Fluoridative degradation of cyclosiloxanes with alkali metal salts of perfluorinated complex anion. Part 5

Article abstract of DOI:10.1016/S0022-328X(00)00537-4

Alkali metal salts of perfluorinated 'non-nucleophilic' complex anions were used for fluoridative degradation of cyclosiloxanes under thermal conditions in the absence and presence of high boiling multifunctional etheral solvent. The degradative products

Full text of DOI:10.1016/S0022-328X(00)00537-4

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 613 (2000) 239–243
Fluoridative degradation of cyclosiloxanes with alkali metal salts
ꢀ
of perfluorinated complex anion. Part 5
Omar Farooq *
Research Laboratory, I&C Sector, Building 201-2W-17, 3M Central Research, St. Paul, MN 55144-1000, USA
Received 8 November 1999; received in revised form 31 July 2000
Abstract
Alkali metal salts of perfluorinated ‘non-nucleophilic’ complex anions were used for fluoridative degradation of cyclosiloxanes
under thermal conditions in the absence and presence of high boiling multifunctional etheral solvent. The degradative products
consist of fluorosilanes and fluorosiloxanes in low to moderate yields. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Nucleophilic fluorination; Alkali metal salts; Perfluorinated complex anion; Cyclosiloxane
[
8a,b]. Boron trifluoride-etherate has also been used in
1
. Introduction
the fluorination of the Si–H bond, e.g. in a-naphthyl
ferrocenylfluorosilane (a-NpFcSiHF) [8c].
−
Procedures for the preparation of aryl, alkyl, aralkyl
−
−
Perfluorinated complex anions, e.g. BF , PF , SbF
6
4
6
fluorosilanes from appropriate functionalized silicon
compounds are known. These procedures include the
use of antimony trifluoride with antimony pentachlo-
ride [1,2], fluorosulfonic acid [3], alkyl- and arylfluo-
rophosphoranes [4] and metal fluorides with mineral
acids [5]. Carbonyl fluorides were used as fluorinating
reagent in organosilicon chemistry. Thus, alkyl- and
phenylsilanols and alkoxyalkylsilanes were converted to
the corresponding fluorosilanes in respectable yields [6].
Reaction of boron trifluoride-etherate with oligo-
meric organosiloxanes under heating gives organo-
fluorosilanes [7a]. The former was also used in the
fluorinations of such functionalized organosilanes as
−
,
and AsF , have been regarded as non-nucleophilic
6
and inert or ‘innocent’ anions. Electrochemical experi-
ments [9] from several controlled-potential oxidations,
have demonstrated that the anion, [BF ] , is not truely
−
4
inert and that high yields of fluorinated products result
from the participation of this anion in the ‘follow-up’
reactions of electrode intermediates. Some of these
anions were used [10] as their (expensive) silver salts,
for halogen-exchange fluorination of chlorosilicon and
chlorogermanium transition-metal complexes. In these
reactions silver-ion assisted rapid elimination of the
halogen is seemingly obvious in accounting for the
reasonable yields of the fluorinated products. Tetra-
fluoroborate anion as its triphenylmethyl salt, under
mild reaction conditions, has been reported [11] to
fluorinate Si–H bond(s) of trialkyl- and dialkylsilanes.
The reagent was further used for succesful fluorination
of HSiMe CH Fe(CO) Cp [Cp=p-cyclopentadienyl]
R4−nSiX [X=H, OR, Cl, Br] [7b,c]. Graphite-interca-
lated SbF was used to fluorinate organo-silicon com-
pounds involving Si–O and Si–Cl bonds [7d].
Under mild conditions, phosphorus pentafluoride
was also found to fluorinate the Si–H bond in (SiH ) O
n
5
3
2
2
2
2
[
11]. Potassium tetrafluoroborate, under similar condi-
ꢀ
Part of this work was presented at the Fluorine Division, ACS
tions, failed to fluorinate the Si–H bond in trialkylsi-
lane [11].
To our knowledge, alkali metal salts of ‘non-nucle-
ophilic’ perfluorinated complex anions have not been
used for fluorination and degradation of such function-
alized organosilicon compounds as cyclosiloxanes. We
National Meeting, New Orleans, 1996. For Parts 1–4, see: J. Fluorine
Chem. 86 (1997) 189; J. Chem. Soc. Perkin Trans 1 (1998) 661; J.
