New insights into hexacoordinated silicon complexes with 8-oxyquinolinato ligands: 1,3-shift of Si-bound hydrocarbyl substituents and the influence of Si-bound halides on the 8-oxyquinolinate coordination features

Article abstract of DOI:10.5560/ZNB.2014-4170

The transsilylation reaction between allyltrichlorosilane and 8-trimethylsiloxyquinoline in the molar ratio 1: 3 yields the hexacoordinated silicon tris-chelate (oxinate)₂Si(adho) ("oxinate" = 8-oxyquinolinate, "adho" = di-anion of 2-allyl-1,2-

Full text of DOI:10.5560/ZNB.2014-4170

New Insights into Hexacoordinated Silicon Complexes with 8-
Oxyquinolinato Ligands: 1,3-Shift of Si-Bound Hydrocarbyl Substituents
and the Influence of Si-Bound Halides on the 8-Oxyquinolinate
Coordination Features
Erik Wächtlera, Alexander Kämpfea, Katrin Krupinskia, Daniela Gerlacha, Edwin Krokea,
Erica Brendlerb, and Jörg Waglera
a
Institut für Anorganische Chemie, TU Bergakademie Freiberg, Leipziger Straße 29, 09596
Freiberg/Sachsen, Germany
Institut für Analytische Chemie, TU Bergakademie Freiberg, Leipziger Straße 29, 09596
b
Freiberg/Sachsen, Germany
Reprint requests to Dr. Jörg Wagler. Fax: (+49) 3731 39 4058.
E-mail: joerg.wagler@chemie.tu-freiberg.de
Z. Naturforsch. 2014, 69b, 1402 – 1418 / DOI: 10.5560/ZNB.2014-4170
Received August 1, 2014
Dedicated to Professor Hubert Schmidbaur on the occasion of his 80th birthday
The transsilylation reaction between allyltrichlorosilane and 8-trimethylsiloxyquinoline in the mo-
lar ratio 1 : 3 yields the hexacoordinated silicon tris-chelate (oxinate)2Si(adho) (“oxinate” = 8-
oxyquinolinate, “adho” = di-anion of 2-allyl-1,2-dihydro-8-oxyquinoline) comprising an SiO3N3
skeleton. The identity of this complex was established by single-crystal X-ray diffraction analysis
and 29Si CP/MAS NMR spectroscopy of its chloroform solvate. Benzyltrichlorosilane and diben-
zyldichlorosilane, comprising benzyl (Bn) as an “aromatically stabilized allyl moiety” did not un-
dergo such rearrangement. Instead, the complexes (oxinate)2SiBnCl and (oxinate)2SiBn2 were ob-
tained even upon using three molar equivalents of 8-trimethylsiloxyquinoline.
We determined the crystal structure of a non-disordered bis-chelate (oxinate)2SiBnCl with Si-
bound hydrocarbyl and halogen substituents (the previously published (oxinate)2SiMeCl was dis-
ordered with alternative Me/Cl site occupancies). (Oxinate)2SiBnCl exhibits surprisingly poor re-
sponse of the N−Si bonds to the different trans-disposed Si−X (X = Bn, Cl) bonds. For com-
parison and deeper insights into the coordination chemistry of oxinato silicon complexes with
halide substituents, we determined the crystal structures of (oxinate)2SiPhCl·CHCl3, (oxinate)2SiCl2,
(oxinate)2SiF2·1.5(CHCl3), and (8-oxyquinaldinate)2SiF2. Furthermore, the crystal structures of
BnSiCl3 and Bn2SiCl2 (and its dibromo analog) are reported. The influence of the Si–C–C–C torsion
angles of the benzyl group on the 29Si NMR shift of benzylsilanes (which is noticeably upfield with
respect to analogous methyl silanes) was analyzed by quantum-chemical calculations.
Key words: Benzylsilanes, Hypercoordination, Isomerism, Oxyquinolinate, Rearrangement
Introduction
we found this coordination pattern to dominate the
portfolio of isomers (found for (oxinate)2SiRR0 with
In 1984 Klebe and Tran Qui reported the first R, R0 = Ph, Ph; Ph, Me; (CH2)3; (CH2)4; (CH2)5
crystal structure of a hexacoordinated silicon bis- and the related complex (8-oxyquinaldinato)2SiPh(8-
chelate with 8-oxyquinolinate (oxinato) ligands, i. e., oxyquinaldinyl) (II)). By contrast, we encountered
(oxinate)2SiMeCl (I) [1]. Their analysis confirmed the the N,N-trans-O,O-cis coordination mode in only
hexacoordination of the Si atom and revealed a sili- one case (the tris-chelate (oxinate)2Si(PhN–CH2CH2–
con coordination sphere with the Si−N bonds trans NPh), III) and the intermediate all-cis coordination
to the monodentate substituents Me and Cl, whereas mode with Ph, 8-oxyquinolinyl (IV). Furthermore,
the O atoms are trans to each other. In our studies we reported three examples for silicon compounds
of silicon bis-chelates with two oxinato ligands [2 – 4] with capped tetrahedral coordination spheres ([4+2]
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E. Wächtler et al. · Hexacoordinated Silicon Complexes
1403
or [4+1] coordination with Si···N separations>2.7 Å), tions, Scheme 1 [4]) served as a motivation for us to
i. e., (oxinate)2SiRR0 with R, R0 = Me, Me (V); (CH2)5 explore the chemistry of oxinato silicon compounds in
(IX, Scheme 1) and (CH2)6 (VI). Further crystallo- more detail.
graphically confirmed hypercoordinated silicon com-
plexes with 8-oxyquinolinate among the ligands bear Results and Discussion
only one such ligand, either as a monodentate sub-
stituent (in (salen*)SiPh(8-oxyquinolinyl), VII, [5]) or Benzylchlorosilanes
as an O,N-chelating ligand (e. g., in complex VIII, [6])
at a hexacoordinated silicon atom, and so far one pen-
tacoordinated silicon oxinato complex (X, Scheme 1) thesized dibenzyldichlorosilane (Bn2SiCl2, δ29Si =
has been confirmed crystallographically [4].
22.6 ppm) and benzyltrichlorosilane (BnSiCl3, δ29Si
In the context of different investigations we had syn-
The still rather limited insights into the coordination = 7.6 ppm) [21], which are relevant starting materi-
behavior of oxinate in the ligand sphere of a silicon als for this study, and from Bn2SiCl2 we had also pre-
atom (whereas various more complex O,N-chelating pared the fluoro and bromo derivatives Bn2SiF2 (δ29Si
ligands have already been utilized in silicon coor- = −10.7 ppm) and Bn2SiBr2 (δ29Si = 17.2 ppm)
dination chemistry [7 – 20]) and the occasional find- (Scheme 2). 29Si NMR investigations of these ben-
ings of surprising reactivity patterns of oxinato sili- zylsilanes revealed noticeably upfield-shifted signals
con complexes (e. g., temperature-dependent coordi- with respect to those of the corresponding methylsi-
nation equilibria and UV-induced rearrangement reac- lanes MeSiCl3 (δ29Si = 12.2 ppm) or Me2SiX2 (δ29Si
Scheme 1.
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E. Wächtler et al. · Hexacoordinated Silicon Complexes
Scheme 2.
Fig. 1 (color online). Molecular structure of (from top) ben-
zyltrichlorosilane and dibenzyldichlorosilane in the crystal.
(Displacement ellipsoids are shown at the 50% probability
level, hydrogen atoms are omitted). Selected bond lengths
(Å) and angles (deg): BnSiCl3: Si1−Cl1 2.031(1), Si1−Cl2
2.032(1), Si1−Cl3 2.032(1), Si1−C1 1.849(2); Si1–C1–
C2 113.6(2), Cl1–Si1–C1–C2 172.2(2); Bn2SiCl2: Si1−Cl1
2.052(1), Si1−Cl2 2.060(1), Si1−C1 1.857(1), Si1−C8
1.854(2); Si1–C1–C2 114.1(1), Si1–C8–C9 115.0(1), C1–
Si1–C8–C9 171.4(1); Bn2SiBr2 (atomic labels correspond to
those in Bn2SiCl2): Si1−Br1 2.210(1), Si1−Br2 2.223(1),
Si1−C1 1.866(2), Si1−C8 1.861(2); Si1–C1–C2 114.6(1),
Si1–C8–C9 115.3(1), C1–Si1–C8–C9 170.5(1).
