Hexafluoropropylene oxide-alcohol: A convenient system for silica dissolution

Article abstract of DOI:10.1080/10426507.2010.530324

A new method of silica dissolution is described. It involves the formation of a stable SiF₄ n ROH complex (1, 1a) just from SiO₂ and anhydrous alcoholic HF generated in situ from commercially available hexafluoropropene oxide. Alcoholic SiF₄ complexes can be easily converted to different organosilicon compounds of the type SiF₄L ₂ and (LH)₂SiF₆ [L = 1,10-phenantroline (2a), 2,2'-dipyridyl (2b), Me₂SO (2c), pyridine (2d), triethanolamine (3a)]. Different silica-containing compounds can be used in this strategysilicagel, sand, alumosilicates, and even rice husk. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426507.2010.530324

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Phosphorus, Sulfur, and Silicon and the
Related Elements
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Hexafluoropropylene Oxide–Alcohol: A
Convenient System for Silica Dissolution
Sergey A. Lermontov a , Alena N. Malkova a , El'mira Kh. Lermontova
b & Andrei V. Churakov b
a Institute of Physiologically Active Compounds, Russian Academy of
Sciences , Chernogolovka, Moscow region, Russia
b N. S. Kurnakov Institute of General and Inorganic Chemistry,
Russian Academy of Sciences , Moscow, Russia
Published online: 13 Jan 2011.
To cite this article: Sergey A. Lermontov , Alena N. Malkova , El'mira Kh. Lermontova &
Andrei V. Churakov (2010) Hexafluoropropylene Oxide–Alcohol: A Convenient System for Silica
Dissolution, Phosphorus, Sulfur, and Silicon and the Related Elements, 186:1, 178-188, DOI:
10.1080/10426507.2010.530324
To link to this article: http://dx.doi.org/10.1080/10426507.2010.530324
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Phosphorus, Sulfur, and Silicon, 186:178–188, 2011
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2010.530324
HEXAFLUOROPROPYLENE OXIDE–ALCOHOL:
A CONVENIENT SYSTEM FOR SILICA DISSOLUTION
Sergey A. Lermontov,1 Alena N. Malkova,1
El’mira Kh. Lermontova,2 and Andrei V. Churakov2
1Institute of Physiologically Active Compounds, Russian Academy of Sciences,
Chernogolovka, Moscow region, Russia
2N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy
of Sciences, Moscow, Russia
GRAPHICAL ABSTRACT
L2/ROH
SiF4 * L2
TEA/ROH
HFPO/ROH
r.t.
(TEAH)2SiF6
SiF4 * n ROH
SiO2
2-
HFPO = hexafluoropropylene oxide
TEA = triethanolamine
L = 1,10-phenantroline, 2,2'-dipyridyl,
Me2SO
OH
O
O
F3C
Py/ROH
SiF4 * n Py +
(n = 1, 2)
* 2 PyH+
O
SiF4
Abstract A new method of silica dissolution is described. It involves the formation of a
stable SiF4 · n ROH complex (1, 1a) just from SiO2 and anhydrous alcoholic HF generated
in situ from commercially available hexafluoropropene oxide. Alcoholic SiF4 complexes can
be easily converted to different organosilicon compounds of the type SiF4L2 and (LH)2SiF6
[L = 1,10-phenantroline (2a), 2,2ꢁ-dipyridyl (2b), Me2SO (2c), pyridine (2d), triethanolamine
(3a)]. Different silica-containing compounds can be used in this strategy—silicagel, sand,
alumosilicates, and even rice husk.
Keywords Hexafluoropropene oxide; hydrogen fluoride; silica dissolution; silicon tetrafluoride
INTRODUCTION
Organosilicon chemicals are almost exclusively prepared from elemental silicon
or silicon tetrachloride, obtained from the carbothermal reduction of silica at around
1200–1300◦C.1 The main problem with any industrial process based on silica as a starting
material is the very strong Si O bond (about 535 kJ/mol in SiO2). The utilization of silica
itself to produce silicon-containing compounds with the aim to exclude high-temperature
processes has been the aim of a number of investigations. Only a few strategies of silica
depolymerization and further dissolution are known to date. Silica dissolution in alkali
Received 28 May 2010; accepted 4 October 2010.
Address correspondence to Sergey A. Lermontov, Institute of Physiologically Active Compounds, Russian
Academy of Sciences, Severny proezd 1, 142432, Chernogolovka, Moscow region, Russia. E-mail: lermon@
ipac.ac.ru
178

