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Tetrakis(tri-tert-butylsilyl)-tetrahedro-tetrasilane (tBu3Si)4Si4 The First Molecular Silicon Compound with a Si4 Tetrahedron.

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metric ligands as chiral inductors see also: 0. Reiser, Angew. Chem. 1992,
According to a b initio calculations, the strain energy of
105, 576;Angew. Chem. Int. Ed. Engl. 1992,31,547.
(SiH), polyhedra increases with the number of three-mem161 U.Nagel, B. Rieger, Chem. Ber. 1988. 121, 1123-1131; U. Nagel, B.
bered rings in the polyhedron framework (see Scheme 1).[” 3l
Rieger, Organomerallics 1989,8, 1534-1538; U. Nagel. B. Rieger, A.
Bublewitz, J Organomet. Chem. 1989,370, 223-239.
[71 U.Nagel, A. Bublewitz, Chem. Ber. 1992, 125, 1061-1072;[l].
[XI K. Burgess, M. J. Ohlmeyer, K. H. Whitmire, Organometdics 1992,
H
I I, 3588-3600. diop = 2,3-O-isopropylidene-2,3-dihydroxy-l,4-b1s(dipheny1phosphino)butane.
191 B. D. Vineyard, W. S. Knowles, M. J. Sabacky, G. L. Bachman, D. J.
\
Weinkauff, J. Am. Chem. SOC.1977,99,5946-5952;U. Nagel, E.Kinzel,
Si
H
J. Andrdde, G. Prescher, Chem. Ber. 1986,119,3326-3343.
[lo] The pyrrolidine nitrogen atom is protected by the Boc group, which can be
removed easily.
hexahedro-octasilane
triprismo-hexasilane
tetrahedra-tetrasilane
[I11 Rotamers of 2 c exist because of the partial double bond character of the
(391kJ mol- 1 239.6pm) (476kJ mol- I ; 237.5 pm) (590kJ mo, - 1 231.4pm)
amide bond of the Boc group; they are evident in the 31P{’H) NMR
spectrum.
Scheme 1. (SiH). Polyhedra; calculated strain energies and Si-Si distances in
[12]Recently the review appeared in this journal “On Quantifying Chirality”:
parentheses [2, 31.
A. B. Buda, T. Auf der Heyde, K. Mislow, Angew. Chem. 1992, 104,
1012-1031;Angew. Chem. Int. Ed. Engl. 1992,31,989-1007.Mislowetal.
attempt to give measures of chirality for geometric shapes. A conclusion of
their investigations is “that the maximum chirality is associated with minOne expects the difficulty of the syntheses of these fascinatimum symmetry.. _ ”
ing polyhedral comp0unds[~1to follow the same trend. In1131 H.Buschmann, H.-D. Scharf, N. Hoffmann, P. Esser, Anxew. Chem. 1991,
103,480-518; Angew. Chem. Int. Ed. Engl. 1991,30,414.BY using the
deed, until now only hexahedro-octasilane derivatives (Si
isoinversion principle one can predict that for this type of catalysis a
substituents: s ~ M ~ , ~C B
M ~ ,,C H M ~ ,2, , 6 - ~ t , c , ~have
~)
catalyst that has been optimally tailored to the substrates will provide the
been synthesized.[51(For the heavier homologue germanium,
best ee values at 49°C and 2.3 bar.
Tetrakis(tri-tert-butylsilyl)-tetuahedvo-tetrasilane
(tBu,Si),Si, : The First Molecular Silicon Compound with a Si, Tetrahedron**
By Nils Wiberg,* Christian M . M . Finger,
and Kurt Polborn
Dedicated to Professor Heinrich Noth
on the occasion of his 65th birthday
In a recently published review on the cluster chemistry of
the heavier elements in the fourth main group (Si, Ge, Sn),
which is still in its infancy, S. Masamune et al. state in their
concluding remarks that the syntheses of tetrasilatetrahedrane 1, disilyne 2, and 1,1,l-pentasilapropellane3 are currently the greatest challenges for silicon chemists.”] We report here on our achievement of one of these goals-the
synthesis of a molecular silicon compound with a Si, tetrahedron (see
with regard to the question of a disilyne).
