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Dimethylamino-Pyrazoles and Pyrazolylium Salts.

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[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Wagner, unpublished results.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
tion of 2d with nitrosyl tetrafluoroborate furnishes 3,5bis(dimethylamino)-4-phenylpyrazol~umtetrafluoroborate
9 in 72% yield as dark blue
On a preparative
scale it was found that protonation of 2d with tetrafluoroboric acid and subsequent oxidation of the isolable pyrazolium salt 8, with dichlorodicyano-p-benzoquinone
(DDQ), was more favorable.
The electronic spectrum of 9I"I is, as expected, similar
to that of a structurally related cyclopentadienylium salt
(6-dimethylamino- 1,4-dimethyl-5,7-diphenyl1,2,3,4-tetrahydrocyclopentapyrazine-6-ylium
A,,, = 624 nrnr3l). Also informative with respect to the electronic properties of the 4n system 9 is a comparison with
the 6x system 8 : In the 'H-NMR spectrum of 9, two signals appear at 6=3.91 and 2.90, which are assigned to the
protons of the dimethylamino groups. Upon increasing the
temperature these signals broaden and the coalescence
temperature is 121°C. From this, an energy barrier of
AG* = 19.45 kcal/mol is calculated for the rotation about
the ring-NMe2 bond. The 'H-NMR spectrum of 8, o n the
other hand, shows only one signal for these protons, indicative of a rapid rotation of the dimethylamino groups.
Apparently-and as expected-the 4n system of 9 is a very
much stronger electron acceptor than the 6n system of 8.
Received: June 21, 1985;
revised: August 6, 1985 [Z 1360 IEI
German version: Angew. Chem. 97 (1985) 998
CAS Registry numbers:
la, 98635-07-5; l b , 98635-09-7; lc, 98635-10-0; l d , 98635-12-2; Za, 26387-780: Zb, 98635-13-3; Zc, 98635-14-4; Zd, 98635-15-5; 3a, 98635-17-7; 3b, 9863519-9: 3e, 98635-21-3; 3d, 98635-23-5; 4a, 98635-16-6; 4b, 98635-18-8; 4c,
98635-20-2: 4d, 98635-22-4; 5,98635-24-6; 6,98635-25-7; I b , 98651-86-6; 7d,
98651-89-9; 8, 98651-90-2; 9, 98635-27-9; 4-methoxybenzenediazonium tetrafluoroborate, 459-64-3; 4-nitrobenzenediazonium tetrafluoroborate, 456-27-9.
R. Gompper, K. Bichlmayer, Angew. Chem. 91 (1979) 170; Angew.
Chem. Int. Ed. Engl. 18 (1979) 156.
R. Gompper, M. Junius, Tetrahedron Lett. 21 (1980) 2883.
R. Gompper, H. Glockner, Angew. Chem. 96 (1984) 48; Angew. Chem.
Int. Ed. Engl. 23 (1984) 53.
L. C. Behr, R. Fusco, C. H. Jarboe in A. Weissherger (Ed.): The Chemistry of Heterocyclic Compounds, Vol. 22, Wiley, New York 1976, p. 3; A.
N. Kost, 1. I. Grandberg, Adu. Heterocycl. Chem. 6 (1966) 347.
E. L. Anderson, J. E. Casey, Jr., L. C. Greene, J. J. Lafferty, H. Reiff, J.
Med. Chem. 7 (1964) 259.
H. J. Gais, K. Hafner, M. Neuenschwander, Helu. Chim. Acta 52 (1969)
H. Beyer, Z . Chem. 9 (1969) 361; H. Beyer, H. Honeck, L. Reichelt, Liebigs Ann. Chem. 741 (1970) 45; R. R. Schmidt, H. Huth, Tetrahedron
Lett 1975. 33; W.-D. Pfeiffer, E. Bulka, Synthesis 1977, 196, 485; S. M.
S. Chauhan, H. Junjappa, ibid. 1975, 798: J. Liehscher, J. Prakt. Chem.
325 (1983) 689; H. Schafer, K. Gewald, ibid. 323 (1981) 332.
H. G. Viehe, Z. Janousek, Angew. Chem. 85 (1973) 837: Angew. Chem.
Int. Ed. Engl. 12 (1973) 806; G . J. Voghel, T. L. Eggerichs, Z. Janousek,
H. G. Viehe, J . Org. Chem. 39 (1974) 1233.
Za: Yield 81%. colorless oil, b.p. 104"C/10-3 torr (Ref. [6]: b.p. 85"C/
torr); Zb: yield 87%. m.p. 122-123°C; Zc: yield 47%, m.p. 149.5150°C; Zd: yield 46%, m.p. 162-162.5"C.
