Synthesis of stable silicon heterocycles by reaction of organic substrates with a chlorosilylene [PhC(NtBu)2SiCl]

Article abstract of DOI:10.1002/chem.201001901

Heteroleptic chlorosilylene (PhC(NtBu)₂SiCl) (1) reacts with unsaturated organic compounds under oxidative addition. Reactions of 1 with cyclooctatetraene (COT) and a diimine afford [1+4]-cycloaddition products 3 and 6, respectively. In the cas

Full text of DOI:10.1002/chem.201001901

FULL PAPER
DOI: 10.1002/chem.201001901
Synthesis of Stable Silicon Heterocycles by Reaction of Organic Substrates
with a Chlorosilylene [PhCACTHNUTRGNEN(UG NtBu)2SiCl]
Shabana Khan, Sakya S. Sen, Daniel Kratzert, Gasˇper Tavcˇar, Herbert W. Roesky,* and
Dietmar Stalke[a]
Dedicated to Professor Dr. Hans H. Karsch
Abstract: Heteroleptic chlorosilylene
(PhC(NtBu)2SiCl) (1) reacts with unsa-
bonds. The facile isolation of silaimine
complexes is probably due to the kinet-
ic protection afforded by the bulky Ar
moiety. When 1 is treated with tert-
butyl isocyanate, cleavage of the C=O
bond is observed, which leads to for-
mation of the four-membered Si2O2
cycle 5. The same product is formed
when 1 is allowed to react with trime-
thylamine N-oxide. When 1 is treated
with diphenyl disulfide, cleavage of the
G
À
turated organic compounds under oxi-
dative addition. Reactions of 1 with cy-
clooctatetraene (COT) and a diimine
afford [1+4]-cycloaddition products 3
and 6, respectively. In the case of COT,
S S bond occurs to form 7. All prod-
ucts have been characterized by multi-
nuclear NMR spectroscopy, EI mass
spectrometry, and elemental analysis.
In addition, the molecular structures of
3–6 have been determined by single-
crystal X-ray diffraction studies. Col-
lectively, these results suggest that
owing to the presence of the lone pair
of electrons, the propensity of 1 to un-
dergo oxidative addition is very high.
À
one Si N bond of the amidinato ligand
is cleaved, resulting in tetracoordinate
silicon, whereas with a diimine a penta-
coordinate silicon is formed. Treatment
Keywords: cycloaddition
gands reactivity small ring
systems · X-ray diffraction
· N li-
of
1 with ArN=C=NAr (Ar =2,6-
·
·
iPr2C6H3) yields silaimine complex 4
with cleavage of one of the C=N
Introduction
Since then, the field of stable silylene research has become a
subject of extensive studies and, by means of tailored syn-
thetic strategies that utilize ligands with exact steric and
electronic balance, a fair number of silylenes that are stable
at room temperature have been synthesized and structurally
characterized.[5] These successful isolations have represented
a classic progression from transient intermediate to matrix-
isolated molecule to stable compound for the silylenes. Sur-
prisingly, very little attention has been paid to the synthesis
of chlorosilylenes, although they can be considered as ana-
logues of gaseous silicon dichloride.[6] Very recently, we suc-
ceeded in synthesizing a stable monomeric chlorosilylene
Taming short-lived reactive intermediates under laboratory
conditions is a strong motivation for preparative chemists.
Silylene, the silicon analogue of carbene, is proposed as a re-
active intermediate in various thermal and photochemical
reactions in organosilicon chemistry.[1] It was first identified
as a transient intermediate by Skell and Goldstein[2a] and
subsequently spectroscopically characterized in an argon
matrix by Michl and West.[2b] In 1986, Jutzi et al. succeeded
in isolating the first silylene stable at room temperature,
which is commonly known as decamethylsilicocene,[3a]
Cp*2Si (Cp*=pentamethylcyclopentadiene). Karsch et al.
subsequently reported a stable s-bonded compound contain-
ing a divalent silicon atom stabilized by a phosphinometha-
nide ligand.[3b] In these two compounds, the formal oxidation
state of the silicon centers is +2, whereas the coordination
number at the silicon atoms is higher than two. In 1994,
West and co-workers isolated the first divalent dicoordinate
N-heterocyclic silylene,[4a] which is analogous to the N-heter-
ocyclic carbene reported by Arduengo et al. in 1991.[4b]
(LSiCl, L=PhCACTHNUTRGNEUNG
(NtBu)2)[7a] (1) and an N-heterocyclic car-
bene (NHC)-stabilized dichlorosilylene (LSiCl2, L=1,3-
bis(2,6-iPr2C6H3)imidazol-2-ylidene) (2).[7b] Another advance
in this discipline was made by Filippou and co-workers, who
isolated an NHC-stabilized dibromosilylene, LSiBr2 (L=1,3-
bis(2,6-iPr2C6H3)imidazol-2-ylidene)[7c] and carbene adducts
of arylchlorosilylenes, SiArCl·
2,6-Trip2C6H3; Mes=2,4,6-Me3C6H2, Trip=2,4,6-iPr3C6H2),
Im-Me4 =(1,3,4,5-tetramethyl)imidazol-2-ylidene).[7d]
The
ACHTUGNTRENNUN(G Im-Me4) (Ar=2,6-Mes2C6H3,
advantage of base-stabilized silylenes is that the number of
coordination sites at the silicon center is three, and this ar-
rangement is responsible for the astonishing thermal stabili-
ty of the halosilylenes, which are otherwise considered as re-
active intermediates.[8] The reactivities of dicoordinate sily-
lenes are well documented,[9] but little is known about the
chemistry of chlorosilylenes. Very recently, Baceiredo et al.
