STUDIES OF THE REACTIONS OF TRIAMINOPHOSPHINES WITH α,β-UNSATURATED NITRILES

Article abstract of DOI:10.1135/cccc19942109

Tris(dialkylamino)phosphines IIIa and IIIb react with furfurylidenemalonitrile (Ia) and its thiophene analogue Ib to give a mixture of 1:1 adducts IV and V.Compounds IV have aminophosphonium dipolar ion structure, while compounds V are the ylide forms.The ratio of the products depends on the reaction conditions.Some reactions of IV and V are described.

Full text of DOI:10.1135/cccc19942109

Short Communication
2109
STUDIES OF THE REACTION OF TRIAMINOPHOSPHINES
WITH α,β-UNSATURATED NITRILES
Ibtisam T. HENNAWY
National Research Centre, Dokki, Cairo, Egypt
Received July 27, 1993
Accepted February 26, 1994
Tris(dialkylamino)phosphines IIIa and IIIb react with furfurylidenemalonitrile (Ia) and its thiophene
analogue Ib to give a mixture of 1 : 1 adducts IV and V. Compounds IV have aminophosphonium
dipolar ion structure, while compounds V are the ylide forms. The ratio of the products depends on
the reaction conditions. Some reactions of IV and V are described.
As a continuation of the work1,2 on the reaction of trialkyl phosphites with α,β-unsatu-
rated nitriles I the present investigation was done to compare the behaviour of
tris(dialkylamino)phosphines (R N) P and trialkyl phosphites (RO) P toward the same
2
3
3
1
,2
species. It was shown that the phosphorus of the phosphites attacks the exocyclic
ethylenic bond in I to give the phosphonate 1 : 1 adducts II (Scheme 1).
Furfurylidenemalonitrile (Ia) or thienylidenemalonitrile (Ib) and tris(dimethyl-
amino)phosphine (IIIa) or tris(diethylamino)phosphine (IIIb) in mole ratio 1 : 3
yielded, after 6 h in refluxing benzene, a crude product which generally precipitated out
of the solution in ≈ 80% yield. The resulting adduct can be isolated by fractional crys-
tallization in two forms, one with ionic phosphorus (IV) in ≈ 43% yield, and the other
with C=P bond (V) in ≈ 28% yield. Compounds IV were obtained as water-sensitive,
red crystals, quite stable for 2 – 3 days. Compounds V, reddish brown crystals, were
SCHEME 1
Collect. Czech. Chem. Commun. (Vol. 59) (1994)

2
110
Hennawy:
formulated as methylenephosphoranes on the basis of spectral data presented below.
Evidently, the unsaturated nitrile underwent 1,2-addition at carbon, but the resulting
phosphonium betaine IV rearranged to the more stable ylide V (Scheme 2). Analogous
proton shifts have been observed in the reaction of triphenylphosphine with maleic
3
4,5
anhydride , and of triaminophosphines with activated double bonds .
The composition and structure of IV were determined by elemental and molecular
weight (MS) analyses. Also, their structure of phosphonium betaines is evident from
3
1
the NMR data (Tables I and II). The P NMR spectra have a high-field resonance
2
1
at δ ≈ 38 ppm, typical of sp -hybridized phosphorus. The H NMR spectrum of IVa
CD SOCD ) showed the exocyclic methine proton as a doublet at δ 4.08 ppm with a
(
3
3
2
rather large coupling constant ( J(H,P) = 24.5 Hz), which confirms the assigned struc-
ture IV and excludes the reverse addition product with a coupling constant in the range
≈
10 – 13 Hz. The six methyl groups attached to nitrogen gave one doublet at δ 2.58
SCHEME 2
Collect. Czech. Chem. Commun. (Vol. 59) (1994)

