Cyclic and polyhedral aluminosiloxanes with Al2Si2O4, Al4Si2O6, and Al4Si4O12 frameworks: X-ray crystal structures of [(2,4,6-Me3C6H<s

Article abstract of DOI:10.1021/om950685p

Reactions of (silylamino)silanetriols RN(SiMe₃)Si(OH)₃ (R = 2,4,6-Me₃C₆H₂ (1) and 2,6-Me₂C₆H₃ (2)) with i-Bu₂AlH in 1:1 molar ratio at -78 °C afford alumino

Full text of DOI:10.1021/om950685p

918
Organometallics 1996, 15, 918-922
Cyclic a n d P olyh ed r a l Alu m in osiloxa n es w ith Al2Si2O4,
Al4Si2O6, a n d Al4Si4O12 F r a m ew or k s: X-r a y Cr ysta l
Str u ctu r es of
[(2,4,6-Me3C6H2)N(SiMe3)Si(OAlBu -i)(OAl(Bu -i)2)O]2 a n d
†
[(2,6-Me2C6H3)N(SiMe3)SiO3Al‚C4H8O2]4
Vadapalli Chandrasekhar,‡ Ramaswamy Murugavel, Andreas Voigt,
Herbert W. Roesky,* Hans-Georg Schmidt, and Mathias Noltemeyer
Institut fu¨r Anorganische Chemie der Universita¨t Go¨ttingen,
Tammannstrasse 4, D-37077 Go¨ttingen, FRG
Received August 31, 1995X
Reactions of (silylamino)silanetriols RN(SiMe3)Si(OH)3 (R ) 2,4,6-Me3C6H2 (1) and 2,6-
Me2C6H3 (2)) with i-Bu2AlH in 1:1 molar ratio at -78 °C afford aluminosiloxanes [RN(SiMe3)-
Si(OH)O(OAlBu-i‚dioxane)]2 (R ) 2,4,6-Me3C6H2 (3) and 2,6-Me2C6H3 (4)) and [RN(SiMe3)-
Si(OAlBu-i)(OAl(Bu-i)2)O]2 (R ) 2,4,6-Me3C6H2 (5) and 2,6-Me2C6H3 (6)), respectively. While
3 and 4 are eight-membered Al2Si2O4 cyclic compounds, 5 and 6 are drum-shaped
aluminosiloxanes with an Al4Si2O6 core. When the same reactions were carried out in 1:2
molar ratio of the reactants at -78 °C, only the drum-shaped polyhedral compounds 5 and
6 are isolated. The reactions between the silanetriols and i-Bu2AlH in 1:1 molar ratio at 65
°C proceed quantitatively to yield the cubic aluminosiloxanes [RN(SiMe3)SiO3Al‚dioxane]4
(R ) 2,4,6-Me3C6H2 (7) and 2,6-Me2C6H3 (8)) with an Al4Si4O12 framework. The X-ray crystal
structures of 5 and 8 have been determined.
In tr od u ction
soluble derivatives might be useful model compounds
for the complex aluminosilicates, and it is also possible
that they can be used as precursors to assemble, by
appropriate chemistry, aluminosilicates such as zeolites
via cage fusion reactions or sol-gel processes under mild
conditions. The greatest obstacle in the preparation of
soluble nonionic aluminosilicate analogues is the lack
of suitable synthons. Feher and co-workers have re-
ported the use of a siloxanetriol (c-C6H11)7Si7O9(OH)3
for the preparation of aluminosilsesquioxanes contain-
ing a Si7O12Al unit.6-8 We have shown that stable and
discrete (silylamino)silanetriols RN(SiMe3)Si(OH)3 are
excellent synthons for the assembly of three-dimen-
sional metallasilsesquioxanes.9,10 In this paper, we
report the synthesis of new polyhedral and cyclic alu-
Aluminosilicates are ubiquitous in nature, being the
constituents of a wide range of naturally occurring
minerals.1,2 Although most of the aluminosilicates are
built upon simple structural principles, a wide range of
structural and compositional diversity is present among
these compounds. For example, among zeolites which
are composed of three-dimensional interconnected net-
works of SiO4 and AlO4 tetrahedra, there is a large
variation in their compositions.2 Even when the Al/O/
Si composition is fixed in a series of aluminosilicates
such as M[Al2Si2O8], different structures are found
depending on the metal.2 These large structural and
compositional variations present also lead to important
reactivity differences. Thus, among the catalytically
important class of zeolites the reactivity of ZSM-5 is
well-known, but modified zeolites such as titanium
containing TS-1 or TS-2 very recently have been found
to be useful catalysts for a range of organic trans-
formations.3-5
(4) (a) Perego, G.; Ballussi, G.; Corno, C.; Tamarasso, M.; Buonomo,
F.; Esposito, A. In Studies in Surface Science and Catalysis, New
Developments in Zeolite Science and Technology; Murakami, Y., Iijima,
A., Word, J . W., Eds.; Elsevier: Amsterdam, 1986. (b) Boccuti, M. R.;
Rao, K. M.; Zecchina, A.; Leofanti, G.; Petrini, G. In Structure and
Reactivity of Surfaces; Morterra, C., Zecchina, A., Costa, G., Eds.;
Elsevier: Amsterdam, 1989.
