Electronic interactions in 1-ethynyl-2-phenyltetramethyldisilanes HC{triple bond, long}CSiMe2SiMe2C6H4X

Article abstract of DOI:10.1016/j.jorganchem.2007.01.024

1-Ethynyl-2-phenyltetramethyldisilanes HC{triple bond, long}CSiMe₂SiMe₂C₆H₄X [X = NMe₂ (1), H (2), CH₃ (3), Br (4), CF₃ (5)] are accessible from ClSiMe₂SiMe₂

Full text of DOI:10.1016/j.jorganchem.2007.01.024

Journal of Organometallic Chemistry 692 (2007) 2046–2055
www.elsevier.com/locate/jorganchem
Electronic interactions in 1-ethynyl-2-phenyltetramethyldisilanes
HC„CSiMe2SiMe2C6H4X
a
a
a
a
´
Jennifer A. Shaw-Taberlet , Jean-Rene Hamon , Thiery Roisnel , Claude Lapinte ,
b
b
b,
*
Michaela Flock , Thomas Mitterfellner , Harald Stueger
a
UMR 6226 Sciences Chimiques de Rennes, CNRS-Universite´ de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France
b
Institut fu¨r Anorganische Chemie, Technische Universita¨t Graz, Stremayrgasse 16, A-8010 Graz, Austria
Received 25 October 2006; received in revised form 10 January 2007; accepted 16 January 2007
Available online 24 January 2007
Abstract
1-Ethynyl-2-phenyltetramethyldisilanes HC„CSiMe2SiMe2C6H4X [X = NMe2 (1), H (2), CH3 (3), Br (4), CF3 (5)] are accessible
from ClSiMe2SiMe2Cl, BrMgC6H4X and HC„CMgBr in a two step Grignard reaction. The crystal structure of 1 as determined by
single crystal X-ray crystallography exhibits a nearly planar PhNMe2 moiety and an unusual gauche array of the phenyl and the acetylene
group with respect to rotation around the Si–Si bond. Full geometry optimization (B3LYP/6-31+G**) of the gas phase structures of
1–5 affords minima for the gauche and the anti rotational isomers, both being very close in energy with a rotational barrier of only
3–5 kJ/mol. Experimental and calculated (time-dependent DFT B3LYP/TZVP) UV absorption data of 1–5 show pronounced electronic
interactions of the HC„C– and the C6H4X p-systems with the central Si–Si bond.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: UV absorption spectra; Disilanes; Hyperconjugation; DFT calculations
1. Introduction
In addition, pronounced substituent effects on polysi-
lane properties such as bathochromically shifted UV/visi-
ble absorption maxima are observed, when unsaturated
organic side groups like phenyl, vinyl or acetylene moieties
or atoms with p symmetric lone pairs like the halogens, O
or N are linked directly to the Si–Si bond [6]. At first such
interactions were rationalized in terms of d–p* hybridiza-
tion in the excited state. Later, the importance of r–p con-
jugation (hyperconjugation) in the ground state between
the Si–Si r-bond and the adjacent p symmetric orbitals
were recognized [2a]. Thus, it has been demonstrated by
photoelectron spectroscopy, that the HOMO of phenylpen-
tamethyldisilane is a linear combination of Si–Si r and
C6H5 p orbitals [1a]. In a related study Sakurai et al. fur-
nished indications of the r-donating character of the Si–
Si bond [7]. Meanwhile it has been generally accepted, that
r–p or r–n conjugation is the key factor for the substituent
effects influencing polysilane properties. In PhMe2SiSiMe3,
for instance, r–p hyperconjugation is responsible for the
observed rise of the energy of the highest occupied Si–Si
It is well known that disilanes possess interesting physi-
cal properties owing to their r-electronic system, which is
characterized by a HOMO high in energy and a LUMO
low in energy [1]. This property is invoked to explain,
why r-bonding electrons are delocalized across a polysi-
lane network in a manner comparable to the delocalization
of conjugated organic p-electrons giving Si–Si bonded spe-
cies quite interesting properties [2] like unusually long
wavelength UV absorption maxima, low ionization ener-
gies, nonlinear optical behavior [3], fluorescence [4] or pho-
tochemical activity. r-Delocalization in Si–Si bonded
compounds has also been treated theoretically on various
levels of theory including simple Hueckel, semiempirical,
ab initio and DFT methods [5].
*
Corresponding author. Tel./fax: +43 316 873 8708.
E-mail address: harald.stueger@tugraz.at (H. Stueger).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.01.024

J.A. Shaw-Taberlet et al. / Journal of Organometallic Chemistry 692 (2007) 2046–2055
2047
Me Me
known methods, adapted to each reaction [11]. The general
procedure is illustrated in Scheme 1. The first step involves
the in situ formation of the para substituted phenyl
Grignard reagent, which displaces a chlorine atom in
ClSiMe2SiMe2Cl by nucleophilic substitution. The
resulting chlorosilane intermediates were partially charac-
terized, the corresponding data can be found in the
experimental section. The second chlorine atom of these
intermediates was then displaced by ethynyl magnesium
bromide.
The yields after purification were moderate to good. For
liquid compounds 3, 4 and 5, the workup consisted of
extraction of the crude mixture with pentane, followed by
distillation and gave the desired product at a spectroscopic
purity level. The Me2N-derivative 1, a salt-like white solid
at room temperature, was crystallized from a concentrated
pentane solution at ꢀ40 ꢁC after distillation. The clear, col-
orless crystals obtained were stored at ꢀ70 ꢁC due to their
tendency to change color to brown upon standing at room
temperature. It is interesting to note that such color
changes were not accompanied by changes in the spectro-
scopic data. Generally all products were characterized by
standard spectroscopic techniques (29Si, 13C and 1H
NMR, IR, HRMS). The results (compare experimental
section) agree well with the proposed structures in all cases.
X
Si Si C CH
Me Me
Fig. 1. General structure of the family of r–p conjugated disilanes
reported herein: 1, X = NMe2; 2, X@H; 3, X@CH3; 4, X@Br; 5, X@CF3.
r-level relative to Me3SiSiMe3 and the concomitant
decrease of the UV-excitation energy [1a].
