Synthesis of a lewis base stabilized dimer of N-substituted hydrosila hydrazone and a silaaziridine

Article abstract of DOI:10.1021/om101066w

The dehydrohalogenation of a silicon(IV)-substituted diphenyl hydrazone derivative leads to a dimer of a N-substituted hydrosila hydrazone, which consists of a four-membered Si₂N₂ core and a hydrogen attached to each of the silicon a

Full text of DOI:10.1021/om101066w

912 Organometallics 2011, 30, 912–916
DOI: 10.1021/om101066w
Synthesis of a Lewis Base Stabilized Dimer of N-Substituted Hydrosila
Hydrazone and a Silaaziridine
Sankaranarayana Pillai Sarish,† Anukul Jana,† Herbert W. Roesky,*,† Prinson P. Samuel,†
Carlos E. Abad Andrade,† Birger Dittrich,† and Carola Schulzke§
†
€
€
Institut fu€r Anorganische Chemie, Universitat Gottingen, Tammannstrasse 4, 37077 Gottingen,
€
Germany, and §School of Chemistry, Trinity College Dublin, Dublin 2, Ireland
Received November 12, 2010
The dehydrohalogenation of a silicon(IV)-substituted diphenyl hydrazone derivative leads to a
dimer of a N-substituted hydrosila hydrazone, which consists of a four-membered Si2N2 core and a
hydrogen attached to each of the silicon atoms instead of giving a substituted hydrosilaneimine. The
compound is obviously formed by dimerization of hydrosilaneimine. Moreover there are no
straightforward synthetic methods known for the synthesis of silaaziridine. The preparation of such
species would be of special importance for the development of a new field of silicon chemistry. The
reaction of chlorosilylene, LSiCl, and PhCHdNPh resulted in a base-stabilized silaaziridine. All
compounds were characterized by NMR spectroscopy, mass spectrometry, microanalysis, and X-ray
structural analysis.
Introduction
and instead rearranged products were obtained.7-9 In
2007 Woerpel et al. reported the synthesis of silaaziridine
by applying silver triflate catalyzed silylene transfer from
silacyclopropane to imines.10 The aziridines are used as
precursors for the synthesis of N-containing heterocyclic
compounds, which are important for producing drugs11
and natural products.12 Stable silaaziridine could be an
alternative precursor for the synthesis of N,Si-containing
heterocyclic compounds. Subsequently a facile synthesis of
stable hydrosilaneimines and silaaziridines would be a real
challenge for the synthetic chemist. Recently we were suc-
cessful in isolating the previously reported stable chloro-
silylene LSiCl (1) (L = PhC(NtBu)2)13 in high yield using
LiN(SiMe3)2 as a dehydrohalogenating agent,14 which
helped to carry out its versatile reactivities. Among them, one
is the convenient synthesis of monosilaepoxide, which was
formed by the reaction of 1 with ketones.15 The successful
stabilization of monosilaoxirane by the benzamidinato
ligand prompted us to probe the reaction of 1 with the
>CdNR precursor. The question arises whether it will
afford [1þ2] cycloaddition compounds or oxidative addition
products.
The stable allotropes of the lighter p block elements
such as nitrogen and oxygen possess triple and double bonds,
respectively. Nitrogen has a ubiquitous nature to form
double as well as triple bonds with carbon. Silicon, the
congener of carbon, forms silane imine complexes,1-3 which
constitute a vital area of research in the last two decades.
However stable hydrosilaneimines, compounds with a SidN
double bond and one hydrogen attached to the silicon atom,
are elusive and have been characterized only in an argon
matrix.4,5 Moreover examples of silaaziridines, which are
constituted of three-membered Si-N-C ring systems, are
scant. The paucity of such compounds is largely related to
their limited synthetic approach. In the case of silaaziridines,
Brook et al. reported for the first time their synthesis using
isocyanides and photochemically generated silenes.6 How-
ever, this method lacks generality. Moreover, silaaziridines
have been proposed as reactive intermediates in thermal and
photochemical silylene transfer reactions to imines, although
the strained three-membered ring compounds were not isolated,
*To whom correspondence should be addressed. E-mail: hroesky@
gwdg.de.
