Free-radical addition of phosphine to vinyl ethers: Atom-economic synthesis of tris(2-organyloxyethyl)phosphines and their derivatives

Article abstract of DOI:10.1016/j.mencom.2011.01.007

Phosphine, generated from red phosphorus in the system KOH-H ₂O-toluene, reacts with vinyl ethers under radical initiation (AIBN, dioxane, 78-80 °C, atmospheric pressure) to give tris(2-organyloxyethyl) phosphines, which are transformed to the

Full text of DOI:10.1016/j.mencom.2011.01.007

Mendeleev
Communications
Mendeleev Commun., 2011, 21, 17–18
Free-radical addition of phosphine to vinyl ethers: atom-economic
synthesis of tris(2-organyloxyethyl)phosphines and their derivatives
Nina K. Gusarova, Svetlana I. Verkhoturova, Tatyana I. Kazantseva,
Valentina L. Mikhailenko, Svetlana N. Arbuzova and Boris A. Trofimov*
A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences,
664033 Irkutsk, Russian Federation. Fax: +7 3952 41 9346; e-mail: boris_trofimov@irioch.irk.ru
DOI: 10.1016/j.mencom.2011.01.007
Phosphine, generated from red phosphorus in the system KOH–H2O–toluene, reacts with vinyl ethers under radical initiation (AIBN,
dioxane, 78–80°C, atmospheric pressure) to give tris(2-organyloxyethyl)phosphines, which are transformed to the corresponding
phosphine chalcogenides (in up to 73% isolated yield) via the reactions with air oxygen, elemental sulfur or selenium.
Organic phosphines and phosphine chalcogenides are widely
used in the synthesis of metal complexes,1 extractants of noble,
rare-earth and transuranic elements,2 precursors and special
solvents for the preparation of conductive nanomaterials,3 flame
retardants4 and building blocks for the design of diverse organo-
phosphorus compounds.5 Currently, a particular emphasis is
placed on functional phosphines and phosphine chalcogenides.
For instance, phosphines bearing ether moieties6 are effective
chelating ligands for the design of metal complex catalysts which
are used for ring-opening metathesis polymerization of norbor-
nene,7 carbonylation of methanol,8 hydroformylation of styrene.9
A conventional method for synthesis of such functional phos-
phines is based on the reaction of alkali metal phosphides with
1,2-chlororganyloxyethanes.7–10
The most convenient, atom-economic and environmentally
benign approach to such compounds is addition of PH reactants11
to vinyl ethers, that has been demonstrated on the example of
secondary phosphines and phosphine chalcogenides.12 Phosphine,
PH3, is one of the most available and efficient phosphinating
agents since a feasible method for its generation from elemental
phosphorus and potassium hydroxide in aqueous-organic sys-
tems has been developed.13 This allowed one to carry out atom-
economic syntheses of primary, secondary and tertiary phosphines
(including functional and unsaturated), based on the addition of
phosphine to alkenes11,13 and acetylenes.11 At the same time, to
the best of our knowledge, there is only one publication14 reporting
that phosphine adds to butyl vinyl ether in the presence of AIBN
under heating in autoclave (33 atm) to give a mixture of primary,
secondary and tertiary phosphines.
Table 1 Reaction of PH3 with vinyl ethers.
RO
X
Pred
RO
OR
OR
KOH / H2O toluene
OR
1a–c
P
P
Xn
PH3 / H2
AIBN,
dioxane
78–80 °C
OR
OR
2a–c
3–7
Phosphine
Entry CH2=CH–OR
R
Phosphinea
X
chalcogenide,
yieldb (%)
1
2
3
4
5
1a
1b
1b
1b
1c
C7H15
Ph
Ph
2a
2b
2b
2b
2c
O
O
S
3, 36c
4, 60
5, 73
Ph
Se 6, 56
O 7, 54
1-naphthyl
aIdentified in the reaction mixture by 31P NMR. bYield of isolated product.
cAlong with phosphine oxide 3, the product contains small amount of bis-
(2-heptyloxyethyl)phosphine oxide (yield, 5%).
