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Hindered Rotation at the Triple Bond.

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(8) indicates the presence of two isomers-probably cisltrans
( 4 ) is also formed on reduction of the dication [(C5H5Co(PMe2H)3]'+, which-similarly to [C5H5C~(PMe3)3]2+[1'za1 isomers.
-is obtainable in good yield by reaction of C5H5Co(CO)12
with PMezH in methanol.
According to M O calculations[61 for [(CO),M(p-PPh2)] 2
the o-electron pair of the metal-metal bond occupies the
HOMO of this molecule. Should this also be the case for
( 4 ) its Co-Co bond ought to have nucleophilic character
cis
trans
and react with electrophiles. It does not react with Me1 at
room temperature. O n the other hand, ( 4 ) reacts rapidly
Trimethylphosphane is bulkier than trimethyl phosphite" O1
and quantitatively with trifluoroacetic acid to give a cationic
and can therefore attack a cobalt atom of (6) only from
p-hydridocobalt complex, which on precipitation with
the more sterically favorable side. The NMR data of (7)
NH4PF6 affords the corresponding hexafluorophosphate (6)
giveno indication in this case whether the cis- or corresponding
as dark-brown, air-stable crystals['!
trans-isomer is present.
No addition takes place on reaction of (6) with anionic
Lewis-bases such as H - or Me-: The reactions with NaH
(in tetrahydrofuran) or with LiCH3 (in ether) lead quantitatively to the neutral complex ( 4 ) .
Our observation that the stepwise addition of a Lewis acid
and a Lewis base to a metal-metal bond is possible, without
disturbing the binuclear structure, could be of general importance. Thus, the increased reactivity of carbonylmetal clusters
(e.g. Ir4(C0),2 ) in the presence of Lewis acids such as AICI,"
We assume that the cation of (6) has a triple-decker-like
could be due to the initial opening of an M-M bond and
structure[*! According to Hofmann et al.[91, binuclear comthe subsequent reaction of the intermediate with a Lewis
plexes of this type ought to be stable when the two metal
base such as e.g. CO. Vahrenkurnp"zl has recently pointed
atoms possess 30 or 34 valence electrons; in the case of (6)
out the possibility that ligand substitution in binuclear comthe 34-electron rule applies. Consistent with the suggested
plexes or clusters is initiated by cleavage of an M-M bond.
bridged structure the NMR signal of the CoHCo proton
is observed at much higher field (6= -21!) than that of the
The marked broadCoH proton of [C,H5Co(PMe3),H] +IZa1.
ening of the signal is due to the fact that the bridge H-atom
is bound to two Co nuclei (which have a quadrupole moment).
Like the 34-electron complex [Ni2(C5H5)3]+[81,(6) also
reacts with Lewis bases: reactions with PMe3 and P(OMe),
afford the compounds (7) and (S), respectively, in very good
yields (>go%). The red crystals of ( 7 ) and (8) are readily
soluble in acetone or nitromethane and are only slightly
sensitive to air.
The opening of the CoHCo bridge during the formation
of (7) and (8) is confirmed by the 'H-NMR spectra (Table
1). For example, the hydride signal in the spectrum of (7)
Table 1 . 'H-NMR data of the complexes ( 4 ) , ( 6 ) , ( 7 ) and ( 8 ) (6 values,
T M S mt.; J in Hz).
Complex Solvcnt
(41
(6)
(7)
(8) [a]
Ce.Hh
CsHS
4.60 t
[JpH=0.8]
[DbI-DMSO 5.23 t
[JpH=0.4]
CD3N02
4.96s
4.80 s
CD,N02
5.07 s
5.02 s
4.83 s
4.77 s
p-PMe2 Co-H
1.7 vt
1.2 vt
1.73 vt
1.54 ~t
2.06 vt
1.47 vt
2.19-
1.45 [b]
I
-21.0 t
[JpH=60]
-13.3 t
[JpH=66]
- 12.7 t (br)
1.73 d
[JpH=lO]
4.09 d
[JPH
=4.2]
3.92 d
[Jp~=4.0]
[a] Mixture oftwo isomers (see text); [h] overlapping of four virtual triplets.
is shifted 7.7ppm downfield compared to the same signal
in the spectrum of ( 6 ) and appears in a similar region as for
[C5H5Co(PMe3)2H]+. While the reaction of ( 6 ) with PMe3
gives essentially only one product, the NMR spectrum of
A n g e i i , Chrni.