1 (here R = SitBu,)
2
a triprismo-hexagermane with CH(SiMe,), substituents on
the germanium atoms has also been generated.c6’) Since compounds with a tetrahedral framework constructed of atoms
of one element exist for most of the elements near silicon in
the periodic table, boron,”’ aluminum,[*]
carbon,[”] phosphorus (P,), and arsenic (As,), it is especially
puzzling that neither a tetrahedra-tetrasilane nor a tetrahedro-germane have been synthesized previously.
A tetrahedro-tetrasilane Si,R, should be more stable than
either a hexahedro-octasilane or a triprismo-hexasilane if it
has sterically demanding R groups (see
Thus
we chose to synthesize the target tetrahedron molecule 1 with
tri-tert-butylsilyl groups (R = SitBu,, “supersilyl”) (for
more on the name supersilyl see comment[81). Since Siztetrahedra are anionic components in alkaline and alkaline
earth silicides such as NaSi, KSi, and BaSi, , it was reasonable to try to give these “molecular freedom” (e.g.
Siz- + 4 R X --* Si,R, + 4X-). All attempts at derivatization have failed thus far (one reason for this is the high
reducing ability of the silicides; see comment[”, 12]).
Another imaginable approach, the dehalogenation of the
previously unknown tBu,Si-SiCI, with sodium, did not
provide access to 1, although the analogous reaction of the
less bulky tBuMe,Si-SiBr, led to hexahedro-octasilane (Si
substituents = SiMe,tBu).[’] Treatment of tBu,Si-SiC1,
with sodium in benzene at 80 “C did not give 1 ; instead NaCl
formation and hydrogen uptake led to a number of products
including 1,2-bis(supersilyl)disilane 4,which can be brominated easily to provide tetrabromobis(supersily1)disilane 5,
and the very interesting tris(supersily1)cyclotrisilane 6.[’
3
t Bu,
tBu,Si-SiH,-SiH,-Si
[**I
Institut fur Anorganische Chemie der Universitat
Meiserstrasse I, D-80333Miinchen (FRG)
Telefax: Int. code + (89)5902-451
Sterically Overloaded Silicon Compounds, Part 6, Silicon Compounds,
Part 96.This research was supported by the Deutsche Forschungsgemeinschaft. We thank Dr. J. Evers (Institut fur Anorganische Chemie der Universitlt Miinchen) for the measurement and interoretation of various rotating crystal and Wemenberg photographs, and Dr. 0 . Seligmann
(Institut fur Pharmazeutische Biologie der Universitat Munchen) for
recording a FAB mass soectrum. Part 5 and 95:J. Kovacs, G.Baum. G.
Fritz, D. Fenske, N. Wiberg, H. Schuster, K. Karaghiosoff, Z . Anorg.
Allg. Chem. 1993,619, 453.
-
1054
0 VCH
, ,H
-,
>I
t Bu,Si-SiEr,-SiBr,-Si
tau,
5
H, / \ H
,
,Si
Si
tBuSSi
‘Sit Eu,
6
At this Doint we found that 1 (R = SitBu,)
“ _ can be obtained according t o Equation (a) by the reaction of 5 with
supersi~y~sodium
t S u 3 ~ i ~ a . [ i ~~~~~~~d
4~
4,the precursor
-
Verlagsgesellschaft mbH, 0-694.51 Wemheim. 1993
tBu,Si
4
[*] Prof. Dr. N. Wiberg, DipLChem. C. M. M. Finger, Dr. K. Polborn
2 5 + 41Bu,SiNa
-
1 (R
0570-0833193/0707-1O54
$ 1 O . O O i .ZSjO
=
SirBu,)
+ 41Bu,SiBr + 4NaBr
(a)
Angew. Chem. In[. Ed. Engl. 1993,32. No. 7
of 5, can be synthesized by treating supersilylchlorosilane
tBu,Si-SiH,Cl, accessible from SiH,Cl, and tBu,SiNa,
with sodium; the yields here are much better than by the
previously mentioned approach.
Compound 1 forms intensely yellow-orange needles,
which change color (to deep-red) reversibly upon heating
and do not melt below 350°C. The crystals display high
thermo- and photostability and are stable to water and air.
