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Cycloadditions with Silver Ion-Stabilized (2RS 3RS)-3-Methoxy-trans-Cycloheptene.

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[ l ] cJ F Vijgtle. W M. Muller, E. Weber, Chem. Ber. 113. 1130 (1980).
I21 a) D. D. MacNicol, J. J. McKendrick. D R. Wilson, Chem. SOC.Rev. 7. 65
(1978). b) K. Pollmer, 2. Chem. 19, 81 (1979).
131 J. H Jones. G. T Young, J. Chem SOC.C 1968. 436
(41 The compounds gave satisfactory elemental analyses and appropriate spectra
(51 Analogous stoichiometry and similar decomposition ranges are observed with
tri-o-thymotide clathrates: cf W. Baker, B. Gilbert. W. D. Ollis. J . Chem SOC
1952, 1443.
[6] a) D. Lawton, J. Chem. SOC.IPS& 2339; b) D. J. Williams. D. Lawton. Tetrahedron Lett. 1975, 111
[7] We thank Prof. Dr. M. R. Truter, Cambridge, for communication of the
structure of [18]crownd.dimethyl sulfone complex. The CH3 hydrogen
atoms of the guest form H bonds with the oxygens of the host crown.
[S] Analogous O H . . - N bonds exist in bipyridine . resorcinol adducts. We thank
Prof. Dr. W. H. Watson, Texas Christian University, for communication this
result prior to publication; cf. C. Oepen. F. Vogtle, Justus Liebigs Ann. Chem.
1979, 2114.
(91 a ) C. Allegro, M. Farina, A . Immirn, A . Colombo, U. Ross;. R. Broggi, G. Natfa, J. Chem. SOC.B 1967, 1020, 1028; b) W. Boker, K. M. Bug& J. F. W
McOmie, D. A. M. Warkins, ibid. 1958, 3594.
Cycloadditions with Silver Ion-Stabilized (2RS,3RS)3-Methoxy-trans-Cycloheptene[**~
By Heiner Jendralla[’]
While compounds having a trans double bond in an eightmembered ring are as a rule stable at room temperature, no
stable trans-cycloheptene or a corresponding bridgehead olefin could be prepared despite continued efforts[’’. Trapping
experiments on photochemically generated rrans-cycloheptene revealed that its lifetime at - 10 “ C is 23 minutes12’.
“Normal” deamination of the nitrosourea (1) in weakly
basic methanol led to the unstabilized title compound (2) as
intermediate together with (8) as primary product13].Though
(2) rapidly isomerizes to the cis-olefin (7) at room tempera-
[‘I
Dr. H. Jendralla
Institut fur Organische Chemie, FB9
Gesamthochschule. D-5600 Wuppertal 1 (Germany)
I”] This work was supported by the Deutsche Forschungsgemelnschaft and the
Zentrale Verfugungsfonds der G H Wuppertal. 1 am indebted to Dr. W. Dietrich
(Universitat Bochum), who kindly recorded the ”C-NMR spectra.
1032
0 Verlag Chemie, CmbH, 6940 Weinheim, 1980
ture[‘], it can be trapped to the extent of 95% in the form of
the cycloadducts ( 3 4 and (3b) on deamination of (1) in methanol/f~ran[~~.
On addition of silver perchlorate or trifluoromethanesulfonate (triflate) to a methanolic solution of (1) the deamination proceeds without the necessity of a base. If the reaction
product is partitioned between ether and water, the ether extracts contain a mixture of the products (7), (S), and small
amounts of (9). If ammonia is now passed through the aqueous solution and the extraction is repeated, practically only
(7) with small amounts of (9) and no (8) are found in the extract. Since the cis-olefin (7) forms no water-soluble silver
perchlorate complex under the reaction conditions, this experiment indicates the reversible stabilization of the transolefin (2) as the water-soluble silver(1) complex (6)IS1.Removal of water in uucuo affords (6) as a colorless, thermally
stable and moderately light-sensitive powder. The triflate
complex could be isolated analytically pure by recrystallization (ethyl acetate/pentane/ - 30 oC)[61.Elemental analysis
gave a n olefin/silver ratio of 1:I[’]. The trans-configuration
of the double bond and the configuration of the methoxy
group follow from the identical ‘H-NMR spectra of (6a) and
(6b). I-H (6=5.80) and 2-H (5.50) form a n AB system; the
large coupling constant J,.2
= 17.9 Hz confirms their trans
orientation. 2-H also couples with 3-H (J2,3=7.9 Hz), whilst
1-H couples differently with the two protons on C-7
= 4.3 Hz). The magnitude of J2.3
confirms
(J1.,= 9.2 Hz, J1.,.