(9) Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F. Organometallics
1998, 17, 1378–1382.
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Dev. 2002, 5, 918–927.
(12) Kametani, T.; Honda, T. Adv. Heteroat. Chem. 1986, 39,
181–236.
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metallics 1988, 7, 2245–2247.
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r
pubs.acs.org/Organometallics
Published on Web 01/05/2011
2011 American Chemical Society

Article
Scheme 1. Preparation of Silicon(IV)-Substituted Diphenyl
Organometallics, Vol. 30, No. 4, 2011 913
Hydrazone (2), N-Substituted Hydrosila Hydrazone (3),
and Silaaziridine (4)
Figure 1. Molecular structure of 2. Thermal ellipsoids are
shown at 50% probability. H atoms except on Si1 and N1 are
˚
omitted for clarity reasons. Selected bond distances (A) and
angles (deg): Si1-Cl1 2.2045(13), Si1-N1 1.722(3), N1-N2
1.364(3), Si1-N3 1.802(3); N2-N1-Si1 124.3(2), N1-Si1-Cl1
90.23(10).
doublet of doublets at δ -99.82 ppm (1J(29Si-1H) =
299.45 Hz, 2J(29Si-1H) = 10.78 Hz). Furthermore the solid-
state structure of compound 2 was confirmed by single-crystal
X-ray structural analysis.
Single crystals of 2 were obtained from a hot saturated
n-hexane solution at room temperature after one day. Com-
pound 2 crystallizes in the triclinic space group P1, with one
monomer in the asymmetric unit as illustrated in Figure 1.
Surprisingly, 2 is monomeric in the solid state, and what is
even more striking, the NH group is not involved in any
kind of hydrogen bonding. Compound 2 is stable in the
solid state as well as in solution for a longer period of time
without any decomposition under an inert atmosphere.
The coordination polyhedron around the silicon atom
features a distorted tetragonal-pyramidal geometry. The
silicon is attached to two nitrogen atoms from the back-
bone of the chelating ligand, the nitrogen atom from the
diphenyl hydrazone moiety, the Cl atom, and a hydrogen
Herein, we report on the synthesis of a stable base-stabi-
lized Si2N2 core [LSi(H)-N-NdCPh2]2 (L = PhC(NtBu)2)
(3) from the reaction of LSiCl(H)N(H)-NdCPh2 (2) with
1,3-bis(tert-butyl)imidazol-2-ylidene under HCl elimina-
tion. Here it is worth mentioning that compound 2 is
obtained from the unprecedented oxidative addition of one
of the N-H bonds of diphenyl hydrazone (Ph2CdN-NH2)
to the silicon(II) center of the base-stabilized chlorosilylene,
LSiCl (1). Furthermore an efficient method is outlined for
the synthesis of stable silaaziridine 4 by the reaction of 1 with
N-benzylideneaniline (PhCHdNPh).
Results and Discussion
˚
atom. The N1-N2 bond length is 1.364(3) A, which is
The reaction of chlorosilylene, LSiCl (1), with diphenyl
hydrazone in toluene leads to the silicon(IV)-substituted
diphenyl hydrazone derivative LSiCl(H)N(H)-NdCPh2 (2)
(Scheme 1). The reaction proceeds via the oxidative addition
of one of the N-H bonds to the silicon(II) center. A similar
reaction was observed when ammonia was reacted with the
silylene L0Si (L0 = CH{(CdCH2)(CMe)(2,6-iPr2C6H3N)2}).16
In contrast to the present results, when L0Si was reacted with
diphenyl hydrazone, there was exclusive formation of the
[1þ4] cycloaddtion product.17 The different reactivity is
mainly due to the difference in coordination numbers around
the silicon atom of the two silylenes.
