Striking stability of a substituted silicon(II) bis(trimethylsilyl)amide and the facile Si-Me bond cleavage without a transition metal catalyst

Article abstract of DOI:10.1021/ja205369h

Silicon(II) bis(trimethylsilyl)amide (LSiN(SiMe₃)₂, L= PhC(NtBu)₂) (2) has been synthesized by the reaction of LSiHCl₂ with KN(SiMe₃)₂ in 1:2 molar ratio in high yield where 1 equiv of the

Full text of DOI:10.1021/ja205369h

ARTICLE
pubs.acs.org/JACS
Striking Stability of a Substituted Silicon(II) Bis(trimethylsilyl)amide
and the Facile SiÀMe Bond Cleavage without a Transition
Metal Catalyst
Sakya S. Sen, Jakob Hey, Regine Herbst-Irmer, Herbert W. Roesky,* and Dietmar Stalke*
Institut f€ur Anorganische Chemie an der Universit€at G€ottingen, Tammannstrasse 4, D-37077, G€ottingen, Germany
S Supporting Information
b
ABSTRACT: Silicon(II) bis(trimethylsilyl)amide (LSiN-
(SiMe3)2, L= PhC(NtBu)2) (2) has been synthesized by the
reaction of LSiHCl2 with KN(SiMe3)2 in 1:2 molar ratio in high
yield where 1 equiv of the latter functions as a dehydrochlor-
inating agent. 2 exhibits a high stability up to 154 °C and can be
handled in open air for a short period of time without any appreciable decomposition. An amazing five-membered cyclic silene (3)
results from the cleavage of one SiÀMe bond of 2 with an adamantyl phosphaalkyne. 3 is the first example of a heavy cyclopentene
derivative which consists of four different elements, C, N, Si, and P. Both compounds are characterized by multinuclear NMR
spectroscopy, EI-mass spectrometry, and single crystal X-ray diffraction studies.
’ INTRODUCTION
of the plethora of reactivities shown by LSiCl, it is highly desirable
to develop new methods for the preparation of heteroatom
substituted silylenes in good yield. The synthesis of silylene with
nitrogen substitution is a nontrivial task. In 1998, Kira and his co-
workers showed that bis(diisopropylamino) silylene, which was
generated photochemically, is stable at room temperature but
only in solution.14a In 2003, West et al. reported that bis(bis-
(trimethylsilyl)amino)silylene is stable only at low temperature
and undergoes rapid decomposition above 0 °C.14b Therefore,
the chemistry of amino silylenes is still unknown and needs
further attention. To develop the chemistry of amino silylenes, it
is essential to find a more convenient and high yield protocol,
rather than the prototypical photochemical generation or alkali
metal reduction technique. In a prior publication,15a we reported
that the reaction of KN(SiMe3)2 with Cp*SiHCl2 (Cp* = Me5C5)
afforded a disilene of composition E-[(Me3Si)N](η1-Cp*)SidSi-
(η1-Cp*)[N(SiMe3)] in 68% yield which was previously reported
by Jutzi et al. in less than 10% yield.15b We presume that the
formation of different products with different metal amides is due
to the difference in the size of the metal cations, which increases
down the group with the result that the basicity of the amide
increases. Hence, we treated LSiHCl2 (1) with KN(SiMe3)2 in
1:2 molar ratio and obtained LSiN(SiMe3)2 (2), a silicon(II)
bis(trimethylsilyl)amide in good yield. The increase in yield is the
requirement to accomplish new reactivity patterns of this unique
compound.
