COMMUNICATIONS
[{(CO)5Cr}6Ge6]2 , A Molecular
Organometallic Derivative of the
Unknown Zintl Ion [Ge6]2 **
T. Kar, B. G. Niyogi, P. Hobza, P. von R. Schleyer, Chem. Rev. 1990,
90, 1061; f) H. Bock, K. Ruppert, C. Näther, Z. Havlas, H. F.
Herrmann, C. Arad, I. Göbel, A. John, J. Meuret, S. Nick, A.
Rauschenbach, W. Seitz, T. Vaupel, B. Solouki, Angew. Chem. 1992,
104, 564; Angew. Chem. Int. Ed. Engl. 1992, 31, 550; g) A.-M. Sapse, P.
von R. Schleyer, Lithium Chemistry: A Theoretical and Experimental
Overview, Wiley, New York, 1995.
Peter Kircher, Gottfried Huttner,* Katja Heinze, and
Gerd Renner
[2] For the recent works on the dynamics of carbanionic inversion, see:
a) H. J. Reich, K. J. Kulicke, J. Am. Chem. Soc. 1995, 117, 6621;
b) R. W. Hoffmann, R. K. Dress, T. Ruhland, A. Wenzel, Chem. Ber.
1995, 128, 861; c) H. J. Reich, K. J. Kulicke, J. Am. Chem. Soc. 1996,
118, 273.
[3] [4]Radialene (1) was isolated as yellow crystals in 11% yield by the
intramolecular reaction of hexadecamethyl-3,5,8,10,13,15,18,20-octa-
silacycloicosa-1,6,11,16-tetrayne with [(C5H4Me)Mn(CO)3] (3 molar
equiv) by irradiation (l >300 nm) under reflux in THF. However,
when one molar equivalent of the manganese complex was used, the
octasilyl-substituted trimethylenecyclopentene derivative was ob-
tained in 17% yield. For p-electron systems, such as 1, derived from
silicon-containing macrocyclic polyacetylene, see H. Sakurai, Pure
Appl. Chem. 1996, 68, 327. For the trimethylenecyclopentene and its
tetraanion tetralithium, see: A. Sekiguchi, T. Matsuo, C. Kabuto,
Angew. Chem. 1997, 109, 2572; Angew. Chem. Int. Ed. Engl. 1997, 36,
2462.
Dedicated to Professor Manfred Weidenbruch
on the occasion of his 60th birthday
The synthesis of [{(CO)5Cr}6Sn6]2 [1] illustrated that clusters
composed exclusively of main group elements could be
prepared from organometallic precursors; the resulting clus-
ter is embedded in a matrix of organometallic protective
groups. At the same time it was shown that octahedral
clusters, which obey the usual counting rules[2] in terms of the
structure and the electron count, were not restricted to
boron[3] in main group chemistry. Whereas the [Sn6]2 ion[1]
protected by organometallic groups was initially the only
example for this, in the meantime octahedral clusters that
obey the counting rules[2] have been established as building
blocks of solids. Both [Ga6]8 and [Tl6]8 exhibit octahedral
structures with 14 framework electrons.[4] Two-dimensional
corner-sharing indium octahedra are present in Rb2In3.[4] The
phase KTl contains tetragonally compressed thallium octahe-
dra with 12 framework electrons.[4] All these octahedral
clusters are built from elements of Group 13.[5, 6] For elements
of other groups the only example to date was the [Sn6]2 ion,
which was protected by organometallic groups.[1]
The reaction principle based on the treatment of pentacar-
bonylchromate with element halides had with K2[Cr(CO)5]
and SnCl2 led to the octahedaral cluster [{(CO)5Cr}6Sn6]2 .[1]
The transfer of this principle to other pentacarbonylmetalates
and other element halides appeared straightforward; how-
ever, numerous attempts proved unsuccessful. We have now
found that the reaction of GeI2 with Na2[Cr2(CO)10] leads to
the desired anionic cluster [{(CO)5Cr}6Ge6]2 (1) provided
that 2,2'-bipyridine is added to the reaction mixture
(Scheme 1).