= 4.4, 31.8, 19.2 ppm for X = F, Cl, Br, respec-
tively) [22]. As we observed the same phenomenon of
relatively upfield-shifted 29Si NMR signals during our
investigation of benzyl-substituted oxinato complexes
(vide infra), we also strived for an investigation of the
molecular structures of benzylhalosilanes and the in-
fluence of the benzyl group on the 29Si NMR shift,
which will be presented in this paragraph.
The reaction of SiCl4 with a commercially avail-
able benzylmagnesiumchloride solution in a 1 : 2 stoi-
chiometric ratio (aiming at maximum yield in diben-
zyldichlorosilane) afforded a mixture of BnSiCl3,
Bn2SiCl2 and Bn3SiCl, the components of which were C sequence of the respective benzyl group. This ar-
isolated in yields of 5, 68 and 0.6%, respectively rangement was also found for Bn2SiBr2 (not depicted),
(based on BnMgCl). Whereas the mono- and disub- which is isostructural with its chloro analog. The pre-
stituted silanes were separated by vacuum distillation, ferred arrangement of electron-donating groups in α-
Bn3SiCl was recrystallized from the residue. The solid- position of silanes towards the positively polarized sil-
state structure of Bn3SiCl has already been reported by icon atom (e. g., in (F3C)F2Si–O–NMe2 the N-lone
Osakada et al. [23]. Bn2SiCl2 crystallized upon cool- pair is directed towards the silicon atom [24]) is well-
ing to room temperature, and a single-crystalline shard known from the literature. This so-called α-effect re-
thereof proved suitable for X-ray diffraction analysis sults in particular features of these so-called α-silanes,
(Fig. 1). BnSiCl3, obtained as the first fraction of the e. g., high-field shifted 29Si NMR resonances due to
vacuum distillation, was placed in a freezer (−20◦C), additional electron donation. The Si–C–C bond an-
whereupon a solid formed which also allowed for man- gles found in the molecular structures of BnSiCl3
ual extraction of single-crystalline pieces on an ice- (113.6(2)◦) and Bn2SiCl2 (114.1(1) and 115.0(1)◦),
cooled Petri dish, thus giving access to their X-ray which are significantly wider than the tetrahedral an-
diffraction analysis (Fig. 1). The molecular structures gle, cannot support the concept of α-silanes with ben-
of BnSiCl3 and Bn2SiCl2 reveal a special arrange- zyl being a special α-substituent. Thus, minimization
ment of one phenyl group with respect to the Si-bound of intermolecular repulsive forces might render the
chlorine atoms (axis through the o-carbon atoms al- present positions of the benzyl groups more favorable
most parallel to Cl1–Cl2 in Bn2SiCl2 and to Cl2–Cl3 rather than the action of significant electrostatic attrac-
in BnSiCl3), which can alternatively be described as tions. In order to analyze the reasonability of retention
an almost perpendicular arrangement of the phenyl of this Ph-CH2–SiX2 arrangement in solution and its
ring with respect to the plane created by the Si–C– effect on the 29Si NMR shift, the gas-phase molecular
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E. Wächtler et al. · Hexacoordinated Silicon Complexes
1405
Fig. 2 (color online). Molecular conformation of benzyl-
trichlorosilane with minimum (left) and maximum energy
(right) in the potential energy surface scan (see Fig. 3).
Fig. 3. Potential energy surface scan of benzyltrichlorosilane
for the rotation about the Si−C bond (front to back) and vari-
ation of the Si–C–C–C dihedral angle (left to right).
structures of benzyltrihalosilanes BnSiX3 (X = F, Cl,
Br) were optimized at the B3LYP/6-311G(d,p) level of the SiX3 moiety about the Si−C bond, however,
of theory. All of them revealed a minimum energy con- are significantly less hindered (2 kcal mol−1). Thus,
formation similar to that found for BnSiCl3 in the solid at least the relative arrangement of the benzene ring
state (Fig. 2, left). A potential energy surface scan was with respect to the silicon atom as depicted in Fig. 2
then performed, in which the SiX3 group was rotated (left) should noticeably contribute to the predominant
about the Si−C bond in increments of 2◦ (60◦ in to- molecular arrangement of benzyltrihalosilanes in solu-
tal), in conjunction with a 180◦ rotation of the phenyl tion.
group about the (Si)C−C(Ph) bond (in increments of
The magnetic anisotropy of π-electron systems,
2◦). Each rotation was followed by relaxation of the e. g., benzene, and the shielding vs. deshielding ef-
atomic coordinates (only keeping the two angles of fects resulting therefrom can significantly contribute
interest restrained). The resulting energy surface pro- to the overall shielding of the nuclei, e. g., protons,
file for BnSiCl3 (∆Emax = 8.3 kcal mol−1) is depicted which are situated in plane with or orthogonal to
in Fig. 3. Benzyltrifluoro- and -tribromosilane deliv- the benzene ring current. Hence, the so-called shield-
ered similar energy surface patterns with ∆Emax being ing cone of the benzene ring might provide an ex-
4.1 and 8.9 kcal mol−1, respectively. For BnSiCl3 the planation for high-field shifted 29Si NMR resonances
molecular conformation of highest energy with respect in benzylhalo- vs. alkylhalosilanes. Quantum-chemical
to the above energy surface scan is depicted in Fig. 2, calculations at the B3LYP/6-311G+(2d,p) and HF/6-
right. One can easily conclude that repulsive forces 311G+(2d,p) levels predicted 29Si NMR shifts of 31.6
result from intramolecular interactions between one and 19.8 ppm, respectively, for BnSiCl3 in the molec-
chlorine atom and an ortho-hydrogen atom of the ben- ular conformation shown in Fig. 2, left, and shifts of
zyl group. The energy differences of about 4 – 8 kcal 35.3 and 21.8 ppm, respectively, for the conformation
mol−1 give rise to the assumption that the most likely shown in Fig. 2, right. Even though the chemical shifts
molecular structures of benzyltrihalosilanes in solu- calculated are noticeably off the experimental value
tion may differ only slightly from the molecular shape (7.6 ppm) and depend on the method and basis set
found for BnSiCl3 in the solid state and in the opti- used, the rather small differences between the shifts
mized gas-phase structures BnSiX3, as far as the ori- calculated for the different molecular conformations
entation of the benzene ring with respect to the silicon clearly indicate that the arrangement of the benzyl
atom is concerned, but rotation of the phenyl group group found in the solid state contributes only to a lim-
is still easily possible at room temperature. Rotations ited extent to an upfield shift of the 29Si resonance.
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E. Wächtler et al. · Hexacoordinated Silicon Complexes
Scheme 3.
Thus, as hypercoordination (α-effect) and magnetic
anisotropy of the aromatic system do not play the key
role for the upfield-shifted 29Si NMR signals of ben-
zylsilanes, we attribute it to the properties of the Si−C
bond to the Bn substituent (i. e., the dia- and paramag-
netic (de)shielding contributions associated therewith).
Reactions of allyl- and benzylchlorosilanes with
8-trimethylsiloxyquinoline
Inspired by the allyl 1,3-shift from allylsilanes to an
imine ligand (e. g., formation of XI, Scheme 3, [25,
26]) and the UV-driven rearrangement of the com-
plexes (oxinate)2Si(CH2)n (n = 3, 4, 5, 6) [4] (as
shown for X in Scheme 1), which proves the oxinate-2-
position to be an “aromatically camouflaged” imine C
atom, we investigated the reaction of allyltrichlorosi-
Fig. 4 (color online). Molecular structure of (oxinate)2-
Si(adho) in a crystal of its 1.5(CHCl3) solvate. (Dis-
placement ellipsoids are shown at the 50% probability
level, hydrogen atoms are omitted). The asymmetric unit
comprises two molecules of the complex and three CHCl3
lane with 8-trimethylsiloxyquinoline (Scheme 3). To molecules, but the doubled size of the unit cell mainly arises
from partial ordering of the otherwise (at room temperature)
our surprise, despite using the rather mild ligand trans-
disordered solvent molecules, while the two complex
fer reagent (oxinate)SiMe3 and allyltrichlorosilane in
molecules are pseudo-symmetry-related and thus exhibit
basically identical structural features. Selected bond lengths
a 1.8 : 1.0 molar ratio, we obtained the complex
(oxinate)2Si(adho) (which requires three equivalents of
the oxinate for its formation) as chloroform solvate in
(Å): Si1−O1 1.783(2), Si1−O2 1.769(2), Si1−O3 1.767(2),
Si1−N1 1.961(2), Si1−N2 1.947(2), Si1−N3 1.811(2),
N3−C19 1.482(3), C19−C20 1.505(4), C20−C21 1.337(4),
60% yield. Its molecular structure is shown in Fig. 4.
