Stable silaimines with three- and four-coordinate silicon atoms

Article abstract of DOI:10.1021/ic301543y

The reactions of silylenes with organic azides are quite diverse, depending on the substituents of the silylene center and on the nature of the azide employed. Elusive silaimine with three-coordinate silicon atom L ¹SiN(2,6-Triip₂-C₆H₃) (5) {L ¹ = CH[(C=CH₂)(CMe)(2,6-iPr₂C₆H ₃N)₂] and Triip = 2,4,6-triisopropylphenyl} was synthesized by treatment of the silylene L¹Si (1) with a sterically demanding 2,6-bis(2,4,6-triisopropylphenyl)phenyl azide (2,6-Triip ₂C₆H₃N₃). The reaction of Lewis base-stabilized dichlorosilylene L²SiCl₂ (2) {L ² = 1,3-bis(2,6-iPr₂C₆H₃)imidazol-2- ylidene} with Ph₃SiN₃ afforded four-coordinate silaimine L²(Cl₂)SiNSiPh₃ (6). Treatment of 2,6-Triip₂C₆H₃N₃ with L ³SiCl (3) (L³ = PhC(NtBu)₂) yielded silaimine L³(Cl)SiN(2,6-Triip₂-C₆H₃) (7) possessing a four-coordinate silicon atom. The reactions of L ³SiN(SiMe₃)₂ (4) with adamantyl and trimethylsilyl azide furnished silaimine compounds with a four-coordinate silicon atom L³(N(Ad)SiMe₃)SiN(SiMe₃) (8) (Ad = adamantyl) and L³(N(SiMe₃)₂)SiN(SiMe ₃) (9). Compound 8 was formed by migration of one of the SiMe ₃ groups. Compounds 5-9 are stable under inert atmosphere and were characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray studies.

Full text of DOI:10.1021/ic301543y

Article
pubs.acs.org/IC
Stable Silaimines with Three- and Four-Coordinate Silicon Atoms
Prinson P. Samuel, Ramachandran Azhakar, Rajendra S. Ghadwal,* Sakya S. Sen, Herbert W. Roesky,*
Markus Granitzka, Julia Matussek, Regine Herbst-Irmer, and Dietmar Stalke*
Institut fur Anorganische Chemie, Universitat Gottingen, Tammannstrasse 4, 37077 Gottingen, Germany
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: The reactions of silylenes with organic azides are quite diverse, depending
on the substituents of the silylene center and on the nature of the azide employed. Elusive
silaimine with three-coordinate silicon atom L1SiN(2,6-Triip2-C6H3) (5) {L1 = CH[(C
CH2)(CMe)(2,6-iPr2C6H3N)2] and Triip = 2,4,6-triisopropylphenyl} was synthesized by
treatment of the silylene L1Si (1) with a sterically demanding 2,6-bis(2,4,6-
triisopropylphenyl)phenyl azide (2,6-Triip2C6H3N3). The reaction of Lewis base-stabilized
dichlorosilylene L2SiCl2 (2) {L2 = 1,3-bis(2,6-iPr2C6H3)imidazol-2-ylidene} with Ph3SiN3
afforded four-coordinate silaimine L2(Cl2)SiNSiPh3 (6). Treatment of 2,6-Triip2C6H3N3 with L3SiCl (3) (L3 = PhC(NtBu)2)
yielded silaimine L3(Cl)SiN(2,6-Triip2-C6H3) (7) possessing a four-coordinate silicon atom. The reactions of L3SiN(SiMe3)2 (4)
with adamantyl and trimethylsilyl azide furnished silaimine compounds with a four-coordinate silicon atom L3(N(Ad)SiMe3)-
SiN(SiMe3) (8) (Ad = adamantyl) and L3(N(SiMe3)2)SiN(SiMe3) (9). Compound 8 was formed by migration of one of the
SiMe3 groups. Compounds 5−9 are stable under inert atmosphere and were characterized by elemental analysis, NMR
spectroscopy, and single-crystal X-ray studies.
azidosilane or silatetrazolines.1a,12 In almost all of these
INTRODUCTION
■
reactions involvement of initial formation of an unstable
silaimine as an intermediate was proposed, which further reacts
with another molecule of organic azide to form azidosilane or
silatetrazolin.
