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Homocyclobutadienes and Cyclopropenes by Reaction of a Stable Cyclobutadiene with Diazo Compounds.

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magnetic species thus generated from 4b did, however,
show a broad ESR signal at g=2.01598, which indicates
substantial unpaired electron spin density at the iron
atom[*].The green radical is persistent for several weeks if
the solution is removed from the sodium. Further contact
with the metal causes the solution to become yellow again
within 15 h; no further change was observed after 3 d.
Table 1. Dihydroacepentalene complexes: reaction conditions, yields, characteristic data (&&.
4a: 3a +7.5 F e 2 ( C 0 h THF, 2 5 ° C 3 d, 64O/n, bright yellow oil.-IR (film):
3050, 2975, 2045 (CO), 1985 (CO), 1955 (CO), 1205, 1070, 760 cm-'.-UV
(THF): /l,,,(log~)=238 (sh, 3.982), 313 (4.011), 361 (3.807).--'H-NMR (270
MHz, CDCIp): 6 ~ 0 . 9 7(t, 6 H , 2'-H, 'J1.,2.=6.8 Hz), 1.05 (t, 6 H , 2"-H,
3J~,,.2-=7.2HZ), 2.40-2.75 (m, BH, 1'-H, 1"-H), 3.70 (d, l H , 3-H, 3J2,3=3.1
Hz), 5.23 (d, 1 H, 2-H), 5.76 (d, 1 H, 6-H, 3J5,6=6.0 Hz), 5.93 (d, 1 H, 5-H),
6.51 (d, 1 H, 8-H, 3Js.9=5.5 Hz, AB system), 6.56 (d, I H , 9-H).-I3C-NMR
(100.63 MHz, CDClp): 6=14.0 (4, C-2', 'Jc,H=I25.3 Hz), 14.8 (4, C-2",
'Jc,~=125.3 HZ), 44.2 (t. C-1', ' J C , H = ~ ~ I Hz),
. O 45.4 (t, C-I", IJe,H=131.0
HZ),~~.O(~~,C-~,'JC.H=I~~.~HZ,~J~,H=~.I
H~),78.3(s,C-4),78.4(dd.C3, IJ~.H=168.7 Hz, ' J c . H = ~ . ~ Hz), 83.5 (s, C-7), 88.6 (s, C-lo), 116.1 (hs, Cl), 125.5 (dd, C-6, ' J c , ~ = 1 7 0 . 9 Hz, 2 J c , ~ = 2 . 8Hz), 137.0 (dd, C-5,
'Jc.1~=167.1Hz, 2 J c . ~ = 2 . 6Hz), 141.2 (d, C-8, -'Jc,H=164.2 Hz), 147.3 (d, C2%), 255
9, ' J ~ , ~ = 1 6 4 . Hz),
9
212.3 (s, CO).-MS (70 ev): m/z=410 (Ma,
(Mm-3CO-NEt2+H, 100%).
4b: 3b 5 Fe2(CO)9, THF, 25"C, 1 d ; 70%, bright yellow oil.
4c: 3e +7.5 Fe2(C0)9, THF, 2 5 T , 1 d ; 24%, orange oil.
4d: 3d +7.SFe2(CO)9, THF, 2 5 T , 3 d ; 26%, yellow oil.
4e: 3e 5 Fe2(C0)9,THF, 2 5 T , 3 d ; 4% (not optimized; losses upon column
chromatography), bright yellow oil.
5b: green, persistent.-ESR (9.236 GHz, [DR]THF):g=2.01598 (bs).
+
+
6a: yellow.--'H-NMR
(270 MHz, [DR]THF): 6=0.99 (t, 12H, 2'-H,
- 14.2 Hz), 3.38 (mc, 4 H , 1'-H),
3Jl:2=7.0 Hz), 2.73 (mc, 4H, 1'-H, zJ,,s.i.b=
4.70 (d, 3(8)-H, 'J3(8,,2(9,=4.9 Hz), 5.97 (s, 5(6)-H), 6.11 (d, 2(9)-H).-I3CNMR (67.92 MHz,[D,]THF):6=14.2 (4, C-2', ' J c , H = 124.1 Hz), 43.7 (t, C-1',
'Jc,11=333.7 HZ), 68.7 (bs, C-lo), 78.7 (bs,C-I), 86.6 (bs, C-4(7)), 122.3 (dd,
158.8 HZ, ' J c . ~ = 4 . 4 Hz), 136.8 (d, C-2(9), - ' J C , H = 160.2 Hz),
C-5, -'Jc.H=
142.8 (C-3(8), ' J c . ~ = l 6 0 . 1Hz), 237.6 (s, CO).