ˇ
[a] Dr. S. Khan, Dr. S. S. Sen, Dr. D. Kratzert, Dr. G. Tavcar,
Prof. Dr. H. W. Roesky, Prof. Dr. D. Stalke
Institute of Inorganic Chemistry
Tammannstrasse 4, 37077 Gçttingen (Germany)
Fax : (+49)551393373
E-mail: hroesky@gwdg.de
Chem. Eur. J. 2011, 17, 4283 – 4290
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4283

and Filippou et al. succeeded in isolating silyne and silyli-
dyne complexes using SiII halides as precursors.[10a,b] From
À
these results, it was apparent that the reactive Si Cl bond
and a lone pair of electrons on silicon in 1 would provide
synthetic access to other stable and fascinating silicon com-
pounds,[10c] but the low yield (10%) of 1 hampered our fur-
ther investigations. Very recently, however, we obtained 1 in
90% yield by treating LSiHCl2 with LiNACTHUNTRGNEU(GN TMS)2, whereby
the latter functions as a dehydrochlorinating agent.[11] The
increased yield of 1 obtained by the new method allowed us
to study its reaction chemistry, which is of fundamental im-
portance to ascertain the hallmark of this special class of
compounds and as well as to compare the reaction patterns
of 1 with those of other reported silylenes. We have commu-
nicated our initial finding that 1 could be added to an
alkyne to afford a 1,2-disilacyclobutene.[11] In addition, we
have reported that 1 reacts with Ph2C=O and PhC(O)-
C(O)Ph to yield a monosilaepoxide[12a] and a 2,5-dioxa-1-si-
lacyclopent-3-ene,[12b] respectively. However, it was deemed
highly desirable to further explore the reactivity of 1 to un-
derstand its electronic and structural properties as well as
the nature of the lone pair of electrons on the silicon atom
in this unique molecule. We present herein a more extensive
study of the reactivity of 1 toward a variety of unsaturated
molecules, namely cyclooctatetraene, carbodiimide, tert-
butyl isocyanate, trimethylamine N-oxide, diimine, and di-
phenyl disulfide.
Scheme 1. Preparation of 3.
1
any change in the H NMR spectrum, even in variable-tem-
perature 1H NMR experiments. This is probably due to a
rapid exchange on the NMR time scale within the NCNSi
part of the molecule. The resonances at d=2.28 and 5.63–
5.93 ppm correspond to two CH and six CH=C protons, re-
spectively. The 29Si NMR spectrum features a sharp reso-
nance at d=À9.49 ppm, which is in accordance with the re-
ported shift for the [1+4]-cycloaddition product.[16] In the EI
mass spectrum, the molecular ion peak was observed at m/z
397 [M+] with high intensity.
The molecular structure of 3 was unequivocally confirmed
by single-crystal X-ray diffraction analysis (Figure 1).[17]
3
¯
crystallizes in the triclinic space group P1 (Table 1). The
Results and Discussion
Reaction of 1 with 1,3,5,7-cyclooctatetraene: Cyclooctate-
traene (COT), the first 8p-electron system to be studied,
adopts an inherently nonplanar tub-shaped geometry of D2d
symmetry with alternating single and double bonds (with
angles C=C-C 126.18 and C=C-H 117.68) and hence behaves
as a nonaromatic polyene rather than as an anti-aromatic
compound.[13] COT has attracted much attention because it
undergoes a conformation change between tub- and planar-
shaped structures with the addition or removal of electrons.
Many COT-bridged molecules are known for s-block and f-
block elements.[14] Cyclic [1+2] derivatives of COT with
phosphorus fragments[15] are known, but to the best of our
knowledge there has been no report concerning the reaction
of COT with a silylene.