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2111
3
ppm, J(H,P) = 10.3 Hz, i.e., the three dimethylamino groups are magnetically equiva-
lent. The IR spectra of IV gave absorption bands at ≈ 2 210 (CN), ≈ 1 610 (C=C,
−
1
thiophene) and at 1 315 and 860 cm (P−N). On heating adducts IV above their melting
points under reduced pressure, they regenerated the starting materials I and III. But,
their refluxing in ethyl acetate for 3 h resulted in their rearrangement to give V, identi-
fied by melting points, mixed melting points and comparison of IR spectra.
On the other hand, structure of the isomeric by-products V is established by the
3
1
elemental and spectral analyses (Tables I and II). The P NMR shifts of V have, as
expected, more positive shifts (δ ≈ 63 ppm) than IV as the electronegativity of P atom
1
in V increased. H NMR data of compounds V indicate that C atom α to P bears no H,
3
since the methine proton appears as a doublet at δ ≈ 4.6 ( J(H,P) = 10 Hz). Moreover,
−1
V showed an IR absorption band at 1 385 cm corresponding to C=P. Isolation of two
stable forms, a dipolar ion with tetravalent phosphorus, and the other with pentacova-
TABLE I
Characteristic of compounds IV and V
Calculated/Found
+
M.p., °C
Yield,
%
Formula
(M.w.)
M
Compound
(
solvent)
m/z
%
C
% H % N
% P
% S
IVa
IVb
IVc
IVd
Va
205
45
53
44
48
28
22
23
18
C H N OP
54.71 7.22 22.79 10.07
54.60 7.12 22.72 10.12
–
307
391
323
407
307
391
323
407
1
4
22
5
(
(
(
(
(
(
(
(
CHCl3)
(307.4)
178
C H N OP
61.36 8.75 17.89 7.91
61.25 8.65 17.69 7.83
–
2
0
34
5
Me2CO)
(391.5)
165
C H N PS
51.99 6.86 21.66 9.58
51.78 6.69 21.76 9.62
9.91
9.76
1
4
22
5
Me2CO)
(323.4)
140
C H N PS
58.94 8.41 17.18 7.60
58.86 8.33 17.20 7.54
7.87
7.78
2
0
34
5
CHCl3)
(407.6)
245
C H N OP
54.71 7.22 22.79 10.07
54.65 7.15 22.71 10.14
–
1
4
22
5
EtOAc)
(307.4)
Vb
230
C H N OP
61.36 8.75 17.89 7.91
61.24 8.62 17.77 7.82
–
2
0
34
5
EtOAc)
(391.5)
Vc
192
C H N PS
51.99 6.86 21.66 9.58
51.82 6.81 21.55 9.62
9.91
9.82
1
4
22
5
CHCl3)
(323.4)
Vd
185
C H N PS
58.94 8.41 17.18 7.60
58.76 8.32 17.22 7.52
7.87
7.76
2
0
34
5
Me CO)
(407.6)
2
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112
Hennawy:
lent phosphorus, from a reaction of (R N) P with α-diketones was previously re-
2
3
6
,7
ported .
Effort was devoted to optimize the yields of the products of the reaction of nitriles I
with aminophosphine IIIa. Thus, the reaction of I and IIIa was carried out in several
solvents of different polarity (benzene, acetonitrile and ethyl acetate) maintaining the
general conditions as in the first experiment (Table III). From the data shown in
Table III, it is obvious that nitriles I react with aminophosphine IIIa in low-boiling
polar solvent to give preferentially the betaine species IV and diminish its conversion to
TABLE II
1
31
IR, H NMR and P NMR data for compounds IV and V
~
−1 a
1
b,c
IR (ν, cm )
H NMR (δ, ppm)
3
1
P
Compound
NMR
δ, ppm
CH N
3
C≡N
N−P
N=P
NCH2
HC−P
HC−CN
CH C
3
IVa
2 220 1 310,
60
–
38.64
2.58 d
–
4.08 d
–
3
1
J(H,P)
0.3
2
2
8
J(H,P) 24.5
IVb
IVc
IVd
Va
2 210 1 305,
75
–
–
–
38.25
42.73
42.84
1.37 t
3.37 q
4.20 d
–
–
–
3
8
J(H,P) 10.0 J(H,H) 6.0 J(H,P) 24.0
2 220 1 310,
65
2 220 1 325,
75
2.54 d
–
4.02 d
3
3
3
3
3
3
2
8
J(H,P) 10.5
J(H,P) 22.4
1.35 t
3.34 q
4.31 d
2
8
J(H,P) 11.2 J(H,H) 6.2 J(H,P) 21.8
2 215
2 210
2 220
2 215
–
–
–
–
1 385 64.20
1 380 64.28
1 390 65.50
1 380 63.57
2.47 d
–
–
–
–
–
4.83 d
3
3
3
3
J(H,P) 9.7
J(H,P) 9.7
Vb
1.31 t
3.25 q
4.6 d
J(H,P) 12.2 J(H,H) 6.2
J(H,P) 10.5
Vc
2.49 d
–
4.52 d
J(H,P) 9.5
J(H,P) 9.5
Vd
1.32 t
3.24 q
4.48 d
J(H,P) 10.2 J(H,H) 6.5
J(H,P) 10.2
a
−1
b
IR spectra also showed bands around 1 610 cm (C=C, furan or thiophene); coupling constant in
c
Hz; furan and thiophene, δ 6.4 – 7.8.
Collect. Czech. Chem. Commun. (Vol. 59) (1994)

