Striking reactivity of a stable, Zwitterionic silylene towards substituted diazomethanes, Azides, and isocyanides

Article abstract of DOI:10.1002/chem.200901337

The reactivity of the zwitterionic N-heterocyclic silylene (NHS) LSi: 1 (L = Ar-N-C(Me)=CH-Q= CH₂)-N-Ar, Ar = 2,6-iPr₂C ₆H₃), towards diphenyldiazomethane (Ph₂CN ₂), trimethylsilyl azide (M

Full text of DOI:10.1002/chem.200901337

DOI: 10.1002/chem.200901337
Striking Reactivity of a Stable, Zwitterionic Silylene Towards Substituted
Diazomethanes, Azides, and Isocyanides
Yun Xiong, Shenglai Yao, and Matthias Driess*[a]
Dedicated to Professor Yitzhak Apeloig on the occasion of his 65th birthday
À
Abstract: The reactivity of the zwitter-
ionic N-heterocyclic silylene (NHS)
CPh2)2 2 (80% yield), whereas the
treatment of 1 with Me3SiN3 gives the
tion of C6H11 NC gives the silyl cya-
nide LSi(R)CN (R=cyclohexyl)
4
À À
À
LSiD
1
(L=Ar N C(Me)=CH C
G
spirobicyclic
ACHTUGNRTEN(NUGN NNSiMe3)2 3 (67% yield), and addi-
silatetrazoline
LSi-
(32% yield) along with the unexpected
azasilacyclobutane 5 (41% yield). The
novel compounds were fully character-
À À
CH2) N Ar, Ar=2,6-iPr2C6H3), to-
wards diphenyldiazomethane (Ph2CN2),
trimethylsilyl azide (Me3SiN3), and cy-
1
ized by H, 13C, and 29Si NMR spectros-
Keywords:
diiminylsilanes
silatetrazolines · silylenes
cyanides
·
·
À
clohexyl isocyanide (C6H11 NC) is re-
ported. The addition of Ph2CN2 to 1
leads to the diiminylsilane LSiACTHNUGRTNEUNG(N=
copy, ESIMS, elemental analysis, and
single-crystal X-ray diffraction.
·
heterocycles
Introduction
For azides, it has been shown that A–C readily react with
Me3SiN3, Ph3CN3, Ph3SiN3, and AdN3 (Ad=adamantyl) to
give the different products D–G (Scheme 2), depending on
Following the successful isolation of the thermally stable N-
heterocyclic silylenes (NHSs) A–C in the last decade
(Scheme 1),[1] their reactivities towards numerous unsaturat-
Scheme 1. Isolable N-heterocyclic stable silylenes.
ed organic and organometallic substrates have been exam-
ined in detail.[2] Among these, the behavior of A–C towards
organic azides, cyanides, and isocyanides has also been stud-
ied.[3]
Scheme 2. Products resulting from the reactions between silylenes A–C
and organic azides, cyanides, and isocyanides.
[a] Dr. Y. Xiong, Dr. S. Yao, Prof. Dr. M. Driess
Technische Universitꢀt Berlin
Institute of Chemistry: Metalorganic and Inorganic Materials
Sekr. C2, Strasse des 17. Juni 135, 10623 Berlin (Germany)
Fax : (+49)30-314-29732
the nature of the reactant and reaction conditions.[3] Similar-
ly, the reactions of A and B with organic cyanides and iso-
cyanides revealed significant differences (Scheme 2): Sily-
E-mail: matthias.driess@tu-berlin.de
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FULL PAPER
lene A is inert towards excess quantities of organic cyanides
even at elevated temperature, whereas B readily reacts with
tert-butyl cyanides to give the disilaazetine H.[3c] Moreover,
silylene B reacts with isocyanide to give either the 1-cyano-
2-organo disilane I or the silacyanide 1,1-adduct J, depend-
ing on the reaction conditions. In contrast, A undergoes con-
version with organo isocyanides to give silacyanides of type
J.[2a]
copy). Compound 2 was obtained in almost quantitative
yield through conversion of 1 with diphenyldiazomethane in
the molar ratio of 1:2. The reactivity of A–C towards
Ph2CN2 is currently unknown.
