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Non-Ergodic Behavior of Excited Radical Cations in the Gas Phase.

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[l] D. Erodullu, D. Mooiz, poster at the Symposium des Arbeitskreises
KSAM der GDCh-Fachgruppe ,,Analytische Chemie" in Martinsried
(Germany), March 1981.
[2] Syntex P2, four-circle diffractometer with modified LT-I cooling unit,
Mo,,,, o-scan, 20,,,, =60", 762 reflections, of which 722 observed
(Fo>3uF), program system EXTL, R , =0.026.
[3] The crystal structure of [(HOC2H,),NH]+SH- (unpublished) shows the
same geometry for the singly protonated molecule.
[4] W.Saenger, Nature 279, 343 (1979).
151 C. K. Johnson, ORTEP 11, Report ORNL-5138, Oak Ridge National La.
boratory, Oak Ridge, Tenn. (1976).
(' : *) proportions. Furthermore, the kinetic energy
release, T, for the I3CH3- and "CH3-eliminations, would
be expected to be closely similar. If, however, the internal
energy of (2,* is distributed non-statistically
to
ciation (i. e. the behavior is non-ergodic), then-despite the
equivalence O f both methyl group-the two I3CH3 and
Non-Ergodic Behavior of Excited Radical Cations
in the Gas Phase[**]
By Gisbert Depke, Chava Lifshitz, Helmut Schwarz, and
Eva Tzidony"l
Dedicated to Professor Hans D. Beckey on the occasion
of his 60th birthday
One of the central questions in reaction dynamics today
is whether highly excited molecules behave ergodically['],
i. e. whether unimolecular dissociations are slower than intramolecular vibrational energy redistribution. It has been
shown for neutral molecules[21that energy randomization
is completed within a few picoseconds and that molecules
behave non-ergodically only under special conditions['"]. If
similar non-ergodic behavior were found in ionic systems,
then one of the basic assumptions of the quasi-equilibrium
theory ( Q E P of mass spectra'31would be violated.
Evidence for the non-statistical behavior of the enol radical cation of acetone ( I ) , through measurements of kinetic energy release distributions T of the dissociation
fragments, has recently appearedl4]. In that study and in
previous ones[51,[2H]-labeled isotopomers of (1) were employed and there was the ever present possibility of kinetic
isotope effects. In order to circumvent this problem, we
have now prepared the [13C]-labeledisotopomers ( l a ) and
(lb). We report here on the unimolecular dissociation of
this radical cation in the gas phase and present evidence
indicating that this system is characterized by non-ergodic
behavior.
The study of ['HI-labeled ions (l),strengthened by thermochemical
has shown that the CH3-cleavage from metastable ions (1) (lifetimes = lo-' s) does not
take place by direct a-cleavage ((1)#(3) + CH3), but by dissociation to ion (5) following a rate determining [1,3]-Hshift ((1)- (4)+(2)) (Fig. 1). A highly excited intermediate
acetone radical cation (2)* is formed, whose lifetime has
been estimated to be 5 x
d4].
If (2)" were to behave ergodically, one would expect, on
the basis of the chemical equivalence of the two methyl
groups, that the two specifically ['3C]-labeled ions ( l a ) and
( l b ) would eliminate the radicals I3CH; and "CH; in
1'
,OH
HZC =c\ ,]
CH3
i 10)
I1
P.7'
C H3
(I h )
0 Verlag Chemie GmbH, 6940 Weinheim, 1981
Fig. 1. Energy profile for the isomerization and dissociation of the en01 radical cation of acetone (1). The reaction coordinate is complex; it involves a
[1.3]-H-shift ((T)-(2*)), followed by a C-C-cleavage leading to formation of
the acyl ion (5).
"CH3 radicals would be expected to cleave-off at different
rates. Previous data[4.5al indicate that discrimination
against the CH3 group, which is originally present in (I), is
to be e ~ p e c t e d [ ~ and
. ' ~ ] that the T-value for the elimination
of this group should be smaller than for the alternative
process in which the methyl radical is formed from the original CH, group and the hydrogen atom of the OH
group.
