Versatile reactivity of a zwitterionic isolable silylene toward ketones: Silicon-mediated, regio- and stereoselective C-H activation

Article abstract of DOI:10.1002/chem.200900318

Reactions of the isolable, ylide-like silylene LSi: (1) (L = CH[(C= CH ₂)CMe][N(Ar)]₂, Ar = 2,6-iPr₂C ₆H₃) with different ketones (benzophenone, benzylideneaceton, acetophenone) have been investigated

Full text of DOI:10.1002/chem.200900318

FULL PAPER
DOI: 10.1002/chem.200900318
Versatile Reactivity of a Zwitterionic Isolable Silylene toward Ketones:
À
Silicon-Mediated, Regio- and Stereoselective C H Activation
Yun Xiong, Shenglai Yao, and Matthias Driess*[a]
Abstract: Reactions of the isolable,
ylide-like silylene LSi: (1) (L=CH[(C=
CH2)CMe][N(Ar)]2, Ar=2,6-iPr2C6H3)
variation of the reaction temperature,
the initial product 2 rearranges under
re-aromatization stereoselectively to
the corresponding siloxindane 3, which
has also been isolated in high yield. In
contrast, reactions of 1 with benzylide-
nacetone and acetophenone furnish the
[4+1] cycloaddition product 4 and the
silyl enol ether 5, respectively. It is pro-
posed that in all reactions the 1,4-dipo-
lar nature of 1 plays key role, leading
to highly reactive donor–acceptor ad-
ducts, which undergo rearrangement
(tautomerization) to the final products.
The new compounds 2, 3, 4, and 5 were
AHCTUNGTRENNUNG
with different ketones (benzophenone,
benzylideneaceton,
acetophenone)
have been investigated. The metastable
dearomatized siloxindane 2, which was
suggested previously as reaction inter-
mediate but could not be detected in
related reactions, has been obtained for
the first time from the regio- and ste-
reoselective addition of silylene 1 to
benzophenone at low temperature. By
1
characterized by H, 13C, and 29Si NMR
spectroscopy, EI-MS, and elemental
analysis, and their structures deter-
mined by single-crystal X-ray diffrac-
tion analysis.
Keywords: cycloaddition · siloxin-
danes · silyl enol ethers · silylation ·
stereoselective addition
Introduction
lenes can be valuable building
blocks in organic synthesis, for
which the generated organosili-
con group can serve as a pro-
tecting group for further chemi-
cal transformations. Likewise,
Silylenes are divalent dicoordinate silicon species typically
with a singlet ground state. They feature a lone pair of elec-
trons and an empty 3p-valence orbital localized at silicon,
which represent the HOMO and LUMO, respectively. Thus,
silylenes can act both as Lewis acids, for example, in reac-
tions with nucleophiles, and as Lewis bases, for example, in
reactions with electrophiles.[1] Moreover, their carbene-like
electron deficiency enables a variety of facile insertion reac-
À
the direct formation of Si C
bonds through insertion and cy-
cloaddition reactions of sily-
lenes with unsaturated organic
precursors in the vicinity to
other functional groups and at
Scheme 1. Zwitterionic, ylide-
like silylene 1.
