Reactions of stable N -heterocyclic silylenes with ketones and 3,5-Di-tert -butyl-o-benzoquinone

Article abstract of DOI:10.1021/om200388a

The reactions of L [PhC(NtBu)₂SiCl] and L [CH{(C=CH ₂)(CMe)(2,6-iPr₂C₆H₃N) ₂}Si] with monoketones and quinone have been examined. The reaction of L with 2-adamantanone furnishes a [1 + 2]-c

Full text of DOI:10.1021/om200388a

ARTICLE
pubs.acs.org/Organometallics
Reactions of Stable N-Heterocyclic Silylenes with Ketones
and 3,5-Di-tert-butyl-o-benzoquinone
Ramachandran Azhakar, Rajendra S. Ghadwal, Herbert W. Roesky,* Jakob Hey, and Dietmar Stalke*
Institut f€ur Anorganische Chemie der Universit€at G€ottingen, Tammannstrasse 4, 37077 G€ottingen, Germany
S Supporting Information
b
ABSTRACT: The reactions of L [PhC(NtBu)2SiCl] and L0 [CH{(Cd
CH2)(CMe)(2,6-iPr2C6H3N)2}Si] with monoketones and quinone have been
examined. The reaction of L with 2-adamantanone furnishes a [1 + 2]ꢀ
cycloaddition product 1, whereas with 3,5-di-tert-butyl-o-benzoquinone leads
to the [1 + 4]ꢀcycloaddition product 2. The treatment of L0 with 3,5-di-tert-
butyl-o-benzoquinone gives [1 + 4]ꢀcycloaddition product 3, and the reaction
with acylferrocene yields compound 4. Compounds 1ꢀ4 were characterized
by single crystal X-ray structural analysis, NMR spectroscopy, EIꢀMS spectro-
metry, and elemental analysis.
’ INTRODUCTION
in 1:1 ratio as shown in Scheme 1, whereas compounds 3and 4were
formed upon reaction of L0 with 3,5-di-tert-butyl-o-benzoquinone
and acylferrocene in 1:1 ratio (Scheme 2). Compounds 1ꢀ4 were
unequivocally established by single crystal X-ray structural analyses.
Furthermore, all structures were fully characterized by NMR
spectroscopy, EIꢀMS, and elemental analysis.
Silylenes are silicon analogues of carbenes and exist with
neutral divalent silicon atoms.1 The first stable N-heterocyclic
silylene (NHSi) was reported by West et al.,2 in 1994. Since then,
many stable NHSis1bꢀd,3 and other silylenes have been isolated.4
The reactivity pattern of NHSis is quite comparable with that of the
N-heterocyclic carbenes (NHCs), where the latter led to many
applications in chemistry.5,6 Silylenes have two nonbonding elec-
trons in the HOMO which possess nucleophilic character, and an
empty 3p-orbital as the LUMO which causes electrophilic proper-
ties. They possess both nucleophilic and electrophilic reactive sites at
the same silicon atom, therefore they are ambiphilic and behave as
Lewis acids as well as Lewis bases.7 Owing to this, there is an
extensive research activity going on in the chemistry of NHSis,
which is very challenging (insertion: CꢀH,8 NꢀH,9 OꢀH,10
SꢀH,9a PꢀP,11 NꢀSi,12 CꢀF,13 CꢀX (Cl, Br, I),14 SiꢀCl,14
PꢀH,15 AsꢀH,15 addition,8a,9c,9d,16 metal complexes,17 Lewis
acids18). In addition, the reactions of silylenes with organic sub-
strates lead to a number of interesting new organosilicon com-
pounds, which are otherwise difficult to achieve.1e,f Recently, we
became interested in the reactivity studies of silylenes L
[PhC(NtBu)2SiCl] and L0 [CH{(CdCH2)(CMe)(2,6-iPr2C6H3-
N)2}Si] toward organic substrates.3b,9bꢀ9d,13,19 Inspired by the
diverse reactivity shown by silylenes with ketones,8a,9d,16a,19a,19d we
report herein the reactions of silylenes L and L0 with 2-adamanta-
none, 3,5-di-tert-butyl-o-benzoquinone, and acylferrocene. The re-
action of L with 2-adamantanone favors a [1 + 2]ꢀcycloaddition
product 1, whereas with 3,5-di-tert-butyl-o-benzoquinone leads to
[1 + 4]ꢀcycloaddition product 2. Treatment of L0 with 3,5-di-tert-
butyl-o-benzoquinone affords the [1 + 4]ꢀcycloaddition product 3,
and the reaction with acylferrocene gives compound 4.
