Thermal and BF3·Et2O-catalyzed cleavage of 1-hydrohexafluoroisobutenyloxytrimethylsilane. Perfluoromethacrolein, its isomers, dimers, and homopolymers

Article abstract of DOI:10.1007/s11172-005-0019-8

During vacuum pyrolysis in a quartz or steel tube, 1- hydrohexafluoroisobutenyloxy- trimethylsilane (1) eliminates fluorotrimethylsilane to give perfluoromethacrolein, which was detected by NMR. Similar pyrolysis of silane 1 over KF results in E- and Z-β-hydro- tetrafluoromethacryloyl fluorides. At 20°C, perfluoromethacrolein undergoes homo- polymerisation and/or cyclodimerization to yield 4,4-difluoro-2- pentafluoroisopropenyl-5- trifluoromethyl-4H-1,3-dioxin, which rearranges into E-7,7,7-trifluoro-2,6-bis(trifluoro- methyl)-4-oxahepta-2,5-dienoyl fluoride under the action of BF₃·Et₂O. The same fluoride is also formed, together with fluorotrimethylsilane, directly from silane 1 under the action of BF₃·Et₂O.

Full text of DOI:10.1007/s11172-005-0019-8

Russian Chemical Bulletin, International Edition, Vol. 53, No. 8, pp. 1693—1699, August, 2004
1693
Thermal and BF3•Et2Oꢀcatalyzed cleavage of
1ꢀhydrohexafluoroisobutenyloxytrimethylsilane.
Perfluoromethacrolein, its isomers, dimers, and homopolymers
†
ꢀ
A. Yu. Volkonskii, E. M. Kagramanova, E. I. Mysov, and N. E. Mysova
A. N. Nesmeyanov Institute of Organoelement Сompounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5085. Eꢀmail: volkonskii@ineos.ac.ru
During vacuum pyrolysis in a quartz or steel tube, 1ꢀhydrohexafluoroisobutenyloxyꢀ
trimethylsilane (1) eliminates fluorotrimethylsilane to give perfluoromethacrolein, which was
detected by NMR. Similar pyrolysis of silane 1 over KF results in Eꢀ and Zꢀβꢀhydroꢀ
tetrafluoromethacryloyl fluorides. At 20 °С, perfluoromethacrolein undergoes homoꢀ
polymerisation and/or cyclodimerization to yield 4,4ꢀdifluoroꢀ2ꢀpentafluoroisopropenylꢀ5ꢀ
trifluoromethylꢀ4Hꢀ1,3ꢀdioxin, which rearranges into Eꢀ7,7,7ꢀtrifluoroꢀ2,6ꢀbis(trifluoroꢀ
methyl)ꢀ4ꢀoxaheptaꢀ2,5ꢀdienoyl fluoride under the action of BF3•Et2O. The same fluoride is
also formed, together with fluorotrimethylsilane, directly from silane 1 under the action of
BF3•Et2O.
Key words: 1ꢀhydrohexafluoroisobutenyloxytrimethylsilane, boron trifluoride—diethyl ether
complex, pyrolysis, perfluoromethacrolein, Eꢀ and Zꢀβꢀhydrotetrafluoromethacryloyl fluoꢀ
rides, Eꢀ and Zꢀ7,7,7ꢀtrifluoroꢀ2,6ꢀbis(trifluoromethyl)ꢀ4ꢀoxaheptaꢀ2,5ꢀdienoyl fluorides,
4,4ꢀdifluoroꢀ2ꢀpentafluoroisopropenylꢀ5ꢀtrifluoromethylꢀ4Hꢀ1,3ꢀdioxin.
It has been reported1,2 that enol trimethylsilyl ethers
and ketene trimethylsilyl acetals containing a СF3 group
in the βꢀposition are thermally rather unstable and elimiꢀ
nate fluorotrimethylsilane at temperatures above 50 °С to
give the corresponding α,βꢀunsaturated carbonyl comꢀ
pounds. This communication reports an attempt to exꢀ
tend this approach to 1ꢀhydrohexafluoroisobutenyl triꢀ
methylsilyl ether (1) in order to synthesize perfluoroꢀ
methacrolein (2), which has been suggested previously3,4
as an intermediate for some reactions.
results in quantitative elimination of Me3SiF, but this
yields Еꢀfluoride 3* as the second product rather than
perfluoromethacrolein (2) (Scheme 1).
Scheme 1
Results and Discussion
It was found unexpectedly that trimethylsilyl ether 1,
which has not been described in the literature and has
been prepared by a slightly modified reported procedure,5
is distillable under atmospheric pressure without decomꢀ
position and withstands prolonged heating at 160 °С in a
sealed glass tube.
The time required for complete conversion of silyl
ether 1 depends appreciably on the amount of the cataꢀ
lyst used. For instance, in the presence of >10 mol.%
BF3•Et2O, the reaction is completed over 24 h at 20 °С,
whereas with 2—4 mol.% BF3•Et2O, the reaction goes to
completion in ∼20 days at 20 °С or in several hours
at 60 °С. A pronounced Е→Z isomerization of fluoride 3
Using
alkylhexafluoroisobutenyl
ethers
(СF3)2С=СXOR (X = F, OR´, NR´2, С2F5) similar in
structure to silane 1, it has been shown6 that 1,4ꢀeliminaꢀ
tion of alkyl fluorides is efficiently catalyzed by SbF5 or
BF3•Et2O. The addition of BF3•Et2O to silyl ether 1 also
† Deceased.
