[2+2+1]cycloadditions of bis(dialkylamino)acetylenes with SiI 2(Idip): Syntheses and reactivity studies of unprecedented 2,3,4,5-tetraamino-1 H-siloles

Article abstract of DOI:10.1002/chem.201403108

A novel method for the synthesis of 1H-siloles is presented. It involves a [2+2+1] cycloaddition of the ynediamines R₂N-C≡C-NR₂ (R=Me, Et) with SiI₂(Idip) (Idip=1,3-bis(2,6-diisopropylphenyl) imidazolin-2-ylidene) to affor

Full text of DOI:10.1002/chem.201403108

DOI: 10.1002/chem.201403108
Full Paper
&
Siloles |Very Important Paper|
[
2+2+1] Cycloadditions of Bis(dialkylamino)acetylenes with
SiI (Idip): Syntheses and Reactivity Studies of Unprecedented
2
2
,3,4,5-Tetraamino-1H-siloles**
Yury N. Lebedev, Ujjal Das, Oleg Chernov, Gregor Schnakenburg, and
[a]
Alexander C. Filippou*
Abstract: A novel method for the synthesis of 1H-siloles is
presented. It involves a [2+2+1] cycloaddition of the ynedia-
mines R NÀCꢀCÀNR (R=Me, Et) with SiI (Idip) (Idip=1,3-
the N-heterocyclic carbene IMe (IMe =1,3,4,5-tetramethyli-
4 4
midazolin-2-ylidene) leads, after displacement of the iodide
groups, to the unprecedented diiodide salt [Si(IMe ) {C -
2
2
2
4 2
4
bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) to afford the
orange-colored, highly water-sensitive 1,1-diiodo-2,3,4,5-tet-
raamino-1H-siloles SiI {C (NR ) } (1-I: R=Me; 2-I R=Et). Treat-
(NEt ) }](I) (3), containing a 1H-silole dication with a four-co-
2 4 2
IV
ordinate Si center. The crystal structure of 3 reveals similar
bonding characteristics for the dicationic 1H-silole to those
of the neutral 1H-siloles 1-I–2-Br. Two-electron reduction of
3 with C K affords, after elimination of one IMe group, the
2
4
2 4
ment of 2-I with an excess of SiBr afforded after I/Br ex-
4
change the 1,1-dibromo-1H-silole SiBr {C (NEt ) } (2-Br). The
2
4
2 4
8
4
1H-siloles 1-I, 2-I, and 2-Br were fully characterized and their
thermolabile, carbene-stabilized 1-silacyclopentadien-1-yli-
molecular structures determined by single-crystal X-ray dif-
fraction. The compounds feature a slightly twisted five-mem-
bered silacyclopenta-2,4-diene ring and a double/single CÀC
bond alternation in the diene fragment. Reaction of 2-I with
dene Si{C (NEt ) }(IMe ) (4), which was characterized by ele-
4
2 4
4
1
13
1
29
1
mental analysis and H,
spectroscopies.
C{ H}, and
Si{ H} NMR
Introduction
of electrons at silicon, these compounds predominantly react
as nucleophiles, as shown by the formation of various transi-
Low-valent silicon chemistry has witnessed a renaissance fol-
lowing recent studies, which have shown that N-heterocyclic
carbenes (NHCs) are very effective bases for the stabilization of
unsaturated Si centers in low oxidation states. Appealing ex-
tion-metal complexes, in which SiX (Idip) act as s-donor li-
2
[6]
gands. Reactions of SiX (Idip) with strong nucleophiles have
2
[5,7]
also been reported,
indicating a certain electrophilic charac-
ter of these compounds, which is, however, much attenuated
in comparison to that of dihalosilylenes. Consequently reac-
[
1]
[2]
amples are the NHC adducts of Si , SiX (X=Cl, Br, I), sila-
2
2
[
3]
nones, and Si(Cl)R (R=C H -2,6-Ar (Ar=C H -2,4,6-Me ; C H -
tions of SiX (Idip) with alkynes have so far proved to be slug-
6
3
2
6
2
3
II
6
2
2
[
4]
[8]
2
,4,6-iPr ); N(SiMe )(C H -2,6-iPr ). Particularly, the Si com-
gish, and only SiCl (Idip) has been reported to react with di-
3
3
6
3
2
2
pounds SiX (Idip) (Idip=1,3-bis(2,6-diisopropylphenyl)imidazo-
phenylacetylene to give an NHC adduct of a 1,2,3-trisilacyclo-
2
[2a]
lin-2-ylidene) and Si(Cl)R(IMe ) (IMe =1,3,4,5-tetramethylimida-
pent-4-ene. In contrast, most silylenes are very reactive to-
wards alkynes. Their reactions have been extensively studied
and have been shown to give silirenes (silacyclopropenes) (A),
1,2-disilacyclobutenes (B), or 1,4-disilacyclohexadienes (C) de-
pending on the reaction conditions and the substituents in the
4
4
zolin-2-ylidene) proved to be very valuable building blocks,
which enabled the synthesis of new classes of unsaturated sili-
con compounds, including zwitterionic silylidene complexes, si-
[5]
lylidyne complexes, metallosilylenes, and metallosilanones.
[9a]
The electronic structure of SiX (Idip) differs considerably from
reactants (Scheme 1).
2
that of dihalosilylenes. As 8VE compounds bearing a lone pair
[a] Dipl.-Chem. Y. N. Lebedev, U. Das, Dr. O. Chernov, Dr. G. Schnakenburg,
Prof. Dr. A. C. Filippou
Institut fꢀr Anorganische Chemie, Universitꢁt Bonn
Gerhard-Domagk-Straße 1, 53121 Bonn (Germany)
E-mail: filippou@uni-bonn.de
[**] Idip=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene.
Supporting information for this article is available on the WWW under
1
http://dx.doi.org/10.1002/chem.201403108. It contains copies of the H and
1
3
1
29
1
C{ H} NMR spectra of 1-I, 2-Br, and 3, the Si{ H} NMR spectra of 2-Br
and 4, and the molecular structure of 1-I.
Scheme 1. Common products of the reactions of silylenes with alkynes.
Chem. Eur. J. 2014, 20, 1 – 11
1
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1
H-Siloles are formed only in traces in these reactions, but
orange, highly water-sensitive crystals, which melt at 858C
are produced in metal-catalyzed reactions of silirenes with
without decomposition.
[
9b]
alkynes.
The fast and selective conversion of SiI (Idip) into the
2
In this work we present a new reaction channel of SiI (Idip)
[2+2+1] cycloaddition products 1-I and 2-I is surprising given
the different reactivity pattern of silylenes towards alkynes (see
Introduction). It can be attributed to the well-known, high nu-
cleophilicity of the ynediamines R NÀCꢀCÀNR . In fact no reac-
2
with the electron-rich alkynes R NCꢀCNR (R=Me, Et) leading
2
2
to unprecedented 2,3,4,5-tetramino-1H-siloles, and we report
on first reactivity studies of these compounds.
2
2
tion of SiX (Idip) (X=Br, I) was observed with alkynes, such as
2
3
-hexyne, p-tolylacetylene, or diphenylacetylene, at ambient
Results and Discussion
[8]
temperature. Two pathways may be envisaged for the
[2+2+1] cycloaddition of SiI (Idip) with R . The first
NÀCꢀCÀNR
Addition of bis(dimethylamino)acetylene to a stirred benzene
2
2
2
solution of SiI (Idip) was accompanied by an instantaneous
one is suggested to involve a substitution of Idip by the ynedi-
amine to give a 1,1-diiodosilacyclopropene intermediate, and
the second one a displacement of one iodide group by the
ynediamine to give a NHC-stabilized 1-iodosilacyclopropenium
salt. Trapping experiments failed so far, the putative intermedi-
ates being presumably trapped very fast by the highly nucleo-
philic ynediamine to give the final product.
2
color change from yellow to orange to afford a mixture of the
2,3,4,5-tetra(dimethylamino)-1H-silole SiI {C (NMe ) } (1-I) and
2 4 2 4
Idip (Scheme 2).