314 [m.p., UV/VIS (CH,CN): A,.,(log&)]: 3a: 194"C, 468 nm (4.42);
4a: 208°C. 423 nm (sh, 4.17); 3b: 254"C, 443 nm (4.46): 4b: 269"C,
467 nm (4.35); 3e: 166"C, 435 nm (4.32); 4c: 178-179"C. 420 nm (sh,
4.06); 36 : 404 nm (4.25); 4d : 206-206.5 "C, 448 nm (4.36).
H. Meerwein, K. F. Zenner, R. Gipp, Justus Liebigs Ann. Chem. 688
(1965) 67; S. H. Smallcombe, M. C. Caseno, J. A m . Chem. SOC. 93
(1971) 5826.
1121 9: m.p. 160-161°C: UV/VIS (CH,CN): A,,,(log&)=209 (3.67), 229
(3.52), 267 (3.73), 337 (s, 3.06), 583 nm (3.71); 'H NMR (CD,CN):
6=2.90 (s; 6 H , NCH,), 3.91 (s; 6 H , NCH3), 7.36 (mc; 5H, phenyl-H);
"C NMR (CD3CN): 6=41.89 (4;NCH,), 44.07 (4;NCH,), 87.02 (s;
C-4), 129.24 (s; Ph-C-11, 129.79 (d: Ph-C-m), 130.09 (d; Ph-C-p), 133.27
(Ph-C-o), 168.35 (s; C-3, C-5).
Angew. Chem. Int. Ed. Engl. 24 (1985) No. I 1
A Novel Route to
PentamethylcyclopentadienyllutetiumAlkoxides and
By Herbert Schurnann,* Ilse Albrecht, and Ekkehard Hahn
Dedicated to Professor Max Schmidt on the occasion of
his 60th birthday
Only very few organometallic compounds of the "hard"
electropositive metals of the lanthanoid series are known
in which, aside from organic groups, other ligands are
bonded via "soft" atoms such as sulfur, phosphorus o r silicon.['] Such compounds are, however, of particular interest as reagents for organic syntheses because of their very
reactive, and possibly strong covalent Ln-X bonds. To our
knowledge only one organolanthanoid-sulfur compound,
has so far been characterized,
whereas several bis(cyclopentadieny1)lanthanoid-phosphane derivatives have been described.[31However, their
unequivocal characterization by X-ray structural determination was, in contrast to that of the first organolanthanoid-silicon complex, [Li(dme)3][(CSH5)2Sm(SiMe3)21'41
(dme = 1,2-dimethoxyethane), hitherto not possible.
We have now found a simple, versatile route to this interesting class of compounds. Bis(pentamethylcyc1opentadienyl)lutetiumdi(~-methyl)bis(tetrahydrofuran)lithi~m~~~
reacts in ether with tert-butyl alcohol at -78°C with formation of bis(pentamethylcyclopentadienyl)lutetium tertbutylate, 1, whereas with tert-butyl hydrosulfide the compound 2 (thf = tetrahydrofuran) is obtained with retention
of the bridged structure. [Li(tmed)2][CsMe5Lu(CHj)3][61
(tmed = tetramethylethylenediamine), which exists as a n
ion pair, reacts with both tBuOH and tBuSH with formation of the bridged organolanthanoid compounds 3 and 4,
Both 3 and 4 are also assumed to contain a LU(F-X)&
unit since in each case only one molecule of tmeda is
bound to lithium. The N M R spectra of both compounds,
however, show only one signal for the three tert-butyl ligands, which can be explained in terms of a rapid exchange of the terminal XtBu group with the two bridging
ligands. An analogous process was observed in the case of
[Li(tmed)]3[Th(CH,),] where six bridging CH3 groups and
+ GO-tBu
+ 2
[*] Prof. Dr. H. Schumann, Dr. I. Alhrecht, Dr. E. Hahn
lnstitut fur Anorganische und Analytische Chemie der Technischen
Universitat Berlin
Strasse des 17. Juni 135, D-1000 Berlin 12
Organometallic Compounds of the Lanthanoids, Part 32. This work was
supported by the Fonds der Chemischen Industrie, by the Deutsche Forschungsgemeinschaft, and special funds from the Technische Universitat Berlin.-Part 31: H. Schumann, W. Genthe, E. Hahn, M. B. Hossain,
D. van der Helm, J. Organomet. Chem., in press.
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0570-0833/85/l1ll-0985 $ 02.50/0
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salt, pyrazole, pyrazolylium, dimethylamino
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