6b: yellow.--'H-NMR (80 MHz, [D,]THF): 6 = 1.20-1.60 (m, 2'-H, 3'-H),
2.10-3.20 (m, l'-H), 4.72 (d, 3(8)-H, 3J2(9,,3(s,=4.8Hz), 5.90 (s, 5(6)-H), 6.16
(d, 2(9)-H).
The 'H-NMR spectra of the new complexes (see Table
1) are simpler than those of the precursors 4a and 4b.
Both this and the number of 13C-NMRsignals indicate the
presence of a plane of symmetry. The number, the chemical shifts, and the multiplicity of the 13C signals are consistent only if the new complexes have structures of the
1,10-q2-type 6 . In particular, the resonances of the quarternary olefinic carbon atoms C-1/C-10 at 78.7/68.7 and the
low-field value of the carbonyl group at 6 = 237.8"' corroborate the structure as tricarbonyl(olefin)ferrate( - 2) 6. All
attempts to isolate these ionic complexes, which are extremely oxygen sensitive, have failed so far.
6a and 6b are the first spectroscopically characterized
representatives of this class of compounds. The few reports
on the reduction of tricarbonyl(diene)iron complexes only
describe indirect evidence for such ferrate complexes from
cyclic voltammetry and polarography["]. The cyclic voltamogram of 4a shows two irreversible reduction waves at
-2.19 and -2.63 V (vs. SCE). This proves the intermediacy of a radical anion as detected in the sodium reductions.
It appears noteworthy that upon reduction of 4 only the
1,lO-q2-complexes 6 are formed and not the less symmetric 2,3-q2-isomers. This may be due to a favorable stabilization of the symmetric intermediate 5. The well-known
708
0 Verlag Chemie GrnbH, 0-6940 Weinheirn, 1984
reduction of Fe(CO), with sodium to afford disodium tetracarbonylferrate( - 2)["l in the presence of benzophenone
as an electron transfer catalyst"'] thus finds its counterpart
in the formation of 6 from 4, where the tetraenic ligand
may act as the electron-transfer catalyst.
Received: April 2, 1984 [Z 785 IE]
German version: Angew. Chem. 96 (1984) 722
[I] G. F. Emerson, L. Watts, R. Peltit, J. Am. Chem. Soc. 87(1965) 131.
[2] E. Weidemiiller, K. Hafner, Angew. Chem. 85 (1973) 958; Angew. Chem.
Inf. Ed. Engl. I2 (1973) 925.
[3] A. Streitwieser, Jr.: Molecular Orbital Theory for Organic Chemists, Wiley. New York 1961, p . 290f: R . Zahradnik, J . Michl, J. Koutecky, Coll.
Czech. Chem. Commun. 29 (1964) 1932; R. Zahradnik, J. Michl, ibid. 30
(1965) 3529.
[4] T. A. Alhright, P. Hofmann, R. Hoffmann, C. P. Lillya, P. A. Dobosh, J.
A m . Chem. SOC.105 (1983) 3396.
[5] H. Butenschon, A. d e Meijere, Tetrahedron Lett. 25 (1984) 1693.
[6] R. Aumann, J . Organomet. Chem. 76 (1974) C32; J. Elzinga, H. Hogeveen, Tetrahedron Lett. 1976, 2383; B. R. Bonazza, C. P. Lillya, J. A m .
Chem. SOC.96 (1974) 2298.
171 Technique described by A. Minsky, A. Y. Meyer, M. Rabinovitz, J. A m .
Chem. SOC.104 (1982) 2475.
[8] An ESR investigation of olefin tricarbonyliron radical anions formed
from tricarbonyl(diene)iron complexes upon reduction with Na/K has
been reported: P. J. Krusic, J. San Filippo, Jr., J . Am. Chem. SOC.104
(1982) 2645.
[9] Cf. M. H. Chisholm, S. Godelski, Prog. Inorg. Chem. 20 (1976) 299ff.;
G. C. Levy: Topics in Carbon-13-NMR-Specfroscopy, Vol. 2, Wiley, New
York 1976, p. 294ff; L. J. Todd, J. R. Wilkinson, J. Organomet. Chem. 77
(1974) 1.
[lo] N. El Murr, M. Rivecci, P. Dixneuf, J. Chem. SOC. Chem. Commun.