Compound 2 represents the first example of a diiminylsi-
lane. Interestingly, the analogous diiminylaluminumACHTUNGTRENNUNG(III)
À À
À
compound
L’Al
(N=CPh2)2
(L’=Ar N C(Me)=CH
À
C(Me)=N Ar, Ar=2,6-iPr2C6H3) was obtained by Roesky
and co-workers from the reaction of the low-valent L’Al(I)
compound with Ph2CN2 at 608C.[6] Its formation was as-
sumed to result from the primary conversion of two molar
Compared with the stable NHSs A–C, the N-heterocyclic
zwitterionic stable silylene LSiD 1[4] (L=Ar N C(Me)=CH
CACHTUNGTRENNUNG(=CH2) N Ar, Ar=2,6-iPr2C6H3), (Scheme 1) possesses a
À À
À
À À
À
remarkably different reactivity pattern towards saturated
and unsaturated substrates owing to the contribution of the
ylide-like resonance structure 1’ (Scheme 1) to the electronic
ground state. This implies the presence of two reactivity
sites in the molecule with an electrophilic silicon site and a
nucleophilic exocyclic methylene group. In fact, the zwitter-
ionic nature of 1 causes a fascinating reactivity pattern:
equivalents of Ph2CN2 to Ph2C=N N=CPh2 and subsequent
À
insertion of Al(I) into the N N bond, which was proven by
carrying out reliable experiments.[6] In contrast, we can con-
clude that the formation of 2 does not result from an inser-
À
tion reaction of 1 to the primarily generated Ph2C=N N=
À
CPh2 moiety, because 1 is resistant towards Ph2C=N N=
CPh2, even after boiling in toluene for several hours. Al-
though the mechanism is still unknown, we suggest that the
reaction of 1 with Ph2CN2 occurs through the diazasilacyclo-
propen [2’] as the initial product (Scheme 3). The formation
of related and even isolable diazametallacyclopropenes con-
taining NiN2 and TiN2 cores have been reported for the re-
action of Ph2CN2 with corresponding transition-metal-com-
plex precursors.[7] Subsequently, the proposed diazasilacyclo-
propen intermediate [2’] could be attacked by Ph2CD, which
i) 1,4-addition with HX (X=BACHTNUGRTNEUNG
(C6F5)4,[5a] OH,[5b] or tri-
flate[4]), that is, electrophilic addition of H+ to the exocyclic
methylene group in 1 and addition of the nucleophile X to
the silicon(II) center; ii) facile insertion reactions of silicon
(II) into element–element bonds, for example, the reaction
of 1 with white phosphorus,[5c] halosilanes and halocar-
bons,[5d] ammonia,[5e] terminal alkynes,[5f] as well as primary
NHC to Si addition and subsequent oxygenation of Si to
form isolable silanones[5g] and dioxasiliranes,[5 h] respectively;
iii) cycloadditions with unsaturated organic substrates, for
example, the [2+1] cycloaddition of 1 to alkynes[5f] and ben-
zylideneacetone;[5i] iv) facile coordination to transition-metal
centers in low oxidation state;[5j,k] and v) silicon-mediated
is produced in situ from Ph2CN2 to give product
2
(Scheme 3). A related conversion was observed that in-
volved titanium complexes.[8]
1
Compound 2 has been fully characterized by H, 13C, and
29Si NMR spectroscopy, mass spectrometry, and elemental
analysis. The formation of 2 is accompanied by a large shift
in the 29Si NMR spectrum of Dd=À160 ppm relative to 1
(d=88 ppm). The molecular structure of 2 was confirmed
by single-crystal X-ray diffraction analysis. The silicon atom
in 2 is tetrahedrally coordinated by four nitrogen atoms
[5l,m]
À
C H activation and tautomerization processes.
The un-
usual electronic features of 1 prompted us to include reac-
tivity studies employing unsaturated organic nitrogen sub-
strates for the exploitation of novel building blocks. Herein,
we wish to report the remarkable reactivity of 1 towards di-
À
phenyldiazomethane
(Me3SiN3), and cyclohexyl isocyanide (C6H11NC).
(Ph2CN2),
trimethylsilyl
azide
(Figure 1). The endocyclic Si N (ring) bond lengths in 2
À
À
(Si1 N1 173.5(2), Si1 N2 174.1(2) pm) are almost identical
to the corresponding values in 1 (173.4(2), 173.5(2) pm), but
À
are slightly longer than those of terminal Si N bond lengths
À
À
À
Results and Discussion
(Si1 N3 170.5(2), Si1 N4 170.0(2) pm). Whereas the N1
À
C6, and N2 C18 bond lengths (145.1(3), 145.6(2) pm) are
typical for N C single bonds, the much shorter N3 C30 and
N4 C43 bond lengths (127.0(2), 127.4(2) pm) are indicative
À
À
Treatment of an equimolar amount of 1 with diphenyldiazo-
methane at 08C affords a red solution from which the diimi-
À
nylsilane LSi
(N=CPh2)2 2 was isolated in the form of
of N=C double bonds.
