3,5-Dimethylpyrazolyl-Substituted Di- and Trisiloxanes

Article abstract of DOI:10.1002/ejic.201600591

The synthesis and characterization of di- and trisiloxanes with 3,5-dimethylpyrazolyl (pz*) moieties are presented. Disiloxanes of the type O(SiMe_3–npz*_n)₂(n = 1, 2, and 3 in 2, 3, and 4, respectively) are easily accessible through a trans-silylation approach. Crystal structure analyses of compound 4 and the two side products 5 and 6 illustrate different coordination motifs of pz* (terminal vs. bridging) in the disiloxane system. The reaction of O₂Si₃Cl₈with Me₃Sipz* led to the unsymmetrically substituted trisiloxane pz*₃SiO-Sipz*₂O-SiCl₂pz* (7) with bridging pz* units and tetra- and pentacoordinate silicon atoms and the fully pyrazolyl-substituted trisiloxane O₂Si₃pz*₈(8), depending on the choice of the reaction conditions. The²⁹Si NMR properties of 7 were investigated by²⁹Si CP/MAS NMR spectroscopy and supporting quantum chemical calculations analyzing the principal components of the chemical-shift tensor for all three silicon atoms in this molecule.

Full text of DOI:10.1002/ejic.201600591

DOI: 10.1002/ejic.201600591
Full Paper
Siloxanes
3,5-Dimethylpyrazolyl-Substituted Di- and Trisiloxanes
Florian Bitto,*[a] Erica Brendler,[b] Uwe Böhme,[a] Jörg Wagler,[a] and Edwin Kroke*[a]
Abstract: The synthesis and characterization of di- and trisilox- cally substituted trisiloxane pz*3SiO-Sipz*2O-SiCl2pz* (7) with
anes with 3,5-dimethylpyrazolyl (pz*) moieties are presented. bridging pz* units and tetra- and pentacoordinate silicon atoms
Disiloxanes of the type O(SiMe3–npz*n)2 (n = 1, 2, and 3 in 2, 3, and the fully pyrazolyl-substituted trisiloxane O2Si3pz*8 (8), de-
and 4, respectively) are easily accessible through a trans-silyl- pending on the choice of the reaction conditions. The 29Si NMR
ation approach. Crystal structure analyses of compound 4 and properties of 7 were investigated by 29Si CP/MAS NMR spectro-
the two side products 5 and 6 illustrate different coordination scopy and supporting quantum chemical calculations analyzing
motifs of pz* (terminal vs. bridging) in the disiloxane system. the principal components of the chemical-shift tensor for all
The reaction of O2Si3Cl8 with Me3Sipz* led to the unsymmetri- three silicon atoms in this molecule.
Introduction
disiloxanes and trisiloxanes substituted by Si–N-bound five-
membered heterocycles has been published so far, that is, silox-
anes functionalized with pyrrolidinonyl (I to III)[3] phthalimidyl
(IV),[4] pyrrolyl (V),[5] and imidazolyl groups (VI)[6] (Scheme 1).
Pyrazole and pyrazolide compounds show manifold coordina-
tion modes in complexes with transition metals.[1a] As parts of
boron-, carbon-, and silicon-based compounds, pyrazolyl units
also show interesting ligand characteristics due to their multi-
ple coordination possibilities.[1b–1f] In our previous studies on
the chemistry of pyrazolyl-substituted silicon compounds, we
Results and Discussion
investigated the reactivity of hydridochlorosilanes and disil- Substituted Disiloxanes
anes.[2] We identified siloxanes with pyrazolyl units as potential
The pz*-substituted disiloxanes were prepared from the corre-
new multidentate ligands for transition metals. Therefore we
expanded our investigations to the reactions of chloro-substi-
tuted disiloxanes O(SiMe3–nCln)2 (n = 1, 2, 3) and octachlorotri-
siloxane O2Si3Cl8 with Me3Sipz*. None of the potential products
are known in the literature. Only a scarce set of examples of
sponding chloro-substituted siloxanes. In the disiloxane series
O(SiMe3–nCln)2 (n = 1, 2, 3) the compounds with n = 1 and 3
were commercially available. 1,1′,3,3′-Tetrachloro-1,3-di-
methyldisiloxane O(SiMeCl2)2 (1) had to be synthesized for our
studies. Even though the literature provides a selection of
routes to 1 (from the high-boiling fraction of the Müller–Ro-
chow process,[7] chlorination of hydrogen-substituted silox-
anes,[8] and partial hydrolysis of methyltrichlorosilane[9]), these
methods have low selectivity, low yield, and/or laborious purifi-
cation in common. Therefore, we employed the Friedel–Crafts
acylation method for replacing Si-bound phenyl substituents by
Si–Cl bonds (Scheme 2).[10] To the best of our knowledge this
is the first report on a siloxane being chlorinated in this manner.
Notably, in n-hexane as solvent this reaction of 1,1,3,3-tetra-
phenyl-1,3-dimethyldisiloxane O(SiMePh2)2 and stoichiometric
amounts of AlCl3 (anhydrous) and acetyl chloride proceeds in a
clean manner and was completed within minutes.
Scheme 1. Di- and trisiloxanes substituted by five-membered heterocycles.
[a] Institut für Anorganische Chemie, TU Bergakademie Freiberg,
Leipziger Str. 29, 09599 Freiberg Germany
E-mail: florian.bitto@chemie.tu-freiberg.de
edwin.kroke@chemie.tu-freiberg.de
www.tu-freiberg.de/fakult2/aoch/agsi
Scheme 2. Synthesis of 1 by Friedel–Crafts acylation.
[b] Institut für Analytische Chemie, TU Bergakademie Freiberg,
Leipziger Str. 29, 09599 Freiberg Germany
The isolation of the pure disiloxane 1 from this reaction mix-
ture is laborious due to carryover by n-hexane (see Experimen-
tal Section and Supporting Information for details). However, as
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under http://dx.doi.org/10.1002/ejic.201600591.
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the raw product is a two-component mixture of n-hexane and of the oxygen position, and thus a significant deviation of the
1 (according to NMR spectroscopic analysis), we decided to use Si–O–Si angle from linearity. Wojnowski et al. have demon-
this hexane solution of 1 (after gas chromatographic analysis) strated the influence of this centrosymmetric constraint of a
in subsequent stoichiometric reactions.
disiloxane O atom in O[Si(OtBu)3]2.[11] Initial refinement in the
space group P1 gave an Si–O–Si angle of 180°, but with large
¯
The disiloxanes of the type O(SiMe3–npz*n)2 2 (n = 1), 3 (n =
2), and 4 (n = 3) were synthesized by a trans-silylation approach
with Me3Sipz* in n-hexane (Scheme 3). The compounds were
isolated by removal of the solvent and the volatile byproduct
Me3SiCl in vacuo. Compounds 3 and 4 are colorless solids, and
2 was obtained as a colorless liquid. The identity of the com-
pounds was confirmed by multinuclear NMR spectroscopy
and very anisotropic thermal ellipsoid for the oxygen atom
[U11 = 143(6), U22 = 212(8), U33 = 57(4), Ueq = 138(4)] indicating
enhanced mobility. They are also much larger than that of the
silicon atoms [Ueq(Si) = 71(1)].
