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Hexavinylogous Porphyrins with Aromatic 30 -Electron Systems.

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these mechanisms by providing independent information on
both. While the overall charge of the phenyl fragments in 1
and 2 differ relatively little, the extreme polarizations in the
osystems of the phenyl cations cause a pronounced shift of
positive charge from the C,H, fragment into the other half of
the molecule. We consider this electron density shift responsible
for the negative reaction constant p F . The phenyl ring gains
n density upon dediazoniation, which is consistent with the positive reaction constant pR.
Received: February 12, 1997
Supplemented version: May 2, 1997 [Z 10106IEl
German version: Angeu.. Chem. 1997, 109, 2324-2328
Keywords: bond theory . dediazoniation * diazonium ions
electronic structure . linear free energy relation
[l] L. P. Hamrnett. Chem. Re!,. 1935, 17, 125.
[2] a) R W Taft. J Am. Chem Sac. 1957, 79, 1045; b) S . Ehrenson, R. T. C.
Brownlee. R W Taft. Prog. Phys. Org. Chem. 1973, 10. 1.
[3] a ) R D. Topsom, Prog. Phvs. Org. Chem. 1976, 12, 1; b) ibid. 1987, 16, 125.
[4] a) E. R Vorpagel, A. Streitwieser, S. D Alexandratos, J. Am. Chem. Sac.
1981. fO3. 3171; b) J. Niwa. Bull. Chem. Sac. Jpn. 1989, 62, 226.
[5] H. Zollinger. J Org. Chem. 1990, 55. 3856.
[6]a ) R. Glaser, C J. Horan. J. 0 r - g . Chem. 1995,60,7518,zit. Lit.; b) R. Glaser,
M.-S Son, J Am. Chem. Sac. 1996, 118.10942.
[7] a) R. Glaser. G . S:C. Choy, M. K. Hall, J. Am. Chem. Sac. 1991, 113, 1109;
b) R. Glaser. G. S.-C. Choy, b i d . 1993, 115, 2340; c) R. Glaser, D. Farmer,
Chmz. Eur J 1997, 3. 1244.
[8] H Zollinger. Drozo Chemistry I , VCH, Weinheim, 1994, chapters 8-10.
191 Gaussian94, revision C.3: M. J. Frisch, G. W Trucks, H. B. Schlegel, P. M. W.
Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson,
J A Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V.
Ortiz, J. B. Foresman, J. Cioslowski, B. B. Stefanov, A. Nanayakkara, M.
Challacombe. C. Y Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres,
E. S . Replogle. R. Gomperts, R. L. Martin, D. J. Fox, J. S . Binkley, D. J. Defrees. 1. Baker. J. J. P Stewart, M. Head-Gordon, C. Gonzalez, J. A. Pople,
Gaussian, Inc.. Pittsburgh, PA, 1995.
[lo] W. J. Hehre, L. Radom, P. von R. Schleyer, J. A. Pople, Ab Inirio Molecular
Orhirul Theor!.. Wiley. New York, 1986.
[If] J. A Pople. A P Scott, M. W. Wong, L. Radom, Isr J Chem. 1993,33, 345.
[12] C. J Horan, R . Glaser, J. Phys. Chem. 1994, 98. 3989.
[13] a) T Kuokkanen, P. 0. I. Virtanen, Acra Chem. Scand. Ser. B 1979,33, 725;
b) T. Kuokkanen. ibid. 1990, 44, 394.
1141 P. Burri, G. H Wahl, H. Zollinger, Helv. Chim. Acra 1974, 57, 2099.
[15] a) R. F W Bader. Afoms in Molecules. A Quunfum Theory, Oxford University
Press. New York. 1990; b) F. W. Biegler-Konig, R. E W. Bader, T.-H. Tang,
J Cornpu8 Chem. 1982, 3. 317; c) R. F.W. Bader, P. L. A. Popelier, T. A.
Keith. Angen. Chem. 1994,106,647; Angew. Chem. Int. Ed. Engi. 19!24,33,620.
1161 Electron-density analyses were also carried out for 1a and 2a at the correlated
levels MP2(full)/6-3lG* (including dissociation pathways) and CISD(full)/
6-31G'i:RHF 6-31G*; similar results were obtained: R. Glaser et a]., unpublished results.
1171 a) R. Glaser. G. S. Chen, C. L. Barnes, Angew. Chem. 1992,104,749; Angen,.
Chem. Inr. Ed Engl. 1992, 31, 740; b) G. S. Chen, R. Glaser, C. L. Barnes,
J Chem. Sac. Chem. Commun. 1993. 1530.