* The corresponding dimethylamide is known.7
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1629—1635, August, 2004.
1066ꢀ5285/04/5308ꢀ1693 © 2004 Springer Science+Business Media, Inc.

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Volkonskii et al.
in the presence of BF3•Et2O takes place only after comꢀ
plete conversion of silane 1, its rate being rather low
at 20 °С.
The use of a stainlessꢀsteel tube allows the temperaꢀ
ture of pyrolysis to be lowered by 100—200 °С; however,
in this case, the reaction is obviously catalytic. The nature
of the catalysis is obscure, because both the temperature
of the onset of the pyrolysis (300—400 °С) and the degree
of conversion of silane 1 at the same temperature depend
appreciably on the tube prehistory.
An even more pronounced lowering of the temperaꢀ
ture was attained by carrying out the pyrolysis in the presꢀ
ence of anhydrous KF, which proceeds with a 100% conꢀ
version of silyl ether 1 even at 300 °С. However, perfluoroꢀ
methacrolein (2) is no longer the major reaction product,
being replaced by its isomers, Еꢀ and Zꢀβꢀhydrotetraꢀ
fluoromethacryloyl fluorides (6) (NMR and GLС/MS
data) (Scheme 3).
Fluoride Eꢀ3 is formally the dimer of perfluoroꢀ
methacrolein (2); however, no such dimers are known
for either methacrolein (cf. Refs 8, 9) or perfluoroꢀ
methacryloyl fluoride (4) (cf. Ref. 10), which is a close
perfluorinated analog of aldehyde 2. The stereospecificity
of the reaction (see Scheme 1) indicates probably that the
reaction proceeds via a cyclic intermediate (or a cyclic
transition state) with cisꢀfixing of the H atom and the СF3
group at the ring double bond, this fragment remaining
intact during the subsequent ring opening.
It is known11,12 that fluoride 4 as well as perfluoro(ethyl
isopropenyl ketone) (5) readily form [4+2]ꢀcycloadducts
with aliphatic aldehydes. This gives grounds for hoping
that intermediate perfluoromethacrolein (2) could be deꢀ
tected using compound 4 or 5. However, it was found that
in the 1—BF3•Et2O—4 (or 5) ternary mixtures, silane 1
and fluoride 4 (or perfluorovinyl ketone 5) behave absoꢀ
lutely independently of each other, in particular, silyl
ether 1 eliminates Me3SiF according to Scheme 1 to give
a mixture of fluorides E,Zꢀ3, while fluoride 4 is rearꢀ
ranged into bis(trifluoromethyl) ketene (cf. Ref. 13), and
perfluorovinyl ketone 5 remains virtually unchanged.
Moreover, fluoride 4 can itself catalyze the reaction shown
in Scheme 1; however, its electrophilicity does not suffice
to ensure Е→Zꢀisomerization of acyl fluoride Eꢀ3. In the
case of ketone 5, this type of catalysis is not involved,
most likely, due to steric restrictions created by the bulky
pentafluoroethyl group.
Scheme 3
Dilute (2—3%) solutions of perfluoromethacrolein (2)
in silyl ether 1 are sufficiently stable to enable unambiguꢀ
ous identification of aldehyde 2 by NMR spectroscopy.
Nevertheless, perfluoromethacrolein (2) enters into subꢀ
sequent reactions over a period of several days at room
temperature; the main of these reactions is cyclodimerizaꢀ
tion to give dioxin 7 (Scheme 4).
Since the lowꢀtemperature cleavage of silyl ether 1
induced by BF3•Et2O did not result in perfluoroꢀ
methacrolein (2), we attempted to carry out vacuum pyꢀ
rolysis of silane 1 in a flowꢀtype reactor. It was found
that pyrolysis in a quartz tube starts at 550 °С and,
at low degrees of conversion, results in a quantitative
formation of Me3SiF and perfluoromethacrolein (2),
which was detected by NMR in the reaction products
(Scheme 2).
Scheme 4
Scheme 2
An increase in the concentration of perfluoroꢀ
methacrolein (2) in the pyrolysis products sharply inꢀ
creases the rate of its further transformations, homoꢀ
polymerization rather than cyclodimerization being
the major reaction route in this case.* The cycloꢀ
dimer 7 : polymer 8 ratio and the exact structure of the
The complete conversion of silane 1 is attained only at
800 °С; however, at temperatures of >700 °С, this comꢀ
pound undergoes more extensive destruction, as indicated,
first of all, by the appearance of perfluoromethylacetylene
in the pyrolysate.
* Although the resulting pyrolysates always contained small
amounts of αꢀhydrohexafluoroisobutyraldehyde, in none of the
cases, was the formation of 2ꢀhexafluoroisopropylꢀsubstituted
analog of dioxin 7 detected (cf. Ref. 4).

Сleavage of hexafluoroisobutenyloxysilane
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
1695
polymer depend on both the composition of the initial
pyrolysate and the schedule of its heating from –196 °С
to room temperature. This implies apparently that diꢀ and
polymerization of perfluoromethacrolein (2) starts with
an electrophilic attack by the carbonyl С atom of one
molecule of aldehyde 2 on the carbonyl O atom of anꢀ
other molecule to give betaine 9 (Scheme 5). When the
concentration of perfluoromethacrolein (2) is low, most
of betaine 9 undergoes intramolecular cyclization into
dioxin 7, while at high concentrations of 2, the betaine is
attacked predominantly by the next molecules of aldeꢀ
hyde 2, which finally results into homopolymer 8.