HEXAFLUOROPROPYLENE OXIDE–ALCOHOL
179
metals hydroxides and in hydrogen fluoride are well known reactions affording inorganic
silicates, H2SiF6, or gaseous SiF4.1 A method of SiO2 depolymerization in alkaline alcohols
with the formation of silicon chelates has been developed by different research groups2–5
(Scheme 1). These procedures usually afford crystalline solvates, frequently containing wa-
ter and/or glycol. This fact makes it difficult to use the products in organometallic synthesis.
O
O
O
200 0C
- 3 H2O
SiO2 + MOH + 3 HOCH2CH2OH
M = K, Na
M
OH
Si
2
N
210 0C
- 2 H2O
SiO2 + HOCH2CH2OH + N(CH2CH2OH)3
O
O
Si
O
OCH2CH2OH
(HOCH2CH2)nN[CH2CH2OSi(OCH2CH2)3N]3-n
SiO2 + (HOCH2CH2)3Nexcess
- 2 H2O
OH
SiO2 + 3
(NH4)2[Si(C6H4O2)3] * H2O
+ 2 aqNH3
OH
Scheme 1
The main goal of our work was to find a method of silica dissolution that was
satisfactory to the following conditions: (i) the method should not need high temperature
and (ii) it should afford products suitable for organometallic synthesis or as a silicon source
for the electronics industry.
RESULTS AND DISCUSSION
Dissolution of Silica
Silicon tetrafluoride reacts rapidly with water, forming H2SiF6 and SiO2.6 Unlike so-
lutions of SiF4 in lower alcohols, (C1–C4) are rather stable at least at ambient temperature.6,7
It is assumed that solvates containing hexacoordinate silicon are formed (Figure 1).
Basing on these facts, we propose a new strategy for silica dissolution under very mild
conditions. The strategy consists in the primary generation of anhydrous HF in an alcohol
R
OR
H
H
O
Si
O
F
F
F
F
RO
H
H
R
Figure 1 Structure of SiF4–alcohol complex.

180
S. A. LERMONTOV ET AL.
followed by the reaction with silica. The idea is based on the assumption that an excess
of the alcohol will replace water from the coordination sphere of SiF4, thus preventing its
hydrolysis. Different compounds producing HF in the reaction with alcohols can be used
for this strategy: SF4,8 perfluoroalkene oxides,9,10 organic acid fluoroanhydrides,11 and, of
course, hydrogen fluoride itself.
We have found that the most convenient source of alcoholic HF in laboratory practice
is hexafluoropropene oxide (HFPO), a commercially available and safe compound, which
reacts rapidly with alcohols producing two moles of HF and an inert ester.9,10 Silica and
silica-containing compounds are easily dissolved in an alcoholic solution of HFPO giving
SiF4 complexes 1 and 1a, which are stable at ambient temperature (Scheme 2).
O
O
+ 2 HF
OR
CF3 CF
OR
+ 2 ROH
CF2
CF3 CF
HFPO
n ROH
SiO2 + 4 HF
SiF4 * 4 ROH + 2 H2O
1
, R = Me
1a , R = Et
Scheme 2
The dissolution reaction proceeds rapidly at room temperature when a stream of
HFPO is passed through a SiO2 suspension in the respective alcohol. We have found esters
of 2-alkoxytetrafluoropropionic acid in the reaction mixture, thus confirming the primary
reaction of HFPO with the alcohol. By a special experiment, we have prepared a solution of
gaseous SiF4 in anhydrous MeOH and have found that its 19F NMR spectrum was identical
with that of 1.
Different silica-containing compounds can be used as a silica source in this pro-
cedure: silicagel, sand, alumosilicates, and even rice husk. Rice husk is one of the most
serious contaminants in rice-producing countries. Its annual worldwide production is about
100 million tons.12 Rice husk is a rather unusual material: the SiO2 content in it is approx-
imately 20% (together with 75% organic matter—mainly cellulose and lignin—and 5%
inorganic salts). Rice husk is hardly burned or milled, and it is very slowly decomposed in
nature.13 Several methods of its use as a silica source are known.13–15 Usually these methods
include controlled burning or anaerobic pyrolysis of rice husk (at 500–600◦C) followed by
a SiO2/C mixture oxidation.
We have shown that up to 97% of silica could be extracted from rice husk using the
described procedure. It is worth mentioning that the organic part of rice husk (cellulose
and lignin) is not destroyed during SiO2 extraction and can be further used as usual wood.
This means that there exists a possibility to elaborate a process of full rice husk processing:
silica extraction → fermentation → bioethanol and biobuthanol.
For the purposes of potential industrial application, we have dissolved silica gel and
have extracted silica from rice husk by an alcoholic solution of inexpensive hydrogen
fluoride. This procedure is not convenient for laboratory use because serious precautions
are needed to prevent personnel from poisoning by the very hazardous hydrogen fluoride.

