Novel heterometallic lanthanide silsesquioxane

Full text of DOI:10.1021/ic990208p

Inorg. Chem. 1999, 38, 3941-3943
3941
complex with structure 5 has been reported.7 The coordination
requirements of the large Y3+ ion (6-coordinate radius 104 pm8)
lead to the formation of a novel dimeric structure 6 where Y2
achieves a coordination number of 6 by means of an interaction
with a framework O atom. The coordination sphere of Y1 is
completed by two Ph3PO ligands.2
Novel Heterometallic Lanthanide Silsesquioxane
Judith Annand, Helen C. Aspinall,* and
Alexander Steiner
Department of Chemistry, Donnan and Robert Robinson
Laboratories, University of Liverpool, Liverpool, L69 7ZD,
U.K.
ReceiVed February 22, 1999
Introduction
The chemistry of rare earth ions in the highly electron
withdrawing environment provided by siloxane ligands might
be expected to show novel reactivity such as electrophilic C-H
activation. The incompletely condensed polyhedral oligosils-
esquioxanes 1 have been widely investigated by Feher and
others, and complexes with a wide range of transition and main
group metals have been prepared.1
Notable by their almost total absence in this chemistry are the
rare earth metals, for which only one complex, a cyclopentyl
silsesquioxane, has been characterized crystallographically.2 The
rare earth ions are significantly larger than any other metals
which have been incorporated into the silsesquioxane frame-
work; their requirement for higher coordination numbers and
the lability of most of their complexes have contributed to the
difficulties in obtaining simple products. Crystallographic
characterization of products has frequently been hampered by
disorder of cyclohexyl groups on the silsesquioxane framework.
Silsesquioxane complexes of M3+ ions show varied coordina-
tion chemistry: due to the facially capping geometry imposed
by the silsesquioxane ligand a monomeric complex in the
absence of other donors would result in a “bare” metal ion. The
highly electrophilic nature of such a complex results in formation
of a variety of dimeric structures. For most M3+ ions (Al,3 Ga,4
V, Cr, Ti5) a dimeric structure of type 2 is formed, in which
the M ion attains a coordination number of 4. Cleavage of the
dimer to form a monomer of structure 4 can be achieved, e.g.,
by the addition of Me3PO. In the case of B, where π interactions
with O favor a trigonal planar geometry, structure 3 is adopted.6
Very recently the synthesis of a bis(silsesquioxane)tungsten
Results and Discussion
We set out initially to prepare lanthanide silsesquioxanes by
reaction of lanthanide tris-silylamides with trisilanol 1. When
the reaction of [Yb{N(SiMe3)2}3] with 1 equiv of 1 was carried
out in the presence of PMDTA (PMDTA is (Me2NCH2CH2)2-
NMe), a solid product analyzing as [(C6H11)7Si7O12Yb-
(PMDTA)] was obtained in good yield. A small number of
good-quality prisms were obtained from THF/MeCN at room
temperature along with poorly crystalline material. A crystal
was selected for a structural study and was found to diffract
reasonably well; structure solution showed this crystal to be
[{(C6H11)7Si7O12}{(C6H11)7Si7O11(OSiMe3)}YbLi2(THF)2-
(MeCN)]‚2.5THF, 7. An ORTEP plot of 7, omitting lattice
(1) Feher, F. J.; Newman, D. A.; Walzer, J. F. Polyhedron 1995, 14,
3239-3253.
(2) Herrmann, W. A.; Anwander, R.; Dufaud, V.; Scherer, W. Angew.
Chem., Int. Ed. Engl. 1994, 33, 1285-1286.
solvent molecules, is shown in Figure 1; Figure 2 shows an
ORTEP plot excluding cyclohexyl groups for clarity. Selected
bond distances and angles are given in Table 1. The Yb atom
(3) Feher, F. J.; Budzichowski, T. A.; Weller, K. J. J. Am. Chem. Soc.
1989, 111, 7288-7289.
(4) Feher, F. J.; Budzichowski, T. A.; Ziller, J. W. Inorg. Chem. 1997,
36, 4082-4086.
(7) Smet, P.; Devreese, B.; Verpoort, F.; Pauwels, T.; Svoboda, I.; Foro,
S.; Van Beeuman, J.; Verdonck, L. Inorg. Chem. 1998, 37, 6583-
6586.
(5) Feher, F. J.; Walzer, J. F. Inorg. Chem. 1990, 29, 1604-1611.