Synthesis of silylene and exploring itschemistry is at the cutting
edge of chemical research not only because it can provide answers
to basic questions related to its chemical bonding, structure, and
reactivity, but also due to the study of silylene that has the
potential of providing useful insights and directions for growing
fields such as silicon-based polymers,1a photolithiography,1b and
silicon surface science.1c,d Since the successful isolation of the first
N-heterocyclic silylene (NHSi) in 1994 by West et al.2a several
other silylenes have been reported by different groups.2bÀi
Parallel to these results, a few numbers of higher coordinate
Si(II) compounds have been isolated by different groups.3 Never-
theless, despite intensive recent research the progress of studying
the chemistry of silylenes is relatively slow which is largely
attributed to the very limited synthetic approaches. The most
common route to access compounds with low valent silicon atom
is the reduction of the parent halogen compounds with strong
reducing agents such as sodium or potassium metal or potassium
graphite (KC8). However, the yield of the reduced products is
usually very small, sometimes merely 5%,4 which certainly
impedes further investigation. Recently, we demonstrated that
Si(II) compounds can be synthesized almost in quantitative yield
using N-heterocyclic carbene (NHC) as a dehydrochlorinating
agent.5a The technique was extended by Cui et al. to access several
four- and five-membered NHSis reported beforehand.5b We
further diversified this dehydrochlorination method by replacing
NHC with commercially available LiN(SiMe3)2 and reproduced
our previously reported silicon(II) chloride, LSiCl (L = PhC-
(NtBu)2) (which was isolated in 10% yield before)3c in 90%
yield.5c The increase in yield was the breakthrough to carry out
systematic reactivity studies with homo-5c and heteroalkyne,6
ketone,7 diketone,8 isocyanate,9 carbodiimide,9 imine,10 diimine,9
COT,9 diazobenzene,11 borane,12 and metal carbonyls.13 In view
’ RESULT AND DISCUSSION
Treatment of 1 with 2 equiv of KN(SiMe3)2 in toluene for 12 h
afforded a new monomeric N-substituted Si(II) compound in
Received: June 10, 2011
Published: July 07, 2011
r
2011 American Chemical Society
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ARTICLE
Scheme 1. Synthesis of 2
Scheme 2. Synthesis of 3
Si1ÀN2ÀC1ÀN3 ring is not planar. The Si(II) atom is shifted
out of the plane defined by C1ÀN2ÀN3 by 0.537(3) Å, thus,
arranged to a distorted trigonal pyramid with the three nitrogen
atoms in the basal positions. The Sil lone pair marks the apex of
the trigonal pyramid. The two Si 1ÀN(ligand) bond lengths are
identical (1.878(1) and 1.878(1) Å), while the Si1ÀN(SiMe3)2
bond length is 1.769(7) Å. The latter is 0.045 Å longer than the
equivalent distance in the previously reported LSiNMe2
(1.724(2) Å)3d but very similar to the theoretically calculated
value of [{(Me3Si)2N}2Si]2 (1.779 Å).14b
Figure 1. Molecular structure of 2 with the anisotropic displacement
parameters depicted at the 50% probability level. Hydrogen atoms and
the disorder of the N(SiMe3)2 group are not shown for clarity. Selected
bond lengths (Å) and angles (deg): N(1)ÀSi(1) 1.769(7), N(2)ÀSi(1)
1.8780(10), N(3)ÀSi(1) 1.8776(10); N(1)ÀSi(1)ÀN(2) 108.3(4),
N(1)ÀSi(1)ÀN(3) 112.2(4), N(3)ÀSi(1)ÀN(2) 69.09(4).
The chemistry of heteroatom substituted silylenes is one of the
foci of current research and no reactivity of silicon(II) bis-
(trimethylsilyl)amide has been mentioned so far. It is under-
standable that the chemistry of 2 will be different from that of
LSiCl due to its higher thermal stability and the presence of a
strong SiÀN bond instead of a labile SiÀCl bond. To compare
the reactivity of 2 with that of LSiCl, we treated 2 with PhCtCPh
and AdCtP. The reactions of LSiCl with PhCtCPh and
AdCtP afforded 1,2-disilacyclobutadiene5c and 1,3-disilacarba-
phosphide derivative,6 respectively. With PhCtCPh, 2 did not
react, but with AdCtP, it furnished a five-membered cyclic silene.