Silylenes are the heavier analogues of carbenes, with the carbon
atom replaced by a silicon atom.1 Initially, these species were
generated as short-lived reactive intermediates and studied by
trapping experiments with other unsaturated substrates. The
first stable silylene was isolated in 1994 by Denk et al.2 as N-
heterocyclic silylene (NHSi) using the same stabilization
concept employed by Arduengo et al. to prepare the carbon
analogue, N-heterocyclic carbene (NHC).3 Since their first
isolation, the stable silylenes emerged as versatile building
blocks for novel silicon compounds, which were otherwise
difficult to access using a conventional protocol. Remarkable
advances in the reactivity studies of silylene compounds were
made possible very recently due to the availability of these
elusive species in high yield using very facile and safe methods.
The search for the formation of multiply bonded silicon
compounds has attracted attention throughout the last decades
and is still one of the most fascinating topics for silicon
chemists. The availability of stable silylenes allows direct access
to compounds with silicon−heteroatom (SiX, X = O,4 P,5 S,6
Se,6a,b Te,6b N7) multiple bonds. Key members of this class of
compounds are silaimines (R2SiNR′, where R or R′ is alkyl
or aryl group), which are considered highly reactive species due
to the polarity of the Siδ+−Nδ− bond.8 The first stable silaimines
were isolated independently by Wiberg9 and Klingebiel10 in
1986 by thermal salt elimination through multistep reactions.
However, direct methods for silaimine synthesis are limited,
and silaimines with less bulky terminal groups are still scarce. A
THF adduct of a silaimine was reported by West et al. by the
reaction of a NHSi with sterically hindered Ph3CN3.7 However,
most of the reactions of NHSis including well-known L1Si (1)
(L1 = CH{(CCH2)(CMe)(2,6-iPr2C6H3N)2}11 with less
bulky organic azides resulted in the formation of either
We have recently reported on the high yield access of Lewis
base-stabilized silylenes,13−16 L2SiCl2 (2) (L2 = :C[N(2,6-
iPr2C6H3)CH]2),13 L3SiCl (3) (L3 = PhC(NtBu)2),14 and
L3SiN(SiMe3)2 (4)15,16a using very mild reducing agents. In the
course of our studies on dichlorosilylene L2SiCl2 (2), we
focused on probing the reactions with various organoazides.
With sterically encumbered terphenyl azides (2,6-Ar2C6H3)N3
(Ar = 2,6-iPr2C6H3, 2,4,6-iPr3C6H2) 2 smoothly afforded the
corresponding silaimine compounds.17 However, when treated
with AdN3, it led to a functionalized N-heterocyclic carbene
through the formation of unstable dichlorosilaimine as an
intermediate.18 From these observations it is evident that the
alkyl or aryl substituent at the nitrogen atom of azides has a
significant role in these reactions. This observation is further
augmented by the reaction of L3SiCl (3) with CH(SiMe3)N2,
which resulted in a four-membered Si2N2 derivative via the
formation of a silaimine complex that dimerizes in a [2 + 2]
cycloaddition reaction due to its kinetic instability.19a A similar
behavior was observed in the dehydrohalogenation of a
silicon(IV) substituted diphenyl hydrazone derivative, where
an unstable hydrosilaimine undergoes dimerization to afford a
four-membered Si2N2 core.19b These results indicate that the
steric protection is a crucial factor for obtaining stable silaimine
compounds due to the polarized nature of the Si−N bond. This
steric protection might be introduced by choosing either a
Received: July 17, 2012
Published: October 4, 2012
© 2012 American Chemical Society
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Scheme 1. Synthesis of Compounds 5−9
bulky ligand at the silicon atom or a sterically crowded
substituent at the nitrogen atom. We recently prepared a stable
bis-silaimine compound with terminal trimethylsilyl groups.20a