The formation of compound 2 was confirmed by elemental
analysis, multinuclear NMR spectroscopy, and EI mass
spectrometry. The 1H NMR spectrum of 2 shows resonances
at δ 6.48 and 6.62 ppm for the Si-H and N-H proton,
respectively, and both exhibit doublets with the same coupling
constant (3J = 3 Hz). The 29Si NMR spectrum exhibits a
indicative of a N-N single bond. A noteworthy feature of
˚
compound 2 is the Si(H)NH moiety (Si1-N1 1.722(3) A).
The Si-N1 bond length can be compared with the
slightly shorter Si-N bond lengths than that in RSi(NH2)3
(R=2,4,6-Ph3C6H2 av 1.709(7) A, R = 2,6-iPr2C6H3-
18
˚
19
˚
NSiMe3 av 1.709(2) A, and R = 2,4,6-tBuC6H2O av
19
˚
1.692(6) A).
Compound 2 exhibits a Si-H as well as a N-H bond,
which both are potential proton donors for the elimination
of HCl. This would occur from either the 1,1 or 1,2 position
while adding a proton scavenger (such as amine, N-hetero-
cyclic carbene). In the case of 1,1 HCl elimination there
would be the formation of LSiN(H)NdCPh2, while 1,2 HCl
elimination would lead to the substituted hydrosilaneimine
derivative LSi(H)dNNCPh2. In the literature there are
protocols on both the formation of silylene compounds by
(18) Ruhlandt-Senge, K.; Bartlett, R. A.; Olmstead, M. M.; Power,
P. P. Angew. Chem. 1993, 105, 459-461. Angew. Chem., Int. Ed. Engl.
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€
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metallics 2009, 28, 6574–6577.

914 Organometallics, Vol. 30, No. 4, 2011
Sarish et al.
each. The coordination polyhedron around the silicon
atom comprises two nitrogen atoms from the supporting
ligand, one hydrogen atom, and two nitrogen atoms of
the hydrazone moiety, featuring a distorted trigonal-
bipyramidal geometry. The axial positions are occupied
by two nitrogen atoms. The axial substituents include
an angle of 80.34° with the silicon atom. The distorted
trigonal-bipyramidal architecture includes different Si-N
bond distances for axial and equatorial substituents. The
Si-N bond lengths in the equatorial positions (Si1-N1
˚
˚
1.752 A and Si1-N21 1.831 A) are shorter than that in the
˚
axial positions (Si-N11 2.028 A). In summary, compound
3 represents a stable crystalline compound with three four-
membered rings that are connected through silicon atoms,
and it exhibits at each silicon center a terminal-bound
hydrogen atom.
After the successful synthesis of an N-substituted hydro-
sila hydrazone, we turned our attention to the synthesis of
silaaziridine. From the retrosynthetic point of view, the
silaaziridines can be prepared by reacting either silene with
nitrene or, alternatively, silaimine with carbene, or imine
with silylene. The preparation of stable silene24-26 and
silaimine1-3 is limited, although nowadays there are numer-
ous reports on stable silylenes.27,28 For developing a new
route to stable silaaziridines we employed the reaction of
stable silylenes with imines. Finally it is noteworthy that in all
the known silaaziridines the silicon atom binds to either
carbon or silicon. So far no compounds are available where
heteroatoms are attached to silicon.
Figure 2. Molecular structure of 3. Thermal ellipsoids are
shown at 50% probability. H atoms except on those on silicon
˚
are omitted for clarity reasons. Selected bond lengths [A]
and angles [deg]: Si1-N11 2.0280(11), Si1-N21 1.8306(10),
Si1-N1 1.7521(10), Si1-H 1.350; N11-Si1-N21 68.18(4),
N11-Si1-N1 99.17(5), Si1-N1-Si1a 99.66(5).
1,1 HCl elimination20,21 and the formation of compounds
with SidN bonds by 1,2 HCl elimination.22 The reaction of
compound 2 with an equivalent amount of 1,3-bis-
(tert-butyl)imidazol-2-ylidene23 leads only to N-substituted
hydrosila hydrazone as a dimer of composition [LSi(H)-
NNdCPh2]2 (3) in good yield (Scheme 1) instead of forming
the hydrosilaneimine derivative LSi(H)dNNCPh2. This is in
contrast to the reaction of LSiHCl2 with the same carbene,14
which yields exclusively LSiCl.
