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The Dependence of Intramolecular Electron Transfer on Structure in a Spiro Compound Containing Two Cyclooctatetraene Moieties.

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191 7: IR (KBr, -30°C): v=3010 c m - ' ( d - H or =C-H), v=1315 c m - '
(CsC), y=756 c m - ' (C-H); 'H-NMR (400 MHz, [D,]THF, rel. TMS,
-30°C): 6=5.96 (m, 2H, C2H2),5.09 (m, 2H, Ni-CH=), 4.85 (m, 2H,
=CH-), 2.20, 2.16 (m, 4H, PCH), 1.94, 1.91 (m, 4H, PCH), 1.5-0.9 (8
multiplets, 48H, PCH,); "C-NMR (75.5 MHz, [D,ITHF, rel. TMS,
-30°C): 6=115.6 (m. 2C, 'J(CH)=ISI Hz, =CH-), 110.8 (m, 2C,
'J(CH)= 143 Hz, Ni-CH=), 98.8 (m, 'J(CH)= 190 Hz, H G C H ) ; "PNMR (32.4 MHz, [D,]THF, rel. 85% aqueous H,P04, -30°C): 6=83.6,
71.4, intensity ratio 1 : I .
zene to formation of the previously unknown spiro[4.4]nona-2,7-diene 6 as sole product (Table 1).
The Dependence of Intramolecular Electron Transfer
on Structure in a Spiro Compound Containing Two
Cyclooctatetraene Moieties**
By Giinter Krummel, Walter Huber, and Klaus Miillen*
Dedicated to Professor Emanuel Vogel on the occasion of
his 60rh birthday
The previously unknown compound 1, 10,10'-spirobi(bicyclo[6.3.0]undeca-2,4,6,8-tetraene), offers the following
advantages over already investigated model systems: 1) the
subunits are fixed orthogonally to each other by the spiro
c o ~ p l i n g ; ' 2)
~ ,both
~ ~ a direct ~1,nconj~gation''-~]as well as
a through-space conjugation161 between the subunits are
ruled out; 3) because of the planarization of the cyclooctatetraene (COT) necessary for ion formation,"'] the reorganization energy required for an intramolecular electron
transfer between the subunits should be increased.
We describe here the synthesis of 1 and structurally related compounds, the generation of lee, lz@,
and 140
and discuss the possibility of electron transfer between
COT subunits of these anions. The method of choice for
the preparation of 1 (Scheme 1) is that previously used by
us on several occasions: cycloannelation by reaction of
dianions with bifunctional electrophiles.l' 'I After alkylation of the cyclooctatetraene dianion Li2-2 (2 equiv.) with
tetrabromoneopentane 3b and aqueous work-up the polycycle 5 is isolated in 56% yield. Apparently a twofold cycloannelation takes place, but the primary product undergoes a valence isomerization under the reaction conditions. The I3C-NMR spectrum of 5 (Table 1) shows that
only one species of several conceivable configurational
isomers exists. Photolysis of 5 leads via cleavage of ben-
Prof. Dr. K. Miillen, Dip].-Chem. G. Krummel
Institut fur Organische Chemie der Universitat
J.-J.-Becher-Weg 18-20, 6500 Maim I (FRG)
Priv.-Doz. Dr. W. Huber
Institut fur Physikalische Chemie der Universitat
Klingelbergstrasse 80, CH-4056 Basel (Switzerland)
Reductive Transformations, Part 9. This work was supported by the
Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.-Part 8: G. Neumann, K. Miillen, J. Am. Chem. SOC. 108 (1986)
0 VCH Veriagsqeseiischaji mbH. 0-6940 Weinheim. 1987
, L G L
The rate constants of the intramolecular electron transfer between separate redox units"' are not only dependent
on the substrate and ion-pair structure[21but also on the
length and conformation of the bridging g r o ~ p . ' ~ We
have generated extended redox sequences of several "biselectrophoric" systems and have been able to alter the energy profiles of intramolecular electron
Scheme 1. a) NHI, -33°C; HzO, 20°C. b) Pentane, 3 x lo-'
c) NH,, -60°C; d) NH3, -6O"C, KNH2. e) CdC12.
Pyrex lamp.
The course of the cycloannelation reaction depends on
the structure of the ion pair of the nucleophile and on the
leaving group of the electrophile 3 (Scheme 1). Alkylation
of Liz-2 with the chloride 3a instead of with the bromide
3b leads to formation of only the monoadduct 7 (Table 1).
O n the other hand, if the potassium salt Kz-2 is allowed to
react with 3b only the polycycle 8 is obtained after dehydrogenation (cf. 4+ 14@+
I ) (Table l), i.e., here a reductively induced three-membered ring formation follows the
The conversion of 4 into 5 can be partially suppressed
by working at lower temperatures (Scheme l), and the target compound 1 is obtained via the tetraanion 148.1121
Table 1. Melting points ( 5 , 7) and "C-NMR data [a] of 5 - 8 .
5 : 83°C; 6 = 127.6, 127.5, 120.6 (C3-C6, C3'-C6'), 57.6 (CIO), 52.0, 51.1 (C2,
C7, C2', C77, 47.4, 46.3 (C1, C8, CI', CS?, 37.0, 36.8 (C9, C11, C9', CII')
6 : 8= 130.1 (C2, C3, C7, CS), 48.7 (C5), 47.5 (Cl, C4, C6, C9)
7:84-85°C; 6= 134.8, 128.2, 127.7 (C2-C7), 51.5, 50.6 (C12, C13), 46.3 (ClO),
43.0, 41.8 (Cl, C8, C9, C11)
8: 6 = 140.2 (C1, CS), 132.5, 131.7, 131.2 (C2-C7), 47.3 (C9, C1 I), 19.0 (CIO),
14.7 (C12, C13)
[a] CDCll; 5 , 6 100 MHz; 7, 8 50 MHz.
