Synthesis, characterization and theoretical calculations of model compounds of silanols catalyzed by TEMPO to elucidate the presence of Si-O-Si and Si-O-N bonds

Article abstract of DOI:10.1039/c5ra10056a

We report the results from the reactions of 1-phenylethanol, 2-methylpropanol, trimethylsilanol and triphenylsilanol with TEMPO, OH-TEMPO and Br-TEMPO salt at different reaction conditions to obtain model functionalized compounds. With 1-phenylethanol, the ketone compound was obtained as expected, but when using triphenylsilanol the corresponding hexaphenyldisiloxane [di(triphenylsilane)ether] was obtained in crystal form, as well as the silaneoxiamine (Si-O-N). The hexaphenyldisiloxane crystal belonged to the triclinic crystal system with a space group P1, a = 8.5829(4) ?, b = 9.4856(4) ?, c = 10.9694(5) ?, α = 95.951(4)°, β = 90.059(3)°, γ = 113.352(4)°, the asymmetric unit comprised of Z = 1. The results showed that the synthetic method to obtain silane ether is simple and can be completed in one step, as well as independently of the type of TEMPO and base used. Also, under the same reactions conditions, we prepared the corresponding TEMPO-containing silanes as triphenylsilaneoxiamine and observed formation of Si-oxide chains through an in situ polycondensation reaction. The resulting compounds were characterized by FT-IR spectroscopy, mass spectrometry (EI), and ¹H-NMR. The best assignment for infrared spectroscopy characterization and the structural parameters by vibrational frequencies were determined by DFT calculations.

Full text of DOI:10.1039/c5ra10056a

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Page 1 of 44
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Synthesis, characterization and theoretical calculations of model
compounds of silanols catalyzed by TEMPO to elucidate the presence of
Si-O-Si and Si-O-N bonds.
1
*
1
1
1
Judith Percino , José A. Pacheco , Guillermo Soriano-Moro , Margarita Cerón , M.
1
1
2
2
Eugenia Castro , Víctor M. Chapela , José Bonilla-Cruz , Tania E. Lara-Ceniceros ,
2
3
Mildred Flores-Guerrero and Enrique Saldivar-Guerra .
1
Lab. de Polímeros, Centro de Química, Instituto de Ciencias, Benemérita Universidad
Autónoma de Puebla, Complejo de Ciencias, ICUAP, Edif. 103H, 22 Sur y San Claudio,
C.P. 72570 Puebla, Puebla, México.
2
Cento de Investigación en Materiales Avanzados S.C. (CIMAV-Unidad Monterrey),
Alianza Norte 202, Autopista Monterrey-Aeropuerto Km 10, PIIT, C.P. 66600 Apodaca,
Nuevo León, México.
3
Centro de Investigación en Química Aplicada, Blvd. Enrique Reyna No. 140, Col. San
José de los Cerritos, C.P. 25294 Saltillo, Coahuila, México.
Corresponding author:
M. Judith Percino,
Centro de Química, Instituto de Ciencias,
Benemérita Universidad Autónoma de Puebla,
Complejo de Ciencias, ICUAP, Edif. 103H,
2
2 Sur y San Claudio, C.P. 72570,
Tel. +52-222-2295500 x 7285
judith.percino@correo.buap.mx
1

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Abstract
We report the results from the reactions of the 1-phenylethanol, 2-methylpropanol,
trimethylsilanol and triphenylsilanol with TEMPO, OH-TEMPO and Br-TEMPO salt at
different reaction conditions to obtain model functionalized compounds. With 1-
phenylethanol, the ketone compound was obtained as expected, but using the
triphenylsilanol the corresponding hexaphenyldisiloxane [di(triphenylsilane)ether] was
obtained in crystal form, as well as, the silaneoxiamine (Si-O-N). The
hexaphenyldisiloxane crystal belonged to the triclinic crystal system with a space group P-
1
, a = 8.5829(4) Å, b = 9.4856(4) Å, c = 10.9694(5) Å, α= 95.951(4)°, β= 90.059(3)°,
γ=113.352(4)°, the asymmetric unit comprised of Z=1. The results showed that the
synthetic method to obtain silane ether is simple and can be completed in one step, as well
as independently of the type of TEMPO and base used. Also, under the same reactions
conditions, we prepared the corresponding TEMPO-containing silanes as
triphenylsilaneoxiamine and observed formation of Si-oxide chains through an in situ
polycondensation reaction. The resulting compounds were characterized by FT-IR
1
spectroscopy, mass spectrometry (EI), and H-NMR. A best assignment for infrared
spectroscopy characterization and the structural parameters by vibrational frequencies were
determined by DFT calculations.
Keywords
Silanols, Oxoammonium salt, TEMPO, crystal structure, hexaphenyldisiloxane,
computational calculation, silicon oxide, DFT calculations.
2