The addition of one equivalent of COT to a colorless so-
lution of 1 in toluene at ambient temperature resulted in a
light-yellow crystalline solid after stirring overnight and re-
moval of the solvent under vacuum (Scheme 1). The solid
was extracted with toluene and colorless crystals of 3 were
obtained by storing the saturated solution at room tempera-
ture for one day. The composition and constitution of 3
were proven by spectroscopic methods and elemental analy-
sis. Surprisingly, the 1H NMR spectrum features only one
sharp singlet for the tBu protons (d=1.12 ppm). Several at-
tempts were made to detect the resonances of the two
chemically different tBu groups, but we could not observe
Figure 1. Crystal structure of 3. Hydrogen atoms and tBu groups have
been omitted for clarity. Anisotropic displacement parameters are depict-
ed at the 50% probability level. Selected bond lengths [ꢁ] and bond
angles [8]: Cl(1)–Si(1) 2.0820(7), N(1)–C(1) 1.413(2), N(2)–C(1) 1.273(2),
Si(1)–C(21) 1.8761(19), Si(1)–C(16) 1.895(2), N(1)–Si(1) 1.7418(14),
C(21)–C(22) 1.513(3), C(22)–C(23) 1.317(3), C(16)–C(23) 1.510(3); N(1)-
Si(1)-C(21) 119.34(7), N(1)-Si(1)-C(16) 114.71(8), N(1)-Si(1)-Cl(1)
114.20(6), C(21)-Si(1)-Cl(1) 111.62(6), C(16)-Si(1)-Cl(1) 103.11(7), C(21)-
Si(1)-C(16) 90.43(9), C(20)-C(21)-C(22) 108.76(16), C(22)-C(23)-C(16)
116.88(18), C(20)-C(19)-C(18) 132.0(2).
structure displays a bicyclic system with a tetracoordinate
silicon center. Si(1) shows a distorted tetrahedral geometry,
with two sites being occupied by carbon atoms C(16) and
C(21) of the COT ring, and the other two sites being occu-
pied by nitrogen N(1) of the amidinato ligand and Cl(1).
4284
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Chem. Eur. J. 2011, 17, 4283 – 4290

Stable Silicon Heterocycles from PhCACTHNURTGNENG(U NtBu)2SiCl
FULL PAPER
Table 1. Crystallographic and structure refinement data at 100.0(2) K.
Reaction with a carbodiimide: Carbodiimides are character-
ized by a functional group with the general formula RN=C=
NR and are representative of the family of heterocumu-
lenes. The reaction of NHC with diisopropylcarbodiimide
that gives rise to the corresponding betaines followed by
cyclization has recently been described.[18] However, we are
not aware of comparable reactions with silylenes. In view of
this, we reacted 1 with ArN=C=NAr (Ar =2,6-iPr2C6H3).
We anticipated the formation of a spiro-centered silicon
compound with the silicon center fused between two four-
membered amidinato rings, but to our surprise the reaction
yielded a silaimine complex with cleavage of one of the C=
N bonds. Although silaimine complexes are known in the lit-
erature,[19] this is a very new and convenient route for pre-
paring such complexes without using dangerous organoa-
zides. The most striking phenomenon of the reaction is the
complete cleavage of one of the C=N bonds with the forma-
tion of a Si=N bond.
3
4
5
6·0.5toluene
CCDC
781631
781628
781629
782243
number
empirical C23H31ClN2Si C27H40ClN3Si C30H46Cl2N4O2Si2 C44.50H63ClN4Si
formula
Fw
399.04
P1
470.16
P21/c
621.79
P1
717.53
P1
¯
¯
¯
space
group
a [ꢁ]
b [ꢁ]
c [ꢁ]
a [8]
b [8]
9.3483(9)
14.9338(10) 9.2385(18)
9.6554(19)
11.7840(11) 20.6236(14) 10.572(4)
10.344(2)
12.140(3)
18.019(4)
81.190(4)
73.558(4)
69.184(3)
2025.1(8)
2
10.7051(10) 9.1862(6)
87.309(2)
72.706(2)
84.442(2)
1120.47(18) 2743.5(3)
2
90
103.061(5)
96.178(5)
112.438(4)
829.2(4)
1
104.145(4)
90
g [8]
V [ꢁ3]
Z
4
1calcd
[gcmÀ3
1.183
1.138
1.245
1.177
]
F
G
428
1016
332
778
]
0.234
0.202
0.301
0.160
q range for 1.81–26.04
data col-
1.41–25.40
2.02–26.39
1.18–26.42
Compound 1 was treated with bis(2,6-diisopropylphenyl)-
carbodiimide in toluene at ambient temperature by stirring
overnight (Scheme 3). The solution was subsequently con-
lection [8]
reflections 26345/4430
collected/
40880/5030
21133/3400
48242/8275
unique
ACHTUNGTRENNUNG[I> 2s(I)]
data/re-
4430/0/250
5030/554/467 3400/0/187
8275/203/536
straints/pa-
rameters
GoF on F2 1.042
1.049
1.056
1.046
R1 [I>
2s(I)],
wR2 (all
data)
0.0405,
0.1045
0.0576,
0.1636
0.0334, 0.0891
0.0414, 0.1105
Largest
diff. peak/
hole
0.207/À0.215 0.884/À0.555 0.336/À0.270
0.302/À0.344
Scheme 3. Preparation of 4.