[18] R. Glaser, C J Horan. Can. J. Chem. 19%. 74, 1200, and references therein.
Hexavinylogous Porphyrins with Aromatic
30 Ic-Electron Systems**
Christian Eickmeier and Burchard Franck*
The seminal work of Sondheimer et al. on the synthesis
of cyclic conjugated compounds, including the aromatic
[18]annulene (1 a), culminated with the preparation of
[30]annulene (1 b)."] Although 1 b follows the (4n + 2) ruler2]for
aromatic systems, it is unstable. Perfect conformational stabilization of a C,, perimeter is achieved in kekulene 2 synthesized
by Staab and Diederi~h.'~]
However, the n-electron sextets of its
annelated benzene rings do not allow the formation of a conjugated 30n perimeter. Recently it has been shown with numerous
examples that planar cyclopolyenes can be stabilized by insertion of pyrrole
but no aromatic compound corresponding to [30]annulene (1 b) has been synthesized so far.
2
lb
3
4:n=O
5:n=l
After we had found that the tetravinylogous porphyrin 4 has
a stable aromatic 26x-electron system,[*] the question arose
whether the stabilizing effect of the pyrrole units would be sufficient for a hexavinylogous porphyrin 5 , which has a conjugated
perimeter corresponding to the [30]annulene (1 b) of Sondheimer et al.[l] One serious impedement was that the synthesis of
5 would have to proceed via the highly reactive pyrrylpolyene 11
(Scheme 1).
We report here on the first synthesis of a hexavinylogous
porphyrin 5 with an aromatic 30~-electronsystem. In addition
to its importance for the understanding of aromaticity, this octaethyl[30]porphyrin is also of practical interest, as its parent
compound, octaethyl[l8]porphyrin 3,[91
is the most extensively
used porphyrin in chemistry and medicine.
[*] Prof. Dr. B. Franck
['*I
Angeu Chem In! Ed Engl 1997,36, N o 20
Organisch-chemisches Institut der Universitat
Corrensstrasse 40, D-48149 Miinster (Germany)
Fax. Int. code +(251)83-39972
e-mail: franck~uni-muenster.de.
Dr. C. Eickmeier
Boehringer Ingelbeim KG
D-55216 Ingelheim am Rhein (Germany)
Novel Porphyrinoids, Part 16. This work was supported by the Deutsche
Forschungsgemeinschaft, the Fonds der Chemischen Industrie. and the BASF
AG (Ludwigshafen).Part 15: [7].
0 WILEY-VCH Vertag GmbH, D-69451 Weinhelm, 1997
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1
7
Ph,P -CHO
6
L
C
1
H
O
*-.
PhCH, , A
I1
I0
5%
65 %
19 %
can be explained by the favored hairpin-type conformation of
11, which results from steric repulsion of the ethyl groups in the
dipyrrylmethane unit (indicated with an arrow in Scheme 1;
"helical effect"[4g1).Of the new [30]porphyrins, the 16-aza[30]porphyrin 13['31is the least stable. Its synthesis required
careful optimization of the conditions for the condensation of
the biladiene salt 11 : NHJMeOH at room temperature in the
presence of a stoichiometric amount of DDQ.
Although the [30]porphyrins 5 and 12 have limited solubility,
their ' H N M R spectra could be recorded in [DJdimethylsulfoxide/[D,]trifluoroacetic acid ([D,]DMSO/[D,]TFA); the
observed diatropic ring current effects provide proof of aromacity (Figure 1). For 5 the maximum difference Ah in the chemical
shifts of the inner (He)and outer (H,) protons is 23.7. This value
is slightly lower than that of the [26]porphyrin 4 (Ah = 24.1),[*]
and indicates that extending the conjugated perimeter from 4 to
5 does not result in a further increase of aromaticity, as expressed by the diatropic ring current effect. Thus we conclude
that the planar stabilization of annulenes through four pyrrole
units ends with the 3071 perimeter 5 because of its two long C,
bridges.
Further evidence for the interdependence of the ring current
effect and planarity of the ring system can be gained from the 6
values of 16-phenyl-[30]porphyrin 12 (Figure 1). The maximum
13.23 12.26
14.39 13.49
''5
- 9.30
-6.47 -6.31
- 9.05
HN
5
12
13
Scheme 1. Synthesis of the hexavinylogous biladiene 11 and its cyclocondensation
to give the octaethyl[30]porphyrins 5, 12, and 13[13].
