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Donor-Acceptor Substituted Anions and Cations in the Cyclopentadienyl System.

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for the conversion of a M-N2 moiety into a M-N,H2 moiety."Zl
Received: July 3, 1985 [ Z 1373 IE]
German version: Angew. Chem. 97 (1985) 984
I l l Cf. also, e.g., R. W. F. Hardy, F. Bottomley, R. C. Burns, A Treatise on
Dinitrogen Fixation. Wiley, New York 1979.
121 S. N. Foner, R. L. Hudson, J . Chem. Phyr. 28(1958)719; S . Hunig, H. R.
Miiller, W. Thier, Angem,. Chem. 77 (1965) 368; Angenr. Chem. Znr. Ed.
Engl. 4 (1965) 271; N. Wiberg, G. Fischer, H. Bachhuber, ihid.84 (1972)
889 and I 1 (1976) 829.
131 E. I. Stiefel in W. E. Newton, J. R. Postgate, C . Rodriguez-Barrueco
(Eds.): Recent Deuelopmenrs in Nitrogen Fixation, Academic Press, London 1977, p. 69.
[4] Cf. also a) G. N. Schrauzer, Angew. Chem. 87(1975) 579; Angew. Chem.
Inr. Ed. Engl. 14 (1975) 514; b) the intermediary occurrence of NlH2 can
also be concluded from the hydrolysis products N2 and NZHI of N2or [{(C,H,),TiPhj,N,]: Y. G. Borodcomplexes such as [{(CSHJ2Tij2N2J
ko, I. N. Ivleva, L. N. Kachapina, S. I. Salienko, A. K. Shilova, A. E.
Shilov, J . Chem. Soc. Chem. Commun. 1972, 1178: F. W. van der Weij, J.
H. Teuben, J . Organornet. Chem. 120 (1976) 223.
[Sl D. Sellmann, J . Organomet. Chem. 34 (1972) C27; D. Sellmann, K. Jodden, Angew Chem. 89 (1977) 480: Angew. Chem. I n t . Ed. Engl. 14 (1977)
464, and references cited therein.
[6] D. Sellmann, E. Bohlen, Z . Nuturforsch. 8 3 7 (1982) 1026.
171 No NH-bands can be observed in the I R spectrum of 1 . Only fragment
ions occur in the FD-mass spectrum, and a Raman spectrum for the
identification, e.g., of the N N double bond could not be recorded because of fluorescence and decomposition. In the visible region of the
electronic spectrum (in CHIC12) two bands can be observed at 480 nm
(&,,,,=6980 L/mol cm) and 610 nm (&,,.,,=2860 L/mol cm), which are
missing in the case of other [ R ~ ( P P h ) ~ ) d t t complexes.
181 X-ray structure analysis of 1 .2CH2CI2:Pi, a = I152.7(6), h= 1256.6(8),
c = 1391.1(8) pm,
a = I16.54(4),
B= 110.41(4),
OJ scan 1.6<0<
V,,,,,=1569.97~I0"pm'; Z = I . T = -35"C, AMoKCcrr
29.3" m i n - ' , I <28<46". Of 4371 independent reflections, 3870 with
I >2m(T(I).(SHELXTL, direct methods, R , =0.051, R2=0.057. The positions of all H atoms were determined by difference Fourier synthesis,
but only the positions of the H atoms on N were refined). Important
bond lengths [ppm] and angles ["I. NN' l30.l(l.4), NH 66.4(15.5), RUN
202.6(5), RuSl 237.2(3), RuS2 234.4(3), RuS3 228.2(2), RuS4 237.4(3),
RuP 231.8(2), SIC2 174.8(9), S2C1 l76.6(l.l), S2C61 182.1(7); RuNN'
129.3(9), N'NH 113.5(8.5), RuNH I16.8(8.2), SIRuS4 168.7(1). SIRuS2
86.1( I ) , S2RuP 176.0( I), S2RuS3 88.4(1). S l R u N 87.3(3), S4RuN 92.2(3).
Further details of rhe crystal structure investigation are available on request from the Fachinformationszentrum Energie, Physik, Mathematik
G m b H , D-7514 Eggenrtein-Leopoldshafen 2, on quoting the depository
number CSD-5 1487, the names of the authors, and the full citation of
the journal.
