Stabilization of low valent silicon fluorides in the coordination sphere of transition metals

Article abstract of DOI:10.1021/ja210697p

Silicon(II) fluoride is unstable; therefore, isolation of the stable species is highly challenging and was not successful during the last 45 years. SiF₂ is generally generated in the gas phase at very high temperatures (～1100-1200 °C) and low pressures and readily disproportionates or polymerizes. We accomplished the syntheses of stable silicon(II) fluoride species by coordination of silicon(II) to transition metal carbonyls. Silicon(II) fluoride compounds L(F)Si·M(CO)₅ {M = Cr (4), Mo (5), W(6)} (L = PhC(NtBu)₂) were prepared by metathesis reaction from the corresponding chloride with Me₃SnF. However, the chloride derivatives L(Cl)Si·M(CO)₅ {M = Cr (1), Mo (2), W(3)} (L = PhC(NtBu)₂) were prepared by the treatment of transition metal carbonyls with L(Cl)Si. Direct fluorination of L(Cl)Si with Me₃SnF resulted in oxidative addition products. Compounds 4-6 are stable at ambient temperature under an inert atmosphere of nitrogen. Compounds 4-6 were characterized by NMR spectroscopy, EI-MS spectrometry, and elemental analysis. The molecular structures of 4 and 6 were unambiguously established by single-crystal X-ray diffraction. Compounds 4 and 6 are the first structurally characterized fluorides, after the discovery of SiF₂ about four and a half decades ago.

Full text of DOI:10.1021/ja210697p

Article
pubs.acs.org/JACS
Stabilization of Low Valent Silicon Fluorides in the Coordination
Sphere of Transition Metals
Ramachandran Azhakar, Rajendra S. Ghadwal,* Herbert W. Roesky,* Hilke Wolf, and Dietmar Stalke*
Institut fur Anorganische Chemie der Universitat Gottingen, Tammannstrasse 4, 37077 Gottingen, Germany
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: Silicon(II) fluoride is unstable; therefore, isolation of the stable species is highly
challenging and was not successful during the last 45 years. SiF2 is generally generated in the gas phase at
very high temperatures (∼1100−1200 °C) and low pressures and readily disproportionates or
polymerizes. We accomplished the syntheses of stable silicon(II) fluoride species by coordination of
silicon(II) to transition metal carbonyls. Silicon(II) fluoride compounds L(F)Si·M(CO)5 {M = Cr (4),
Mo (5), W(6)} (L = PhC(NtBu)2) were prepared by metathesis reaction from the corresponding
chloride with Me3SnF. However, the chloride derivatives L(Cl)Si·M(CO)5 {M = Cr (1), Mo (2),
W(3)} (L = PhC(NtBu)2) were prepared by the treatment of transition metal carbonyls with L(Cl)Si.
Direct fluorination of L(Cl)Si with Me3SnF resulted in oxidative addition products. Compounds 4−6 are stable at ambient
temperature under an inert atmosphere of nitrogen. Compounds 4−6 were characterized by NMR spectroscopy, EI-MS
spectrometry, and elemental analysis. The molecular structures of 4 and 6 were unambiguously established by single-crystal X-ray
diffraction. Compounds 4 and 6 are the first structurally characterized fluorides, after the discovery of SiF2 about four and a half
decades ago.
were not successful. However, we succeeded in the synthesis of
L(F)Si·BH3 and L(H)Si·BH3 in which each silylene base forms
an adduct with the Lewis acid BH3. L(F)Si·BH3 was only
characterized by NMR and mass spectrometry.13 Silylene has a
stereoactive lone pair of electrons, which acts as a σ-donor
ligand and forms complexes with transition metals by ligand
substitution reactions.14,15 We have reported the properties of
silylenes as σ-donor ligands for the synthesis of transition metal
complexes,15 as well as on its oxidative addition reactions with
organic substrates16 and Lewis bases.17 Stabilization of highly
reactive species in the coordination sphere of transition metals is
of current interest;18 however, no fluorosilylene coordinate with a
transition metal has been isolated so far. Herein, we report the
stable silicon(II) fluoride species {L(F)Si·M(CO)5, M = Cr (4),
Mo (5), W(6)} (L = PhC(NtBu)2), where 4 and 6 are the first
structurally characterized silicon(II) fluoride derivatives.