The reaction of L with an equimolar amount of 2-adamanta-
none resulted in silaoxirane 1. Compound 1 is soluble in toluene
and benzene and insoluble in n-hexane and n-pentane. It is stable
both in the solid state as well as in solution without any
decomposition under an inert gas atmosphere. The 29Si NMR
spectrum of 1 shows a single resonance at δ ꢀ104.80 ppm, which
is upfield shifted when compared with that of L (δ 14.6 ppm).3a
1
The tBu protons of compound 1 in the H NMR spectrum
exhibit a singlet which is observed at δ 1.16 ppm and is downfield
shifted compared to that of L (δ 1.08 ppm). In addition, 1 shows
its molecular ion in the mass spectrum at m/z 444.
The silaoxirane product 1 was unambiguously established by
single crystal X-ray structural analysis. 1 crystallizes in the triclinic
space group P21/c, and the molecular structure is shown in
Figure 1. We propose that the reaction of L with 2-adamantanone
followed the [1 + 2]ꢀcycloaddition reaction. The silicon atom is
in a distorted square pyramidal geometry, made up from two
nitrogen atoms, a single oxygen atom, a carbon atom, and a
chlorine atom. The structural index τ which defines the extent of
deviation from trigonal bipyramidal to square pyramidal geome-
try (τ = 1 for perfect trigonal bipyramidal; τ = 0 for perfect square
based pyramid20) is 0.14, indicating strong deviation from the
regular TBP geometry and closer to square pyramidal geometry.
Such a silicon atom with almost distorted square pyramidal
geometry is rare.21 There is little change in the NꢀSiꢀN bite
angle at the silicon atom with the backbone ligand. In 1 it is
’ RESULTS AND DISCUSSION
Compounds 1 and 2 were obtained in good yield when L was
treated with 2-adamantanone and 3,5-di-tert-butyl-o-benzoquinone
Received: May 10, 2011
Published: June 23, 2011
r
2011 American Chemical Society
3853
dx.doi.org/10.1021/om200388a Organometallics 2011, 30, 3853–3858
|

Organometallics
ARTICLE
Scheme 1. Synthesis of 1 and 2
Figure 1. Molecular structure of 1. The anisotropic displacement
parameters are depicted at the 50% probability level. Hydrogen atoms
are omitted for clarity. Selected bond lengths (Å) and angles (deg):
Si(1)ꢀN(1) 1.8997(13), Si(1)ꢀN(2) 1.8176(13), Si(1)ꢀO(1)
1.6462(11), Si(1)ꢀCl(1) 2.0930(5), Si(1)ꢀC(16) 1.8461(15), O(1)ꢀC-
(16) 1.5485(17), C(1)ꢀN(1) 1.3188(18), C(1)ꢀN(2) 1.3559(18), O-
(1)ꢀSi(1)ꢀN(2) 131.79(6), O(1)ꢀSi(1)ꢀC(16) 52.26(6), N(2)ꢀ
Si(1)ꢀC(16) 114.56(6), O(1)ꢀSi(1)ꢀN(1) 98.50(6), N(2)ꢀSi(1)ꢀN-
(1) 70.48(5), C(16)ꢀSi(1)ꢀN(1) 146.59(6), O(1)ꢀSi(1)ꢀCl(1)
117.33(4), N(2)ꢀSi(1)ꢀCl(1) 110.73(5), C(16)ꢀSi(1)ꢀCl(1) 109.40-
(5), N(1)ꢀSi(1)ꢀCl(1) 98.08(4), C(16)ꢀO(1)ꢀSi(1) 70.52(7), O-
(1)ꢀC(16)ꢀSi(1) 57.22(6).