3 is a yellow solid soluble in benzene, toluene, diethyl
ether, and THF, respectively, and shows no decomposition
on exposure to dry air. 3 was characterized by multinuclear
spectroscopy, EI mass spectrometry, elemental analysis, and
X-ray structural analysis. The 1H NMR spectrum of 3
exhibits a singlet (δ 4.86 ppm) that can be assigned to the
Si-H proton, accompanied by two 29Si satellite resonances.
The 29Si NMR spectrum exhibits a doublet resonance
(δ -96.65 ppm) with a coupling constant of J(29Si-H) =
286.18 Hz. Suitable crystals for X-ray structural analysis
were obtained from a hot saturated THF solution of 3
after storing this solution overnight at room temperature.
3 crystallizes in the monoclinic space group P21/n, with
one-half molecule of 3 in the asymmetric unit and one
slightly disordered THF molecule. 3 exists as a dimer in the
solid state (Figure 2). There are no classical intermolecular
hydrogen bonds observed in the crystal lattice. Geometry
The addition of N-benzylideneaniline (PhCHdNPh) to a
solution of 1 in toluene leads to compound 4 (Scheme 1). The
colorless solution was evaporated, and the residue extracted
with hot n-hexane to yield colorless crystals of 4 in 88% yield.
The exact mechanism for the formation of 4 is unknown, but
two mechanistic pathways can be envisioned. Either an
electrophilic attack of 1 could occur at the imine nitrogen
of N-benzylideneaniline to give a sila ylide, or alternatively, a
nucleophilic attack of 1 to the imine carbon of N-benzylide-
neaniline might be possible to result in a charge-separated
species. Both pathways can lead to compound 4 after suc-
cessive ring closure. Compound 4 is well soluble in benzene,
toluene, THF, and diethyl ether and shows no decomposi-
1
tion on exposure to dry air. 4 was characterized by H and
29Si NMR spectroscopy, EI mass spectrometry, elemental
analysis, and X-ray structural analysis.
1
The H NMR spectrum of 4 exhibits a singlet resonance
(δ 4.07 ppm) that can be assigned to the C-H proton of the
three-membered silaaziridine ring. The 29Si NMR spectrum
exhibits a singlet resonance (δ -131.35 ppm) consistent with
a neutral pentacoordinate silicon.26 Single crystals of 4 were
obtained from a saturated hot n-hexane solution after one
day. Compound 4 crystallizes in the triclinic space group P1,
with two molecules in the asymmetric unit. Interestingly, the
criteria suggest one attractive C--H
N hydrogen bond
3 3 3 3
(20) Ghadwal, R. S.; Roesky, H. W.; Merkel, S.; Henn, J.; Stalke, D.
Angew. Chem. 2009, 121, 5793–5796. Angew. Chem., Int. Ed. 2009, 48,
5683-5686.
(24) Ishikawa, M.; Kikuchi, M.; Watanabe, K.; Sakamoto, H.; Kunai
J. Organomet. Chem. 1993, 443, C3–C5.
(25) Bravo-Zhivotovskii, D.; Dobrovetsky, R.; Nemirovsky, D.; Molev,
V.; Bendikov, M.; Molev, G.; Botoshansky, M.; Apeloig, Y. Angew. Chem.
2008, 120, 4415–4417. Angew. Chem., Int. Ed. 2008, 47, 4343-4345.
(26) Corriu, R.; Lanneau, G.; Priou, C. Angew. Chem. 1991, 103,
1153–1155. Angew. Chem., Int. Ed. Engl. 1991, 30, 1130-1132.
(27) So, C.-W.; Roesky, H. W.; Gurubasavaraj, P. M.; Oswald, R. B.;
Gamer, M. T.; Jones, P. G.; Blaurock, S. J. Am. Chem. Soc. 2007, 129,
12049–12054.