INTRODUCTION
■
Taming of highly reactive species to be isolable at normal
laboratory conditions is a challenging task in synthetic
chemistry.1 Carbenes and silylenes R2E: (where R = alkyl,
aryl, H, or halogen and E = C or Si) are highly reactive and play
a constantly growing important role in synthetic organic and
organosilicon chemistry as well as in material sciences.2−4
Stable analogues of carbenes and silylenes have been isolated as
N-heterocyclic carbenes (NHCs)5 and N-heterocyclic silylenes
(NHSis).6 The reactivity of NHSis is comparable with that of
the NHCs. The latter find many applications in chemistry.7,8
Gaseous dihalosilylenes X2Si: (X = F or Cl)9,10 have been
known for many years. However, they are not stable at room
temperature; they condense to polymeric (X2Si)x or dispro-
portionate to (SiX)x and perhalosilanes. The properties and
reactivity of gaseous X2Si: and polymeric (X2Si)x have been
studied, but no stable analogue of halosilylene was known.11 In
2006,6e we reported on a base-stabilized monochlorosilylene
L(Cl)Si (L = PhC(NtBu)2), and later developed a facile
method to access L(Cl)Si in almost quantitative yield using
LiN(SiMe3)2 as a reducing agent.6f Moreover, we isolated NHC
stabilized dichlorosilylene NHC·Cl2Si (NHC= 1,3-bis-(2,6-
diisopropylphenyl)imidazol-2-ylidene or 1,3-bis-(2,4,6-
trimethylphenyl)imidazol-2-ylidene) in high yield without
using hazardous reducing agents such as alkali metals or KC8.
NHC·Cl2Si was obtained by a new synthetic procedure com-
prising the reductive elimination of HCl from trichlorosilane in
the presence of NHC under mild reaction conditions.12 After
the report of the chloro-derivatives, we focused our atten-
tion on the synthesis of stable silicon(II) fluoride. Due to the
high propensity of fluorosilylene toward polymerization or dis-
proportionation, attempts to isolate fluoro-analogues of LSiF
RESULTS AND DISCUSSION
■
For the preparation of compounds 4−6 {L(F)Si·M(CO)5, M = Cr
(4), Mo (5), W(6)}, we assembled first the chloride derivatives
1−3 {L(Cl)Si·M(CO)5 {M = Cr (1), Mo (2), W(3)} and
treated these in 1:1 ratio with Me3SnF as a fluorinating agent.19
Compounds 1−3 {L(Cl)Si·M(CO)5, M = Cr (1), Mo (2),
W(3)} were obtained in good yield in one pot reactions of L(Cl)Si
with the respective M(CO)5(THF) in 1:1 ratio (Scheme 1). All
compounds are soluble in benzene, toluene, and THF and insoluble
in hexane and pentane. They are stable both in solution and solid
state for a long period of time without any decomposition under an
inert gas atmosphere. Compounds 1−3 were fully characterized by
Received: November 24, 2011
Published: December 19, 2011
© 2011 American Chemical Society