(6) Feher, F. J.; Budzichowski, T. A.; Ziller, J. W. Inorg. Chem. 1992,
31, 5100-5105.
(8) Shannon, R. D. Acta Crystallogr. 1976, A32, 751-767.
10.1021/ic990208p CCC: $18.00 © 1999 American Chemical Society
Published on Web 08/03/1999

3942 Inorganic Chemistry, Vol. 38, No. 17, 1999
Notes
O atoms (O2 and O14), and its distorted tetrahedral coordination
sphere is completed with one molecule of THF and one MeCN
ligand. Space-filling models of the complex indicate that there
is insufficient room for coordination of two THF molecules to
Li1, but the small, linear MeCN molecule fits well. Li2 also
has approximately tetrahedral coordination geometry, bonding
to two siloxy O atoms (O13 and O1), one framework O atom
(O23), and one OSiMe3 group (O24). The bonds to O23 and
O24 are somewhat longer than those between Li1 or Li2 and
the siloxy oxygens. Although bonding between metal ions and
framework O atoms of zeolites is well characterized, the only
other reported example of bonding between a metal atom and
a silsesquioxane framework O atom is in the Y complex 6; there
are no known examples of Li bonding in this manner. A
complex of Ti coordinated to two (C6H11)7Si7O11(OSiMe3)
ligands has been reported, but the crystal structure of this
complex has not been published, and there is no evidence that
the OSiMe3 groups are coordinated to the metal atoms.9
Spectroscopic and analytical data indicated that 7 was present
only as a very minor impurity in the reaction product. Its
formation is ascribed to the presence of a very small quantity
of LiN(SiMe3)2 in the [Yb{N(SiMe3)2}3] starting material.
Although HN(SiMe3)2 does not react with (C6H11)7Si7O9(OH)3
on standing at room temperature overnight, it is known to silylate
alcohols in the presence of Brønsted or Lewis acids,10a,b and
therefore the formation of small quantities of [(C6H11)7Si7O9-
(OH)2(OSiMe3)], probably catalyzed by a Lewis acidic lan-
thanide species, is not unreasonable. Complex 7 forms very
much better quality crystals than other Ln silsesquioxane
complexes we have worked with, and so it is not surprising
that the small quantity of material was selected for X-ray
structural studies. A crystal of [{(C6H11)7Si7O12}{(C6H11)7-
Si7O11(OSiMe3)}YLi2(THF)2(MeCN)]‚2.5THF, 7a, was isolated
from the analogous reaction of [Y{N(SiMe3)2}3].
Figure 1. ORTEP plot of 7.
Figure 2. ORTEP plot of 6 showing atom-numbering scheme.
Cyclohexyl groups are omitted for clarity.
We then attempted a rational preparation of 7 and 7a by
reaction of [(C6H11)7Si7O12Ln(THF)2] (Ln ) Yb, Y) with
[(C6H11)7Si7O9(OLi)2(OSiMe3)] (prepared by the reaction of
(C6H11)7Si7O9(OH)2(OSiMe3)11 with 2 equiv of BunLi in
toluene). Crystallization of the reaction product from THF/
MeCN yielded colorless prisms analyzing as [{(C6H11)7Si7O12}-
{(C6H11)7Si7O11(OSiMe3)}LnLi2(THF)2(MeCN)]‚2.5THF. Unit
cell determinations of these crystals confirmed that they were
identical to 7 and 7a and the complex NMR data obtained for
the Y complex were consistent with the low-symmetry structure
7a. The OSiMe3 group of 7a, which is coordinated to a Li atom,
showed a chemical shift of 17.01 ppm in the 29Si NMR
spectrum, significantly shifted from the value of 11.39 ppm for
the OSiMe3 group in (C6H11)7Si7O9(OH)2(OSiMe3). Addition
of 1 equiv of [(C6H11)7Si7O9(OLi)3] (see Experimental Section)
to a THF solution of [(C6H11)7Si7O12Ln(THF)2] and heating to
65 °C led to formation of a clear colorless solution, from which
crystalline material deposited on cooling to room temperature.
The clear colorless crystals broke down to a powder in the
absence of solvent. Elemental analysis12 indicated that the
product was [Li3{(C6H11)7Si7O12}2Ln], but low solubility pre-
cluded further characterization.
