Formyl azide: Properties and solid-state structure

Article abstract of DOI:10.1002/anie.201209288

The simplest acyl azide, HC(O)N₃, has been prepared as the neat substance and characterized by IR and Raman spectroscopy and low-temperature X-ray crystallography (see solid-state structure; C white, H gray, N blue, O red). Photolysis of the azide in CO-doped solid noble-gas matrices furnished the first experimental proof of the elusive parent acyl isocyanate HC(O)NCO.

Full text of DOI:10.1002/anie.201209288

Angewandte
Chemie
DOI: 10.1002/anie.201209288
Covalent Azides
Formyl Azide: Properties and Solid-State Structure**
Xiaoqing Zeng,* Eduard Bernhardt, Helmut Beckers,* Klaus Banert, Manfred Hagedorn, and
Hailiang Liu
[
12]
Covalent azides are important reagents in chemistry, biology,
important small molecules, such as cyclo-N CO,
OPN/
2
[1]
[13]
[14]
medicine, and materials science. Owing to the explosive
nature of this class of compounds, some simple azides had not
been isolated as neat substances, although they have been
known to exist for a long time, and it took several decades to
fully disclose their structures and properties. For instance, the
ONP, and SPN/SNP/cyclo-PSN. By analogy, formyl azide
would be the ideal precursor of the elusive parent acyl nitrene
intermediate (HC(O)N), which has been extensively explored
by quantum-chemical calculations. As a continuation of our
work on covalent azides and their decomposition intermedi-
ates, we report herein on the properties of neat formyl azide,
its single-crystal structure, and also the interception of the
short-lived formyl nitrene.
[
15]
solid-state structure of the simplest covalent azide, HN ,
3
[
2]
which was first synthesized by Curtius in 1890, has only very
recently been reported by Klapçtke et al. The same is true
for the simple halogen azides ClN3, BrN3, and IN3, while
[
3]
[4]
[5]
[6]
For the synthesis of neat HC(O)N , the low-temperature
3
the molecular structure of highly explosive FN is up to now
reaction (ꢁ30 to ꢁ158C) of triformamide with hexadecyltri-
3
[7]
only available from a gas-phase microwave study.
Preparation and characterization of relatively unstable
butylphosphonium azide (QN ), which affords HC(O)N with
3
3
[
8a]
yields up to 50%, was chosen. Both solid precursors are
soluble in the high-boiling-solvent propylene carbonate,
which allows the separation of the highly volatile HC(O)N3
from the reaction mixture with an estimated yield of 40% at
[8]
azides, such as the parent acyl azide HC(O)N and alkynyl
3
[
9]
azide HCCN3, is particularly challenging. The simplest
member of the widely used acyl azides, namely formyl azide,
HC(O)N , has been the target of many computational
low temperatures. Solid HC(O)N sublimes at low temper-
3
3
[8]
studies. According to calculations, it may easily decompose
into HNCO through a concerted elimination of N2 and
Curtius rearrangement. This prediction was supported by
atures in vacuo, which allows its purification and transfer
without noticeable decomposition (see the Supporting Infor-
mation for details).
[
8a]
a recent experimental study
in which formyl azide was
Solid HC(O)N melts sharply at ꢁ50.58C to yield a color-
3
generated and its thermal decomposition in solution was
less liquid that could be frozen into the solid again without
studied. The activation barrier was found to be (20.3 ꢀ
incident. Thermal decomposition of gaseous HC(O)N into
3
ꢁ1
1
.1) kcalmol , and the half-life in CDCl at room temper-
HNCO and N was monitored by IR spectroscopy. Similar to
3
2
ature was found to be merely 20 min.
We have been interested in the synthesis, structure, and
decomposition reactions of covalent azides, and a number of
the observations in solution, the decomposition follows a first-
order rate kinetics (Supporting Information, Figures S1,S2),
ꢁ
5
ꢁ1
but with a much slower rate (25.58C, k = 8.80 ꢀ 10 s , t
=
/2
1
[10]
ꢁ4 ꢁ1
highly explosive azides, such as OC(N ) ,
OP(N ) , and
2.2 h) than that observed in CDCl (258C, k = 5.96 ꢀ 10 s ,
3
2
3
3
3
[
11]
[8a]
SP(N ) ,
have been isolated as neat substances and
t1/2 = 20 min).