Compound 1 cannot be reduced by sodium in benzene in the
presence of [18]crown-6 but reacts with oxidants like tetracyanoethylene and Br,.
X-ray quality crystals of pure 1 have not yet been obtained; however, when a mixture of 1 and hexa-tert-butyldisilane tBu,Si-SitBu, ("superdisilane") was recrystallized
from hexadeuteriobenzene!
yellow-orange rectangular
cubes formed with the composition 2(tBu,Si),Si;
(tBu,Si), C,D, 1 a, whose structure was established by Xray crystallography."61 The cubic unit cell (Fig. 1) contains
two sets of four molecules of 1 (tetrahedra 1 and IA), which
are located in the eight cube quadrants, as well as four molecules of superdisilane (occupation of the middle of every
edge and the center of the cube) and four molecules of hexadeuteriobenzene (occupation of all corners and middles of all
the faces of the cube). All the molecules are positioned on
threefold symmetry axes. The superdisilane molecules fill the
large gaps between the almost sphere-shaped molecules of 1
and thereby apparently stabilize the structure of the crystal.
tetrahedron 1A: 237.1 and 235.6 pm; for
the
Si-Si distance in Me,%-SiMe, 234.0 pm, in tBu,Si-SitBu,
268.5 pm). The elongated Si-C bonds (range 191.2197.0 pm) are rationalized in the same way.
Fig. 2. Structure of 1 in the crystal of 1a (ORTEP; Si atoms: thermal ellipsoids
at the 50% level; C atoms with arbitrary radii for clarity; no H atoms). Selected
bond lengths [pm] and angles ["I: Tetrahedron 1 : Sil-Si2 235.5(2), Si3-Si4
236.5(2), 3 2 3 3 232.0(2), Si3-Si3' 231.5(2), Sil-Cl 194.7(5), Si4-C5 194.0(5),
Si4-C9 196.2(5),Si4-Cl3 191.7(5); Sil-Si2-Si3 144.8(1)(idealized value 144.75),
Si2-Si3-Si4 144.9(1). Si4-Si2-Si3' 59.9 (1) (idealized value 60). Si2-Sil-Cl
106.1(1),Si3-Si4-C5 105.8(2), Si3-Si4-C9 106.0(2). Tetrahedron 1 A: Sil A-Si2A
237.1(1), Si3A-Si4A 235.6(2), Si2A-Si3A 232.6(2), Si3A-Si3A' 234.1(2), Sil AC I A 194.1(5), Si4A-C5A 194.1(5),Si4A-C9A 191.2(5), Si4A-Sil3A 197.0(5);
Sil A-SiZA-Si3A 144.5(1), Si2A-Si3A-Si4A 144.9(1), Si3A-Si2A-Si3A' 60.4(1),
Si2A-SilA-Cl A 105.8(2), Si3A-Si4A-CSA 107.1(2),si3A-Si4A-C9A 106.6(2)
Si3A-Si4A-Cl3A 105.8(2).
The superdisilane molecules tBu,Si-SitBu, in crystals 1a
display almost the same Si-Si distance (268.5 pm) as in crystals containing only superdisilane. As in the pure crystal
of superdisilane,[20] in l a the two tBu,Si halves are not
staggered but twisted out of this symmetric position
by 5.2".
Fig. 1. Cubic unit cell of l a (all rBu groups were left out for clarity, the C
atoms ofC,D, haveeffective radii; all molecules are found on threefold symmetry axes).