Fluorine Chem. (submitted); J. Chem. Soc. Perkin Trans 1 (submit-
ted).
*
Fax: +1-651-7375101.
E-mail address: ofarooql@mmm.com (O. Farooq).
0
022-328X/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00537-4

2
40
O. Farooq / Journal of Organometallic Chemistry 613 (2000) 239–243
cussed reaction mixture also identified 1,3,3,-trifluoro-
,1,3-triphenyldisiloxane which was formed by
1
disproportionation of 1,1-difluoro-1,1,3,3-tetraphenyld-
isiloxane under the reaction conditions used. The solid
residue of the reaction mixture was analyzed in deu-
11
terium oxide. B-NMR spectra shows two signals at
1
1
19
l B 2.92 (q, J
16 Hz) and 1.10 (s) and F-NMR
B–F
19
spectra shows two signals at l F −142.3(s) and −
46.8(s). These NMR signals were assigned to
FPh SiOBF ] and [BF ] , respectively.
1
−
2 3 4
−
Scheme 1.
[
The reaction of hexaphenylcyclotrisiloxane with te-
trafluoroborate was repeated in 1:1 molar ratio for 2 h.
Analysis of the products after work-up show unreacted
starting material and the same five products (1–5)
altogether in the ratio 30:70. The fluorinated products
have almost similar distributions and none of them was
formed in a higher ratio worth of isolation by distilla-
tion. The reaction was repeated with sodium hex-
afluorophosphate in the same ratio (1:1) for 1.5 h and
the same five products were found to be formed in the
ratio 10:35:25:12:18. On work-up the reaction mixture
in water, extraction in methylene chloride, drying on
anhydrous magnesium sulfate and removal of solvent,
the same five products in the ratio 33:33:17:4:13 were
obtained.
have recently reported the use of alkali metal salts of
perfluorinated complex anions for the conversion of
halo- and alkoxysilanes [12–16] to the corresponding
fluorosilanes and haloboranes [17] to the corresponding
fluoroboranes in high yield. We have also reported the
use of the same reagents for the conversion of organo-
chlorophosphorus compounds to their corresponding
fluoro-derivatives in respectable yield [18–20]. We now
want to report the use of these salts as potential sources
of fluoride ions for the fluoridative degradation of
cyclosiloxanes
leading
to
fluorosilanes
and
fluorosiloxanes.
When the above discussed reaction of hexaphenylcy-
clotrisiloxane was repeated with potassium te-
trafluoroborate in 1:6 molar ratio, a rather slow
reaction was observed. For a reaction of 45 min, no
diphenyldifluorosilane was formed. Other products viz.,
2
. Results and discussion
When a mixture of hexaphenylcyclotrisiloxane and
sodium tetrafluoroborate (Scheme 1) in the ratio 1:6
was heated to about 200°C for 45 min, a semi-solid
resulted on cooling. Vacuum distillation gave a mixture
of distillate which were identified by the NMR analysis.
1
1
,3-difluoro-1,1,3,3-tetraphenyldisiloxane, 1,5-difluoro-
,1,3,3,5,5-hexaphenyltrisiloxane and 1-fluoro-5-hy-
droxy-1,1,3,3,5,5-hexaphenyltrisiloxane were formed in
0% in the ratio 3:2:11, the remaining being unreacted
7
2
9
Si-NMR spectra shows multiple signals due to
starting material. When the reaction was prolonged for
about 2 h, about 6% diphenyldifluorosilane was found
to be formed.
diphenyldifluorosilane and monofluorinated organo-sil-
icons together with other products in the ratio 80:20.
