N-heterocyclic carbene (NHC)-stabilized silanechalcogenones: NHC→Si(R2)=E (E = O, S, Se, Te)

Article abstract of DOI:10.1002/chem.200902467

A series of N-heterocyclic carbene-stabilized silanechalcogenones 2a,b (Si=O), 3a,b (Si=S), 4a,b (Si=Se), and 5a,b (Si=Te) are described. The silanone complexes 2a,b were prepared by facile oxygenation of the carbenesilylene adducts 1a,b with N₂O, whereas their heavier congeners were synthesized by gentle chalcogenation of 1a,b with equimolar amounts of elemental sulfur, selenium, and tellurium, respectively. These novel compounds have been isolated in a crystalline form in high yields and have been fully charac-terized by a variety of techniques including IR spectroscopy, ESIMS, and multinuclear NMR spectroscopy. The structures of 2 b, 3 a, 4 a, 4 b, and 5 b have been confirmed by single-crystal X-ray crystallography. Due to the NHC-→Si donor-acceptor electronic interaction, the Si=E (E = O, S, Se, Te) moieties within these compounds are well stabilized and thus the compounds possess several ylide-like resonance structures. Nevertheless, these species also exhibit considerable Si=E doublebond character, presumably through a nonclassical Si=E π-bonding interaction between the chalcogen lone-pair electrons and two antibonding Si-N σz.ast; orbitals, as evidenced by their high stretching vibration modes and the shortening of the Si-E distances (between 5.4 and 6.3%) compared with the corresponding Si-E single-bond lengths.

Full text of DOI:10.1002/chem.200902467

FULL PAPER
DOI: 10.1002/chem.200902467
N-Heterocyclic Carbene (NHC)-Stabilized Silanechalcogenones:
NHC!Si(R2)=E (E=O, S, Se, Te)
Shenglai Yao, Yun Xiong, and Matthias Driess*[a]
Dedicated to Professor Hubert Schmidbaur
Abstract: A series of N-heterocyclic
terized by a variety of techniques in-
cluding IR spectroscopy, ESIMS, and
multinuclear NMR spectroscopy. The
structures of 2b, 3a, 4a, 4b, and 5b
have been confirmed by single-crystal
X-ray crystallography. Due to the
NHC!Si donor–acceptor electronic
interaction, the Si=E (E=O, S, Se, Te)
moieties within these compounds are
well stabilized and thus the compounds
carbene-stabilized silanechalcogenones
2a,b (Si=O), 3a,b (Si=S), 4a,b (Si=Se),
and 5a,b (Si=Te) are described. The si-
lanone complexes 2a,b were prepared
by facile oxygenation of the carbene–
silylene adducts 1a,b with N2O, where-
as their heavier congeners were synthe-
sized by gentle chalcogenation of 1a,b
with equimolar amounts of elemental
sulfur, selenium, and tellurium, respec-
tively. These novel compounds have
been isolated in a crystalline form in
high yields and have been fully charac-
possess several ylide-like resonance
structures. Nevertheless, these species
also exhibit considerable Si=E double-
bond character, presumably through a
nonclassical Si=E p-bonding interac-
tion between the chalcogen lone-pair
ꢀ
electrons and two antibonding Si N s*
orbitals, as evidenced by their high
stretching vibration modes and the
shortening of the Si–E distances (be-
tween 5.4 and 6.3%) compared with
Keywords: carbenes · chalcogens ·
heterocycles
silanones
· multiple bonds ·
ꢀ
the corresponding Si E single-bond
lengths.
Introduction
The chemistry of multiply bonded heavier main-group ele-
ments is currently one of the main areas of research in or-
ganometallic chemistry. Of especially great interest are com-
pounds with a double bond that involves heavier Group 14
and Group 16 elements as heavier congeners of ubiquitous
ketones.[1] Since Corriu et al. reported in 1989 the first
stable silanethione (Si=S) and silaneselone (Si=Se) deriva-
tives I and II (Scheme 1) supported by a intramolecular N!
Si donor–acceptor bond,[2] several series of stable doubly
bonded species have been developed by taking advantage of
the kinetic protection from the bulky ligands and/or the
thermodynamic stabilization from Lewis donors as well as
acceptors. Striking examples, including a series of fascinating
stable heavier diarylsilanechalcogenones III (Scheme 1)[3]
and dialkylsilanechalcogenones IV (Scheme 1)[4] without in-
Scheme 1. Isolable compounds with a double bond involving silicon and
Group 16 elements.
[a] Dr. S. Yao, Dr. Y. Xiong, Prof. Dr. M. Driess
Institute of Chemistry: Metalorganics and Inorganic Materials
Sekretariat C2, Technische Universitꢁt Berlin
Strasse des 17. Juni 135, 10623 Berlin (Germany)
Fax : (+49) 30-314-29732
tramolecular donor support, were described by Tokitoh,
Okazaki et al. as well as by Iwamoto and Kira et al., respec-
tively. Recently, a novel bis(silaneselone) with two donor-
supported Si=Se double bonds was reported by Mꢀller and
West et al.[5]
E-mail: matthias.driess@tu-berlin.de
Chem. Eur. J. 2010, 16, 1281 – 1288
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1281

Although a “free” silanone derivative (R2Si=O) still re-
mains elusive, we recently succeeded in synthesizing the re-
markably stable silaformamide–borane complex[6] with a
donor–acceptor-supported silicon–oxygen double bond start-
ing from a zwitterionic silylene.[7]
Moreover, we reported the synthesis and characterization
of an entire series of heavier congeners of silanoic silylesters
V (Scheme 1)[8] that bore an N!Si-supported Si=E (E=O,
S, Se, Te) moiety from gentle monochalcogenation of a
stable siloxysilylene.[6] Inspired by the isolation of N-hetero-
cyclic carbene (NHC)-stabilized main-group element species
reported by Robinson et al.,[9] we preliminarily communicat-
ed the isolation of the NHC-supported silanone 2a
(Scheme 2) by facile oxygenation of a NHC–silylene adduct
uene to N2O at ꢀ788C leads to a gradual loss of color. The
desired product 2b can be obtained as colorless crystals by
crystallization of the resulting reaction solution at ꢀ208C in
88% yield.
The NHC-stabilized heavier silanechalcogenones 3a,b,
4a,b, and 5a,b are readily accessible by direct chalcogena-
tion applying the respective elemental chalcogens. Thus,
treatment of equimolar amounts of the NHC–silylene ad-
ducts 1a and 1b with elemental sulfur S8 in toluene at ambi-
ent temperature, respectively, leads to a color change from
yellow to pale yellow and the formation of colorless precipi-
tates (Scheme 2). Subsequent workup of the resulting mix-
tures affords 3a and 3b as a colorless crystalline solid in 79
and 71% yields, respectively. Similarly, the conversions of
1a and 1b with elemental selenium and tellurium enable the
formation and isolation of 4a (76%) and 4b (69%) in the
form of colorless crystals as well as 5a (74%) and 5b (68%)
in the form of yellow crystals. Notably, the free silylene[7]
without NHC is resistant towards elemental selenium and
tellurium under the same conditions, whereas the treatment
of the free silylene with sulfur slowly results in complex un-
identified products. This finding confirms the increase of nu-
cleophilicity of the silicon(II) center in 1a and 1b by coordi-
nation of the NHC moiety.
