Phenylhalosilazanes

Article abstract of DOI:10.1134/S1070363211120127

A method of synthesis of phenylhalosilazanes by the reaction of phenyl(fluoro)chlorosilanes PhSiF_3-nCl_n (n = 0-3) with hexamethyldisilazane at room temperature is elaborated. The thermolysis of 1,1,1- trimethyl-3-phenyl-3,3-difluorodisilazane affords cyclic phenylfluorosilazanes (PhSiFNHSiMe₃)_n (n = 3-5). The process may occur via the intermediate formation of phenylfluorosilimine. Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S1070363211120127

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 12, pp. 2493–2497. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © S.V. Basenko, L.E. Zelenkov, M.G. Voronkov, A.I. Albanov, 2011, published in Zhurnal Obshchei Khimii, 2011, Vol. 81, No. 12,
pp. 2046–2050.
Phenylhalosilazanes
S. V. Basenko, L. E. Zelenkov, M. G. Voronkov, and A. I. Albanov
Favorskii Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
e-mail: sv_basenko@irioch.irk.ru
Received April 12, 2011
Abstract—A method of synthesis of phenylhalosilazanes by the reaction of phenyl(fluoro)chlorosilanes
PhSiF3–nСln (n = 0–3) with hexamethyldisilazane at room temperature is elaborated. The thermolysis of 1,1,1-
trimethyl-3-phenyl-3,3-difluorodisilazane affords cyclic phenylfluorosilazanes (PhSiFNHSiMe3)n (n = 3–5).
The process may occur via the intermediate formation of phenylfluorosilimine.
DOI: 10.1134/S1070363211120127
Earlier we have shown that organylfluoro- [1] and
organylchlorosilanes [2] split the Si–N bond in hexa-
methyldisilazane I even at room temperature to form
the corresponding organylchloro- and fluorodisilazanes.
does not change the course of the reaction. The substi-
tution of the fluorine atom of 1,1,1-trimethyl-3-phenyl-
3,3-difluorodisilazane by the trimethylsilylamino
group proceeds at room temperature very slowly, after
72 h the conversion is only 15%.
In continuation of this research we have studied the
reaction of phenyl(fluoro)chlorosilanes with compound
I [3]. Phenyl(difluoro)chlorosilane was found to react
with compound I (25°С, molar ratio 1:1, 2 h) to form
1,1,1-trimethyl-3-phenyl-3,3-difluorodisilazane in up
to 92% yield.
PhSiF2NHSiMe3 + Me3SiNHSiMe3
→ PhSiF(NHSiMe3)2 + Me3SiF.
The reaction of phenyl(difluoro)chlorosilane with
the equimolar mixture of compound I and hexamethyl-
disiloxane II (molar ratio 1:1:1, 25°С) proceeds
exclusively with the cleavage of the Si–N bond.
PhSiF2Cl + Me3SiNHSiMe3 → PhSiF2NHSiMe3 + Me3SiCl.
In the reaction of phenyl(fluoro)dichlorosilane with
compound I (molar ratio 1:1, 25°С, 4 h) the 1,1,1-
trimethyl-3-phenyl-3-fluoro-3-chlorodisilazane is formed
in up to 73% yield.
Therefore, only the Si–Cl bond of phenyl(difluoro)-
chlorosilane enters the reaction.
The increase of the molar content of compound I
SiFCl2
Cl
Si
F
+ Me3SiCl
+ (Me3Si)2NH
NHSiMe2
The formed 1-phenyl-1,1-difluoro- and 1-phenyl-1-
fluoro-1-chloro-3,3,3-trimethyldisilazanes do not react
with the starting phenylfluorochlorosilanes under the
studied conditions.
SiF3−nCln
+
+ Me3SiCl
SiF2−mClm−Ν−SiF3−nCln−1
H
SiF2−mClm−ΝΗ−SiMe3
n = 1, 2; m = 0, 1.
2493

2494
BASENKO et al.
The reaction of phenyl(fluoro)dichlorosilane with
compound I (molar ratio 1:2, 25°С, 24–36 h) results in
the formation of 1,1,1,5,5,5-hexamethyl-3-phenyl-3-
fluorotrisilazane in a high yield (79–87%).