The key building block for the synthesis of the octaethyl[30]porphyrin 5 was the hexavinylogous biladiene bishydrobromide or bilaoctaene 11 (Scheme 1). The deep green
bishydrobromide 11 was prepared starting from pyrrylacrolein
614"7
by chain extension through Wittig reaction with phosphorane 711']and acid-catalyzed condensation with dipyrrylmethane 10." '1 7-(3,4-Diethylpyrrol-2-yl)hepta-2,4,6-trienal8/9
was obtained as a mixture of the (4E) and (42) isomers, from
which the (all-E) product 9 was separated as rust-colored reddish crystals by column chromatography (silica gel, ether/cyclohexane 2: 1) and recrystallization (etherln-hexane) . The oily
(42) isomer 8 yielded a further amount of 9 by isomerization
with iodinelhv (24 h, daylight).
The bilaoctaene salt 11, which contains two heptavinylogous
amidine structures, is stable to air but decomposed in solution.
Its cyclocondensation with formaldehyde was achieved in
methanol/HBr. After subsequent in situ dehydrogenation with
2,3-dichloro-5,6-dicyano-1,4-benzoquinone
(DDQ), 2,3,13,14,
18,19,29,30-octaethyl[30]porphyrin(7.1.7.1)(5)['"] was isolated
and purified by twofold flash chromatography[' 5 1 (silica gel,
CH,CI,/MeOH 1O:l). Compound 5 is deep violet in solution,
and despite its limited stability as a solid and in solution, it could
be completely characterized.['31 The considerably more stable
36-phenyl[30]porphyrin 12 was obtained by acid-catalyzed conIn this
densation of biladiene 11 with excess ben~aldehyde.~'~]
case air oxidation sufficed for the dehydrogenation of the initially formed cyclic intermediate. After column chromatography
(silica gel, CH,Cl,/MeOH 20: 1) 12 was obtained as thin green
needles. As in earlier investigations[4g,71 the high yield of 65 %
2214
0 WILEY-VCH
Verlag GmbH, D-69451 Weinheim, 1997
5
12
Figure 1. 'H NMR chemical shifts of I301porphyrin 5 and 16-phenyl-[30]porphyrin
12[13].
difference A8 in the chemical shifts of the inner (H,) and outer
protons (Ha) amounts to 19.7,which is four units less than for
5. In agreement with earlier results['61 this may be explained by
distortion of the 30x perimeter due to interactions of the phenyl
group with adjacent ethyl groups.
It can be concluded that even [30]annulene systems are aromatic and follow E. Huckel's (4n 2) rule['] when they are stabilized and held planar. The stabilization of the [30]R systems in
5, 12, and 13 by insertion of four pyrrolic units follows the
porphyrin model in nature.
+
Received: March 24, 1997 [210275IE]
German version: Angew. Chem. 1997, f09,2302-2304
Keywords: annulenes
reactions
-
aromaticity
- porphyrinoids
*
Wittig
[l] a) F. Sondheimer, R. Wolovsky, Y. Amiel, J Am. Chem. SOC.1962, 84, 274284; b) F.Sondheimer, Acr. Chem. Res. 1972,5, 81 -91
[2] a) E. Hiickel, 2. Phys. 1931, 70,204-286; b) S. Kikuchi, J Chem. Educ. 1997,
74, 194-201.
[3] H. A. Staab, E Diederich, Chem. Eer 1983, 116, 3487-3503
[4] Vinylogous porphyrins: a) R. A. Berger, E. LeGoff, Tetrahedron Lett. 1978,
4225-4228; b) E. LeGoff, 0.G. Weaver, J Org. Chem. 1987,52,710-711; c)
M. Gosmann, B. Franck, Angew. Chem. 1986, 98, 1107-1108; Angeu. Chem.
Int. Ed. Engl 1986, 25, 1100-1101; d) B. Franck, M. Gosmann, DOS DE
3635820, 28. April 1988, BASF AG [Chem. Ahstr. 1988, 109, 94748~1;e) B.
Franck, H. Konig, C . Eickmeier, DOS DE 4029768, 26. March 1992, BASF
AG [Chem. Ahstr. 1992, 117, 26197dl; f) B. Franck, H. Konig, C. Eickmeier,
M. Volker, T. Wessel, DE 4029768. Eur. Pat. Appl. EP 477,611, 1. April 1992.
BASF AG [Chem.Ahstr. 1992. If 7,7740j1; g) B. Franck, A. Nonn, K. Fuchs,
M. Gosmann, Liebigs Ann. Chem. 1994, 503-510.
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[5] Vinylogous porphycenes: a) N. Jux, P. Koch, H. Schmickler, J. Lex. E. Vogel,
Angew. Chem. 1990, 102, 1429-1431; Angew. Chem. Int. Ed. Engl. 1990, 29,
1385-1387; b) E. Vogel, Pure Appl. Chem. 1993,65, 143-152.