HEXAFLUOROPROPYLENE OXIDE–ALCOHOL
181
Properties of the Complexes Prepared
Complexes 1 and 1a afford crystalline products after the reaction with tertiary amines
(Scheme 3). Compounds 2 are formed immediately after addition of the ligand and are usu-
ally pure enough after filtration, washing, and drying. They are colorless, stable crystalline
substances that are soluble in polar solvents like Me2SO and DMF. The structures of both
2a and 2b were established by NMR spectroscopy and elemental analysis and were con-
firmed by X-ray diffraction.16,17 The 19F NMR spectra of 2a,b show two triplets (A2X2 spin
systems), confirming the formation of cis-complexes.
L2/ROH
SiF4 * L2
SiF4 * n ROH
, L - 1,10-phenantroline
2a
1, R = Me
, R = Et
1a
2
, L - 2,2'-dipyridyl
2b
2
Scheme 3
More complex mixtures of silicon-containing compounds are usually formed with
nonchelating ligands (Scheme 4). Thus, dimethylsulfoxide gives a “normal” 1:2 adduct
2c. In the case of triethanolamine (TEA), only hexafluorosilicate 3a was formed as a Si-F-
containing product. Our attempt to prepare pure compounds of type 2 or 3 from compound 1
and pyridine were unsuccessful. The reaction affords a mixture of products. The formation
of 2d is consistent with data in the literature for SiF4-pyridine adducts—both types of
products (1:2 and 1:1) are described.18,19
Me2SO/ROH
SiF4 * 2 Me2SO
2c
2-
OH
O
O
F3C
Py/ROH
SiF4 * n Py +
2d
(n = 1, 2)
SiF4 * n ROH
1,1a
R = Me, Et
* 2 PyH+
O
SiF4
4
TEA = triethanolamine
Py = pyridine
TEA/ROH
(TEAH)2SiF6 + [Si(OR)4]
3a
Scheme 4
We were able to obtain single crystals of a minor product 4, which were suitable
for X-ray diffraction. Compound 4 is a rare example of the hexacoordinate silicon anion
with mixed oxygen bonded and halogen ligands.20 The organic part of this anion is a
derivative of trifluoropyruvic acid hydrate, which is probably formed from hydrolysis of
the methyl ester of 2-methoxytetrafluoropropionic acid by water present in the reaction
mixture (Scheme 5).
The formation of compound 4 looks very unusual because a transformation of
alkoxytetrafluoropropionic esters into trifluoropyruvic acid derivatives needs high tem-
perature and strong acids as catalysts10 (Scheme 5). In our case it proceeds at ambient
temperature without any catalyst.