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Introduction
1
Symmetrical disiloxanes are an important class of compounds in silicon chemistry. Some
of the symmetrical disiloxanes are known to have important applications as liquid
2
-7
8-9
crystals, and pharmacologically active compounds. Recently, some of these compounds
1
0
have drawn attention as useful intermediates in organic synthesis. Napier et al. and Sore et
1
1
al. have shown novel applications of aryl disiloxanes and vinyl disiloxanes, respectively,
as efficient coupling partners in Hiyama cross-coupling reactions. The general methods
available in the literature for the preparation of symmetrical disiloxanes are intermolecular
1
2,13
14,15
condensation of silanols,
and reaction of polysiloxanes with Grignard reagents.
On the other hand, it is well know that silica plays an important role in nature,
1
6-18
science, and technological applications.
The chemical properties of the silica surface are
mainly determined by several silanol and siloxane groups that are present on both the
external and internal surfaces. Silanol groups (SiOH) can be easily functionalized by
1
6-23
different chemical procedures,
due to its applications in chromatography among others.
of silicon dioxide (SiO ) surfaces with silane molecules is an important technique for a
and the importance of functionalized silica materials is
2
4-27
The chemical functionalization
2
2
8-31
32-33
variety of device,
and sensor applications.
However, the quality control of self-
assembled monolayers (SAMs) is difficult to achieve because of the lack of a method to
directly measure the formation of new interfacial Si-O bonds. Tian et al. reported a direct
3
4
characterization of the interfacial Si-O bond formation, which extended our understanding
of the surface reaction mechanisms and improved the quality of the SAM. Infrared
spectroscopy has also been used in the silica powder surface silanization studies for
3
5
monitoring Si-O-Si bond formation. By monitoring the Si-O-Si region of the IR spectrum,
3

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it is possible to distinguish between an organosilane that is covalently bound through Si-O-
Si surface bonds and an organosilane polymer deposited on the surface.
Moreover, various functionalized alkoxyamines have been designed and synthesized
as initiators for living free radical polymerization, leading to well-defined macromolecular
3
6-41
architectures, such as block, graft, and star polymers.
Since Hawker et al. reported the
synthesis of 2,2,6,6-tetramethyl-l-(1-pheny1ethoxy)-piperidine from the reaction of 2,2,6,6-
tetramethylpiperidine-1-oxyl (TEMPO) and an excess amount of styrene in the presence of
3
8
benzoyl peroxide, a few synthetic methods for alkoxyamines have been reported. For
example, ethylbenzene derivatives were reacted with the tert-butoxyl radical (tert-BuO)
3
9,40
and then coupled with the nitroxyl radical.
In addition, the polymer-coated nanoparticles are of great interest because of their
applications, one of the most effective methods to polymer-coated nanoparticles is surface
functionalization by grafting of polymer. The surface properties can be widely varied by
4
1-49
choosing diverse functional monomers.
Thus, different nanoparticles, such as silica,
carbon, could be functionalized with well defined polymers of the desired grafting density,
to interact wih iron, gold, silver particles. To date, surface initiated graft polymerization can
be used to control the molecular weight of the graft chains on nanoparticles by using of
living radical polymerization technique, i.e. atom transfer radical polymerization (ATRP),
and reversible addition-fragmentation transfer (RAFT). For example, Matyjaszewski et al.
has been synthetized organic/inorganic hybrid nanoparticles by ATRP using silica
5
0
functionalized with ATRP initiator groups. Benicewicz et al. has been grafted silica
5
1
nanoparticles by RAFT in order to obtain dye labeled polymers or stabilize magnetic
5
2
nanoparticles with biomedical applications. Recently, Bonilla et al. had proposed the
functionalization of particles of silica using a TEMPO-bromide salt (Br-TEMPO) in order
4

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3
to grow styrene-maleic anhydride copolymers from the functionalized silica surface.
These investigators proposed that the hydroxyl groups on the silica surface are potential
sites for attack by Br-TEMPO salt, according to Scheme 1. By use of undirected
experiments by GPC and DSC, these studies showed that the particles were functionalized
41,53
and verified the growth of the polymers chains.
However, there was no direct
observation of the formation of the N-O-O-Si moiety in the silica.
5
3
Scheme 1. Procedure for preparing PSMA-NMRP particles, as proposed by Bonilla et al.
Therefore, it is important to understand the surface reaction mechanisms. Present
methodology cannot determine whether the newly formed organosilanes are parts of the
silica network or are attached through just one bond. The difficulty in discovering the
nature of the interfacial Si-O bonds arises from the complexity of distinguishing if the bond
is present as Si-O-Si, Si-O-N, or as the proposed Si-O-O-N bond formation in the model
compounds. In the present work we report model compounds from reactions of silanols
catalyzed by TEMPO to determine the type of bond present (e.g., N-O-Si or Si-O-Si) after
surface-grafting of nanomaterials via the surface-initiated nitroxide-mediated radical
polymerization (Si-NMRP) approach.
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Experimental
Materials and Instrumentation
1
-Phenylethanol, 2-methylpropan-2-ol, trimethylsilanol, triphenylsilanol, TEMPO, OH-
TEMPO, oxo-TEMPO and NH -TEMPO were acquired from Aldrich Chemical Co.
2
Melting points were measured with an SEV (0-300 °C) apparatus and were reported as
uncorrected values. IR spectra of the products were recorded on a Vertex (model 70, Bruker
1
Optics, Germany) 750 FT-IR spectrophotometer by attenuated total reflectance (ATR). H
1
3
NMR and C NMR spectra were obtained in CDCl and DMSO-d on a Bruker 500 MHz
3
6
NMR spectrometer (Varian NMR, Walnut Creek, CA). The electron ionization (EI) spectra
were acquired on a Jeol MStation 700-D mass spectrometer (Jeol USA, Peabody, MA).
Differential scanning calorimetry (DSC) curves were acquired with a TA
Instruments DSC Q200. Typically, 1–2 mg of the sample was added to an aluminum pan
−
1
(
Tzero®) and heated at 10 °C min in the range of -10 °C to 400 °C. The sample was
-1
cooled at the same rate of 10 °C min up to 25°C. Scanning electron microscopy (SEM) of
Field Emission Model 200 Nova NanoSEM (FEI Company) was utilized at 15kV to
investigate the morphology of new compouds.
The synthesis of 2,2,6,6-tetramethyl-1-oxopiperidinebromide salt (Br-TEMPO) was
5
4
carried out according to a literature procedure (Scheme 2). Bromine (1.64 mL, 32 mmol)
was carefully measured using a glass syringe and was added slowly to a solution of
TEMPO (5 g, 32 mmol in 100 mL of CCl anhydrous). A brown solid (Br-TEMPO) was
4
formed instantaneously and was purified by washing with CCl . The Br-TEMPO salt was
4
1
dried under vacuum at room temperature overnight (yield 92%). H NMR (400 MHz,
CDCl ): 2.32–2.74 ppm (m, 6H, CH ), 1.71–1.99 ppm (s, 12H, CH ).
3
2
3
6