As expected, the units of 1 in crystal 1a (Fig. 2) are constructed of Si, tetrahedra, which have two different Si-Si
distances (tetrahedron 1 : 233.0 and 231.5 pm; tetrahedron
IA: 232.6 and 234.1 pm) as a consequence of the crystal
symmetry. These distances are somewhat longer than those
calculated for unsubstituted tetrahedro-tetrasilane (231.4 pm;
for comparison, in cyclotrisilanes: Si-Si distance in
[(tBuCH,),Si], 239.1 pm, in (tBu,Si), 251.1 pm;['81 see also
comment [I9]). The exocyclic Si-Si separations are somewhat
longer than normal Si-Si single bonds as a result of the bulk
of the supersilyl groups (tetrahedron 1: 235.5 and 236.5 pm;
Angebt. Chem. Int Ed. Engl. 1993, 32, N o . 7
0 VCH
Experimental Procedure
To a solution of 5 (0.428 g, 0.553 mmol) in T H F (50 mL) at -20°C was added
dropwise a 0 . 5 6 ~solution of tBu,SiNa (2.00mL, 1.12 mmol). The reaction
mixture was allowed to warm to room temperature, the T H F removed under
vacuum, the residue dissolved in pentane (70 mL), the precipitated NaBr filtered off, and the pentane removed by distillation. The crude product was
recrystallized a number of times from tBuOMe to provide 0.144 g (0.158 mmol,
57%) pure, yellow-orange 1 (R = SirBu,), m.p. > 350°C. - 'H NMR (C,D,):
6 = 1.357; (CDCI,): 6 = 1.185; 29Si{1H}NMR (C,D,): 6 = 38.89 (Si4), 53.07
(SitBu,); "C{'H} NMR (C,D,): 6 = 24.68 (CMe,), 32.16 ( C M e , ) ; MS
(KratosBO RFA,Xe(7 kV, 10 W)):m/z(%)908/909/910/911/912/913/914(8.5/
100/86.3/64.5/31.9/17.6/7.4) [ M '1. 7101711/712/713/714 (51.9/47.4/24.5/14.3/
7.2) [ M +- SitBu,]; UVjVIS (isooctane): A,., = 210/235/310/451 nm (extinction 75870/70891/19867/3583). Si,C,8H,,8 ( M , = 908.7): calcd. C 63.33 H
11.97. found C 63.53 H. 12.28.
Verlagsgesellscha) mbH, D-694S1 Weinheim, 1993
Received: March 27, 1993 [Z5949IE]
German version: Angel*. Chem. 1993, 105, 1140
0S70-0833/93/0707-10553 10.0Oi .25/0
1055
[l] T. Tsumuraya, S. A. Batcheller, S. Masamune, Angew. Chem. 1991, 103,
916; Angew. Chem. Ini. Ed. Engi. 1991, 30, 902.
[2] S. Nagase, Angew. Chem. 1989, 101, 340; Angew. Chem. I n t . Ed. Engl.
1989, 28, 329.
[3] According to calculations triprismo-hexasilane is considerably more stable
than the isomeric hexasilahenzene; tetrahedra-tetrasilane is more stable
than tetrasilacyclobutadiene but not as markedlyjl]. Bulky R groups help
stabilize structure 1.
[4] M. Weidenbruch, Angew. Chem. 1993, 105, 574; Angew. Chem. Int. Ed.
Engl. 1993.32, 545.
[5] H. Matsumoto, K. Higuchi, Y. Hoshino, H. Koike, Y. Naoi, Y. Nagai. J.
Chem. Sac. Chem. Commun. 1988, 1083; H. Matsumoto, K. Higuchi, S.
Kyushin, M. Goto, Angew. Chem. 1992,104,1410; Angew. Chem. Int. Ed.
Engl. 1992, 31, 1354; A. Sekiguchi, T. Yatabe, H. Kamatani, C. Kabuto,
H. Sakurai, J. Am. Chem. Sac. 1992, 1f4,6260.
[6] A. Sekiguhi, C. Kabuto, H. Sakurai, Angew. Chem. 1989,101, 97; Angew.
Chem. Ini. Ed. Engl. 1989, 28, 55.
171 T. Mennekes, P. Paetzold, R. Boese, D. Bliser, Angew. Chem. 1991, 103,
199; Angew. Chem. h l . Ed. Engl. 1991,30, 173.
[S] N. Wiberg in Frontiers ofOrganosilicon Chemistry (Eds.: A. R. Bassindale,
P. P. Gaspar), R. SOC.Chem. Cambridge, 1991, p. 263; C. Dohmeier, C.
Robl, M. Tacke, H. Schnockel, Angew. Chem. 1991, 103, 594; Angew.
Chem. I n f . Ed. Engl. 1991, 30, 564.
[9] W. Uhl, W. Hiller, M. Layh, W. Schwarz, Angew. Chem. 1992,194, 1378;
Angew. Chem. Int. Ed. Engi. 1992, 31, 1364.