(NMR data). New NMR signals appear that can be atꢀ
tributed to difluoroborane 10 (Scheme 7).
Scheme 7
After complete conversion of dioxin 7, the concentraꢀ
tion of difluoroborane 10 continues to increase gradually
at 20 °С, which is accompanied by the corresponding
change in the content of silane 1, BF3•Et2O, and Me3SiF,
whereas the content of acyclic dimer Eꢀ3 virtually does
not change. Meanwhile, heating of the reaction mixture
to 60 °С induces fast consumption of borane 10 with
simultaneous restoration of the initial concentration of
BF3•Et2O, which is followed by slower transformation of
silyl ether 1 into dimer Eꢀ3 and Me3SiF according to
Scheme 1. A similar intermediate formation of difluoroꢀ
borane 10 occurs upon mixing of pure silane 1 with
∼3 mol.% BF3•Et2O at 20 °С. In addition, the reaction
mixture was found to contain cyclic dimer 7.
Scheme 5
To summarize the foregoing, one can propose the folꢀ
lowing sequence of transformations of silane 1 in the presꢀ
ence of BF3•Et2O (Scheme 8).
After the complete conversion of perfluoromethacroꢀ
lein (2), the pyrolysate formed in a quartz tube at 730 °С
was subjected to vacuum distillation to give a mixture of
lowꢀboiling products consisting mainly of silyl ether 1,
Me3SiF, and cyclic dimer 7. After addition of BF3•Et2O
in an amount nearly equimolar to dioxin 7, compound 7
rearranged over a period of 4 days at 20 °С to give acyclic
dimer Eꢀ3, apparently, through a fluoride ion eliminaꢀ
tion—addition reaction sequence (Scheme 6).
First, BF3•Et2O cleaves the Si—O bond of silyl ether 1
in a usual way to give Me3SiF and difluoroborane 10
(cf., for example, Ref. 14). The F atoms of the trifluoroꢀ
methyl groups in borane 10 remain fairly mobile, and the
next BF3•Et2O molecule detaches the allylic F atom; the
resulting tetrafluoroborate salt 11 decomposes to give
perfluoromethacrolein (2) and two recovered BF3 molꢀ
ecules. Subsequently, perfluoromethacrolein (2) cycloꢀ
dimerizes to give dioxin 7, which, in turn, rearranges to
fluoride Eꢀ3 (see Schemes 4 and 6). Moreover, BF3•Et2O
apparently participates directly in the cyclodimerization
of perfluoromethacrolein (2), which suppresses its polyꢀ
merization. On the one hand, BF3•Et2O activates the
carbonyl group of aldehyde 2 and accelerates the formaꢀ
tion of betaine 12, thus decreasing the concentration of
perfluoromethacrolein (2) in the solution. On the other
hand, it appears likely that betaine 12, which retains the
possibility of intramolecular cyclization, is much less
prone to intermolecular addition of the next molecule of
aldehyde 2 than betaine 9 (see Scheme 5).
Scheme 6
In conclusion, it should be noted that the susceptibilꢀ
ity of perfluoromethacrolein (2) for the electrophilic atꢀ
tack by the carbonyl С atom with the С=С bond remainꢀ
ing intact discovered in this study makes this compound
similar to standard aldehydes and emphasizes its essential
difference from a close analog, fluoride 4.
In addition to relatively fast opening of cyclic dimer 7,
a slow decrease in the content of silyl ether 1 and
BF3•Et2O and an increase in the amount of Me3SiF occur

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Volkonskii et al.
Scheme 8
At an evaporator temperature of ∼150 °С, the results of GLС
and GLС/MS are in good agreement with NMR data; however,
an increase in the evaporator temperature to >200 °С is accomꢀ
panied by partial thermal destruction of silane 1, as indicated by
the sharp increase in the concentration of impurities having
short retention time, in particular, a noticeable amount of
Me3SiF appears.
Study of the thermal stability of silane 1. After heating (6 h at
160 °С) in a sealed glass tube, silyl ether 1 remains unchanged
(NMR data).
Experimental
1
H and 19F NMR (СF3СOOH as the external standard) and
19F{1H} NMR spectra were recorded on Perkin—Elmer Rꢀ32
and Bruker WPꢀ200SY spectrometers, IR spectra were meaꢀ
sured on a URꢀ20 spectrometer, the Raman spectrum was reꢀ
corded on a Ramanor HGꢀ2S instrument, and mass spectra and
GС/MS analysis were run on a VG 7070E mass spectrometer
(EI, 70 eV).
The starting compounds and solvents were purified and dried
by standard procedures; the experiments were carried out under
dry argon. The molar ratios of the main components are always
given for mixtures. The NMR and MS spectral data for the
synthesized compounds are presented in Table 1.