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Journal of the American Chemical Society
Article
Scheme 1. Synthesis of 1−6
Table 1. Crystal and Structure Refinement Parameters for Compounds 1, 2, 3, 4, and 6
parameter
1·toluene
2
3·toluene
4
6
empirical formula
fw
C27H31ClCrN2O5Si
579.08
C20H23ClMoN2O5Si
530.88
C27H31ClN2O5SiW
710.93
C20H23CrFN2O5Si
470.49
C20H23FN2O5SiW
602.34
cryst syst
monoclinic
orthorhombic
P212121
triclinic
monoclinic
triclinic
space group
P21/m
P1
̅
P21/n
P1
̅
unit cell
a = 9.896(3) Å
b = 13.060(5) Å
c = 11.577(4) Å
β = 98.60(2)°
a = 9.791(2) Å
b = 13.307(2) Å
c = 18.432(2) Å
a = 9.873(2) Å
b = 11.621(3) Å
c = 13.1260(10) Å
α = 94.910(10)°
β = 93.04(2)°
γ = 97.560(10)°
1484.4(5) Å3, 2
1.591 g/cm3
a = 10.538(2) Å
b = 18.0290(10) Å
c = 12.411(3) Å
β = 109.130(2)°
a = 9.203(3)Å
b = 10.2800(10) Å
c = 13.187(2) Å
α = 110.720(10)°
β = 99.33(2)°
γ = 91.24(4)°
dimensions
volume, Z
1479.4(9) Å3, 2
1.300 g/cm3
2401.5(7) Å3, 4
1.468 g/cm3
2.044 mm−1
1080
2227.7(7) Å3, 4
1.403 g/cm3
0.322 mm−1
976
1147.2(4) Å3, 2
1.744 g/cm3
density (calcd)
abs coeff
−1
−1
0.292 mm
2.187 mm−1
2.765 mm
F(000)
crystal size/mm3
604
704
588
0.30 × 0.21 × 0.13
1.40−20.28°
0.20 × 0.20 × 0.15
1.74−20.09°
0.18 × 0.16 × 0.10
1.23−20.81°
0.20 × 0.15 × 0.12
1.63−21.35°
0.20 × 0.20 × 0.15
1.32−20.91°
θ range for data
collection
limiting indices
−12 ≤ h ≤ 12; −16 ≤ k
≤ 14; −14 ≤ l ≤ 10
−11 ≤ h ≤ 11; −16 ≤
k ≤ 16; −22 ≤ l ≤ 22
−12 ≤h ≤ 12; −14 ≤ k
≤ 14; 0 ≤ l ≤ 16
−12 ≤ h ≤ 13; −23 ≤ k
≤ 23; −16 ≤ l ≤ 16
−11 ≤ h ≤ 11; −13 ≤ k
≤ 13; −16 ≤ l ≤ 16
reflns collected
indep reflns
13 702
17 349
62 539
36 069
68 180
3068 (Rint = 0.0229)
99.9% (θ = 20.28°)
4609 (Rint = 0.1123)
99.8% (θ = 20.09°)
6280 (Rint = 0.0303)
99.2% (θ = 20.81°)
5057 (Rint = 0.0285)
99.1% (θ = 21.35°)
4949 (Rint = 0.0419)
99.6% (θ = 20.91°
completeness to θ
refinement
method
full-matrix least-squares
full-matrix least-squares
full-matrix least-squares
full-matrix least-squares
full-matrix least-squares
on F2
on F2
on F2
on F2
on F2
data/restraints/
params
GOFon F2
3068/363/284
4609/0/278
6280/111/353
5057/0/277
4949/0/277
1.062
1.042
1.087
1.039
1.065
final R indices [I >
2σ (I)]
R1 = 0.0313,
wR2 = 0.0877
R1 = 0.0472,
wR2 = 0.1175
R1 = 0.0205,
wR2 = 0.0509
R1 = 0.0253,
wR2 = 0.0670
R1 = 0.0139,
wR2 = 0.0341
R indices (all data)
R1 = 0.0372,
wR2 = 0.0917
0.306 and −0.363 e Å−3
R1 = 0.0558,
wR2 = 0.1208
1.001 and −1.021 e Å−3
R1 = 0.0211,
wR2 = 0.0514
1.965 and −1.182 e Å−3
R1 = 0.0287,
wR2 = 0.0684
0.352 and −0.370 e Å−3
R1 = 0.0154,
wR2 = 0.0352
1.098 and −0.861 e Å−3
largest diff peak
and hole
NMR spectroscopy, EI-MS spectrometry, elemental analysis, and
single crystal X-ray structural analysis (Table 1).
from one silicon and five carbon atoms of the carbonyl groups.