(21) Filippou, A. C.; Chernov, O.; Blom, B.; Stumpf, K. W.;
Schnakenburg, G. Chem.;Eur. J. 2010, 16, 2866–2872.
(22) Li, B.; Matsuo, T.; Hashizume, D.; Fueno, H.; Tanaka, K.;
Tamao, K. J. Am. Chem. Soc. 2009, 131, 13222–13223.
(23) (a) Arduengo, A. J.; Bock, H.; Chen, H.; De, M.; Dixon, D. A.;
Green, J. C.; Herrmann, W. A.; Jones, N. L.; Wagner, M.; West, R.
J. Am. Chem. Soc. 1994, 116, 6641–6649. (b) Scott, N. M.; Dorta, R.;
Stevens, E. D.; Correa, A.; Cavallo, L.; Nolan, S. P. J. Am. Chem. Soc. 2005,
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Article
Organometallics, Vol. 30, No. 4, 2011 915
techniques or inside a MBraun MB 150-GI glovebox main-
tained at or below 1 ppm of O2 and H2O. All solvents were
distilled from Na/benzophenone prior to use. The starting
material 1 was prepared using a literature procedure.14 Other
chemicals were purchased and used as received. 1H, 13C, and 29Si
NMR spectra were recorded on a Bruker Avance DRX instru-
ment and referenced to the deuterated solvent in the case of
1
the H and 13C NMR and SiMe4 for the 29Si NMR spectra.
Elemental analyses were performed by the Analytisches Labor
€
€
des Instituts fur Anorganische Chemie der Universitat
Gottingen. EI-MS were measured on a Finnigan Mat 8230
€
or a Varian MAT CH5 instrument. Melting points were mea-
€
sured in sealed glass tubes with a Buchi melting point B 540
instrument.
Figure 3. Molecular structure of 4 shows the two different
isomers in the asymmetric unit. Thermal ellipsoids are shown
at 50% probability. H atoms except on C1 and C29 are omitted
Synthesis of 2. A solution of Ph2CdNNH2 (0.19 g, 1 mmol) in
toluene (10 mL) was added to a toluene solution (35 mL) of 1
(0.29 g, 1 mmol) at -78 °C. The reaction mixture was allowed to
warm slowly to room temperature and stirred for 12 h at this
temperature. After that all volatiles were removed under vacu-
um. The residue was dissolved in n-hexane (45 mL), and the
solution was warmed and filtered over a Celite pad. The result-
ing solution was kept overnight at room temperature to afford
colorless crystals of 2. Yield: 0.39 g, 80%. Mp: 138-140 °C. 1H
NMR (500 MHz, C6D6): δ 7.85-7.84, 7.18-6.84 (m, 15H,
C6H5), 6.62 (d, 1H, NH), 6.48 (d, 1H, SiH), 1.15 (s, 18H,
C(CH3)3) ppm. 13C NMR (125 MHz, C6D6): δ 172.08, 147.08,
140.00, 134.78, 129.87, 129.67, 129.63, 128.84, 128.69, 128.31,
127.72, 127.01, 54.68, 31.67 ppm. 29Si NMR (99.35 MHz,
˚
for clarity reasons. Selected bond lengths [A] and angles [deg]:
Si1-Cl1 2.0800(17), Si1-N1 1.733(4), Si1-C1 1.858(4), Si1-
N2 1.914(4); N1-Si1-C1 49.58(16), N1-Si1-Cl1 105.35(13),
N2-Si1-N3 70.89(15).
unit cell contains two different isomers. C1 and C29 exhibit
chirality that is distinct in the two cases. The hydrogens at
these carbon atoms were found and refined freely with
respect to the location but constrained with respect to the
displacement parameters. X-ray crystal structure analysis
afforded the structure as illustrated in Figure 3. Compound 4
is stable in the solid state as well as in solution for a longer
period of time without any decomposition under inert atmo-
sphere. The coordination polyhedron around the silicon
atom features a distorted trigonal-bipyramidal geometry,
with the chlorine atom at an axial position. The silicon is
attached to two nitrogen atoms from the backbone of the
chelating ligand, one carbon and one nitrogen atom from the
imine moiety, and a chlorine atom. The three nitrogen atoms
are in equatorial positions, whereas the carbon is in between
an equatorial and axial position, giving rise to the distortion.
