Octahedral adducts of dichlorosilane with substituted pyridines: Synthesis, reactivity and a comparison of their structures and29Si NMR chemical shifts

Article abstract of DOI:10.1002/chem.200701412

H₂SiCl₂ and substituted pyridines (Rpy) form adducts of the type all-trans-SiH₂Cl₂·2 Rpy. Pyridines with substituents in the 4- (CH₃, C₂H₅, H ₂C=CH, (CH₃)₃C (CH₃)₂N) and 3-positions (Br) give the colourless solids 1a-f. The reaction with pyrazine results in the first 1:2 adduct (2) of H₂SiCl₂ with an electron-deficient heteroaromatic compound. Treatment of Id and 1e with CHCl₃ yields the ionic complexes [SiH₂(Rpy) ₄]Cl₂·6 CHCl₃ (Rpy = 4-methylpyridine (3d) and 4-ethylpyridine (3e)). All products are investigated by single-crystal X-ray diffraction and ²⁹Si CP/MAS NMR spectroscopy. The Si atoms are found to be situated on centres of symmetry (inversion, rotation), and the Si-N distances vary between 193.3 pm for 1c (4-(dimethylamino)pyridine complex) and 197.3 pm for 2. Interestingly, the pyridine moieties are coplanar and nearly in an eclipsed position with respect to the SiH₂ units, except for the ethyl-substituted derivative 1e, which shows a more staggered conformation in the solid state. Calculation of the energy profile for the rotation of one pyridine ring indicates two minima that are separated by only 1.2 kJmol ^-1 and a maximum barrier of 12.5 kJ mol^-1. The ²⁹Si NMR chemical shifts (δ_iso) range from -145.2 to -152.2 ppm and correlate with the electron density at the Si atoms, in other words with the +I and + M effects of the substituents. Again, compound 1e is an exception and shows the highest shielding. The bonding situation at the Si atoms and the ²⁹Si NMR tensor components are analysed by quantum chemical methods at the density functional theory level. The natural bond orbital analysis indicates polar covalent Si-H bonds and very polar Si-Cl bonds, with the highest bond polarisation being observed for the Si-N interaction, which must be considered a donor-acceptor interaction. An analysis of the topological properties of the electron distribution (AIM) suggests a Lewis structure, thereby supporting this bonding situation.

Full text of DOI:10.1002/chem.200701412

DOI: 10.1002/chem.200701412
Octahedral Adducts of Dichlorosilane with Substituted Pyridines:
Synthesis, Reactivity and a Comparison of Their Structures
29
and Si NMR Chemical Shifts
Gerrit W. Fester,[a] Jçrg Wagler,[a] Erica Brendler,[b] Uwe Bçhme,[a]
Gerhard Roewer,[a] and Edwin Kroke*[a]
Abstract: H2SiCl2 and substituted pyri-
dines (Rpy) form adducts of the type
all-trans-SiH2Cl2·2Rpy. Pyridines with
substituents in the 4- (CH3, C2H5,
H2C=CH, (CH3)3C, (CH3)2N) and 3-po-
sitions (Br) give the colourless solids
1a–f. The reaction with pyrazine results
in the first 1:2 adduct (2) of H2SiCl2
with an electron-deficient heteroaro-
matic compound. Treatment of 1d and
1e with CHCl3 yields the ionic com-
for 2. Interestingly, the pyridine moiet-
ies are coplanar and nearly in an
eclipsed position with respect to the
SiH2 units, except for the ethyl-substi-
tuted derivative 1e, which shows a
more staggered conformation in the
solid state. Calculation of the energy
profile for the rotation of one pyridine
ring indicates two minima that are sep-
arated by only 1.2 kJmolꢀ1 and a maxi-
mum barrier of 12.5 kJmolꢀ1. The
29Si NMR chemical shifts (diso) range
from ꢀ145.2 to ꢀ152.2 ppm and corre-
late with the electron density at the Si
atoms, in other words with the +I and
+M effects of the substituents. Again,
compound 1e is an exception and
shows the highest shielding. The bond-
ing situation at the Si atoms and the
29Si NMR tensor components are ana-
lysed by quantum chemical methods at
the density functional theory level. The
natural bond orbital analysis indicates
ꢀ
polar covalent Si H bonds and very
ꢀ
polar Si Cl bonds, with the highest
bond polarisation being observed for
ꢀ
plexes [SiH
2A
the Si N interaction, which must be
4-methylpyridine (3d) and 4-ethylpyri-
dine (3e)). All products are investigat-
ed by single-crystal X-ray diffraction
and 29Si CP/MAS NMR spectroscopy.
The Si atoms are found to be situated
on centres of symmetry (inversion, ro-
considered a donor–acceptor interac-
tion. An analysis of the topological
properties of the electron distribution
(AIM) suggests
a Lewis structure,
thereby supporting this bonding situa-
tion.
Keywords: hypercoordination
NMR spectroscopy
·
·
·
ꢀ
tation), and the Si N distances vary
quantum chemistry
X-ray diffraction
·
silicon
between 193.3 pm for 1c (4-(dimethyl-
amino)pyridine complex) and 197.3 pm
Introduction
date.[1–4] Most of these chlorosilane–amine adducts are only
stable in the solid state and dissociate quantitatively on
melting, dissolution, or evaporation,[5] which explains why
only limited information about their molecular structure is
available. The adducts described in the literature mainly in-
volve those with unsubstituted or methyl-substituted pyri-
dines as donor molecules.[6]
The tendency of the chlorosilanes SiHnCl4ꢀn to form coordi-
nation compounds with tertiary amines appears to be a
good way of studying their Lewis acidity, although only a
few compounds of this type have been synthesised to
The relative stability of such octahedral complexes de-
pends on the basicity of the Lewis base, the energy differ-
ence between the tetrahedral and the planar structures of
H2SiCl2 as well as the steric demands of the donor mole-
cules and the resulting intramolecular repulsive interactions.
Dismutation reactions of chlorosilanes in the presence of
[a] G. W. Fester, Dr. J. Wagler, Dr. U. Bçhme, Prof. Dr. G. Roewer,
Prof. Dr. E. Kroke
Institut für Anorganische Chemie, TU Bergakademie Freiberg
Leipziger Strasse 29, 09596 Freiberg (Germany)
Fax : (+49)3731-39-4058
[7]
E-mail: kroke@chemie.tu-freiberg.de
[b] Dr. E. Brendler
ꢀ
amine bases are also known. For example, an Si H dismuta-
Institut für Analytische Chemie, TU Bergakademie Freiberg
Leipziger Strasse 29, 09596 Freiberg (Germany)
tion process occurs when SiH3Cl is added to an excess of
3164
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 3164 – 3176

FULL PAPER
pyridine to give
[Eq. (1)]:
a
hexacoordinate silicon complex[3]
pyridine (lutidine) and 2,4,6-trimethylpyridine (collidine),
do not form octahedral silicon complexes, nor does 2-vinyl-
pyridine. We initially expected the formation of octahedrally
coordinated silicon compounds in analogy to the complexa-
tion of H2SiCl2 with 2,4-dimethylpyridine.[6] The steric de-
mands of the 2,6-dimethyl and 2-vinyl substituents may be
responsible for this lack of reactivity.
2 SiH3Cl þ 2 NC5H5 ! SiH2Cl2ðNC5H5Þ2 þ SiH4
ð1Þ
Another route to hexacoordinate SiH2Cl2 derivatives is
based on the decomposition of NMe(SiHCl2)2 into the di-
ACHTREUNG
chlorosilane pyridine complex and a mixture of by-products
The hexacoordinate silicon complexes were characterised
by CP/MAS NMR spectroscopy, single-crystal X-ray diffrac-
tion and Raman spectroscopy. The low solubilities of the
compounds reported herein precluded their characterisation
by solution NMR spectroscopy. As expected, all seven com-
by the action of tertiary amines[5] [Eq. (2)]:
NMeðSiHCl2Þ2 þ 2 NC5H5 ! SiH2Cl2ðNC5H5Þ2
ð2Þ
þ1=nð-SiCl2-NMe-Þn
ꢀ
pounds 1a–f and 2 exhibit a characteristic Si H valence vi-
bration band at 2050–2103 cmꢀ1 in the Raman spectrum (see
These reactions suggest that H2SiCl2 is a suitable Lewis
acid for complex formation with pyridines, tertiary amines
and other Lewis bases, and this result was recently support-
ed theoretically and compared to the Lewis acidity of relat-
ed compounds such as SiCl4, SiH4 and GeF4.[8] This sugges-
tion is further supported by an unexpected redistribution re-
action of trichlorosilane. This redistribution occurs in the
presence of N,N,N’,N’-tetraethylethylenediamine (teeda)
and leads to an octahedral dichlorosilane complex with
SiH2Cl2N2 coordination,[9] as shown in Equation (3):
Table 1). The 29Si NMR chemical shifts are all around d=
Table 1. 29Si CP/MAS NMR spectroscopic data, selected bond lengths
and nACHTERU(GN SiH) resonance bands for compounds 1a–f, 2 and H2SiCl2 (com-
pounds are ordered according to their 29Si NMR shift).
ꢀ
ꢀ
R
diso 29Si
[ppm]
d
[pm]
(Si N)
d
[pm]
G
nACHTREUNG
(SiH)
G
A
]
H2SiCl2
ꢀ11.3
204.8(8)
228.8(1)
228.1(1)
228.5(1)
227.5(1)
226.7(1)
226.9(1)
230.3(1)
227.7(1)
2200[8]
2075
2103
2078
2080
2094
2075
2050
2061
H
3-Br
4-CHCH2
4-CH3
ꢀ145.1
ꢀ145.2
ꢀ147.2
ꢀ148.8
ꢀ148.9
ꢀ149.5
ꢀ151.8
ꢀ152.2
196.9(1)[5]
196.9(1)
195.6(1)
196.6(1)
197.3(1)
196.3(1)
193.1(3)
195.9(1)
1a
1b
1d
2
1 f
1c
1e
4-C
4-[N
4-CH2CH3
ACHTREUNG
AHCTREUNG
Herein we report the systematic synthesis and investiga-
tion of the hexacoordinate compounds H2SiCl
2A
ꢀ145 ppm, which is characteristic for octahedral silicon
compounds.[10] The Si atoms gain electron density with in-
creasing +M and/or +I effects of the substituents at the
pyridine moiety, which leads to a high-field shift of the
29Si NMR signal. This is most obvious for 1c due to the
strong +M effect of the dimethylamino substituent
(Scheme 2).
exhibit various substitution patterns at the donor molecule.
These solid adducts are stable at room temperature and are
directly accessible from dichlorosilane.
Results and Discussion
Synthesis and structural characterisation of 1a–f and 2:
Compounds 1a–f and 2 (Scheme 1) were synthesised in
aprotic solvents such as n-hexane, toluene or THF. There
was no indication for the formation of dichlorosilane/solvent
complexes. 2,6-Disubstituted pyridines, such as 2,6-dimethyl-
Scheme 2. Mesomeric effects of substituents in 4-(dimethylamino)pyri-
dine adduct 1c.
A decrease of the nACHTRE(UNG Si-H) wavenumber correlates with a
ꢀ
decrease of the Si N bond length (Table 1). This is due to
an increase of the electron-donating capacity of the pyridine
Scheme 1. The reaction of dichlorosilane with substituted pyridines.
base, which is highest for the [NAHCTRE(UNG CH3)2] substituent, lowest
Chem. Eur. J. 2008, 14, 3164 – 3176
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3165

