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Direct 13C-NMR Spectroscopic Observation of Cyclopropylidene Bromolithiocarbenoids.

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(3): a) Metalation of (2) (1 g, 5.9 mol) in pentane (10 ml)
with one equivalent of t-BuLi at 0 ° C for 12 h furnishes a
product, which, after removal of solvent, has the composition
corresponding to (3a); dec. pt. 90 "C, soluble in ether, THF,
dioxane.-b) Addition of TMEDA and of pentane to an
ethereal solution of (34 leads on cooling to quantitative precipitation of the crystalline complex (3); m. p. 70 "C.
(4): Reaction of (3a) with excess benzyl bromide in pentane at 20 "C for 12 h and separation of LiBr affords (4) in
74% yield; m.p. 123 "C (from THF).
(6): Metalation of (5)I5]with excess CH3Li in ether at 0 "C,
followed by reaction with excess CHJ and hydrolytic
workup, furnishes (6) in 95% yield; m.p. 197 "C (dec., from
(7): HBr gas is passed into a solution of (2) (2.61 g, 15.9
mmol) in benzene (100 ml) until evolution of H2 ceases.
Yield 75% after removal of benzene and crystallization from
CH2C12at -78°C; m.p. 131 "C.
(9): A solution of (8)[61(0.9 g, 6 mmol) in THF (10 ml) is
allowed to react with one equivalent of H3B.C4Hs0 for 1 h
at 20°C. Removal of solvent, dissolution of the residue in
benzene, filtration, removal of benzene, and crystallization
from pentane affords (9) in 80% yield; m. p. 46 "C.
Received: June 1, 1979 [Z 296b IE]
German version: Angew. Chem. 91, 848 ( 1 979)
[I] H. Schmidbaur, G. Miiller, U. Schubert, 0. Orama, Angew. Chem. 90. 126
(1978); Angew. Chem. Int. Ed. Engl. 17, 126 (1978).
121 H. H. Karsch, H. Sehmidbaur, 2.Naturforsch. B 32. 762 (1977).
[3] Monoclinic, P2,/c; a=9.30(1), b=20.07(3), c=16.31(2)
V= 2854(8)
=0.94 g cm - 7 . MoK, radiation, Syntex four circle diffractometer, R = 0.095.
141 H. Schmidbaur, E. Weiss, Angew. Chem. 91, 847 (1979); Angew. Chem. Int.
Ed. Engl. 18, 781 (1979)
[5] K. C. Nainan, G. E. Ryschkewizsch, Inorg. Chem. 8, 2671 (1969).
[6] H. Schmidbaur, W.Tronich, Chem. Ber. 101. 3545 (1968).
in tetrahydrofuran solution at - 100 "C from the I3C-labeled
( 0 )dibromides['] (2u)-(4u) and n-butyllithium (solution in
R/R = H , Alkyl,
$ -
, ,C=,
= Alkyl-metal
= Alkyl-halogen,
>-o, <Si-X
Scheme 1. Acceptor and donor reactivity of brornocdrhenoids (1)
For comparison we also determined the "C-( 0 ) - N M R
shifts of the corresponding Br/Br, Br/H, Li/H, and H/H
compounds ( 2 4 c-e)-(4a,
c-e). All the data are compiled
in Table 1. The signals of the lithium derivatives are on average ca. 8 ppm wide at -100°C and are without structure;
they become sharper at higher temperature. Chemical proof
of the identity of the organometallic species was provided by
protonation (in the sample tube and on a preparative scale['')
to the corresponding CH compounds (212, e)-(4c, e) and
their NMR analysis and isolation. In the case of (3b), the
rearrangementis1 to the 1,2-cyclononadiene (6 C2= 208r9')
which occurs on warming could be monitored: the signal of
(3b) became increasingly sharp at -80 and -7O"C, and
reached normal line width (as for solvent signals) at - 60 "C;
at the same time it loses intensity in favor of the allene-C2
Direct I3C-NMR Spectroscopic Observation of Cyclopropylidene Bromolithiocarbenoids
By Dieter Seebach, Herbert Siegel, Klaus Miillen, and Kurt
The first detection of a halolithiocarbenoid by Kobrich
and Trappila]was followed by initially extensive mechanistic
studies[ib1while the preparative scope of this class of substances, which are stable only at very low temperatures, was
not fully appreciated until the 1 9 7 0 ' ~ ' The
~ ~ . geminal position
of the positive (metal) and negative (halogen) leaving group,
i. e. the joint acceptor and donor properties of the C atom of
compounds such as (I),leads to the versatile and surprisingly
reaction behavior shown in Scheme 1. In
spite of, or precisely because of, the plethora of chemical results available the nature of the bond in intermediates like
( I ) is still unclear; they have hitherto escaped direct observation in the temperature rangeI41 in which the reactions mentioned take place.