Much better results were obtained by refinement of a disor-
der model (rigid-body model), which decreased the Si–O–Si an-
gle to 144°. Unfortunately, neither structure refinement in a
lower-symmetry space group (P1) nor refinement of split posi-
tions for O1 proved suitable to solve this problem.
1
(29Si{1H}, 13C{1H}, H), Raman spectroscopy, and elemental anal-
yses.
Therefore, we employed quantum chemical methods to ad-
dress this issue and to obtain information regarding the true
Si–O–Si angle. The variation of the Si–O–Si angle in 4 was calcu-
lated by means of a relaxed potential-energy surface (PES) scan
at the B3PW91-6-31G(d) level of theory (for details, see Support-
ing Information). Bending of the Si–O–Si angle revealed a very
flat PES between 170 and 180° with the minimum at 175° (Fig-
ure S9 and Table S2). This explains the rather large anisotropic
thermal ellipsoid for the oxygen atom in the X-ray structure of
4. These results are in line with findings from quantum chemical
calculations on a range of disiloxanes O(SiR3)2 (R = H,[12,13] F,[13]
Cl,[13] Me,[13] OH[14]) at the DFT and MP2 levels of theory. The
results consistently show a flat PES in the range of 140–180°
with a barrier of 5–10 kJ/mol for linearization. This low barrier
enables great mobility of this unit. Hence, the crystallographi-
cally imposed Si–O–Si angle of 180° in 4 does not reflect the
true situation, but calculations confirmed the true angle (ener-
getic minimum) to be close to 180°. The negative hyperconju-
gation from the oxygen lone pairs to the Sipz*3 units stabilizes
this almost linear arrangement.
Scheme 3. Synthesis of the disiloxanes 2, 3, and 4.
29Si NMR spectroscopy revealed an upfield shift of the reso-
nance on replacing Si–Cl by Si–pz* for each set of disiloxanes
(Table 1).
Table 1. 29Si NMR shifts [ppm] of the series of disiloxanes O(SiMe3–nRn)2 (n =
1–3, R = pz*, Cl) recorded in C6D6.
O(SiMe2R)2
O(SiMeR2)2
O(SiR3)2
R = Cl
R = pz*
6.6
–6.1
–15.0
–36.2
–45.3
–77.6
Compound 4 was also characterized by single-crystal XRD.
Suitable crystals were obtained by recrystallization from n-hex-
ane. The structure was refined in the triclinic space group P1
¯
with one half-molecule in the asymmetric unit (Figure 1).
The coordination geometry around the silicon atom is best
described as a distorted Si(N3O) tetrahedron with N–Si–N(O) an-
gles in the range of 106.91(6)–111.21(6)°. The pyrazolyl ring at
N1 is nearly perpendicular to the Si–O bond [O1–Si1–N1–N2
74.64(13)°], while the other two rings show cis (N3–N4) and
trans orientation (N5–N6) of their second N atom with respect
to the Si–O bond [O1–Si1–N5–N6 30.84(12)°, O1–Si1–N3–N4
–168.56(10)°]. The two Sipz*3 moieties adopt a pseudostag-
gered conformation along the central Si–O–Si unit. The Si–N
bond lengths [1.728(1) Å–1.737(2) Å] are in line with those of
other silicon compounds with terminal pz* units.[2,15] The Si–O
bond length [1.593(1) Å] is slightly shorter than that of O(SiPh3)2
[1.616(1) Å], which conforms to the higher electronegativity of
the substituents in 4.[16]
Our attempts at synthesizing partially pz* substituted disilox-
anes by treating O(SiCl3)2 with substoichiometric amounts of
Me3Sipz* failed (we did not succeed in isolating defined com-
pounds). These reactions produced mixtures of partially substi-
tuted chlorosiloxanes and compound 4. Nonetheless, our at-
Figure 1. Molecular structure of 4 in the crystal (ellipsoids set at 50 %,
hydrogen atoms omitted for clarity).
The Si–O–Si angle is constrained to 180° due to positioning tempts to isolate pure compounds by recrystallization resulted
of the oxygen atom on a crystallographic center of inversion. in small amounts of crystals of decomposition products [(4)(5)2
The larger thermal displacement factor of O1 [Uiso = 41(1)] with and 6]. Their molecular structures demonstrate the variable co-
respect to that of Si1 [35(1)], however, hints at dynamic disorder ordination modes of Si-bound pz* units. They complement the
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terminal bonding mode in 4 by a bridging mode of pz* and, as
their characteristic feature as hydrolysis products, ligation by
Hpz*. [(μ-pz*)2(O){SiCl2(Hpz*)}2] (5) is an Hpz* adduct of the in-
tended partially pz* substituted siloxane O(SiCl2pz*)2 and co-
crystallizes with 4 as (4)(5)2 in the monoclinic space group
C2/c. The asymmetric unit consists of one half-molecule
of 4 and one molecule of 5. The two silicon atoms in 5 are
octahedrally coordinated by their mutual O atom, two chloro
substituents, two bridging pyrazolyl units, and a coordinated
Hpz* molecule (Figure 2).
Figure 3. Molecular structure of 6 (ellipsoids set at 50 %, C-bound hydrogen
atoms omitted for clarity).
Table 2. Comparison of structural features of compounds 4, 5, and 6.
4
5
6
Si–N [Å]
N1 1.734(2)
N3 1.737(2)
N5 1.728(2)
N7
N8
N9
N10
N11
N13
Si2
1.915(3)
1.921(3)
1.923(3)
1.927(3)
1.946(3)
1.948(3)
1.673(3)
1.680(2)
120.35(14)
N1
N2
N3
N5
1.881(1)
1.927(2)
1.913(2)
1.853(2)
Si–O [Å]
1.594(1)
180
Si1
Si2
1.624(1)
1.636(1)
133.51(9)
Si3
Figure 2. Molecular structure of 5 in a crystal of (4)(5)2 (ellipsoids set at 50 %,
C-bound hydrogen atoms omitted for clarity). The N-bound hydrogen atoms
were located as residual electron-density peaks.
Si–O–Si [°]
Compared with the other disiloxanes discussed here, the Si–
O–Si angle in 5 is noticeably small [120.35(14)°] because of its
location in a five-membered ring system, and the Si–O bonds
are the longest because of the hexacoordination of the Si at-
oms. The molecular structure of 5 is stabilized by intramolecular
N–H···Cl hydrogen bonds [H12n···Cl2 2.55 Å, N12–H12n···Cl2
170.1°, H14n···Cl3 2.68 Å, N14–H14n···Cl3 174.4°].
