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Is Hexazine Stable.

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JI,l,=448.9 Hz. The chemical shift of the central phosphorus
continues the trend found for the other L 2 Pcompounds mentioned above (tip= - 188 to -218), as ’Jppcorresponds to the coupling constants found in those compounds.
According to an X-ray structure analysis, 2 crystallizes
with two molecules of CH2C12.The five-membered ring of
the cation (Fig. 1) has an envelope conformation. While in
most other cases the PP bond length is “remarkably constant at 220-225 pm and seems insensitive to the bonding
situation at the p h o s p h ~ r u s ” ~here
~ ~ , it is considerably
shorter. The angle at the central phosphorus is very small,
but is also just as small at the doubly coordinated phosphorus in diazaphospholene”’.
the discussion of evidence, three theoretical papers were
cited, one of whichlZhlwas effectively interpreted as indicating that N , “is slightly stabilized”. A considerably more
accurate calculation is presented in the following; earlier
work is shown in a critical light.
The semiempirical studies of Dewar1”] involve two calculations: A MI N D 0 / 3 calculation predicts that hexaazine is more stable than dinitrogen; this result is considered to be unreliable by Dewar. because repulsion between
the lone pairs of electrons is not considered. A MNDDO/ 1
calculation indicates that N(, is approximately 135 1 kJ/mol
higher in energy than 3 N’. and decomposes without an activation barrier.
In their ab initio SCF calculation, without geometrical
optimization, Palmer et
used a minimal basis. The energies thus obtained are shown in Table I . N o statement
was made about the stability of hexazine.
Table I . Theoretical comparison of stabilities of hexazine/dinitrogen
bl
a1
Fig. I . a) Structure of the cation in 2’2CHKI:: monoclinic, space group Pi,
1165.5(2), b = 1317.4(3), c = 1098.2(6) pm, a = 100.38(2), p=98.55(3),
y=68.20(20)”, Z = 2 , p<,,t<
= 1.47 g/cm - ‘. 4091 independent reflections
(Mo,,., P’22.0o(F’), 2eSSOo), R=0.042, R, =0.040.-b) Bond lengths
[ppm] and angles
in the triphospholane ring.
(I=
r]
Further experiments show that the “complexes” L2Po
are variable, both with respect to the phosphane ligands L,
and as regards the generation of Pa; in particular, acyclic
species can also be prepared.
Method
N,,,€ / E l ,
NI, E / E I ,
(N,.-3N2), €/kJ mol
Ref. [Za]
Ref. [2b]
FOGO
-325.290
- 108.526
- 325.468
- 325.988
- 108.569
756
63 I
1089
- 108.801
WrightIZh1
also used a minimal basis in his a b inirio S C F
calculations with geometrical optimization under Dhhsymmetry. The energies for the optimal bond lengths of 137.9
pm are also included in Table I. By comparison with
standard bond energies, and the corresponding calculation
for N4, he comes to the conclusion that hexazine exhibits
“a genuine stabilizing effect”. However, whether the decomposition N(,-+3N 2 is hindered by an activation barrier
was not investigated. Such a decomposition would only be
possible if the symmetry were lowered from D,, to DjI,.
Received: August 10, 1981 ( 2 974 IE]
German version: Angew. Chem. 94 (1982) 72
[I]a) S. F. Spangenberg, H. H. Sisler, Inorg. Chem. 8 (1969) 1006; b) C. B.
Lindahl, W. L. Jolly, ibid. 3 (1964) 1634; M. Baudler, G. Wetter, Z. Anorg.
Chem. 329 (1964) 3 : c) W. Malisch, R. Alsmann, Angew. Chem. 88 (1976)
809: Angew. Chem. In!. Ed. Engl. I S (1976) 769.
[2] a) A. Schmidpeter, F. Zwaschka, Angew. Chem. 89 (1977) 747; Angew.
Chem. In!. Ed. Eng/. 16 (1977) 704; b) A. Schmidpeter, S. Lochschmidt,
unpublished: c) D. Weber, G. Heckmann, E. Fluck, Z . Nalurjiorsch. 8 3 1
(1976) 81: d ) D. Weber, E. Fluck, 2. Anorg. Allg. Chem. 424 (1976) 103.
