Synthesis and reactivity of N-aryl substituted N-heterocyclic silylenes

Article abstract of DOI:10.1016/j.jorganchem.2009.10.034

The synthesis of two N-aryl substituted 2-silaimidazolidenes 9a, b by metal-reduction of the appropriate silicon(IV) heterocycles is reported. Structural as well as spectroscopic data obtained for the N-aryl substituted N-heterocyclic silylenes (NHSi) are very close to those obtained previously for their N-alkyl substituted counterparts. NHSis 9a, b are used as starting materials for the synthesis of a series of dichalcogenadisiletanes 19-24 and for of a mono silylene tungsten complex 29. The reactivity studies revealed only marginally differences between the N-aryl substituted NHSis 9a, b and previously described N-alkyl substituted silylenes.

Full text of DOI:10.1016/j.jorganchem.2009.10.034

Journal of Organometallic Chemistry 695 (2010) 398–408
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and reactivity of N-aryl substituted N-heterocyclic silylenes q
P. Zark a, A. Schäfer a, A. Mitra b, D. Haase a, W. Saak a, R. West b, T. Müller a,
*
a Institut für Reine und Angewandte Chemie, Carl von Ossietzky Universität Oldenburg, Carl von Ossietzky Strasse 9-11, 26129 Oldenburg, Federal Republic of Germany
b Organosilicon Research Center, Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, WI 53706, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of two N-aryl substituted 2-silaimidazolidenes 9a, b by metal-reduction of the appropriate
silicon(IV) heterocycles is reported. Structural as well as spectroscopic data obtained for the N-aryl
substituted N-heterocyclic silylenes (NHSi) are very close to those obtained previously for their N-alkyl
substituted counterparts. NHSis 9a, b are used as starting materials for the synthesis of a series of dichalc-
ogenadisiletanes 19–24 and for of a mono silylene tungsten complex 29. The reactivity studies revealed
only marginally differences between the N-aryl substituted NHSis 9a, b and previously described N-alkyl
substituted silylenes.
Received 12 August 2009
Accepted 25 October 2009
Available online 30 October 2009
Keywords:
Carbene homologues
Metallacycles
N-heterocyles
Si-ligands
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
ing the general scheme for the synthesis of N-heterocyclic carbene
analogues, we considered the reduction of N-aryl substituted 1,4-
Stable silylenes 1–8 [1–11] are known for several years and
most of the well-characterized examples are N-heterocyclic silyl-
enes (NHSi), in which the di-coordinated silicon atom is substi-
tuted by two nitrogen atoms. Although the synthesis of NHSis 1
[1], 2a [2], 3a [4] were reported already 15 years ago, the chemistry
of these compounds and their use in synthesis is still very limited,
in particular when compared with the analogous N-heterocyclic
carbenes. The extremely bulky and inflexible substituents at the
nitrogen atoms are one of the reasons for the limited use of NHSis
1, 2a, 3. In the course of our investigation of low coordinated sili-
con cations the quest for stable silylenes with different substitu-
tion patterns at nitrogen arose. Therefore, we established
convenient synthetic routes which afford N-aryl substituted silyl-
enes 9 in moderate to high isolated yields and studied the principal
reactivity of these NHSis versus Brønstedt acids, chalcogens and
reactive transition metal complexes (Charts 1 and 2).
diazabutadienes 10 by lithium metal and subsequent cyclization
of the dianion 11 with silicon(IV)chloride as a viable synthetic
route to the N-heterocyclic dichloride 12 (see Scheme 1). Reductive
elimination of the dichlorides 12 would then afford the NHSi 9a, b.
Following this lead, the dichloride 12a was synthesized in a 20 g
scale by treatment of diazabutadiene 10a with 2.2 eq. lithium in
thf at 0 °C, addition of tetrachlorosilane to the resulting suspension
of dianion 11a in thf at liquid nitrogen temperature and subse-
quent warming of the reaction mixture to room temperature.
The synthesis of the analogue Xyl (Xyl: 2,6-dimethylphenyl)
substituted diaminodichlorosilane 12b proved to be more
demanding. At temperatures below T = À45 °C the solubility of
the intermediate dilithiodiazabutadiene 11b in thf is low and reac-
tion with silicon tetrachloride yielded a mixture of the disilylated
product 14 and the N-heterocyclic silyldichloride 12b (Scheme 2).
When the reaction is performed at 0 °C, instead, the spiro com-
pound 13 was the only isolated product (Scheme 2). Performing
the reaction at T = À40 °C and using diluted solutions of 11b al-
lowed however the isolation of dichloride 12b in high yields. In a
similar way the dibromide 15 was obtained by reaction of 11b with
silicon tetrabromide (Scheme 2).
2. Results and discussion
2.1. Syntheses
For the subsequent reduction step of the dichlorides 12 by alkali
metals a careful monitoring of the reaction by 1H NMR is war-
ranted since over-reduction and decomposition easily occurs and
purification of the NHSis proved to be tedious. We found, that
the reduction of dichloride 12a with lithium naphthalide in thf at
room temperature affords the NHSi 9a in high yields (Scheme 3),
while using the same reaction conditions NHSi 9b was produced
only in low yields in a not tractable product mixture together with
A low yield synthesis of the Dipp (Dipp: 2,6-di-iso-propyl-phe-
nyl) substituted silylene 9a has been reported earlier [12] and the
less-bulky substituted NHSi 9b was previously unknown. Follow-
q
Presented in part at the International Symposium on Organosilicon Chemistry
XV (ISOS XV) Jeju, Korea 2008 (S10-1, book of abstract p. 65).
* Corresponding author. Tel.: +49 (441) 798 3874; fax: +49 (441) 798 3352.
E-mail address: thomas.mueller@uni-oldenburg.de (T. Müller).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.10.034

P. Zark et al. / Journal of Organometallic Chemistry 695 (2010) 398–408
399
Scheme 1. General synthesis of N-heterocyclic silyldichlorides 12 (a: R = Dipp, b:
R = Xyl).
Chart 2.
elemental silicon, compound 11b and the spiro compound 13. On
the other hand the dibromide 15 was reduced by magnesium to
give the NHSi 9b in high isolated yields (80%). Using the less reac-
tive magnesium as reductant over-reduction does not occur, there-
fore monitoring of the reaction course is not needed in this case.
Crystals from NHSis 9 which proved to be suitable for X-ray diffrac-
tion analysis were obtained in both cases from n-hexane solution
at À20 °C.
2.2. Reactivity
Chart 1.
The reactivity of the N-alkyl substituted heterocyclic silylenes 1,
2a, 3a is well investigated and is documented in several literature
Scheme 2. Reaction of dilithiated diazabutadiene 11b with silicon tetrahalides at various temperatures.

400
P. Zark et al. / Journal of Organometallic Chemistry 695 (2010) 398–408
Scheme 3. Synthesis of NHSi 9a, b.
