Phosphorus-containing disiloxanes: Synthesis and thermal rearrangement of the 1,2-shift type

Article abstract of DOI:10.1007/s11172-005-0388-z

Methods for the synthesis of tetramethylbis(ω-phosphoryloxyalkyl) disiloxanes were developed. Thermal rearrangement of the 1,2-shift type of tetramethylbis(phosphoryloxymethyl)disiloxanes was studied. The 1,2-shift rearrangement of dimethyl(diphenoxyphosp

Full text of DOI:10.1007/s11172-005-0388-z

Russian Chemical Bulletin, International Edition, Vol. 54, No. 5, pp. 1245—1249, May, 2005
1245
Phosphorusꢀcontaining disiloxanes: synthesis and thermal
rearrangement of the 1,2ꢀshift type
ꢀ
G. N. Molchanova, T. M. Shcherbina, P. V. Petrovskii, and E. E. Nifant'ev
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5085. Eꢀmail: zaq@ineos.ac.ru
Methods for the synthesis of tetramethylbis(ωꢀphosphoryloxyalkyl)disiloxanes were develꢀ
oped. Thermal rearrangement of the 1,2ꢀshift type of tetramethylbis(phosphoryloxymethyl)diꢀ
siloxanes was studied. The 1,2ꢀshift rearrangement of dimethyl(diphenoxyphosphoryloxyꢀ
methyl)silyl hydrogen sulfate was found.
Key words: phosphorusꢀcontaining disiloxanes, synthesis, thermal 1,2ꢀshift rearrangement.
Thermally initiated rearrangements of the 1,2ꢀshift
type have been discovered and rather widely studied1—8 to
date for many silylmethyl esters of oxygenꢀcontaining acꢀ
ids of pentavalent phosphorus. The rearrangement is the
migration of radical R from the silicon atom to the
methylenic carbon atom to form the corresponding silyl
esters of phosphorus acids (Scheme 1).
The classical method for the synthesis of functionalized
disiloxanes is the reaction of the corresponding triꢀ
methylsilyl compounds with concentrated sulfuric acid
followed by hydrolysis.11 In this case, the functional group
should be stable toward hydrolysis under the reaction conꢀ
ditions. We have shown that for phosphates 2a,b, which
are potentionally stable to the 1,2ꢀshift rearrangement
due to the remote position of the silicon atom from the
functional group, this method produces disiloxanes 3a,b
(Scheme 2).
Scheme 1
Scheme 2
In all cases studied, the R substituent is a hydrogen
atom or a hydrocarbon radical (alkyl or aryl). The migraꢀ
tion of heteroatomic substituents from the silicon atom in
the 1,2ꢀshift rearrangements is poorly studied and deꢀ
scribed only for several chloromethylsilanes (the migratꢀ
ing group is PhMeN, PhO,9 or Me3Si10).
We studied the 1,2ꢀshift rearrangement in the series
of disiloxanes, viz., diphosphorylated derivatives of
2,2,4,4ꢀtetramethylꢀ2,4ꢀdisilaꢀ3ꢀoxapentaneꢀ1,5ꢀ
diol (1a,b).
The reaction accompanied by methane evolution beꢀ
gins already on heating to 45 °C, and after hydrolysis
with water the target disiloxanes 3a,b are formed in
~100% yield.
Thus, both diphenoxylꢀ and bis(trifluoroethoxy)phosꢀ
phoryl groups are stable on heating with concentrated
sulfuric acid, whereas the resulting disiloxanes 3a,b are
thermally stable (at least on heating at 200 °C for 5 h).
When Me3SiCH2OP(O)(OR)2 (4a,b) is treated with
concentrated sulfuric acid, the reaction begins only on
R = Ph (a), CH2CF3 (b)
* Dedicated to Academician N. K. Kochetkov on the occasion
of his 90th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1210—1214, May, 2005.
1066ꢀ5285/05/5405ꢀ1245 © 2005 Springer Science+Business Media, Inc.

