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Kinetics of the Homotropilidene Valence Tautomerism.

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except in cyclohexane, methylcyclohexane, or pentane ;
this property depends strongly on the nature of the metal
atom M (Mo > W) and the substituents on the silicon :
(CH,),Si > CH,SiHCI
= CH,SiCI,
> HSiCl, z SiBr, > SiCI,
The fact that compounds of type
(n-C,H,)(CO),M-M(CO),(x-C,H,)
are found after decomposition indicates that the metal-silicon bond is more
labile in these cases than in the Co, Fe, and Mn analogs.
Kinetics of the Hornotropilidene Valence
Tautornerisrn["]
By H a r d Giirither, Josef Bernd Pawliczek, Joachim Ulmen,
and Woifram Grirnme[*]
The ability to detect fluxionalsystemsby NMR spectroscopy
was impressively demonstrated for the first time in the case
of bicyclo[5.1 .O)octa-2,5-diene(3,4-homotropilidene)( I ) ['I.
There has as yet, however, been no study of the kinetics of
this rearrangement, which is preceded by a conformational
equilibrium [(A)+(B)][1*21,
because the spin system of (1 )
(10H)%.toocomplicated for exact NMR line shape analysis.
This is also shown in the smooth replacement of the trimethylsilyl group in reactions with hetero~iloxanes['~~
:
T - C ~ H ~ ( C O ) ~ M - S ~ (+C (CH3),XOSi(CH3),
H~)~
-
The strong tendency to form the siloxane group provides
additional driving force in this reaction['61.
General procedure:
A 3-5-fold excess of the halosilane (12-20mmol) is
added to a suspension of Na[Mo(CO),(n-C,H,)] (1.1 g,
4.1 mmol). After 15-45 hours' stirring in a closed vessel
at 25 "C the insoluble material is removed from the reaction
mixture, and the filtrate is evaporated to dryness in an oilpump vacuum. The crude product is extracted with pentane;
from this solution the silyl complex can be obtained pure
on cooling (- 78 "C).
We have therefore synthesized the mixture of octadeuteriobicyclo[5.l.0]octa-2,5-dienes (2)+(2'), each component
having one dihydro-methylene group[31,and have, for the
Received: December 28,1971 [Z 590 I€]
German version: Angew. Chem. 84,538 (1972)
[I] L. H . Sommer, Pure Appl. Chem. 19, 525 (1969).
[2] A. D. Berry and A. G . MacDiarmid, Inorg. Nucl. Chem. Lett. 5,
601 (1969).
[3] Y: L . Baay and A . G. MacDiarmid, Inorg. Chem. 8,987 (1969).
[4] M . A . Nasta and A. G . MacDiarmid, J. Organometal. Chem. 18,
P 11 (1969).
[5] W Jetz and W A . G . Graham, J. Amer. Chem. SOC.89,2773 (1967).
[6] D. J . Cardin, S . A . Keppie, B. M . Kingston, and M . F . Lappert,
Chem. Commun. 1967, 1035; D. J . Cardin, S. A. Keppie, and M . F .
Lappert, J. Chem. SOC.A 1970,2594.
[7] A. P . Hagen, C . R. Higgins, and P . J . Russo, Inorg. Chem. 10, 1657
(1971).
[8] H . R. H . Patil and W A . G . Graham, Inorg. Chem. 5,1401 (1966).
[9] D.J . Cardin, S . A. Keppie, and M . F . Lappert, Inorg. Nucl. Chem.
Lett. 4, 365 (1968).
[lo] R. B. King,K . H . Pannel, C . R. Bennett, and M . Ishaq, J. Organometal. Chem. 19, 327 (1969).
[ I l l R. B. King, Accounts Chem. Res. 3,424 (1970).
1121 We thank N . Pelz for determining the mass spectra
[13] ,A part of the substance is decomposed during the ligand exchange
reaction.
[I41 H . Schmidbaur, Angew. Chem. 77, 206 (1965); Angew. Chem.
internat. Edit. 4, 201 (1965).
[I51 H . Schmidbaur and H . Hussek, J. Organometal. Chem. I , 244
(1964).
[I61 H . Schmidbnur and W Tronich, Chem. Ber. 101,3545 (1968).
Angew. Chem. internat. Edit.
Vo1. 11 (1972) 1 No. 6
k = 55s.'
L
Fig. 1. Temperature-dependent experimental (left) and theoretical
(right) 'H-NMR spectra of the methylene protons of ( 2 /+ ( 2 ' )
on H ( D) -decoupling ; signals of incompletely deuteriated material
appear below vA.
[*] Prof. Dr. H. Giinther, Dr. J. B. Pawliczek,
DipLChem. J. Ulmen, and Prof. Dr. W. Grimme
Institut fur Organische Chemie der Universitat
5 Koln, Zulpicher Str. 47 (Germany)
[**I Support of this work by the Landesamt fur Forschung of Nordrhein-Westfalen and the Deutsche Forschungsgemeinschaft is gratefully acknowledged.
517
+
first time, derived data for the rearrangement (2) (2')
between - 65 and 102"C from the temperature-dependent
line shape of the 'H-NMR spectrum (solvent [D,]toluene,
frequency 100 MHz, internal reference benzene).
With H(D}-decoupling, two AB systems (v, =620.6,, vb=
685.4,, and J=2.6, Hz, and v:=424.0,, vb=474.9,, and
J=20.6, Hz) are observed for (2)+(2') in the slow exchange region (-65°C) which must be assigned to the
CH, groups in structure ( 2 ) and (Z'), respectively (Fig. 1).