Scheme 2. Synthesis of 3 and 4
is depicted in Figure 2. The right absolute structure is confirmed
by the refinement of the Flack-x-parameter to 0.03(5).22 Com-
pared to 1, the silicon atom is also pentacoordinate, made up of
two nitrogen atoms, two oxygen atoms, and a chlorine atom. The
coordination polyhedron of the central silicon atom is located
halfway between that of a trigonal bipyramid and a square
pyramid with τ = 0.50. Like in 1, there is a small variation of
the NꢀSiꢀN bite angle (70.00(7)°) at the silicon atom with the
backbone ligand. The SiꢀCl bond length is 2.0858(8) Å, and the
distances of Si(1)ꢀO(1) and Si(1)ꢀO(2) are 1.7204(14) Å and
1.6906(14) Å, respectively.
However, the reaction of 3,5-di-tert-butyl-o-benzoquinone with
L0 afforded the [1 + 4]ꢀcycloaddition product 3. It is soluble in n-
hexane, n-pentane, toluene, and benzene. In addition, it is stable
both in the solid state as well as in solution. The 29Si NMR spectrum
of 3 shows a single resonance (δ ꢀ49.36 ppm), which is shifted
upfield compared to that of L0 (δ 88.4 ppm).3c The γꢀCH proton
for compound 3 in the 1H NMR spectrum is observed at δ 5.38
ppm and is upfield shifted when compared with that of L0 (δ 5.44
ppm). The NCCH2 protons in 3 exhibit sharp singlets at 3.42 and
4.02 ppm (δ for L0 = 3.32 and 3.91 ppm). Compound 3 shows its
molecular ion in the mass spectrum at m/z 664.4.
Compound 3 crystallizes in the triclinic space group P1, and
the structure is shown in Figure 3. In 3, the silicon atom is
tetracoordinate in a distorted tetrahedral geometry comprising
two nitrogen atoms (from the supporting ligand) and two oxygen
atoms. The silicon atom is dislocated from N2C3 ligand plane by
0.304(2) Å. There is a shortening of bonds observed between the
Si atom and the nitrogen atoms of the supporting ligand. The
average bond distance between SiꢀNav in 3 is 1.6992(18) Å,
whereas in L0 it is 1.7345(10) Å. The bite angle (NꢀSiꢀN) at
the silicon atom with the backbone ligand is 106.06(8)°,
compared to 99.317(54)° in L0. The bond lengths Si1ꢀO1
(1.6647(15) Å) and Si1ꢀO2 (1.6607(15) Å) are indicating
single bonds.23 The newly formed SiC2O2 five-membered ring
is nearly orthogonal arranged to the SiN2C3 six-membered ring.
The dihedral angle between the two planes is 85.68(5)°.
The reaction of L0 with an equimolar amount of acylferrocene in
n-hexane at room temperature proceeds rapidly with the formation
70.48(5)°, whereas in L it is 71.15(7)°. There is shortening of the
SiꢀCl bond length (2.0930(5) Å) in 1 when compared to that of
L [SiꢀCl of L 2.156(1) Å]. The angles of the newly formed OSiC
three-membered ring are OꢀSiꢀC (52.26(6)°), SiꢀCꢀO
(57.22(6)°), andCꢀOꢀSi(70.52(7)°). Correspondingly, the bond
distances within the three-membered ring are SiꢀO (1.6462(11) Å),
OꢀC (1.5485(17) Å), and SiꢀC (1.8461(15) Å). These values
are quite comparable to those of other silaoxirane compounds
reported in the literature.16a,19a
Treatment of L with 3,5-di-tert-butyl-o-benzoquinone af-
forded the [1 + 4]ꢀcycloaddition product 2. Compound 2 is
soluble in all common organic solvents. Similar to 1, it is stable
both in the solid state as well as in solution under an inert gas
atmosphere. Like 1, the 29Si NMR spectrum of 2 is upfield shifted
with a single resonance at δ ꢀ94.58 ppm. The tBu protons for
compound 2 in the 1H NMR spectrum show a single resonance
at δ 1.24 ppm. In addition, the tBu protons of the 3,5-di-tert-
butyl-o-benzoquinone exhibit resonances at 1.34 and 1.69 ppm.