We have successfully examined by "C-NMR spectroscopy
the carbenoids (2b)-(4b) generated in an NMR sample tube
Prof. Dr. D. Seebach, Dr. H. Siegel. Prof. Dr. K. Mullen [**I,
K. Hiltbrunner
Laboratorium fur Organische Chemie der Eidgenossischen Technischen
ETH-Zentrum, Universitatstrasse 16, CH-8092 Zurich (Switzerland)
[**I Present address: Institut Fur Organische Chemie der Universitat, Greinstrasse 4, D-5000 Koln 4 (Germany)
0 Verlag Chemie, GmbH. 6940 Weinherm, 1979
(a): R' = R~ = ~ i ( b ) : R' = Li, R Z = B r
( c ) : R' = H , R~ = B r
( d ) : R'
= H, RZ = L1
( e ) : R' = R2 = H
Table 1. "C-NMR shifts of the 90% "C-labeled ( 0 )compounds (2)-(4) in 6
values relative to TMS. Temperature - 100"C, solvent C4H,0/C4Dx0 (9: 1);
Varian XL-100 spectrometer, 25 MHz measuring frequency; F T recording technique up to 2500 pulses.
Chemical shift or shift difference
(41 161
The pronounced downfield shift Asbc of the Li/Br carbenoid C atoms ( 0 )by values of up to 67 relative to the H/Br
compounds is surprising (cf. Table 1): large shift differences
are not normally found for the saturated (sp') C atom between CH and CLi
as is confirmed by the
cyclopropanes ( 2 4 e)-(4d, e) (Asd, in Table 1). The observed deshielding is also unexpectedly large in cornparison
0570-0833/79/1010-0784 $ 02.50/0
Angew. Chem. Int. Ed. Engl. 18 (1979) No. 1 0
with sulfur- and phosphorus-substituted carbanionoid cent e r ~ [ '(AS
~ ' ca. - 10 to + 10). Replacement of H by Br leads
in the Li derivatives (2)-(4) (AShd=70-90) to a four- to
five-fold greater downfield shift than that in the H compounds (AS,, = 14-24). Thus it may be concluded that considerable weakening (54 of the CBr bond['41or even rehy-
(7), 6 = 2 1 0
bridization (56) have taken place in the cyclopropylidene
carbenoids, cf. ( 0 )shift in (6)[IZ1and (7)[15]. Further studies['*' (variation of halogen and metal, measurement of I3C"C coupling constants, etc.) are necessary to obtain more
precise information["].
13C-NMR Spectra of Tribromomethyllithium and
By Herbert Siegel, Kurt Hiltbrunner, and Dieter Seebach"]
After addition of n-butyllithium to a solution of I3C-labeled tetrabromomethaneI'] [(la), 6 = - 29.81 in tetrahydrofuran, i.e. after bromine/lithium exchange to give (Ib), at
- 100 " C in an NMR sample tube[*],the I3C-NMR spectrum
shown in Figure 1A is observed. Almost the entire intensity
of the label appears in three stable (at least for several hours)
low-field signals: a quartet (ql, J = 4 3 Hz) at 6=101.5, a
sharp singlet (s) at 6=144.1, and a second quartet (q2, J = 4 0
Hz) at S = 152.2. Addition of methanol immediately
quenches all three resonances. On warming to - 80 "C, ql
disappears in favor of q,, which concomitantly becomes less
structured: at - 70 " C only s is still present; its intensity decreases on further warming but reaches zero only at
- 40 CI3l. Addition of methanol at - 70 " C to the solution
displaying only the singlet does not lead to tribromomethane
[(lc),6 3c =9.7]; the hydrolysis product character is ti^'^' of tribromomethyllithium ( l b ) is formed only so long as the two
other signals are visible.
Received: June 21, 1979 [Z297a IE]
German version: Angew. Chem. 91, 844 (1979)
CAS Registry numbers:
(Za), 2415-79-4(26). 57640-05-8;(Zc), 1121-39-7;(Zd), 61 184-95-4;(Ze), 286-088; (3a), 1196-95-8;(3b), 58681-23-5;(Sc), 36616-95-2;(3d), 71648-11-8; (3e). 28660-2;(4a). 4578-96-5;(4b), 71648-12-9;(4c), 4622-37-1;14d), 71648-13-0;(4e).