C19−C28 1.548(3), C28−C29 1.499(4), C29−C30
1.313(4). The sum of the angles about N3 amounts to 359.9◦.
Both the crystallographic analysis and the 29Si CP/
MAS NMR spectroscopic data (δiso = −146.6 ppm)
confirmed the rearrangement of the allyl group to the
formal imine C atom of one oxinate ligand with forma- we thus conclude that the allyl rearrangement product
tion of the hexacoordinated silicon tris-chelate. Chang- (oxinate)2Si(adho) is the favored reaction product in
ing the molar ratio of the starting materials to 2.7 : 1.0 this system of reactants under these conditions. Kost
had only a marginal impact on the yield (62%), and et al. [27] had reported the rearrangement of a tBu
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E. Wächtler et al. · Hexacoordinated Silicon Complexes
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Scheme 4.
group to an unsaturated ligand moiety upon the entry of
a third chelating ligand into the Si coordination sphere.
In order to check whether the third oxinate ligand is
essential to induce allyl rearrangement from the Si
atom to the oxinate C2 atom or whether the rearrange-
ment would also proceed at the stage of a bis-chelate
(oxinate)2SiAllCl, we performed the analogous reac-
tion with allylphenyldichlorosilane (Scheme 3), which
should result either in the formation of a bis-chelate
(oxinate)2SiAllPh or of its rearrangement product (oxi-
nate)SiPh(adho) with a pentacoordinated silicon atom.
As found in the reaction with allyltrichlorosilane, we
also observed the formation of a red product solution
in this case, and 29Si NMR spectroscopic investiga-
tions of the crude product solution confirmed the for-
mation of compounds with a pentacoordinated silicon
atom (δ29Si = −84.3, −87.9, −90.9 ppm). The pres-
ence of three signals in the characteristic shift range
of pentacoordinated silicon atoms gives rise to the as-
sumption that different isomers of (oxinate)SiPh(adho)
coexist in solution.
As an oxinate ligand contains a “camouflaged imine
moiety” which can react in an imine-like manner in
this allyl-1,3-shift reaction, we aimed at introduc-
ing benzyl as a “camouflaged allyl moiety” into the
complex as well. In sharp contrast, the reactions of
the benzylchlorosilanes BnSiCl3 and Bn2SiCl2 with
two equivalents of 8-trimethylsiloxyquinoline only af-
forded the transsilylation products (oxinate)2SiBnCl
and (oxinate)2SiBn2, respectively (Scheme 4, Fig. 5).
Even the reaction of BnSiCl3 with three equiv-
alents of 8-trimethylsiloxyquinoline only afforded
(oxinate)2SiBnCl, and the third equivalent of the lig-
and did not react with the Si-bound Cl atom of this
bis-chelate complex.
Fig. 5 (color online). Molecular structures of (from top)
(oxinate)2SiBnCl, (oxinate)2SiBn2 (in its CHCl3 solvate)
and (oxinate)2SiPhCl (in its CHCl3 solvate) with displace-
ment ellipsoids set at the 50%, 50% and 30% probability
level, respectively (hydrogen atoms are omitted). Selected
bond lengths (Å) and angles (deg): (oxinate)2SiBnCl:
Si1−Cl1 2.230(1), Si1−O1 1.767(2), Si1−O2 1.771(2),
Si1−N1 2.013(2), Si1−N2 1.982(2), Si1−C19 1.915(2);
Si1–C19–C20 118.1(2); (oxinate)2SiBn2: Si1−O1 1.784(1),
Si1−O2 1.789(1), Si1−N1 2.073(2), Si1−N2 2.055(2),
Si1−C19 1.931(2), Si1−C26 1.933(2); Si1–C19–C20
121.8(1), Si1–C26–C27 120.9(1); (oxinate)2SiPhCl:
Si1−Cl1 2.203(1), Si1−O1 1.763(2), Si1−O2 1.753(2),
Si1−N1 2.013(2), Si1−N2 2.012(2), Si1−C19 1.903(3).
In addition to underlining that benzyl does not re-
flect a “camouflaged allyl” in terms of the intended stage (oxinate)2SiAllCl (which is generally possible
1,3-shift reaction, the formation of (oxinate)2SiBnCl as shown by the reaction of 8-trimethylsiloxyquinoline
provides support for the hypothesis that the allyl with allylphenyldichlorosilane, vide supra), because
1,3-shift reaction already proceeds at the bis-chelate the rearrangement product (oxinate)SiCl(adho) with
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E. Wächtler et al. · Hexacoordinated Silicon Complexes
a pentacoordinated silicon atom can be expected to
be more susceptible to further ligand exchange reac-
tions, i. e., transsilylation with a third equivalent of
8-trimethylsiloxyquinoline, whereas the hexacoordi-
nated Si complex (oxinate)2SiAllCl should be rather
inert towards further transsilylation (in analogy to
(oxinate)2SiBnCl).
The comparison of the Si−N bonds in (oxinate)2-
SiBnCl (2.01 and 1.98 Å) and (oxinate)2SiBn2 (2.07
and 2.06 Å) indicates that the trans-disposed Si−X
bond (X = Cl vs. C) plays a less pronounced role than
the overall (“spherical”) Lewis acidity caused by the
more or less electron-withdrawing substituents (i. e.,
introduction of one Cl substituent causes shortening
of both Si−N bonds and has only a marginal effect
on the particular shortening of the trans-Si−Cl-located
Si−N bond). As the available literature data of Si−N
bond lengths in (oxinate)2SiRX complexes are only
of limited value for a comparison (heavy disorder of
the structure with R, X = Me, Cl [1], similar bonds
in the structure with R, R0 = Me, Ph [2], O trans to
Scheme 5.
X for R, X = Ph, 8-oxyquinolinyl [3]), we synthesized dinated silicon complex (oxinate)2SiCl2 by quantum-
(oxinate)2SiPhCl as another example of complexes of chemical calculations, 29Si CP/MAS NMR and IR
the type (oxinate)2SiRX with two Si−N bonds trans spectroscopy, and we had come to the conclusion
to the two different monodentate substituents (Fig. 5). that this complex most likely crystallizes as the all-
In case of this compound we found basically identi- trans isomer. In order to solve this contradiction,
cal (both 2.01 Å) Si−N bond lengths despite the two we recorded a 29Si CP/MAS NMR spectrum of the
different trans-disposed substituents. Furthermore, the (oxinate)2SiCl2 obtained in the current study. The
Si−N bond lengths for the compounds with R, X = Bn, spectrum basically resembles that of the previous study
Cl and Ph, Cl are similar to one another, and the (i. e., only one signal located at −158.7 ppm). In con-
Si−N bond lengths in the compounds with R, R0 = Ph, trast to the previously recorded spectrum (with a signal
Ph (2.09 Å) [2], Ph, Me (2.09 – 2.11 Å) [2], (CH2)5 located at −157.9 ppm) the signal is slightly shifted
(2.09 – 2.13 Å) [4], and Bn, Bn (2.07, 2.06 Å) are also upfield. We cannot rule out contributions of experi-
similar.
mental errors and the effect of crystal size to cause
this shift, but the width of the signal (caused by the
chloro substituents) would at least allow for the ap-
pearance as a single signal even in case of a su-
perposition of signals of two isomers. Therefore, we
Syntheses of bis-chelates with two Si–X (X = F, Cl)
bonds
Motivated by the successful preparation of crys- also recorded a powder X-ray diffractogram of our
talline bis-oxinato silicon complexes suitable for X- product (oxinate)2SiCl2 and found a good match with
ray diffraction via the transsilylation route and the still the pattern predicted from the single-crystal structure.
present lack of crystal structure data of complexes of Some reflections of moderate intensity, however, could
the type (oxinate)2SiX2 (X = halide), we synthesized not be assigned, neither to the crystal structure of
(oxinate)2SiCl2 and (oxinate)2SiF2 (Scheme 5, Fig. 6). (oxinate)2SiCl2 nor to the crystal structure of the po-
Both complexes exhibit the same coordination mode tential contaminant 8-oxyquinoline hydrochloride [28]
(O,O-trans, N atoms trans to the monodentate sub- (see Supporting Information). These findings, and the
stituents) as most of the other crystallographically very similar relative energies calculated for the herein
characterized oxinato silicon bis-chelates. In 2005 [2] found isomer of (oxinate)2SiCl2 and its all-trans alter-
we had analyzed the potential isomers of the hexacoor- native [2] now give rise to the assumption that both
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E. Wächtler et al. · Hexacoordinated Silicon Complexes
1409
Scheme 6.