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2113
the more stable form V. On the other hand, it was demonstrated that the use of a higher-
boiling solvent (even polar) leads to the predominance of the C=P form.
Exposure of IV or V to air or quenching the crude reaction products with water re-
sulted in their conversion to VI (Scheme 2). Hexamethylphosphortriamide was also
3
1
identified in solution, P NMR δ = +24 ppm. The structure assignment of VI is based
1
on molecular weight determination and H NMR spectrum (3.26 d, 2 H, J(H,H) = 8
(
CH ) and 3.91 t, 1 H, J(H,H) = 8 (CH)).
2
Moreover, IVa and/or Va could be converted into the stable phosphonium salt VIIa
by anhydrous hydrogen chloride in methylene chloride solution. The elemental analysis
3
1
showed that one mol HCl had combined with one mol IVa or Va. The P NMR shift of
4
31
VIIa (δ 52.5 ppm) is consistent with the fact that the P NMR resonances of triamino-
phosphine ylides occur, in contrast to triphenylphosphine ylides, at higher magnetic
fields than the resonance of corresponding phosphonium betaines or phosphonium salts.
1
H NMR spectrum of VIIa is also in accordance with the assigned structure. It shows
2
the exocyclic protons (2 H) as two doublets: CH α to P is centered at δ 4.2 ( J(H,P) =
2
3
3.5 Hz), while CH β to P is centered at δ 4.55 ppm ( J(H,P) = 10.5 Hz).
Furthermore, we have also investigated whether V would undergo reaction with
8
benzaldehyde in the Wittig reaction . Such a reaction would be expected to lead to the
formation of hexamethylphosphortriamide and an alkene. Indeed, when a mixture of Va
3
1
and benzaldehyde was heated in ethyl acetate for 8 h, P NMR spectroscopy indicated
the formation of P=O (δ = +24 ppm) and the olefinic product VIII was isolated. Its
1
structure assignment is based on mass, infrared and H NMR data. Compound VIII had
+
the molecular formula C H N O and m/z = 234 (M ). Its IR spectrum showed a new
1
5
10
2
−1
band at 1 618 cm corresponding to C=C. Also, it had absorption bands at 2 230 (CN)
and 1 600 (arom.) cm . Its H NMR spectrum (CDCl ) had signals at δ 4.05 d, 1 H,
−1
1
3
TABLE III
Yields of compounds IV and V in the reaction of nitriles I with tris(dimethylamino)phosphine (IIIa)
Yield, %
Compound
Solvent
Time, h
IV
V
Ia
Ia
Ia
Ib
Ib
Ib
Benzene
CH3CN
EtOAc
6
10
5
43
65
–
28
10
75
25
12
78
Benzene
CH3CN
EtOAc
6
40
60
–
10
5
Collect. Czech. Chem. Commun. (Vol. 59) (1994)

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114
Hennawy:
J(H,H) = 4 (CHCN); 5.65 d, 1 H, J(H,H) = 4 (=CH−Ar); 6.2 – 8.15 m, 9 H (furan and
arom.).
Summarizing, it seems clear that the relative stability of compounds with quintuply
and quadruply bonded phosphorus, obtained from the reaction of trivalent phosphorus
compounds, (RO) P or (R N) P with α,β-unsaturated nitriles may vary significantly
3
2
3
1
,2,7–11
with the structure of both reagents
. Moreover, we showed that additions of
triaminophosphines to activated double bond are readily accomplished whereby the
products can be treated in a variety of ways (thermolysis, hydrolysis, acidolysis and
Wittig reaction) which increases the synthetic use of the phosphorus reagents.
EXPERIMENTAL
~
−1
All melting points are uncorrected. The IR spectra (ν in cm ) were recorded in KBr pellets, using
1
Perkin–Elmer Infracord Spectrophotometer Model 197 (Grating). The H NMR spectra were
measured in CDCl on Varian Spectrometers at 90 MHz, using TMS as an internal reference; δ are
3
3
1
given in ppm, J in Hz; P NMR spectra were recorded with a Varian FT-80 Spectrometer (vs 85%
H PO ). The mass spectra were run at 70 eV on Kratos MS-50 equipment provided with a data sys-
3
4
tem. Elemental analyses were carried out at the microanalysis laboratory of National Research
Centre, Cairo. All the reactions were performed under nitrogen.
Reaction of α,β-Unsaturated Nitriles Ia, Ib with Triaminophosphines IIIa, IIIb. General Procedure
1
2
13
To a stirred suspension of nitrile Ia (ref. ) or Ib (ref. ) (0.01 mol) in dry benzene (30 ml) a solution
of IIIa or IIIb (0.015 mol) in 25 ml of benzene was added at room temperature and the reaction
mixture was refluxed for ≈ 6 h. Benzene was removed under reduced pressure and the residue was
triturated with boiling methylene chloride. Crystallization of the residue from suitable solvents af-
forded products V. Evaporation of CH Cl solution to dryness and crystallization of the residual sub-
2
2
stance from the proper solvent (see Table I) yielded compounds IV. For yields, melting points, and
physical and analytical data, see Table I. The reactions in acetonitrile or ethyl acetate were carried
out in the same way (Table III).
Thermal Treatment of IVa
Betaine IVa (0.2 g) was heated to 240 °C for one hour in a cold finger sublimator, under reduced
pressure (657 Pa). The reaction vessel was left to cool and ethanol (3 ml) was added. The crystals
which separated were recrystallized from ethanol to give nitrile Ia which was identified by melting
1
2
point, mixed melting point and comparison of the IR spectra .
Conversion of IVa into Va
A solution of IVa (0.2 g) was refluxed in ethyl acetate (25 ml) for 3 h. The reaction mixture was
evaporated to dryness and the residual substance was crystallized from chloroform to give Va (0.17 g,
8
6%), identified by melting point, mixed melting point, and comparison of the IR spectra.
Reaction of IVa or Va with Water
A solution containing IVa or Va (0.2 g) in benzene (4 ml) was added dropwise to water (20 ml) with
vigorous stirring. Removal of the volatile components under reduced pressure (60 °C, 2 105 Pa) gave
Collect. Czech. Chem. Commun. (Vol. 59) (1994)