(5) (a) J oseph, R.; Ravindranathan, T.; Sudalai, A. Tetrahedron Lett.
1995, 36, 1903 and references cited therein. (b) Sheldon, R. A.; Dakka,
J . Catal. Today 1994, 19, 215. (c) Sonawane, H. R.; Pol, A. V.; Moghe,
P. P.; Biswas, S. S.; Sudalai, A. J . Chem. Soc., Chem. Commun. 1994,
1215. (d) Kumar, P.; Hegde, V. R.; Pandey, B.; Ravindranathan, T. J .
Chem. Soc., Chem. Commun. 1993, 1553. (e) Blasco, T.; Camblor, M.
A.; Corma, A.; Pe´rez-Pariente, J . J . Am. Chem. Soc. 1993, 115, 11806.
(f) Notari, B. Stud. Surf. Sci. Catal. 1988, 37, 413.
(6) Feher, F. J .; Budzichowski, T. A.; Weller, K. J . J . Am. Chem.
Soc. 1989, 111, 7288.
(7) Feher, F. J .; Weller, K. J . Organometallics 1990, 9, 2638.
(8) Feher, F. J .; Weller, K. J .; Ziller, J . W. J . Am. Chem. Soc. 1992,
114, 9686.
(9) Montero, M. L.; Uso´n, I.; Roesky, H. W. Angew. Chem. 1994, 106,
2198; Angew. Chem., Int. Ed. Engl. 1994, 33, 2103.
Given this background, it is surprising that there
have been very few attempts to prepare nonionic soluble
analogues of these highly complex materials. Such
* To whom correspondence should be addressed.
† Dedicated to Prof. Dr. Rudolf Taube on the occasion of his 65th
birthday.
‡ On sabbatical leave from the Department of Chemistry, Indian
Institute of Technology, Kanpur-208 016, India.
X Abstract published in Advance ACS Abstracts, J anuary 1, 1996.
(1) Wells, A. F. Structural Inorganic Chemistry; Oxford: London,
1984; pp 998-1000.
(2) Liebau, F. Structural Chemistry of Silicates; Springer: Berlin,
1985; pp 244-260.
(3) (a) Bhaumik, A.; Kumar, R. J . Chem. Soc., Chem. Commun.
1995, 869. (b) Zhao, D.; Goldfarb, D. J . Chem. Soc., Chem. Commun.
1995, 875. (c) Gao, H.; Suo, J .; Li, S. J . Chem. Soc., Chem. Commun.
1995, 835. (d) Serano, D. P.; Li, H.-X.; Davis, M. E. J . Chem. Soc.,
Chem. Commun. 1992, 745. (e) Reddy, J . S.; Kumar, R.; Ratnasamy,
P. App. Catal. 1990, 58, L1. (f) Reddy, J . S.; Kumar, R. J . Catal. 1991,
130, 440.
(10) (a) Winkhofer, N.; Voigt, A.; Dorn, H.; Roesky, H. W.; Steiner,
A.; Stalke, D.; Reller, A. Angew. Chem. 1994, 106, 1414; Angew. Chem.,
Int. Ed. Engl. 1994, 33, 1352. (b) Montero, M. L.; Voigt, A.; Teichert,
M.; Uso´n, I.; Roesky, H. W. Angew. Chem. 1995, 107, 2761; Angew.
Chem., Int. Ed. Engl. 1995, 34, 2504. (c) Voigt, A.; Murugavel, R.;
Chandrasekhar, V.; Winkhofer, N.; Roesky, H. W.; Schmidt, H.-G.;
Uso´n, I. Organometallics, in press.
0276-7333/96/2315-0918$12.00/0 © 1996 American Chemical Society

Cyclic and Polyhedral Aluminosilicates
Organometallics, Vol. 15, No. 3, 1996 919
Sch em e 1
Sch em e 2
one can assume that the formation of 5 and 6 should
have proceeded via the intermediacy of the eight-
membered rings. The initially formed eight-membered
rings probably further react stepwise with 2 equiv of
i-Bu2AlH and subsequently fold to form the resultant
drum structures which contain coordinatively saturated
aluminum centers.
minosiloxanes. The polyhedral aluminosiloxanes exist
in two different cage structural forms containing a Al4-
Si2O6 or Al4Si4O12 framework.