Scheme 4. Reaction of NHSi 9a with ethanol.
overviews [13–16]. Their reactivity is dominated by the Lewis base
character which is conferred by the lone electron pair at the silicon
atom. On the other hand, the conjugation between the lone pairs at
the nitrogen atoms and the 3p(Si) orbital dramatically decrease the
Lewis acidity of the NHSi to such an extent, that even with strong
bases such as triethylamine and pyridine no reaction occurs. The
formation of a complex with a N-heterocyclic carbene is the only
well documented example for a Lewis acid like reactivity of silyl-
ene 2a [17]. The most important reaction mode for silylenes 1,
2a, 3a is oxidative addition to give tetracoordinated silicon(IV)
compounds [18–21]. For these transformations concerted [19] as
well as stepwise radical mechanisms [20–22] are suggested. We
examined several reactions which are characteristic for silylenes
to review the effect of the N-aryl substituent on the reactivity of
NHSis 9.
grown from n-hexane/thf solutions at À20 °C over a period of sev-
eral days. The use of phospha chalcogenides instead of the elemen-
tal chalcogenes Se and Te permitted shorter reaction times and
allowed lower reaction temperatures. Previous low temperature
NMR investigations of the reaction of NHSi 1 with sulfur reported
by West and colleagues suggested the presence of a reactive inter-
mediate for which a silathione structure was put forward [24]. In
addition the groups of Kira and Tokitoh reported the synthesis
and characterization of donor-free heavy silachalcogenons R2Si@E
(E = S, Se, Te) by reaction of silylenes with chalcogens [25]. Re-
cently several other groups reported the isolation of intra-, or
intermoleculary stabilized heavy silaketones [26–29]. Our at-
tempts to use the modified steric requirements of N-aryl substi-
tuted NHSis 9 to stabilize or to trap putative silachalcogenon
Unlike non-stabilized silylenes but similar to their N-alkyl
substituted counterparts, silylenes 9 do not react with silanes such
as Et3SiH even at elevated temperatures. That is 1H and 29Si NMR
spectra of the reaction mixture indicate even after 12 h at room
temperature only the presence of the starting material. In the same
way, like NHSis 1–3 and unlike typical silylenes the NHSis 9 did not
show any [1,4]-cycloaddition reactivity versus 2,3-dimethyl-buta-
diene and in contrast to NHSi 1 [23] also no activity in polymeriza-
tion of alkenes. As a test case for the stability and chemical
behaviour of aryl substituted NHSi 9 versus H acidic compounds,
silylene 9a was treated with 1 eq. ethanol at room temperature.
The NMR spectroscopic results indicate the formation of three
main compounds 16, 17, 18, which integrate in the 1H NMR and
in GC to 1:2:1, see Scheme 4. These three compounds were identi-
fied in the mixture by their characteristic NMR spectroscopic data
and by their mass spectra obtained from GC/MS. While the forma-
tion of ethoxysilanes 16, 17 is as anticipated, based on the experi-
ence with N-alkyl substituted silylenes [24] the formation of the
degradation product, enamin 18, is unexpected and hints to lower
stability of the Si–N linkage in 9a versus Brønstedt acids.
Scheme 5. Synthesis of dichalcogena-disiletanes 19–24.
Table 1
Syntheses and yields of dichalcogena-disiletanes 19–24.
Compound
R
E
Reaction
Yield (%)
19
20
21
22
23
24
Xyl
S
6b + S8
45
50
46
82
69
5
In analogy to the reactivity of NHSi 1–3 versus chalcogens, the
N-aryl substituted silylenes 9 afford dichalcogena–disiletanes 19–
24 by reaction with elemental sulphur, Et3PSe or Et3PTe in low to
moderate yields (Scheme 5 and Table 1). Crystals of compounds
19–22, which were suitable for X-ray diffraction analysis were
Xyl
Xyl
Dipp
Dipp
Dipp
Se
Te
S
Se
Te
6b + Et3PSe
6b + Et3PTe
6a + S8
6a + Et3PSe
6a + Et3PTe

P. Zark et al. / Journal of Organometallic Chemistry 695 (2010) 398–408
401
Table 2
intermediates failed however. That is, reactions of NHSi 9a with
Et3PE (E = Se, Te) at temperatures as low as À100 °C in the presence
of 2,3-dimethyl-butadiene give as only detectable products disile-
tanes 23 and 24. In particular no bicyclic products 27, 28 which
would result form a [4 + 2] cycloaddition reaction between the
butadiene and the putative heavy silanones 25, 26 were observed
(Scheme 6). In addition the disiletanes 23, 24 are stable towards
cycloreversion up to temperatures T = 65 °C as no trapping prod-
ucts, 27, 28, were detected even after heating to reflux in thf for
12 h in the presence of excess 2,3-dimethyl-butadiene (Scheme 6).
The nucleophilic properties of N-heterocyclic silylenes are
underlined by their ability to form transition metal complexes with
group 6 and group 8 metals [30,31]. As an example for a transition
metal complex having a N-aryl substituted silylene as ligand, the
deep violet tungsten pentacarbonyl complex W(CO)5(9b), 29, was
synthesized by reaction of NHSi 9b with W(CO)5(thf), 30
(Scheme 7). The particular advantage of using the solvent complex
30 is the exclusive formation of the mono silylene complex 29,
indicated by only one signal in the 29Si NMR spectra
Selected NMR data of compounds NHSi 9, diazasilacyclopentenes 12, 13, 15,
disiletanes 19–24 and silylene complex 29.
Compound
R
d1H(NCH)
d
13C(NCH)
d
29Si
Other nuclei
9b
9a
12a
12b
13
15
19
20
21
Xyl
Dipp 6.48
Dipp 5.73
Xyl
Xyl
Xyl
Xyl
Xyl
Xyl
6.27
124.1
125.4
125.1
118.5
117.5
119.5
118.3
118.7
119.0
76.5
75.9
d
d
d
15N = À190.7
15N = À196.3
15N = À297.8
À38.4
5.51
5.38
5.53
5.49
5.37
5.28
À41.0
À48.1
À64.9
d
15N = À290.1
À39.5
À63.0
d
d
77Se = 186.0
125Te = 483.0
À137.9
(1JSi,Te = 315 Hz)
À38.8
22
23
24
Dipp 5.63
Dipp 5.64
Dipp 5.60
124.1
124.1
124.3
À61.7
d
d
77Se = 197.3
125Te = 451.9
À131.2
(1JSi,Te = 310 Hz)
109.1
29
Xyl
6.07
124.7
d
15N = À209.3
(1JSi,W = 163 Hz)
1
(d29Si = 109.1, JSi,W = 164 Hz). In reactions using W(CO)6 as start-
ing material complex 29 is formed in a mixture with a second spe-
cies which features a Si–W linkage . This new product became
noticeable by an additional 29Si NMR signal at d29Si = 111.7
(1JSi,W = 198 Hz).