The Si−M bond distances in 1−3 are 2.3458(7), 2.4550(14),
and 2.5086(11) Å. The average metal carbonyl bond lengths
are 1.884(2), 1.998(6), and 2.038(4) Å, respectively. The Si−
Cl bond length each in 1−3 is 2.1006(9), 2.1182(19), and
2.1012(14) Å [Si−Cl of L(Cl)Si, 2.156(1) Å]. The bite angle
(N−Si−N) for 1−3 is 71.62(8)°, 71.34(18)°, and 71.41(12)°,
respectively [N−Si−N of L(Cl)Si, 71.15(7)°].
Like 1−3, the respective fluorine derivatives 4−6 are soluble
in benzene, toluene, and THF and insoluble in hexane and
pentane. Furthermore, they are stable both in solution and the
solid state for a long period of time without any decomposition
provided they are stored in an inert gas atmosphere. Com-
pounds 4−6 were characterized by NMR spectroscopy, EI-MS
spectrometry, and elemental analysis. The molecular structures
of 4 and 6 were unequivocally established by single crystal
X-ray diffraction studies (Table 1).
The 1H and 13C NMR spectra of 1−3 show usual resonances
expected for the amidinate (L) and carbonyl groups. The 29Si
NMR spectra of 1−3 exhibit a single resonance each at δ 92.34,
72.75, and 52.99, which is shifted downfield when compared to
L(Cl)Si (δ 14.6).6e In compounds 1−3, the silicon atom is
deshielded upon coordination to the metal atom. The chemical
shifts are pertinent to the reported value of δ 62.69 for L(Cl)Si
Ni(CO)3.15d Moreover 1−3 show their molecular ions in their
mass spectra at m/z 486, 532, and 618, respectively.
The molecular structure of 1 is shown in Figure 1 (for 2 and
3, see Supporting Information). The selected bond parameters
for compounds 1−3 are given in Table 2. The silicon atom is
tetracoordinate and features distorted tetrahedral geometry
comprising two nitrogen atoms from the supporting amidinato
ligand, one chlorine atom, and one metal atom. The metal atom
is hexacoordinate with a distorted octahedral geometry derived
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Table 3. NMR and EI-MS Data for Compounds 4−6
[M+]/
amu
compound 29Si (δ/ppm), JSi−F /Hz 19F (δ / ppm), JSi−F / Hz
4
5
6
73.98, 440
56.65, 442
41.79, 428
−89.95, 440
−90.33, 442
−93.20, 428
470
516
602
The molecular structure of 4 is shown in Figure 2 (for 6, see
Supporting Information), and the selected bond parameters for
Figure 1. Molecular structure of 1. Anisotropic displacement
parameters are depicted at the 50% probability level.
Formation of the silicon(II) fluorides 4−6 was readily observed
in their related 19F NMR spectrum. Compounds 4−6 exhibit a
single 19F NMR resonance at δ −89.95, −90.33, and −93.20,
respectively. They show satellite signals due to the coupling to the
silicon atom with JSi−F of 440, 442, and 428 Hz (Table 3). The
29Si NMR spectra of 4−6 exhibit a doublet centered at δ 73.98
(JSi−F = 440 Hz), 56.65 (JSi−F = 442 Hz), and 41.79 (JSi−F = 428
Hz) each, which is shifted upfield compared to those of the
silicon(II) chlorides 1−3. It is interesting to set side by side the
above NMR data with those of LSiF319d {19F NMR, δ −132.38
(JSi−F = 219 Hz); 29Si NMR, δ −124.91 (JSi−F = 219 Hz)}. In
LSiF3 both the 19F and 29Si NMR resonances are shifted to higher
field as expected when compared with those of 4−6. The reason
might be due to the higher coordinate silicon in LSiF3 which is
unmatched to those of 4−6. The EI-MS spectra of compounds
4−6 exhibit their molecular ions at m/z 470, 516, and 602,
respectively. In 4−6 the silicon atom is tetracoordinate with a
distorted tetrahedral geometry comprising two nitrogen atoms
from the amidinate ligand, one fluorine atom, and one metal
atom. The metal atom each in 4, 5, and 6 features distorted
octahedral geometry derived from one silicon atom and five
carbon atoms of the carbonyl groups.