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Scheme 2. Synthesis of the oxoammonium salt (Br-TEMPO).
Oxidation of methylbenzylalcohol to acetophenone
The Br-TEMPO salt is well known to be a good oxidant. We used Br-TEMPO as an
oxidizing agent in the following manner (Scheme 3): under magnetic stirring, 1-
phenylethanol (0.15 g, 1.27 mmol) was added dropwise to Br-TEMPO (0.3 g, 1.27 mmol)
dissolved in 3.5 mL of dichloromethane simultaneously with a 37% NaOH solution. The
reaction mixture changed from brown to orange over approximately 5 min. At the end of
reaction, the solid phase was isolated by filtration and the liquid phase solvent was
1
evaporated under vacuum. The liquid concentrate was analyzed by IR and H-NMR.
Scheme 3. Synthesis of acetophenone (top) and the reaction of 2-methylpropan-2-ol
(bottom) using Br-TEMPO
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Reactions of 2-methylpropan-2-ol, trimethylsilanol, triphenylsilanol at different
reaction conditions
The reaction conditions of temperature, time, and amount of Br-TEMPO were
examined to optimize the functionalization of the nanoparticles through the formation of
5
3
the peroxide bond as: –N-O-O-Si- (Table 1). Additional reaction conditions were selected
because preliminary experiments demonstrated that the reaction did not require the use of
the bromine salt of TEMPO. Hence, we developed the following general reaction
procedure: a mixture of triphenylsilanol (1.08 mmol, 0.3 g) with TEMPO at molar ratio
(1:1) was maintained at reflux and stirred at 67 °C. Triphenylsilanol (1.08 mmol, 0.3 g) was
dissolved in 0.5 mL of DMF giving a colorless solution. To the solution was added
TEMPO (1.08 mmol, 0.17 g). Then, was it added KOH (1.08 mmol, 0.062 g). The reaction
was maintained for 24 h until the precipitate formed. The precipitate was separated and a
white powder was purified. The liquid phase was treated with acetone and THF until a
beige precipitate formed. The products were characterized by EI Mass and IR.
Table 1 summarizes the different reactions that were carried out to determine the
effects of using TEMPO, Br-TEMPO, and derivatives of TEMPO. The conditions were
chosen according to the observed results from experiments I and II which indicated that the
three reagents 2-methylpropan-2-ol (1), trimethylsilanol (2), and triphenylsilanol (3) did not
undergo reaction. The solvent DMF was used due to the very low solubility of (Ph) SiOH
3
in other solvents. For reactions II-VIa a strong base (KOH) was used. Condition VI(b) was
used the Br-TEMPO and triethylamine in dichloromethane as solvent. Also various
derivatives TEMPO were used to prove the reaction occurred with alcohols.
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Table 1. Reaction conditions used to evaluate the preparation of the precursor with the
-C-O-O-N- or Si-O-O-N- bond.
(1)
(2)
(3)
Chemical
(CH ) COH
(CH ) SiOH
(Ph) SiOH
3
3
3 3
3
reagent
Experiment
Conditions used
I
TEMPO/36-38 °C or 66-68 °C/48 h
II
TEMPO/DMF/ KOH/36-38 °C/48 h
III
IV
V
-
-
-
Oxo-TEMPO/ DMF/ KOH/66-68 °C/48 or 24 h
OH-TEMPO/DMF/ KOH/66-68 °C/48 or 24 h
NH
-TEMPO/DMF/ KOH/66-68 °C/48 or 24 h
2
VI
(a) Br-TEMPO/DMF/KOH/
6-38 °C and 66-68 °C/48 h
(b) Br-TEMPO/CH Cl /Et N /4 °C/4 h
2
2
3
3
Crystallization of hexaphenyldisiloxane
In the reactions II, III and VI(b) the crystals of hexaphenyldisiloxane were formed
before the liquid was treated with THF. These crystals were washed with ethanol. The
melting point of crystals was of 225 °C.
X-ray crystallography
All reflection intensities of hexaphenyldisiloxane was measured at 110(2) K using a
SuperNova diffractometer (equipped with Atlas detector) with Cu Kα radiation (λ =
1
2
.54178 Å) under the program CrysAlisPro (Version 1.171.36.32 Agilent Technologies,
013). The cell dimensions were refined and solved with the program SHELXS-2013
5
5
(
Sheldrick, 2013) and were refined on F2 with SHELXL-2013. Analytical numeric
absorption corrections based on a multifaceted crystal model were applied using
CrysAlisPro (Version 1.171.36.32 Agilent Technologies, 2013). The temperature of the
data collection was controlled using a Cryojet system (manufactured by Oxford
Instruments). The H atoms were placed at calculated positions using the instructions AFIX
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4
3 with isotropic displacement parameters having values 1.2 times Ueq of the attached C
atoms.
Result and discussion
The Br-TEMPO salt was characterized by IR spectroscopy to determine if the
+
characteristic signal for N =O was present. To confirm if the Br-TEMPO could oxidize a
1
primary alcohol, we used 1-phenylethanol as a model compound. The IR and H-NMR
spectra showed the characteristics bands for both the starting material and the oxidized
product. The IR and NMR signals were comparable with the reported values and the
melting point matched with the expected temperature. The IR spectrum presented the
signals characteristic for the acetophenone product in the oxidation reaction, indicating that
-1
-1
the TEMPO is in the form of salt. The signal at 1650 cm was for νC=O, at 910 cm for
-1
1
δC-H in plane and at 775 cm for δC-H out-of-plane. The H-NMR (CDCl ν ppm): s, 2.6
3
ppm, 3H (CH ), 8 ppm, dd: 2H (o-Ar), 7.45-755 ppm, [m:2H at (m- Ar) and at 7.55 ppm
3
1
H (para-H in phenyl group)].
Previous reports had led us to expect that formation of TEMPO-containing
56
alkylsilanes could be difficult. Using the conditions in Table 1, we had an indication that
the reaction had taken place by the slight yellow color of the solution due to the
consumption of the TEMPO. The characterization of reactions I and II using 2-
methylpropan-2-ol (1), trimethylsilanol (2), and triphenylsilanol (3), indicated that no
reaction had occurred because the starting reagents were recovered. However, with reagent
(3) under reaction conditions II, we obtained two white powders, one with a melting point
of 225 °C with a yield of 20% and another that did not melt even at temperatures up to >
1
0