Short Communication
2115
3
1
an oil which was shown to contain only hexamethylphosphortriamide ( P NMR δ = +24 ppm) and
VIa. The former was removed by distillation at 60 °C/0.657 Pa whereby the latter remained; yield 59 mg
(
62.3%), m.p. 62 – 64 °C (hexane). For C H N O (146.1) calculated: 65.75% C, 4.12% H, 19.17% N;
8 6 2
1
found: 65.55% C, 4.07% H, 19.03% N. IR spectrum (KBr): 2 225 (CN), 1 610 (C=C, furan). H NMR
spectrum (CDCl ): 3.26 d, 2 H, J(H,H) = 8 (CH ); 3.91 t, 1 H, J(H,H) = 8 (CH); 6.4 – 7.8 m, 3 H (furan).
3
2
+
Mass spectrum, m/z: 146 (M , 100%).
Reaction of Va with Hydrogen Chloride
A stirred suspension of Va in CH Cl (20 ml) was cooled to 0 – 5 °C and treated with anhydrous HCl
2
2
gas to saturation. The red solution became yellow; after 15 min the solvent was removed at 2 368 Pa.
The solid (224 mg, 90%) of the aminophosphonium salt VIIa was obtained, m.p. 183 °C (ethanol).
For C H ClN OP (343.8) calculated: 48.90% C, 6.74% H, 10.31% Cl, 20.37% N, 9.01% P; found:
1
4
23
5
1
4
8.86% C, 6.35% H, 10.08% Cl, 20.25% N, 9.27% P. H NMR spectrum (CDCl ): 4.2 dd, 1 H
J(H,P) = 23.5, J(H,H) = 13.5 (CH−P); 4.55 dd, 1 H, J(H,P) = 10.5, J(H,H) = 13.5 (C−CH); 6.4 – 7.8 m,
H (furan). P NMR spectrum (CDCl ): 52.5. Mass spectrum, m/z: 343 (M , 55%).
3
2
3
3
1
+
3
3
Wittig Reaction of Compound Va
A solution of Va (0.2 g) in ethyl acetate (25 ml) was heated under reflux with benzaldehyde (2 ml)
for 8 h. The precipitate formed on cooling was washed with cold benzene and then recrystallized
from benzene to give VIII (100 mg, 67%), m.p. 176 °C. For C H N O (234.3) calculated: 76.91% C,
1
5
10
2
4
.30% H, 11.96% N; found: 76.82% C, 4.18% H, 11.09% N. IR spectrum (KBr): 2 230 (CN), 1 618
1
(
C=C), 1 600 (arom.). H NMR spectrum (CDCl ): 4.05 d, 1 H, J(H,H) = 4 (CHCN); 5.65 d, 1 H,
3
+
J(H,H) = 4 (C=CH−Ph); 6.2 – 8.15 m, 9 H (furan and arom.). Mass spectrum, m/z: 234 (M , 100%).
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