Received: December 12, 1978 [Z 143b IE]
German version: Angew. Chem. 91, 172 (1978)
CAS Registry numbers:
( 4 ) , 69277-85-6; ( 6 ) , 69277-87-8; (7), 69277-89-0: cis-(R), 69292-12-2;
trans-(8), 69277-91-4: C O ( C ~ H ~1277-43-6
)~,
Basic Metals. Part 17. This work was supported by the Deutsche Forschungsgemeinschaft,the Fonds der Chemischen Industrie and by donations of chemicals from BASF, Ludwigshafen, and Bayer AG, Leverkusen. We wish to thank J . Wolf for experimental assistance.-Part
16: A. Spencer, H. Werner, J. Organomet. Chem., in press.
[2] a) H. Werner, 19: Hofmann. Chem. Ber. 110, 3481 (1977): b) Angew.
Chem. 89, 835 (1977): Angew. Chem. Int. Ed. Engl l h . 794 (1977).
131 a ) H . Neukornm, H. Werner, Helv. Chim. Acta 57. 1111,- , i'l?4): b) H.
Werner, B. Juthani, unpublished.
R . G . Huyter, L . F. Williams, J. Inorg. Nncl. Chcm 3. 1'177 (1964).
K . Leonhard, H. Werner, Angew. Chem. 89, 656 (1977). Angcw. Chern.
Int. Ed. Engl. 16, 649 (1977); K . Leunhurd, B. Jutharri, H . Werner,
unpublished.
B. K . To,, M . B. Hull, R. F. Fenske, L. F. Dahl, Inorg. Chem. 14,
3103 (1975).
On the protonation of binuclear complexes and the isolation of stable
PF6 salts cf. K . Fauuel, R. Mathieu, R . Poilblanc, Inorg. Chem. 15,
976 (1976).
H. Werner, Angew. Chem. 89. 1 (1977); Angew. Chem. Int. Ed. Engl.
16, 1 (1977).
J . Ct: Lauher, M . Eliun, R. H . Summerville, R . Hoffmanii. J. Am. Chem.
Soc. 98, 3219 (1976).
C. A. Tolman, Chem. Rev. 77, 313 (1977).
G. C. Demitras, E. L. Muettertws, J. Am. Chem. Soc. 99, 2796 (1977).
H . Vahrenkamp, Angew. Chem. 90, 403 (1978); Angew. Chem. Int. Ed.
Engl. 17, 379 (I 978).
[I]
Hindered Rotation at the Triple Bond
By Phiiippe Koo Tze Mew and Fritz Vogtle[*]
While rotation about the C-C single bond in ethanes
is hindered even by small substituents[laXIb],
it is foreseeable
that bulkier substituents are necessary to bring about such
p]
Prof. Dr. F. Vogtle, DipLChem. P. Koo Tze Mew
Institut fur Organische Chemie und Biochemie der Universitat
Gerhard-Domagk-Str. 1, D-5300 Bonn (Germany)
lnt. Ed. Engl. 18 ( 1 9 7 9 ) N o . 2
0 Verlag Chemir, GmbH, D-6940 Weinhelm, 1979
159
0570-0833179 '0202-0159 $01 .00/0
hindrance in the case ofthe extended triple-bond system ( 1 )["I.
We have found that suitably substituted triptycene groups
hinder rotation not only in butynes (1) but also in butenes
(2) and butanes (3).
a~-(Lbl
111
121
Thus, in ( 4 b ) we have an obvious case of steric hindrance
of the "nonbonded interaction" type by (methyl) substituents,
which touch each other face-to-face without substantial steric
contributions from neighboring groupsC6.'I.