However, as the decomposition of formyl
3
3
structurally characterized. The decomposition of these
azides provides unique approaches to some fundamentally
azide was found to be slower in non-polar solvents such as
cyclohexane, the smaller rate of this reaction in the gas phase
is not surprising.
IR and Raman spectra of HC(O)N are shown in Figure 1.
3
[
+]
[
*] Dr. X. Zeng, Dr. E. Bernhardt, Dr. H. Beckers
FB C—Anorganische Chemie, Bergische Universitꢀt Wuppertal
Gaussstrasse 20, 42119 Wuppertal (Germany)
E-mail: zeng@uni-wuppertal.de
The observed vibrational frequencies agree well with calcu-
lated anharmonic values using the CCSD(T)-F12a method
[8a]
(
Table 1).
Assignments of the spectra are supported by
beckers@uni-wuppertal.de
a higher-resolved IR spectrum (Supporting Information,
1
4/15
Figures S3,S4) and
tion, Table S1).
N isotopic shifts (Supporting Informa-
Prof. Dr. K. Banert, Dr. M. Hagedorn, H. Liu
Technische Universitꢀt Chemnitz, Organische Chemie
Strasse der Nationen 62, 09111 Chemnitz (Germany)
Carbonyl azides can, in principle, exist as a mixture of two
close-in-energy conformers by adopting syn or anti config-
uration of the C=O and N groups with respect to the CꢁN
+
[
] Permanent address: College of Chemistry
Chemical Engineering and Materials Science
Soochow University, 215123 Suzhou (China)
3
a
bond. Theoretical calculations suggest the dominance of a syn
[
**] This work was supported by the Deutsche Forschungsgemeinschaft
conformation for HC(O)N , and the anti conformer has
3
(
WI 663/26-1, BA 903/12-3). We gratefully acknowledge Prof. H.
a contribution of a few percent (Supporting Information,
Willner (Universitꢀt Wuppertal) for generously supporting this work
and helpful discussions, and Prof. G. Rauhut (Universitꢀt Stuttgart)
for sharing the full set of anharmonic frequencies for HC(O)N3
calculated with the CCSD(T)-F12a method.
Table S2). The latter can be distinguished from syn by
ꢁ
1
a higher C=O stretching frequency of 46 cm (Supporting
Information, Table S3). Indeed, a very weak shoulder
ꢁ
1
appeared at 1764 cm
1717 cm
beside the strong band (n ) at
3
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201209288.
ꢁ
1
in the IR spectrum of the gaseous sample
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1
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The Raman spectrum of solid HC(O)N3 is shown in
Figure 1. In the C=O stretching region, only one strong band
ꢁ1
appears red-shifted by ꢁ43 cm from the corresponding gas-
ꢁ1
phase IR band (1717 cm ). In contrast, the CꢁH stretch is
ꢁ1
blue-shifted by +27 cm . These shifts clearly indicate the
existence of so-called improper hydrogen bonds in the solid
[
16]
state.
The IR spectrum of HC(O)N isolated in an Ar
3
matrix was also measured (Figure 1), and only one band for
the C=O stretch of syn HC(O)N was observed.
3
Crystallization of HC(O)N was performed in a similar
3
[10]
way to that of OC(N3)2 by slow sublimation of a small solid
sample inside a glass tube (o.d. 6 mm, length 15 cm) at ꢁ788C.
However, handling of HC(O)N3 crystals is challenging
because of the low melting point (ꢁ50.58C) and the risk of
explosion caused by pressure variations (for details, see the
Supporting Information).