Table 1. Selected Bond Distances (Å) and Angles (deg) for 7
Yb1-O1
Yb1-O2
Yb1-O3
Yb1-O13
Yb1-O14
Yb1-O25
Li1-O2
2.200(11)
2.222(12)
2.115(12)
2.236(11)
2.220(12)
2.411(11)
1.98(4)
Li1-O14
Li1-O26
Li1-N1
1.83(4)
1.98(4)
2.07(4)
1.84(4)
1.95(4)
2.18(4)
2.19(4)
Li2-O1
Li2-O13
Li2-O23
Li2-O24
O1-Yb1-O2
O1-Yb1-O3
O1-Yb1-O13
O1-Yb1-O14
O1-Yb1-O25
O2-Yb1-O3
O2-Yb1-O13
O2-Yb1-O14
O2-Yb1-O25
O3-Yb1-O13
O3-Yb1-O14
O3-Yb1-O25
O13-Yb1-O14
O13-Yb1-O25
O14-Yb1-O25
O2-Li1-O14
O2-Li1-O26
O14-Li1-O26
100.1(4)
94.4(4)
79.6(4)
98.3(4)
174.5(4)
98.3(4)
165.6(4)
77.0(4)
85.4(4)
96.1(4)
167.1(4)
84.4(4)
88.8(4)
95.1(4)
83.2(4)
92.7(16)
117.6(17)
112.8(18)
O2-Li1-N1
115.6(17)
98.2(16)
121.5(18)
97.0(19)
128(2)
O26-Li1-N1
O14-Li1-N1
O1-Li1-O13
O1-Li2-O23
O1-Li2-O24
O13-Li2-O23
O23-Li2-O24
O13-Li2-O24
Si1-O1-Yb1
Si2-O2-Yb1
Si3-O3-Yb1
Si8-O13-Yb1
Si9-O14-Yb1
Si12-O23-Si14
Li2-O24-Si14
Li2-O24-Si15
Si14-O24-Si15
127(2)
113.2(19)
70.6(13)
123(2)
135.8(7)
142.9(7)
160.9(7)
147.8(7)
131.0(7)
148.8(8)
93.0(12)
126.6(13)
137.4(9)
(9) Crocker, M.; Herold, R. H. M.; Orpen, A. G. J. Chem. Soc., Chem.
Commun. 1997, 2411-2412.
(10) (a) Anderson, B. A. in Encyclopaedia of Reagents for Organic
Synthesis; Paquette, L. A., Ed.; J. Wiley: New York, 1995; Vol. 4, p
2661. (b) Kumar, P.; Pais, G. C. G.; Keshavaraja, A. J. Chem. Res.,
Synop. 1996, 376-377.
(11) Feher, F. J.; Newman, D. A.; Walzer, J. F. J. Am. Chem. Soc. 1989,
111, 1741-1748.
(12) Found: C, 49.01; H, 7.63; Li, 0.70. C84H154Si14O24Li3Y requires: C,
49.19; H, 7.57; Li, 1.01.
is coordinated to five siloxy O atoms and one THF molecule to
give approximately octahedral geometry. Because of the large
size of the Yb atom, cyclohexyl groups closest to the metal (on
Si1-3 and Si8 and Si9) do not show any steric interactions of
the type reported for compound 5.7 Li1 is bonded to two siloxy

Notes
The lithiated silsesquioxanes [(C6H11)7Si7O9(OLi)3] and
Inorganic Chemistry, Vol. 38, No. 17, 1999 3943
Preparation of (C6H11)7Si7O9(OLi)3. (C6H11)7Si7O9(OH)3 (2.1 g,
2.157 mmol) was suspended in toluene (40 cm3). n-BuLi (2.88 M in
hexanes, 2.3 cm3, 6.470 mmol) was added, and the resulting solution
was stirred at room temperature for 16 h. After this time, the solvent
was removed in vacuo to give a white solid. This was washed with
THF and separated by filtration. Yield ) 1.64 g (77%). Anal. Found:
C, 50.52; H, 7.82. C42H77O12Li3 requires: C, 50.88; H, 7.83. 13C
NMR: 27.74, 27.57, 27.04, 26.93, 26.77, 26.62 ppm (CH2); 25.12,
23.96, 23.22 ppm (ipso C; relative intensities 3:3:1). 29Si NMR: -58.30,
-67.19, -69.30 ppm (relative intensities 3:3:1). 7Li NMR: -2.23 ppm.