orange-red crystals in 40% yield (Scheme 3). Note that the
Treatment of 1 with excess trimethylsilyl azide at ambient
temperature quantitatively afforded the silatetrazoline 3
(Scheme 4). The iminosilane [3’] has been proposed as a re-
active intermediate, which undergoes immediate conversion
with trimethylsilyl azide in a [3+2] cycloaddition process to
give the silatetrazoline 3 (Scheme 4). The formation of 3 is
reminiscent of the result of the reaction of L’Al(I) with
Me3SiN3.[9]
expected silaethene LSi=CPh2 could not be detected in the
1
reaction mixture (by using H, 13C, and 29Si NMR spectros-
Notably, and in contrast to the result mentioned above,
the reactions of the stable silylenes A–C with an excess of
Me3SiN3 exclusively afforded the corresponding azido(trime-
thylsilylamido)silanes D[3] (Scheme 2). The formation of a si-
Scheme 3. Formation of 2.
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8543

M. Driess et al.
Figure 2. Molecular structure of 3. Thermal ellipsoids are drawn at the
50% probability level. Hydrogen atoms (except for those at C1) are
À
omitted for clarity. Selected bond lengths (pm) and angles (8): Si1 N1
Figure 1. Molecular structure of 2. Thermal ellipsoids are drawn at the
50% probability level. Hydrogen atoms (except for those at C1) are
À
À
À
À
173.9(2), Si1 N2 173.07(1), Si1 N3 175.7(1), Si1 N6 172.1(1), N1 C2
À
À
À
À
141.7(2), N1 C6 145.8(2), N2 C4 143.1(2), N2 C18 146.3(2), Si2 N3
À
À
omitted for clarity. Selected bond lengths (pm): Si1 N4 170.00(2), Si1
À
À
À
À
178.1(1), Si3 N6 176.9(1), N3 N4 140.7(2), N4 N5 125.9(2), N5 N6
À
À
À
À
N3 170.6(2), Si1 N1 173.5(2), Si1 N2 174.1(2), N1 C2 142.2(2), N1 C6
À
À
À
À
142.6(2), C1 C2 139.6(3), C2 C3 141.5(2), C3 C4 138.1(3), C4 C5
144.6(3); N1-Si1-N2 103.07(7), N3-Si1-N6 89.81(6).
À
À
À
À
145.1(3), N2 C4 140.7(2), N2 C18 145.6(2), N3 C30 127.0(2), N4 C43
À
À
À
À
127.4(2), C1 C2 134.4(3), C2 C3 145.9(3), C3 C4 134.4(3), C4 C5
149.4(3); N1-Si1-N2 103.48(8), N3-Si1-N4 110.01(8), N1-Si1-N3 109.31(8),
N1-Si1-N4 113.24(8), N2-Si1-N3 117.52(8), N2-Si1-N4 103.19(8).
À
SiN4 ring in 3 (Si1 N3 175.7(2), 172.1(2) pm) vary a little.
The six-membered SiN2C3 ring is puckered with a folding
angle of 41.68 between the plane defined by the Si1, N1, and
N2 atoms and that by the N1, C2, C3, C4, and N2 atoms. In
contrast, the five-membered SiN4 ring is almost planar
À
(mean deviation from the plane=2.2 pm.). The N3 N4 and
À
N5 N6 bond lengths (140.6(3) and 142.6(2) pm) are typical
À
À
of N N single bonds, whereas the much shorter N4 N5
bond length of 125.9(2) pm is indicative of a N=N double
bond. The N-Si-N angles are in the range of 89.8 to 119.078,
and thus the Si atom is coordinated in a distorted tetrahe-
dral fashion.
Similar to silylene A,[2a] 1 is chemically inert towards or-
ganic cyanides (MeCN, tBuCN). However, 1 readily reacts
with cyclohexyl isocyanide in hexane solutions at room tem-
perature, affording the orange silacyanide 4 and the red aza-
silacyclobutane 5, which can be isolated by fractional crys-
tallization in 32 and 41% yield, respectively (Scheme 5). In-
terestingly, the formation of 5 encompasses a silicon-mediat-
Scheme 4. Treatment of 1 with trimethylsilyl azide.
À
latetrazoline 3, instead of the corresponding azido-
ed coupling of three isocyanide molecules and twofold C H
activation.