182
S. A. LERMONTOV ET AL.
2-
OH
O
O
OH
OH
O
O
F3C
H2O
SiF4/Py
* 2 PyH+
CF3 CF
OMe
CF3
O
OH
OMe
SiF4
O
4
150-170 0C
H2SO4 conc.
CF3
OMe
O
Scheme 5
Compound 4 crystallizes in the space group P-1. The diamond representation of
the complex is given in Figure 2; selected bond lengths and bond angles are listed in
Table 1. The coordination polyhedron of the silicon atom in complex 4 displays a slightly
distorted octahedral geometry. All of the cis bond angles are close to 90◦ [86.3(7)–95.8(7)◦],
while trans angles are greater than 170◦ [174.0(1)–177.8(1)◦]. The five-membered ring is
´
almost planar, with atom O1 displaced from the least-squares plane by 0.180(3) Å. The
O1 C1 C3 O2 torsion angle is 7.2(3)◦.
Figure 2 Crystal structure of 4 showing anion–cation interactions. Hydrogen atoms are omitted for clarity except
those participating in hydrogen bonding. Thermal ellipsoids are given at the 50% probability level, except for H
atoms, which have arbitrary radii. [Please see the color version of this figure online.]

HEXAFLUOROPROPYLENE OXIDE–ALCOHOL
183
Table 1 Selected bond lengths (Å) and angles (◦) of 4
Bond length (Å)
Bond angle (◦)
Si1 F4
Si1 F3
Si1 F2
Si1 F1
Si1 O1
Si1 O2
O1 C1
O2 C3
O3 C1
O4 C3
1.6497(14)
1.6576(14)
1.6678(14)
1.7137(14)
1.8017(15)
1.8135(17)
1.385(3)
1.303(3)
1.402(3)
1.212(3)
∠F2 Si1 F1
∠F4 Si1 O1
∠F3 Si1 O2
177.78(7)
175.14(8)
173.98(7)
The pyridinium counter ions are linked to a central dianion through N H O hydro-
gen bonds. Only one oxygen atom of the ligand is involved in both hydrogen bonds. Two
centrosymmetrically related anions form dimers by O(3) H(3) F(1) hydrogen bond (Fig-
ure 3). The latter results in a noticeable elongation of the Si(1) F(1) bond. The structural
parameters of the hydrogen bonds are given in Table 2.
CONCLUSION
In summary, a novel, convenient strategy for the dissolution of silicon dioxide has been
developed, which uses available reagents and proceeds at ambient temperature affording
pure complexes of SiF4. This procedure can make SiO2 a good starting material for inorganic
and organometallic synthesis.
In our opinion, the most interesting application of SiF4 complexes is their conversion
to tetraalkoxysilanes. Several methods for the synthesis of tetraalkoxysilanes Si(OR)4 from
tetrafluorosilane are patented21–25 (Scheme 6).
3 SiF4 + 4 ROH + 4 NH3
3 SiF4 + 4 ROH + 2 Fe
SiF4 + 4 ROH + 2 CaO
SiF4 + 4 ROH + 2 Na2S
Si(OR)4 + 2 (NH4)2SiF6
Si(OR)4 + 2 FeSiF6
Si(OR)4 + 2 CaF2 + 2 H2O
Si(OR)4 + 4 NaF + 2 H2S
Scheme 6
When performed on an industrial scale, these processes can become the basis for the
use of SiO2 as a starting material in organosilicon chemistry.
The developed method of silica dissolution can also be useful for the extraction of
silica from different silicon-containing compounds including serious agricultural contami-
nants such as rice husk.
EXPERIMENTAL
1H and 19F NMR spectra were recorded with a Bruker DPX-200 spectrometer at 200
MHz and 188 MHz, respectively. Chemical shifts are given relative to TMS (1H) and CFCl3
(19F) as external standards.