Silenes are usually prepared by thermal and photochemical
rearrangement of suitable acyl silanes, easily accessible from
reactions of acid chlorides with silyl anions, by sila-Peterson
reaction, and β-elimination of inorganic salts.17 Apeloig, Kira,
and Sekiguchi independently showed that the sila-Peterson
reaction is very useful for synthesizing stable silenes.17bÀe Kira
et al. also reported that dialkyl silylene isomerizes to the
corresponding silaethene via an apparent 1,2-silyl migration at
room temperature.2e Recently, some disilenides are indepen-
dently brought to the fore by Sekiguchi18a,b and Scheschkewitz
et al.18c,d,e Several cyclic silenes were obtained by the reactions of
disilenides with acid chlorides.19 Herein, we present a convenient
synthesis of a cyclic silene from a heteroleptic Si(II) compound.
Treatment of an equimolar mixture of AdCtP and 2 in
toluene for 12 h furnished the cyclic product 3, which was formed
in about 65% yield as red crystals (Scheme 2). Compound 3
crystallizes in the triclinic space group P1 with the asymmetric
unit containing two whole molecules.16 Only one of the nearly
identical molecules will be discussed. The molecular structure of 3
with relevant bond lengths and angles is shown in Figure 2. It is
the first example of a five-membered cyclic silene formed by four
different elements. The sum of the internal bond angles of 3 is
533°. The CNSi2P ring does not exhibit a slight envelope
conformation but is twisted. The P and Si2 atoms are removed
from the plane defined by CÀSi1ÀN by more than 0.3 Å, each
arranged at opposite sides of the plane. The ring can be
considered as a heavy cyclopentene derivative consisting of two
Si atoms, and one each of C, N, and P atoms. Both of the silicon
atoms display a distorted tetrahedral coordination geometry and
almost 78% yield (Scheme 1). Compound 2 is the second
example of a system stable at room temperature that contains a
Si(II)ÀN bond. 2 is isolated as a colorless crystalline solid with
good solubility in diethyl ether, toluene, and THF. 2 exhibits a
high stability up to 154 °C and can be handled in open air for a
short period of time without any appreciable decomposition.
This remarkable stability is presumably due to the presence of
two helmet-like trimethylsilyl groups which shield the Si(II)
center.
The 1H NMR spectrum of 2 displays two sets of resonances
(δ = 0.44 and 0.63 ppm) for the two SiMe3 groups. A sharp
resonance is exhibited at δ = 1.23 ppm for 18 tBu protons, which
are shifted downfield relative to those in LSiCl (δ = 1.08 ppm).3c
The 29Si NMR spectrum of 2 displays three resonances
(δ = À8.07, 2.81, and 3.71 ppm). The first corresponds to the
Si(II) center while the other two are assigned to the two SiMe3
groups. There is an upfield shift of the Si(II) atom in the 29Si
NMR spectrum when compared to that of LSiCl (δ = 14.6
ppm).3c This is apparently due to the donation of a lone pair of
electrons from the nitrogen atoms to the vacant p orbital of the
Si(II) atom so that the deshielding of the Si atom is reduced. In
the EI-mass spectrum, the molecular ion is observed as the most
abundant peak with highest relative intensity at m/z 419.
The molecular structure of 2 is shown in Figure 1 while the
important bond lengths and angles are provided in the legend
of Figure 1. 2 crystallizes in the triclinic space group P1.16 The
bis(trimethylsilyl)amino group is involved in disorder with
nearly equivalent site occupation factors (s.o.f.) and restrained
bond lengths and angles. For this reason, only values for one of
each the disordered moieties will be given. The coordination
geometry around the Si1 atom is trigonal pyramidal with the sum
of the bond angles around Si1 atom of 290°. The geometry is
consistent with the presence of a stereochemically active lone
pair of electrons at the Si(II) atom.3c,d The four-membered
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Journal of the American Chemical Society
ARTICLE
Scheme 3. Tentative Mechanism for the formation of 3
but, to our knowledge, there is no example of C(sp3)ÀSi bond
cleavage of trimethylsilyl group without catalytic support of a
transition metal at room temperature.