Careful redistillation (b.p. 70–74°C/0.5 Torr) gave
diphenyldifluorosilane in 60% yield . The monofluori-
nated organo-silicon products were idenfied by Si-
NMR and by mass spectra as 1,3-difluoro-1,1,3,3-
tetraphenyldisiloxane,
phenyltrisiloxane and 1-fluoro-5-hydroxy-1,1,3,3,5,5-
hexaphenyltrisiloxane in the ratio 50:40:10. Si-NMR
analysis (vide infra) of the residue of the reaction
mixture shows all the four products in the ratio
1
When a reaction mixture of octaphenylcyclote-
trasiloxane and sodium tetrfluoroborate in the ratio 1:8
was heated for 45 min, a similar reaction mixture
resulted. Vacuum distillation gave a mixture of prod-
2
29
29
1,5-difluoro-1,1,3,3,5,5-hexa-
ucts which were identified by their Si-NMR spectra as
diphenyldifluorosilane, 1,3-difluoro-1,1,3,3-tetraphenyl-
disiloxane, 1,5-difluoro-1,1,3,3,5,5-hexaphenyltrisilox-
ane and 1-fluoro-5-hydroxy-1,1,3,3,5,5-hexaphenyl-
trisiloxane in the ratio 21:54:15:10. Redistillation gave
1,3-difluoro-1,1,3,3-tetraphenyldisiloxane in 15% yield.
The reaction was repeated for 1.5 h and the same five
products were found to be formed in the ratio
2
9
2
1
6:20:16:12. An additional product, 1,5-dihydroxy-
,1,3,3,5,5-hexaphenyltrisiloxane, as identified by its
Si-NMR and mass spectra was formed in 26% relative
2
9
4
3
0:30:10:15:5. Diphenyldifluorosilane was distilled in
5% yield. The residue of this reaction mixture was
abundance. Repeating the reaction, quenching the reac-
tion products in water and appropriate work-up gave
the same products. Mass spectral analysis of the dis-
29
analyzed, after appropriate work-up, by Si-NMR and
mass spectra and was found to consist of the same
reaction products in the ratio 3:16:21:18 together with
the same additional product as identified in the reaction
of hexaphenylcyclotrisiloxane in 42% relative abun-
dance.
1
2
0
B.p. 66–70 C/0.4 Torr: see Ref. [12].
Yield is based on the assumption that all the silicons are difluori-
nated.

O. Farooq / Journal of Organometallic Chemistry 613 (2000) 239–243
241
distillation gave 1,3-difluoro-1,3-dimethyl-1,3-diphenyl-
disiloxane in 30% yield.
The reactivity of cyclosiloxanes is different from that
of alkoxysilanes. We have recently reported [13–16]
that the later reacts with alkali metal salts of perfluori-
nated complex anions even in a fluoride-equivalent
ratio of the complex salts leading to near-quantitative
yield of fluoro-silanes. Thus, diphenyldiethoxysilane,
methylphenyldimethoxysilane and n-octadecyl dime-
thylethoxysilane react with alkali metal salts of complex
anions in the fluoride-equivalent ratio to give near-
quantitative yield of the fluorinated silanes. The cy-
closiloxanes with the complex salts at even
siloxy-equivalent ratio, generally, gives poor yield of
the fluorosilanes and fluorosiloxanes. Lower ratio of
salt:cyclosiloxane provides lower yield of fluorinated
products.
It should be mentioned here that alkali metal
fluorides, e.g. sodium fluoride does not react with cy-
closiloxanes in the presence or absence of solvents.
Therefore, salts of perfluorinated complex anions
provide a route to the fluorinated silanes and -siloxanes
from the cyclosiloxane precursors albeit reduced in
yield.
Scheme 2.
When the above reaction was repeated in tetraglyme
with sodium hexafluorophosphate in the same molar
ratio for 15 min, the same products 1–5 were identified
in the ratio.50:5:5:8:32 after appropriate work-up. Re-
distillation gave diphenyldifluorosilane in 42% yield.
The reaction was repeated in the absence of solvent for
0 min to obtain the same products in the ratio
0:22:9:7:2. Diphenyldifluorosilane was distilled in 50%
yield. The solid residue of the reaction mixture was
analyzed in deuterium oxide and Si-NMR spectra
shows the products 1–3 in the ratio 5:17:22. P-NMR
spectra shows a doublet and a singlet at l P −11.24
d, JP–F 1288 Hz) and −18.48 (s). These NMR signals
In the discussed cases, that the reaction of cyclosilox-
ane with the complex salt gives poor yield of the
expected fluorosilane may be attributed to poor polar-
ization of the Si–O–Si bond by the in situ generated
Lewis acid. In some reactions of cyclosiloxane with
alkali metal complex salts monitored for a short time,
silylfluorophosphate or -fluoroborate intermediates
could be identified in the reaction mixture.