While the methyltriptycene-substituted ethene ( 5 b ) and
the analogous cthanc ( 6 h ) do not show temperature-dependent ' H - N M R spcctr;i. in the case of umubstituted ditriptycenylethane ( 6 u ) a sharpening of the multiplets of the arene
protons and singlet of the methylene protons compared to the
singlet of the bridgehead protons is observed on increasing
the temperature. Cooling to - 20 "C leads to increased broadening of the multiplets of the arene protons, especially of
the multiplet of H-I, H-8 and H-13. At -40°C H-1, H-4
and H-2, H-3 split at 6=7.42 and 7.00 in the intensity ratio
1 : 1. These findings are consistent with free rotation of the
triptycenyl groups about the C-9--CH2 bond in ( 6 a ) at room
temperature and the freezing out of rotation at lower temperature, for Ph' in the conformation ( 6 a A ) differs from the
equivalent phenylene groups Ph2 and Ph3[*1. At -30°C the
free energy of activation is 4 G = 58.5 kJ 'mol (14 kcal/mol)191.
The sharp singlet of the four / i t ~ ~ r / i protons
j h ~
in ( 6 a )
at room temperature indicates time-averaged predominance
131
DNMR spectroscopic investigation of the unsubstituted
ditriptycenyl-ethyne ( 4 a), -ethene ( 5 a)[21,and -ethane ( 6 a )
(see Table 1) revealed detectable steric interactions only for
the ethane system at low temperature.
6
151
14)
101 R i =R,=
(b!
.
sc-ICbl
161
H
Ri = Rn= CH3
+
Hindrance to rotation could, however, be achieved also
in the ethyne system ( 4 ) by incorporation of internal substit-
Table 1. Yields, melting points and 'H-NMR data (room temperature) of the synthesized triptycenes of type ( 4 )
CDd.
Yield
[ %]
(4u)
10
(4h)
16
(5a)
14
(Sh)
12
(6a)
51
16h)
47
~
M. D.
. r"C1 ral
(solvent)
CH(pheny1ene)
450 [b]
(Nitrobenzene)
423 (dec.)
(Nitrobenzene)
480 [c]
(Nitrobenzene)
435 (dec.)
(Nitrobenzene)
475 (dec.)
(Toluene)
443 (dec.)
(Toluene)
7-08 (m, i2H), 7.48 (m, 6 H )
8.01 (m, 6H)
6.71 (4. 4 H , JAB=7Hz), 7.09 (m, 8 H )
7.46 (m, 4H), 8.22 (m, 4 H )
7.07 (m, 12H), 7.51 (m, 6 H )
7.86 (m,6 H )
6.65 (4. 4 H, JAB= 7 Hz), 7.10 (m, 8 H)
7.51 (m, 4H), 8.20 (m, 4 H )
7.06 (m, 12H). 7.46 (m, 6 H )
7.X9 (m, 6 H)
,
(m. XH)
6.57 (4, 4 H , J A B = 7 H z ) 7.13
7.50 (m, 4H), 8.33 (m, 4 H )
(6).
IH-NMR (CDCIJTMS int., ii values, 90 MHz)
5.54 (s, 2 H )
5.73 (s, 2 H )
5.54 (s, 2 H )
7.53 (s, 2 H )
5.75 (s, 2 H )
8.02 (s, 2 H)
5.44 (s, 2 H )
4.1 1 (s, 4 H )
5.68 (s, 2H)
4.33 (s, 4 H )
2.78
(s. 6 H )
2.53
(s, 6 H )
2.53
is, 6 H )
2.34
(s. 6 H )
2.49
(s, 6 H )
2.31
(s, 6 H )
~~~
[a] All melting points (uncorrected) were determined under nitrogen in sealed tubes. [b] Temperature at which decomposition commences; no melting
is observed up to 500°C. [c] Partial decomposition above 389°C.