Although the mechanism of the reaction remains vague, we
propose that it is a concerted one (Scheme 3). The P atom
attacks the Si(IV) center of one of the SiMe3 groups and the lone
pair of electrons on Si(II) center attacks the electron deficient
carbon of phosphaalkyne. Consequently, there is an oxidative
addition under the migration of one Me group from Si(IV)
center to the adjacent P atom and simultaneous formation of a
SidC bond.
Figure 2. Molecular structure of 3 with the anisotropic displacement
parameters depicted at the 50% probability level. Hydrogen atoms and
NtBu methyl groups are not shown for clarity. Only one of the two nearly
identical molecules of the asymmetric unit is shown and discussed. Selected
bond lengths (Å) and angles (deg): Si1ÀN3 1.7292(13), Si1ÀC16
1.7536(13), N3ÀSi2 1.7801(12), C16ÀP1 1.8071(13), P1ÀSi2
2.2155(9); N3ÀSi1ÀC16 112.34(6), C16ÀP1ÀC17 107.87(7),
C16ÀP1ÀSi2 94.30(5), C17ÀP1ÀSi2 100.74(6), N3ÀSi2ÀC18
111.52(7), C18ÀSi2ÀC19 109.20(8), N3ÀSi2ÀP1 104.10(4),
C18ÀSi2ÀP1 108.36(6), C16ÀSi1ÀN1 120.83(6), Si(1)ÀC(16)À
P(1) 114.06(7), Si(1)ÀN(3)ÀSi(2) 108.05(6).
The spectroscopic data are in agreement with the structures of
3 deduced from single crystal X-ray diffraction studies. In the EI-
MS spectrum of 3, the molecular ion was observed at m/z 597.4
although with low intensity. However, the most abundant peak
was observed at m/z 582.3 which corresponds to [3-Me].
The 31P NMR spectrum of 3 shows a singlet with 29Si satellites
(δ = À116.7 ppm). The 29Si NMR spectrum of 3 displays three
resonances for three chemically different Si atoms. The most low-
field resonance at δ = 14 ppm corresponds to the silene Si (Si1).
A resonance at δ = À0.2 ppm corresponds to SiMe3 group.
Another resonance at δ = À21.8 ppm corresponds to Si2 which is
attached to P with a unusually low SiÀP coupling constant
the two SiÀN bond lengths are of 1.729(1) and 1.780(1) Å,
respectively. The Si 1ÀC 16 bond length (1.754(1) Å) is even
shorter than in Brook’s first disilene,20 (TMS)2SidC(OTMS)-2-
Ad (1.764 Å) and only slightly longer than in Scheschkewitz’s 1,2-
disilacyclobut-2-ene (1.7459(15) Å),19a suggesting a SiÀC dou-
ble bond in 3.21 The small increase in the SiÀC bond length
compared to that of Scheschkewitz’s cyclic disilene is due to the
formation of a five-membered ring instead of a four-membered
ring which resulted in ring strain reduction. This may be
attributed to the presence of π-donating N atom to Si1 which
reduces the polarity of the SidC double bond significantly,
thereby increasing the bond length. The sum of the bond angles
around C16 is 360°. This implies that the carbon atom contribut-
ing to the SiÀC double bond in 3 adopts an essentially planar
environment which is in sharp contrast to the strongly pyrami-
dalized Si atom of the SiÀC doubly bonded compounds.19 The
planar arrangement may be due to the presence of electronegative
substituentslike N andP at Si andC, respectively. Thepresence of
electronegative substituents reduces the gap between π and σ*,
thereby enabling stronger mixing of these two orbitals. The
geometry of the P atom can best be described as distorted trigonal
pyramidal with the sum of the bond angles of 303°. The SiÀP and
CÀP bond lengths are 2.2155(9) and 1.807(1) Å, respectively,
which matcheswith common values for single bonds.22 N3 adopts
a trigonal planar coordination geometry with the sum of bond
angles of 360°.
