Crystal structures and 29Si NMR calculations of amino-functionalized silyllithium compounds

Article abstract of DOI:10.1002/1099-0682(200104)2001:4<1013::AID-EJIC1013>3.0.CO;2-5

X-ray structural analysis of the amino-functionalized silyllithium compounds tris(tetrahydrofuran)[bis(diethylamino)phenylsilyl]lithium (4·3THF) and tris(tetrahydrofuran)[(diethylamino)bisphenylsilyl]lithium (7·3THF) are presented. Both compounds are mono

Full text of DOI:10.1002/1099-0682(200104)2001:4<1013::AID-EJIC1013>3.0.CO;2-5

FULL PAPER
29
Crystal Structures and Si NMR Calculations of Amino-Functionalized
Silyllithium Compounds
Carsten Strohmann,*[a] Oliver Ulbrich,[a] and Dominik Auer[a]
Keywords: Ab initio calculations / Lithium / NMR spectroscopy / Silanes / Si ligands
˚
˚
X-ray structural analysis of the amino-functionalized silylli-
thium compounds tris(tetrahydrofuran)[bis(diethylamino)-
(4·3THF), 2.682(8) A (7·3THF) and 2.732(7) A {tris(tetrahydro-
furan)[bis(diphenylamino)phenylsilyl]lithium} (1·3THF). N−Si
phenylsilyl]lithium (4·3THF) and tris(tetrahydrofuran)[(di- orbital interactions, influenced by the type of substituents
ethylamino)bisphenylsilyl]lithium (7·3THF) are presented. located at the nitrogen centre, affect these structural para-
Both compounds are monomeric in the solid state as well as
in solution. Despite the formal negative charge at the silicon
atom, the nitrogen centres are flattened. No Li−N interactions
were observed, in contrast to the homologous (lithiomethyl)-
meters as well as the 29Si NMR chemical shifts. The appar-
ently unusual experimental values of the 29Si NMR reson-
ance signals at δ = 20.3 (for 7·3THF) and δ = 28.4 (for 4·3THF)
can be explained by DFT-IGLO calculations and are a con-
amines. RI-DFT calculations give an explanation for the vari- sequence of the combination of electronegative and electro-
˚
ation of experimental Si−Li bond lengths of 2.627(4) A
positive substituents at the silicon centre.
Introduction
shifts of such compounds is still not well understood. More
structural information about dialkylamino-functionalized
silyllithiums can be concluded from the solid state struc-
ture of tris(tetrahydrofuran)[(diphenylamino)bisphenylsilyl]-
lithium (1·3THF) (Figure 1).[5]
Silyllithium compounds are useful and important re-
agents for silyl-group transfer reactions to organic mole-
cules or organometallic systems.[1a,1b] Generally, silyllithi-
ums can be prepared by reaction of a chlorosilane with li-
thium metal and cleavage of the disilane intermediate
(Scheme 1),[2aϪ2c] although that method is limited to sys-
tems bearing at least one aryl group.[2c]
Figure 1. Structural formula of 1·3THF
The crystal structure shows a monomeric silyllithium sys-
tem with the lithium centre being coordinated by three THF
molecules. A closer look at the structural parameters re-
˚
veals a quite long SiϪLi bond of 2.732(7) A and a planar
nitrogen centre. The phenyl substituents at the nitrogen
centre enhance the planarisation of this centre, and there-
fore it is not clear if this system is comparable to the syn-
thetically useful dialkylamino-functionalized silyllithiums.
Elongation of the SiϪLi and SiϪN bonds in compound
1·3THF should be caused by the additional interaction of
the lone pair at the amino group with the phenyl substitu-
ents.
We attach importance to the clarification of the struc-
tural facts of dialkylamino-functionalized silyllithiums in
order to study structure/reactivity patterns. The most im-
portant questions are: i) What are the structures of bis(di-
ethylamino)phenylsilyllithium (4) or (diethylamino)bisphen-
ylsilyllithium (7) in the solid state? and ii) How can we ex-
plain the unusual downfield shifts of the 29Si NMR reson-
ance signals?[3a,5]
Scheme 1.
