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Bridgehead Reactivities of Trishomobarrelene and Trishomobullvalene.

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occupied molecular
orbitals becomes E = 014 x
(- 5f
Qualitatively the orbital scheme
given for ( 2 a ) in Figure 1 is retained, i.e. AE1,,z4AE2,,
is valid for the energy differences AE1,’ and AE2,3between
the three highest occupied orbitals. 0 and p’ are of the same
order. The energy level diagram for the ion (3) should be
similar.
v-).
Received: August 10,1971;
supplemented: November 22,1971 [Z 533 IE]
German version: Angew. Chem. 84,65 (1972)
Bridgehead Reactivities of Trishomobarrelene
and Trishomobullvalene[*”]
By Arrnin de Meijere, Otto Schallner, and
Christian Weit erneyer 1’’
The extent to which a carbonium ion is stabilized by acyclopropyl substituents depends upon the orientation of
the cyclopropane rings relative to the axis of the adjacent
vacant p orbital of the carbonium ion“]. Whereas the tricyclopropylmethyl cation is about as stable as the triphenylmethyl cation[’], destabilization is observed in a
Hb
(3c), m.p. 91°C. Photochlorination of (2) in carbon
tetrachloride with tert-butyl hypochlorite at - 20°C yielded 30% of pure I-chlorotrishomobullvalene (3d), m. p.
128-129 “C. I-Chlorotrishomobarrelene ( 4 ) , m. p. 114 to
116”C, could be obtained analogously in the same yield.
The NMR- and mass spectra as well as elemental analyses
of compounds (3b) -(3d) and ( 4 ) are in accord with the
proposed structures.
The exclusive substitution at the bridgehead positions in
( 1 ) and (2) observed in the reported reactions suggests a
special reactivity of these positions. In order to obtain
some information about the stabilization of the bridgehead carbonium ions of (1) and ( 2 ) , we measured the
half-reaction times of the solvolysis of (3d) and ( 4 ) in
90% aqueous ethanol171.The rate constants which were
estimated from these data (see Table 1) indicate that at
25°C ( 4 ) reacts about 300 times faster than tert-butyl
chloride ( 5 a ) and more than lo9 times faster than l-chlorobicyclo[2.2.2]octane ( 6 a ) [*I.
(3d) is so reactive that it is readily hydrolyzed to the alcohol
(3 b ) upon exposure to moist air; in 90% aqueous ethanol
even at 0°C it is solvolyzed so rapidly that the half-reaction
time could not be measured very accurately. At 0°C (3d)
reacts more than 10” times faster than (6u) at 25°C.
The geometry of ( I ) and (2) which is pertinent to this
reactivity may be estimated from NMR-spectroscopic
data (see Table 2). The 13C,H coupling constants indicate
that the bridgehead carbon in (2) is sp3 hybridized whereas
the bridgehead C-H bond in (1) exhibits a slightly higher
( 6 ~ 1x
, = CI
(6b). X = B r
Table 1. Relative solvolysis rate constants of some tertiary halides in
90% aqueous ethanol.
t (“C)
case in which the plane of the cyclopropane ring and the
axis of the vacant p orbital are held perpendicular to each
otherc3]. In “trishomobarrelene” ( I ) and “trishomobullvalene” (2)[“l the “propeller”-cyclopropane rings are
arranged in such a way that a partial stabilization of the
corresponding bridgehead carbonium ions should result.
Bridgehead substituted derivatives of ( I ) and (2) are
accessible by radical substitution reactions. (2) is readily
autoxidized; upon standing in the presence of air the
hydroperoxide (3a) is formed. (3a) decomposes upon
heating to 100°C to give the alcohol (3b), m.p. 183 to
186”C, which could be isolated in 10-15% yield by gas
chromatography. The reaction of (2) with dichlorocarbene,
generated by the method of Makosza and Wawrzyniewicz15.61, gave a 60% yield of the dichloromethyl derivative
[*I
Dr. A. de Meijere, Dip1.-Chem. 0. Schallner, and
DipLChem. C. Weitemeyer
Organisch-chemisches Institut der Universitat
34 Gottingen, Windausweg 2 (Germany)
Presented at the “International Symposium,on the Chemistry of
Small Ring Compounds and Activated Multi~ leBonds”, Louvain,
Belgium, Sept. 13-16, 1971.
[**I
56
25
0
25
25
25
25
k (sec- I )
5.5 x
[a]
(7 x lo-’) [a]
1.73~10-~
7.14~
<4x1O-I3
4.05 x lo-’’
k,d
3x102
(4 x lo4)
1.o
41
< 2.3 x 10- 7
2.34 x
k.4
>lo9
> 10“
5x106
5x10’
1.0
> 10
Ref.
