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Aromatic Systems with Polymethine-like Structures A Structural Comparison of Bis- and Tris(dimethylamino)phenalenium Ions.

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By electron transfer to tris(4-bromopheny1)amminium
hexachloroantimonate or by oxidation with iodine also the
radical cation T@ can be generated, whose ESR spectrum in
dichloromethane at 220 K is shown in Figure 3. The analysis
was achieved with the aid of the 'H-hyperfine structure coupling constants determined by ENDOR and general triple
a(H) = + 3.55, a(H) = + 3.78,
and a(H) = - 1.51 G. Simulation of the ESR spectrum
(Fig. 3, bottom) gave a(N) = 2.65 (4N), a(H) = 3.54 (12H),
a(H) = 1.77 (12H) and a(H) = 1.53 (4H) G. The g factor
(2.0029) lies in the expected range.["] The appearance of
different N-methyl proton signals in the ESR spectrum of
2'@at 220 K indicates a restricted rotation about the Car,,-N
bond with two different arrangements of the methyl
groups. This effect was also observed in the case of the
radical cation of 1,2,4,5-tetrakis(dimethylamino)benzene
but not in the case of the radical cation 3'@isomeric with
Aromatic Systems with Polymethine-like
Structures: A Structural Comparison of Bisand Tris(dimethy1amino)phenalenium Ions **
By Heinz A . Staab," Jorg Hofmeister,and Clam Krieger
The structure analysis of the dication of 1,2,4,5-tetrakis(dimethylamino)benzenerl] showed quite clearly that the
cyclic delocalization of aromatic rc-systems can be largely
removed as a result of the formation of only weakly coupled
polymethine-like partial structures. From absorption spectroscopic studies Duhne et a1.12] have been able to classify
conjugated n-electron systems into aromatic, olefinic, and
polymethine-like partial structures; Fabiant3]has supported
such a "building-block model" by quantum chemical calculations. However, the validity and limits of this heuristic
concept require further experimental verification.
Received: February 8, 1991 [Z 4432 I€]
German version: Angew,. Chem. 103 (1991) 1006
CAS Registry numbers:
2, 134180-29-3; 2 ' HBF,, 134208-55-2; 2 . (HBF,),, 134180-30-6; 2 (HBr),,
134180-31-7;2*', 134180-32-8; 2", 134180-33-9;4,2306-08-3; 5,134180-25-9;
6, 134180-26-0; 7, 134180-27-1;8, 134180-28-2.
[l] R. W. Alder, M. R. Bryce, N. C. Goode, N. Miller, J. Owen. J. Chem. SOC.
Perkin Truns. 1 1981, 2840.
[2] Recent review on "proton sponge" compounds: H. A. Staab, T. Saupe.
Angew. Chern. 100 (1988) 895; Angew. Chem. Inl. Ed. Engl. 27 (1988) 865.
[3] K. Elbl-Weiser, C. Krieger, H. A. Staab, Angew. Chem. 102 (1990) 183;
Angew. Chem. Int. Ed. Engl. 29 (1990) 211; cf. also K. Elbl, C. Krieger,
H. A. Staab, ibid. 98 (1986) 1024 and 25 (1986) 1023.
[4] 0. Christmann, Chem. Ber. 98 (1965) 1282; cf. also A. F. Pozharskii. I. S.
Kashparov, Khim. Geterotsikl. Soedin. fY72, 860.
[5] Elemental analyses and spectroscopic data are consistent with the given
[6] H. Quast, W. Risler, G. Dollscher, Synfhesis 1972, 558.
[7] Crystal structure data of2: orthorhombic crystals (from pentane), space
group Phcn (No. 60, Int. Tables), u = 1007.1(1), b = 1746.3(2), c =
1018.5(1)pm; Z = 4. eCAlcd
= 1.114 gcm-'; 2158 symmetry independent,
measured reflections, 1300 with I > 3.0u(1)classed as observed; solution of
structure by direct methods (MULTAN 82); R = 0.042 [18].
