± 2076
Keywords: ammonolysis ´ ceramics ´ nitrides ´ sol ± gel
processes
Scheme 1. Possible photoexcitations of a substrate molecule in a xenon
matrix.
substance absorbing in the wavelength region of the irradiat-
ing light can be induced to undergo a photoreaction also in a
[
1] Better Ceramics Through Chemistry, Vol. I and II (Eds.: C. J. Brinker,
D. E. Clark, D. R. Ulrich), Materials Research Society, Pittsburgh,
1984.
xenon matrix (S1 S0 absorption; direct route A ). For
1
[
[
[
2] C. J. Brinker, G. W. Scherer, Sol-Gel Science, Academic Press, San
Diego, 1990.
3] R. Riedel, E. Kroke, A. Greiner, A. O. Gabriel, L. Ruwisch, J.
Nicolich, P. Kroll, Chem. Mater. 1998, 10, 2964.
instance, matrix irradiation (l ˆ313 nm) of 2-diazo-2H-imi-
dazole in argon as well as in xenon leads to 2H-imidazol-2-
ylidene.[ In this case the special feature of xenon lies only in
its ability to stabilize the generated carbene by complex-
1]
4] C. K. Narula, R. T. Paine, R. Schaeffer, Mater. Res. Soc. Symp. Proc.
1986, 73, 383.
[1]
ation.
[
[
5] M. Siebold, C. Rüssel, Mater. Res. Soc. Symp. Proc. 1988, 121, 477.
6] A. O. Gabriel, R. Riedel, Angew. Chem. 1997, 109, 371; Angew. Chem.
Int. Ed. Engl. 1997, 34, 384.
Surprisingly, in a xenon matrix even those molecules are
accessible for photoreactions, which cannot absorb light at the
wavelength employed. This phenomenon can be observed
[
[
[
7] A. O. Gabriel, R. Riedel, S. Storck, W. F. Maier, Appl. Organomet.
Chem. 1997, 11, 833.
8] W. Schnick, Angew. Chem. 1993, 105, 846; Angew. Chem. Int. Ed.
Engl. 1993, 32, 806.
when the xenon matrix is doped with halogen atoms (indirect
[2]
route B ). Hereby the halogen atoms absorb the excitation
1
energy, which is stored in xenon halogen exciplexes, whose
9] T. Schlieper, W. Schnick, Z. Anorg. Allg. Chem. 1995, 621, 1037.
[
[
10] W. Schnick, H. Huppertz, Chem. Eur. J. 1997, 3, 679.
11] R. E. King; B. Kammer, P. Hopper, C. L. Schilling (Union Carbide
Corp.), US-A 4,675,424, 1987.
12] M. Jansen, J. Löffelholtz, Adv. Mater. 1992, 4, 746.
13] O. Wagner, M. Jansen, H.-P. Baldus, Z. Anorg. Allg. Chem. 1994, 620,
[
*] Prof. Dr. G. Maier, Dipl.-Chem. C. Lautz
Institut für Organische Chemie der Universität
Heinrich-Buff-Ring 58, D-35392 Giessen (Germany)
Fax: (‡49)641-99-34309
[
[
366.
[**] This work was supported by the Volkswagenstiftung, the Fonds der
Chemischen Industrie, and the Deutsche Forschungsgemeinschaft.
[
14] J. Hapke, G. Ziegler, Adv. Mater. 1995, 7, 380.
2
038
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1433-7851/99/3813-2038 $ 17.50+.50/0
Angew. Chem. Int. Ed. 1999, 38, No. 13/14