Another surprising finding is that both complexes
(oxinate)2SiCl2 and (oxinate)2SiF2 crystallize as the
same isomer (O,O-trans mode). In studies of hexacoor-
dinated silicon bis-chelates with other (O,N)-bidentate
chelators (Scheme 6 [29, 30]) the size difference of Cl
vs. O vs. F led to the formation of different isomers
for the dichloro vs. the difluoro complex. That is, the
substituent in close proximity to the sp2-hybridized N
atom prefers to face the smaller O atom in case of the
chloro complex but faces the F atom in the difluoro
complex because of the lower steric repulsion with the
smaller F atom (relative to the O atom). In case of the
oxinato complexes we have shown [2, 3] that hydrogen
contacts between the H atom in 2-position of the oxi-
nate and a lone-pair donor atom stabilize the Si coordi-
nation sphere. Apparently, the H contact to the neigh-
boring oxinate O atom is favored over the alternative
H contact to a fluorine atom, thus over-compensating
the influence of steric repulsion by the slightly bigger
O atom. Replacement of the CH moiety in 2-position
by a CMe moiety (i. e., using the 8-oxyquinaldinate
ligand) eventually drives the still hexacoordinated sil-
icon complex into the alternative N,N-trans coordina-
tion mode, now with the CMe moieties facing the F
atoms (Scheme 5, Fig. 6).
Fig. 6 (color online). Molecular structures of (from top)
(oxinate)2SiCl2, (oxinate)2SiF2 (in its solvate·1.5(CHCl3))
and (8-oxyquinaldinate)2SiF2 with displacement ellipsoids
set at the 50% probability level (hydrogen atoms are
omitted). The structure of (oxinate)2SiF2 contains four inde-
pendent complex molecules in the asymmetric unit, but only
one of them is depicted as a representative example. The
asymmetric units of each of the other two structures consist
of half a molecule, with the Si atom located on a two-fold
axis. Atom labels with asterisks indicate symmetry equiva-
lent positions. Selected bond lengths (Å): (oxinate)2SiCl2:
Si1−Cl1 2.187(1), Si1−O1 1.749(1), Si1−N1 1.966(2);
(oxinate)2SiF2: Si2−F3 1.644(1), Si2−F4 1.642(1), Si2−O3
1.765(1), Si2−O4 1.752(1), Si2−N3 1.983(1), Si2−N4
1.977(1); (8-oxyquinaldinate)2SiF2: Si1−F1 1.658(1),
Si1−O1 1.769(2), Si1−N1 1.947(2).
For comparison of the energetics of these two alter-
native isomers (depending on the chelating ligand oxi-
nate vs. 8-oxyquinaldinate and on the size of the halide
Cl vs. F) we have performed quantum-chemical calcu-
lations (full optimization of the gas-phase molecular
conformation at the DFT MPW1PW91 6-311G(d,p)
level, single-point energy calculations at the MP2 6-
31G(d) level). The relative energies are shown in Ta-
isomers coexist in solution and precipitate/crystallize ble 1, atomic coordinates of the optimized molecular
as mixtures with the fractions of the isomers depending structures are available in the Supporting Information
on subtle differences between the individual syntheses (available online, see note at the end of the paper for
performed.
availability). This analysis confirms that the complexes
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E. Wächtler et al. · Hexacoordinated Silicon Complexes
Table 1. Relative energies of sets of two isomers O,O- Table 2. Solid-state 29Si NMR shifts δiso (in ppm relative to
trans and N,N-trans (kcal mol−1
) of the complexes
TMS) of various hexacoordinated silicon chelates with two
oxinato (or related) ligands.
(chelator)2SiX2. The first entry corresponds to the optimized
structure at the DFT MPW1PW91 6-311G(d,p) level, the en-
try in parentheses corresponds to the single-point calculation
at the MP2 6-31G(d) level.
δiso29Si
remarks
Lit.
(oxinate)2SiPhMe
(oxinate)2SiPh2
−126
[2]
[2]
this work
[4]
[4]
[4]
this work
this work
[3]
−137
a
Chelator
Oxinate
X
F
Cl
F
Cl
O,O-trans
N,N-trans
(oxinate)2SiBn2
(oxinate)2Si(CH2)3
(oxinate)2Si(CH2)4
(oxinate)2Si(CH2)5
(oxinate)2SiPhCl
(oxinate)2SiBnCl
(oxinate)2SiPh
−124/−130
−130
2.7 (0)
1.8 (0)
6.7 (2.4)
0 (0)
0 (0.7)
0 (1.9)
0 (0)
−99
b
8-Oxyquinaldinate
−112/−114
−152
2.0 (5.9)
−140
−147
(8-oxyquinolinyl)
(oxinate)2SiX2 exhibit similar energies for their alter- (oxinate)2SiF2
−163
this work
[2] and
this work
[2]
[2]
this work
[2]
c
(oxinate)2SiCl2
−158/−159
native O,O-trans and N,N-trans coordination modes,
whereas for (8-oxyquinaldinate)2SiX2 the response to
the steric demand of the halide is clearly reflected in
N,N-trans being the favored coordination mode for the
fluoro derivative, whereas O,O-trans is more favorable
for the chloro derivative.
d
(oxinate)2SiBr2
−170
−152
−147
−151
−114
(oxinate)2Si(PhN(CH2)2NPh)
(oxinate)2Si(adho)
(oxinate)3Si+
e
f
(8-oxyquinaldinate)2SiPh
(8-oxyquinolinyl)
(8-oxyquinaldinate)2SiF2
[3]
In the crystal structures of the complexes shown
in Fig. 6 we find surprisingly similar bond lengths.
Neither the transition from (oxinate)2SiCl2 to its flu-
oro analog caused any noteworthy changes in Si−O
−158
this work
a
We attribute the presence of two signals to a phase transformation
upon partial loss of solvent of crystallization; b the crystallographic
c
asymmetric unit comprises two independent molecules; only for
and Si−N bond lengths, nor did the change of the 2nd entry the crystal structure has been determined; d broad sig-
e
nal, no crystal structure reported; the counter ion is chloride, no
coordination mode and steric repulsion by a dif-
f
crystal structure reported; the Si−N bonds in this complex are
ferent ligand cause any significant changes to the
noticeably longer (2.18 and 2.26 Å) than in the other complexes
Si−F, Si−O and Si−N separations (upon switch-
(1.95 – 2.12 Å).
ing to (8-oxyquinaldinate)2SiF2). In comparison with
the complexes (oxinate)2SiRR0 and (oxinate)2SiRX
we find systematically shorter Si−N bonds in the for (oxinate)2SiF2·1.5(CHCl3), −158 ppm for (8-oxy-
(oxinate)2SiX2 compounds (to a less pronounced ex- quinaldinate)2SiF2).
tent this trend is also reflected in the Si−O bond
With the current study the portfolio of crystallo-
lengths), with the shortest Si−N separation en- graphically and 29Si NMR spectroscopically (solid
countered in (8-oxyquinaldinate)2SiF2 (1.95 Å). This state) characterized bis-chelates (oxinate)2SiRR0 and
bond length corresponds nicely to the Si−N(oxinate) analogs has grown noticeably. Table 2 shows their 29Si
bond lengths in (oxinate)2Si(PhN(CH2)2NPh) [2] and CP/MAS NMR shifts (δiso), which now allow for fur-
(oxinate)2Si(adho), which are also 1.95/1.96 Å; this ther comparison within this class of complexes. The
compound exhibits the same N,N-trans coordination hydrocarbyl-substituted compounds with Si(CH2)5,
mode of the O,N-chelators.