The composition and constitution of the resulting new
compounds were proven by elemental analysis, ESIMS, and
multinuclear NMR spectroscopy. Although the 1H and
13C NMR signals of 2a,b–5a,b for the N-heterocyclic sup-
porting ligands are similar to those observed for their pre-
cursor 1a,b, their 29Si NMR spectra exhibit significant high-
field shifts (Table 1) compared to those found for 1a (d-
Table 1. NMR spectroscopic data of 2a,b–5a,b.
Complex
d(29Si) [ppm]
d(77Se) [ppm]
d(125Te) [ppm]
Scheme 2. Synthesis of 2a,b–5a,b from NHC–silylene adducts 1a and 1b.
2a
2b
3a
3b
4a
4b
5a
5b
ꢀ74.2[a]
ꢀ72.9[a]
ꢀ34.9[b]
ꢀ33.5[b]
ꢀ33.3[b]
ꢀ32.9[b]
ꢀ46.0[b]
ꢀ49.6[b]
–
–
–
–
–
–
–
–
1a with N2O.[10] To extend this work, we probed the possibil-
ity for direct chalcogenation of the NHC–silylene adducts
1a and 1b with elemental heavier chalcogens for the prepa-
ration of the respective NHC-supported silanechalcoge-
nones. Here we report on the synthesis as well as the spec-
troscopic and structural characterization of the first series of
NHC-stabilized silanechalcogenones, which includes 2b (Si=
O), 3a,b (Si=S), 4a,b (Si=Se), and 5a,b (Si=Te) (Scheme 2).
–
ꢀ374.4
ꢀ470.2
–
–
ꢀ1010.4
–
ꢀ982.5
[a] Measured in [D6]benzene. [b] Measured in [D2]dichloromethane.
G
U
29Si NMR chemical shifts of 2a (d=ꢀ74.2 ppm) and 2b (d=
ꢀ72.9 ppm) lie between the values observed for the two dia-
stereomers of the N-donor-stabilized silanoic ester V (d=
ꢀ85.1 and ꢀ85.8 ppm)[8a] and the silaformamide–borane
complex (d=ꢀ61.5 ppm).[6] As expected, the 29Si NMR
spectra of the heavier NHC–silanechalcogenones 3a,b–5a,b
exhibit less-shielded silicon nuclei (ranging from d=ꢀ32.9
to ꢀ49.6 ppm) relative to the NHC-supported silanones 2a
and 2b. These chemical shifts of 3a,b–5a,b are comparable
to the corresponding chemical shifts of related silanoic thio-,
Results and Discussion
Synthesis and spectroscopic characterization: In a prelimina-
ry communication we reported that the NHC–silanone
adduct 2a is easily accessible by oxygenation of the NHC–si-
lylene adduct 1a with N2O (Scheme 2).[10] The same proce-
dure is also suitable for the synthesis of the sterically more
hindered NHC–silanone adduct 2b. Accordingly, exposure
of a yellow solution of the NHC–silylene adduct 1b[11] in tol-
seleno-, and telluroesters V, with dACTHNUTRGNEUNG
(29Si) values ranging from
ꢀ38.4 to ꢀ52.2 ppm.[8b] Expectedly, the 29Si nuclei of the un-
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Chem. Eur. J. 2010, 16, 1281 – 1288

Silanechalcogenones
FULL PAPER
supported Si=E (E=S, Se, Te) compounds III and IV reso-
nate at much lower field; they range from d=166.6 to
229.5 ppm.[3,4] Even the intramolecular N-donor-supported
silanechalcogenones I (dACTHUNTGRENNUG ACHUTNGTRENNUGN
(29Si)=22.3 ppm) and II (d(29Si)=
29.4 ppm)[2] are less shielded than 3a,b and 4a,b, respective-
ly. Apparently, this observation is indicative of greater per-
turbation of the Si=E (E=O, S, Se, Te) double bonds
caused by both the C3N2 p system in the backbone and the
NHC moiety, thereby leading to several resonance struc-
tures as depicted in Scheme 3.
Figure 1. IR spectra of 2b (c), 3b (b), 4b (g), and 5b (d) in
the characteristic region of 550–1250 cmꢀ1
.
numbers of V.[8b] Nevertheless, these n˜
ACTHNUTRGNE(NUG Si=E) (E=O, S, Se,
Te) stretching modes are drastically larger than the corre-
Scheme 3. Resonance structures of 2a,b–5a,b (E=O, S, Se, Te; Ar=2,6-
iPr2C6H3; R=Me, iPr).
ꢀ
sponding values observed for Si E single-bond species (i.e.,
for (MeH2Si)2E, in which E=O, S, Se, Te),[12] which might
suggest considerable double-bond character in 2a,b–5a,b.
The latter Si=E multiple-bond character can be rationalized
as previously discussed by a nonclassical Si=E p-binding in-
teraction between the chalcogen lone-pair electrons and two
The 77Se NMR spectra of 4a and 4b show a singlet signal
at d=ꢀ374.4 and ꢀ470.2 ppm, respectively, which are in
sharp contrast to the downfield shifts of the unsupported
Si=Se species III (d=635 ppm).[3] The latter chemical shifts
are, however, comparable to those of V (E=Se; d=ꢀ384.8
and ꢀ401.3 ppm).[8b] Likewise, the 125Te NMR spectra of 5a
and 5b display singlet signals (d=ꢀ1010.4 for 5a and
ꢀ982.5 ppm for 5b) very close to those of the two diastereo-
mers of V (E=Te ; d=ꢀ1076.7 and ꢀ1105.5 ppm).[8b] The
shielding of the 77Se and 125Te nuclei of the Si=E moiety in
4a,b–5a,b is in accordance with their 29Si NMR spectroscopy
and implies again the resonance stabilization of the silicon–
chalcogen double bonds (Scheme 3).
ꢀ
antibonding Si N s* orbitals that are located mainly at the
silicon site.[6,8b]
Molecular structures: The molecular structure of 2a has al-
ready been reported in a preliminary communication.[10] The
molecular structures of 2b, 3a, 4a, 4b, and 5b were estab-
lished by single-crystal X-ray diffraction analysis and their
ORTEP drawings are shown in Figures 2, 3, 4, 5, and 6 to-
gether with their structural parameters. For comparison, the
selected interatomic distances (d) and angles are compiled
in Table 3. The structures of 3b and 5a have also been con-
firmed by X-ray diffraction but they cannot be discussed
due to poor crystal quality. Whereas compounds 2b, 4b, and
5b crystallize in the monoclinic space groups P21/c (2b, 5b)
and P21/n (4b), respectively, compounds 3a and 4a result in
Interestingly, a considerable Si=E p-bond character of
complexes 2a,b–5a,b can also be concluded from the vibra-
tional stretching frequencies of the Si=E moieties (Table 2).
Table 2. Comparison of the vibrational stretching frequencies [cmꢀ1] of
¯
the Si=E moieties in 2a,b–5a,b with the silanoic chalcogenesters V.[8]
the triclinic space group P1. Two independent molecules of
2b are found in the asymmetric unit as shown in Figure 2.
Similar to 2a, the new compounds are monomeric in the
crystal, and the silicon centers adopt a strongly distorted tet-
rahedral coordination geometry with a terminal chalcogen
atom. Whereas the six-membered C3N2Si rings in the com-
pounds are slightly puckered, the five-membered NHC rings
remain planar.
