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Organic-Soluble Neutral and Ionic Indium Siloxane Cages Potential Precursors for Indium-Containing Silicates.

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Organic-Soluble Neutral and Ionic Indium
Siloxane Cages: Potential Precursors for
Indium-Containing Silicates**
2 : 4, lnMe3
Andreas Voigt, Mrinalini G. Walawalkar,
Ramaswamy Murugavel, Herbert W. Roesky,*
Emilio Parisini, and Paolo Lubini
6 CH4
Dedicated to Professor Achim Muller
on the occasion of his 60th birthday
Zeolites and metal-doped zeolites have attracted increasing
attention from chemists and material scientists because of their
excellent catalytic and ion exchange properties, which also find
wide applications in the chemical industry. While aluminumcontaining silicates have been well known and studied over the
decades, there has been a recent upsurge in the study of Gadoped molecular sieves and phosphate compounds in the light
of their usefulness in catalytic conversions." - 3 1 In spite of the
widespread applications of A1 and Ga zeolites, there are only a
very few reports on the synthesis or on the catalytic activity of
In-containing zeolites.[41Studies on In-based zeolites warrant
attention in the light of their recently reported utility in the
catalytic reduction of nitrogen oxides (NO,) ,[41 a process that
has implications in cleaning up exhaust gases of combustion
Studies on metallasiloxanes are also important because of
their ability to act as model compounds for complex zeolite
Starting from a series of stable silanetriols we have
synthesized a range of metallasiloxanes incorporating metals
such as Al, Ga, Sn, Ti, Zr, Ta, and Re that exhibit novel structural features.I6,71 IR particular, silanetriols are excellent starting materials for three-dimensional Al- and Ga-containing
siloxanes, which could function as models for zeolites.['] Continuing our efforts in the utilization of stable and discrete
silanetriols for the preparation of useful metallasiloxanes, we
report here on the first successful synthesis of new polyhedral
indium siloxanes 2-5 (Scheme 1) that are soluble in common
organic solvents such as pentane, diethyl ether, THF, and
toluene. While the reaction between 1 and InMe, in the ratio 1:2
results in the partial elimination of methyl groups on indium
leading to the drum-shaped In-siloxane 2, a 1:1 reaction between the same reactants under similar conditions leads to the
complete elimination of all the methyl groups on indium and the
isolation of the cube-shaped In-siloxane 3. The reactions between 1 and the ionic alkylindium compounds Li[InMe,] and
Na[InMe,] lead to the ionic In-siloxanes 4 and 5, respectively
(Scheme 1).
The reaction leading to the Na-In-siloxane 5 is particularly
interesting. The formation of this product should have proceeded by a self-condensation of the silanetriol 1 resulting in the
tetrahydroxydisiloxane [ (OH),RSi],O and water.['] This process is presumably catalyzed by highly ionic reactants such as
Na[InMe,] in the reaction
Evidently, the reactive
N-SiMe, bonds in the initially formed In-siloxane are partial[*] Prof Dr. H. W. Roesky, Dr. A. Voigt, M. G . Walawalkar, Dr. R. Murugavel,
Dr. E. Parisini, Dr. P. Lubini
lnstitut fur Anorganische Chemie der Universitat
Tammannstrasse 4. D-37077 Gotringen (Germany)
Fax: Int. code +(551) 39 33 73
e-mail : hroesky(u
This work was supported by the Deutsche Forschungsgemeinschaft and the
Witco GmbH. Bergkamen. R. M. thanks the Alexander-von-Humboldt
foundation, Bonn, for a research fellowship. E. P. and P. L. are grateful to
the European Union for post-doctoral grants (ERB CHBG CT 940731 and
BBW 94.0162 CHBG C T 940731).
Angeu, Chem Int. Ed. Engl 1997.36.No. 20
C WILEY-VCH Verlag GmbH,
4 : 4, InMes
- 12 CH4
4, Li[lnMe4]
12 CHd
I 3, Na[lnMe4]
2 SiMesOti
H ~
Scheme 1 Synthesis of indium siloxanes 2-5.
ly hydrolyzed over the period of crystallization (ca. three
months) to yield the siloxane 5, which contains NHAr groups.