In order to probe whether other structures are pos-
sible between the reactions of these two reactants under
different experimental conditions, we carried out the
reactions of silanetriols 1 and 2 with i-Bu2AlH in a 1:1
stoichiometry at 65 °C. The result is the complete
elimination of all the isobutyl and hydride groups on
aluminum with the formation of the three-dimensional
aluminosiloxanes 7 and 8 (Scheme 2). In contrast, the
reaction between the silanetriol RN(SiMe3)Si(OH)3 (R
) 2-Me-6-i-PrC6H3 (9)) and AlMe3 proceeds cleanly at
room temperature. All the methyl groups of AlMe3
react, and the cubic aluminosiloxane [RN(SiMe3)SiO3-
Al‚THF]4 (10) is formed as the only product (Scheme
2). Spectroscopic examination of the isolated product
did not show the presence of any cyclic or drum
compounds, an observation that demonstrates the steric
role played by the bulky isobutyl groups in stabilizing
the cyclic and drum structures 3-6.
The new aluminosiloxanes 3-8 and 10 are freely
soluble in common organic solvents such as pentane,
diethyl ether, tetrahydrofuran, and toluene.12 While the
ring and drum aluminosiloxanes 3-6 are air- and
moisture-sensitive, the cubic aluminosiloxanes 7, 8, and
10 can be handled in air for short periods (ca. 1 h)
without any detectable decomposition. The cyclic alu-
minosiloxanes 3 and 4 were not isolated in an analyti-
cally pure form, and the crude products were charac-
terized by means of IR, mass, and NMR spectroscopy.
The drum and cubic aluminosiloxanes do not melt up
to ca. 200 °C and decompose without melting on further
heating.
Resu lts a n d Discu ssion
Syn th esis a n d Sp ectr a . We have recently synthe-
sized air-stable and lipophilic (silylamino)silanetriols
RN(SiMe3)Si(OH)3 (R ) 2,4,6-Me3C6H2 (1) and 2,6-
Me2C6H3 (2)) starting from hindered primary aromatic
amines as shown in eq 1.11
RNH2 1. n-BuLi 8 RN(SiMe3)H 1. n-BuLi8
2. SiMe3Cl
2. SiCl4
H2O/aniline
RN(SiMe )Si(OH)
RN(SiMe3)SiCl3
8
(1)
3
3
1, 2
Addition of i-Bu2AlH to solutions of silanetriols 1 and
2 in hexane and 1,4-dioxane (5:1 v/v) at -78 °C in 1:1
stoichiometry affords the mixtures of aluminosiloxanes
[RN(SiMe3)Si(OH)O(OAlBu-i‚dioxane)]2 (R ) 2,4,6-
Me3C6H2 (3) and 2,6-Me2C6H3 (4)) and [RN(SiMe3)Si-
(OAlBu-i)(OAl(Bu-i)2)O]2 (R ) 2,4,6-Me3C6H2 (5) and
2,6-Me2C6H3 (6)) (Scheme 1). The cyclic compounds 3
and 4 could not be isolated in an analytically pure form.
However, the polyhedral derivatives 5 and 6 were
obtained in good purity by fractional crystallization.
Compounds 5 and 6 are isolated as the only products
directly from 1:2 stoichiometric reactions of silanetriols
(1 and 2) with i-Bu2AlH (Scheme 1).
We had earlier reported, in a preliminary com-
munication, that in an analogous 1:1 reaction between
i-Bu2AlH and a more sterically hindered silanetriol RN-
(SiMe3)Si(OH)3 (R ) 2,6-i-Pr2C6H3) only the eight-
membered Si-O-Al ring aluminosiloxane [RN(SiMe3)-
Si(OH)O(OAlBu-i‚THF)]2 with an unreacted OH group
on silicon was isolated and structurally characterized.9
However, in the present case, the replacement of the
isopropyl groups by methyl groups in the ortho positions
of the aryl ring is sufficient to tilt the steric balance
required for the isolation of the polyhedral drum com-
pounds 5 and 6 in minor quantities along with the eight-
membered ring compounds 3 and 4.
The IR spectra of 3 and 4 contain a strong broad
absorption around 3400 cm-1 due to the free -OH group
on each silicon. Peaks due to [M - Bu]+ ions are
1
observed in their EI mass spectrum. In the H NMR
spectra of 3 and 4, in addition to the resonances due to
aryl, SiMe3, and i-Bu groups, two additional signals
around δ 3.4 and 3.7 are observed due to the OCH2
protons of the 1,4-dioxane molecules coordinated to the
aluminum centers. Compounds 3 and 4 show two 29Si
NMR resonances each. The resonances due to SiO3
silicon centers are seen around δSi -80, while those due
to the SiMe3 group are seen around δSi 1. These
chemical shifts are characteristic of the eight-membered
Treatment of the crude product mixtures of 3 and 5
or 4 and 6 with 2 equiv of i-Bu2AlH in hexane at room
temperature leads to the complete conversion of the
cyclic aluminosiloxanes 3 and 4 to the drum compounds
5 and 6, respectively (Scheme 1). From this observation,
(11) Murugavel, R.; Chandrasekhar, V.; Voigt, A.; Roesky, H. W.;
Schmidt, H.-G.; Noltemeyer, M. Organometallics 1995, 14, 5298.