Reaction of 2-I with an excess of SiBr in benzene proceeded
4
smoothly at ambient temperature to give, after I/Br exchange,
the 1,1-dibromo-1H-silole 2-Br, which, after work-up, was iso-
lated as a highly water-sensitive, orange, low-melting solid
(
m.p. 548C) in 71% yield (Scheme 3). Interestingly, 2-I did not
react with SiBr in n-hexane, which indicates a strong influence
4
2 2 2 2
Scheme 2. [2+2+1] cycloaddition of SiI (Idip) with the ynediamines C (NR )
of the solvent polarity on the I/Br exchange rate of this
reaction.
(dip=2,6-diisopropylphenyl; two dots have been used to denote a lone pair
of electrons).
Rapid work-up was necessary to avoid complete decomposi-
tion of the 1H-silole 1-I, leading to a mixture of unidentifiable
organic compounds. Decomposition was observed when the
reaction mixture was stirred for a longer period of time at am-
bient temperature (>15 min). Separation of 1-I from the liber-
ated Idip by fractional crystallization proved difficult due to
the similar solubility of the two compounds in common organ-
4
Scheme 3. I/Br exchange reaction of 2-I with SiBr .
ic solvents. For this reason, one equivalent of SiI was added to
4
the reaction mixture to trap Idip as the much less soluble tri-
The molecular structures of 1-I, 2-I, and 2-Br were deter-
mined by single-crystal X-ray diffraction analyses (Figure 1). Se-
lected bonding parameters of these compounds are listed in
Table 1. All tetraamino-1H-siloles feature a slightly twisted sila-
cyclopenta-2,4-diene ring, as evidenced by the dihedral angle
of the four-ring carbon carbons C1-C2-C3-C4 (1-I: 11.0(14)8; 2-
I: 15.2(2)8; 2-Br: 16.2(3)8). They also display a CÀC double–
single bond alternation as shown by the C ÀC and C ÀC
iodosilylimidazolium salt [SiI (Idip)]I, which could be easily sep-
3
arated from 1-I after extraction of 1-I with benzene or n-
hexane. The 1H-silole 1-I was isolated as orange, highly water-
sensitive crystals after crystallization from n-hexane solution at
À608C. Compound 1-I decomposes upon heating at 1118C to
a black mass. The solid deteriorates slowly even at room tem-
perature, but can be stored for weeks at low temperatures
a
b
b
b
[10]
(
À308C).
bond lengths of 1.37 and 1.52 ꢁ, respectively (Table 1). An-
other common structural feature of the 1H-siloles 1-I, 2-I, and
2-Br is the distorted tetrahedral coordination geometry of Si
with an acute endocyclic C -Si-C angle of approximately 968
The analogous diethylamino derivative 2-I was prepared in
a similar manner upon treatment of SiI (Idip) with two equiva-
2
lents of Et NÀCꢀCÀNEt in benzene (Scheme 2). Compound 2-I
2
2
a
a
was found to be more robust than 1-I, and no decomposition
of 2-I was observed in solution at ambient temperature upon
stirring the reaction mixture for a longer period of time (3 h).
Separation of 2-I from the liberated Idip was achieved after
(Table 1). The SiÀC distances (1.827(11)–1.854(2) ꢁ) correspond
to those of typical SiÀC single bonds, and compare well with
[10]
those of other structurally characterized 1H-siloles.
The
mean SiÀI bond length of 1-I (2.463 ꢁ) and 2-I (2.466 ꢁ) is simi-
lar to that of SiI (2.432(5) ꢁ), MesSiI (2.453 ꢁ), 1,4-diiodo-
[11]
[12]
trapping Idip with one equivalent of SiI as described above
4
4
3
[
13]
for 1-I, or after addition of (NEt H)Cl to give the hexane-insolu-
2,3,5,6-tetraphenyl-1,4-disilacyclohexa-2,5-diene (2.436(2) ꢁ),
3
[14]
ble imidazolium salt (IdipH)Cl. Compound 2-I could be easily
and other silicon(IV) iodides. Similarly, the mean SiÀBr dis-
tance of 2-Br (2.235 ꢁ) compares well with that of other four-
separated from [SiI (Idip)]I or (IdipH)Cl by extraction with n-
3
IV
[15]
hexane, and was isolated after crystallization at À308C as
coordinate Si compounds (2.253 ꢁ).
&
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the N - and N -bonded alkyl substituents, indicating a rapid ro-
a
b
tation of the amino groups about the C ÀN and C ÀN bonds
a
a
b
b
as well as a rapid inversion of the Na and N atoms on the
b
NMR time scale at ambient temperature (see the Supporting
13
1
Information). The C{ H} NMR spectra of 1-I, 2-I, and 2-Br dis-
2,5
play one diagnostic signal for the Ca (C ) carbons at d=
3,4
1
22.7–124.5 ppm and one for the Cb (C ) carbons at d=
1
45.5–147.8 ppm, which were assigned by comparing the
n
1
2
J(Si,C) coupling constants (2-I: J(Si,C )=71 Hz, J(Si,C )=
a
b
29 Hz) (Table 2).
As observed for other 1H-siloles, the relative chemical shifts
Figure 1. DIAMOND plot of the molecular structure of 2-I. Thermal ellipsoids
are set at the 40% probability level. Hydrogen atoms are omitted for clarity.
Selected bond lengths [ꢁ] and bond angles [8] (bond lengths and angles in
square brackets are of 2-Br): SiÀI1 2.4654(5) [SiÀBr1 2.2340(6)], SiÀI2
of the Ca and C carbon signals of 1-I, 2-I, and 2-Br are re-
versed, when compared with those of furans or pyrroles.
b
[17]
2
9
The Si NMR signals of 1-I (d in C D =À87.8 ppm) and 2-I (d
6
6
2
.4672(5) [SiÀBr2 2.2363(7)], SiÀC1 1.849(2) [1.849(2)], SiÀC4 1.854(2)
in C D =À83.5 ppm) appear at considerably lower field than
6
6
29
[
1
1.841(2)], C1ÀC2 1.370(2) [1.365(3)], C2ÀC3 1.524(2) [1.521(3)], C3ÀC4
that of SiI (d in C D =À346.6 ppm), and the Si NMR signal
4
6
6
.370(2) [1.378(3)], C1ÀN1 1.426(4) [1.422(3)], C2ÀN2 1.392(2) [1.416(3)], C3À
of 2-Br (d in C D =À13.4 ppm) appears at considerably lower
6
6
N3 1.402(2) [1.393(3)], C4ÀN4 1.420(2) [1.422(3)]; I1-Si-I2 104.57(2) [Br1-Si-Br2
field than that of SiBr (d in C D =À90.8 ppm). The observed
104.15(3)], C1-Si-C4 96.58(7) [97.3(1)].
4
6
6
1
3
1
29
1
All amino groups in 1-I, 2-I, and 2-Br are rotated
Table 2. Selected C{ H} NMR and Si{ H} NMR data of the 1H-siloles and 4.
out of the five-membered ring, the C -bonded amino
a
13
1
29
Comp.
C{ H} NMR
Si NMR
groups (C =C1,C4) slightly more than the C -bonded
2,5
3,4
a
b
C
a
(C
)
C
b
(C
)
amino groups (C =C2,C3). Thereby, the mutual steric
b
[a]
1
2
-I
-I
122.7
145.5
À87.8
À83.5
À13.4
À29.2
À69.6
repulsion between adjacent amino groups is mini-
mized. Moreover, the amino groups are pyramidal as
evidenced by the sum of the bonding angles at the
Na (N1,N4) and Nb (N2,N3) atoms (Table 1). The Na
alkyl substituents are bent away from the neighbor-
ing N alkyl substituents towards the SiX (X=I, Br)
[a]
1
2
124.3 ( J(Si,C)=71 Hz)
124.5
122.6 ( J(Si,C)=79 Hz)
153.0 ( J(Si,C)=20 Hz)
146.7 ( J(Si,C)=29 Hz)
147.8
151.3 ( J(Si,C)=23 Hz)
141.9 ( J(Si,C)=8.1 Hz)
[
a]
2-Br
[
b]
1
2
3
4
[
a]
1
2
[a] [D
6
]benzene, 298 K. [b] [D
2
]dichloromethane, 298 K.
b
2
group, and the alkyl substituents at the two Nb
2
9
atoms are bent away from each other. In combination with the
lower pyramidalization of the Nb atoms (Table 1), this alkyl
group arrangement minimizes further the steric repulsion es-
pecially between the adjacent N and N amino groups, which
shift of the Si NMR signal to lower field upon replacing
iodine by bromine substituents in 2-X (X=I, Br) is a common
phenomenon in Si chemistry.
