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Distanna-closo-dodecaborate.

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Angewandte
Chemie
mixture of decaborane and bis(dimethylamino)methylsilane
((Me2N)2SiHMe).[2] The incorporation of tin atoms into the
skeleton of boranes or carbaboranes is possible for a variety
of clusters. The following heteroboranes with naked tin atoms
as cluster vertices have been prepared through typical saltelimination reactions between deprotonated nido clusters and
tin(ii) halides: closo-[1-Sn-2,3-(SiMe3)2-2,3-C2B4H4],[3] closo[1-Sn-2,4-(SiMe3)2-2,4-C2B4H4],[3] closo-[1,2,3-SnC2B8H10],[4]
closo-[1,2,3-SnC2B9H11],[5] closo-[4,1,6-SnC2B10H12].[6] However, 1,2-distanna-closo-dodecaborate, a higher homologue
of o-carbaborane and o-silaborane, was unknown prior to our
investigation.
Herein, we present the first synthesis of a distanna-closododecaborate with adjacent tin atoms. First, one tin vertex
was incorporated into the decaborane cluster skeleton by
applying an adaptation of the method published by Gaines et
al.;[7] accordingly, stanna-nido-undecaborate [C14H19N2][7-Cl7-SnB10H12] (1) was synthesized from a mixture of decaborane, proton sponge (1,8-bis(dimethylamino)naphthalene,
C14H18N2), and tin(ii) chloride (Scheme 1).
Borane Chemistry
Scheme 1. Formation of stanna-nido-undecaborate 1 with proton
sponge (C14H18N2) as base.
DOI: 10.1002/anie.200503197
Distanna-closo-dodecaborate**
Reaction of the nido-borate 1 with additional equivalents
of proton sponge and tin(ii) chloride did not lead to the
incorporation of a second tin atom into the cluster skeleton.
However, use of a different base in the reaction was
successful: the interesting derivative [Et3NH]2[(Sn2B10H10)2]
(2) of the distanna-closo-dodecaborate was isolated from a
mixture of the eleven-vertex cluster 1, triethylamine, and
tin(ii) chloride. In 2, two clusters are joined together by a Sn
Sn bond (Scheme 2).
Dominik Joosten, Ingo Pantenburg, and
Lars Wesemann*
Dedicated to Professor Hansgeorg Schnckel
on the occasion of his 65th birthday
Dicarba-closo-dodecaborane ([C2B10H12]) is by far the most
prominent and best investigated heteroborane. The chemistry
of this nearly icosahedral cluster has been a field of active
research for more than forty years.[1] Fifteen years ago, the
higher homologue of the o-carbaborane, disila-closo-dodecaborane ([Me2Si2B10H10]), was fortuitously isolated from a
[*] D. Joosten, Prof. Dr. L. Wesemann
Institut f1r Anorganische Chemie
Universit5t T1bingen
Auf der Morgenstelle 18, 72076 T1bingen (Germany)
Fax: (+ 49) 7071-295-306
E-mail: lars.wesemann@uni-tuebingen.de
Dr. I. Pantenburg
Institut f1r Anorganische Chemie
Universit5t zu KAln
Greinstrasse 6, 50939 KAln (Germany)
[**] This work was supported by the Deutsche Forschungsgemeinschaft.
Angew. Chem. Int. Ed. 2006, 45, 1085 –1087
Scheme 2. Formation of the dimeric closo-heteroborate 2.
According to the 11B{1H} NMR spectra, this surprising
reaction proceeds almost quantitatively. However, the fate of
the chlorine substituent is unknown. A comparable intermolecular Sn Sn bond formation occurs in the synthesis of [7,7’(SnB10H12)2]2 ; this species was postulated by Gaines et al. to
be formed after oxidative elimination of C2H6 from [7-Me-7-
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1085
Communications
SnB10H12] .[7] The structure of the dimeric distannaborate salt
2 in the solid state was unequivocally determined by singlecrystal X-ray structure analysis (Figure 1).[8] The Sn Sn
distances of 2.795(1) and 2.794(1) ? within the clusters are
Figure 1. Structure of the dianion of 2 in the solid state (ORTEP plot,
hydrogen atoms omitted, 50 % probability ellipsoids). Selected
distances [F] and angles [8], standard deviations in parentheses: Sn1
Sn2 2.7945(4), Sn1 B3 2.673(4), Sn1 B4 2.379(4), Sn1 B5 2.383(4),
Sn1 B6 2.686(4), Sn2 B3 2.375(4), Sn2 B6 2.373(4), Sn2 B7
2.319(4), Sn2 B8 2.321(4), Sn2 Sn2a 2.7240(4), Sn1a Sn2a
2.7954(4), Sn1a B3a 2.689(4), Sn1a B4a 2.390(4), Sn1a B5a
2.403(4), Sn1a B6a 2.699(4), Sn2a B3a 2.388(4), Sn2a B6a 2.390(4),
Sn2a B7a 2.333(4), Sn2a B8a 2.327(4); Sn1-Sn2-Sn2a 137.42(1),
Sn1a-Sn2a-Sn2 153.57(1), Sn1-Sn2-Sn2a-Sn1a 145.12(2).