À
tions into X Y s- bonds of substrates to yield heteroatom-
substituted silanes[2,3] and new classes of organosilicon com-
pounds that are otherwise difficult to achieve. Since the suc-
cessful synthesis and isolation of several stable silylenes,[4]
including the zwitterionic silylene 1 (Scheme 1),[5] their fasci-
nating reactivity toward a variety of substrates, such as hal-
oalkanes, halosilanes,[6] alkali metal amides,[7,8] alkenes, al-
kynes,[9,10] alcohols,[11–13] as well as white phosphorus,[14] has
been a matter of numerous investigations. Accordingly, sily-
the same time encoding stereochemical information is a
challenging tool in synthetic chemistry.[15] Unexpectedly,
data on the reactivity of stable silylenes toward heteroatom-
ic C=X bonds, in particular to the C=O bond in ketones, is
relatively scarce. In the latter case, merely one isolable N-
heterocyclic silylene,[16] transient silylenes generated in situ
either by thermolysis[17] or photolysis of the corresponding
precursors,[18] and decamethylsilocene[19,20] were employed to
study the reactivity of divalent silicon toward ketones. The
[a] Dr. Y. Xiong, Dr. S. Yao, Prof. Dr. M. Driess
Technische Universitaet Berlin
À
À
conversions led to unexpected new Si C- and Si O-func-
tionalized products, including siloxindanes[17–20] and silyl enol
ethers,[17] depending on the electronic nature of the applied
silylenes and the ketones. The mechanism is unknown and
intermediates could not be observed but it has been pro-
Institute of Chemistry: Metalorganic and Inorganic Materials
Sekr. C2, Strasse des 17. Juni 135, 10623 Berlin (Germany)
Fax : (+49)30-314-29732
E-mail: matthias.driess@tu-berlin.de
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ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5545

posed that [2+1] cycloaddition occurs as an initial step to
give the respective three-membered SiCO cycles, which sub-
rate experiments using isolated 2 dissolved in hexane. Quan-
titative formation of 3 can be achieved after one week at
458C, and colorless crystals of the desired product are acces-
sible by fractional crystallization in 85% yield.
À
sequently rearrange to the final products. Since the new Si
À
C- and Si O-functionalized heterocyclic products could be
valuable precursors for organic transformations in natural
product synthesis,[21] it seems desirable to extend their syn-
thetic access for facile applications in regio- and stereoselec-
tive synthesis by using other silylenes.
Apparently, 2 represents the kinetic product and results
from a [4+1] cycloaddition under concomitant de-aromati-
zation of one phenyl group, whereas 3 is the thermodynamic
product, which benefits from re-aromatization of the cross-
conjugated methylene–cyclohexadiene p-system in 2. Relat-
ed intermediates of 2 with a non-aromatic siloxindane ring
system have been previously proposed but could not be de-
tected for similar reactions of transient silylenes[17,18] and a
stable silylene[16] with benzophenone, respectively. A close
example shows decamethylsilicocene which reacts slowly
with benzophenone in toluene to give the corresponding an-
alogue of 2. However, the latter product does not undergo
re-aromatization and formation of the corresponding ana-
logue of 3.[20]
Recently we reported the reactivity of silylene 1 towards
a variety of saturated and unsaturated substrates.[5,6e,10,13,14,22]
Owing to its 1,4-dipolar nature, 1 shows a markedly distinct
reactivity compared with other stable silylenes. For instance,
H+ addition to 1 occurs solely in position 4 leading to a sily-
liumylidene cation,[22] and a siloxy silylene is formed through
addition of water onto 1.[13] Moreover, the ylide-like nature
of 1 opens up new reaction channels for silylene transforma-
tions with unsaturated substrates such as terminal alkynes
[10]
À
(C H insertion vs. [2+1] cycloaddition). Thus we antici-
pated that the versatile reactivity of 1 (ylide vs. silylene re-
activity) has a drastic influence on the nature of products
yielded by the reaction of 1 with heteroatomic C=X bonds.
In fact, utilization of 1 facilitates for the first time the isola-
tion of a reaction intermediate for the conversion of a stable
silylene with a ketone. Herein, we describe the striking reac-
tivity of 1 toward ketones, which proceeds via silicon-medi-
Although the mechanism is still unknown, it is proposed
that the 1,4-dipolar nature of 1 plays an important role in
the reaction: First, the charge separation in 1 favors a nucle-
ophilic attack of the oxygen atom in benzophenone at the
positively charged, divalent Si atom, leading to the donor–
acceptor adduct A as an initial product (Scheme 3). Owing
to the high Lewis basicity of the SiII lone pair electrons, the
formation of a [2+1] cycloaddition compound in the follow-
ing step seems possible but unlikely due to steric congestion
and strain energy of the Si-O-C three-membered ring.
Therefore, we propose that A isomerizes to B and subse-
quently to the [4+1] cycloaddition product 2. The latter re-
À
ated C H activation and an unprecedented tautomerization.
Results and Discussion
À
The reaction of silylene 1 with an equimolar amount of ben-
zophenone in hexane proceeds readily even at À788C.