(12) Quantities of 3 mmol of all the compounds can be dissolved in
10 mL of THF or diethyl ether at 25 °C.

920 Organometallics, Vol. 15, No. 3, 1996
Ta ble 1. 29Si NMR Da ta for Cyclic a n d P olyh ed r a l Alu m in osiloxa n es
Chandrasekhar et al.
compd
structure
δ(SiMe3), ppm
δ(SiO3), ppm
[(2,4,6-Me3C6H2)N(SiMe3)Si(OH)O(OAlBu-i‚dioxane)]2 (3)
[(2,6-Me2C6H3)N(SiMe3)Si(OH)O(OAlBu-i‚dioxane)]2 (4)
ring
ring
ring
drum
drum
drum
cube
cube
cube
1.0
0.8
1.3
11.5
11.8
12.5
0.8
-80.0
-79.8
-77.0
-65.5
-65.6
-65.3
-79.8
-79.7
-79.3
a
[(2,6-i-Pr2C6H3)N(SiMe3)Si(OH)O(OAlBu-i‚THF)]2
[(2,4,6-Me3C6H2)N(SiMe3)Si(OAlBu-i)(OAl(Bu-i)2)O]2 (5)
[(2,6-Me2C6H3)N(SiMe3)Si(OAlBu-i)(OAl(Bu-i)2)O]2 (6)
a
[(2,6-i-Pr2C6H3)N(SiMe3)Si(OAlBu-i)(OAl(Bu-i)2)O]2
[(2,4,6-Me3C6H2)N(SiMe3)SiO3Al‚dioxane]4 (7)
[(2,6-Me2C6H3)N(SiMe3)SiO3Al‚dioxane]4 (8)
[(2-Me-6-i-PrC6H3)N(SiMe3)SiO3Al‚THF]4 (10)
0.8
0.7
a
From ref 9.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 5a
Bond Lengths for Molecule 1
Si(1)-O(1)
Si(1)-O(2)
Al(1)-O(1)
Al(1)-O(3a)
Al(2)-O(3a)
Al(2)-C(51)
1.603(7)
1.685(6)
1.731(7)
1.883(6)
1.871(6)
1.954(10)
Si(1)-N(1)
Si(1)-O(3)
Al(1)-O(2a)
Al(1)-C(31a)
Al(2)-O(2)
Al(2)-C(41)
1.670(8)
1.692(6)
1.879(6)
1.929(10)
1.880(7)
1.964(10)
Bond Angles for Molecule 1
O(1)-Si(1)-N(1)
N(1)-Si(1)-O(2)
N(1)-Si(1)-O(3)
O(1)-Al(1)-O(2a)
O(2a)-Al(1)-O(3a)
113.3(3) O(1)-Si(1)-O(2)
114.7(3) O(1)-Si(1)-O(3)
115.2(4) O(2)-Si(1)-O(3)
103.8(3) O(1)-Al(1)-O(3a)
80.3(2) O(1)-Al(1)-C(31a)
109.5(3)
110.4(3)
91.9(3)
103.9(3)
123.3(4)
O(2a)-Al(1)-C(31a) 120.3(4) O(3a)-Al(1)-C(31a) 116.4(4)
O(3a)-Al(2)-O(2)
O(2)-Al(2)-C(51)
O(2)-Al(2)-C(41)
Si(1)-O(1)-Al(1)
Si(1)-O(2)-Al(2)
Si(1)-O(3)-Al(2a)
95.8(3) O(3a)-Al(2)-C(51)
108.1(4) O(3a)-Al(2)-C(41)
109.3(4) C(51)-Al(2)-C(41)
125.1(3) Si(1)-O(2)-Al(1a)
121.6(3) Al(1a)-O(2)-Al(2)
121.2(3) Si(1)-O(3)-Al(1a)
108.2(4)
109.2(4)
122.9(4)
93.8(3)
117.6(3)
93.5(3)
F igu r e 1. Core structure of 5 showing the drum polyhe-
dron.
cyclic aluminosiloxanes and compare well with an
analogous cyclic aluminosiloxane [RN(SiMe3)Si(OH)O-
(OAlBu-i‚THF)]2 (R ) 2,6-i-Pr2C6H3), whose crystal
structure has been reported earlier (Table 1).9
Al(2a)-O(3)-Al(1a) 117.3(3)
Bond Lengths for Molecule 2
Si(3)-O(4)
Si(3)-N(2)
Al(3)-O(4)
Al(3)-O(6b)
Al(4)-O(5)
Al(4)-C(101)
1.574(6)
1.681(7)
1.758(6)
1.873(6)
1.880(7)
1.951(11)
Si(3)-O(6)
Si(3)-O(5)
Al(3)-O(5b)
Al(3)-C(81)
Al(4)-O(6b)
Al(4)-C(91)
1.673(6)
In the drum compounds 5 and 6, both the 29Si
resonances due to the SiO3 and SiMe3 groups are shifted
downfield and are observed around δSi -66 and 12,
respectively. These significant shifts are a likely con-
sequence of the presence of the four-membered Si-O-
Al-O rings in these compounds (vide infra). It is
interesting to note that in the cubic structures 7, 8, and
10 which are composed of only eight-membered Si-O-
Al rings (vide infra), the 29Si chemical shifts again move
upfield (Table 1).
