Reaction of diphenyl[2-(triethoxysilyl)ethyl]phosphine oxide with boron trifluoride etherate

Article abstract of DOI:10.1134/S107036321010004X

Diphenyl[2-(trifluorosilyl)ethyl]phosphine oxide was synthesized by the reaction of diphenyl[2-(triethoxysilyl)ethyl]phosphine oxide with boron trifluoride etherate. As shown by the ¹H, ¹³C, ¹⁹F, ³¹P, ²⁹Si multinuclear NMR spectroscopy data, the silicon atom in the molecule is tetracoordinate. The absence of P=O→Si interaction in diphenyl[2-(trifluorosilyl)ethyl]phosphine oxide, as follows from the comparison of the calculated [GIAO B3LYP/6-311++G(2d,p)] and experimental δ(²⁹Si) and δ(³¹P) values, is due to the formation of complex with BF₃ by the phosphoryl oxygen.

Full text of DOI:10.1134/S107036321010004X

ISSN 1070-3632, Russian Journal of General Chemistry, 2010, Vol. 80, No. 10, pp. 1913–1917. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © А.Е. Pestunovich, E.P. Doronina, А.I. Albanov, М.G. Voronkov, 2010, published in Zhurnal Obshchei Khimii, 2010, Vol. 80,
No. 10, pp. 1603–1607.
Reaction of Diphenyl[2-(triethoxysilyl)ethyl]phosphine Oxide
with Boron Trifluoride Etherate
А. Е. Pestunovich†, E. P. Doronina, А. I. Albanov, and М. G. Voronkov
Favorskii Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
e-mail: voronkov@irioch.irk.ru
Received January 14, 2010
Abstract―Diphenyl[2-(trifluorosilyl)ethyl]phosphine oxide was synthesized by the reaction of diphenyl[2-
1
(triethoxysilyl)ethyl]phosphine oxide with boron trifluoride etherate. As shown by the H, 13C, 19F, 31P, 29Si
multinuclear NMR spectroscopy data, the silicon atom in the molecule is tetracoordinate. The absence of
P=O→Si interaction in diphenyl[2-(trifluorosilyl)ethyl]phosphine oxide, as follows from the comparison of the
calculated [GIAO B3LYP/6-311++G(2d,p)] and experimental δ(29Si) and δ(31P) values, is due to the formation
of complex with BF3 by the phosphoryl oxygen.
DOI: 10.1134/S107036321010004X
Among monocyclic intramolecular complexes with
the pentacoordinate silicon of special interest are those
having the endocyclic O→Si bond, the so-called
“dragonoids”, first of all, corresponding to the general
formula RC(O)YCH2SiF3, A [1]. The presence of
heteroatom (Y = O, S, NR) in their coordination five-
membered ring results in the strengthening of the donor-
acceptor contact O→ Si as compared to Y = CH2. This
occurs due to the p–π conjugation in the fragment
Y–C=O, in which Y is a heteroatom containing one or
two lone electron pairs that increases the donor ability
of the carbonyl oxygen. As shown by the IR spec-
troscopy data, (2-benzoylethyl)trifluorosilane PhC(O)·
CH2CH2SiF3 exists as a mixture of the cyclic
(coordinated) and acyclic (noncoordinated) forms both
in the crystal and in solutions [2]. The replacement of
the silicon atom in А by germanium or tin atoms
possessing higher electrophilicity allowed to obtain
stable intramolecular complexes O=CCH2M with five-
membered ring (M = Ge, Sn) [3]. We expected that the
silicon-containing phosphine oxides R2P(O)CH2CH2·
SiF3 with the phosphoryl group, possessing higher than
the carbonyl group coordinating potential [4–5] would
preferably exist in the coordinated form. On the other
hand, the О,О-dialkyl(trifluorosilylethyl)phosphonates
(RO)2P(O)CH2CH2SiF3 (R = Me, Et) we obtained
earlier according to the multinuclear NMR spectroscopy
data and quantum chemical calculation at the
B3LYP/6-31G(d) level of theory contained tetra-
coordinate silicon atom [6]. Calculations by the same
method predicted that the substitution of the alkoxy
groups at the phosphorus atom by alkyl groups would
lead to stable intracomplex coordination structure of
dialkyl[2-(trifluorosilyl)ethyl]phosphonate [6].