E. Kroke et al.
for the Br substituent and intermediate for the alkyl-substi-
tuted pyridines.
As shown by the X-ray structural data (see below), the
pyridine moiety of compound 1c exhibits a quinoid reso-
nance structure unlike the remaining octahedral complexes,
which have bond lengths typical of aromatic pyridine rings.
The 4-ethyl-substituted derivative 1e is the only compound
which obviously does not match the M/I effect induced
trend of the 29Si NMR chemical shifts. This is most likely
caused by the special molecular conformation of 1e (see
below), that is, the torsion angle between the pyridine rings.
A more detailed analysis of the 29Si NMR spectroscopic
data is provided later in this discussion (measurement and
calculation of the 29Si NMR chemical shift tensor).
Figure 2. Molecular structure of 1c·2CHCl3 (ORTEP plot with 50%
probability ellipsoids; most hydrogen atoms omitted for clarity). Selected
bond lengths are summarised in Tables 1and 2.
All (Rpy)2SiH2Cl2 complexes 1a–f crystallise in centro-
symmetric space groups and with half of a molecule as the
asymmetric unit in each case. The molecular structures of
1a, 1b, 1d and 1 f are depicted in Figure 1. The pyridine N-
play a role in achieving a dense molecular packing due to
the modified steric demands of the substituent at the pyri-
dine system. Intermolecular interactions, however, are also
ꢀ
found: the C8 H8 bond points towards chlorine atom Cl1
ꢀ
of
a
neighbouring molecule (Cl3C H!Cl distance of
2.61Š; Table 2).
The common features of the three previously published
complexes[5,6] and the pyridine adducts 1a–f are the coplanar
arrangement of the two pyridine ring systems, the slight out-
ꢀ
of-plane position of the Si H bonds and the orthogonal ar-
rangement of the chlorine atoms with respect to the SiH2
unit (Figure 3, left). This preferred conformation can be in-
terpreted as a result of only small repulsive interactions be-
tween the Si-bonded H atoms and the pyridine H atoms in
ꢀ
ꢀ
the 2-position. Thus, substitution of Si H for Si X moieties
leads to significant out-of-plane positions of all four sub-
stituents, as can easily be seen in the structures of the pyri-
dine adducts of SiCl4.[11,12]
Contrasting the conformational behaviour of the com-
pounds discussed above, the Si atom of complex 1e is not
situated on a centre of inversion and its H-Si-H axis is locat-
ed on a twofold axis of rotation, which means that the pyri-
dine ring systems are not coplanar (Figure 3, right,
Figure 4). Despite this conformational difference, the coor-
ꢀ
dination behaviour of the pyridine ligand (Si N separation)
is similar to those in complexes 1a, 1b, 1d and 1 f.
All complexes have five independent pyridine carbon
atoms in the solid state, although C2,6 and C3,5 are not
always resolved in the 13C CP/MAS NMR spectrum (see Ex-
perimental Section).
Figure 1. Molecular structures of (top to bottom) 1a, 1b, 1d and 1 f
(ORTEP plots with 50% probability ellipsoids; C-bonded hydrogen
atoms omitted for clarity). Selected bond lengths are provided in
Tables 1and 2.
Compound 1b was chosen as a representative example to
analyze the relative stabilities of the different conformations
of the pyridine rings by quantum chemical methods. The tor-
sion angle C5-N1-Si1-Cl1 was varied in 58 steps from 0 to
1908 and the geometry of the molecule was optimised at
every step with only the torsion angle fixed. The results of
this potential energy surface (PES) scan are summarised in
Figure 5. The local minimum at a torsion angle of 608 corre-
sponds to the conformation found in the X-ray structure of
1b. The solid-state structure, however, has a more “perpen-
atoms, silane H-atoms and Cl atoms in these adducts are sit-
uated trans to each other in a pattern that makes these com-
plexes structurally related to the adducts (pyridi-
[5]
ne)2SiH2Cl2,[5] (3-methylpyridine)2SiH2Cl2 and (2,4-dime-
thylpyridine)2SiH2Cl2.[6]
Complex 1c crystallises as the chloroform solvate
1c·2CHCl3 (Figure 2) and the chloroform molecules may
3166
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 3164 – 3176

Octahedral Pyridine Adducts of Dichlorosilane
FULL PAPER
ꢀ
ꢀ
Table 2. Selected bond lengths [pm] for 1a–f and 2 (standard deviation in parentheses). The Si N and Si Cl bond lengths are summarised in Table 1.
1a
1b
1c
1d
1e
1 f
2
ꢀ
Si1 H1A
137(1)
140(2)
144(3)
137(1)
137(1)
141(1)
139(2)
138(1)
ꢀ
Si1 H1B
ꢀ
N1 C1
134.3(1)
134.5(1)
138.0(1)
139.1(1)
138.4(1)
138.5(1)
134.1(2)
134.4(2)
137.5(2)
139.8(2)
139.4(2)
137.5(2)
132.2(2)
134.4(4)
134.7(4)
135.4(5)
140.2(5)
141.6(5)
135.9(5)
134.1(2)
134.7(1)
138.0(2)
139.6(2)
139.8(2)
138.3(2)
149.7(2)
134.1(1)
134.2(1)
138.5(1)
139.5(1)
139.6(1)
138.0(1)
150.1(1)
152.3(1)
133.7(2)
133.7(2)
137.9(2)
138.9(2)
139.7(2)
137.5(2)
152.2(2)
153.2(2)
153.1(2)
153.3(2)
133.1(1)
138.3(1)
138.2(1)
ꢀ
N1 C5
ꢀ
C1 C2
ꢀ
C2 C3
ꢀ
C3 C4
ꢀ
C4 C5
ꢀ
C3 C6
ꢀ
C6 C7
ꢀ
C6 C8
ꢀ
C6 C9
ꢀ
N2 C3
134.4(4)
133.2(1)
133.5(1)
ꢀ
N2 C2
ꢀ
N2 C6
145.5(5)
145.8(4)
ꢀ
N2 C7
Figure 3. View along the N-Si-N axis in molecules 1b (left) and 1e
(right). Ethyl- and vinyl groups as well as C-bonded hydrogen atoms
have been omitted for clarity. The Cl1-Si1-N1-C5) dihedral angles are
76.4 (1)8 (1b) and 70.2 (1)8 (1e). The pyridine planes in 1e are twisted
with respect to each other by 39.67(2)8. The dihedral angles between the
pyridine planes are 08 for the other molecules.
Figure 5. A representation of the PES scan of 1b (top) and figures show-
ꢀ
ing the rotation of one pyridine ring and a view along the N1 Si axis at
different C5-N1-Si1-Cl1 torsion angles (bottom).
Figure 4. Molecular structure of 1e (ORTEP plot with 50% probability
ellipsoids; C-bonded hydrogen atoms omitted for clarity). Selected bond
lengths are provided in Tables 1and 2.
nearly equivalent. Both conformations lead to minimal
steric repulsion between the axial pyridine rings and the
equatorial substituents at the silicon atom.
dicular” conformation, that is, the chlorine atoms are nearly
perpendicular to the plane of the pyridine rings, with torsion
angles of 76.48. The difference between the calculated and
experimentally determined torsion angles can be attributed
to packing effects in the solid state.
There is a very flat energy barrier separating the local
minimum at 608 from the global minimum at 1208. Such a
“staggered” conformation is found for 1e in the solid state.
The energy difference between the rotamers at 608 and 1208
is only 1.2 kJmolꢀ1, which means that these two minima are
The overall energy barrier for rotation of the pyridine
ꢀ1
ꢀ
ring around the Si N bond is about 12.5 kJmol , a value
which is easily reached in solution at room temperature. A
similar rather shallow energy potential has been found for
SiH2Cl2·2Rpy.[5] A global minimum at a torsion angle of
60.48 was calculated, which deviates only slightly from the
value found in the solid state.
ꢀ
ꢀ
The Si Cl bonds are also of similar length and the C C/
ꢀ
C N bond systems of the pyridine ligands are comparable.
Chem. Eur. J. 2008, 14, 3164 – 3176
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3167