IV
[18]
The 1,1-diiodo-1H-siloles 1-I and 2-I are promising starting
materials for further reactivity studies, since they bear two
iodide groups, which are good leaving groups and should be
easily displaced from silicon. In fact, reaction of 2-I with two
equivalents of the N-heterocyclic carbene IMe (IMe =1,3,4,5-
a
b
are separated by a much shorter C=C bond. The CringÀN bond
lengths range from 1.39–1.43 ꢁ and are close to those of C
2
–
sp
[
16]
Nsp
3
single bonds.
They suggest, in connection with the
other parameters presented above, a small p-conjugative inter-
action of the amino groups with the C=C bonds. This is further
4
4
tetramethylimidazolin-2-ylidene) in toluene was instantaneous,
and led, after replacement of both iodide groups, to the iodide
1
13
1
confirmed by the H and C{ H} spectra of 1-I, 2-I, and 2-Br in
2
+
2+
C D at 298 K, which all display a single set of resonances for
salt of the dicationic 1H-silole [Si(IMe ) {C (NEt ) }]
(3 )
6
6
4 2
4
2 4
2 2
Table 1. Selected bond lengths [ꢁ] and angles [8] of the 1H-siloles 1-I, 2-I, 2-Br, and 3·4(CH Cl ).
[
a]
[a]
[a]
[a]
[a]
[b]
[b]
Comp.
SiÀC
1.827(11)
a
C
a
ÀC
b
C
b
ÀC
b
SiÀX
C
a
-Si-C
a
SN
a
SN
b
1
2
2
3
-I
1.370(14)
1.350(14)
1.370(2)
1.370(2)
1.365(3)
1.378(3)
1.367(4)
1.508(14)
1.524(2)
1.521(3)
1.522(12)
2.455(3)
2.470(3)
96.2(5)
343.8
343.5
341.0
341.8
340.0
339.8
358.3
356.5
355.2
351.4
348.9
354.1
355(2)
1
.836(10)
1.849(2)
.854(2)
1.849(2)
.841(2)
1.862(3)
-I
2.4654(5)
2.4672(5)
2.2340(6)
2.2363(7)
1.898(4)
96.58(7)
97.3(1)
95.8(3)
1
-Br
1
[c]
350(2)
[
a] C
and N
of 3·4(CH
respective individual value and n is the total number of individual values.
a
= C1,C4; C
(N2,N3) atoms, respectively. [c] The unweigthed mean values x
Cl ) are given; the standard deviations s of x (values in parentheses) were calculated from the equation s =S(x
b
= C2,C3; X=I1,I2 (for 1-I and 2-I), Br1,Br2 (for 2-Br), C1,C4 (for 3). [b] SN
a b a
and SN are the sums of the bonding angles at the N (N1,N4)
b
u
of the individual bonding parameters of the three independent 1H-silole dications
2
2
2
2
2
u
i
Àx
u
) /(n Àn), in which x
i
is the
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Scheme 4. Stepwise synthesis of the NHC-stabilized 1-silacyclopentadien-1-
ylidene 4 from 2-I via the 1H-silole salt 3 (two dots have been used to
denote a lone pair of electrons).
Figure 2. DIAMOND plot of the molecular structure of one of the three inde-
2
+
2 2
pendent cations, 3 in 3·4(CH Cl ). Thermal ellipsoids are set at the 40%
probability level. Hydrogen atoms are omitted for clarity. Selected bond
(
Scheme 4). Salt 3 precipitated out of the solution, and was
isolated after crystallization as yellow-orange crystals in 66%
yield. The salt is well soluble in CH Cl , but insoluble in toluene
lengths [ꢁ] and bond angles [8] (bond lengths and angles in square brackets
2
+
2
2
are of the other two independent cations of 3 found in the asymmetric
unit): Si1ÀC1 1.865(7) [1.867(6), 1.858(7)], Si1ÀC4 1.854(6) [1.858(7), 1.870(7)],
Si1ÀC21 1.909(7) [1.898(7), 1.893(6)], Si1ÀC28 1.894(6) [1.886(7), 1.906(6)],
C1ÀC2 1.378(9) [1.361(10), 1.350(10)], C2ÀC3 1.511(9) [1.509(10), 1.545(11)],
C3ÀC4 1.368(9) [1.371(9), 1.373(10)], C1ÀN1 1.390(8) [1.415(9), 1.432(9)], C2À
N2 1.391(8) [1.408(8), 1.392(9)], C3ÀN3 1.382(8) [1.392(9), 1.374(9)], C4ÀN4
1.417(8) [1.403(9), 1.408(10)], C1-Si-C4 96.3(3) [95.6(3), 95.5(3)], C21-Si1-C28
and diethyl ether.
Attempts to stop the reaction of 2-I with IMe at the mono-
4
substitution step have failed so far. For example, reaction of 2-I
with one equivalent of IMe4 at À308C in toluene afforded,
after work-up, a 1:1 mixture of the starting material and 3. This
observation suggests that substitution of the first iodide group
in 2-I by IMe to give the putative ionic intermediate [SiI{C -
106.4(3) [107.1(3), 104.1(3)].
4
4
+
+
(
NEt ) }(IMe )] is slower than that in [SiI{C (NEt ) }(IMe )] by
2
4
4
4
2 4
4
2
+
IMe in the second step leading to the final product.
tive charge of 3 is delocalized via strong covalent SiÀC
4
carbene
Compound 3 is the first salt of a dicationic 1H-silole to be re-
single bonds over the IMe groups. Further substantiation of
4
ported, and to the best of our knowledge an unprecedented
this suggestion is provided by the similar magnitude of the
IV
1
1
1
dicationic Si compound with a tetrahedral coordinated Si
J(Si,C) coupling constants of 3 ( J(Si,C
=72 Hz; J(Si,Ca-
carbene
center. The crystal structure of 3·4(CH Cl ) was determined by
=79 Hz), which also compare well with those of SiÀC
sp2
2
2
(ring)
[20]
single-crystal X-ray diffraction analysis. Three independent
pairs of cations/anions with very similar bonding parameters
were found in the asymmetric unit. The unweighted mean
single bonds in silanes (64–70 Hz).
In addition, the NMR
chemical shift of the Ccarbene atoms of 3 (d in CD Cl =
2
2
138.8 ppm) is similar to that of the
2
+
values of selected bond lengths and angles of 3 are listed in
imidazolium salt (IMe H)Cl (d in
4
[4a]
Table 1 and were used for the discussion below. The molecular
CD Cl =136.9 ppm),
but differs
2
2
2
+
structure of one of the three independent cations 3 is de-
very much from that of IMe (d in
4
[
21]
picted in Figure 2.
C D =212.7 ppm),
indicating
6
6
2
+
2+
The crystal structure of 3·4(CH Cl ) shows well-separated 3
that 3 should be best considered
2
2
ions and iodide counter anions, the closest Si···I contact
5.49 ꢁ) being much longer than the sum of the van der Waals
radii of silicon and iodine of 4.08 ꢁ (r (Si)=2.10 ꢁ; r (I)=
as a bis(imidazolium) salt bridged
(
by
a
1-silacyclopenta-dien-1-yli-
dene group (Figure 3).
w
w
[
19]
2+
13
1
1
.98 ꢁ). The 1H-silole dication 3 displays similar bonding
parameters to those of the neutral 1H-siloles 1-I, 2-I, and 2-Br
Table 1). The slightly twisted silacyclopenta-2,4-diene ring (di-
hedral angle (C -C -C -C )=19(3)8) in 3·4(CH Cl ) contains as in
The C{ H} NMR spectrum of 3
Figure 3. Stereochemical for-
mula of the dication 3
displays at 298 K one singlet for
2+
2,5
(
the Ca(ring) (C ) atoms at d= pointing out its bis-imidazoli-
um salt character.