1246
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 5, May, 2005
Molchanova et al.
heating to 70 °C and is accompanied by the complete
decomposition of the starting substrate. Since sulfuric
acid eliminates the phenyl group from the silicon atom
under milder conditions than the methyl group does,12
the target disiloxanes 1a,b were synthesized by the reacꢀ
tion between dimethyl(phenyl)silylmethyl phosphates
Me2PhSiCH2OP(O)(OR)2 (5a,b) and sulfuric acid folꢀ
lowed by the hydrolysis of the intermediate reaction prodꢀ
uct, namely, silyl hydrogen sulfate (6a,b) (Scheme 3).
the 1H NMR spectrum increases gradually during the
reaction. After 9 h, the doublet signal disappears comꢀ
pletely, and the only signal is observed in the region of
CH2 protons: the singlet at δ 5.18. Similarly, after 20 min,
the 31P NMR spectrum of the reaction mixture contains
the signal of silyl hydrogen sulfate 6a´ at δ –11.33 and an
additional signal at δ –18.16. After 9 h, the single signal
appears in the 31P NMR spectrum at δ –14.64, which
corresponds, most likely, to free diphenylphosphoric acid.
These data suggest that phosphate 6a´ undergoes the
rearragement at room temperature: the hydrogen sulfate
group migrates from the silicon atom to the methylenic
carbon atom to form silyl phosphate 7a´ (Scheme 4).
Scheme 3
Scheme 4
Probably, this rearrangement is a reason for the deꢀ
crease in the yield of disiloxanes on prolonged storage of
the reaction mixture. Therefore, the reactions of phosꢀ
phates 5a,b with concentrated sulfuric acid were further
carried out in methylene chloride with cooling to 0 °C,
and the reaction mixture was hydrolyzed 5 min after the
reactants were mixed. This procedure enabled us to obꢀ
tain disiloxanes 1a and 1b in 77 and 73% yields, respecꢀ
tively.
According to the data of the 31P NMR spectra, after
5 min the reaction mixture contains no starting phosꢀ
phate 5a,b. However, the yield of disiloxanes 1a,b deꢀ
creases substantially with an increase in the duration of
the first reaction step. If the hydrolysis is carried out sevꢀ
eral hours after sulfuric acid addition, the disiloxane canꢀ
not be isolated. To study this fact, we carried out the
reaction of phosphate 5a with deuterated sulfuric acid and
monitored the reaction course by NMR. At 20 °C, alꢀ
ready after 20 min, the 1H NMR spectrum of the reaction
mixture contains a singlet signal at δ 5.79 (~10%) along
with the doublet of the CH2 protons of silyl hydrogen
sulfate 6a´ at δ 5.59. The intensity of the singlet signal in
Phosphorylated disiloxanes 1a,b were heated at 150 °C.
1
According to the data of the H and 31P NMR spectra
(Table 1), at this temperature the disiloxanes undergo the
1,2ꢀshift rearrangement.* The siloxy group migrates durꢀ
* According to the NMR spectral data, the rearrangement of
disiloxanes 1a,b begins already on heating to 125 °C.
Table 1. Some parameters of the 1H and 31P NMR spectra of compounds 1, 8, and 9 in the reaction mixtures after heating of
phosphorusꢀcontaining disiloxanes 1a,b at 150 °C for 5 h
Starꢀ
ting
comꢀ
pound
NMR, δ, J/Hz
1H (region of SiCH2 protons)
31P
1
8
9
1
8
9
SiCH2OP
(d)
SiCH2OP
(d, JH,P = 6.2)
SiCH2OSi SiCH2OCH2 SiCH2OP
SiCH2OP
CH2SiOP
CH2SiOP
(s)
(s)
(s)
(s)
1a
1b
3.70 (JH,P = 6.2)
3.71 (JH,P = 5.8)
3.87
3.92
2.81
3.00
2.96
3.19
–9.87
–0.07
–10.01
–0.24
–20.50 (br.s)
–10.43 (br.s)

Phosphorusꢀcontaining disiloxanes
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 5, May, 2005
1247
ing the rearrangement from the silicon atom to the
methylenic carbon atom to form intermediate silylmethyl
ester 8a,b, and then the silylmethoxy group of the latter
migrates to produce ether 9a,b (Scheme 5).