E. Kroke et al.
The influence of the dimethylamino group in complex 1c,
ꢀ
however, is striking. The formation of much shorter Si N
ꢀ
bonds causes significant lengthening of the Si Cl bonds and
the +M effect of the dimethylamino substituent leads to
quinoid-type bond lengths in the pyridine system.
Complex 2, which represents the first structurally charac-
terised hexacoordinate silicon complex with a nitrogen-rich
six-membered heterocycle as additional donor, also crystalli-
ses in a centrosymmetric space group (P21/c) with the Si
atom situated on a centre of symmetry (Figure 6). The pyra-
Scheme 3. Dissociation of 3d and 3e in boiling CHCl3 to yield the adduct
[(Rpy)4SiH2]2+
.
ꢀ
Kost et al. have shown that Si X dissociation depends
strongly on a variety of parameters, particularly temperature
(ionisation is enhanced at low temperature), solvent (ionisa-
tion takes places in hydrogen-bond donor solvents) and the
nature of the anion.[13,14] In the present case, the hydrogen-
bond donor solvent CHCl3 stabilises the chloride ion.
Figure 6. Molecular structure of 2 (ORTEP plot with 50% probability el-
lipsoids; C-bonded hydrogen atoms omitted for clarity).
The crystal structure of 3d has already been described by
Bolte et al.[15] therefore it is not discussed further here. The
crystal structure of 3e (Figure 7) also contains half of the di-
ꢀ
ꢀ
zine ring systems are coplanar and even the Si H and Si Cl
bonds are aligned in the same manner as in complexes 1a–f.
Due to the electron deficiency of the pyrazine ligand, the
ꢀ
Si N bond [197.3(1) pm] is significantly longer than in the
pyridine adducts. This slightly stretched interatomic dis-
ꢀ
tance, however, is still notably shorter than the Si N bond
length in the adduct (2,4-dimethylpyridine)2SiH2Cl2
[6]
(201.6 pm) as a result of the steric hindrance due to the
methyl group in the 2-position.
Reactivity: As mentioned in the introduction, most hyper-
coordinate Lewis base adducts of chlorosilanes are only
stable in the solid state and dissociate upon dissolution or
heating (melting). A simple method to investigate the rela-
tive stabilities of SiH2Cl2·2Rpy adducts involves exchange
reactions using pyridines with different substituents. The ob-
served exchange of the pyridine ligands upon treatment of
the complex H2SiCl2·2py with 4-(dimethylamino)pyridine
suggests that 1c is more stable:
Figure 7. Structure of the dication [(4-Et-py)4SiH2]2+ in
3e·6CHCl3 (ORTEP plot with 50% probability ellipsoids; C-bonded hy-
drogen atoms omitted for clarity). Selected bond lengths and bond angles
are provided in Table 3.
a crystal of
cation [(4-ethylpyridine)4SiH2]2+ as well as a chloride ion
and three chloroform molecules in the asymmetric unit. In
contrast to the structure of 1c, the chloroform molecules
solvate the chloride anion in the crystal of 3e. Two of these
chloroforms are rotationally disordered around their C H
bonds, which are directed towards the chloride ion. The
same two molecules as well, as their symmetry equivalents,
H2SiCl2 Á 2 py þ 2ð4-DMAPÞ ! H2SiCl2 Á 2 ð4-DMAPÞ þ 2 py
ð4Þ
ꢀ
Exchange of the pyridine ligands was also observed in the
absence of any other substituted pyridine ligands. Thus, the
extraction of 1d and 1e with boiling CHCl3 caused the for-
mation of dicationic silicon complexes 3d and 3e, respec-
ꢀ
surround one ethyl group of the cation (C13 C14), which is
necessarily also disordered due to the varying steric de-
mands of the disordered solvent molecules. It is worth men-
ꢀ
tively, where both Si Cl bonds have been substituted by the
ꢀ
respective pyridine molecules (Scheme 3). The chloride
counterions are stabilised by chloroform molecules. In con-
trast, the extraction of 1a–c and 1 f with boiling CHCl3 does
tioning that the other ethyl group (C6 C7) seems unaffected
even though some slightly disordered CHCl3 molecules are
found in close proximity (see Table 3 for bond lengths and
angles of 3d and 3e).
ꢀ
not cause any ionisation of the Si Cl bonds. Single crystals
of 3d and 3e suitable for X-ray structure analyses were ob-
tained (see Experimental Section). The extraction of 2 with
boiling CHCl3 or CH3CN causes the complex to decompose.
The overall configuration of the dication, the Si atom of
which is located on a centre of symmetry, is related to the
structures of the cations in the compounds [(4-methylpyridi-
3168
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 3164 – 3176

Octahedral Pyridine Adducts of Dichlorosilane
FULL PAPER
Table 3. Selected bond lengths [pm] and angles [8] for 3d and 3e (stan-
dard deviations in parentheses).
3d
3e
ꢀ
Si1 N1
196.0(1)
196.0(1)
141(2)
196.4(2)
196.3(2)
138(2)
ꢀ
Si1 N2
ꢀ
Si1 H1A
ꢀ
N1 C1
134.3(1)
134.5(1)
138.0(1)
139.1(1)
138.4(1)
138.5(1)
149.8(2)
–
134.8(1)
134.5(1)
138.0(2)
137.7(2)
139.5(2)
139.1(2)
149.5(2)
–
134.0(3)
134.8(3)
137.5(2)
139.8(2)
139.4(2)
137.5(2)
150.7(3)
150.6(4)
133.7(3)
134.9(3)
137.3(4)
139.2(4)
137.8(4)
136.9(3)
153.9(4)
146.6(7)
90.5(9)
ꢀ
N1 C5
ꢀ
C1 C2
ꢀ
C2 C3
ꢀ
C3 C4
ꢀ
C4 C5
ꢀ
C3 C6
ꢀ
C6 C14
ꢀ
N2 C7
Figure 8. Top: 29Si CP/MAS spectrum of 1e calculated using the principal
ꢀ
N2 C11
ꢀ
C10 C11
components given in Table 4; bottom: spectrum at
1.25 kHz.
a spin rate of
ꢀ
C7 C8
ꢀ
C8 C9
ꢀ
C9 C10
ꢀ
C9 C12
ꢀ
cording to the Herzfeld–Berger convention.[18,19] The 29Si
CP/MAS spectrum of 1e is given in Figure 8 as an example.
We also calculated the 29Si NMR principal components by
the GIAO method based on the geometries of the crystal
structures (see Table 4). The observed and calculated spans
are quite large in comparison with those for other hexacoor-
dinate Si complexes. Figure 9 shows the orientation of the
principal components in the molecular structure of com-
pound 1b.
C12 C13
H1A-Si1-N1
H1A-Si1-N2
89.2(7)
89.4(7)
90.6(9)
ne)4SiH2]2+, [(3-methylpyridine)4SiH2]2+, [(3,4-dimethylpyri-
dine)4SiH2]2+, [(3,5-dimethylpyridine)4SiH2]2+ and [(pyridi-
ne)4SiH2]2+ (chloride and/or bromide salts; octahedral coor-
dination, trans H-Si-H, four
pyridine N-atoms on equatorial
Table 4. 29Si MAS NMR spectroscopic data and results of GIAO calculations (B3LYP/6-311+G
ACHTRE(UNG 2d,p)) of the
sites).[15–17] Irrespective of the
synthesis path described above,
single crystals of the hexacoor-
dinate complexes 1a–c and 1 f
were obtained directly upon ex-
29Si NMR shifts of compounds 1a–f and 2.
[a]
Molecule
diso
d11
d22
d33
W[b]
k[b]
1a
exp
calc
exp
calc
exp
calc
exp
calc
exp
calc
exp
calc
exp
calc
ꢀ145.4
ꢀ159.8
ꢀ147.2
ꢀ165.0
ꢀ152.1
ꢀ173.1
ꢀ148.8
ꢀ164.3
ꢀ152.3
ꢀ166.3
ꢀ149.6
ꢀ165.9
ꢀ149.1
ꢀ160.4
ꢀ47.5
ꢀ74.3
ꢀ51.0
ꢀ87.4
ꢀ75.7
ꢀ106.4
ꢀ51.8
ꢀ83.4
ꢀ66.1
ꢀ95.2
ꢀ49.5
ꢀ83.7
ꢀ49.0
ꢀ74.0
ꢀ185.9
ꢀ187.7
ꢀ187.3
ꢀ190.5
ꢀ180.9
ꢀ195.0
ꢀ185.1
ꢀ191.5
ꢀ185.1
ꢀ186.7
ꢀ189.3
ꢀ192.3
ꢀ187.8
ꢀ184.9
ꢀ202.8
ꢀ217.4
ꢀ203.3
ꢀ217.1
ꢀ199.7
ꢀ217.8
ꢀ209.5
ꢀ217.9
ꢀ205.7
ꢀ216.9
ꢀ210.0
ꢀ221.6
ꢀ210.5
ꢀ222.4
155.3
143.1
152.2
129.7
124.0
111.3
157.7
134.5
139.6
121.6
160.5
138.0
161.5
148.4
ꢀ0.8
ꢀ0.6
ꢀ0.8
ꢀ0.6
ꢀ0.7
ꢀ0.6
ꢀ0.7
ꢀ0.6
ꢀ0.7
ꢀ0.5
ꢀ0.7
ꢀ0.6
ꢀ0.7
ꢀ0.5
1b
1c
1d
1e
1 f
2
ꢀ
traction with CHCl3. The Cl3C
H!Cl contacts to the chloride
ion in complexes 3d and 3e
(approx. 245 pm) are shorter
ꢀ
than the Cl3C H!Cl distance
between the chloroform mole-
cule in 1c and the Si-bonded Cl
atom (261pm) because of the
ꢀ
anionic charge. The short Si N
bonds in 1c and the resulting
[a] Chemical shift in the solid state. [b] Herzfeld–Berger convention, W=d11ꢀd33, k=3(d22ꢀdiso)/W.
C
ꢀ
longer Si Cl bonds, which rep-
resent a step on the way to
ꢀ
base-supported Si Cl dissociation and chloride ion forma-
tion, can be related to the incorporation of the chloroform
The principal components of the investigated compounds
1 point along the E-Si-E (E=Cl, H, N) bond axes, with the
ꢀ
molecule in the structure of 1c.
highest shielding being observed in the direction of the Si
ꢀ
N bonds (d33) and the lowest shielding along the Si Cl
Measurement and calculation of the 29Si NMR chemical
shift tensor: The 29Si NMR chemical shift tensors were de-
termined in order to get a better understanding of the
29Si NMR shielding of these compounds. The principal com-
ponents, and subsequently the isotropic chemical shift, the
span (W; anisotropy) and skew (k) of the tensor were ex-
tracted from spinning side-band 29Si CP/MAS spectra ac-
bonds (d11). Both the calculated and the experimental values
of the skew range between ꢀ0.5 and ꢀ0.9, which means that
ꢀ
the shielding in the direction of the Si H bonds (d22) is only
slightly smaller than d33. The silicon nucleus is therefore
strongly shielded in the direction of the hydrogen and pyri-
dine substituents and less shielded in the direction of the
ꢀ
Si Cl bonds. The span decreases for both the experimental
Chem. Eur. J. 2008, 14, 3164 – 3176
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3169