SiFCl2
NHSiMe3
Si
F
+ 2 Me3SiCl
+ 2 (Me3Si)2NH
NHSiMe3
The difference in the reactivity of the Si–N and Si–O
bonds of compounds I and II, respectively, allowed
obtaining the earlier unknown mixed phenyl(fluoro)-
siloxazanes. Thus, the successive reaction of phenyl
(fluoro)dichlorosilane with siloxane II (molar ratio
1:1, 25°С, 12–24 h) and silazane I leads to 1,1,1,5,5,5-
hexamethyl-3-phenyl-3-fluorosiloxazane.
bond, which results in the selective substitution of the
chlorine atom in the studied reactions.
The available literature data [5] suggest that these
reactions are assisted by the effect of n,σ*-interaction,
which should result in stabilization of the lone electron
pair of the fluorine atom, in the shortening of the Si–F
bond and the elongation of the Si–Cl bond, favoring
the rupture of the latter in the studied reactions.
OSiMe3
+ (Me3Si)2NH
Si
F
An alternative point of view on the electronic
effects in the systems containing the chlorine and
fluorine atoms at the same silicon or carbon atom is
named “the effect of positive charge” [6]. This effect is
also consistent with the data obtained in the present
study.
Cl
OSiMe3
+ Me3SiCl
Si
F
NHSiMe3
Note that the reaction of 1-phenyl-1-fluoro-1-
chloro-3,3,3-trimethyldisilazane with hexamethyldi-
siloxane does not give the above product under the
studied conditions.
The thermolysis of 1,1,1-trimethyl-3-phenyl-3,3-
difluorodisilazane results in the formation of cyclic
structures, which were identified by the methods of
19F, 29Si NMR spectroscopy and chromatomass spec-
trometry. It can be assumed that the thermolysis
proceeds with the intermediate formation of phenyl-
fluorosilimine, which undergoes further cyclization.
NHSiMe3
+ (Me3Si)2O
Si
F
Cl
NHSiMe3
F
Me
F
F
NH
+ Me3SiCl
NH
Si
F
Si
Si
Si
Me
225оС
OSiMe3
Me
10 h
Our investigations suggest that the ammonium salts
which could be formed in small amounts due to the
reaction of ammonia dissolved in silazane with
hydrogen halides in halosilanes do not possess
catalytic activity [4].
Me
Me
Si
+
F
Me
The investigation of the three-component concurrent
reactions of the mixtures of phenylhalosilanes PhSiF3–nСln
(n = = 0–3) with hexamethyldisilazane (molar ratio of
the reagents 1:1:0.9, 25°С) gives the following order
of activity of phenylhalosilanes with respect to hexa-
methyldisilazane: PhSiF2Cl > PhSiFCl2 > PhSiCl3 >
PhSiF3.
Phenylfluorocyclosilazanes with 3- and 4-phenyl-
fluorosilazane links are predominantly formed.
The products of insertion of phenylfluorosilimine
into the molecules of the starting 1,1,1-trimethyl-3-
phenyl-3-fluorosilazane were registered only by the
19F NMR spectroscopy method and are contained as
admixtures (see the table). Apparently, the formed
linear products of insertion undergo further thermal
decomposition with the formation of phenylfluoro-
The ease of the reaction of phenylfluorochloro-
silanes (especially of PhSiF2Cl) with hexamethyldi-
silazane is due to much larger polarizability and less
strength of the Si–Cl bond as compared to the Si–F
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PHENYLHALOSILAZANES
F
HN
Si
F
Si
NH
Si
F
HN
Si
Si
Si
NH
F
+
NH
F
HN
Si
NH
F
F
F
NH
Si
+
n
F
NH
Si
Si
F
Si
NH
HN
F
Si
F
Si
NH
NH
F
n = 3–5.
silimine, whereas phenylfluorocyclosilazanes may be
more stable under the conditions of the reaction.
Number of amino groups
n = 1
5.9
0
n = 2
n = 3
–17.2
23
n = 4
–28.6
35
δSi
–1.7
7.6
Earlier it was mentioned that the increase in the
number of aminogroups in silazanes Me4–nSi(NR2)n
from 1 to 4 leads to successive shielding of the silicon
atom [7].