All the new In-siloxanes have been characterized based on
their analytical, spectroscopic (IR, 'H and "Si NMR), and
mass spectrometric (EI MS) data. In addition the solid-state
structures of 2, 4, and 5 have been unambiguously established
by single-crystal X-ray diffraction studies.'' In the case of 3, it
has so far not been possible to obtain suitable single crystals.
The spectroscopic data are consistent with the structural formulation of all the compounds. The EI mass spectra of all compounds yield molecular ion peaks or the peaks due to loss of
solvent molecules or methyl groups. Three 29Si NMR signals
are observed for the three different types of silicon centers in 5
(6 = - 73.9, - 72.8, and 2.3); the spectra of all the other compounds show only two 29SiNMR signals corresponding to the
SiMe, and SiO, moieties.
The molecular structure of the heterosiloxane 2 (Figure 1) can
best be described as a cylindrical-drum whose top and bottom
faces are made up of six-membered In,O,Si rings. The side faces
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seems to provide a greater flexibility to the cubic core. In particular, the chair conformation for the four eight-membered
In,O,Si, rings facing the coordinated Li+ ions is absent in the
other two faces of the cage. Also there is a pronounced deviation
from regular tetrahedral coordination of the four-coordinate In
atoms. The Li+ ions adopt a nearly ideal square-pyramidal coordination geometry. AS a consequence of the side-on coordination of the oxygen atoms to the Li' ions, the cubic cage is
slightly squeezed along the axis perpendicular to the plane defined by these four lithium ions. The conformation adopted by
the N-bonded ligands in 2 and 4 is almost identical; owing to the
bulkiness of the isopropyl groups, the aromatic ring is forced to
lie perpendicular to the Si-N-Si plane.
The molecular structure of In-siloxane 5 is made up of a
central In,Na,O,,Si, core that resembles the shape of a birdcage (Figure 3 ) . Two formal [(N(Ar)(SiMe,))0,(p-O)02Si(NHAr)J4- ligands coordinate to two [InMeJ2+,one [InMe,J+,
and three Na+ moieties. There are two InO,Si, six-membered
Figure 1 Molecular structure of 2 in the crystal. Selected bond lengths [A] and
angles ["I: In(l)-O(l) 2.148(6), In(1)-0(2) 2.150(6), In(l)-C(18) 2.100(9), In(?)O(3A) 2.033(6), Si(l)-O(l) 1.654(6), Si(l)-0(2) 1.666(6), Si(1)-0(3) 1.590(6),
Si(1)-N(1) 1.722(7), I n @ - C( 16) 2.1 36(6), In(2)-C( 17) 2.1 32( 10); O(I)-In( 1)-O(2)
71.0(2), O(l)-In(1)-0(3A) 97.8(2), 0(2)-In(l)-0(3A) 100.1(2), C( 16)-In(2)-C(17)
are composed of two such six-membered rings (existing in a boat
conformation) in addition to two planar four-membered In0,Si
rings. The shape of the In,O,Si, framework in compound 2 is
similar to that observed for the previously characterized A1 and
Ga analogues.l8I Given the differences in the covalent radii of
the metal atoms, the I n - 0 distances (2.1 1 A) are longer than the
G a - 0 (1.91 A) and A1-0 (1.83 A) distances in the corresponding compounds. As a consequence, the internal 0 - M - 0 angles
of the drum also decrease on going from A1 to In. The I n - 0
distances in 2 are comparable with the values reported
for [(InC(Me,Si),)40(OH),J (2.12 A)[1Za1and [{In(OH)(O,PPh,)Me(py)),] (2.23 A) (py = pyridine)
Both 3 and 4 are made up of a central In,O,,Si, cubic core
(Scheme 1). In the ionic compound 4 (Figure 2), four of the six
faces of the In,O,,Si, cube are further surrounded by Li+ ions.