SiMePh and SiPh2 moieties reflect the trend of upfield-
As (oxinate)2SiF2 and (8-oxyquinaldinate)2SiF2 shifted 29Si NMR signals upon replacing alkyl by aryl
contain Si−F bonds cis to each other, we expected substituents, which has also been observed with other
a
29Si CP/MAS NMR signal shape similar to that silicon compounds [32]. The “outlier” complexes with
of other hexacoordinated difluorosilicon complexes [6, Si(CH2)4 and Si(CH2)3 moieties simply reflect the
30, 31], i. e., a dublettoid signal caused by dipo- trend of alternating up- and downfield-shifted signals
lar coupling of the cis-arranged fluorine atoms in- of homologous silacycloalkanes, which has already
stead of an intentionally expected triplet-like sig- been reported [4]. The complex (oxinate)2SiBn2 seems
nal. Indeed, this signal shape was observed in both to represent another outlier from this series, but the in-
cases (spectra available in the Supporting Informa- vestigation of other benzylhalosilanes (vide supra) al-
tion), but at different chemical shifts (δiso = −163 ppm ready shows that benzyl does not reflect typical alkyl
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E. Wächtler et al. · Hexacoordinated Silicon Complexes
1411
character in terms of its influence on 29Si NMR shifts were recorded on a Bruker Avance III 500 MHz spectrom-
eter or on a Bruker DPX 400 spectrometer (Me4Si as inter-
nal standard), solid-state 29Si NMR spectra were recorded
on a Bruker AvanceTM 400 MHz WB spectrometer in 4 mm
ZrO2 rotors or in 7 mm ZrO2 rotors with KelF inserts. El-
emental analyses were performed using an Elementar vario
MICRO cube.
but causes an upfield shift of the resonance with re-
spect to “regular” alkyl groups. Replacing one hydro-
carbyl group by a more electronegative substituent (Cl
or aryloxy) causes a further upfield shift of the 29Si
resonance, and the same is observed even more pro-
nounced for systems with both hydrocarbyls replaced
by ligands with more electronegative donor atoms. In
the series (oxinate)2SiX2 (X = F, Cl, Br) some kind of
“sagging pattern” is observed as in case of the silicon
halides SiX4 with SiCl4 exhibiting the most downfield
resonance. This behavior can be attributed to the differ-
ent dia- and paramagnetic and relativistic contributions
to the 29Si shielding in silicon halides [33].
Dibenzyldichlorosilane
A solution of benzylmagnesiumchloride (100 mL of
a 2.0 M solution in THF, 200 mmol) was added dropwise
to a cooled solution (−10◦C) of tetrachlorosilane (19.5 g,
115 mmol) in THF (350 mL). The resulting cloudy yellow
solution was allowed to reach room temperature and was
stirred for another 2 h. The clear and almost colorless solu-
tion thus obtained was stored at room temperature for 1 d.
Then the solvent was removed under reduced pressure, and
the colorless oily residue was dissolved in hexane (200 mL).
Immediately magnesium chloride precipitated. After stirring
at room temperature for 1 h the precipitate was filtered off
and washed with hexane (3 × 40 mL). From the combined
filtrate and washings the solvent was removed in a vacuum,
and the cloudy oily residue was again dissolved in hexane
(100 mL), whereupon more magnesium chloride precipitated
which, after stirring at room temperature for 1 h, was fil-
tered off and washed with hexane (30 mL). Again, from the
clear colorless filtrate the solvent was removed under re-
duced pressure, and the resulting oily product was distilled
in a vacuum (3.0 mm Hg). Fraction 1 (benzyltrichlorosilane,
yield: 2.36 g, 10.5 mmol, 5% with respect to benzylmag-
nesiumchloride) was obtained between 65 and 75◦C. Some
drops of an intermediate fraction (from 75 to 140◦C) were
discarded before fraction 2 (dibenzyldichlorosilane, yield:
19.1 g, 68.0 mmol, 68%) was received between 140 and
147◦C as a colorless liquid which crystallized upon cool-
ing to room temperature. The yellow oily residue was dis-
solved in hexane (19 mL), and colorless crystals of triben-
zylchlorosilane were obtained at room temperature (yield:
1.40 g, 0.42 mmol, 0.6% with respect to benzylmagnesium-
chloride).
Conclusion
Our continuation of the exploration of syntheses of
hypercoordinated silicon compounds with oxinate and
8-oxyquinaldinate ligands has proven oxinate suscep-
tible to an allyl-1,3-shift from silicon to the oxinate C2
atom. Benzyl, although resembling a camouflaged al-
lyl group, was retained bound to the hexacoordinated
silicon atom, e. g., in (oxinate)2SiBnCl. New insights
into oxinate coordination patterns (coordination modes
and Si−N bond lengths depending on the other Si-
bound substituents) were obtained from this and other
halide-substituted silicon complexes which have been
prepared in the course of this study. Last but not least,
the solid-state structures of BnSiCl3, Bn2SiCl2 and
Bn2SiBr2 were determined, which enhance the portfo-
lio of crystallographically characterized benzylsilanes
significantly, and which allowed a closer look at the in-
fluence of the Si-bound benzyl group on the 29Si NMR
shift.
Experimental Section
General considerations: Most of the starting materials
The identity of benzyltrichlorosilane was confirmed by
were commercially available and were used as received 29Si NMR (79.49 MHz, CDCl3, 25◦C): δ = 7.6 ppm [10].
without further purification. Triethylamine and some sol-
Dibenzyldichlorosilane: Yield: 19.1 g (68.0 mmol, 68%).
vents were distilled from sodium benzophenone (THF and – 1H NMR (400.13 MHz, CDCl3, 25◦C): δ = 2.60 (s, 4 H,
diethyl ether) or sodium (hexane and toluene) and were CH2), 7.05 – 7.35 ppm (mm, 10 H, ar). – 13C{1H} NMR
stored over sodium wire (diethyl ether, hexane, toluene) (100.62 MHz, CDCl3, 25◦C): δ = 28.7 (CH2), 125.8 (p),
or activated molecular sieves 3 Å under argon atmosphere 128.6, 129.1 (o and m), 133.8 ppm (i) (ar). – 29Si{1H} NMR
(THF). Amylene-stabilized chloroform and acetonitrile were (79.74 MHz, CDCl3, 25◦C): δ = 22.6 ppm. – C14H14SiCl2
received in spectroscopic grade and were stored over acti- (281.25): calcd. C 59.79, H 5.02; found C 59.20, H 5.08.
vated molecular sieves 3 Å. All reactions were carried out
The identity of tribenzylchlorosilane was confirmed NMR
under an atmosphere of dry argon utilizing standard Schlenk spectroscopically: 1H NMR (400.13 MHz, CDCl3, 25◦C):
3
techniques. Solution-state 1H, 13C and 29Si NMR spectra δ = 2.33 (s, 6 H, CH2), 7.05 (d, 6 H, ar, JHH
=
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1412
E. Wächtler et al. · Hexacoordinated Silicon Complexes
7.6 Hz), 7.14 – 7.30 ppm (mm, 9 H, ar). – 29Si{1H} NMR To this solution allyltrichlorosilane (1.32 g, 7.50 mmol) was
(79.74 MHz, CDCl3, 25◦C): δ = 21.1 ppm.
added at 0◦C to afford a yellow solution, which turned or-
ange and red within one day. The product was obtained
after 3 d as a red crystalline solid which was filtered off,
washed with chloroform (10 mL) and dried in vacuo. Yield:
1.93 g (2.84 mmol, 62%). – 29Si CP/MAS NMR (79.5 MHz,
νspin = 4 kHz): δiso = −146.6 ppm. – C63H49Cl9N6O6Si2
(1361.31): calcd. C 55.58, H 3.63, N 6.17; found C 55.62, H
3.61, N 6.20. (The characterization of this compound in so-
lution was hampered by the very poor solubility in solvents
such as chloroform or DMSO.)
Reaction 2: 8-Trimethylsiloxyquinoline (from 2.00 g,
13.7 mmol of 8-oxyquinoline) was prepared as described
above, and it was dissolved in chloroform (20 mL). To this
solution allyltrichlorosilane (0.88 g, 5.0 mmol) was added at
0◦C to afford a yellow solution, which turned orange and red
within one day. The product was obtained after 3 d as a red
crystalline solid which was filtered off, washed with chloro-
form (10 mL) and dried in vacuo. Yield: 1.86 g (2.73 mmol,
60%). – 29Si CP/MAS NMR (79.5 MHz, νspin = 4 kHz):
Dibenzyldifluorosilane
To
a
solution of dibenzyldichlorosilane (1.57 g,
5.58 mmol) in THF (10 mL) zinc fluoride (1.15 g,
11.2 mmol) was added. After stirring at room tempera-
ture for 3 d the solvent was removed under reduced pressure.
The colorless residue was dissolved in a mixture of hexane
(10 mL) and toluene (5 mL) and allowed to stand overnight,
and the zinc halides were filtered off. Removal of the sol-
vents from the clear filtrate under reduced pressure afforded
dibenzyldifluorosilane as a colorless oil. Yield: quantitative.
