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Isolation of Tetrazene N4H4.

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The resultsdescribed here indicate that measurement of optical
activity on oriented systems yields not only information about
absolute configurations but also provides further structural
P
[7] Owing to theorientation with an electrical field. the phase has a symmetry
axis in the direction of the field (optical axis of system). Measurement
perpendicular to the optical axis is impossible at present because the linear
dichroism is very large. O n filling the cells care should be taken that no
additional linear dichroism arises at the cell windows.
[ 8 ] C . Djrrusci. R . Rinikrr. and B. Rinikur. J . Amer. Chem. S O C . 78. 6377
(1956);H . Z i f e r and C . H . Robinson, Tetrahedron 14, 5803 119681.
01
Isolation of Tetrazene, N&[ll
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By Nils Wiberg, Heiner Bayer, and Heinz Bachhubrr[']
The only hydrogen compounds of nitrogen that have previously been unambiguously characterized are ammonia
(NH,), hydrazine (N2H4), diimine (N2H2)"' and hydrogen
azide (N3H). We have now succeeded in preparing a further
nitrogen hydride, namely tetrazene (N4H4). which, unlike the
previously known compoundscontaininga one-, two- or threemembered nitrogen chain, is based on a skeleton of four
nitrogen atoms.
For synthesis of this compound, tetrakis(trimethylsily1)tetrazenel4]which is readily accessible by acid-catalyzed dimerization of bi~(trimethylsilyl)diimine[~~
is treated with trifluoroacetic acid in methylene dichloride at -78°C. The tetrazene,
being only sparingly soluble in methylene dichloride, is thus
precipitated as a colorless solid; it can be purified by sublimation.
A C
(Me3Si)2N-N=N-N(SibIe,)2
10
+ 1 v3<'-rool~
- P,t-roosi,~HzN-N=N-NH2
E
30
05
15
Fig. 2. 3 P-Acetoxy-5-cholesten-7-one
(Z), dissolved in cholesteryl chloridejcholesteryl laurate (cf. text and legend to Fig. 1).
information, e. g. regarding the arrangement of the chromophore relative to the molecular axis. Theoretical evaluation
and the consequences of applying the sector rules, eft., will
be reported later.
The following facts indicate that the nitrogen hydride isolated
has the structure ofa trans-Ztetrazene: 1 . Quantitative analysis
of the thermolysis products (see below) yields a nitrogenbydrogen ratio of 1 :1, i. e. the nitrogen hydride has the molecular
formula (NH),.-2. The mass spectrum obtained for the isolated compound at an ionization energy of 70eV in the gas
phase at 5 x lo-' torr shows the molecular ion N4H; as an
intense line at m/e=60. If the ionization energy is lowered
from 70 to IOeV, then, as expected, the mass groups of ionic
fragments N,H; with one, two or three nitrogen atoms disappear almost completely and there remains only the signal
of the molecular ion. Thus x in the molecular formula (NH)x
that follows from the analytical investigations must be replaced
by the number 4.-3. By germylation with N,N-diethyl(trimethylgermy1)amine the nitrogen hydride N4H4 can be converted by the reaction (E = Ge)
Received: September 16, 1974 [Z 140 IE]
German version: Angew. Chem. 87, 2M) (1975)
CAS Registry numbers:
( I ) , 601-51-0: (Z), 809-51-8
[I] 1. Tinoco, J r . and W G . Hammerle, J. Phys. Chem. 60, 1619 (1956):
N . Go,J. Chem. Phys. 43, 1275 (1965);J. Phys. SOC. Jap. 23, 88, 1094 (1967);
Y N . Chiu, J . Chem. Phys. 52, 1042 (1970);A. D. Buckinykam and M . B.
Soc. A 1971, 1988.
[2] I . Tinoco, Jr., J. Amer. Chem. SOC. 81, 1540 (1959); R. Mandel and
G. Holiwarrh, J. Chem. Phys. 57, 3469 (1972);Biopolymers 12, 655 (1973);
and references cited therein.