In contrast to alkyl- and arylsilyllithiums, functionalized
silyllithium species have been studied less extensively. Some
dialkylamino-functionalized silyllithium compounds with
phenyl substituents at the central silicon atom have been
developed by Tamao et al.[3aϪ3c] These compounds, espe-
cially 4 and 7, can be prepared according to Scheme 1 and
are stable in solution at room temperature. Nevertheless,
structural information about these dialkylamino-func-
tionalized silyllithium compounds is scarce.[4a,4b,5] Tamao
and co-workers were able to prove that dialkylamino-func-
tionalized silyllithiums are monomeric in solution by obser-
vation of 29SiϪ7Li coupling (quadruplet) in the 29Si NMR
spectra in the temperature range of Ϫ100 to Ϫ110 °C.[5]
However, the nature of the unusual 29Si NMR chemical
Results and Discussion
[a]
Institut für Anorganische Chemie, Universität Würzburg
Am Hubland, 97074 Würzburg, Germany
Fax: (internat.) ϩ49-931/888-4605
The silyllithium compound 4 was prepared starting from
chlorosilane 2 and lithium metal in THF, as described by
E-mail: c.strohmann@mail.uni-wuerzburg.de
Eur. J. Inorg. Chem. 2001, 1013Ϫ1018
WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ1948/01/0404Ϫ1013 $ 17.50ϩ.50/0
1013

C. Strohmann, O. Ulbrich, D. Auer
[9]
FULL PAPER
Tamao and co-workers (Scheme 2).[3c] In the 29Si NMR (Me3Si)3SiLi·3THF;[8] 2.67 A in Ph3SiLi·3THF; 2.65 A in
spectrum of the reaction mixture of 2 with lithium metal at (Me3SiLi)6].[10a,10b] The two nitrogen centres in 4·3THF
temperatures above 0 °C we observe a resonance signal for show an almost planar environment; the deviations from
˚
˚
˚
the disilane 3 (main product), as well as a signal for 4. Fur- the plane are 0.057 and 0.088 A. The total sum of the bond
thermore we also found chlorosilane 2 at shorter reaction angles at the nitrogen centres are 354.9° and 358°, respect-
times, allowing us to conclude that the reaction of 2 with 4 ively (360° in 1·3THF[5]). The SiϪN bond lengths in
˚
to give 3 is slow. Disilane 3 is not cleaved by lithium to 4·3THF are relatively long [1.772(2) and 1.781(2) A] com-
˚
give the silyllithium compound 4. We assume the following pared to other aminosilanes [1.73 and 1.72 A in
reaction pathway: the silyllithium compound 4 is the prim- (Et2N)2PhSiSiPh(NEt2)2],[11] but shorter than the corres-
˚
ary product of the reaction of chlorosilane 2 with lithium ponding bonds of 1.824(3) A in 1·3THF (see Table 1).
metal, compound 4 reacts to form the disilane 3 at temper-
atures above 0 °C and a cleavage of the disilane by lithium
is not observed. Reaction of 2 at low temperatures (Ͻ 0 °C)
leads to 4, which is stable and does not react with chlorosil-
ane 2 at that temperature.
Figure 2. Molecular structure of tris(tetrahydrofuran)[bis(diethyl-
amino)phenylsilyl]lithium (4·3THF) in the crystal; selected bond
˚
lengths [A] and angles [°]: SiϪLi 2.627(4), SiϪN(1) 1.781(2),
Scheme 2.
SiϪN(2) 1.772(2), SiϪC(9) 1.926(2), LiϪO(1) 1.987(5), LiϪO(2)
1.972(5),
LiϪO(3)
1.971(4);
N(2)ϪSiϪN(1)
112.66(11),
The analogous synthesis of the silyllithium species 7, also N(2)ϪSiϪC(9) 100.14(11), N(1)ϪSiϪC(9) 100.01(11), N(2)ϪSiϪLi
described by Tamao and co-workers,[3c] follows a different
120.05(13), N(1)ϪSiϪLi 110.26(13), C(9)ϪSiϪLi 111.39(12),
C(1)ϪN(1)ϪC(3)
C(3)ϪN(1)ϪSi
113.4(2),
116.6(2),
C(1)ϪN(1)ϪSi
C(7)ϪN(2)ϪC(5)
124.9(2),
114.2(2),
reaction path (Scheme 3). The primary product of the reac-
tion of chlorosilane 5 with lithium metal at temperatures of
Ϫ40 to Ϫ20 °C is the disilane 6. Raising the temperature of
the reaction mixture to 0 °C results in the cleavage of the
SiϪSi bond and the formation of the silyllithium species 7.