Moreover, Kira et al. reported four base free silaimines with
terminal Ph, CH2Ph, SiMe3, and Ad groups.20b
resonance (δ −44.29), which is shifted upfield when compared
to that of 1 (δ 88.4).11 The γ-CH proton for compound 5 in
the H NMR spectrum is observed at δ 5.20 and is upfield
1
shifted when compared to that of 1 (δ 5.44). The NCCH2
protons in 5 exhibit sharp singlets at δ 3.36 and 3.91 (for 1 δ
3.32 and 3.91). The molecular ion of 5 is exhibited in its EI-
mass spectrum at m/z 940. Compound 5 crystallizes in the
monoclinic space group P21/c, and the structure is shown in
Figure 1. In 5 the silicon atom is three-coordinate and in a
planar geometry comprising three nitrogen atoms (two from
the supporting ligand). There is a shortening of bonds observed
between the Si atom and the nitrogen atoms of the supporting
ligand. The average bond distance between Si1−N1 and Si1−
Apart from the chemistry of dichlorosilylene 2, we have also
investigated the reactions of two functionalized silylenes 3 and
4, each of which possesses the same benzamidinato backbone,1e
but no reactions with organic azides are known. Inspired by the
varied reactivity shown by silylenes and in search for the
silaimines with a three- and four-coordinate silicon atom, and
for those with less bulky substituents at nitrogen, we carried out
the reaction of the stable silylenes 1−4 with various organic
substituted azides. Treatment of L1Si (1) with 2,6-bis(2,4,6-
triisopropylphenyl)phenyl azide resulted in the silaimine
L1SiN(2,6-Triip2-C6H3) (5) (Triip = 2,4,6-triisopropylphenyl)
containing a three-coordinate silicon atom. The reaction of
base-stabilized dichlorosilylene L2SiCl2 (2) with Ph3SiN3
afforded L2(Cl2)SiNSiPh3 (6) possessing a four-coordinate
silicon atom. Similarly, treatment of stable monochlorosilylene
L3SiCl (3) with 2,6-Triip2C6H3N3 yields the four-coordinate
silaimine L3(Cl)SiN(2,6-Triip2C6H3) (7). The reactions of
L3SiN(SiMe3)2 (4) with adamantyl and trimethylsilyl azides
furnished four-coordinate silaimine compounds L3(N(Ad)-
SiMe3)SiN(SiMe3) (8) (Ad = adamantyl) and L3(N(SiMe3)2)-
SiN(SiMe3) (9), respectively. Silaimines 5−9 are stable under
an inert atmosphere and were fully characterized by physical
methods. The molecular structures of 5, 6, 8, and 9 were
established unambiguously by single-crystal X-ray structure
analyses.
Figure 1. Molecular structure of 5. The anisotropic displacement
parameters are depicted at the 50% probability level. The bulky
substituents at the phenyl group attached to N3 and all hydrogen
atoms are omitted for clarity. Selected bond lengths [Å] and angles
[deg]: Si1−N1 1.7051(13), Si1−N2 1.7206(13), Si1−N3 1.5698(13),
C30−N3 1.3848(18); N1−Si1−N2 106.44(6), N1−Si1−N3
120.58(6), N2−Si1−N3 132.86(6), Si1−N3−C30 148.68(11).
RESULTS AND DISCUSSION
■
The reaction of 1 with 2,6-bis(2,4,6-triisopropylphenyl)phenyl
azide in equimolar ratio afforded the three-coordinate silaimine
derivative 5 (Scheme 1). Compound 5 is soluble in all common
organic solvents. The 29Si NMR spectrum of 5 shows a single
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N2 in 5 is 1.7129(13) Å, whereas the corresponding distance in
1 is 1.7349(11) Å. The bite angle (N−Si−N) at the silicon
atom with the backbone ligand is 106.44(6)°, as compared to
99.31(5)° in 1. The Si1−N3 bond length of 1.5698(13) Å
indicates a double bond character.8a
SiMe3 groups from one nitrogen atom to the other nitrogen.
The proposed mechanism is illustrated in Scheme 2.
Scheme 2. Formation of Compound 8
The reaction of dichlorosilylene L2SiCl2 (2) with triphe-
nylsilyl azide in equimolar ratio afforded the four-coordinate
silaimine derivative 6 (Scheme 1). Like 5, this compound is also
soluble in toluene, benzene, and THF. The 29Si NMR spectrum
of 7 shows resonances at δ −29.64(SiPh3) and −75.25(SiCl2).