Although the overall shape of the cage appears to be comparable to that of the A1 analogue,'8b1the substitution of A1 by In
Figure 2. Structure of the central core in 4 in the crystal. Selected bond lengths [A]
and angles ["I: In(l)-0(2) 2.036(3), In(l)-O(lB) 2.068(3), In(l)-0(2A) 2.056(3),
In(lA)-C(20A) 2.131(4), Si(1)-O(1) 1.609(3), Si(I)-0(2) 1.618(3), Si(l)-0(3)
1.615(3), Li(1)-0(4) 1.953(8), Li(1)-O(1B) 2.561(10), Li(l)-0(2) 1.933(8), Li(1)O(3A) 1.974(8); 0(2)-In(l)-0(2A) 115.65(1 l ) , 0(2)-In(l)-O(lB) 92.19(12), O(2A)In(1)-O(1B) 95.21(12).
0 WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1997
Figure 3. Structure of the central core in 5 in the crystal. Selected bond lengths
and angles I"]: In(l)-0(3) 2.078(5), In(l)-0(4) 2.069(5), In(l)-O(8) 2.080(5),
In( 1)- C( 1) 2.144(8), Si( 1)- O( 1) 1.640(5 ) , Si( 1)-0(2) 1.606(5), Si(1)-O( 3)
1.619(5), Na(1)-O(1) 2.647(5), Na(l)-0(2) 2.512(6), Na(1)-O(5) 2.313(6),
Na(l)-0(9) 2.310(6), Na(1)-O(1 I ) 2.295(6); Si(I)-O(l)-Si(2) 141.4(3), Si(1)-0(2)In(2) 137.4(3), Si( 1)-0(3)-In( 1) 123.2(3).
rings in the molecule that are linked by two In-0-Si bridges. All
the oxygen atoms in the molecule are triply bridging ( p 3 )the In,
Na, and Si centers. All In atoms have a tetrahedral coordination
While the two pentacoordinate Na' ions (bonded to four
cage oxygen atoms and one THF molecule) have an approximate square-pyramidal geometry, the third Na+ ion is tetrahedrally coordianted by two cage oxygen atoms and two T H F
molecules. There are two distinct types of Si-0 distances in the
molecule: the Si -O(Si) bonds are considerably longer (av
1.65 A) than the Si-O(In) bonds (av 1.60 A). All the I n - 0
distances are nearly equal; the average value is 2.08A. The
N a - 0 distances in the molecule vary from 2.28 to 2.66 A.
In summary, small variations in the reaction conditions
and the choice of starting materials has allowed us to prepare
indium siloxanes with different polyhedral structures, which
would potentially model the In-silicate frameworks. Furthermore, the hydrolyzable functionalities make compounds 2 - 5
promising starting materials for the synthesis of new synthetic
In-containing zeolites under mild conditions or by sol-gel processes.
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Angeu. Chem. Inl. Ed. Engl. 1997, 36, No. 20
Experimental Section
2. A solution of InMe, (1 60 g, 10 mmol) in n-hexane/THF (10 mL/5 mL) was
added to a suspension of 1 (1.64 g. 5 mmol) in n-hexane (40 mL) at room temperature. The resulting clear solution was heated under reflux for 2 h and then slowly
allowed to cool to room temperature to yield colorless crystals of 2 after two days.
Yield 2.45 g (82%); MS (EI, 70eV): miz ( Y o ) : 1198 (20) [M'], 1183 (100)
[M' - Me]. ' H NMR (CDCI,): 6 = - 0.10 (s, 6H; InMe), 0.04 (s, 12H; InMe,),
0.30 (s. 18H. S I M P J .1.32 (m, 24H; CHMr,), 3.57 (m. 4H; CHMe,). 7.05 (s, 6H;
aromat 1. *'Si NMR (CDCI,): 6 = -70.9 (SO,), 6.3 (SiMe,); IR (Nujol):
i. =1500,1317,1260,1249,1180,1106,1043,1014,969,955,905,875,838,802,752,
688. 61 3.542 cm- ' .elemental analysis (%) calcd for C,6H,,In,N,0,Si,:
C 36.1, H
5.8, N 2.4; found: C 35.1. H 5.2. N 2.1.