Еꢀ7,7,7ꢀTrifluoroꢀ2,6ꢀbis(trifluoromethyl)ꢀ4ꢀoxaheptaꢀ2,5ꢀ
diеnoyl fluoride (Eꢀ3). А. A mixture of silyl ether 1 (1.5179 g,
6.018 mmol) with BF3•Et2O (0.6408 g, 4.515 mmol) was kept at
20 °С to complete conversion of silane 1. After 24 h, the mixture
consisted of fluoride Eꢀ3, Me3SiF, BF3•Et2O (1.0 : 2.2 : 1.7),
and a small amount (<5%) of other components (NMR and
GLС data). The solution was cooled (–78 °С) and allowed to
warm spontaneously to 20 °С, volatile products being distilled in
vacuo into a trap (–78 °С). At 20 Torr, this gave 0.5433 g (98%)
of Me3SiF with 98% purity (NMR and GLС data); at 20 °С
(1 Torr), 0.6085 g of a mixture mainly consisting of BF3•Et2O
(85—90%), some fluoride Eꢀ3 (5—7%), and unidentified subꢀ
stances (NMR and GLС data) was obtained. The solid residue
was sublimed at 40 °С (1 Torr), the sublimate was dissolved in
СH2Сl2, the solution was filtered, and the filtrate was diluted
with hexane until it became turbid and left for 14 h at –10 °С.
The cold solution was filtered and the precipitate was dried in
vacuo over Р2O5 to give 0.6095 g (63%) of fluoride Eꢀ3 as colorꢀ
less crystals with m.p. 49—55 °С and 98% purity (GLС data).
Repeated reprecipitation from СH2Сl2 with hexane gave a
sample with m.p. 55—56.5 °С. Found (%): С, 29.9; H, 0.67;
F, 59.7. С8H2F10O2. Сalculated (%): С, 30.0; H, 0.63; F, 59.4.
IR, ν/cm–1: 1815 vs (СOF), 1710 m (С=С), 1650 vs (С=С).
B. A mixture of silyl ether 1 (∼1.5 mmol) and BF3•Еt2O
(∼0.06 mmol) was heated at 60 °С in a sealed glass tube. Afꢀ
ter 5 h, the reaction mixture did not contain the starting silane 1
and consisted of fluoride Eꢀ3, Me3SiF (1 : 2), and minor amounts
of BF3•Et2O and unidentified components (NMR data).
Е→ZꢀIsomerization of fluoride Eꢀ3. A solution of fluoride
Eꢀ3 (0.0788 g, 0.246 mmol) and BF3•Et2O (0.0088 g,
0.062 mmol) in СH2Сl2 (0.1761 g) was heated at 90—95 °С in a
sealed glass tube. After 7 h, the solution contained a mixture of
fluorides Eꢀ3 and Zꢀ3 in ∼1 : 1 ratio (NMR data). Similar
heating of a 25% solution of fluoride Eꢀ3 in СH2Сl2 for 17 h
1ꢀHydrohexafluoroisobutenyloxytrimethylsilane (1). Bis(triꢀ
fluoromethyl) ketene (122 mL at –78 °С; ∼200 g, ∼1.12 mol)10
was passed with stirring through liquid trimethylsilane (88.4 g,
1.19 mol) precooled to –78 °С and containing crystalline
H2PtСl6•6H2O (0.0876 g, 1.69•10–4 mol) at such a rate that
boiling of the reaction mixture (reflux condenser, –78 °С) was
not too vigorous and the temperature did not rise above 35—40 °С
(for passing of the last 30 mL, water cooling at intervals was
required). After completion of the ketene addition, the mixture
was stirred for 1 h for cooling down to ∼20 °С. Distillation of the
reaction mixture gave 271.1 g (∼96%) of silane 1, b.p. 59—61 °С
(50 Torr) (130—132 °С (760 Torr)), purity >99% (NMR and
GLС data). Found (%): С, 33.4; H, 3.95; F, 45.3; Si, 10.7.
С7H10F6OSi. Сalculated (%): С, 33.3; H, 4.00; F, 45.2; Si, 11.1.
IR (Raman), ν/cm–1: 1670 s (1670 s) (С=С).
The impurities present were as follows:
1ꢀHydrohexafluoroisobutenyl 2ꢀhydrohexafluoroisobutyrate,
(СF(1)3)2СH(1)СOOСH(2)=С(СF(2)3)(СF(3)3)
(0.4%).
3
1H NMR, δ: 4.52 (hept, 1 H, H(1), JH(1),F(1) = 7.1 Hz); 8.53
(br.s, 1 H, H(2)). 19F NMR, δ: 12.7 (d, 6 F, F(1), JF(1),H(1)
=
3
4
7.1 Hz); 13.8 (q, 3 F, F(3), JF(3),F(2) = 6.2 Hz); 17.2 (q, 3 F,
4
F(2), JF(2),F(3) = 6.2 Hz).
Trimethylsilyl
2ꢀhydrohexafluoroisobutyrate,
(СF3)2СHСOOSiMe3 (0.2%). 1H NMR, δ: 4.21 (hept, СH,
3JH,F = 7.5 Hz); the signal of the Me3Si group coincides
with that in the spectrum of silane 1. 19F NMR, δ: 12.2 (d,
3JF,H = 7.4 Hz).
The freshly distilled product almost does not contain
(СF3)2СHСHO or (Me3Si)2O.