Compound 2 shows its molecular ion in the mass spectrum at
m/z 514.
The [1 + 4]ꢀcycloaddition product 2 was confirmed by single
crystal X-ray structural analysis. Compound 2 crystallizes in the
orthorhombic space group P212121, and the molecular structure
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Organometallics
ARTICLE
Figure 2. Molecular structure of 2. The anisotropic displacement
parameters are depicted at the 50% probability level. Hydrogen atoms
are omitted for clarity. Selected bond lengths (Å) and angles (deg):
Si(1)ꢀN(2) 1.9060(18), Si(1)ꢀN(1) 1.8164(18), Si(1)ꢀO(1)
1.7204(14), Si(1)ꢀCl(1) 2.0858(8), Si(1)ꢀO(2) 1.6906(14), O(1)ꢀC-
(16) 1.378(2), C(1)ꢀN(1) 1.362(3), C(1)ꢀN(2) 1.3606(3), O(2)ꢀC-
(17) 1.375(2), C(16)ꢀC(17) 1.389(3), O(2)ꢀSi(1)ꢀO(1) 90.59(7),
O(2)ꢀSi(1)ꢀN(1) 131.49(8), O(1)ꢀSi(1)ꢀ N(1) 99.30(7), O(2)ꢀSi-
(1)ꢀN(2) 88.38(7), O(1)ꢀSi(1)ꢀN(2) 164.15(7), N(1)ꢀSi(1)ꢀN(2)
70.00(7), O(2)ꢀSi(1)ꢀCl(1) 116.01(6), O(1)ꢀSi(1)ꢀCl(1) 98.05(5),
N(1)ꢀSi(1)ꢀCl(1) 109.43(6), N(2)ꢀSi(1)ꢀCl(1) 96.61(6).
Figure 4. Molecular structure of 4. The anisotropic displacement
parameters are depicted at the 50% probability level. Hydrogen atoms
are omitted for clarity except over silicon atom. Selected bond lengths
(Å) and angles (deg): N(1)ꢀSi(1) 1.7192(15), N(2)ꢀSi(1) 1.7215-
(15), O(1)ꢀSi(1) 1.6446(12), Si(1)ꢀH(1) 1.457(19), C(30)ꢀO(1)
1.383(2), C(30)ꢀC(32) 1.476(3), C(30)ꢀC(31) 1.322(3), C(1)ꢀC-
(4) 1.476(3), C(3)ꢀC(5) 1.375(3), O(1)ꢀ Si(1)ꢀN(1) 108.56(7),
O(1)ꢀSi(1)ꢀN(2) 112.37(7), N(1)ꢀSi(1)ꢀN(2) 103.88(7), O-
(1)ꢀSi(1)ꢀH(1) 104.9(8), N(1)ꢀSi(1)ꢀH(1) 115.0(8), N(2)ꢀSi-
(1)ꢀH(1) 112.3(8), C(30)ꢀO(1)ꢀSi(1) 125.51(11), C(31)ꢀC(30)ꢀ
O(1) 121.72(17), O(1)ꢀC(30)ꢀC(32) 113.34(15).
3.72(1H), and 3.78(1H)). Moreover compound 4 exhibits its
molecular ion in the mass spectrum at m/z 672.
Compound 4 crystallizes in the triclinic space group C2c and
the molecular structure is shown in Figure 4. The silicon atom is
in a distorted tetrahedral geometry, made up from two nitrogen
atoms, one oxygen atom, and a hydrogen atom. The two nitrogen
atoms are derived from the chelating ligand. There is a little
deviation in the distance between the Si atom and the nitrogen
atoms of the supporting ligand. The average SiꢀNav bond
distance in 4 is 1.7204(15). The bite angle at the silicon atom
with the backbone ligand is 103.88(7)°. The Si1ꢀO1 bond
length is 1.6446(12) Å and C30ꢀO1 is 1.383(2) Å. The distance
C30ꢀC31 of 1.3222(3) Å indicates a CdC double bond. The
position of the silicon bound hydrogen atom was taken from the
difference Fourier map and refined freely to a SiꢀH distance of
1.457(19) Å, which is quite comparable with that of similar
reported compounds.24 The silicon atom is dislocated from the
N2C3 plane by 0.362(2) Å.