The Si=O bond lengths of 1.527(2) and 1.534(2) ꢃ in 2b
are even shorter than that observed for 2a (1.541(2) ꢃ) and
in the silanoic ester V (1.579(3) ꢃ).[8a] To our knowledge,
they are the shortest Si=O bond lengths hitherto reported
among stable molecular silicon–oxygen compounds with ter-
minal oxygen atoms.[6,8a,10] In contrast, although the Si=E
(E=S, Se, Te) bond lengths in 3a (Si=S: 2.006(1) ꢃ), 4a
(Si=Se: 2.1457(9) ꢃ), 4b (Si=Se: 2.1399(9) ꢃ), and 5b (Si=
E=O
E=S
E=Se
E=Te
V[8]
2a–5a
2b-5b
ꢁ1150
1134
1133
739
683
679
695
614
606
678
595
588
As depicted in Figure 1, the assignment of the respective n˜-
(Si=E) stretching vibration results from overlapping of the
N
IR spectra; the characteristic frequencies are listed in
Table 2.
The n˜ACHTUNGTRENNUNG
(Si=O) stretching vibration modes of 2a (1134 cmꢀ1)
and 2b (1133 cmꢀ1) are around 20–30 cmꢀ1 smaller than that
observed for the silanoic ester (ꢁ1150 cmꢀ1)[8a] and the sila-
formamide–borane complex (1165 cmꢀ1).[6] Similarly, the n˜-
G
ACHTUNGTRENNUNG(Si=Se), and n˜ACHTUNGTNER(NUGN Si=Te) values are also significantly
ꢀ
Te: 2.383(2) ꢃ) are significantly shorter than respective Si
Chem. Eur. J. 2010, 16, 1281 – 1288
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1283

M. Driess et al.
Figure 3. Molecular structure of 3a. Thermal ellipsoids are drawn at the
50% probability level. Hydrogen atoms are omitted for clarity. Selected
ꢀ
ꢀ
ꢀ
bond lengths [ꢃ] and angles [8]: S1 Si1 2.006(1), Si1 N2 1.749(2), Si1
ꢀ
ꢀ
ꢀ
ꢀ
N1 1.752(2), Si1 C30 1.963(3), N1 C2 1.407(4), N2 C4 1.414(4), N3
ꢀ
ꢀ
ꢀ
ꢀ
C30 1.357(4), N3 C31 1.391(4), N4 C30 1.356(4), N4 C32 1.378(4), C2
ꢀ
C3 1.431(4), C3 C4 1.370(4); N2-Si1-N1 102.1(1), N2-Si1-S1 115.53(9),
N1-Si1-S1 115.88(9), C30-Si1-S1 110.4(1), N4-C30-N3 103.7(3).
Figure 2. The two independent molecules of 2b in the asymmetric unit.
Thermal ellipsoids are drawn at the 50% probability level. Hydrogen
atoms, except those at C1 and C41, are omitted for clarity. Selected bond
ꢀ
ꢀ
ꢀ
lengths [ꢃ] and angles [8]: Mol. 1: Si1 O1 1.527(2), N1 C2 1.407(4), N1
ꢀ
ꢀ
ꢀ
ꢀ
Si1 1.751(3), Si1 N2 1.741(3), Si1 C30 1.978(3), N2 C4 1.418(4), C2 C3
ꢀ
ꢀ
ꢀ
ꢀ
1.450(5), N3 C30 1.356(4), N3 C31 1.377(4), C3 C4 1.334(5), N4 C30
1.361(4), N4 C32 1.383(4); N1-Si1-N2 101.8(1), N1-Si1-O1 118.8(1), N2-
Si1-O1 114.0(1), C30-Si1-O1 107.8(1), N3-C30-N4 104.9(2); Mol. 2: Si2
O2 1.534(2), Si2 N6 1.744(3), Si2 N5 1.754(3), Si2 C70 1.963(3), N5
Figure 4. Molecular structure of 4a. Thermal ellipsoids are drawn at the
50% probability level. Hydrogen atoms are omitted for clarity. Selected
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
bond lengths [ꢃ] and angles [8]: Se1 Si1 2.1457(9), Si1 N2 1.754(3), Si1
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
N1 1.759(2), Si1 C30 1.977(3), N1 C2 1.405(4), N2 C4 1.416(4), N3
ꢀ
ꢀ
ꢀ
ꢀ
C42 1.408(4), N6 C44 1.418(4), N7 C70 1.355(4), N7 C71 1.385(4), N8
ꢀ
ꢀ
ꢀ
ꢀ
C30 1.356(3), N3 C31 1.379(4), N4 C30 1.356(4), N4 C32 1.386(4), C2
ꢀ
ꢀ
ꢀ
C70 1.359(3), N8 C72 1.388(4), C42 C43 1.458(5), C43 C44 1.324(5);
O2-Si2-N6 115.0(1), O2-Si2-N5 118.4(1), N6-Si2-N5 101.6(1), O2-Si2-C70
107.6(1), N7-C70-N8 105.1(2).
ꢀ
C3 1.433(4), C3 C4 1.362(4); N2-Si1-N1 101.7(1), N2-Si1-Se1 114.98(9),
N1-Si1-Se1 115.92(9), C30-Si1-Se1 111.6(1), N4-C30-N3 104.6(2).
ꢀ
E single bonds, they are a little longer than the correspond-
ing values observed in the series of silanoic esters V (Si=S
1.980(2), Si=Se 2.117(1), Si=Te 2.346(1) ꢃ),[8b] respectively.
The latter elongations correspond well with the bathochro-
mic shifts of the Si=E stretching modes observed in the IR
spectra (Table 2). However, as can be seen from the per-
centage of bond shortening with regard to the corresponding
Interestingly, the Si N bond lengths in these new struc-
tures (ranging from 1.741(3) to 1.766(5) ꢃ) are significantly
shorter than those observed in precursors 1a (1.802(3) and
1.805(3) ꢃ) and 1b (1.794(2) and 1.820(2) ꢃ) in spite of the
increased coordination number of the silicon atom in these
NHC-supported silanechalcogenones. In addition, although
ꢀ
the Si Ccarbene bond lengths (ranging from 1.963(3) to
2.007(6) ꢃ) in these species are much longer than a typical
Si C single-bond length in organosilanes (1.86 ꢃ), they are
ꢀ
Si E single bonds (%Dd) in Table 3, the Si=E moieties in
ꢀ
2a,b–5a,b could have significant double-bond character, al-
ꢀ
though zwitterionic Si+
excluded.
bonding character could not be
shorter than those found for 1a (2.016(3) ꢃ) and 1b
ꢀ
E
(2.065(2) ꢃ).[10,11] This shortening of the Si N and Si C
ꢀ
ꢀ
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Chem. Eur. J. 2010, 16, 1281 – 1288

Silanechalcogenones
FULL PAPER
Table 3. Selected structural parameters of 2a,b–5a,b.
ꢀ
ꢀ
ꢀ
d(Si=E)
[ꢃ]
%Dd[a] d(Si C)
d(Si N)
[ꢃ]
d(Si N)
[ꢃ]
[ꢃ]
2a
(E=O)
2b
1.541(2)
5.5
6.3
1.930(2)
1.745(2)
1.750(2)
1.527(2)
1.978(3)
1.751(3)
1.741(3)
(E=O)
3a (E=S) 1.534(2)
5.9
6.3
1.963(3)
1.963(3)
1.754(3)
1.752(2)
1.744(3)
1.749(2)
4a
2.006(1)
2.1457(9)
2.1399(9)
2.383(2)
(E=Se)
4b
5.5
5.7
5.4
1.977(3)
1.978(3)
2.007(6)
1.759(2)
1.754(3)
1.766(5)
1.754(3)
1.762(3)
1.758(5)
(E=Se)
5b
(E=Te)
ꢀ
ꢀ
[a] %Dd=[1ꢀd(Si=E)/d(Si E)]ꢄ100%. Standard values for Si O
ꢀ
ꢀ
ꢀ
(1.63 ꢃ), Si S (2.14 ꢃ), Si Se (2.27 ꢃ), and Si Te single-bond lengths
(2.52 ꢃ) from ref. [13].