Table I . "CH3- versus 12CH3-eliminationfrom the radical cations ( l a ) and
(lb). The relative intensities were obtained from MIKE-spectra and the
translational energy values (calculated from the widths at half-height of the
metastable peaks) were obtained from high voltage scans (MAT 31 1 mass
spectrometer at 70 eV ionizing energy; 3 kV acceleration potential, 300 pA
emission current) [a].
Ion
(la)
(1b)
rel. intensity [%]
"CH,
12CH3
*
42.3 2 2.5
53.5 f 1.6
57.1 2.5
46.Sk1.6
T [meV
"CH3
12CH3
59.4
74
71.5
62.2
[a] Details concerning the methodology may be found in [5]. The ions ( l a )
and ( l b ) were produced from the ["C1-[abelled ketones. [l-'3C]-2-hexanone
and 13-"C]-2-hexanone. respectively, via McLafferty rearrangements.
The data presented in Table 1 (different loss of 13CH3
and I2CH3; LCH,
demonstrate quite convincingly
that the electron impact-induced unimolecular methyl
eliminations from the enol radical cation of acetone (1) do
not behave statistically. Hence, a fundamental assumption
of the quasi-equilibrium theory, namely that the distribution of internal energy between the vibrational states is statistical, is apparently violated by (1).
+
HzC=C\
[*I Prof. Dr. H. Schwarz, DipLChem. G. Depke
Institut fur Organische Chemie der Technischen Universitat
Strasse des 17. Juni 135, D-1000 Berlin 12 (Germany)
Prof. Dr. C. Lifshitz, E. Tzidony, M. Sc.
Department of Physical Chemistry, Hebrew University
Jerusalem 91 904 (Israel)
[*'I This work has been supported by the Fonds der Chemischen Industrie,
the Deutsche Forschungsgemeinschaft and the Technische Universitat
Berlin (Exchange Program TUBIHUJ).
792
(1)
Received: February 24, 1981 [Z 852 IE]
German version: Angew. Chem. 93, 824 (1981)
CAS Registry numbers:
(la), 78790-65-5; (lb), 78790-66-6.
OS70-0833/81/0909-0792 $02.50/0
Angew. Chem. fni. Ed Engl. 20 (1981) No. 9
[I] I . OreL B. S. Rubinouitch, Acc. Chem. Res. 12. 166 (1979).
121 a) J. D. Rynbrandt. B. S. Rubinouitch, J. Phys. Chem. 74, 4175 (1970);
ibid. 75, 2164 (1971); J. Chem. Phys. 54, 2275 (1971); b) R. A. Coueleskie.
D. A. Dolson. C . S. Purmenter. J. Chem. Phys. 72, 5774 (1980).
131 H. M. Rosenstock, M . B. Wallenstein. A. L. Wahrhu/tig, H. Eyring, Proc.
Natl. Acad. Sci. USA 38, 667 (1952); C. L ~ s h i t z .Adv. Mass Spectrorn.
7A. 3 (1977).
[41 C. Lifshitz. E. Tzidony, Int. J. Mass Spectrom. Ion Phys. 39, 181 (1981).
151 a) F. W. McLnflerty, D. J . McAdoo. J. S . Smith, R. Kornfeld, J. Am.
Chem. SOC.93,3720 (1971); b) J. H. Beynon, R. M . Cuprioli, R. G. Cooks,
Org. Mass Spectrom. 9, 1 (1974); c) C. Lifshirz, E. Tzidony, D . T. Tenuillinger. C. E. Hudson, Adv. Mass Spectrom. 8, 859 (1980).
[6] R. G. Cooks. J . H . Beynon, R. M . Cuprioli, R. G. Lester: Metastable Ions,
Elsevier, Amsterdam, 1973.
Synthesis of Hydrido(phenyl)osmium(n)- from
Benzeneosmium(o)-Complexes: Intramolecular
Insertion of a Lewis Basic Metal Atom into an sp2C-H Bond"'
By Ruiner Werner and Helmut Werner"]
In recent years, considerable interest has been shown in
the problem of activating C-H bonds by transition metals. Green et a1.l2] found that e. g. bis(cyc1opentadieny1)tungsten ("tungstenocene"), prepared in situ by photolysis of (C,H5),WH2 or thermolysis of (C,H,),WH(CH,),
can react with arenes by insertion into an sp2-C-H
bond.