(amido)silane (Scheme 4), could be rationalized through the
larger steric congestion of 1 compared with those of A–C.
This is supported by the fact that A–C react similarly with
more bulky substituted azides such as Ph3CN3 and Ph3SiN3
to give silatetrazolines.
It is reasonable to assume that the initial step for the for-
mation of both 4 and 5 is a Lewis acid–base reaction be-
tween 1 and cyclohexyl isocyanide, leading to the silylene–
isocyanide adduct [4’] as an initial intermediate (Scheme 5).
The formation of [4’] appears to be favored owing the high
electrophilicity of Si(II) and the ylide-like structure of 1.
Likewise, related silylene–isocyanide adducts were previous-
ly observed by Tokitoh and co-workers.[10] Moreover, em-
ploying the cycloorganosilylene reported by Kira and co-
workers led to the isolation of a [5’]-type adduct (Scheme 5)
that contains a heteroallenic Si=C=N moiety.[11] Apparently,
in the case of 1, the adducts [4’] and [5’] undergo further re-
The 29Si NMR spectrum of 3 shows three resonances at
d=9.45 and 11.5 (SiMe3) and À40.8 ppm (Sisilylene), respec-
tively. An X-ray diffraction analysis proves that 3 consists of
a spirobicyclic skeleton (Figure 2) with two SiN2C3 and SiN4
rings orthogonal to each other (dihedral angle=89.58). The
À
À
Si N bond lengths of the C3N2Si ring in 3 (Si1 N1 173.9(2),
À
Si1 N2 173.1(2) pm) are similar to those in 1 (173.4(2),
À
173.5(2) pm), whereas those of the Si N bond lengths of the
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Reactivity of a Stable, Zwitterionic Silylene
FULL PAPER
Figure 3. Molecular structure of 4. Thermal ellipsoids are drawn at the
50% probability level. Hydrogen atoms are omitted for clarity. Selected
À
À
À
bond lengths (pm) and angles (8): Si1 N1 172.0(4), Si1 N2 172.5(4), Si1
À
À
À
À
C30 188.5(2), Si1 C31 187.4(2), N3 C30 111.3(2), N1 C2 138.4(5), N2
À
À
C4 145.6(5), N2 C18 145.8(5), N1 C6 144.8(6); C30-Si1-C31 104.69(7),
N1-Si1-N2 104.67(6), N2-Si1-C31 116.4(2), N1-Si1-C31 115.7(2), N2-Si1-
C30 107.5(2), N1-Si1-C30 107.5(2).
Scheme 5. Formation of 4 and 5 through the proposed intermediates [4’],
[5’], [5’’], and [5’’’].
actions either to afford compound 4 through cyclohexyl mi-
gration to the divalent silicon center, or they react with two
isocyanide molecules to yield the novel azasilacyclobutane
5. We assume that the adduct [5’] initially reacts with one
molecule of isocyanide through [2+2] cycloaddition to give
the transient carbene [5’’], which couples to one molecule of
isocyanide to yield the transient species [5’’’] that contains
an excocyclic C=C=N moiety at the SiC2N ring (Scheme 5).
À
The mechanism for the twofold C H activation of a cyclo-
hexyl group and the concomitant dihydrogen transfer to a
C=N moiety in hypothetical [5’’’] to give the final product 5
remains unknown. The driving force for the latter process
could be attributed to the close proximity of the basic C=C=
N group to the cyclohexyl group attached to the exocyclic
C=N group in [5’’’]. Clearly, further investigations are neces-
sary to elucidate the mechanism.
Both products 4 and 5 were fully characterized by NMR
spectroscopy, ESIMS, and elemental analysis. Their molecu-
lar structures were established by single-crystal X-ray dif-
fraction analyses as shown in Figures 3 and 4, respectively.
Compound 4 crystallizes in the monoclinic space group P21.
As expected, the silicon atom adopts a tetrahedral coordina-
tion geometry. The SiN2C3 heterocycle is puckered with a
Figure 4. Molecular structure of 5. Thermal ellipsoids are drawn at the
50% probability level. Hydrogen atoms (except for those at N5, C32,
and C50) are omitted for clarity. Selected bond lengths (pm) and angles
À
À
À
À
(8): Si1 N1 173.0(2), Si1 N2 172.6(2), Si1 N3 170.6(2), Si1 C30 190.6(2),
À
À
À
À
C30 C31 147.0(3), C31 C32 134.7(3), N4 C30 129.6(3), N5 C32
À
À
À
À
138.3(3), N4 C45 142.2(3), C45 C50 133.0(3), N3 C31 144.8(2), N1 C2
142.3(2), N2 C4 141.7(2), C1 C2 137.4(3), C2 C3 143.0(3), C3 C4
136.7(3), C4 C5 146.1(3); N3-Si1-N2 117.36(8), N3-Si1-N1 118.00(8), N2-
Si1-N1 103.83(8), N3-Si1-C30 76.34(8), N2-Si1-C30 120.71(9), N1-Si1-C30
119.83(8), C31-N3-Si1 96.12(12), C30-N4-C45 120.50(18).