Figure 3. Molecular structure of 3. The anisotropic displacement para-
meters are depicted at the 50% probability level. Hydrogen atoms are omitted
for clarity. Selected bond lengths (Å) and angles (deg): N(1)ꢀSi(1)
1.6955(18), N(2)ꢀSi(1) 1.7028(17), O(1)ꢀSi(1) 1.6647(15), O(2)ꢀSi-
(1) 1.6607(15), C(35)ꢀO(2) 1.396(2), C(30)ꢀO(1) 1.385(2), C-
(30)ꢀC(35) 1.387(3), C(1)ꢀC(2) 1.477(3), C(4) ꢀ C(5) 1.364(3),
O(2)ꢀSi(1)ꢀO(1) 96.04(7), O(2)ꢀSi(1)ꢀN(1) 118.62(8), O(1)ꢀSi-
(1)ꢀN(1) 110.09(8), O(2)ꢀSi(1)ꢀN(2) 109.28(8), O(1)ꢀSi(1)ꢀN-
(2) 117.13(8), N(1)ꢀSi(1)ꢀN(2) 106.06(8), C(35)ꢀO(2)ꢀSi(1)
108.91(12), C(30)ꢀO(1)ꢀSi(1) 108.87(12), C(30)ꢀC(35)ꢀO(2)
112.51(17), O(1)ꢀC(30)ꢀC(35) 113.37(17).
’ CONCLUSION
of an orangeꢀred colored solution of compound 4. Like 3,
compound 4 is soluble in n-hexane, n-pentane, toluene, and
benzene. Furthermore, 4 is stable both in the solid state as well as
in solution for a long period of time without any decomposition
under an inert gas atmosphere. Similar to 3, the 29Si NMR spectrum
of 4 shows a single upfield resonance (δ ꢀ51.25 ppm). The γꢀCH
proton for compound 4 exhibits a single resonance, which is
We have shown the versatile reactivity of silylenes L and L0
toward monoketones and quinone. The reaction of L with
2-adamantanone and 3,5-di-tert-butyl-o-benzoquinone furnish a
[1 + 2]ꢀcycloaddition product 1 and [1 + 4]ꢀcycloaddition
product 2, respectively. Treatment of L0 with 3,5-di-tert-butyl-o-
benzoquinone and acylferrocene leads to [1 + 4]ꢀcycloaddition
product 3 and compound 4, respectively.
1
observed at δ 5.35 ppm in its H NMR spectrum. The SiꢀH
proton shows a single resonance (δ 5.28 ppm), which was
1
29
’ EXPERIMENTAL SECTION
confirmed by Hꢀ Si HSQC experiment. The CdCH2 unit of
4 results in two doublets (2.83 and 4.26 ppm) with J = 2 Hz. The
NCCH2 protons in 4 resonate at δ 3.45 and δ 4.02 ppm. The
unsubstituted cylcopentadienyl part of the ferrocenyl unit exhibits a
single resonance (δ 3.90 ppm), while the substituted part of the
ferrocenyl unit exhibits multiplets (δ 3.11 (1H), 3.54(1H),
All manipulations were carried out in an inert atmosphere of dinitro-
gen using standard Schlenk techniques and in a dinitrogen filled glove-
box. Solvents were purified by MBRAUN solvent purification system
MB SPS-800. All chemicals were purchased from Aldrich and used
without further purification. L was prepared as reported in literature.3c
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Organometallics
ARTICLE
Table 1. Crystal and Structure Refinement Parameters for Compounds 1, 2, 3, and 4
parameters
1
2
3 0.5pentane
4
3
empirical formula
CCDC no.