[lo] G. Maier, S. Pfriem, U. Schafer, R. Matusch, Angew. Chem. 1978, 90, 552;
Angew. Chem. Int. Ed. Engl. 1978, f7,520. H. Irngartinger, A. Goldmann,
R. Jahn, M. Nixdorf, H. Rodewald, G. Maier, K.-D. Malsch, R. Emrich,
ibid. 1984, 96,967 and 1984.23.993.
[ l l ] E. Hey-Hawkins, H:G. von Schnering, Chem. Be,. 1991, 124, 1167; Z.
Naturforsch. B 1991, 46, 307; ibid. 1991, 46, 621.
112) H. Bock, K. Don, R. Schlogl, Universitat Frankfurt, have attempted to
prepare tetrahedra-tetrasilane Si,X, by rapid solidification processing of
BaSi, ( 2 0 0 0 T melt under argon on a rotor at 20000 rpm and with additional cooling by n-hexane) with halogens; however, only halosilanes like
Si,CI, and SiI, could be isolated (lecture at the 25th National Organosilicon Symposium, University of Southern California, Los Angeles, USA,
April 3, 1992, and Diplomarbeit, G. Herrmann, Universitat Frankfurt,
1991).
N. Wiberg, T. PassIer, unpublished.
The idea that the conversion of 5 into 1 could proceed by the dimerizais quite fascinattion of bis(superdisily1)disilyne tBu,Si-SiS-SiBu,
ing:
5 tBu,SiNa --t (tBu,Si)BrSi=SiBr(SitBuJ
tBu,SiBr + NaBr;
(tBu,Si)BrSi=SiBr(SitBu,)
tBu,SiNa + tBu,Si-SiSi-SitBu,
tBu,SiBr NaBr.
N. Wiberg, H. Schuster, A. Simon, K. Peters, Angew. Chem. 1986,98,100;
Angew. Chem. I n f . Ed. Engl. 1986,25, 79.
M , = 2303.15, cuX-ray analysis of l a : 2Si,C,,H,,,.Si2C2,H,,.C,D,,
=
bic, P2,3 (no. 198), a = 2473.3(8) pm, Y = 15.1304 nm3, Z = 4(!), pcalod
1.011 Mgm--', p = 0.185 mm-', T = 296K, data collection on a yelloworange crystal with dimensions of0.4 x 0.53 x 0.53 mm. 16621 Reflections
were collected on an Enraf-Nonius CAD4 diffractometer, of which 6761
were independent and observed, 5940 with ( F > 3uF). @-Scan,scan width
0.50" 0.35tan0, maximum measurement 180 s per reflection; range:
2 " 2 0 < 46". Complete measurement of i h , k , f with (hl < / a n d k < k
additional reflections without this restriction, i.e. ca. 78% of I h , k . I
(R,= 0.019), then interruption because of decomposition. Correction for
anisotropic disintegration (0.9949,1.2071). Weissenbergphotographs confirm the unit cell found and showed only weak reflections for Okl when
k = 2n + 1 ; the reflections h were extinguished when h = 2n + I . The tBu
groups of the hexa-tert-butyldisilane molecules are more disordered and
require geometric constraints; the C atoms of C,D, were also quite disordered; in the final model the D atoms were not included. Solution:
SHELX86, block refinement with SHELX76[17]. Riding hydrogen atoms
at geometrical positions, all non-hydrogen atoms refined anisotropically.
R = 0.057, R, = 0.051, w = l/a2(Fo).433 Parameters. The ratio of reflections to refined parameters is 13.7: 1, The absolute configuration was not
determined. Further details of the crystal structure investigation may be
obtained from the Fachinformationszentrum Karlsruhe, Gesellschaft fur
wissenschaftlich-technische Information mbH, D-76344 Eggenstein-Leopoldshafen (FRG) on quoting the depository number CSD-57184, the
names of the authors, and the journal citation.
[I71 G. M. Sheldrick, SHELX76, Program for the Crysraf Structure Derermination. University of Cambridge, 1976; SHELX86, Program for rhr Solution
of Crystal Structures, Gottingen, 1985.