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1
2
80 °C, with yield of 80%. The IR, H-NMR, EI mass spectrometry characterizations of the
powder which melted at 225 °C are showed in Figure 1. The characteristics bands (Figure
-1
-1
1
a) were at 3066 and 3016 cm and were assigned to νC-H of Ar, δC-H of Ar 1428 cm
-1
-1
56
-1
and 1117 cm . The signal at 1095 cm was assigned to νSi-O-Si, and at 709 cm and 515
-1
1
cm were due to νSi-Ph. The H-NMR spectrum, Figure 1(b), showed a high degree of
symmetry, as indicated by a multiplet with three signals at 7.51-7.49 ppm, 7.42-7.38 ppm,
and at 7.30-7.27 ppm for the protons of the aromatic rings. The EI mass spectrum, Figure
1
3
(c), showed the following mass fragments: 457 m/z [C H OSi ], 379 m/z [C H OSi ],
30 25 2 24 19 2
03 m/z [C H OSi ], 257 m/z [C H Si], 181 m/z [C H Si], 44 m/z [SiO]. The
18
15
2
18 15
12 10
spectroscopic results showed that the powder was either a di(triphenylsilane)ether or
hexaphenyldisiloxane.
It was possible to isolate the product hexaphenyldisiloxane in crystal form and its
structure was determined to be an ordered structure. The ORTEP structure of
hexaphenyldisiloxane, including the atomic numbering scheme is shown in Figure 2, which
also includes a view of tridimensional packing. Selected crystal data, the structure solution
and refinements are listed in Table 2 and 3.
1
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(a)
(b)
1
2

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(c)
1
Figure 1. The IR (a), H-NMR (b) and EI mass (c) spectra for the di(triphenylsilane)ether
1
3

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The molecule belongs to the triclinic system and is of the P-1 space group. It has an
inversion center through C(1)-O-C(1), C(7)-O-C(7), C(13)-O-C13) of each of the phenyl
groups and the central fragment Si--O--Si is linear along the crystallographic c axis. The
cell contains Z=1, in contrast to the structure solvated hexaphenyldisiloxane previously
5
7
reported. The principal interatomic distances are Si(1)---O(1) of 1.6198(3) and 1.6199(3)
Å, the Si(1)—C(1)- 1.8692(13) and 1.8654 (13)Å, and Si(1)—O(1) of 1.6198(3) and
1
.699(3) finally the S(1)—C of 1.8692 (13)Å, 1.8654(13) and 1.8627(1) for each aromatic
ring due to the inversion center. The angle of 180° is indicative of the linearity of the
Si(1)—O(1)—Si(1) fragment. Furthermore, angles between O(1)-Si(1)-C(13) of
1
09.69(4)°, O(1)-Si(1)-C(7) of 108.53(4)° and C(13)-Si(1)-C(7) of 109.80(6)° indicate the
tetrahedral geometry of the Si atom.
A
B
Figure 2. Molecular structure (A) of hexaphenyldisiloxane, the displacement ellipsoids are
drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary
radii. (B) Stereoscopic view of the packing on the crystallographic c axis.
1
4