Сleavage of hexafluoroisobutenyloxysilane
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
1697
Table 1. 1H and 19F NMR and mass spectra of the products
Comꢀ
pound
NMR, δ (J/Hz)
MS, m/z
(Irel (%))
1H
19F
1 a
0.71 (s, 9 H, Me);
7.69 (m, 1 H, CH)
15.8 (qd, 3 F, F(2), 4JF(2),F(1) = 6.4,
4JF(2),CH = 1.9); 18.3 (qd, 3 F, F(1),
4JF(1),F(2) = 6.4, 4JF(1),CH = 1.4)
252 [M]+ (0.8), 237 [M – Me]+ (18.3), 179
[C4HF6O]+ (2.4), 159 [C4F5O]+ (1.3), 141
[C4HF4O]+ (100), 113 [C3HF4]+ (23.7), 77
[Me2SiF]+ (82.2), 73 [Me3Si]+ (43.7)b
—
2 c
10.09 (br.dq, 1 H,
8.7 (dq, 1 F, F(1), 2JF(1),F(2) = 31.0,
4JF(1),F(3) = 9.0); 17.6 (ddd, 3 F, F(3),
4
CHO, JH,F(2)
4JH,F(3) ≈ 2.3)
≈
4
4JF(3),F(2) = 23.5, JF(3),F(1) = 9.0,
4JF(3),H = 3.0); 20.0 (dqd, 1 F, F(2),
2JF(2),F(1) = 31.0, 4JF(2),F(3) = 23.5,
4JF(2),H = 1.8)
Eꢀ3 d
Zꢀ3 f
Eꢀ6 a
7.37 (qdq, 1 H,
14.0 (dd, 3 F, F(3), 4JF(3),F(4) = 10.3,
4JF(3),H(2) = 1.6); 14.6 (qd, 3 F, F(2),
320 [M]+ (22.5), 301 [M – F]+ (12.7), 163
[C4HF6]+ (89.7), 159 [C4F5O]+ (18.5), 141
[C4HF4O]+ (40.1), 138 [C4HF3O2]+ (100), 110
[C3HF3O]+ (55.2), 91 [C3HF2O]+ (28.5), 90
[C3F2O]+ (16.5), 82 [C2HF3]+ (17.5), 75
[C3HF2]+ (47.2), 69 [CF3, C3HO2]+ (95.5),
53 [C3HO]+ (13.5), 51 [CHF2]+ (15.3), 47
[COF]+ (14.2), 29 [CHO]+ (33.1)e
320 [M]+ (11.8), 301 [M – F]+ (10.1), 163
[C4HF6]+ (75.8), 159 [C4F5O]+ (21.8), 141
[C4HF4O]+ (39.1), 138 [C4HF3O2]+ (100), 113
[C3HF4]+ (12.7), 110 [C3HF3O]+ (46.1), 91
[C3HF2O]+ (23.0), 90 [C3F2O]+ (10.8), 82
[C2HF3]+ (12.6), 75 [C3HF2]+ (36.2), 69 [CF3,
C3HO2]+ (71.8), 51 [CHF2]+ (11.4), 29
[CHO]+ (13.3)
160 [M]+ (89.1), 159 [M – H]+ (34.0), 141
[M – F]+ (59.2), 140 [M – HF]+ (11.8), 132
[M – CO]+ (14.2), 113 [M – COF]+ (29.6),
112 [C3F4]+ (10.2), 93 [C3F3]+ (15.3), 91
[M – CF3]+ (78.7), 82 [C2HF3]+ (47.1), 75
[C3HF2]+ (19.1), 71 [C3FO]+ (11.2), 69 [CF3]+
(100), 63 [C2HF2]+ (11.8), 51 [CHF2]+ (77.7),
47 [COF]+ (29.7), 44 [C2HF]+ (16.6), 31 [CF]+
(48.2)g
H(1), 4JH(1),F(2)
=
1.6, 4JH(1),F(1)
=
4JF(2),F(1) = 6.4, JF(2),H(1) = 1.6);
4
6JH(1),F(4) = 0.8);
17.6 (qdd, 3 F, F(1), 4JF(1),F(2) = 6.4,
8JF(1),F(4) = 2.1, 4JF(1),H(1) = 0.8);
7.64 (dq, 1 H,
4
H(2), JH(2),F(4)
=
117.1 (qdqd, 1 F, F(4), 4JF(4),F(3)
=
4.1, 4JH(2),F(3) = 1.6)
10.3, 4JF(4),H(2) = 4.1, JF(4),F(1) = 2.1,
6JF(4),H(1) = 0.8)
8
∼7.37 (m, 1 H, H(1),
∆(δ – δ ) ≈ 0.00);
14.55 (qd, 3 F, F(2), 4JF(2),F(1) = 6.5,
4JF(2),H(1) = 1.8); 17.0 (br.d, 3 F,
F(3), 4JF(3),F(4) = 10.5); 17.5 (br.q,
3 F, F(1), 4JF(1),F(2) = 6.5); 100.4
(br.q, 1 F, F(4), 4JF(4),F(3) = 10.5)
Z
E
7.77 (m, 1 H, H(2))
2
7.52 (ddq, 1 H,
CH, 2JH,F(1) = 70.9,
4JH,F(3) = 4.6,
4JH,F(2) = 1.6)
–13.1 (ddq, 1 F, F(1), JF(1),H = 71.2,
4JF(1),F(3) = 58.5, 4JF(1),F(2) = 6.4); 13.0
(ddd, 3 F, F(2), 4JF(2),F(3) = 10.2,
4JF(2),F(1) = 6.4, 4JF(2),H = 1.9); 116.6
(dqd, 1 F, F(3), 4JF(3),F(1) = 58.5,
4
4JF(3),F(2) = 10.2, JF(3),H = 4.6)
Zꢀ6 a
7.61 (d, 1 H, CH,
2JH,F(1) = 71.2)
–9.8 (dqd, 1 F, F(1), 2JF(1),H = 71.4,
4JF(1),F(2) = 26.0, 4JF(1),F(3) = 5.9);
16.1 (dd, 3 F, F(2), 4JF(2),F(1) = 26.0,
4JF(2),F(3) = 10.2); 101.0 (qd, 1 F, F(3),
4
4JF(3),F(2) = 10.2, JF(3),F(1) = 5.9)
7 h
6.66 (br.s, 1 H,
H(1)); 7.91 (m,
1 H, H(2))
–7.9 (d.br.q, 1 F, F(5), 2JF(5),F(4)
=
320 [M]+ (6.4), 301 [M – F]+ (0.3), 163
[C4HF6]+ (46.4), 161 [C4H2F5O]+ (68.3), 159
[C4F5O]+ (71.1), 141 [C4HF4O]+ (100), 113