The molecular structure of 6 is shown in Figure 2. Compound
The 1H NMR spectrum of 8 exhibits three single resonances
at δ 0.59, 0.87, and 1.22, which correspond to two SiMe3
groups and one tBu group, respectively. In the 1H NMR
spectrum of 9, four single resonances have been observed (δ
0.41, 0.57, 0.73, and 1.15). The first three belong to the SiMe3
groups, whereas the latter one correponds to the tBu protons,
which is shifted slightly high-field when compared to that of 4
(δ 1.23).6 The 29Si NMR spectrum of 8 shows three resonances
(δ −64.53, −24.14, and 1.78) for the three chemically different
Si atoms. While the first one corresponds to the Si atom that is
coordinated by the amidinate ligand, the second one originates
from the SiMe3 group that is bonded to the SiN unit, and the
third one from the remaining SiMe3 moiety attached to the N−
Ad group. Similarly, in the 29Si NMR spectrum of 9, the Si
atom that is coordinated by the amidinate ligand resonates at δ
−65.35, and the SiMe3 group attached to the SiN unit
displays a resonance at δ −23.68. The latter two resonances (δ
−1.76, and 4.16) correspond to the remaining SiMe3 groups in
9. In the EI-mass spectra of 8 and 9, the molecular ions are
observed as the most abundant peaks at m/z 568 and 506. The
molecular structures of 8 and 9 were established by single-
crystal X-ray diffraction studies. Figures 3 and 4 portray the
Figure 2. Molecular structure of 6. The anisotropic displacement
parameters are depicted at the 50% probability level. Hydrogen atoms
and disordered toluene solvent molecules are omitted for clarity.
Selected bond lengths [Å] and angles [deg]: C1−Si1 1.924(3), Si1−
N3 1.581(2), Si1−Cl1 2.0783(11), Si1−Cl2 2.0698(10), Si2−N3
1.658(2); C1−Si1−N3 109.17(11), Si1−N3−Si2 156.73(15), Cl1−
Si1−N3 117.24(9), Cl2−Si1−N3 118.78(9), Cl1−Si1−Cl2 100.57(4).
6 crystallizes in the monoclinic space group P21/c. Here, the
silicon atom is four-coordinate and displays a distorted
tetrahedral geometry. The silicon coordination environment
is derived from one carbon atom of the NHC, two chlorine
atoms, and one nitrogen atom. The average Si−Cl distance in 6
is 2.0745(11) Å [Si−Clav of 2 is 2.1664(16) Å]. Compound 6
exhibits a Si−C bond distance of 1.924(3) Å, which is shorter
when compared to that of 2 [Si−C 1.985(4) Å]. The Si−N
bond length of 6 (1.581(2) Å) is consistent with those reported
for silaimine species with four-coordinate silicon atoms.17
The reaction of 2,6-bis(2,4,6-triisopropylphenyl)phenyl azide
with 3 in an equimolar amount afforded the four-coordinate
silaimine derivative 7 (Scheme 1). The 29Si NMR spectrum of 6
shows a resonance at δ −104.78, which is upfield shifted when
compared to that of 3 (δ 14.6).14 The tBu protons of
Figure 3. Molecular structure of 8. The anisotropic displacement
parameters are depicted at the 50% probability level. Hydrogen atoms
are omitted for clarity. Selected bond lengths [Å] and angles [deg]:
Si1−N1 1.8482(13), Si1−N2 1.8447(13), Si1−N3 1.5936(14), Si1−
N4 1.7202(13); N3−Si1−N4 114.25(7), N3−Si1−N2 116.73(7),
N4−Si1−N2 114.54(6), N3−Si1−N1 115.97(7), N4−Si1−N1
117.73(6), N2−Si1−N1 70.88(6), N3−Si1−C1 119.21(7), N4−
Si1−C1 126.50(6), N2−Si1−C1 35.53(5), N1−Si1−C1 35.70(5).
1
compound 7 in the H NMR spectrum exhibit a singlet that is
observed at δ 0.75. In addition, 7 shows its molecular ion in the
mass spectrum at m/z 790.