In connection with this, we have synthesized di-
phenyl[2-(trifluorosilyl)ethyl]phosphine oxide Ph2P(O)·
CH2CH2SiF3 by the reaction of BF3·Et2O with
diphenyl[2-(triethoxysilyl)ethyl]phosphine oxide (I)
according to reaction 2 (n = 3). The latter was prepared
by addition of diphenylphosphine oxide to vinyl-
triethoxysilane in the presence of dinitrile of azo-
bisisobutyric acid [reaction (1)].
Ph2PHO + CH2=CHSi(EtO)3
Ph2P(O)CH2CH2Si(OEt)3,
I
(1)
Ph2P(O)CH2CH2Si(OEt)3
I
.
BF3 Et2O
(2)
_
Ph2P(O)CH2CH2SiFn(OEt)3 n
,
II, III
†
n = 2 (II), 3 (III).
Deceased.
1913

1914
PESTUNOVICH et al.
Table 1. 1H,19F,29Si, and 31P NMR parameters of I–III
EtOSi
Comp.
no.
CH2Si
CH2P
Ph
δSi
δF
δP
MeCH2О
1.18 t, 9Н
1.21 t, 3Н
–
MeCH2O
3.77 q, 6Н
3.90 q, 2Н
–
0.84 m, 2Н
1.17 m, 2Н
1.27 m, 2Н
2.29 m, 2Н
2.65 m, 2Н
2.75 m, 2Н
7.44–7.43 m, 10Н
7.44–7.75 m, 10Н
7.54–7.74
–47.4
–
34.38
54.99
I
–62.9 t.d
–61.35 q.d
–134
II
III
–137.5 54.58
Table 2. 13С NMR parameters of I–III
EtOSi
Comp.
CH2Si
1.13 d
CH2P
Ph
no.
MeCH2О MeCH2O
2
3
22.70 d
18.18
58.48
128.51 d (Co, JCP 11.0 Hz), 130.86 D (Cm, JCP 8.8 Hz), 131.54 d (Cp,
4JCP 2.9 Hz), 132.70 d (Ci, 1JCP 97.6 Hz)
I
–0.45 t.d
–1.7 q.d
19.51 d
18.6 d
17.13
–
58.71
–
123.5 d (Ci, 1JCP 106.4 Hz), 128.72 (Co), 130.71 (Сm), 131.91 (Ср)
II
122.9 d (Ci, 1JCP 106.8 Hz), 129.73 (Co), 131.52 (Сm), 134.75 (Ср)
III
At room temperature in ether and with the ratio of
the reagents I:BF3·Et2O = 1:1 only two ethoxy groups
were replaced by fluorine atoms (II, n = 2). When the
ratio was 1:2, a mixture of compounds II and III was
formed. When the ratio was 1:3 and after heating of
the reaction mixture at 70°С for 1 h we succeeded in
preparation of the target product III in 67% yield.
Phosphine oxides II, III are colored hygroscopic
liquids.
and spatial structure of diphenyl[2-(trifluorosilyl]ethyl)-
phosphine oxide III using the density functional theory
method B3LYP/6-31G(d). Two minima corresponding
to the cyclic (closed) and acyclic (open) forms were
found on the potential energy surface of the molecule.