[8] H. Einspahr, J. B. Robert, R. E. Marsh, J. D. Roberts. Acru Cr.ystu//ogr.
Secf. B29 (1973) 1611.
[9] An even stronger twisting of the naphthalene skeleton resulting in even
longer N ... N distances were revealed in an X-ray structure analysis of
1,8-bis(dimethylamino)-4,5-dinitronaphthalene7 : C. Krieger, unpublished.
[lo] Cf. also H. A. Staab, K. Oberdorf, C. Krieger, unpublished.
[ l l ] 'H NMR (500 MHz, [D,]dimethyl sulfoxide) of 2 HBF,: 6 = 2.76 (s,
12H), 3.04 (d, 35=1.8Hz, 12H), 7.02 (d, ' J =8. 5Hz , 2H). 7.79
(d,'J= 8.5 Hz, 2H), 18.75 (br. s, 1 H); of 2 . (HBF4)>:6 = 3.14 (s, 24H),
8.39 (s, 4H), 18.80 (br. s, 2H).
[12] T. Barth, Diplomnrberr, Universitit Heidelberg 1990.
[13] Cf. R. L. Benoit, D. Lefebvre, M. Frichette, Can. J. Chem. 65 (1987) 996.
[14] Crystal structure data of 2 . (HBr), . (H,O),: tetragonal crystals, space
group P4/n (No. 85, Int. Tables), u = 1814.2(2). c =793.2(1) pm, Z = 4;
ec.,oa= 1.406 gcm-'; 3329 symmetry independent, measured reflections,
1579 classed as observed with I > 3.00(/); solution of structure by direct
methods (MULTAN 82); R = 0.046 [18].
[lS] Cyclic voltammetry in acetonitrile/O.l M tetrabutylammonium perchlorate. glassy carbon electrode versus Ag/AgCI; ferrocene standard
Fc/Fce = 0.0 V.
[16] H. Kurreck, B. Kirste, W. Lubitz, Angew. Chem. 96 (1984) 171; Angew,.
Chem. I n f . Ed. Engl. 23 (1984) 173, and references cited therein.
[17] K. Elbl-Weiser, F. A. Neugebauer, H. A. Staab, Terruhedron Left.30
(1989) 6161.
1181 Further details of the crystal structure analyses are available on request
from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschafthch-technische Information mbH, W-7514 Eggenstein-Leopoldshafen 2, on quoting the depository number CSD-55233, the names of the
authors, and the journal citation.
Verlugsgesellschufi mbH, W-6940 Weinheim, 1991
In this connection our interest focussed on a comparison
of the structures of the 1,3- and 1,9-bis(dimethylamino)phenalenium salts 1 and 2. In both cases trimethinecyanine partial substructures can be formulated, of which that in the
case of 1 has the all-trans arrangement, whereas in the case
of 2 the peri position of the dimethylamino substituents enforce an all-cis arrangement. More important in connection
with the problem outlined above is, however, that 1 and 2
differ with respect to the part of the n-electron system not
incorporated in the polymethine moiety: in 1 this would be
a naphthalene system, in 2 a benzene system; the benzene
system would be bound to the polymethine fragment via
double bonds and the central single bond.
In contrast to 1 and 2, in the case of the 1,4,7-tris(dimethylamino)phenalenium ion 3 polymethine substructures with
only weak coupling to the remaining n-electron system were
not to be expected since, here, three equivalent mesomeric
structures should prevail.