The reactions of 4 with AdN3 and Me3SiN3 led to the four-
coordinate silaimines 8 and 9, respectively (Scheme 1). It is
interesting to mention that treatment of AdN3 with 2 showed a
functionalized N-heterocyclic carbene through the formation of
an unstable dichlorosilaimine as the intermediate.18 In the
present study the reaction of 4 with AdN3 resulted in a
silaimine compound with terminal SiMe3 group through an
unexpected migration of one SiMe3 group. The route of this
migration remains unclear. However, we propose that an
unstable silaimine compound with a terminal adamantyl group
has been formed as an intermediate under the elimination of
dinitrogen. Subsequently, there is a 1,3-migration of one of the
molecular representation of 8 and 9, respectively. Both 8 and 9
crystallize in the triclinic space group P1. The central Si atoms
̅
in 8 and 9 are four-coordinate and exhibit a distorted
tetrahedral geometry with the sum of the bond angles of
345.52° and 347.12°, respectively. The Si1−N3 bond lengths
for 8 and 9 (1.5936(14) and 1.5885(14) Å) are slightly longer
when compared to those of L2Si(Cl)2N−2,6-iPr2C6H3
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Synthesis of 5. n-Hexane (60 mL) was placed in a Schlenk flask
(100 mL) containing 1 (0.36 g, 0.81 mmol) and 2,6-bis(2,4,6-
triisopropylphenyl)phenyl azide (0.43 g, 0.82 mmol). The reaction
mixture was stirred at room temperature for 12 h. The solution was
filtered, and the solvent was reduced in vacuo to 20 mL and stored in a
freezer at −26 °C for 3 days to obtain single crystals of 5 (0.50 g,
64%). Mp 196−198 °C. Anal. Calcd for C65H89N3Si (940.51): C,
1
83.01; H, 9.54; N, 4.47. Found: C, 82.85; H, 9.49; N, 4.45. H NMR
(300 MHz, C6D6, 25 °C): δ 0.39−1.47 (m, 60H, CH(CH3)2), 2.26
(m, 1H, CH(CH3)2), 2.56 (m, 1H, CH(CH3)2), 2.66−2.98 (m, 4H,
CH(CH3)2), 3.12 (m, 1H, CH(CH3)2), 3.36 (s, 1H, NCCH2), 3.43
(m, 1H, CH(CH3)2), 3.54−3.79 (m, 2H, CH(CH3)2), 3.91 (s, 1H,
NCCH2), 5.20 (s, 1H, γ-CH), 6.54−7.28 (m, 13H, ArH) ppm.
29Si{1H} NMR (59.63 MHz, C6D6, 25 °C): δ −44.29 ppm. EI-MS: m/
z 940 [M+].
Figure 4. Molecular structure of 9. The anisotropic displacement
parameters are depicted at the 50% probability level. Hydrogen atoms
and disordered toluene lattice molecules are omitted for clarity.
Selected bond lengths [Å] and angles [deg]: Si1−N1 1.8360(13),
Si1−N2 1.8326(14), Si1−N3 1.5885(14), Si1−N4 1.7218(14); N3−
Si1−N4 116.58(7), N3−Si1−N2 117.46(7), N4−Si1−N2 113.10(7),
N3−Si1−N1 118.04(7), N4−Si1−N1 112.50(6), N2−Si1−N1
71.25(6), N3−Si1−C1 121.63(7), N4−Si1−C1 121.79(6), N2−Si1−
C1 35.87(6), N1−Si1−C1 35.64(5).
Synthesis of 6. Toluene (60 mL) was added to a Schlenk flask
(100 mL) containing 2 (0.49 g, 1.01 mmol) and triphenylsilyl azide
(0.30 g, 1.00 mmol). The reaction mixture was stirred at room
temperature for 12 h. The solution was filtered, and the solvent was
reduced in vacuo to about 30 mL and stored at −26 °C in a freezer for
5 days to obtain colorless single crystals of 6 (0.60 g, 78.9%). Mp
171−174 °C (decomp). Anal. Calcd for C45H51Cl2N3Si2 (760.98): C,
1
71.02; H, 6.74; N, 5.52. Found: C, 71.05; H, 6.71; N, 5.38. H NMR
(200 MHz, C6D6, 25 °C): δ 0.93 (d, 12 H, CH(CH3)2), 1.20 (d, 12 H,
CH(CH3)2), 2.82 (m, 4H, CH(CH3)2), 6.36 (s, 2H, CH), 6.98−7.20
(m, 12H ArH), 7.68−7.82 (m, 9H ArH) ppm. 29Si{1H} NMR (99.36
MHz, C6D6, 25 °C): δ −29.64 (SiPh3), −75.25 (SiCl2) ppm.