After 90 h, the signal of silyl ether 9 remains the only
signal in the 31P NMR spectrum.
The product of complete rearrangement, viz., phosꢀ
phorusꢀcontaining ether 9a,b, was hydrolyzed with water
and extracted with ether; phenol and (PhO)2P(O)OH were
removed by washing out with a
Scheme 5
saturated solution of Na2CO3. Afꢀ
ter the solvent was distilled off, the
disiloxane fraction was partially poꢀ
lymerized. According to the data
1
of GCꢀMS and H NMR spectroꢀ
scopy, the structure of cyclic diꢀ
siloxane 10 can be ascribed to the main monomeric comꢀ
ponent of the resulting disiloxane fraction (see Experiꢀ
mental). This structure indirectly confirms the structure
of silyl ether 9.
Thus, we developed the methods for the synthesis of
phosphorusꢀcontaining disiloxanes and showed that phosꢀ
phates based on dimethylsilylmethanol containing the oxy
substituent at the silicon atom undergo the 1,2ꢀshift therꢀ
mal rearrangement that consists in the migration of the
oxy substituent (OSO3H, OSiMe2CH2—, OCH2SiMe2—)
from the Si atom to the methylenic carbon atom. The
presence of the oxy group at the silicon atom decreases
substantially the thermal stability of silylmethyl phosphates
compared to that of silylmethyl phosphates containing
three carbon substituents at the silicon atom. In addition,
the thermal stability of silylmethyl phosphates decreases
with an enhancement of the electronꢀwithdrawing ability
of the oxy substituent. For example, phosphates 6a,b conꢀ
taining the most withdrawing sulfate group are rearranged
even at room temperature, whereas trialkylsilylmethyl
phosphates are stable3 on heating to 175 °C. The rearꢀ
rangement of compounds 1, 6, and 8 involved no migraꢀ
tion of the methyl group, which is well consistent with the
previously8 obtained data that the most electronegative
substituent migrates predominantly from the silicon atom
during the 1,2ꢀshift.
After compound 1a was heated for 5 h, two signals of
approximately equal intensities appeared along with the
doublet signal of the starting compound (δ 3.70) in the
1H NMR spectrum in the region of signals of the CH2
protons: a doublet signal at δ 3.87 and a singlet at δ 2.81.
They are attributed, most likely, to the SiCH2OP protons
and SiCH2OSi protons of phosphate 8a (13% in the mixꢀ
ture). This spectrum also contains a lowꢀintensity signal
at δ 2.96 (the CH2OCH2 protons of the products of comꢀ
plete rearrangement of 9a, 2%). The further heating reꢀ
sults in a decrease in the intensity of the signal of the
methylene protons of the starting compound and an inꢀ
crease followed by a decrease in the intensity of the douꢀ
blet downfield signal and the singlet signal at δ 2.81. The
intensity of the singlet signal at δ 2.96 increases gradually.
After 90 h, this signal remains the only one in the region
where methylene protons appear. A similar transformaꢀ
tion of the signal of the methylenic protons is detected in
Experimental
NMR spectra were recorded on a Bruker WPꢀ200SY instruꢀ
ment in CDCl3. The signals of residual protons of the deuterated
1
solvent were used as the internal standard for H NMR spectra,
1
and the external standard for 31P NMR spectra was H3PO4.
GCꢀMS analysis was carried out on a Varianꢀ3400 chromatoꢀ
graph with the DBꢀ1 capillary column (30 m×0.32 mm; layer
thickness 0.25 µm) in the temperatureꢀprogrammed regime
from 60 to 250 °C. The rate of the programmed temperature
increase was 6 °C min–1, a FinniganꢀMAT 800 AT ion trap was
used as the detector, and electron impact energy was 70 eV.
The yields, physicochemical constants, and results of elꢀ
emental analyses of phosphates 1—3 are presented in Table 2.
