Dismutation of diamidoarylphosphites

Article abstract of DOI:10.1080/714040960

Some examples of spontaneous dismutation of diamidoarylphosphites in different solvents were studied, and features of the process were revealed.

Full text of DOI:10.1080/714040960

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Phosphorus, Sulfur, and Silicon and the Related
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Dismutation of Diamidoarylphosphites
Edward E. Nifantyev a , Elena N. Rasadkina a , Pavel V. Slitikov a & Larisa K. Vasyanina a
a Moscow Pedagogical State University, Moscow, Russia
Available online: 18 Jun 2010
To cite this article: Edward E. Nifantyev, Elena N. Rasadkina, Pavel V. Slitikov & Larisa K. Vasyanina (2003): Dismutation of
Diamidoarylphosphites, Phosphorus, Sulfur, and Silicon and the Related Elements, 178:11, 2465-2477
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Phosphorus, Sulfur, and Silicon, 178:2465–2477, 2003
ꢀC
Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500390235578
DISMUTATION OF DIAMIDOARYLPHOSPHITES
Edward E. Nifantyev, Elena N. Rasadkina, Pavel V. Slitikov,
and Larisa K. Vasyanina
Moscow Pedagogical State University, Moscow, Russia
(Received May 6, 2003; accepted June 12, 2003)
Some examples of spontaneous dismutation of diamidoarylphosphites
in different solvents were studied, and features of the process were
revealed.
Keywords: Diamidoarylphosphites; dismutation; equilibrium; process
features
We studied the phosphorylation of aromatic diols with neutral amides
of phosphorous acid and noted a spontaneous transformation of the re-
sulting diamidoarylphosphites to cyclo(bis-amidoarylphosphites) with
the release of phosphorous acid triamides at room temperature.1,2
SCHEME 1
In fact, this is dismutation, a spontaneous irreversible process, which
proceeds without change in the valence of phosphorus.
Transition processes with the participation of identical molecules
of trivalent phosphorus derivatives have been known since long ago.
They can have unexpected results. Most of them proceed with a change
in the coordination of the phosphorus atom3−5 and require heating,
catalyst, or irradiation. The possibility of exchange processes between
molecules with similar substituents is noteworthy. In the P(OPh)3–
P(NEt2)3 system, two weeks after the starting reagents were mixed
The work was supported by the Foundation “Russian Universities” (grant no. 990
986).
Address correspondence to Edward E. Nifantyev, 26 Baku Komissarov, 12-3, Flat 60,
Moscow 117526, Russia.
2465

2466
E. E. Nifantyev et al.
at 25◦C, four compounds—P(OPh)3, PhOP(NEt2)2, (PhO)2PNEt2, and
P(NEt2)3—were detected by 31P NMR spectroscopy at a molar ratio of
5:7:9:6, which did almost not change for 8.5 months.6 Thus, sponta-
neous exchange of acceptor substituents at the trivalent phosphorus
atom is a real process. Unfortunately, features of these processes and
their motive forces were not discussed in the literature.
RESULTS AND DISCUSSION
Based on the aforesaid, we began the study of reasons and main fea-
tures of dismutation with simplest diamidoarylphosphites in order to
trace the effects of solvent, reagent concentrations, the structure of
aromatic substituent, and the character of amide function in the initial
compounds on the process studied. The first stage included the study
of behavior of the following diamidoarylphosphites:
SCHEME 2
The reaction was performed in solutions at room temperature be-
cause it was shown in preliminary experiments that the reaction does