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Table 2. Crystallography Data for hexaphenyldisiloxane
Empirical formula
C H O Si
36 30 2
Crystal system
Color, Habit
Formula weight
Space group
T(K)
triclinic
colorless block
534.78
P-1
110(2)
a( Å)
b (Å)
c (Å)
α(°)
8.5829(4)
9.4856(4)
10.9694(5)
95.951(4)
90.059(3)
113.352(4
727.71(6)
1
1.220
282
1.305
1.54178
β (°)
γ (°)
V (Å )
3
Z
-3
Dc(g cm )
F (000)
-1
ꢀ
(mm )
λ (Å)
Crystal size (mm )
θmax(°)
3
0.31 × 0.21 × 0.20
143.8
2
N
9218
N° (I>2.0 σ(I))
R1
2707
3.18
wR2
8.21
goodness-of-fit
Largest diff peak and hole (e Å )
1.046
0.49 and -0.27
-3
1
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Table 3. Selected interatomic distances (Å) and angles (°) for hexaphenyldisiloxane
Bond lenght (Å)
C(1)-Si(1)
C(7)-Si(1)
C(13)-Si(1)
O(1)-Si(1)
C(8)-C(9)
C(10)-C(11)
1.8692(13)
1.8654(13)
1.8627(13)
1.6198(3)
1.391(2)
1.385(2)
Angle bond(°)
C(12)-C(7)-Si(1)
C(8)-C(7)-Si(1)
C(6)-C(1)-Si(1)
C(2)-C(1)-Si(1)
C(14)-C(13)-Si(1)
C(18)-C(13)-Si(1)
Si(1)-O(1)-Si(1)
O(1)-Si(1)-C(13)
O(1)-Si(1)-C(7)
C(13)-Si(1)-C(7)
O(1)-Si(1)-C(1)
C(13)-Si(1)-C(1)
C(7)-Si(1)-C(1)
122.53(10)
119.86(10)
120.71(10)
121.44(10)
120.17(10)
122.39(10)
180.0
109.69(4)
108.53(4)
109.80(6)
108.72(4)
110.30(6)
109.77(6)
In addition to hexaphenyldisiloxane, the powder with the melting point higher than
2
80 °C was also obtained with the III, IV and V reaction conditions using reagent (3) even
though these reactions used derivatives of TEMPO. Only a small difference was observed
with the OH-TEMPO. Although this other product was present in small yield, it was
possible to characterize it. From the IR spectrum (Figure 3) we observed the signal at 1428
-1
-1 57
cm assigned to Si-C(Ph) which was reported as a sharp and intense band (1430 cm );
-1
the band at 1117 cm is also due to the presence of a νSi-C(Ph), but the new band at 1095
-1
cm (which was not present in the spectra of the starting reagents), could be due to the Si-
-1
O. The three bands in the range of 760-710 cm of approximately equal intensity are
typical for the presence of Si-phenyl. The difference in the spectrum for the ether
1
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-1
compound was the signal at 1350 cm , which in TEMPO has been reported to correlate
-1
with the C-N in the range of 1250–1000 cm (m). For OH-TEMPO, a band appeared at
-1
-1
1
350 cm corresponding to C-N, as well as another broad band at 1590 cm . We
questioned if these bands gave evidence of the presence of Si-O-N bond?
Figure 3. IR spectrum for silaneoxiamine compound
In order to identify better the signals was performed theoretical calculations of the
fully optimized structures of the compound with moieties Si-O-Si and Si-O-N. The
5
8
calculations were carried out using DFT calculations with the hybrid functional B3LYP,
5
9
60
with the basis set 6-311++G(d,p), in the Gaussian09 computational package. For
calculations, the initial guess of the system (hexaphenyldisiloxane) was obtained from X-
ray coordinates data, while for system (triphenylsilaneoxiamine) was computationally built.
Vibrational frequencies of both compounds were calculated at the same level of theory in
gas phase and including the effect of n,n-dimethylformamide (DMF) with ε=37.219 using
1
7