191 D. Sellmann, A. Brandl, R. Endell, J . Orqanomet. Chem. 49 (1973) C 2 2 ;
G. Huttner, W. Gartzke, K. Allinger, Angew,. Chem. 86 (1974) 860: Angew. Chem. In!. Ed. Enql. I3 (1974) 822; J . Organomet. Chem. 9 / (1975)
[lo] D. Sellmann, M. Waeber, G. Huttner, L. Zsolnai, unpublished.
[ I I] Cf. also: W. C. Hamilton, J. A. Iber,, Hrdrogen Bonding in Solids. Benjamin. New York 1968, p. 168; I. Olovsson, P. G. Jonssen in P. Schuster,
G. Zundel, C. Sandorfy (Eds.): The HJ'drogen Bond. Vol. 11. North Holland, Amsterdam 1976, p. 401.
[I21 Estimating a bonding enthalpy of only 12 kJ/mol per H-bridge, the four
S-H(N,H2) bridges in the title complex would lower by about 25% the
bonding enthalpy of the complexed N2HZcompared to that of the free
N,H2 of AHr,zuxl=212 kJ [13].
[I31 S. N. Foner, R. L. Hudson, J . Cbem. Phy.7. 48 (1978) 3162.
cyclopentadienes, since the pyridiniocyclopentadienides
obtained from them should absorb at longer wavelengths
than analogues without substituents in the five-membered
ring. Donor-acceptor substituted derivatives should at the
same time, however, be more stable than donor-substituted
derivatives, which are likewise expected to exhibit bathochromism.
130-140 'C
The well known reaction of glutaric acid dinitrile with
diethyl oxalate['] can be considerably improved by the use
of potassium tert-butoxide/tetrahydrofuran (THF). The dipotassium salt 1 is formed in quantitative crude yields. It
reacts with N,N'-dimethylethylenediamine dihydrochloride to yield the ammonium salt, which can be converted
by heating in ethylene glycol into the desired donor-acceptor substituted cyclopentadiene 2 (yield 52%, colorless
needles, m.p. 248 "C (decomp.)). Protonation of 1 provides
the dihydroxy compound 3 (colorless powder, m.p. 222°C
(decomp.)). The analogous reaction of 1 with o-phenylenediamine dihydrochloride affords the cyclopentadiene derivative 4 (yield 57%, orange-yellow crystals, decomp. above
Like other cyclopentadienes, 2 is suitable for the preparation of fulvenes. Reaction with dimethylformamide di-
ethyl acetal affords the 6-dimethylaminofulvene 5 (yield
659'0, orange-yellow needles, m.p. 128-130°C), while reaction with benzaldehyde furnishes the 6-phenylfulvene 6
Donor-Acceptor Substituted Anions and Cations in
the Cyclopentadienyl System**
By Rudolf ComppeP and Thomas Gessner
In connection with studies on the color and reactivity of
pyridiniocyclopentadienides"' we have concerned ourselves with the preparation of donor-acceptor substituted
['I Prof. Dr. R. Gompper, DipLChem. T. Gessner
lnstitut fur Organische Cbemie der Universitiit
Karlstrasse 23, D-8000 Miinchen 2 (FRG)
This work was supported by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie.
0 VCH Verlagsges~lls~haji
mbH, 0-6940 Weinherm. 1985
0570-0833/85/1111-U982 $ 02.51VO
Angew. Chem. I n f . Ed. Engl. 24 11985) No. I 1
(yield 5 1%, orange-yellow needles, m.p. 228-230°C). Fulvalenes are also accessible from 2. The yellowish potassium salt 7 ['H NMR (CD,CN): 6=2.66 (s; 6 H , NCH3),
2.79 (s; 4 H , NCH2), 6.05 (s; 1 H, 5-ring-H)], obtained from
2 with potassium tert-butoxide, reacts with iodine to give
the colorless dihydrofulvalene 9 (m.p. 190°C (decomp.)),
from which the donor-acceptor substituted fulvalene 8 is
formed by reaction with n-butyllithium and then with iodine [yield 66%, shiny green prisms, m.p. 317-318°C; UV/
VIS (CH,CN): A,,,(log&)=230 (4.44), 265 (sh, 3.94), 301
(sh, 3.68), 335 (sh, 3.33), 520 nm (4.47)].