When the reaction mixture is allowed to warm up to 08C
within 4 h, quantitative formation of the remarkable silyl
enol ether 2 is observed, which is isolated in the form of col-
orless crystals in 87% yield. However, performing the reac-
tion at ambient temperature produces a mixture of 2 and its
silyl ether tautomer 3 (Scheme 2). The amount of 3 can be
easily increased at the expense of 2 by prolonging the reac-
tion time and increasing the temperature. In other words, 2
rearranges completely to 3, which has been proven by sepa-
arranges through silicon-mediated C H activation and re-ar-
omatization to give compound 3.
Compounds 2 and 3 have been unambiguously character-
ized by H, 13C, and 29Si NMR spectroscopy, mass spectrom-
1
etry, and elemental analysis. Since two chiral centers are
present in both compounds, the formation of two diastereo-
mers is possible in each case. However, only one diastereo-
mer of 2 is formed with the R,S configuration as shown by
1H NMR spectroscopy of the resulting reaction mixture. Ap-
parently, the formation of 2 proceeds in a regio- and stereo-
selective manner. Similarly in the case of 3, one diastereo-
mer (with S,S or R,R configuration) dominates (>93%) in
the resulting reaction mixture. The characteristic multiplet
1
at d=3.35 ppm in the H NMR spectrum of 2 results from
the proton bound to a sp3-hybridized g-C atom of the cyclo-
hexadiene ring. Accordingly, this signal is absent in the
1H NMR spectrum of 3. Instead, two new singlets at d=5.10
(93% of a diastereomer) and 5.02 ppm (7% of another dia-
stereomer) appear for the corresponding resonances of the
benzylic a-protons. The molecular structures of 2 and 3 have
been confirmed by single-crystal X-ray diffraction analyses
(Figure 1 and Figure 2).
Compound 2 crystallized in the monoclinic space group
P21/c with R,S configuration (Figure 1). The silicon center is
À
tetrahydrally coordinated, featuring a Si O (166.3(2) pm)
À
and a Si C (186.1(2) pm) single bond. The non-aromatic cy-
Scheme 2. Formation of 2 and 3 from silylene 1 and benzophenone.
clohexadiene-like six-membered ring (C30 to C35) in 2 is
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Reactions of Zwitterionic Silylene toward Ketones
FULL PAPER
Compound 3 with S,S and
R,R configuration crystallizes in
¯
the triclinic space group P1
(Figure 2). Similar to the mo-
lecular structure of 2, the sili-
con atom possesses a tetrahe-
dral coordination. The two an-
nelated rings of the siloxindane
skeleton are almost coplanar
À
and the C35 C36 distance of
152.6(2) pm represents a typical
single bond. Despite the afore-
mentioned difference, the geo-
metric parameters within the
six-membered C3N2Si ring are
comparable to those observed
in 2.
Treatment of the stable sily-
lene 1 with one equivalent of
benzylideneacetone at room
temperature leads to the quan-
titative formation of the [4+1]
cycloaddition
product
4
Scheme 3. Proposed mechanism for the formation of 2 and 3 via the intermediate B.
(Scheme 4), which is analogous
Figure 2. Molecular Structure of 3. Thermal ellipsoids are drawn at the
50% probability level. Hydrogen atoms (except for those at C1, C3, and
C36 are omitted for clarity. Selected bond lengths [pm] and angles [8]:
Figure 1. Molecular structure of (R,S)-2. Thermal ellipsoids are drawn at
the 50% probability level. Hydrogen atoms (except for those at C1, C3,
and C30) are omitted for clarity. Selected bond lengths [pm] and angles
À
À
À
À
Si1 O1 164.5(1), Si1 N1 171.4(1), Si1 N2 172.2(1), Si1 C30 184.9(1),
À
À
À
À
[8]: Si1 O1 166.3(2), Si1 N1 171.8(2), Si1 N2 171.3(2), Si1 C30 186.1(2),
À
À
À
O1 C36 143.8(1), C36 C35 152.6(2), C35 C30 139.5(2); N2-Si1-N1
105.11(10), O1-Si1-C30 93.86(9), N1-Si1-N2 104.91(6), O1-Si1-C30
94.03(6).