Diamidoarylphosphites
2467
not occur in block and that a rise in temperature (≤90◦) has no effect
on the rate of the process.
The reaction was monitored with 31P NMR spectroscopy, by the de-
crease in signal intensities in the range of 127–132 ppm typical for
diamidoesters and by the accumulation of signals in the ranges of 136–
147 ppm (typical for amidodiesters) and 115–122 ppm (typical for phos-
phorous triamides). The reaction was considered gone to completion
(complete dismutation) when the signal from the initial diamidoester
completely disappeared from the 31P NMR spectrum. Note that, in some
experiments, we observed only partial exchange of substituents and
equilibrium established between the initial diamidoesters (1–8) and
the resulting amidodiesters (1ꢀ–8ꢀ) and triamides.
SCHEME 3
Amidodiesters 1ꢀ–8ꢀ were identified by 31P NMR spectroscopy in the
reaction mixture because of isolation problems. However, thionophos-
phates (1ꢀꢀc, 1ꢀꢀd, 1ꢀꢀf, 1ꢀꢀg, 6ꢀꢀb, 7ꢀꢀa,f, 8ꢀꢀb) were obtained in some cases,
which were isolated by column chromatography and characterized.
SCHEME 4
It also should be noted that the resulting diarylamidoalkylphosphites
1ꢀ–8ꢀ are not subjected to further dismutation.
It is important that the nature of solvent is a factor that can be used
for the regulation of dismutation rate (Tables I and II).
For phenyl derivatives, it was noted that the highest transition rate
of diamidoesters 1 to monoamidodiesters 1ꢀ is observed in methylene
chloride, benzene, and diethyl ether; the lowest rate is observed in
1,4-dioxane. An exception is provided by dipiperidyl and dimorpholi-
dophenyl phosphites 1d and 1e, whose dismutation rate is maximal
in dioxane and minimal in methylene chloride. We believe that this
is related to the structural correspondence of 1,4-dioxane with the

2468
E. E. Nifantyev et al.
TABLE I The Complete Dismutation Time of Diethylamidoarylphosphites
1b–8b in Different Solvents at Room Temperature (days)
No.
CH3CN
CH2Cl2
1,4-Dioxane
C6H6
(C2H5)2O
C6H14
1b
2b
3b
4b
5b
6b
7b
8b
45
—
—
90
—
48
44
74
62
—
180
76
68
130
—
27
44
25
—
—
—
—
23
40
88
32
—
—
—
—
150
80
a
—
Equilibrium
—
18
Equilibrium
175
35
Equilibriumb
Equilibrium
Equilibrium
Equilibrium
Equilibrium Equilibrium
68 Equilibrium
20
aNo dismutation is observed.
bEquilibrium is a stable state of the system established at a specific reagent ratio
(usually, diesteroamidophosphite:esterodiamidophosphite = 1:4).
piperidyl and morpholine fragments of the molecule. In the case of
para-substituted phenyl phosphites 2–5, dismutation is observed only
in methylene chloride and dioxane; it does not occur in other solvents
(except for 4b). This is probably determined by the effect of substituents,
i.e., by the shift of electron density on the benzene ring, which hampers
the polarization of the “working” P O and P N bonds in this case. In
chloro and bromo derivatives 4b and 5b, the electron density is pulled
away from the ester oxygen included in the conjugation of the aromatic
fragment, which in turn affects the pπ -dπ interactions in the amide
fragment and its stability. In the methyl derivative 2b, the effect is en-
hanced by hyperconjugation, which leads to an opposite result in the
aromatic fragment and finally enhances the pπ -dπ conjugation of the
amide function. This results in the deactivation of the molecule during
dismutation. Methylene chloride and dioxane most probably exert a di-
rected solvating action and thus decrease the conjugation effects and
make dismutation most possible. In the case of reagent 3b, which has a
bulky substituent in the para position of the aromatic ring with respect
to oxygen, both a strong +J effect and a steric factor are essential. As
TABLE II The Complete Dismutation Time of Phenyldiamidophosphites
1a,b,d,e in Different Solvents at Room Temperature (days)
No.
CH3CN
CH2Cl2
1,4-Dioxane
C6H6
(C2H5)2O
C6H14
1a
1b
1d
1e
Equilibrium
37
48
100
130
130
130
39
60
25
100
56
37
40
66
88
—
89
45
40
Equilibrium
Equilibrium
Equilibrium
20

