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The First closo-Monosilaborane.

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The First closo-Monosilaborane**
Lars Wesemann* and Ulli Englert
In comparison to the thoroughly investigated carboranes"]
the study of silaboranes is still very young; until now only two of
these compounds have been structurally characterized.", Recently we were able to establish that the nucleophilic fragmentation of l ,2-dimethyl-o-silaborane forms l and thereby achieved
the synthesis of the first nido-~ilaborane.'~~
Here we report on the
first reaction of 1, which can be described as the first cluster
construction reaction with a silaborane. Compound 1 reacts with
an excess of Et,N. BH, [41 in boiling bis(2-methoxyethyl)ether to
form 1-methyl-I-sila-closo-dodecaborate(1-) 2 in 93 % yield.
I-CH3
1-
+ Et3N.BH3
Experimental Procedure
*
- 2 H,,
- Et3N
2
1
The constitution of 2 can be ascertained unequivocally from
its NMR spectra. The appearance of only three signals in the
IIB NMR with an intensity ratio of 5 : 1 : 5 for eleven B atoms
indicates that the cluster
framework has fivefold
symmetry. The assignment of the signals for
the groups B2-B6 and
B7-Bll as well as for
B12 (for numbering
scheme see Fig. 1) can be
confirmed by the 2D
IIB-llB NMR spectrum. Interestingly the
influence of the heteroatom on the "B NMR
shifts of EBllHll in
comparison to those of
[Bl,Hl,]2- (6 = -15.3)
is especially significant
for the B atom directly
opposite to the heteroatom (B12).['] This pheFig. 1. Structure of the anion 2 in the crystal
nomenon has also been
(PLATON representation [9], ellipsoids at
the 30% probability level). Selected distances
termed an "antipodal ef[A], standard deviations in parentheses.
fect". In the above-menSil-C1 1836(2), Sil-B2 2.024(2), Sil-B3
tioned example the value
2.030(2), Sil-B4 2.025(2). Sil-B5 2.026(2),
of the shift for B12 (6 =
Sil-B6 2.028(2). B2-B3 1.855(3), B2-B6
1.854(3), B2-B7 1.769(3), B2-Bll 1.766(3),
- 14.6) deviates
only
B3-B4 1.860(3), B3-B7 1.76813). B3-B8
slightly
from
that
for
1.78214). B4-B5 1.854(3). B4-B8 1.776(3), B4[Bl2Hl,IZ-. The signals
B9 1.771(4), B5-B6 1.847(3), B5-B9 1.76413).
for the B-bound H atoms
B5-Bl0 1.762(3), B6-Bl0 1.770(3). B6-Bll
1.772(3), B7-B8 1.780(3), B7-Bll 1.783(3),
can be assigned to the
B7-Bl2 1.766(3), BX-B9 1.786(4), B8-Bl2
respective B groups by
1.770(4), B9-Bl0 1.779(4). B9-BI2 1.770(3),
interpretation
of the 2D
B10-Bll 1.785(3), B10-BI2 1.774(3), Bll-Bl2
'H-"B NMR spectrum.
1.772(3).
[*] Dr. L. Wesemann, Dr. U. Englert
Institut fur Anorganische Chemie der Technischen Hochschule
Professor-Pirlet-Strasse, D-52056 Aachen (Germany)
Fax: Int. code +(241)8888-288
[**I This work was supported by the Deutsche Forschungsgemeinschaft (DFGSchwerpunktprogramm "Polyeder")
Angen. Chem. Int. Ed. Engl. 1996, 35, N o . 5
The results of the crystal structure analysis[61(Fig. 1) are in
agreement with the structure in solution determined from spectroscopic data. The distances between the B atoms of the fivemembered ring (B2-B6) capped by the Si atom are, as expected,
larger [1.847(3)- 1.860(3) A] than the remaining B-B distances
[I .762(3)- 1.786(4) A]. These are in turn only insignificantly
longer than those in [B12H12]2-[1.755(7)-1.780(7) A].[101The
Si-B distances are similar to those in the starting material l.[31
Surprisingly many examples of the class of compounds
EB, ,HI 1, to the which the title compound belongs, are already
known: E = MeA12-,["] RC-,[12] MeGe-,[l3] MeSn-,[l3]
Pb2-,[131 HN,"4] MeP,[151 As- 1161 Sb- >1171 S, [I81 Se,[l91Te,[lsl
While the carbon compound homologous to 2 was synthesized
as early as 1963, the higher homologues (Ge, Sn, Pb), which are
formed by metathesis from [B,lH,,]4- and the metal dihalide,
were first prepared in 1992.
