α,β- and β,γ-unsaturated phosphonium salts in reactions with halogenating agents

Article abstract of DOI:10.1134/S1070363210110046

Reaction of 1,4-bisphosphonium salts containing common buta-1,3-dienylene group with the halogenating agenst such as halogens and copper halides is studied. It was found than in all the cases instead of the expected products of the 1,2- or 1,4-addition to

Full text of DOI:10.1134/S1070363210110046

ISSN 1070-3632, Russian Journal of General Chemistry, 2010, Vol. 80, No. 11, pp. 2243–2248. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © M.Zh. Ovakimyan, A.S. Pogosyan, M.L. Movsisyan, M.G. Indzhikyan, R.A. Tamazyan, A.G. Aivazyan, 2010, published in Zhurnal
Obshchei Khimii, 2010, Vol. 80, No. 11, pp. 1779–1784.
α,β- and β,γ-Unsaturated Phosphonium Salts in Reactions
with Halogenating Agents
M. Zh. Ovakimyana, A. S. Pogosyana, M. L. Movsisyana,
M. G. Indzhikyana, R. A. Tamazyanb, and A. G. Aivazyanb
a Institute of Organic Chemistry of National Academy of Sciences of Armenia,
ul. Z. Kanakertsi 167a, Yerevan, 375091 Armenia
e-mail: ioc_phos@mail.ru
b Center of Investigation of Molecular Structure, National Academy of Sciences of Armenia, Yerevan, Armenia
Received December 14, 2009
Abstract―Reaction of 1,4-bisphosphonium salts containing common buta-1,3-dienylene group with the
halogenating agenst such as halogens and copper halides is studied. It was found than in all the cases instead of
the expected products of the 1,2- or 1,4-addition to the above-mentioned salts the adducts with complex anions
were formed quantitatively. According to the X-ray studies of bis(tributylphosphonio)buta-1,3-dienotri-
bromocuprate the positive charge on phosphorus is compensated with the complex [Cu2Br6]2– anion.
DOI: 10.1134/S1070363210110046
Great number of studies deals with the reactions of
nucleophilic addition to α,β-unsaturated phosphonium
salts. Due to structural features special place among
them belongs to 1,4-diphosphonium salts with the
common 1,3-butadienylene group. It is established that
the above-mentioned substrates in the reactions with
A–H and also HA–CH2–CH2–AH nucleophiles behave
as two isolated vinylphosphonium salts. This means
that nucleophilic attack is directed on the β-carbon
atoms of 1,3-butadienylene system [1, 2].
are practically absent. Keough et al. [3] described the
bromination of tributylvinylphosphonium bromide with
bromine in carbon tetrachloride at moderate heating.
The authors stated that the product of the double bond
bromination is formed, but no H NMR data concern-
ing this product was presented in the Experimental.
1
It should be expected that the reaction of 1,4-bis-
(triphenylphosphonio)buta-1,3-dienedichloride I with
halogens would lead to the products of 1,2- or the
conjugated 1,4-addition due to the initial attack of the
halogen cation on one of α-carbon atoms of the
common carbon bridge of the diphosphonium salt
according to the following scheme.
We have found that the reports concerning the
reactions of electrophilic addition (halogenation,
hydro-halogenation, etc.) to vinylphosphonium salts
+
+
1,4-
CH CHX
Ph3P CHX CH
PPh3
Cl−
Cl−
+
+
Ph3P CH CH CH CH
PPh3
Cl−
Cl−
1,2-
+
+
Ph3P CHX CHX CH CH PPh3
X
X
Cl−
Cl−
I
We have shown that the reaction of compound I
with two moles of bromine in chloroform at room
temperature leads to formation of yellow crystalline
compound which was characterized by elemental
analysis as the adduct of starting salt with two
molecules of bromine. In the 31P NMR spectrum of the
compound obtained the signal at 24 ppm characteristic
of the starting substance is observed. 1H NMR
spectrum contains the signals of four protons at sp2-
hybridized carbon atoms of the carbon bridge. The
2243

2244
OVAKIMYAN et al.