This can also be recognized by a change of colour during
the reaction or from the analogous synthesis of 7 starting
from 6.
C(7)ϪN(2)ϪSi 119.0(2), C(5)ϪN(2)ϪSi 124.8(2)
Crystals from the amino-functionalized silyllithium com-
pound 7·3THF could be obtained by fast crystallization
from a solution in n-pentane at Ϫ30 °C. The compound
crystallises in the monoclinic crystal system, space group
P21/c with two molecules in the asymmetric unit (Figure 3
and 4, and Table 2). The structure analysis was performed
at Ϫ10 °C, because single crystals of 7·3THF are very sensi-
tive to strong cooling, which results in a slow decomposi-
tion and bad quality of the collected reflection data. Like
4·3THF the silyllithium species 7·3THF is monomeric in
the solid state and no intramolecular coordination of the
lithium centre by the nitrogen atom was found. The lithium
centres are surrounded by three THF molecules in a tetra-
Scheme 3.
hedral geometry. The SiϪLi bond lengths [2.682(8) and
˚
Compounds 4 and 7 were isolated as crystalline THF ad- 2.678(8) A] are longer than in the comparable compound
ducts. The amino-functionalized silyllithium compound 4·3THF. An elongation of the SiϪN bond relative to other
4·3THF crystallized from n-pentane at Ϫ90 °C in the tri- aminosilanes can also be observed. The nitrogen centre
¯
clinic crystal system, space group P1 (Figure 2 and Table 2). shows an almost planar environment, as in compound
The crystals melt at temperatures above Ϫ20 °C. 4·3THF is 4·3THF, with deviations from the plane of 0.061 and
˚
monomeric in the solid state with the lithium centre being 0.095 A and a sum of angles of 357.6° and 354.1°, respect-
surrounded by three THF molecules in a tetrahedral geo- ively.
metry. Neither an intramolecular coordination of the li-
The structure of 4·3THF in [D8]toluene solution is also
thium centre by the nitrogen atoms nor a chelating effect monomeric, which is confirmed by an observed 29SiϪ7Li
could be observed. This is not unusual but is in contrast to coupling [quadruplet for the resonance signal, 1J(29Si,7Li)ϭ
(lithiomethyl)amines.[6] Nevertheless the SiϪLi bond length 56.8 Hz] in the 29Si NMR spectrum at Ϫ40 °C. Further
˚
is relatively short [2.627(4) A] compared to other silylli- cooling causes an asymmetric spreading and a splitting of
thium species [2.732(7) A in 1·3THF;[5] 2.70 A in the signal set at Ϫ75 °C indicating a freezing of a dynamic
˚
˚
(Me3SiLi)2·3 (Me2NCH2CH2NMe2)3;[7]
2.66 A
in process. Compound 7·3THF also shows monomeric behavi-
˚
1014
Eur. J. Inorg. Chem. 2001, 1013Ϫ1018

Amino-Functionalized Silyllithium Compounds
FULL PAPER
Table 1. Selected data taken from crystal structure analysis and quantum chemical calculations
Crystal structure analysis
Calculated values[a]
1·3THF[5]
4·3THF
7·3THF
1·3THF
4·3THF
7·3THF
˚
SiϪLi [A]
2.732(7)
1.824(3)
360.0
2.627(4)
2.682(8)
2.678(8)
1.764(4)
1.763(4)
357.6/354.1
2.770
1.873
360.0
2.680
2.732
1.824
354.0
˚
SiϪN [A]
1.781(2)
1.772(2)
354.9/358
1.837
1.827
N (Sum of angles) [°]
354.8/357.9
[a]
Values taken from RI-DFT calculations at the BP86/TZVP level.