The composition of 4 was also confirmed by mass spec-
trometry and elemental (C, H, N) analysis. The most intense
peak in the EI mass spectrum appeared at m/z = 475 [M]þ.
2
C6D6): δ -99.82 ppm (dd, J = 299.45 and J = 10.78 Hz).
EI-MS (70 eV) m/z (%): 453(100%) [M - 2H - Cl]þ, 489 (10%)
[M - H]þ. Anal. Calcd for C28H35ClN4Si: C, 68.47; H, 7.18; N,
11.41. Found: C, 68.47; H, 7.35; N, 11.46.
Synthesis of 3. A solution of 1,3-bis(tert-butyl)imidazol-
2-ylidene (0.18 g, 1 mmol) in THF (20 mL) was added to a
THF solution (30 mL) of 2 (0.49 g, 1 mmol) at -78 °C. The reac-
tion mixture was allowed to warm gradually to room tempera-
ture and stirred overnight. After that all volatiles were removed
under vacuum. The residue was dissolved in n-hexane (40 mL),
and the solution was warmed and filtered over a Celite pad.
Single crystals of 3 suitable for X-ray structural analysis were
obtained by storing the solution overnight at room temperature.
Yield: 0.38 g, 85%. Mp: 299-301 °C. 1H NMR (300 MHz,
C4D8O): δ 7.44-7.09 (m, 30H, C6H5), 4.86 (s, 2H, SiH), 1.06 (s,
36H, C(CH3)3) ppm. 13C NMR (75.47 MHz, C4D8O): δ
169.81,143.46, 142.30, 137.11, 132.60, 130.50, 130.17, 128.81,
128.25, 128.12, 127.95, 127.50, 126.99, 54.58, 32.01(br) ppm.
29Si NMR (59.63 MHz, C4D8O): δ -96.65 ppm (d, J = 286.18
Hz). EI-MS (70 eV) m/z (%): 728.4 (100) [Mþ - NdCPh2],
908.5(55) [M]þ, 454.2(30) [M/2]þ. Anal. Calcd for C56H68N8Si2:
C, 73.96; H, 7.54; N, 12.32. Found: C, 73.12; H, 8.07; N, 12.12.
Synthesis of 4. A solution of PhCHdNPh (0.18 g, 1 mmol) in
toluene (10 mL) was added to a toluene solution (35 mL) of 1
(0.29 g, 1 mmol) at -30 °C. The reaction mixture was allowed to
warm slowly to room temperature and stirred for an additional
1 h at the same temperature. After that all volatiles were
removed under vacuum. The residue was dissolved in n-hexane
(40 mL), and the solution was warmed and filtered over a Celite
pad. The resulting solution was stored overnight at room
temperature to afford colorless crystals of 4. Yield: 0.42 g,
Conclusions
In summary, we have demonstrated that base-stabilized
chlorosilylene, LSiCl, allows for a convenient oxidative
addition reaction of one of the N-H bonds of phenyl
hydrazone under the formation of a silicon(IV)-substituted
hydrazone derivative. The latter undergoes a 1,2 HCl elim-
ination by a N-heterocyclic carbene to generate a stable
N-substituted hydrosila hydrazone as a dimer that contains
a chain of three four-membered rings, and in the spirocyclic
structure each Si atom is part of two four-membered rings
and a hydrogen atom on silicon. Moreover we have shown a
convenient method for an efficient synthesis of a stable
silicon-heteroatom (chlorine, nitrogen) bound silaaziridine.