122.6 ppm, one singlet for the C
a
b
b
a
2
2
b
3,4
the neutral congeners 1-I–2-Br a distorted tetrahedral coordi-
(C ) atoms at d=151.3 ppm, but
two singlets in each case for the C -ring carbons, the N -
4
,5
1,3
nated silicon atom with an acute endocyclic C -Si-C angle of
a
a
4,5
9
5.8(3)8 (Table 1). The mean length of the SiÀC
bonds
bonds
bonded and the C -bonded methyl groups of the IMe
4
carbene
(
(
1.898(4) ꢁ) is slightly larger than that of the SiÀC
groups (see Figure 7 in the Supporting Information). In combi-
a(ring)
1.862(3) ꢁ) and approximates those of the silylimidazolium
nation with the observed orientation of the IMe groups in the
4
[
2b]
13
salts [SiX (Idip)]X (X=Br: SiÀC 1.880(9) ꢁ;
X=I: SiÀC
solid-state structure of 3, the C NMR spectrum let us suggest
3
[
2c]
1.911(3) ꢁ ). This comparison indicates that the double posi-
that rotation of the two symmetry-equivalent IMe4 groups
&
&
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about the SiÀC
bonds is frozen out at ambient tempera-
ric structure in solution with the symmetry plane bisecting the
silacycle. It also indicates that inversion as well as rotation of
all amino groups about their respective CringÀN bonds is fast
on the NMR time scale. On the other hand two singlets are ob-
carbene
ture, rendering the two halves of each IMe group chemically
4
inequivalent.
1
H-Siloles have been shown to have a low-lying LUMO re-
1,3
4,5
sulting from the orbital interaction (s*–p* conjugation) be-
served for the N -bonded methyl groups, the C -bonded
4,5
tween a s* orbital of the SiR unit with a p* orbital of the bu-
methyl groups and the C -ring atoms of the IMe group in 4
2
4
[
22]
tadiene moiety.
Occupation of this orbital by electrons is
(Figure 4 and 5). The signal splitting suggests that the carbene
ring plane lies in the symmetry plane of the molecule and that
therefore expected to weaken the SiÀR bonds leading to bond
cleavage. In fact, reduction of 1H-siloles by alkali metals has
been shown to give, after cleavage of the SiÀR bonds, mono-
anions of siloles (silolides (silacyclopentadienides)) or dianions
rotation of the IMe group about the SiÀC
bond is hin-
4
carbene
dered presumably due to the large steric demand of the dieth-
ylamino groups. In comparison, free rotation of the IMe group
4
[
23]
of siloles (silolediides).
was observed by NMR spectroscopy in the related tetraphenyl
derivative Si(C Ph )(IMe ), which was obtained upon dehydro-
In this context, 2e reduction of 3 was an appealing reaction
to study. After stirring a mixture of 3 and two equivalents of
potassium graphite (C K) in 1,4-dioxane for 18 h, the bronze
4
4
4
[
24]
chlorination of the 1H-silole SiClH(C Ph )(IMe ).
4
4
4
29
The Si NMR resonance of 4 (d=À69.6 ppm) is shifted up-
field relative to that of the parent 1H-silole 3 (d=À29.2 ppm)
8
color of C K had disappeared. Solvent evaporation followed by
8
[25]
extraction with toluene afforded a dark orange extract, which
and appears in the region expected for silyl anions. More-
over, the relative position of C - and C -ring carbon signals is
1
according to H NMR spectroscopy contained a new com-
a
b
pound (4) and IMe in the molar ratio 1:1. Repeated fractional
reversed compared with that in the 1H-siloles 1-I–3 (Table 2).
4
1
1
crystallization from toluene enabled the separation of the two
products, and the isolation of 4 as yellow crystals in 49% yield.
Despite numerous attempts no suitable single crystals of 4
could be grown. The obtained crystals had a morphology remi-
niscent of asbestos fibers but did not diffract. However, the
NMR spectra of 4 allowed, in combination with the elemental
The J(Si,C ) and J(Si,Ccarbene) coupling constants of 4 (20 and
a
25 Hz, respectively) have similar values, but are considerably
smaller than those of the parent 1H-silole 3 (79 and 72 Hz, re-
1
spectively) (Table 2). They approximate the J(Si,C) coupling
1
constants of SiCl(C H -2,6-Mes )(IMe ) ( J(Si,Caryl)=48 Hz;
6
3
2
4
1
[4a]
II
J(Si,Ccarbene)=33 Hz), and indicate that the Si center in 4
analysis, the identification of this compound as the IMe -stabi-
uses mainly p orbitals for the s-bonding to its three carbon
substituents.
4
lized
Scheme 4). Thus, the H and C{ H} NMR spectra of 4 display
a single set of signals for the C - and C -bonded amino groups
silacyclopentadien-1-ylidene
Si{C (NEt ) }(IMe )
4 2 4 4
1
13
1
(
Finally, the Ccarbene resonance of 4 (d=168.5 ppm) is shifted
to considerably lower field than that in the parent 1H-silole 3
(d=138.8 ppm), and appears at a similar position to those of
a
b
(
Figure 4 and 5). This suggests that 4 has an overall C -symmet-
s
1
Figure 4. H NMR spectrum of 4 in [D
6
]benzene at 298 K.
Chem. Eur. J. 2014, 20, 1 – 11
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5
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1
3
1
6
Figure 5. C{ H} NMR spectrum of 4 in [D ]benzene at 298 K (enlarged sections of the NMR spectrum are shown in the insets).
[
28]
the NHC-stabilized silylenes SiCl(C H -2,6-Mes )(IMe ) (d=
carrier properties, making them very promising materials for
6
3
2
4
[
4a]
[2b]
[29]
165.2 ppm),
58.4 ppm).
SiBr (IDip) (d=164.5 ppm),
SiI (IDip) (d=
2
organic photoelectronic and photovoltaic devices.
2
[
2c]
1
All these NMR parameters clearly indicate
In this context, the novel method reported in this work
a quite different electronic structure of 4, which can be de-
scribed either as a NHC-stabilized 1-silacyclopentadien-1-yli-
dene (A) or a zwitterionic silacyclopentadienide (B) (Figure 6).
based on the [2+2+1] cycloaddition of SiI (Idip) with ynedia-
2
mines may be of particular interest, since it provides access to
polyamino-substituted 1H-siloles, which are not available by
the various methods reported so far for 1H-siloles. Moreover,
the obtained 2,3,4,5-tetraamino-1H-siloles allow further func-
tionalization as shown by the isolation and full characterization
of the 1H silole salt 3, an unprecedented dicationic compound
IV
of Si in a tetrahedral environment. On the other hand 2e-re-
duction of 3 provides access to the zwitterionic silacyclopenta-
dienide 4, which belongs to a very rare class of compounds.
Prospective studies should clarify whether 4 can be used as
a silacyclopentadien-1-ylidene transfer reagent.
Figure 6. Two ways to view compound 4 as a NHC-stabilized 1-silacyclopen-
tadien-1-ylidene (A) or as a zwitterionic silacyclopentadienide (B).
Experimental Section
Discussion and Outlook
General
Several methods have been developed for the synthesis of 1H-
[
17]
siloles. The most important synthetic methods involve the
reaction of 1,4-dilithiobuta-1,3-dienes with halosilanes or
All experiments were carried out under an atmosphere of argon
using Schlenk or glove-box techniques. The glassware was dried in
the oven at approximately 1108C and heated in vacuo prior to use.
The solvents were refluxed over the corresponding drying agent
[
26]
Si(OMe)4, and the intramolecular reductive cyclization of bis-
phenylethynyl) silanes with lithium naphthalenide leading to
(
(n-hexane: sodium wire/benzophenone/tetraglyme; diethyl ether:
2
,5-dilithio-1H-siloles, which can be converted into a series of
sodium wire/benzophenone; benzene: sodium wire/benzophe-
none; 1,4-dioxane, toluene: sodium wire; dichloromethane: Sica-
pent followed by Na/Pb alloy), purged several times during reflux
with argon and distilled under argon. All solvents except CH Cl
[
27]
2
,5-difunctionalized 1H-siloles. The latter compounds are key
building blocks for the synthesis of 1H-silole based p-conjugat-
ed polymers with interesting photoluminescent and charge
2
2
&
&
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were stored in the glove box. CH Cl was stored in a Schlenk flask
over 4 ꢁ molecular sieves.