show a directed SiϪLi interaction[7Ϫ10b] in contrast to the
alkyl homologues.[12]
Comparing the structures of the dialkylaminosilyllithium
compounds 4·3THF and 7·3THF with other structural data
from known silyllithium compounds shows, that the SiϪLi
˚
bonds are among the shortest [2.627 (4) A for 4·3THF] and
˚
the longest [2.732(7) A for 1·3THF] of such systems. In or-
der to distinguish between crystallographic (e.g. packing)
and substituent effects at the silicon centre we performed
quantum chemical calculations on compounds 1·3THF,
4·3THF and 7·3THF. RI-DFT calculations at the BP86/
TZVP level were used for structure optimization of these
molecules. The relative values of important structural para-
meters, such as SiϪLi and SiϪN distances, are reproduced
by these quantum chemical calculations (see Table 1). The
performed DFT calculations overestimate the values of the
bond lengths, as is common for such methods.[13a,13b]
Figure 3. Molecular structure of tris(tetrahydrofuran)[(diethylami-
no)bisphenylsilyl]lithium (7·3THF) (molecule 1) in the crystal; se-
˚
lected bond lengths [A] and angles [°]: Si(1)ϪLi(1) 2.682(8),
Si(1)ϪN(1) 1.764(4), Si(1)ϪC(5) 1.909(5), Si(1)ϪC(11) 1.917(5),
Li(1)ϪO(1) 1.966(10), Li(1)ϪO(2) 1.944(9), Li(1)ϪO(3) 1.978(10);
N(1)ϪSi(1)ϪC(5)
N(1)ϪSi(1)ϪLi(1)
C(11)ϪSi(1)ϪLi(1)
C(1)ϪN(1)ϪC(3)
100.7(2),
109.2(2),
115.2(2),
112.8(5),
N(1)ϪSi(1)ϪC(11)
C(5)ϪSi(1)ϪLi(1)
C(5)ϪSi(1)ϪC(11)
C(1)ϪN(1)ϪSi(1)
106.3(2),
123.4(2),
100.1(2),
125.8(4),
C(3)ϪN(1)ϪSi(1) 119.0(4)
NBO analyses show that the lone pair of the dialkyamino
group interacts with an antibonding orbital located at the
silicon centre, resulting in an increase in the charge at this
centre compared to triorganosilyllithium compounds. These
interactions cause a contraction of the polar SiϪLi bond
and therefore 4·3THF has the shortest SiϪLi distance of
all three systems. Since 7·3THF has only one dialkylamino
group, the SiϪLi bond length is longer than in 4·3THF.
The lone pair at the nitrogen centre in 1·3THF is delocal-
ized onto the phenyl groups; this results in a weaker interac-
tion with the silicon centre and therefore the SiϪN and
SiϪLi bonds are elongated.