[6] Expanded porphyrins: a) J. L. Sessler, S . J. Weghorn, V Lynch, M. R. Johnson,
A n g e w Chrm. 1994, 106, 1572-1575; Angew. Chem. Int. Ed. Engl. 1994, 33,
1509-1512; b) J. L. Sessler, A . K. Burrel, Top. Curr. Chem. 1991, 161, 177273.
[7] B. Franck, A . Nonn, Angew. Chem. 1995,107,1941-1957; Angew. Chem. Int.
Ed. Engl. 199534, 1795-1811.
[S] T. Wessel, B. Franck, M. Moller, U. Rodewald, M. Lage, Angew. Chem. 1993,
105, 1201-1203; Angew. Chem. Int. Ed. Engl. 1993, 32, 1148-1151.
191 a) H. Fischer, R. Haumler, Justus Liebigs Ann. Chem. 1929, 468, 58-98; b)
H. H. Inhoffen. J:H. Fuhrhop. H. Voigt, H. Brockmann, Justus Liebigs Ann.
Chem. 1966, 695. 133-143.
[lo] M. Gosmann. A. Vogt. B. Franck, Liebigs Ann. Chem. 1990, 163-168.
[ l l ] M. J. Berenguer, J. Castells, R. M. Gdiard, M. Moreno-Manas, Tetrahedron
Lerr. 1971. 495-496.
(121 J. B. Paine, R B Woodward, .
I
Org. Chem. 1976, 41. 2826-2835.
[13] Selected spectroscopic and analytical data. 5: ' H NMR (300 MHz,
6 = - 9.30
(t, J =12.8 Hz,
2H,
[D,]DMSO,[D,]TFA.
TMS):
(CH),CH(CH),). --9.05 (m, 4H. CHCH(CH),CHCH), -5.38 (s, NH), 12.19
(s. 2 H . monomethine bridge-CH), 13.49 (d, J = 1 3 . 9 Hz, 4 H , CH(CH),CH),
14 39 (t, .I = 12.8 Hz, 4 H , (CH,)CHCHCH(CH),); IR (KBr): V = 2960,2920,
2860(CH). 1440 CIII-' (conj. C=C);UV/Vis(CH,CI,);d,,,(Igs)= 545(5.62),
(Igc)
, = 562 (5.77). 588 (5.36),
7.17 nm (4.55); U\'/Vis (CH,CI,/TFA). i.,,
761 nm (4 56). M S (70 eV): m / z (YO)= 690 (34) [ M i ] ,661 (8) [ M + - C,H,],
calcd 690.4662, found 690.4679. 12:
345 (8) [M' 11; HRMS: C,,H,,N,:
'H NMR (300 MHI, [D,]DMSO/[D,]TFA,TMS): 6 = - 6.72. -6.47, -6.31
(3 t. J = 13.3 Hz. ? H each, CHCHCHCHCHCHCH), -3.09, - 1 72 (2s,
NH). 8.15-8.21 (n. 3H, n?- and p-phenyl-H). 8.86 (d. J = 6 5 Hz, 2H, ophenyl-H). 1095 (s. l H , monomethine bridge-CH), 12.26 (br. d, 2 H ,
(CH),CH), 12.42 (d, J = 1 3 . 3 H ~ ,2 H , CH(CH),), 13.23 (t, J = 1 2 . 9 H z ,
(CH),CHCHCH(CH),); IR (KBr): i. = 3400 (NH), 2960, 2920, 2860 (CH),
(Iga)
, = 553 (5.67), 599 (5.00),
1590 cm-' (conj. C=C); UV/Vis (CH,CI,): i,,
(Igs) = 574 (5.741, 778 nm (4.64);
726 nm (4.66). UViVis (CH,CI,/TFA): imBX
MS (70eV) ni'r (X) =766 (100) [M'], 736 (32) [M' - C,H,], 689 (20)
[M' - C,H,]. 383 (100) [M+:2]; HRMS: C,,H,,N,:
calcd 766.4975, found
766.4989, correct C,H,N analyses. 13: UV/Vis (CH,CI,): i,,, = 519 nm; UV/
Vis (CH,CI, + 1'10 TFA): i,,, = 550,567 nm, MS (70 eV): m/z (%) = 691 (38)
calcd 691.4614, found
[ M i ] , 662 (4) [M' - C,H,]; HRMS: C,,H,,N,:
691.4600.