Figure 5. Molecular structure of 4b. Thermal ellipsoids are drawn at the
50% probability level. Hydrogen atoms are omitted for clarity. Selected
ꢀ
ꢀ
ꢀ
bond lengths [ꢃ] and angles [8]: Se1 Si1 2.1399(9), N1 C2 1.414(4), N1
ꢀ
ꢀ
ꢀ
ꢀ
Si1 1.754(3), Si1 N2 1.762(3), Si1 C30 1.978(3), N2 C4 1.420(4), C2 C3
spectroscopy and X-ray diffraction. The Si=E (E=O, S, Se,
Te) moieties within these compounds are electronically well
supported by the C3N2 backbone and the NHC ligands,
thereby resulting in several ylide-like resonance structures.
However, these species possess considerable Si=E double-
bond character as indicated by their Si=E vibration modes
and relatively short Si=E bond lengths. Due to the highly
nucleophilic chalcogen centers in 2a,b–5a,b, they represent
a fascinating new type of strong s-donor ligands capable of
the synthesis of low-coordinate transition-metal complexes
that could find applications in homogeneous catalysis. Re-
spective investigations are currently underway.
ꢀ
ꢀ
ꢀ
ꢀ
1.457(4), N3 C30 1.366(4), N3 C31 1.391(4), C3 C4 1.336(4), N4 C30
1.371(4), N4 C32 1.395(4); N1-Si1-N2 102.43(1), N1-Si1-Se1 120.41(9),
N2-Si1-Se1 109.50(9), C30-Si1-Se1 111.2(1), N3-C30-N4 105.2(3).
ꢀ
Experimental Section
General considerations: All experiments and manipulations were carried
out under dry oxygen-free nitrogen using standard Schlenk techniques or
in an MBraun inert atmosphere drybox containing an atmosphere of pu-
rified nitrogen. Solvents were dried by standard methods and freshly dis-
tilled prior to use. The starting materials 1a[10] and 1b,[11] were prepared
according to literature procedures. Compound 2a was prepared accord-
ing to the preliminary communication.[10] ESIMS were measured using a
Thermo Scientific LTQ orbitrap XL. 1H, 13C, 77Se, 125Te, and 29Si NMR
spectra were recorded using Brucker spectrometers ARX 200 and AV
400 with residual solvent signals as internal reference (1H and 13C{1H}) or
with an external reference (SiMe4 for 29Si, SeMe2 for 77Se, (PhTe)2 for
125Te, respectively). Abbreviations: s=singlet; d=doublet; t=triplet;
sept=septet; m=multiplet; br=broad.
Figure 6. Molecular structure of 5b. Thermal ellipsoids are drawn at the
50% probability level. Hydrogen atoms are omitted for clarity. Selected
ꢀ
ꢀ
ꢀ
bond lengths [ꢃ] and angles [8]: Te1 Si1 2.383(2), Si1 N2 1.758(5), Si1
ꢀ
ꢀ
ꢀ
ꢀ
N1 1.766(5), Si1 C30 2.007(6), N1 C2 1.402(7), N2 C4 1.410(7), N3
ꢀ
ꢀ
ꢀ
ꢀ
C31 1.387(8), N3 C30 1.387(7), N4 C30 1.368(7), N4 C32 1.385(8), C2
ꢀ
C3 1.463(8), C3 C4 1.350(8); N2-Si1-N1 101.8(2), N2-Si1-Te1 112.4(2),
N1-Si1-Te1 113.1(2), C30-Si1-Te1 114.1(2), N4-C30-N3 104.0(5).
bond lengths is ascribed to the presence of a ylide-like reso-
nance stabilization of the Si=E double bonds.
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 2b, 3a, 4a, 4b, and 5b were collected using an Oxford Dif-
fraction Xcalibur S Sapphire at 150 K (MoKa radiation, l=0.71073 ꢃ).
The structures were solved by direct methods and refined on F2 with the
SHELX-97[14] software package. The positions of the hydrogen atoms
were calculated and considered isotropically according to a riding model.
Conclusion
The first entire series of NHC-stabilized silanechalcoge-
nones 2a,b (Si=O), 3a,b (Si=S), 4a,b (Si=Se), and 5a,b (Si=
Te) has been successfully prepared by gentle oxidation of
the carbene–silylene adducts with N2O (in the case of 2a,b)
and elemental chalcogens. They were isolated in a crystal-
line form in high yields and characterized by NMR and IR
Compound 2b: Monoclinic; space group P21/c; a=21.202(1), b=
16.8240(7), c=21.427(1) ꢃ; b=94.281(3)8; V=7621.9(7) ꢃ3; Z=8;
ACTHNUTRGNEUNG
1calcd =1.117 Mgmꢀ3; m(MoKa)=0.096 mmꢀ1; 38707 collected reflections;
12890 crystallographically independent reflections (Rint =0.0949); 7044
reflections (I>2s(I)); qmax =25.008; R(Fo)=0.0707 (I>2s(I)), wR(F2o)=
0.1278 (all data); 859 refined parameters.
Chem. Eur. J. 2010, 16, 1281 – 1288
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1285

M. Driess et al.
¯
Compound 3a: Triclinic, space group P1; a=9.8537(4), b=11.9875(4),
6 mL and subsequent cooling to ꢀ208C for 24 h afforded colorless crys-
tals of 3a (0.47 g, 0.77 mmol, 79%). M.p. 2458C (decomp); 1H NMR
(400.13 MHz, [D2]dichloromethane, 258C): d=0.40 (d, 3J(H,H)=7 Hz,
3H; CHMe2), 0.51 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.08 (d, 3J(H,H)=
7 Hz, 3H; CHMe2), 1.11 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.16 (d,
c=19.6748(7) ꢃ; a=76.60(3), b=79.852(3), g=86.764(3)8; V=
2225.63(14) ꢃ3; Z=2; 1calcd =1.277 Mgmꢀ3; m(MoKa)=0.492 mmꢀ1; 16683
collected reflections; 7817 crystallographically independent reflections
(Rint =0.0440); 5115 reflections (I>2s(I)); qmax =258; R(Fo)=0.0567 (I>
2s(I)), wR(F2o)=0.1248 (all data); 473 refined parameters.