3: A solution of InMe, (0.80 g, 5 mmol) in n-hexane/THF (10 mL/5 mL) was added
to a suspension of 1 (1.64 g, 5 mmol) in n-hexane (40 mL) at 60 'C. After the evolution of methane gas ceased, the heating was continued for an additional 1.5 h. The
solvent was removed in vacuo to afford 3 as a white solid which was purified by
crystallization from hot n-hexane. Yield 2.43 g (95%). MS (EI, 70 eV): miz (%):
2045 (10) [ M ' ] . 1756 (100) [M' - 4THFI. ' H N M R (CDCI,): b = 0.15 ( s , 36H;
S I M P , ) . 1.26 (m.48H. CHMe,), 1.28 (m. 16H, OCH,CH,), 3.46(m, 16H; OCH,).
3.74 (m. 8H. CHMe,). 7.10 (m. 12H; aromat.); '9Si NMR (CDCI,): 6 = -72.4
(SiO,). 6.4 (SiMe,). IR (NuJol): i.=1499, 1321, 1258. 1180, 1109, 1046. 1012,968,
954. 908. 879. 836. 801. '755. 656, 617, 551, 474, 443, 397cm-'; elemental analysis
(%) calcd for C ~ ~ , H , , ~ I i i ~ N ~ O 1C6 S
51i ,9,
: H 7.7, N 3.2; found: C 50.1, H 7.1,
N 2.9.
4: A solution of LilnMe, [I31 (0.91 g, 5 mmol) in n-hexane/THF (10 mL/5 mL) was
slowly added to a suspension of 1 (1.64 g, 5 mmol) in n-hexane (40 mL). The reaction mixture was heated under reflux for 1.5 h and then allowed to cool to room
temperature From this solution, colorless crystals of 4 were obtained after two
- 4 T H F ] , 1770
days. Y i e l d 2 2 7 g ( 8 5 % ' 1 , M S ( E I , 7 0 e V ) ~ m / z ( % )1844(5)[M+
(100) [M' - 4 T H F - SiMe,]; ' H N M R (C,D,): 6 = - 0.15 (s, 12H; InMe),
0.15 (s. 36H: SiMr,), 1.23 (m, 16H; OCH,CH,), 1.37 (m, 4XH; CHMe,), 3.54
(m. 16H. OCH,). 3.82 (m, 8H; CHMe,), 7.12 (m, 12H; aromat.); 29Si NMR
(CDCI,): d = -75 9 (SO,), 5.8 (SiMe,); elemental analysis (%) calcd for
C 45.0. H 6.9, N 2 6; found. C 44.3, H 6.4, N 2.4.
5 : A solution of Na[InMe,] (131 (0.59 g, 3 mmol) in n-hexaneiTHF (10 mL/5 mL)
was slowly added to a suspension of 1 (1.31 g, 4 mmol) in n-hexane (40 mL). The
reaction mixture was heated under reflux for 1.5 h a n d and then allowed to cool to
room temperature and left to crystallize. The colorless solution turned brown over
three months with the formation of large colorless single crystals of 5. Yield: 0.94 g
(40% based on 1). m . p 2OO'C (decomp), MS (EI, 70eV): miz (%): 1839 (2)
[ M i - 3MeI. 1695 (3) [ M - 3Me - 2THFl. 162 (100) [rPr,C,H,NH, - Me];
' H N M R (C,D,) j = - 0.77 (s, 12H; InMe), 0.41 (s, 18H; SiMe,), 1.23 (d,
,J(H,H) = 6 8 Hz. 24H: CHMe,), 1.29 (d. ,J(H.H) = 6.8 Hz, 24H; CHMe,), 1.40
(t, '4H.H) = 6 4 Hz. 16H; OCH,CH,), 3.45 (I, 'J(H,H) = 6.4 Hz, 16 H ; OCH,),
4.04 (sept.. 4H: CHMe,,, 4.14 (sept., 4H; CHMe,). 6.82-7.20 (m, 12H; aromat.);
"Si NMR (C,D,) 6 = -73.86 (SiO,). -72.76 (SO,), 2.30 (SiMe,); IR ( N u J o ~ ) :
C = 1319,1256,1245.11115,1099,1049,1019.941,919,834,801,720,592,546,515,
462 c m - ' . elemental andysis: calcd for C,,H,,,In,N,Na,O,,Si,:
C 47.2, H 7.1,
N 3.0; found. C 46.8. H 7.3. N 2.6 The observed low values ofcarhon analysis for
2-5 are due to the formation of silicon carbide during the combustion process.