C
25H37ClN2OSi
C29H43ClN2O2Si
CCDC 824155
515.19
C45.5H66N2O2Si
C41H52FeN2OSi
CCDC 824157
672.79
CCDC 824154
445.11
CCDC 824156
701.09
formula wt
temperature/K
wavelength/Å
crystal system
space group
90 (2)
100 (2)
100 (2)
100 (2)
0.71073
0.71073
0.71073
0.71073
monoclinic
orthorhombic
P212121
triclinic
monoclinic
C2c
P21/c
P1
unit cell dimensions
a = 15.4914 (14) Å
b = 11.6071 (10) Å
c = 13.5417 (12) Å
R = 90°
β = 104.728 (2)°
γ = 90°
2354.9 (4) Å3, 4
1.255 g/cm3
0.233 mmꢀ1
960
a = 10.8117 (10) Å
b = 14.4507 (14) Å
c = 18.4194 (18) Å
R = 90°
β = 90°
γ = 90°
2877.8 (3) Å3, 4
1.189 g/cm3
0.202 mmꢀ1
1112
a = 12.9856 (9) Å
b = 12.9963 (9) Å
c = 13.3486 (9) Å
R = 73.1430(10)°
β = 79.4280(10)°
γ = 88.4660(10)°
2118.5 (3) Å3, 2
1.098 g/cm3
a = 21.2031 (5) Å
b = 10.0796 (2) Å
c = 35.5186 (8) Å
R = 90°
β = 104.5550°
γ = 90°
7347.4 (3) Å3, 8
1.216 g/cm3
0.476 mmꢀ1
2880
volume, Z
density (calcd)
absorption coefficient
F (000)
0.092 mmꢀ1
766
crystal size
0.16 ꢁ 0.12 ꢁ 0.05 mm3
1.36ꢀ27.20°
ꢀ19 e h e 19,
ꢀ14 e k e 14,
ꢀ17 el e 17
39086
0.07 ꢁ 0.07 ꢁ 0.07 mm3
1.79ꢀ26.03°
ꢀ12 e h e 13,
ꢀ17 e k e 17,
ꢀ22 el e 22
29073
0.12 ꢁ 0.08 ꢁ 0.06 mm3
1.60ꢀ26.75°
ꢀ16 e h e 16,
ꢀ16 e k e 16,
ꢀ16 e l e 16
59261
0.12 ꢁ 0.10 ꢁ 0.08 mm3
θ range for data collection
limiting indices
1.98ꢀ25.35°
ꢀ25 e h e 20,
ꢀ12 e k e 9,
ꢀ42 e l e 41
reflections collected
58971
independent reflections
completeness to θ
5224 (Rint = 0.0305)
99.9% (θ = 27.20)
5657 (Rint = 0.0549)
99.7% (θ = 26.03)
8992 (Rint = 0.0269)
99.7% (θ = 26.75)
6648 (Rint = 0.0340)
98.8% (θ = 25.35)
refinement method
full-matrix least-squares on F2 full-matrix least-squares on F2 Full-matrix least-squares on F2 Full-matrix least-squares on F2
data/restraints/parameters
goodness-of-fit on F2
final R indices [I > 2σ (I)]
R indices (all data)
5224/0/277
5663/0/359
8992/143/485
6648/0/428
1.122
1.038
1.028
1.037
R1 = 0.0366, wR2 = 0.0942
R1 = 0.0403, wR2 = 0.0964
R1 = 0.0351, wR2 = 0.0729
R1 = 0.0427, wR2 = 0.0764
0.03(5)
0.193 and ꢀ0.203 eÅꢀ3
R1 = 0.0439, wR2 = 0.1090
R1 = 0.0535, wR2 = 0.1151
R1 = 0.0335, wR2 = 0.0774
R1 = 0.0407, wR2 = 0.0809
absolute structure parameter
largest diff peak and hole
0.373 and ꢀ0.322 eÅꢀ3
0.455 and ꢀ0.557 eÅꢀ3
0.420 and ꢀ0.370 eÅꢀ3
1H and 29Si NMR spectra were recorded with Bruker Avance DPX 200,
Bruker Avance DRX 300, Bruker Avance DRX 400, or a Bruker Avance
DRX 500 spectrometer, using C6D6 as solvent. Chemical shifts (δ) are
given relative to SiMe4. EIꢀMS 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.