E. Kroke et al.
Figure 10. Molecular representation of 1b showing the BCPs (small black
dots on the bond paths). The atomic spheres are drawn with arbitrary
radii.
at the BCPs. Table 5 shows these properties for the BCPs
that connect the silicon atoms with their surrounding ligands
and substituents in the compounds under investigation.
Figure 9. Orientation of the principal shielding tensor components in 1b.
2
Table 5. Electron density (1), Laplacian (5 1) and bond ellipticity (e) at
selected BCPs in 1a–f and 2.
2
1
5 1
e
ꢀ3
ꢀ5
and the calculated tensors nearly in the same order: 1 f >
1d > 1a > 1b > 1e > 1c (exp. values). Compound 1c has
a noticeably smaller span than the other complexes 1, which
we attribute to the quinoid-like resonance structure of this
derivative (see Scheme 2). The differences in the spans of
the complexes are due to changes in both d11 and d33, al-
though d11 seems to have a higher contribution to W. The
pyrazine derivative has the highest span and a skew of ꢀ0.7
as a result of two directions with higher shielding, similar to
the pyridine derivatives.
[eŠ
]
ACHTRE[UNG eŠ ]
ꢀ
Si H
1a
1b
1c
1d
1e
1 f
2
1.035
0.983
0.920
1.024
1.027
0.998
1.019
5.995
4.802
3.424
5.790
5.860
5.154
5.590
0.029
0.032
0.036
0.029
0.030
0.030
0.029
ꢀ
Si Cl
1a
1b
1c
1d
1e
1 f
2
.320
0.4311
0.428
0.413
0.433
0.432
0.438
0.443
0.440
There are some deviations between the experimental and
calculated tensor components, with the calculated span
being smaller than the experimental one. The highest devia-
tion between calculated and measured isotropic shift values
(diso) is 22 ppm. A comparison between the calculated and
experimental principal components shows a good accord-
ance for d22, but significant deviations for d33 and especially
d11, the components which are nearly perpendicular to the
1.288
1.128
1.427
1.388
1.463
1.432
0.418
0.447
0.431
0.419
0.413
0.416
ꢀ
Si N
1a
1b
1c
1d
1e
1 f
2
0.513
0.530
0.563
0.519
0.528
0.522
0.508
4.927
5.120
5.5610.1
4.946
5.057
4.990
0.194
0.165
[20,21]
ꢀ
Si H bonds. It has been shown previously
that silicon-
29
bound hydrogen atoms cause inaccuracies in 29Si NMR shift
calculations, and this problem has not yet been solved theo-
retically.
0.185
0.176
0.175
0.194
4.877
Densityfunctional theory(DFT) calculations : Quantum
chemical calculations were performed to obtain a better in-
sight into the bonding features of the compounds under in-
vestigation. Topological analysis of the electron-density dis-
tribution is a powerful tool for that purpose, and this analy-
sis can be carried out using the atoms-in-molecules theory
(AIM) developed by Bader and others.[22–25] This method
partitions the electron density of a molecule 1(r) into indi-
vidual non-overlapping atomic fragments by rigorously de-
fined interatomic surfaces.[23]
The bond critical points (BCPs) between the atoms of the
molecules 1a–f and 2 represent the topology one would
expect for a classical Lewis structure. Figure 10 shows one
such example. A more detailed analysis is only possible,
however, by looking at the properties of the electron density
2
The graphical representation of the Laplacian 5 1 and
the electron density maps (1(r)) in Figure 11 shows that
there is very low electron density at the BCPs between Si
and Cl and slightly positive values of the Laplacian, which
suggests a predominantly ionic interaction. The graphical
representation of the Laplacian, with its nearly spherical
charge concentration around the chlorine atom, confirms
this assumption. The remarkable bond ellipticity at the
BCPs between Si and Cl hints at some p-donation from lone
pairs at chlorine atoms into unoccupied orbitals at silicon.
However, if we classify the interaction between Si and Cl as
ionic, it would be unreasonable to designate a “partial
double-bond character” to these bonds. A closer look at
3170
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 3164 – 3176

Octahedral Pyridine Adducts of Dichlorosilane
FULL PAPER
Figure 12. Contour map of 1 at the BCP between Si and Cl. The plane of
ꢀ
the plot is perpendicular to the Si Cl axis and shows the elliptical defor-
mation of the electron density into the SiCl2H2 plane.
types are the higher positive value of the Laplacian (see
Table 6) and the small but clearly visible charge concentra-
tion at the nitrogen atom in the former, which reflects the
donor–acceptor interaction between N and Si. The results of
the AIM analysis suggest that the canonical form C is the
best description of the bonding features between silicon and
the surrounding ligands and substituents in compounds of
type 1 (Scheme 4). Similar conclusions have been drawn
from experimental and theoretical charge-density studies in
hexacoordinate silicon complexes with an [SiO2N2F2] coordi-
nation framework.[27]
An alternative description of the chemical bonding be-
tween the silicon atom and its surrounding atoms is provid-
ed by the natural bond orbital (NBO) analysis. This method,
developed by Weinhold et al.,[28] uses the one-electron
matrix as a starting point to find the best Lewis structure of
the molecule. Bond polarisations, hybridisations of the
atoms, partial charges and the electron configuration of the
atoms can all be calculated by this method, which has been
described previously in detail.[28–30]
The four valence structures of 1b depicted in Scheme 4
were investigated by the NBO method. The valence struc-
ture with six covalent bonds from the silicon atom, which
corresponds to an sp3d2 hybridisation (A), has 96.31%
Lewis character, in other words the electrons are located to
a degree of 96.31% in localised hybrid orbitals. The other
valence structure with four covalent bonds to hydrogen and
chlorine, which has an sp2d configuration at the central sili-
con atom, has 97.56% Lewis character (B). The remaining
valence structures with covalent bonds to the hydrogen and
the nitrogen atoms (C) and solely to the hydrogen atoms
(D) have 97.40% and 97.34% Lewis character, respectively.
Thus, the valence structures B–D represent similarly good
descriptions for this type of compound. Further valence
Figure 11. Representation of the topological properties of 1b in different
planes: SiH2Cl2 (top), SiN2Cl2 (middle) and SiH2N2 (bottom). Left
2
column: Laplacian of the electron density. Positive values of 5 1 are
drawn with dashed lines and represent regions of charge depletion; nega-
2
tive values of 5 1 are drawn with solid lines and represent regions of
charge concentration. Right column: electron density. Selected bond
paths and bond critical points are included in the figures. The contour
values for both representations in atomic units are: 0.001, 0.002, 0.004,
0.008, 0.02, 0.04, 0.08, 0.2, 0.4, 0.8, 2, 4, 8, 20, 40, 80, 200, 400 and 800.
electron density distribution at the BCP between Si and Cl
shows that the electronic charge is preferentially accumulat-
ed in the SiCl2H2 plane (see Figure 12). The charge density
of the hydrogen atom is polarised towards the positively
charged silicon atom, which leads to a notable charge con-
ꢀ
centration at the Si H bond axis and higher electron density
at the BCPs. This can be interpreted in terms of a polar co-
valent bond, although the positive value of the Laplacian
would suggest otherwise. A closer examination of the posi-
tion of the BCP in this case shows that this point is located
2
close to the nodal surface in 5 1, where the atomic basins
ꢀ
of Si and H exhibit an opposite behaviour with respect to
the sign of the Laplacian of 1. Such interactions have been
classified as “intermediate interactions” and range from
closed-shell to shared interactions.[26]
structures with ionic Si H interactions are imaginable but,
due to the lower bond polarity of these bonds, such valence
structures are less probable and will not be considered here.
All four valence structures are discussed in the following
paragraphs. Structure A has a large non-Lewis character
(3.69%, 5.97 e), which makes this structure less probable.
The Si hybridisation can be denoted as sp3d2 with ideal par-
ꢀ
The Si N bonds are polar with considerable ionic contri-
bution to the bonding, with similar values for 1 as for the
ꢀ
Si Cl bonds. The main differences between these two bond
Chem. Eur. J. 2008, 14, 3164 – 3176
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3171