[lo]
[lo]
[8]
191
[a] Estimated from the measured half-reaction time.
s character, i. e. the C-C-C
angles at the bridgehead in
( I ) are smaller than in (2). The dihedral angles (cpHH) between the bridgehead protons (Ha) and the adjacent
tertiary cyclopropyl protons (Hb) can be estimated from
between the two“
the vicinal coupling constants (35HH)
(see Table 2). The angle between the plane of a cyclois
propane ring and a vacant bridgehead p orbital (cp,-J
approximately 90” - pHH.
Since the energy of interaction
between two %-electron systems is proportional to cos’ cp
of the torsional angle cp between the two”21,one may derive
the crude approximation that the stabilization of the
bridgehead carbonium ion per a-cyclopropyl group in ( I )
should be about 67% and in (2) about 45% of the greatest
possible stabilization.
The experimentally determined reactivities of (3d) and
( 4 ) are in satisfactory agreement with these estimates.
Angew. Chem. internat. Edit. 1 Vol. I1 (1972) / No. I
Table 2. 13C,H- and vicinal H,H-coupling constants of the bridgehead
protons in ( 1 ) and (2).
Cpd.
J,,<H
(Hz)
scharacter
3J,ie,(Hz)
(%)
(I)
(2)
137
127
27 [a]
25 [a]
4.24
5.44
Ti,,,
qp-,, E, E ,
(7
(")
55
42
35
0.67
48[14] 0.45
[a] Calculated from !he equation % S = J ~ ~ ~ , , / S O[13]
O
Although the effect of stabilization in ( 4 ) is predicted to
be larger than in (3d), the latter reacts about 10' to l o 3
times faster than ( 4 ) because the bridgehead in ( 3 d ) is
less strained and therefore the corresponding carbonium
ion should more readily attain planarity.
Received: September 24, 1971 [Z 530 IE]
German version: Angew. Chem. 84,63 (1972)
[I] For references see [3a].
[2] H . A. Hart and J . M . Sandri, J. Amer. Chem. SOC.81, 320 (1959);
H . A . Hart and P. A. Law, ibid. 84, 2462 (1962);86, 2959 (1964).
[3] a) P. con R. Schieyer and 1/: Buss, J. Amer. Chem. SOC.91, 5880
(1969); b) J . C . Martin and B. R. Ree, ibid. 91, 5882 (1969).
[4] A. de Meijere and C . Weitemeyer, Angew. Chem. 82, 359 (1970);
Angew. Chem. internat. Edit. 5, 376 (1970).
[5] M . Makosza and M . Wawrzyniewicz, Tetrahedron Lett. 1969,4659.
161 Cf. I . Tabushi, Z . Yoshida, and '
I
Takahashi, J. Amer. Chem. SOC.
92, 6670 (1970).
[7] Exact kinetic determinations are in progress
[8] The solvolysis rate constant of ( 6 a ) is unknown, therefore it was
estimated from the value for ( 6 6 ) [9] and the known difference between
the rates of ( S a ) and ( 5 b ) .
191 Calculated from the measured value for 80% aqueous ethanol;
P. Brenneisen, C. A . Grob, R. A . Jackson, and M . Ohta, Helv. Chim.
Acta 48,146 (1965).
[lo] E. Grunwald and S . Winstein,J. Amer. Chem. SOC.70, 846 (1948).
[I13 M . Karplus, J. Chem. Phys. 30, 11 (1959); in the present case a
Karplus equation was used which was fitted for the vinylcyclopropane
system with empirical constants: H. Kiose, Dissertation, Universitat
Koln 1969.
[I21 I . Fischer-Hjalmars, Tetrahedron 19,1805 (1963).
1131 D.Seebach,Angew. Chem. 77,119 (1965);Angew. Chem. internat.
Edit. 4, 121 (1965).
[I41 Noreadded inproof(Dec. 5,1971):An electron diffraction structure
analysis of ( 2 ) has indicated that the angle cpp-. is actually about 65",
i.e. larger than the crude estimate obtained from the H,H-coupling
constant. This will probably also apply to (1) (B.Andersen, A . de Meijere,
and 0.Schallner, unpublished results).