Figure 1. Upper trace: IR spectrum (absorbance A, resolution
ꢁ1
0
.25 cm ) of Ar-matrix-isolated HC(O)N at 16 K. Middle trace: IR
3
Formyl azide crystallizes in a monoclinic space group (Pc)
ꢁ1
spectrum (transmittance T, resolution 2 cm ) of gaseous HC(O)N at
[17]
3
with four molecules in the unit cell,
and there are two
2
2
98 K. Bottom trace: Raman spectrum (Raman intensity I, resolution
ꢁ
1
crystallographically nonequivalent molecules (I and II,
Figure 2) with essentially identical (within standard devia-
tion) molecular parameters (Supporting Information,
Table S4). They form coplanar pairs linked by CꢁH
(II)···O=C (I) bonds of 2.46 ꢁ, while these pairs are further
cm ) of solid HC(O)N at 77 K.
3
(
Supporting Information, Figure S5). When this weak feature
is taken as evidence for the presence of the anti conformer, its
relative abundance can be estimated based on calculated and
observed IR intensities for these two bands to be less than
linked to infinite zigzag chains through slightly shorter
(2.43 ꢁ) CꢁH (I)···O=C (II) interactions (Supporting Infor-
[
8a]
2
%. In fact, in the IR spectrum of HC(O)N in CCl , an
mation, Figure S6). The shorter H···O contact (2.43 ꢁ)
3
4
ꢁ1
unassigned weak band (1734 cm ) also occurred beside the
strong band of syn HC(O)N (n , 1699 cm ). It is likely to be
corresponds to
a
heavy-atom CꢁH···O distance of
ꢁ
1
3.241(2) ꢁ along with an angle of 143.3(1)8, whereas the
longer H···O contact of 2.46 ꢁ correlates to a CꢁH···O
3
3
associated with the anti conformer, and its estimated abun-
dance is about 10%.
distance of 3.321(2) ꢁ and an angle of 150.6(1)8. Similar
ꢁ1
Table 1: Experimental and calculated vibrational frequencies [cm ] of HC(O)N3.
[
a]
[e]
[f]
Experiment
Calculated
Assignment
IR
Raman
Solid
77 K
[
b]
[d]
CCl4
98 K
Gas phase
Ar matrix
16 K
CCSD(T)
[
c]
2
298 K
D(PR)
3
3
3
423 vvw
301 vvw
093 vvw
3402 vvw
3416 (4)
3302 (1)
3095 (3)
2938 (52)
2288 (29)
2172 (192)
2087 (15)
1887 (8)
1718 (258)
1360 (<1)
1332 (4)
1175 (163)
1151 (357)
993 (<1)
947 (101)
844 (9)
2n (A’)
3
n +n (A’)
2
5
3098.5 vw
2939.9 w
2282.3 w
2159.7 vs
2079.2 w
1875.4 w
1708.1 s
3067 m
2964 s
2267 vw
2172 s
n +n (A’)
3 4
2
932 w
2937 w
288 w
2164 vs
17
16
n , CꢁH stretch (A’)
1
2
2n (A’)
5
2
1
152 s
699 s
n , out-of-phase NꢁN stretches (A’)
2
2
1
085 w, sh
883 w
n +n (A’)
5
6
2n (A’)
6
1717 s
17
1674 s
1374 ms
n3, C=O stretch (A’)
n4, in-plane HCO bend (A’)
n +n (A’)
1
370.1 vvw
1323 vw
1322 vvw
1173.1 s
1149.1 vs
5
9
1
1
169 s
146 s
1174 s, sh
1151 vs
20
17
1171 w
1142 vw
2n11 (A’)
n , in-phase NꢁN stretches (A’)
5
1006 vw
n , CꢁH out-of-plane bend (A’’)
1
0
9
42 m
27 w
945 ms
17
16
941.3 s
842 vw
824.6 m
581.4 w
956 vs
n , CꢁN stretch (A’)
6
8
47 w, sh
820 m
82 vw
n +n (A’)
11 12
8
831 s
581 vw
829 (42)
584 (8)
n7, in-plane OCN bend (A’)
n , out-of-plane N bend (A“)
5
1
1
3
496 m
286 w
190 s
491 (<1)
251 (14)
171 (<1)
n , in-plane N bend (A’)
8
3
n , torsion (A’’)
1
2
n9, in-plane CNN bend (A’)
[
a] Observed band positions and relative intensities: vs=very strong, s=strong, ms=medium strong, w=weak, vw=very weak, vvw=very very
ꢁ1
weak. [b] In CCl solution; see Ref. [8a]. [c] P, R separation in cm . [d] Most intense matrix site. [e] Calculated anharmonic frequencies and IR
intensities (kmmol , in parenthesis) using the CCSD(T)-F12a method. [f] Tentative assignments for the vibration modes of the syn conformer
4
ꢁ
1
according to calculated displacement vectors.