À
À
À
À
O1 C36 140.2(3), C36 C35 135.0(3), C35 C34 144.8(3), C34 C33
À
À
À
À
134.4(3), C33 C32 144.7(4), C32 C31 132.7(3), C31 C30 149.4(3), C35
C30 150.3(3); N2-Si1-N1 105.11(10), O1-Si1-C30 93.86(9).
puckered with a folding angle of 17.68 between the planes
defined by C30, C31, C35, and the plane defined by C31–
to that observed with another stable silylene.[16] The reaction
mechanism should be similar to that for compound 2. Com-
pound 4 was isolated in the form of colorless crystals in
94% yield. The latter was fully characterized by NMR spec-
À
C35. In line with that, the distances of C30 C31 (149.4 pm)
À
and C30 C35 (150.3 pm) show typical single-bond character,
1
whereas that of C35 C36 (135.0 pm) is indicative for a C=C
troscopy, EI-MS, and elemental analysis. The H, 13C, and
À
double bond.
29Si NMR spectra of the resulting reaction solution show
Chem. Eur. J. 2009, 15, 5545 – 5551
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5547

M. Driess et al.
equivalent of acetophenone at room temperature. In fact,
À
sole formation of 5 is a result of the relatively high C H
acidity of the a-methyl group (Scheme 4).
The formation of 5 is analogous to that observed with a
transient silylene and acetophenone.[17] Its generation can be
rationalized by a reaction pathway involving prior formation
of donor–acceptor adduct C followed by intramolecular
proton abstraction and enolization through the divalent Si
atom (Scheme 5, pathway i). An alternative pathway to 5 is
the formation of a 1,4-addition intermediate based on reac-
tion of silylene 1 with the enol form of the acetophenone
(Scheme 5, pathway ii). Unfortunately, attempts to detect a
reaction intermediate by means of low-temperature
1H NMR spectroscopy (À808C) failed.
Scheme 4. Synthesis of 4 and 5.
only one set of signals, indicating a highly regio- and stereo-
specific reaction. The doublet of doublets at d=1.49 ppm in
1
the H NMR spectrum can be assigned to the resonance of
the methyl group of the OCMe protons, which undergo
long-range coupling with the two protons on the five-mem-
bered ring. The latter protons in turn resonate at d=3.22
and 4.52 ppm, respectively. The molecular structure of 4 was
established by a single-crystal X-ray diffraction analysis
(Figure 3). Compound 4 crystallizes in the triclinic space
Scheme 5. Proposed mechanism for the formation of 5.
Compound 5 was isolated as colorless crystals in 86%
1
yield and fully characterized by H, 13C, 29Si NMR spectros-
copy, mass spectrometry, and elemental analysis. The dou-
blets at d=3.06 and 4.49 ppm in the H NMR spectrum with
Figure 3. Molecular Structure of 4. Thermal ellipsoids are drawn at 50%
probability level. Hydrogen atoms (except for those at C1, C3, C32, and
C33) are omitted for clarity. Selected bond lengths [pm] and angles [8]:
1
a coupling constant of J=2 Hz can be assigned to the germi-
nal protons of the PhCCH2 moiety, while the singlet at d=
5.37 ppm represents the SiH proton of the silyl enol ether.
According to X-ray diffraction analysis (Figure 4), com-
pound 5 crystallizes in the monoclinic space group C2/c. The
À
À
À
À
Si1 O1 166.4(1), Si1 N1 171.8(1), Si1 N2 172.0(1), Si1 C33 188.7(2),
À
À
À
O1 C31 139.3(2), C31 C32 132.5(2), C32 C33 151.1(2); N1-Si1-N2
105.15(6), O1-Si1-C33 95.00(6).