[31 M. Baudler, J. Vesper, H. Sandmann, 2. Narurjiorsch. 8 2 7 (1972) 1007.
141 1. Emsley, D. Hall: R e Chemisrry of Phosphorus. Harper and Row. London 1976, p. 458.
[5] P. Friedrich, G. Huttner, J. Luber, A. Schmidpeter, Chem. Eer. 1 1 1 (1978)
1558. and references cited therein.
Is Hexazine Stable?
By Hanspeter Huber*
Dedicated / o Professor Edgar Heilbronner on the occasion
of his 60th birthday
Vogler ef a / . [ ’ ] on
, the basis of experimental evidence,
have recently postulated that N, (hexazine, hexaazobenzene, cyclohexaazatriene) exists at low temperatures. In
[*I
64
Dr. H. Huber
Physikalisch-chemisches Institut der Universitar
Klingelbergstrasse 80, CH-4056 Basel (Switzerland)
0 Verlag Chemie GmhH. 6940 Weinheim. 1982
Starting from Wright’s geometry[2h1we optimized the
structure of N, with Dhh symmetry. We used the FOGO
method[31 with sliding orbitals; this corresponds to a
(DZ+ P) basis and is, hence, a considerable improvement
on the earlier calculations with minimal bases (the total energy lies approximately 1360 kJ/mol lower than that of the
previous best calculation[‘h1). The energy for an NN separation of 13 l . l pm, which is found for the stationary point,
is also reproduced in Table I.
In order to decide whether this stationary point is a genuine minimum, the force constant matrix was calculated
using Pulay’s “force” method‘“I. Normal coordinate analysis indicated that this is no/ a minimum, but, rarher. a saddlepoint. From the results of our calculations, N , with D,,,
symmetry is not stable, but decomposes without an activation barrier in accord with Dewar’s MNDDO/I calculation. Based on experience with calculations of this level,
the result should not differ substantially by extending the
basis. A geometrical optimization including electron correlation (and a sufficiently large basis) is too involved at
present. The influence of the electron correlation on the
stability is difficult to estimate. Also, stabilization by solvation cannot be completely excluded.
0S70-083~/82/~101-0064
$ OZ,SO/O
Angeu,. Chem. I I ~ Ed.
I . Engf. 21 (19821 No. I
In summary, none of the calculations yield an activation
energy and (with the exception of the MIND0/3 calculation) all predict that in the gas phase N6 is ca. lo3 kJ/mol
less stable than 3 N2. For as long as n o direct experimental
proof for the existence of N6 exists we must assume that
hexazine is neither thermodynamically nor kinetically stable.
Received: February 16, 1981 [ Z 973 IE]
German version: Angew. Chem. 94 (1982) 71
111 A. Vogler, R. E. Wright. H. Kunkely, Angew. Chem. 92 (1980) 745; Angew.
Chem. In!. Ed. Engl. 19 (1980) 717.
[2] a ) M. H. Palmer, A. J. Gaskell, R. H. Findlay, J. Chem. Soc. Perkin Trans.
I 1 1974. 778; b) J. S . Wright, J. Am. Chem. Soc. 96 (1974) 4753: c) M. S. J.
Dewar, Pure Appl. Chem. 44 (1975) 767.
[31 H. Huber, Theor. Chim. Acta 55 (1980) 117: 1. Mol. Struct. Theochem. 76
(1981) 277
[4] P. Pulay. M o l . Phys. 1 7 (1969) 197.
2,4,6-Cycloheptatrienylidenemalondialdehyde
(8,s-Diformylheptafulvene) **
By Christian ReichardP and Kyeong- Ye01 Yun
We report here on the preparation of the title compound
7, which belongs to the hitherto rarely investigated cycloalkylidenemalondialdehydes.Starting from the sodium
salt 1 of malondialdehyde, 71'01
is obtainable as orange-red
crystals (m.p. 132- 133 "C, dec.) uia the isolable intermediates 2 to 6 (Scheme I).
According to NMR spectra, 7 is in equilibrium with the
valence isomer 3-formyl-8aH-cyclohepta[b]furan
8 in solution (DzO: 100% 7; CCI,: 37% 7).
