Angewandte
Chemie
DOI: 10.1002/anie.201001826
Silicon Azides
Neutral Lewis Base Adducts of Silicon Tetraazide**
Peter Portius,* Alexander C. Filippou,* Gregor Schnakenburg, Martin Davis, and
Klaus-Dieter Wehrstedt
[1]
The field of binary main-group element azides has enjoyed a
renaissance in the last decade, leading to many fascinating
[
2]
compounds. Binary azides of Group 14 elements are a class
of rare, highly endothermic compounds. Their isolation and
handling poses considerable challenges to experimentalists
due to the combination of high energy content, excessive
[3]
sensitivity and thermal lability. Therefore, it is not surprising
[
4]
that to date only the primary explosive a-Pb(N ) and the
3
2
+
[5]
2À
3 6
[3,6,7]
ions [C(N ) ]
and [E(N ) ] (E = Si–Pb)
have been
3
3
Scheme 1. Syntheses and reactions of Si(N ) and its Lewis base
adducts. For an alternative synthesis of compound 4, see Ref. [6].
structurally characterized. Recently, the extremely hazardous
compound C(N ) was isolated in tiny amounts and trans-
3 4
3
4
[
8]
formed into various organic products. Si(N3)4 has been
reported to be a violently explosive substance, which could
[9]
not be obtained in pure form. Experimental evidence for the
appear at the same positions as those reported for
[
10]
+
+
[6]
presence of pure Ge(N3)4 is lacking,
and Sn(N3)4 and
(PPN) [Si(N ) ] (4; PPN = N(PPh ) ).
Compound 1
2
3
6
3 2
Pb(N3)4 are presently not known. Nitrogen-rich silicon
compounds are of special interest due to their potential as a
viable replacement for lead azide to avoid its deleterious
forms colorless solutions in acetonitrile that are sensitive to
hydrolysis but can be stored for several weeks under exclusion
of air at À288C and used as stock for the syntheses of
derivatives of Si(N ) . Treatment of 1 with a slight excess of
[
11]
environmental impact and as precursors for new materi-
3
4
[
12]
als. Herein we present the large-scale synthesis and full
characterization of conveniently accessible, thermally stable,
and highly energetic Lewis base adducts of Si(N ) , and the
the Lewis bases 2,2’-bipyridine (bpy) and 1,10-phenanthroline
(phen) afforded, after precipitation of NaN , exclusively the
3
Lewis base adducts [Si(N ) (bpy)] (2) and [Si(N ) (phen)] (3),
3
4
3
4
3 4
safe synthesis and handling of solutions of pure Si(N ) .
respectively (Scheme 1). After work-up and recrystallization
from acetonitrile, compound 2 and the MeCN hemisolvate of
3 were isolated as colorless, analytically pure needles in 57–
3
4
Addition of SiCl to a suspension of 7.3 equiv of NaN in
4
3
acetonitrile at room temperature afforded selectively the
[
13]
disodium salt of hexaazidosilicate (1; Scheme 1). Evidence
for the formation of 1 was provided by its selective chemical
functionalization (see below) and the solution IR spectra,
which displayed one strong n (N ) absorption band at
60% yields (from SiCl ). No explosions occurred during the
4
repeated preparations of 2 and 3·0.5MeCN, which can be
scaled-up to several grams of the desired compound. Both
compounds are not sensitive to friction and are moderately
soluble in CH Cl , THF, and MeCN. Although solutions of 2
asym
3
À1
À1
2
1
109 cm
and one weak nsym(N ) absorption band at
3
317 cm after completion of the reaction. Both bands
2
2
and 3·0.5MeCN are rapidly hydrolyzed, releasing HN and
3
the Lewis bases (bpy or phen), the crystalline compounds can
be stored and handled safely at ambient temperature under
dry air. Under vacuum, compound 2 melts at 2128C, whereas
[
*] Dr. P. Portius, Dr. M. Davis
Department of Chemistry, The University of Sheffield
Brook Hill, Sheffield, S3 7HF (UK)
Fax: (+44)114-222-9346
[14]
3
decomposes upon melting at 2158C.
The remarkable
thermal stability of 2 and 3·0.5MeCN is surprising in view of
E-mail: p.portius@sheffield.ac.uk
their reactive nitrogen contents of 44–48% and the extreme
sensitiveness of Si(N ) . The thermochemical properties of 2
Prof. Dr. A. C. Filippou, Dr. G. Schnakenburg
Institut fꢀr Anorganische Chemie, Universitꢁt Bonn
Gerhard-Domagk-Strasse 1, 53121 Bonn (Germany)
Fax: (+49)228-735-327
3 4
and 3·0.5MeCN were studied in more detail by differential
scanning calorimetry (DSC) and compared with those of the
analogous germanium compounds [Ge(N ) (bpy)] (2a) and
3
4
E-mail: filippou@uni-bonn.de
[13]
[
Ge(N ) (phen)]·0.5MeCN (3a·0.5MeCN). Representative
3 4
Prof. Dr. K.-D. Wehrstedt
BAM Bundesanstalt fꢀr Materialforschung und -prꢀfung
Division II.2
thermograms of 2 and 3·0.5MeCN are depicted in Figure 1.
The thermogram of 2 reveals that melting at the extrapolated
ex
on
onset temperature T = 2118C (endothermic peak temper-
Unter den Eichen 87, 12205 Berlin (Germany)
endo
À1
ature Tp = 2128C, DH = + 110 Jg ) is followed by a
m
[
**] We thank the Deutsche Forschungsgemeinschaft SFB 813 (A.C.F.),
ex
distinct decomposition process, which begins at T = 2658C
(Tp = 2948C), and liberates a large heat of decomposition
the EPSRC (fellowship to P.P.), and the Humboldt-Universitꢁt zu
Berlin for financial support.
on
exo
À1
(
DH = À2.4 kJg ). The germanium analogue 2a shows a
d
[13]
similar behavior.
In comparison, compound 3·0.5MeCN
Angew. Chem. Int. Ed. 2010, 49, 8013 –8016
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
8013