We recently reported the synthesis of a series of benzeneosmium(o) complexes of the type C6H60SLL'r3! If tertiary
phosphanes or phosphites are selected as the ligands L and
L', the compounds obtained, as shown in eq. (a), are
thermolabile; they decompose even during attempts to
separate off the naphthalene formed as by-product.
ture both (I) and (2) react very slowly with trimethylphosphane; after 24 h only a slight reduction in the concentration of the alkene complex is detected as indicated by
NMR spectroscopy. Upon warming the solution (C&,) to
70°C [for ( I ) after 20 h, for (2) after 5 h] compound (3) is
formed practically quantitatively. Instead of the expected
exclusive displacement of the alkene, insertion of the osmium into a C-H bond of the benzene also occurs.
Repetition of the reaction in C6D6 indicates that an intramolecular oxidative addition has occured; only (3). and no
complex containing the OS(C&)D grouping, is formed.
Hence, the insertion of the metal does not proceed via a
benzene/phosphane exchange.
The changes in the 'H-NMR spectrum provide information on the course of the reaction. While no intermediate
product is observed in the formation of (3) from (2), such a
species can be unequivocally detected in the reaction of (I)
with PMe3. Its spectroscopic data (Table 1) confirm the
structure (C2H4)(PMe3)30s(C6H5)H(4). When the reaction
of (1) with PMe3 (molar ratio I :4) in benzene is interrupted after 2 h, a mixture of 80% (41, 10%( I ) , and 10%(3)
is obtained. Almost pure (4) was obtained by recrystallization and this was characterized by mass spectroscopy. In
the presence of excess trimethylphosphane, (4) reacts completely to give (3). An ethylosmium complex cannot be detected, i.e. no insertion of the coordinated ethylene into
the 0s-H bond occurs. Furthermore, a reductive elimination of benzene from (3) in the presence of trimethylphosphane cannot be observed.
In order to clarify the stereochemistry of the final step in
the synthesis of (3) from (I), (4) was reacted with PMe2Ph.
The ethylene coordinated in the trans-position to the hydride ligand is quantitatively exchanged after 7 h (C&,
70 "C). In a reaction which proceeds with rigorous stereospecificity, the phosphane occupies the alkene-site, which
was verified by selective decoupling experiments. The formation of (3) and (PMe3)3(PMeZPh)Os(C6H,)H(5) from (I)
can therefore be formulated as follows:
The alkene(trimethy1phosphane)complexes
C6H60s(PMe3)C2H3Rare considerably more stable and
are obtained in an analogous way to that shown in eq. (a).
They can be isolated in pure form by reaction of the hydrido cations [C6H60~H(PMe)3C2H3R]e
with NaHI3].
H
C6H60s(PMe,)C2H,R
HQ
[C6H60sH(PMe3)C2H3RIm
H
(b)
(I), R = H
(2). R = M e
Our attempt to synthesize the bis(trimethy1phosphane)
complex C,&oS(PMe3)2,
which should be an even
stronger
Lewis
base
than
the
homologous
C6H6RU(PMe3)2f4',by exchange of the coordinated alkene
in (I) or (2) for PMe, was unsuccessful. At room tempera[*] Prof. Dr. H. Werner, DipLChem. R. Werner
Institut fiir Anorganische Chemie der UniversitSt
Am Hubland, D-8700 Wiirzburg (Germany)
Angew. Chern. Ini. Ed. Engl. 20 (1981) No. 9
In the intermediate product (Z),we postulate a q4-c00rdination of the benzene, which is not without precedent in
the chemistry of areneruthenium(0) and osmium(o) complexe~[~].
The question of whether the hydrido(o1efin) compound (4) is formed from (7) via a one-step reaction or
0 Verlag Chemie GmbH. 6940 Weinheim, 1981
0570-0833/81/0909-0793 $02.50/0
793
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