Figure 2. Molecular structure of 4. Hydrogen atoms are omitted for
clarity. Anisotropic displacement parameters are depicted at the 50%
probability level.
compounds 4 and 6 are given in Table 2. There is a small
variation in the Si−M bond distances in 4 and 6 after the
replacement of the chlorine by the fluorine atom. The average
metal carbonyl bond lengths in 4 and 6 are 1.8893(14) and
2.039(2) Å, respectively. These values are quite comparable to
the chloro analogues of 1 and 3. The Si−F bond lengths in
4 and 6 are 1.6168(8) and 1.6245(14) Å and are close to those
found in LSiF3.19d The bite angle (N−Si−N) for 4 and 6 is
71.62(5)° and 70.93(8)°. A comparison of gaseous SiF2 with its
Table 2. Selected Bond Parameters for Compounds 1−4 and 6
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Article
Si−F bond length of 1.59 Å20 indicates an increase in the bond
length of only 0.03 Å. In contrast to that are the physical
properties. SiF2 is a gas at 25 °C and has a half-life of 150 s at
<1 mmHg,10a whereas the complexes 4−6 can be stored at
room temperature in an inert atmosphere for a long period of
time without decomposition.
Compound 3. Quantity used: W(CO)6, 1.00 g (2.84 mmol),
L(Cl)Si, 0.84 g (2.85 mmol); yield (1.50 g, 85.2%). Mp 142−145 °C
(d). Elemental analysis (%) calcd for C20H23ClN2O5SiW (618.79): C,
1
38.82; H, 3.75; N, 4.53. Found: C, 38.72; H, 3.72; N, 4.51. H NMR
(500 MHz, C6D6, 25 °C): δ 1.09 (s, 18H, C(CH3)3), 6.81−6.93 (m,
5H, C6H5) ppm. 13C{1H} NMR (125.75 MHz, C6D6, 25 °C): δ 30.71
C(CH3)3, 54.98 (C(CH3)3), 128.29, 128.40, 128.47, 129.53, 130.05,
130.88 (C6H5), 174.47 (NCN), 199.06 (CO), 200.07 (CO) ppm.
29Si{1H} NMR (99.36 MHz, C6D6, 25 °C): δ 52.99 ppm. EI-MS: m/z:
CONCLUSION
■
618 [M+], 590 [M+ − CO], 562 [M+ − 2CO], 534 [M+ − 3CO], 506
Four and a half decades ago, Margrave, Timms, and co-workers
generated the silicon(II) fluoride in the gas phase at high
temperatures (∼1100−1200 °C) and low pressures. They published
their results in this journal. However, SiF2 is unstable and
readily disproportionates or polymerizes. Herein, we report on
the first structurally characterized stable silicon(II) fluoride com-
pounds that have been accomplished by utilizing the coordina-
tion sphere of transition metals. The compound L(F)Si·M(CO)5
{M = Cr (4), Mo (5), W(6)} (L = PhC(NtBu)2) contains the
fluorosilylene moiety LSiF which coordinates to a transition
metal carbonyl M(CO)5 fragment. These compounds were
prepared for the first time by metathesis reaction from the
corresponding chloride with Me3SnF. This approach marked a
route to an easy access of low valent silicon fluorides.