X-r a y Cr yst a l St r u ct u r e of 5. The molecular
structure of the Al/Si/O core of 5 is shown in Figure 1.
Selected structural parameters are listed in Table 2. The
compound crystallizes in the triclinic space group P1h
with two half molecules in the asymmetric unit. The
structure of 5 can be described as a cylindrical drum
with the top and bottom faces of the polyhedron being
made of six-membered Al2SiO3 rings. The side faces are
composed of two such six-membered rings in addition
to two four-membered AlSiO2 rings. All the six-
membered rings are puckered and exist in a boat
conformation. The four-membered rings are planar.
There are two types of Si-O distances in the mol-
ecules. The longer distance (average 1.68 Å) is associ-
ated with the Si-O bonds in the planar four-membered
ring. Similarly, there also are two types of Al-O
distances, with the Al-µ3-O distance being substantially
longer (1.88 Å) than the Al-µ2-O distances (1.74 Å).
These differences also extend to the Si-O-M and
O-Si-O angles. Thus, the expected tetrahedral values
around silicon fall to 94.0°. Even the angles around µ3-
1.692(6)
1.868(7)
1.919(11)
1.885(6)
1.958(9)
Bond Angles for Molecule 2
O(4)-Si(3)-O(6)
O(6)-Si(3)-N(2)
O(6)-Si(3)-O(5)
O(4)-Al(3)-O(5b)
O(5b)-Al(3)-O(6b)
O(5b)-Al(3)-C(81)
O(5)-Al(4)-O(6b)
110.5(3) O(4)-Si(3)-N(2)
114.5(4) O(4)-Si(3)-O(5)
91.3(3) N(2)-Si(3)-O(5)
102.6(3) O(4)-Al(3)-O(6b)
80.1(3) O(4)-Al(3)-C(81)
119.9(4) O(6b)-Al(3)-C(81)
95.2(3) O(5)-Al(4)-C(101)
113.5(3)
110.4(3)
114.7(3)
103.9(3)
122.9(4)
118.7(5)
109.4(4)
108.7(4)
O(6b)-Al(4)-C(101) 108.5(4) O(5)-Al(4)-C(91)
O(6b)-Al(4)-C(91)
Si(3)-O(4)-Al(3)
Si(3)-O(5)-Al(4)
Si(3)-O(6)-Al(3b)
109.7(3) C(101)-Al(4)-C(91) 122.0(5)
125.2(3) Si(3)-O(5)-Al(3b)
121.0(3) Al(3b)-O(5)-Al(4)
94.3(3) Si(3)-O(6)-Al(4b)
93.8(3)
118.7(3)
121.4(3)
Al(3b)-O(6)-Al(4b) 117.0(3)
a
Positions: (a) -x, -y + 1, -z + 1; (b) -x + 1, -y, -z + 2.
oxygen are smaller (91.4°). All these geometrical pa-
rameters compare well with values found in the related
compound [RN(SiMe3)Si(OAlBu-i)(OAl(Bu-i)2)O]2 (R )
2,6-i-Pr2C6H3).9
X-r a y Cr yst a l St r u ct u r e of 8. The molecular
structure of the Al/Si/O core of 8 is shown in Figure 2.
Selected structural parameters are summarized in
Table 3. The molecule crystallizes in the tetragonal
space group P421c as a 1,4-dioxane solvate.13 A cubic
polyhedron can be defined with 4 silicon atoms and 4
(13) The lattice 1,4-dioxane solvate does not show any interaction
with the aluminosiloxane molecule.

Cyclic and Polyhedral Aluminosilicates
Organometallics, Vol. 15, No. 3, 1996 921
Exp er im en ta l Section
Gen er a l Da ta . All experimental manipulations were car-
ried out under an atmosphere of dinitrogen rigorously exclud-
ing air and moisture. The samples for spectral measurements
were prepared in a drybox. Solvents were purified according
to conventional procedures and were freshly distilled prior to
use. Diisobutylaluminum hydride (1 M solution in hexanes,
Aldrich) and trimethylaluminum (2 M solution in hexanes,
Aldrich) were used as received. The silanetriols 1, 2, and 9
were prepared as described.11 NMR spectra were recorded on
a Bruker AM 200 or a Bruker AS 400 instrument, and the
chemical shifts are reported with reference to TMS. The
upfield shifts are negative. IR spectra were recorded on a Bio-
Rad Digilab FTS7 spectrometer (only the strong absorption
bands are given; vide infra). Mass spectra were obtained on
Finnigan MAT System 8230 and a Varian MAT CH5 mass
spectrometer. Melting points were obtained on a HWS-SG
3000 apparatus and are uncorrected. CHN analyses were
performed at the Analytical Laboratory of the Institute of
Inorganic Chemistry at Go¨ttingen, Germany.