3
6
29
3
1
3
1
(
were assigned to tris(fluorodiphenylsilyl) phosphate and
tris(fluorotetraphenylsiloxysilyl)phosphate. The reac-
tion of octaphenylcyclotetrasiloxane with sodium te-
trafluoroborate was repeated, in the absence of any
solvent, in 1:1 ratio for 2 h. Analysis of the reaction
We previously reported [12,17] that when alkyl- or
arylhalosilane or -haloborane was heated with alkali
metal salts of perfluorinated complex anion in the
presence or absence of any etheral solvent, correspond-
ing fluorosilane or fluoroborane was formed in near
quantitative yield. The reactions in the absence of sol-
vent have shown the evolution of boron trifluoride gas
29
products, after appropriate aqueous work-up, by Si-
NMR and mass spectra shows the same compounds
1
–5 in the ratio 20:17:10:15:38. The same reaction was
[17] and the release of fluoride ion from the thermal
−
repeated, in the absence of any solvent, with sodium
hexafluorophosphate in the ratio 1:1 for 3 h. The
reaction mixture was found to consist of the same
products 1–5 in the ratio 17:30:20:20:10.
decomposition of the complex anion, [BF ] . The
4
fluoride ion causes nucleophilic halogen-exchange
fluorination in the halosilanes or haloboranes. We have
further reported that alkoxysilanes [13,14] also react
with the salts of ‘non-nucleophilic’ anions to give
fluorosilanes and that the reactions provide a source of
anhydrous fluoride ions and thermally liberated Lewis
acids which undergo complexation with the alkoxysi-
lane. In the present reactions, under similar conditions,
thermally liberated Lewis acid undergoes complexation
with oxygen in cyclosiloxane wherein the silicon center
becomes polarized for nucleophilic attack by the liber-
ated anhydrous fluoride ion (Scheme 2). The fluori-
nated ate anion undergoes further thermal
decomposition forming difluorosilane, fluorinated silox-
anes and fluorosilylfluoroborates, -phosphates and -an-
Reaction of trimethyltriphenylcyclotrisiloxane with
sodium hexafluoroantimonate in the ratio 1:6 was also
investigated under the same reaction conditions as de-
scribed above. Aqueous work-up of the reaction mix-
ture shows two main products viz., methylphenyl-
difluorosilane and 1,3-dihydroxy-1,3-dimethyl-1,3,-
diphenyldisiloxane in the ratio 50:50. Vacuum distilla-
tion gave methylphenyldifluorosilane in 45% yield.
When the same reaction was repeated, in the absence of
any solvent, using sodium hexafluorophosphate in the
ratio 1:1 for 45 min, all the five products 1–5 (for
R=Me) were obtained in the ratio 8:40:24:16:12. Re-

2
42
O. Farooq / Journal of Organometallic Chemistry 613 (2000) 239–243
2
9
timonates which undergo further thermal decomposi-
tion leading to more difluorosilanes and fluorosilox-
anes. Thermal decomposition of the fluorinated
siloxanes also leads to the formation of difluorosilanes.
This decomposition may involve participation of any
intermediate complex fluoride ion or even the parent
perfluorinated complex anion itself.
FPh SiOSiPh F (2): Si-NMR [400 MHz, CDCl ]: l
2
2
3
−35.15 (d, JSi–F 278 Hz) [Lit. [12] −36.15 (d, JSi–F 286
Hz).
2
9
FPh SiOSi(Ph )OSiPh F (3): Si-NMR [400 MHz,
CDCl ]: l −36.10 (d, J
FPh SiOSi(Ph )OSiPh OH (4): Si-NMR [400 MHz,
CDCl ]: l −36.51 (d, J
2
2
2
284 Hz), −42.00 (s).
3
Si–F
29
2
2
2
284 Hz), −42.50 (s),
3
Si–F
‘
Non-nucleophilic’ perfluorinated complex anions are
−32.90 (s).
thermally labile and can be used as a source of anhy-
drous fluoride ions for nucleophilic fluorination of cy-
closiloxanes. The process further involves fluoridative
degradation of cyclosiloxanes leading to fluoro- and
fluorosiloxy-silanes.