[C3HF4]+ (30.2), 112 [C3F4]+ (21.0), 75
[C3HF2]+ (15.1), 69 [CF3]+ (29.2)
4
163.6, JF(5),F(6) = 6.4); 8.6 (qd, 1 F,
2
F(1), 4JF(1),F(3) = 9.7, JF(1),F(2) = 7.0);
4
11.7 (qd, 1 F, F(2), JF(2),F(3) = 20.1,
2JF(2),F(1) = 7.0); 15.3 (ddd, 3 F, F(6),
4JF(6),F(5) = 6.3, 4JF(6),F(4) = 4.0,
4JF(6),H(2) = 1.4); 19.2 (dd, 3 F, F(3),
4JF(3),F(2) = 20.1, 4JF(3),F(1) = 9.7); 23.0
(ddq, 1 F, F(4), 2JF(4),F(5) = 163.6,
4
4JF(4),H(2) ≈ JF(4),F(6) ≈ 4.2)
a Without a solvent.
b For Siꢀcontaining ions, data only for the 28Si isotope are given.
c In silyl ether 1.
d In СD2Сl2.
e The assignment was done with allowance for analysis of metastable ions.
f In СH2Сl2.
g For a mixture of Eꢀ and Zꢀisomers.
h In a mixture of silyl ether 1 and Me3SiF (1 : 2).

1698
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
Volkonskii et al.
without a catalyst did not result in a change in the composition
(NMR data).
gel and, according to NMR, consisted of silane 1, Me3SiF,
perfluoromethacrolein (2), 4,4ꢀdifluoroꢀ2ꢀpentafluoroisoꢀ
propenylꢀ5ꢀtrifluoromethylꢀ4Hꢀ1,3ꢀdioxin (7), polymer 8
(1.0 : 1.7 : 0.07 : 0.05 : 1.4), and several minor components,
including F3СС≡СF (19F NMR, δ: –121.6 (q, 1 F, СF, 4J =
4.4 Hz); 28.0 (d, 3 F, СF3, 4J = 4.4 Hz) (cf. Ref. 15)). After
16 days, volatile substances consisting of silane 1, Me3SiF, and
dioxin 7 (1.0 : 2.0 : 0.07) with a small amount of other compoꢀ
nents (NMR data) were distilled in vacuo (1 Torr) at 20 °С from
the mixture containing no perfluoromethacrolein (2) (NMR
data) into a trap (–196 °С); the residue was a creamishꢀwhite
waxy material. BF3•Et2O (0.0054 g, 0.038 mmol) was added to
0.2318 g of the volatile products (1 : Me3SiF : 7 : BF3•Et2O =
1.0 : 2.0 : 0.07 : 0.08 (NMR data)) and the mixture was left in a
sealed glass tube at 20 °С. After 4 days, the mixture did not
contain dioxin 7 and consisted of silyl ether 1, Me3SiF, Еꢀ3,
BF3•Et2O, and difluoroborane 10 (1.0 : 2.5 : 0.06 : 0.04 : 0.04)
(NMR data); the composition of the mixture after 7 days was as
follows: 1 : Me3SiF : Eꢀ3 : BF3•Et2O : 10 = 1.0 : 2.7 : 0.06 :
0.025 : 0.06 (NMR data). After 3 h at 60 °С, the mixture did not
contain borane 10 and consisted of silane 1, Me3SiF, Еꢀ3, and
BF3•Et2O (1.0 : 3.9 : 0.24 : 0.1) (NMR data), and after 24 h at
60 °С, the conversion of silyl ether 1 was >99% and the mixture
contained Me3SiF, fluoride Еꢀ3, and BF3•Et2O (1.0 : 0.16 : 0.02)
and also 5—7% of minor components (NMR data).
Transformation of silane 1 in the presence of perfluoroꢀ
methacryloyl fluoride (4). А. A mixture of silyl ether 1 (0.1361 g,
0.539 mmol), fluoride 4 10 (0.0999 g, 0.561 mmol), and
BF3•Et2O (0.0028 g, 0.020 mmol) was heated at 100 °С in a
sealed glass tube. After 5 h, the mixture did not contain the
starting silane 1 and consisted of Me3SiF, fluorides Eꢀ3 and Zꢀ3,
perfluoromethacryloyl fluoride (4), bis(trifluoromethyl) ketene
(1.0 : 0.30 : 0.15 : 0.72 : 0.37), and a small amount of impurities
(
19F NMR data). The composition of the mixture after 12 h was
as follows: Me3SiF : Еꢀ3 : Zꢀ3 : 4 : (СF3)2С=С=O = 1.0 : 0.24 :
0.31 : 0.64 : 0.38 (19F NMR data). Further heating resulted
in only an insignificant change in the Eꢀ3
: Zꢀ3 and
4 : (СF3)2С=С=O ratios, but the amount of impurities in the
mixture gradually increased (19F NMR data).