6
2: A solution of Et4N-l (0.40 g, 1.36 mmol) and BH,.NEt, (2.00 g, 17.4mmol) in
5 m L of bis(2-methoxyethyl) ether was heated at reflux for 64 h. After all the volatile
components were removed in vacuum, the residue was dissolved in 15 mL of T H F
and filtered. The product crystallized at room temperature when Et,O was layered
on top of the T H F solution. Yield. 0.38 g (93%) Et,N-2. Correct C, H analysis.
N M R spectra at 25°C in [DJTHF: ' H N M R (500MHz. TMS): 6 =1.49 (H7H11, H12), 1.41 (H2-H6), 0.75 (s, SiMe), measurement and assignment of the
B-H signalsascrosspeaksin the2D "B-'HNMRspectrum; "BNMR(160 MHz,
Et,O.BF,): 6 = -12.6 (d, J = 1 4 7 H z , B7-Bll), - 1 4 6 (d. J = 1 3 4 H z , B12),
- ~ ~ . ~ ( ~ , J = ~ ~ ~ H z , B ~ - B ~ ) ; ~ ~ C=N-12.1
M R ((s,SiMe);
I~~MH~,TM
z9S~
N M R (100 MHz, TMS). d = - 28 (s).
Received: October 26. 1995 [ZXSOOIE]
German version: Angew. Chem., 1996, 108, 586-587
-
Keywords: boron compounds clusters
- silaboranes
[I] R. N . Grimes, Curhoranes, Academic Press, London, 1970.
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911-913; Angew. Chem. In[. Ed Engl. 1990. 29, 918-920; b) D. Seyferth, K.
Biichner, W S. Rees. Jr., L. Wesemann, W. M. Davis, S. S Bukalov. L. A.
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131 L. Wesemann, U. Englert, D. Seyferth, Angew. Chem. 1995, 107,2435-2436;
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[5] S. Heimanek. Chem. Rev. 1992. 92, 325-362.
[6] a) Single crystals of Et,MeN-2 were obtained from THF/Et,O at room temperature. b) Crystal structure analysis: ENRAF-Nonius CAD4 diffractometer; Mo,, radiation, graphite monochromator; intensity data with w scans
collected at 253 K. Et,MeN-2: colorless, transparent parallelepiped, 0.60 x
0.45 x 0.40 mm, monoclinic space group P2Jn (No. 14); u = 8.573(2), b =
14.242(3), c = 16.40416) A, fi = 105.07(3)", V = 1934(1) A3, Z = 4, pFIlrrl=
0.994 gcm-', p(Mo,,) =1.03 cm-', F(000) = 624; 4232 reflections with
3<0<26", 2816 symmetry-independent reflections with I > a ( I ) in the structure solution [7] and refinement [XI for 323 parameters; R = 0.048, R, = 0.058.
6'
= uz(Fo);hydrogen atoms were isotropically refined. In the cation there is
orientational disorder of the methyl group versus one of the ethyl groups. This
does not interfere with the packing of the crystals. c) Further details of the
crystal structure determination of Et,MeN-Z may he obtained from the Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen (Germany) on quoting the depository number CSD-404522.
[7] G. M. Sheldrick, SHELXS-86, Gottingen, 1986.
[XI B. A. Frenz. ENRAF-Nonius, SDP, Version 5.0, 1989.
[9] A. L. Spek, A r m Crystal/ogr. Sect. A 1990, 46, C34.
[lo] J. A. Wunderlich, W. N. Lipscomb. J: A m . Chem Soc. 1960. 82. 4427-4428.
[ l l ] T. D. Getman, S. G. Shore, Inorg. Chem. 1988, 27, 3439-3440.
[12] W. H. Knoth, J. A m . Chem. Soc. 1967,89, 1274-1275.
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1992, 31, 979-983.
[14] J. Muller, J. Runsink, P. Paetzold. Angew. Chem. 1991. /03,201; Angew Chem.
Int. Ed. Engl. 1991, 30, 175.
[15] T. D. Getman, H.-B. Deng, L.-Y Hsu, S. G. Shore, Inorg. Chem. 1989, 28,
3612-3616.
[16] J. L. Little, S. S. Pao, K. K. Sugathan, Inorg. Chem. 1974, 13, 1752-1756.
[17] J. L. Little, Inorg. Chem. 1979. 18, 1598-1600.
[18] J. PleSek, S. Heimanek, J. Chem. Soc. Chern. Commun. 1975, 127-128.
1191 G. D. Friesen, L. J. Todd, J. Chem. Soc. Chem. Commun. 1978, 349-350.
VCH Verlagsgrsellschaft nibH, 0-69451 Weinheim, 1996
0570-0#33/96/3505-05273 15.00+ ,2510
527
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