31
(1J(29SiÀ P) = 14.79 Hz).26
In summary, we have demonstrated a very convenient synth-
esis of N-substituted heteroleptic silylene and its reaction with
adamantyl phosphaalkyne which leads to the facile formation of
stable cyclic silene. Especially interesting is the facile SiÀMe
bond cleavage at room temperature without any transition metal
catalyst which was not observed before. Therefore, this reaction
raises a broad variety of possibilities, which are currently being
explored in our laboratory.
’ EXPERIMENTAL SECTION
All manipulations were carried out in an inert gas atmosphere of
dinitrogen using standard Schlenk techniques and in a dinitrogen filled
glovebox. The solvents used were purified by a MBRAUN solvent
purification system MB SPS-800. Compound 1 was prepared by
literature methods.5c All chemicals purchased from Aldrich were used
without further purification. 1H, 13C, 31P, and 29Si NMR spectra were
recorded in C6D6 using a Bruker Avance DPX 200 or a Bruker Avance
DRX 500 spectrometer. EI-mass spectra were obtained using a Finnigan
MAT 8230 instrument. Elemental analyses were performed by the
Institut f€ur Anorganische Chemie, Universit€at G€ottingen. Melting
points were measured in a sealed glass tube on a B€uchi B-540 melting
point apparatus.
Preparation of 2. Toluene (200 mL) was added to a mixture of 1
(3.31 g, 10.00 mmol) and potassium bis(trimethylsilyl)amide (3.99 g,
20.00 mmol) at ambient temperature. Immediately, the solution turned
to a red color with the formation of KCl. The resulting suspension was
stirred for 12 h. The solvent was then removed in vacuo, and the residue
The most intriguingfeature of the reaction isthe cleavage of one
of the SiÀC bonds of SiMe3 unit followed by a methyl group
migration to the phosphorus atom. Usually, the cleavage of the
C(sp3)ÀSi bonds requires extremely vigorous conditions,23 but
there are very few exceptions using a transition metal catalyst. For
example, a Pd catalyzed oxidative methylation of alkenes using
trimethylsilyl group as a methyl source has been reported.24
Following this, the catalytic cleavage of C(sp3)ÀSi bond in
25
trialkylsilyl groups has also been described using [RhCl(cod)]2
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Table 1. Crystallographic Data for the X-ray Structural Analyses of Compounds 2 and 3
2
3
Empirical formula
F. w.
C
21H41N3Si3
C32H56N3PSi3
598.04
419.84
Temperature (K)
CCDC no.
Wavelength (Å)
Crystal system
Space group
a (Å)
100(2)
101(2)
828727
828728
0.56086
triclinic
P1
0.71073
triclinic
P1
8.439(2)
12.866(2)
16.639(2)
17.090(3)
90.72(2)
108.43(3)
91.83(2)
3468.2(11)
4
b (Å)
10.943(2)
c (Å)
14.350(3)
R (deg)
95.67(2)
β (deg)
103.27(3)
γ (deg)
Volume (Å3)
93.68(2)
1278.3(5)
Z
2
Density (calculated) (Mg/m3)
1.091
1.146
Absorption coefficient (mmÀ1
)
0.196
0.113
F(000)
460
1304
Crystal size (mm3)
θ range for data collection (deg)
Index ranges
0.35 Â 0.30 Â 0.15
1.47 to 26.73
À10 e h e 10
À13 e k e 13
À18 e l e 18
41035
0.18 Â 0.10 Â 0.08
1.32 to 22.75
À17 e h e 17
À22 e k e 22
À23 e l e 23
119976
Reflections collected
Independent reflections
Completeness to
5420 [R(int) = 0.0182]
99.9%
19013 [R(int) = 0.0310]
99.8%
Absorption correction
Max. and min transmission
Refinement method
Semiempirical from equivalents
0.970 and 0.934
Full-matrix least-squares on F2
5420/325/332
1.028
Semiempirical from equivalents
0.930 and 0.864
Full-matrix least-squares on F2