[3] J . K u n z and A. McLean, Nature 136,795 (1935);J . Kunz and A . Babkock,
Phil. Mag. 23, 616 (1936);J . K u n z and R . G. La E m . Nature 140, 194
( 1937).
[4] A . D. Buckinykam, G. P . Caesar, and M. 8. Dunn, Chem. Phys. Lett.
3, 540 ( 1969).
[5] E . Friedel, C. R. Acad. Sci. Paris 1923,475;H . Stegemrier, K . J . Mainusch,
and E . Striyner, Chem. Phys. Lett. 8, 425 (1971).
161 J . M . Pochan and P . F. Erhardr, Phys. Rev. Lett. 27, 790 (1971): E.
Frirdrl, Ann. Phys. Paris 18, 273 (1922); H . Baesslrr and M . M . Labrs,
J. Chem. Phys. 51, 1846 (1969):52, 631 (1970);E. Sackmann, Chem. Phys.
Lett. 3,253 (1969);J. Amer. Chem. SOC. YO, 3569 (1968).
Dunn, J. Chem.
Anyew. Chem. intrrnat. Edit. J Vol. 14 ( 1 9 7 5 1
No. 3
into the derivative, tetrakis(trimethylgermyl)-2-tetrazene
which could be synthesized by an independent routeL5'.N4H4
also reacts analogously with N,N-diethyl(trimethylstanny1)amine (E = Sn). Thence we conclude that N4H4has the structure
2-tetrazene.-4. The synthetic route leading to tetrazene consists of protolysis of tetrakis(trimethylsilyl)-2-tetrazenewhich
according to X-ray structure analysis[6fhas the trans-configuration; and, since a change of configuration during protolysis
is unlikely, the 2-tetrazene prepared in this way probably
also has the trans-configuration['!
Thermolysis of tetrazene
XzN + H2N-NHZ
HZN-N-N-NH,
N=N=N
['I
Prof. Dr. N. Wiberg, Dipl.-Chem. H. Bayer, and Dr. H . Bachhuber
tnstitut fur Anorganische Chemie der UniversitPt
8 Miinchen 2, Meiserstr. I (Germany)
171
leads by decomposition to nitrogen and hydrazine and by
isomerization to ammonium azide[81.If pure tetrazene is thus
decomposed, the decomposition and isomerization products
are formed in about 75 and 25% yields, respectively (e.9.
found: 1.18mmol of N2, 1.18mmol of N2H4, 0.39mmol of
NH3, 0.38mmol of HN3). However, decomposition and isomerization of tetrazene in methanol affords about 40 and
60%, respectively. Thermolysis of solid tetrazene begins only
at ca. 0°C (gaseous tetrazene is metastable even at room
temperature); trans-2-tetrazene is thus unexpectedly thermostable.
Experimental:
Trifluoroacetic acid (6.00mmol) in methylene dichloride
(15ml) is dropped very slowly into a well-stirred solution
of tetraki~(trimethylsilyl)tetrazene[~~
in methylene dichloride
(25 ml) cooled to - 78 "C. The tetrazene is isolated by condensation: the reaction mixture is warmed slowly to 0°C and
the vapor is passed in a high vacuum through a glass trap
cooled to -78°C into one cooled to -196°C. A11 the methylene dichloride then collects in the second trap (- 196°C)
together with trimethylsilyl acetate; the 2-tetrazene remaining
in the first trap (- 78 "C) is purified by repeated sublimation
in a high vacuum from - 15"C into a tube cooled to - 78 "C
(yield 90%).
Received: August 15, 1974 [Z 143a lE]
German version: Angew. Chem. 87, 202 (1975)
I
b899
II
7
Fig. 1. Photoelectron spectrum of trans-2-tetrazene
Derivation of the orbital sequence of tetrazene (Fig. 2)
is based on the vertical ionization energies of trans-azomethane[3a1and ammonia[3b1together with consideration of the
inductive effects of azo ( - I ) and amino groups ( + I ) .