R ea ct ion s of 1 a n d 2 w it h i-Bu 2AlH a t -78 °C (1:1
Ra tio). A solution of RN(SiMe3)Si(OH)3 (0.56 of 1 or 0.54 g
of 2, 2 mmol) in hexane (10 mL) and 1,4-dioxane (2 mL) was
cooled to -78 °C. To this was added i-Bu2AlH (2 mmol, 2 mL
of 1 M solution in hexane) dropwise using a syringe. The
reaction mixture was allowed to attain room temperature and
stirred for 24 h. The solvent was removed in vacuo affording
mixtures of 3 and 5 and 4 and 6, respectively. From these
mixtures the drum compounds 5 and 6 could be obtained in a
pure form in small quantities (20%) by fractional crystalliza-
tion at -20 °C from hexane/1,4-dioxane (4:1 v/v).
F igu r e 2. Core structure of 8 showing the cubic polyhe-
dron.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 8a
Si(1)-O(3)
Si(1)-O(1)
Al(1)-O(3a)
Al(1)-O(2b)
1.615(4)
1.623(4)
1.703(4)
1.712(4)
Si(1)-O(2)
Si(1)-N(1)
Al(1)-O(1)
Al(1)-O(4)
1.616(4)
1.739(5)
1.708(4)
1.877(4)
O(3)-Si(1)-O(2)
O(2)-Si(1)-O(1)
O(2)-Si(1)-N(1)
O(3a)-Al(1)-O(1)
O(1)-Al(1)-O(2b)
O(1)-Al(1)-O(4)
Si(1)-O(1)-Al(1)
111.1(3) O(3)-Si(1)-O(1)
111.7(2) O(3)-Si(1)-N(1)
106.7(2) O(1)-Si(1)-N(1)
108.9(3)
110.0(2)
108.4(3)
113.5(2) O(3a)-Al(1)-O(2b) 117.5(2)
115.5(2) O(3a)-Al(1)-O(4)
104.1(2) O(2b)-Al(1)-O(4)
135.5(3) Si(1)-O(2)-Al(1b)
102.2(2)
101.0(2)
140.1(3)
R ea ct ion s of 1 a n d 2 w it h i-Bu 2AlH a t -78 °C (1:2
Ra tio). A solution of RN(SiMe3)Si(OH)3 (0.56 of 1 or 0.54 g
of 2, 2 mmol) in hexane (10 mL) and 1,4-dioxane (4 mL) was
cooled to -78 °C. To this was added i-Bu2AlH (4 mmol, 2 mL
of 1 M solution in hexane) dropwise using a syringe. The
reaction mixture was allowed to attain room temperature and
stirred for 24 h. The solvent was removed in vacuo affording
5 or 6 in nearly quantitative yields.
Si(1)-O(3)-Al(1c) 144.4(3)
a
Positions: (a) y - 1, -x - 1, -z; (b) -x - 2, -y, z; (c) -y - 1,
x + 1, -z.
aluminum atoms occupying its alternate corners. The
Si‚‚‚Al edges of the cube are bridged by an oxygen atom
in a µ2 fashion. The cube is composed of six puckered
Al2Si2O4 eight-membered rings, each of which exists in
a C4 crownlike conformation.
Syn th esis of Cu bic Alu m in osiloxa n es 7 a n d 8. Com-
pounds 7 and 8 were synthesized in a similar manner.
A
solution of RN(SiMe3)Si(OH)3 (0.56 of 1 or 0.54 g of 2, 2 mmol)
in hexane (10 mL) and 1,4-dioxane (2 mL) was cooled to -78
°C. To this was added i-Bu2AlH (2 mmol, 2 mL of 1 M solution
in hexane) dropwise using a syringe. The reaction mixture
was allowed to attain room temperature and was heated under
reflux for 6 h until the gas evolution ceased. Subsequently,
the solvent was removed in vacuo affording 7 or 8 as white
solid residues in quantitative yields. The products were dried
thoroughly for 24 h under high vacuum and recrystallized from
hexane and dioxane at 5 °C.
The average Al-O bond length within the polyhedron
(1.71(4) Å) is considerably shorter than the exocyclic
Al-O bond length (1.88(4) Å). This is consistent with
the bonding type differences within and outside the
framework. The average Si-O bond length (1.62 Å) is
shorter than the Si-O distances observed in the parent
silanetriol.11 The average Si-O-Al angle within the
framework is 140.0°.