A series of recent investigations revealed, that the UV/
vis absorption spectra and other photophysical properties
of polysilanes are drastically influenced by the silicon back-
bone comformation. The topic was comprehensively
reviewed lately [8]. It has been widely accepted that the anti
conformation effectively extends r-delocalization while the
gauche form does not. As a consequence, an all-anti
conformer of a polysilane is supposed to afford a batho-
chromically shifted first UV absorption maximum. The
UV absorption spectra of r–p conjugated systems also
show remarkable conformational dependence. A careful
study of the absorption spectra of conformationally con-
strained aryldisilanes demonstrated that a torsion angle
between the phenyl ring plane and the Si–Si bond of 90ꢁ
effects in maximum r–p conjugation [9]. Similar conforma-
tional dependence of UV absorption and emission proper-
ties was also observed, when the 1,2-diphenyldisilane
moiety is conformationally constrained by incorporation
into cyclic structures [10].
2.2. NMR Spectroscopy
The present contribution describes the synthesis and
characterization of several previously unknown conjugated
disilanes of the general type shown in Fig. 1. NMR and
UV/vis spectroscopic data are used together with the
results of an X-ray crystal structure determination of 1 to
study the degree of electron delocalization in 1–5 and to
detect possible interactions of the phenyl and acetylene
p-systems via the silicon–silicon bond. Furthermore, exper-
imental data are rationalized by appropriate DFT
calculations.
Only weak electronic effects of the substituents attached
to the aromatic ring are apparent in the 29Si NMR spectra.
Thus, compounds 1–5, exhibit very similar 29Si chemical
shift values for the silicon atom a to the phenyl ring within
the close range of only 2 ppm. The same is true for the 13
C
chemical shifts of the acetylene carbons, which are nearly
unaffected by the presence of electron withdrawing or elec-
tron donating substituents attached to the phenyl ring. Sub-
stituent effects as expected for p-disubstituted benzene
derivatives, however, are found for the 13C resonance lines
of the aromatic carbon atoms. A simple empirical method
based on substituent increments Zi can be used to predict
benzene ring 13C shifts according to following equations [12]:
2. Results and discussion
2.1. Preparation
Zi ¼ diðC6H5XÞ ꢀ 128:5ðppmÞ
ð1Þ
ð2Þ
Novel disilanyl acetylides 1, 3, 4 and 5 were synthesized
in three steps from tetramethyldichlorodisilane via well
X
diðC H
¼ 128:5 þ
ZiðppmÞ
6ꢀnXnÞ
6
Me Me
Mg
ClMe2SiSiMe2Cl
X
Br
X
MgBr
X
Si Si Cl
Me Me
THF, 0oC
HC CMgBr
X = -NMe2, -H, -CH3, -Br, -CF3
Me Me
Si Si
X
C
CH
Me Me
Scheme 1.

2048
J.A. Shaw-Taberlet et al. / Journal of Organometallic Chemistry 692 (2007) 2046–2055
Originating from monosubstituted benzenes, however,
these shift increments do not take into account interactions
between multiple phenyl substituents. Deviation of experi-
mental and predicted values, therefore, are to be expected,
if substituents show interactions like strong resonance or
inductive effects of opposite signs. Experimental and pre-
dicted 13C chemical shift values of the aromatic carbons
in 1–5 are collected in Table 1. Excellent correlation
between experimental and calculated values is observed
for 3 containing the weakly donating methyl group (maxi-
mum deviation, 1 ppm), while 1, 4 and 5 exhibit somewhat
larger deviations of different magnitude and sign pointing
towards enhanced interaction of the disilanyl moiety with
the p-NMe2, Br and CF3 substituents, respectively.
Fig. 2. ORTEP drawing and numbering of 1. Thermal ellipsoids are
shown at the 50% probability level. Hydrogen atoms have been omitted
for clarity.
2.3. Molecular structure of 1
The molecular structure of 1 was determined by X-ray
crystallography on a monocrystal. The data are summa-
rized along with DFT calculated values in Table 2. An
ORTEP diagram can be found in Fig. 2.
With a sum of the C–N–C angles being 359.8ꢁ the Me2N-
moiety is nearly perfectly planar. Furthermore, this substi-
tuent crystallizes nearly coplanar to the phenyl ring as
shown by the C2–N3–C4–C5 dihedral angle of 178.2ꢁ.
The N3–C4 bond with a bond length of 137.5 pm is signif-
icantly shorter as compared to the C1–N3 and C2–N3 single
bonds (144.2 and 144.4 pm). Both facts indicate a strong
degree of resonance delocalization from the nitrogen lone
Table 1
Experimental and calculated 13C chemical shifts of 1–5
3
2
1 SiMe2SiMe2 C CH
4
X
X
dC1
dC2
dC3
dC4
Exp.a
Calc.b
Exp.a
Calc.b
Exp.a
Calc.b
Exp.a
Calc.b
–Hc
–NMe2
–CH3
–Br
138.0
122.6
134.2
136.9
143.5
134.0
135.1
134.1
135.5
134.3
128.0
112.2
128.8
131.0
124.8
128.9
150.9
138.6
125.7
127.2
126.2
135.0
136.5
141.3
134.2
134.7
135.5
134.3
113.1
127.8
130.9
124.8
150.0
138.2
123.0
131.2
–CF3
a
Signal assignment is based on decoupled experiments.
b
c
Data calculated by Eq. (2). Values for Zi are taken from Ref. [11b].
Experimental spectrum recorded in order to calculate Zi using Eq. (1).
Table 2
Experimental and calculated bond lengths, angles and torsion angles for gauche-1
Bond length (pm)
Exp.
Calc.
Bond angle (ꢁ)
Exp.
Calc.
Si1–Si2
Si1–C9
Si2–C14
Si–Cmethyl (mean)
C14–C15
C4–C5
C5–C6
C6–C9
C9–C8
C8–C7
233.64(4)
187.02(10)
184.98(11)
187.1
237.48
188.79
185.27
C1–N3–C2
C1–N3–C4
C2–N3–C4
Si2–C14–C15
C4(Ph centroid)–C9–Si1
119.22(10)
120.24(10)
120.37(10)
172.20(11)
176.90
117.0
119.1
119.0
178.8
179.1
119.10(16)
140.83(15)
138.39(15)
140.00(14)
140.11(14)
138.58(15)
140.75(15)
144.23(15)
144.41(15)
137.54(14)
121.86
141.54
139.25
140.87
140.70
139.41
141.43
145.53
145.52
139.25
Torsion angle (ꢁ)
C2–N3–C4–C7
C1–N3–C4–C5
C9–Si1–Si2–C14
C8–C9–Si1–Si2
C6–C9–Si1–Si2
1.14
6.60
ꢀ66.92
ꢀ97.14
79.24
13.3
ꢀ12.8
ꢀ71.7
ꢀ107.3
72.1
C7–C4
C1–N3
C2–N3
N3–C4

J.A. Shaw-Taberlet et al. / Journal of Organometallic Chemistry 692 (2007) 2046–2055
2049
pair across the aromatic ring. Accordingly we observe some
quasi-quinoidal character of the phenyl ring as evidenced by
slightly shortened C5–C6 and C7–C8 bond lengths,
although the difference is not large enough to allow more
definite conclusions.