184
S. A. LERMONTOV ET AL.
Figure 3 Centrosymmetric dimers in the structure of 4. Hydrogen atoms are omitted for clarity except those
participating in hydrogen bonding. The pyridine rings are not shown for clarity. Thermal ellipsoids are given at
the 50% probability level, except for H atoms, which have arbitrary radii. [Please see the color version of this
figure online.]
Hexafluoropropene oxide (HFPO) was a commercial product from Kirovo-Chepetsk
chemical plant (Russia) (99.7% purity). Silica gel (Chemapol, L 100/250) was dried at
150◦C during 2 h before a reaction. Rice husk was obtained from one of south Russia rice
mills and was washed with aqueous HCl according to the method of Liou et al.26
Table 2 Hydrogen bonding interactions in the compound 4(Å, ◦)
d(D H)
d(H . . . A)
d(D . . . A)
∠(D H . . . A)
O3 H3 . . . F1i
N1 H1 . . . O1ii
N2 H2 . . . O1iii
0.82(3)
0.79(3)
0.97(5)
1.81(3)
2.24(3)
1.86(5)
2.626(2)
2.984(3)
2.814(3)
174(3)
156(3)
168(4)
Symmetry codes: (i) − x + 2, −y, −z + 2; (ii) x − 1, y, z − 1; (iii) x − 1, y, z.

HEXAFLUOROPROPYLENE OXIDE–ALCOHOL
185
2,2ꢁ-Dipyridyl (Lancaster), 1,10ꢁ-phenanthroline (Chemapol), triethanolamine
(Merck), N-pyridine oxide (Aldrich), anhydrous methanol (Aldrich, 0.05% water content),
and ethanol (Aldrich, 0.1% water content) were used as purchased. Other solvents and
reagents were purified and dried by standard procedures.
Anhydrous SiF4 was prepared from a SiO2/Na2SiF6 mixture by treatment with con-
centrated sulfuric acid.
SiO2 Dissolution: General Procedure
Anhydrous MeOH (10 mL) and silica gel (0.6 g, 0.01 mol) were placed in a polytet-
rafluoroethylene (PTFE) flask equipped with a PTFE gas-injection tube, and HFPO (3.32
g, 0.02 mol, determined from the weight increase) was introduced with magnetic stirring
at room temperature. The reaction was slightly exothermic. When HFPO addition was
complete, the reaction mixture was stirred for 1 h (the whole amount of silica gel was dis-
solved). Then a solution of 0.01 mol of 1,10-phenanthroline or 2,2ꢁ-bipyridyl in anhydrous
MeOH (5 mL) was added. A precipitate was formed immediately, which was stored for 1
h, separated by filtration, washed with MeOH, and dried in vacuo.
The 19F NMR spectrum of the filtrate after evaporation of the solvent contained the
signals of CF3CF(OCH3)COOCH3: δ = −80.5 (d, 3JFF = 3 Hz, 3F, CF3), −133.5 (m, 1F),
which coincided with those of the separately prepared ester.10
The reaction in dry ethanol produced compound 1a.
Compound 2a was isolated from a Me2SO/MeOH mixture, 69% yield, mp > 230◦C.
The H NMR spectrum (DMSO-d6) contained two sets of signals corresponding to the
1
1,10-phenanthroline ligand in a 1.5:1 intensity ratio: δ = 8.0 (m, 2H), 8.2 (s, 2H), 8.6
(m, 2H), 9.2 (m, 2H); δ = 8.2 (m, 2H), 8.4 (s, 2H), 9.0 (m, 2H), 9.3 (m, 2H). 19F NMR
(DMSO-d6): δ = −118.3 (t, 2JFF = 18.4 Hz, 2F, SiF2; JSiF = 164 Hz), −143.1 (t, 2JFF
=
18.4 Hz, 2F, SiF2; JSiF = 146 Hz), −135.0 (broad). Anal. Calcd for C12H8N2SiF4: C, 50.69;
H, 2.84; F, 26.73. Found: C, 50.67; H, 2.79; F, 26.67%. Single crystals suitable for X-ray
diffraction were obtained from the Me2SO/MeOH mixture. X-ray analysis revealed that
compound 2a crystallized isostructurally to a substance described earlier in the literature.16
Compound 2a was also obtained from 1a in 76% yield.
Compound 2b was isolated from a Me2SO/MeOH mixture, 74% yield, mp > 230◦C.
1H NMR spectrum (DMSO-d6) contained signals corresponding to the 2,2ꢁ-bipyridyl ligand:
δ = 8.0 (m, 2H), 8.5 (m, 2H), 8.6 (m, 2H), 9.0 (m, 2H). 19F NMR (DMSO-d6): δ = −118.7
2
2
(t, JFF = 14.4 Hz, 2F, SiF2; JSiF = 160 Hz), −142.0 (t, JFF = 13.0 Hz, 2F; SiF2,
JSiF = 161 Hz). Anal. Calcd. for C10H8N2SiF4: C, 46.14; H, 3.09; F, 29.20. Found: C,
46.08; H, 3.06; F, 29.35%. Single crystals suitable for X-ray diffraction were obtained
from the Me2SO/MeOH mixture. X-ray analysis revealed that compound 2b crystallized
isostructurally to a substance described earlier in the literature.17
Dissolution of Sand
Compound 2a was synthesized from washed sand according to the above procedure
in 40% yield after 20 h of stirring (unreacted sand was separated by filtration).
Dissolution of Zeolite
Compound 2a was prepared from 1 g of zeolite 4A (Na12[(AlO2)12/(SiO2)12] · 27
H2O, dried at 300◦C during 6 h) in 74% yield after 25 h of stirring (unreacted zeolite was
separated by filtration).