3
3J(H,H)=7 Hz, 3H; CHMe2), 1.21 (d, J(H,H)=7 Hz, 3H; CHMe2), 1.37
(d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.40 (d, 3J(H,H)=7 Hz, 3H; CHMe2),
1.50 (s, 3H; NCMe), 2.09 (s, 3H; C2Me2), 2.29 (s, 3H; C2Me2), 2.49 (sept,
3J(H,H)=7 Hz, 1H; CHMe2), 2.61 (sept, 3J(H,H)=7 Hz, 1H; CHMe2),
2.83 (s, 1H; NCCH2), 3.66 (s, 1H; NCCH2), 3.81 (sept, 3J(H,H)=7 Hz,
1H; CHMe2), 3.84 (sept, 3J(H,H)=7 Hz, 1H; CHMe2), 4.08 (s, 3H;
NMe), 4.23 (s, 3H; NMe), 5.37 (s, 1H; g-CH), 6.97–7.25 ppm (m, 6H;
2,6-iPr2C6H3); 13C{1H} NMR (100.61 MHz, [D2]dichloromethane, 258C):
d=9.1, 9.5 ppm (C2Me2); 23.1, 23.6, 23.7, 24.2, 24.5, 24.7, 25.6, 25.8, 26.3,
27.9, 28.3, 29.2, 29.3 (NCMe, CHMe2); 34.3, 36.2 (NMe); 86.6 (NCCH2);
105.1 (g- C); 123.1, 123.5, 124.7, 125.2, 126.7, 126.9, 128.8, 1389.0, 140.1,
143.1, 146.9, 147.6, 150.2, 150.3, 150.6 (NCMe, NCCH2, 2,6-iPr2C6H3,
C2Me2); 153.6 ppm (SiC); 29Si NMR (79.49 MHz, [D2]dichloromethane,
258C): d=ꢀ34.9 ppm; IR (KBr): n˜ =433 (w), 452 (m), 467 (m), 523 (w),
547 (w), 562 (m), 599 (w), 649 (w), 682 (m), 734 (w), 748 (w), 759 (w),
802 (m), 852 (w), 917 (m), 936 (w), 975 (w), 1045 (m), 1056 (s), 1103 (m),
1175 (m), 1192 (m), 1243 (m), 1254 (m), 1307 (m), 1316 (m), 1352 (s),
1379 (s), 1441 (m), 1465 (m), 1528 (w), 1583 (w), 1637 (s), 2864 (m), 2926
(m), 2948 (m), 2966 (s), 3011 (m), 3054 (m), 3111 cmꢀ1 (w); ESIMS (ion
spray voltage 5 kV, flow rate 5 mLminꢀ1, in dichloromethane): m/z: calcd
for C36H53N4SiS [M+H]+: 601.38, found: 601.37; elemental analysis calcd
(%) for C36H52N4SiS: C 71.95, H 8.72, N 9.32; found: C 71.42, H 8.74, N
9.28.
¯
Compound 4a: Triclinic; space group P1; a=10.3516(3), b=11.8219(4),
c=16.8403(6) ꢃ; a=104.200(3), b=99.470(3), g=92.487(2)8; V=
1963.07(11) ꢃ3; Z=2; 1calcd =1.240 Mgmꢀ3; m(MoKa)=1.153 mmꢀ1; 16482
collected reflections; 6887 crystallographically independent reflections
(Rint =0.0509); 4761 reflections (I>2s(I)); qmax =258; R(Fo)=0.0483 (I>
2s(I)), wR(F2o)=0.0793 (all data); 419 refined parameters.
Compound 4b: Monoclinic; space group P21/n; a=11.2340(4), b=
17.2401(5), c=19.8093(7) ꢃ; b=91.474(3)8; V=3835.3(2) ꢃ3; Z=4;
1calcd =1.219 Mgmꢀ3; m(MoKa)=1.043 mmꢀ1; 18505 collected reflections;
6756 crystallographically independent reflections (Rint =0.0599); 4692 re-
flections (I>2s(I)); qmax =258; R(Fo)=0.0466 (I>2s(I)), wR(F2o)=0.1003
(all data); 430 refined parameters.
Compound 5b: Monoclinic; space group P21/c; a=11.6985(5), b=
20.0099(9), c=18.4557(7) ꢃ; b=103.791(4)8; V=4195.7(3) ꢃ3; Z=4;
1calcd =1.326 Mgmꢀ3; m(MoKa)=0.898 mmꢀ1; 20485 collected reflections;
7334 crystallographically independent reflections (Rint =0.0664); 5208 re-
flections (I>2s(I)); qmax =258; R(Fo)=0.0645 (I>2s(I)), wR(F2o)=0.1532
(all data); 457 refined parameters.
CCDC-746660 (2b), -746661 (3a), -746662 (4a), -746663 (4b), and
-746664 (5b) 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.
Synthesis of 3b: Elemental sulfur (0.037 g, 1.17 mmol) was added to a so-
lution of 1b (0.73 g, 1.17 mmol) in toluene (20 mL) at room temperature.
After stirring overnight, the yellow color of the solution vanished and a
colorless precipitate was formed. Volatiles were removed in vacuo, the
residue washed with diethyl ether (25 mL) and extracted with dichloro-
methane (15 mL). Concentration of the clear solution to approximately
8 mL and subsequent cooling to ꢀ208C for 24 h afforded colorless crys-
tals of 3b (0.52 g, 0.83 mmol, 71%). M.p. 1778C (decomp); 1H NMR
(400.13 MHz, [D2]dichloromethane, 258C): d=0.52 (d, 3J(H,H)=7 Hz,
3H; CHMe2), 0.85 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 0.94 (d, 3J(H,H)=
7 Hz, 3H; CHMe2), 1.04 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.09 (d,
Synthesis of 2b: A solution of 1b (0.62 g, 0.99 mmol) in toluene (15 mL)
was cooled to ꢀ788C. The N2 atmosphere in the flask was exchanged by
N2O and the reaction mixture was allowed to warm to room temperature.
Subsequently, the concentrated reaction solution (5 mL) was chilled to
ꢀ208C for 48 h, thus affording colorless single crystals of 2b qualified for
X-ray diffraction analysis (0.56 g, 0.87 mmol, 88%). M.p. 271–2738C
(decomp); 1H NMR (200.13 MHz, [D6]benzene, 258C): d=0.37 (d,
3J(H,H)=7.0 Hz, 3H; CHMe2), 0.53 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2),
0.93 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2), 0.95 (d, 3J(H,H)=7.0 Hz, 3H;
CHMe2), 1.13 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2), 1.29 (d, 3J(H,H)=
7.0 Hz, 6H; CHMe2), 1.39 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2), 1.46 (d,
3J(H,H)=7.0 Hz, 3H; CHMe2), 1.49 (s, 3H; Me), 1.52 (s, 3H; Me), 1.63
(s, 3H, Me), 1.53 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2), 1.67 (d, 3J(H,H)=
7.0 Hz, 3H; CHMe2), 1.82 (d, 3J(H,H)=7.0 Hz, 3H; CHMe2), 2.84 (sept,
3J(H,H)=7.0 Hz, 1H; CHMe2), 3.29 (sept, 3J(H,H)=7.0 Hz, 1H;
CHMe2), 3.38 (s, 1H; NCCH2), 3.94 (s, 1H; NCCH2), 4.15 (sept,
3J(H,H)=7.0 Hz, 1H; CHMe2), 4.44 (sept, 3J(H,H)=7.0 Hz, 1H;
CHMe2), 5.51 (s, 1H; g-CH), 5.63 (sept, 3J(H,H)=7.0 Hz, 1H;
NCHMe2), 6.99–7.48 (brm, 6H; 2,6-iPr2C6H3), 8.48 ppm (sept, 3J(H,H)=
7.0 Hz, 1H; NCHMe2); 13C{1H} NMR (100.61 MHz, [D6]benzene, 258C):
d=10.2, 10.4 (C2Me2); 20.8, 21.3, 21.4, 21.6, 22.5, 23.3, 23.4, 24.4, 24.6,
25.0, 25.2, 26.3, 26.9, 27.7, 27.8, 29.2, 29.5 (CHMe2,NCHMe2, NCMe);
49.8, 51.3 (NCHMe2); 85.8 (NCCH2), 107.7 (g-C); 123.0, 123.8, 124.9,
125.6, 126.4, 126.7, 127.0, 129.3, 138.0, 140.0, 142.8, 146.2, 146.7, 149.9,
150.2, 152.0 (NCMe, NCCH2, 2,6-iPr2C6H3, C2Me2); 155.9 ppm (SiC);
29Si NMR (79.49 MHz, [D6]benzene, 258C): d=ꢀ72.9 ppm (s); IR (KBr):
n˜ =460 (m), 485 (m), 509 (w), 522 (w), 544 (w), 566 (w), 578 (w), 738(w),
761 (m), 771 (w), 804 (m), 920 (m), 938 (w), 979 (w), 1045 (w), 1053 (m),
1081 (w), 1110 (w), 1134 (s), 1177 (w), 1193 (m), 1207 (w), 1244 (w), 1254
(w), 1307 (m), 1323 (w), 1352 (s), 1378 (s), 1441 (m), 1466 (m), 1529 (w),
1583 (w), 1626 (w), 1645 (m), 2695 (w), 2865 (m), 2946 (m), 2973 (s),
3057 cmꢀ1 (w); EIMS: m/z (%): 640.37 (4) [M]+, 625.33 (8) [MꢀMe]+,
597.31 (100) [MꢀiPr]+; elemental analysis calcd (%) for C40H60N4SiO: C
74.95, H 9.43, N 8.74; found: C 74.33, H 9.04, N 8.61.