Tamao and co-workers observed that the 29Si NMR spec-
tra of (aminosilyl)lithiums and (alkoxysilyl)lithiums show a
downfield shift relative to the corresponding chlorosilanes,
in contrast to (triorganosilyl)lithiums.[3a,5] In order to un-
derstand these downfield shifts and the observed structural
parameters we optimized the energy of the simplified model
compounds Ph(Me2N)2SiLi and Ph2(Me2N)SiLi by DFT
methods [B3LYP/6Ϫ31ϩG(d)] and calculated the NMR
resonance signals using the GIAO method [HF/
Figure 4. Molecular structure of tris(tetrahydrofuran)[(diethylami-
no)bisphenylsilyl]lithium (7·3THF) (molecule 2) in the crystal; se-
˚
lected bond lengths [A] and angles [°]: Si(2)ϪLi(2) 2.678(8),
Si(2)ϪN(2) 1.763(4), Si(2)ϪC(33) 1.926(4), Si(2)ϪC(39) 1.916(5),
Li(2)ϪO(4) 1.954(9), Li(2)ϪO(5) 1.969(9), Li(2)ϪO(6) 1.970(9);
N(2)ϪSi(2)ϪC(33)
N(2)ϪSi(2)ϪLi(2)
C(39)ϪSi(2)ϪLi(2)
C(29)ϪN(2)ϪC(31)
106.0(2),
116.4(2),
111.4(2),
112.9(4),
N(2)ϪSi(2)ϪC(39)
C(33)ϪSi(2)ϪLi(2)
C(33)ϪSi(2)ϪC(39)
C(29)ϪN(2)ϪSi(2)
101.6(2),
119.2(2),
99.7(2),
122.4(3),
C(31)ϪN(2)ϪSi(2) 118.8(3)
our in [D8]toluene solution. At Ϫ68 °C a 29SiϪ7Li coupling 6Ϫ311ϩG(2d,p)].[14a,14b] The geometrical parameters of the
[quadruplet for the resonance signal, 1J(29Si,7Li) ϭ 50.6 Hz] minimized model systems show similar structural character-
can be observed in the 29Si NMR spectrum. Further cool- istics as the molecular structures of 4·3THF and 7·3THF
˚
ing does not lead to an asymmetric spreading as in com- in the crystal, but with too short SiϪLi bonds [2.476 A for
pound 4·3THF. These 29SiϪ7Li couplings do not allow us Ph(Me2N)2SiLi and 2.490 A for Ph2(Me2N)SiLi]. This ef-
˚
to reach any definite conclusion about the nature of the fect can be explained by the absence of coordinating solvent
SiϪLi bond (contribution of covalency), although it is con- molecules. The calculated values for the 29Si NMR reson-
spicuous that lithiated silanes with coordinating solvents ance signals of our model compounds are δ ϭ 21.0
Eur. J. Inorg. Chem. 2001, 1013Ϫ1018
1015

C. Strohmann, O. Ulbrich, D. Auer
FULL PAPER
SiϪLi 2.490, SiϪN 1.786, SiϪC(3) 1.921, SiϪC(9) 1.934,
C(3)ϪSiϪN 104.3, C(9)ϪSiϪN 108.5, N (sum over angles) 352.4;
absolute SCF energy: Ϫ894.925802514 Hartree.
[Ph(Me2N)2SiLi] and δ ϭ 18.9 [Ph2(Me2N)SiLi], close to
the experimental values of δ ϭ 28.4 for 4 and δ ϭ 20.3 for
7. These results confirm the trend of the downfield shift of
functionalized silyllithiums compared to (triorgano)silylli-
thiums, and therefore coordinating solvent molecules can
be omitted in model systems for 29Si NMR calculations.
Calculations performed on the simplified model systems
Me3SiLi, Me2(H2N)SiLi and Me(H2N)2SiLi within the
bounds of the DFT-IGLO method allow a thorough ana-
lysis of the shielding tensors concerning paramagnetic con-
tributions of localised molecular orbitals (LMO).[15a,15b]
The result is that, with the change from Me3SiLi (calculated
chemical shift: δ ϭ Ϫ5.7) to Me2(H2N)SiLi (calculated
chemical shift: δ ϭ 14.9), the significant contribution for
the shielding tensors of the remaining two LMOs of the
The RI-DFT[18] calculations on compounds 1·3THF, 4·3THF and
7·3THF were done with the TURBOMOLE[19] program at the
BP86/TZVP level with starting coordinates taken from the crystal
˚
structure analyses. Selected bond lengths [A] and angles [°] for
1·3THF: SiϪLi 2.770, SiϪN 1.873, SiϪC(1) 1.950, SiϪC(7) 1.939,
C(1)ϪSiϪN 103.4, C(7)ϪSiϪN 103.9, N (sum over angles) 360.0;
absolute SCF energy: Ϫ1976.437591873 Hartree; Ϫ selected bond
˚
lengths [A] and angles [°] for 4·3THF: SiϪLi 2.688, SiϪN(1) 1.827,
SiϪN(2) 1.837, SiϪC(9) 1.948, C(9)ϪSiϪN(1) 100.8,
C(9)ϪSiϪN(2) 100.5, N (sum over angles) 357.9; absolute SCF en-
˚
ergy: Ϫ1653.023345787 Hartree; Ϫ selected bond lengths [A] and
angles [°] for 7·3THF: SiϪLi 2.732, SiϪN 1.824, SiϪC(5) 1.964,
SiϪC(11) 1.947, C(5)ϪSiϪN 105.8, C(11)ϪSiϪN 101.4, N (sum
SiϪC bond as well as the SiϪLi LMO increase consider- over angles) 354.0; absolute SCF energy: Ϫ1671.469514876
Hartree. The criterion for convergence for these calculations was
lowered to a change in absolute SCF energy of 5 ϫ 10Ϫ5 Hartree,
due to the size of these systems. Minimizing the energy starting
from the second conformer of 7·3THF in the crystal showed no
significant differences in the results compared to the calculated
values of the other conformer of 7·3THF.