1978, 552; N. El Murr, M. Rivecci, E. Laviron, G. Deganello, Tetrahedron Lett. 1976, 3339; L. I. Denisovich, 1. A. Suskina, S . P. Gubin, Nou.
Polyarogr., Tezisy Dokl. Vses. Srtueshch. Polyarogr. 6 (1975) 133; Chem.
Abstr. 86 (1977) 23505h; L. 1. Denisovich, S. P. Gubin, Usp. Khirn. 46
(1977) 50; Russ. Chem. Rev. 46 (1977) 27.
I l l ] H. Behrens, R. Weher, Z . Aitorg. Allg. Chem. 281 (1955) 190.
I121 J. P. Collman, Acc. Chem. Res. X (1975) 342.
Homocyclobutadienes and Cyclopropenes by
Reaction of a Stable Cyclobutadiene with Diazo
Compounds**
By Uwe-Josef Vogelbacher, Philipp Eisenbarth, and
Manfred Regitz*
Bicyclo[2.l.O]pentenes ("homocyclobutadienes")
are
prepared by irradiation of I ,3-cyclopentadienes ; they are
thermally unstable and undergo electrocyclic retro-reactions even at room temperature"]. Herein, we report a
novel entry to this class of compounds: Reaction of the cyclobutadiene 1 with diazo compounds leads, inter alia, to
formation of the dihydropyrazoles 2, whose photolysis
furnishes thermally stable hornocyclobutadienes. The
scope of this synthetic strategy depends upon the pattern
of substitution in the diazo compounds and is restricted,
by an as yet unknown diazoalkane reaction, to cyclopropenylazines.
The reaction of lCz1
with diazomethane (fourfold excess)
is extraordinarily rapid, but in no way specific. [3 2]-Cycloaddition at the electron-deficient and sterically best accessible double bond dominates, giving the stable dihydropyrazoles 2 (24%) and 3 (30%); cycloaddition at the di-terfbutyl-substituted double bond to give 4 also takes place,
+
[*] Prof. Dr. M. Regitz, DipLChem. U.-J. Vogelbacher, Dr. P. Eiseubarth
Fachbereich Chemie der Universitat
Erwin-Schrodinger-Strasse,
D-6750 Kaiserslautern (FRG)
[**I Syntheses with Cyclobutadienes, Part 6. This work was supported by the
Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Indust&-Part 5: M. Regitz, P. Eisenbarth, Chem. Ber. 117(1984) 1991.
0570-0833/84/0909-0708$ 02.50/0
Angew. Chern. I n t . Ed. Engl. 23 (1984) N o . 9
but only to the extent of 4% (separation of products by column chromatography on silica gel with hexane/ether
4 : 1).
1
Photolysis of 2 in pentane (Philips HPK 125W, Pyrex
filter) leads quantitatively-presumably via the diradical
5-to formation of the homocyclobutadiene 6,which does
not isomerize to the corresponding cyclopentadiene, even
on distillation (b.p. l10°C/3 x
mbarL3]).
The irradiation of 3 is much more complex, since the diradical 7 cyclizes to the isomeric homocyclobutadienes 6
and 8 (65 :35, 'H-NMR). 6 is photostable, whereas the
a,O-unsaturated ester 8 slowly rearranges photochemically
in an electrocyclic reaction to the cyclopentadiene 9 ['HNMR, 90 MHz, CDCI,: 6=1.20, 1.30, 1.36, 1.53 (4s, each
9H, tBu, 1,3,4 and ester), 3.05 (s, 2H, CH,)]. The same
product pattern results on photolysis of 4, a further proof
of its structure and composition.
Table 1. Selected physical data of compounds 2-4, 6, 8, 12a, and 12f.
2 : Colorless oil; IR (film): v = 1705 cm-l (CO); 'H-NMR (90 MHz, CDCI,):
S = 1.17, 1.19, 1.34, 1.48 (4s, 9H, tBu-1,6,7, ester), 4.47, 4.98 (2d, AB system,
J=18 Hz, 2H, 4-H); "C-NMR (50.28 MHz, CDCI3): 6=27.86, 28.69, 31.70,
32.50 [(H,Q3C-1,6,7, ester], 33.88, 34.02, 32.25 [(H3C),C-l,6,7], 57.31 (C-5),
77.70 (t. J = 142.2 Hz, C-4), 82.04 [(H,C),C-ester], 113.36 (C-1), 152.00, 160.54
(C-6/71, 172.49 (CO); MS (18 ev): m/i=334 (Ma-N2, 5.9), 222
(Mm- Nz-2CdH8, 81%).