iletanes 19–24. All Si(IV) compounds are characterized by 1H
NMR chemical shift for the NCH hydrogen atom of
d1H(NCH) = 5.28–5.73. Compared to the Xyl substituted heterocy-
cles the NCH proton of the Dipp substituted analogous species res-
onate at slightly lower field (
are characterized by a significant low field shift of this 1H reso-
nance by
d1H (NCH(Si(II)/Si(IV))) = 0.75 (9a) and 0.76 (9b) com-
pared to the corresponding silyldichlorides 12. This low energy
shift is less pronounced as reported for NHSi 1 (
d1H (NCH(Si(II)/
D
d1H (NCH) = 0.14–0.32). The NHSis 9
2.3. Spectroscopic properties
D
Selected NMR data for the NHSis 9, and the tungsten silylene
complex 29 are compared in Table 2 with those obtained for the
Si(IV) containing diazasilacyclopentenes 12, 13, 15, and with dis-
D
Si(IV))) = 1.02) [1] but still remarkable. The deshielding of the
NHC protons in N-heterocyclic silylenes such as 1 and 9 was put
forward as an indication of cyclic conjugation across the five-mem-
bered heterocycle [32]. For the tungsten silylene complex 29 this
low field shift is smaller but still noticeable (D
d1H (NCH(Si(II)/
Si(IV))) = 0.46). The analysis of the 13C NMR shift data obtained
for the sp2 hybridized NCH carbon atoms in compounds 9, 12,
13, 15, 19–24, 29 is of little informative value. The substituent ef-
fect of the different aryl groups attached to nitrogen atom on
d
13C(NCH) is as large as the effect of the different oxidation states
of the inner-cyclic silicon atom. More instructive is a comparison of
the nitrogen NMR chemical shift of the silyldihalides 12a and 15
with that obtained for NHSis 9. The replacement of the tetracoor-
dinated silicon center in 12a and 15 by a di-coordinated silicon
atom in 9 results in a marked deshielding of the ring nitrogen
atoms by approximately 100 ppm. The 15N NMR signal is trans-
ferred from a chemical shift region typical for aromatic enamines
to a region characteristic for imidazols [33]. This deshielding of
the nitrogen atoms in NHSis 9 suggests a certain degree of multiple
bonding between the innercyclic nitrogen and carbon atoms. Obvi-
ously, the effect of metal complexation on d15N NMR chemical shift
is relatively small, since for the tungsten complex 29 d15N = À209.3
is detected, still in the chemical shift region typical for NHSi (i.e.
Scheme 6. Formation of disiletanes 23, 24 in the presence of 2,3-
dimethylbutadiene.
d
15N (1) = À170 d15N (2a) = À225). The strongly deshielded 29Si
resonances of NHSis 9 at d29Si = 75.9 (9a) and 76.5 (9b) are very
close to that reported for their N-t-butyl substituted counterpart
1 (d29Si (1) = 78.3) [34,35] and are clearly the most significant
and characteristic NMR spectroscopic parameters for this class of
compounds. In the series of disiletanes 19–24 a marked high field
shift of the 29Si NMR resonance is noticed along the chalcogen ser-
ies which places the 29Si NMR signal of the tellurium compounds
21, 24 in an unusual high field region for tetracoordinated silicon
compounds (i.e. d29Si (21) = À137.9 d29Si (24) = À131.2). The low
field 29Si NMR resonance of silylene pentacarbonyl tungsten com-
plex 29 (d29Si = 109.1) is very close to that found for the tetracar-
bonyl complex trans-W(CO)4(1)2 (d29Si = 97.8) and is located at
the high field end of the chemical shift region previously reported
Scheme 7. Synthesis of the NHSi tungsten carbonyl complex 29.

402
P. Zark et al. / Journal of Organometallic Chemistry 695 (2010) 398–408
for base-free
g
1-silylene tungsten complexes (d29Si = 380.9-97.8)
Table 3
1
Experimental structural parameters of compounds 9b, 15, 19–22 and 29 (bond
distances d in pm, bond angels in (°), all data are given as average values of chemical
identical linkages). Selected data for NHSi 1 is also given for comparison [43].
[30,36–39], The large value of the JSi,W coupling constant of
a
163 Hz testifies the direct Si–W linkage. Due to the limited number
of reported values [36,39] the size of the JSi,W coupling constant
can not be securely correlated to the degree of bonding between
the silicon and tungsten atoms in complex 29.
1
Compound
d(C,C)
d(C,N)
d(N,Si)
a
(NSiN)
d(SiX)
a(XSiX)
1
132.0
131.8
133.4
133.3
132.8
133.0
133.2
138.2
138.8
138.5
142.2
141.7
141.9
142.1
141.8
138.6
174.7
174.7
171.4
171.9
172.0
173.2
171.8
171.8
88.1
87.6
93.7
92.6
92.7
92.7
92.9
90.3
9b
15
19
20
21
22
29
Silylenes 9a, b are pale yellow substances and accordingly they
show absorptions in the UV–vis spectra also in the visible region
(9a: kmax (n-hexane): 225, 268, 278, 290, 374, 452; 9b: kmax (n-hex-
ane): 225, 268, 278, 289, 382, 462). The comparison with the UV
data obtained for the 2-silaimidazoles 12a and 15 suggests that
the chromaticity of the silylenes is solely due to the N-arylated
silaimidazole moiety (12a : kmax (n-hexane): 225, 268, 278, 291,
374, 452; 15: 225, 268, 278, 291, 385, 462). A distinct UV band
which could be assigned to the lone pair Si?3p(Si) transmission
was not detected in the UV–vis spectra of silylenes 9a, b, most
probably due to the low intensity of this formally forbidden band.
222.8a
213.1b
228.0c
251.5d
213.5b
245.6e
101.2a
96.7b
97.6c
98.2d
96.4b
a
b
c
X = Br.
X = S.
X = Se.
X = Te.
X = W.
d
e
2.4. Crystal structure data
The molecular structures of silylenes 9a, b in the crystal are
shown in Figs. 1 and 2 and pertinent data for NHSi 9b are summa-
rized in Table 3. The basic structural feature in both molecules is
the central planar five-membered k2-2-sila-1,3-diazole ring (dihe-
dral angles CCNSi = À2.7–3.0°) with the aryl substituents at the
nitrogen atoms oriented almost perpendicular to the heterocycle
(dihedral angles C8C3NSi 95.7–106.1°). Crystals of NHSi 9a show
a statistical side disorder (see Fig. 3) which prevents a careful anal-
ysis of the structural data. In this case the crystal symmetry of the
monoclinic space group C2/c generates a centre of inversion at the
midpoint of the two nitrogen atoms and allows for two different
orientations of the five membered heterocycle in the crystal. In
Fig. 3. Statistical side disorder in the crystal structure of silylene 9a, only the
central five membered ring and the ipso atoms of the Dipp-substituents are shown.
contrast, crystals of the N-aryl substituted silylene 9b show no dis-
order and the crystal structure was refined to high accuracy. The
bond parameter of NHSi 9b are nearly identical to those obtained
previously for the N-alkyl substituted NHSi 1 (see Table 3) [40].
This indicates a negligible substituent effect on the structure of
the central k2-2-sila-1,3-diazole ring when the substituent at the
nitrogen atom is changed from alkyl to bulky aryl groups. The most
notable differences in the molecular structures of NHSi 9b and its
precursor compound, the cyclic dibromide 15, are the shorter
innercyclic CN bonds and the longer SiN bonds in NHSi 9b. While
the long SiN bond is a result of the divalency of the silicon atom
in NHSi 9b, the shorter CN bond suggests a bond order larger than
one, in qualitative agreement with the 15N NMR results.
Fig. 4 shows as an example for the tricyclic disiletanes, the
molecular structure of the ditellura-disiletane 21 in the crystal.
Pertinent data for all structurally experimentally investigated dis-
iletanes are summarized in Table 3. Inspection of the bond param-
eters reveals the close structural similarity between these
compounds. Bond lengths and bond angles of the planar five-mem-
bered rings are nearly identical. In all investigated cases also the
central four-membered 1,3-disiletane rings are planar and in the
case of the selenium 20 and sulfur compounds 19, 22 they are ori-
ented nearly orthogonal to both diazasilacyclopentene cycles. In
the case of the tellurium compound 21 the rings are tilted. That
is, the planes of the central four-membered ring and five-mem-
bered ring form a torsion angle of 75°. The silicon-chalcogen dis-
tances and the innercyclic bond angles found in the experimental
structures of disilaetanes 19–22 are very similar to those found
for related compounds [24,41,42].
