Dual behavior of sulfur trioxide-hexaethyltriamidophosphite system

Full text of DOI:10.1134/S0012500806120020

ISSN 0012-5008, Doklady Chemistry, 2006, Vol. 411, Part 2, pp. 226–229. © Pleiades Publishing, Inc., 2006.
Original Russian Text © I.V. Bodrikov, V.K. Bel’skii, I.Yu. Shebelova, A.Yu. Subbotin, A.A. Sazhin, 2006, published in Doklady Akademii Nauk, 2006, Vol. 411, No. 5, pp. 629–632.
CHEMISTRY
Dual Behavior of Sulfur
Trioxide–Hexaethyltriamidophosphite System
I. V. Bodrikov, V. K. Bel’skii, I. Yu. Shebelova, A. Yu. Subbotin, and A. A. Sazhin
Presented by Academician G.A. Abakumov April 19, 2006
Received May 24, 2006
DOI: 10.1134/S0012500806120020
In donor–acceptor complexes and adducts with
We have established for the first time that sulfur tri-
donor trivalent phosphorus compounds, sulfur trioxide oxide reacts with hexaethyltriamidophosphite as an
is coordinated to phosphorus through the sulfur atom ambident electrophile and is coordinated to the donor
[
1]. In particular, sulfur trioxide reacts with trialkyl- center either through an oxygen atom (formation of
phosphines and trialkyl phosphites to give adducts I adduct III with the P–O bond) or through the sulfur
and II containing the P–S bond:
atom (formation of adduct IV with the P–S bond).
⊕
ꢀ
The reaction was carried out at –75°C in anhydrous
methylene chloride in a dry nitrogen flow.
R P + SO
R P–SO
3
3
3
3
I
In the course of isolation, adduct III released sulfur
dioxide to form hexaethyltriamidophosphate V. Adduct
IV is a colorless crystalline solid stable in air.
⊕
ꢀ
(
RO) P + SO
(RO) P–SO .
3 3
3
3
II
(
(
Et N) P–OSO
(Et N) P=O
2
3
2
3
III
2
–
SO2
V
(
Et N) P + SO
3
2 3
⊕
ꢀ
Et N) P–SO
2
3
IV
3
The structures of the compounds obtained were proved by the treatment of the resulting products with
established by X-ray diffraction, IR spectroscopy, antimony pentachloride in methylene chloride at –40°C
NMR, and independent synthesis. The structure of to produce donor–acceptor complexes VI and VII.
adduct III was confirmed by quantum-chemical calcu- Antimony pentachloride as a strong Lewis acid dis-
lation.
places sulfur dioxide from adduct III and sulfur triox-
ide from adduct IV to yield complexes VI and VII,
respectively:
The ratio between adducts III and IV varies in a
wide range depending on reaction conditions. The ratio
between adducts III and IV isolated from the reaction
mixture obtained by reacting hexaethyltriamidophos-
⊕
ꢀ
⊕
ꢀ
(
Et N) P–OSO + (Et N) P–SO
2 2 2 3
3 3
SbCl
5
phite with SO at –75°C in methylene chloride is close
to 1 : 3. Vacuum pyrolysis of the adducts at 160°C
results in triamidophosphate V and sulfur dioxide in
(Et N) P=O ⋅ SbCl + (Et N) P ⋅ SbCl
3 3
2 5 2 5
3
VI
VII
The structure of complexes VI and VII was proved by
elemental analysis data, IR spectroscopy, and indepen-
dent synthesis.
7
3% yield. Hexaethyltriamidophosphite reacts with
3
SO preliminarily bound to pyridine (as pyridine–sulfur
trioxide) to give adduct IV in quantitative yield. The
concurrent formation of two kinds of adducts was
Our semiempirical quantum-chemical calculations
MNDO and AM1 [2]) of probable reaction pathways
(
for the hexaethyltriamidophosphite–sulfur trioxide sys-
tem show that P–O coordination of the reactants is
energetically more favorable as compared with P–S
binding. Thus, when the reactants approach each other
Nizhni Novgorod State Technical University,
ul. Minina 24, Nizhni Novgorod, 603600 Russia
2
26