2. BrCH2C02Me
7 also reacts with carbon disulfide. The resulting dithiocarboxylic salt reacts, e.g. with methyl bromoacetate to
give the bis(methoxycarbony1thio)fulvene 10 (yield 71%,
orange-yellow needles, m.p. 190'C). Treatment of 7 with
3-methyl-2-methylthiobenzothiazolium tetrafluoroborate
leads to the thiaazafulvalene 11 [yield 57%, shiny metallic
green prisms, m.p. 248-250°C; UV/VIS (CH,CN):
A,, (log&)= 225 (4.52), 520 nm (4.58)], which can be oxidized with iodine to the blackish-violet radical cation salt 12
[yield 91%, m.p. 156°C; UV/VIS (CH,CN): Amax(1og&)
=212 (4.53), 236 (4.36), 291 (4.71), 365 (4.50), 424 (4.39),
568 (sh, 3.66), 609 (3.79), > 900 nm].
The distinctive effect of the combination of donor- and
acceptor-substituents in 2 is illustrated in a dramatic way
by the fact that not only can the (yellow) cyclopentadienides 13 be prepared (e.g. 7, M=K), which contain the
"aromatic" 6n system of the cyclopentadienide anion,
from 2, but also the green cyclopentadienylium tetrafluoroborate 14, which contains the "antiaromatic" 4n system
of the cyclopentadienylium cation [yield practically quantitative, m.p. 160°C (decomp.); UV/VIS (CH,CN):
?L ,".,%(log&)=225
(4.25), 307 (4.13), 350 (sh, 3.59), 426 (sh,
2.46). 810 nrn (2.52); ' H NMR (CD,CN): 6=3.65 (s; 6 H ,
NCH?), 4.00 (s; 4 H , NCH2), 8.15 (s; 1 H, 5-ring-H)l. The
signal of the five-membered ring H atom in the anion of 7
(6(H-6) = 6.05) is shifted somewhat downfield compared to
that of t h e (unsubstituted) cyclopentadienide anion[31
Angew. Chem. I n t . Ed. Engl. 24 (1985) No. I 1
(6= 5.49). This difference, taking into account the relationship between charge density (according to PPP: qc.6=
- 0. 12Sr4I) and chemical shift (AS, = (10.7AqJ ppm"])
shows 7 to be a typical aromatic compound with diamagnetic ring current. As expected, the substituents in 7 d o not
influence the aromatic properties of the anionic cyclopentadienide system. The signal of the corresponding proton
in the cation of 14 (6=8.15) appears between the proton
signals of the tropylium ion (6=9.2616]) and of benzene
(6 = 7.27"l) and not, as one would expect from the size of
the ring, between those of the cyclopropenylium ion
(6= ll.lLgl)
and of the tropylium ion. The charge-induced
shift on going from 13 to 14 (A6,=3.58 ppm) calculated
from the charge density on C-6 of 14 (according to PPP:
q = 0.207141)using the above equation is considerably
larger than that observed (A6=2.10 ppm) and leads to a
calculated paratropic shift of AS,, = 1.48 ppm in 14. This
value is actually smaller than, for instance, that in the bicyclo[5.4.l]dodecapentaenide anion (3.7-6.8 ppm),['I but is
comparable with that observed in tri-tert-butylcyclobutadiene (1.04 ppm).["I Like other paratropic compounds (cf.,
e.g.,'"I) 14 may therefore be counted among the antiaromatic systems. The yellow salt 15["] (Amax=421nm) can be
regarded as a non-aromatic compound for comparison
with 14.
ClO: 15
Compared to this model ( ' H NMR: 6(H-3)=8.3; PPP:
qc.3= +0.129'41) the signal of H-6 in the 'H NMR spectrum of 14 shows a small upfield shift. Particularly striking
is the enormous difference in color (green/yellow, AAmax
ca. 400 nm) between 14 and its open-chain analogue 15.