Diamidoarylphosphites
2469
a result, molecules cannot approach each other closely, and almost no
dismutation is observed.
For naphthalene derivatives 7 and 8, the higher transition rate is
observed in methylene chloride, and the lowest rate in diethyl ether
and acetonitrile (an equilibrium is established). It should be noted that
β-naphthol derivatives are dismutated better and more rapidly than α-
naphthol derivatives. We attribute this to the different arrangements
of aromatic fragments with respect to the phosphorus unit.
It also was interesting to trace how the rupture of conjugation be-
tween the benzene ring and the phosphorus unit affects the process rate.
For this purpose, we used derivatives 6 with a benzyl radical at the oxy-
gen atom. It was shown that the dismutation of benzyl derivatives, if
any, is extremely slow compared to the reagents considered above. The
highest rate is attained in methylene chloride, but it decreases in the
sequence: phenyl > naphthyl > benzyl.
The study of the effect of amide substituents on the dismutation rate
showed that the highest transition rate is observed for compounds with
aliphatic amide substituents (methyl, ethyl, and isopropyl) (1a–c) and
usually in polar solvents. Heterocyclic amides (piperidyl and morpholyl)
(d, e) are dismutated more slowly, regardless of the ester component.
When reagents containing an aromatic amide component are used,
dismutation probably follows another scheme:
SCHEME 5
This direction of the reaction is well observed in 31P NMR spectra.
Along with the signals from the resulting diesteroamides, a signal of
similar integral intensity appeared in the region of triesters (130 ppm)
some time after the beginning of the reaction. The first direction fol-
lows the scheme considered above. The second direction, in our opinion,

2470
E. E. Nifantyev et al.
TABLE III The Dismutation Time (days) of
Tetraethyldiamide of Phosphorous Acid Phenyl Ester 1b as
Depending on its Molar Concentration in Different Solvents
Solvent
<1.5 M
1.5 M–3 M
>3
CH3CN
CH2Cl2
1,4-Dioxane
C6H6
90
29
145
45
48
130
25
—
16
190
77
Equilibrium
Equilibrium
Et2O
Equilibrium
40
includes the interaction between diesteroamide accumulated in the
course of reaction and the initial diamidoester. This is probably related
to the fact that the ester and amide fragments containing aromatic
substituents have similar departure rates. It should be noted that no
complete dismutation was observed in this case.
The study of the effect of reagent concentrations showed that the
process rate attains maximal values when the initial diamidophos-
phite concentration is between 0.15 and 3 M. Beyond this concentration
range, the dismutation rate decreases in all solvents, except methylene
chloride (where the reaction rate increases abruptly (Table III).
We believe that the presence of an aromatic fragment in the molecule
is one of the key factors inducing this type of transition. When the
phenyl group in the initial compound is substituted by cyclohexyl, no
transition is observed either in block, in solution, or under heating.
Based on the foregoing, we suppose the following scheme for the
dismutation of dialkylamidoarylphosphites:
SCHEME 6

Diamidoarylphosphites
2471
In solution, two molecules approach each other by aromatic frag-
ments under the effect of attraction and form a molecular associate
due to the stacking interaction. It is known that stacking interactions
are most frequent in monosubstituted phenols.7 The approach of aro-
matic fragments entails an approach of phosphorus units, i.e., of amide
fragments. At some time, two of these fragments can be arranged in
the same plane, which creates conditions for the redistribution of elec-
tron density to form new bonds and, hence, reaction products. It should
be noted that stacking interaction plays a part in the initial approach
of molecules. Solvent is also essential for this process. It is capable to
enhance (methylene chloride and 1,4-dixane) or weaken the stacking
interaction due to solvation and polarization. However, stacking inter-
action in the resulting diarylamidophosphite is weakened because of
its low energy (0–50 kJ/mol),7 and aromatic nuclei are separated.
Stacking interaction can also be responsible for the effect of reagent
concentrations on the process rate. The formation of an associate, which
can be considered as an important factor of the process, requires an op-
timal distribution of substance molecules among the solvent molecules.
Thus, an increase in the concentration of the initial diamidoester de-
creases the possibility of its complete solvation. On the other hand,
when the diamidoester concentration decreases significantly, the dis-
tance between its molecules increases and molecular associates cannot
be formed.
In these terms, it is clear that the dismutation of para-substituted
phenols is usually hampered and the presence of an aromatic amide
fragment changes the process pathway. It is evident that, along with
the conjugation effects, steric factors also contribute.
As was shown previously in the literature,6 diphenyldiethylami-
dophosphite is more stable than tetraethyldiamidophenylphosphite. We
confirmed this fact during the optimization of the geometry of these
molecules and the computations of their steric energies in the gas phase
using the MM2 program.8 We also performed similar computations for
all synthesized compounds and showed that the steric effects for com-
pounds 1–8 are higher than those for compounds 1ꢀ–8ꢀ . An exception is
provided by cyclohexyl derivatives (9), for which an opposite situation
is observed. Therefore, no dismutation occurs for these compounds, as
was noted above. Results of calculations are given in Table IV.
On generalizing the results obtained, it can be noted that the dis-
mutation of diamidoarylphosphites is a complex multicomponent pro-
cess, which depends on the structural and electron parameters of sub-
stituents at the phosphorus atom, polarity and polarizing capacity of
solvents, and concentration parameters. The study of the process con-
tinues, and we would attract attention of colleagues, because many of us