3
3J(H,H)=7 Hz, 3H; CHMe2), 1.12 (d, J(H,H)=7 Hz, 3H; CHMe2), 1.21
(d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.23 (d, 3J(H,H)=7 Hz, 3H; CHMe2),
1.36 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.37 (d, 3J(H,H)=7 Hz, 3H;
3
CHMe2), 1.53 (s, 3H; NCMe), 1.66 (d, J(H,H)=7 Hz, 3H; CHMe2), 1.68
(d, 3J(H,H)=7 Hz, 3H; CHMe2); 2.25 (s, 3H; C2Me2), 2.40 (s, 3H;
C2Me2), 2.57 (sept, 3J(H,H)=7 Hz, 1H; CHMe2), 2.92 (s, 1H; NCCH2),
3.02 (sept, 3J(H,H)=7 Hz, 1H; CHMe2), 3.72 (s, 1H; NCCH2), 3.74
(sept, 3J(H,H)=7 Hz, 1H; CHMe2), 3.90 (sept, 3J(H,H)=7 Hz, 1H;
CHMe2), 5.45 (s, 1H; g-CH), 5.81 (sept, 3J(H,H)=7 Hz, 1H; NCHMe2),
7.01–7.22 (m, 6H; 2,6-iPr2C6H3), 8.18 ppm (sept, 3J(H,H)=7 Hz, 1H;
NCHMe2); 13C{1H} NMR (100.61 MHz, [D2]dichloromethane, 258C): d=
11.3, 11.6 (C2Me2); 21.3, 21.7, 22.6, 23.3, 23.6, 23.8, 24.3, 24.6, 24.8, 24.9,
26.0, 26.3, 27.1, 27.7, 27.8, 29.2, 29.3 (NCHMe2, NCMe, CHMe2), 49.5,
52.2 (NCHMe2); 87.4 (NCCH2); 107.1 (g-C); 123.2, 123.9, 124.6, 125.1,
126.5, 126.9, 127.4, 130.1, 138.6, 141.1, 142.8, 146.7, 147.2, 149.2, 150.2,
150.9 (NCMe, NCCH2, 2,6-iPr2C6H3, C2Me2); 153.7 ppm (SiC); 29Si NMR
(79.49 MHz, [D2]dichloromethane, 258C): d=ꢀ33.5 ppm; IR (KBr): n˜ =
430 (w), 452 (m), 470 (m), 523 (w), 547 (w), 565 (m), 599 (w), 650 (w),
679 (s), 735 (w), 761 (w), 772 (w), 801 (m), 916 (m), 936 (w), 978 (w),
1044 (m), 1057 (s), 1105 (m), 1172 (m), 1190 (m), 1203 w), 1243 (m),
1256 (m), 1306 (m), 1320 (m), 1353 (s), 1379 (s), 1441 (m), 1466 (m),
1538 (w), 1583 (w), 1625 (m), 1643 (m), 2864 (m), 2943 (m), 2968 (s),
3057 cmꢀ1 (w); ESIMS (ion spray voltage 5 kV, flow rate 5 mLminꢀ1, in
dichloromethane): m/z: calcd for C40H61N4SiS [M+H]+: 657.44, found:
657.43; elemental analysis calcd (%) for C40H60N4SiS: C 73.12, H 9.20, N
8.53; found: C 72.88, H 9.17, N 8.29.
Synthesis of 3a: Elemental sulfur (0.032 g, 0.98 mmol) was added to a so-
lution of 1a (0.56 g, 0.98 mmol) in toluene (15 mL) at room temperature.
After stirring overnight, the yellow color of the solution vanished and a
colorless precipitate was formed. Volatiles were removed in vacuo, the
residue washed with diethyl ether (20 mL) and extracted with dichloro-
methane (10 mL). Concentration of the clear solution to approximately
Synthesis of 4a: Elemental selenium (0.052 g, 0.67 mmol) was added to a
solution of 1a (0.38 g, 0.67 mmol) in toluene (10 mL) at room tempera-
ture. After stirring for 3 h, the yellow color of the solution vanished and
a colorless precipitate was formed. Volatiles were removed in vacuo, the
1286
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 1281 – 1288

Silanechalcogenones
FULL PAPER
residue washed with diethyl ether (10 mL) and extracted with dichloro-
methane (10 mL). Concentration of the clear solution to approximately
4 mL and subsequent cooling to ꢀ208C for 24 h afforded colorless crys-
tals of 4a (0.33 g, 0.51 mmol, 76%). M.p. 2568C (decomp); 1H NMR
(400.13 MHz, [D2]dichloromethane, 258C): d=0.44 (d, 3J(H,H)=7 Hz,
3H; CHMe2), 0.56 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.08 (d, 3J(H,H)=
7 Hz, 3H; CHMe2), 1.09 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.17 (d,
Synthesis of 5a: Elemental tellurium (0.18 g, 1.41 mmol) was added to a
solution of 1a (0.80 g, 1.41 mmol) in toluene (30 mL) at room tempera-
ture. After stirring for 3 h, a yellow precipitate was formed. Volatiles
were removed in vacuo, the residue washed with diethyl ether (30 mL)
and extracted with dichloromethane (20 mL). Concentration of the clear
solution to approximately 10 mL and subsequent cooling to ꢀ208C for