DUAL BEHAVIOR OF SULFUR TRIOXIDE–HEXAETHYLTRIAMIDOPHOSPHITE SYSTEM
227
C(2)
C(1)
C
O(2)
O(3)
C
C(4)
N(1)
C
O
C
C
N
S
C(3)
P
C
S
C(9)
P
N3
O
O(1)
C
O
C(7)
N(2)
C
C(12)
C(11)
N
C(10)
C
C
C
C(8)
C(5)
C(6)
Fig. 2. Structure of adduct IV.
Fig. 1. Structure of adduct III.
along the P–S line, the SO molecule turns out of the coordinated to the phosphorus atom via oxygen and
3
plane perpendicular to the trajectory of approach; in so sulfur atoms. The quantum chemical calculations show
doing, one of the oxygen atoms is oriented to the phos- that the coordination of the reactants to form the P–O
phorus atom. In the calculations of approach of the bond is energetically more favorable.
reactant molecules from different initial positions upon
full optimization of system geometry, the phosphorus
atom is oriented toward the nearest oxygen atom of the
Taking into account the very low energy barrier for
the P–O coordination of the reactants, one can suppose
this pathway to be dominant. The resulting P–O adduct
further produces hexaethyltriamidophosphate and iso-
SO molecule. If the oxygen atoms are restrained
3
within the plane perpendicular to the direction of reac- meric adduct VI with the P–S coordination.
tant approach until attaining the equilibrium P–S bond
In conclusion, it is worth noting that the revealed
length, there is no energy minimum corresponding to
ambident electrophilicity of sulfur trioxide is likely to
complex formation. When the constraint on the reaction
appear not only in the system with hexaethyltriami-
coordinate is lifted, the molecules spontaneously move
dophosphite but also in reactions with other donor com-
apart.
pounds. The resulting complexes or adducts cannot
If the reactants approach each other when the phos- always be isolated by the usual methods owing to fast
phorus atom is oriented toward one of the oxygen isomerization or transformation into other products.
atoms of the SO molecule, the reactants produce a rel- Therefore, the behavior of systems of sulfur trioxide
3
atively weak complex with the P–O coordination of the with electron-donating components and, first of all,
molecules. The complex formation is virtually barrier- with trivalent phosphorus compounds requires system-
less, and the flat sulfur trioxide molecule thereby atic analysis.
becomes slightly pyramidal. Adduct III with the P–O
coordination of the reactants is unambiguously
detected upon full optimization of all geometry param-
eters for the excited singlet electronic state of the
donor–acceptor system. The structure of the adduct is
shown in Fig. 1.
Thus, the results obtained indicate that the hexaeth-
yltriamidophosphite–sulfur trioxide system consists of
two isomeric adducts where the components are linked
through P–O and P–S bonds. The ratio of the isomers
varies within a wide range depending on preparation
conditions.
Our calculation results also show that the decompo-
sition of adduct III into hexaethyltriamidophosphate
and sulfur dioxide has an energy barrier of 17 kcal/mol.
EXPERIMENTAL
1
13
Thus, the results obtained indicate that sulfur triox-
The H and C NMR spectra were recorded on a
ide behaves as an ambident electrophile with respect to Gemini-300 spectrometer (operating frequency
a typical donor, hexaethyltriamidophosphite, and is 300 MHz), solutions in DMSO-d
, hexamethyldisilox-
6
DOKLADY CHEMISTRY Vol. 411 Part 2 2006