Pred
PhO
KOH / H2O toluene
Me
OPh
1b
MeI
I–
P
PH3 / H2
2b
AIBN,
dioxane
78–80 °C
20–22 °C
OPh
8
Scheme 1
Here we report on the convenient atom-economic synthesis of
tertiary phosphines (isolated as the corresponding phosphine
chalcogenides or phosphonium salts) based on radical addition
of phosphine to vinyl ethers under atmospheric pressure. The
reaction proceeds upon passing phosphine, generated as a phos-
phine–hydrogen mixture from red phosphorus and potassium
hydroxide in aqueous-toluene medium,13 through a solution of
vinyl ethers 1a–c in dioxane heated to 78–80°C in the presence
of AIBN. To achieve the complete organyloxyethylation of phos-
phine, vinyl ethers are introduced into the reaction vessel by two
portions: the first one (two thirds) is placed into the flask at the
initial reaction stage, while the remaining portion is added after
the phosphine feeding is stopped. Under these conditions,† the
major reaction products are the corresponding tris(2-organyl-
oxyethyl)phosphines 2a–c (identified in the reaction mixture by
†
The 1H, 31P and 77Se NMR spectra were recorded on a Bruker DPX 400
spectrometer (400.13, 161.98 and 76.31 MHz, respectively). The yields
were calculated with an allowance for the conversion of the vinyl ether.
The phosphine–hydrogen mixture (PH3 / H2, ~1:1) was generated13 in a
separate flask by dropwise addition of 50% aqueous solution of KOH
(150 g) to a mixture of red phosphorus (30 g) in 100 ml of toluene at
70–75°C. The gas mixture was passed through a washing bottle contain-
ing mixture of KOH (10 g), H2O (10 g) and 15 ml of DMSO (for sca-
venging of flammable diphosphine) and further through the reaction flask,
all connections of equipment were made gas-tight, the outlet of the reac-
tion flask was connected with two washing bottles containing aqueous
solutions of CuSO4 (to catch residual phosphine). Thus, only small
amounts of hazardous phosphine diluted with hydrogen was present in
the system at every moment, so the synthesis was safe.
© 2011 Mendeleev Communications. All rights reserved.
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Mendeleev Commun., 2011, 21, 17–18
the 31P NMR peaks at –40.3 to –38.5 ppm). The latter are trans-
formed by the reactions with air oxygen, elemental sulfur or
selenium to give tris(2-organyloxyethyl)phosphine chalcogenides
3–7 (Table 1).†
When iodomethane was used as a ‘trap’ for phosphine 2b,
methyl[tris(2-phenyloxyethyl)]phosphonium iodide 8 was ob-
tained in 61% yield (Scheme 1).†
Thus, the reaction of phosphine with vinyl ethers, proceeding
under mild conditions (atmospheric pressure, AIBN) represents
a convenient approach to the atom-economic synthesis of new func-
tional tertiary phosphines with an ether moiety and their deriva-
tives, prospective hemilabile ligands for metal complex catalysis.
Tris(2-organyloxyethyl)phosphines 2a–c (general procedure). A solu-
tion of AIBN (0.065 g) in dioxane (25 ml) contained in the reaction flask,
was blown with argon and saturated with phosphine–hydrogen mixture.
To the solution obtained, vinyl ether 1 (8.3 mmol) in 5 ml of dioxane was
added dropwise over 1 h at 78–80°C, while bubbling phosphine at a rate
of 15 ml min–1, with the following heating (78–80°C) of the reaction
mixture for additional 4 h upon passing phosphine. The phosphine feeding
was stopped, the system was blown with argon, then 0.033 g of AIBN was
introduced and a solution of vinyl ether 1 (4.2 mmol) in 3 ml of dioxane
was added dropwise over 10 min into the reaction mixture, which was
then stirred at 78–80°C for additional 2 h (for 1a), 1.5 h (for 1b) or 3 h
(for 1c). The reaction mixtures containing only or predominately tertiary
phosphines 2a–c (31P NMR data, d: –38.5, –39.8, –40.3, respectively)
were then used (without isolation) for the preparation of phosphine
chalcogenides 3–7 and phosphonium iodide 8.
This work was supported by the President of the Russian
Federation (grant no. NSH-3230.2010.3 for leading scientific
schools).
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Tris(2-organyloxyethyl)phosphine oxides 3–5 (general procedure). The
reaction mixture, containing phosphine 2, was blown with air and allowed
to stay for 2 days, then dioxane and unreacted vinyl ether were removed
under reduced pressure, the residue was washed with diethyl ether (1 ml)
and dried in vacuo.
Tris(2-heptyloxyethyl)phosphine oxide 3. A product (0.65 g), contain-
ing according to the 31P NMR, phosphine oxide 3 and bis(2-heptyloxy-
1
ethyl)phosphine oxide [dP 28.1 (d, JPH 462.2 Hz)] in the molar ratio
of 5:1 was obtained. Yields are 36% and 5%, respectively (conversion of
1
vinyl ether 1a is 80%), yellowish oil. H NMR (CDCl3) d: 0.87 (t, 9H,
Me, 3JHH 6.9 Hz), 1.19–1.50 (m, 30H, CH2), 2.04 (m, 6H, CH2P), 3.31
and 3.64 (2m, 12H, CH2O). 31P NMR (CDCl3) d: 46.9.