Si–Si and Si–C bond lengths measure at the expected
values for single bonds. The geometry around the silicon
atoms is approximately tetrahedral. Interestingly, the bond
angle formed between the ethynyl triple bond and Si2 devi-
ates from linearity (172.20ꢁ), which could be rationalized
by hyperconjugational type r–p interactions within the
C„C–Si–Si moiety of 1. In a similar fashion the phenyl
plane is bent towards to the Si1–Si2 r bond as evidenced
by the CPh centroid–C9–Si1 bond angle of 176.90ꢁ.
Compound 1 exhibits an unusual gauche-array of the
phenyl relative to the acetylene group (C9–Si1–Si2–
C14 = 66.9ꢁ), while 1,2-diaryldisilanes usually adopt an
anti-geometry of the central X–Si–Si–X moiety [3b,13].
Theoretical calculations (see below) suggest that the gauche
conformation observed for 1 in the crystalline state could
be favored due to packing, rather than electronic effects.
The roughly perpendicular arrangement of the plane of
the phenyl ring relative to the Si–Si bond with a dihedral
angle C8–C9–Si1–Si2 of 97.14ꢁ allows effective overlap
for r–p conjugation between these groups.
ers, a series of calculations has been performed for 1, in
which the Csp–Si–Si–Csp2 dihedral angle a was varied from
0ꢁ to 180ꢁ (see Fig. 4). Minima were found at a = ꢀ178.9ꢁ
(anti) and 71.7ꢁ (gauche) with rotational barriers of 3 kJ/
mol for anti ! gauche and 5 kJ/mol for gauche ! anti.
The small rotational barrier and the negligible energy dif-
ference between the gauche and the anti form indicate
nearly unhindered rotation around the Si–Si bond and
equal population of both rotamers in the gas phase at room
temperature.
Bond lengths, bond angles and dihedral angles calcu-
lated for 1–5 do not show significant variations with the
substituents attached to the phenyl ring. The correspond-
ing data can be found in the Supplementary material.
Agreement between the calculated and the experimental
10
8
6
4
Full geometry optimization (B3LYP/6-31+G**) of the
gas phase molecular structures of 1–5 affords two minima
very close in energy, which can be considered as rotational
isomers with respect to rotation around the silicon–silicon
bond. The calculated structures for compound 1 are illus-
trated in Fig. 3. In all cases the gauche isomer is slightly less
stable than the anti isomer with an energy differences
between 1.34 kJ/mol (5) and 1.63 kJ/mol (1). In order to
estimate the rotational barrier between the two conform-
2
0
0
20
40
60
80
100
120
140
160
180
torsion angle α [°]
Fig. 4. Variation of the relative energy of 1 as the dihedral angle a
(C9–Si1–Si2–C14) is varied from 0ꢁ to 180ꢁ.
Fig. 3. DFT (B3LYP/6-31+G**) optimized geometries and relative energies for 1.

2050
J.A. Shaw-Taberlet et al. / Journal of Organometallic Chemistry 692 (2007) 2046–2055
molecular structure of 1 is reasonably good (compare
Table 2), although the calculations were carried out for
the gas phase. A weak quinoidal character of the phenyl
ring is also observed computationally, which clearly
reflects the influence of the Me2N– donor on the aromatic
system. However, many structural indications of elec-
tronic conjugation found experimentally are less pro-
nounced in the theoretical model. Thus, the environment
of the N atom is calculated to be slightly pyramidal with
a sum of the C–N–C bond angles of 354.6ꢁ (anti) and
355.1ꢁ (gauche), respectively. Furthermore, the torsion
angles between the planes formed by the Me2N-group
and the phenyl ring are much larger in the calculated
structure, while the calculated torsion angles formed
between the phenyl plane and the disilyl substituent devi-
ate much more from the ideal 90ꢁ than the experimental
value. The deviation of the Si2–C„C bond angle from
linearity and the bending of the plane of the phenyl ring
towards the Si–Si bond axis are not reflected by the quan-
tum chemical calculations at all. Because the computa-
tional method used in the present study usually reflects
structural features arising from r–p delocalization quite
well, the observed discrepancy of calculated and experi-
mental structures are most likely due to crystal packing
effects and intermolecular interactions occurring exclu-
sively in the solid state.
obtained for 1–5 with the corresponding data of their
Me5Si2-analogues.
Two basic types of absorption spectra are observed
within the series 1–5. The absorption spectra of 2–5 are sur-
prisingly similar with kmax values between 233 and 239 nm
and slightly red shifted first absorption bands for the Br-
and CF3 derivatives 4 and 5 relative to 2 and 3. The
Me2N– substituted compound 1, however, exhibits a first
absorption maximum at 271 nm with unusually high inten-
sity, the position of which is much less affected by the nat-
ure of the organosilicon substituent attached to the
benzene ring. Thus, going from Me2N–C6H4–SiMe3
(kmax = 266 nm) [14] to 1, a bathochromic shift of just
5 nm is observed, while the first absorption maximum of
compound 2, for instance, is shifted to the red by 22 nm
as compared to PhSiMe3 (kmax = 211 nm) [4a].
In order to achieve a tentative assignment of the low
energy absorption bands the absorption spectra of 1–5
were calculated by time-dependent DFT at the B3LYP/
TZVP level. The features apparent in spectra of 2–5 can
be interpreted straightforwardly assuming r–p conjugation
between the Si–Si r-orbital and the p systems of the unsat-
urated substituents as described in the introductory section.
A qualitative molecular orbital diagram for 2 is depicted in
Fig. 5 together with the shape of the calculated frontier
orbitals (B3LYP/6-31+G**).