[eꢁÀ3
]
centrated and stored at room temperature for crystalliza-
tion, whereupon colorless crystals of 4 suitable for X-ray
crystallography were deposited. Compound 4 was found to
be soluble in solvents such as toluene, diethyl ether, and
THF. The structure of 4 was further confirmed by multinu-
clear NMR spectroscopy, EI mass spectrometry, and ele-
mental analysis. The 1H NMR spectrum features a reso-
nance at d=1.05 ppm attributable to the tBu protons. Two
sharp resonances at d=1.13 and 1.56 ppm indicate the
twelve CH3 protons. A septet is observed at d=4.00–
4.14 ppm due to the two CH protons of the isopropyl
groups. The methine proton signal at d=4.00 ppm shows a
3J correlation with the two CH3 proton signals at d=1.13 (d,
J=6.90 Hz) and 1.56 ppm (d, J=6.90 Hz), which confirms
the position of the iPr groups. Since the signals of the aro-
matic protons are overlapped, the COSY correlation could
not be assigned for individual aromatic protons. The
29Si NMR spectrum features a sharp resonance at d=
À104.79 ppm. In the EI mass spectrum, the molecular ion
was observed as the most abundant peak at m/z 469 with
the highest relative intensity.
The COT ring in the final structure has a nonplanar geome-
À
try with alternating C C and C=C bonds. The bond angles
C(20)-C(21)-C(22)
108.76(16)8,
C(22)-C(23)-C(16)
116.88(18)8, and C(20)-C(19)-C(18) 132.0(2)8 in the cycload-
duct 3 are also in the range for the nonplanar and distorted
tub-shaped geometry of COT.
The mechanism of formation of 3 involves a rare example
of a [1+4] cycloaddition of a silylene to the COT ring to
generate a silicon-substituted bicyclic system with three C=
C bonds (Scheme 2). However, we did not observe any reac-
tion of compound 1 with 1,5-cyclooctadiene or cyclooctene.
Although we are not sure about the mechanism of forma-
tion of 4 and no intermediates could be isolated, we suggest
that the reaction may take place in the following way
Scheme 2. Mechanism for the formation of 3.
Chem. Eur. J. 2011, 17, 4283 – 4290
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4285

H. W. Roesky et al.
Reaction with tert-butyl isocyanate: Isocyanate presents two
unsaturated functional sites and may therefore show some
fascinating reactivities with stable silylenes. We are not
aware of any previous reports of such reactions. We antici-
pated that these reactants would undergo a putative [2+3]
cycloaddition, but to our surprise the formation of a Si2O2
ring with cleavage of the C=O bond was observed. The for-
mation of tert-butyl isocyanide as a side product of the reac-
tion was confirmed by 1H NMR spectroscopy.
A reaction mixture consisting of 1 and tert-butyl isocya-
nate in toluene at ambient temperature was stirred over-
night. Subsequent removal of the solvent in vacuo afforded
a colorless solid (Scheme 5), which was extracted with tolu-
Scheme 4. Suggested mechanism for the formation of 4.
(Scheme 4). The lone pair on nitrogen first attacks the elec-
trophilic silylene, and donation of this pair forms a double
bond. This intermediate further rearranges to 4 with the for-
mation of an isonitrile, which has been confirmed by
1H NMR spectroscopy.
Single crystals of 4 were grown from a concentrated solu-
tion in toluene. The crystal structure of 4 was determined by
single-crystal X-ray diffraction analysis (Figure 2).[17] Com-
Scheme 5. Preparation of 5.
ene. Colorless crystals of 5 were obtained by storing the
concentrated solution in toluene at room temperature. The
composition and constitution of 5 were proven by spectro-
1
scopic methods and elemental analysis. The H NMR spec-
trum shows one set of resonances due to the amidinato
ligand. The 29Si NMR spectrum features a sharp resonance
at d=À113.54 ppm. This chemical shift is consistent with
those of previously reported compounds with five-coordi-
nate silicon atoms.[20] The EI mass spectrum showed the mo-
lecular ion peak at m/z 620, although with low intensity.
The molecular structure of 5 is shown in Figure 3.[17] Com-
Figure 2. Crystal structure of 4. Hydrogen atoms have been omitted for
clarity. Anisotropic displacement parameters are depicted at the 50%
probability level. Selected bond lengths [ꢁ] and bond angles [8]: Si(1)–
N(1) 1.545(2), Si(1)–N(3) 1.803(2), Si(1)–N(2) 1.809(2), Si(1)–Cl(2)
2.087(10); N(1)-Si(1)-N(3) 121.63(12), N(1)-Si(1)-N(2) 122.71(12), N(3)-
Si(1)-N(2) 72.73(9), N(1)-Si(1)-Cl(2) 121.33(9), N(3)-Si(1)-Cl(2)
103.57(8), N(2)-Si(1)-Cl(2) 104.10(7), Si(1)-N(1)-C(16) 171.1(4).
¯
pound 5 crystallizes in the triclinic space group P1 (Table 1).
pound 4 crystallizes in the monoclinic space group P21/c
(Table 1). The two phenyl rings are each disordered over
two positions. The silicon atom exhibits a distorted tetrahe-
dral geometry. Two sites of the silicon atom are occupied by
the N atoms from the amidinato ligand, and a further site is
occupied by a chlorine atom. The nitrogen atom from the
carbodiimide group fills the remaining coordination site.