1
only difference is that the signals of α-carbon atoms
are shifted upfield as compared to the substance I. At
heating with styrene in methanol the product obtained
almost quantitatively gives dibromostyrene, while at
the attempt of repeated crystallization decomposes to
form the starting salt. On the basis of the result
obtained we concluded that the adduct is 1,4-bis-
(triphenylphosphonio)buta-1,3-dienedichloride–bromine
(1:2) II. We have also found that the phosphonium salt
I does not react with chlorine. Our attempt to
chlorinate it under the conditions of free-radical
addition by heating in the chlorine flow under the
irradiation by the light of the 500 W lamp in presence
of benzoyl peroxide also failed. Substance I also does
not react with hydrochloric and hydrobromic acid
either at room temperature or at heating. Such behavior
can be probably explained by the association of its
anions with the added acid.
copper(II) bromide. H NMR spectrum of the product
obtained is complicated, and in 31P NMR spectrum the
same signal at 24 ppm as in the starting salt was
observed. On the basis of the above-presented and the
elemental analysis data we have ascribed structure III
to this substance.
We have shown that treating complex III with
aqueous ammonia causes its decomposition with the
liberation of the starting salt I. Reaction of complex III
with styrene similarly to the case of compound II
quantitatively yields dibromostyrene. Bromination of
the unsaturated carbon bridge of complex III with
molecular bromine in methanol was unsuccessful. This
reaction unexpectedly led to formation of the complex
II and copper(II) bromide.
Reaction of salt I with two moles of copper(II)
chloride in methanol at room temperature yielded the
compound which on the basis of elemental analysis
and 1H and 31P NMR data was characterized as 1,4-bis-
(triphenylphosphonio)buta-1,2-dienotrichlorocuprate IV.
We failed to obtain UV spectrum of the complex IV
due to its poor solubility in methanol.
We made an attempt to brominate the unsaturated
carbon bridge of the salt I with copper(II) bromide.
Reaction of substrate with two moles of this reagent in
methanol led to the quantitative formation of black
crystalline adduct of the salt I with two molecules of
+ 2Br2
+
+
Ph3P CH CH CH CH
PPh3 2Br2
Cl−
Cl−
II
+ 2Br2
+ 2 CuBr2
+
+
CH
Ph3P
Cl−
CH
CH CH
I
PPh3
2 CuBr2
2 CuCl2
Cl−
III
+ 2 CuCl2
+
+
Ph3P CH CH CH CH
PPh3
Cl−
Cl−
IV
Unlike salt I its bis(tributylphosphoniobromide)
analog reacts with two moles of bromine to give an
adduct which according to 31P NMR data cannot be
The UV spectrum of the salt V contains an
absorption band with a maximum at ~254 nm. The
spectrum of copper complex VI has two bands with
the maxima at ~251 nm and ~300 nm. The latter band
is characteristic of complex compounds.
1
regarded as an individual product. In the H NMR
spectrum of this preparation the signals of four protons
belonging to sp2-hybridized carbon atoms of the
central carbon bridge of the salt V are observed. On
the basis of this data it can be suggested that a mixture
of bromine complexes is formed leaving intact the
unsaturated carbon bridge. The reaction of salt V with
copper(II) bromide in methanol at room temperature
led to the quantitative formation of complex of the salt
Molecular structure of compound VI was
established by the X-ray diffraction analysis. Already
in the preliminary studies the increased background
irradiation characteristic of the disordered structures
was found. Parameters of the tetragonal body-centered
unit cell measured on the Enraft-Nonius automatic
CAD-4 diffractometer at room temperature and refined
by 24 reflexes with 11 < θ < 14 are equal to a 32.724 Å,
V
with two molecules of CuBr2, 1,4-bis(tri-
butylphosphonio)buta-1,3-dienotribromocuprate VI.
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α,β– AND β,γ-UNSATURATED PHOSPHONIUM SALTS IN REACTIONS
2245
c 16.004 Å, V 17143(5) Å3. Diffraction experiments
were carried out on the same apparatus. Intensities of
8384 reflections in the ranges 0 ≤ h ≤ 39, 0 ≤ k ≤ 39,
and 0 ≤ l ≤ 19, θmax 25o were measured, MoKα-
radiation, graphite monochromator. Systematical
extinctions unambiguously indicated I41/acd (z = 32)
space group. All the calculations were carried out
according to the SHELXTL complex of programs [4].
After averaging the symmetrically equivalent re-
flections the array contained 3769 nonequivalent
reflections, among them 791 observed with I > 2σ(I).