186
S. A. LERMONTOV ET AL.
Extraction of SiO2 from Rice Husk
Rice husk [3 g, containing approximately 0.6 g (0.01 mol) of SiO2] were stirred
for 4 h with a solution of 3.32 g (0.02 mol) of HFPO in anhydrous MeOH (20 mL) at
room temperature. The organic part of rice husk was separated by filtration, and a solution
of 1,10-phenanthroline (0.01 mol) in anhydrous MeOH (5 mL) was added to the filtrate.
Compound 2a was obtained in 73% yield.
A sample of organic part of rice husk was burnt at 500◦C in a steam of air, revealing
that 97% of SiO2 was extracted.
Use of Alcoholic Solution of HF
Dissolution of SiO2. Anhydrous MeOH (10 mL) and silica gel (0.6 g, 0.01 mol)
were placed in a PTFE flask equipped with a PTFE gas-injection tube, and gaseous HF
(0.8 g, 0.04 mol, determined from the weight increase) was introduced with magnetic
stirring at room temperature. The reaction was slightly exothermic. After HF addition was
complete, the reaction mixture was stirred during 1 h. During this time, the whole amount
of silicagel was dissolved. Then a solution of 0.01 mol of 1,10-phenanthroline in anhydrous
MeOH (5 mL) was added. A precipitate was immediately formed, stored for 1 h, separated
by filtration, washed with MeOH, and dried in vacuo. Compound 2a was obtained in 57%
yield.
Extraction of SiO2 from rice husk. Anhydrous MeOH (20 mL) and rice husk
[3 g, containing approximately 0.6 g (0.01 mol) of SiO2] were placed in a PTFE flask
equipped with a PTFE gas-injection tube and gaseous HF (0.8 g, 0.04 mol, determined
from the weight increase) was introduced with magnetic stirring at room temperature. The
reaction was slightly exothermic. After HF addition was complete, the reaction mixture
was stirred during 5 h. The organic part of rice husk was filtered off, and a solution of
0.005 mol of 1,10-phenanthroline in anhydrous MeOH (5 mL) was added to the filtrate.
A precipitate was immediately formed, stored for 1 h, separated by filtration, washed with
MeOH, and dried in vacuo. Compound 2a was obtained in 49% yield.
Preparation of SiF4L2 with Nonchelating Ligands
A solution of 0.02 mol of Me2SO, triethanolamine, or pyridine in anhydrous MeOH
(5 mL) was added to a solution of 1, prepared from SiO2 (0.6 g, 0.01 mol). A precipitate was
usually formed immediately, stored for 1 h, separated by filtration, washed with MeOH,
and dried in vacuo. Compound 2с was soluble in MeOH, and after removal of the solvent,
it was purified by crystallization from toluene, 74% yield, mp 101–104◦C. Anal. Calcd.
for C4H12S2O2SiF4: C, 18.45; H, 4.65; F; 29.19. Found: C, 17.85; H, 5.32; F; 29.13%. 1H
NMR (CD3CN): δ = 2.9 (s, 6H, CH3S), 7.0 (s, 1H, SOH). 19F NMR (CD3CN): δ = −137.5
(s). Alternatively, compound 2c was prepared as described in the literature18 by passing
SiF4 (0.0035 mol), prepared from conc. H2SO4 and 1, through a solution of Me2SO (0.6 g,
0,007 mol) in benzene (5 mL). A precipitate was immediately formed. The reaction mixture
was stored for 1 h, the precipitate was separated by filtration, washed with benzene, and
dried in vacuo. 1Н and 19F NMR spectra and the melting point of both samples of 2c were
identical.
Compound 3a was isolated from MeOH, 71% yield, mp 100–101◦C. 1H NMR (D2O):
δ = 3.4 (t, 3JHH = 5.2 Hz, 2H, NCH2), 3.9 (t, 3JHH = 5.0 Hz, 2H, OCH2). 19F NMR (D2O):