ΔδSi
However, the replacement of the fluorine atom in
1,1,1-trimethyl-3-phenyl-3,3-difluorodisilazane with
the second trimethylsilylamino group results in
deshielding of the silicon atom by 14 ppm, with the
chlorine atom, by 20 ppm, whereas its replacement
with trimethylsiloxy group, on the contrary, leads to
the shielding of the silicon atom by 5 ppm. The
correlation relationship δSi–χx can be represented as
follows.
Parameters of 19F, 29Si NMR spectra of phenyl(fluoro)-
chlorodisilazanes (CCl4, 20%)
δSi, ppm
Compound
PhSiF2NHSiMe3
δF, ppm JSiF, Hz
PhSi≡
–46.5
–26.1
–33.0
SiMe3
6.2
–134.57 262.5
–122.26 289.9
–131.44 257.9
PhSiFClNHSiMe3
PhSiF(NHSiMe3)2
–6.9
4.3
χx
δSi
−51.6 3.5
PhSiFOSiMe3(NHSiMe3) –51.6 4.5/11.1 –130.53 254.4
(OSiMe3)
3
−46.5 3.9
PhSiCl2NHSiMe3
(PhSiFNH)3
–11.5
–35.7
–35.6
–35.0
7.3
–
–
–
X
PhSiFXNHSiMe3
=
H
N
S
i
M
e
−33.0
−26.1
3.0
3.1
–126.28 272.4
–125.45 273.8
–125.23 269.2
(PhSiFNH)4
–
(PhSiFNH)5
–
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BASENKO et al.
Oppositely directed variation in the 29Si chemical
kept for 2–4 h. On opening the ampule the content was
transferred to the distillation flask pre-filled with argon
and pre-heated, and the mixture was distilled. Yield
13.9–14.2 g (90–92%), n2D0 1.4510, bp 55–58°С (2 mm
Hg). 19F NMR spectrum, δF: –134.57 ppm. 29Si NMR
spectrum, δSi, ppm: –46.5 t (PhSi≡), 6.2 (SiMe3, JSiF
262.5 Hz). Mass spectrum, m/z, %: 231(1) [M]+, 216
(100) [M – Me]+, 200(6) [M – Me – MeH]+, 188(4)
[M – C3H7]+, 143(5), 135(27) [PhSiMe2]+, 132(3), 91
(4), 77(6) [Ph]+, 73(12) [SiMe3]+.
shifts in Me4–nSi(NR2)n and PhSiF4–n(NHSiMe3)n with
variation in the number of the Si–N bonds can be
explained as follows: 29Si chemical shifts in these
series of compounds lie on the branch of the δ ~ f(χx)
relationship, where the increase in the electronegativity
of the substituents leads to the shielding of the silicon
atom [8]. Whereas the increased number of amino-
groups in amino(methyl)silanes increases the Σχx, for
compounds PhSiF4–n(NHSiMe3)n it has the opposite
effect. The replacement of the fluorine atom in PhSiF2·
(NHSiMe3) by chlorine also decreases the sum of
electronegativities at the silicon atom Σχx and, hence,
causes deshielding of 29Si.
PhSiFCl(NHSiMe3). Yield 73%, bp 71–71.5°С
19
29
(2 mm Hg). F NMR spectrum, δF: –122.26 ppm. Si
NMR spectrum, δSi, ppm: –26.1 d (PhSi≡), 6.9 (SiMe3,
JSiF 289.9 Hz).
The increase of the silicon shielding upon the
replacement of the fluorine atoms in these molecules
by trimethylsiloxy group is anomalous since the latter
is less electronegative as compared to fluorine atom.
However, a larger shielding of the silicon atom by the
trimethylsiloxy group has already been mentioned in
the literature [7].
PhSiF(NHSiMe3)2. Yield 87%, bp 106–108°С
19
29
(2 mm Hg). F NMR spectrum, δF: –131.44 ppm. Si
NMR spectrum, δSi, ppm: –33.0 d (PhSi≡), 4.3 (SiMe3,
JSiF 257.9 Hz). Mass spectrum, m/z, %: 300(1) [M]+,
285(41) [M – Me]+, 269(3) [M – Me – MeH]+, 257(13)
[M – C3H7]+, 253(9), 175(14), 135(100) [PhSiMe2]+,
77(6) [Ph]+, 73(30) [SiMe3]+.