Synthesis of 1. Toluene (60 mL) was added to a 100 mL Schlenk
flask containing L (0.29 g, 0.98 mmol) and 2-adamantanone (0.15 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 ꢀ32 °C in a freezer for 2 days to obtain
colorless single crystals of 1; (0.31 g, 70%); mp 171ꢀ174 °C (decomp).
Elemental analysis (%) calcd for C25H37ClN2OSi (445.11): C, 67.46; H,
8.38; N, 6.29. Found: C, 67.29; H, 8.25; N, 6.38. 1H NMR (200 MHz,
C6D6, 25 °C): δ 1.16 (s, 18H, 2 ꢁ C(CH3)3), 1.66ꢀ1.69 (m, 2H,
C10H14), 1.88 (s, 2H, C10H14), 1.98ꢀ2.07 (m, 4H, C10H14), 2.20 (br,
2H, C10H14), 2.58 (br, 2H, C10H14), 2.98 (br, 2H, C10H14), 6.80ꢀ6.94
(m, 5 H, C6H5) ppm. 29Si{1H} NMR (59.63 MHz, C6D6, 25 °C):
δ ꢀ104.80 ppm. EIꢀMS: m/z 444.0 (M+).
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 ꢀ32 °C for 3 days to
obtain colorless single crystals of 2; (0.32 g, 73%); mp 150ꢀ153 °C
(decomp). Elemental analysis (%) calcd for C29H43ClN2O2Si (515.20): C,
67.61; H, 8.41; N, 5.44. Found: C, 67.27; H, 8.51; N, 5.36. 1H NMR (200
MHz, C6D6, 25 °C): δ 1.24 (s, 18H, 2 ꢁ C(CH3)3), 1.34 (s, 9H, C(CH3)3),
1.69 (s, 9H, C(CH3)3), 6.79ꢀ7.26 (m, 7H, C6H5 and C6H2) ppm; 29Si{1H}
NMR (79.49 MHz, C6D6, 25°C): δꢀ94.58 ppm. EIꢀMS: m/z514.0 (M+).
Synthesis of 3. n-Pentane (60 mL) was placed in a 100 mL Schlenk
flask containing L0 (0.24 g, 0.54 mmol) and 3,5-di-tert-butyl-o-benzo-
quinone (0.12 g, 0.54 mmol). The reaction mixture was stirred at room
temperature for 12 h. The solution was filtered, and the solvent was
reduced in vacuo to 10 mL and stored in a freezer at ꢀ32 °C for a week
to obtain colorless single crystals of 3. For elemental analysis, 3 0.5pen-
3
tane was treated under vacuum for 6 h to remove the pentane molecule;
(0.28 g, 78%); mp 135ꢀ138 °C (decomp). Elemental analysis (%) calcd
for C43H60N2O2Si (665.03): C, 77.66; H, 9.09; N, 4.21. Found: C,
77.70; H, 9.15; N, 4.15. 1H NMR (500 MHz, C6D6, 25 °C): δ 0.69 (d,
3H, J = 7 Hz, CH(CH3)2), 1.00 (s, 9H, C(CH3)3), 1.08 (d, 3H, J = 7 Hz,
CH(CH3)2), 1.14 (s, 9H, C(CH3)3), 1.29 (d, 3H, J = 7 Hz, CH(CH3)2),
1.37 (m, 6H, 2 ꢁ CH(CH3)2), 1.44 (s, 3H, NCCH3) 1.48 (m, 6H, 2 ꢁ
CH(CH3)2), 1.56 (d, 3H, J = 7 Hz, CH(CH3)2), 3.30 (m, 1H, J = 7 Hz,
CH(CH3)2), 3.42 (s, 1H, NCCH2), 3.64 (m, 1H, J = 7 Hz, CH(CH3)2),
Synthesis of 2. Toluene (60 mL) was added to a 100 mL Schlenk
flask containing L(0.25 g, 0.85 mmol) and 3,5-di-tert-butyl-o-benzoquinone
(0.19 g, 0.86 mmol). The green-colored reaction mixture was stirred at
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ARTICLE
3.83 (m, 1H, J = 7 Hz, CH(CH3)2), 4.02 (s, 1H, NCCH2), 5.38 (s, 1H,
γꢀCH), 6.69 (br, 1H, C6H2), 6.86 (br, 1H, C6H2), 6.98ꢀ7.14 (m, 6 H,
2 x iPr2C6H3) ppm. 29Si{1H} NMR (79.49 MHz, C6D6, 25 °C):
δ ꢀ49.36 ppm. EIꢀMS: m/z 664.4 (M+).