À
The most significant bond lengths are those of the Si N
bonds. The two silicon–amidinato nitrogen bond lengths are
almost the same (1.803(2) and 1.809(2) ꢁ), whereas the
Figure 3. Crystal structure of 5. Hydrogen atoms have been omitted for
clarity. Anisotropic displacement parameters are depicted at the 50%
probability level. Selected bond lengths [ꢁ] and bond angles [8]: O(1)–
Si(1) 1.6574(12), O(1)–Si(1A) 1.7177(12), Si(1)–O(1A) 1.7177(12), Cl(1)–
Si(1) 2.0972(6), N(1)–C(1) 1.356(2), N(1)–C(12) 1.486(2), N(1)–Si(1)
1.8080(14), N(2)–C(1) 1.311(2), N(2)–C(8) 1.481(2), N(2)–Si(1)
1.9416(14); O(1)-Si(1)-O(1A) 85.63(6), Si(1)-O(1)-Si(1A) 94.37(6), O(1)-
Si(1)-N(1) 126.02(6), O(1A)-Si(1)-N(1) 100.07(6), O(1)-Si(1)-N(2)
94.31(6), O(1A)-Si(1)-N(2) 166.96(6), N(1)-Si(1)-N(2) 69.46(6), N(1)-
Si(1)-Cl(1) 113.78(5).
À
other Si N bond length is 1.545(2) ꢁ, clearly indicating the
formation of an Si=N double bond,[19] which is kinetically
stabilized by the bulky 2,6-iPr2C6H3 group. The geometry
about N(1) can best be described as distorted trigonal
planar, with two sites being occupied by Si(1) and C(16).
The lone pair of electrons occupies the remaining coordina-
À
tion site. The Si Cl bond length (2.087(10) ꢁ) is shorter
than that in 1 (2.156(1) ꢁ).[7a]
4286
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Chem. Eur. J. 2011, 17, 4283 – 4290

Stable Silicon Heterocycles from PhCACTHNURTGNENG(U NtBu)2SiCl
FULL PAPER
The structure consists of a rectangular cyclodisiloxane ring
orthogonal to a slightly distorted planar skeleton containing
the silicon atoms and their pendant nitrogen substituents.
À
The two independent Si O bond lengths are very similar
(1.6574(12) and 1.7177(12) ꢁ) and are slightly longer than
the normal bond lengths found in other cyclic siloxanes.[21]
The amidinate ligands and Cl atoms are disposed above and
below the Si2O2 ring in such a way that the Si centers exhibit
Scheme 7. Preparation of 6.
À
a distorted square-pyramidal geometry. The Si Cl bond
length is 2.0972(6) ꢁ. Another striking feature of this struc-
À
ture is the Si Si distance of 2.48 ꢁ, which is 0.13 ꢁ longer
case of compound 4, a COSY correlation was observed be-
tween the methine proton signal and that of the iPr protons.
The 29Si NMR spectrum features a sharp resonance at d=
À101.89 ppm,[20] and the EI mass spectrum shows the molec-
ular ion at m/z 670 as the most abundant peak with highest
relative intensity.
[22]
À
than the normal Si Si s bond length (2.35 ꢁ). From these
values, it can be assumed that there is no bond between the
two Si atoms. This assumption is also supported by MNDO
calculations on the parent cyclodisiloxane, H4Si2O2, which
provided no evidence for bonding between the silicon
atoms.[21] In agreement with this, recent ab initio calculations
on H4Si2O2 have indicated that the cyclodisiloxane is best
described as containing four equivalent localized Si O
bonds with no appreciable s bonding between the silicon
atoms. Here, it is worth pointing out that a similar kind of
Single crystals of 6 suitable for X-ray diffraction analysis
were grown from a saturated solution in toluene at room
temperature (Figure 4). Compound 6 crystallizes in the tri-
À
¯
clinic space group P1; the other crystallographic data are
summarized in Table 1.[17] In the spirocyclic structure, the sil-
À
Si2O2 cycle was obtained when LSi SiL (L=PhC
was reacted with benzophenone under cleavage of the C=O
(NtBu)2)
bond and abstraction of a proton from THF.[23]
Reaction with trimethylamine N-oxide: Trimethylamine N-
oxide is well known as an oxidizing agent, which is used to
convert alkyl halides into aldehydes. As 1 has a chlorine
atom bound to silicon, we were keen to probe the reaction
of 1 with trimethylamine N-oxide in this context. It is also
noteworthy that the isolation of a silanone (R2Si=O) that is
stable at room temperature (Kippingꢂs dream)[24,25] is still
elusive. With these possibilities in mind, we treated Me3N+
OÀ with 1 in THF, which afforded 5 (Scheme 6), the same
product that we obtained from
the reaction between tert-butyl
isocyanate and 1 (Scheme 5).
The NMR spectroscopic data
and EI mass spectrum were in
accordance with those of 5 ob-
Scheme 6. Alternative synthe-
sis of 5.
tained previously.