It was noted [9] that the decrease in the size of the
ring of dimethylcyclosilazanes results in deshielding of
the silicon atom by 3–5 ppm. In the case of phenyl-
fluorocyclosilazanes the ring size has practically no
effect on the chemical shifts of silicon, fluorine, and
the coupling constants (JSiF).
PhSiFOSiMe3(NHSiMe3). Yield 84%. 19F NMR
spectrum, δF: –130.53 ppm. 29Si NMR spectrum, δSi,
ppm: –51.6 d (PhSi≡), 4.5 (NHSiMe3), 11.1 (OSiMe3,
J
SiF 254.4 Hz) Mass spectrum, m/z %: 301(5) [M]+, 217
(95) [M – Me]+, 270(5) [M – Me – MeH]+, 254(5), 208
(10); 194(35); 176(4), 162(2), 136(28), 135(100)
[PhSiMe2]+, 132(19), 121(6), 107(6), 91(9), 77(12)
[Ph]+, 74 (13), 73(33) [SiMe3]+.
EXPERIMENTAL
1H, 19F and 29Si spectra were recorded on a Bruker
DPX 400 spectrometer at working frequencies 400
(1H), 100.13 (13C), 376.47 (19F), 79.49 (29Si) MHz in
The obtained compounds are very sensitive to
heating and air moisture.
1
CCl4 (for H CDCl3 was added), internal reference
Thermolysis of PhSiF2NHSiMe3. The calcined
ampule was charged with 1.16 g (5 mmol) of PhSiF2·
NHSiMe3 in a nitrogen atmosphere, sealed, and
maintained at 225°С for 8 h. After opening and removal
of solvent the residue was analyzed. On attempt to
distillate in a vacuum (1 mm Hg) the mixture poly-
merizes.
tetramethylsilane (1H, 13C, 29Si), and CCl3F (19F).
Mass spectra were taken on a Shimadzu GCMS-
QP5050A chromatomass spectrometer, injector
temperature 200–250°С, carrier gas helium, tempera-
ture of detector 250°С, quadruple mass analyzer,
electron ionization with the ionization voltage 70 eV.
(PhSiFNHSiMe3)3. 19F NMR spectrum, δF:
–126.28 ppm. 29Si NMR spectrum, δSi, ppm: –35.7 d
(JSiF 272.4 Hz). Mass spectrum, m/z %: 417(48) [M]+,
399(2), 340(100) [M – Ph]+, 323(44), 321(7), 303(11),
262(29), 260(4), 242(6), 219(5), 199(8), 197(7), 169
(16), 166(7), 161(7), 77(17) [Ph]+.
(PhSiFNHSiMe3)4. 19F NMR spectrum, δF:
–125.45 ppm. 29Si NMR spectrum, δSi, ppm: –35.6 d
(JSiF 273.8 Hz).
Mixed phenyl(fluoro)chlorosilanes PhF3–nCln (n =
1–2) were prepared by disproportionation of PhSiF3
with PhSiСl3 [10].
Reaction of phenylfluorochlorosilanes with
silazanes. PhSiF2NHSiMe3. An ampule was charged
with 10 ml (0.067 mol) of dry PhSiF2Cl under dry
argon, degassed five times in a vacuum, 14 ml
(0.067 mol) of the similarly degassed (Me3Si)2NH was
added, and the ampule was sealed. The mixture was
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PHENYLHALOSILAZANES
(PhSiFNHSiMe3)5. 19F NMR spectrum, δF:
–125.23 ppm. 29Si NMR spectrum, δSi, ppm: –35.0 d
(JSiF 269.2 Hz).
4. Basenko, S.V., Mirskov, R.G., and Voronkov, M.G.,
Russ. J. Gen. Chem., 1999, vol. 69, no. 3, p. 387.
5. Egorochkin, A.N. and Voronkov, M.G., Elektronnoe
stroenie organicheskikh soedinenii kremnija, germanija
i olova (Electron Structure of Organic Compounds of
Silicon, Germanium, and Tin), Novosibirsk: Sib. Otd.
Ross. Akad. Nauk, 2000.
(PhSiFNHSiMe3)n (n = 4–5) could not be detected
mass-spectrometrically because of technical limitations
of the detector.
6. Suvorov, B.A., Russ. J. Gen. Chem., 2006, vol. 76,
no. 9, p. 1401.
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