Upon UV irradiation an electron is excited from the
HOMO, which is delocalized over the whole Ph–Si–Si–
C„C framework, to a LUMO of predominant p*(Ph)
character. Because the highest occupied p-MO’s of the
Ph–X and C„C substituents in 3, 4 and 5 are also found
well below the highest r(Si–Si) level as shown by the first
ionization potentials estimated by photoelectron spectros-
copy (C6H5CH3: IP1 = ꢀ8.89 eV; C6H5CF3: IP1 = ꢀ9.75
eV [15]; C6H5Br: IP1 = ꢀ9.02 eV; HC„CH: IP1 = ꢀ11.4
eV [16]; Me3SiSiMe3: IP1 = ꢀ8.69 eV [1a]), the HOMO’s
in the whole series are best described by highly delocalized
2.4. UV/vis absorption spectra
UV absorption data of 1–5 are presented in Table 3
together with calculated values (Turbomole 5.6 B3LYP/
TZVP) and literature data for the corresponding Me5Si2-
derivatives.
All compounds exhibit absorption maxima in the near
UV region. The impact of the HC„C-group on the
absorption characteristics is negligibly small as can be eas-
ily judged by comparing the kmax and absorptivity values
Table 3
Experimental and calculated UV/vis data
X
SiMe2SiMe2 Y
e (l molꢀ1 cmꢀ1
X
Y
kmax exp.a (nm)
)
kmax Calc.b gauche
kmax Calc.b (nm) trans
d
Me2N–
Me2N–
Me
Me
H
Me
HC„C–
Me
HC„C–
Me
HC„C–
HC„C–
Me
270c
271e
233c
233
–
–
–
39000
d
262.5 (HO ! LU + 1)
265.4 (HO ! LU + 1)
–
–
–
13400
10800
13900
13800
6820
236 (HO ! LU)
243 (HO ! LU)
231c
233
–
–
H
Br
235.2 (HO ! LU)
245 (HO ! LU)
–
252 (HO ! LU)
239.5 (HO ! LU)
249 (HO ! LU)
–
256 (HO ! LU)
239
F3C–
F3C–
a
239.5f
239
HC„C–
6200
C6H12 solution, c = 5 · 10ꢀ5 mol Æ lꢀ1
.
b
c
d
e
f
Time-dependent DFT B3LYP/TZVP.
Data taken from Ref. [4a].
Not reported.
Data taken from Ref. [4b].
c = 5 · 10ꢀ6 mol lꢀ1
.

J.A. Shaw-Taberlet et al. / Journal of Organometallic Chemistry 692 (2007) 2046–2055
2051
Fig. 6. Frontier orbital diagram for 1 (c). Energies of highest occupied
MO’s of (a) benzene, (b) N,N-dimethylaminobenzene and (d) hexameth-
yldisilane and acetylene are derived from PES measurements [17]. Orbital
shapes were calculated using density functional theory (Gaussian 03;
B3LYP/6-31+G**).
Fig. 5. Frontier orbital diagram for 2 (b). Energies of highest occupied
MO’s of (a) benzene and (c) hexamethyldisilane and acetylene are derived
from PES measurements [17]. Orbital shapes were calculated using density
functional theory (Gaussian 03; B3LYP/6-31+G**).
polysilane chains and cycles [2d,18,19]. The gauche and the
anti rotational isomers of 1–5, however, were calculated to
exhibit very similar absorption spectra. Combined with the
low rotational barrier around the Si–Si bond calculated for
1 and 2 this result clearly rules out, that the differences in
the absorption spectra of 1–5 arise from variable contribu-
tions of the gauche and the anti rotational isomers.
orbitals with a large r(Si–Si) contribution and 2 may serve
as a model substance for the understanding of the absorp-
tion behavior of 3, 4 and 5 as well. This picture is perfectly
in line with the computational results obtained for 3–5,
which are included in the Supplementary material. The
low energy UV absorption bands observed for 2–5 between
233 and 239 nm, thus, can be assigned to r(Si–Si) ! p*
electron transitions. The small difference of the excitation
energies within the series 2–5 indicates only minor impact
of the X-groups attached to the phenyl ring on the extent
of r–p conjugation.
The strong absorption maximum at 271 nm visible in the
spectrum of 1 is characteristic for compounds containing
the Me2N–phenyl moiety. In p-sila-N,N-dimethylanilines
it is usually found around 270 nm and can be assigned to
a localized transition within the aromatic system with
minor contributions of the p-silanyl substituent [17]. This
model is fully supported by our computational results
(compare Fig. 6) obtained for 1. Due to the effective mixing
of the n(N) and benzene p orbitals the highest occupied p–
MO is raised above the r(Si–Si) level, and the HOMO in 1
is primarily p in character with negligible r(Si–Si) contri-
bution. The 271 nm band in the absorption spectrum of 1
is assigned computationally to the HOMO ! LUMO + 1
transition, where the electron is excited from this p(Ph)
type HOMO to an orbital with p*ph/p*C„C/rSi–C character.
In the literature, contributions of several conformers are
frequently invoked to explain the UV absorption spectra of
3. Conclusions
Experimental and computational results presented in
this paper provide significant evidence for extended r–p
conjugation within the family of disilanes 1–5. Experimen-
tal absorption spectra exhibit absorption maxima in the
near UV, the position and intensity of which are influenced
by the presence of electronically active substituents
attached to the phenyl ring in para position. DFT calcula-
tions allow the assignment of the observed absorption
bands to r(Si–Si) ! p*(ph) or p(ph) ! p*(ph) electron
transitions depending on the substituents attached to the
benzene ring. Unusual structural features found for 1
experimentally by single crystal X-ray crystallography,
however, are rather due to crystal packing and solid state
effects than intramolecular electronic interactions, because
they are much less pronounced in the calculated gas phase
structure of the molecule. Currently attempts are made in
our laboratories to link the terminal acetylene group in
1–5 to electron rich transition metal centers in order to
study donor–acceptor substituent interactions via the sili-
con–silicon bond.

2052
J.A. Shaw-Taberlet et al. / Journal of Organometallic Chemistry 692 (2007) 2046–2055
4. Experimental section
4.1. General procedures
NMe2); 0.46 (s, 6H, SiMe2Cl); 0.44 (s, 6H, SiMe2–Caryl).
29Si NMR (THF/ext. lock D2O, ext. TMS, ppm):
d = 22.53 (SiMe2Cl); ꢀ22.79 (SiMe2–Caryl).