The syntheses of 1-3 are based on previous work of other
author^,^^.^] especially of Hiinig and W~lff.~']
1 (X = BF,)
(red needles, m.p. 201 "C; 91 YOyield) was formed upon reaction of 1,3-dimethoxyphenaleniumtetraflu~roborate['~
dimethylamine in dichl~romethane.['~
For X-ray structure
analysis the tetrafluoroborate was converted by bromide
ion-exchange (QAE-Sephadex A-25, water) into 1 (X = Br),
which crystallized from dichloromethane/ethyl acetate as the
[*] Prof. Dr. H. A. Staab, Dr. J. Hofmeister, C. Krieger
Abteilung Organische Chemie
Max-Planck-Institut fur medizinische Forschung
Jahnstrasse 29, W-6900 Heidelberg (FRG)
[**I Electron Donor Acceptor Compounds, Part 48. Part 47: K. Elbl-Weiser,
C. Krieger, H. A. Staab, Angew. Chem. 102 (1990) 183; Angew, Chem. Inr.
Ed. EngL 29 (1990) 2 1 1.
Angew. Chem. Inf. Ed. Engl. 30 (i991) No. 8
hemihydrate (red prisms, m.p. 230-231 "C (decomp.); 82%
For the synthesis of 2,9-dimethylaminophenalenonewas
allowed to react with trimethyloxonium tetrafluoroborate (dichloromethane, 20 "C) to give 1-dimethylamino-9-methoxyphenalenium tetrafluoroborate (m.p. 192-194°C (decomp.);
79% yield),[7' from which 2 (X = BF,) was obtained (m.p.
172"C; 63 % yield) by reaction with dimethylamine.['] The
halogenides 2 (X = CI, Br, I) can be obtained by ion-exchange ; in contrast to the chloride and bromide, which are
very hygroscopic, 2 (X = I) can be obtained pure (m.p.
214 "C, from dichloromethane/ethyl acetate).l7I 1,4,7-Tris(dimethy1amino)phenalenium salts 3 were synthesized from
which was methylated with diazomethane (ether/dichloromethane, - 10 "C ; 46 % yield)
to give 4,7-dimethoxyphenalenone (m.p. 180'C).17] Upon
treatment with trimethyloxonium tetrafluoroborate (dichloromethane, 20 "C) 3,4,7-trimethoxyphenaleniumtetrafluoroborate was formed (m.p. 300-310°C (decomp.); 83%),17]
whose reaction with dimethylamine in acetonitrile gave 3
(X = BF,) (m.p. 300-303°C (decomp.); 93% yield).I7]Subsequent anion-exchange reactions furnished 3 (X = I), which
crystallized from dichloromethane/diethyl ether with dichloromethane in the ratio 1:l (dark red crystals, m.p. 289°C
(decomp.)), and 3 (X = Br) (dark red prisms, m.p. 272"C,
from dichloromethane/ethyl acetate).I7I
According to the structure analysis of 1 (X = Br),@]the
bond lengths (Fig. 1 A) for the N(l')-C(l)-C(3)-N(3') region
are consistent with a symmetrical polymethine structure: the
C(l)-C(2) and C(2)-C(3) bonds show the characteristic
bond equalization of such a mesomeric system; the C(1)N(1') and C(3)-N(3') distances are consistent with a partial
double bond character of these bonds. This polymethine
structural unit is coupled via two single bonds with the second substructure of the x-electron system, whose bond
lengths correspond to a naphthalene unit. Figure 1 B shows
that this naphthalene subunit is almost planar, whereas the
polymethine moiety is twisted from this plane so that it can
assume an essentially planar arrangement with inclusion of
the dimethylamino groups.