E. Kroke et al.
Table 6. Results of the NBO analysis for 1b and H2SiCl2.[a]
ꢀ
The longer Si Cl bond requires
spatially more extended d-orbi-
Molecule/bond
Occ.
% Si
AO of Si [%]
p
AO of E [%]
p
s
d
s
d
ꢀ
tals at Si than the short Si H
H2SiCl2
bond. Nevertheless, sp2d hy-
bridisation represents a suitable
bonding model for this Lewis
ꢀ
Si Cl
ꢀ
Si H
1.99
1.97
26.71
42.75
21.98
28.15
75.67
70.84
2.35
1.02
20.19
99.88
79.33
0.12
0.48
–
1b (valence structure A)
ꢀ
structure. The Si Cl bonds are
strongly polarised toward the
Cl atom (83.08%), although the
Si H bonds are less polarised
(64.24% H). The pz orbital at
Si is occupied by only 0.40 e
ꢀ
Si Cl
ꢀ
Si H
1.88
1.79
1.90
15.86
32.61
9.91
15.69
23.58
16.16
50.0
50.0
50.0
34.31
26.42
33.84
20.61
99.33
32.71
79.25
0.67
67.28
0.14
–
0.02
ꢀ
Si N
1b (valence structure B)
ꢀ
ꢀ
Si Cl
ꢀ
Si H
1.90
1.87
16.92
35.76
20.73
33.94
50.0
50.0
29.27
16.06
20.59
99.33
79.27
0.67
0.14
–
1b (valence structure C)
ꢀ
Si N
ꢀ
Si H
1.91
1.84
10.64
35.01
21.37
29.42
50.0
50.0
28.63
20.58
32.70
99.33
67.28
0.67
0.02 and is suitable for donor–ac-
ceptor interactions with the
1b (valence structure D)
lone pairs of the
N atoms,
ꢀ
Si H
1.98
40.62
49.64
50.0
0.36
99.33
0.67
–
which are occupied by 1.73 e.
The second-order perturbation
theory analysis gives a stabiliz-
ing effect of 502 kJmolꢀ1 for
[a] Occ: occupancy of the bond; % Si: share of the atomic orbitals of Si in the molecule orbital; AO: atomic
orbitals that contribute to the bonds
ꢀ
each N Si interaction, although
this value must not be interpreted as the bond energy.
The hybridisation of the silicon atom in structure C is also
sp2d. The combination of s, px, pz and dz2 orbitals produces
ꢀ
four hybrid orbitals in the xz plane. The Si N bonds are
ꢀ
strongly polarised toward the N atom (89.36%) and the Si
H bonds are less polarised (64.99% H). The py orbital at Si
is occupied by 0.58 e and this orbital is suitable for donor–
acceptor interactions with the lone pairs of the Cl atoms,
which are occupied by 1.61 e. The second-order perturbation
theory analysis gives a stabilizing effect of 847 kJmolꢀ1 for
Scheme 4. Possible Lewis structures for compounds of type 1.
ꢀ
each Cl Si interaction.
The hybridisation of the silicon atom in structure D can
be categorised as sp. This is indeed found for these bonds,
with 49.64% s, 50% p and a minor share of d-character in
tition of the hybrid orbitals of 16.7% s, 50% p and 33.3% d.
The only major deviation from this ideal state is observed
ꢀ
ꢀ
for the Si H bonds, which have 23.58% s-character at Si.
the hybrid orbitals at Si. The Si H bonds in this valence
structure are only weakly polarised (40.62% Si). All other
ꢀ
ꢀ
The shorter Si H bond has a higher s-character than the Si
ꢀ
ꢀ
ꢀ
ꢀ
Cl and Si N bonds. All three bond types (Si Cl, Si H, Si
N) are occupied by nearly two electrons. Information about
the bond polarity can be obtained from the percentage of Si
in the bond orbital. A non-polar covalent bond has percen-
tages close to 50% for both atoms, whereas a share of
orbital interactions in this structure must be treated with
second-order perturbation theory. The N Si interaction has
ꢀ
already been discussed in the previous section, and each in-
teraction between Cl and Si gives a stabilizing effect of
864 kJmolꢀ1 if it is treated as a perturbation of this valence
structure.
The natural charges of 1b and of selected reference mole-
cules are shown in Table 7. The charge of the silicon atom
increases from 1.02 to 1.17 upon complex formation. A simi-
ꢀ
32.61% Si for the Si H bond indicates a polar bond where
the electron density is shifted towards the H atom. The Si
Cl bond, which has an Si contribution of 15.86%, is even
more polar. The highest polarity in A is observed for the
ꢀ
ꢀ
Si N interaction (90.09% N and 9.91% Si). This interaction
is a borderline case which should be considered as a donor–
acceptor interaction.
Table 7. Natural charges of the atoms in 1b and selected reference mole-
cules.
The Si-atom hybridisation in B can be categorised as sp2d.
The combination of s, px, py and dx2ꢀy2 orbitals produces
hybrid orbitals in the xy plane. Ideal sp2d-hybridisation in-
volves 25% s, 50% p and 25% d character. There are devia-
tions from the ideal bonding state in this structure since
there is a higher proportion of s character (33.94%) in the
Molecule
Atom
Natural charge
pyridine
H2SiCl2
N
ꢀ0.46
1.02
ꢀ0.35
ꢀ0.16
1.17
ꢀ0.55
ꢀ0.24
ꢀ0.53
Si
Cl
H
Si
Cl
H
N
1b
ꢀ
Si H bond (Table 6) and a higher proportion of d character
ꢀ
(29.27%) in the Si Cl bond. These differences can be corre-
lated with the different bond lengths, as discussed above.
3172
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 3164 – 3176