19013/0/727
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
1.026
R1 = 0.0277, wR2 = 0.0739
R1 = 0.0291, wR2 = 0.0750
0.365 and À0.246
R1 = 0.0366, wR2 = 0.0937
R1 = 0.0471, wR2 = 0.0998
0.979 and À0.393
Largest diff. peak and hole (e.ÅÀ3
)
was extracted with toluene (100 mL). The filtrate was concentrated to
yield colorless crystals of 2 (3.30 g, 78.62%). Mp 154À158 °C. For the
elemental analysis, 2 was treated in vacuo overnight. Anal. calcd for 2,
C21H41N3Si3 (419.8): C, 60.08; H, 9.84; N, 10.01; found: C, 59.68; H,
MHz, C6D6, 25 °C): δ 2.5 (Si(CH3)2), 5.5 (SiMe3), 15.9 (P-CH3,
1J(31PÀ C) = 42.79 Hz), 30.7(CCH3), 31.8 (CCH3), 37.7, 38.1, 46.9,
13
47.1 (adamantyl), 54.8 (CCH3), 55.2 (CCH3), 126.9, 127.4, 128.5,
13
130.2, 131.9 (Ph), 127.7 (Si-C-P, 1J(31PÀ C) = 12.78 Hz), 175.2
1
9.55; N, 10.02; H NMR (300 MHz, C6D6, 25 °C): δ 0.44 (s, 9H,
(NCN) ppm; 31P NMR (121.5 MHz, C6D6, 25 °C): À116.7 ppm;
SiMe3), 0.63 (s, 9H, SiMe3), 1.23 (s, 18H, tBu), 6.86À6.96 (m, 5H, Ph)
ppm; 13C{1H} NMR (75.46 MHz, C6D6, 25 °C): δ 5.19 (SiMe3), 5.7
(SiMe3), 32.1 (CMe3), 57.7 (CMe3), 127.6, 127.7, 127.9, 128.1, 128.3,
129.2 (Ph), 156.8 (NCN) ppm; 29Si{1H} NMR (59.62 MHz, C6D6,
25 °C): δ À8.07 (SiN(SiMe3)2), 2.81 (SiMe3), 3.71(SiMe3) ppm. EI-
MS: m/z: 419 [M+] (100%).
29Si{1H}NMR (99.36 MHz, C6D6, 25 °C): δ À21.8 (Me2Si-P),
31
1J(29SiÀ P) = 14.79 Hz), À0.2 (SiMe3), 14 (SidC) ppm. EI-MS:
m/z: 597 [M+] (20%), 582 [M+-Me] (100%).
Crystal Structure Determination. Shock cooled crystals were
selected and mounted under nitrogen atmosphere using the X-TEMP.16
The data for 2 were collected at 100(2) K on an INCOATEC Mo
microfocus source27 with Quazar mirror optics and APEX II detector on
a D8 goniometer. An INCOATEC Ag microfocus source was used for
data collection of 3 employing an APEX II detector with Ag KR-
radiation enhanced fluorescent layer on a Bruker D8 goniometer. Both
diffractometers were equipped with a low-temperature device and used
Mo KR radiation, λ = 0.71073 Å and Ag KR radiation, λ = 0.56086 Å,
respectively. The data of 2 and 3 were integrated with SAINT28 and an
empirical absorption correction (SADABS) was applied.29 The struc-
tures were solved by direct methods (SHELXS-97) and refined by full-
matrix least-squares methods against F2 (SHELXL-97).30 All non-
Preparation of 3. Toluene (25 mL) was added to the mixture of 2
(0.42 g, 1.00 mmol) and adamantyl phosphaalkyne (0.18 g, 1.00 mmol)
at ambient temperature. The mixture was stirred for 12 h. The solvent
was removed under vacuum and the residue was treated with 20 mL
toluene. Storage of the filtrate at room temperature for 7 days afforded
red crystals of 3 (0.39 g, 65.3%). Mp 212À215 °C. Elemental analysis
(%) calcd for C32H56N3PSi3 (597.35): C, 64.27; H, 9.44; N, 7.03; found:
C, 64.66; H, 9.43; N, 7.06. 1H NMR (500 MHz, C6D6, 25 °C): δ 0.33 (s,
6H, SiMe2), 0.46 (s, 9H, SiMe3), 0.63 (s, 3H, P-Me), 1.16 (br, 18H, tBu),
1.38 (br, 10H, Ad), 6.8À7.1 (m, 5H, Ph) ppm; 13C{1H}NMR (75.46
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Journal of the American Chemical Society
ARTICLE
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 to
1.5 times the Ueq of their pivot atoms for terminal sp3 carbon atoms and
1.2 times for all other carbon atoms. In 2, the N(SiMe3)2 group is
disordered over two positions. It was refined using distance restraints
and displacement parameters restraints.
