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Attempts to Synthesize Zwitterionic Donor-Acceptor Cyclophanes The Diastereomeric 12 15-Bis(dimethylamino)-[2](2 5)-p-benzoquinono[2]paracyclophanes.

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assignment of the signal at 6 = 7.94 to the twelve equivalent
protons H-1,2,4,5,7,8..., of the absorption at 6 = 8.37 to the
second group of equivalent external protons H-3,6,9,12,15,18
and of the signal at 6=10.45 to the six internal protons
H-19,20,21,22,23,24[numbering as in ( 9 ) ] .The peculiar downfield shift just of the internal protons of (1) is taken as a strong
experimental argument against the dominance of an annulenoid ring-current in the macrocyclic system and in favor of
a strong coupling between the inner and outer perimeters
according to the benzenoid formulation ( I b). This result is
inconsistent with calculations of the diamagnetic anisotropy
for ( I ) using the semi-classical approach of P a ~ l i n g [ ' ~ "it] ;
agrees qualitatively, however, with more recent MO calculations['31.
Received: March 2, 1978 [Z 954a I E ]
German version: Angew. Chem. 90,383 (1978)
CAS Registry numbers:
( I ) , 15123-47-4; (2), 66183-91-3; ( 3 ) , 66183-90-2; ( 4 ) , 66183-89-9; (j),
19576-05-7;(61,661 83-88-8; (7), 66183-87-7;(S), 21273-84-7; (9), 66183-86-6
Conjugation in Macrocyclic Systems, Part 27.-Part 26: li. E. Meissner,
A. Gender, H.A. Staub, Tetrahedron 1977, 3.
H.A. Staab, Plenary Lecture at the Annual Meeting, Gesellschaft Deutscher Chemiker (Kekul6 Centennial) in Bonn on 14.9.1965.
The naming of ( I ) as a polycyclic system according to the IUPAC
rules on nomenclature leads to an extraordinarily complicated name
which does not give any direct information about structure and symmetry of the molecule (see also [4]).
F . Mgtle, H. A. Staab, Chem. Ber. 101, 2709 (1968).
K. Burri, @! Jenny, Helv. Chim. Acta 50, 1978, 2542 (1967); W Jenny,
R. Paioni, Chimia 22, 248 (1968); 23, 41 (1969); Helv. Chim. Acta
53, 141 (1970); P . Baumgarfner, R. Paioni, W Jenny, ibid. 54, 266 (1971).
H. A. Sraab, M . Haeuei, Chem. Ber. 106, 2190 (1973); cf. also J . u.
Braun, Ber. Dtsch. Chem. Ges. 70, 979 (1937).
Elemental analyses, molecular weights and spectroscopic data are in
agreement with the structures mentioned.
For the 'phane-nomenclature' cf. F. M g t l e , P. Neumann, Tetrahedron
26, 5847 (1970).
Cf. the results obtained for the sterically similar [2.2](2,7)naphthaIenophane: J . R . Dauy, J . A. Reiss, Aust. J. Chem. 29, 163 (1976).
We thank Dr. W Otting, Max-Planck-lnstitut fur medizinische Forschung Heidelberg, for the recording of the mass spectra, which for
most of the compounds mentioned here was very difficult.
I). Schweitzer, unpublished.
We thank Professor J . Dabrowski and D. Griebel of our Department
for the great erfort made by them in overcoming the unusual technical
difficulties in the 'H-NMR-measurements of ( I ) .
a) R. McWeeny, Proc. Phys. Soc. London A 6 4 , 261, 921 (1951); c t
also L. Pauling, J. Chem. Phys. 4, 673 (1936); b) G. Ege, H. Fischer,
Tetrahedron 23, 149 (1967); G. Ege, H . Vogler, Theor. Chim. Acta
26, 55 (1972).
Attempts to Synthesize Zwitterionic Donor-Acceptor
Cyclophanes: The Diastereomeric 12,15Bis(dirnethylarnino)-[2](2,5)-p-benzoquinono[2]paracyclophanes[
By Renate Reimann and Heinz A . Staabr]
Previous investigations of charge-transfer interactions in
donor-acceptor cyclophanes[21led to the question of the existence of 'paracyclophane-zwitterions' in which, as a consequence of an especially low ionization potential of the donor
or a high electron affinity of the acceptor, an electron transfer
[*] Prof. Dr. H. A. Staab, DipLChem. R. Reimann
Abteilung Organische Chemie, Max-Planck-Institut fur medizinische
Jahnstrasse 29, D-6900 Heidelberg 1 (Germany)
from donor to acceptor occurs already in the ground state
of the molecule. Such paracyclophanes for which the radical
cation and the radical anion components would be fixed in
close proximity and definite orientation were of interest regarding the interaction between the radical electrons: strong
coupling should lead to a singlet (or a triplet?) ground state
of the molecule, whereas with weak transanular interaction
the single radical ion units of such a molecule should exist
in doublet spin states. Furthermore, we wondered whether
a zwitterionic structure of donor-acceptor cyclophanes would
result in a crystal structure comprising stacked cyclophane
moieties where the stacking axis is perpendicular or nearly
perpendicular to the cyclophane planes and, therefore, the
radical cation side of one cyclophane directly faces the radical
anion side of the neighboring molecule. For such lattice structures peculiar anisotropic crystal properties (e. g., changes in
electrical conductivity) might be expected.