[4] Spectral data for 1: m.p. 219 ± 2208C; 1H NMR ([D1]chloroform,
TMS): d 0.05 (s, 8H, CH2), 0.14 (s, 48H, CH3); 13C{1H} NMR
([D1]chloroform, TMS): d 2.1 (CH3), 10.8 (CH2), 134.7 (C), 167.5
(C); 29Si{1H} NMR ([D1]chloroform, TMS): d 7.8.
[5] The [4]radialene dianion, which was obtained by metalating 1,2-
dimethyl-3,4-bismethylenecyclobutene with nBuLi/KOtBu or nBuLi/
N,N,N',N'-tetramethylethylenediamine, has been characterized by the
quenching experiments, see: W. T. Thorstad, N. S. Mills, D. Q. Buck-
elew, L. S. Govea, J. Org. Chem. 1989, 54, 773.
[6] Crystal structure analysis of 2: A single crystal (0.35 Â 0.30 Â 0.25 mm)
was sealed in a capillary glass tube for the data collection. Diffraction
data were collected at 150 K on a Mac Science DIP2020 Image Plate
Diffractometer employing graphite-monochromated MoKa radiation
(l 0.71073 ); C36H72Li2O2Si8, Mr 767.47, a 9.506(1), b
22.105(1), c 11.869(1) , b 112.197(1)8, V 2309.20(1) 3, mono-
clinic, space group P21/c, Z 2, 1calcd 1.164 gcm 3. The final R
factor was 0.031 (Rw 0.038) for 4208 reflections with Io > 2s(Io).
Crystallographic data (excluding structure factors) for the structure
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC-101 602. Copies of the data can be obtained free of charge
on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(fax: (44) 1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
[7] The variable-temperature NMR experiment cannot be conducted in
[D8]toluene. When the temperature is lowered, the crystals of the bis-
contact ion pair precipitate which hampers the dynamic NMR study.
[8] Spectral data for 2 in [D8]THF: 1H NMR ([D8]THF, 298 K, TMS): d
0.23 (d, J 12.6 Hz, 4H, CH2), 0.17 (d, J 12.6 Hz, 4H, CH2), 0.04
(s, 48H, CH3); 13C{1H} NMR ([D8]THF, 298 K, TMS): d 6.4 (CH3),
6.9 (CH3), 11.4 (CH2), 66.8(C), 180.7 (C); 29Si{1H} NMR ([D8]THF8,
298 K, TMS): d 13.5; 6Li{1H} NMR ([D8]THF, 298 K, LiCl in
MeOH, external standard): d 0.38, 0.66.
After the reaction 2,2'-bipyridine (bpy) is mainly contained
as ligand in the main product [{(CO)5Cr}2Ge(bpy)].[7] The role
of the 2,2'-bipyridine in the formation of 1 is not clear;
however, without it compound 1 is not obtained. Since the
[9] The signal at d 0.38, which is assigned to the solvated Li ion,
becomes more intense on addition of 6LiBr due to the rapid exchange.
However, the intensity of the signal at d 0.66 for the Li ion of the
CIP remains unchanged because this ion is bound to the p-electron
system of the framework.
[10] The Li ion walk of the CIP is suppressed at 173 K so that Li is fixed
at one site of the framework. This gives rise to eight 13C NMR signals
for SiMe2 and three methylene groups (d 9.7, 10.4, and 11.4), two
endocyclic carbons (d 185.9 and 177.8), and two exocyclic carbons
(d 83.5 and 50.2). In the 29Si NMR spectrum, four signals were
observed at d 15.7, 14.3, 12.6, and 11.6.
Scheme 1. Synthesis of 1. bpy 2,2'-bipyridine.
[*] Prof. Dr. G. Huttner, Dipl.-Chem. P. Kircher, Dipl.-Chem. K. Heinze,
G. Renner
Anorganisch-chemisches Institut der Universität
Im Neuenheimer Feld 270, D-69120 Heidelberg (Germany)
Fax: (49)6221-545707
[**] This work was supported by the Fonds der Chemischen Industrie and
by the Deutsche Forschungsgemeinschaft (SFB 247).
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Angew. Chem. Int. Ed. 1998, 37, No. 12