Temperature increase leads to line broadening, coalescence
(ca. 35°C) and finally in the region of fast exchange (40°C)
to an averaged spectrum: 3=523.0,, Cb=582.2,, and .f=
11.4, Hz. Integration of the low-temperature spectrum
gave different concentrations for (2) and (2') : K ( - 35 "C)
~ 0 . 9A
. similar isotope effect, namely that hydrogen in
competition with deuterium prefers the cyclopropyl to the
ally1 position, was recently observed for barbaralone14]and
for octadeuteriobicyclo[5.1.0]octa-2,4-diene~31.
To determine the rate constants k, the temperature-dependent line shape of the spectrum was calculated quantummechanically'51for the exchange process AB+ A'B' (Fig. I),
taking into account changes in the spectral parametersc6'
and the mole fractions. With 20 experimental points the
best Arrhenius equation for the reaction (2')-(2) was:
k
= 1011.5 *
0.1
exp [-(I2450 +220)/RT]s-'
and from a log (k/T)/(l/T)diagram the activation parameters AH* =11.8iO.2 kcal/mol and AS* = -8.Oi0.3
clausius were obtained. For 1,3,4,6-tetramethy1-3,4-homotropilidene AG* (OOC)was previously['] estimated as 13.6
kcal/mol. From the temperature-dependence of the K
values a AHo of 240k 25 cal/mol in favor of (2) was calculated by van't Hoffs equation.
Our results also make it possible to decide whether the
rearrangement ( l ) $ ( l ' ) proceeds through a transoid or a
cisoid transition state"]. From the 33,,, values found the
proton assignments (3A ) or ( 4 B ) can be made according
to whether the ground state of ( I ) has the conformation
( A ) or ( B ) :
symmetry according to whether it is derived from ( A )
(transoid) or ( B ) (cisoid), and the proton exchange must
follow this symmetry. Since the results of photoelectron
spectroscopy indicate conformation ( A ) for the ground
state of (I)['], the rearrangement must occur through the
cisoid transition state['*'I.
The energy profile { C ) or (D) may be discussed for the
reaction ( I ) + (1') that is accompanied by the conformational equilibrium ( A ) e( B ) . If the energy barriers for the
valence tautomerism in dihydrobullvalene ( 5 ) (12.6 kcal/
mol)['oland barbaralane ( 6 ) (8.6 kcal/mol)["] and for the
ring inversion of 1,3,5-cycloheptatriene(6 kcal/mol)['21are
considered, preference must be given to (C). The energy
difference between conformations ( A ) and ( B ) thus
amounts to 3 kcal/mol at most.
Received: January 10,1972 [Z 592 IE]
German version: Angew. Chem. 84,539 (1972)
[I]W ti. Doering and W R. Roth, Tetrahedron 19, 715 (1963); Angew.
Chem. 75, 27 (1963); Angew. Chem. internat. Edit. 2, 115 (1963).
[2] L. Birladeanu, D. L. Harris, and S . Winstein, J. Amer. Chem. SOC.
92, 6387 (1970).
[3] W Grimme and W uon E. Doering, to be published.
[4] J . C . Barborak, S. Chari, and P . uon R. Schleyer, J. Amer. Chem.
SOC.93, 5275 (1971).
[5] C. J . Cresswell and R . K . Harris, J. Magn. Res. 4, 99 (1971). We
thank Drs. R . K . Harris and M . Kinns for supplying a listing of their
program.
[6] The temperature-dependence of the resonance frequencies was
determined below the coalescence point.
[7] S . Forsen and R. A . Hoffmann, J. Chem. Phys. 39, 2892 (1963).
[8] P . Bischof, R. Gleirer, E . Heilbronner, V Hornung, and G . Schroder,
Helv. Chim. Acta 53,1645 (1970).
[9] Ref. [2] contains similar interpretations, but closer examination
shows that the experimental evidence given there is not sufficient
to answer the question about the conformation of the transition state
for the valence tautomerism ( 1 ) ( 1 ' ) satisfactorily.
[lo] G Schroder, J . F . M . Oth, and R. Merenyt, Angew. Chem. 77,
774 (1965); Angew. Chem. internat. Edit. 4, 752 (1965).
[I13 W ti. E. Doering, B. M . Ferrier, E. 7: Fossel, J . H . Hartenstein,
M . Jones, Jr., G . Klumpp, R. M . Rubin, and M . Saunders, Tetrahedron
23, 3943 (1967).
[12] a) F . A . L. Anet, J. Amer. Chem. SOC.86,458 (1964); b) F . R. Jensen
and L. A . Smith, ibid. 86, 956 (1964).
On the other hand, double resonance experiment^^^] yielded
theexchangeschemes H,+HI,and H,+Hb,i. e . A B e A ' B ' .
These agree with the assignments only if the valence tautomerism is preceded and followed by a conformational
change into the respective alternative conformations
[( 3 A ) -+ ( 3 B ) or ( 4 B ) + ( 4 A ) ] , because the transition
state for the rearrangement ( I ) e(1') has either C,, or C,,
Does 1-Norbornene Exist?
By Reinhart Keese and Ernst-Peter Krebs"'
We have reported that 1,2-exo-dihalonorbornanes
are bisdehalogenated by butyllithium and that in the presence of
furan the two diastereoisomers (6) and (7) result. The
constant product ratio led us to assume that l-norbornene was formed as an intermediate'']. We now have strong
evidence for the assumption that I-norbornene is actually
[*] Dr. R. Keese and E.-P. Krebs, Dip1.-Natw. ETH
Organisch-chemisches Laboratorium der
Eidg. Techn. Hochschule
CH-8006 Zurich, Universitatsstrasse 6 (Switzerland)
518
Angew. Chem. internat. Edit. 1 Val. 11 ( 1 9 7 2 ) 1 N o . 6
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