As in 13, the substituents in 14 also change the properties of the parent compound only slightly. 14 is more stable than the unsubstituted cyclopentadienylium cation
(inter alia because of the removal of degeneration of the
frontier orbitals), but the paratropic and thus antiaromatic
properties are retained, albeit to a lesser extent.
There are only very few fully conjugated monocyclic
systems which, with the same ring size and same substituents, exist both as a cation as well as an anion, with the
latter possessing two additional x-electrons. In the case of
the pentachloro- and pentaphenylcyclopentadienide derivatives, the (aromatic) metal cyclopentadienides are stable,1'41 whereas the (antiaromatic) cyclopentadienylium
salts could previously only be obtained in
and 14 are, in contrast, the first pair of carboxylic ions in
which the partners have comparable stability.
Received: June 10, 1985:
revised: August 6, 1985 [Z 1346 IE]
German version: Angew. Chem. 97 (1985) 996
CAS Registry numbers:
1, 98689-16-8: 2, 98689-19-1; 3, 10528-59-3: 4, 98689-20-4: 5, 98689-21-5; 6,
98689-22-6: 7,98689-23-7; 8, 98689-25-9; 9, 98689-24-8; 10, 98689-27-1 ; 11,
98689-28-2: 12, 98689-30-6: 14, 98703-78-7; (EtO),CCOZEt, 95-92- I;
2-H2NCaH4NH2.2HCI,615-28-1; (Et0)2CHNMe2, 1188-33-6; PhCHO, 10052-7: C S 2 ,75- 15-0: BrCH2C'02Me, 96-32-2: 4,5-dioxo-l,3-cyclopentandicarbonitrile N,N'-dimethylethylenediamine salt, 98689-1 8-0; 5.7-dicyano- 1,4-dimethyl- 1,2,3,4-tetrahydro-6H-cyclopentapyrazine-6-dithiocarboxylic
acid potassium salt, 98689-26-0; 3-methyl-2-(methylthio)benzothiazoliumtetratluoroborate, 36530-03-1.
[ I ] V. Figala, Dissertation, Universitat Munchen 1970; cf. R. Gompper, Angew. Chem. 81 (1969) 348: Angew. Chem. l n t . Ed. Engl. 8 (1969) 312.
[21 A. Michae1,Am. Chem. J . 30 (1903) 156; R. C. Cookson. K. R. Friedrich,
J. Chem. SOC.C1966. 1641.
0 VCH Verlagsgesellschafi mbH, 0-6940 Weinheim, 1985
0570-0833/85/1111-0983 $ 02.SO/O
[31 G. Fraenkel, R. E. Carter, A. McLachlan, J. H. Richards, J. Am. Chem.
Soc. 82 (1960) 5846.
[41 H:U.
Wagner, unpublished results.
[ 5 ] T. Schaefer, W. G. Schneider, Can. J. Chem. 41 (1963) 966.
[61 R. H. Cox, L. W. Harrison, W. K. Austin, J. Phys. Chem. 77 (1973)
[7] Cf. M. Hesse, H. Meier, B. Zeeh, Spektroskopische Methoden in der Organischen Chemie, Thieme, Stuttgart 1979, p. 155.
[S] R. Breslow, J. T. Groves, J. Am. Chem. Soc. 92 (1970) 984.
[9] S. W. Staley, A. W. Orvedal, J. Am. Chem. Soc. 95 (1973) 3382.
[lo] S. Masamune, N. Nakamura, M. Suda, H. Ona, J. Am. Chem. SOC.95
(1973) 8481.
[ I l l A. Minsky, A. Y. Meyer, M. Rabinovitz, Tetrahedron 41 (1985) 785.
[I21 J. Dale, S. Kriiger, C. Romming, Acta Chem. Scand. 8 3 8 (1984) 117.
[I31 R. Breslow, R. Hill, E. Wasserman, J. Am. Chem. SOC.86 (1964) 5349; R.
Breslow,Acc. Chem. Res. 6 (1973) 393; W. Broser, H. Kurreck, P. Siegle,
Chem. Ber. 100 (1967) 788.