Figure 4. Crystal structure of 6·0.5toluene. Hydrogen atoms, iPr and tBu
groups, and disordered toluene have been omitted for clarity. Anisotropic
displacement parameters are depicted at the 50% probability level. Se-
lected bond lengths [ꢁ] and bond angles [8]: Cl(1)–Si(1) 2.2138(7), N(1)–
C(1) 1.3446(19), N(1)–C(12) 1.4862(19), N(1)–Si(1) 1.8290(13), N(2)–
C(1) 1.324(2), N(2)–C(8) 1.494(2), N(2)–Si(1) 1.9115(13), N(3)–C(28)
1.407(2), N(3)–C(16) 1.446(2), N(3)–Si(1) 1.7883(14), N(4)–C(29)
1.412(2), N(4)–C(30) 1.4508(19), N(4)–Si(1) 1.7892(13), Si(1)–C(1)
2.3215(16); C(1)-N(1)-C(12) 131.75(13), C(1)-N(1)-Si(1) 92.76(9), C(12)-
N(1)-Si(1) 135.41(10), C(1)-N(2)-C(8) 128.71(13), C(1)-N(2)-Si(1)
89.80(9), C(8)-N(2)-Si(1) 136.77(10), C(28)-N(3)-C(16) 114.44(13), C(28)-
N(3)-Si(1) 111.80(10), C(16)-N(3)-Si(1) 133.42(11), C(29)-N(4)-C(30)
110.86(12), C(29)-N(4)-Si(1) 111.65(10), C(30)-N(4)-Si(1) 132.87(10),
N(3)-Si(1)-N(4) 87.65(6), N(3)-Si(1)-N(1) 108.57(6), N(4)-Si(1)-N(1)
116.52(6), N(3)-Si(1)-N(2) 92.98(6), N(4)-Si(1)-N(2) 172.86(6), N(1)-
Si(1)-N(2) 70.00(6), N(3)-Si(1)-Cl(1) 155.40(5), N(4)-Si(1)-Cl(1) 90.11(5),
N(1)-Si(1)-Cl(1) 94.33(5), N(2)-Si(1)-Cl(1) 86.36(4), N(3)-Si(1)-C(1)
105.18(6), N(4)-Si(1)-C(1) 151.39(6), N(1)-Si(1)-C(1) 35.35(5), N(2)-
Si(1)-C(1) 34.78(5), Cl(1)-Si(1)-C(1) 88.15(4).
Reaction with a diimine: The reaction between glyoxal-
bis(2,6-diisopropylphenyl)imine and 1 was conducted by stir-
ring an equimolar mixture in toluene for 12 h. Evaporation
of the solvent afforded air- and moisture-sensitive colorless
crystals of 6. The mechanism of product formation would
seem to be unequivocal, with 1 undergoing a [1+4] oxidative
addition reaction with the diimine to yield 6 (Scheme 7).
Compound 6 was isolated as a colorless crystalline solid
with good solubility in solvents such as diethyl ether, tolu-
ene, and THF. It was characterized by spectroscopic meth-
1
ods and X-ray crystallography. The H NMR spectrum fea-
tures a septet at d=4.15 ppm attributable to the four CH
protons of the iPr groups, as well as a doublet at d=
5.72 ppm with a coupling constant J=6.68 Hz, which indi-
cates the olefinic nature of the relevant protons. As in the
Chem. Eur. J. 2011, 17, 4283 – 4290
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www.chemeurj.org
4287

H. W. Roesky et al.
icon atom is part of both a four- and a five-membered ring
and is coordinated by two nitrogen atoms from the amidina-
to ligand, two nitrogen atoms from the diimine, and one
chlorine atom. The silicon atom thus displays unambiguous
Conclusion
In conclusion, we have prepared a variety of silicon hetero-
cycles by treating 1 with different types of unsaturated or-
ganic compounds. The experimental data for the reactions
of 1 show its propensity for oxidative addition due to the
presence of a lone pair of electrons on the silicon center.
This is in good agreement with the reactivity of previously
reported silylenes. Further investigations of the reactions of
1 are currently in progress and will be reported in due
course.
À
distorted trigonal-bipyramidal geometry. The Si N bonds
are the most notable structural features of 6. Inspection of
the structural data shows that N(2) and N(4) occupy the
axial positions with bond lengths of 1.9115(13) ꢁ and
1.7892(13) ꢁ, while N(1), N(3), and Cl(1) reside in equatori-
À
al positions. All of the Si N bond lengths are in good ac-
À
cordance with those of Si N single bonds reported in the lit-
erature.[19] The Si Cl bond length in 6 (2.2138(7) ꢁ) is
À
slightly longer than that in 1 (2.156(1) ꢁ).