The data of 1H, 19F {1H}, and 31P{H} NMR spectra are given in
Table 3. The data of 1H and 31P{1H} NMR spectroscopy for
compounds 9a,b are presented in Table 4.
the H NMR spectrum when disiloxane 1b is heated (see
Table 1).
The 31P NMR spectra of phosphorusꢀcontaining
disiloxanes 1a,b after their heating at 150 °C for 5 h exꢀ
hibit, along with the signal of the starting phosphate, the
appearance of an additional closely lying singlet, which
corresponds, most likely, to the phosphorus atom of the
nonꢀrearranged fragment of disiloxane 8, and a broad
signal in the region where silyl phosphates appear. This
signal is assigned to nonꢀseparated signals of the phosꢀ
phorus atom of the CH2SiOP group of phosphates 8 and 9.

1248
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 5, May, 2005
Molchanova et al.
Table 2. Yields, physicochemical constants, and elemental analysis data for phosphates 1—3
20
Comꢀ
pound
Yield
(%)
nD
Found
Calculated
Molecular
formula
(%)
P
С
Н
Si
1a
1b
2a
2b
3a
3b
77
73
50
69
94
97
1.5282
1.3775
1.4810
1.3720
1.4851
1.3745
55.14
54.70
24.99
24.64
53.41
53.80
31.75
31.45
52.20
51.93
29.27
29.28
5.63
5.51
3.56
3.54
5.58
5.87
4.47
4.40
5.45
5.28
3.91
3.80
8.99
9.40
8.66
9.08
9.96
6.94
6.39
6.76
7.05
7.05
6.77
6.68
8.64
8.53
8.34
8.23
6.30
6.29
6.22
6.13
6.21
6.39
6.13
6.22
C30H36O9P2Si2
C14H24F12O9P2Si2
C20H26F3O4PSi
C12H20F9O4PSi
C38H46F6O9P2Si2
C22H34F18O9P2Si2
1
Table 3. H, 19F, and 31Р NMR spectral data for phosphates 1—3a,b
Comꢀ Solꢀ
pound vent
NMR, δ, J/Hz
1H
19F {1H}
CF3CH CF3CH2
31Р {1H}
(s)
MeSi
(s)
SiCH2
CH2CH2CH2 CH2CH
CH
(m)
R
(m)
(m)
—
(m)
—
(s)
(s)
1a
1b
2a
2b
3a
CDCl3 0.15
CDCl3 0.31
C6D6 –0.39
C6D6 –1.23
3.93
(d, JH,P = 6.2)
3.93
(d, JH,P = 5.8)
0.24—0.55
(m)
0.34—0.57
(m)
0.31—0.67
(m)
—
—
7.21—7.39
4.50—4.96
—
—
—
–9.89
0.17
—
—
1.18—1.52 1.58—1.82 5.73—5.91 7.05—7.32
1.19—1.56 1.58—1.87 4.52—4.72 4.16—4.39
—
–11.87
–2.48
–12.01
0.05
0.83
2.42,
2.29*
—
C6D6
0.12
1.31—1.99
1.32—1.93
5.05—5.26 6.85—7.00
(рꢀН);
7.03—7.10
(mꢀН);
7.34—7.38
(оꢀН)
3b
C6D6
0.19 0.37—0.79 (m)
4.74—5.00 3.94—4.24 –0.08
2.10,
2.28*
–2.65
* Signals of magnetically nonequivalent CF3CH2 groups.
1
Table 4. H and 31P NMR spectral data for ethers 9a,b
stirring and iceꢀcooling (~0 °C) for 1—2 min to a mixture of
concentrated H2SO4 (5 mL) and anhydrous CH2Cl2 (15 mL).
The reaction mixture was stirred for 5 min, poured onto ice, and
extracted with ether (3×30 mL). The organic extracts were
washed with a saturated solution of NaHCO3 (20 mL), dried
with MgSO4, and chromatographed on Al2O3 (eluent ether).
The solvent was distilled off in vacuo.