À
À
À
À
À
strongly puckered six-membered SiN2C3 ring and a planar
four-membered SiNC2 ring, which are orthogonal to each
other. Remarkably, the C50, C45, N4, C32, and N5 atoms, as
well as the four-membered SiNC2 ring have a co-planar ori-
entation to each other, which implies the presence of a con-
À
folding angle of 25.28. The Si N bond length of the C3N2Si
ring are similar to the corresponding values in 2 and 3 and
À
À
À
À
those in the precursor 1. The Si1 C30 and Si1 C31 lengths
jugated p system. Accordingly, the respective C C and C N
bond lengths show expected alternations.
À
represent common values for Si C single bonds, whereas
À
the C30 N3 bond length of 111.3(2) pm is typical of a cya-
nide group.
¯
Compound 5 crystallizes in the triclinic space group P1.
The structure of 5 consists of a spirobicyclic skeleton with a
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M. Driess et al.
collected reflections; 8401 crystallographically independent reflections
(Rint =0.0387); 5612 reflections with I>2s(l); qmax =258; R(Fo)=0.0491
(I>2s(l)); wR(F2o)=0.0839 (all data); 545 refined parameters.
Conclusion
We have found that the reaction of the zwitterionic stable si-
lylene 1 with unsaturated nitrogen substrates opens facile
access to unprecedented building blocks in organosilicon
heteroatom chemistry. Thus, conversion of 1 with diphenyl-
diazomethane leads to the isolation of the first diiminylsi-
lane LSiACHTUNGTRENNUNG(N=CPh2) 2. In contrast to the behavior of the relat-
ed stable NHSs A–C, reaction of 1 with trimethylsilyl azide
solely affords the corresponding silatetrazoline 3, instead of
Syntheses of 2: Ph2CN2 (0.60 g, 3.1 mmol) was added to a solution of 1
(0.68 g, 1.5 mmol) in n-hexane (10 mL)at 08C. The reaction mixture was
allowed to warm to room temperature. Recrystallization of the crystalline
material obtained from hexane at À208C in diethyl ether at room tem-
perature yielded orange-red single crystals of 2 that were suitable for X-
ray diffraction analysis. Yield: 1.00 g (1.24 mmol, 80%); m.p. 1588C (de-
composed); 1H NMR (200.13 MHz, [D6]benzene, 258C): d=0.79 (d,
3J(H,H)=7.0 Hz, 9H; CHMe2), 1.16 (s, 6H; CHMe2), 1.40 (d, 3J(H,H)=
7.0 Hz, 9H; CHMe2), 3.22–3.35 (m, 1H; CHMe2), 3.50 (s, 1H; NCCH2),
3.50–3.74 (m, 3H; CHMe2), 4.15 (s, 1H; NCCH2), 5.62 (s, 1H; g-CH),
6.29–7.27 ppm (m, br, 26H; Ph, 2,6-iPr2C6H3); 13C{1H} NMR
(100.61 MHz, [D6]benzene, 258C): d=22.4–28.8 (CHMe2, NCMe), 86.9
(NCCH2), 108.9 (g-C), 124.5–150.1 ppm (NCMe, NCCH2, 2,6-iPr2C6H3,
N=CPh2); 29Si NMR (79.49 MHz, [D6]benzene, 258C): d=À72.0 ppm (s);
ESIMS: m/z (%): 804 (13) [M+], 789.6 (100) [M+ÀMe], 761.5 (98) [M+
ÀiPr]; elemental analysis calcd (%) for C55H60N4Si: C 82.04, H 7.51, N
6.96; found: C 82.22, H 7.40, N 6.91.
formation of the corresponding azidoACTHNUTRGNEUNG(amido)silane. Conver-
sion of 1 with cyclohexyl isocyanide gives the silacyanide 4,
but also the remarkable azasilacyclobutane 5. The latter re-
sults from a cascade of coupling reactions of three isocya-
À
nide molecules, twofold C H activation, and intramolecular
dihydrogen transfer.