In the case of 2 (X = I), an X-ray structure analysis revealed a polymethine substructure, two nearly isolated double bonds and a benzenoid six-membered ring.['] Due to
high vibration amplitudes in the region C(3 a)-C(4)-C(5)C(6)-C(6 a) the exact determination of bond lengths and
angles was limited. The structure analysis of a mixed crystal
of 2 (X = C1, Br)["] (measured in a sealed capillary because
of the hygroscopicity) led, however, to a confirmation of
these results. Characteristic features of this structure are the
polymethine moiety with mesomeric bond equalization in
the region N( l')-C(l)-C(9a)-C(9)-N(9'),the high double
bond character with bond lengths of 133.9(4) and 134.3(4) pm
for C(2)-C(3) and C(7)-C(8), respectively, and the benzenoid
character of the remaining six-membered ring (Fig. 2 A). The
side view (viewed along the central C(9 a) ...C(5) axis) shows
that the polymethine system of 2, in contrast to that of 1, is
not completely planar due to the peri-arrangement, but that
the steric interaction between the dimethylamino groups
leads to a stronger torsion about the C-N bonds (torsion
angle C(9a)<(ljN(l')C(l''B) 19.5" and C(9a)-C(9)-N(9)C(9"B) 25" (Fig. 2 B).
Whereas X-ray structure analyses confirmed the "building
block model" of polymethine-like, olefinic and aromatic
structural units in the case of 1 and 2, the results of the
structure analyses of the salts of 3 are consistent with expectation that no such substructures are definable in these cases.
In the case of 3 (X = I) an approximate C , symmetry of the
Angew. Chem. Int. Ed. Engl. 30 (1991) No. 8
Fig. 1. Structure of the phenalenium ion of 1 (X = Br) viewed perpendicular to
the "naphthalene" plane (A) with bond lengths [pm] and angles I"] (in brackets
standard deviations in units of the last decimal place) and side view along the
C(2)...C(6A) axis (B) [8].
Fig. 2. Structure of the phenalenium ion of 2 (X = CI, Br) viewed perpendicular to the phenalenium plane (A) with bond lengths [pm] and angles ["I (in
brackets standard deviations in units of the last decimal given) and side view
along the C(9a)...C(5) axis (B) [lo].
Verlagsgesellschaft mbH, W-6940 Weinheim. 1991
the shorter distance is apparently linked to the hexagonal
network of bromide ions, which surround the pair of
phenalenium ions with the shorter interplanar distance
(Fig. 4).[lZ1
Received: February 8, 1991 [Z 4431 IE]
German version: Angew. Chem. 103 (1991) 1003
Fig. 3. Structure of the phenalenium ion o f 3 . CH,CI, (X = I) viewed perpendicular to the phenalenium plane with bond lengts [pm] and angles ['I (in
brackets, standard deviations in units of the last decimal given) 1111.
cation was found for the phenalenium moiety, and individual polymethine units could not be identified. Remarkable,
however, is the high bond order, which can be deduced from
the short C(2)-C(3), C(S)-C(6), and C(8)-C(9) distances
(Fig. 3).11
3 (X = Br), which has the same structure as the iodide
with respect to the phenalenium ion, exhibits a particularly
interesting lattice packing: the cations of 3 are stacked with
an ecliptical arrangement of the phenalene skeletal frameworks along the c-axis, whereby the dimethylamino groups
of neighboring cations are in exactly staggered positions.
The interplanar distances alternate between 376 and 396 pm;
[l] K. Elbl, C. Krieger, H. A. Staab, Angew. Chem. 98 (1986) 1024; Angew.
Chem. Inf. Ed. Engl. 25 (1986) 1023.
[2] S. Dahne, D. Leupold, Angew. Chem. 78 (1966) 1029; Angew. Chem. int.
Ed. Engl. 5 (1966) 984; S . Dahne, F. Moldenhauer Prog. Phys. Org. Chem.
15 (1985) 1, and references cited therein.
[3] J. Fabian, 1 Prakt. Chem. 320 (1978) 361, and references cited therein.
141 S . Hiinig, E. Wolff, JUSIUSLiebigs Ann. Chem. 732 (1970) 26.
[5] K. D. Franz, R. L. Martin, Tetrahedron 34 (1978) 2147; cf. also K. D.
Franz, J. Org. Chem. 44 (1979) 1704; R. Neidlein, Z. Behzadi, Chem. Z f g .
102 (1978) 199.
[6] M. Jarcho, J. Am. Chem. Soc. 90 (1968)4644; J. K. Elwood, J Org. Chern.