Received: April 10, 1997 [Z 10331IE]
German version: Angeu. Chem. 1997, 109, 2313-2315
Keywords: alkali metals
- cage compounds - indium . silicon
[I] G. Giannetto. R. Monque, R. Galiasso, Catal. Rev. Scr. Eng 1994, 36, 271.
[2] M. Estermann, L. 13. McCusker, C. Baerlocher, A. Merrouche, H. Kessler,
Nature 1991. 352. 320.
[3] a) M . Guisnet. N . S. Gnep, F. Alario, Appl. Curd. A 1992, 8Y, 1; b) Y. Ono,
Curd Re,. Scr Eng. 1992, 34, 179; c) L. S . Marchenko, D. Z. Levin, V. A.
Plakhotnik. E.S . Mortikov. Bull. Atud. Sci. USSR Div. Chem. Sci. Engi.
E-uml 1986. 35. 81.
[4] a ) E Kikuchi. M. Ogura, I. Terasaki, Y Goto, J Card. 1996, 161, 465; b) E.
Kikuchi, K. Yogo, Cafal. Toduy 1994, 22. 73.
151 a ) R. Murugavel. '1.Voigt, M G. Walawalkar, H. W. Roesky, Chem. Rev.
1996,96,2205, b) M. G. Voronkov, E. A. Maletina, V. K. Roman, Heterosiloxunes. (Sovier Scrent!fic Review Supplemenr. Series Chemistry, Vol. I ) , Academic
Press. London. 1988; c ) F. J. Feher, T. A. Budzichowski, Polyhedron 1995, 14,
[61 R. Murugavel. V. Chandrasekhar, H. W. Roesky, Acc. Chem. Res. 1996, 29,
[7] A. Voigt. R. Murugavel, M. Montero, H. Wessel, F.-Q. Liu, H. W Roesky, I.
Uson. T. Albers. E. Parisini. Angew. Chem. 1997, 109, 1020-1022, Angew.
Chrm. Inr. E d Eng' 1997, 36, 1001-1003, and references therein.
[81 a) M. Montero. I Lson, H. W. Roesky, Angeu. Chem. 1994,106,2198; Angew.
Chem. In1 Ed. Engi. 1994, 33. 2103; b) M. Montero, A. Voigt, M. Teichert, I.
Uson. H. W. Roesky. ihid. 1995, 107, 2761 and 1995, 34, 2504, c) A. Voigt, R.
Murugavel. E. Pariiini, H. W. Roesky. ihid. 1996, 108, 823 and 1996, 35, 748;
Angrn. Chrm. /nr. Ed. Lngl. 1997, 36, No. 20
d) V. Chandrasekhar, R. Murugavel, A. Voigt, H. W. Roesky, H.-G. Schmidt,
M. Noltemeyer, Organomerallics 1996, 15, 918.
[9] R. Murugavel, P. Bottcher, A. Voigt, M. G . Walawalkar. H W. Roesky. E.
Pansini, M. Teichert, M. Noltemeyer, Chem. Commun. 1996, 2417.
[lo] Self-condensation of silanols in the presence of ionic acidic or basic impurities
IS well known, see ref. 191.