Fig. 1. Molecular structure of silylene 9a in the crystal (hydrogen atoms are
omitted; ellipsoids are drawn at 50% probability).
Fig. 5 shows the molecular structure of the silylene pentacar-
bonyl tungsten complex 29. The compound crystallizes in the
Fig. 2. Molecular structure of silylene 9b in the crystal (hydrogen atoms are
omitted; ellipsoids are drawn at 50% probability).

P. Zark et al. / Journal of Organometallic Chemistry 695 (2010) 398–408
403
relative strong back bonding for the Si–W bond. Finally, the Toll-
man angle for NHSi 9b was established with a value of 123.7° close
to that reported for NHSi 1.
3. Conclusion
The multi-gramme synthesis of two silylenes, 9a, b, of the 2-
silaimidazolidene type which have aryl substituents at the ring
nitrogen atoms is reported. The investigations revealed no signifi-
cant differences in structures, spectroscopic properties or reactivi-
ties of these new NHSis to those of previously known N-alkyl
substituted silylenes, such as 1. Minor differences such as deviating
solubility and modified spatial requirements around the low coor-
dinated silicon atom, however, might be of importance for their
further application in synthesis and catalysis.
4. Experimental
4.1. General information
Fig. 4. Molecular structure of the tellurium compound 21 in the crystal (hydrogen
atoms are omitted; ellipsoids are drawn at 50% probability).
All procedures were carried out in oven-dried glassware under
inert argon atmosphere using Schlenk techniques. Benzene, tolu-
ene, thf, hexane and triethylsilane were distilled from sodium. Eth-
anol was dried as described in literature [45]. [D6]Benzene,
[D8]toluene and [D1]chloroform were stored over molecular sieves.
All reagents were obtained from commercial suppliers and were
used without further purification. Tetrabromosilane [46], triethyl-
phosphane selenide [47], -telluride [48] and the 1,4-diazabutadi-
enes 10a [49], b [50] were prepared according to literature
procedures. IR spectra were recorded on a Bruker Vector 22 spec-
trometer. UV–vis spectra were obtained on a Zeiss (Jena) Specord
100 spectrometer. Mass spectra and high resolution mass spectra
were carried out on a Finnigan-MAT95 spectrometer with electron
impact ionization (EI) and chemical ionization (CI), using iso-bu-
tane. GC–MS studies were performed on a thermo focus, DSQ.
NMR spectra were recorded on a Bruker DRX 500 and DRX 300.
1H NMR spectra were calibrated using residual protio signals of
the solvent as internal reference d1H (C6D5H) = 7.20, d1H
(C6D5CD2H = 2.03, d1H (CHCl3) = 7.24 and 13C NMR spectra using
the central line of the solvent signal
d
13C(C6D6) = 128.0,
Fig. 5. Molecular structure of the tungsten pentacarbonyl silylene complex 29 in
the crystal (hydrogen atoms are omitted; ellipsoids are drawn at 50% probability).
d
13C(C6D5CD3) = 20.4, d13C (CDCl3) = 77.0. 15N, 29Si, 77Se, 125Te
NMR spectra were calibrated using external standards. 15N NMR:
d
15N (Me2NCHO) = À267.5 versus CH3NO2. 29Si NMR: d29Si (Me2-
SiHCl) = 11.1 versus TMS). 77Se NMR: d77Se (Ph2Se2) = 275.0 versus
Me2Se. 125Te NMR: d125Te (Ph2Te2) = 422.0 versus Me2Te. The def-
inite assignment of the signals resulted from DEPT and 2D H,H
COSY, H,C HMQC, H,C HMBC and H,N HMBC (3JN,H = 10 Hz) mea-
surements. Single-crystal X-ray diffraction data for compound 9a,
9b, 15, 19–24 and 29 were recorded on a STOE-IPDS-diffactometer
space group Cmcm and the molecules are located on the Wyckoff
position c (m2m). The planar five-membered ring and two of the
cis-carbonyl groups are located in one mirror plane. The orthogonal
cis-carbonyl ligands are placed in the second mirror plane and the
N-aryl substituent are oriented perpendicular relative to the cen-
tral diazasilole ring. The bond lengths and angles in the diazasilole
ring are nearly identical compared to those in the free silylene 9b
with the exception of a slightly elongated C@C bond in complex 29.
The Si–W bond is short (d(SiW) = 245.62(16) pm), regarding the
range of typical Si–W bonds (d(SiW) = 238.9–270.8 pm) [43]. It is
in the same range as reported previously for the tetracarbonyl
tungsten complex trans W(CO)4(1)2 (d(SiW) = 247.1 pm) but it is
using Mo Ka (k = 71.073 pm) radiation at 153 K. Structural solu-
tions were obtained with direct methods using SHELXS-97 [51] and
refined SHELXL-97 [51]. All shown molecular structures designed
with DIAMOND. Crystallographic data are summarized in Table 4.
4.2. Synthesis of 1,3-bis(2,6-diisopropylphenyl)-1,3-diaza-2,2-
dichloro-2-silacyclopent-4-ene, 12a
significantly longer than the Si–W bond found in
g
1-silylene tung-
sten complexes with non-stabilized silylenes (d(SiW) = 235 pm
[37] and 238.5 pm [36]). The CO bond lengths of the cis-carbonyl
groups (d(CO) = 114.18(62) and 113.97(62) pm) are close to the
bond length in W(CO)6 with 113.9 pm [44], while the trans CO
Lithium (387 mg, 55.9 mmol), cut into small pieces was added
to a solution of 10a (10 g, 26.6 mmol) in thf (110 mL, c = 236 mmol
L
À1) at 0 °C. The cooling bath was removed and the mixture was
bond
is
markedly
shortened
for
about
4 pm
stirred for 16 h. Excess of lithium was removed with a pincer and
the reaction mixture was frozen using a liquid nitrogen bath. Tet-
rachlorosilane (15.5 mL, 133 mmol), pre cooled to À25 °C, was
added in one portion. After the addition was completed the mix-
ture was allowed to warm to room temperature and stirred for
(d(CO) = 109.90(72) pm). Concomitantly the trans W–CO bond
(d(W–COtrans) = 207.75(58) pm) is the longest W–C bond in the
molecule (d(W–COcis = 204.32(51), 205.10(48) pm). This indicates
the weakest degree of W–C
p-back bonding for this group and a

404
P. Zark et al. / Journal of Organometallic Chemistry 695 (2010) 398–408
Table 4
Crystallographic data of compound 9, 15, 19–22 and 29.
Compound
9b
9a
15
19
Formula
SiN2C2H2(C8H9)2
731875
C18H20N2Si
292.45
Si(N2C2H2)(C12H17
731877
C26 H36 N2 Si
404.66
)
2
SiBr2(N2C2H2)(C8H9)2
731876
C18H20Br2N2Si
452.27
Si2S2(N2C18H20
731881
C36H40N4S2Si2
649.02
)
2
CCSD number
Empirical formula
Mf
T (K)
153(2)
153(2)
153(2)
153(2)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
0.71073
0.71073
Monoclinic
C2/c
20.1834(13)
6.5053(7)
20.1801(14)
90
0.71073
Monoclinic
P21/c
9.8400(7)
14.0110(6)
13.7925(10)
90
0.71073
Monoclinic
P21/n
11.0010(2)
14.3957(4)
21.6609(5)
90
Triclinic
ꢀ
P1
8.3255(14)
10.526(2)
11.109(2)
99.14(3)
a
(°)
b (°)
105.25(2)
112.91(2)
826.9(4)
102.61(1)
90
2585.7(4)
4
1.039
0.104
95.070(9)
90
1894.1(2)
4
1.586
4.344
96.466(2)
90
3408.55(14)
4
1.265
0.258
c
(°)
VUC (Å3)
Z
2
qcalc (mg mÀ3
)
1.175
0.138
l
(mmÀ1
)
F(0 0 0)
312
880
904
1376
Crystal size (mm3)
h Range (°)
0.22 Â 0.11 Â 0.02
2.49–26.25.