À
short C30 C31 distance of 131.4(3) pm is indicative for a
double bond. The metric parameters for 5 are similar to
¯
group P1 with R,R or S,S configurations. The five-membered
SiOC3 ring is nearly planar and perpendicular to the six-
membered SiN2C3 ring. The spiro-silicon atom is tetrahe-
drally coordinated, featuring four single bonds, which are
each within the respective normal bond length range.[23]
To learn whether the possible keto–enol tautomerism in
acetophenone changes the nature of the addition product,
we probed the conversion of silylene 1 with one molar
those of other silyl enol ether.[23]
Conclusions
In conclusion, reaction of the zwitterionic stable silylene 1
with benzophenone at À788C leads to the isolation of the
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Reactions of Zwitterionic Silylene toward Ketones
FULL PAPER
phire at 150 K (MoKa radiation, l =0.71073 ꢁ). The structures were
solved by direct methods and refined on F2 with the SHELX-97[24] soft-
ware package (Table 1). The positions of the H atoms were calculated
Table 1. Crystal and refinement data for 2, 3, 4, and 5.
Compound
2
3
4
5
empirical
formula
M
C42H50N2SiO C42H50N2SiO C39H50N2SiO C37H48N2SiO
626.93
626.93
90.90)
564.86
crystal system monoclinic
triclinic
P1
triclinic
P1
monoclinic
C2/c
21.2473(5)
10.1482(2)
30.7649(8)
90
¯
¯
space group
a [ꢁ]
b [ꢁ]
c [ꢁ]
P21/c
9.3263(3)
22.0602(7)
17.9069(7)
90
11.3945(3)
11.8961(4)
14.8824(3)
78.296(2)
82.767(2)
68.200(3)
1831.26(9)
2
8.9500(2)
12.7001(6)
15.5694(5)
95.481(3)
96.704(3)
97.307(3)
1732.36(11) 6629.4(3)
2
1.133
0.099
a [8]
b [8]
104.129(4)
90
3572.7(2)
4
91.980(2)
90
g [8]
V [ꢁÀ3
]
Z
8
dcalcd [MgmÀ3
]
1.166
1.137
0.098
1.132
0.101
m (MoKa
)
0.100
[mmÀ1
]
Figure 4. Molecular Structure of 5. Thermal ellipsoids are drawn at 50%
probability level. Hydrogen atoms (except for those at C1, C3, Si1, and
C30) are omitted for clarity. Selected bond lengths [pm] and angles [8]:
reflections
collected
independent
reflections
18951
6261
17089
6447
15096
6086
26495
5805
À
À
À
À
Si1 O1 163.2(1), Si1 N1 171.6(2), Si1 N2 171.8(2), O1 C31 133.8(2),
À
C30 C31 131.4(3); N2-Si1-N1 104.18(8), O1-Si1-C31 127.5(1), O1-C31-
C30 120.7(2), O1-C31-C32 113.2(2), C30-C31-C32 126.0(2).
R
A
0.0569
4468
0.0167
5597
0.0263
4877
0.0371
4936
with I> 2s(I)
data/
parameters
final R indices 0.0615
[I>2s(I)] R1
6261/424
6447/424
0.0380
6086/398
0.0421
5805/382
0.0561
unusual [4+1] cycloaddition product 2, which contains a
methylenecyclohexadiene moiety that results from de-aro-
matization of a phenyl group. The tendency of 2 to undergo
re-aromatization facilitates its slow tautomerization to 3 al-
ready at room temperature. The latter has also been isolated
and structurally characterized. Reaction of 1 with benzylide-
R indices (all
data) wR2
0.1107
0.1087
0.1041
0.1121
À
neacetone and the higher C H acidic acetophenone yields
and considered isotropically according to a riding model (exception is the
hydrogen atom on silicon in 5 which has been found in the electron den-
sity map). CCDC-719074, CCDC-719075, CCDC-719076, and CCDC-
719077 contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge Crystal-
lographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif
the expected [4+1] cycloaddition product 4 and the corre-
sponding silyl enol ether 5, respectively. Remarkably, forma-
tion of 2, 3, and 4 occurs regio- and stereospecifically. It is
proposed that in all reactions the 1,4-dipolar nature of 1
plays a key role in facilitating the facile attack of the oxygen
atom on the silicon atom, leading to the formation of
donor–acceptor intermediates, which subsequently undergo
rearrangement (tautomerization) to yield the respective
thermodynamic products.