Syn th esis of Cu bic Alu m in osiloxa n e 10. To a solution
of (2-Me-6-i-PrC6H3)N(SiMe3)Si(OH)3 (9) (0.6 g, 2 mmol) in
hexane (10 mL) and THF (2 mL) was added AlMe3 (2 mmol, 1
mL of 2 M solution in hexane) dropwise using a syringe. The
evolution of CH4 ceased within 10 min, and the reaction
mixture was stirred at room temperature for another 6 h.
Subsequently, the solvent was removed in vacuo affording 10
as white solid residue in quantitative yield. The solid was
recrystallized from 10:1 v/v hexane and THF.
Con clu sion
We have demonstrated that the (silylamino)silanetri-
ols are excellent synthons for the preparation of soluble,
neutral aluminosiloxanes with different types of Al/Si/O
frameworks which might serve as model compounds for
many naturally occurring insoluble, ionic aluminosili-
cates. Small changes in the reaction temperature or the
bulkiness of the substituents on aluminum or nitrogen
have allowed the isolation of aluminosiloxanes with
different polyhedral structures. Further, the synthesis
involves only the elimination of alkane or hydrogen
during the reaction, thereby making the workup pro-
cedure very simple. We have also been recently suc-
cessful in synthesizing soluble, anionic aluminosilicates
using this synthetic method.10b Hence, this synthetic
route appears to be general and may be applicable to
the preparation of hitherto unknown metallasiloxanes.
3. IR (Nujol): 3415, 1423, 1230, 1055, 970, 798, 680 cm-1
.
1H NMR (C6D6): 0.01 (s, 18H, SiMe3), -0.30 (d, 4H, CH2CH-
(CH3)2), 0.71 (m, 2H, CH2CH(CH3)2), 0.84 (d, 12H, CH2CH-
(CH3)2), 2.14 (s, 6H, CH3), 2.21 (s, 12H, CH3), 3.35 (s, 8H,
OCH2), 3.68 (s, 8H, OCH2), 6.80 (s, 4H, aromatic). 29Si NMR
(C6D6): -80.0 (SiO3), 1.0 (SiMe3). MS (EI, 70 eV): m/e 853
([M - Bu]+).
4. IR (Nujol): 3400, 1431, 1235, 1061, 966, 787, 678 cm-1
.
1H NMR (C6D6): 0.03 (s, 18H, SiMe3), -0.28 (d, 4H, CH2CH-
(CH3)2), 0.67 (m, 2H, CH2CH(CH3)2), 0.81 (d, 12H, CH2CH-
(CH3)2), 2.20 (s, 12H, CH3), 3.38 (s, 8H, OCH2), 3.66 (s, 8H,

922 Organometallics, Vol. 15, No. 3, 1996
Chandrasekhar et al.
OCH2), 6.8-7.0 (m, 6H, aromatic). 29Si NMR (C6D6): -79.8
(SiO3), 0.8 (SiMe3). MS (EI, 70 eV): m/e 825 [M - Bu]+).
5. Mp > 200 °C (dec). IR (Nujol): 1320, 1302, 1257, 1218,
1183, 1155, 1129, 1057, 1020, 960, 894, 875, 839, 797, 757,
Ta ble 4. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for 5 a n d 8
compd
5
8
736, 722, 681, 568, 561, 476 cm-1
.
29Si NMR (C6D6): -65.5
(SiO3), 11.5 (SiMe3). MS (EI, 70 eV): m/e 957 ([M - Bu]+,
100%). Anal. Calcd for C48H94Al4N2O6Si4: C, 56.8; H, 9.3; N,
2.8. Found: C, 56.2; H, 9.1; N, 3.0.
empirical formula
fw
C48H94Al4N2O6Si4 C60H104Al4N4O20Si8‚C4H8O2
1015.53
223(2)
1622.22
153(2)
temp, K
wavelength, Å
cryst system
space group
a, Å
0.710 73
triclinic
P1h
0.710 73
tetragonal
P421c
6. Mp > 200 °C (dec). IR (Nujol): 1319, 1296, 1259, 1206,
1185, 1129, 1047, 1020, 966, 949, 912, 894, 876, 839, 800, 767,
683, 559, 547, 493, 481 cm-1 29Si NMR (C6D6): -65.6 (SiO3),
.
12.408(2)
12.550(3)
22.822(5)
82.37(3)
80.85(3)
63.60(3)
3135(1)
2
18.810(2)
11.8 (SiMe3). MS (EI, 70 eV): m/e 929 ([M - Bu]+, 100%).
Anal. Calcd for C46H90Al4N2O6Si4: C, 56.0; H, 9.2; N, 2.8.
Found: C, 55.7; H, 9.1; N, 2.9.
b, Å
c, Å
12.717(2)
90
90
90
4500(1)
2
R, deg
â, deg
7. Mp > 220 °C (dec). IR (Nujol): 1303, 1258, 1219, 1154,
1129, 1082, 1049, 955, 894, 876, 839, 802, 756, 735, 723, 682,
γ, deg
V, Å3
638, 574, 550, 477 cm-1 1H NMR (C6D6): 0.30 (s, 36H, SiMe3),
.