B. A mixture of silyl ether 1 (0.1412 g, 0.560 mmol) and
fluoride 4 (0.1038 g, 0.583 mmol) was heated at 120 °С in a
sealed glass tube. After 24 h, the degree of conversion of 1 was
>95% and the mixture consisted of fluoride Еꢀ3, Me3SiF,
perfluoromethacryloyl fluoride (4) (1.0 : 1.8 : 2.1), and a small
amount of other components (19F NMR data).
The transformation of silane 1 in the presence of perꢀ
fluoro(ethyl isopropenyl ketone) (5). А. A mixture of silyl ether 1
(0.2009 g, 0.796 mmol), vinyl ketone 5 12 (0.2102 g) with >87%
purity (0.66 mmol), and BF3•Et2O (0.0148 g, 0.104 mmol) was
heated at 85 °С in a sealed glass tube. After 5 h, the mixture did
not contain the initial silane 1 and mainly consisted of Me3SiF,
fluorides Eꢀ3 and Zꢀ3, and vinyl ketone 5 (1.0 : 0.47 : 0.14 : 0.9).
In addition, the total amount of impurities slightly increased
and their composition somewhat changed (19F NMR data).
B. A mixture of silyl ether 1 (0.1807 g, 0.716 mmol) and
vinyl ketone 5 (0.1632 g) with >87% purity (0.51 mmol) was
heated at 150 °С in a sealed glass tube. After 7 h, the key compoꢀ
sition of the mixture virtually has not changed (1 : 5 = 1.0 : 0.69,
total content 1 + 5 > 90%); however, the total amount of impuꢀ
rities slightly increased and their composition somewhat changed
1
Polymer 8. H NMR, δ: 6.90 (0.65 H); 7.71 (0.35 H); 7.80
(0.4 H); 7.97 (0.5 H); 8.05 (1 H) (all br.s). 19F NMR, δ: 6.4
(6.3 sh, 6.0 sh) (0.2 F); 8.3 (1 F); 8.6—9.1 (0.25 F); 9.25 (0.2 F);
9.4 (0.2 F); 9.8 (0.3 F); 10.2 (0.15 F); 10.5 (0.1 F); 10.7 (0.04 F);
11.0 (0.02 F); 14.5 (0.25 F); 15.1 (0.08 F); 17.7 (2.1 F); 18.0
(0.9 F) (all br.s); 19.1 (br.dd(q), 1 F, Jd = 18.5 Hz, Jd(q) = 9 Hz).
The molar content was calculated from the total integral intenꢀ
sity of the signals for all H and F atoms of polymer 8 and
converted for monomer С4HF5O.
(1ꢀHydrohexafluoroisobutenyloxy)difluoroborane
(10).
1H NMR, δ: 7.99 (br.s). 19F NMR, δ: –75.4 (br.s, 1.4 F, F(3));
16.3 (m, 3 F, F(2)); 18.6 (m, 3 F, F(1)). The markedly reduced
integral for the F(3) atom may indicate the partial formation of
dialkoxyꢀsubstituted analog of borane 10.
(
19F NMR data).
Vacuum pyrolysis of silane 1. А. Silyl ether 1 (3.12 g,
12.4 mmol) was passed for 10 min in vacuo (1 Torr) through a
quartz tube 8 mm in diameter preheated to 610 °С (a thermoꢀ
couple on the outer side of the tube in the middle of the 25ꢀcm
long heated section), the pyrolysis products being collected in
successively connected traps (–78 and –196 °С). The pyrolyꢀ
sates were heated to ∼20 °С to give ∼0.05 g (∼0.5 mmol) of
Me3SiF with ∼97% purity in the –196 °С trap (GLС data) and
3.05 g of a mixture of silyl ether 1, perfluoromethacrolein (2),
Me3SiF (1.0 : 0.03 : 0.02), and several minor compoꢀ
C. Silyl ether 1 (1.29 g, 5.11 mmol) was passed for 20 min
in vacuo (1 Torr) through a stainlessꢀsteel tube 15 mm in
diameter filled with a 15ꢀcm long bed of anhydrous KF
(1 mm < d < 2 mm)* and maintained at 310 °С (the heated
length is 25 cm). During this period, 1.27 g of the pyrolysate
containing no silane 1 was collected in a trap (–196 °С). The
pyrolysate collected after 10 min at 20 °С consisted of Me3SiF,
fluorides Eꢀ6, Zꢀ6, dioxin 7, polymer 8 (1.0 : 0.30 : 0.34 :
0.03 : 0.17) and a slight amount of minor components (NMR,
GLС, and GLС/MS data).
nents
((СF3)2СHСHO,
(СF3)2СHСOOСH=С(СF3)2,
(Me3Si)2O, etc.) in the –78 °С trap (NMR data). After 20 days
at 20 °С, the pyrolysate collected at –78 °С did not contain
pentafluoromethacrolein (2) and consisted of silane 1, dioxin 7,
Me3SiF (1.0 : 0.01 : 0.02), and a number of minor compoꢀ
nents ((СF3)2СHСHO, (СF3)2СHСOOСH=С(СF3)2, etc.)
(NMR data).
B. Silyl ether 1 (0.69 g, 2.7 mmol) was pyrolyzed in a similar
way at 730 °С, the products being collected in a trap (–196 °С).