Octahedral Pyridine Adducts of Dichlorosilane
FULL PAPER
lar effect has already been discussed for antimony, tin and
silicon complexes.[5,8,31] The negative charge on the pyridine
nitrogen atom also increases upon complex formation. Fur-
thermore, the chlorine and hydrogen atoms also bear higher
negative charges in complex 1b than in H2SiCl2. These
changes in the charge distribution are evidence for a bond-
ing situation in the complex that involves generally more
polar bonds than in the starting molecule H2SiCl2. This as-
sumption is confirmed by the bond polarities shown in
Experimental Section
Caution: Handling of dichlorosilane is not trivial due to its low boiling
point of 8.48C and oxidative and hydrolytic sensitivity. All reactions were
carried out under dry argon using Schlenk techniques. Solvents were
dried and purified by standard methods. CP/MAS NMR spectra were re-
corded with a Bruker Avance 400 MHz WB spectrometer by using a 7-
mm probehead with zirconia rotors and KelF inserts operating at 400.23,
100.61 and 79.51 MHz for 1H, 13C and 29Si, respectively. Chemical shifts
are reported in ppm relative to TMS. Raman spectra were recorded with
a Bruker RFS 100/S instrument equipped with an Nd/YAG Laser. X-ray
single crystal structure analyses were carried out with a Bruker Nonius
X8 APEX2 CCD diffractometer. Elemental analysis (determination of
the chlorine content of product 1c) was performed by hydrolysis of
0.15 g of 1c in 100 mL of dilute sodium hydroxide solution followed by
chloride quantification by ion chromatography (Dionex, ICS-2000;
eluent: 22 mm KOH; column: AS11 HC, electrical conductivity measure-
ment).
ꢀ
Table 6. The Si Cl bond has 26.71% Si character in H2SiCl2,
and this value decreases to 15.86% and 16.92% for the va-
lence structures A and B, respectively. A similar effect is ob-
ꢀ
served for the Si H bond.
Conclusion
The structures were solved by direct methods and refined by full-matrix
least-squares methods. All non-hydrogen atoms were refined anisotropi-
cally. Carbon-bonded hydrogen atoms were placed in idealised positions
and refined isotropically (riding model). Si-bonded hydrogen atoms were
found by analysis of the residual electron density and refined without
bond length restraints. Structure solution and refinement of F2 against all
reflections were carried out with the software SHELXS-97 and
SHELXL-97 (G. M. Sheldrick, Universität Gçttingen (1986–1997)).
Structure determination and refinement data for the crystal structures
Hexacoordinate dichlorosilane/pyridine adducts have been
synthesised in various aprotic solvents by the direct reaction
of H2SiCl2 with pyridine. The first example of an
H2SiCl2·2Rpy compound bearing non-coplanar pyridine
rings has been found, although a coplanar arrangement of
the pyridine ligands seems to be the most typical conforma-
tion in the solid state. Quantum chemical analysis demon-
strates that both coordination modes may be favourable.
Some of these pyridine adducts (those bearing 4-methyl-
and 4-ethylpyridine) have been shown to undergo ligand re-
distribution when extracted with hot chloroform to yield the
presented in this paper are summarised in Tables 8,
9 and 10.
CCDC 621840 (1a), 621841 (1b), 621839 (1c), 634403 (1d), 621844 (1e),
621843 (1 f), 621845 (2), 621846 (3d) and 621842 (3e) contain the supple-
mentary 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.
The Quantum chemical calculations were carried out using the GAUSSI-
AN 03 program suite.[32] The solid-state geometries obtained from X-ray
structure analyses were used for the calculations without further optimi-
sation. The calculations were performed at the density functional theory
level (DFT), using Beckeꢁs three-parameter hybrid exchange functional
and the correlation functional of Lee, Yang and Parr (B3LYP),[33,34] with
the 6-311+G
The AIM analyses[22] were performed at the B3LYP/6-311+G
AHCTRE(UGN 2d,p) level
with the geometries obtained from the X-ray structure analyses.
hexacoordinate siliconium salts [H2SiACHTER(UGN RPy)4]Cl2, the anion
of which is stabilised by chloroform molecules.
The 29Si CP/MAS NMR spectra of the adducts
H2SiCl2·2Rpy reveal large spans for the shielding tensors of
their octahedrally coordinated silicon nuclei, and GIAO cal-
culations have provided an insight into the directions of the
principal components [(11), (22) and (33)] of the shielding
tensors, which point almost along the Cl-Si-Cl, H-Si-H and
N-Si-N axes, respectively. The highest shielding is observed
(2d,p) basis set for all atoms.[35–37]
ACHTREUNG
The wavefunction files for the AIM analysis were generated in Cartesian
coordinates with a basis set containing 6d functions (option “6D 10F” in
Gaussian 03). The electron-density topology was analysed by using the
programs AIM2000[38] and Xaim.[39]
The NBO analyses were performed with NBO 3.0.[28] The different va-
lence structures A–D were generated with the “CHOOSE” option in the
NBO programme.
ꢀ
ꢀ
in the direction of the Si H and Si N bonds, and the shield-
ꢀ
ing is considerably lower in the direction of the Si Cl bonds.
Quantitative descriptions of those shielding tensors, howev-
er, are difficult due to general problems with the modelling
of H Si bond influences on 29Si NMR properties, which
ꢀ
Relaxed potential energy surface (PES) scans were performed with the
Opt=ModRedundant utility in Gaussian 03 with B3LYP/6-31G(d). This
option includes the specification of redundant internal coordinates. In
these cases, a specific torsion angle was changed in 58 steps. The geome-
try of the molecule was completely optimised in every step whilst restrict-
ing only the torsion angle to the specified value. This method allows
access to a defined section of the potential energy surface.
have not yet been overcome.
Four possible valence structures A–D have been investi-
gated with the NBO method, with the valence structures B,
C and D being equally good descriptions of the bonding sit-
uation. The NBO analysis reveals that these structures con-
ꢀ
ꢀ
tain polar covalent Si H bonds, strong polar Si Cl bonds,
and that the highest bond polarisation is observed for the
The principal components of the NMR shielding tensor were extracted
from the spectra using the HB-MAS program (D. Fenzke, Universität
Leipzig 1989).
ꢀ
Si N interaction, which therefore has to be considered as a
donor–acceptor interaction. Analysis of the topological
properties of the electron density distribution (AIM) sug-
gests that the Lewis structure C is the best description for
the bonding situation in molecules of the type
H2SiCl2·2Rpy.
NMR shielding tensors were calculated by the Gauge-Independent
Atomic Orbital method (GIAO)[40] at the B3LYP/6-311+G
ACHTRE(UGN 2d,p) level
of theory with the geometries obtained from the X-ray structure analyses.
Calculated absolute shielding values were converted to relative shifts (d)
by calculating the shielding of tetramethylsilane at the same level of
theory.
H2SiCl2 (Degussa), 4-methylpyridine (Alfa Aesar), 4-ethylpyridine
(Merck), 3-bromopyridine (ABCR), 4-tert-butylpyridine (Fluka), 4-vinyl-
Chem. Eur. J. 2008, 14, 3164 – 3176
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3173

E. Kroke et al.
Table 8. Crystal data and structure refinement for 1a, 1b and 1c·2CHCl3.
1a
1b
1c·2CHCl3
empirical formula
formula weight
T [K]
C10H10Br2Cl2N2Si
417.01
93(2)
C14H16Cl2N2Si
311.28
93(2)
C16H24Cl8N4Si
584.08
93(2)
l [Š]
0.71073
monoclinic
C2/c
18.8249(8)
5.6038(2)
14.6931(6)
90
117.762(2)
90
1371.57(10)
4
2.019
6.365
808
0.71073
monoclinic
P21/n
7.0686(5)
8.1304(6)
13.5961(10)
90
101.653(2)
90
765.27(10)
2
1.351
0.490
324
0.71073
triclinic
P1
crystal system
space group
a [Š]
b [Š]
c [Š]
¯
7.1762(10)
8.9359(12)
10.6509(15)
113.895(6)
93.773(6)
94.148(6)
619.42(15)
1
1.566
0.970
298
0.28”0.10”0.04
2.86–26.99
a [8]
b [8]
g [8]
V [Š3]
Z
1calc [Mgmꢀ3
]
absorption coefficient [mmꢀ1
(000)
crystal size [mm3]
]
F
A
0.67”0.12”0.06
3.84–36.99
0.30”0.22”0.05
3.58–27.50
q range for data collection [8]
index ranges
reflections collected
ꢀ29ꢁhꢁ31, ꢀ9ꢁkꢁ9, ꢀ24ꢁlꢁ23
ꢀ9ꢁhꢁ9, ꢀ9ꢁkꢁ10, ꢀ17ꢁlꢁ17
ꢀ9ꢁhꢁ9, ꢀ11ꢁkꢁ10, 0ꢁlꢁ13
11221
5584
6384
independent reflections, Rint
completeness to qmax [%]
absorption correction
max./min. transmission
data/restraints/parameters
final R indices [I>2s(I)]
R indices (all data)
3485, 0.0222
99.5
semiempirical
0.6803/0.1524
3485/0/83
R1 =0.0202, wR2 =0.0496
R1 =0.0286, wR2 =0.0513
1.045
1.175, ꢀ1.031
1744, 0.0336
99.8
2644, 0.0308
98.7
semiempirical
0.9622/0.7004
4086/0/137
R1 =0.0489, wR2 =0.0962
R1 =0.0926, wR2 =0.1047
0.882
0.582, ꢀ0.435
semiempirical
0.9759/0.8155
1744/0/92
R1 =0.0304, wR2 =0.0644
R1 =0.0477, wR2 =0.0683
0.998
goodness-of-fit on F2
ꢀ3
largest diff. peak and hole [eŠ
]
0.292, ꢀ0.196
Table 9. Crystal data and structure refinement for 1d, 1e and 1 f.
1d
1e
1 f
empirical formula
formula weight
T [K]
C12H16Cl2N2Si
287.26
90(2)
C14H20Cl2N2Si
315.31
90(2)
C18H28Cl2N2Si
371.41
153(2)
l [Š]
0.71073
monoclinic
P21/n
5.9012(7)
8.0579(9)
14.8296(18)
90
0.71073
monoclinic
C2/c
11.8426(4)
9.2001(3)
14.3452(4)
90
0.71073
monoclinic
C2/c
19.6243(7)
8.0608(2)
13.7150(4)
90
crystal system
space group
a [Š]
b [Š]
c [Š]
a [8]
b [8]
105.374(6)
90
679.93(14)
2
1.403
0.545
99.199(2)
90
1542.85(8)
4
1.357
0.487
111.674(2)
90
2016.16(11)
4
1.224
0.383
g [8]
V [Š3]
Z
1 [Mgmꢀ3
]
absorption coefficient [mmꢀ1
(000)
crystal size [mm3]
]
F
A
300
664
792
0.65”0.38”0.25
2.82–34.00
0.50”0.40”0.25
2.82–48.00
0.43”0.35”0.02
2.23–30.00
q range for data collection [8]
index ranges
reflections collected
ꢀ9ꢁhꢁ9, ꢀ12ꢁkꢁ12, ꢀ23ꢁlꢁ22 ꢀ24ꢁhꢁ24, ꢀ11ꢁkꢁ19, ꢀ29ꢁlꢁ29 ꢀ27ꢁhꢁ27, ꢀ11ꢁkꢁ11, ꢀ18ꢁlꢁ19
15534
24634
15622
independent reflections, Rint
completeness to qmax [%]
absorption correction
max./min. transmission
data/restraints/parameters
final R indices [I>2s(I)]
R indices (all data)
2691, 0.0512
96.9
semiempirical
0.8758/0.7130
2691/0/84
R1 =0.0536, wR2 =0.1736
R1 =0.0562, wR2 =0.1751
1.161
1.167, ꢀ0.669
7361, 0.0242
99.7
semiempirical
0.8879/0.7952
7361/0/92
R1 =0.0308, wR2 =0.0842
R1 =0.0490, wR2 =0.0899
1.046
0.659, ꢀ0.328
2943, 0.0298
100.0
semiempirical
0.9924/0.9072
2943/0/110
R1 =0.0328, wR2 =0.0774
R1 =0.0538, wR2 =0.0839
1.039
0.358, ꢀ0.236
goodness-of-fit on F2
ꢀ3
largest diff. peak and hole [eŠ
]
3174
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 3164 – 3176