Experimental Section
Reaction with diphenyl disulfide: Reactions of silylenes with
many sulfur-containing moieties are known, for example
CS2, S8, and PhNCS.[7q,26] However, to the best of our knowl-
edge, there has been no report of a silylene reacting with di-
General: All manipulations were carried out in an inert atmosphere of
dinitrogen using standard Schlenk techniques and in a dinitrogen-filled
glove box. The solvents used were purified by means of a MBRAUN MB
SPS-800 solvent purification system. Compound 1[11] and glyoxal-bis(2,6-
diisopropylphenyl)imine[28] were prepared by literature methods. All
chemicals purchased from Aldrich were used without further purification.
1H, 13C, and 29Si NMR spectra were recorded on Bruker Avance
DPX 200 or Bruker Avance DRX 500 spectrometers from solutions in
C6D6 or C7D8. Chemical shifts d are given relative to SiMe4. EI mass
spectra were obtained using a Finnigan MAT 8230 instrument. Elemental
analyses were performed at the Institut fꢃr Anorganische Chemie, Uni-
versitꢄt Gçttingen. Melting points were measured in sealed glass tubes
on a Bꢃchi B-540 melting point apparatus.
À
phenyl disulfide. The disulfide bond (S S) is covalent in
À1
À
nature, with a bond dissociation energy of 60 kcalmol . S S
[27a]
À
bonds are weaker than C C bonds
and are thus suscepti-
ble to scission by polar reagents, such as electrophiles and
more especially nucleophiles. Recently, Stephan et al. and
À
Alcarazo et al. independently reported S S bond cleavage
by frustrated Lewis pairs.[27b,c] Treatment of diphenyl disul-
À
fide with silylene 1 resulted in cleavage of the S S bond
with the formation of product 7 (Scheme 8).
Preparation of 3: Toluene (30 mL) was added to a mixture of 1 (0.294 g,
1.00 mmol) and 1,3,5,7-cyclooctatetraene (0.104 g, 1.00 mmol) and the re-
sulting solution was stirred for 12 h. The solvent was then removed in
vacuo, and the residue was extracted with toluene (20 mL). The filtrate
was concentrated to yield colorless crystals of 3 (0.29 g, 75%). M.p. 175–
1798C; elemental analysis calcd (%) for C23H31ClN2Si (398.19): C 69.23,
H 7.83, N 7.02; found: C 68.96, H 7.02, N 7.55; 1H NMR (200 MHz,
C6D6, 258C): d=1.12 (s, 18H; tBu), 2.28 (br, 2H; CH), 5.63–5.93 (m, 6H;
COT), 6.76–7.00 ppm (m, 5H; Ph); 13C{1H} NMR (125.75 MHz, C6D6,
258C): d=31.8 (CMe3), 37.7 (CH), 54.7 (CMe3), 125.8, 127.5, 128.0, 128.5,
128.9, 129.3, 135.9 (Ph), 169.3 ppm (NCN); 29Si{1H} NMR (99.36 MHz,
C6D6, 258C): d=À9.49 ppm; EI-MS: m/z: 397 [M+] (44%),319 [M+ÀPh
(100%).
Scheme 8. Preparation of 7.
Preparation of 4: Toluene (25 mL) was added to a mixture of 1 (0.30 g,
1.02 mmol)
and
bis(2,6-diisopropylphenyl)carbodiimide
(0.36 g,
0.99 mmol) at room temperature. The mixture was stirred overnight. The
solvent was then removed under vacuum and the remaining solid was ex-
tracted with toluene (20 mL). The resulting solution was concentrated
and stored at room temperature for 2 days to yield colorless crystals of 4
(0.11 g, 42%). M.p. 165–1708C; elemental analysis calcd (%) for
C27H40ClN3Si (470.17): C 68.97, H 8.58, N 8.94; found: C 67.95, H 8.14, N
8.35; 1H NMR (300 MHz, C7D8, 258C): d=1.05 (s, 18H; tBu), 1.13 (d,
6H, J=6.90 Hz; CHMe2), 1.56 (d, 6H, J=6.90 Hz; CHMe2), 4.00–4.14
(sept, 2H; CHMe2), 6.82–7.30 ppm (m, 8H; Ph); 13C{1H} NMR
(75.45 MHz, C7D8, 258C): d=22.5 (CHMe2), 23.3 (CHMe2), 30.8
(CHMe2), 32.9 (CMe3), 54.9 (CMe3), 117.3, 122.5, 123.4, 130.9, 133.4,
137.5, 140.4, 145.4 (Ph), 176.1 ppm (NCN); 29Si{1H} NMR (59.62 MHz,
C6D6, 258C): d=À104.79 ppm; EI-MS: m/z: 469 [M+] (100%).
Preparation of 5: Toluene (25 mL) was added to a mixture of 1 (0.29 g,
1.00 mmol) and tert-butyl isocyanate (0.10 g, 1.01 mmol) and the solution
was stirred overnight. After removal of the solvent in vacuo, the solid
was extracted with toluene (30 mL). Concentration and storage of the so-
lution at room temperature afforded colorless crystals of 5 (0.41 g, 67%).