So small number of the reflections observed is
explained by the weak scattering ability of the crystal
because of the disordered structure. Despite the fact
that the reflections were measured up to θmax 25°,
practically the observed reflections were located below
θ 18°. The structure was solved by the direct method,
hydrogen atom coordinates were determined by
calculations. Disordered structure model was refined
by means of the full-matrix root mean square method
with the restrictions of C–C interatomic distances in
the butyl groups. For the consideration of the
disordering the split positions of copper and bromine
atoms were refined. Final diversion factor was R =
0.087, S = 0.9245. Comparatively high diversion factor
and high values of thermal parameters are due to the
weak scattering ability of the crystal which did not
permit the accounting for the disordering of the butyl
groups. Atomic coordinates and the equivalent thermal
parameters are presented in the table. General view of
molecule is shown in Fig. 1.
Coordinates of the symmetrically nonequivalent atoms of
molecule of the 1,4-bis(tributylphosphonio)buta-1,3-diene-
tribromocuprate
Atom
x/a
y/b
z/c
Ueq [Å2]
P
0.6710(2)
0.7064(5)
0.7350(5)
0.6801(6)
0.6836(2)
0.7126(5)
0.7375(4)
0.6873(6)
0.7879(4)
0.136(3)
C1
0.7379(13) 0.150(12)
0.7704(11) 0.101(10)
0.8963(14) 0.180(14)
0.9542(18) 0.34(3)
C2
C3
C4
0.6617(11) 0.6560(7)
C5
0.6513(8)
0.6878(7)
0.6217(7)
0.6131(9)
0.5699(9)
0.5558(8)
0.6824(7)
0.7228(7)
0.6764(8)
0.6545(9)
0.6995(7)
0.7441(7)
0.7440(8)
0.7868(7)
0.6293(6)
0.6097(10)
1.036(2)
0.44(5)
C6
1.0723(11) 0.26(2)
C7
0.7563(15) 0.193(14)
C8
0.773(2)
0.739(2)
0.759(2)
0.30(3)
0.33(3)
0.30(2)
C9
C10
C11
C12
C13
C14
Br1
Br2
Br3
Br3A
Br4
Br4A
Cu
0.7538(13) 0.180(13)
0.776(2)
0.727(2)
0.776(3)
1
0.29(2)
0.7255(11) 0.5704(10)
0.7623(15) 0.5568(10)
0.35(3)
0.49(5)
3/4
0.76793(7)
0.1177(12)
0.7448(13) 0.87219(10) 1.0193(15) 0.163(9)
0.6804(5)
0.6772(4)
0.6392(7)
0.6437(7)
0.8466(6)
0.8430(3)
0.7950(5)
0.7978(6)
0.8428(12) 0.268(9)
0.8300(8) 0.121(4)
X-ray studies showed that the positive charge on
phosphorus in this structure is compensated by the
complex [Cu2Br6]2– anions. Each of this anions is
surrounded by four molecules of 1,4-bis(butylphos-
phonio)buta-1,3-diene in such a manner that two
molecules coordinate the anion with two phosphorus
atoms, while another two only with one. In the
complex [Cu2Br6]2– anion two bromine atoms provide
the bond between two atoms of copper, and the
negative charge of anion is distributed obviously be-
tween the rest four ones. This conclusion is confirmed
by the fact that each of these bromine atoms is
surrounded by four atoms of phosphorus and is located
in one plane with them (Fig. 2).
1.0067(12) 0.174(7)
1.0248(12) 0.200(8)
0.70099(7) 0.82136(7)
0.96213
(13)
0.1224(11)
lapping of four double bonds of the phosphonium salt
with d-orbitals of two positively charged atoms of
phosphorus preventing the approach of halogenating
agent. In connection with that we have studied the
reaction of β,γ-unsaturated phosphonium salt, allyltri-
phenylphosphonium bromide VII, with the equimolar
amount of bromine in methanol. The process resulted
in the quantitative formation of the bromine-containing
complex VIII in the 1:1 ratio similarly to the above-
described case of the salt I.
By analogy with the salt V and its copper complex
VI it may be suggested that compounds III and IV
have the analogous structure.
Failure of the attempt of halogenation of the salts I
and V can be explained theoretically by partial over-
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2246
OVAKIMYAN et al.