2
28
BODRIKOV et al.
–
4
Coordinates of the non-hydrogen atoms (Å × 10 ) in ad- warmed to ambient temperature. The solvent was
duct IV
Atom
removed in a vacuum, and the residue was washed with
hexane (3 × 5 mL) to give 2.48 g (75%) of adduct IV,
mp 99°C (CH Cl –CCl ).
x
y
z
2
2
4
S
3456(1)
6000(1)
2221(3)
3427(3)
3513(4)
7510(3)
5973(3)
6269(3)
7367(7)
8313(13)
9192(5)
9490(10)
6528(5)
8148(7)
5346(6)
3721(9)
7810(6)
8857(7)
4895(5)
3977(10)
2234(1)
2932(1)
2962(2)
1566(2)
1855(2)
2149(2)
3571(2)
3577(2)
1231(3)
1107(5)
2336(3)
1906(8)
4541(2)
4720(4)
3186(3)
3640(5)
3536(3)
4384(4)
4238(3)
4013(5)
2250(1)
2629(1)
2226(2)
2897(2)
1431(2)
2862(2)
3449(2)
1844(2)
2489(4)
1781(5)
3450(3)
4314(5)
3531(3)
4206(4)
4181(3)
4339(5)
1458(3)
1542(6)
1463(3)
565(4)
For C H N O PS anal. calcd. (%): C, 44.02; H,
.24; N, 12.83; S, 9.79.
1
2
30
3
3
9
P
O(1)
O(2)
O(3)
N(1)
N(2)
N(3)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
Found (%): C, 43.89; H, 9.43; N, 12.71; S, 9.65.
1
H NMR (DMSO-d , δ, ppm): 1.06 (t, 18H, 6CH ),
6
1
3
3
3.14 (m, 12H, 6CH ). C NMR (DMSO-d , δ, ppm):
9.23 (CH ), 12.76 (CH ). IR (ν, cm ): 1060, 1170,
2
6
–
1
3
1
2 3
220 (overlapping bands of the C–N bond and SO3
fragment vibrations). Vacuum evaporation of the hex-
ane solution gave 0.65 g (25%) of hexaethyltriami-
2
D
0
20
dophosphate V, n = 1.4635 (lit. [3]: nD = 1.4650).
Reaction of hexaethyltriamidophosphite with
pyridine–sulfur trioxide. Pyridine–sulfur trioxide
(
0.64 g, 4.0 mmol) was added to a solution of 1.00 g
(4.0 mmol) of hexaethyltriamidophosphite in 15 mL of
CH Cl under a dry nitrogen flow at –20°C. The mix-
2
2
ture was stirred at –20°C until the precipitate was dis-
solved (about 1 h) and then warmed to ambient temper-
ature. The mixture was subjected to reduced pressure
and washed with hexane (3 × 5 mL) to give 1.25 g
(95%) of adduct IV, mp 99°C.
Pyrolysis of the adducts. The reaction mixture
after solvent removal (0.16 g, 0.50 mmol) was kept for
3
0 min at 160°C in a vessel connected to a vacuum
pump through a tube filled with solid NaOH at a resid-
ual pressure of 100 mmHg. Then, the mixture was
cooled and treated with hexane (3 × 1 mL). After vac-
uum treatment, the residue was applied to a column of
Al O (hexane as the eluent) to give 0.094 g (73%) of
2
3
ane as the external reference. The IR spectra were
recorded as CH Cl solutions on a UR-20 spectropho-
tometer with solvent compensation. The X-ray diffrac-
tion study of a single crystal of compound IV was car-
ried out on a CAD4 automated diffractometer (λ MoKα,
graphite monochromator, 2θ scan, 2θmax = 60°). Com-
pound IV forms monoclinic crystals, a = 7.775(2) Å, tachloride. A solution of 0.17 mL (1.32 mmol) of
b = 14.661(3) Å, c = 16.074(3) Å, α = 90°, β = SbCl in 5 mL of CH Cl was added dropwise under a
02.54(3)°, γ = 90°, V = 1788.6(7) Å , Z = 4, space
group P2 /c. The structure was solved by direct meth-
ods and refined by least squares to R = 0.0281 for
hexaethyltriamidophosphate. The gain in the weight of
2
2
the absorbent was found to be 0.023 g (71% calculated
with respect to SO ). The sulfite ions in the absorbent
2
were determined by iodometric titration [4].
Reaction of the adducts with antimony pen-
5
2
2
3
1
dry nitrogen flow to a solution of 0.42 g (1.28 mmol) of
1
the reaction mixture in 7 mL of CH Cl at –10°C. The
2
2
mixture was kept for 4 h while it warmed to ambient
2
1
443 independent reflections with F > 2σ. The coordi- temperature. The residue obtained after vacuum treat-
nates of non-hydrogen atoms are shown in the table. ment was washed with benzene (3 × 3 mL). Insoluble
The molecular structure of adduct IV is shown in Fig. 2.
residue was recrystallized from a methylene chloride–
hexane mixture to give 0.48 g (69%) of complex VII,
mp 65–67°C.
Reaction of hexaethyltriamidophosphite with
SO . A solution of 2.46 g (10 mmol) of hexaethyltri-
3
amidophosphite in 10 mL of anhydrous methylene
chloride was added over one hour under a dry nitrogen
flow to a solution of 0.42 mL (10 mmol) of freshly dis-
tilled sulfur trioxide in 10 mL of the same solvent at
For C H Cl N PSb anal. calcd. (%): C, 26.38;
H, 5.53; Cl, 32.44; N, 7.69; P, 5.67.
1
2
30
5
3
Found (%): C, 26.1; H, 5.37; Cl, 32.66; N, 7.80;
75°C. The mixture was kept for 2 h at –70°C and then P, 5.74.
−
DOKLADY CHEMISTRY Vol. 411 Part 2 2006

DUAL BEHAVIOR OF SULFUR TRIOXIDE–HEXAETHYLTRIAMIDOPHOSPHITE SYSTEM
229
The benzene washings were treated with hexane to
REFERENCES
precipitate 0.21 g (28%) of complex VI, mp 127–
1
2
3
. Ando, F., Koketsu, J., and Ishii,Y., Bull. Chem. Soc. Jpn.,
981, vol. 54, pp. 3495–3499.
. Voityuk, A.A., Zh. Strukt. Khim., 1988, vol. 29, no. 1,
1
28°C.
1
For C H Cl N OPSb anal. calcd. (%): C, 25.63;
1
2
30
5
3
pp. 138–162.
H, 5.38; Cl, 31.52; N, 7.47; P, 5.51.
. Kodolov, V.I. and Spasskii, S.S., Usp. Khim., 1964,
vol. 33, p. 1501.
Found (%): C, 25.01; H, 5.17; Cl, 31.69; N, 7.38;
P, 5.34.
4. Williams, W.J., Handbook of Anion Determination,
Edinburgh: Butterworth-Heinemann, 1979. Translated
under the title Opredelenie anionov, Moscow: Khimiya,
1982.
Complexes VI and VII were also obtained by inde-
pendent syntheses.
DOKLADY CHEMISTRY Vol. 411 Part 2 2006