As an effort aimed in this direction we synthesized the
donor-acceptor cyclophanes ( 1 ) and (2) in which p-benzoquinone as acceptor is combined in pseudo-ortho and pseudogeminal orientations with the especially strong donor
N,N,N,N'-tetramethyl-p-phenylene diamine (TMPD). The
zwitterions (1 a ) and ( 2 a ) corresponding to (1) and (2),
respectively, would include as components the semiquinone
radical anion and the 'Wurster's Blue' radical cation, both
of which are known as relatively stable radical ions. Although,
in intermolecular CT complexes of TMPD, the formation
of radical ions apparently requires acceptors with higher electron affinity (e.g., chloranil)r31.due to the specific interactions
in [2.2]paracyclophanes, no definite conclusions could be
drawn regarding the stability of the zwitterions ( l a ) and
( 2 a ) as against ( 1 ) and (2).
For the syntheses of (1 ) and ( 2 ) , after the failure of more
direct synthetic routes, we had to adopt the multi-step course
starting from the diastereomeric 4,7-dimethoxy-12,15-dimethoxycarbonyl[2.2]paracyclophanes (3) and ( 4 ) which had
already been synthesized as donor-acceptor cyclophanes previously"].
Hydrolysis of (3) (potassium hydroxide, methanol; 24 h,
97 % yield) afforded the dicarboxylic acid (5)r41 (dec. > 320°C),
which on reaction with sulfinyl chloride (chloroform/dimethylformamide; 85 % yield) gave thedichloride (7)[41 (m.p. 152°C).
Treatment of (7) with sodium azide in acetone/water afforded
the diazide (9)C41 (dec. > 9 0 T , 85 % yield). Subsequent Curtius
reaction of (9) (boiling toluene, 2 h) led to the diamino derivative which, on account of its extraordinary instability, without
further purification and characterization was methylated with
methyl iodide/potassium carbonate (methanol, 2 0 T , under
argon) to pseudo-ortho-4,7-dimethoxy-12,15-bis(dimethylamino)[2.2]paracyclophane (11)14] (colorless crystals, m.p.
98 "C, overall yield 3 1 %).
Angew. Chem. Int. Ed. Engl. 17 (1978) No. 5
131, X =OMe
151, X = OH
171, X : C l
191, X = N,
141, X = O M e
161 , X = OH
iiai x :N ,
Analogously, in the pseudogeminal series, starting from
( 4 ) we obtained the dicarboxylic acid (6)[41 (dec. >320°C,
94.5 % yield), the dichloride
(m.p. 214°C; 88 % yield),
and the diazide
(dec. > 114°C; 81 % yield). Curtius
reaction of ( I 0) and immediate subsequent methylation
yielded the pseudogeminal bis(dimethy1amino) derivative
(12)r41(pale yellow crystals, m. p. 181"C, overall yield 11 %).For all pairs of diastereomers of the two series the assignment
to the pseudo-ortho and pseudogeminal structures, respectively, is confirmed by comparison of 'H-NMR data; particularly characteristic is the transannular substituent effect of the
methoxy groups which, for the aromatic protons in pseudogeminal positions of the neighboring ring, results in a downfield
absorption intensity of the pseudogeminal compound is higher
by a factor of about 10 than that of the pseudo-ortho isomer
[ ( I ) : ,A = 545 nm (E = 147), in cyclohexane; A, = 595 nm
(e = 160),in methylene chloride; (2): h,,, = 531 nm (E = 1670),
in cyclohexane; h,,,=577 nm (E = 1930), in methylene chloride]. The solvent-dependence of the absorption maxima as
well as the orientation dependence of the absorption intensities,
similar to those of [2.2]paracyclophane quinhydronesf61,indicate that the long-wavelength absorption is to be assigned
to a CT-transition from a less polar ground state to a more
polar excited state. On the other hand, the 'Wurster's Blue'
radical cation derived from 4,7-bis(dimethylamino)[2.2]paracyclophane, which has been synthesized for comparison[71,
shows absorptions in the same wavelength region
[Amax= 585 nm, in 1,2-dichloroethane]. Hence, on the basis
of the absorption spectra alone an unambiguous distinction
between (1)/(2) and the corresponding zwitterions (I a)J(2a)
is rather difficult. ESR measurements on (I) and (2) in the
solid state and on (2) in solution in 1,2-dimethoxyethane
between 20 and 7O0C[*l,as well as the regular line-width
of the 'H-NMR absorptions of ( I ) and (2), exclude paramagnetic ground states of zwitterionic structures. The problem
of the existence and electronic structure of cyclophane-zwitterions of the type ( I a ) and (2a) needs, however, further investigation including the synthesis of TMPD-[2.2]paracyclophanes
with stronger acceptors than p-benzoquinone.