Ph
Ph
Ph
Ph
P
P
O
O
F
Si
The structure of the synthesized compounds I–III
was studied by the method of multinuclear NMR
spectroscopy (Tables 1, 2). The 29Si signals in the
spectra of compounds II and III are split into a triplet
of doublets or quartet of doublets, respectively, due to
the spin-spin coupling with the fluorine and
phosphorus atoms. The 19F and 29Si NMR parameters
of diphenyl[2-(trifluorosilyl]ethyl)phosphine oxide
Ph2P(O)CH2CH2SiF3 [III: 29Si (–61.35 ppm q.d), 19F
(–137.5 ppm), J(29Si–19F) 278 Hz] practically coincide
with those in the spectrum of the earlier synthesized
compound (OEt)2P(O)CH2CH2SiF3 with tetracoor-
dinate silicon atom [6]: 29Si (–61.2), 19F (–137.61),
J(29Si–19F) (277.5). This is suggestive of the absence
(or too weak to be detected by the NMR) coordination
O→Si in molecule III. However, it is hard to explain
the observed downfield shift of the 31P signal by 20 ppm
on going from triethoxy- I to trifluoroderivative III.
F
F3Si
Acyclic form
F
Cyclic form
In the isolated state, judged from the value of the
relative internal energy of the complex formation, ΔЕ,
the equilibrium occurs between the cyclic and acyclic
forms of diphenyl[2-(trifluorosilyl]ethyl)phosphine
oxide (Table 3). At room temperature, as follows from
the value of the relative free energy, ΔG, it is shifted to
the open form. In the chloroform solution (with only
polar effects being taken into account in the SCRF
model) molecule III exists in the closed form (ΔЕ =
–4.5 kcal mol–1, ΔG = –2.4 kcal mol–1). The latter is
characterized by rather short contact OSi (dSiO
=
2.017 Å). The geometry of the coordination node
OSiCF3 is close to the trigonal bipyramid (TBP, ηα =
74 %).
The calculated chemical shift δtheor(29Si) of the
cyclic form III in the chloroform solution is shifted
upfield with respect to that of the open form (see Table 3),
which is indicative of pentacoordination of the silicon
Why the structure stabilized by the Р=О→Si
attractive interaction is not formed in the experiment?
To answer this question, we have studied the electronic
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REACTION OF DIPHENYL[2-(TRIETHOXYSILYL)ETHYL]PHOSPHINE OXIDE
1915
Table 3. Calculated data [B3LYP/6-31G(d)] for [2-(trifluorosilyl]ethyl)-phosphine oxide (III) molecule and its complexes
with CHCl3 and BF3
ΔЕ
(ΔG)
0.7
δtheor(29Si),а dexp(29Si), dtheor(31P),а
dexp(31P),
ppm
Medium, model
dSiO
dSiF
ηα
ΔSi
ppm
–88.3
–57.8
ppm
ppm
32.9
16.4
2.146
1.633
62
0.218
–61.4
54.6
Gas, isolated state
(–1.2)
2.017
2.703
2.149
1.650
1.608
1.636
74
27
62
0.151
0.413
0.221
4.5
(2.4)
–0.1
(–1.6)
2.6
–94.6
–57.5
–66.0
–59.0
–85.9
–58.0
39.4
18.8
28.0
19.6
39.1
21.5
CHCl3, SCRF (ε = 4.9)
CHCl3, supermolecule
III·HCCl3
CHCl3, hybrid model
III·HCCl3 + SCRF (ε = 4.9)
Gas, supermolecule
III·BF3
2.833
2.802
1.603
1.606
19
22
0.457
0.444
–1.8
(–2.9)
–0.02
–65.4
–60.4
–64.5
–59.6
45.8
42.8
47.9
46.0
CHCl3, hybrid model
III·BF3 + SCRF (ε = 4.9)
a
Calculated [GIAO B3LYP/6-311++G(2d,p)] and experimental chemical shifts δ(29Si) and δ(31P), ppm, B3LYP/6-31G(d) internuclear
distances SiO (dSiO, Å) and SiF (dSiF, Å), degree of pentacoordination of silicon atom (ηα, %), shift of the silicon atom from the equatorial
plane (ΔSi, Å), relative internal, ΔЕ, and free, ΔG, energies (298.15 K, 1 atm) for complex formation [ΔЕ(ΔG) = Е(G)cycl – Е(G)acycl
,
kcal mol–1] of compound III in the gas phase and in CHCl3 (SCRF model, ε = 4.7). Calculated chemical shifts of nonbonded forms of III
are given in italics. Positive value of ΔSi corresponds to the shift of the silicon atom towards fluorine.