À608C to afford large orange crystals of 1-I. Yield 252 mg
2
2
(0.498 mmol, 27% based on SiI (Idip)). Compound 1-I starts to de-
2
[
2c]
[21]
compose above 1118C turning to a black mass. Elemental analysis
SiI (Idip),
1,3,4,5-tetramethyl-imidazolin-2-ylidene (IMe4),
and
2
[
30]
calcd (%) for C H I N Si (506.24): C 28.47, H 4.78, N 11.07; found:
C8K were prepared as described in the literature. SiI was pre-
pared from silicon powder and iodine as described in the litera-
ture. The obtained crude pink-colored SiI was heated to reflux
in toluene with copper powder to remove the excess of iodine,
and the resulting mixture filtered to give a light yellow filtrate,
12 24 2
4
4
1
C 28.26, H 5.00, N 10.75%. H NMR (300.1 MHz, [D ]benzene, 298 K,
6
3
,4
2,5
[
31]
ppm): d=2.54 (s, 12H, C -N(CH ) ), 2.87 ppm (s, 12H, C -N(CH3)2);
3 2
C{ H} NMR (75.47 MHz, [D ]benzene, 298 K, ppm): d=39.6 (s, 4C,
-N(CH ) ), 44.8 (s, 4C, C -N(CH ) ), 122.7 (s, 2C, C ), 145.5 ppm
s, 2C, C ); Si{ H} NMR (59.6 MHz, [D ]benzene, 298 K, ppm): d=
4
1
3
1
6
3
,4
2,5
2,5
C
(
3 2
,4
3 2
3
29
1
from which pure SiI was isolated as a white crystalline solid after
6
4
29
1
À87.8 ppm (s).
crystallization at À308C and shown by Si{ H} NMR spectroscopy
2
9
to be pure ( Si NMR (59.6 MHz, [D ]benzene, 298 K, ppm): d=
6
1,1-Diodo-2,3,4,5-tetrakis(diethylamino)-1H-silole, SiI {C (NEt ) }
2
4
2 4
À346.6 (s)). Similarly, SiBr was prepared from silicon powder and
4
(2-I): Bis(diethylamino)acetylene (0.355 g, 2.11 mmol) was added
bromine following the procedure described in reference [32] and
isolated after purification as a colorless liquid, which was shown by
within 1 min to a solution of SiI (Idip) (671 mg, 1.00 mmol) in ben-
2
zene (4 mL). During addition the solution turned from yellow to
orange. After the reaction mixture had been stirred for 10 min, a so-
lution of SiI4 (0.536 g, 1.00 mmol) in benzene (5 mL) was added
dropwise. The resulting suspension was stirred for 5 min, and n-
hexane (10 mL) were added. The suspension was filtered from
a brown sticky material, which was discarded. The dark orange fil-
trate was evaporated to dryness in vacuo and the residue extract-
ed with n-hexane (10 mL). The extract was filtered from some in-
soluble material, the filtrate was concentrated in vacuo to approxi-
mately 2 mL and stored at À308C. Large orange crystals of 2-I
were grown, which were separated from the mother liquor by fil-
tration at À308C and dried in vacuo at ambient temperature for
2
9
1
29
Si{ H} NMR spectroscopy to be pure ( Si NMR (59.6 MHz,
[
D ]benzene, 298 K, ppm): d=À90.8 (s)). The syntheses of the yne-
6
[33,34]
diamines R NCꢀCNR (R=Me, Et)
were modified and the ynedi-
2
2
amines isolated as colorless, air-sensitive liquids, which were
1
13
1
[35]
shown by H and C{ H} NMR spectroscopy to be pure.
The C, H, N analyses were carried out in triplicate for each sample
using an Elementar Vario Micro elemental analyzer. The individual
C, H, N values did not differ by more than Æ0.3%. The mean C, H,
N values are given below for each compound. The melting points
were determined in duplicate for each sample using a calibrated
Bꢂchi melting point apparatus. The samples were sealed in capilla-
ry tubes under vacuum and rapidly heated to a temperature ap-
proximately 20 K lower than that at which melting or decomposi-
tion started. Heating was then continued with a rate of approxi-
3 h. Yield 0.26 g (0.42 mmol, 42% from SiI
mental analysis calcd (%) for C20 Si (618.45): C 38.84, H 6.52,
N 9.06; found: C 38.39, H 6.31, N 8.85; H NMR (400.1 MHz,
(Idip)). M.p. 858C. Ele-
2
H I N
40 2 4
1
À1
3
3,4
mately 3 Kmin until the sample melted or decomposed. NMR
[D
N(CH
6
]benzene, 298 K): d=0.95 (t, J(H,H)=7.1 Hz, 12H,
C
-
3
2,5
spectra were recorded on a Bruker Avance DMX-300, DPX-300,
DPX-400 NMR or DMX-500 NMR spectrometer in dry deoxygenated
2
CH
3
)
2
), 1.16 (t, J(H,H)=7.1 Hz, 12H, C -N(CH
2
3
CH
3
)
2
), 3.17 (q,
), 3.22 ppm (q, J(H,H)=7.1 Hz,
); C{ H} NMR (75.47 MHz, [D ]benzene, 298 K):
), 15.5 (s, 4C, C -N(CH CH ), 44.3 (s,
), 124.3 (s, J(Si,C)=
3
3,4
J(H,H)=7.1 Hz, 4H, C -N(CH
CH )
3 2
2
2,5
13
1
[
D ]benzene or [D ]dichloromethane. [D ]Benzene was trap-to-trap
4H, C -N(CH
d=13.9 (s, 4C, C -N(CH
4C, C -N(CH
2
CH
3
)
2
6
6
2
6
3,4
2,5
condensed from sodium powder and [D ]dichloromethane from
2
CH
)
3
2
2
)
3 2
2
1
13
1
3,4
2,5
1
CaH . The H and C{ H} NMR spectra were calibrated against the
residual proton and natural abundance C resonances of the deu-
2
2,5
CH
3
)
2
), 49.7 (s, 4C, C -N(CH
2
CH
71 Hz, 2C, C ), 146.7 ppm (s, J(Si,C)=29 Hz, 2C, C ); Si{ H} NMR
(59.6 MHz, [D
]benzene, 298 K): d=À83.5 ppm (s); EI-MS (70 eV):
)
3 2
2
13
2
3,4 29
1
terated solvent relative to tetramethylsilane ([D ]benzene, d =
6
6
H
+
+
7
5
.15 ppm and d =128.0 ppm; [D ]dichloromethane, d =5.32, d =
3.8 ppm). The Si NMR spectra were calibrated against external
m/z (rel. intensity in%)=618 (100, [M ]), 589 (5, [M ÀC
H ]), 560
2 5
C
2
2
H
C
9
+
+
+
(47, [M À2C
H
2
]), 545 (20, [M À2C
H
2
ÀCH
]), 534 (67, [M
5
5
3
pure SiMe . The standard was filled in a capillary, which was
À2C
H
2
5
ÀCN].
4
sealed-off and introduced in a 5 mm NMR tube containing the cor-
responding deuterated solvent. The NMR tube was finally vacuum-
sealed and used for the calibration. The following abbreviations
were used for the forms and multiplicities of the NMR signals: s:
Alternative synthesis of 2-I: Bis(diethylamino)acetylene (350 mg,
2
.08 mmol) was added within 1 min to a solution of SiI (Idip)
2
(670 mg, 1.00 mmol) in benzene (15 mL). During addition the solu-
tion turned orange. The reaction mixture was stirred for 3 h, and
the solvent was removed in vacuo. The residue was extracted with
n-hexane (5 mL) and the extract was filtered. The orange filtrate
was evaporated to dryness in vacuo to give 590 mg of a yellow-
1
singlet, t: triplet, q: quartet, m: multiplet, br: broad. The H and
1
3
C NMR signals of all compounds were assigned by a combination
of H,H-COSY, HMQC, HMBC, and DEPT experiments. This allowed in
n
combination with the J(Si,C) coupling constants an unequivocal
1
orange powder, which was shown by H NMR spectroscopy to con-
assignment of all proton and carbon resonances.
tain the product 2-I and Idip in a molar ratio of 10:1.5. The powder
was dissolved in THF (10 mL), and Et N·HCl (16 mg, 0.12 mmol) was
3
added to the solution. The suspension was stirred for 1 h and all
volatiles were removed in vacuo. The residue was extracted with n-
hexane (2ꢃ10 mL), and the extract was filtered. The filtrate was
concentrated in vacuo to approximately 2 mL and stored at À608C
for 18 h. Large orange crystals of 2-I were obtained, which were
collected by filtration at À608C and dried in vacuo at ambient
Synthesis
1
,1-Diodo-2,3,4,5-tetrakis(dimethylamino)-1H-silole,
SiI {C -
2 4
(
NMe ) } (1-I): Bis(dimethylamino)acetylene (430 mg, 3.83 mmol)
2
4
was added within 1 min to a yellow solution of SiI (Idip) (1.25 g,
2
1
.86 mmol) in benzene (30 mL). After the mixture had been stirred
for 1 min at ambient temperature, a solution of SiI4 (1.00 g,
.87 mmol) in benzene (20 mL) was added within 30 s. During ad-
temperature for 3 h. Yield: 0.27 g (0.44 mmol, 44% from SiI (Idip)).