[M+ − 4CO], 478 [M+ − 5CO].
General Procedure for the Synthesis of L(F)Si·M(CO)5 {M =
Cr (4), Mo (5), W(6)}. THF (60 mL) was added to a 100 mL Schlenk
flask containing corresponding L(Cl)Si·M(CO)5 and Me3SnF. The
reaction mixture was stirred at room temperature for 36 h. After the com-
pletion of reaction, the solvent was removed in vacuo and the remaining
substrate extracted with toluene (60 mL) to yield L(F)Si·M(CO)5.
Compound 4. Quantity used: L(Cl)Si·Cr(CO)5, 0.30 g (0.62
mmol), Me3SnF, 0.12 g (0.66 mmol); yield (0.24 g, 82.7%). Mp 107−
110 °C (d). Elemental analysis (%) calcd for C20H23FCrN2O5Si
(470.49): C, 51.06; H, 4.93; N, 5.95. Found: C, 50.96; H, 4.88; N,
1
5.86. H NMR (300 MHz, C6D6, 25 °C): δ 1.05 (s, 18H, C(CH3)3),
6.82−6.91 (m, 5H, C6H5) ppm. 13C{1H} NMR (125.75 MHz, C6D6,
25 °C): δ 30.91 C(CH3)3, 54.39 (C(CH3)3), 127.85, 128.20, 128.50,
128.62, 129.64, 130.75 (C6H5), 175.51 (NCN), 211.51 (CO), 220.34
(CO), 222.92 (CO) ppm. 29Si{1H} NMR (59.63 MHz, C6D6, 25 °C):
δ 73.98 (d) ppm (JSiF = 440 Hz). 19F{1H} NMR (282.40 MHz, C6D6,
25 °C): δ −89.95 ppm (JFSi = 440 Hz). EI-MS: m/z: 470 [M+], 442
[M+ − CO], 414 [M+ − 2CO], 386 [M+ − 3CO], 358 [M+ − 4CO],
330 [M+ − 5CO].
EXPERIMENTAL SECTION
■
Syntheses were carried out under an inert gas atmosphere of
dinitrogen in oven-dried glassware using standard Schlenk techniques,
and other manipulations were accomplished in a dinitrogen filled
glovebox. Solvents were purified by MBRAUN solvent purification
system MB SPS-800. All chemicals were purchased from Aldrich and
used without further purification. L(Cl)Si was prepared as reported in
the literature.6e,f 1H, 13C, 19F, and 29Si NMR spectra were recorded
with a Bruker Avance DPX 300, or a Bruker Avance DRX 500 spectro-
meter, using C6D6 as solvent. Chemical shifts δ are given relative to
SiMe4. EI-MS spectra were obtained using a Finnigan MAT 8230
Compound 5. Quantity used: L(Cl)Si·Mo(CO)5, 0.35 g (0.66
mmol), Me3SnF, 0.12 g (0. 66 mmol); yield (0.26 g, 76.5%). Mp 100−
103 °C (d). Elemental analysis (%) calcd for C20H23FMoN2O5Si
(514.43): C, 46.70; H, 4.51; N, 5.45. Found: C, 46.66; H, 4.42; N,
1
5.38. H NMR (300 MHz, C6D6, 25 °C): δ 1.06 (s, 18H, C(CH3)3),
6.80−6.93 (m, 5H, C6H5) ppm. 13C{1H} NMR (125.75 MHz, C6D6,
25 °C): δ 30.87 C(CH3)3, 54.16 (C(CH3)3), 127.90, 128.20, 128.53,
128.70, 130.22, 130.65 (C6H5), 174.59 (NCN), 208.66 (CO), 209.13
(CO) ppm. 29Si{1H} NMR (99.36 MHz, C6D6, 25 °C): δ 56.65 (d) ppm
(JSiF = 442 Hz). 19F{1H} NMR (282.40 MHz, C6D6, 25 °C): δ −90.33
ppm (JFSi = 442 Hz). EI-MS: m/z: 516 [M+], 488 [M+ − CO], 460
[M+ − 2CO], 432 [M+ − 3CO], 404 [M+ − 4CO], 376 [M+ − 5CO].