2
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Angewandte
Chemie
[8a]
a broad UV absorption at lmax = 233 nm. Photolysis of the
azide isolated in an Ar matrix at 16 K using UV irradiation of
either 193 or 255 nm solely furnished HNCO (Supporting
Information, Figure S7). The failure to detect HC(O)N in the
photolysis products might be consistent with the preference of
[8a]
a concerted decomposition mechanism for HC(O)N3.
However, the possible formation of the singlet nitrene with
subsequent Curtius rearrangement under the photolysis
conditions cannot be ruled out. Thus a conventional nitrene
trapping experiment with CO was performed by irradiating
Figure 2. Packing of HC(O)N molecules (I and II) in the unit cell.
Short intermolecular H···O distances are indicated by dashed lines and
their distances in [ꢁ].
3
(
l = 255 nm) HC(O)N in a CO-doped Ar matrix (azide/CO/
3
Ar= 1:50:500). Along with the IR bands of HNCO, another
ꢁ1
set of new bands at 2248, 1733, 1425, and 963 cm was
1
4/15
CꢁH···O hydrogen bonds were also found in solid formalde-
obtained (Supporting Information, Figure S8). Their
N
[
18]
12/13
hyde (3.246(1) and 3.321(2) ꢁ).
The presence of these
and C isotopic shifts have been determined in experiments
using a N-labeled sample (Supporting Information, Fig-
1
5
hydrogen bonds is also supported by aforementioned spec-
troscopic results.
1
3
ure S9) and a CO-doped Ar matrix, respectively (Support-
ing Information, Table S5). The collected IR data of the
photoproduct strongly suggest the formation of formyl
isocyanate, HC(O)NCO. Surprisingly, calculated IR frequen-
cies and their relative intensities show better agreement for
the higher-energy anti conformer (Supporting Information,
Tables S5–S7). The relative amounts of HNCO and
HC(O)NCO produced by photolysis of HC(O)N3 in the
CO-doped Ar matrix was roughly estimated from the
observed and calculated intensities of the IR bands for
these two species (Supporting Information, Table S8), and it
appears that both were formed in nearly equal amounts.
Taking into account the preference of a concerted decom-
The HC(O)N molecule in the solid state adopts an almost
3
planar syn conformation (Figure 3), and the dihedral angles
OCN N and CN N N are 1.3 and 178.88, respectively. Its
a
b
a
b
g
molecular structure is comparable to those of related covalent
position pathway for HC(O)N , the formation of HC(O)NCO
3
from photolysis of the azide in the presence of CO is
Figure 3. Solid-state structures of HC(O)N (molecule I). Ellipsoids are
set at 50% probability. Bond lengths are given in [ꢁ]; angles are given
in the Supporting Information, Table S4.
3
[
8a]
intriguing. According to the calculations,
the transition
ꢁ1
state for the concerted decomposition is 6.5 kcalmol lower
in energy than that for the formation of the nitrene. This small
energy difference implies that both processes could occur
when a large excess of energy is applied to the azide, such as
UV light irradiation (l = 193 or 255 nm). This reasoning may
explain the formation of both HNCO and HC(O)NCO by UV
photolysis of CO matrix-isolated azide. The stereoselective
formation of the higher-energy anti HC(O)NCO can be
explained by considering the molecular structure of the
singlet nitrene HC(O)N intermediate. A planar cyclic struc-
ture with a significantly smaller OCN angle (88.08) in the
singlet than that in the triplet (121.08) was calculated for
[
10]
[3]
azides OC(N3)2
(
and HN3 in the solid state. The CꢁO
1.204(2) ꢁ) and the CꢁN (1.418(2) ꢁ) bond lengths in
HC(O)N3 are (within the standard deviations) similar to
those in OC(N3)2 (CꢁO 1.200(6) ꢁ, CꢁN 1.412(7) and
1
.407(8) ꢁ), while the OCN angle (125.21(16)8) is slightly
smaller than that of OC(N ) (127.2(5)8), which is probably
3
2
due to the lower spatial requirement of the hydrogen atom
compared to that of a second N group. The N ꢁN bond
3
a
b
lengths are also similar in the carbonyl azides HC(O)N3
+
+
(
1.256(2) ꢁ) and OC(N3)2 (1.265(7) and 1.274(7) ꢁ), but
HC(O)N (B3LYP/6-311 G(3df, 3pd)). Similar results were
also found for other singlet nitrenes, and attributed to an
longer than that of HN (1.233(5) ꢁ), while the N ꢁN bond
3
b
g
[
15a,19]
lengths in HC(O)N3 (1.121(2) ꢁ), HN3 (1.121(5) ꢁ) and
OC(N ) (1.111(6) and 1.111(7) ꢁ) show much less variations.