2
1
The product was shown by H NMR spectroscopy to be pure.
1
dition the solution turned orange and formation of a yellow pre-
cipitate was observed. The reaction mixture was subsequently
stirred for 2 min and then filtered via a cannula. The filtrate was
evaporated to dryness in vacuo and the residue was extracted
with n-hexane (2ꢃ10 mL). The extract was filtered, and the filtrate
was concentrated in vacuo to approximately 2 mL and stored at
Synthesis of 1,1-dibromo-2,3,4,5-tetrakis(diethylamino)-1H-
silole, SiBr {C (NEt ) } (2-Br): SiBr (1.0 mL, 2.8 g, 8.1 mmol) was
added rapidly to a solution of 2-I (550 mg, 0.889 mmol) in benzene
(20 mL). The orange reaction solution was stirred for 20 h at ambi-
ent temperature, and all volatiles were removed in vacuo. The resi-
due was extracted with n-hexane (2ꢃ10 mL), filtered, and the
2
4
2
4
4
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4
5
orange filtrate was concentrated in vacuo to approximately 2 mL
and stored at À608C for 18 h. The formed orange crystals of 2-Br
were collected by filtration at À608C and dried in vacuo at ambi-
ent temperature for 3 h. Yield: 331 mg (0.631 mmol, 71% from 2-I).
M.p. 548C. Elemental analysis calcd (%) for C H Br N Si (524.45): C
6H, 2 ꢃ C -Me, IMe ), 2.42 (s, 6H, 2 ꢃ C -Me, IMe ), 2.61 (m br, 4H,
4 4
2,5
2,5
2
C
-N(CH CH ) ), 2.76 (m br, 4H, C -N(CH CH ) ), 3.06 (dq, J(H,H)=
2 3 2 2 3 2
13.5 Hz, J(H,H)=7.1 Hz, 4H, C -N(CH H CH ) ), 3.58 (dq, J(H,H)=
13.5 Hz, J(H,H)=7.1 Hz, 4H, C -N(CH H CH ) ), 3.93 (s, 6H, 2 ꢃ N -
Me, IMe ), 4.03 ppm (s, 6H, 2 ꢃ N -Me, IMe ); C{ H} NMR
(75.47 MHz, [D ]dichloromethane, 298 K): d=10.3 (s, 2C, 2 ꢃ C -Me,
2
IMe ), 10.7 (s, 2C, 2 ꢃ C -Me, IMe ), 14.1 (s, 4C, C -N(CH CH ) ), 15.0
4 4 2 3 2
(s br, w1/2 =47 Hz, 4C, C -N(CH CH ) ), 35.0 (s, 2C, 2 ꢃ N -Me, IMe ),
39.1 (s, 2C, 2 ꢃ N -Me, IMe ), 44.3 (s br, w =68 Hz, 4C, C -
4 1/2
3
3,4
2
A
B
3 2
3
3,4
1
A
B
3
3 2
13
1
20
40
2
4
4
4
1
5
4
5.80, H 7.69, N 10.69; found: C 45.04, H 7.45, N 10.40%. H NMR
3
4
3,4
(
300.1 MHz, [D ]benzene, 298 K): d=0.95 (t, J(H,H)=7.1 Hz, 12H,
6
3
,4
3
2,5
2,5
1
C
-N(CH CH ) ), 1.15 (t, J(H,H)=7.1 Hz, 12H, C -N(CH CH ) ), 3.08
2
3 2
2
3 2
3
2
3 2
4
3
2,5
3
3,4
(
q, J(H,H)=7.1 Hz, 8H, C -N(CH CH ) ), 3.17 ppm (q, J(H,H)=
2
3 2
3
,4
13
1
2,5
7
2
4
2
.1 Hz, 8H, C -N(CH CH ) ); C{ H} NMR (75.47 MHz, [D ]benzene,
N(CH CH ) ), 50.6 (s br, w =51 Hz, 4C, C -N(CH CH ) ), 122.6 (s,
2
3 2
,4
6
2
3 2
1/2
2
3 2
5
3
2,5
1
2,5
98 K): d=13.9 (s, 4C, C -N(CH CH ) ), 15.1 (s, 4C, C -N(CH CH ) ),
J(Si,C)=79 Hz, 2C, C -N(CH CH ) ), 133.1 (s, 2C, 2 ꢃ C -Me, IMe ),
133.9 (s, 2C, 2 ꢃ C -Me, IMe ), 138.8 (s, J(Si,C)=72 Hz, 2C, 2 ꢃ NCN,
4
IMe ), 151.3 ppm (s, J(Si,C)=23 Hz, 2C, C -N(CH CH ) ); Si{ H}
4 2 3 2
2
3 2
2
3 2
2
3 2
4
3
,4
2,5
4
1
4.4 (s, 4C, C -N(CH CH ) ), 49.6 (s, 4C, C -N(CH CH ) ), 124.5 (s,
2
3 2
2
3 2
2
,5
3,4
29
1
2
3,4
29
1
C,
C
), 147.8 ppm (s, 2C,
C
);
Si{ H} NMR (59.6 MHz,
[
D ]benzene, 298 K): d=À13.4 ppm (s).
NMR (59.6 MHz, [D ]dichloromethane, 298 K): d=À29.2 ppm (s).
6
2
Synthesis of 1,1-bis(1,3,4,5-tetramethylimidazolin-2-ylidene)-
,3,4,5-tetrakis(diethylamino)-1H-silole diiodide, [Si(IMe ) {C -
Synthesis of 1-(1,3,4,5-tetramethylimidazolin-2-ylidene)-2,3,4,5-
tetrakis(diethylamino)-silacyclopentadiene-1-ylidene Si(IMe ){C -
2
4
2
4
4
4
(
NEt ) }](I) (3): An orange solution of 2-I (1.00 g, 1.62 mmol) in tol-
(NEt ) } (4): In a Schlenk tube the 1H-silole salt 3 (2.48 g,
2
4
2
2 4
uene (10 mL) was added to a stirred suspension of IMe (400 mg,
2.86 mmol) and C K (780 mg, 5.77 mmol) were suspended in 1,4-di-
4
8
3
1
.22 mmol) in toluene (10 mL) at ambient temperature within
min. voluminous, yellow-orange precipitate was rapidly
oxane (50 mL). The suspension was stirred for 18 h. During this
time the bronze color of the potassium-graphite had disappeared,
and the color of the solution had changed from orange to dark
orange. The solvent was removed in vacuo and the residue extract-
ed with toluene (2ꢃ30 mL). The extract was filtered from graphite
and the filtrate was concentrated in vacuo to approximately 15 mL
and stored for 18 h at À308C. The crude product was recrystallized
three times from toluene to afford compound 4 as yellow crystals.
Yield: 680 mg (1.39 mmol, 49%). M.p. 1298C. Elemental analysis
calcd (%) for C H N Si (488.83): C 66.34, H 10.72, N 17.20; found:
A
formed. The suspension was stirred for 1 h, filtered off, and dried
in vacuo for 30 min at ambient temperature to give a yellow-
orange powder. The powder was crystallized from a dichlorome-
thane–diethyl ether mixture (1:2, v/v) at À608C to give 3 as
yellow-orange crystals. The crystals were collected by filtration at
À608C and dried in vacuo at ambient temperature for 3 h. Yield:
1
9
30 mg
(1.07 mmol,
66%).
H NMR
(300.1 MHz,
2,5
[
D ]dichloromethane, 298 K): d=0.84 (s br w =28 Hz, 12H, C -
2
1/2
3,4
27 52
6
3
1
N(CH CH ) ), 1.07 (t, J(H,H)=7.1 Hz, 12H, C -N(CH CH ) ), 2.39 (s,
C 66.48, H 11.15, N 16.29%. H NMR (300.1 MHz, [D ]benzene,
6
2
3 2
2
3 2
2 2
Table 3. Crystal data and structure refinement parameters of 1-I, 2-Br, 2-I, and 3·4(CH Cl ).