The second side product 6 is also an Hpz* adduct of disilox-
ane O(SiCl2pz*)2, but features only one Hpz* ligand and only
one bridging pz* group, whereas the second pz* substituent is
terminal. It crystallized directly from the reaction solution in n-
hexane in monoclinic space group P21/m (Figure 3). The asym-
metric unit contains one half-molecule, which is located on a
bisecting plane with most of its atoms; only the Cl atoms are
out of this plane. The coordination around the silicon atoms is
nearly ideal trigonal-bipyramidal [τ(Si1) = 0.98, τ(Si2) = 0.97][17]
with N–Si–N axes. The structure features a N–H···N hydrogen
bond between the terminal pz* unit and the coordinated Hpz*
moiety [N4–H4n···N6 171.71°, H4n···N6 2.01 Å] which stabilizes
this flat conformation.
Substituted Trisiloxanes
Our initial aim was to synthesize the fully pz*-substituted tri-
siloxane O2Si3pz*8 (8). During the experiments we found that
the solvent (solv) is the most important factor for success. Using
n-hexane, n-pentane, or diethyl ether did not lead to the
desired product 8 but yielded the asymmetrically substituted
trisiloxane 7 (Scheme 4).
Scheme 4. Synthesis of 7 and 8 by a one- or two-stage trans-silylation proc-
ess.
Table 2 compares structural data for 4–6.
Compounds 4–6 reflect different coordination modes of the
The fully pz* substituted siloxane can be prepared by trans-
pyrazolyl unit: pz* as terminal substituent or in a bridging mode silylation in dichloromethane. Product 7, obtained by trans-silyl-
between two silicon atoms, and Hpz* as a bifunctional ligand ation in the above-mentioned solvents, can be converted to 8
having a polar N–H bond available for establishing N–H···Cl/N in a second stage trans-silylation reaction. Both trisiloxanes
hydrogen bonds, which enhances the binding of this ligand in were characterized by multinuclear NMR spectroscopy (29Si{1H},
1
addition to its primary N–Si coordination.
13C{1H}, H), Raman spectroscopy, and elemental analysis. For 7
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the single-crystal structure and 29Si CP/MAS NMR spectrum of spectra were recorded at different spinning frequencies (1.3,
the crystalline compound were obtained.
Compound 7 crystallizes in the triclinic space group P1 with
one molecule in the asymmetric unit directly from the reaction
2.3, 5 kHz). The three isotropic shifts (δ = –63.4, –123.8, and
–135.2 ppm) are in accord with the expected three signals of
one tetra- and two pentacoordinate silicon atoms. The signal
broadening of the peak at δ = –123.8 ppm, which can be attrib-
uted to residual dipolar coupling to the quadrupolar chlorine
nuclei, already hints at an assignment of this signal to the
chloro-substituted Si atom Si1. This assignment was then con-
firmed by the agreement of the principal components of the
CSA tensors of the three Si atoms extracted from the spinning-
sideband spectra and the corresponding data predicted by
computational methods (Table 4 and Figure S3).[19,20]
¯
mixture in n-hexane (Figure 4).
Table 4. Experimental and calculated 29Si CSA tensor principal components
δ
11, δ22, δ33 and parameters derived therefrom (isotropic shift δiso, span Ω,
skew κ) of compound 7.[21]
Si
δiso
δ11
δ22
δ33
Ω
κ
Si1 exp.[a]
–123.8
–16.7
–4.7
–26.4
–25.6
–29.3
–33.3
–157.6
–159.2
–173.4
–185.7
–64.4
–195.6
–185.2
–205.9
–211.3
–96.1
178.8
180.5
179.5
185.7
66.3
–0.58
–0.71
–0.64
–0.72
0.04
calcd.[b] –116.3
Si2 exp.
calcd.
Si3 exp.
calcd.
–135.2
–140.9
–63.4
–66.9
–63.8
–103.7
70.4
0.13
Figure 4. Molecular structure of 7 (ellipsoids set at 50 %, hydrogen atoms and
methyl groups of the pz* units are omitted for clarity).
[a] Experimental: extracted from the 29Si CP/MAS data at a spinning fre-
quency of 2.0 kHz. [b] Calculated: B3PW91/6-311+G(2d,p) using the atomic
coordinates from the crystal structure.
Silicon atoms Si1 and Si2 adopt distorted trigonal-bi-
pyramidal coordination spheres [τ(Si1) = 0.88, τ(Si2) = 0.92] with
Cl2–Si1–N3 and N4–Si2–N7 as the axes. The coordination envi-
ronment around the third silicon atom is best described as
pseudotetrahedral [N–Si3–N(O) 97.46°···115.06°]. The Si–N
bonds of the nitrogen atoms that occupy the axial positions of
the trigonal bipyramids (N3, N4, N7) are significantly longer
than the other Si–N bonds in the molecule (Table 3). This is in
accord with structural data from the literature and the concept
of 3c–4e bonds in the axial position of trigonal-bipyramidal sili-
con complexes.[18] The Si–O bond lengths and Si–O–Si angles
(Table 3) are in line with those found for compounds 5 and 6.
The signal at δ = –63.4 ppm is easily related to Si3 in the
crystal structure, which is the only four-coordinate silicon atom.
Taking into account the results of the quantum chemical calcu-
lations [B3PW91/6-311+G(2d,p), calculated with the coordinates
of the crystal structure], the other two peaks can now be as-
signed to Si1 (OSiCl2pz*, –123.8 ppm) and Si2 (O2Sipz*2,
–135.2 ppm). 29Si NMR spectroscopic data obtained for the di-
siloxanes already showed that pz*-substituted silicon atoms ex-
hibit pronounced shielding with respect to similar chloro-sub-
stituted Si atoms. This is in agreement with the situation here:
two silicon atoms in comparable bonding situation (five-coordi-
nate, oxygen and chloro/pz* substituents), the one with more
pz* units has an isotropic 29Si NMR signal shifted to higher field.
Interestingly, the isotropic chemical shift is noticeably differ-
ent for Si1 and Si2, whereas their contributors (principal compo-
nents of the shift tensor) are simultaneously shifted, and thus
the CSA tensors of Si1 and Si2 have very similar span and skew
(in accord with the calculated data, Table 4). The influence of
the different types of substituents with respect to the orienta-
tion of the CSA tensor components in the molecule (Figure 5)
provides an explanation. For the pentacoordinate silicon atoms
(Si1, Si2), the orientation of principal component δ11 corre-
sponds to the axis of the trigonal bipyramid. The other two
components are situated in the equatorial plane of the coordi-
nation environment. With the rather wide span and negative
skew (one significantly less shielded direction, i.e., along the
bipyramidal axis), the CSA tensors of Si1 and Si2 match the
Table 3. Selected bond lengths [Å] and angles [°] in the structure of 7.