intramolecular O!N interaction.
Thus, nucleophilic
attack of CO to the nitrene center is expected to occur from
3
2
On the other side, the N N N angle in HC(O)N3
the opposite side of this supposed NꢁO interaction, that is, the
a
b
g
(
174.49(17)8) is slightly larger than those in HN (172.8(2)8)
anti position with respect to the carbonyl oxygen.
3
and OC(N ) (172.1(5)8, 172.6(6)8).
The intervention of formyl nitrene during the photo-
3
2
According to recent ab initio calculations, formyl nitrene
is one of the rare nitrenes that has a singlet ground state with
decomposition of HC(O)N is also supported by the forma-
3
tion of traces of either N-(1,1-dimethylpropyl)formamide or
N-cyclopentylformamide during its photolysis in 2-methylbu-
tane or cyclopentane solutions. These formamides can be
regarded as trapping products of HC(O)N by insertion into
CꢁH bonds of the solvents (Supporting Information, Figur-
ꢁ1
a rather small singlet–triplet gap (DE = ꢁ0.13 kcalmol ,
S-T
[
15a]
CCSD(T)/cc-pVQZ);
however, such a small DE implies
S-T
that the ground state multiplicity of formyl nitrene can hardly
be assured using theoretical calculations. This precarious
situation encouraged us to study the photolysis of HC(O)N3
isolated in solid noble gas matrices. Formyl azide exhibits
es S10–S12).
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3
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.
Angewandte
Communications
In summary, the unstable parent acyl azide HC(O)N has
[7] D. Christen, H. G. Mack, G. Schatte, H. Willner, J. Am. Chem.
Soc. 1988, 110, 707 – 712.
3
been isolated as a neat substance and structurally character-
ized. While solely the lower-energy syn conformer was
observed in cryogenic Ar matrices and in the solid state,
traces of the anti conformer (< 2%) were detected in the gas
phase. In the solid state, the molecules are linked by two
different types of intermolecular CꢁH···O=C hydrogen bonds.
[
8] For examples, see: a) K. Banert, C. Berndt, M. Hagedorn, H.
Liu, T. Anacker, J. Friedrich, G. Rauhut, Angew. Chem. 2012,
1
24, 4796 – 4800; Angew. Chem. Int. Ed. 2012, 51, 4718 – 4721;
b) R. Kakkar, S. Zaidi, R. Grover, Int. J. Quantum Chem. 2009,
09, 1058 – 1069; c) G. O. Jones, K. N. Houk, J. Org. Chem. 2008,
1
73, 1333 – 1342; d) C. Wentrup, H. Bornemann, Eur. J. Org.
Chem. 2005, 4521 – 4524; e) S. A. Glover, A. Rauk, J. Chem. Soc.
Perkin Trans. 2 2002, 1740 – 1746; f) H. M. Badawi, J. Mol.
Struct.: THEOCHEM 2002, 583, 89 – 97.
UV photodecomposition of HC(O)N in a CO-doped Ar
3
matrix yields, along with HNCO, the parent acyl isocyanate
HC(O)NCO in an anti conformation. The stereoselective
formation of anti HC(O)NCO with CO was rationalized by
capturing elusive singlet HC(O)N and by considering a planar
cyclic structure for this nitrene that is due to intramolecular
O!N interaction.