À9 6 h 6 9
À13 6 k 6 13
À13 6 l 6 13
10334
0.50 Â 0.47 Â 0.29
2.59–26.09.
À23 6 h 6 24
À7 6 k 6 8
0.60 Â 0.32 Â 0.08
2.54–26.23.
À12 6 h 6 12
À17 6 k 6 17
À17 6 l 6 17
20099
0.28 Â 0.12 Â 0.02
3.51–28.04
Index ranges
À13 6 h 6 14
À17 6 k 6 19
À27 6 l 6 28
31681
À24 6 l 6 24
10846
Reflections collected
Independent reflections
Observed reflections
Completeness to h = 25.00°
Absorption correction
3077 [Rint = 0.1608]
2384 [Rint = 0.0515]
3738 [Rint = 0.0681]
8216 [Rint = 0.1008]
916 [I > 2
94.1%
r(I)]
1498 [I > 2
93.8%
r(I)]
2547 [I > 2
97.8%
r(I)]
4338 [I > 2r(I)]
99.4%
None
None
None
Numerical
Maximum and minimum transmission
Refinement method
0.9973 and 0.9704
0.9705 and 0.9500
0.7226 and 0.1803
0.9943 and 0.9324
Full-matrix least-squares on Full-matrix least-squares on Full-matrix least-squares on Full-matrix least-squares on
F2
F2
F2
F2
Data/restraints/parameters
3077/0/194
0.584
2384/0/149
1.034
3738/0/212
0.831
8216/0/405
0.974
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0442
wR2 = 0.0625
R1 = 0.1814
wR2 = 0.0818
0.152 and À0.208
R1 = 0.0558
wR2 = 0.1224
R1 = 0.0919
wR2 = 0.1307
0.148 and À0.136
R1 = 0.0276
wR2 = 0.0534
R1 = 0.0513
wR2 = 0.0567
0.528 and À0.609
R1 = 0.0534
wR2 = 0.1013
R1 = 0.1363
wR2 = 0.1263
0.408 and À0.340
Largest difference in peak and hole
(e ÅÀ3
)
20
21
22
29
Formula
Se2Si2(N2C18H20
731879
C36H40N4Se2Si2
742.82
)
Si2Te2(N2C18H20)2½ (C7H8)
731880
C39.5H44N4Si2Te2
886.17
Si2S2(N2C26H36
731878
C52H72N4S2Si2
873.44
)
W(CO)5Si(N2C2H2(C8H9)2)
731882
C23H20N2O5SiW
616.35
2
2
CCSD number
Empirical formula
Mf
T (K)
153(2)
153(2)
153(3)
153(2)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
0.71073
Monoclinic
P21/n
11.1542(2)
14.3715(6)
21.6091(13)
90
0.71073
Monoclinic
P21/n
11.3582(4)
11.0611(5)
30.9109(9)
90
0.71073
Monoclinic
P21/c
20.8619(5)
15.2564(4)
15.9470(4)
90
0.71073
Orthorhombic
Cmcm
9.7089(5)
14.3926(5)
17.1781(5)
90
a
(°)
b (°)
95.371
90
3448.8(3)
4
1.431
96.241(4)
90
3860.5(2)
4
1.525
1.606
94.733(2)
90
5058.3(2)
4
1.147
0.190
90
90
c
(°)
VUC (Å3)
2400.40(16)
4
1.706
Z
qcalc (mg mÀ3
)
l
(mmÀ1
)
2.245
4.897
F(0 0 0)
1520
1764
1888
1200
Crystal size (mm3)
h Range (°)
0.45 Â 0.27 Â 0.13
0.60 Â 0.24 Â 0.08
1.96–26.10.
À14 6 h 6 14
À13 6 k 6 13
À37 6 l 6 36
33050
0.31 Â 0.20 Â 0.11
0.50 Â 0.26 Â 0.13
2.53–28.21
À12 6 h 6 12
À19 6 k 6 19
À21 6 l 6 22
18725
2.83–26.15
2.77–28.96
Index ranges
À13 6 h 6 13
À17 6 k 6 17
À26 6 l 6 26
31555
À28 6 h 6 28
À20 6 k 6 20
À21 6 l 6 21
73816
Reflections collected
Independent reflections
Observed reflections
Completeness to h = 25.00°
Absorption correction
6695 [Rint = 0.0741]
7180 [Rint = 0.0650]
13287 [Rint = 0.0616]
1585[Rint = 0.0784]
3865 [I > 2
r
(I)]
5462 [I > 2
r
(I)]
8288 [I > 2
99.3%
r(I)]
1585 [I > 2r(I)]
97.3%
Numerical
94.4%
Numerical
97.6%
Numerical
None
Maximum and minimum transmission
Refinement method
0.7590 and 0.4315
Full-matrix least-squares on
F2
0.8823 and 0.4458
Full-matrix least-squares on
F2
0.9797 and 0.9427
0.5685 and 0.1933
Full-matrix least-squares on Full-matrix least-squares on
F2
F2
Data/restraints/parameters
6695/0/405
7180/3/415
13287/0/557
1585/0/93

P. Zark et al. / Journal of Organometallic Chemistry 695 (2010) 398–408
405
Table 4 (continued)
20
21
22
29
Goodness-of-fit (GOF) on F2
0.601
0.928
1.001
1.042
Final R indices [I > 2
r
(I)]
R1 = 0.0239
wR2 = 0.0358
R1 = 0.0573
wR2 = 0.0389
0.312 and À0.55
R1 = 0.0307
wR2 = 0.0763
R1 = 0.0440
wR2 = 0.0807
1.586 and À0.919
R1 = 0.0399
wR2 = 0.0886
R1 = 0.0922
wR2 = 0.1122
0.340 and À0.314
R1 = 0.0199
wR2 = 0.0473
R1 = 0.0221
wR2 = 0.0478
3.477 and À0.690
R indices (all data)
Largest difference in peak and hole
(e ÅÀ3
)
one hour. The solvent was evaporated in vacuum, the residue was
treated with n-hexane and the remaining salts were removed by
filtration. Finally, the solvent was evaporated in vacuum until
incipient crystallization. Storage of the solution at À20 °C results
in quantitative crystallization of the product. Yield: 7.91 g
(16.6 mmol, 62%). 1H NMR (500.133 MHz, 300 K, C6D6): d = 1.20
(NCH, 12b), 127.4 (Cpara, 12b), 127.8 (Cpara, 14), 129.0 (Cmeta, 12b),
129.4 (Cmeta, 14), 137.4 (Cipso, 14), 137.7 (Cipso, 12b), 138.3 (Cortho
,
14), 138.4 (Cortho, 12b). 29Si{1H} NMR (99.357 MHz, 300 K, C6D6):
d = À41.0. (NNSiCl2, 12b), À30.0 (NSiCl3, 14). 12.80 min, m/z (%)
362.1 (5) [12+], 132.0 (72) [C9H10N+], 105.0 (100) [C8H9+].