Atoms
Si1
Value
Si–N
N1
N3
N4
N5
N7
N8
N9
N11
O1
O1
O2
O2
O1
O2
1.769(1)
1.933(1)
1.870(1)
1.770(1)
1.950(1)
1.749(1)
1.721(1)
1.729(1)
1.645 (1)
1.639 (1)
1.669 (1)
1.618 (1)
133.58(6)
125.20(6)
Si2
Si3
Si–O
Si1
Si2
Si3
Si–O–Si
To assign the 29Si NMR signals to the individual Si atoms of expected pattern for pentacoordinate silicon compounds.[22,23]
7, two of which are pentacoordinate, we combined 29Si CP/MAS It has been shown that the principal components of the shield-
NMR spectroscopy for determination of the principal compo- ing tensor are strongly influenced by the ligands that are per-
nents of the chemical-shift anisotropy (CSA) tensor with the pendicular to them.[22,24] Thus, in case of Si1 and Si2, Si–Cl ver-
results of quantum chemical calculations. The CP/MAS NMR sus Si–N bonds have been exchanged both in equatorial and
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axial position, and therefore greater shielding of Si2 in all direc-
tions is observed.
Figure 6. 29Si NMR spectra of 7 in different solvents and in the solid state.
For the purpose of comparison the positions of the signals of Si1, Si2, and
Si3 (labels correspond to the crystal structure) are marked in the CP/MAS
spectrum. The asterisk marks a spinning sideband of Si1.
ent species, resulting in line broadening to an extent that pre-
vents the detection of signals. This is supported by a compari-
1
son of the H NMR spectra of 7 in C6D6 and CDCl3 (Figure 7).
The former shows narrow individual lines, indicating slow ex-
change, and the latter broad signals due to coalescence, typical
for fast exchange.
Figure 5. Orientation of the CSA tensor principal components (calculated) in
7 (Herzfeld–Berger convention);[19–21] from top to bottom: Si1, Si2, Si3. The
arrows show only the direction not the magnitude.
Depending on the solvent, the 29Si NMR spectrum of 7 in
solution reveals complex dynamic behavior. This is not limited
to the silyl transfer between the nitrogen atoms of the pz*
units, as observed for pyrazolyl-substituted monosilanes,[25] it
also includes changes in the coordination environment of the
silicon atoms.
For solutions in C6D6 and THF, signals in the typical region
of four- and five-coordinate silicon atoms are found (Table 5).
The signal of the four-coordinate silicon atom is considerably
shifted upfield compared to the solid state, while for the silicon
atoms with higher coordination numbers two sets of signals
can partially be observed (Figure 6). This is attributed to the
presence of diastereomeric species, which originate from the
change of the bridging pz* units between Si1 and Si2 or Si2
and Si3 by breaking the Si2–N4 and Si3–N8 bonds while form-
ing Si2–N2 and Si3–N6 bonds. Unequal intensity of the signals
is due to energetic differences between the isomers.
Figure 7. 1H NMR spectra of 7 in the regions of the pz* signals.
The 29Si NMR spectrum of the fully pz*-substituted trisilox-
ane 8 shows two signals in the upfield region of tetracoordinate
Si atoms (Figure 8). The signals at δ = –77 and –91 ppm occur
with an intensity ratio of 2:1 and are noticeably shifted upfield
with respect to the starting material O2Si3Cl8 (Cl3SiO:
–46.0 ppm, Cl2SiO2: –72.0 ppm, ratio 2:1). We assign the signal
at δ = –77 ppm to the terminal silicon atoms (pz*3SiO). The
shift is similar to that of the pz*3SiO group in the disiloxane 4
(δ = –77.6 ppm) and only slightly shifted upfield relative to
that of 7. The remaining upfield-shifted signal (δ = –91 ppm) is
assigned to the central pz*2SiO2 unit. As for 7 no 29Si NMR
signal was obtained from a CDCl3 solution of 8. The solid-state
NMR spectrum of 8 shows signals in the same region as that in
benzene solution. The terminal –OSipz*3 units show two signals
of similar intensity. This could be due to inequivalence of the
two terminal groups of one molecule in the solid state or differ-
ent conformer sites (crystallographically independent mol-
ecules). The CP/MAS spectrum of 8 at 4 kHz shows no spinning
sidebands and a small span comparable to that for Si3 in com-
Table 5. 29Si NMR shifts [ppm] of 7 in the solid state and in different solvents.
Si1
Si2
Si3
CP/MAS
C6D6
THF
–123.8
–120.9/–121.7
–122.5
–135.2
–133.2/–135.7
–134.4/–137.2
–63.4
–68.9
–70.3
For a solution of 7 in CDCl3 no 29Si NMR signals could be pound 7. These are further hints at tetracoordination of all Si
observed. We attribute this to fast exchange between the differ- atoms.
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O(SiMe3–npz*n)2 are easily obtained by trans-silylation with
Me3Sipz*. Their 29Si NMR signals are upfield-shifted with in-
creasing replacement of Cl atoms by pz* units. The molecular
structures determined for O(Sipz*3)2 (4) and the two side prod-
ucts 5 and 6 demonstrate the coordinative possibilities of the
(H)pz* unit in combination with the flexible Si–O–Si moiety.
The trans-silylation reaction with O2Si3Cl8 yielded the asym-
metrically substituted siloxane 7, which has two pentacoordi-
nate silicon atoms. Analysis of its 29Si NMR shifts (CP/MAS meas-
urements and quantum chemical calculations of the principal
components of the CSA tensor) allowed for unequivocal assign-
ment of the chemical shifts to the individual Si atoms of this
compound. Dynamic behavior of the Si-bound pz* moieties was
observed depending on the choice of the solvent, and coales-
cence was almost reached in CDCl3.
Figure 8. 29Si NMR spectra of 8 and O2Si3Cl8.
Isolation of the fully substituted trisiloxane O2Si3pz*8 (8) by
an optimized protocol showed the importance of the choice of
the solvent. The comparison of the solution and solid-state 29Si
NMR spectra of 8 showed four-coordinated silicon atoms in
both cases.