Compound 6. Quantity used: L(Cl)Si·W(CO)5, 0.49 g (0.79
mmol), Me3SnF, 0.15 g (0.82 mmol); yield (0.42 g, 87.5%). Mp 110−
113 °C (d). Elemental analysis (%) calcd for C20H23FN2O5SiW
(602.33): C, 39.88; H, 3.85; N, 4.65. Found: C, 39.83; H, 3.81; N,
instrument. Elemental analyses were performed by the Institut fur
̈
Anorganische Chemie, Universitat Gottingen. Melting points were
̈
̈
measured in sealed glass capillaries on a Buchi B-540 melting point
̈
apparatus.
General Procedure for the Synthesis of LSi(Cl)·M(CO)5 {M =
Cr (1), Mo (2), W(3)}. The respective M(CO)5(THF) complex was
prepared by UV irradiation of the corresponding M(CO)6 in THF as
described in the literature.21 The prepared M(CO)5(THF) solution
was added to the flask containing L(Cl)Si. The mixture was stirred for
14 h at room temperature. Finally the solvent was removed in vacuo and
extracted with toluene to obtain the corresponding L(Cl)Si·M(CO)5.
Compound 1. Quantity used: Cr(CO)6, 1.00 g (4.54 mmol),
L(Cl)Si, 1.34 g (4.54 mmol); yield (2.02 g, 91.4%). Mp 147−150 °C
(d). Elemental analysis (%) calcd for C20H23ClCrN2O5Si (486.94): C,
1
4.62. H NMR (500 MHz, C6D6, 25 °C): δ 1.07 (s, 18H, C(CH3)3),
6.80−6.91 (m, 5H, C6H5) ppm. 13C{1H} NMR (125.75 MHz, C6D6,
25 °C): δ 30.86 C(CH3)3, 54.19 (C(CH3)3), 127.81, 128.30, 128.62,
128.64, 130.17, 130.75 (C6H5), 175.53 (NCN), 199.18 (CO), 200.48
(CO) ppm. 29Si{1H} NMR (59.63 MHz, C6D6, 25 °C): δ 41.79 (d) ppm
(JSiF = 428 Hz). 19F{1H} NMR (282.40 MHz, C6D6, 25 °C): δ −93.20
ppm (JFSi = 428 Hz). EI-MS: m/z: 602 [M+], 574 [M+ − CO], 546
[M+ − 2CO], 518 [M+ − 3CO], 490 [M+ − 4CO], 462 [M+ − 5CO].
Crystal Structure Determination. Suitable single crystals for
X-ray structural analysis of 1−4 and 6 were obtained by slow evaporation
of their corresponding toluene solutions, and the crystals were
mounted at low temperature in inert oil under argon atmosphere by
applying the X-Temp2 device.22 The diffraction data were collected at
100 K on a Bruker D8 three circle diffractometer equipped with a
SMART APEX II CCD detector and an INCOATEC Ag microsource
with INCOATEC Quazar mirror optics (λ = 0.5608 Å). The data were
integrated with SAINT,23 and an empirical absorption correction with
SADABS24 was applied. The structures were solved by direct methods
(SHELXS-97) and refined against all data by full-matrix least-squares
methods on F2 (SHELXL-97).25 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 1.5Ueq of their pivot atoms for terminal
sp3 carbon atoms and 1.2 times for all other carbon atoms.