38 (1973) 2425,2430.
[7] Elemental analysis and spectroscopic data are consistent with the assumed
[8] Crystal structure data of 1 (X = Br)-hemihydrate: monoclinic, space
group 12/a;a = 2016.3(4), b = 745.6(2), c = 21 15.0(4)pm, p = 107.72(2)";
Z = 8, eralcd= 1.492 gem--'; 2923 measured reflections, 1768 classed as
observed with i t 3.00(0. Solution of structure by direct methods (MULTAN), R = 0.038 [13].
[9] Crystal structure data of 2 (X = I): monoclinic, space group C2/c;
a = 874.6(2), b = 2543.8(3), c =745.5(2) pm, p = 109.26(2)"; 2 = 4,
= 1 . 6 0 2 4 g ~ m - ~1899
; measured reflections, 1175 classed as observed with I t 3.00(1). Solution of structure by direct methods (MULTAN), R = 0.031 [13].
[lo] Crystal structure data of 2 (X = CI, Br): monoclinic, space group P2,la;
a = 826.6(2), b = 1805.7(4), c = 1096.4(2) pm, fl = 107.49(2)"; Z = 4,
eealcd= 1.315 g ~ m - 2730
~ ; measured reflections, 1633 classed as observed
with I 2 3.00(0, solution of structure by direct methods (MULTAN),
R = 0.053 [13].
1111 Crystal structure data of 3 (X = I): monoclinic, space group P2,/a;
a =769.0(2), b = 1265.7(3), c = 2197.4(4) pm, /? = 93.34(2)"; 2 = 4,
= 1.575 g ~ m - 2208
~ ; measured reflections, 1814classed as observed
with I > 3.00(0. Solution of structure by Patterson synthesis (heavy atom
method); difference Fourier synthesis for the establishment and solution
of the structure of the cation; after usual refinement R = 0.025 [13].
[12] Crystal structure data of 3 (X = Br): trigonal, space group P312;
a = 1143.0(1), c =772.4(1) ppm; Z = 2,
= 1.422 g ~ m - 769
~ ; measured reflections, 514 classed as observed with I 2 S.Oo(f). Solution of
structure by Patterson synthesis with the help of detailed symmetry considerations; R = 0.056 1131.
[13] Further details of the crystal structure investigations are available on request from the Fachinfomationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH, W-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository number CSD-55232, the
names of the authors, and the journal citation.
Enediyne Compounds Equipped with Acid-, Baseand Photo-Sensitive Triggering Devices. Chemical
Simulation of the Dynemicin A Reaction Cascade **
By K . C. Nicolaou,* W-M. Dai, S . I/: Wendeborn,
A . L. Smith, I: Torisawa, P . Maligres, and C.-K. Hwang
The recent isolation of the novel anticancer agent dynemicin A (1)l1] and the proposed cascade of reactions
Fig. 4. Structure of 3 (X = Br): view of a pair of phenalenium ions along the
stacking axis (c-axis) [12].
0 VCH Verlagsgesellrschaft mbH. W-6940 Weinheim. 1991
Prof. K. C. Nicolaou, Dr. W-M. Dai, S . V. Wendeborn, Dr. A. L. Smith,
Dr. Y Torisawa, P. Maligres, and Dr. C.-K. Hwang
Department of Chemistry, Research Institute of Scripps Clinic
10666 N. Torrey Pines Road, La Jolla, CA 92037 (USA)
Department of Chemistry
University of California, San Diego
La Jolla, CA 92037 (USA)
This work was supported by the National Institutes of Health (USA) and
the National Science Foundation (USA). A. L.S. thanks the Science and
Engineering Research Council (SERC) for the award of a NATO fellowship.
Angew. Chem. 1n1. Ed. Engl. 30 (1991) No. 8
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like, structure, dimethylamino, phenalenium, system, bis, trish, ions, comparison, aromatic, polymethine
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