[ I ] a) G. K6brich. H. Trapp, Z. Naturforsch. B 18, 1125 (1963);b) G. Kobrich,
Angew. Chem. 84, 557 (1972);Angew. Chem. Int. Ed. Engl. 11, 473 (1972);
P. J. Stung, Chem. Rev. 78, 383 (1978).
[2] T. Hiyama, H. Saimoto, K . Nishio, M. Shinoda, H. Yamamofo, H. Nozaki,
Tetrahedron Lett. 1979, 2043;R. Dammann, D. Seebach, Chem. Ber. 112.
2167 (1979); D. Masure, C. Chiut, R. SauwCtre, J. F. Normant, Synthesis
1978. 458;D. Seyferth, R. L. Lambert, M. Massol, J. Organomet. Chem. 88.
255 (1975)and earlier work cited therein.
[3]For (a) retention of olefin configuration; for (c) retention at the carhenoid C
atom: for (b) stereoselectivity of hitherto unelucidated configuration [2].
[4] Matrix IR measurements on M'CCI; at 15 K: D. A. Hatrenbiihler, L. And r e w F. A . Carey. I. Am. Chem. Soc. 97, 187 (1975).
[ S ] (2a)-(4a) are obtained from "CHBr, and the olefins by Doering's method:
H. Siegel. D. Seebach. J. Lab. Compd. 1979, in press.
161 We thank Prof. E. Voge!. Koln, for a sample of bicyclo[4.4.0]deca-l(6)3,8triene, the precursor of (4a).
(71 M. Braun, R. Dammann, D. Seebach, Chem. Ber. 108, 2368 (1975).
[S] L. Skattebrrl, Acta Chem. Scand. 17, 1683 (1963).
[9] C. Charrier, D. E. Dorman, J. D. Roberts, J. Org. Chem. 38, 2644 (1973).
[lo] J. P. C. van Dongen, H. W. D. wan Dokman, M. J. A . de Bie, Rec. Trav.
Chim. Pays-Bas 93, 29 (1974).
1111 Ethenyl [lo](sp2) and ethynyl 1121 (sp) C atoms undergo a downfield shift
on replacement of H by Li, probably due to polarization of the 71 system: J.
E. WiNiams. Jr.. A. Sfreitwieser, Jr., 1. Am. Chem. SOC.97, 2634 (1975).The
A& values are therefore more compatible with the sp' model of cyclopropane (Coulson-Moffil, banana bonds) than with Walsh's sp* model.
[I21 H. Siege!, K . Hiltbnmner, D. Seebach, unpublished results.
1131 G. Chassaing, A . Marque!, Tetrahedron 34, 1399 (197R); T. Bottin-Strralko,
1. Seyden-Penne, M. J. Pouef, M. P. Simonnin, J. Org. Chem. 43, 4346
[I41 Formulations of this kind are already found in Ksbrich's publications [ib]
and were deduced from purely chemical evidence.
[ 151 G. A . Olah, C Liang, D. B. Ledlie, M. G. Costopoulos, J. Am. Chem. SOC.99,
4196 (1977).
(161 (5b) could be regarded as the LiBr complex of singlet cyclopropylidene
whose carbene C is calculated to have a charge of -0.21 [R. Gleiter, R.
Hoffmann,J. Am. Chem. SOC.90, 5457 (1968)l.The well-documented destabilization on going from pyramidal to planar-trigonal arrangement of atoms
in the three-membered rings appears at first sight to disfavor formulation
(5b) based on the geometry [P. W Dillan, C. R. Underwood, J. Am. Chem.
SOC.99. 2435 (1977);D. J. Pasto. M. Haley, D. M. Chipman, ;bid. 100, 5272
(1978)]of cyclopropylidene.
Angew. Chem. Inr. Ed. Engl. 18 (1979) No. 10
l + O "
Fig. I . "C-NMR spectra (H-decoupled) of solutions of f i b J . A, and fZb). B. ~n
THF/perdeuterio-THF ( Y 1 ) at 100°C As in the text. the shift\ arc given as 6
values relative to TMS. Varian XL 100 spectrometer. 1:T mode.
Figure 1B shows the sole low-field signal obtained in the
same way for 1,1,l-tribromoethane [(Za), 90% 13CBr3, 20%
I3CH3;produced from (16) and labeled iodomethane]: it is a
45 Hz quartet having 8 Hz of fine structure (JI3~13c). As in
the case of (lb), warming to - 80 " C leads to a loss of structure; however, no singlet occurs even at high temperatures.
Prof. Dr. D. Seebach, Dr. H. Siegel, K. Hiltbrunner
Laboratorium fur Organische Chemie der Eidgenossischen Technischen
ETH-Zentrum, Universitatstrasse 16, CH-8092 Zurich (Switzerland)
0 Ver!ag Chemie, GmbH, 6940 Weinheim, 1979
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spectroscopy, nmr, 13c, observations, direct, bromolithiocarbenoids, cyclopropylidene
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