Syntheses of 3: Trimethylsilyl azide (0.39 mL, d=0.88 gmLÀ1, 3.0 mmol)
was added to a solution of silylene 1 (0.29 g, 0.65 mmol) in hexane
(10 mL) at room temperature. The reaction was completed in three days.
The solution was concentrated to approximately 5 mL and cooled to
Experimental Section
General methods and materials: All experiments and manipulations were
carried out under dry oxygen-free nitrogen by using standard Schlenk
techniques or in an MBraun inert atmosphere dry box, which contained
an atmosphere of purified nitrogen. Solvents were dried by standard
methods and freshly distilled prior to use. The starting materials silylene
À208C. Product
3 crystallized as colorless crystals. Yield: 0.28 g
(0.44 mmol, 67%); m.p. 2358C (decomposed); 1H NMR (200.13 MHz,
[D6]benzene, 258C): d=À0.32 (s, 9H; SiMe3), 0.55 (s, 9H; SiMe3), 1.06
(d, 3J(H,H)=7.0 Hz, 3H; CHMe2), 1.17 (d, 3J(H,H)=7.0 Hz, 3H;
CHMe2), 1.18 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2), 1.22 (d, 3J(H,H)=
7.0 Hz, 3H; CHMe2), 1.26 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2), 1.38 (d,
3J(H,H)=7.0 Hz, 3H; CHMe2), 1.39 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2),
1.45 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2), 1.47 (s, 3H, NCMe), 3.25 (sept
3J(H,H)=7.0 Hz, 1H; CHMe2), 3.44 (sept 3J(H,H)=7.0 Hz, 1H;
CHMe2), 3.46 (s, 1H; NCCH2), 3.63 (sept 3J(H,H)=7.0 Hz, 1H;
CHMe2), 3.78 (sept 3J(H,H)=7.0 Hz, 2H; CHMe2), 4.02 (s, 1H;
NCCH2), 5.25 (s, 1H; g-CH), 7.02–7.16 ppm (m, 6H; iPrC6H3);
13C{1H} NMR (100.61 MHz, [D6]benzene, 258C): d=À0.10 (Si(CH3)3),
1.06 (Si(CH3)3), 23.0, 24.7, 24.8, 25.3, 25.4, 25.7, 26.1, 26.4, 27.2, 28.1, 28.5,
28.9, 29.0 (NCMe, CHMe2), 91.1 (NCCH2), 109.0 (g-C), 124.7, 125.2,
125.3, 125.6, 127.5, 127.6, 137.0, 137.7, 144.0, 147.3, 148.0, 148.2, 148.3,
149.8 ppm (NCMe, NCCH2, 2,6-iPr2C6H3); 29Si{1H} NMR (79.49 MHz,
[D6]benzene, 258C): d=À40.8 (LSi), 9.45 (SiMe3), 11.5 ppm (SiMe3);
ESIMS: m/z (%): 647.1 (3) [M+], 632.3 (3) [M+ÀMe], 604.3 (5) [M+
ÀiPr]; elemental analysis calcd (%) for C35H58N6Si3: C 64.96, H 9.03, N
12.99; found: C 64.96, H 8.84, N 12.96.
À
1 and Ph2CN2, as well as Ph2C=N N=CPh2 were prepared according to
the literature procedures in Refs. [4], [12], and [13], respectively. NMR
spectra were recorded with Bruker spectrometers (ARX200, AV400) and
with residual solvent signals as internal references (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. High-resolu-
tion ESIMS were measured on a Thermo Scientific LTQ orbitrap XL.
Single-crystal X-ray structure determination: Crystals were each mounted
on a glass capillary in perfluorinated oil and measured under a flow of ni-
trogen. The data of 2, 3, 4, and 5 were collected on an Oxford Diffraction
Xcalibur S Sapphire at 123 K (MoKa radiation, l=0.71073 ꢂ). The struc-
tures were solved by direct methods and refined on F2 with the SHELX-
97[14] software package. The positions of the H atoms were calculated and
considered isotropically according to a riding model. CCDC-732602,
732603, 732604, and 732605 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.
Syntheses of 4 and 5: Cyclohexyl isocyalide (0.53 mL, d=0.878 gmLÀ1
,
4.3 mmol) was added to a solution of silylene 1 (0.63 g, 1.4 mmol) in
hexane (10 mL) at room temperature. After three days at room tempera-
ture the solution was concentrated to 5 mL and cooled to À208C. The
orange compound 4 (0.25 g, 0.45 mmol, 32%) first crystallized, followed
by the formation of red crystals of 5 (0.45 g, 0.58 mmol, 41%).