In spite of two out of three Si atoms having the same substi-
tution pattern, the Si atoms of 7 exhibit different coordination
features to those of 8. For an explanation of the formation of
the unusual compound 7 one must consider different aspects:
1) Me3Sipz* is a mild reagent, in contrast to pz*– (e.g., 3,5-di-
methylpyrazole in the presence of triethylamine), as shown by
the reaction with H2SiCl2 and HSiCl3;[2] 2) the low solubility of
7 in some solvents helped with its isolation; 3) the formation
of compound 8 is observed at room temperature only in
CH2Cl2. This is in line with the results of calculations for the
isodesmic reaction 7 → 8 (Scheme 5) at the B3PW91/6-31G(d)
Experimental Section
General: All manipulations were performed under an inert atmos-
phere of dry argon by using standard Schlenk techniques or a
MBraun Glovebox with a concentration of O2 and H2O below
5 ppm. CDCl3 was distilled from CaH2, n-hexane was distilled from
sodium, n-pentane was dried with a column of molecular sieves,
and C6D6 was used as received. All solvents were stored with molec-
level of theory. The computational analysis predicts a positive ular sieves under argon. Me3SiCl, O(SiMe2Cl)2, O(SiCl3)2, O(SiM-
ePh2)2, AlCl3 (anhydrous), acetyl chloride, O2Si3Cl8, and 3,5-dimeth-
ylpyrazole were used as received from commercial suppliers. Tri-
methyl-3,5-dimethylpyrazolylsilane (Me3Sipz*) was synthesized as
described before.[1] Raman spectra were recorded with a Bruker Op-
tik RFS 100/S spectrometer equipped with an Nd-YAG laser
(1500 mW, 1064 nm) in the range 3600–90 cm–1. Elemental analyses
were carried out with a Vario Micro Cube analyzer of the company
Elementar (Hanau, Germany).
small Gibbs free energy of +20 kJ/mol in the gas-phase and
+28 kJ/mol in CH2Cl2, which disfavors the formation of 8 from
7, but could still be compensated by solvent effects (for more
details, see the Supporting Information).
1,1,3,3-Tetrachloro-1,3-dimethyldisiloxane [O(SiMeCl2)2, 1]:
Acetyl chloride (19.1 g, 243.5 mmol) was added to a stirred suspen-
sion of anhydrous AlCl3 (32.5 g, 234.5 mmol) and O(SiMePh2)2
(25.0 g, 60.9 mmol) in n-hexane (300 mL) at room temperature in
several portions through a dropping funnel. The reaction com-
menced after a short induction period and proceeded in boiling n-
hexane with occurrence of two liquid phases. After cooling the reac-
tion mixture, the n-hexane phase was separated by decantation.
Distillation at ambient pressure (details in Supporting Information)
gave 1 as a colorless liquid (at 143 °C), yield 7.8 g, 32 mmol, 53 %.
1H NMR (400.13 MHz, C6D6, 20 °C, TMS): δ = 0.47 ppm (s, 6 H, SiCH3);
13C{1H} NMR (100.63 MHz, C6D6, 20 °C, TMS): δ = 5.4 ppm [1J(Si,C) =
47.0 Hz, SiCH3]; 29Si{1H} NMR (79.48 MHz, C6D6, 20 °C, TMS): δ =
Scheme 5. Reaction leading from 7 to 8 for calculation of the Gibbs free
energy.
Thus, both kinetic effects (poor solubility of 7 in some sol-
vents, mild trans-silylation reagent pz*-SiMe3) and thermody-
namic effects (disfavored formation of 8, unless compensated
by favorable solvent effects) contribute to the formation and
isolation of compound 7 and serve as an explanation why the
choice of a different solvent eventually gave rise to the forma-
tion of 8.
–15.0 ppm [OSiCH3(Cl2)]. Raman: ν = 142 (w), 173 (vw), 195 (vw),
˜
232 (vw), 340 (vw), 446 (s) [Si–Cl], 1270 (vw), 1404 (vw), 2914 (vs),
2985 (w) cm–1
.
Conclusion
1,3-Bis(3,5-dimethylpyrazolyl)-1,1,3,3-tetramethyldisiloxane
[O(SiMe2pz*)2, 2]: Me3Sipz* (19.9 g, 118.4 mmol) was added to a
stirred solution of O(SiMe2Cl)2 (12.0 g, 59.2 mmol) in n-hexane
(50 mL), and the reaction mixture was heated to reflux for 9.5 h.
After removal of the solvent and volatile components under re-
The synthesis of O(SiMeCl2)2 by Friedel–Crafts acylation is sim-
ple and effective. The procedure used by us results in the pure
product or n-hexane solutions thereof. Both can be used
for subsequent reactions. The pz*-substituted disiloxanes duced pressure (condensation into a cold trap), the raw product
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was distilled in vacuo to yield 2 as a colorless liquid (126 °C, 2 mbar),
yield 8.59 g, 26.6 mmol, 45 %. 1H NMR (400.13 MHz, C6D6, 20 °C,
TMS): δ = 5.71 (s, 2 H, pz*C-H), 2.11 (s, 12 H, pz*C-CH3) 0.39 ppm
[s, 12 H, Si(CH3)2]; 13C{1H} NMR (100.63 MHz, C6D6, 20 °C, TMS): δ =
151.13 (pz*C-CH3), 145.6 (pz*C-CH3), 107.9 (pz*C-H) 13.6 (pz*C-CH3),
12.5 (pz*C-CH3), 0.7 ppm [1J(Si,C) = 36.0 Hz, Si(CH3)2]; 29Si{1H} NMR
(79.48 MHz, C6D6, 20 °C, TMS): δ = –6.1 ppm [OSi(CH3)2pz*]. Raman:
–123.8 (OSiCl2pz*), –63.4 ppm (pz*3SiO). Raman: ν = 100 (s), 149 (m),
˜
202 (m), 241 (w), 267 (w), 307 (w), 328 (w), 367 (w), 462 (w), 497 (w),
535 (w), 593 (m), 968 (vw), 1020 (w), 1067 (vw), 1155 (vw),
1189 (vw), 1189 (vw), 1350 (vw), 1380 (vw), 1439 (m), 1467 (w),
1538 (vw),1556 (vw), 1574 (vw), 2732 (vw), 2866 (w), 2927 (vs),
2960 (m), 2982 (m), 2998 (w), 3109 (vw), 3129 (w) cm–1
.
C30H42Cl2N12O2Si3 (757.91): calcd. C 47.54, H 5.59, N 22.18; found C
47.74, H 5.55, N 21.87.
ν = 100 (vw), 171 (vw), 193 (vw), 412 (vw), 469 (vw), 491 (vw),
˜
589 (w), 709 (vw), 799 (vw), 1019 (vw), 1443 (w), 1556 (vw),
2728 (vw), 2743 (vw), 2869 (w), 2905 (vs), 2922 (s), 2983 (m),
3090 (vw), 3123 (vw) cm–1. C14H26N4OSi2 (322.56): calcd. C 52.13, H
8.12, N 17.73; found C 52.42, H 8.08, N 17.34.