– 1H NMR (400.13 MHz, CDCl3, 25◦C): δ = 2.26 (s, 4 H,
CH2), 7.02 (d, 4 H, ar, 3JHH = 7.2 Hz), 7.10 – 7.25 ppm (mm,
6 H, ar). – 13C{1H} NMR (100.62 MHz, CDCl3, 25◦C):
δ = 21.0 (t, 2JFC 14.0 Hz, CH2), 125.6 (p), 128.7, 128.8 (o
and m), 133.7 (i) ppm (ar). – 29Si{1H} NMR (79.74 MHz,
CDCl3, 25◦C): δ = −10.7 ppm (t, 1JSiF = 310 Hz).
δ
iso = −146.6 ppm.
(Oxinate)SiPh(adho)
To stirred solution of 8-oxyquinoline (2.00 g,
Dibenzyldibromosilane
To
a
solution of dibenzyldichlorosilane (2.03 g,
7.21 mmol) in toluene (5 mL) tetrabromosilane (2.51 g,
7.21 mmol) was added at room temperature. The mixture
was stirred under reflux for 2 h. After cooling to room
temperature the volatiles were removed in vacuo, the viscous
residue was again dissolved in toluene (4 mL), and tetra-
bromosilane (1.30 g, 3.74 mmol) was added. After stirring
under reflux for 1 h and cooling to room temperature the
volatiles were again removed under reduced pressure, and
toluene (4 mL) and tetrabromosilane (1.50 g, 4.31 mmol)
were added to the residue once again, followed by stirring
the mixture under reflux for 1 h. Final removal of volatiles
under reduced pressure afforded an oil which solidified at
room temperature to yield beige crystals. Yield: quantitative.
a
13.7 mmol) and triethylamine (2.10 g, 20.6 mmol) in
THF (50 mL) chlorotrimethylsilane (1.64 g, 15.1 mmol)
was added at 0◦C. After 1 h stirring at this temperature
the precipitated triethylammonium chloride was filtered
off and washed with THF (10 mL). From the combined
filtrate and washings the solvent was removed under reduced
pressure, and the remaining oil was dissolved in chloroform
(25 mL). To this solution allylphenyldichlorosilane (1.49 g,
6.86 mmol) was added at 0◦C to afford a yellow solution,
which turned orange and red within few days. The volume
of this still clear product solution was reduced to about
10 mL (by condensation of volatiles into a cold trap under
reduced pressure), and a 29Si NMR spectrum was recorded
(79.74 MHz, D2O insert, 25◦C): δ = 31.0 (Me3SiCl),
20.4 (residual 8-trimethylsiloxyquinoline), −84.3, −87.9,
−90.9 ppm. So far, we have not been able to isolate one or
more of the products from this solution by crystallization.
–
1H NMR (400.13 MHz, CDCl3, 25◦C): δ = 2.83 (s, 4
3
H, CH2), 7.14 (d, 4 H, ar, JHH = 6.8 Hz), 7.17 – 7.30 ppm
(mm, 6 H, ar). – 13C{1H} NMR (100.62 MHz, CDCl3,
25◦C): δ = 30.6 (CH2), 125.9 (p), 128.5, 129.2 (o and m),
134.0 (i) ppm (ar). – 29Si{1H} NMR (79.74 MHz, CDCl3,
25◦C): δ = 17.5 ppm.
(Oxinate)2SiBnCl
(Oxinate)2Si(adho)·1.5(CHCl3)
8-Oxyquinoline (1.00 g, 6.85 mmol) and triethylamine
Reaction 1: To a stirred solution of 8-oxyquinoline (1.00 g, 9.78 mmol) were dissolved in THF (30 mL) and
(2.00 g, 13.7 mmol) and triethylamine (2.10 g, 20.6 mmol) the mixture cooled to 0◦C; chlorotrimethylsilane (0.78 g,
in THF (50 mL) chlorotrimethylsilane (1.78 g, 16.4 mmol) 7.2 mmol) was added dropwise. The triethylammonium chlo-
was added at 0◦C. After 1 h stirring at this temperature the ride precipitate was filtered off and washed with THF (6 mL).
precipitated triethylammonium chloride was filtered off and From the filtrate and washings the solvent was removed un-
washed with THF (10 mL). From the combined filtrate and der reduced pressure. The residue was dissolved in chloro-
washings the solvent was removed under reduced pressure, form (3 mL), and benzyltrichlorosilane (0.78 g, 3.42 mmol)
and the remaining oil was dissolved in chloroform (20 mL). was added. The yellow product, which crystallized within
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E. Wächtler et al. · Hexacoordinated Silicon Complexes
1413
2 d, was filtered off, washed with THF and dried in vacuo. tion. The mixture was stored at a temperature of −50◦C,
Yield: 1.42 g (3.21 mmol, 94%). – M. p. > 200◦C (decompo- and the product was obtained as a crystalline solid (0.62 g,
sition without melting). – 29Si CP/MAS NMR (79.5 MHz, 1.0 mmol), which was filtered off, washed with chloroform
νspin = 5 kHz): δiso = −139.8 ppm. – C25H19ClN2O2Si (6 mL) and dried in vacuo. The filtrate and washings were
(442.96): calcd. C 67.78, H 4.32, N 6.32; found C 67.68, H, concentrated by removing some solvent under reduced pres-
4.42, N 6.23. (The characterization of this compound in so- sure, and a second charge of product was obtained upon
lution was hampered by the very poor solubility in solvents storage at 6◦C (0.38 g, 0.62 mmol). Combined yield: 1.00 g
such as chloroform or DMSO.)
(1.62 mmol, 46%). – 1H NMR (CDCl3, 400 MHz): δ =
3
2.56 (bs, 2 H; CH2); 6.57 (d, JHH = 7.5 Hz, 2 H); 6.66
(Oxinate)2SiBn2·CHCl3
3
(mm, 3 H); 6.90 (m, 1 H); 7.05 (d, JHH = 8.22 Hz, 1
3
3
H); 7.12 (d, JHH = 7.5 Hz, 1 H); 7.46 (t, JHH = 8.08 Hz,
To an ice-cooled stirred solution of 8-oxyquinoline
(1.00 g, 6.85 mmol) and triethylamine (1.00 g, 9.78 mmol)
in THF (30 mL) chlorotrimethylsilane (0.79 g, 7.3 mmol)
was added. After 1 h the triethylammonium chloride pre-
cipitate was filtered off, washed with THF (6 mL) and dis-
carded. From the combined filtrate and washings the sol-
vent was removed under reduced pressure, and the remain-
ing oil was dissolved in chloroform (3 mL), and solid diben-
zyldichlorosilane (0.98 g, 3.5 mmol) was added to the solu-
3
1 H); 7.90 (d, JHH = 8.48 Hz, 1 H); 8.10 ppm (m, 1 H,
HC=N). – 13C{1H} NMR (CDCl3, 100 MHz): δ = 36.8
(CH2), 111.4, 114.1, 121.3, 122.0, 126.8, 128.0, 128.7,
129.9, 135.9, 137.6, 141.7, 144.8, 154.4 ppm (HC=N). –
29Si CP/MAS NMR (79.5 MHz, νspin = 5 kHz): δiso
=
−124.3, −129.8 ppm (two signals were detected because of
loss of chloroform from the crystalline product upon drying;
loss of chloroform was also confirmed by elemental analy-
Table 3. Crystal structure data for BnSiCl3, Bn2SiCl2 and Bn2SiBr2.
BnSiCl3
Bn2SiCl2
Bn2SiBr2
Empirical formula
Mr
C7H7Cl3Si
225.27
C14H14Cl2Si
281.24
C14H14Br2Si
370.16
T, K
90(2)
90(2)
90(2)
Crystal size, mm3
Crystal system
Space group
a, Å
0.45 × 0.42 × 0.23
monoclinic
P21
6.0773(6)
7.3273(6)
10.7882(10)
90.357(5)
480.39(8)
2
1.56
10
228
−8 ≤ h ≤ +8
−10 ≤ k ≤ +10
−16 ≤ l ≤ +16
0.75
0.41 × 0.32 × 0.24
monoclinic
P21/n
9.8002(2)
13.8222(3)
10.4841(3)
102.976(1)
1383.91(6)
4
1.35
5
584
−14 ≤ h ≤ +14
−20 ≤ k ≤ +16
−15 ≤ l ≤ +15
0.75
32/100
19 230
0.26 × 0.24 × 0.10
monoclinic
P21/n
9.9011(5)
13.8650(7)
10.5256(5)
102.015(3)
1413.29(12)
4
1.74
58
728
−14 ≤ h ≤ +12
−20 ≤ k ≤ +20
−13 ≤ l ≤ +15
0.75
32/95
24 858
b, Å
c, Å
β, deg
V, Å3
Z
Dcalcd., g cm−3
µ(MoKα ), cm−1
F(000), e
hkl range
((sinθ)/λ)max, Å−1
θmax, deg/% completeness 32/98.5
Refl. measured
Refl. unique/Rint
Param. refined
R(F)/wR(F2)a
[I > 2 σ(I)]
R(F)/wR(F2)a
(all refls.)