Received: March 2, 1978 [Z 954b IE]
German version: Angew. Chem. YO, 385 (1978)
In the following reaction steps the ether cleavage in (1 1)
and (12) and the oxidation to the benzoquinone had to
be accomplished under reaction conditions under which the
TMPD part of the molecule is not affected. According to
model experiments with mixtures of TMPD and hydroquinone
dimethylether, this could be achieved by demethylation with
methyl magnesium iodide [ ( I I ) : 190°C, 50min; ('12): 195"C,
75 min] and oxidation with silver oxide in ether. After chromatography on silica gel from toluene/methanol (1O:l) and recr)\tdlization from pet. ether (40-60) ( I ) was obtained in
15.5 y g , yield, and (2) in 18 % ~ield.-(l)[~J: black crystals,
m.p. 183°C; MS: M C calc. for C20H24NZ0z324.1838, obs.
324.1844; 'H-NMR (CDC13): 6=2.0-3.7 (m, 8H), 2.67 (s,
12H), 5.93 (s, 2H), 6.14 (s, 2H).--(2)[41: black crystals, m.p.
204°C; MS: M + calc. for CzoHz4N202 324.1838, obs.
324.1828; 'H-NMR (CDC13): 6=2.0-3.7 (m, 8H), 2.68 (s,
12H), 5.80 (s, 2H), 6.1 S (s, 2H).
( I ) and (2) shoM uiiusually broad absorption bands which
extend from about 4jOnm through the whole visible region
into the near infrared. Long-wavelength initial absorptions
and absorption maxima are strongly solvent-dependent and,
in general, show a bathochromic shift with increasing polarity
of the solvent; a strict correlation with dielectric constants
or dipole moments of the solvent is, however, not observed.
In the whole region of the long-wavelength absorption the
Angew. Chem. Inr. Ed. Engl. 17 (1978) No. 5
CAS Registry numbers:
(I), 66212-55-3; (2), 66183-93-5; (3), 66212-59-7; (4), 66183-99-1; ( 5 ) ,
66212-58-6; ( 6 ) , 66183-98-0; (71,6621 2-57-5; (a), 66183-97-9; (9). 66212-564; (lo), 66183-96-8; (11). 66289-65-4; f 121, 66183-95-7; p-benzoquinone,
106-51-4; TMPD, 100-22-1
Orientation Dependence ofcharge-Transfer Interactions, 16th Communication.-I 5th Communication: H . A. Sruab, H.-E. Henke, Tetrahedron
Lett. (in press).
For further references see H . A. Sraab, U . ZapL A. Gurke, Angew. Chem.
89, 841 (1977); Angew. Chem. Int. Ed. Engl. 16, 801 (1977).
Cf. the partly contradictory statements of H . Kainer, D . Bijl, A. C .
Rose-lnnes, Naturwissenschaften 41, 303 (1954); D. Bijl, H . Kainer, A .
C. Rose-innes, J. Chem. Phys. 30,765 (1959); L Matsunaga, C. A . McDowell, Nature (London) 185, 916 (1960); M . E . Browne, A . Ortenberg, R .
L. Brandon, J. Chem. Phys. 4 1 , 3265 (1964); G . ?: Port, J . Kommandeur,
Mol. Phys. 13, 373 (1967).
Element analyses and spectroscopic data are in agreement with the
structures mentioned.
Cf. H . J . Reich, D. J . Cram, J. Am. Chem. Soc. 97, 3534 (1969); H .
A . Staab, W Rebafka, Chem. Ber. 110, 3333 (1977); H . A. Staab, H .
Haffner, ihid. 110, 3358 (1977).
W Rebafka, H . A . Staab, Angew. Chem. 85, 831 (1973); 86, 234 (1974);
Angew. Chem. Int. Ed. Engl. 12, 776 (1973); 13, 203 (1974); H . A. Staah,
W Rebafka, Chem. Ber. 110, 3333 (1977); H . A . Staab, C. P. Herz,
H.-E. Henke,ibid. 710,3351 (1977); H . A. Staab, C . P . Herr, Angew. Chem.
89, 839 (1977); Angew. Chem. Int. Ed. Engl. 16, 799 (1977).
Starting from 4-amino[2.2]paracyclophane via the 4-acetylamino-, 4-acetylamino-7-nitro- and 4-amino-7-nitro[2.2]paracyclophanes, 4,7-diamino[2.2]paracyclophane was obtained which was methylated to the
4,7-bis(dimethylamino) compound ( R . Reimann, Diplomarbeit, Universitat Heidelberg 1976).
We thank H . Zimmermann, Department of Molecular Physics, for the
ESR measurements and Dr. H . Weger for preliminary investigations,
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cyclophanes, synthesis, zwitterion, acceptor, benzoquinone, donor, dimethylamino, bis, paracyclophanes, attempts, diastereomeric
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