1111 Crystal structure analysis for 2: C3,H,,In,N,0,Si,,
M , = 1198.55, triclinic,
rl = 98.01(3), 6 = 96.16(3),
P I , a =10.086(2), h =10.462(2), c =13.151(3)
y = 113.80(3)', V = 1237(1)
Z = 1, pc.,cd = 1.609 gcm-'. 3679 independent
reflections, R1 = 0.0518 for 1>2u(/), u R 2 = 0.1215 for all data. Crystal
M , = 2133.8, tetragonal,
data for 4: C,,H, ,,In,Li,N,O,,Si,.(OC.H,),,
V = 10974(3) A3. 2 = 4, pralcd
14,/0, u = h = 29.200(4), c = 12.870(3)
1.344 gem-,. 4061 independent refelctions, R1 = 0.0424 for 1>2u(/),
wR2 = 0.1172 for all data. Crystal structure analysis for 5:
M , = 1883.81, triclinic, Pi. a = 14.799(3),
rl = 91.03(3), 6 =106.18(3). 7 = 97.49(3)",
h = 15.520(3), c = 23.361(5)
V = 5101(2)
2 = 2, pCalcd
= 1.227 gcm-', 13329 independent reflections,
R1 = 0.0530 for 1>2u(Z), wR2 = 0.1376 for all data The data were collected
on a Stoe-Siemens-AED2 four-circle diffractometer equipped with a graphite
monochromator, Mo,, radiation (Z = 0.71073 A). The measurements were
made with a cooled crystal coated with an oil drop by using the Learnt Profile
Method [14]. The structures were solved by direct methods (SHELXS-90) [15]
and refined on all data by full-matrix least-squares on F* [16]. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were added in idealized positions and included in the refinement. Crystallographic data (excluding
structure factors) for the structures reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-100353. Copies of the data can be obtained free of charge on
application to The Director, CCDC, 12 Union Road, Cambridge, CB2 lEZ,
UK (fax: int. code +(1223)336-033; e-mail: uk)
[12] a) S . S. Al-Juaid, N. H. Buttrus, C. Eaborn, P. B. Hitchcock, A. T. L. Roberts,
1. D. Smith, A. C. Sullivan, J Chem. Soc. Chmn?.Commun. 1986,908, b) A. M.
Arif, A R Barron, Polyhedron 1988, 7. 2091.
1131 K. Hoffmann, E. Weiss. J Orgunomel. Chem. 1972, 37, 1.
[14] W. Clegg, Acra Crystallogr. Sect. A 1981, 37, 22.
[15] G. M. Sheldrick, SHELXS-90/96, Program for Structure Solution: A c f a Crysrallogr. Seer. A 1990, 46, 467.
1161 G . M. Sheldrick, SHELXL-93/96, Program for Crystal Structure Refinement,
Universitdt Gottingen, 1993.
The Distortive Tendency of Benzene n: Electrons:
How Is It Related to Structural Observables?**
Avital Shurki and Sason Shaik*
Many computational experiments have demonstrated that
benzene x electrons tend to distort to a localized D,,structure,
while the final D,, symmetry is determined by the o framework.['"] However, the notion of x distortive tendency would
have remained elusive without experimental probes. Although
the exalted b,, frequency of the 'B,, excited state was recently
pointed out as such an
there is still a need for
a more "chemical" observable which can be associated with
x distortive tendency. Structure is an essential chemical observable, and the recent exciting syntheses of cyclohexatriene mot i f ~ [ ~(for
* ~ example
I, in which there is strong bond alternat i ~ n ) [ ~pose
~ I an excellent opportunity for drawing a link
between x distortive tendency and structure as well as predicting
novel structures.
Our approach for establishing the requisite link between
x distortive tendency and structural probes relies on the struc[*I Prof. S. Shaik, A. Shurki
Department of Organic Chemistry and
The Lise Meitner-Minerva Center for Computational Quantum Chemistry
The Hebrew University
91904 Jerusalem (Israel)
Fax: Int. code +(2)658-5345
e-mail: sason(a
[**I This work was supported by the Israel Science Foundation , which was founded by the Israel Academy of Sciences and Humanities.
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