Br2
Br3''
Br4
Cu
C14'
Cu''
C13'
C11'
C10
C5
Br3
Br1
Br4''
C8
C6
C12'
C1'
P
C3
C2'
C9
C7'
C4
C4'
C2
C3'
C9'
C7
P
C1
C8'
C6'
C11
C5'
C12
C10'
C14
C13
Fig. 1. Molecular structure of 1,4-bis(tributylphosphonio)buta-1,3-dienetribromocuprate (VI). Hydrogens and disordered atoms are
not shown for the sake of clarity. Symmetry codes i (1.5 – x, 1.5 – y, 1.5 – z); ii (1.5 – x, y, 2 – z).
As was expectable, compound VIII when heated
with styrene gave dibromostyrene and salt VII. The
latter one analogously to the salts I and V forms
copper complex, allyltriphenylphosphoniumtribromo-
cuprate IX. Unlike the complexes III, VI it is a black
viscous substance having the absorption band with the
maximum at ~300 nm characteristic of the complex
compounds.
While searching the reported data concerning
complexes of phosphonium salts with copper halides it
was found that analogous complexes formed by the
saturated phosphonium compounds were described in
[5, 6].
According to the preliminary data complexes III,
IV exhibit high bactericide activity, but regretfully at
the same time they are highly toxic.
EXPERIMENTAL
1H and 31P NMR spectra were taken on a Varian
1
Mercury-300 spectrometer (300.077 MHz for H) at
303 K. Chemical shifts were measured against internal
TMS. Starting salts I and V were prepared according
to the procedures [7, 8].
Fig. 2. Surrounding of the [Cu2Br6]2– polyanion with
phosphorus atoms. Butyl groups of the molecule are not
shown for the sake of clarity.
1,4-bis(Triphenylphosphonio)buta-1,3-diene di-
chloride–bromine (1:2) (II). To a solution of 2 g of
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α,β– AND β,γ-UNSATURATED PHOSPHONIUM SALTS IN REACTIONS
2247
salt I in 50 ml of chloroform 1 g of bromine was
added. The mixture obtained was stirred for 2 h and
left overnight. Chloroform was removed, and the
residue was thoroughly washed with anhydrous diethyl
ether and dried in a vacuum to give 3 g (100%) of the
yellowish orange crystalline substance II, mp 190°C.
1H NMR spectrum (CDCl3), δ, ppm (J, Hz): 7.80 m
filtered off, washed with the anhydrous diethyl ether
and dried in a vacuum to give 2.8 g (98.5%) of black
1
powder, mp 145–147°C . H NMR spectrum (DMSO-
d6), δ, ppm (J, Hz): 7.80 m [30H, (C6H5)3P+], 8.10
3
quintet (2H, P+CH=CH, JPH 21.6, JHH 14.7), 9.10 d.d
2
(2H, P+CH=, JPH 24.4, JHH 14.8). 31P NMR spectrum
(DMSO-d6), δP 23.9 ppm. Found, %: C 52.56; H 3.79;
Cl 23.27, P 6.81. C40H34Cl6Cu2P2. Calculated, %: C
52.40, H 3.71, Cl 23.25, P 6.77.
3
[30H, (C6H5)3P+]. 8.10 quintet (2H, P+CH=CH, JPH
2
21.6, JHH 14.7). 9.10 d.d (P+CH=, JPH 24.4, JHH 14.8).
31P NMR spectrum (CDCl3), δP 23.9 ppm. Found, %:
C 48.93, H 3.86, P 6.34. C40H34Br4Cl2P2. Calculated,
%: C 49.60, H 3.51, P 6.41.
1,4-bis(Tributylphosphonio)buta-1,3-dienedibro-
mocuprate (VI). To a solution of 2 g of the salt V in
15 ml of methanol a solution of 1.45 g of copper(II)
bromide in 50 ml of methanol was added. The
resulting mixture was stirred for 6 h and left for 24 h.
Methanol was removed, and the residue was
thoroughly washed with the anhydrous diethyl ether
and dried in a vacuum to give 3.45 g (100%) of black
crystalline substance, mp 192–194°C . UV spectrum
(MeOH), λmax, nm: 251, 300. Found, %: C 31.54, H
5.39, Br 45.18, Cu 11.91, P 5.72. C28H58Br6Cu2P2.
Calculated, %: C 31.61; H 5.45, Br 45.15, Cu 11.95, P
5.83.
1,4-bis(Triphenylphosphonio)buta1,3-dienedi-
chloride dibromocuprate (III). To a solution of 2 g
of salt I in 40 ml of methanol a solution of 1.4 g of
copper(II) bromide in 50 ml of methanol was added.