ably. This is caused by the very large induced coupling of
these LMOs with the σ*(SiϪN) orbital, resulting in a de-
creased shielding [and increased chemical shift of
Me2(H2N)SiLi]. At the same time the number of SiϪC
LMOs decreases (SiϪN LMOs make a lower paramag-
netic contribution than SiϪC LMOs). The latter effect
predominates with the addition of a second H2N group
[Me(H2N)2SiLi] causing, in total, an increase of the shield-
ing compared to Me2(H2N)SiLi [calculated chemical shift
for Me(H2N)2SiLi: δ ϭ 9.9]. A similar trend was observed
for the gradual replacement of the methyl groups of Me4Si
with chloro substituents.[16] That effect can also be observed
for other metallated silanes with R2N or RO substituents
and explained by NMR calculations. Further calculations
on this topic are in progress.
The
GIAO
method-based
NMR
calculations
[HF/
6Ϫ311ϩG(2d,p)] of Ph(Me2N)2SiLi and Ph2(Me2N)SiLi were per-
formed with GAUSSIAN 98.[14a,14b] Calculated absolute shieldings
σ were converted into relative shifts δ with σ calculated at the same
level for TMS [σcalcd(Si) ϭ 385.9]; calculated value of σ for
Ph(NMe2)2SiLi: 364.83; calculated value of σ for Ph2(NMe2)SiLi:
367.18.
The structures of the model systems Me3SiLi, Me2(H2N)SiLi and
Me(H2N)2SiLi were optimized at the B3LYP/6Ϫ31ϩG(d) level us-
ing GAUSSIAN 98.[14b] Selected bond lengths [A] and angles [°]
˚
for Me3SiLi: SiϪLi 2.516, SiϪC 1.928, CϪSiϪC 104.2, CϪSiϪLi
114.4; absolute SCF energy: Ϫ416.770639118 Hartree; selected
bond lengths [A] and angles [°] for Me2(H2N)SiLi: SiϪLi 2.509,
˚
Experimental Section
SiϪC(1) 1.921, SiϪC(2) 1.930, SiϪN 1.790, C(1)ϪSiϪN 101.9,
C(2)ϪSiϪN 109.8; absolute SCF energy: Ϫ432.828715216 Hartree;
General: All preparations were performed using standard Schlenk
techniques under an oxygen-free and water-free argon atmosphere.
Tetrahydrofuran was dried over Na/benzophenone and freshly dis-
tilled under argon. 29Si NMR spectra were recorded on a Bruker
DRX-300 (59.6 MHz) spectrometer with an external standard of
tetramethylsilane (δ ϭ 0.0).