M.p. 182–1858C; elemental analysis calcd (%) for C30H46Cl2N4O2Si2
(620.25): C 57.95, H 7.46, N 9.01; found: C 57.02, H 7.14, N 8.95;
1H NMR (500 MHz, C6D6, 258C): d=1.42 (s, 36H; tBu), 6.86–7.13 ppm
(m, 10H; Ph); 13C{1H} NMR (75.45 MHz, C6D6, 258C): d=32.27 (CMe3),
Addition of diphenyl disulfide to a solution of 1 in tolu-
ene at ambient temperature and stirring overnight gave a
colorless solution. Evaporation of the solvent in vacuo yield-
ed 7 as a colorless solid. Compound 7 was found to be solu-
ble in toluene and THF. The composition of 7 was estab-
lished by NMR spectroscopy, EI mass spectrometry, and ele-
mental analysis. The 1H NMR spectrum features a reso-
nance at d=1.42 ppm attributable to the eighteen tBu pro-
tons. The resonances of the fifteen phenyl protons appear in
the range d=6.90–7.91 ppm. The formation of 7 is accompa-
nied by a large shift (Dd=97.66 ppm) in the 29Si NMR
signal (d=À83.26 ppm) compared to that of 1. The chemical
shift of the product is consistent with those of reported five-
coordinate silicon compounds.[20] The EI mass spectrum fea-
tures a peak at m/z 477 as the most abundant ion, which cor-
responds to a fragment formed by the elimination of one
chlorine atom from the molecular ion.
4288
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 4283 – 4290

Stable Silicon Heterocycles from PhCACTHNURTGNENG(U NtBu)2SiCl
FULL PAPER
54.2 (CMe3), 127.5, 128.0, 129.2, 137.8 (Ph), 172.69 ppm (NCN);
29Si{1H} NMR (59.62 MHz, C6D6, 258C): d=À113.54 ppm; EI-MS: m/z:
620 [M+] (40%), 585 [M+ÀCl (100%).
Alternative preparation of 5: THF (25 mL) was added to a mixture of 1
(0.3 g, 1.02 mmol) and trimethylamine N-oxide (0.08 g, 1.06 mmol) and
the suspension was stirred until a clear solution was obtained. After re-
moval of the solvent in vacuo, the solid was extracted with toluene
(30 mL). Concentration and storage of the solution at À328C afforded 5
(0.24 g, 40%) as a colorless solid.
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Preparation of 6: Toluene (40 mL) was added to a mixture of 1 (0.29 g,
1.00 mmol)
and
glyoxal-bis(2,6-diisopropylphenyl)imine
(0.38 g,
1.01 mmol) at ambient temperature. The resulting mixture was stirred for
12 h. The solvent was then removed in vacuo, and the residue was ex-
tracted with toluene (20 mL). The extract was filtered and the filtrate
was concentrated to yield colorless crystals of 6 (0.35 g, 52.2%). M.p.
189–1928C; elemental analysis calcd (%) for C41H59ClN4Si (671.47): C
73.34,
H 8.86, N 8.34; found: C 73.67, H 9.02, N
9.35; 1H NMR
(200 MHz, C6D6, 258C): d=0.76 (s, 18H; tBu), 1.25 (d, 12H, J=6.91 Hz;
CHMe2), 1.44 (d, 12H, J=6.84 Hz; CHMe2), 4.15–4.18 (sept, 4H;
CHMe2), 5.72 (d, 2H, J=6.68 Hz; CHCN), 6.80–7.30 ppm (m, 11H; Ph);
13C{1H} NMR (125.75 MHz, C6D6, 258C): d=25.6 (CHMe2), 28.2
(CHMe2), 30.6 (CMe3), 32.1 (CHMe2), 55.6 (CMe3), 117.7 (NCC), 123.5,
123.8, 129.3, 129.9, 131.2, 133.8, 149.1, 149.6 (Ph), 169.4 ppm (NCN);
29Si{1H} NMR (59.62 MHz, C6D6, 258C): d=À101.89 ppm; EI-MS: m/z:
670 [M+] (100%).
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1.00 mmol) and diphenyl disulfide (0.22 g, 1.00 mmol) and the suspension
was stirred until a transparent solution was obtained after 12 h. The sol-
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127.5, 127.81, 128.0, 129.1, 129.8, 133.8, 135.8, 136.6 (Ph), 170.7 ppm
(NCN); 29Si{1H} NMR (99.36 MHz, C6D6, 258C): d=À83.26 ppm; EI-
MS: m/z: 477 [MÀCl] (100%).
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length restraints and isotropic displacement parameter restraints.
CCDC 781631 (3), CCDC 781628 (4), CCDC 7816329 (5), CCDC 781643
(6·0.5 toluene) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements
Support of the Deutsche Forschungsgemeinschaft is gratefully acknowl-
edged. S.K. is indebted to the Deutscher Akademischer Austausch
Dienst for a research fellowship. G.T. thanks the Alexander von Hum-
boldt Foundation for a research grant. We are grateful to the reviewers
for their useful suggestions.
Chem. Eur. J. 2011, 17, 4283 – 4290
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Received: July 6, 2010
Revised: January 17, 2011
Published online: March 8, 2011
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