Octakis(3,5-dimethylpyrazolyl)trisiloxane [O2Si3pz*8, 8]:
Me3Sipz* (4.04 g, 24.0 mmol)was added to a solution of O2Si3Cl8
(1.20 g, 3.0 mmol) in CH2Cl2 (8.0 mL), and the mixture heated to
reflux for 6 h. After the solvent and volatile components were re-
moved in vacuo, the residue was dissolved in n-pentane (8.0 mL)
and stored in a refrigerator (8 °C). After 7 d a colorless precipitate
appeared. The supernatant solution was removed by decantation
and the solid immediately dried in vacuo. Compound 8 was ob-
1,1,3,3-Tetrakis(3,5-dimethylpyrazolyl)-1,3-dimethyldisiloxane
[O(SiMepz*2), 3]: Me3Sipz* (2.2 g, 13.3 mmol) was added to a solu-
tion of O(SiMeCl2)2 (0.81 g, 3.3 mmol) in n-hexane (10 mL) and the
mixture stirred at room temperature for 27 h. After evaporation of
the solvent and volatile components, 3 was obtained as a colorless tained as a colorless solid, yield 1.52 g, 1.7 mmol, 58 %, m.p. 280 °C
solid, yield 1.57 g, 3.25 mmol, 98 %, m.p. 95 °C (decomposition,
sealed capillary). H NMR (400.13 MHz, C6D6, 20 °C, TMS): δ = 5.68
(decomposition, sealed capillary). 1H NMR (500.13 MHz, C6D6, 20 °C,
TMS): δ = 5.75 (8 H, pz*C-H), 2.30 (24 H, pz*C-CH3); 1.90 ppm (24 H,
pz*C-CH3); 13C{1H} NMR (125.76 MHz, C6D6, 20 °C, TMS): δ = 155.2
1
(s, 4 H, pz*C-H), 2.05 (s, 24 H, pz*C-CH3), 1.22 ppm (s, 6 H, SiCH3);
13C{1H} NMR (100.63 MHz, C6D6, 20 °C, TMS): δ = 149.3 (pz*C-CH3), (pz*C-CH3), 143.9 (pz*C-CH3), 108.7 (pz*C-H), 12.8 (pz*C-CH3),
108.4 (pz*C-H), 12.7 (pz*C-CH3), –0.6 ppm (SiCH3); 29Si{1H} NMR 10.7 ppm (pz*C-CH3); 29Si{1H} NMR (99.36 MHz, C6D6, 20 °C, TMS):
(79.48 MHz, C6D6, 20 °C, TMS): δ = –36.3 ppm [OSiCH3(pz*2)]. Ra- δ = –77.0 (pz*3SiO), –91.1 ppm (OSipz*2O). Raman: ν = 101 (s),
˜
man: ν = 84 (w), 117 (w), 167 (w), 188 (w), 209 (w), 343 (vw),
149 (w), 203 (w), 269 (vw), 307 (w), 340 (vw), 462 (vw), 498 (vw),
˜
462 (vw), 593 (m), 1019 (w), 1441 (w), 1465 (w),1562 (vw), 2684 (vw), 535 (vw), 593 (s), 642 (vw), 699 (vw), 739 (vw), 776 (vw), 967 (vw),
2914 (vs), 2955 (w), 2976 (w) cm–1. C22H34N8OSi2 (482.74): calcd. C 1019 (vw), 1067 (vw), 1152 (vw), 1191 (vw), 1308 (vw), 1351 (vw),
54.74, H 7.10, N 23.21; found C 54.65, H 7.20, N 22.97.
1380 (vw), 1441 (w), 1537 (vw), 2733 (vw), 2928 (vs), 3128 (w)
cm–1. C40H56N16O2Si3 (877.25): calcd. C 54.77, H 6.43, N 25.55; found
C 54.53, H 6.21, N 25.39.
Hexakis(3,5-dimethylpyrazolyl)disiloxane [O(Sipz*3)2, 4]:
Me3Sipz* (9.14 g, 54.3 mmol) was added to a solution of O(SiCl3)2
(2.58 g, 9.0 mmol) in n-hexane (15 mL) and the mixture heated to
reflux for 2.5 h. After cooling, a colorless solid formed, which was
collected by filtration, washed with n-hexane (4 × 10 mL), and dried
in vacuo, yield 5.16 g, 8.0 mmol, 88 %, m.p.114 °C (decomposition,
Single-Crystal Structure Determination: The XRD data sets were
collected with a Stoe IPDS2 diffractometer by using Mo-Kα (λ =
0.71073 Å) radiation. The structures were solved by direct methods
(SHELXS-97) and refined to convergence on F2 against all of the
independent reflections by the full-matrix, least-squares method
with the SHELXL-97 program.[26] Non-hydrogen atoms were refined
anisotropically, C-bound hydrogen atoms were refined in idealized
positions (riding model), and N-bound H atoms were located as
residual electron-density peaks and refined isotropically without re-
straints (Table 6).
1
sealed capillary). H NMR (400.13 MHz, CDCl3, 20 °C, TMS): δ = 5.82
(s, 6 H, pz*C-H), 2.02 ppm (s, 36 H, pz*C-CH3); 13C{1H} NMR
(100.63 MHz, CDCl3, 20 °C, TMS): δ = 153.3 (pz*C-CH3), 148.9 (pz*C-
CH3), 108.8 (pz*C-H), 13.2 (pz*C-CH3) 12.2 ppm (pz*C-CH3); 29Si{1H}
NMR (79.48 MHz, CDCl3, 20 °C, TMS): δ = –78.1 ppm (OSipz*3). Ra-
man: cm–1 ν = 111 (s), 201 (w), 288 (vw), 325 (vw), 363 (vw),
˜
437 (vw), 591 (s), 647 (vw), 759 (vw), 797 (vw), 971 (vw), 1021 (w),
1085 (vw), 1144 (vw), 1310 (vw), 1372 (vw), 1439 (m), 1472 (w),
1567 (vw), 2730 (vw), 2867 (vw), 2922 (vs), 2964 (m), 3108 (vw)
cm–1. C30H42N12OSi2 (642.91): calcd. C 56.05, H 6.58, N 26.14; found
C 56.25, H 6.66, N 26.15.
CCDC 1470248 (for 4), 1470251 (for 4·5), 1470249 (for 6), and
1470250 (for 7) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre.
NMR Spectroscopy: Solution NMR spectra were recorded with a
Bruker DPX 400 spectrometer operating at 400.13 MHz (1H) or
Bruker Avance III 500 operating at 500.13 MHz (1H). The spectra
were referenced internally to TMS or residual (protic) solvent signals.