Manipulations of air-sensitive compounds were per-
formed under a nitrogen atmosphere using standard
Schlenk techniques. Solvents were dried using a column
solvent purification system [20]. p-Bromo-N,N-dimethylan-
iline, p-bromotoluene and 1-bromo-4-trifluoromethylben-
zene (Aldrich, Acros) were purchased and used as
obtained. ClSiMe2SiMe2Cl [21], ClMe2SiSiMe2PhBr [3a]
and compound 2 [22] were prepared using published proce-
dures. Reaction completion was verified with GC/MS on a
HP 5890 II and HP 5971 with a 25 m long poly-
dimethylsiloxane column. Infrared spectra were obtained
as Nujol mulls or as films between KBr windows with a
Bruker IFS28 FT-IR infrared spectrophotometer (4000–
400 cmꢀ1). UV–visible spectra were recorded on a Per-
kin–Elmer Lambda 35 spectrometer. 1H and 13C NMR
spectra were recorded on a Bruker DPX200, 29Si NMR
spectra were recorded on a Varian INOVA 300 MHz at
room temperature. Chemical shifts are reported in parts
per million (d) relative to tetramethylsilane (TMS), using
the residual solvent resonances as internal references.
Coupling constants (J) are reported in hertz (Hz), and inte-
grations are reported as numbers of protons. The following
abbreviations are used alone or together to describe peak
patterns: singlet = s, doublet = d, triplet = t, quartet = q,
quintet = p, septet = h, m = multiplet. High-resolution
mass spectra (HRMS) were recorded on a high-resolution
VARIAN MAT 311 analytical spectrometer operating in
4.3. 1-(p-Trifluoromethylphenyl)-2-chlorotetra-
methyldisilane
The procedure followed was that used for the Me2N-
derivative as described above with 5.0 g (0.022 mol) of
p-F3CPhBr, 0.7 g (0.029 mol) Mg, 4.5 g (0.025 mol) of
ClSiMe2SiMe2Cl and 35 mL of THF. After the evapora-
tion of THF, 4.9 g (74%) of the title compound were iso-
lated from the crude product mixture by extraction with
pentane. The slightly yellow, air- and moisture-sensitive
liquid was used without further purification.
1H NMR (C6D6, ext. TMS, ppm, rel. Int.): d = 7.40–
7.25 (AA’BB’, 4H, C6H4); 0.25 (s, 6H, SiMe2Cl); 0.23
(s, 6H, SiMe2Caryl). 29Si NMR (THF/ext. lock D2O, ext.
TMS, ppm): d = 21.34 (SiMe2Cl); ꢀ21.30 (SiMe2–Caryl).
4.4. 1-(p-N,N-Dimethylaminophenyl)-2-ethynyl-
tetramethyldisilane (1)
A solution of HC„CMgBr (36 mL, 0.5 M) in THF
was added dropwise to 5.0 g (0.018 mol) of Me2NPh-
SiMe2SiMe2Cl dissolved in 25 mL of THF. After stirring
the resulting solution at room temperature overnight GC/
MS analysis revealed that the reaction had gone to com-
pletion. The solvent was evaporated and the resulting
solid extracted three times with pentane. After removal
of the pentane in vacuum the crude product was purified
by distillation to yield a white solid that readily formed
air- and moisture-stable crystals of pure 1 from a satu-
rated pentane solution at ꢀ40 ꢁC with a yield of 2.5 g
(53%).
´
the EI mode, at the Centre Regional de Mesures Physiques
de l’Ouest (CRMPO), Rennes. Polyethyleneglycol (PEG)
was used as internal reference, and methanol was used as
solvent. All mass measurements refer to peaks for the most
common isotopes (1H, 12C, 14N, 19F, 28Si). Elemental anal-
yses were conducted on a Thermo-FINNIGAN Flash EA
1112 CHNS/O analyzer by the Microanalytical Service of
the CRMPO at the University of Rennes 1, France.
B.p. (0.08 mbar): 95 ꢁC. Anal. Found: C, 63.55; H, 8.91;
N 5.33%. Calc. for C14H23NSi2: C, 64.30; H, 8.86; N
5.36%. FT-IR (Nujol, cmꢀ1): 2022 (s) m(C„C). H NMR
1
(CDCl3, ext. TMS, ppm, rel. Int.): d = 7.47–6.83 (AA’BB’,
4H, C6H4); 3.04 (s, 6H, NMe); 2.56 (s, 1H, C„CH); 0.47
(s, 6H, SiMe2); 0.30 (s, 6H, SiMe2). 13C NMR (CDCl3,
4.2. 1-(p-N,N-Dimethylaminophenyl)-2-chlorotetramethyl-
disilane
1
ext. TMS, ppm): 150.9 (s, C4Ar); 135.1 (dd, JC–H = 155.4
1
Hz, C2Ar); 122.6 (s, C1Ar); 112.2 (dd, JC–H = 157.2 Hz,
1
4
A solution of p-Me2NPhMgBr prepared from 2.15 g
(88.46 mmol) of Mg and 15.0 g (0.075 mol) of p-
Me2NPhBr in 50 mL of THF was added at 0 ꢁC to 13.9 g
(0.075 mol) of ClSiMe2SiMe2Cl dissolved in 100 mL of
THF over a period of 2 h. After stirring the resulting solu-
tion at room temperature for 16 h the reaction was shown
by GC/MS to have gone to completion. Work-up was
achieved by evaporating the solvent and extracting the
solid residue with a 50:1 mixture of toluene and THF.
Upon removal of the solvents in vacuum, the desired prod-
uct (10.2 g, 50%) appeared as a white air- and moisture-
sensitive solid, which was used without further purification.
1H NMR (THF/ext. lock D2O, ext. TMS, ppm, rel.
Int.): d = 7.42–6.81 (AA’BB’, 4H, C6H4); 3.01 (s, 6H,
C3Ar); 95.3 (dh, JC–H = 236.43 Hz, JC–H = 3.3 Hz,
2
C„CH); 89.5 (d, JC–H = 41.7 Hz, C„CH); 40.3
1
4
(qq, JC–H = 135.2 Hz, JC–H = 3.8 Hz, NMe); ꢀ2.85 (qq,
1JC–H = 121.6 Hz, JC–H = 2.2 Hz, SiMe2); ꢀ3.8 (qq,
4
1JC–H = 120.7 Hz, JC–H = 2.4 Hz, SiMe2). 29Si NMR
4
(THF/ext. lock D2O, ext. TMS, ppm): d = ꢀ23.16
ðSiMe2–Csp2Þ; ꢀ37.10 (SiMe2–Csp). HRMS (C14H23NSi2,
[M+]): 261.1369 (calc.); 261.1362 (found).