In 3, relatively high residual density stays in the final structure. It can
be modeled with a disorder of Si2 and P1 resembling the two possible
twisted conformers of the five-membered ring. Consequentially, the
hydrocarbon substituents are involved in the disorder as well. Even
though high quality data up to relatively high resolution (d = 0.725 Å)
were employed in the refinement, only the two heavy atoms can properly
be refined and no residual density peaks could directly be assigned to
substituents because of the very low site occupation factors of about 0.04
and 0.02, respectively, for both of the two molecules in the asymmetric
unit. Using strong constraints and restraints enabled refinement of a
model of the disordered methyl groups. It was decided not to include a
model of the disorder in the final refinement. Further details and a model
of the disorder can be found in the Supporting Information.
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Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge Crystal-
lographic Data Centre. The crystal data are listed in Table 1. Copies of
the data can be obtained free of charge from The Cambridge Crystal-
lographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
’ ASSOCIATED CONTENT
S
Supporting Information. CIF files for 2 and 3. Details
b
about the crystal structure refinement of 3 (PDF). This material
is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Authors
hroesky@gwdg.de; dstalke@chemie.uni-goettingen.de
(9) Khan, S.; Sen, S. S.; Kratzert, D.; Tavꢁcar, G.; Roesky, H. W.;
Stalke, D. Chem.—Eur. J. 2011, 17, 4283–4290.
(10) Sarish, S. P.; Jana, A.; Roesky, H. W.; Samuel, P. P.; Andrade,
C. E. A.; Dittrich, B.; Schulzke, C. Organometallics 2011, 30, 912–916.
(11) Khan, S.; Sen, S. S.; Michel, R.; Kratzert, D.; Roesky, H. W.;
Stalke, D. Organometallics 2011, 30, 2643–2645.
(12) Jana, A.; Leusser, D.; Objartel, I.; Roesky, H. W.; Stalke, D.
Dalton Trans. 2011, 40, 5458–5463.
(13) (a) Tavꢁcar, G.; Sen, S. S.; Azhakar, R.; Thron, A.; Roesky, H. W.
Inorg. Chem. 2010, 49, 10199–10202. (b) Azhakar, R.; Sarish, S. P.;
Roesky, H. W.; Hey, J.; Stalke, D. Inorg. Chem. 2011, 50, 5039–5043.
(14) (a) Tsutsui, S.; Sakamoto, K.; Kira, M. J. Am. Chem. Soc. 1998,
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’ ACKNOWLEDGMENT
We thank the Deutsche Forschungsgemeinschaft for support-
ing this work. D.S. is grateful for funding from the DFG Priority
Programme 1178, the DNRF funded Center for Materials
Crystallography (CMC) for support and the Land Niedersachsen
for providing J.H. with a fellowship in the Catalysis for Sustain-
able Synthesis (CaSuS) Ph.D. program. Dedicated to Professor
Karl Otto Christe on the occasion of his 75th birthday.
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