After the completion, 0.69 g of the pyrolysate was carefully
heated to melting and homogenization at the lowest possible
temperature, transferred into a tube, sealed, and heated to ∼20 °С.
After 1—2 min at 20 °С, the contents of the tube turned into a
Polymer 8. 19F NMR, δ: 6.7 (6.6 sh) (0.25 F); 8.5 (1.7 F);
8.8—9.6 (0.65 F); 10.1 (0.45 F); 10.4 (0.25 F); 14.6 (0.45 F);
17.7 (3.4 F); 18.0 (0.85 F) (all br.s); 19.3 (br.dd, 1 F, J1 = 19 Hz,
J2 = 10 Hz).
Detection of intermediate products in the reaction of silane 1
with BF3•Et2O. A mixture of silyl ether 1 (0.3115 g, 1.235 mmol)
with BF3•Et2O (0.0049 g, 0.0345 mmol) was kept at 20 °С in a
sealed glass tube and NMR spectra were recorded at intervals.
* After filling the tube with preliminarily dried and sieved KF,
the tube was heated for 1 h at 300—340 °С and for 1 h at
350—380 °С in vacuo (1 Torr).

Сleavage of hexafluoroisobutenyloxysilane
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
1699
After 8 h, a small amount of a white solid precipitated from the
solution (apparently, the product of replacement of all F atoms
in BF3•Et2O), and traces of difluoroborane 10 appeared in the
solution. The composition of the supernatant after 5 days was as
follows: 1 : Me3SiF : BF3•Et2O : 10 : 7 : Eꢀ3 = 1.0 : 0.1 : 0.007 :
0.01 : 0.003 : 0.02; the liquid contained also several minor comꢀ
ponents. After 6 days, the precipitate completely dissolved, the
conversion of silane 1 was ∼20%, borane 10 was not detected in
the solution, and the content of BF3•Et2O increased almost to
the starting level (∼1% of the total fluorine integral). After 7 days,
with the conversion of silyl ether 1 equal to ∼35%, cyclic dimer 7
was not detected in the solution either. After 18 days, conversion
of silane 1 was 100%, and the mixture consisted of fluoride Еꢀ3,
Me3SiF, BF3•Et2O (1.0 : 2.2 : 0.04), and a small amount (<5%)
of minor components. After 26 days, the composition of the
mixture almost did not change and traces of fluoride Zꢀ3 were
detected.
4. A. V. Popov, A. N. Pushin, and E. L. Luzina, Izv. Akad.
Nauk. Ser. Khim., 1997, 1069 [Russ. Сhem. Bull., 1997, 46,
1032 (Engl. Transl.)].
5. V. D. Sheludyakov, V. P. Kozyukov, E. A. Rybakov, and
V. F. Mironov, Zh. Obshch. Khim., 1967, 37, 2141 [J. Gen.
Сhem. USSR, 1967, 37 (Engl. Transl.)].
6. N. P. Gambaryan and E. M. Rokhlin, Usp. Khim., 1986, 55,
885 [Russ. Сhem. Rev., 1986, 55 (Engl. Transl.)].
7. A. N. Сhekhlov, A. V. Popov, and A. N. Pushin, Dokl. Akad.
Nauk, 1993, 331, 62 [Dokl. Сhem., 1993 (Engl. Transl.)].
8. US Pat. 2250520; Сhem. Abstrs, 1941, 35, 69836; US Pat.
2256544; Сhem. Abstrs, 1942, 36, 994.
9. H. Schulz and H. Wagner, Angew. Сhem., 1950, 62, 105.
10. D. С. England and С. G. Krespan, J. Am. Сhem. Soc., 1966,
88, 5582.
11. D. С. England, L. Solomon, and С. G. Krespan, J. Fluor.
Сhem., 1973—1974, 3, 63.
12. D. С. England, J. Org. Сhem., 1981, 46, 147.
13. E. M. Rokhlin, E. G. Abduganiev, and U. Utebaev, Usp.
Khim., 1976, 45, 1177 [Russ. Сhem. Rev., 1976, 45 (Engl.
Transl.)].
14. M. G. Voronkov, O. M. Trofimova, and N. F. Сhernov, Izv.
Akad. Nauk SSSR. Ser. Khim., 1985, 2148 [Bull. Acad. Sci.
USSR, Div. Сhem. Sci., 1985, 34, 1987 (Engl. Transl.)].
15. R. E. Banks, M. G. Barlow, and K. Mullen, J. Сhem. Soc. С,
1969, 1331; R. E. Banks, M. G. Barlow, W. D. Davies, R. N.
Haszeldine, K. Mullen, and D. R. Taylor, Tetrahedron Lett.,
1968, 3909.
The authors are grateful to M. V. Galakhov for reꢀ
cording the NMR spectra of fluoride Eꢀ3.
This work was partially supported by the Russian
Scientific Сenter "Applied Сhemistry" (StꢀPetersburg)
(Agreement No. 17/01).
References
1. T. Yokozawa, T. Nakai, and N. Ishikawa, Tetrahedron Lett.,
1984, 25, 3987.
2. T. Yokozawa, M. Yamaguchi, T. Nakai, and N. Ishikawa,
Nippon Kagaku Kaishi, 1985, 2202.
3. Yu. A. Сheburkov and I. L. Knunyants, Fluorine Сhem. Rev.,
1967, 1, 107.
Received November 28, 2003;
in revised form January 5, 2004