4.5. 1-(p-Tolyl)-2-ethynyltetramethyldisilane (3)
The synthesis of 3 was carried out in a one-pot fashion
starting from p-bromotoluene and ClSiMe2SiMe2Cl. A
solution of p-tolylMgBr prepared from 1.6 g (0.065 mol)

J.A. Shaw-Taberlet et al. / Journal of Organometallic Chemistry 692 (2007) 2046–2055
2053
of Mg and 10.9 g (0.064 mol) of p-bromotoluene in 50 mL
of THF was added at 0 ꢁC to 11.9 g (0.064 mol) of ClSi-
Me2SiMe2Cl dissolved in 100 mL of THF over a period
of 2 h. After stirring the resulting solution at room temper-
ature for 16 h the reaction was shown by GC/MS to have
gone to completion. After dropwise addition of 130 mL
of a 0.5 M solution of HC„CMgBr in THF, the resulting
mixture was stirred at room temperature overnight to
achieve complete conversion (GC/MS monitoring recom-
mended). After aqueous workup with 1 M H2SO4 and
extraction with pentane, the combined organic layers were
dried over Na2SO4. Removal of the solvent and fractional
distillation of the liquid residue gave 10.9 g (74%) of pure 3
as a colorless oily liquid.
tional distillation of the crude product gave 5.6 g (79%)
of pure 5 as a colorless air- and moisture-stable liquid.
B.p. (0.03 mbar): 46 ꢁC. FT-IR (Nujol, cmꢀ1): 2029 (s)
m(C„C). 1H NMR (CDCl3, ext. TMS, ppm, rel. Int.):
d = 7.85–7.75 (AA’BB’, 4H, C6H4); 2.55 (s, 1H, C„CH);
0.51 (s, 6H, SiMe2); 0.28 (s, 6H, SiMe2). 13C NMR (CDCl3,
1
ext. TMS, ppm): d = 143.5 (s, C1Ar); 134.3 (dd, JC–H
=
160.7 Hz, C2Ar); 127.2 (m, C1Ar); 130.9 (qt,
1
1JCꢀF = 128.0 Hz, CF3); 124.8 (dm, JC–H = 160.7 Hz,
1
C3Ar); 96.0 (d, JC–H = 237.3 Hz, C„CH); 88.3 (dm,
3
2JC–H = 45.5 Hz, JC–H = 3.3 Hz, C„CH); -3.1 (qq,
4
1JC–H = 121.9 Hz, JC–H = 2.4 Hz, SiMe2); ꢀ4.35 (qq,
4
1JC–H = 121.2 Hz, JC–H = 2.5 Hz, SiMe2). 29Si NMR
(THF/ext. lock D2O, ext. TMS, ppm): d = ꢀ22.28
ðSiMe2–Csp2Þ; ꢀ37.77 (SiMe2–Csp). HRMS (C13H17F3Si2,
[M+]): 286.0821 (calc.); 286.0823 (found).
B.p. (0.03 mbar): 58–60 ꢁC. FT-IR (Nujol, cmꢀ1): 2028
1
(s) m(C„C). H NMR (CDCl3, ext. TMS, ppm, rel. Int.):
d = 7.59–7.34 (AA’BB’, 4H, C6H4); 2.62 (s, 1H, C„CH);
2.51 (s, 3H, Aryl-Me); 0.59 (s, 6H, SiMe2); 0.39 (s, 6H,
SiMe2). 13C NMR (CDCl3, ext. TMS, ppm): d = 138.6 (q,
2JC–H = 6.5 Hz, C4Ar); 134.2 (s, C1Ar); 134.1 (dd,
4.8. X-ray crystallography
Single crystals suitable for X-ray crystallography of 1
were obtained as described above, and were mounted with
epoxy cement on the tip of a glass fiber. Crystal, data col-
lection, and refinement parameters are given in Table 4.
The compound was studied on a Kappa-CCD Enraf-
Nonius FR590 diffractometer equipped with a bidimen-
1
1JC–H = 157.2 Hz, C2Ar); 128.8 (dm, JC–H = 157.2 Hz,
1
C3Ar); 95.60 (d, JC–H = 237 Hz, C„CH); 88.97 (dm,
3
2JC–H = 41.9 Hz, JC–H = 3.3 Hz, C„CH); 21.6 (qt,
3
1JC–H = 126.3 Hz, JC–H = 4.5 Hz, ArMe); ꢀ2.9 (qq,
4
1JC–H = 121.7 Hz, JC–H = 2.3 Hz, SiMe2); ꢀ4.0 (qq,
4
1JC–H = 121.0 Hz, JC–H = 2.4 Hz, SiMe2). 29Si NMR
(THF/ext. lock D2O, ext. TMS, ppm): d = ꢀ22.26
ðSiMe2–Csp2Þ; ꢀ36.78 (SiMe2–Csp). HRMS (C13H20Si2,
[M+]): 232.1104 (calc.); 232.1112 (found).
Table 4
Crystallographic data for compound 1
Empirical formula
Formula weight
C14H23NSi2
261.51
4.6. 1-(p-Bromophenyl)-2-ethynyltetramethyldisilane (4)
Collection temperature (K)
Crystal system
Crystal size (mm)
173(2)
The procedure followed was that used for 1 with 3.5 g
(0.011 mol) of BrPhSiMe2SiMe2Cl, 28 mL of 0.5 M
HC„CMgBr in THF and 15 mL of THF. Fractional dis-
tillation of the crude product gave 3.0 g (86%) of pure 4
as a colorless air- and moisture-stable liquid.