3: Colorless crystals, m.p. 85°C; IR (KBr): v = 1705 cm-' (CO); 'H-NMR
(CDCI3):6=1.03, 1.21, 1.28, 1.48 (4s, 9H,tBu-5,6,7,ester),4.26,4.52(2d,AB
system, J=18 Hz, 2H, 4-H); "C-NMR (CDCI,): 6=27.84, 28.60, 31.60,
32.74 [(H3Q3C-5,6,7, ester], 33-21, 33.82, 34.27 [(H3C),C-5,6,7), 62.61 (C-5),
77.29 (t, J = 139.0 Hz, C-4); 82.39 [(H,C),C-ester], 102.61 (C-1), 156.99, 157.30
(M", l), 233
(C-6/7), 170.30 (CO); MS (18 eV): m/z=362
(Mm-N2-CdH9-CO?, 12), 222 (Mm-N2-2C4H8, 55).
4 : Colorless crystals, m.p. 107°C (pentane); IR (film): v = 1700 (CO), 1635
cm-' (C=C); 'H-NMR (CDCI,): 6=1.11, 1.27 (each s, 9 bzw. 18H, tBn1,5,7), 1.46 (s,9H, tBu-ester), 4.07, 4.83 (2d, AB system, JH,H=19.2Hz, 2H,
4-H); "C-NMR (CDCI,): 6=27.96, 29.85 [(HaC)aC-1,5,7, ester], 31-69, 32.48,
35.46 [(H,C),C-1,5,7], 82.04 [(H,C),C-ester], 115.00 (C-l), 64.75 (C-5), 139.22
(C-6), 160.78 (C-7), 166.72 (CO).
6 : Colorless oil; IR (film): v = 1705 cm-' (CO); 'H-NMR (CDC13): 6 = 1.12,
1.15, 1.17, 1.44 (4s, 9H, tBu-2,3,4, ester), 2.00, 2.23 (2d, AB system, 5=3.4
Hz, 2H, 5-H); "C-NMR (CDCI,): S=27.94, 29.41, 31.54, 31.62 [(H,C),C2,3,4, ester], 31-94 (C-4), 34.24, 34.35, 34.43 [(H,C),C-2,3,4], 46.94 (C-1), 52.84
(dd, J = 148.2, 166.4 Hz, C-5), 80.00 [(H,C)C-ester], 154.01, 155.90 (C-2/3),
172.78 (CO).-5-Methyl derivative of 6: colorless oil; IR (film): v = 1700
cm-' (CO); 'H-NMR(CDC13): 6=1.12, 1.15, 1.20, 1.47 ( 4 ~ 9, H , tBu-2,3,4,
ester), 1.28 (d, J=6.6 Hz, 3H, 5-Me), 2.97 (9. J = 6 . 6 Hz, 1 H, 5-H).
8: Colorless oil; 'H-NMR (CDCI,): 6=1.11, 1.12, 1.17, 1.44 (4s, 9H, IBU1,3,4, ester), 1.78, 2.30 (2d, AB system, J = 3 . 2 Hz, 2H, 5-H).
12a: IR (film): v = 1718,1672 cm-' (CO); 'H-NMR (CDCI,): S= 1.25 (s, 9 H ,
tBu-azomethine), 1.26 (s, 18H, tBu-2/3), 1.40 (s, 9H, rBu-ester), 2.35, 2.47
(2s, 3H, Me-acetyl); %NMR (CDCI,): 6=25.98, 30.48 (CO-CHa), 27.85,
28.53, 30.03 [(H,C),C-2/3, azomethine, ester], 32.36, 39.60 [(H3C),C-2/3,
azomethine], 39.10 (C-1), 80.23 [(H,C),C-ester], 119.30 (C-2/3), 157.80
(C=N), 173.36 (CO-ester), 177.10 (C=N), 197.20, 201.42 (CO-acetyl).
12fI12'f (E/Z-isomers): IR (KBr): v = 1712 cm-' (CO); 'H-NMR (CDCI,):
6= 1.08, 1.29 (2s, together 9H, ratio 50:50, tBu-azomethine), 1.29 (2, 18H,
tBu-2/3), 1.40, 1.51 (2s, together 9H), ratio 50 :50, IBu-ester), 7.1-8.6 (m,
8 H , aromat. H); "C-NMR (CDCI?): 6=27.05, 27.76, 28.20, 29.60, 30.11,
30.43 [(H30)~C-2/3,azomethine, ester], 3 1.90,32.80,38.53, 39.60 [(H3C),C-2/
3, azomethine], 37.64, 42.60 (C-1), 79.32, 80.34 [(H,C),C-ester], 118.18 (C-2/
3), 120-142 (aromat. C), 147.78, 157.60, 165.03, 173.88 (C=N), 175.08,
175.31 (CO); MS (70 eV): m/z=512 ( M a s I), 455 (Mm-C4H9, 3).