Compound 2: Monoclinic; space group P21/n; a=19.7641(3), b=
11.9909(2), c=20.2938(4) ꢂ; b=107.144(2)8; V=4595.72(4) ꢂ3; Z=4;
1calc =1.164 mg/m3; m (MoKa)=0.092 mmÀ1; 41293 collected reflections;
8077 crystallographically independent reflections (Rint =0.0350); 6964 re-
flections with I>2s(l); qmax =25.008; R(Fo)=0.0567 (I>2s(l)); wR(F2o)=
0.1347 (all data); 550 refined parameters.
4: M.p. 1988C (decomposed); 1H NMR (200.13 MHz, [D6]benzene,
258C): d=0.58–1.07 (m, 7H; cyclohexyl), 1.14 (d, 3J(H,H)=7.0 Hz, 3H;
CHMe2), 1.20 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2), 1.27 (d, 3J(H,H)=
7.0 Hz, 3H; CHMe2), 1.31 (d, 3J(H,H)=7.0 Hz, 6H; CHMe2), 1.35 (d,
3J(H,H)=7.0 Hz, 3H; CHMe2), 1.43 (s, 3H; NCMe), 1.52 (d, 3J(H,H)=
7.0 Hz, 3H; CHMe2), 1.61 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2), 3.43 (s,
1H; NCCH2), 3.50–3.60 (m, 1H; CHMe2), 3.62–3.72 (m, 1H; CHMe2),
3.71–3.85 (m, 2H; CHMe2), 4.04 (s, 1H; NCCH2), 5.36 (s, 1H; g-H),
6.96–7.18 ppm (m, br, 6H; 2,6-iPr2C6H3); 13C{1H} NMR (100.61 MHz,
[D6]benzene, 258C): d=21.4, 23.8, 24.2, 24.3, 24.9, 25.1, 26.1, 26.2, 26.3,
26.4, 26.5, 26.6, 27.1, 27.4, 27.7, 28.6, 28.7, 29.1, 29.2 (cyclohexyl, NCMe,
CHMe2), 89.6 (NCCH2), 106.2 (g-C), 124.0, 124.2, 124.5, 125.4, 126.0,
128.5, 128.6, 136.0, 141.1, 147.0, 147.1, 148.2, 149.0, 149.7 ppm (NCMe,
NCCH2, NC, 2,6-iPr2C6H3); 29Si{1H} NMR (79.49 MHz, [D6]benzene,
258C): d = À45.3 ppm (s); ESIMS: m/z (%): 553.4 (18) [M+], 538.4
(100) [M+ÀMe], 10.3 (75) [M+ÀiPr]; elemental analysis calcd (%) for
C36H51N3Si: C 78.06, H 9.28, N 7.59; found: C 77.86, H 9.15, N 7.74.
Compound 3: Monoclinic; space group P21/n; a=12.4172(3), b=
21.7559(5), c=14.0023(3) ꢂ; b=92.208(2); V=3776.83 (15) ꢂ3; Z=2;
1calc =1.138 mg/m3; m (MoKa)=0.157 mmÀ1; 23445 collected reflections;
6641 crystallographically independent reflections (Rint =0.0356); 4545 re-
flections with I>2s(l); qmax =258; R(Fo)=0.0352 (I>2s(l)); wR(F2o)=
0.0882 (all data); 412 refined parameters.
Compound 4: Monoclinic; space group P21; a=8.8465(3), b=20.1261(6),
c=9.9234(3) ꢂ; b=111.857(4); V=1639.81(9) ꢂ3; Z=2; 1calc =1.122 mg/
m3; m (MoKa)=0.099 mmÀ1; 9516 collected reflections; 5466 crystallo-
graphically independent reflections (Rint =0.0156); 4421 reflections with
I> 2s(l), qmax =258; R(Fo)=0.0347 (I>2s(l)); wR(F2o)=0.0907 (all data);
370 refined parameters.
¯
Compound 5: Triclinic, space group P1, a=10.3377(3), b=12.7802(5),
c=20.0685(8) ꢂ; a=101.868(3), b=94.871(3); g=109.864(4)8; V=
2405.59(15) ꢂ3; Z=2; 1calc =1.066 mg/m3; m (MoKa)=0.086 mmÀ1; 21149
8546
www.chemeurj.org
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 8542 – 8547

Reactivity of a Stable, Zwitterionic Silylene
FULL PAPER
5: M.p. 2388C (decomposed); 1H NMR (200.13 MHz, [D6]benzene,
258C): d=0.38–2.85 (m, 33H; cyclohexyl), 1.21 (d, J(H,H)=7.0 Hz, 3H;
[4] M. Driess, S. Yao, M. Brym, C. van Wꢃllen, D. Lenz, J. Am. Chem.