(1.545(2) Å)17 and L3Si(Cl)N−2,6-iPr2C6H3 (1.545(2) Å).21
The Si2−N3 bond distances in 8 and 9 (1.6594(15) and
1.6575(15) Å) correspond to the Si−N single bond
lengths.19,22 The geometry about N3 can best be described as
distorted trigonal planar, with two sites being occupied by two
Si atoms.
Synthesis of 7. Toluene (60 mL) was added to a Schlenk flask
(100 mL) containing 3 (0.30 g, 1.02 mmol) and 2,6-bis(2,4,6-
triisopropylphenyl)phenyl azide (0.53 g, 1.01 mmol). The reaction
mixture was stirred at room temperature for 12 h. The solution was
filtered, and the solvent was reduced in vacuo to about 30 mL and
stored at −26 °C in a freezer for a week to obtain 7 as a crystalline
solid (0.60 g, 75%). Mp 161−164 °C. Anal. Calcd for C51H72ClN3Si
(790.68): C, 77.47; H, 9.18; N, 5.31. Found: C, 77.39; H, 9.15; N,
CONCLUSION
■
1
Stable silaimine L1SiN(2,6-Triip2-C6H3) (5) with three-
coordinate silicon atom has been prepared using the bulky
azide, 2,6-bis(2,4,6-triisopropylphenyl)phenyl azide. Lewis
base-stabilized chlorosilaimines L2(Cl2)SiN(SiPh3) (6) and
L3(Cl)SiN(2,6-Triip2C6H3) (7) were synthesized by the
reaction of chlorosilylenes with appropriate azides. We obtained
the unusual silaimine compound L3(N(Ad)SiMe3)SiN(SiMe3)
(8) (Ad = adamantyl) under the 1,3-migration of one SiMe3
group and L3(N(SiMe3)2)SiN(SiMe3) (9) featuring a terminal
SiMe3 group. A recent communication from our laboratory
documented the reduction of dichlorosilaimines resulting in the
formation of dimeric silaisonitriles.20a The herein reported
chlorosilaimines are expected to be valuable precursors for the
preparation of various silaisonitriles.
5.38. H NMR (500 MHz, C6D6, 25 °C): δ 0.75 (s, 18H, C(CH3)3),
1.19−1.41 (m, 30H, CH(CH3)2), 1.53 (d, 6H, CH(CH3)2), 2.80−3.10
(m, 4H, CH(CH3)2), 3.48 (m, 2H, CH(CH3)2), 6.80−7.24 (m, 12H,
ArH) ppm. 29Si{1H} NMR (99.36 MHz, C6D6, 25 °C): δ −104.78
ppm. EI-MS: m/z 790 [M+].
Synthesis of 8. Toluene (30 mL) was added to a Schlenk flask
(100 mL) containing 4 (0.50 g, 1.19 mmol) and adamantyl azide (0.21
g, 1.19 mmol). The reaction mixture was stirred at room temperature
for 6 h. The solvent was reduced in vacuo to about 15 mL and stored
at −4 °C to obtain single crystals of 8 in a day (0.52 g, 77%). Mp 210−
212 °C. Anal. Calcd for C31H56N4Si3 (569.06): C, 65.43; H, 9.92; N,
1
9.85. Found: C, 65.35; H, 9.83; N, 9.94. H NMR (500 MHz, C6D6,
25 °C): δ 0.58 (s, 9H, Si(CH3)3), 0.87 (s, 9H, Si(CH3)3), 1.22 (s,
18H, tBu), 1.59−1.67 (m, 6H, Ad CH2), 2.02 (br, 3H, Ad CH), 2.35
(br, 6H, Ad CH2), 6.87−6.96 (m, 5H, ArH) ppm. 29Si{1H} NMR
(99.36 MHz, C6D6, 25 °C): δ −64.53 (LSi), −24.14 (SiNSiMe3),
1.776 (Si−NSiMe3) ppm. EI-MS: m/z 568 [M+].