Mossbauer Measurements on
Neptunium(vI1) Compounds[**]
By Klaus Frohlich, Philipp Giitlich, and Cornelius Keller[']
Until a few years ago neptunium(vr1)compounds were unknown. Recently, a number of neptunium compounds were
prepared, which, on the basis of the preparation method
and stoichiometric composition, are supposed to contain
heptavalent neptunium (nominal valency with electronic
configuration [Rn]5p 6d0 SO)['-^^. We have carried out
Mossbauer measurements on a few of these compounds,
namely Li,NpO, ( I ) , [C0(en),]Np0,.xH,O[~~ ( 2 ) ,
[*] Prof. Dr. P. Giitlich and Dr. K. Frohlich
Eduard-Zintl-Institut fur Anorganische und Physikalische Chemie
der Technischen Hochschule
61 Darmstadt, Hochschulstrasse 4 (Germany)
Prof. Dr. C. Keller
Kernforschungszentrum
7 5 Karlsruhe, Postfach 3640 (Germany)
[**I This work was supported by the Deutsche Forschungsgemeinschaft and the Bundesministerium fur Bildung und Wissenschaft.
Angew. Chein. internat. Edit. J Vol. I I (1972) J No. 1
Ba,(NpO,),~xH,O (3), and Ca,(NpO,),.xH,O ( 4 ) , to
prove the oxidation state of the neptunium and to learn
more about the structural and bond properties[*].
All measurements were made with source and absorber at
4.2K. The compounds were used as absorber and the
source was an alloy of 241Am(5%) in thorium metal.
A more negative isomer shift (6) than that for NpF, was
obtained for all the materials studied (see Table). [According to previous Mossbauer spectroscopic investigations of
neptunium(v1) compounds, NpF, is the most ionic in
character and consequently exhibits the most negative
isomer shift : its value, 6 = - 58 mm/s (relative to N P O , ) [ ~ ~ ,
is the lower limit of the assumed characteristic isomer-shift
range for Npv' compounds.] Since A(r2)/(r2) for 237Np
is negative"'], it follows from the 6 values that the electron
density at the neptunium nucleus of the compounds under
investigation is greater than in the case of NpF,. In the
oxygen-bonded compounds the valence electrons of the
oxygen, which tends to be more covalent than fluorine,
mainly occupy orbitals of the neptunium atom which
shield s electrons from the nucleus. The covalent contribution to the Np-0 bonding must introduce additional
shielding to the s electrons of the central neptunium atom
and thus lead to a lower electron density at the Np nucleus
in Np-0 compounds compared to Np-F compounds.
The higher electron densities following from the measured
6 values can be adequately explained only by the presence
of heptavalent neptunium. The absence of the last 5f electron in Np(v1r)-compared to Np(v1)-results in a weaker
shielding of the s electrons (mainly on the 6s shell) and thus
leads to the observed increase in electron density at the
Np nucleus.
Table. Isomer shift (6), quadrupole splitting ( A E Q ) ,and asymmetry
parameter (q)of neptunium compounds (1) - (4). Source (24'Am/Th)
and absorber at 4.2 K.
Absorber
(11
(21
(31
(4)
8 [a1
[mm s-'I
AEQ
[mm
-68.7t2.9
-61.1 f2.6
-60.2k2.8
-60.7k3.0
15.3+0.5
44.6k1.0
43.2k1.0
33.7k1.0
rl
SC']
0.33 kO.01
0.23 i0.02
0.40 _+ 0.03
0.38f 0.03
_-
[a] Isomer shift relative to NpO,.
The occurrence of quadrupole splitting AEQ(see Table) in
the case of Li,NpO, ( I ) disproves the previously presumed
0, symmetry of the NpOiPresent findings are
more consistent with a compressed octahedron (neptunyl
group in the z direction). The deviation of the asymmetry
parameter q from zero (see Table) indicates that the central
Np atom is not situated at the symmetry center (e.g. due to
presence of a non-linear neptunyl group) or that the xy
plane formed by oxygen atoms is rhombically distorted.
The AEQ values for compounds ( 2 ) , ( 3 ) , and ( 4 ) are two
to three times greater than the value for ( I ) . This is explained as being due to the Np-0 bond lengths of the neptunyl
group in these compounds being shorter than in Li,NpO,.
The more positive 6 values measured for these three compounds support this explanation. The deviations of the q
values from zero suggest that the common anion formed
by all three compounds is [Np0,(OH),]3and not
NpO:-. The presence of both trans-0 atoms and trans-OH
groups in this anion in addition to the neptunyl group
readily explains the observed values of the quadrupole
splitting and asymmetry parameters (the two Np-0 bond
lengths in the xy plane are smaller than the Np-OH dis57
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