Compound
1-I
2-I
2-Br
2 2
3·4(CH Cl )
empirical formula
C
12
H
24
I
2
N
4
Si
C
20
H
40
I
2
N
4
Si
C
20
H
40Br
2
N
4
Si
106 8 6 4 3
C H200Cl I N N24Si
formula weight
temperature [K]
506.24
123(2)
618.45
123(2)
524.47
123(2)
2940.17
123(2)
wavelength [ꢁ]
0.71073
0.71073
0.71073
0.71073
crystal system, space group
triclinic, P¯ 1
monoclinic P2
1
/n
triclinic, P¯ 1
1
monoclinic, P2 /c
unit cell dimensions
a [ꢁ]
b [ꢁ]
c [ꢁ]
a [8]
b [8]
g [8]
9.3845(4)
9.8371(4)
10.3605(3)
18.1591(4)
14.3958(4)
90
107.776(2)
90
2579.08(12)
4, 1.593
2498
9.5183(4)
10.7177(5)
13.8357(4)
77.520(2)
87.776(3)
67.483(2)
1271.52(9)
2, 1.370
3.247
20.269(1)
33.761(2)
21.730(1)
90
112.375(2)
90
13750.1(1)
4, 1.420
1.587
11.9831(5)
100.940(2)
100.247(2)
117.023(2)
922.38(7)
2, 1.823
3.470
488
3
volume [ꢁ ]
À3
Z, calculated density [gcm
absorption coefficient [mm
F(000)
]
À1
]
1232
544
6000
crystal size [mm]
q range for data collection
limiting indices
0.36ꢃ0.15ꢃ0.10
1.82 to 26.008
À11 ꢁhꢁ11,
À12ꢁkꢁ12,
À13ꢁlꢁ14
0.33ꢃ0.20ꢃ0.17
2.89 to 28.008
À13ꢁhꢁ13,
À23ꢁkꢁ23,
À19ꢁlꢁ19
0.91ꢃ0.82ꢃ0.24
2.70 to 28.008
À12ꢁhꢁ12,
À13ꢁkꢁ14,
À17ꢁlꢁ18
0.60ꢃ0.40ꢃ0.08
1.18 to 26.008
À24ꢁhꢁ25,
À38ꢁkꢁ41,
À26ꢁlꢁ26
reflections collected/unique
completeness to q=28.00
absorption correction
15742/3630 [R(int)=0.0898] 39327/6229 [R(int)=0.0557] 15498/5942 [R(int)=0.0483] 164223/26984 [R(int)=0.0476]
99.9%
99.9%
96.5%
99.9%
semi-empirical from equivalents
max. and min. transmission
refinement method
0.91741 and 0.46909
0.7044 and 0.4361
0.5096 and 0.1561
0.8736 and 0.5381
2
full-matrix least-squares on F
data/restraints/parameters
goodness-of-fit on F
3630/0/182
1.155
6229/0/252
1.000
5942/0/252
1.015
26984/12/1372
1.048
2
final R indices [I>2s(I)]
R indices (all data)
largest diff. peak and hole [eꢁ
R
R
1
=0.0584, wR
=0.0669, wR
2
2
=0.1594
=0.1660
R
R
1
=0.0218, wR
=0.0279, wR
2
2
=0.0485
=0.0499
R
R
1
1
=0.0327, wR
=0.0498, wR
2
2
=0.0751
=0.0788
R
R
1
1
=0.0669, wR
=0.0872, wR
2
2
=0.1790
=0.1979
1
1
À3
]
2.160 and À1.540
0.646 and À0.996
0.525 and À0.785
5.451 and À2.205
&
&
Chem. Eur. J. 2014, 20, 1 – 11
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8
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Full Paper
4
3
2
C
1
3
98 K): d=1.18 (s, 3H, C -Me, IMe ), 1.22 (t, J(H,H)=7.1 Hz, 12H,
[2] a) R. S. Ghadwal, H. W. Roesky, S. Merkel, J. Henn, D. Stalke, Angew.
Chem. 2009, 121, 5793–5796; Angew. Chem. Int. Ed. 2009, 48, 5683–
5686; b) A. C. Filippou, O. Chernov, G. Schnakenburg, Angew. Chem.
2009, 121, 5797–5800; Angew. Chem. Int. Ed. 2009, 48, 5687–5690;
c) A. C. Filippou, Y. N. Lebedev, O. Chernov, M. Straßmann, G. Schnaken-
burg, Angew. Chem. 2013, 125, 7112–7116; Angew. Chem. Int. Ed. 2013,
4
2
,5
5
3
-N(CH CH ) ), 1.31 (s, 3H, C -Me, IMe ), 1.39 (t, J(H,H)=7.0 Hz,
2 3 2 4
2H, C -N(CH CH ) ), 2.94 (q, J(H,H)=7.1 Hz, 8H, C -N(CH CH ) ),
3
,4
3
2,5
2
3 2
2
3 2
3,4
1
3
.26 (s, 3H, N -Me, IMe ), 3.55 (q br, J(H,H)=7.0 Hz, 4H, C
-
4
3
13
1
N(CH CH ) ), 3.76 ppm (s, 3H, N -Me, IMe );
75.47 MHz, [D ]benzene, 298 K): d=7.9 (s, 1C, C -Me, IMe ), 8.3 (s,
C{ H} NMR
2
3 2
4
5
(
1
6
4
5
2, 6974–6978.
4
2,5
3,4
C, C -Me, IMe ), 14.7 (s, 4C, C -N(CH CH ) ), 15.2 (s, 4C, C -
4 2 3 2
[
3] Y. Xiong, S. Yao, M. Driess, J. Am. Chem. Soc. 2009, 131, 7562–7563.
4] a) A. C. Filippou, O. Chernov, B. Blom, K. W. Stumpf, G. Schnakenburg,
Chem. Eur. J. 2010, 16, 2866–2872; b) H. Cui, C. Cui, Dalton Trans. 2011,
40, 11937–11940.
1
3
N(CH CH ) ), 32.5 (s, 1C, N -Me, IMe ), 33.6 (s, 1C, N -Me, IMe ), 45.7
2
3 2
,4
4
4
[
3
2,5
4
(
s, 4C, C -N(CH CH ) ), 51.6 (s, 4C, C -N(CH CH ) ), 124.8 (s, 1C, C -
2
3 2
2
3 2
2
5
Me, IMe ), 125.1 (s, 1C, C -Me, IMe ), 141.9 (s, J(Si,C)=8.1 Hz, 2C,
4
4
3
,4
1
2,5
C
1
(
-N(CH CH ) ), 153.0 (s, J(Si,C)=20 Hz, 2C,
68.5 ppm (s, J(Si,C)=25 Hz, 1C, NCN, IMe4);
59.6 MHz, [D ]benzene, 298 K): d=À69.6 ppm (s).
Crystal structure determination of 1-I, 2-I, 2-Br, and 3·4(CH Cl ):
Single crystals of 1-I (red blocks), 2-Br (yellow plates), and 2-I
orange-yellow blocks) were grown upon slow cooling of n-hexane
C
-N(CH CH ) ),
Si{ H} NMR
[5] a) A. C. Filippou, O. Chernov, K. W. Stumpf, G. Schnakenburg, Angew.
Chem. 2010, 122, 3368–3372; Angew. Chem. Int. Ed. 2010, 49, 3296–
3300; b) A. C. Filippou, O. Chernov, G. Schnakenburg, Chem. Eur. J.
2
3 2
2
3 2
1
29
1
6
2
011, 17, 13574–13583; c) A. C. Filippou, B. Baars, O. Chernov, Y. N. Leb-
2
2
edev, G. Schnakenburg, Angew. Chem. 2014, 126, 576–581; Angew.
Chem. Int. Ed. 2014, 53, 565–570.
(
[
[
6] R. S. Ghadwal, R. Azhakar, H. W. Roesky, Acc. Chem. Res. 2013, 46, 444–
solutions from ambient temperature to À608C (Table 3). Orange
456.
plates of 3·4(CH Cl ) were obtained upon diffusion of diethyl ether
2
2
7] a) Y. Xiong, S. Yao, S. Inoue, E. Irran, M. Driess, Angew. Chem. 2012, 124,
10221–10224; Angew. Chem. Int. Ed. 2012, 51, 10074–10077; b) K. C.