1
49.33; H, 4.76; N, 5.75. Found: C, 49.22; H, 4.62; N, 5.78. H NMR
(500 MHz, C6D6, 25 °C): δ 1.09 (s, 18H, C(CH3)3), 6.79−6.93 (m,
5H, C6H5) ppm. 13C{1H} NMR (125.75 MHz, C6D6, 25 °C): δ 30.52
C(CH3)3, 55.15 (C(CH3)3), 127.91, 128.19, 128.29, 128.35, 129.68,
130.77 (C6H5), 174.22 (NCN), 217.61 (CO), 219.76 (CO), 222.95
(CO) ppm. 29Si{1H} NMR (99.36 MHz, C6D6, 25 °C): δ 92.34 ppm.
EI-MS: m/z: 486 [M+], 458 [M+ − CO], 430 [M+ − 2CO], 402 [M+ −
3CO], 374 [M+ − 4CO], 346 [M+ − 5CO].
Compound 2. Quantity used: Mo(CO)6, 1.00 g (3.79 mmol),
L(Cl)Si, 1.12 (3.80 mmol); yield (1.70 g, 84.2%). Mp 140−143 °C
(d). Elemental analysis (%) calcd for C20H23ClMoN2O5Si (530.89): C,
1
45.25; H, 4.37; N, 5.28. Found: C, 45.16; H, 4.32; N, 5.12. H NMR
(500 MHz, C6D6, 25 °C): δ 1.09 (s, 18H, C(CH3)3), 6.79−6.94 (m,
5H, C6H5) ppm. 13C{1H} NMR (125.75 MHz, C6D6, 25 °C): δ 30.72
C(CH3)3, 54.94 (C(CH3)3), 127.91, 128.25, 128.40, 128.56, 130.16,
130.77 (C6H5), 173.48 (NCN), 208.65 (CO), 210.50 (CO) ppm.
29Si{1H} NMR (99.36 MHz, C6D6, 25 °C): δ 72.75 ppm. EI-MS: m/z:
532 [M+], 504 [M+ − CO], 476 [M+ − 2CO], 448 [M+ − 3CO], 420
[M+ − 4CO], 392 [M+ −5CO].
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Journal of the American Chemical Society
Article
Wright, J.; Zafar, M. N. Inorg. Chem. 2011, 50, 10522−10524. (i) Hess,
J. L.; Hsieh, C.-H.; Reibenspies, J. H.; Darensbourg, M. Y. Inorg. Chem.
2011, 50, 8541−8552. (j) Phillips, E. M.; Riedrich, M.; Scheidt, K. A.
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C. H. Inorg. Chem. 2010, 49, 4665−4669. (l) Jana, A.; Azhakar, R.;
ASSOCIATED CONTENT
* Supporting Information
Molecular structures of 2, 3, and 6. CIF files for 1, 2, 3, 4, and 6.
This material is available free of charge via the Internet at
http://pubs.acs.org.
■
S
̌
Tavcar, G.; Roesky, H. W.; Objartel, I.; Stalke, D. Eur. J. Inorg. Chem.
2011, 3686−3689. (m) Kronig, S.; Theuergarten, E.; Holschumacher,
D.; Bannenberg, T.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Inorg.
Chem. 2011, 50, 7344−7359.
AUTHOR INFORMATION
Corresponding Author
hroesky@gwdg.de, rghadwal@uni-goettingen.de; dstalke@
chemie.uni-goettingen.de
■
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ACKNOWLEDGMENTS
■
Dedicated to Professor Rudolf Hoppe on the occasion of his
90th birthday. We are thankful to the Deutsche Forschungsge-
meinschaft and Prohama, Ludwigshafen, for supporting this
work. R.A. is thankful to the Alexander von Humboldt Stiftung
for a research fellowship. D.S. and H.W. are grateful to the
DNRF funded Center for Materials Crystallography (CMC) for
support, and the Land Niedersachsen for providing a fellowship
in the Catalysis of Sustainable Synthesis (CaSuS) Ph.D. program.
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