The 29Si solid-state CP/MAS NMR spectra were recorded with a
Bruker Avance 400 MHz WB spectrometer operating at 79.51 MHz
1,1-Dichloro-1,3,3,5,5,5-hexakis(3,5-dimethypyrazolyl)trisilox-
ane ([(pz*2Si)(μ-pz*)O(Sipz*)(μ-pz*)O(SiCl2pz*)], 7): Me3Sipz*
(2.70 g, 16.0 mmol) was added in one portion to a solution of
O2Si3Cl8 (0.80 g, 2.0 mmol) in n-hexane . The reaction mixture was
stirred thoroughly for a few seconds and then stored undisturbed.
After 48 h the crystallization of the product had finished. The super-
natant solution was decanted, and the crystals washed with n-hex-
ane (2 × 10 mL) and dried in vacuo. Compound 7 was obtained as
a colorless solid, yield 1.13 g, 1.5 mmol, 74 %, m.p. 177 °C (decom-
position, sealed capillary). Due to exchange reactions it is not possi-
ble to assign individual chemical shifts to the pyrazolyl units, so
ranges for the components are reported. 1H NMR (400.13 MHz,
C6D6, 20 °C, TMS): δ = 5.78–5.43(6 H, pz*C-H), 2.49–1.86 ppm (36 H,
pz*C-CH3); 13C{1H} NMR (100.63 MHz, C6D6, 20 °C, TMS): δ = 149.3–
146.5 (pz*C-CH3), 110.3–107.3 (pz*C-H), 13.9–12.1 ppm (pz*C-CH3);
29Si{1H} NMR (79.48 MHz, C6D6, 20 °C, TMS): δ = –133.3/–135.7 (I=
(
29Si) by using a 7 mm probe and a spinning frequency of 5 kHz, if
not otherwise specified. The chemical shift scale was referenced to
TMS.
Quantum Chemical Calculations: The DFT calculations were car-
ried out by using Gaussian 03.[27] NMR shielding tensors were calcu-
lated with the Gauge-Independent Atomic Orbital method
(GIAO)[28] by using the B3PW91[29] density functional in combina-
tion with the 6-311+G(2d,p)[30] basis set for all atoms, and the ge-
ometries from X-ray structure analyses. Calculated absolute shield-
ing values were converted to relative shifts δ by means of the calcu-
2/1, OSipz*2O), –120.9/–121.2 (I=1/2, OSiCl2pz*), –68 ppm (pz*3SiO); lated shielding for tetramethylsilane at the same level of theory.
29Si CP/MAS NMR (79.51 MHz, 20 °C, TMS): δ = –135.2 (OSipz*2O), Energy calculations and the relaxed PES scan (Gaussian 09)[31] were
Eur. J. Inorg. Chem. 2016, 4207–4215
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Table 6. Selected crystallographic and refinement data for 4, (4)(5)2, 6, and 7.
4
(4)(5)2
6
7
Formula
M [g mol–1
T [K]
C30H42N12OSi2
642.94
200(2)
C70H102Cl8N28O3Si6
1835.94
150(2)
C15H22Cl4N6OSi2
500.37
200(2)
C30H42Cl2N12O2Si3
757.93
180(2)
]
Crystal size [mm]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
0.25 × 0.20 × 0.10
triclinic
0.23 × 0.11 × 0.03
monoclinic
C2/c
32.121(2)
9.0573(3)
30.554(2)
90
99.681(5)
90
8762.4(9)/4
1.392
0.40 × 0.15 × 0.03
monoclinic
P21/m
12.0257(6)
7.1971(4)
13.3270(7)
90
103.464(4)
90
1121.75(10)/2
1.481
0.35 × 0.25 × 0.13
triclinic
P1
P1
¯
¯
9.2409(8)
9.9622(8)
10.9282(9)
68.525(7)
66.749(6)
74.890(7)
852.20(12)/1
1.253
8.0624(4)
14.0076(7)
17.6607(8)
97.655(4)
100.215(4)
100.352(4)
1902.67(16)/2
1.323
α [°]
ꢀ [°]
γ [°]
V [Å3]/Z
ρcalcd. [g cm–3
]
μ(Mo-Kα) [mm–1
F(000)
]
0.148
342
0.402
3848
0.654
516
0.311
796
Θ range [°]
2.4 to 25.5
10462
3153 (Rint = 0.0683)
99.4
2.3 to 25.0
22496
7651 (Rint = 0.1000)
99.2
2.6 to 27.0
15554
2637 (Rint = 0.0392)
99.9
2.6 to 30.0
31503
11086 (Rint = 0.0323)
99.9
Measured reflections
Independent reflections
Completeness [%]
Data/restraints/parameters
Goodness of fit on F2
R1/wR2 [I > 2σ(I)]
3153/0/211
1.038
0.0412/0.1060
0.0559/0.1132
0.386/–0.232
7651/0 /542
0.952
0.0480/0.0846
0.1120/0.1021
0.374/–0.443
2637/0/172
1.083
0.0267/0.0700
0.0322/0.0738
0.304/–0.274
11086/0/454
1.036
0.0388/0.1010
0.0503/0.1074
0.457/–0.374
R1/wR2 (all data)
Largest diff. peak/hole [e Å3]
[7]
a) A. N. Polivanov, N. N. Troitskaya, E. V. Los, N. N. Silkina, A. S. Shapatin,
M. Gavars, O. D. Gracheva, A. G. Trufanov, V. N. Bochkarev, Zh. Obshch.
Khim. 1987, 57, 1570–1573; b) M. Kumada, M. Yamaguchi, Nippon Kagaku
Zasshi 1954, 57, 175–177.
N. N. Sokolov, K. A. Andrianov, Russ. Chem. Bull. 1958, 6, 827–832.
H. Manami, S. Nishizaki, Nippon Kagaku Zasshi 1958, 79, 60–65.
a) A. G. Russell, T. Guveli, B. M. Kariuki, J. S. Snaith, J. Organomet. Chem.
2009, 694, 137–141; b) U. Herzog, H. Borrmann, J. Organomet. Chem.
2003, 681, 5–11; c) U. Herzog, H. Borrmann, J. Organomet. Chem. 2004,
689, 564–574.
done with the B3PW91 density functional in combination with the
6-31G(d) basis set for all atoms, on the fully optimized geometries.
Supporting Information (see footnote on the first page of this
article): 1. color figures of the presented crystal structures. 2. Details
of the solid-state NMR measurements of 7. 3. Relaxed PES scan of
4, reaction enthalpies and atomic coordinates. 4. Details concerning
the isolation of 1.
[8]
[9]
[10]
Acknowledgments
[11]
W. Wojnowski, W. Bochenska, K. Peters, E.-M. Peters, H. G. von Schnering,
Z. Anorg. Allg. Chem. 1986, 533, 165–174.
F. Weinhold, R. West, Organometallics 2011, 30, 5815–5824.
G. Tsantes, N. Auner, T. Müller, in: Organosilicon Chemistry V: From Mol-
ecules to Materials (Eds.: J. Weis, N. Auner), Wiley-VCH, Weinheim, Ger-
many, 2003.