I
11
US
t
1 reacts stereospecifically with diazoethane to give exclusively the 4-methyl derivative of 2 (yield 65%, b.p.
125"C/3 x
mbarr3]); the homocyclobutadiene prepared from this compound is also thermally stable (95%,
b.p. 125"C/3 x
mbar"'). Whether the methyl group of
the two compounds is endo- or exo-oriented can not be deduced from the spectroscopic data. The high activation
barrier of the homocyclobutadiene/cyclopentadiene isomerization is obviously due to steric reasons.
1 reacts with the doubly acylated or arylated diazomethanes 10 at 20°C in pentane in a novel reaction involving
ring contraction[61to give the yellow (12a-e, f) or red cyclopropenylazines (12d). We presume that the sterically
less favorable cycloaddition is circumvented by attack of
Angew. Chern. Int. Ed. Engl. 23 (1984) N o . 9
12
10, 11,12
a
Yield [%]
M.p.["C]
b
C
d
e
f
65
61
45
56
51
52
-
-
106
142
129
60
-
-
1 4 5 / 3 ~ 1 0 -160/10-'
~
-
B.p. [oC/mbar]
0 Verlag Chemie GmbH. 0-6940 Weinheim, 1984
PI
-
(3 I
0570-0833/84/0909-0709 $ 02.50/0
709
the terminal, electrophilic nitrogen atom of 10 at C-2 of
the cy~lobutadiene[~];
initially the homocyclopropenylium
betaines 11[” are formed in which the charge is optimally
stabilized.
The constitution of the azines is supported not only by
their colors and analytical data but, in particular, by the
I3C-NMR spectra (50.28 MHz, CDCl3); the spectra show,
inter aha, separated signals for two azomethine C atoms
(6 = 141.10- 177.04); the olefinic three-membered ring
atoms (6= 117.89-119.30) as well as the two C-type atoms
of the tert-butyl groups attached to this ring, and the sp3
cyclopropene C-atom (6= 37.64-42.60) each give only
one signal. The signals of the cyclopropene C atoms are
virtually identical with those observed for tert-butyl(l,2,3tri-ter~-butyl-2-cyclopropenyl)diazoacetate~z~.
Since the diazomethane substituents are identical, the
azines occur only as E / Z isomers 12 and 12‘, as also follows from the NMR spectra in the case of 12e and 12f (see
Table 1 ; the isomeric ratios are 60 :40 and 50 : 50, respectively). That the same phenomenon is not observed in the
case of 12a - 12d can only be ascribed to a rapid inversion
at N-I, enforced by the other half of the azomethine moiety, which is a stronger electron-a~ceptor[’~.
Me3SnE(CF& 3 0 ( l ~ CR3E=CF2
~ ~ ~ n ~
1
2
a , E = P ; b, E = A s
The heteroalkenes 2 are formed on thermolysis of 1 at
torr in a pyrolysis tube and are quenched from the
gas phase at - 196°C. Pyrolysis experiments at the inlet of
a mass spectrometer showed that an optimal temperature
range for this process is 300-340°C. Unreacted 1 is repeatedly fed through the hot zone until the conversion into
2 is complete[41.The phosphaalkene 2a can be recondensed in a high vacuum at l o p 3 torr without any detectable loss, whereas the new arsaalkene 2b rapidly dimerizes
or polymerizes. Despite its high reactivity, 2b could be unequivocally characterized by its I9F-NMR spectrum at
- 110°C (Fig. 1) and finally identified by its dimerization
products.
2a.
F’
I
I
Received: April 26, 1984;
supplemented: July 9, 1984 [Z 810 IE]
German version: Anyew. Chem. 96 (1984) 691
CAS Registry numbers:
1 83747-03-9; 2 91181-02-1; 3 91181-03-2; 4 91181-04-3; 6 91181-05-4; 8
91181-06-5; 9 91181-01-6; 10a 29397-21-5; 10b 6773-29-1; 1Oc 2085-31-6;
1Od 85-41-6; 10e 883-40-9; 10f 832-80-4; 12a 91181-08-7; 12b 91181-09-8;
12c 91181-10-1; 12d 91181-11-2; 12e 91181-12-3; 12e‘ 91181-14-5; 12f
91181-13-4; 12f‘ 91181-15-6
[l] The half-life of unsubstituted bicyclo[2.1.0]pentane (CCI4, 20°C) is ca.