16 716
3231/0.0254
101
4811/0.0332
154
0.0323/0.0789
4666/0.0406
154
0.0282/0.0593
0.0231/0.0644
0.0246/0.0662
0.0478/0.0831
0.0474/0.0622
x(Flack)
0.03(7)b
1.189
0.30/−0.45
–
–
GoF (F2)a
1.063
0.45/−0.23
1.079
0.54/−0.53
∆ρfin (max/min), e Å−3
a
R(F) = Σ||Fo| − |F ||/Σ|Fo| for the observed reflections with F2 > 2 σ(F2); wR(F2) = [Σw(Fo2
−
c
F2)2/Σw(Fo2)2]1/2; GoF = [Σw(Fo2 − F2)2/(nobs − nparam)]1/2; w = [σ2(Fo2) + (aP)2 + bP]−1, where
c
c
P = (Max(Fo2,0)+2F2)/3: b The structure was refined as a twin (1 0 0 0 1 0 0 0 1, BASF 0.331(1)).
c
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E. Wächtler et al. · Hexacoordinated Silicon Complexes
−152.1 ppm. – C25H18Cl4N2O2Si (548.30): calcd. C 54.76,
sis). – C33H27Cl3N2O2Si (618.01): calcd. C 64.14, H 4.40,
N 4.53 vs. C32H26N2O2Si·0.18(CHCl3) (520.13): calcd. C H 3.31, N 5.11; found C 54.61, H, 3.29, N 5.09. (The char-
74.31, H 5.07, N 5.39; found C 74.37, H 5.04, N 5.45.
acterization of this compound in solution was hampered by
the very poor solubility in solvents such as chloroform or
DMSO.)
(Oxinate)2SiPhCl·CHCl3
8-Oxyquinoline (3.00 g, 20.6 mmol) and triethylamine
(3.14 g, 30.8 mmol) were dissolved in THF (60 mL) and
cooled to 0◦C, whereupon chlorotrimethylsilane (2.46 g,
(Oxinate)2SiF2·1.5(CHCl3)
To a solution of 8-hydroxyquinoline (0.58 g, 4.0 mmol)
22.6 mmol) was added dropwise. The triethylammonium and triethylamine (0.43 g, 4.3 mmol) in THF (20 mL) was
chloride precipitate was filtered off and washed with THF added trimethylchlorosilane (0.46 g, 4.2 mmol) dropwise,
(20 mL). From the filtrate and washings the solvent was re- and the resulting suspension was stirred for 1 h. After fil-
moved under reduced pressure. The residue was dissolved tration the colorless solid residue was washed with THF
in chloroform (30 mL) and cooled to 0◦C. At this temper- (3 × 2 mL), and from the combined filtrates and washings
ature, phenyltrichlorosilane (2.39 g, 11.3 mmol) was added, the volatiles were removed in vacuo. In another Schlenk
and the solution was stored at room temperature. The yel- tube SiF4Py2 [34, 35] (0.53 g 2.0 mmol) was stirred in chlo-
low crystalline product was filtered off, washed with chloro- roform (2 mL), and the resulting suspension was layered
form and dried in vacuo. Yield: 4.55 g (8.31 mmol, 81%). with additional 5 mL of pure chloroform followed by a layer
–
29Si CP/MAS NMR (79.5 MHz, νspin = 4 kHz): δiso
=
of the previously prepared 8-trimethylsiloxyquinoline which
Table 4. Crystal structure data for (oxinate)2SiF2·1.5 CHCl3, (oxinate)2SiPhCl·CHCl3 and (oxinate)2(adho)Si·1.5 CHCl3.
(oxinate)2SiF2
(oxinate)2SiPhCl
(oxinate)2(adho)Si
·1.5 CHCl3
·CHCl3
·1.5 CHCl3
Empirical formula
Mr
C39H27Cl9F4N4O4Si2
1066.88
C25H18Cl4N2O2Si
548.30
C63H49Cl9N6O6Si2
1361.31
T, K
150(2)
296(2)
100(2)
Crystal size, mm3
Crystal system
Space group
a, Å
0.30 × 0.28 × 0.18
0.20 × 0.20 × 0.10
0.38 × 0.12 × 0.06
triclinic
triclinic
triclinic
P1
P1
P1
16.2316(5)
16.6957(6)
17.4505(6)
72.468(3)
78.518(3)
80.500(3)
4391.1(3)
4
1.61
7
2152
−21 ≤ h ≤ +21
−22 ≤ k ≤ +22
−23 ≤ l ≤ +23
0.66
8.2014(3)
11.0054(4)
13.7955(5)
78.239(2)
88.439(2)
85.604(2)
1215.36(8)
2
1.50
6
560
−9 ≤ h ≤ +10
−14 ≤ k ≤ +14
−17 ≤ l ≤ +17
0.64
11.2522(3)
14.0343(3)
19.9637(5)
77.977(1)
79.815(1)
75.471(1)
2958.89(13)
1
1.53
5
1396
−10 ≤ h ≤ +13
−16 ≤ k ≤ +16
−20 ≤ l ≤ +22
0.60
b, Å
c, Å
α, deg
β, deg
γ, deg
V, Å3
Z
Dcalcd., g cm−3
µ(MoKα ), cm−1
F(000), e
hkl range
((sinθ)/λ)max, Å−1
θmax, deg/%
28/99.9
27/98.6
25/99.9
completeness
Refl. measured
Refl. unique/Rint
Param. refined
R(F)/wR(F2)a
[I > 2 σ(I)]
63 808
21 174/0.0298
1192
19 697
5236/0.0359
355
30 305
10 054/0.0443
788
0.0394/0.0996
0.0485/0.1261
0.0433/0.0905
R(F)/wR(F2)a
(all refls.)
0.0622/0.1086
0.0819/0.1387
0.0894/0.1009
GoF (F2)a
1.030
0.57/−0.45
1.134
0.36/−0.45
0.985
0.40/−0.39
∆ρfin (max/min), e Å−3
a
See Table 3 for definition of R values and GoF, as well as information on the weighting scheme applied.
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E. Wächtler et al. · Hexacoordinated Silicon Complexes
1415
has been dissolved in chloroform (2 mL). This reaction mix- (0.91 mmol, 45%). – 29Si CP/MAS NMR (79.5 MHz,
ture was stored undisturbed overnight at room tempera- νspin = 4 kHz): δiso = −158 ppm (signal consists of two
ture after which a yellow crystalline solid suitable for X- peaks, at −155.6 and −160.3 ppm). – C20H16N2O2SiF2
ray diffraction was obtained. The product was filtered off, (382.44): calcd. C 62.81, H 4.22, N 7.33; found C 62.86, H
washed with chloroform (2 × 1 mL) and dried in vacuo. 4.37, N 7.50. (The characterization of this compound in so-
Yield 0.66 g (1.8 mmol, 88% referring to C18H12N2O2SiF2 lution was hampered by the very poor solubility in solvents
· 0.14 CHCl3). – 29Si CP/MAS NMR (79.5 MHz, νspin
=
such as chloroform or DMSO.)
5 kHz): δiso = −163 ppm (signal consists of two peaks,
at −160.9 and −165.0 ppm). – C18H12N2O2SiF2 · 0.14
CHCl3 (371.10): calcd. C 58.71, H 3.30, N 7.55; found C
58.56, H 3.33, N 7.93. (The characterization of this com-
pound in solution was hampered by the very poor solubility
in solvents such as chloroform or DMSO.)
(Oxinate)2SiCl2
To a solution of 8-trimethylsiloxyquinoline (prepared
analogously as described for (oxinate)2SiF2·1.5(CHCl3)
but starting from 10 mmol 8-hydroxyquinoline, 12.5 mmol
Me3SiCl and 15 mmol Et3N in 50 mL THF) in acetonitrile
(20 mL) was quickly added SiCl4 (0.85 g, 5.0 mmol) in one
portion under stirring at room temperature. Stirring was dis-
(8-Oxyquinaldinate)2SiF2
This compound was prepared in an analogous manner continued immediately after complete SiCl4 addition, and
from 4 mmol 8-hydroxyquinaldine and 2 mmol SiF4Py2 [34, the mixture was stored undisturbed overnight at room tem-
35]. Crystals appeared after one week. Yield: 0.35 g perature yielding a yellow crystalline solid suitable for X-ray
Table 6. Crystal structure data for (oxinate)2SiCl2 and
(oxyquinaldinate)2SiF2.