24 h afforded yellow crystals of 5a (0.59 g, 1.04 mmol, 74%). M.p. 1938C
(decomp); 1H NMR (400.13 MHz, [D2]dichloromethane, 258C): d=0.49
(d, 3J(H,H)=7 Hz, 3H; CHMe2), 0.66 (d, 3J(H,H)=7 Hz, 3H; CHMe2),
1.06 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.08 (d, 3J(H,H)=7 Hz, 3H;
CHMe2), 1.17 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.22 (d, 3J(H,H)=7 Hz,
3H; CHMe2), 1.41 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.46 (d, 3J(H,H)=
7 Hz, 3H; CHMe2), 1.54 (s, 3H; NCMe), 2.10 (s, 3H; C2Me2), 2.31 (s,
3H; C2Me2), 2.44 (sept, 3J(H,H)=7 Hz, 1H; CHMe2), 2.58 (sept,
3J(H,H)=7 Hz, 1H; CHMe2), 2.94 (s, 1H; NCCH2), 3.69 (s, 1H;
NCCH2), 3.76 (sept, 3J(H,H)=7 Hz, 1H; CHMe2), 3.80 (sept, 3J(H,H)=
7 Hz, 1H; CHMe2), 4.12 (s, 3H; NMe), 4.21 (s, 3H; NMe), 5.44 (s, 1H; g-
CH), 6.98–7.27 ppm (m, 6H; 2,6-iPr2C6H3); 13C{1H} NMR (100.61 MHz,
[D2]dichloromethane, 258C): d=9.0, 9.7 (C2Me2); 23.0, 23.7, 24.3, 24.4,
24.7, 24.9, 25.5, 25.6, 26.6, 28.0, 28.6, 29.3, 29.4 (NCMe, CHMe2); 34.4,
40.4 (NMe); 89.1 (NCCH2); 107.1 (g-C); 123.0, 123.6, 124.7, 125.3, 126.3,
127.0, 127.2, 129.2, 139.8, 141.9, 142.7, 147.0, 147.8, 149.0, 149.7, 150.1
(NCMe, NCCH2, 2,6-iPr2C6H3, C2Me2); 152.6 ppm (SiC); 29Si NMR
(79.49 MHz, [D2]dichloromethane, 258C): d=ꢀ46.0 ppm (s); 125Te NMR
(126.24 MHz, [D2]dichloromethane, 258C): d=ꢀ1010.4 ppm; IR (KBr):
n˜ =409 (w), 446 (m), 513 (m), 559 (w), 569 (w), 595 (m), 651 (w), 733
(w), 744 (w), 757 (m), 772 (w), 800 (m), 851 (w), 916 (m), 935 (w), 974
(w), 1047 (m), 1101 (w), 1108 (w), 1173 (m), 1188 (m), 1240 (m), 1253
(m), 1306 (m), 1316 (m), 1350 (s), 1378 (s), 1394 (w), 1438 (m), 1464 (m),
1540 (w), 1583 (w), 1637 (m), 2864 (m), 2925 (m), 2945 (m), 2962 (s),
3012 (w), 3054 cmꢀ1 (w); ESIMS (ion spray voltage 5 kV, flow rate
5 mLminꢀ1, in dichloremethane): m/z: calcd for C36H53N4SiTe [M+H]+:
699.31; found: 699.31; elemental analysis calcd (%) for C36H52N4SiTe: C
62.08, H 7.52, N 8.04; found: C 62.40, H 7.67, N 7.79.
3
3J(H,H)=7 Hz, 3H; CHMe2), 1.22 (d, J(H,H)=7 Hz, 3H; CHMe2); 1.39
(d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.43 (d, 3J(H,H)=7 Hz, 3H; CHMe2),
1.51 (s, 3H; NCMe), 2.11 (s, 3H; C2Me2), 2.30 (s, 3H; C2Me2), 2.47 (sept,
3J(H,H)=7 Hz, 1H; CHMe2), 2.59 (sept, 3J(H,H)=7 Hz, 1H; CHMe2),
2.87 (s, 1H; NCCH2), 3.70 (s, 1H; NCCH2), 3.82 (sept, 3J(H,H)=7 Hz,
1H; CHMe2), 3.83 (sept, 3J(H,H)=7 Hz, 1H; CHMe2), 4.10 (s, 3H;
NMe), 4.25 (s, 3H; NMe), 5.41 (s, 1H; g-CH), 6.98–7.26 ppm (m, 6H;
2,6-iPr2C6H3); 13C{1H} NMR (100.61 MHz, [D2]dichloromethane, 258C):
d=9.1, 9.6 (C2Me2); 23.1, 23.7, 24.0, 24.2, 24.5, 24.7, 25.6, 25.7, 26.4, 28.0,
28.4, 29.3, 29.4 (NCMe, CHMe2); 34.4, 37.4 (NMe); 87.5 (NCCH2); 105.8
(g- C); 123.0, 123.5, 124.7, 125.2, 126.6, 126.9, 127.0, 129.0, 139.3, 140.6,
143.0, 146.8, 147.7, 149.8, 150.1, 150.4 (NCMe, NCCH2, 2,6-iPr2C6H3,
C2Me2); 153.1 ppm (SiC); 29Si NMR (79.49 MHz, [D2]dichloromethane,
258C): d=ꢀ33.3 ppm (s); 77Se NMR (76.31 MHz, [D2]dichloromethane,
258C): d=ꢀ374.4 ppm (s); IR (KBr): n˜ =419 (w), 454 (m), 524 (w), 535
(m), 547 (w), 560 (w), 570 (w), 598 (w), 614 (s), 654 (w), 734 (w), 746
(w), 758 (m), 769 (w), 800 (s), 853 (m), 918 (m), 936 (m), 975 (m), 1052
(s), 1102 (m), 1174 (m), 1190 (m), 1242 (m), 1253 (m), 1307 (m), 1317
(m), 1330 (w), 1352 (s), 1378 (s), 1440 (m), 1465 (m), 1530 (w), 1583 (w),
1637 (s), 2867 (m), 2926 (m), 2946 (m), 2965 (s), 3011 (m), 3053 (m),
3111 cmꢀ1 (w); ESIMS (ion spray voltage 5 kV, flow rate 5 mLminꢀ1, in
dichloromethane): m/z: calcd for C36H53N4SiSe [M+H]+: 649.32; found:
649.32; elemental analysis calcd (%) for C36H52N4SiSe: C 66.74, H 8.09,
N 8.65; found: C 66.51, H 8.00, N 8.57.