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6
1
the Polarizable Continuum Model (PCM). The selected parameters are shown in Table 4.
The effect of the solvent DMF was not significant on the structural parameters. Geometry
parameters obtained in gas phase MP2/6-31G(d) calculations were in good agreement with
the parameters for hexaphenyldisiloxane, see Table 3. For Si-O-N compound good results
were obtained in comparison to other siliceoxiamine systems containing Si-O-N fragments
in its structure. Geometry parameters obtained in gas phase MP2/6-31G(d) calculations
were Si−O= 1.623(3) Å, O−N= 1.479(6) Å and Si−O−N= 105.6(8)° reported in reference
6
2
for Cl SiONMe compound. The structures of H SiONMe and H Si(ONMe ) showed
3
2
3
2
2
2 2
parameters of Si−O= 1.682 and 1.699 Å, O−N= 1.459 and 1.477 Å, and Si−O−N= 102.5
6
3
and 94.2, respectively, while ClH SiONMe showed Si−O= 1.678 Å, O−N= 1.468 Å and
2
2
6
4
Si−O−N= 91.6° in MP2/6-311G(d,p).
Parameters of H SiON(BH )Me ,
3 3 2
FH SiON(BH )Me and H SiOC(CH )Me were calculated at MP2/6-311G(d,p) level of
2
3
2
3
3
2
theory, obtaining similar values to those previously reported (Si−O= 1.707, 1.700 and 1.657
6
5
Å, O−N= 1.433 and 1.428 Å and Si−O−N= 121.4 and 119.7°). For F SiONMe calculated
3
2
values at MP2/6-311G(d,p) level of theory were reported with values of Si−O= 1.626 Å,
6
6
O−N= 1.478 Å and Si−O−N= 103.5°.
.
..
For the compounds containing Si-O-N fragments N Si interaction has been
6
1-65
calculated in the range of 1.963−2.768 Å,
which indicate a intramolecular donor-
acceptor interaction between silicon and nitrogen, leading to noticeably narrow Si-O-N
angles (at range of 82.9-113.2°) for systems containing pyrrole, pyrrolidine and piperidine
6
7
groups. More recently, one structure containing TEMPO-SiCl3 was characterized
6
8
crystallographically and using DFT calculations. In this work, authors reported similar
.
..
characteristics parameters Si−O= 1.638 Å, O−N= 1.469 Å, N Si=2.748 and Si−O−N=
1
8

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1
24.3° for their compound TEMPO-SiCl which contains the similar fragment Si−O−N,
3
showed structural features that gave an indication of possible presence of the Si-O-N bonds,
that corresponding to a silaneoxiamine, Table 4. Figure 4 shows the optimized structures
with moieties Si-O-Si and Si-O-N calculated at B3LYP/6-311++G(d,p) theory level.
Table 4. Theoretical B3LYP/6-311++G(d,p) selected structural parameters of the optimized
structures with moieties SiOSi and SiON. Internuclear distances in (Å), and valence
angles in (º).
Parameter
Si-O-Si
Si-O-N
Gas
1.64983
1.88638
----
----
1.39337
----
1.08560
----
180.00000
----
108.49329
120.34040
110.43251
----
DMF
1.65023
1.88749
----
----
1.39423
----
1.08547
----
180.00000
----
108.57186
120.42375
110.36428
----
Gas
1.69395
DMF
1.69336
Si−O
Si−C
N−O
C−N
C=C
C−C
1.89287
1.45801
1.50345
1.39228
1.54654
1.08580
1.09464
----
124.05473
111.42343
119.37505
109.70218
107.92266
118.23619
1.89432
1.45983
1.50394
1.39311
1.54682
1.08582
1.09437
----
124.28608
110.81206
119.32609
110.12654
108.01966
118.34112
C −H
Ph
C−H
Si−O−Si
Si−O−N
C−Si−O
C−C−Si
C−Si−C
C−N−O
C−N−C
----
----
1
9

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hexaphenyldisiloxane
triphenylsilaneoxiamine
Figure 4. Optimized structures with moeties Si-O-Si and Si-O-N calculated at B3LYP/6-
11++G(d,p) theory level.
3
2
0

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On the other hand, the vibration wavelengths form theoretical calculations are
-1
resumed in Table 5. Stretching vibrations Si-O were found at 1088.56 and 1076.98 cm for
-1
compound hexaphenyldisiloxane and at 832.02 and 828.01 cm for compound
triphenylsilaneoxiamine, in gas and solvent phases, respectively. Bending vibrations of Si-
-1
O were located at 527.8 and 519.1 cm for hexaphenyldisiloxane in the gas and solvent
phases, while for triphenylsilaneoxiamine, two bending vibrations are located at 517.92 and
-1
-1
5
27.25 cm in gas phase and at 512.27 and 522.60 cm in solution, due to the non-
symmetrical structure of triphenylsilaneoxiamine compound in comparison to
6
9
-1
hexaphenyldisiloxane structure. In early work, an IR band appeared at 1080 cm for the
Si-O-Si bond for the formation of a gel of silica. In this work, Orcel et al. indicated the
-1
absorption bands due to the silica network were located between 1100 and 800 cm and the
-
1
deformation of the Si-O-Si appeared at 455 cm . The vibrational frequencies in the IR
7
0
spectra have been reported for compounds with bridged Si-O-Si groups, which are in
agreement, to a certain degree, according to the silicon precursor (Table 5). For the
triphenylsilaneoxiamine compound, several vibrational frequencies were in agreement with
7
1
those assigned for TEMPO compound (Table 5).
1
Furthermore, the H-NMR and EI mass spectra (Figures 5 and 6) showed that
presence of triphenylsilane and OH-TEMPO. The m/z resulting fragmentation gave the EI
mass spectrum, which indicated the presence of the silaneoxiamine moiety, Figure 6.
However, the ether compound always was obtained in greater yield in almost all reactions
performed and a very little yield the corresponding the silaneoxiamine, even though the
5
3
reaction was performed with the reaction conditions reported.
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1