[
9] a) K. Banert, R. Arnold, M. Hagedorn, P. Thoss, A. A. Auer,
Angew. Chem. 2012, 124, 7633 – 7636; Angew. Chem. Int. Ed.
2012, 51, 7515 – 7518; b) N. Jung, S. Brꢂse, Angew. Chem. 2012,
124, 12335 – 12337; Angew. Chem. Int. Ed. 2012, 51, 12169 –
12171.
[
[
[
10] X. Q. Zeng, M. Gerken, H. Beckers, H. Willner, Inorg. Chem.
010, 49, 9694 – 9699.
11] X. Q. Zeng, E. Bernhardt, H. Beckers, H. Willner, Inorg. Chem.
011, 50, 11235 – 11241.
2
Received: November 20, 2012
Revised: December 18, 2012
Published online: && &&, &&&&
2
12] a) X. Q. Zeng, H. Beckers, H. Willner, J. F. Stanton, Angew.
Chem. 2011, 123, 1758 – 1761; Angew. Chem. Int. Ed. 2011, 50,
1720 – 1723; b) X. Q. Zeng, H. Beckers, H. Willner, J. F. Stanton,
Eur. J. Inorg. Chem. 2012, 3403 – 3409.
Keywords: azides · formyl azide · matrix isolation ·
reactive intermediates · solid-state structures
.
[
13] X. Q. Zeng, H. Beckers, H. Willner, J. Am. Chem. Soc. 2011, 133,
20696 – 20699.
[
1] See, for example: a) Organic Azides: Syntheses and Applications
Eds.: S. Brꢂse, K. Banert), Wiley, Chichester, 2010; b) M. S.
[
14] X. Q. Zeng, H. Beckers, H. Willner, J. S. Francisco, Angew.
Chem. 2012, 124, 3390 – 3395; Angew. Chem. Int. Ed. 2012, 51,
(
Platz in Reactive Intermediates (Eds.: R. A. Moss, M. S. Platz,
M. J. Jones), Wiley-Interscience, 2004, p. 501; c) E. F. V. Scriven,
Azides and Nitrenes; Reactivity and Utility, Academic Press, New
York, 1984; d) S. Brꢂse, C. Gil, K. Knepper, V. Zimmermann,
Angew. Chem. 2005, 117, 5320 – 5374; Angew. Chem. Int. Ed.
3
334 – 3339.
[
15] For examples, see: a) E. A. Pritchina, N. P. Gritsan, A. Maltsev,
T. Bally, T. Autrey, Y. Liu, Y. Wang, J. P. Toscano, Phys. Chem.
Chem. Phys. 2003, 5, 1010 – 1018; b) S. A. Stoffregen, R. D.
McCulla, R. Wilson, S. Cercone, J. Miller, W. S. Jenks, J. Org.
Chem. 2007, 72, 8235 – 8242; c) D. A. Pantazis, A. C. Tsipis, C. A.
Tsipis, J. Phys. Chem. A 2002, 106, 1425 – 1440.
2005, 44, 5188 – 5240; e) C. Knapp, J. Passmore, Angew. Chem.
2004, 116, 4938 – 4941; Angew. Chem. Int. Ed. 2004, 43, 4834 –
4836; f) T. M. Klapçtke, Chem. Ber. 1997, 130, 443 – 452; g) I. C.
[
[
16] J. Joseph, E. D. Jemmis, J. Am. Chem. Soc. 2007, 129, 4620 – 4632.
17] Crystal structure analysis of HC(O)N (for details of measure-
Tornieporth-Oetting, T. M. Klapçtke, Angew. Chem. 1995, 107,
59 – 568; Angew. Chem. Int. Ed. Engl. 1995, 34, 511 – 520.
3
5
ments and structure solutions, see the Supporting Information):
[
[
2] T. Curtius, Ber. Dtsch. Chem. Ges. 1890, 23, 3023 – 3033.
3] J. Evers, M. Gçel, B. Krumm, F. Martin, S. Medvedyev, G.
