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DTA Studies on Formation of Dehydrobenzene and Dichlorocarbene from Haloorganolithium Compounds.

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Decomposition of the complex is evidently initiated by
thermal dissociation of the L i e 0 coordinative bond. A
free coordinative site becomes available at the lithium,
DTA Studies on Formation of Dehydrobenzene and
Dichlorocarbene from Haloorganolithium
Compounds
By Oleg M . Nefedov and Andrej I . Dyachenko"]
Dedicated to Professor Georg Wittig on the occasion
of his 75th birthday
In the present communication we report differential thermal analysis (DTA)"] studies on the decomposition of
o-halophenyllithiums, o-XC,H,Li ( I )
and trichloromethyllithium ( 2 j f 3 - ' ] in the presence of ethers and
amines. Compounds ( I ) and (2) were obtained by the
addition of 1.0-10ml of a 1 . 0 ~
solution of o-XC,H,Br
(I), X
=
F, C1, B r
thus resulting in immediate elimination of lithium halide
owing to intramolecular coordinationX+Li. If this concept
is correct complexes of ( I ) with cyclic ethers and other
ligands of high basicity (e.g . dimethoxyethane or tetramethylethylenediamine) should be more stable that those
with dialkyl ethers owing to a stronger L i t 0 bond.
Since the stability of complexes of (1) with cyclic ethers,
dimethoxyethane, and tetramethylethylenediamine was
indeed found to be independent of polarity, it seems reasonable to conclude that the L i c O bond strength is mainly
determined by the steric requirements of the solvent in connection with its ability to undergo inversion.
(2)
(X=F, C1, Br) or C1,CX' (X'=H, Br) in isopentane or npentane to an equal volume of 1.0N n-C,H,Li in the same
solvent at - 150°C. The mixture was then allowed to warm
to room temperature ( z l h) in a DTA instrument. The
results are shown in Table 1.Independent experiments have
shown that the observed exothermic effects are due to the
decomposition of ( I ) or (2)16].
As is also evident from the data in Table 1, the stability of
complexes ( I ) increases in the sequence X = Br < C1< F.
This corresponds to the donor strengths of the halogenst7*'!
An analogous, albeit less pronounced, stabilization was
also found for (2) in polar solvents (Table 1).This doubtless
means that dichlorocarbene formation does not proceed
Table 1. Thermal stability of haloorganolithium compounds in polar solvents
Dipole
moment
(D)
Solvent
Decomposition temperature (T)[a]
o-XC,H,Li ( 1 ) from o-XC,H,Br CI,CLi 12) from C1,CX'
X=CI
X=Br
X'=H
X'=Br
X=F
~
Diethyl ether
Di-n-propyl ether
Di-n-butyl ether
Triethylamine
Tetrahydropyran
Tetrahydrofuran
Oxetane
Methyloxirane
1,2-Dirnethoxyethane
Tetramethylethylenediamine
[a] Average of 3-4
1.15
1.18
1.22
0.82
1.55
1.75
1.92
1.95
1.72
-
- 48
- 73
-50
-73
- 70
-
-21
-20
- 19
- 20
- 19
-16
- 50
-51
- 50
- 52
- 50
- 48
-
-I 5
- 75
- 76
- 13
- 80
-
- 88
- 84
- 87
- 87
- 65
- 66
- 65
-
- 89
-
75
- 75
-
-
- 76
- 85
- 85
-
67
- 66
-
65
-
experiments.
As is seen from Table 1 the thermal stability of ( I ) increases substantially only on going from acyclic to cyclic
ethers. Within the two series of ethers the stability remains
practically unchanged in spite of the varying polarity.
These results are not in accord with formation of dehydrobenzene (3) via an o-halophenyl anion intermediate ( 4 ) [71,
since such a mechanism would require a decrease in stability of ( I ) with increasing solvent polarity. Hence, we
assume that (3) is formed by a concerted p-elimination of
LiX from a complex of ( I ) with ether (or trialkylamine)['. 'I.
[*I
- 85
- 83
Prof. Dr. 0. M. Nefedov and A. I. Dyachenko
N. D. Zelinsky Institute of Organic Chemistry
Academy of Science of the USSR
Moscow B-334, Leninsky prospect 47 (UdSSR)
Angew. Chem. infernat. Edit. 1 Vol. I 1 (1972) 1 N o . 6
[I] 0. M . Nefedoc and A. I . Dyachenko, Doklady Akad. Nauk SSSR
198, 593 (1971).
[2] 0.M . Nefedou, A. I . Dynchenko, and A . Yn. Shteinshneider, Izv
Akad. Nauk SSSR, Ser. Khim. 1971, 1845.
[ 3 ] 0 .M . Nefedou, A. 1. Dyachenko, and A. Ya. Shteinshneider: V. International Conference on Organometallic Chemistry, Abstracts. Moscow
1971, Vol. 1, p. 598.
[4] G. KBbrich, Angew. Chem. 79, 15 (1967); Angew. Chem. internat.
Edit. 6, 41 (1967).