Monoclinic
0.7 · 0.4 · 0.12
P21/a
12.3423(5)
8.2962(4)
16.4090(7)
90.00
108.405(2)
90.00
1594
Space group
˚
a (A)
˚
b (A)
˚
c (A)
B.p. (0.03 mbar): 75 ꢁC. FT-IR (Nujol, cmꢀ1): 2028 (s)
m(C„C). 1H NMR (CDCl3, ext. TMS, ppm, rel. Int.):
d = 7.56–7.44 (AA’BB’, 4H, C6H4); 2.55 (s, 1H, C„CH);
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
0.49 (s, 6H, SiMe2); 0.28 (s, 6H, SiMe2). 13C NMR (CDCl3,
Volume (A )
1
Z
4
ext. TMS, ppm): d = 136.9 (s, C4Ar); 135.5 (dd, JC–H
=
Absorption coefficient (mmꢀ1
)
0.204
1.090
568
2.72–27.52
ꢀ16 < h < 9,
ꢀ10 < k < 10,
ꢀ20 < l < 20
21163
1
Density calc. (g cmꢀ3
F(000)
)
160 Hz, C2Ar); 131.0 (dd, JC–H = 167 Hz, C3Ar); 125.7
1
(s, C1Ar); 95.9 (d, JC–H = 237 Hz, C„CH); 88.5 (dm,
2JC–H = 42.0 Hz, JC–H = 3.3 Hz, C„CH); ꢀ2.30 (qq,
3
h Range (ꢁ)
Limiting indices
1JC–H = 122 Hz, JC–H = 2.3 Hz, SiMe2); ꢀ3.49 (qq,
4
1JC–H = 121 Hz, JC–H = 2.4 Hz, SiMe2). 29Si NMR
4
(THF/ext. lock D2O, ext. TMS, ppm): d = ꢀ21.12
ðSiMe2–Csp2Þ; ꢀ36.67 (SiMe2–Csp). HRMS (C12H17BrSi2,
[M+]): 296.00522 (calc.); 296.031 (found).
Reflections collected
Independent reflections
Completeness to h = 27.52ꢁ
Max. and min. transmission
Data/restraints/parameters
Final R indices [I > 2r(I)]
3654
99.8%
0.976 and 0.867
3654/0/154
R1 = 0.0264
wR2 = 0.0759
R1 = 0.0290
wR2 = 0.0779
1.039
4.7. 1-(p-Trifluoromethylphenyl)-2-
ethynyltetramethyldisilane (5)
R indices (all data)
The procedure followed was that used for 1 with 7.4 g
(0.025 mol) of F3CPhSiMe2SiMe2Cl, 60 mL of 0.5 M
HC„CMgBr in THF and 15 mL of diethyl ether. Frac-
Goodness-of-fit on F2
Largest difference in peak and hole (e A
ꢀ3
˚
)
0.349 and ꢀ0.180

2054
J.A. Shaw-Taberlet et al. / Journal of Organometallic Chemistry 692 (2007) 2046–2055
sional CCD detector employing graphite-monochromated
Mo Ka radiation (k = 0.71073 A). The cell parameters were
References
˚
[1] (a) C.G. Pitt, H. Bock, J. Chem. Soc., Chem. Commun. (1972) 28;
(b) C.G. Pitt, R.N. Carey, E.C. Toren, J. Am. Chem. Soc. 94 (1972)
3806.
[2] (a) For some reviews concerning the electronic properties of polysil-
anes, consult: C.G. Pitt, in: A.L. Rheingold (Ed.), Homoatomic
Rings, Chains and Macromolecules of Main Group Elements,
Elsevier, New York, 1977, p. 203;
obtained with Denzo and Scalepack with 10 frames (psi
rotation: 1ꢁ per frame) [23]. The data collection provided
21163 reflections (Table 4). Subsequent data reduction
with Denzo and Scalepack gave the independent reflections
(Table 4). The space group was chosen based on the sys-
tematic absences in the diffraction data. The structure
was solved with SIR-97 which revealed the non-hydrogen
atoms [24]. After anisotropic refinement, the remaining
atoms were found in Fourier difference maps. The complete
structure was then refined with SHELXL97 by the full-matrix
least-squares procedures on reflection intensities (F2) [25].
The absorption was not corrected. The non-hydrogen
atoms were refined with anisotropic displacement coeffi-
cients, and all hydrogen atoms were treated as idealized
contributions. Atomic scattering factors were taken from
the literature [26].
(b) H. Sakurai, J. Organomet. Chem. 200 (1980) 261;
(c) H. Sakurai, Pure Appl. Chem. 59 (1987) 1637;
(d) R.D. Miller, J. Michl, Chem. Rev. 89 (1989) 1359;
(e) R. West, in: G. Wilkinson, F.G.A. Stone, E.W. Abel (Eds.),
Comp. Organomet. Chem. II, vol. 2, Pergamon Press, 1995, p. 77;
(f) E. Hengge, H. Stueger, in: S. Patai, Z. Rappoport, Y. Apeloig
(Eds.), The Chemistry of Organic Silicon Compounds, vol. 2, Wiley,
Chichester, 1998, p. 2177.
[3] (a) G. Mignani, M. Barzoukas, J. Zyss, G. Soula, F. Balegroune, D.
Grandjean, D. Josse, Organometallics 10 (1991) 3660;
(b) D. Hissink, P.F. van Hutten, G. Hadziioannou, J. Organomet.
Chem. 454 (1993) 25;
(c) H.K. Sharma, K.H. Pannell, I. Ledoux, J. Zyss, A. Ceccanti, P.
Zanello, Organometallics 19 (2000) 770;
(d) C. Grogger, H. Rautz, H. Stueger, Mh. Chem. 132 (2001) 453.
[4] (a) H. Sakurai, H. Sugiyama, M. Kira, J. Phys. Chem. 94 (1990)
1837;
4.9. Computational methods
Geometry optimizations and analytical vibrational
frequency calculations were carried out with the Gaussian
03 program suite [27] at the density functional level using
the B3LYP hybrid functional and 6-31+G** basis sets as
implemented. The UV spectra obtained by time-
dependent B3LYP/TZVP calculations were performed
with the Turbomole V5.6 program [28]. Relative energies
given include zero point vibrational energy (ZPVE)
corrections.
(b) M. Kira, T. Miyazawa, H. Sugiyama, M. Yamaguchi, H. Sakurai,
J. Am. Chem. Soc. 115 (1993) 3116;
(c) M. Yamamoto, T. Kudo, M. Ishikawa, S. Tobita, H. Shizuka, J.
Phys. Chem. A 103 (1999) 3144.
[5] For reviews consult Ref. [2a,2d] and H.A. Fogarty, D.L. Casher, R.
Imhof, T. Schepers, D.W. Rooklin, J. Michl, Pure Appl. Chem. 75
(2003) 999.
[6] (a) D.N. Hague, R.H. Prince, J. Chem. Soc. (1965) 4690;
(b) H. Gilman, W.H. Atwell, G.L. Schwebke, J. Organomet. Chem. 2
(1964) 369;
(c) H. Sakurai, S. Tasaka, M. Kira, J. Am. Chem. Soc. 94 (1972)
9285;
Acknowledgements
(d) C.G. Pitt, J. Am. Chem. Soc. 91 (1969) 6613;
(e) H. Stueger, E. Hengge, Mh. Chem. 119 (1988) 873;
(f) H. Stueger, G. Fuerpass, K. Renger, Organometallics 24 (2005)
6374.