Mondal, H. W. Roesky, M. C. Schwarzer, G. Frenking, I. Tkach, H. Wolf, D.
Kratzert, R. Herbst-Irmer, B. Niepoetter, D. Stalke, Angew. Chem. 2013,
125, 1845–1850; Angew. Chem. Int. Ed. 2013, 52, 1801–1805; c) Y.
Xiong, S. Yao, S. Inoue, J. D. Epping, M. Driess, Angew. Chem. 2013, 125,
7287–7291; Angew. Chem. Int. Ed. 2013, 52, 7147–7150.
into a saturated CH Cl solution at ambient temperature. The data
collection of 1-I, 2-Br, and 3·4(CH Cl ) was performed on a Nonius
2
2
2
2
KappaCCD diffractometer (area detector), and the data collection
of 2-Br on a STOE IPDS-2T diffractometer (area detector). The dif-
fractometers used graphite-monochromated MoKa radiation (l=
.71073 ꢁ) and were equipped with low-temperature devices
Nonius KappaCCD diffractometer: Cryostream 600er series, Oxford
Cryosystems, 123 K; STOE IPDS-2T diffractometer: Cryostream
00er series, Oxford Cryosystems). Intensities were measured by
fine-slicing w and f scans and corrected for background, polariza-
tion and Lorentz effects. An empirical absorption correction was
applied for all data sets. The structures were solved by direct meth-
ods and refined anisotropically by the least-squares procedure im-
plemented in the SHELX program system. Hydrogen atoms were
included isotropically by using the riding model on the bound
carbon atoms. Compound 2-Br crystallized also in a different modi-
0
(
[
[
8] S. Reis, Diplomarbeit, Universitꢅt Bonn, 2012.
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therein; b) W. S. Palmer, K. A. Woerpel, Organometallics 1997, 16, 4824–
7
4827.
[
10] A CSD survey (11.04.2014) of 1H-siloles gave 173 hits and mean values
of 1.362, 1.500, and 1.870 ꢁ for the C
lengths, respectively.
a
ÀC
b
, C
b
ÀC
b
and SiÀC
a
bond
[
11] M. Kolonits, M. Hargittai, Struct. Chem. 1998, 9, 349–352.
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[
2
[13] J. Yang, I. Guzei, J. G. Verkade, J. Organomet. Chem. 2002, 649, 276–288.
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ters gave 77 hits and a mean SiÀI bond length of 2.489 ꢁ.
fication (2-Br ) featuring very similar bonding parameters. This
a
structure is also deposited in the CSD database and is not dis-
cussed in this manuscript. The salt 3 crystallized kinetically con-
trolled within a rather large unit cell containing three independent
cation/anion pairs of 3 and four dichloromethane molecules in the
asymmetric unit. The solvent molecules could be fully located in
the difference density map and refined anisotropically applying
a soft ISOR restraint at the carbon atoms of the solvent molecules.
[15] According to a CSD survey (11.04.2014, 149 hits) the mean SiÀBr bond
length of four-coordinate silicon atoms is 2.253 ꢁ.
[
16] F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G. Orpen, R. Taylor,
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[
[
[
[
CCDC-997162 (1-I), CCDC-997163 (2-I), CCDC-997164 (2-Br), CCDC-
97165 (2-Br ), and CCDC-997166 (3) contain the supplementary
a
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.
9
[21] N. Kuhn, T. Kratz, Synthesis 1993, 561–562.
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Acknowledgements
[
[
We thank the Deutsche Forschungsgemeinschaft (SFB 813) and
the University of Bonn for the generous support of this work.
We also thank Dr. J. Tirrꢄe for discussions, C. Schmidt, K. Proch-
nicki, and H. Spitz for recording the solution NMR spectra, and
A. Martens for the elemental analyses.
2
630–2632.
[26] a) E. H. Braye, W. Hꢂbel, I. Caplier, J. Am. Chem. Soc. 1961, 83, 4406–
4413; b) S. Yamaguchi, R.-Z. Jin, K. Tamao, F. Sato, J. Org. Chem. 1998,
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3, 10060–10062; c) S. Yamaguchi, R.-Z. Jin, S. Ohno, K. Tamao, Organo-
metallics 1998, 17, 5133–5138.
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[
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53, 223–228; c) J. Braddock-Wilking, Y. Zhang, J. Y. Corey, N. P. Rath, J.
Keywords: 1H-siloles
cycloaddition · dihalosilylenes · N-heterocyclic carbenes
·
1-silacyclopentadien-1-ylidenes
·
Organomet. Chem. 2008, 693, 1233–1242.
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28] a) K. Tamao, S. Yamaguchi, Pure Appl. Chem. 1996, 68, 139–144; b) K.
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Barlow, S. R. Marder, Chem. Commun. 2009, 1948–1955.
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Chem. Eur. J. 2014, 20, 1 – 11
www.chemeurj.org
9
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
1
[
29] a) S. Yamaguchi, C. Xu, T. Okamoto, Pure. Appl. Chem. 2006, 78, 721–
[35] NMR spectroscopic data of Me
298 K, ppm): d=2.50 (s, 12H, 2 ꢃ N(CH
298 K, ppm): d=45.7 (s, 2 ꢃ N(CH ), 75.3 (s, 2 ꢃ C
2
NCꢀCNMe
2
:
H NMR ([D
6
6
]benzene,
]benzene,
1
3
1
730; b) S.-C. Lo, P. L. Burn, Chem. Rev. 2007, 107, 1097–1116; c) J. Chen,
3
)
2
); C{ H} NMR ([D
alkyne
Y. Cao, Acc. Chem. Res. 2009, 42, 1709–1718.
3
)
2
); NMR spectro-
1
[
[
[
30] a) K. Fredenhagen, G. Cadenbach, Z. Anorg. Allg. Chem. 1926, 158, 249–
scopic data of Et
2
NCꢀCNEt
2
:
H NMR ([D
6
]benzene, 300.1 MHz, 298 K,
3
263; b) W. Rꢂdorff, E. Schulze, Z. Anorg. Allg. Chem. 1954, 277, 156–171.
ppm): d=1.09 (t, J(H,H)=7.1 Hz, 12H,
2
13
ꢃ
1
N(CH
2
CH
C{ H}-NMR ([D
75.5 MHz, 298 K, ppm): d=13.2 (s, 4C, 2 ꢃ N(CH CH ), 49.9 (s, 4C, 2 ꢃ
3
)
2
), 2.71 (q,
3
31] Handbuch der Prꢁparativen Anorganischen Chemie, Vol. 2, (Ed.: G.
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dam, 1988, pp. 185–186.
J(H,H)=7.1 Hz, 8H,
2
ꢃ
N(CH
2
CH
3
)
2
);
6
]benzene,
2
3 2
)
alkyne
N(CH
2
CH
3
)
2
), 74.1 (s, 2 ꢃ C
).
[
[
Received: April 15, 2014
Published online on && &&, 0000
&
&
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www.chemeurj.org
10
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Full Paper
FULL PAPER
&
Siloles
Y. N. Lebedev, U. Das, O. Chernov,
G. Schnakenburg, A. C. Filippou*
&& – &&
2
,3,4,5-Tetraamino-1H-siloles SiI {C -
yl-imidazolin-2-ylidene) leads to [Si-
2
4
[
2+2+1] Cycloadditions of
(NR ) } (1-I: R=Me; 2-I R=Et) were syn-
(IMe ) {C (NEt ) }](I) (3), containing a 1H-
2
4
4 2
4
2 4
2
Bis(dialkylamino)acetylenes with
SiI (Idip): Syntheses and Reactivity
Studies of Unprecedented 2,3,4,5-
Tetraamino-1H-siloles
IV
thesized by a [2+2+1] cycloaddition of
R NÀCꢀCÀNR (R=Me, Et) with NHC-
silole dication with a four-coordinate Si
2
center. Two-electron reduction of 3 with
C8K affords the carbene-stabilized 1-sila-
cyclopentadien-1-ylidene Si{C (NEt ) }-
2
2
1
stabilized SiI (L =1,3-bis(2,6-diisopro-
2
pylphenyl)imidazolin-2-ylidene). Reac-
4
2 4
tion of 2-I with the N-heterocyclic car-
(IMe ) (4).
4
2
bene IMe (IMe (L )=1,3,4,5-tetrameth-
4
4
Chem. Eur. J. 2014, 20, 1 – 11
www.chemeurj.org
11
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