3.1.1. Mass spectra
Ph SiF (1): m/e 220–222 (Ph SiF , 86%), 154–156
2
2
2
2
(Ph SiF –SiF , 99%), 77 (Ph. from Ph–Ph).
2
2
2
FPh SiOSiPh F (2): m/e 418–420 (Ph FSiOSiFPh ,
2
2
2
2
5
5%), 341–343 (Ph FsiOSiFPh–Ph, 25%), 340–342
2
(
Ph FSiOSiFHPh, 25%), 263–265 (Ph FSiOSiFHPh–
2
2
3. Experimental
Ph, 99%), 154 (Ph–Ph), 77 (Ph from Ph–Ph).
FPh SiOSi(Ph )OSiPh F (3): m/e 616–618 [FPh -
2
2
2
2
Hexaphenylcyclotrisiloxane, octaphenylcyclotetracy-
SiOSi(Ph )OSiPh F, 32%], 415–417 [FPh SiOSi(Ph )-
2 2 2 2
losiloxane, methylphenylcyclotrisiloxanes (from Pe-
trarch/Gelest), sodium salts of perfluorinated complex
anions (from Aldrich) were of reagent grade and were
used as received. Tetraglyme was dried over sodium
under reflux. Boiling and melting points are uncor-
OSiPh F–SiPh F, 52%], 402–404 [(SiPhF) , 20%], 201
2 2 2
(SiPhF, 40%), 154 (Ph–Ph, 40%), 77 (Ph from Ph–Ph,
20%).
F PhSiOSiPh F: m/e 360–362 [F PhSiOSiPh F,
2
2
2
2
45%], 282–284 [F PhSiOSiPhF, 10%], 205–207
2
1
13
31
19
rected. H-, C-, P- and F-NMR spectra were
recorded on a Varian superconducting NMR spectrom-
[F SiOSiPhF, 100%), 154 [Ph–Ph, 65%].
2
1
eter at 400 MHz operating frequency for the H-,
3.2. Reaction of octaphenylcyclotetrasiloxane
1
3
31
1
3
00.58 MHZ for the C-, 162 MHz for the P- and
1
9
76 MHz for the F-NMR spectroscopy. In these
experiments, TMS (internal) was used for H- and C-,
5% phosphoric acid (external) for P- and CFCl3
external) for F-NMR spectroscopy as references,
A mixture of 4 g (5.02 mmol) octaphenylcyclote-
trasiloxane and 4.82 g (44.2 mmol) sodium te-
trafluoroborate was heated for 1.5 h as described
above. Vacuum distillation gave a mixture of products
consisting of diphenyldifluorosilane, 1,4-difluoro-1,1-
1
13
31
8
(
1
9
respectively.
3
,3-tetraphenyldisiloxane and other fluorinated silox-
anes in the ratio 21:54:25. Redistillation gave
,3-difluoro-1,1,3,3-tetraphenyldisiloxane in 35% yield.
3.1. Reaction of hexaphenylcyclotrisiloxane
1
A mixture of 4 g (6.6 mmol) of hexaphenylcyclotri-
The residue in the reaction flask was similarly analyzed
as described above. Reaction with sodium hex-
afluorophosphate was similarly carried out for 30 min
to obtain diphenyldifluorosilane in 50% yield. NMR
and mass spectra of the products are similar as de-
scribed above.
siloxane and 4.8 g (44.0 mmol) of sodium tetrafluorob-
orate was heated for 45 min at about 200°C. Vacuum
distillation at 80–90°C/0.5 Torr gave 2.4 g of distillate
consisting of diphenyldifluorosilane and other difluori-
nated siloxanes together in the ratio 80:20. Redistilla-
tion gave diphenyl-difluorosilane in 45% yield (b.p.
70–74°C/0.5 Torr) in 99% purity. The yield is based on
3.3. Reaction of trimethyltriphenylcyclotrisiloxane
difluorination of each silicon moiety. The residue in the
reaction flask was diluted with methylene chloride,
filtered and dried over anhydrous magnesium sulfate.