G
1
CAS Registry numbers:
Tetrakis(trimethylsilyl)tetrazene, 52164-24-6; trifluoroacetic acid, 76-05-1 ;
trans-tetrazene, 54410-57-0
i
[ l ] Part 3 of Tetrazene and Its Derivatives. This work was supported by
the Deutsche Forschungsgemeinschaft.-Part 2: N. Wiberg and W Uhlenbrork, Chem. Ber. I O S , 63 (1972); Part 1 : [4].
[Z] N . Wiberg, H . Bachhuber, and G . Fischer, Angew. Chem. 84, 889 (1972):
Angew. Chem. internat. Edit. 11, 829 (1972). N . Wiberg, G. Fiscker, and
H . Backkuber, Chem. Ber. 107, 1456 (1974).
[3] N . Wiberg and W Uhlenbrock, J. Organometal. Chem. 70, 239 (1974).
[4] N . Wiberg and W Uhlenbrock. Angew. Chem. 82, 47 (1970); Angew.
Chem. internat. Edit. 9, 70 (1970).
[ 5 ] N . Wiberg and S . K . Vasisht, unpublished work
[ 6 ] M . Veirh, Acta Crystallogr., in press.
[7] The amine nitrogen atoms in trans-2-tetrazene are most probably sp'and not sp'-hybridized (cf. J . Kronur, N. Wiberg. and H . Bayer, Angew.
Chem. 87. 203 (1975);Angew. Chem. internat. Edit. 14. 178 (1975)).
[8] For decomposition, isomerization and other possible degradations of
azo-compounds cf. [3].
Photoelectron Spectrum of Tetrazene"'
By Jurgen Kroner, Nils Wiberg, and Heiner Bayed']
The nitrogen hydride N J i 4 recently isolated for the first
time has the geometrical structure of a trans-2-tetrazene['].
To obtain the first preliminary information about its electronic
structure we have measured the photoelectron (PE) spectrum
of tetrazene''! In the energy range up to 21.21 eV it shows eight
bands (Fig. l), which can be assigned by qualitative MO
considerations (Fig. 2).
[*I Dr. I. Kroner, Prof. Dr. N. Wiberg, and Dipl.-Chem. H. Bayer
Institut fur Anorganische Chemie der Universitat
8 Miinchen 2, Meiserstr. 1 (Germany)
178
1
la2
s
NLHL
e
Fig. 2. M O scheme of n- and n-interactions in trans-ttetrazene (vertical
ionization energies in eV).
The first PE bands of tetrazene is undoubtedly to be assigned
to ionization of the x3-orbital because of its shape and vibrational fine structure (v@ = 650 cm-', ca. 15 progressions; cf.
also ammonia" bJ and ~ y a n a m i d e'I').~ In view of the inductive
effect (CH,+NH,) and of a small interaction effect between
the n-orbital of the azo group and the energetically low-lying
o-orbitals of the amino group (IE2H3= 15.8 eV[3b1),the second
band should refer to ionization of the n+-orbital of the azo
group. If as an approximation one assumes an equal inductive decrease in n, and n- on going from azomethane
to tetrazene ( x1 eV), the fourth band can be assigned to
ionization of the corresponding n combination[41. Thus the
third PE band must be assigned to x 2 which mixes symmetrycorrectly with the n*-orbital of the azo group. For nl there
remains the fifth PE band.
The qualitatively derived interaction diagram (Fig. 2) has
been confirmed by CNDO/S calculations[51on the assumption
of "pyramidal" amino-nitrogen atoms: n3 (8.51), n, (10.13),
x 2 (11.67), n- (13.92), x t (14.44eV); it was impossible to
~
Anyew. Chem. infernal. Edit. J Vol. 14 ( 1 9 7 5 ) No. 3
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