13.20 min, m/z (%) 531.9 (32) [14+]; 265.9 (100) [C9H5Cl4N2Si2+],
132.0 (62) [C9H10N+], 105.0 (84) [C6H9+].
3
(d, 12H, CH(CH3)2, JH,H = 6.8 Hz), 1.36 (d, 12H, CH(CH3)2,
3
3JH,H = 6.8 Hz), 3.69 (sept., 4H, CH(CH3)2, JH,H = 6.8 Hz), 5.73 (s,
2H, NCH), 7.13–7.22 (m, 6H, C6H3). 13C{1H} NMR (125.758 MHz,
300 K, C6D6): d = 24.5 (CH(CH3)2), 24.9 (CH(CH3)2), 28.6 (CH(CH3)2),
118.6 (CH), 125.1 (NCH), 129.4 (CH), 134.3 (Cq), 147.9 (Cq). 15N{1H}
INEPT NMR (50.678 MHz, 300 K, C6D6): d = À297.8. 29Si{1H} NMR
(99.362 MHz, 300 K, C6D6): d = À38.4. UV–vis (n-hexane): kmax
[nm] = 225, 268, 278, 291, 374, 452 (shoulder).
4.6. Synthesis of 1,3-bis(2,6-dimethylphenyl)-1,3-diaza-2,2-dibromo-
2-silacyclopent-4-ene, 15
Lithium (551 mg, 79.4 mmol), which was cut into small pieces,
was added to a solution of 10b (10 g, 37.8 mmol) in thf (500 mL,
c = 75 mmol LÀ1) at 0 °C. The cooling bath was removed and the
mixture was stirred for 16 h. Excess of lithium was removed by a
pincer and the mixture was cooled to À40 °C. Degassed tetrabro-
mosilane (4.7 mL, 37.7 mmol) was added in one portion. When
the addition was completed the mixture was allowed to warm to
room temperature and stirred for one hour. The solvent was evap-
orated in vacuum, the residue was treated with n-hexane and the
salts were removed by filtration. Finally, the solvent was evapo-
rated in vacuum until incipient crystallization. Crystals suitable
for single-crystal X-ray diffraction were obtained after complete
crystallization at À20 °C. Yield: 9.55 g (21.1 mmol, 63%). 1H NMR
(500.133 MHz, 300 K, C6D6): d = 2.50 (s, 12H, CH3), 5.53 (s, 2H,
NCH), 7.01 (m, 6H, C6H3). 13C{1H} NMR (125.758 MHz, 300 K,
C6D6): d = 19.5 (CH3), 119.5 (NCH), 127.4 (Cpara), 129.1 (Cmeta),
137.7(Cipso), 138.3 (Cortho). 15N{1H} INEPT NMR (50.678 MHz,
300 K, C6D6): d = À290.1. 29Si{1H} NMR (99.362 MHz, 300 K,
C6D6): d = À64.9. EI MS m/z (%): 453.8 (23) [15++4], 451.8 (51)
4.3. Synthesis of 1,3-bis(2,6-dimethylphenyl)-1,3-diaza-2,2-dichloro-
2-silacyclopent-4-ene, 12b
Similar to the preparation of 12a using a solution of 10b in thf
with a concentration of c = 75 mmol LÀ1. Tetrachorosilane was
added at T = À40 °C. Yield: 65%. 1H NMR (300.132 MHz, 303 K,
C6D6): d = 2.46 (s, 12H CH3), 5.51 (s, 2H, NCH), 7.00 (s, 6H, C6H3).
13C{1H} NMR (125.773 MHz, 300 K, C6D6): d = 18.9 (CH3), 118.5
(NCH), 127.4 (Cpara), 129.0 (Cmeta), 137.7 (Cipso), 138.4 (Cortho).
29Si{1H} NMR (99.357 MHz, 300 K, C6D6): d = À41.0. GC/MS: RT:
12.80 min, m/z (%) 362.1 (5) [12b+], 132.0 (72) [C9H10N+], 105.0
(100) [C6H9+].
4.4. Reaction of 10b with lithium and tetrachorosilane at 0 °C
Similar to the preparation of 12a using a solution of 10b in thf
with c = 236 mmol LÀ1. Tetrachorosilane was added at 0 °C. After
evaporation of the reaction solvent thf, the residue was extracted
with toluene. After recrystallization from toluene the spiro com-
[15++2], 449.8 [15+] (20), 121.0 (100) [C8H9NH2+]. EI HRMS calc.
12
for [
C
18
1H2079Br214N228Si] m/z 449.9763, found m/z 449.9763.
4.7. Synthesis of 1,3-bis(2,6-dimethylphenyl)-1,3-diaza-2-
pound
1,4,6,9-tetrakis(2,6-dimethylphenyl)-1,4,6,9-tetraaza-5-
silacyclopent-4-en-2-ylidene, 9b
silaspiro[4,4]nona-2,7-diene, 13 was isolated. Yield: 10%. 1H NMR
(300.132 MHz, 303 K, C6D6): d = 2.09 (s, 24H CH3), 5.38 (s, 4H,
NCH), 6.97 (s, 12H, C6H3). 13C{1H} NMR (125.773 MHz, 300 K,
C6D6): d = 19.2 (CH3), 117.5 (NCH), 125.7 (Cpara), 129.0 (Cmeta),
137.1 (Cipso), 143.1 (Cortho). 29Si{1H} NMR (99.357 MHz, 300 K,
C6D6): d = À48.1. GC/MS: RT: 21.68 min, m/z (%) 556.3 (100)
[13+], 292.1 (58) [10b+].
A mixture of magnesium turnings (620 mg, 25.6 mmol) and 15
(10.52 g, 23.3 mmol) were stirred in thf (150 mL) at room temper-
ature until the magnesium was consumed. The complete reduction
of 15 is verified by 1H NMR. The solvent was evaporated in vacuum,
the residue was dissolved in n-hexane and the salts were removed
by filtration. Finally, the solvent was evaporated in vacuum until
incipient crystallization. Crystals suitable for single-crystal X-ray
diffraction were obtained after complete crystallization from n-
hexane at À20 °C. Yield: 6.01 g (20.6 mmol, 80%). 1H NMR
(500.133 MHz, 300 K, C6D6): d = 2.27 (s, 12H, CH3), 6.27 (s, 2H,
NCH), 7.07 (m, 6H, C6H3). 13C{1H} NMR (125.772 MHz, 300 K,
C6D6): d = 18.5 (CH3), 124.1 (NCH), 126.7 (Cpara), 128.6 (Cmeta),
135.2 (Cortho), 142.8 (Cipso). 15N{1H} INEPT NMR (50.683 MHz,
300 K, C6D6): d = 190.7. 29Si{1H} NMR (99.362 MHz, 300 K, C6D6):
d = 76.5. CI MS m/z (%): 602.4 (2) [9b2+H2O+], 349.3 (19)
4.5. Reaction of 10b with lithium and tetrachorosilane at À70 °C
Similar to the preparation of 12a using a solution of 10b in thf
with c = 236 mmol LÀ1 was used. Tetrachorosilane was added at
À70 °C. A 1:2 mixture of 1,4-bis(2,6-dimethylphenyl)-1,4-bis(tri-
chlorosilyl)-1,4-diaza-buta-2-ene, 14 and 12b was isolated and
no further separation was performed. 1H NMR (300.132 MHz,
303 K, C6D6): d = 2.27 (s, 24H, CH3, 14), 2.46 (s, 12H CH3, 12b),
5.51 (s, 2H, NCH, 12b), 5.93 (s, 2H, NCH, 14), 6.91 (s, 6H, C6H3,
14), 7.00 (s, 6H, C6H3, 12b). 13C{1H} NMR (125.773 MHz, 300 K,
C6D6): d = 18.5 (CH3, 14), 18.9 (CH3, 12b), 117,0 (NCH, 14), 118.5
[9b+C4H9+], 293.3 (100) [9b+H+]. CI HRMS calc. for
12
[
C
18
1H2014N228Si] m/z 293.1474, found m/z 293.1476. UV–vis
(n-hexane): kmax [nm] = 225, 268, 278, 289, 385, 462 (shoulder).