the (2RS, 3RS)-configuration of @)[’I
previously deducedr3]
from the adducts ( 3 4 and (3b). The very good agreement of
the proton coupling constants of ( 6 4 and (66) with those of
3-methoxy-trans-~yclooctene[~~
would suggest that the homologous olefins have a similar conformation. If one assumes
that the olefin in (6) has the crown conformation (“eight-
shaped loop”) already demonstrated in the case of trans-cyclooctene[*l, C-5 is found to be located exactly “behind” the
double bond, i. e. should lie centrally in the shielding cone of
anisotropism. The I3C-NMR spectra of (6a) and (6b) contain four triplets. C-5 is shielded by about the same amount
0570-0~33/80/1212-10~2 S 02.50/0
Angew. Chem. In(. Ed. Engl. 19 (1980) No. 12
(8 ppm) compared to C-4 and C-6 as C-7 is deshielded due to
its allylic
An X-ray structure analysis of (6b) is in
progress.
The silver complex ( 6 4 reacts with dienes at room temperature to give the corresponding cycloadducts (3) and (10)(33). Gas chromatographically, the sole impurity found in all
cases was the cis-olefin (7) (2-13%). The following diastereomeric ratios a / b were determined by capillary gas chromatography: (3): 4.4:l; (11): 2.0:l; (12): 2.4:l. The ratio a/
b = 4.4 :1 of the furan adducts (3)differs drastically from that
found in the trapping of free trans-olefin (2) ( a / b = 0.95 :l)l3l
and suggests that part of the cycloaddition takes place in the
ligand sphere of the silver ion. The insolubility of ( 6 4 in solvents suitable for anthracene hinders cycloaddition of the
complex. However, (13) (m.p. 122°C) was obtained when
ammonia was passed into the stirred suspension of (6a) in
the saturated anthracene solution in dichloromethane. Reaction of (6a) with trans-cyclooctene (5) gave tris(trans-cyc1ooctene)silver perchlorate (4),m. p. 197 "C (decomp.). Preliminary experiments show that cis,trans-cycloheptadienes
can also be stabilized as silver complexes.
Received: January 4, 1980 IZ 645 IE]
supplemented: April 15, 1980
German version: Angew. Chem. 92, 1068 (1980)
[I] J. F Liebman. A. Greenberg, Chem. Rev. 76, 31 1 (1976); E. J. Carey, F A.
Carey, R. A. E. Winler, J. Am. Chem. SOC.87, 934 (1965).
[2] J. Inoue, S. Takamuku, H Sakurai. J. Chem. SOC.Perkin Trans. I1 1977,
1635.
[3] W. Kirmse, H . Jendralla, Chem. Ber. 111, 1857 (1978).
[4] N o cycloadducts can be detected if furan is added after 3 h.
[5] A similar stabilization of photochemically generated trans-cycloheptene by
copper(1) triflate was recently reported J. Th. M. Evers, A. Mackor, Recl.
Trav. Chim. Pays-Bas 98, 423 (1979); Tetrahedron Lett. 1980, 415.
161 16a) could not be crystallized. A rough purification was achieved by saltingout (6a) from a saturated solution with NaNO,.
[7] Whirham and Wright, J. Chem. SOC.C 1971, 883, prepared the diastereomers
of 3-methoxy-( I I?-cyclooctene via a stereochemically unambiguous route.
They found for the (2RS,3SR)-isomer J2.)= 2.1 Hz. for the (2RS,3RS)-isomer
J z 2 = 9 . 0Hz. They also quoted J, "=9.1 Hz, J,.8 =3.55 Hz.
181 0.Ermer. Angew. Chem. 86, 672 (1974); Angew. Chem. Int. Ed. Engl 13,
604 (1974)
191 All the new compounds gave satisfactory 'H-NMR spectra. (6a): m.p. 157159°C (dec.) 161, 'H-NMR (DzO. TMS ext.): S=5.80 (ddd, I-H, J,.z=17.9
Hz. J 1 7 = 9 2 Hz. J 1 . 7 =4.3 Hz). 5.50(dd, 2-H, Jl,2=t7.9 Hz. J2,,=7.9 Hz),
4.20 (rn, 3-H). 3.50 ( s . OCH,). 2.73-1.30 (m. 8H); "C-NMR (D20. TMS
ext.) 6 = 123.0 (d, C-l), 120.6 (d, C-2). 81.7 (d, C-3), 57.5 (q, OCH,), 39.2 (t.
C-7). 31.3 (I). and 31.1 (1) (C-4, C-6). 23.0 (1, C-5); essentially in agreement
with MS of (7). (66): m.p. 142-143 "C (dec.), 'H-NMR. as (6a); "C-NMR
(DIO/TMS ext.): 6 = 121.7 (d, JcH=161.6 Hz. C-I), 120.9 (9. JcF=317.7 Hz.
CF,). 119.9 (d, J c ~ = 1 6 1 . 6Hz, C-2). 81.3 (d. J0=150.4 Hz, C-3). 57.2 (4.