Sons: NewYork, 1999; Vol. 2, Part 3, pp 2463ꢀ2568. (b) Nagendran,
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Synthesis of 4. n-Hexane (60 mL) was placed in a 100 mL Schlenk
flask containing L0 (0.24 g, 0.54 mmol) and acylferrocene (0.12 g, 0.53
mmol). The orange red colored reaction mixture was stirred at room
temperature for 12 h. The solution was filtered, and the solvent was
reduced in vacuo to 40 mL and stored in a freezer at ꢀ32 °C for 12 h to
obtain reddishꢀorange colored single crystals of 4; (0.26 g, 72%); mp
212ꢀ215 °C (decomp). Elemental analysis (%) calcd for C41H52FeN2OSi
(672.79): C, 73.19; H, 7.79; N, 4.16. Found: C, 72.85; H, 7.89; N, 4.00. 1H
NMR (300 MHz, C6D6, 25 °C): δ 1.02 (d, 3H, J = 7 Hz, CH(CH3)2), 1.06
(d, 3H, J = 7 Hz, CH(CH3)2), 1.26ꢀ1.29 (2d, 6H, 2 ꢁ CH(CH3)2), 1.30
(d, 3H, J = 7 Hz, CH(CH3)2), 1.44 (d, 3H, J = 7 Hz, CH(CH3)2), 1.49
(s, 3H, NCCH3), 1.52 (d, 3H, J = 7 Hz, CH(CH3)2), 1.56 (d, 3H, J = 7 Hz,
CH(CH3)2), 2.83 (d, 1H, J = 2 Hz, CdCH2), 3.11 (m, 1H, C5H4), 3.40
(m, 1H, J = 7 Hz, CH(CH3)2), 3.45 (s, 1H, NCCH2), 3.54 (m, 2H,
CH(CH3)2, C5H4), 3.72(m, 1H, C5H4), 3.78 (m, 1H, C5H4), 3.84 (m, 2H,
J = 7 Hz, 2 ꢁ CH(CH3)2), 3.90 (s, 5H, C5H5), 4.02 (s, 1H, NCCH2), 4.26
(d, 1H, J = 2 Hz, CdCH2), 5.28 (s, 1H, SiH), 5.35 (s, 1H, γꢀCH),
6.97ꢀ7.30 (m, 6 H, 2 ꢁ iPr2C6H3) ppm. 29Si{1H} NMR (59.62 MHz,
C6D6, 25 °C): δ ꢀ51.25 ppm. EIꢀMS: m/z 672 (M+).
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Crystal Structure Determination. Suitable single crystals for
Xꢀray structural analysis of 1, 2, 3, and 4 were mounted at low temperature
in inert oil under argon atmosphere by applying the X-Temp2 device.25 The
data were collected on a Bruker D8 three circle diffractometer equipped
with a SMART APEX II CCD detector and an INCOATEC Mo micro-
focus source with INCOATEC Quazar mirror optics.26 The data were
integrated with SAINT,27 and an empirical absorption correction with
SADABS28 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).29 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 1.5 Ueq of their pivot atoms for terminal sp3
carbon atoms and 1.2 times for all other carbon atoms (Table 1).
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’ ASSOCIATED CONTENT
S
Supporting Information. CIFs for 1(CCDCꢀ824154),
b
2(CCDCꢀ824155), 3(CCDCꢀ824156), and 4(CCDCꢀ824157).
This material is available free of charge via the Internet at http://
pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: hroesky@gwdg.de (H.W.R.); dstalke@chemie.
uni-goettingen.de (D.S.).
’ ACKNOWLEDGMENT
We are thankful to the Deutsche Forschungsgemeinschaft for
supporting this work. R.A. is grateful to the Alexander von Humboldt
Stiftung for a research fellowship. D.S. and J.H. 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) PhD program.
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