Syntheses: 2: Ph2CO (0.14 g, 0.77 mmol) was added to a solution of sily-
lene 1 (0.34 g, 0.77 mmol) in hexane (10 mL) at À788C. The reaction
temperature was allowed to warm slowly to 08C within 4 h. At 48C com-
pound 2 crystallized from concentrated hexane solution (5 mL) as color-
less plates in a yield of 0.42 g (0.67 mmol, 87%). M.p. 1598C (decomp);
1H NMR (200.13 MHz, [D6]benzene, 258C):
7.0 Hz, 3H; CHMe2), 1.28 (d, 3J
(H,H)=7.0 Hz, 3H; CHMe2), 1.30 (d,
3J(H,H)=7.0 Hz, 3H; CHMe2), 1.32 (d, 3J
(H,H)=7.0 Hz, 3H; CHMe2),
1.33 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2), 1.35 (d, 3J
(H,H)=7.0 Hz, 3H;
CHMe2), 1.39 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2), 1.47 (d, 3J
(H,H)=
7.0 Hz, 3H; CHMe2), 1.59 (s, 3H; NCMe), 3.35 (m, 1H; OSiCH CH=),
3.47 (s, 1H; NCCH2), 3.60 (sept., 3J
(H,H)=7.0 Hz, 1H; CHMe2), 3.88
d ACHTUNGTRENNUNG(H,H)=
=1.15 (d, 3J
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
Experimental Section
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
À
General considerations: All experiments and manipulations were carried
out under dry oxygen-free nitrogen using standard Schlenk techniques or
in an MBraun inert atmosphere dry box, containing an atmosphere of pu-
rified nitrogen. Solvents were dried by standard methods and freshly dis-
tilled prior to use. The starting material silylene 1 was prepared accord-
ing to a literature procedure.[5] The NMR spectra were recorded with
Bruker spectrometers ARX200, AV400, and with residual solvent signals
as internal reference (1H and 13C{H}) or with an external reference
(SiMe4 for 29Si). Abbreviations: s=singlet; d=doublet; t=triplet; sept=
septet; m=multiplet; br=broad.
AHCTUNGTRENNUNG
(m, 3H; CHMe2), 4.06 (s, 1H; NCCH2), 5.39 (m, 1H; OSiCHCH=), 5.50
(s, 1H; g-CH), 5.56 (m, 2H; OSiCH CH=CHCH=), 6.37 (d, 3J
C
À
9.7 Hz, 1H; PhC=CCH=), 7.01–7.22 ppm (m, br, 11H; C6H5, 2,6-
iPr2C6H3), 7.69 (m, 1H); 13C{1H} NMR (100.61 MHz, [D6]benzene, 258C):
d=21.7 (NCCH3), 23.6, 24.3, 25.1, 25.4, 25.5, 25.8, 26.6, 26.7 (CHMe2,
OSiCHCH=), 28.4, 28.8, 28.9 (CHMe2), 88.7 (NCCH2), 108.9 (g-C),
114.5, 123.3, 123.8, 124.9, 124.4, 124.6, 124.7, 125.5, 127.4, 127.8, 127.9,
128.1, 128.7, 134.3, 135.4, 137.2, 141.4, 147.4, 148.1, 148.2, 149.0, 149.1,
À
149.8 ppm (NCMe, NCCH2, vinyl CH=(cyclohexadiene system), CPh,
Single-crystal X-ray structure determination: Crystals were each mounted
on a glass capillary in perfluorinated oil and measured in a cold N2 flow.
The data of 2–5 were collected on an Oxford Diffraction Xcalibur S Sap-
2,6-iPr2C6H3); 29Si{1H} NMR (79.49 MHz, [D6]benzene, 258C): d=
À22.0 ppm (s); EI-MS: m/z (%): 626.5 (31) [M+], 611.4 (100) [M+ÀMe],
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5549

M. Driess et al.
583.3 (55) [M+ÀiPr]; elemental analysis calcd (%) for C42H50N2SiO: C
(NCMe, NCCH2, PhCCH2, 2,6-iPr2C6H3); 29Si{1H} NMR (79.49 MHz,
[D6]benzene, 258C): d=À51.5 ppm (s); EI-MS: m/z (%): 564.4 (14) [M+],
549.3 (100) [M+ÀMe], 521.3 (15) [M+ÀiPr]; elemental analysis calcd
(%) for C37H48N2SiO: C 78.67, H 8.56, N 4.96; found: C 78.47, H 8.46, N
4.97.