atom. On the contrary, the experimentally determined
chemical shift δexp(29Si) of diphenyl[2-(trifluorosilyl]
ethyl)phosphine oxide unambiguously points to the
tetracoordinate silicon atom. Moreover, the calculated
chemical shifts of phosphorus δtheor(31P) both for the
cyclic and acyclic form also differ from the
experimental value δexp(31P) by more than 15 and
37 ppm, respectively.
To resolve the alternative of SiV versus SiIV in
compound III, we have employed a more realistic
model of its solvation with chloroform. Namely, not
only the polarity of the solvent but also its ability to
form hydrogen bonds with III was taken into account
in the supermolecule approximation. Apparently, the
energetic preference of the intermolecular coordination
bond РО···Н over the intramolecular РО→Si in
complex III·HCCl3 will result in a decrease in the
degree of pentacoordination of the silicon atom and a
downfield shift of the δtheor(29Si). This was found to be
the case (Table 3). Moreover, according to the relative
energies, the equilibrium is shifted towards the form
(IIIacycl)·HCCl3. Nevertheless, even when taking into
account the formation of hydrogen bonds of molecule
III with chloroform, the calculated and experimental
values of δ(31Р) are strongly different. No satisfactory
agreement was achieved between the δtheor and δexp
values neither for silicon nor for phosphorus nuclei
also within the framework of the hybrid model, which
included the effects of the nonspecific and specific
solvation of III with chloroform, (Table 3).
As mentioned above, compound III was prepared
by the reaction of compound I with BF3·Et2O = 1:3. In
the presence of a more strong (as compared to Et2O)
Lewis base in the reaction mixture (like compound III)
decomposition of complex BF3·Et2O and participation
of the formed BF3 in interaction with the phosphoryl
oxygen atom of Ph2P(O)CH2CH2SiF3 is possible. This
rules out the coordination of the РО group with the
silicon atom. Indeed, calculations prove the energetic
preference of the intermolecular complexes of BF3
with cyclic and acyclic forms of Ph2P(O)CH2CH2SiF3
over the complex BF3·Et2O:
Et2O + BF3 → Et2O·BF3 {ΔЕ = Е(Et2O·BF3) – [Е(Et2O) + Е(BF3)] = –9.5 kcal mol–1}
(IIIcycl) + BF3 → (IIIcycl)·BF3 {ΔЕ = Е[(IIIcycl)·BF3] – [Е(IIIcycl) + Е(BF3)] = –16.3 kcal mol–1}
(IIIacycl) + BF3 → (IIIacycl)·BF3 {ΔЕ = Е[(IIIacycl)·BF3] – [Е(IIIacycl) + Е(BF3)] = –18.8 kcal mol–1}
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 10 2010

1916
PESTUNOVICH et al.
3
Ph
Ph
Ph
Ph
109.5 – 1/3 nΣ=1θn
P
BF3
P
ηα =
×100%,
O
109.5 – 90
O
BF3
F
Si
where θ is the angle between the axial and equatorial
F3Si
F
F
bonds [11].
(IIIcycl) BF3
(IIIacycl) BF3
.
.
Chemical shifts δtheor(29Si) and δtheor(31Р) were
calculated relative to TMS and PH3 [12–14],
respectively, at the GIAO B3LYP/6-311++G(2d,p))
level of theory [15]. δtheor(29Si) = σtheor(ТМС) –
The calculated values of δtheor(29Si) and δtheor(31P)
for complexes III·BF3 approach the experimental
chemical shifts, and taking into account the polarity of
the solvent leads to even better agreement (Table 3).