Oehlinger, F. X. Steemann, I. Troyan, T. M. Klapçtke, M. I.
Eremets, J. Am. Chem. Soc. 2011, 133, 12100 – 12105.
4] a) R. L. Cook, M. C. Gerry, J. Chem. Phys. 1970, 53, 2525 – 2528;
b) B. Lyhs, D. Blꢂser, C. Wçlper, S. Schulz, G. Jansen, Angew.
Chem. 2012, 124, 13031 – 13035; Angew. Chem. Int. Ed. 2012, 51,
HC(O)N , Mo-Ka radiation (l = 0.71073 ꢁ), sample temper-
ature 150(2) K, colorless crystal (0.05 ꢀ 0.30 ꢀ 1.24 mm ), mono-
3
3
clinic, space group Pc (No. 7), a = 11.890(3), b = 3.6943(14), c =
3
ꢁ3
7
(
.004(4) ꢁ, V= 299.35(3) ꢁ , Z = 4, 1calcd = 1.576 gcm
,
m-
[
ꢁ1
MoKa) = 0.138 mm , F(000) = 144, 5524 measured, 2004 inde-
pendent reflections [Rint = 0.0464, R = 0.0382], thereof 1775
s
with I > 2s(I) (3.54 < q < 32.87), completeness 99.9% (to q =
12859 – 12863, and references therein.
2
3
0.58, d = 0.7 ꢁ). Refinement of the structure based on F with
[
5] a) M. Hargittai, I. C. Tornieporth-Oetting, T. M. Klapçtke, M.
Kolonits, I. Hargittai, Angew. Chem. 1993, 105, 773 – 774; Angew.
Chem. Int. Ed. Engl. 1993, 32, 759 – 761; b) B. Lyhs, D. Blꢂser, C.
Wçlper, S. Schulz, G. Jansen, Angew. Chem. 2012, 124, 2008 –
2004 independent reflections, 91 variables, and 2 restraints. All
non-hydrogen atoms were refined anisotropically. R1 = 0.0441
2
(
I > 2s(I)), Goodness-of-fit on F 1.023. CCDC 909289 contains
the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
2013; Angew. Chem. Int. Ed. 2012, 51, 1970 – 1974, and
references therein.
[
6] a) P. Buzek, T. M. Klapçtke, P. v. R. Schleyer, I. C. Tornieporth-
Oetting, P. S. White, Angew. Chem. 1993, 105, 289 – 290; Angew.
Chem. Int. Ed. Engl. 1993, 32, 275 – 277; b) M. Hargittai, J.
Molnar, T. M. Klapçtke, I. C. Tornieporth-Oetting, M. Kolonits,
I. Hargittai, J. Phys. Chem. 1994, 98, 10095 – 10097; c) H. O.
Munz, H. K. Bodenseh, M. Ferner, J. Mol. Struct. 2004, 695 – 696,
[
[
18] T. S. Thakur, M. T. Kirchner, D. Blꢂser, R. Boese, G. R. Desiraju,
Phys. Chem. Chem. Phys. 2011, 13, 14076 – 14091.
19] For a very recent example, see: S. Vyas, J. Kubicki, H. L. Luk, Y.
Zhang, N. P. Gritsan, C. M. Hadad, M. S. Platz, J. Phys. Org.
Chem. 2012, 25, 693 – 703, and references therein.
189 – 202.
4
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ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2013, 52, 1 – 5
These are not the final page numbers!

Angewandte
Chemie
Communications
Covalent Azides
The simplest acyl azide, HC(O)N , has
3
been prepared as neat substance and
X. Zeng,* E. Bernhardt, H. Beckers,*
K. Banert, M. Hagedorn,
characterized by IR and Raman spectros-
copy and low-temperature X-ray crystal-
lography (see solid-state structure;
C white, H gray, N blue, O red). Photol-
ysis of the azide in CO-doped solid noble-
gas matrices furnished the first experi-
mental proof of the elusive parent acyl
isocyanate HC(O)NCO.
H. Liu
&&&& — &&&&
Formyl Azide: Properties and Solid-State
Structure
Angew. Chem. Int. Ed. 2013, 52, 1 – 5
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!