very similar to the Sn Sn distance of 2.724(1) ? between the
clusters, and are somewhat longer than the distance of
2.587(1) ? between the tin atoms in [7,7’-(SnB10H12)2]2 .
Interestingly, the Sn B distances involving the substituted tin
atoms (Sn2/Sn2a) are shorter than those involving the
unsubstituted ones (Sn1/Sn1a).
In the 11B{1H} NMR spectrum of the Cs-symmetrical
cluster units in solution, six signals with an intensity ratio of
1:1:2:2:2:2 are detected, as expected. However, even with a
supplementary two-dimensional 11B–11B COSY NMR spectrum, only the resonance at d = 14.4 ppm with five cross
peaks can unequivocally be assigned to boron atoms B9/B9a
and B11/B11a.
The signals in the 119Sn{1H} NMR spectrum of 2 (Figure 2)
can be assigned according to stannaborate chemistry: upon
substitution at the naked tin vertex in [SnB11H11]2 , a downfield shift from d = 546 to between 350 to 150 ppm is
observed.[12, 13] Therefore, we conclude that in 2 the tin atoms
Sn1/Sn1a and Sn2/Sn2a show signals at d = 452 and
228 ppm, respectively. Furthermore, a 119Sn{1H} NMR simulation[11] corroborates this assignment of the 119Sn{1H} NMR
spectrum. The 117/119Sn satellites of the unsubstituted atoms
Sn1/Sn1a (at d = 452 ppm) show a coupling to Sn2/Sn2a
(1J(119Sn1, 119Sn2/117Sn2, 119Sn1a, 119Sn2a/117Sn2a) = 3705 Hz),
whereas the 117/119Sn satellites of the substituted atoms Sn2/
Sn2a (at d = 228 ppm) show couplings to both Sn1/Sn1a and
Sn2a/Sn2 (1J(119Sn2, 117Sn2a, 119Sn2a, 117Sn2) = 2190 Hz, in
addition to the former ones).
To cleave the Sn2 Sn2a bond we reacted the dimeric
stannaborate salt 2 with an excess of the reducing agent
K[HBEt3] (Scheme 3). 11B{1H} NMR spectroscopy reveals
Scheme 3. Formation of 1,2-distanna-closo-dodecaborate 3 by reductive
cleavage of the dimeric closo-heteroborate 2.
that this cleavage proceeds quantitatively. After cation
exchange, the 1,2-distanna-closo-dodecaborate was isolated
from an aqueous solution of the potassium salt as the
tetraalkylammonium salt [Bu3MeN]2[Sn2B10H10] (3). The
distannaborate dianion was characterized by NMR spectroscopy, mass spectrometry, and elemental analysis. The
11
B{1H} NMR spectrum of 3, which comprises four signals
with an intensity ratio of 2:2:4:2, is consistent with the C2v
symmetry of the distannaborate cluster. On the basis of the
two-dimensional 11B–11B COSY NMR spectrum, we were
able to assign the four resonances to the respective boron
atoms by taking into account that heteroatom-bridged B–B
contacts usually show weak cross peaks. In the 119Sn{1H} NMR
spectrum, one resonance was detected at d = 349 ppm for
the two tin atoms in the distannaborate cluster, as expected.
In conclusion, with the three-step procedure presented herein
we are able to prepare the 1,2-distanna-closo-dodecaborate
cluster from decaborane. The coordination chemistry of this
dianion is now under investigation.
Experimental Section
Figure 2. The 119Sn{1H} NMR spectrum of 2.
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All manipulations were carried out under a dry argon atmosphere in
Schlenk glassware. Solvents were purified by standard methods and
stored under an argon atmosphere. The mass spectrometry measurements were recorded in positive- and negative-ion mode using a
Bruker esquire 3000plus spectrometer equipped with an ESI interface.