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1
Figure 5. H-NMR spectrum for silaneoxiamine
-156
-16
-39
Si
O
N
OH
Si
O
Si
Si
m/z 431
m/z 275
m/z 259
m/z 220
-39
-39
-39
-78
Si
Si
Si
Si
m/z 29
m/z 39
m/z 107
m/z 182
m/z 142
CH
2
Si
O
N
N
OH
Si
N
Si
N
m/z 155
m/z 400
m/z 321
m/z 292
Si
N
CH
2
m/z 193
2
2

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Figure 6. EI mass spectrum and proposed fragmentation for silaneoxiamine
2
3

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-1
Table 5. Theoretical B3LYP/6-311++G(d,p) vibrational frequencies in (cm ) of the optimized structures with moieties Si-O-Si and Si-O-N in gas
phase and solvent DMF phases. Vibrational frequencies of TEMPO are included by sake of comparison at the same level of theory.
Hexaphenyldisiloxane
Triphenylsilaneoxiamine TEMPO
-
1
Band (cm )
Structural unit
Si-O-Si
Gas
527.78
DMF
519.00
519.25
----
Gas
DMF
Gas
----
----
530.96
550.78
629.63
----
DMF
----
----
528.49
549.80
627.73
----
----
----
----
----
δ(Si-O)
517.92
527.25
----
512.27
522.60
----
5
27.84
δ(C-H)wagging
δ(N-C)wagging
δ(N-O)bending
δ(C-H)wagging
-CH
2
, -CH
3
----
C-N-C
C-N-O
-Ph
----
----
556.00
687.12
711.74
713.33
715.00
717.66
721.77
750.74
755.81
758.32
952.21
832.02
968.40
984.79
1063.99
1116.95
1124.61
1127.20
1149.74
1202.41
1226.66
1259.27
1280.27
1298.50
1300.39
553.61
685.45
711.93
713.08
714.33
715.49
718.81
750.35
758.16
758.92
943.86
828.01
966.69
982.51
1061.56
1114.72
1121.47
1124.88
1146.55
1198.83
1224.31
1256.45
1276.67
1295.66
1297.73
----
----
714.74
713.59
713.81
714.15
717.92
718.03
752.95
758.12
758.20
----
7
7
14.92
15.79
----
----
----
----
----
----
----
----
δ (C-C)ring puckering -Ph (five adjacent H)
722.13
22.17
753.62
7
δ(C-H)wagging
-Si-Ph
----
----
----
----
7
7
58.20
58.24
ν(N-O)
-N-O
-Si-O-Si, Si-O
----
ν(Si-O)asym
δ(C-H)rocking
1088.56
----
1076.98
----
----
----
-CH
, -CH
968.86
983.24
1060.88
----
----
----
967.94
981.36
1058.96
----
----
----
1141.18
1190.15
1211.78
1258.35
1271.54
----
2
3
-
-
---
---
----
----
ν(Si-C)asym
Si-Ph
1121.07
1118.29
1126.98
1127.20
----
1
1
130.04
130.19
δ(C-H)twisting
δ(C-C)bending
δ(C-C)wagging
ν(C-C)sym
ν(C-N)asym
ν(C-C)sym
-CH
2
----
1144.61
1195.68
1213.93
1265.15
1276.67
----
Ring vibration
Ring vibration
-C-CH2
C-N-C
-Ph
----
----
----
----
----
----
----
----
1299.59
1296.91
1299.32
1
302.48
----
----
2
4

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1
----
----
302.57
1299.46
----
----
----
----
1304.08
----
1300.87
----
----
----
•
•
ν(NO )
-NO
1372.90
1390.22
1395.84
1413.31
1422.35
----
----
----
1499.64
1507.69
1511.17
----
----
----
----
----
----
----
----
----
3056.25
3056.69
3066.57
3014.31
3015.46
3027.36
3097.40
3099.25
3103.12
3115.43
3119.92
3132.03
----
1372.3
1388.21
1393.34
1406.67
1417.08
----
----
----
1489.27
1499.58
1498.95
----
----
----
----
----
----
----
----
----
3061.61
3062.34
3069.55
3017.06
3018.22
3030.10
3098.91
3101.77
3104.36
3112.40
3119.66
3125.42
----
δ(C-H)wagging
δ(C-H)wagging
δ(C-H)bending
-CH
-CH
-Ph
2
1379.71
1395.95
1412.66
1417.28
1456.35
1457.47
1459.02
1493.54
1505.36
1510.54
1515.78
1517.16
1517.44
1605.65
1606.54
1607.11
1628.01
1628.72
1629.03
3051.80
3056.69
3066.73
3015.62
3017.78
3026.36
3100.81
3103.65
3110.34
3129.01
3140.09
3143.15
3167.12
1377.07
1390.60
1405.73
1409.59
1454.00
1455.36
1456.80
1484.39
1498.56
1504.23
1513.65
1515.14
1516.23
1602.12
1602.91
1603.53
1623.94
1624.62
1625.01
3053.99
3057.76
3066.99
3015.26
3016.03
3027.43
3099.97
3102.46
3108.85
3122.19
3137.76
3140.21
3168.96
-
---
----
---
1457.10
3
-
----
1455.12
1455.47
1455.81
----
----
----
1513.75
1514.34
1514.51
1602.60
1603.06
1603.18
1624.38
1624.83
1624.94
----
----
----
----
----
----
----
----
----
1
1
----
457.94
457.96
δ(C-H)twisting
δ(C-C)bending
ν(C-C)asym
ν (C-C)sym
ν(C-H)asym
ν(C-H)sym
-CH
-Ph
-Ph
-Ph
3
-
-
---
---
1515.68
1
1
1606.12
1
1
1628.29
1
1
516.60
516.78
606.88
606.94
628.84
628.86
-CH2
-CH2
-CH3
-CH3
-Ph
----
-
-
---
---
----
----
----
ν(C-H)asym
ν(C-H)sym
----
-
-
---
---
----
----
---
----
3166.59
---
----
ν(C-H)asym
3164.86
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5