2472
E. E. Nifantyev et al.
TABLE IV Calculated Steric Energies for Compounds 1b–9b, 1ꢀb–9ꢀb, 1a–f,
1ꢀa–f
E steric,
kcal/mol
E steric,
kcal/mol
E steric,
kcal/mol
E steric,
kcal/mol
No.
No.
No.
No.
1b
2b
3b
4b
5b
6b
7b
8b
9b
12.7
14.6
18.9
14.4
20.6
18.0
16.0
11.3
25.8
1ꢀꢀb
2ꢀꢀb
3ꢀꢀb
4ꢀb
5ꢀb
6ꢀb
7ꢀb
8ꢀb
9ꢀb
4.0
11.0
15.3
10.6
5.9
1a
1b
1c
1d
1e
1f
7.2
12.7
26.8
16.7
21.0
4.6
1ꢀa
1ꢀb
1ꢀc
1ꢀd
1ꢀe
1ꢀf
0.82
4.0
14.2
12.9
14.9
3.4
7.4
−6.8
−6.4
35.6
work with similar unsymmetrical systems capable to dismutate under
specific conditions.
EXPERIMENTAL
All syntheses were conducted in dry solvents under a dry nitrogen at-
mosphere. Reactions were monitored by 31P NMR spectroscopy.
1H NMR spectra were recorded in CDCl3 on a Bruker AC-200
(200 MHz). 31P NMR spectra were recorded on a Bruker WP-80SY
(32.4 MHz) against 85% H3PO4.
Column adsorption chromatography was operated on silica gel L
100/250; TLC was performed on Silufol plates using (A) hexane:dioxane
(5:1) and (B) benzene:dioxane (5:1) systems as eluents. Detection was
achieved using iodine vapor treatment and calcination. Reaction solu-
tions were filtered through freshly calcinated alumina according to the
Brockman II procedure (d = 3.5 cm; h = 1 cm).
Dichloroanhydrides of phosphorous acid aryl esters were synthesized
by the peocedure, introduced by Tolkmith9 neutral amides were syn-
thesized by the method, introduced by Michaelis10 phosphorous acid
diamidoesters 1–8 (a,b) were synthesized by the method introduced by
Petrov et al. and Bloshin et al.11,12
Diamidoarylphosphites
Amide Method (General Procedure) (1–8 a,b)
The initial aromatic alcohol (0.1 mmol) in 20 ml of dry dioxane was
added to 0.3 mmol of phosphorous triamide. The mixture was stirred
at room temperature and left to stand for 36 h. The resulting diamine,
solvent, and excess of the initial triamide were removed in vacuo; the