Octahedral Pyridine Adducts of Dichlorosilane
FULL PAPER
Table 10. Crystal data and structure refinement for 2, 3d·6CHCl3 and 3e·6CHCl3.
2
3d·6CHCl3
3e·6CHCl3
empirical formula
formula weight
T [K]
C8H10Cl2N4Si
261.19
90(2)
C30H36Cl20N4Si
1189.72
90(2)
C34H44Cl20N4Si
1245.82
203(2)
l [Š]
0.71073
0.71073
0.71073
crystal system
space group
a [Š]
b [Š]
c [Š]
monoclinic
P21/c
7.29226(2)
8.5929(2)
9.5100(3)
90
triclinic
P1
9.3107(3)
11.0529(4)
12.7008(4)
93.209(2)
triclinic
P1
9.7197(4)
11.0942(5)
13.3461(7)
90.778(2)
¯
¯
a [8]
b [8]
107.6629(16)
90
567.85(3)
2
1.528
0.649
100.801(2)
97.862(2)
1267.34(7)
1
1.559
1.130
101.771(2)
96.028(1)
1400.18(11)
1
1.477
1.026
g [8]
V [Š3]
Z
1 [Mgmꢀ3
]
absorption coefficient [mmꢀ1
(000)
crystal size [mm3]
]
F
A
268
598
630
0.23”0.17”0.08
2.93–34.00
ꢀ11ꢁhꢁ11, ꢀ13ꢁkꢁ13,
ꢀ14ꢁlꢁ14
17761
0.75”0.50”0.40
2.25–35.00
ꢀ15ꢁhꢁ15, ꢀ17ꢁkꢁ17,
ꢀ20ꢁlꢁ20
57513
0.35”0.25”0.20
2.37–28.00
ꢀ11ꢁhꢁ12, ꢀ14ꢁkꢁ14,
ꢀ17ꢁlꢁ17
18146
q range for data collection [8]
index ranges
reflections collected
independent reflections, Rint
completeness to qmax [%]
absorption correction
max./min. transmission
data/restraints/parameters
final R indices [I>2s(I)]
R indices (all data)
2317, 0.0312
100.0
11138, 0.0245
99.9
6724, 0.0208
99.4
semiempirical
0.9499, 0.8549
2317/0/74
R1 =0.0406, wR2 =0.0732
R1 =0.0734, wR2 =0.0793
0.804
semiempirical
0.6343, 0.566
11138/0/256
R1 =0.0334, wR2 =0.0823
R1 =0.0426, wR2 =0.0862
1.085
semiempirical
0.8211, 0.7554
6724/68/358
R1 =0.0476, wR2 =0.1250
R1 =0.0660, wR2 =0.1327
1.083
goodness-of-fit on F2
largest diff. peak and hole
0.536, ꢀ0.454
1.412, ꢀ1.203
0.457, ꢀ0.411
ꢀ3
[eŠ
]
pyridine (Aldrich), 4-(dimethylamino)pyridine (Fluka), pyridine (Riedel
de Haen) and pyrazine (Fluka) were obtained commercially. Liquid sub-
stituted and unsubstituted pyridines were heated over CaH2 for several
hours and then distilled and stored over 3-Š molecular sieves. Solid com-
pounds were dried under vacuum for several hours. Dichlorosilane was
used as supplied (Degussa 99.999%) and employed as a 40 vol% solution
for ease of handling. Dichlorosilane (4 mL) was condensed in a flask and
the desired solvent (6 mL) was added.
(w), 2929 (w), 3011 (w), 3064 (s), 3089 (w), 3129 (w), 3203 cmꢀ1 (w).
Single crystals of 1a were obtained by extraction with boiling CHCl3.
Dichlorodihydridodi(4-vinylpyridine)silane
(1b):
Yield:
1.40 g
(4.53 mmol; 91%), 29Si CP/MAS NMR (nspin =5 kHz): diso =ꢀ147.2 ppm;
13C CP/MAS NMR (nspin =5 kHz): diso =123.8, 127.0, 134.7, 141.8,
151.9 ppm; Raman: n˜ =249 (m), 289 (w), 464 (w), 666 (w), 807 (w), 856
(w), 954 (w), 1002 (w), 1028 (m), 1045 (m), 1073 (m), 1211 (m), 1262 (w),
1305 (w), 1338 (w), 1421 (m), 1438 (m), 1506 (w), 1551 (w), 1621 (s),
1632 (s), [nACHTER(UNG Si-H)] 2078 (w), 2514 (w), 2919 (w), 2978 (w), 2990 (w),
Compounds 1a–f and
2 were synthesised as follows. Dichlorosilane
3072 cmꢀ1 (m). Single crystals of 1b were obtained by extraction with
(5 mmol) was dissolved in toluene (30 mL) at ꢀ788C and the pyridine
base (10 mmol) was added dropwise. The products precipitated as colour-
less solids. The suspension was stirred for one hour at this temperature
and than slowly heated to room temperature. The resultant white precipi-
tate was filtered off, washed with toluene and dried under vacuum.
boiling CHCl3.
Dichlorobis[4-(dimethylamino)pyridine]dihydridosilane (1c): THF was
used for the synthesis of 1c instead of toluene. Yield: 1.59 g (4.63 mmol;
93%); 29Si CP/MAS NMR (nspin =5 kHz): diso =ꢀ151.8 ppm; 13C CP/
MAS NMR (nspin =4 kHz): diso =38.9, 39.6, 107.2, 141.8, 143.4, 156.1 ppm;
Dichlorodihydridodipyridinesilane: H2SiCl
previously by dismutation of HSiCl3 in the presence of pyridine[3] or by
decomposition of N(CH3)(SiHCl2)2 also in the presence of pyridine (see
2ACHTRE(UNG NC5H5)2 has been obtained
(SiH)] at about 2050 cmꢀ1; elemental analysis
Raman: Dual bands for [nACHTREUNG
calcd (%) for C14H22Cl2N4Si (344.10): Cl 20.6; found: Cl 18.9. Single crys-
tals of 1c were obtained by extraction with boiling CHCl3.
G
ACHTREUNG
introduction). We, however, synthesised the compound directly from
H2SiCl2 and pyridine as described above. Yield: 1.26 g (4.90 mmol; 98%),
29Si CP/MAS NMR (nspin =5 kHz): diso =ꢀ145.3 ppm; 13C CP/MAS NMR
(nspin =5 kHz): diso =126.9, 141.2, 144.5 ppm; Raman: n˜ =650 (m), 923
(w), 1020 (s), 1065 (w), 1153 (w), 1205 (m), 1262 (w), [nACHTER(UNG SiH)] 2075 (m),
2515 (w), 2928 (w), 2968 (w), 3008 (w), 3034 (w), 3063 (m), 3075 (s),
3149 cmꢀ1 (m).
Dichlorodihydridodi(4-methylpyridine)silane
(1d):
Yield:
1.32 g
(4.63 mmol; 93%); 29Si CP/MAS NMR (nspin =5 kHz): diso =ꢀ148.8 ppm;
13C CP/MAS NMR (nspin =6.5 kHz): diso =23.1, 128.1, 140.4, 144.7,
157.3 ppm; Raman: n˜ =256 (m), 292 (m), 364 (w), 555 (w), 668 (m), 878
(m), 941 (w), 1005 (w), 1042 (m), 1067 (m), 1204 (m), 1226 (m), 1261 (w),
1324 (w) 1377 (w), 1563 (w), 1626 (m), [nCAHTRE(UGN Si-H)] 2080 (w), 2515 (w), 2919
(s), 2998 (w), 3068 cmꢀ1 (s). Single crystals of 1d were obtained by ex-
Di(3-bromopyridine)dichlorodihydridosilane
(1a):
Yield:
1.43 g
traction with boiling CH3CN.
(3.45 mmol; 69%), 29Si CP/MAS NMR (nspin =5 kHz): diso =ꢀ145.2 ppm;
13C CP/MAS NMR (nspin =4 kHz): diso =111.4, 117.1, 128.8, 143.6 ppm;
Raman: n˜ =251(m), 300 (m), 334 (m), 487 (w), 655 (w), 723 (w), 825
(w), 928 (w), 1034 (s), 1062 (w), 1101 (w), 1126 (w), 1192 (w), 1253 (w),
Dichlorodi(4-ethylpyridine)dihydridosilane
(1e):
Yield:
1.53 g
(4.89 mmol; 98%); 29Si CP/MAS NMR (nspin =5 kHz): diso =ꢀ152.2 ppm;
13C CP/MAS NMR (nspin =6.5 kHz): diso =17.4, 29.1, 128.0, 143.2,
162.5 ppm; Raman: n˜ =248 (m), 332 (w), 400 (w), 526 (w), 585 (w), 650
(w), 666 (m), 745 (w), 799 (m), 970 (w), 1005 (m), 1039 (m), 1064 (m),
1317 (w) 1417 (w), 1468 (w), 1563 (w), 1603 (m), [nACHTRE(UNG Si-H)] 2103 (w), 2501
Chem. Eur. J. 2008, 14, 3164 – 3176
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3175