σtheor(compound), and δtheor(31P)
= –
σtheor(PH3)
σtheor(compound) – 266.1 (where 266.1 is the gas phase
chemical shift of PH3) [13, 14]; σ is the shielding
constant, stheor(TMS) = 327.4 [328.1](CHCl3) and
Therefore, good agreement between the experi-
mental and theoretical values of δ 29Si and δ 31P can be
obtained only by taking into account the donor-
acceptor interaction of BF3 with the phosphoryl
oxygen of diphenyl[2-(trifluorosilyl)ethyl]phosphine
oxide III, and this is the reason of tetracoordination of
the silicon atom in molecule III.
σ
theor(PH3) = 558.9 [558.2](CHCl3).
Solvents were purified according to [16]. All syn-
theses were performed in hermetically closed vessels
in an argon atmosphere.
Diphenyl[2-(triethoxysilyl)ethyl]phosphine oxide
(I). The mixture of 0.7 g (5 mmol) of triethoxy-
vinylsilane, 0.29 g (1.4 mmol) of diphenyloxide, and
0.01 g of dinitrile of azobisisobutyric acid was heated
with stirring with a magnetic stirrer for 10 h at 80°С.
The precipitate formed was filtered off, washed with
hexane. Compound I was obtained in practically
quantitative yield, mp 78°С. Found, %: H 7.56; Si
6.86; P 7.59. C20H29PO4Si. Calculated, %: H 7.44; Si
7.15; P 7.90. NMR spectra are given in Tables 1, 2. In
the IR spectrum the band at 1160 cm–1 (Р=О) is
observed. Mass spectrum, m/z (Irel %): 391 ([M – H]+,
5), 364 (25) [M – C2H4]+ , 363 (16) [M – Et]+, 347 (99)
[M – OEt]+, 346 (90) [M – EtOH]+, 317 (11), 259 (53),
230 (14), 203 (22), 202 (100), 184 (18), 183 (25), 163
(30), 153 (24), 139 (12), 119 (34), 105 (52), 91 (26),
78 (58), 77 (43), 72 (26), 63 (33), 59 (65), 51 (29), 46
(36), 44 (43), 43 (46), 40 (44), 38 (15).
EXPERIMENTAL
Electron impact mass spectrum of compound I was
obtained on a chromatomass spectrometer GCMS-
QP505 A (SHIMADZU) with direct injection of the
sample into the ion source. Temperature of the source
200°С, temperature of injector 175оС. Energy of
electrons 70 eV, quadruple mass analyzer, range of
detected masses 34–650 Da. IR spectra were taken on
a Specord IR-75 instrument in thin layer and in pellets
with KBr. NMR spectra were registered on a Bruker
DPX-400 spectrometer for 5–10% solutions in СDCl3
with HMDS as an internal standard.
All calculations were performed with full geometry
optimization at the B3LYP/6-31G(d) level of theory
using the Gaussian03 program package [7]. Belonging
of the calculated structures to minima on the potential
energy surface was proved by positive values of the
corresponding Hessians. The relative energy, ΔE, of
the cyclic and acyclic forms of compounds was deter-
mined as the difference of their electronic energies
ΔЕel and the zero point energies ΔZPE: ΔЕ = ΔЕel –
ΔZPE. The free energy of complex formation ΔG was
calculated at standard conditions (298.15 K, 1 atm).
For the hybrid model, ΔЕ was estimated without
ΔZPE. Polarity effects were estimated using the
Onsager model (SCRF) [8–10].