80.46, H 8.04, N 4.47; found: C 80.21, H 7.94, N 4.45.
3: Ph2CO (0.26 g, 1.41 mmol) was added to a solution of silylene 1
(0.63 g, 1.41 mmol) in hexane (15 mL) at room temperature and the solu-
tion was warmed to 458C. After one week the reaction was completed
and the solution was concentrated to 5 mL and cooled at 48C. The col-
lected colorless crystals amounted to 0.76 g (1.20 mmol, 85%). M.p.
1
2078C (decomp); H NMR (200.13 MHz, [D6]benzene, 258C): d=0.01 (d,
3J
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(H,H)=7.0 Hz, 3H; CHMe2), 0.04 (d, 3J
1.12–1.22 (3
ꢂ
d, 3J(H,H)=7.0 Hz, 9H; CHMe2), 1.35–1.43 (3
ꢂ
Acknowledgements
3J(H,H)=7.0 Hz, 9H; CHMe2), 1.57 (s, 3H; NCMe), 3.28 (s, 1H;
NCCH2), 3.34 (m, 2H; CHMe2), 3.88 (m, 2H; CHMe2), 3.95 (s, 1H;
This work was supported by the Deutsche Forschungsgemeinschaft.
NCCH2), 5.10 (s, 1H; PhCH), 5.38 (s, 1H; g-H), 5.93 (d, 3J
ACHTUNGTRENNUNG
6.5 Hz, 2H; C6H4), 6.32 (d, 3J
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
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13C{1H} NMR (100.61 MHz, [D6]benzene, 258C): d=22.1 (NCCH3), 24.5,
24.6, 24.7, 24.9, 25.2, 25.4, 26.4, 26.8 (CHMe2), 27.8, 28.2, 29.1, 29.2
(CHMe2), 80.3 (CHPh), 86.2 (NCCH2), 103.8 (g-C), 123.6, 124.5, 124.6,
124.8, 124.9, 126.8, 127.4, 127.6, 127.7, 128.1, 128.2, 128.3, 130.1, 133.5,
134.6, 136.0, 141.5, 142.4, 148.2, 148.7, 148.9, 149.7, 150.5, 155.0 ppm
(NCMe, NCCH2, C6H4, C6H5, 2,6-iPr2C6H3); 29Si{1H} NMR (79.49 MHz,
[D6]benzene, 258C): d=À33.3 ppm (s); EI-MS: m/z (%): 626.3 (31)
[M+], 611.4 (100) [M+ÀMe], 583.2 (56) [M+ÀiPr]; elemental analysis
calcd (%) for C42H50N2SiO: C 80.46, H 8.04, N 4.47; found: C 80.21, H
7.96, N 4.53.
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Chem. 2000, 78, 1526.
4: Benzylideneacetone (0.23 g, 1.53 mmol) was added to a solution of si-
lylene 1 (0.68 g, 1.53 mmol) in hexane (15 mL) at room temperature. The
reaction was completed within one hour. The solution was concentrated
to about 5 mL and cooled at 48C. The product 4 crystallized as colorless
1
crystals. Yield: 0.85 g (1.44 mmol, 94%). M.p. 1368C (decomp); H NMR
(200.13 MHz, [D6]benzene, 258C): d=0.63 (d, 3J
ACHTUNGTRENNUNG
CHMe2), 0.94 (d, 3J
N
ACHTUNGTRENNUNG
[5] M. Driess, S. Yao, M. Brym, C. van Wꢃllen, D. Lenz, J. Am. Chem.
Soc. 2006, 128, 9628.
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
[6] a) D. F. Moser, A. Naka, L. A. Guzei, T. Mꢃller, R. West, J. Am.
Chem. Soc. 2005, 127, 14730; b) M. Delawar, B. Gehrhus, P. B.
Hitchcock, Dalton Trans. 2005, 2945; c) B. Gehrhus, P. B. Hitchcock,
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Yao, M. Driess, Organometallics 2009, 28, 1927.