E. Kroke et al.
1074 (m), 1216 (m), 1279 (w), 1320 (m), 1373 (w), 145 (m), 1461 (m),
[14] D. Kost, V. Kingston, B. Gostevskii, A. Ellern, D. Stalke, B. Walfort,
I. Kalikhman, Organometallics 2002, 21, 2293–2305.
[15] M. Bolte, A. Faber, Acta Crystallogr. Sect. E 2001, 57, o207–o208.
[16] H. Fleischer, K. Hensen, T. Stumpf, Chem. Ber. 1996, 129, 765–771.
[17] M. Bolte, K. Hensen, B. Spangenberg, J. Chem. Crystallogr. 2000,
30, 245–249.
[18] J. Mason, Solid State Nucl. Magn. Reson. 1993, 2, 285–288.
[19] J. Herzfeld, A. E. Berger, J. Chem. Phys. 1980, 73, 6021–6030.
[20] T. Heine, A. Goursot, G. Seifert, J. Weber, J. Phys. Chem. A 2001,
105, 620–626.
[21] C. Corminboeuf, T. Heine, J. Weber, Chem. Phys. Lett. 2002, 357, 1 –
7.
1560 (w), 1626 (m), [nACHTREUNG(SiH)] 2061(m), 2552 (w), 2725 (w), 2874 (m),
2899 (m), 2939 (m), 2972 (m), 2999 (w), 3071cm ꢀ1 (s). Single crystals of
1e were obtained by extraction with boiling CH3CN.
Di-(4-tert-butylpyridine)dichlorodihydridosilane (1 f): Yield: 1.76 g
(4.77 mmol; 95%); 29Si CP/MAS NMR (nspin =5 kHz): diso =ꢀ149.5 ppm;
13C CP/MAS NMR (nspin =6.5 kHz): diso =31.3, 37.3, 124.2, 141.9,
169.7 ppm; Raman: n˜ =252 (m), 337 (w), 370 (w), 397 (w), 550 (w), 667
(m), 734 (m), 753 (m), 844 (w), 928 (m), 940 (w), 1039 (m), 1077 (m),
1129 (m), 1203 (m), 1226 (m), 1274 (m), 1399 (w), 1448 (m), 1466 (m),
1624 (m), [nACHTREUNG(SiH)] 2075 (m), 2529 (w), 2715 (w), 2733 (w), 2865 (w), 2907
(m), 2933 (s), 2954 (m), 2968 (m), 2999 (s), 3077 cmꢀ1 (s). Single crystals
[22] R. F. W. Bader, Atoms in Molecules, Clarendon Press, Oxford, 1994.
[23] R. J. Gillespie, J. Chem. Educ. 2001, 78, 1688–1690.
[24] Explanation taken from: R. A. Gillespie, P. L.A. Popelier, Chemical
Bonding and Molecular Geometry, Oxford University Press, New
York, 2001.
[25] Explanation taken from: N. Kocher, C. Selinka, D. Leusser, D. Kost,
I. Kalikhman, D. Stalke, Z. Anorg. Allg. Chem. 2004, 630, 1777–
1793.
[26] R. F. W. Bader, H. EssØn, J. Chem. Phys. 1984, 80, 1943–1960.
[27] N. Kocher, J. Henn, B. Gostevskii, D. Kost, I. Kalikhman, B. Engels,
D. Stalke, J. Am. Chem. Soc. 2004, 126, 5563–5568.
[28] A. E. Reed, L. A. Curtiss, F. Weinhold, Chem. Rev. 1988, 88, 899–
926.
of 1 f were obtained by extraction with boiling CHCl3.
Dichlorodihydridodipyrazinesilane (2): The above-described synthesis
route was followed but with a smaller amount of solvent. Thus, dichloro-
silane (5 mmol) was condensed in a flask and a solution of 10 mmol of
pyrazine in 1mL of toluene was added. Yield: 1.04 g (3.98 mmol; 80%);
29Si CP/MAS NMR (nspin =5 kHz): diso =ꢀ148.9 ppm; 13C CP/MAS NMR
(nspin =6.5 kHz): diso =136.0, 149.9 ppm; Raman: n˜ =199 (m), 251 (ms),
471 (w), 649 (w), 680 (w), 696 (m), 920 (w), 939 (w), 1023 (s), 1066 (m),
1119 (w), 1170 (w) 1227 (m), 1421 (w), 1533 (m), 1577 (w), 1606 (m),
ꢀ1
2094 (m), 2346 (w), 2900 (w), 2972 (w), 3051(s), 3063 (s), 3092 cm (m).
Tetrakis(4-ethylpyridino)dihydridosiliconium chloride (3e): Compound 1e
(1.57 g, 5 mmol) was extracted with 15 mL of boiling CHCl3 and colour-
less crystals formed within several days after cooling to room tempera-
ture. One of these single crystals was selected for X-ray diffraction.
[29] Explanation taken from: J. T. Nelson, W. J. Pietro, Inorg. Chem.
1989, 28, 544–548.
Dihydridotetrakis(4-methylpyridino)siliconium chloride (3 f): Compound
1 f (1.43 g, 5 mmol) was extracted with 15 mL of boiling CHCl3 and col-
ourless crystals formed within several days after cooling to room temper-
ature. One of these single crystals was selected for X-ray diffraction.
[30] A. E. Reed, R. B. Weinstock, F. Weinhold, J. Chem. Phys. 1985, 83,
735–746.
[31] O. K. H. Poleshchuk, E. L. Shevchenko, V. Branchadell, M. Lein, G.
Frenking, Int. J. Quantum Chem. 2005, 101, 869–877.
[32] Gaussian 03, Revision C.02, M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M.A. Robb, J. R. Cheeseman, J.A. Montgomer-
y Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyen-
gar, 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. Fores-
man, 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. Na-
nayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, C. Gonzalez, J.A. Pople, Gaussian, Inc., Wallingford
CT, 2004.
Acknowledgments
We thank Daniela Gerlach, Institut für Anorganische Chemie, TU Ber-
gakademie Freiberg, Leipziger Str. 29, 09596 Freiberg (Germany), for
performing the X-ray structure analyses of 1d. Degussa AG (Rheinfel-
den, Germany) is acknowledged for a gift of H2SiCl2.
[1] U. Wannagat, R. Schwarz, H. Voss, K. G. Knauff, Z. Anorg. Allg.
Chem. 1954, 227, 73–88.
[2] A. B. Burg, J. Am. Chem. Soc. 1954, 76, 2674–2675.
[3] H. J. Campbell-Ferguson, E. A. V. Ebsworth, J. Chem. Soc. A 1966,
1508–1514.
[4] H. J. Campbell-Ferguson, E. A. V. Ebsworth, J. Chem. Soc. A 1967,
705–712.
[5] K. Hensen, T. Stumpf, M. Bolte, C. Näther, H. Fleischer, J. Am.
Chem. Soc. 1998, 120, 10402–10408.
[6] K. Hensen, M. Kettner, T. Stumpf, M. Bolte, Z. Naturforsch. Teil B
2000, 55, 901–906.
[7] I. Ignatyev, H. Schaefer III, J. Phys. Chem. A 2001, 105, 7665–7671.
[8] H. Fleischer, Eur. J. Inorg. Chem. 2001, 393–404.
[9] P. Boudjouk, S. D. Kloos, B. K. Kim, M. Page, D. Thweatt, J. Chem.
Soc. Dalton Trans. 1998, 877–879.
[10] J. P. Kintzinger, C. Marsmann, NMR-Basic Principles and Progress,
Vol 17, Springer Verlag, Berlin, Heidelberg, New York, 1981.
[11] O. Bechstein, B. Ziemer, D. Hass, S. J. Troyanov, V. B. Rybakov,
G. N. Maso, Z. Anorg. Allg. Chem. 1990, 582, 211–216.
[12] K. Hensen, R. Mayr-Stein, B. Spangenberg, M. Bolte, Acta Crystal-
logr. Sect. A 2000, 56, 610–613.
[13] B. Gostevskii, G. Silbert, K. Adear, A. Sivaramakrishna, D. Stalke,
S. Deuerlein, N. Kocher, M. Voronkov, I. Kalikhman, D. Kost, Orga-
nometallics 2005, 24, 2913–2920.
[33] A. D. Becke, J. Chem. Phys. 1993, 98, 5648–5652.
[34] P. J. Stevens, F. J. Devlin, C. F. Chablowski, M. J. Frisch, J. Phys.
Chem. 1994, 98, 11623–11627.
[35] W. J. Hehre, L. Radom, P. v. R. Schleyer, J.A. Pople, Ab Initio Mo-
lecular Orbital Theory, J. Wiley & Sons, Chichester, 1986.
[36] P. C. Hariharan, J.A. Pople, Theor. Chim. Acta 1973, 28, 213–222.
[37] M. M. Francl, W. J. Pietro, W. J. Hehre, J. S. Binkley, M. S. Gordon,
D. J. DeFrees, J.A. Pople, J. Chem. Phys. 1982, 77, 3654–3665.
[38] F. Biegler-Kçnig, J. Schçnbohm, D. Bayles, AIM2000—A Program
to Analyze and Visualise Atoms in Molecules, J. Comput. Chem.
2001, 22, 545–559.
[39] Xaim: This program was developed by Jose Carlos Ortiz and Carles
Bo, Universitat Rovira i Virgili, Tarragona, Spain.
[40] K. Wolinski, J. F. Hinton, P. Pulay, J. Am. Chem. Soc. 1990, 112,
8251–8260.
Received: September 6, 2007
Published online: February 12, 2008
3176
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 3164 – 3176