Diphenyl[2-(ethoxydifluorosilyl)ethyl]phosphine
oxide (II). The mixture of 0.5 g (1 mmol) of
compound I, 0.14 g (1 mmol) of BF3·Et2O, and 4 ml of
anhydrous ether was stirred for 3 h at room
temperature, kept at this temperature for 24 h, ether
was removed in a vacuum, the residue was dried in a
vacuum for 2 h at room temperature to obtain liquid
compound II. Found, %: Н 5.25, P 7.86, Si 7.34.
C16H19F5BPO2Si. Calculated, %: Н 5.09, Р 8.24, Si
7.47. NMR spectra are given in Tables 1, 2. IR spec-
trum contains absorption bands at 1170, 1140 cm–1
(Р=О), F2Si at 910, 870 cm–1.
The degree of pentacoordination of the silicon
atom, ηα, in the cyclic forms was calculated as
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 10 2010

REACTION OF DIPHENYL[2-(TRIETHOXYSILYL)ETHYL]PHOSPHINE OXIDE
1917
7. Frisch, M.J., Trucks, G.W., Schlegel, H.B., Scuseria, G.E.,
Robb, M.A., Cheeseman, J.R., Montgomery, J.A.,
Vreven, Jr.T., Kudin, K.N., Burant, J.C., Millam, J.M.,
Iyengar, S.S., Tomasi, J., Barone, V., Mennucci, B.,
Cossi, M., Scalmani, G., Rega, N., Petersson, G.A.,
Nakatsuji, H., Hada, M., Ehara, M., Toyota, K., Fukuda, R.,
Hasegawa, J., Ishida, M., Nakajima, T., Honda, Y.,
Kitao, O., Nakai, H., Klene, M., Li, X., Knox, J.E.,
Hratchian, H.P., Cross, J.B., Adamo, C., Jaramillo, J.,
Gomperts, R., Stratmann, R.E., Yazyev, O., Austin, A.J.,
Cammi, R., Pomelli, C., Ochterski, J.W., Ayala, P.Y.,
Morokuma, K., Voth, G.A., Salvador, P., Dannenberg, J.J.,
Zakrzewski, V.G., Dapprich, S., Daniels, A.D., Strain, M.C.,
Farkas, O., Malick, D.K., Rabuck, A.D., Raghavachari, K.,
Foresman, J.B., Ortiz, J.V., Cui, Q., Baboul, A.G.,
Clifford, S., Cioslowski, J., Stefanov, B.B., Liu, G.,
Liashenko, A., Piskorz, P., Komaromi, I., Martin, R.L.,
Fox, D.J., Keith, T., Al-Laham, M.A., Peng, C.Y.,
Nanayakkara, A., Challacombe, M., Gill, P.M.W.,
Johnson, B., Chen, W., Wong, M.W., Gonzalez, C., and
Pople, J.A., Gaussian, 2003. Pittsburgh PA: Gaussian.
Inc. 2003.
Diphenyl[2-(trifluorosilyl)ethyl]phosphine oxide
(III). The mixture of 0.38 g (1 mmol) of compound I
and 0.4 g (3 mmol) of BF3·Et2O was heated at 70°С
with stirring for one hour. Volatile products were
removed in a vacuum at heating on a water bath, the
residue was kept at this temperature in a vacuum for
2 h to obtain compound III as a brown liquid. Found,
%: H 3.95, P 8.15, Si 7.85. C14H14F6BPOSi.
Calculated, %: H 3.96, P 8.11, Si 7.35. NMR spectra
are given in Tables 1, 2. IR spectrum, ν, cm–1: 1160,
1140 (Р=О), 930, 870, 815 (F3Si).
ACKNOWLEDGMENTS
The authors are grateful to V. F. Sidorkin for the
help in performing the research and discussion of the
results.
The work was performed with the support from the
Council on Grants of the President of Russian
Federation (grant no. NSh 255.2008.3).
8. Wong, M.W., Frisch, M.J., and Wiberg, K.B., J. Am.
Chem. Soc., 1991, vol. 113, p. 4776.
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