ACHTUNGTRENNUNG
G
G
ACHTUNGTRENNUNG
3H; OCMe), 3.00 (sept. 3J
ACHTUNGTRENNUNG
3.40 (s, 1H; NCCH2), 3.60 (sept. 3J
R
3
(sept. J
(H,H)=7.0 Hz, 2H; CHMe2), 4.02 (s, 1H; NCCH2), 4.52 (m, 1H;
OCCH), 5.44 (s, 1H; g-CH), 6.76–7.23 ppm (m, 11H; Ph, iPr2C6H3);
13C{1H} NMR (100.61 MHz, [D6]benzene, 258C): d=18.1 (NCCH3), 21.6,
23.9, 24.0, 24.6, 24.7, 25.1, 25.2, 26.2, 26.5, 28.2, 28.3, 28.4, 29.0, 31.7
(NCMe, OCMe, PhCH, CHMe2), 88.4 (NCCH2), 104.8 (OCCH), 107.0 (g-
C), 124.1, 124.4, 125.0, 125.1, 125.2, 127.9, 128.1, 128.4, 128.9, 136.5, 137.1,
139.7, 142.2, 147.8, 148.5, 148.6, 149.1, 149.9, 153.6 ppm (NCMe, NCCH2,
PhC, 2,6-iPr2C6H3); 29Si{1H} NMR (79.49 MHz, [D6]benzene, 258C): d=
À23.8 ppm (s); EI-MS: m/z (%): 590.4 (100) [M+], 575.4 (82) [M+ÀMe],
547.2 (50) [M+ÀiPr]; elemental analysis calcd (%) for C39H50N2SiO: C
79.27, H 8.53, N 4.74; found: C 79.60, H 8.39, N 4.76.
5: Acetophenone (0.12 mL, d=1.03 gmLÀ1, 1.01 mmol) was added to a
solution of silylene 1 (0.45 g, 1.01 mmol) in hexane (8 mL) at room tem-
perature. The reaction mixture was completed immediately. The solution
was concentrated to about 5 mL and cooled at 48C. The product 5 crys-
tallized as colorless crystals. Yield: 0.49 g (0.87 mmol, 86%). M.p. 1468C
(decomp); 1H NMR (200.13 MHz, [D6]benzene, 258C): d=0.98 (d,
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3J
1.24 (d, 3J
CHMe2), 1.36 (d, 3J
7.0 Hz, 3H; CHMe2), 1.51 (s, 3H; NCMe), 3.06 (d, JACHTUNGTRENNUNG
R
ACHTUNGTRENNUNG
E
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
2
PhCCH2), 3.45 (sept. 3J
ACTHNUTRGNENU(G H,H)=7.0 Hz, 1H; CHMe2), 3.48 (s, 1H;
NCCH2), 3.57 (sept. 3J (H,H)=7.0 Hz, 1H; CHMe2), 3.83 (sept.
3J(H,H)=7.0 Hz, 2H; CHMe2), 4.02 (s, 1H; NCCH2), 4.49 (d, J (H,H)=
2
2.0 Hz, 1H; PhCCH2), 5.35 (s, 1H; g-CH), 5.37 (s, 1H; SiH), 6.50–
7.29 ppm (m, 11H; Ph, iPrC6H3); 13C{1H} NMR (100.61 MHz,
[D6]benzene, 258C): d=21.5 (NCCH3), 24.1, 24.3, 24.6, 24.8, 25.0, 25.4,
26.0, 26.1 (CHMe2), 28.2, 28.5, 28.7, 28.8 (CHMe2), 86.6 (NCCH2), 94.7
(PhCCH2), 103.1 (g-C), 124.7, 124.8, 125.0, 125.2, 125.4, 128.1, 128.5,
134.9, 135.7, 136.4, 140.9, 148.3, 148.4, 148.7, 149.7, 149.8, 154.5 ppm
5550
www.chemeurj.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 5545 – 5551

Reactions of Zwitterionic Silylene toward Ketones
FULL PAPER
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Received: February 5, 2009
Published online: April 22, 2009
Chem. Eur. J. 2009, 15, 5545 – 5551
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5551