Synthesis of 4b: Elemental selenium (0.069 g, 0.90 mmol) was added to a
solution of 1b (0.56 g, 0.90 mmol) in toluene (15 mL) at room tempera-
ture. After stirring for 3 h, the yellow color of the solution vanished and
a colorless precipitate was formed. Volatiles were removed in vacuo, the
residue washed with diethyl ether (15 mL) and extracted with dichloro-
methane (15 mL). Concentration of the clear solution to approximately
7 mL and subsequent cooling to ꢀ208C for 24 h afforded colorless crys-
tals of 4b (0.43 g, 0.62 mmol, 69%). M.p. 2248C (decomp); 1H NMR
(400.13 MHz, [D2]dichloromethane, 258C): d=0.55 (d, 3J(H,H)=7 Hz,
3H; CHMe2), 0.90 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 0.98 (d, 3J(H,H)=
7 Hz, 3H; CHMe2), 1.04 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.09 (d,
Synthesis of 5b: Elemental tellurium (0.098 g, 0.78 mmol) was added to a
solution of 1b (0.49 g, 0.78 mmol) in toluene (30 mL) at room tempera-
ture. After stirring for 3 h, a yellow precipitate was formed. Volatiles
were removed in vacuo, the residue washed with diethyl ether (30 mL)
and extracted with dichloromethane (20 mL). Concentration of the clear
solution to approximately 10 mL and subsequent cooling to ꢀ208C for
24 h afforded yellow crystals of 5b (0.33 g, 0.53 mmol, 68%). M.p. 1988C
(decomp); 1H NMR (400.13 MHz, [D2]dichloromethane, 258C): d=0.62
(d, 3J(H,H)=7 Hz, 3H; CHMe2), 0.99 (d, 3J(H,H)=7 Hz, 3H; CHMe2),
1.02 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.05 (d, 3J(H,H)=7 Hz, 3H;
CHMe2), 1.10 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.18 (d, 3J(H,H)=7 Hz,
3H; CHMe2), 1.22 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.23 (d, 3J(H,H)=
7 Hz, 3H; CHMe2), 1.45 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.48 (d,
3J(H,H)=7 Hz, 3H; CHMe2), 1.58 (s, 3H; NCMe), 1.65 (d, 3J(H,H)=
7 Hz, 3H; CHMe2), 1.69 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 2.28 (s, 3H;
C2Me2), 2.43 (s, 3H; C2Me2), 2.45 (sept, 3J(H,H)=7 Hz, 1H; CHMe2),
2.98 (sept, 3J(H,H)=7 Hz, 1H; CHMe2), 2.99 (s, 1H; NCCH2), 3.72
(sept, 3J(H,H)=7 Hz, 1H; CHMe2), 3.84 (s, 1H; NCCH2), 3.87 (sept,
3J(H,H)=7 Hz, 1H; CHMe2), 5.50 (s, 1H; g-CH), 5.91 (sept, 3J(H,H)=
7 Hz, 1H; NCHMe2), 7.04–7.26 (m, 6H; 2,6-iPr2C6H3), 8.26 ppm (sept,
3
3J(H,H)=7 Hz, 3H; CHMe2), 1.14 (d, J(H,H)=7 Hz, 3H; CHMe2), 1.21
(d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.23 (d, 3J(H,H)=7 Hz, 3H; CHMe2),
1.38 (d, 3J(H,H)=7 Hz, 3H; CHMe2), 1.40 (d, 3J(H,H)=7 Hz, 3H;
3
CHMe2), 1.54 (s, 3H; NCMe), 1.66 (d, J(H,H)=7 Hz, 3H; CHMe2), 1.68
(d, 3J(H,H)=7 Hz, 3H; CHMe2); 2.26 (s, 3H; C2Me2), 2.41 (s, 3H;
C2Me2), 2.53 (sept, 3J(H,H)=7 Hz, 1H; CHMe2), 2.93 (s, 1H; NCCH2),
2.99 (sept, 3J(H,H)=7 Hz, 1H; CHMe2), 3.74 (sept, 3J(H,H)=7 Hz, 1H;
CHMe2), 3.76 (s, 1H; NCCH2), 3.90 (sept, 3J(H,H)=7 Hz, 1H; CHMe2),
5.47 (s, 1H; g-CH), 5.84 (sept, 3J(H,H)=7 Hz, 1H; NCHMe2), 7.01–7.22
(m, 6H; 2,6-iPr2C6H3), 8.25 ppm (sept, 3J(H,H)=7 Hz, 1H; NCHMe2);
13C{1H} NMR (100.61 MHz, [D2]dichloromethane, 258C): d=11.3, 11.7
(C2Me2); 21.4, 21.8, 22.6, 23.4, 23.6, 24.2, 24.3, 24.4, 24.8, 24.9, 26.0, 26.1,
27.2, 27.7, 29.3, 29.4 (NCHMe2, NCMe, CHMe2); 49.8, 52.3 (NCHMe2);
88.3 (NCCH2); 107.4 (g-C); 123.2, 123.9, 124.6, 125.2, 126.6, 127.0, 127.3,
130.4, 139.1, 141.6, 142.6, 146.7, 147.3, 148.8, 150.2, 150.7 (NCMe,
NCCH2, 2,6-iPr2C6H3, C2Me2); 152.6 ppm (SiC); 29Si NMR (79.49 MHz,
[D2]dichloromethane, 258C): d=ꢀ32.9 ppm; 77Se NMR (76.31 MHz,
[D2]dichloromethane, 258C): d=ꢀ470.2 ppm (s); IR (KBr): n˜ =418 (w),
449 (m), 468 (m), 529 (w), 547 (w), 561 (w), 606 (m), 660 (w), 759 (m),
772 (w), 801 (m), 815 (w), 914 (m), 934 (w), 975 (m), 1044 (m), 1054 (s),
1076 (w), 1103 (m), 1109 (m), 1172 (m), 1188 (m), 1201 (w), 1242 (w),
1254 (w), 1306 (m), 1319 (m), 1351 (s), 1378 (s), 1439 (m), 1465 (m), 1541
(m), 1583 (w), 1623 (m), 1644 (m), 2864 (m), 2927 (m), 2944 (m), 2967
3J(H,H)=7 Hz,
1H;
NCHMe2);
13C{1H} NMR
(100.61 MHz,
[D2]dichloromethane, 258C): d=11.2, 11.7 (C2Me2); 21.4–30.1 (NCHMe2,
NCMe, CHMe2); 50.0, 52.3 (NCHMe2); 90.1 (NCCH2); 108.1 (g-C);
122.9–150.0 (NCMe, NCCH2, 2,6-iPr2C6H3, C2Me2); 150.2 ppm (SiC);
29Si NMR (79.49 MHz, [D2]dichloromethane, 258C): d=ꢀ49.6 ppm;
125Te NMR (126.24 MHz, [D2]dichloromethane, 258C): d=ꢀ982.5 ppm;
IR (KBr): n˜ =445 (m), 466 (w), 510 (w), 545 (w), 559 (w), 588 (m), 657
(w), 732 (w), 758 (m), 799 (m), 912 (m), 934 (w), 973 (w), 1040 (m), 1073
(w), 1107 (m), 1170 (m), 1185 (m), 1221 (w), 1241 (w), 1254 (w), 1306
(m), 1318 (m), 1351 (s), 1377 (s), 1437 (m), 1464 (m), 1550 (w), 1584 (w),
1635 (m), 2864 (m), 2928 (m), 2940 (m), 2964 (s), 3055 (w), 3110 cmꢀ1
(w); ESIMS (ion spray voltage 5 kV, flow rate 5 mLminꢀ1, in dichlorome-
thane): m/z: calcd for C40H60N4SiTe [M+H]+: 755.37; found: 755.37; ele-
mental analysis calcd (%) for C40H60N4SiTe: C 63.84, H 8.04, N 7.44;
found: C 63.29, H 8.15, N 7.25.
(s), 3054 cmꢀ1 (m); ESIMS (ion spray voltage 5 kV, flow rate 5 mLminꢀ1
,
in dichloromethane): m/z: calcd for C40H60N4SiSe [M+H]+: 705.38;
found: 705.38; elemental analysis calcd (%) for C40H60N4SiSe: C 68.25, H
8.59, N 7.96; found: C 67.96, H 8.68, N 7.70.
Chem. Eur. J. 2010, 16, 1281 – 1288
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1287

M. Driess et al.
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P. von R. Schleyer, G. H. Robinson, J. Am. Chem. Soc. 2008, 130,
14970.
Acknowledgements
Financial support from the Deutsche Forschungsgemeinschaft is highly
acknowledged.
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prepared by using a procedure similar to 1a described in refer-
ence [10]. 1H NMR (200.13 MHz, [D6]benzene, 258C): d=0.38–1.66
(m, 45H; CHMe2, C2Me2, NCHMe2, NCMe), 3.20–4.27 (m, 6H;
NCHMe2, CHMe2), 3.32 (s, 1H; NCCH2), 3.94 (s, 1H; NCCH2), 5.55
(s, 1H; g-CH), 7.00–7.27 ppm (brm, 6H; 2,6-iPr2C6H3);
29Si{1H} NMR (79.49 MHz, [D6]benzene, 258C): d=ꢀ7.6 ppm (s).
ˇ
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the Cambridge Crystallographic Database (http://www.ccdc.cam.
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Received: September 7, 2009
Published online: December 9, 2009
1288
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 1281 – 1288