Comꢀ
pound
NMR, δ
1H
31P{1H}
(s)
MeSi (s) SiCH2 (s)
R (m)
Rearrangement of disiloxanes 1a,b. Disiloxane 1a or 1b was
heated in a sealed NMR tube for 90 h at 125 °C. The course of
rearrangement was monitored by 1H and 31P NMR spectroꢀ
scopy.
9a
9b
0.26
0.56
3.20
3.53
6.86—7.46 –20.29
3.99—4.03 –10.88
Synthesis of disiloxanes 1a,b (general procedure). Phosphate
5a,b 5 (0.01 mol) in anhydrous CH2Cl2 (15 mL) was added with
(1,1,1ꢀTrifluoroꢀ5ꢀtrimethylsilylpentꢀ2ꢀyl)diphenyl phosphate
(2a). A mixture of 1,1,1ꢀtrifluoroꢀ5ꢀtrimethylsilylpentanꢀ2ꢀol13

Phosphorusꢀcontaining disiloxanes
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 5, May, 2005
1249
(2.35 g, 0.011 mol), diphenyl chlorophosphate (2.67 g,
0.010 mol), and Mg (0.012 g, 0.0005 mol) was heated at 160 °C
for 12 h until HCl evolution ceased. The reaction mixture was
cooled, kept for 0.5 h in a vacuum of a waterꢀjet pump, and
chromatographed on Al2O3 (ether as eluent). The solvent was
distilled off, and the residue was distilled in vacuo. Phosphate 2a
(2.23 g) was obtained, b.p. 178—179 °C (1 Torr).
(1,1,1ꢀTrifluoroꢀ5ꢀtrimethylsilylpentꢀ2ꢀyl)bis(2,2,2ꢀtrifluoroꢀ
ethyl) phosphate (2b). Similarly to the synthesis of 2a, phosꢀ
phate 2b (2.51 g, b.p. 78—79 °C (1 Torr)) was obtained from
1,1,1ꢀtrifluoroꢀ5ꢀtrimethylsilylpentanꢀ2ꢀol (1.87 g, 0.009 mol),
bis(2,2,2ꢀtrifluoroethyl) chlorophosphate (2.22 g, 0.008 mol),
and Mg (0.0095 g, 0.0004 mol) by the 5ꢀh reaction at 160 °C.
Synthesis of disiloxanes 3a,b (general procedure). A mixture
of phosphate 2a,b (0.01 mol) and concentrated H2SO4 (5 mL)
was heated at 45 °C until methane evolution ceased. The reacꢀ
tion mixture was poured onto ice and extracted with ether
(3×30 mL). The organic extracts were washed with a saturated
solution of NaHCO3 (20 mL), dried with MgSO4, and chromatoꢀ
graphed on Al2O3 (ether as eluent). The solvent was distilled off
in vacuo.
1,4ꢀDioxaꢀ2,6ꢀdisilaꢀ2,2,6,6ꢀtetramethylhexane (10). Phosꢀ
phate 1a (6.6 g, 0.01 mol) was heated for 4 h at 200 °C. The
reaction mixture was hydrolyzed with water (10 mL) and exꢀ
tracted with ether (30 mL). The organic layer was washed with a
saturated solution of Na2CO3 (3×10 mL) and dried with MgSO4.
The solvent was distilled off. A siloxane fraction (1.7 g, 96%)
was obtained. Cyclic disiloxane 10 (purity 80%, 0.3 g, 17%) was
obtained from this fraction on heating to 200 °C in a vacuum of
a waterꢀjet pump (10 Torr). Mass spectrum, m/z (Irel (%)): 177
[M + 1]+ (12), 161 [M – Me]+ (71), 133 [Me2SiOSiMe2 + 1]+
(100), 103 [M – SiMe2 + 1]+ (48), 73 [Me2SiCH2 + 1]+ (87), 59
[Me2Si + 1]+ (70). 1H NMR (C6D6), δ: 0.21 (s, 12 H, MeSi);
3.30 (s, 4 H, CH2).
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This work was financially supported by the Council on
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Received February 2, 2005;
in revised form March 30, 2005