uents RIf3]:for the internal methyl groups (CH3)i of ( 4 b )
a broadened absorption is already observed at room temperaturer4];at higher temperatures it converts into a sharp singlet
(6=2.80 at 7 0 ° C in C2D2C14),and on cooling it splits into
two singlets (6= 2.66, 3.16, in CD2CI2)(coalescence temperature T,= + IOOC), the intensity ratio of which is temperature
dependent. We interpret this behavior as indicative of the
presence of two conformers at lower temperature, and their
interconversion at higher temperature. We assign the more
intense singlet to the antiperiplanar conformation (up-4 b ) ,
the less intense singlet to the synclinal conformation (sc-4 b ) .
On cooling, the population of the more stable up- compared
to the sc-conformer increases from 2.7:l (OOC) to 7.6:l
(-SOT). Taking into account the difference in population of
the conformers the threshold of the rotation is approximatelyI5l: AGp = 63.1 kJ/mol(15.1 kcal/mol) for the sc-ap conversion and 65.2 kJ/mol (1 5.6 kcal/mol) for the ap+sc conversion.
Tr.ipt
16aAl
16081
of the sterically more favorable antiperiplanar conformation
( 6 a B ) withequivalent methyleneprotons. The increased broadening with decreasing temperature (down to - S O T ) indicates a slowing-down of the to-and-fro rotation of the triptycenylmethylene groups about the central CH2-CH2 bond.
In the process sc-conformers can be formed, but the s p barrier
is not crossed.
Consistent with these explanations is the temperatureindependence ofthe proton resonances of ( 5 b ) and ( 6 b ) which
have predominantly up conformations and whose rotational
barriers should even be higher.
rz
14, 1978
'35 IEI
Received:
German version: Angew. Chem. 91, l h i (1979)
CAS Registry numbers:
( 4 ~ ) .69224-93-7; ( 4 h ) , 69224-94-8; ( S a ) , 69224-95-9; ( 5 b ) , 69224-96-0;
(6121,69224-97-1 : (6b), 69224-98-2
[I]
121
[3]
[4]
[S]
161
[7]
[8]
[9]
a) G Binsch. Top. Stereochem. 3, 97 (1968); b) F . Viigtle, H . FBrsfer,
Angew. Chem. 89. 443 (1977); Angew. Chem. Int. Ed. Engl. 16, 429
(1977); c) S. Pafai: The Chemistry of the Carbon-Carbon Triple Bond.
Interscience, London 1978.
( 5 u ) appears to have been prepared from 9-formyltriptycenetosylhydrazone: 1. 1. Brunoi:lrizskuya, 7: A. Gudasheoa, V R. Skvarchenko, Zh.
@re. Khim. 10, 1495 (1974); but the melting point (388°C) and 'H-NMR
data [6=7.4 (m, 12H), 7.0 (m, 14H), 5.4 (s, 2H), in thionyl chloride],
are not in agreement with those found by us (Table 1, CDCI2), nor
those recorded in thionyl chloride for comparison.
We syntlic.\i7cd ( 4 ) - ( 6 1 by reaction of the corresponding anthracenes
with h c n n ne and 3,6-dimethylbenzyne respectively. Elemental analyses
and q x ~ ~ i o w ~data
p i c are consistent with the given structures.
I lic nuli'i I I groups appear as a sharp singlet; the absorption of H-8,
1 1 - 1 3. ho\\crer, is likewise broadened at room temperature; cooling
leads to a sharp multiplet.
H . Shunan-Aridi, K . H . Bur-Eli, J . Phys. Chem. 74, 961 (1970).
According t o Stuart-Briegleb space-filling models such marked steric
interactions are not to he expected, while CPK models suggest a very
rigid structure. Present-day space-filling models are thus of limited use
for predicting such steric interactions in large molecules.
For the spatial requirements of methyl groups cf. [I b] and Ch. Riichardt,
H:D Br~ckhuur, G. Hrlimann, S. Weiner, R . Winiker, Angew. Chem.
89.913 (1977): Angew. Chem. Int. Ed. Engl. 16, 875 (1977); and references
cited therein.