Table 5. Crystal structure data for (oxinate)2SiBnCl and
(oxinate)2SiBn2·CHCl3.
(oxinate)2SiBnCl
C25H19ClN2O2Si
442.96
(oxinate)2SiBn2·CHCl3
(oxinate)2SiCl2
C18H12Cl2N2O2Si C20H16F2N2O2Si
387.29
150(2)
(oxyquinaldinate)2SiF2
Empirical formula
Mr
C33H27Cl3N2O2Si
618.01
Empirical formula
Mr
382.44
100(2)
T, K
100(2)
200(2)
T, K
Crystal size, mm3
Crystal system
Space group
a, Å
0.30 × 0.10 × 0.03 0.45 × 0.35 × 0.03
Crystal size, mm3
Crystal system
Space group
a, Å
0.35 × 0.30 × 0.10 0.30 × 0.20 × 0.05
monoclinic
P21/n
monoclinic
P21/c
monoclinic
C2/c
monoclinic
C2/c
11.3434(3)
10.2509(2)
17.9446(4)
97.182(1)
2070.23(8)
4
1.42
3
920
13.7917(4)
16.4454(5)
14.1748(4)
112.868(1)
2962.30(15)
4
1.42
4
1280
−17 ≤ h ≤ +15
−18 ≤ k ≤ +20
−16 ≤ l ≤ +17
0.62
13.9866(16)
8.1132(7)
14.9864(16)
109.907(8)
1599.0(3)
4
1.61
5
792
17.2309(13)
7.6145(5)
13.5351(11)
112.998(5)
1634.7(2)
4
1.55
2
792
−20 ≤ h ≤ +20
−9 ≤ k ≤ +9
−16 ≤ l ≤ +16
0.60
b, Å
c, Å
b, Å
c, Å
β, deg
β, deg
V, Å3
V, Å3
Z
Z
Dcalcd, g cm−3
µ(MoKα ), cm−1
F(000), e
hkl range
Dcalcd., g cm−3
µ(MoKα ), cm−1
F(000), e
hkl range
−13 ≤ h ≤ +13
−12 ≤ k ≤ +12
−21 ≤ l ≤ +22
−19 ≤ h ≤ +19
−11 ≤ k ≤ +11
−21 ≤ l ≤ +16
((sinθ)/λ)max, Å−1 0.62
((sinθ)/λ)max, Å−1 0.70
θmax, deg/
26/99.9
26/99.9
θmax, deg/
30/100
25/99.9
% completeness
Refl. measured
Refl. unique/Rint
Param. refined
R(F)/wR(F2)a
[I > 2 σ(I)]
% completeness
Refl. measured
Refl. unique/Rint
Param. refined
R(F)/wR(F2)a
[I > 2 σ(I)]
17 706
4062/0.0608
280
26 740
5816/0.0439
386
9129
2335/0.0286
114
8547
1440/0.1341
124
0.0453/0.0978
0.0414/0.0846
0.0404/0.1068
0.0396/0.0882
R(F)/wR(F2)a
(all refls.)
0.0799/0.1056
0.0858/0.0941
R(F)/wR(F2)a
(all refls.)
0.0501/0.1126
0.0639/0.0956
GoF (F2)a
1.046
1.013
GoF (F2)a
1.076
1.029
∆ρfin (max/min),
0.33/−0.33
0.31/−0.29
∆ρfin (max/min),
0.63/−0.27
0.22/−0.23
e Å−3
e Å−3
a See Table 3 for definition of R values and GoF, as well as informa-
a See Table 3 for definition of R values and GoF, as well as informa-
tion on the weighting scheme applied.
tion on the weighting scheme applied.
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1416
E. Wächtler et al. · Hexacoordinated Silicon Complexes
diffraction. The product was collected by filtration, washed of the solvent molecules (in case of two-fold disordered
with diethyl ether (2 × 10 mL) and dried in vacuo. Yield: chloroform, the site occupancies are far off the 50 : 50 ratio).
1.92 g (4.96 mmol, 99%). – 29Si CP/MAS NMR (79.5 MHz, In addition to solvent disorder (which also applies to the
νspin = 5 kHz): δiso = −158.7 ppm. – C18H12N2O2SiCl2 chloroform molecule in (oxinate)2SiBn2), the SiPhCl moiety
(387.29): calcd. C 55.82, H 3.12, N 7.23; found C 55.55, H of (oxinate)2SiPhCl is disordered with site occupancies of
3.39, N 7.54. (The characterization of this compound in so- 0.961(4) and 0.039(4). The phenyl group of the low occu-
lution was hampered by the very poor solubility in solvents pancy part was refined as an idealized hexagon (SHELXL
such as chloroform or decomposition in DMSO.)
code AFIX 66). Details of the structure determinations are
summarized in Tables 3 – 6.
Computational analyses
CCDC 999917 (for (oxinate)2SiCl2), 999918
(for (oxinate)2SiF2·1.5(CHCl3)), 999919 (for (8-oxy-
quinaldinate)2SiF2), 999920 (for (oxinate)2SiPhCl·CHCl3),
999921 (for (oxinate)2Si(adho)·1.5(CHCl3)), 999922 (for
(oxinate)2SiBnCl), 999923 (for (oxinate)2SiBn2·CHCl3),
999924 (for BnSiCl3), 999925 (for Bn2SiCl2) and 999926
(for Bn2SiBr2) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Geometry optimization (at DFT MPW1PW91 6-
311G(d,p) level) and single point energy analyses (at MP2
6-31G(d) level) of hexacoordinated silicon complexes with
oxinato ligands were performed on isolated molecules
(pseudo gas phase) using GAUSSIAN 09 [36]. For potential
energy surface scans of benzyltrihalosilanes (B3LYP/6-
311G(d,p)) and calculations of 29Si NMR shifts for different
conformations of benzyltrichlorosilane and TMS (at the
B3LYP/6-311G+(2d,p) and HF/6-311G+(2d,p) level)
GAUSSIAN 03 was employed.
Supporting information
X-Ray structure determinations
Cartesian coordinates of the optimized (DFT MPW1
PW91/6-311G(d,p)) molecular structures of O,O-trans
and N,N-trans isomers of (oxinate)2SiCl2, (oxinate)2SiF2,
(8-oxyquinaldinate)2SiCl2 and (8-oxyquinaldinate)2SiF2;
29Si CP/MAS NMR spectra of (oxinate)2SiF2 and (8-
oxyquinaldinate)2SiF2; powder X-ray diffractogram of
(oxinate)2SiCl2 are given as Supporting Information (16
pages) available online (DOI: 10.5560/ZNB.2014-4170).
Single-crystal X-ray diffraction data were collected
on a Stoe IPDS 2/2T single-crystal diffractometer (for
(oxinate)2SiCl2, (oxinate)2SiF2·1.5(CHCl3) and (8-
oxyquinaldinate)2SiF2) or on a Bruker X8 APEX2 CCD
diffractometer (for the other crystal structures) using MoKα
radiation. The structures were solved by Direct Methods
using SHELXS-97 and refined with full-matrix least-
squares methods on F2 of all reflections with SHELXL-97
[37−39] in WINGX [40, 41]. Graphics of the molecular
structures were generated with ORTEP-32 [42, 43] and
Acknowledgement
Parts of this work were performed within the Cluster of
POV-RAY [44]. All non-hydrogen atoms were refined Excellence “Structure Design of Novel High-Performance
anisotropically. C-bound hydrogen atoms were refined Materials via Atomic Design and Defect Engineering
isotropically in idealized positions (riding model). In (ADDE)” that is financially supported by the European
the crystal structures of (oxinate)2SiF2·1.5(CHCl3) and Union (European regional development fund) and by the
(oxinate)2Si(adho)·1.5(CHCl3) the independent molecules Ministry of Science and Art of Saxony (SMWK). We thank
of the Si complex in the asymmetric unit (4 and 2, re- M. Sc. Sebastian Bette (Institut für Anorganische Chemie,
spectively) are related to one another by pseudosymmetry, TU Bergakademie Freiberg) for the powder X-ray diffraction
but this symmetry is heavily violated by the ordering analysis of (oxinate)2SiCl2.
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