406
P. Zark et al. / Journal of Organometallic Chemistry 695 (2010) 398–408
4.8. Synthesis of 1,3-bis(2,6-diisopropylphenyl)-1,3-diaza-2-
4.9.3. Di-l-telluro-di-1,3-bis(2,6-dimethylphenyl)-1,3-diaza-2-
silacyclopent-4-en-2-ylidene, 9a
silacyclopent-4-en-2-ylidene, 21
From silylene 9b by reaction with triethylphosphane telluride.
Oxygen and water sensitive, red crystals for single-crystal X-ray
diffraction were obtained after complete crystallization from
[D8]toluene at À20 °C. For recrystallization the solid was sus-
pended in n-hexane (2 mL) and thf was added until a homogenous
solution was obtained at room temperature. Yield: 193 mg
(0.23 mmol, 46%). 1H NMR (500.133 MHz, 300 K, C6D5CD3):
d = 2.18 (s, 24H, CH3), 5.28 (s, 4H, NCH), 6.88–6.95 (m, 12H,
C6H3). 13C{1H} NMR (125.773 MHz, 300 K, C6D5CD3): d = 20.4
(CH3), 119.0 (NCH), 126.4 (Cpara), 128.9 (Cmeta), 137.3 (Cortho),
140.1 (Cipso). 29Si{1H} NMR (99.357 MHz, 300 K, C6D5CD3):
d = À137.9 (1JSi,Te = 314 Hz). 125Te{1H} NMR (157.845 MHz, 300 K,
C6D5CD3): d = 483.0 (1JSi,Te = 315 Hz). CI MS m/z (%): 844.2 (58)
Naphthalene (420 mg, 3.2 mmol) was dissolved in thf (150 mL)
and lithium (228.3 mg, 32.9 mmol), cut into small pieces, was
added. When the green color of lithium naphthalide appeared, silyl
dichloride 12a (7.11 g, 14.9 mmol), dissolved in thf (40 mL) was
slowly added. The mixture was stirred at room temperature for
20 h. The reduction of 12a was monitored by 1H NMR. After the
reduction was completed the solvent was evaporated in vacuum,
the residue was treated with n-hexane and the salts were removed
by filtration. Finally, the solvent was evaporated in vacuum until
incipient crystallization. Crystals suitable for single-crystal X-ray
diffraction were obtained after complete crystallization from n-
hexane at À20 °C. Yield: 4.37 g (10.8 mmol, 72%). 1H NMR
(500.133 MHz, 300 K, C6D6): d = 1.22 (d, 12H, CH(CH3)2,
[23+], 842.2 (96) [21+À2], 840.1 (100) [21+À4], 838.1 (68)
3JH,H = 6.7 Hz), 1.30 (d, 12H, CH(CH3)2, JH,H = 6.7 Hz), 3.29 (sept.,
[21+À6]. CI HRMS calc. for
[ C
1H4014N428Si2130Te2] m/z
3
12
36
3
2H, CH(CH3)2, JH,H = 6.7 Hz), 6.48 (s, 2H, NCH), 7.11–7.27 (m, 6H,
844.0926, found m/z 844.0938. UV–vis (thf): kmax [nm] = 216,
C6H3). 13C{1H} NMR (125.758 MHz, 300 K, C6D6): d = 24.4
(CH(CH3)2), 25.6 (CH(CH3)2), 28.7 (CH(CH3)2), 123.7 (Cmeta), 125.4
(NCH), 127.8 (Cpara), 139.3 (Cipso), 146.0 (Cortho). 15N{1H} INEPT
NMR (50.678 MHz, 300 K, C6D6): d = À196.3. 29Si{1H} NMR
(99.362 MHz, 300 K, C6D6): d = 75.9. UV–vis (n-hexan): kmax
[nm] = 225, 268, 278, 290, 374 (shoulder).
246, 251, 259, 266, 345 (shoulder), 450.
4.9.4. Di-l-sulfo-di-1,3-bis(2,6-diisopropylphenyl)-1,3-diaza-2-
silacyclopent-4-en-2-ylidene, 22
From silylene 9a by reaction with elemental sulphur. Colorless
crystals for single-crystal X-ray diffraction were obtained after
recrystallization and storage at À20 °C. For recrystallization the so-
lid was suspended in n-hexane (2 mL) and thf was added until a
homogenous solution was obtained at room temperature. Yield:
144 mg (0.2 mmol, 82%). 1H NMR (500.133 MHz, 300 K, C6D6):
4.9. General method to synthesize the silicon chalcogene four-
membered ring compounds 19–24
3
The corresponding silylene 9 (0.5 mmol) and the chalcogene
source (octasulfur 0.0625 mmol, triethylphosphane selenide, -tel-
luride, 0.5 mmol) were dissolved in toluene and stirred 16 h at
room temperature. The solvent was evaporated in vacuum and
the residue was dried under reduced pressure.
d = 1.15 (d, 24H, CH(CH3)2, JH,H = 6.8 Hz), 1.17 (d, 24H, CH(CH3)2,
3JH,H = 6.8 Hz), 3.49 (sept, 8H, CH(CH3)2, JH,H = 6.8 Hz), 5.63 (s,
3
4H, NCH), 7.05–7.22 (m, 12H, C6H3). 13C{1H} NMR (125.773 MHz,
300 K, C6D6): d = 23.6 (CH(CH3)2), 26.3 (CH(CH3)2), 28.8 (CH(CH3)2),
120.1 (Cmeta), 124.1 (NCH), 127.6 (Cpara), 137.3 (Cipso), 148.0 (Cortho).
29Si{1H} NMR (99.361 MHz, 300 K, C6D6): d = À38.8. CI MS m/z (%):
872.8 (80) [22+H+], 871.8 (100) [22+], 377.0 (95) [C26H36N2+H+],
4.9.1. Di-l-sulfo-di-1,3-bis(2,6-dimethylphenyl)-1,3-diaza-2-
silacyclopent-4-en-2-ylidene, 19
178.0
(84)
[ C
1H7214N432S228Si2] m/z 872.4737, found m/z 872.4738.
52
[C12H17NH2+H+].