˚
selected bond lengths [A] and angles [°] for Me(H2N)2SiLi: SiϪLi
2.494, SiϪC 1.915, SiϪN(1) 1.788, SiϪN(2) 1.788, CϪSiϪN(1)
100.5, CϪSiϪN(2) 100.6; absolute SCF energy: Ϫ448.891440368
Hartree. DFT-IGLO calculations of chemical shifts for Me3SiLi,
Me2(H2N)SiLi and Me(H2N)2SiLi have been done at the sum-over-
states density-functional perturbation theory level (SOS-
DFPT),[15b,20] varying the gradient-corrected PW91[21aϪ21c] ex-
change-correlation functional. A compromise strategy discussed
earlier[15b,22a,22b] was applied to obtain accurate KohnϪSham MOs
with moderate effort, by adding an extra iteration with a larger
integration grid and without fit of the exchange-correlation poten-
tial after SCF convergence had been reached. FINE[22a,22b] angular
grids with 32 points of radial quadrature were used. All of the
DFT-IGLO calculations were carried out using the deMon NMR
code.[22a,22b,23] IGLO-II all-electron basis sets were used on all
atoms with density and exchange-correlation potential fitting aux-
iliary basis sets of the sizes 5.1 (H), 5.2 (C, Li, N) and 5.4 (Si).
Calculated absolute shieldings σ were converted into relative shifts
δ with σ calculated at the same level for TMS [σcalcd(Si) ϭ 368.1].
Absolute shielding σ and selected contributions of certain LMOs
Synthesis of Tris(tetrahydrofuran)[bis(diethylamino)phenylsilyl]-
lithium (4·3THF): The synthesis was performed as described by Ta-
mao and co-workers[3c] but with a reaction temperature of Ϫ40 to
Ϫ20 °C. Ϫ 29Si{1H} NMR (C7D8, 233 K): δ ϭ 28.4 (q, JSiLi
ϭ
1
56.8 Hz).
Synthesis of Tris(tetrahydrofuran)[(diethylamino)bisphenylsilyl]-
lithium (7·3THF): The synthesis was performed as described by Ta-
mao and co-workers[3c]. Ϫ 29Si{1H} NMR (C7D8, 205 K): δ ϭ 20.3
1
(q, JSiLi ϭ 50.6 Hz).
Computational Methods: All calculations were carried out on gas-
phase structures.[17] Structure optimizations of Ph(Me2N)2SiLi and
Ph2(Me2N)SiLi at the B3LYP/6Ϫ31ϩG(d) level were performed
using GAUSSIAN 98.[14b] Selected bond lengths [A] and angles [°]
˚
for Ph(Me2N)2SiLi: SiϪLi 2.481, SiϪN(1) 1.788, SiϪN(2) 1.788, for Me3SiLi: σ ϭ 373.8, SiϪC LMO Ϫ100.5, SiϪLi LMO Ϫ103.7;
SiϪC(5) 1.922, C(5)ϪSiϪN(1) 102.8, C(5)ϪSiϪN(2) 102.8, N (sum absolute shielding σ and selected contributions of certain LMOs
over angles) 355.0; absolute SCF energy: Ϫ797.855415745 Hartree; for Me2(H2N)SiLi: σ ϭ 353.2, SiϪC(1) LMO Ϫ116.0, SiϪC(2)
˚
Ϫ selected bond lengths [A] and angles [°] for Ph2(Me2N)SiLi: LMO Ϫ111.2, SiϪN LMO Ϫ91.0, lone pair N LMO 7.4, SiϪLi
1016
Eur. J. Inorg. Chem. 2001, 1013Ϫ1018

Amino-Functionalized Silyllithium Compounds
FULL PAPER
Table 2. Selected crystallographic data for 4·3THF and 7·3THF
4·3THF
7·3THF
Empirical formula
Formula weight [g/mol]
Temperature [K]
C26H49LiN2O3Si
472.70
C28H44LiNO3Si
477.67
173(2)
263(2)
˚
Wavelength [A]
0.71073
0.71073
Crystal system
Space group
Triclinic
Monoclinic
¯
P1
P21/c
˚
a [A]
8.981(2)
10.274(2)
˚
b [A]
10.424(2)
33.791(7)
˚
c [A]
17.668(4)
17.996(4)
α [°]
β [°]
γ [°]
74.36(3)
90
76.67(3)
103.14(3)
67.16(3)
90
3
˚
Volume [A ]
1453.1(5)