2473

2474

Diamidoarylphosphites
2475
residue was distilled in vacuo (1 mm Hg) or passed through an Al2O3
column and dried (70◦C, 2 mm Hg).
Chloroanhydride Method (General Procedure) (1c–g,
6–8c–f, 2, 4, 5b,d)
A solution of 0.25 mmol of dichloroarylphosphite in 20 ml of dry
hexane was added to 1 mmol of dry amine in 50 ml of dry hexane (or
benzene) under intensive stirring and cooling to 0◦C. After the phos-
phorylating agent was added, cooling was removed and the reaction
mixture was stirred for 3 h and left to stand overnight. The resulting
solution was filtered through an Al2O3 layer; solvent was evaporated
in vacuo (15 mm Hg), and the residue was dried (70◦C, 2 mm Hg).
Physicochemical and spectral parameters of the initial amidodi-
arylphosphites phosphorous diamidoesters (1–8) are given in Table V.
Dismutation Procedure
Diamidoarylphosphite 1–8 (0.2 ml) was placed in an ampoule, and 1.2–
1.5 ml of dry solvent was added. The ampoule was sealed, and 31P NMR
spectra were recorded in specified time intervals. The reaction was con-
sidered terminated when the signal from the initial diamidoarylphos-
phite disappeared completely.
Physicochemical and spectral parameters of amidodiarylphosphites
(1ꢀ–8ꢀ) are given in Table VI.
TABLE VI Physicochemical and Spectral Parameters of
Amidodiarylphosphites (1ꢀ–8ꢀ)
Compound no.
Rf (eluent)
31P-NMR, δ, ppm. (solvent)
1ꢀa
1ꢀb
1ꢀc
1ꢀd
1ꢀe
1ꢀf
0.56 (A), 0.88 (B) 139.09 (C6H6), 140.22 (CH3CN)
0.52 (A), 0.89 (B) 140.77 (Et2O), 141.4 (CH2Cl2)
0.6 (A)
142.31 (C6H6)
0.57 (A), 0.88 (B) 136.46 (C6H6)
0.42 (A), 0.56 (B) 135.42 (C6H12), 136.45 (CH3CN)
—
0.68 (A)
0.6 (A)
0.71 (A)
0.7 (A), 0.82 (B)
0.71 (A)
—
0.53 (A)
0.5 (A)
134.94 (C6H12), 135.47 (CH2Cl2)
141.56 (CH2Cl2)
140.58 (C6H12), 141.01 (C4H8O2)
141.79 (CH3CN)
135.35 (C6H12), 137.31 (CH3CN)
141.31 (Et2O)
147.79 (CH3CN), 148.23 (CH2Cl2)
139.9 (C6H6), 140.89 (CH3CN)
135.09 (C6H12), 136.41 (CH3CN)
140.32 (C6H12), 141.32 (CH3CN)
2ꢀb
3ꢀb
4ꢀb
4ꢀd
5ꢀb
6ꢀb
7ꢀb
7ꢀd
8ꢀb
0.5 (A), 0.87 (B)

2476
E. E. Nifantyev et al.
TABLE VII Physicochemical and Spectral Parameters of
Amidodiaryltionphosphates (1ꢀꢁ–8ꢀꢀ)
Compound
31P-NMR, δ,
ppm. (solvent)
no.
Rf (eluent)
1H-NMR, δ, ppm (J, Hz) (CDCl3)
1ꢀꢀd
0.7 (A), 5 0.65 (B) 1.61 m (6H, CH2, 3JHH 6.21), 3.47 m 65.13 (CH2Cl2)
(4H, CH2, 3JPH 11.14), 7.27 d (4H,
CH), 7.35 t (6H, CH)
1ꢀꢀf
0.59 (A)
0.55 (A)
2.77 s (3H, CH3), 6.75–7.8 m (5H,
Ar)
61.09 (CH2Cl2)
59.59 (C6H6)
N
1ꢀꢀg
6.94 t (2H, O Ar, 3JHH 7.32), 7.07 t
(4H, O-Ar, 3JHH 7.33), 7.13 d (4H,
O-Ar), 7.16–7.4 m (10H, N Ar)
1.12 t (6H, CH3, 3JHH 6.95), 3.49 m
(4H, CH2), 5.37 d (4H, CH2, 3JHH
9.35), 7.3 d (4H, CH), 7.38 t (6H,
CH)
6ꢀꢀb
0.59 (A)
66.68 (CH2Cl2)
7ꢀꢀf
0.43 (A)
0.71 (A)
2.73 s (3H, CH3), 6.72–7.74 m (5H,
62.45 (CH2Cl2)
N
Ar), 7.65–7.81 m (12H, O-Ar)
8ꢀꢀb
1.24 t (6H, CH3, 3JHH 7.15), 3.57 m
(4H, CH2, 3JPH 13.75), 7.5–7.85 m
(12H, CH)
66.74 (CH3CN),
67.44 (CH2Cl2)
Thionophosphoric Acid Amidodiesters (1ꢀꢀ–8ꢀꢀ)
The calculated amount of sulfur was added to the reaction mixture of
amidodiester and triamide obtained after the dismutation. The reaction
mixture was heated at 70◦C for 40 h and filtered; solvent was removed
in vacuo, and the residue was subjected to column chromatography.
Physicochemical and spectral parameters of thionophosphates (1ꢀꢀ–
8ꢀꢀ) are given in Table VII.
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Diamidoarylphosphites
2477
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