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3
3
3
3
3
164.90
165.15
173.40
173.44
173.47
3166.67
3166.83
3174.47
3174.48
3174.54
3185.49
3185.56
3185.75
3169.55
3169.55
3175.17
3181.18
3181.55
3183.94
3187.80
3193.46
3171.15
3173.32
3176.35
3180.46
3183.23
3185.85
3187.63
3194.62
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
ν(C-H)sym
-Ph
3183.58
3
3
183.60
183.78
2
6

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The sol-gel process is a well-known method for converting chemical precursors
into ceramics and glasses with the desired properties. The process can produce a wide range
of compositions (mostly oxides) in various forms, including powders, fibers, coatings and
7
0, 73-75
thin films, monoliths and composites, and porous membranes.
By controlling the
synthesis conditions carefully, sol morphology can be directed towards branched polymeric
7
3
systems or toward particulate systems. Control of relative rates of hydrolysis and
polycondensation, the respective mechanism (Scheme 4), as well as the factors of pH,
process temperature, pressure, solvent, concentration of alkoxide, type and concentration of
catalysts and DCCA (Drying Control Chemical Additive), play important roles in
7
3,74,76
determining morphology of the resulting polymeric structure.
Besides the possibility
of modifying the hydrolysis and polycondensation reactions, it is now well known that
addition of DCCA to a mixture of alkoxide, water, and alcohol improves the processing
7
6-80
control of gel structures and processability.
The sol-gel process of silica involves the
hydrolysis [i] and condensation [ii, iii] of alkoxides, such as tetraethoxysilane or
tetramethoxysilane. These monosilanes form in these reactions [i-iii] various diverse linear,
7
3-76
branched and cyclic intermediates (Scheme 4).
Si
OR + H O
Si
OH + ROH
i
2
Si
Si
OH
OH
+
+
Si
Si
OR
OH
Si
Si
O
Si
Si
+
+
ROH ii
O
H O
2
iii
Scheme 4. Hydrolysis and polycondensation mechanism
The compounds as powder white, which was obtained in good percentage in the
reactions II-IV (for 3) and for the reagent (2) at reactions conditions V(a) with a melting
point > 280 °C, could be due to process that carried out during the funtionalized, i.e. the
2
7

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formation of an oxide network or in linear chain through polycondensation reactions of a
molecular precursor (hexaphenyldisiloxane) that is formed in situ, Scheme 5.
TEMPO
Si
OH
Si
O
Si
+
H O
2
DMFA/base
Si
O
Si
Si
O
Si
O
Si
O
Si
+
HO
Si
Scheme 5. Proposed mechanism to form a silica oxide.
The characterization was made for IR, Figure 7 shows the spectra for products from
the reactions of 2 at conditions of VI(a) (Figure 7i) and 3 at II (Figure 7ii). In Figure 7i, the
bands are broad, which is an indication of a polymer type structure. The principal signals at
-1
-1
1
095 cm and 514 cm assigned to νSi-O-Si and δSi-O for the ether forms are missing.
-1
-1
The signal at 704 cm was assigned to δ(C-H) wagging and at 1416 cm is due to δC-H of
7
1
Si-Ph according to reference. The new signals for the Si-O(H) stretching band around of
-1
-1
9
82 cm and one due to Si-O of ≡Si-OH, for reagent triphenylsilanol appeared at 856 cm .
-1
71
The band at around 915 cm was associated with non-bridging free broken Si-O bonds.
-1
Spectrum analysis revealed the bands at 833, 665, 598, 481 and 424 cm that corresponded
to νSi-C (Si-R), νSi-O-Si (structural unit ≡Si-O-Si≡), νSi-O (SiO ) defect, and the
2
7
0,71
important unit, the -O-Si-O- bond for the formation of a gel of silica.
The spectrum also
-1
presented a strong band at about 1662 cm characteristic of a C=O bond which, belonging
to formate or amide groups, was present in the spectra of sols containing formamide, since
74-76
formamide is a typical DCCA, as shown for previous studies.
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8

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(i)
(ii)
Figure 7. The IR spectra from reactions 2 at V(a) (i) and 3 at II (ii).
Finally, in the IR spectrum of the product obtained from the reaction carried out
-1
with trimethylsilanol (Figure 7b), the νSi-CH was assigned at 1269 cm , the band at 865,
3
-1
8
19 and 726 cm corresponded to the weak band in polysiloxanes. We did not observe the
presence of a band for C=O corresponding to an amide as for the II reaction. The IR
2
9