[5] G. Kobrich, H . Biittner, and E . Wagner, Angew. Chem. 82, 177
(1970); Angew. Chem. internat. Edit. 9, 169 (1970).
[6] Reaction mixtures of ( I ) or (2), preheated to temperatures 10 to
20°C below the decomposition temperature, gave o-XC,H,COOH or
C1,CCOOH (80-100% yields) with CO, (after acidification), and
XC,H, or CI,CH (S5-100% yields) with alcohols.
r.71 R. H! Hoffmann: Dehydrobenzene and Cycloalkynes. Academic
Press, New York 1967, pp. 9ff, 43ff.
[8] H . Gilman and R . D. Gorsich, J. Amer. Chem. SOC.78, 2217 (1956)
[9] EHT calculations on the C1,CLi molecule have shown that an
electron transfer from C1 to Li corresponds to the transition from the
ground state of the molecule to the first excited state.
[lo] H . L. Lewis and T L.Brown, J. Amer. Chem. Sac. 92,4664 (1970).
507
via the intermediate anion (C1,C-) but occurs as a concerted a-elimination of LiCl from the complex of (2) with ether
or amineIQl.
It is noteworthy that the temperatures of decomposition of
(2) in triethylamine and acyclic ethers are the same. This
fact may serve as further evidence for the above mechanism, because, according to Lewis and Brown[1oJ,
complexes
of alkyllithium compounds with dialkyl ethers and corresponding trialkylamines are equally stable.
Received: February 28,1972 [Z 610 IE]
German version: Angew. Chem. 84, 527 (1972)
Formation of Macrocyclic Polyolefins
on Autoxidation of Bifunctional
Alk ylenephosphoranes
By Hans Jiirgen Bestmann and Hans Pfiiller["
Dedicated to Professor Georg Wittig on his 75th birthday
Autoxidation of alkylenephosphoranes (ylides)of structure
R-CH=P(C,H,),
affords olefins R-CH=CH-R[']
and triphenylphosphane oxide. If bifunctional alkylenephosphoranes (bisylides) ( I ) are used, cycloolefins (2) ['* 31
are obtained. ( I ) , R=-(CH,),--,
reacts with cyclizing
dimerization to yield 1,5-cyclooctadiene[ZJ.Our further
investigations have given the following results :
If the structure of the starting bisylide of type ( I ) permits
intramolecular ring closure on autoxidation, yielding a
five-, six- or seven-membered ring, such a ring is formed
either mainly or exclusively. A compound such as ( 3 ) ,
however, does not yield any medium-size ring compounds,
e. g. ( 4 ) , but macrocyclic polyolefins such as ( 5 ) -(9) are
obtained by dimerization, trimerization etc. Further
examples are collected in Table 1.
Correct analytical data and NMR and mass spectra are
available for all the pure mono-, di-, and tri-mers listed in
the Table. Formation of further cyclooligomers, of which
in some cases only the trimer could be isolated, can be recognized by C, H analyses, NMR spectra, and clearly from
the field ions in the mass spectrum; here the molecular ions
gave the strongest mass lines, e.g. (6) M' =414, ( 7 )
M' = 552, (S} M' = 690, (9) M' = 828. After hydrogenation, correspondingly heavier molecular ions appear.
For examples 4,6 and 7, the proportion of cis,cis-isomer in
the dimer was determined (silver nitrate complex). It was
then shown that this isomer was formed preferentially:
cis,cis-1,9-cyclohexadecadiene.2AgN03, m.p. 142 to
143"C, 78 % ; cis,cis-l,l0-dioxa-5,14-cyclooctadecadiene~
2AgN03, rn.p. 153"C, 62%; &,cis-1,ll-cycloeicosadiene.2AgN03, m.p. 135-136°C (m.p. 136-137°C[61)
78 %.
All the bifunctional alkylenephosphoranes, except that
used for No. 5 of the Table (poor yield), are sparingly
soluble in dimethyl sulfoxide. We therefore assume that
formation of macrocyclic rings on autoxidation of the bisylides in an intermolecular Wittig reaction (according to
begins with formation of a cis-double bond. SubRef. [I])
sequently, either an intramolecular reaction may occur or
the chain may grow by further intermolecular C=C junctions before ring closure to the cyclooligomer follows.
1,lI-Cycloeicosadiene ( 5 ) and oligomers (6)-
(9)
1,1O-Decamethylenebis(triphenylphosphonium bromide)
(49.5 g, 0.06 mol) is converted by the dimethyl sulfinate
rnethodI4' into a suspension of the corresponding bisylide
in dimethyl sulfoxide, through which, in the apparatus
(3)
[*] Prof. Dr. H. J. Bestmann and Dr. H. Pfuller
Institut fur Organische Chemie der Universitat Erlangen-Numberg
8520 Erlangen, Henkestrasse 42 (Germany)
508
described previously"], oxygen is passed with ice-cooling
and magnetic stirring until the ylide precipitate has dissolved and a brown solution results (oxidation time 3 h ;
Angew. Chem. internat. Edit. i Vol. 11 (1972) i No. 6
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