CI
HRMS
calc.
for
12
From silylene 9b by reaction with elemental sulphur. Colorless
crystals for single-crystal X-ray diffraction were obtained after
recrystallization and storage at À20 °C. For recrystallization the so-
lid was suspended in n-hexane (2 mL) and thf was added until a
homogenous solution was obtained at room temperature. Yield:
149 mg (0.23 mmol, 45%). 1H NMR (500.133 MHz, 300 K,
C6D5CD3): d = 2.21 (s, 24H, CH3), 5.49 (s, 4H, NCH), 7.02 (m, 12H,
C6H3). 13C{1H} NMR (125.773 MHz, 300 K, C6D5CD3): d = 19.0
(CH(CH3)2), 118.3 (NCH), 126.3 (Cpara), 128.8 (Cmeta), 133.3 (Cortho),
139.4 (Cipso). 29Si{1H} NMR (99.357 MHz, 300 K, C6D5CD3):
d = À39.5. CI MS m/z (%): 705.5 (11) [19+C4H9+], 650.4 (43)
4.9.5. Di-
l-seleno-di-1,3-bis(2,6-diisopropylphenyl)-1,3-diaza-2-
silacyclopent-4-en-2-ylidene, 23
From silylene 9a by reaction with triethylphosphane selenide.
Colorless solid were isolated after recrystallization and storage at
À20 °C. For recrystallization the solid was suspended in n-hexane
(2 mL) and thf was added until a homogenous solution was ob-
tained at room temperature. Yield: 165 mg (0.17 mmol, 69%). 1H
NMR (500.133 MHz, 300 K, C6D6): d = 1.18 (d, 48H, CH(CH3)2,
3JH,H = 6.7 Hz), 3.50 (sept., 8H, CH(CH3)2, JH,H = 6.7 Hz), 5.64 (s,
3
[19++2], 649.4 (79) [19++1], 648.4 (100) [19+]. CI HRMS calc. for
4H, NCH), 7.08–7.24 (m, 12H, C6H3). 13C{1H} NMR (125.773 MHz,
300 K, C6D6): d = 23.7 (CH(CH3)2), 26.5 (CH(CH3)2), 29.0 (CH(CH3)2),
120.2 (Cmeta), 124.1 (NCH), 127.6 (Cpara), 137.3 (Cipso), 148.2 (Cortho).
29Si{1H} NMR (99.362 MHz, 300 K, C6D6): d = À61.7. 77Se{1H} NMR
(95.402 MHz, 300 K, C6D6): d = 197.3. CI MS m/z (%): 871.8 (7)
[23+C4H9+], 967.4 (100) [23+H+], 379.0 (38) [C26H38N2+H+], 178.0
12
[
C
1H4014N432S228Si2] m/z 648.2233, found m/z 648.2242.
36
4.9.2. Di-l-seleno-di-1,3-bis(2,6-dimethylphenyl)-1,3-diaza-2-
silacyclopent-4-en-2-ylidene, 20
From silylene 9b by reaction with triethylphosphane selenide.
Colorless crystals for single-crystal X-ray diffraction were obtained
after recrystallization and storage at À20 °C. For recrystallization
the solid was suspended in n-hexane (2 mL) and thf was added un-
til a homogenous solution was obtained at room temperature.
Yield: 185 mg (0.25 mmol, 50%) 1H NMR (500.133 MHz, 300 K,
C6D5CD3): d = 2.13 (s, 24H, CH3), 5.37 (s, 4H, NCH), 6.84–6.95 (m,
12H, C6H3). 13C{1H} NMR (125.773 MHz, 300 K, C6D5CD3): d = 19.5
(CH3), 118.7 (NCH), 126.2 (Cpara), 128.7 (Cmeta), 137.3 (Cortho),
139.7 (Cipso). 29Si{1H} NMR (99.357 MHz, 300 K, C6D5CD3):
d = À63.0. 77Se{1H} NMR (95.397 MHz, 300 K, C6D5CD3): d = 186.0.
CI MS m/z (%): 801.3 (10) [20+C4H9+], 745.2 (72) [20++1], 744.2
(20) [C12H17NH2+H+]. CI HRMS calc. for [12C52 H7214N480Se228Si2]
m/z 968.3626, found m/z 968.3629.
1
4.9.6. Di-l-telluro-di-1,3-bis(2,6-diisopropylphenyl)-1,3-diaza-2-
silacyclo-pent-4-en-2-ylidene, 24
From silylene 9a by reaction with triethylphosphane telluride. A
red solid was isolated after recrystallization and storage at À20 °C.
For recrystallization the solid was suspended in n-hexane (2 mL)
and thf was added until a homogenous solution was obtained at
room temperature. Yield: 26 mg (25 l
mol, 5%) 1H NMR
(500.133 MHz, 300 K, C6D6): d = 1.18 (d, 24H, CH(CH3)2,
(70) [20+], 742.2 (71) [20+À2]. CI HRMS calc. for
3JH,H = 6.6 Hz), 1.26 (d, 24H, CH(CH3)2, JH,H = 6.6 Hz), 3.47 (sept.,
3
1H4014N480Se228Si2] m/z 744.1122, found m/z 744.1112.
8H, CH(CH3)2, JH,H = 6.6 Hz), 5.60 (s, 4H, NCH), 7.14–7.29 (m,
12
3
[
C
36

P. Zark et al. / Journal of Organometallic Chemistry 695 (2010) 398–408
407
12H, C6H3). 13C{1H} NMR (125.758 MHz, 300 K, C6D6): d = 24.2
(CH(CH3)2), 26.1 (CH(CH3)2), 29.4 (CH(CH3)2), 120.0 (Cmeta), 124.3
(NCH), 127.6 (Cpara), 137.4 (Cipso), 148.3 (Cortho). 29Si{1H} NMR
(99.354 MHz, 300 K, C6D6): d = À131.2 (1JSi,Te = 310 Hz). 125Te{1H}
NMR (157.861 MHz, 300 K, C6D6): d = 451.9 (1JSi,Te = 309 Hz). CI
MS m/z (%): 1063.7 (0.2) [24+H+], 379.3 (19) [C26H38N2+H+],
(100) [16+]; RT: 23.15 min, m/z (%) 378.2 (32) [18+]; RT:
24.02 min, m/z (%) 494.3 (100) [17+].
Acknowledgments
P.Z. thanks the Fonds der Chemischen Industrie for scholarship
(No. 183191).
178.2
(16)
C
1H7214N428Si2130Te2] m/z 1068.3430, found 1068.3430. UV–
52
[C12H17NH2+H+].
CI
HRMS
calc.
for
12
[
vis (thf): kmax [nm] = 215, 246, 251, 257, 266, 350 (shoulder), 450.
Appendix A. Supplementary material
4.9.7. Synthesis of 23 and 24 in presence of 2,3-dimethyl-butadiene
Compound 9a (400 mg, 0.98 mmol) and 2,3-dimethyl-1,3-buta-
diene (0.56 mL, 4.9 mmol) were dissolved in thf (30 mL). At
À100 °C the corresponding triethylphosphane chalcogenide, dis-
solved in thf (10 mL), was added slowly. The mixture was warmed
slowly to room temperature and stirred for additional 24 h. The
analysis of the reaction mixture by 1H NMR only showed the for-
mation of the corresponding four-membered hetero cycles 23
and 24. The mixture was heated to reflux for another 12 h. Finally,
the thf was evaporated in vacuum and the residue was dried under
reduced pressure. NMR spectroscopy indicated only the formation
of 23 and 24.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2009.10.034.
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1
193.7 (CO, JC,W = 120.8 Hz), 196.6 (CO, JC,W = 144.3 Hz). 15N{1H}
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12
IR(nujol)
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l
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