The resulting mixture was stirred for 2 h and left for
24 h. Methanol was removed, and the residue was
thoroughly washed with the anhydrous diethyl ether
and dried in a vacuum to give 3.4 g (100%) of black
crystalline substance, mp 243°C . 31P NMR spectrum
(DMSO), δP 23.9 ppm. Found, %: C 44.27, H 3.24, Cu
11.67, P 5.67. C40H34Br4Cl2Cu2P2. Calculated, %: C
43.91; H 3.10, Cu 11.71, P 5.67.
Allyltriphenylphosphonium bromide–bromine
(1:1) (VIII). To a solution of 1 g of salt VII in 20 ml
of methanol 0.42 g of bromine was added. The mixture
obtained was stirred for 3 h and left for 24 h. Methanol
was removed, the residue was thoroughly washed with
the anhydrous diethyl ether and dried in a vacuum to
give 1.4 g (98.5%) of yellow crystalline substance, mp
102–105°C . Found, %: C 46.52, H 3.75, Br 44.31, P
5.82. C21H20Br3P. Calculated, %: C 46.40, H 3.68, Br
44.19, P 5.71.
Reaction of 1,4-bis(triphenylphosphonio)buta-
1,3-dienedichloride dibromocuprate (III) with
aqueous ammonia. Compound III, 0.6 g, was treated
with 10 ml of 25% aqueous ammonia. The white
powder formed was filtered off, washed with the
anhydrous diethyl ether, and dried in a vacuum to give
0.35 g of 1,4-bis(triphenylphosphonio)butadiene di-
chloride I. Its spectral and physicochemical data
coincide with data for the authentic sample.
Allyltriphenylphosphonium tribromocuprate (IX).
To a solution of 0.5 g of salt VII in 20 ml of methanol
a solution of 0.29 g of copper(II) bromide in 15 ml of
methanol was added. The mixture obtained was boiled
with stirring for 4 h. Methanol was removed, the
residue washed with the anhydrous diethyl ether and
dried in a vacuum to give 0.79 g (100%) of the viscous
black mass. UV spectrum (MeOH) λmax 300 nm.
Found, %: C 41.38, H 3.31, Br 19.52, Cu 10.43, P
5.17. C21H20Br3CuP. Calculated, %: C 41.54, H 3.29,
Br 39.57, Cu 10.47, P 5.11.
Reaction of 1,4-bis(triphenylphosphonio)buta-
1,3-dienedichlotidedibromocuprate (III) with bro-
mine. A solution of 0.6 g of compound III in 30 ml of
methanol was treated with 0.176 g of bromine.
Resulting mixture was stirred for 4 h and left for 24 h.
The precipitate formed was separated, washed with
small amount of water, and dried over phosphorus
pentoxide to give 0.38 g (71%) of compound II. Its
spectral, physicochemical, and elemental analysis data
coincide with that of the sample obtained by the
reaction of the salt I with bromine.
Bromination of styrene with the compounds II,
III, and VIII. An equimolar mixture of the cor-
responding complex and styrene (in the case of
compound VIII two moles per one mol of styrene was
used) was refluxed in methanol for 10 h. Methanol was
removed, and the residue was washed with the
1,4-bis(Triphenylphosphonio)buta-1,3-dienetri-
chlorocuprate (IV). To a solution of 2 g of the salt I
in 15 ml of methanol 0.85 g of copper(II) chloride in
20 ml of methanol was added. The resulting mixture
was stirred for 48 h. The precipitate formed was
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OVAKIMYAN et al.
4. Sheldrick, G.M., SHELXL97 and SHELXL97, Program
for the Refinement of Crystal Structure, Gottingen
University, Gottingen (Germany), 1997.
anhydrous diethyl ether. Ether extracts were joined,
ether was removed, and the residue was dried in a
vacuum. In all the cases styrene dibromide was
obtained in 95–97% yield, mp 70–74°C . No melting
point depression of the mixture with the authentic
sample was observed.
5. Hafiz, A.A., J. Iran Chem. Soc., 2008, vol. 5, no. 1,
p. 106.
6. Tawfik, A.M., Synthesis and Reactivity in Inorganic,
Metal-Organic, and Nano-Metal Chemistry, 1992,
vol. 22, issue 2, p. 161.
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