NMR spectra were recorded by using a Bruker DRX400 spectrometer. Elemental analyses were performed by the Institut fEr Anorganische Chemie, UniversitGt TEbingen using a Vario EL analyzer.
2: Triethylamine (0.7 mL, 1 = 0.726 g cm 3, 5.022 mmol) in dimethoxy ethane (DME; 20 mL) was added dropwise over 1.5 h to a
solution of 1 (561.7 mg, 1.147 mmol) and tin(ii) chloride (224.1 mg,
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2006, 45, 1085 –1087
Angewandte
Chemie
1.182 mmol) in DME (40 mL). After stirring for 48 h, the yellow
solution was filtered, and the solvent was evaporated in vacuo. The
residue was washed with hexane (3 J 10 mL), water (3 J 10 mL), and
diethyl ether (3 J 10 mL), and then dried in vacuo to give 2 (349.4 mg,
ca. 67 %) as a yellow powder. 11B{1H} NMR ([D6]acetone, 128 MHz):
d = 0.9 (1 B), 1.1 (1 B), 1.9 (2 B), 7.1 (2 B), 8.1 (2 B), 14.4 ppm
(2 B, B9/B9a, B11/11a); 119Sn{1H} NMR ([D6]acetone, 149 MHz): d =
119
Sn1a, 119/117Sn2a) = 3705 Hz,
232
[1J(119Sn1, 119/117Sn2,
1 119
117
119
117
J( Sn2, Sn2a,
Sn2a, Sn2) = 2190 Hz]; 448 ppm [1J(119Sn1,
119/117
Sn2, 119Sn1a, 119/117Sn2a) = 3705 Hz]; C,H,N analysis (%) calcd
for C12H52B20N2Sn4 : C 15.74, H 5.72, N 3.06; found: C 13.56, H 3.70, N
2.42. Even after a series of elemental analyses from different samples,
there was no better correspondence.
3: A potassium triethylhydridoborate solution (3.2 mL, 1m in
THF) was added dropwise to a suspension of 2 (723.3 mg,
0.790 mmol) in THF (40 mL) and stirred for 45 min. The mixture
turned dark brown, and the hydrogen gas evolved was removed
through an argon bubbler. The solvent was evaporated in vacuo. The
dark gray residue was dissolved in water (30 mL) and filtered into a
solution of [Bu3MeN]Cl (slight excess) in water (20 mL). The
precipitate was collected by filtration, washed with diethyl ether,
and dried in vacuo to give 3 as a white powder (394.8 mg, 66 %).
11
B{1H} NMR ([D8]THF, 128 MHz): d = 1.6 (2 B, B3, B6), 0.1 (2 B,
B10, B12), 6.1 (4 B, B4, B5, B7, B8), 11.7 ppm (2 B, B9, B11);
119
Sn{1H} NMR ([D6]acetone, 149 MHz): d = 349 ppm; MS (ESI):
m/z: 956.7 {[Bu3MeN]3[Sn2B10H10]}+, 556.1 {[Bu3MeN][Sn2B10H10]} ,
355.0 [Sn2B10H10]C ; C,H,N analysis (%) calcd for C26H70B10N2Sn2 : C
41.29, H 9.33, N 3.70; found: C 41.01, H 8.92, N 3.62.
Received: September 8, 2005
Published online: December 28, 2005
.
Keywords: boranes · cluster compounds · tin
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[8] a) Crystals of the proton sponge salt [C14H19N2]2[(Sn2B10H10)2]
(Mr = 1141.74) suitable for X-ray structure analysis were
obtained by slow diffusion of diethyl ether into the reaction
mixture at room temperature; b) crystal-structure analysis:
STOE IPDS II diffractometer: MoKa radiation, T = 150 K;
yellow transparent needle, 0.45 J 0.18 J 0.12 mm3, monoclinic
space group P21/a (no. 14); a = 14.2322(1), b = 13.3667(1), c =
24.685(2) ?, b = 103.142(5)8, V = 4573.1(5) ?3, Z = 4, 1calcd =
1.658 g cm 3, m(MoKa) = 21.87 cm 1, F(000) = 2216; 67 103 reflections with 3.4 < 2q < 54.78, 10 207 independent in structure
solution and refinement for 737 parameters;[9] R1 = 0.0460,
wR2 = 0.0716, w = 1/{s2(F 2o) + [0.0378(F 2o + 2 F 2c)/3]2}; numerical
absorption correction based on an optimized crystal shape;[10] all
hydrogen atoms were found and isotropically refined; c) CCDC283258 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The
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ac.uk/data_request/cif.
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2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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