[18] H. Watanabe, M. Kato, T. Okawa, Y. Nagai, M. Goto, J. Organornet.
Chem. 1984,271,225; A. Schafer, M. Weidenbruch. K. Peters, H. G. von
Schnering, Angew. Chem. 1984,96,311 :Angew. Chem. Int. Ed. Engl. 1984,
23, 302.
[I91 H. Griitzmacher, Angw. Chem. 1992, 104, 1358; Angew. Chem. Int. Ed
Engl. 1992,31, 1329; R. Janoschek, Chem. Unserer Zeir, 1988,21, 128.
[20] H. Bock, J. Meuret, K. Ruppert, Angew. Chem. 1993, 105,413; Angew.
Chent. lnt. Ed. Engl. 1993, 32, 414; J. Organomet. Chem. 1993, 445, 19.
+
+
+
+
+
+
1056
0 VCH Yeriagsgeseilschafi mbH. 0-69451
Weinherm, 1993
(C,F,NGaMe), and (C,F,NInMe), : The First
Gallium-Nitrogen and Indium-Nitrogen
Compounds with Cubane Structures**
By Thomas Belgardt, Herbert U! Roesky,*
Mathias Noltemeyer, and Hans-Georg Schmidt
Dedicated to Professor Hans Bock
on the occasion of his 65th birthday
Compounds with heterocubane frameworks have been
known for a long time for main group elements.[lJThe first
aluminum-nitrogen compound with cubane structure (PhNAlPh), was prepared in 1962 and structurally characterized ten years later.''' In the meantime several more compounds of this type have been de~cribed.1~'
In contrast, there
are no indications of analogous gallium-nitrogen and indium-nitrogen compounds. Starting materials for the synthesis of the aluminum-nitrogen compounds with a central cubic AI,N, unit are the aminoalanes (RNHAlR;),, which
form cubanes through intermolecular reactions. Power et al.
have transferred these reactions to the corresponding aminogallanes and have thus observed that under C-H activation
an intramolecular elimination of hydrocarbons takes
place.[3b1Corresponding reactions of the aminoindanes are
not known. In order to prevent a C-H activation, we have
now treated GaMe, and InMe, each with pentafluoroaniline
(Scheme 1).
H
R
1, 3
Scheme 1. 1, 2: M = Ga; 3, 4: M
=
In. R
= C,F,
The aminometallanes 1 and 3 are obtained as intermediates, which precipitate in the form of needlelike crystals in
high yield. The compounds 2 and 4, the first gallium-nitrogen and indium-nitrogen compounds with cubane frameworks, respectively, can be prepared by heating the appropriate aminometallanes without solvent, and subsequent
recrystallization of the products from n-hexane. Compound
2 belongs to the class of iminogallanes (RNGaR),, for
which to our knowledge only one compound with a complex
4 is the first struccage structure is k n o ~ n . [Compound
~l
turally characterized iminoindane (RNInR'), .
The crystal structure of 2 is shown in Figure I.['] The
framework consists of fourfold coordinated Ga and N
atoms, which together form a regular cube (angles at Ga and
N lie between 85.9(2) and 94.0(2)"). However, the angles here
deviate significantly from the 90" angle of a perfect cube, in
contrast to (PhAlNPh),, for which angles of almost 90" are
observed. The Ga-N bond lengths lie between 197.2 and
203.9 pm (mean 200.8(4) pm). Thus, they correspond to the
atomic distances in aminogallanes, for example those of
(Me,GaNHPh), .IJb1 As expected, the distances are somewhat longer than those for iminoalanes with cubane struc['I
Prof. Dr. H. W Roesky, T. Belgardt, Dr. M. Noltemeyer, H.-G. Schmidt
Institut fur Anorganische Chemie der Universitat
Tammannstrasse 4, D-37077 Gottingen (FRG)
Telefax: Int. code (551)39-3373
This work was supported by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie.
+
["'I
0570-0833j93jO707-1056S 10.00+.25/0
Angew. Chem. h t . Ed. Engl 1993, 32, No. 7
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molecular, compounds, butylsilyl, tbu3si, silicon, tert, tetrasilanes, tetrakis, tetrahedral, 4si4, first, tri, si4
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