The latter is prone to further functionalization and might
have a similar impact on organic chemistry to that realized
for carbon-heteroatom-bound aziridines.29
1
88%. Mp: 117 °C. H NMR (C6D6, 500 MHz): δ 7.54-6.62
(m, 15H, C6H5), 4.07 (s, 1H, CH), 1.15 (s, 9H, C(CH3)3), 1.02 (s,
9H, C(CH3)3) ppm. 13C NMR (125 MHz, C6D6): δ 174.16,
159.97, 150.66, 145.71, 131.26, 131.22, 130.15, 129.34, 129.22,
129.11, 128.81, 128.75, 128.24, 126.02, 124.89, 124.22, 121.27,
118.36, 117.79, 54.65, 54.29, 53.28, 31.80, 30.47 ppm. 29Si NMR
(C6D6, 59.62 MHz): δ -131.35 ppm. EI-MS (70 eV) m/z (%):
475 (100) [M]þ. Anal. Calcd for C28H34ClN3Si: C, 70.63; H,
7.20; N, 8.83. Found: C, 71.45; H, 7.49; N, 9.08.
Experimental Section
General Procedures. All manipulations were performed under
a dry and oxygen-free atmosphere (N2) using standard Schlenk
X-ray Crystal Structure Determination. Suitable crystals of 2
and 4 were mounted on a glass fiber, and data was collected on
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916 Organometallics, Vol. 30, No. 4, 2011
Sarish et al.
an IPDS II Stoe image-plate diffractometer (graphite-mono-
˚
with the Cambridge crystallographic data center. Copies of
the data can be obtained free of charge from the Cambridge
crystallographic data center via www.ccdc.cam.ac.uk/data_request/
chromated Mo KR radiation, λ = 0.71073 A) at 133(2) K. The
data for 3 were collected from a shock-cooled crystal at 100(2) K
on a Bruker SMART 6000 diffractometer equipped with a
rotating anode and INCOATEC mirror optics. The structures
were solved by direct methods (SHELXS-97)30 and refined by
full-matrix least-squares methods against F2 (SHELXL-97).30
All non-hydrogen atoms were refined with anisotropic displace-
ment parameters. The hydrogen atoms were refined isotropi-
cally at calculated positions using a riding model with their Uiso
values constrained to 1.5 times the Ueq of their pivot atoms for
terminal sp3-carbon atoms and 1.2 times for all other carbon atoms.
Hydrogen atoms bound to nitrogen, silicon and the chiral carbon
atoms of 4 were located and refined freely; for the latter only, unlike
their location Uiso was refined as being dependent on the pivot
atoms.
˚
cif. Compound 2: Space group: P1; a = 8.2690(17) A, b =
˚
˚
9.7193(19) A, c = 17.875(4) A; R = 101.04(3)°, β = 102.46(3)°,
γ= 96.72(3)°, R1 = 0.0647 for [I>2σ(I)], wR2 (all data) = 0.1500
(CCDC number for 2: 778977). Compound 3: Space group: P21/n;
˚
˚
˚
a = 12.7543(3) A, b =18.2098(4) A, c = 13.9106(3) A; R = 90.0°,
β = 113.1287(7)°, γ =90.0°, R1 = 0.0367 for [I >2σ(I)], wR2 (all
data) = 0.0960 (CCDC number for 3: 781161). Compound 4: Space
group: P1; a = 11.161(2) A, b = 15.987(3) A, c = 16.576(3) A;
R = 89.93(3)°, β = 83.27(3)°, γ = 71.19(6)°, R1 = 0.0873 for
[I > 2σ(I)], wR2 (all data) = 0.1633 (CCDC number for 4:
776751).
˚
˚
˚
Acknowledgment. Support by the Deutsche Forschungs-
gemeinschaft is highly acknowledged.
Disordered moieties were refined using bond length re-
straints, rigid bond restraints, similarity restraints, and ADP
restraints. Crystallographic data (excluding structure factors)
for the structures reported in this paper have been deposited
Supporting Information Available: X-ray data for 2, 3, and 4
(CIF). This material is available free of charge via the Internet at
http://pubs.acs.org.
(30) Sheldrick, G. M. Acta Crystallogr. Sect. A 2008, A64, 112–122.