The X-ray structure analysis shows that exclusively the
valence isomer 7 exists in the crystal. As a result of steric
interactions, between 2-H/7-H on the one hand, and the
two aldehyde oxygen atoms on the other, the seven-membered ring and the malondialdehyde group are rotated
through 18.1" with respect to each other. This and the participation o f the dipolar mesomeric resonance structure 7b
lead to a relatively long C-I/C-8
bond (143 pm; C,,--C,,.
single bond: 148 pm; double bond: 134 pm).
MNDO calculations["] give a dipole moment of 3.0 D
for a partially optimized completely planar conformation
of 7. An experimental determination of the dipole moment
of 7 was not possible owing to the concomitant presence
of the valence isomer 8 in solution.
Since they cannot be enolized, 2,f-substituted malondialdehydesl'] and alkylidenemal~ndialdehydesl~~
are real
C 3 dialdehydes and therefore valuable C,-synthetic building blocks.
Received: May I I , 1981 [ Z 958 IE]
German version: Angew. Chem. 94 (1982) 69
Angew. Chem Suppl 1982. 113
[I] R. Dersch, C. Reichardt, Synthesis 1980. 940.
[ 5 ] C. Reichardt, W. Pressler. E - U . Wiirthwein, Angew. Chem. 88 (1976) 8 8 :
Angew. Chem. In/. Ed. Engl. I5 (1976) 112.
[I01 T h e constitution of 7 follows from the elemental analysis, the 'H-and
"C-NMR spectra, as well a s an X-ray structure analysis. We thank Dr.
W. Massa and R. Schmidt, Fachbereich Chemie, Universitat Marburg,
for carrying out the X-ray structure analysis.
1161 M. J. S. Dewar, W. Thiel, J. Am. Chem. Soc. 99 (1977) 4899: we thank
Dr. E.-U. Wiirthwein, Universitat Erlangen-Nurnberg, for the M N D O
calculations.
+ NaOH
H
J
L
- H2O
93%
H
2
1
J
Convenient General Synthesis of
A1kynylcyclopropanes* *
J
3
4
By Thomas Liese and Armin de Meijere*
Dedicated to Professor Oskar Glemser on the occasion
of his 70th birthday
1
J
5
6
5t
0
0
H
Q
.....
,
......'
cf
Q
*
H
7a
H
H
7b
H
8
Scheme I .
['I
[**I
Prof. Dr. C h r . Reichardt, K.-Y. Yun
Fachbereich Chemie d e r Universitat
Hans-Meerwein-Strasse, D-3550Marburg (Germany)
Syntheses with Aliphatic Dialdehydes, Part 30. This work was supported
by the Deutsche Forschungsgemeinschaft and the Fonds d e r Chemischen I n d u s t & - P a n 29: [I].
Angew. Chem. In,. Ed. Engl. 21 (1982) No. I
Although donor-, acceptor-, as well as vinyl-substituted
cyclopropanes have become established synthetic tools, alkynylcycIopr~panes[~~,
which because of the junction of a
cyclopropyl and an alkynyl group offer an interesting and
powerful synthetic potential, have not been widely recognized.
We recently found that the easily accessible I-chloro-l(trichloroviny1)cyclopropanes 1l5)react cleanly with 2
moles of n-butyllithium to give (I-chlorocyclopropy1)-substituted lithium acetylides 6 (Scheme I), which can be solvolyzed by methanol o r water to yield (I-chlorocyclopropy1)acetylenes 7 (Table I ) or trapped by a wide variety of
electrophiles EX to give acetylene derivatives 5a (Table 2).
The 1-chloro-I-alkynylcyclopropanes5 and 7 are polyfunctional molecules, and as such valuable building blocks
for organic synthesis. Among the reactions which can be
[*] Prof. Dr. A. d e Meijere, Dipl.-Chem. Th. Liese
lnstitut fur Organische Chemie und Biochemie d e r Universilet
Martin-Luther-King-Platz 6, D-2000 Hamburg 13 (Germany)
[**I This work was supported by the Fonds d e r Chemischen lndustrie a n d
the Hoechst AG.
0 Verlag Chemie GmhH, 6940 Weinheim. 1982
0 5 7 0 - ~ / 8 ~ 3 / 8 2 / 0 1 0 / - 0 0 S6 502.511/0
65
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