6084.1(22)
Z
2
8
Density (calcd.) [g/cm3]
F(000)
1.080
1.043
520
2080
Crystal size [mm3]
Theta range for data collection [°]
Index ranges (h,k,l)
Reflections collected
Independent reflections
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I Ͼ 2σ(I)]
0.60 ϫ 0.40 ϫ 0.20
2.26 to 27.00
Ϫ11,11; Ϫ13,13; Ϫ23,23
10362
0.80 ϫ 0.80 ϫ 0.50
2.40 to 24.00
Ϫ13,13; Ϫ44,43; Ϫ23,23
30076
5922 [R(int) ϭ 0.0616]
9344 [R(int) ϭ 0.1266]
Full-matrix least-squares on F2
5913/0/302
1.008
9333/0/618
1.050
R1 ϭ 0.0606
wR2 ϭ 0.1450
R1 ϭ 0.1048
wR2 ϭ 0.1680
Ϫ
R1 ϭ 0.0832
wR2 ϭ 0.1927
R1 ϭ 0.1701
wR2 ϭ 0.2216
0.0019(7)
R indices (all data)
Extinction coefficient
Largest diff. peak and hole [eA
Ϫ3
˚
]
0.422 and Ϫ0.361
0.306 and Ϫ0.300
[1b]
Trans. 1 1998, 1215Ϫ1228. Ϫ
U. Schubert, A. Schenkel,
LMO Ϫ120.0; absolute shielding σ and selected contributions of
certain LMOs for Me(H2N)2SiLi: σ ϭ 358.2, SiϪC LMO Ϫ116.3,
SiϪN(1) LMO Ϫ85.6, lone pair N(1) Ϫ3.6, SiϪN(2) LMO Ϫ100.6,
lone pair N(2) LMO 4.5, SiϪLi LMO Ϫ126.9.
Transition Met. Chem. 1985, 210Ϫ212.
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[2b]
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[2c]
323Ϫ328. Ϫ
K. Tamao, A. Kawachi, Adv. Organomet.
X-ray Crystal Structure Analysis: Suitable crystals of 4·3THF and
7·3THF were obtained from n-pentane solutions at Ϫ30 °C
(7·3THF) or Ϫ90 °C (4·3THF) as THF adducts. The crystals were
mounted in inert oil on a glass fibre and transferred to the cold
gas stream of the diffractometer [Stoe IPDS; graphite monochrom-
Chem. 1995, 38, 1Ϫ58.
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A. Kawachi, K. Tamao, Bull. Chem. Soc. Jpn. 1997, 70,
945Ϫ955; selected 29Si NMR spectroscopic data of alkylsilylli-
thium-, aminosilyllithium- and alkoxysilyllithium compounds
and the corresponding chlorosilanes: Ph2MeSiCl (δ ϭ 10.0),
Ph2MeSiLi (δ
ϭ Ϫ20.5), (Et2N)PhMeSiCl (δ ϭ 2.3),
˚
ated Mo-Kα radiation (λ ϭ 0.71073 A)]. The structures were solved
(Et2N)PhMeSiLi (δ ϭ 14.4), (Et2N)2PhSiCl (δ ϭ Ϫ18.8),
using direct and Fourier methods (SHELXS-86[24a]); refinement by
(Et2N)2PhSiLi (δ ϭ 28.7), (tBuO)2PhSiCl (δ ϭ Ϫ56.5), (tBu-
[3b]
O)2PhSiLi (δ ϭ 41.8). Ϫ
K. Tamao, A. Kawachi, Y Ito,
full-matrix least-squares methods (based on Fo , SHELXL-93[24b]);
2
Organometallics 1993, 12, 580Ϫ582. Ϫ [3c] K. Tamao, A. Kawa-
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5765Ϫ5772.
anisotropic thermal parameters for all non-H atoms in the final
cycles; the H atoms were refined on a riding model in their ideal
geometric positions. Crystal data and refinement details of struc-
tures 4·3THF and 7·3THF are reported in Table 2.
Crystallographic data (excluding structure factors) for the struc-
tures included in this paper have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary publication
nos. CCDC-139102 (4·3THF) and -151411 (7·3THF). Copies of the
data can be obtained free of charge on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK [Fax: (internat.) ϩ 44-
1223/336-033; Email: deposit@ccdc.cam.ac.uk].
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