[(C6H11)7Si7O9(OLi)2(OSiMe3)] are worthy of comment as Feher
has reported that attempts fully to deprotonate 1 with NaOBut
resulted in decomposition and presumed skeletal degradation
of the silsesquioxane framework, and that [(C6H11)7Si7O9(OH)2-
(ONa)] is stable in solution only for very short periods.1 Stable
sources of silsesquioxane anions have been limited to Tl(I)13
or SbMe414 derivatives. We prepared [(C6H11)7Si7O9(OLi)3] by
reaction at room temperature of a toluene suspension of 1 with
3 equiv of BunLi in hexanes. Removal of solvent in vacuo
followed by washing with THF gave a high isolated yield of
white solid, characterized by NMR spectroscopy (1H, 13C, 7Li,
and 29Si) and elemental analysis. This solid was indefinitely
stable in the air at room temperature, and hydrolysis of a one-
year-old sample with HCl in THF produced 1 cleanly and
quantitatively, indicating that no skeletal degradation had
occurred. There was no evidence of decomposition in solution
over the periods of time required to obtain NMR spectra.
[(C6H11)7Si7O9(OLi)2(OSiMe3)] was prepared similarly by reac-
tion of (C6H11)7Si7O9(OH)2(OSiMe3) with 2 equiv of BunLi in
hexanes; it was much more difficult to isolate in high yield due
to its increased solubility, but small amounts of crystalline solid
were obtained from toluene/petroleum ether and characterized
by 13C NMR spectroscopy and elemental analysis. Again there
was no spectroscopic evidence for decomposition in solution.
Hydrolysis of (C6H11)7Si7O9(OLi)3. (C6H11)7Si7O9(OLi)3 (0.113 g,
0.114 mmol) was suspended in THF (5 cm3). Aqueous HCl (1M, 0.5
cm3, 4.4 equiv) was added, and the reaction mixture was stirred,
resulting in instant dissolution of solid. Stirring at room temperature
was continued for 15 min, after which time solvent was removed in
vacuo to leave a white solid, which was extracted into CH2Cl2 (ca. 20
cm3). The resulting solution was filtered to remove a small quantity of
colorless solid (LiCl), and the filtrate was evaporated to give a colorless
crystalline solid (0.93 g), shown by NMR spectroscopy to be 1. Isolated
yield ) 0.93 g (84%). 13C NMR: 23.91, 23.64, 23.19 ppm (ipso C;
1
relative intensities 3:3:1). H NMR: 6.75 ppm (OH), 1.73, 1.24, 0.76
ppm (C6H11).15
Preparation of [{(C6H11)7Si7O12}{(C6H11)7Si7O11(OSiMe3)}YLi2-
(THF)2(MeCN)]‚2.5THF. A solution of (C6H11)7Si7O9(OSiMe3)(OLi)2
(0.226 g, 0.214 mmol) was added to a THF solution of (C6H11)7Si7O12Y-
(THF)2 (0.242 g, 0.214 mmol). The resulting colorless solution was
stirred at room temperature for 16 h. Solvent was removed in vacuo to
yield a white glass, which was extracted into pentane. Removal of
solvent in vacuo gave crude product (0.498 g), which crystallized as
colorless prisms from THF/MeCN. Anal. Found: C, 49.70; H, 8.16;
N, 0.50; Li, 0.43. C107H202Li2NO28.50Si15Y requires: C, 51.76; H, 8.20;
N, 0.56; Li, 0.56. 29Si NMR: 17.01 ppm (OSiMe3), -57.79, -64.44,
-65.62, -66.92, -67.04, -67.31, -67.51, -68.27, -70.28, -71.10
ppm. [{(C6H11)7Si7O12}{(C6H11)7Si7O11(OSiMe3)}YbLi2(THF)2(MeCN)]‚
2.5THF was prepared in an analogous manner.
Conclusions
We have prepared, and characterized by X-ray diffraction,
the first examples of heterometallic silsesquioxanes containing
a lanthanide and lithium, and a rare example of a complex where
two silsesquioxane cages are bonded to a single central metal
atom. The basicity of the Si-O-Si bridging O atom is
demonstrated by unprecedented coordination to a Li atom. The
first stable Li derivatives of silsesquioxanes have been prepared.