The spectroscopic characterization of 1 at room temperature (Table 2) indicates a structure with effective Dzd symmetry. Cooling leads to a line-broadening of the singlet
signal of the methylene protons and finally at -60°C to
the appearance of the signals of two AB systems. This dynamic behavior confirms that both rings are present in a
tub conformation.
When a solution of 1 in [D8]tetrahydrofuran is brought
into contact with lithium the tetraanion 14@
is formed
again. The number and position of the NMR signals (Table 2) indicate a structure with &d symmetry which contains two planar COTZe units. If one monitors the reduction of 1 N M R spectroscopically it is possible to detect the
dianion 1'' as intermediate. The number of the 'H- and
I3C-NMR signals (Table 2) shows beyond doubt that the
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Angew. Chem. hi.Ed. Engl. 26 (1987) No. 12
Table 2. 'H[6,,]- and ''C[&]-NMR chemical shifts of I , Li21, and Lidl [a].
T ["CI
C I , C8
H9a'. H9b'.
Hlla', H l l b '
2.36 (s)
2.42 (AB), 2.25 (AB)
2.42 (s)
2.38 (AB)
3.48 (5)
3.53 (s). 3.33 (s)
3.52 (s)
CI', C8'
133.2, 132.7, 132.1
133.6, 133.2, 131.1
87.0, 86.7, 85.0
86.7, 85.7, 85.0
H9a, H9b,
Hlla, Hllb
C2' -C7'
c 9 , c11
C9', C11'
[a] [Da]THF; 200 MHz ('H), 50 MHz ("'2)
excess charge remains localized in a single eight-membered ring and, as a consequence, a charged and a neutral
71-unit are present alongside each other. The equivalence of
H9a and H1 l a and non-equivalence of H9a' and H1 la' observable at - 60°C points to planarity of the charged eightmembered ring and the tub conformation of the uncharged
eight-membered ring (Scheme 2). Above 10°C, a rapid inversion of the uncharged ring, recognizable by the coalescence of the signals of H9a' and Hlla', takes place. No
change in the I3C-NMR spectra is observed on heating to
40"C, so that an intramolecular electron transfer on the
time scale accessible in the experiment can be ruled out.
Scheme 2. NMR spectroscopically derived structures of 1, lZe, and lAe.
During the reduction of 1, the NMR signals of 1 and
1 2 Q are observed alongside each other without significant
line-broadening. This shows that no rapid intermolecular
electron transfer takes place and that the intermediate
disproportionates. The ion 1 Be, which
radical anion 1
apparently is present in only low concentration, cannot be
detected ESR spectroscopically. Its characterization can
only be achieved if it is generated from the dianion by
photooxidation. The ESR coupling constants a H(0.40 (6H,
COT-ring), 0.40 (2 H, CHJ, 0.88 mT (2 H, CH,)) show that
the unpaired electron is localized in one COT moiety.
Take-up of an electron by 1 forces, as also in COT 2, a
planarization of the eight-membered ring, which contains
the additional electron. Such a change of conformation
would have to occur alternately in the two eight-membered
rings if an intramolecular charge fluctuation between the
subunits were to take place in l o oor 1". As a result of
the associated increased reorganization
the excess charge of 1 O G and 120 therefore remains localized in
one subunit. The activation energy for the ring inversion of
Angew. Chem. Int. Ed. Engl. 26 (1987) No. I2
the uncharged ring of 1 ' O , which we determined as 12 kcal
mol-', should comply with the activation barrier of the
charge fluctuation. This is also consistent with the fact that
the spatial separation of COT subunits is not solely responsible for the charge localization, since rapid intramolecular electron transfer processes can take place in ion
pairs with separate rigid subunits.r131
Received: June 30, 1987;
revised: September 9, 1987 [ Z 2320 IE]
German version: Angew. Chem. 99 (1987) 1305
[I] J. R. Miller, L. T. Calcaterra, G. L. Closs, J. Am. Chem. Sac. 106 (1984)
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Chem. Inr. Ed. EngL 25 (1986) 443.
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171 L. Echegoyen, R. Maldonado, J. Nieves, A. Alegria, J . A m . Chem. Sac.
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Reoct. Urg. Chem., Visby (Sweden), June 1987.
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(1987) 204.
[I21 The yield of 1 of only 6% referred to 2 is explained by the formation of
5 also occurring under these reaction conditions and by the large losses
in the HPLC separation of 1 and 5.
[I31 F. Gerson, W. Huber, W. B. Martin, Jr., P. Caluwe, T. Pepper, M.
Szwarc, Helm Chim. Acto 67 (1984) 416.
DibenzoIfg,mmnloctalene and
CyclooctaIdefphenanthrene. New Models for the
Conformational Analysis of Biphenyl Systems**
By Willi Heinz, Peter Langensee, and Klaus Miillen*
Dedicated to Professor Klaus Hafner on the occasion of
his 60th birthday
An important step in the conformational analysis of biphenyl systems is the bridging of the ortho
The compounds 1, 2, and 3r3,41
are particularly attractive
[*] Prof. Dr. K. Miillen, DipLChem. W. Heinz, Dr. P. Langensee
Institut fur Organische Chemie der Universitat
J.-J.-Becher-Weg 18-20, D-6500 Mainz 1 (FRG)
[**I This work was supported by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie.
0 VCH Verlagsgesellschafi mbH. 0-6940 Weinheim, 1987
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two, structure, containing, intramolecular, compounds, transfer, spiro, cyclooctatetraene, electro, dependence, moieties
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