JCH
= 142.6 Hz. OCH,), 38 9 (1, JCH
= 129.4 Hz, C-7). 31.0 and 30.7 (t, C-4,
C-6). 22.6 (t, C-5).
Lii2Si7, a Compound Having a Trigonal Planar Si,
Cluster and Planar Si5 Rings
By Hans Georg von Schnering, Reinhard Nesper, Jan Curda,
and Karl-Friedrich Tebbe"'
In a renewed study of the lithium-silicon system we were
able to showlll that the long-known violet compound "Li2Si"
actually has the composition Lit4Si6(Li2.33Si).The metallic
gray compound immediately adjacent on the silicon-rich side
has now been identified as Lii2Si7.This is the silicon-richest
phase in the Li/Si system; it was formerly described as
[*] Prof. Dr. H. G . von Schnering ['I, Dr. R. Nesper, Dipl.-Ing. J. Curda
Max-Planck-Institut fur Festkorperforschung
Heisenbergstrasse I . D-7000 Stuttgart 80 (Germany)
Prof. Dr. K.-F. Tebbe
lnstitut fur Anorganische Chemie der Universitat
Greinstrasse 6, D-5000 Koln 41 (Germany)
Si
".I
si \
Fig. 1. Crystal structure of Lit2Si,, projection of the unit cell along the a axis (Li,
large circles; Si, small circles). Space group Pnrna (No. 62); a=861.0(2),
b = 1973.8(4), c = 1434.1(4) pm; 8 formula units in the unit cell; 2190 reflections
hkl, MoK<. radiation. R=0.035 (anisotropic). None of the atoms shows anomaor occupation densities. Subsequent A€ synthesis is wlthout
lous coefficients U,,
notable contours [6].
Lil3Si7I2l.Preparation of the pure compound from the elements was accomplished in well baked-out, sealed tantalum
ampoules at 1270 K. Syntheses under various conditions,
thermal analysis, and coulometric titration demonstrate that
Li12Si7coexists in equilibrium with Si and Lii4Si6.The compound has a almost negligible phase width (1.69sLi/
S i s 1.71); it melts congruently at 890 K and is extraordinarily sensitive to moisture and oxygen.
Li12Si7is unequivocally a semiconductor with a band gap
of EG = 0.6 eV and a specific conductivity at room temperature of ~ ( 2 9 8 ) = 1 0 -0 ~- l c m -' . The compound is diamagnetic with a considerably greater susceptibility than silicon
(xmol= - 23 x
cm3 mo1-l for Lit 7i4Si).These physical
properties are important for a n understanding of the bonding
because they are indicative of a normal valence compound.
The structure should therefore fulfil the rules of Zintl and
KZemm[31and of Mooser and Pearson141.
Li12Si7forms orthorhombic crystals (Fig. 1) with a surprising new kind of anionic Sin cluster: Planar Sis rings-analogues are already known in the germanide Li, ,Ge,['I-are
accompanied by hitherto unknown star-shaped trigonal planar
Si, clusters of 3/m-D3,, symmetry. The bond lengths d(Si-Si)
in the Si5 ring vary between 235.6 and 238.1 pm (d=236.8
pm) and those in the Si4 star between 236.5 and 239.3 pm
(8=238.0 pm); they are only slightly longer than the interatomic distance of a Si-Si single bond (235.1 pm).
Attempts to describe this structure in terms of the model of
formal ions run into difficulties: for Li24Si,42 (Li +)24(Si4x
-)
(Si5y-)*, the expression x + 2y= 24 would apply. The formal
charge assigned to silicon (Si2-) owing to the homonuclear
divalency of the Si atoms in the Sis ring gives y = 10 as solution. However, this leads directly to Si44-, a 20e system normally found for the tetrahedrane structure of the isoelectronic P4 molecule. Is the Si44- star a n excited tetrahedrane
state then? Assuming a n (sp' + p) configuration for all four
Si atoms, a plausible description can be formulated with
three three-center bonds and seven nonbonding electron
pairs. Another remarkable variant results with the solution
x = y = 8 . The polyanion Si4'- would be isoelectronic with
the carbonate anion C 0 3 2 - and the polyanion Sisx- with cyclopentene. We hope that this interesting structure will rouse
the interest of theoreticians. The isostructural compound
Li12Ge7has likewise been prepared.
Received. July 28. 1980 [Z 639 IE]
German version: Angew Chem 92. 1070 (1980)
[ '1 To whom correspondence thould be addressed.
Angew. Chem Inr. Ed. Engl. I9 (1980) No. 12
si
I
- Si
0 Verlag Chemre, GmbH. 6940 Wernherm, 1980
0570-0833/80/12l2-l033
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silver, ion, stabilizer, cycloadditions, 3rs, 2rs, cycloheptene, transp, methoxy
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