2h: J. 1. Brauman, L. E. Ellis, E. E. van Tamelen, J . A m . Chem. SOC.88
(1966) 846; methyl-substituted bicyclo[2.1 .O]pentenes behave analogously: W. R. Roth, F . 4 . Klarner, H.-W. Lennartz, Chem. Ber. I13 (1980)
1818; F.-G. Klarner, F. Adamsky, ibid. 116 (1983) 299.
121 P. Eiseubarth, M. Regitz, Chem. Ber. f 15 (1982) 3796.
[3] Kugelrohr distillation.
[4] The mass spectra of 12c--1 support this by the fragments m/z=251 ( 7 13%) and 194 (19-100%), that is the tert-butoxycarbonyl-di-tert-butylcyclopropenylium ion and that of the same fragment minus an isobutene
moiety.
[5] For the stability of homocyclopropenylium ions see G. A. Olah, J. S. Staral, R. J. Spear, G. Liang, J. A m . Chem. SOC.97 (1975) 5489; P. B. J.
Driessen, H. Hogeveen, ibid. 100 (1978) 1193; R. C. Haddon, K. Raghavachari, ibid. 105 (1983) 118.
[6] Ring contraction also occurs in the 1 :2 reaction of tetra-tert-butylcyclobutadiene with tetracyanoethylene: G. Maier, K.-A. Schneider, K.-D.
Malsch, H. Irngartinger, A. Lenz, Anyew. Chem. 94 (1982) 446; Anyew.
Chem. Int. Ed. Engl. 21 (1982) 437; Anyew. Chem. Suppl. 1982, 1061.
[7] D. Wurmb-Gerlich, F. Vogtle, A. Mannschreck, H. A. Staab, Justus tiebigs Ann. Chem. 708 (1967) 36.
Facile Synthesis of Heteroalkenes CF3E=CF2
(E=P, AS)**
By Joseph Grobe* and DUCLe Van
The phosphaalkene CF3P=CF2 2a was previously prepared by base-induced cleavage of H F from (CF3),PH”] or
by base-catalyzed reaction of dimethylzinc with
(CF3)2PH[21,i.e. by methods which afford 2a in impure
form or in low yield. On re-investigating the decomposition reaction of the stannanes 1r31,we have now discovered
a simple method for the quantitative synthesis of 2.
40
2b.
I
70
60
F”
,E=C
-
20
30
/F’
I
- 2 8 0 - 2 9 0 -300-
6
I
6
I
-100 -110 - 120
50-6
6
-c-
Flg. I. Sections from the I9F-NMII spectra of 2a (top) and 2b (bottom); in
each case the region for the CF2-group is shown.
Apart from the molecular peaks [2a: m/z 150 (M’);2b:
m/z 194 ( M a ) ] the mass spectra of the two compounds
show similar degradation patterns. CF3As=CF2 is the
smallest As=C-(p-p)n-system so far isolated[’].
The kinetic stability observed for 2a in ca. 10% organic
solutions (e.g. toluene, pentane) is surprising: thus, the
dimer is first detectable after about 10 h, even at 25°C. In
contrast, rapid thawing of the monomer in the condensed
phase from - 196°C to room temperature leads to formation of the polymer (CF3PCF,),[31.If the heteroalkenes are
torr the
passed through a U-tube cooled to - 78 “C at
dimers 3-5 are formed along with small amounts of the
trimer 6 . The new cyclic arsenic compounds 3b-6b could
be identified by comparison of their ”F-NMR spectra
with those given in the literature for 3a-6a[2,61.
3
4
5
[*] Prof. Dr. J. Grobe, Dr. D. Le Van
[**I
Anorganisch-chemisches Institut der Universitat
Corrensstrasse 36, D-4400 Munster (FRG)
Reactive E=C-(p-p)n Systems, Part I. This work was supported by the
Landesamt fur Forschung des Landes Nordrhein-Westfalen.
710
0 Verlay Chemie GmbH, 0-6940 Weinheim. 1984
0570-0833/84/0909-0710 $ 02.50/0
Angew. Chem. I n t . Ed. Engl. 23 (1984) No. 9
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