Removal of solvent gave a semi-solid which was ana-
To a solution of 4 g (8.74 mmol) of trimethylt-
riphenylcyclotrisiloxane in 4 g of tetraglyme was added
12.34 g (52.42 mmol) of sodium hexafluoroantimonate
and the mixture was heated for 30 min as described
2
9
lyzed by Si-NMR and mass spectra. Reactions with
potassium tetrafluoroborate and sodium hex-
afluorophosphate were similarly carried out.
2
9
above. The reaction mixture was analyzed by Si-
NMR and mass spectra. Vacuum distillation gave
methylphenyldifluorosilane in 45% yield (b.p. 115–
120°C/760 Torr). Reaction with sodium hex-
afluorophosphate was similarly carried out and
analyzed.
1
Ph SiF (1): H-NMR [400 MHz, CDCl ]: l 7.87 (d,
2
2
3
8
.1 Hz; dd, 1.4 Hz), 7.66 (t, 7.5 Hz), 7.56 (t, 7.5 Hz)
2
9
[
Lit. [12] 7.90(m), 7.28 (t), 7.14(t)]; Si-NMR [400
MHz, CDCl ]: l −28.70 (t, J 290 Hz) [Lit. [12–14]
3
Si–F
1
−
−
28.65 (t, JSi–F 292), −28.50 (t, JSi–F 290 Hz),
29.53 (t, JSi–F 291 Hz].
PhMeSiF : H-NMR [400 MHz, CDCl ]: l 7.64 (d, 8
2
3
Hz, dd, 1.6 Hz), 7.52 (t, 8 Hz, tt, 2 Hz), 7.43 (t, 8 Hz),

O. Farooq / Journal of Organometallic Chemistry 613 (2000) 239–243
243
[
5] (a) US Patent 3 655 714; CA 77, 75336. (b) German Patent
DD 74271; CA 74, 142 044.
6] R. Mueller, D. Mross, Z. Chem. 11 (1971) 382.
0
.58 (t, 9 Hz) [Lit. [12] 7.45 (d, 8.1 Hz; dd, 1.5 Hz), 7.42
(
t, 7.5 Hz, tt, 2.2 Hz), 7.32 (t, 7.5 Hz), 0.49 (t, 7.5 Hz);
[
[
2
9
Si-NMR [400 MHz, CDCl ]: l −11.80 (t, JSi–F 287
3
7] (a) L.H. Sommer, G.R. Anisul, J. Am. Chem. Soc. 77 (1955)
2482. (b) C. Eaborn, Organosilicon Compounds Butterworths,
London, 1969, p. 167. (c) V. Bazant, V. Chvalovsky, J.
Rathousky, Organosilicon Compounds, Vol. 1, Academic
Press, New York, 1965. (d) R.J.P. Corriu, J.M. Fernandez,
C.Guerin, J. Organomet. Chem. 192 (1980) 347.
8] (a) E.W. Kifer, C.H. Dyke Van, Chem Commun. (1969) 1330,
(b) E.W. Kifer, C.H. Van, Inorg. Chem. 11 (1972) 404. (c)
R.J.P. Corriu, F. Larcher, J. Organomet. Chem. 102 (1975)
C25.
Hz) [Lit. [13,14] −10.95 (t, JSi–F 291 Hz), −10.94 (t,
JSi–F 289 Hz)]
2
9
FPhMeSiOMePhF: Si-NMR [400 MHz, CDCl ]: l
3
−
20.5 (d, J 280 Hz).
FPhMeSiOSi(Ph)(Me)OSiMePhF:
29
Si-NMR [400
[
[
MHz, CDCl ]: l −21.56 (d, J 280 Hz), −31.47 (s).
3
2
9
FPhMeSiOSi(Ph)(Me)OSi(OH)MePh:
Si-NMR
[400 MHz, CDCl ]: l −21.89 (d, J, 278 Hz), −31.94
3
9] (a) V.R. Koch, L.L. Miller, D.B. Clark, M. Fleischman, T.
Joslin, D. Pletcher, Electroanal. Chem. Interface Electrochem.
(
s), 30.65 (s).
4
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nat’ev, O.V. Parakin, Yu.M. Kargin, Zh. Obshch. Khim. 53
1983) 230.
(
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