X-ray Data Collection, Structure Determination, and Refinement
for [{(C6H11)7Si7O12}{Cy7Si7O11(OSiMe3)}YbLi2(THF)2(MeCN)]‚
Experimental Section
2.5THF.
[{(C6H11)7Si7O12}{(C6H11)7Si7O11(OSiMe3)}YLi2(THF)2-
All of the preparations described below were performed under strictly
anaerobic conditions using standard Schlenk techniques. Solvents were
distilled from sodium/benzophenone ketyl (nondeuterated) or CaH2
(deuterated) and stored under N2 over 4 Å molecular sieves prior to
(MeCN)]‚2.5THF were grown at room temperature from THF/MeCN.
A colorless prism of approximate dimensions 0.3 × 0.25 × 0.25 mm
was mounted on a glass fiber in Nujol oil and cooled to -120 °C in a
stream of N2 gas. Crystal data: C107H202Li2NO28.50Si15Yb; colorless
prism (0.30 × 0.25 × 0.25 mm) triclinic, P1h; a ) 16.812(10) Å, b )
16.960(12) Å, c ) 25.17(2) Å, R ) 78.05(7)°, â ) 78.35(6)°, γ )
70.65(5)°, V ) 6556(9) Å3, Z ) 2, Dcalc ) 1.300 g cm-3, F(000) )
2730, µ(Mo KR) ) 0.917 mm-1, T ) -120 °C. A total of 12 999
reflections were measured in the range 2.51° < θ < 20.15°, of which
12 425 were unique (R(int) ) 0.1222). The structure was solved by
direct methods (SHELXS-97) and refined by full-matrix least squares
on F2 (all reflections) (SHELXL-97) to a final R1 ) 0.0940 (5586
reflections with I > 2σ(I)), wR2 ) 0.2630; goodness-of-fit on F2 )
0.988. Residual density in a final Fourier map was 1.263 and -1.286
1
use. Samples for NMR spectroscopy were sealed under vacuum. H
and 13C NMR spectra were recorded in CDCl3 on a Gemini 300
spectrometer; chemical shifts were measured relative to residual 1H (δ
7
7.26) or 13C (δ 77.00) solvent resonances. 29Si and Li NMR spectra
were recorded on a Bruker WM250 spectrometer. The 29Si spectra were
recorded with inverse-gated 1H decoupling to minimize nuclear
Overhauser effects and increase resolution. [Cr(acac)3] was added to a
concentration of ca. 0.02 M as a relaxation agent to ensure accurate
integrated intensities. Elemental analyses were performed in duplicate
by Mr. S. Apter of this department.
Preparation of [(C6H11)7Si7O9(OSiMe3)(OLi)2]. (C6H11)7Si7O9-
(OSiMe3)(OH)2 (1.750 g, 1.67 mmol) was dissolved in toluene (25 cm3).
This solution was cooled to 0 °C, and n-BuLi (2.88 M in hexanes,
1.16 cm3, 3.347 mmol) was added. After stirring at 0 °C for 1 h, and
then at 25 °C for 24 h, the solvent was removed in vacuo to yield a
white solid, which was recrystallized from toluene/petroleum ether at
-20 °C. Yield of crystalline solid ) 0.69 g (39%).
e A-3
.
Acknowledgment. We are grateful to EPSRC for financial
support (studentship to J.A.), to Rhoˆne-Poulenc for a gift of
rare earth oxides, and to Professor F. J. Feher for useful
comments.
Anal. Found: C, 51.34; H, 8.38. C45H86O12Si8Li2 requires: C, 51.10;
H, 8.19.
Supporting Information Available: A listing of experimental
details, positional and thermal parameters, intramolecular bond distances
and angles and torsional angles. This material is available free of charge
via the Internet at http://pubs.acs.org.
13C NMR: 28.01, 27.69, 27.53, 26.92, 26.65 ppm, (CH2); 25.62,
25.05, 24.50, 23.76, 23.17 ppm (ipso C; relative intensities 2:1:2:1:1);
1.94 ppm (OSiMe3).
IC990208P
(13) Feher, F. J.; Rahimian, K.; Budzichowski, T. A.; Ziller, J. W.
Organometallics 1995, 14, 3920-3926.
(14) Feher, F. J.; Budzichowski, T. A.; Rahimian, K.; Ziller, J. W. J. Am.
Chem. Soc. 1992, 114, 3859-3866.
(15) Feher, F. J. J. Am. Chem. Soc. 1986, 108, 3850-3852.