Soc. 2006, 128, 9628.
3
CHMe2), 1.31 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2), 1.33 (d, 3J(H,H)=
7.0 Hz, 3H; CHMe2), 1.34 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2), 1.36 (d,
3J(H,H)=7.0 Hz, 3H; CHMe2), 1.43 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2),
1.44 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2), 1.47 (d, 3J(H,H)=7.0 Hz, 3H;
CHMe2), 1.48 (s, 3H; NCMe), 3.27–3.37 (m, 1H; CHMe2), 3.35–3.45 (m,
1H; CHMe2), 3.42 (s, 1H; NCCH2), 3.67–3.77 (m, 1H; CHMe2), 3.79–
3.89 (m, 1H; CHMe2), 4.02 (s, 1H; NCCH2), 5.29 (s, 1H; g-H), 5.53 (d,
3J(H,H)=10.0 Hz, 1H; C=CH-NHR), 6.13 (t, 3J(H,H)=3.9 Hz, 1H;
[5] a) M. Driess, S. Yao, M. Brym, C. van Wꢃllen, Angew. Chem. 2006,
118, 6882; Angew. Chem. Int. Ed. 2006, 45, 6730; b) S. Yao, M.
Brym, C. van Wꢃllen, M. Driess, Angew. Chem. 2007, 119, 4237;
Angew. Chem. Int. Ed. 2007, 46, 4159; c) Y. Xiong, S. Yao, M. Brym,
M. Driess, Angew. Chem. 2007, 119, 4595; Angew. Chem. Int. Ed.
2007, 46, 4511; d) Y. Xiong, S. Yao, M. Driess, Organometallics 2009,
28, 1927; e) A. Jana, C. Schulzke, H. W. Roesky, J. Am. Chem. Soc.
2009, 131, 4600; f) S. Yao, C. van Wꢃllen, X.-Y. Sun, M. Driess,
Angew. Chem. 2008, 120, 3294; Angew. Chem. Int. Ed. 2008, 47,
3250; g) Y. Xiong, S. Yao, M. Driess, J. Am. Chem. Soc. 2009, 131,
7562; h) Y. Xiong, S. Yao, M. Driess, unpublished results; i) Y.
Xiong, S. Yao, M. Driess, Chem. Eur. J. 2009, 15, 5545; j) A. Meltzer,
C. Praesang, C. Milsmann, M. Driess, Angew. Chem. 2009, 121,
3216; Angew. Chem. Int. Ed. 2009, 48, 3170; k) A. Meltzer, C. Prae-
sang, M. Driess, J. Am. Chem. Soc. 2009, 131, 7232; l) Y. Xiong, S.
Yao, M. Driess, Dalton Trans. 2009, 421; m) Y. Xiong, S. Yao, M.
Driess, unpublished results.
À
SiC=N C=CHCH2), 7.00–7.19 (m, br, 6H; 2,6-iPr2C6H3), 7.52 ppm (t,
3J(H,H)=10.0 Hz, 1H; NH); 13C{1H} NMR (100.61 MHz, [D6]benzene,
258C): d=21.2–29.2 (cyclohexyl, NCMe, CHMe2), 35.0, 53.6, 56.6
À
À
( CH(CH2)5), 89.6 (NCCH2), 105.0 (g-C), 117.6 (C=CH NHR), 120.5
(NC=CHCH2), 123.6–149.7 (NCMe, NCCH2, CNSi, NC(CH2)(=CHCH2),
2,6-iPr2C6H3), 178.0 ppm (SiCNR, R=cyclohexyl); 29Si{1H} NMR
(79.49 MHz, [D6]benzene, 258C): d = À42.9 ppm (s); ESIMS: m/z (%):
771.6. (100) [M+], 728.5 (7.7) [M+ÀiPr], 688.5 (13.6) [M+ÀC6H11]; ele-
mental analysis calcd (%) for C50H73N5Si: C 77.77, H 9.53, N 9.07; found:
C 77.58, H 9.30, N 9.07.
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Received: May 19, 2009
Published online: July 16, 2009
Chem. Eur. J. 2009, 15, 8542 – 8547
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8547