´
The authors are grateful to Drs P. Jehan and P. Guenot
(CRMPO, Rennes) for skillful assistance in recording high-
resolution mass spectra. Financial support from the Aus-
trian-French scientific exchange program (AMADEUS
20/2004-05), the Centre National de la Recherche Scientif-
ique (CNRS), the Technische Universita¨t Graz, the Univer-
[7] H. Sakurai, M. Kira, T. Uchida, J. Am. Chem. Soc. 95 (1973)
6826.
[8] (a) R. West, in: Z. Rappoport, Y. Apeloig (Eds.), The Chemistry of
Organic Silicon Compounds, vol. 3, Wiley, Chichester, 2001, p. 541;
(b) H. Tsuji, J. Michl, K. Tamao, J. Organomet. Chem. 685 (2003) 9.
[9] M. Kira, T. Miyazawa, N. Mikami, H. Sakurai, Organometallics 10
(1991) 3793.
´
`
site de Rennes 1, and the Ministere de l’Education
Nationale de l’Enseignement Superieur et de la Recherche
´
(MENESR, Grant for J.S.-T.) is gratefully acknowledged.
We wish to thank the WACKER CHEMIE GMBH (Burghausen,
Germany) for the donation of silane precursors.
[10] (a) K. Tamao, H. Tsuji, M. Terrada, M. Asahara, S. Yamaguchi, A.
Toshimitsu, Angew. Chem. 112 (2000) 3425;
(b) H. Tsuji, Y. Shibano, T. Takahashi, M. Kumada, K. Tamao,
Bull. Chem. Soc. Jpn. 78 (2005) 1334.
[11] (a) E.A. Williams, J.D. Cargioli, P.E. Donahue, J. Organomet.
Chem. 192 (1979) 319;
Appendix A. Supplementary material
(b) E.R.H. Jones, L. Skatterbol, M.C. Whiting, J. Chem. Soc. (1956)
4765.
[12] (a) D.F. Ewing, Org. Magn. Res. 12 (1979) 499;
(b) E. Breitmaier, W. Voelter, Carbon-13 NMR Spectroscopy, third
ed., VCH, Weinheim, 1987, p. 259.
CCDC 613923 contains the supplementary crystallo-
graphic data for 1. These data can be obtained free of
charge
via
http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2007.01.024.
[13] (a) C. Grogger, H. Fallmann, G. Fuerpass, H. Stueger, G. Kickelbick,
J. Organomet. Chem. 665 (2003) 186;
(b) H. Stueger, M. Braunwarth, G. Fuerpass, J. Baumgartner, R.
Saf, Mh. Chem. 137 (2006) 595.
[14] G. Mignani, A. Kra¨mer, G. Pucetti, I. Ledoux, G. Soula, J. Zyss,
Mol. Eng. 1 (1991) 11.
[15] B.G. Ramsey, J. Organomet. Chem. 135 (1977) 307.

J.A. Shaw-Taberlet et al. / Journal of Organometallic Chemistry 692 (2007) 2046–2055
2055
[16] V.F. Traven, Frontier Orbitals and Properties of Organic Molecules,
Ellis Horwood, New York, 1992.
[17] (a) D. Hissink, H. Bolink, J.W. Eshuis, G.G. Malliaras, G.
Hadziioannou, Polym. Prepr. 34 (1993) 721;
[26] A.J.C. Wilson (Ed.), International Tables for X-ray Crystallography,
vol. C, Kluwer Academic Publishers., Dordrecht, The Netherlands,
1992.
[27] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb,
J.R. Cheeseman, J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C.
Burant, J.M. Millam, S.S. Iyengar, J. Tomasi, V. Barone, B.
Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H.
Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene,
X. Li, J.E. Knox, H.P. Hratchian, J.B. Cross, C. Adamo, J.
Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin,
R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma,
G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S.
Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D.
Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G.
Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A.
Liashenko, P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T.
Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challa-
combe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C.
Gonzalez, J.A. Pople, Gaussian 03, Rev. C.02, Gaussian, Inc.,
Wallingford CT, 2004.
(b) G. Hadziioannou, J. Wildeman, J. Herrema, P. Soeteman, D.
Hissink, J. Brouwer, R. Flipse, Polym. Prepr. 32 (1991) 90;
(c) P.F. vanHutten, G. Hadziioannou, R. Bursi, D. Feil, J. Phys.
Chem. 100 (1996) 85.
[18] H.S. Plitt, V. Balaji, J. Michl, Chem. Phys. Lett. 213 (1993) 158.
[19] Recently we were able to show, that different conformers contribute
to the UV absorption spectra of cyclohexasilane derivatives
Si6Me6ꢀnXn: H. Stueger, G. Fuerpass, M. Flock, Lecture presented
at the 38th Organosilicon Symposium, Boulder CO, USA, 2–5 June,
2005.
[20] A.B. Pangborn, M.A. Giardello, R.H. Grubbs, R.K. Rosen, F.J.
Timmers, Organometallics 15 (1996) 1518.
[21] M. Ishikawa, M. Kumada, H. Sakurai, J. Organomet. Chem. 23
(1970) 63.
[22] M. Ishikawa, H. Sugisawa, K. Yamamoto, M. Kumada, J. Organo-
met. Chem. 179 (1979) 377.
[23] Nonius Kappa CCD Software, Nonius B.V., Delft, Netherlands,
1999.
[24] M.C. Altomare, M. Burla, G. Camalli, C. Cascarano, A. Giacovazzo,
A.G.G. Guagliardi, G. Moliterni, R. Polidori, R. Spagna, J. Appl.
Crystallogr. 31 (1998) 74.
[25] G.M. Sheldrick, SHELX97. Program for the Refinement of Crystal
Structures, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[28] R. Ahlrichs, M. Baer, H.P. Baron, R. Bauernschmitt, S. Boecker, M.
Ehrig, K. Eichkorn, S. Elliott, F. Furche, F. Haase, M. Haeser, H.
Horn, C. Huber, U. Huniar, M. Kattannek, C. Koelmel, M. Kollwitz,
K. May, C. Ochsenfeld, H. Oehm, A. Schaefer, U. Schneider, O.
Treutler, M. von Arnim, F. Weigend, P. Weis, H. Weiss, TURBO-
MOLE (Vers. 5.6), Universitaet Karlsruhe, 2002.