EXPERIMENTAL SECTION
Synthesis of 9. To a toluene (30 mL) solution of 4 (0.50 g, 1.19
mmol) in a Schlenk flask (100 mL) was added trimethylsilyl azide
(0.14 g, 1.19 mmol) in toluene (10 mL) drop by drop at −40 °C. The
solution was warmed to room temperature and stirred for 2 h. The
solvent was reduced in vacuo to about 10 mL and stored at −4 °C to
obtain single crystals of 9 in 2 days (0.48 g, 81%). Mp 192−194 °C.
Anal. Calcd for C24H50N4Si4 (507.02): C, 56.85; H, 9.94; N, 11.05.
■
Syntheses were carried out under an inert gas atmosphere of
dinitrogen in oven-dried glassware using standard Schlenk techniques.
Other manipulations were accomplished in a dinitrogen filled
glovebox. Solvents were purified by the MBRAUN solvent purification
system MB SPS-800. All chemicals were purchased from Aldrich and
used without further purification. Compounds 1,11 2,13 3,14 and 415
were prepared as reported in literature. Triphenylsilyl azide23 and 2,6-
1
Found: C, 56.71; H, 9.99; N, 11.18. H NMR (500 MHz, C6D6, 25
24
1
Triip2C6H3N3 were prepared as reported in the literature. H and
29Si NMR spectra were recorded with a Bruker Avance DPX 200,
Bruker Avance DRX 300, or a Bruker Avance DRX 500 spectrometer,
using C6D6 as solvent. Chemical shifts δ are given relative to SiMe4.
EI-MS spectra were obtained using a Finnigan MAT 8230 instrument.
°C): δ 0.41 (s, 9H, Si(CH3)3), 0.57 (s, 9H, Si(CH3)3), 0.73 (s, 9H,
Si(CH3)3), 1.15 (s, 18H, tBu), 6.86−7.01 (m, 5H, ArH) ppm. 29Si{1H}
NMR (99.36 MHz, C6D6, 25 °C): δ −65.35 (LSi), −23.68 (Si
NSiMe3), −1.76 (Si−NSiMe3), 4.16 (Si−NSiMe3) ppm. EI−MS: m/z
506 [M+].
Elemental analyses were done in the Institut fur Anorganische Chemie,
Crystal Structure Determination. Single crystals were selected
from a Schlenk flask under an argon atmosphere and covered with
perfluorated polyether oil on a microscope slide, which was cooled
with a nitrogen gas flow using the X-TEMP2.25 An appropriate crystal
was selected using a polarized microscope, mounted on the tip of a
̈
Universitat Gottingen. For elemental analysis, the compounds were
̈
̈
under vacuum for 6 h to remove the solvent molecules. Melting points
were measured in a sealed glass tube on a Buchi B-540 melting point
̈
apparatus.
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dx.doi.org/10.1021/ic301543y | Inorg. Chem. 2012, 51, 11049−11054

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Article
Table 1. Crystal and Structure Refinement Parameters for Compounds 5, 6, 8, and 9
parameters
CCDC no.
5
6·toluene
8
(9·toluene)3
891040
891041
891042
891043
empirical formula
formula weight
crystal system
space group
C65H89N3Si
940.48
C52H59Cl2N3Si2
853.10
C31H56N4Si3
569.07
C93H174N12Si12
1797.52
monoclinic
P21/c
monoclinic
triclinic
triclinic
P21/c
P1
̅
P1
̅
unit cell dimensions a = 20.144(2) Å
b = 12.315(2) Å
a = 12.102(2)Å
b = 16.373(2) Å
c = 24.055(3) Å
β = 92.06(3)°
a = 9.875(2) Å
b = 9.906(2) Å
c = 19.285(2) Å
α = 91.21(2)°
β = 104.27(2)°
γ = 111.65(2)°
1686.1(5) Å3, 2
1.121 Mg/m3
0.166 mm−1
a = 13.269(2) Å
b = 16.300(2) Å
c = 25.856(3) Å
α = 87.86(2)°
β = 82.51(2)°
γ = 82.79(2)°
5499.4(12) Å3, 6
1.086 Mg/cm3
0.187 mm−1
c = 22.761(3) Å
β = 93.35(2)°
volume, Z
5636.7(13) Å3, 4
1.108 g/cm3
0.083 mm−1
4763.3(11) Å3, 4
1.190 g/cm3
0.224 mm−1
density (calcd)
absorption
coefficient
F(000)
2056
1816
642
1968
crystal size/mm
0.15 × 0.15 × 0.09