HEXAFLUOROPROPYLENE OXIDE–ALCOHOL
187
δ = −127.5; JSiF = 108 Hz. Anal. Calcd for C12H32N2O6SiF6: C, 32.57; H, 7.29; F,
25.76. Found: C, 32.07; H, 7.36; F, 25.14%. Alternatively, compound 3a was prepared as
described in the literature27 by passing SiF4 (0.01 mol), prepared from conc. H2SO4 and 1,
through a solution of triethanolamine (2.98 g, 0,02 mol) in anhydrous MeOH (5 mL). A
precipitate was immediately formed, the reaction mixture was stored for 1 h, the precipitate
1
was separated by filtration, washed with MeOH, and dried in vacuo. Н and 19F NMR
spectra and the melting point of both samples of 3a were identical.
Compound 2d was isolated from MeOH, 1.92 g yield. Anal. Calcd for C10H12N2SiF4
(SiF4 · 2 py): C, 45.79; H, 3.84; F, 28.98. Anal. Calcd for C5H5NSiF4 (SiF4 · py): C, 32.78;
H, 2.75; F, 41.49. Found: C, 37.53; H, 3.61; F, 35.53%. The elemental analysis data reveal
that the composition of isolated 2d is between that of SiF4 · 2 py and of SiF4 · py. The 1H
NMR spectrum (DMSO-d6) contained signals corresponding to the pyridine ligand: δ =
7.9 (m, 2H), 8.4 (m, 1H), 8.9 (m, 2H). 19F NMR (DMSO-d6): δ = −133.9; JSiF = 107 Hz.
A single crystal of compound 4 was prepared by a slow evaporation of methanol from
the mother liquid. Its structure was established by X-ray diffraction.
X-Ray Structure Determination
Experimental intensities were collected on a Bruker Smart Apex II diffractometer
using graphite monochromatized Mo-Kα radiation (λ = 0.71073 Å, ω-scan). The structures
were solved by direct methods and refined by full-matrix least-squares on F2 (SHELXL-
97)28 with anisotropic displacement parameters for all nonhydrogen atoms (Table 3).
All hydrogen atoms were found from difference Fourier synthesis and refined isotrop-
ically. Crystallographic data (excluding structure factors) for the structure in this article
have been deposited with the Cambridge Crystallographic Data Centre as supplementary
publication No. CCDC-683674. Copies of the data can be obtained free of charge upon
Table 3 Crystal structure and data refinement parameters
Compound
4
Empirical formula
Formula weight
C13H13F7N2O4Si
422.34
Crystal system/space group
P-1
a/Å
b/Å
8.8583(17)
10.062(2)
10.163(2)
71.698(3)
69.623(3)
72.258(3)
786.5(3)
c/Å
α/◦
β/◦
γ /◦
V/Å3
Z
2
D calc (g/cm3)
1.783
0.254
µ (mm−1
)
Temp (K)
150(2)
Theta range for collection
Reflections collected
Independent reflections
R indices (all data)
2.19 < θ < 26.99
5831
3327 [Rint = 0.0418]
0.0610; 0.1040

188
S. A. LERMONTOV ET AL.
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, (fax: +44 1223 336033
or e-mail: deposit@ccdc.cam.ac.uk).
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