[14] For the nomenclature of vinylogous porphyrins see refs.[4c,g]. Following the
designation of the annulenes, the number of x-electrons in the aromatic perimeter precedes in brackets. The name finishes with the C-atom numbers of the
meso bridges between the pyrrole units, starting in the upper left, in parentheses. Thus the porphyrin system of 5 is [30]porphyrin(7.1.7.1).
[15] Flash column chromatography according to W C. Still, M . Kahn, A . Mitra, J.
Org Chem. 1978, 43, 2923-2925; silica gel (Merck), particle size 10.063 mm,
N, pressure 1 3 bar.
[16] B. Franck. G. Krautstrunk. L&gs Ann. Chem. 1993, 1069-1073.
structure determination of this simplest nitrogen heterocycle at
low temperature.
The toxic, extremely carcinogenic, and teratogenic free
aziridine, which tends to polymerize spontaneously (potentially
explosively), was prepared following a known synthetic procedure[61starting with b-aminoethylsulfate. It was purified by repeated distillation and condensed into a thin-walled glass capillary. A single crystal was grown by carefully cooling the melt
after generation of a suitable seed crystal. X-ray diffraction
intensities were collected at 145K and analyzed following established procedures.[']
Aziridine crystallizes with three independent molecules in the
asymmetric unit, which show very similar geometries. As in
crystalline oxirane studied by Luger et a1.,[*] aziridine is an equilateral triangle (Figure l ) , although the bond lengths are
Hli
significantly longer in aziridine
[average values aziridine/oxirane: C-C 1.462(2)/1.438(4)A,
C-N and C - 0 1.467(2)/
H12
1.431(4) A, respectively]. Cyclopropane, also isoelectronic,
Figure I . Molecukar structure of
shows even longer C-C disaziridine in the crystal at 145 K Setances of 1.500 A on average,'']
lected bond lengths and angles
which suggests that the ring
for the three independent molecules. C-C 1.45911). 1.465(2),
bond lengths are primarily deC-N
1.463(2),
1.463(2) A;
pendent on the electronegativi1.464(2);
1.469(2).
1.470(2);
ty of the heteroatom.
1.465(2).
1.468(2) A, C-N-C
Using all available lone pairs
59.8(1), 59.8(1). 59.8(lfi; N-C-C
60.1(1), 60.1(1). 60 1(1), 60.2(1);
of electrons and hydrogen
60 0(1), 60.2(1)
atoms, aziridine forms a hydrogen-bonded chain aggregate
(Figure 2). In contrast to crystal structures of other very small
secondary amines like F,NH, which shows a zig-zag arrangement of molecules ABAB, the chains of aziridine follow an
ABCABC motif with three molecules per repeat unit, although
an ideal N - H . . . N angle of 180" cannot be attained (the NH . . .N angles are 157, 179, and 161O ) . Two molecules are oriented toward one side of the chain axis, while the third one
points in the other direction. The cavity generated on the side of
the latter molecule is filled by a symmetry-equivalent molecule
from the neighboring chain.
A comparison of the structure of aziridine in the crystal and
in the gas phase (Table 1) shows that the molecule suffers no
The Crystal Structure of Aziridine""
Norbert W. Mitzel,* Jiirgen Riede, and Christoph Kiener
Dedicated to Dr. c'. Arnold Beevers
on the occasion of his 89th birthday
The structure of the aziridine molecule in the gas phase is well
established by microwave spectroscopy"] and electron diffractionr2]studies. Ab initio calculations on aziridine confirm most
of the experimental results.[3]The structures of crystalline, substituted aziridines, elucidated by X-ray diffraction, deviate from
these results in some cases.141We report here on the crystal
[*] Dr. N. W. Mitrel. J Riede, C. Kiener
[**I
Anorganisch-chemisches lnstitut der Technischen Universitat Munchen
Lichtenbergstrasse $, D-85747 Garching (Germany)
Fax: Int. code +(89)289-13125
e-mail: N.Mitzel(o Irz.tu-muenchen de
This work was supported by the Bayerisches Staatsministerium fur Unterricht,
Kultus. Wissenschaft und Kunst (Bayerischer Habilitationsforderpreis 1996 to
N. W. M.) We thark Professor H. Schmidbaur for his generous support.
A n g e ~ .07t.m.
.
Ini. Ed. Engl. 1997, 36, No. 20
0 WILEY-VCH
Figure2. View of the hydrogen-bonded molecules in the crystal showing the
ABCABC arrangement in the chains. The intermolecular N -N distances are
3.085(2). 3.069(2), and 3.082(2)w.
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