Tris(2-phenyloxyethyl)phosphine oxide 4. Yield 0.55 g (60%, conver-
sion of vinyl ether 1b is 53%), white powder, mp 139–140°C. 1H NMR
(CDCl3) d: 2.50 (m, 6H, CH2P), 4.43 (m, 6H, CH2O), 6.80–7.40 (m,
15H, Ph). 31P NMR (CDCl3) d: 44.9. Found (%): C, 70.52; H, 6.93;
P, 7.45. Calc. for C24H27O4P (%): C, 70.23; H, 6.63; P, 7.55.
Tris[2-(1-naphthyloxy)ethyl]phosphine oxide 5. Yield 0.33 g (54%, con-
version of vinyl ether 1c is 26%). A paraffin-like yellowish product. 1H NMR
(CDCl3) d: 2.77 (m, 6H, CH2P), 4.63 (m, 6H, CH2O), 6.77–8.26 (m,
21H, naphthyl). 31P NMR (CDCl3) d: 44.6. Found (%): C, 76.83; H, 5.90;
P, 5.81. Calc. for C36H33O4P (%): C, 77.13; H, 5.93; P, 5.52.
Tris(2-phenyloxyethyl)phosphine sulfide 6. To the reaction mixture,
containing phosphine 2b, a solution of 0.13 g (4.1 mmol) of elemental
sulfur in 2 ml of benzene was added and the mixture was stirred at ambient
temperature for 1.5 h, then the solvents and unreacted vinyl ether 1b (con-
version 44%) were removed under reduced pressure, the residue was
washed with ethanol (1 ml) and dried in vacuo to give a paraffin-like
yellowish product. Yield 0.57 g (73%). 1H NMR (CDCl3) d: 2.55 (m,
6H, CH2P), 4.42 (m, 6H, CH2O), 6.81–7.31 (m, 15H, Ph). 31P NMR
(CDCl3) d: 46.9. Found (%): C, 67.29; H, 6.25; P, 6.96; S, 7.81. Calc. for
C24H27O3PS (%): C, 67.59; H, 6.38; P, 7.26; S, 7.52.
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Tris(2-phenoxyethyl)phosphine selenide 7. To the reaction mixture
containing phosphine 2b, elemental selenium (0.33 g, 4.2 mmol) was
added and the mixture was stirred at 65–66°C for 2 h and left overnight.
Then unreacted selenium was filtered off, dioxane and unreacted vinyl
ether 1b (conversion 61%) were removed under reduced pressure, the
residue was washed with ethanol (1 ml) and dried in vacuo to afford a
yellowish oil.Yield 0.67 g (56%). 1H NMR (CDCl3) d: 2.69 (m, 6H, CH2P),
4.45 (m, 6H, CH2O), 6.80–7.38 (m, 15H, Ph). 31P NMR (CDCl3) d: 35.2.
77Se NMR (CDCl3) d: –392.2 (d, 1JSeP 723.7 Hz). Found (%): C, 60.79;
H, 5.95; P, 6.24; Se, 16.38. Calc. for C24H27O3PSe (%): C, 60.89; H, 5.75;
P, 6.54; Se, 16.68.
Methyl[tris(2-phenoxyethyl)]phosphonium iodide 8. To the reaction
mixture containing phosphine 2b, a solution of 1.2 g (8.45 mmol) of iodo-
methane in 5 ml of dioxane was added dropwise for 5 min and the mixture
was left overnight. Then dioxane and unreacted vinyl ether 1b (conversion
64%) were removed under reduced pressure, the residue was washed with
diethyl ether (1 ml) and dried in vacuo to afford a yellowish oil. Yield
0.87 g (61%). 1H NMR (CDCl3) d: 2.38 (d, 3H, Me, 2JHP 14.3 Hz), 3.37
(m, 6H, CH2P), 4.52 (m, 6H, CH2O), 6.81–7.37 (m, 15H, Ph). 31P NMR
(CDCl3) d: 33.2. Found (%): C, 56.18; H, 5.94; I, 23.81; P, 5.84. Calc. for
C25H30IO3P (%): C, 55.98; H, 5.64; I, 23.66; P, 5.77.
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Received: 8th July 2010; Com. 10/3562
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