[I41 G. Wulfsberg, R. West, J. Am. Chem. SOC.94 (1972) 6069; R. Zhang, M.
Tsutsui, D. E. Bergbreiter, J. Organomel. Chem. 229 (1982) 109.
In investigations into stable five-membered ring cations
which are formally to be counted among the antiaromatic
species, we have previously prepared imidazolylium
salts,"] pyrrolylium salts,['] and finally also crystallized cyclopentadienylium
The gradation in the color of
these compounds (yellow/red/blue to green) is consistent
with the HOMO-LUMO distances calculated by HMO.
According to these calculations the longest wavelength absorption maxima in the electronic spectra of pyrazolylium
salts, i.e. of 1,2-diazacyclopentadienylium salts, should approach the maxima of the cyclopentadienylium salts, and
the stabilities of the two systems should also be comparable. Since dialkylamino groups had proven to be stabilizing groups for the previously prepared five-membered ring
cations, it seemed to us that 3-dialkylamino- and 3,5bis(dia1kylamino)pyrazoles would be the most suitable
starting materials. Due to their richness in electrons, they
ought to be more susceptible to electrophilic substitution
than simple pyrazoles, and, moreover, they ought to be
easily oxidizable.
1-Substituted dialkylaminopyrazoles have long been
known,[41while compounds not substituted in the l-position are relatively
Viehe et al.[" have prepared 3,5dichlorovinamidinium salts, but only in the case of one 4phenoxy derivative has a corresponding 1-unsubstituted
pyrazole been reported.
We have now found that the 5-dimethylamino- and 3,5bis(dimethy1amino)pyrazoles 2a-dL9]are readily accessible
in good yields by reaction of the 1-chloro- and 1,3-dichloro-vinamidinium tetrafluoroborates l a - d , respectively,
with hydrazine in dichloromethane. The chlorides 1, CIQ
instead of B E , are sensitive to hydrolysis and are therefore unsuitable for this reaction.
Upon coupling 2a and 2b with benzenediazonium chlorides in dilute mineral acids and subsequent addition of
sodium acetate, or benzenediazonium tetrafluoroborates in
acetonitrile (in the case of 2b this usually leads to improved yields), the azo dyes 4 and their salts 3 " O 1 are obtained. 2b reacts with dimethyl(methylthio)sulfonium tetrafluoroborate"'] in dichloromethane to give, depending
on the molar ratio, either the 3,5-bis(dimethylamino)-4-methylthio-1H-pyrazole 5 (yield 82%, m.p. 101-102°C) or the
(yield 70%, m.p. 151 "C).
x 0.5 T C N Q
7b, R'
= H;
7d, R'
= Ph
When a hot saturated solution of tetracyanoquinodimethane (TCNQ) in acetonitrile is treated with 2b or 2d the
solution immediately turns deep-green, the color typical
for the TCNQ radical anion, and upon cooling, blackishblue needles of 7b and 7d, respectively, crystallize out (7b:
m.p. 234°C (decomp.); 76 : m.p. 216-218°C (decomp.)).
The electrical conductivities (two-electrode measurement,
P = 1800 kp/cm') of pellets of these salts at room temperature are CT= 1.6 x
S/cm and 6.1 x
S/cm, respecti ve 1y .
Attempts to eliminate a methylthio group from 6 to give
a pyrazolyl cation met without success. However, oxida-
[*] Prof. Dr.
By Rudolf Gompper,* Rainer Guggenberger, and
Rolf Zentgraf
Dimethylamino-Pyrazoles and Pyrazolylium Salts**
R. Gompper, Dr. R. Guggenberger, Dr. R. Zentgraf
lnstitut fur Organische Chemie der Universitat
Karlstrasse 23, D-8000 Miinchen 2 (FRG)
This work was supported by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie. We thank Dr. J. Hocker, Bayer AG
Leverkusen, for measuring the electrical conductivities.
0 VCH Verlagsgesellschafr mbH, 0-6940 Weinheim, 1985
0570-0833/85/1111-0984 $ 02.50/0
Angew. Chem. Inr. Ed. Engl. 24 (1985) No. I 1
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acceptor, donor, anion, system, cation, substituted, cyclopentadienyl
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