Z
Dcalcd, g‚cm-3
µ, mm-1
F(000)
1.076
1.197
2.20 (s, 12H, Me), 2.51 (s, 24H, Me), 3.34 (s, 8H, CH2, free
dioxane), 3.38 (t, 16H, CH2), 3.64 (t, 16H, CH2), 6.80 (s, 8H,
aromatic). 29Si NMR (C6D6): -79.8 (SiO3), 0.8 (SiMe3). Anal.
Calcd for C68H120Al4N4O22Si8: C, 48.7; H, 7.2; N, 3.3. Found:
C, 48.5; H, 7.7; N, 3.6.
0.191
0.222
1104
1728
cryst size, mm
θ range, deg
index range
0.5 × 0.4 × 0.2
3.5-20.0
-11 e h e 11
-11 e k e 12
-21 e l e 21
9266
1.2 × 1.0 × 1.0
3.5-22.5
-20 e h e 20
-1 e k e 20
0 e l e 13
3014
8. Mp > 200 °C (dec). IR (Nujol): 1257, 1208, 1128, 1084,
1069, 1047, 966, 947, 913, 876, 839, 766, 684, 636, 613, 560,
tot. reflcns
545, 494 cm-1 1H NMR (C6D6): 0.28 (s, 36H, SiMe3), 2.48 (s,
.
indepdt reflcns
refinement method
data/restraints/
params
5780
1643
24H, Me), 3.35 (s, 8H, CH2, free dioxane), 3.38 (t, 16H, CH2),
full-matrix least squares on F2
3.64 (t, 16H, CH2), 6.80 (m, 12H, aromatic). 29Si NMR (C6D6):
5740/0/601
1636/14/249
-79.7 (SiO3), 0.8 (SiMe3). Anal. Calcd for C64H112Al4N4O22
Si8: C, 47.4; H, 7.0; N, 3.5. Found: C, 46.7; H, 6.8; N, 3.5.
-
R1, R2 (I > 2σ(I))
R1, R2 (all data)
S
0.090, 0.234
0.132, 0.321
1.013
0.063, 0.172
0.068, 0.190
1.069
10. Mp > 250 °C (dec). IR (Nujol): 1251, 1195, 1175, 1074,
964, 910, 837, 783, 752, 610, 548 cm-1 1H NMR (C6D6): 0.06
.
largest diff peak
0.555, -0.428
0.714, -0.411
and hole, e‚Å-3
(s, 36H, SiMe3), 1.20 (d, 24H, Me), 2.20 (s, 12H, Me), 3.75 (m,
4H, CH), 6.95 (m, 12H, aromatic), 1.80 (m, 8H, thf), 3.60 (m,
8H, thf). 29Si NMR (C6D6): -79.3 (SiO3), 0.7 (SiMe3). Anal.
Calcd for C68H120Al4N4O16Si8: C, 51.6; H, 7.6; N, 3.3. Found:
C, 51.1; H, 7.8; N, 3.3.
collection was carried out at -50 °C. This resulted in large
thermal parameters for the carbon atoms of the isobutyl
groups. Other details pertaining to the data collection,
structure solution, and refinement are listed in Table 4.
X-r a y Str u ctu r e Deter m in a tion of 5 a n d 8. Colorless
single crystals suitable for X-ray diffraction studies were grown
from 5:1 v/v hexane/1,4-dioxane at -20 °C for 5 and at 5 °C
for 8. A suitable crystal of each compound was mounted on a
glass fiber and coated with paraffin oil. Diffraction data were
collected on a Siemens-Stoe AED2 four-circle instrument (at
-50 °C for 5 and at -120 °C for 8), with graphite-monochro-
mated Mo KR radiation (λ ) 0.710 73 Å). The structures were
solved by direct methods using SHELXS-9014 and refined
against F2 on all data by full-matrix least squares with
SHELXL-93.15 All non-hydrogen atoms were refined aniso-
tropically. Hydrogen atoms were included at geometrically
calculated positions and refined using a riding model. The
crystals of 5 developed cracks at -120 °C, and hence, the data
Ack n ow led gm en t. This work was supported by the
Deutsche Forschungsgemeinschaft. V.C. and R.M. thank
the Alexander von Humboldt-Stiftung for research
fellowships. We thank the reviewers for their useful
comments.
Su p p or tin g In for m a tion Ava ila ble: Listings of crystal
data, atomic coordinates and equivalent isotropic displacement
parameters for all non-hydrogen atoms, hydrogen positional
and thermal parameters, anisotropic displacement parameters,
and bond distances and bond angles and plots (16 pages).
Ordering information is given on any current masthead page.
(14) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(15) Sheldrick, G. M. SHELXL-93, program for crystal structure
refinement, Go¨ttingen, 1993.
OM950685P