1.01−25.71°
0.12 × 0.10 × 0.06
1.50−25.39°
0.20 × 0.20 × 0.10
1.10−26.73°
0.15 × 0.08 × 0.08
1.26−26.04°
θ range for data
collection
limiting indices
−24 ≤ h ≤ 24; −15 ≤ k ≤ 15;
−27 ≤ l ≤ 27
101 565
−14 ≤ h ≤ 14; −19 ≤ k ≤ 19;
−28 ≤ l ≤ 28
99 203
−12 < h < 9, −12 < k < 12, −24 −16 ≤ h ≤ 16; −20 ≤ k ≤ 20;
< l < 24
13 997
−31 ≤ l ≤ 31
reflns collected
109 840
independent reflns 10 683 (Rint = 0.0447)
completeness to θ 99.6% (θ = 25.71°)
refinement method full-matrix least-squares on F2
8737 (Rint = 0.1243)
99.8% (θ = 25.39°)
full-matrix least-squares on F2
8737/591/656
7128 (Rint = 0.0258)
99.4% (θ = 26.73°)
full-matrix least-squares on F2
7128/0/355
21 603 (Rint = 0.0357)
99.5% (θ = 26.04°)
full-matrix least-squares on F2
21 603/415/1177
data/restraints/
parameters
GOF on F2
10 683/76/660
1.015
1.012
1.038
1.043
final R indices [I > R1 = 0.0398, wR2 = 0.0926
2σ(I)]
R1 = 0.0481, wR2 = 0.1067
R1 = 0.0379, wR2 = 0.0928
R1 = 0.0368, wR2 = 0.0953
R indices (all data) R1 = 0.0525, wR2 = 0.0995
R1 = 0.0841, wR2 = 0.1245
0.410 and −0.343 e Å−3
R1 = 0.0478, wR2 = 0.0985
0.472 and −0.252 e Å−3
R1 = 0.0490, wR2 = 0.1004
0.404 and −0.264 e Å−3
largest diff. peak
and hole
0.306 and −0.354 e Å−3
MiTeGen MicroMount fixed to a goniometer head, and shock cooled
by the crystal cooling device. The data for 5, 6, 8, and 9 were collected
from shock-cooled crystals at 100(2) K.25 The data for 8 and 9 were
collected on an Incoatec Mo microsource26 with mirror optics and an
APEX II detector with a D8 goniometer. The data for 5 and 6 were
measured on a Bruker TXS Mo rotating anode with mirror optics and
an APEX II detector with a D8 goniometer. Both diffractometers used
Mo Kα radiation, λ = 71.073 pm. The data for all structures were
integrated with SAINT,27 and an empirical absorption correction
(SADABS)28 was applied. The structures were solved by direct
methods (SHELXS-97)29a and refined by full-matrix least-squares
methods against F2 (SHELXL-97)29b,c within the SHELXLE GUI.29d
All non-hydrogen atoms were refined with anisotropic displacement
parameters. The hydrogen atoms were refined isotropically on
calculated positions using a riding model with their Uiso values
constrained to equal 1.5 times the Ueq of their pivot atoms for terminal
sp3 carbon atoms and 1.2 times for all other carbon atoms. The
disordered lattice toluene molecules in 6 and 9 and iPr group in the
para position of one of the Triip substituents attached to the phenyl
group at N3 in 5 were refined using distance restraints and restraints
for anisotropic displacement parameters. Crystallographic data
(excluding structure factors) for the structures reported in this Article
have been deposited with the Cambridge Crystallographic Data
Centre. The CCDC numbers, crystal data, and experimental details for
the X-ray measurements are listed in Table 1.
AUTHOR INFORMATION
Corresponding Author
*E-mail: hroesky@gwdg.de (H.W.R.), rghadwal@uni-
goettingen.de (R.S.G.), dstalke@chemie.uni-goettingen.de
(D.S.).
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are thankful to the Deutsche Forschungsgemeinschaft for
supporting this work. R.A. is thankful to the Alexander von
Humboldt Stiftung for a research fellowship. We thank the
Danish National Research Foundation (DNRF)-funded Center
for Materials Crystallography (CMC) for support.
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