Cf. t'. + a) Yu. K . Grishin, N . M . Sergrgeu, 0.A . Subhofin, Yu. A . Ustynyuk,
Mol. Phys. 25, 297 (1973); b) F . Vagr/e, P . Kim Tze Mew, Angew. Chem.
90. 58 (1978); Angew. Chem. Int. Ed. Engl. 1 7 , 60 (1978).
"Temperature of stereochemical rigidity": N . M . Seryeyeo, K . F. Ahdulla,
V, R. Skourcheiiko. J . Chem. Soc. Chem. Commun. 1972, 368.
Surprising Transformation of Azulene by Cycloaddition
with 1-(Diethylamino)propyne[**]
By Klaus Hafner, Hans Jurg Lindner, and Werner Ude"]
Azulene ( I ) reacts as the prototype of nonbenzenoid "aromatic" hydrocarbond' with electrophiles and nucleophiles via
substitution at positions I ( = 3) and 4(= 8), respectively, or 6.
With electron-poor alkynes such as dimethyl acetylenedicarboxylate, ( I ) can undergo not only additive
but-like electron-rich alkenes[2bl also thermally induced
dipolar cycloaddition at the five-membered ring; subsequent
valence isomerization of the primary adduct (2) yields the
next-higher homologue of ( I ) , uiz. the heptalene derivative
(3)['"l. We have now attempted reaction of ( I ) with electronrich alkynes such as 1-(diethy1amino)propyne ( 4 ) in order to
obtain the adduct ( 5 ) via (presumably also dipolar) cycloaddition to the seven-membered ring. Valence isomerization
of ( 5 ) could lead to the hitherto unknown cyclopentacyclononene system (6)13J.
Surprisingly, (1) and ( 4 ) give a colorless crystalline 1 : 1
adduct (7), m. p. 7 6 T , even at room temperature. Compound
(7) was isolated after 20d in 83 "/, yield (based on reacted
azulene)l4I. The constitution of the bridged spiro[4.5]decatetraene (7) has been confirmed by X-ray structure analysis[51
and 'H- and I3C-NMR spectra (Table 1). Thus ( 7 ) exists
in the crystal as a dimer ( 8 ) formed by [4 21 cycloaddition
of its cyclopentadiene moiety whereas a rapid retro-Diels-
+
Alder raction to give (7) occurs in solution (benzene, trichloromethane). This indicates only low activation energy for
dimerization of (7) and for the cycloreversion of ( 8 ) (E,<25
kcal,/mol)['].
Formation of (7) probably involves the primary adduct
( 5 ) containing the structural unit of a spiro[3.4]octa-l,5,7triene, which has been shown by R. D.Miller et al.['I to resist
isolation at - IO'C, partly due to a presumably 1,5 sigmatropic
ring expansion to form a dihydropentalene. Analogous rearrangement of the 1,3-diene-bridged derivative ( 5 ) should lead
to (7).
In the presence of catalytic amounts of glacial acetic acid
at room temperature, ( 7 ) undergoes fast isomerization in
solution (CH30H)-possibly by renewed 1,5 sigmatropic alkyl
shift-to give 20 % of the 1,8a-dihydrocyclopent[c,d]azulene
derivative ( 9 ) (lemon yellow needles, m.p. 87°C; see Table
I ) , which is transformed under the same reaction conditions
Hp
E
[*] Prof. Dr. K. Hafner. Prof. Dr. H. J. Lindner, DipLIng. W. Ude
Institut fur Organiache Chemie der Technischen Hochschule
Petersenstrasse 22, D-6100 Darmstadt (Germany)
[**I Thls work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
(21
within ca. 3 h to give 2-(diethylamino)-l -rnethyl-3,4-dihydrocyclopent[cd]azulene (10) (brown platelets, m. p. 52"C, yield
8 0 % ; See Table 1). In boiling tetralin, on the other hand,
( 7 ) gives (10) directly in 30 %, yield. The same tricyclic com161
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