G. V. Gibbs, M. B. Boisen, L. L. Beverly, K. M. Rosso, Rev. Mineral. Geochem.
2001, 42, 345–381.
a) S. Vepachedu, R. T. Stibrany, S. Knapp, A. J. Potenza, H. J. Schugar, Acta
Crystallogr., Sect. C 1995, 51, 423–426; b) F. Armbruster, I. Fernández, F.
Breher, Dalton Trans. 2009, 5612–5626.
C. Glidewell, D. C. Liles, J. Chem. Soc., Chem. Commun. 1977, 632–633.
The structural factor τ is defined for five-coordinate geometries as τ =
(ꢀ – α)/60 where α is the widest and ꢀ the second widest angle in the
coordination sphere. τ = 1 indicates an ideal trigonal bipyramid and τ =
0 an ideal square pyramid as coordination polyhedron; see: A. W. Addi-
son, T. N. Rao, J. Reedijk, J. van Rijn, G. C. Verschoor, J. Chem. Soc., Dalton
Trans. 1984, 1349–1355.
a) N. Kocher, J. Henn, B. Gostevskii, D. Kost, I. Kalikhman, B. Engels, D.
Stalke, J. Am. Chem. Soc. 2004, 126, 5563–5568; b) K. Akiba, in: Chemistry
of hypervalent compounds (Ed.: K. Akiba), Wiley-VCH, New York, 1999; c)
C. Chuit, Robert J. P. Corriu, C. Reye, in: Chemistry of hypervalent com-
pounds (Ed.: K. Akiba), Wiley-VCH, New York, 1999.
Determined according to the Herzfeld–Berger convention, see: J. Herz-
feld, A. E. Berger, J. Chem. Phys. 1980, 73, 6021–6030.
J. Mason, Solid State Nucl. Magn. Reson. 1993, 2, 285–288.
R. K. Harris, E. D. Becker, S. M. C. De Menezes, P. Granger, R. E. Hoffman,
K. W. Zilm, Magnetic Resonance in Chemistry: MRC 2008, 46, 582–598.
The authors thank the German Research Foundation (DFG) and
the TU Bergakademie Freiberg, Germany for financial support.
[12]
[13]
Keywords: Silicon · Siloxanes · Nitrogen heterocycles ·
Coordination modes · Density functional calculations
[14]
[15]
[1] a) M. A. Halcrow, Dalton Trans. 2009, 38, 2059–2073; b) S. Trofimenko,
Scorpionates. The coordination chemistry of polypyrazolborate ligands, Im-
perial College Press, River Edge, NJ, 1999; c) C. Pettinari, Scorpionates II.
Chelating Borate Ligands, Imperial College Press, Covent Garden, 2008;
d) I. Kuzu, I. Krummenacher, J. Meyer, F. Armbruster, F. Breher, Dalton
Trans. 2008, 5836–5865; e) S. Styra, S. González-Gallardo, F. Armbruster,
P. Oña-Burgos, E. Moos, M. Vanderach, P. Weis, O. Hampe, A. Grün, Y.
Schmitt, M. Gerhards, F. Menges, M. Gaffga, G. Niedner-Schattenburg, F.
Breher, Chem. Eur. J. 2013, 19, 8436–8446; f) F. Armbruster, T. Augenstein,
P. Oña-Burgos, F. Breher, Chem. Eur. J. 2013, 19, 17899–17906.
[2] a) F. Bitto, J. Wagler, E. Kroke, Eur. J. Inorg. Chem. 2012, 2402–2408; b) F.
Bitto, K. Kraushaar, U. Böhme, E. Brendler, J. Wagler, E. Kroke, Eur. J. Inorg.
Chem. 2013, 2954–2962.
[3] a) K. A. Andrianov, A. I. Nogadielli, L. M. Khananashvili, D. S. Akhobadze,
T. N. Vardosanidze, Soobshch. Akad. Nauk Gruz. SSR 1971, 63, 605–608;
b) J. B. Davison, K. J. Wynne, Macromolecules 1978, 11, 186–191.
[4] N. Gotoh, T. Nakajima, j. H. Li, Seisan Kenkyu 1971, 23, 114–116.
[5] J. L. Webb, S. A. Nye, M. M. Grade, EP0398049A219901122, 1990.
[6] Y. Inaki, Polym. Mater. Sci. Eng. 1989, 60, 165–169.
[16]
[17]
[18]
[19]
[20]
[21]
Eur. J. Inorg. Chem. 2016, 4207–4215
www.eurjic.org
4214
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Full Paper
[22]
[23]
[24]
lez, J. A. Pople, Gaussian 03, revision D.02, Gaussian, Inc., Wallingford CT,
2004.
[28] K. Wolinski, J. F. Hinton, P. Pulay, J. Am. Chem. Soc. 1990, 112, 8251–8260.
[29] a) A. D. Becke, J. Chem. Phys. 1993, 98, 5648–5652; b) J. P. Perdew, Y.
Wang, Phys. Rev. B 1992, 45, 13244–13249.
[30] a) W. J. Hehre, Ab initio molecular orbital theory, Wiley, New York, 1986;
b) P. C. Hariharan, J. A. Pople, Theor. Chim. Acta 1973, 28, 213–222; c)
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.
[31] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R.
Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Na-
katsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G.
Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hase-
gawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A.
Montgomery Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Broth-
ers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghava-
chari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega,
J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J.
Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi,
C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski,
G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö.
Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian 09,
revision D.01, Gaussian, Inc., Wallingford CT, 2013.
E. Brendler, T. Heine, A. F. Hill, J. Wagler, Z. Anorg. Allg. Chem. 2009, 635,
1300–1305.
L. E. Paul, I. C. Foehn, A. Schwarzer, E. Brendler, U. Böhme, Inorg. Chim.
Acta 2014, 423, 268–280.
a) L. A. Truflandier, E. Brendler, J. Wagler, J. Autschbach, Angew. Chem.
Int. Ed. 2011, 50, 255–259; Angew. Chem. 2011, 123, 269–273; b) D. Ger-
lach, E. Brendler, T. Heine, J. Wagler, Organometallics 2007, 26, 234–240.
[25] a) D. H. O'Brien, C.-P. Hrung, J. Organomet. Chem. 1971, 27, 185–193; b)
V. N. Torocheshnikov, N. M. Sergeyev, N. A. Viktorov, G. S. Goldin, V. G.
Poddubny, A. N. Koltsova, J. Organomet. Chem. 1974, 70, 347–352.
[26] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
[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, V. Bakken,
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. Ragha-
vachari, 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. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonza-
Received: May 18, 2016
Published Online: August 16, 2016
Eur. J. Inorg. Chem. 2016, 4207–4215
www.eurjic.org
4215
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim