Stoichiometry of the reaction of diphenylchlorophosphine with dimethylformamide in the presence of NaI

Article abstract of DOI:10.1134/S1070363210010123

Stoichiometric relations of initial compounds and reaction products in the synthesis of N,N-dialkyl-(diphenylphosphinomethylene)iminium are established; the second reaction product is diphenylphosphinic iodide. Bringing triphenylphosphine into the reaction increases the N,N- dialkyl(diphenylphosphinomethylene)-iminium yield approximately twice. One of the reaction intermediates is shown to be iododiphenylphosphine. The reaction can be regarded as disproportionation.

Full text of DOI:10.1134/S1070363210010123

ISSN 1070-3632, Russian Journal of General Chemistry, 2010, Vol. 80, No. 1, pp. 100–105. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © V.P. Morgalyuk, P.V. Petrovskii, K.A. Lysenko, E.E. Nifant’ev, 2010, published in Zhurnal Obshchei Khimii, 2010, Vol. 80, No. 1,
pp. 105–110.
Stoichiometry of the Reaction of Diphenylchlorophosphine
with Dimethylformamide in the Presence of NaI
V. P. Morgalyuk, P. V. Petrovskii, K. A. Lysenko, and E. E. Nifant’ev
Nesmeyanov Institute of Organoelemental Compounds, Russian Academy of Sciences,
ul. Vavilova 28, Moscow, 119991 Russia
fax: (+7495)1356549
e-mail: zaq@ineos.ac.ru
Received July 30, 2008
Abstract―Stoichiometric relations of initial compounds and reaction products in the synthesis of N,N-dialkyl-
(diphenylphosphinomethylene)iminium are established; the second reaction product is diphenylphosphinic
iodide. Bringing triphenylphosphine into the reaction increases the N,N-dialkyl(diphenylphosphinomethylene)-
iminium yield approximately twice. One of the reaction intermediates is shown to be iododiphenylphosphine.
The reaction can be regarded as disproportionation.
DOI: 10.1134/S1070363210010123
Functionalized phosphines and related phosph-
amides have not been sufficiently studied so far. Mean-
while, they are valuable objects for solving important
structural problems [1, 2] and developing organophos-
phorus synthesis [3–5], including the design of stable
aminophosphine carbene ligands for potentially cata-
lytically active metal complexes [5].
In course of the study we found that after the
completion of the reaction between chlorodiphenyl-
phosphine (I) and DMF (II) in the presence of NaI, the
31Р NMR spectra of the reaction mixture always
contained two signals of equal intensity. Besides the
signal of target N,N-dimethyl(diphenylphosphino-
methylene)iminium iodide (IIIa) in the spectral region
of negative chemical shift values (–3.4 ppm) always a
signal at 28 ppm appeared identified as corresponding
to diphenylphosphinic iodide Ph2P(O)I (IV) [7].
Similar pattern was observed in the reaction mixture
after the reaction of chlorodiphenylphosphine (I) with
other N,N-dialkylformamides. Unfortunately we failed
to isolate proper Ph2P(O)I (IV) from the reaction
mixture owing to its high reactivity. To prove the
presence of iodide IV in the reaction mixture, to the
filtrate after first precipitation of IIIa was added water
to hydrolyse the Ph2P(O)I. The precipitate thus
obtained actually belonged to diphenylphosphinic acid
Ph2P(O)ОН (V) formed at the hydrolysis of Ph2P(O)I
In the preceding communication [6] we showed that
the reaction of chlorodiphenylphosphine with N,N-
dialkylformamides in the presence of NaI affords N,N-
dialkyl(diphenylphosphinomethylene)iminium iodides:
O
Ph
R
N
C
P
Cl
+
R
H
Ph
I
II
I_
R
R
Ph
NaI
+
N
P
C
1
as showed the data of 31Р NMR spectroscopy [8], Н
Ph
H
IIIa_IIIc
NMR spectrum, and the melting point [9]. This ex-
periment confirms the presence of diphenylphosphinic
iodide (IV) in the reaction product. Thus, the studied
reaction can be described as shown in Scheme 1.
R = Me (IIIа), Et (IIIb), i-Pr (IIIc).
However, these compounds were obtained in 50%
or worse yield and the stoichiometric ratio of reagents
and reaction products was not established. We per-
formed a series of experiments to clear these problems.
Therefore per one mol of DMF involved in the
reaction 2 moles of chlorodiphenylphosphine (I) are
consumed, hence we can state that the reaction
100

STOICHIOMETRY OF THE REACTION OF DIPHENYLCHLOROPHOSPHINE
101
Scheme 1.
I _
N
H3C
H3C
Ph
Ph
Ph
O
I
O
Ph
CH3
CH3
Ph
Ph
NaI
+
+
+
2
P
Cl
P
N
C
P
C
H
H
Ph
I
II
IIIa
IV
O
Ph
Ph
O
+
P
P
H2O
OH
I
Ph
V
IV
Ph
Ph
stoichiometry (Ph2PCl/DMF ratio) is 2:1. This result
explains why the yields of target products IIIa–IIIc in
all cases were not higher than 50%.
NaI
NaCl
+
Cl
+
I
P
P
Ph
Ph
I
VI
The final compounds of the reaction contain
phosphorus atoms of different degree of oxidation,
therefore this rection formally can be assigned to the
disproportionation type. From the fact that the degree
of oxidation of phosphorus atom in the obtained
compound IIIa is lower than that in the parent
chlorodiphenylphosphine (I) while in the di-
phenylphosphinic iodide Ph2P(O)I (IV) it is higher
follows the involvement of redox processes in the
intermediate stages of the reaction.
The iododiphenylphosphine VI that was obtained in
93% purity (by 31Р spectrum) [10] was without a
purification brought into the reaction with DMF
(Scheme 2).
This reaction afforded the target product IIIa and
diphenylphosphinic iodide IV in 1:15 ratio (by the data
of 31Р NMR spectroscopy [7] of reaction mixture).
Hence we can state that the real compound reacting
with DMF is iododiphenylphosphine VI which
probably also plays a role of reducing agent and
therefore the yield of the final product could not
exceed 50%. Therefore it seemed interesting to add to
the reaction mixture another reducing agent to provide
a complete consumption of iododiphenylphosphine VI
for the formation of target compound IIIa.
Triphenylphosphine VII was chosen as reducer which
we introduced into the reaction in the amount
equimolar to chlorodiphenylphosphine I and NaI
(Scheme 3).
In the beginning of this work preliminary
experiments showed that chlorodiphenylphosphine did
not react with DMF directly at room temperature or at
heating to 60°C. Proceeding from this observation we
conclude that propably the real reagent reacting with
DMF is iododiphenylphosphine VI formed in situ from
chlorodiphenylphosphine I in the reaction mixture. To
confirm this assumption we synthesized iododiphenyl-
phosphine VI separately by the reaction of chlorodiphe-
nylphosphine with NaI in dioxane at room temperature:
Scheme 2.
Ph
I_
CH3
CH3
O
H
H3C
H3C
Ph
Ph
O
I
+
P
C
H
N
+
P
P
I
+
N
C
2
Ph
Ph
Ph
VI
II
IIIa
IV
Scheme 3.
I_
CH3
CH3
O
Ph
Ph
H3C
H3C
Ph
NaI
+
N
C
P
C
N
+ Ph3P
Ph3P
O
+
P
Cl +
Ph
H
H
I
II
VII
IIIa
VIII
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 1 2010

102
MORGALYUK et al.
In this case the 31Р NMR spectra of reaction
reaction mixture a white substance was isolated that by
1
mixture were analogous to those observed at the
synthesis of IIIa in the absence of triphenylphosphine
VII. The second signal at 29.5 ppm turned out to be
the signal of triphenylphosphine oxide VIII [11]
formed in the amount equal to that of the target
substance IIIa. Therewith, the yield of IIIa increased
approximately twice. We conclude that in this case the
reaction stoichiometry also corresponds to the ratio of
the reagents Ph2PCl : DMF : Ph3P equal to 1:1:1. From
the filtrate after separation of compound IIIa from the
the data of 31Р [11] and Н NMR spectroscopy and by
melting point [12] corresponded to triphenylphosphine
oxide VIII obtained in 81% yield. Thus, at the use of
triphenylphosphine VII as a reducer, no iododi-
phenylphosphine I is consumed in the reduction, and it
is completely converted into the target compound IIIa.
To confirm that the addition of triphenylphosphine VII
always resulted in the increased yield we synthesized a
series of compounds by analogous procedure without
and with triphenylphosphine VII:
I_
R
R
Ph
O
O
Ph
Ph
NaI
+
2
P
Cl
+
P
+
N
C
P
C
H
N
I
Ph
Ph
Ph
R
C
H
R
IIIa_IIId
IV
I
II
I_
R
R
Ph
O
H
Ph
Ph
+
NaI
P
C
N
Ph3P
+
O
Ph3P
N
+
+
Cl
P
Ph
R
R
H
IIIa_IIId
VIII
I
II
VII
R = Me (IIIa), Et (IIIb), i-Pr (IIIc), Pr (IIId).
Table 1. Yield, %, of compounds IIIa–IIId in the syntheses
In all the cases the addition of triphenylphosphine
VII led to the increased yield. The data on yields are
listed in Table 1.
without and with Ph3P
Products
No Ph3P
41%
With Ph3P
72%
To prove unambiguously the structures of the
obtained compounds we subjected compounds IIIb
and IIIc to XRD analysis (Figs. 1 and 2). The basic
bond lengths and bond angles in IIIb and IIIc
practically do not differ from those in the earlier
studied salt IIIa, except for a significant elongation of
Р1–C1 bond (Table 2). This difference in bond lengths
probably is a result of the special features of cation–
anion interactions in the IIIa crystal.
I_
CH3
CH3
Ph
+
P
P
C
N
Ph
H
IIIa
I_
C
C2H5
C2H5
Ph
Ph
+
N
45%
82%
H
In the studied crystals the cation–anion contacts
I1···C1 are shortened. Taking into account the direction
of this contact (I1C1N1 angle is nearly 90°) it can be
considered as a charge transfer from the anion onto the
cation. The length of this contact is probably defined
first of all by steric size of substituents at the nitrogen
atom. Really, the shortest contact is observed for
methyl substituents, the longest one, for isopropyl
groups (Table 2). The shortening of I···C distance
probably significantly affects the value of charge
transfer and also the character of charge delocalization
in the PCN fragment. Actually, from the value of the
pseudo-torsion angle formed by the lone electron pair
(Lp) of phosphorus atom with C1=N1 bond the
IIIb
CH3
CH3
CH3
I _
HC
Ph
+
P
C
H
N
24%
39%
64%
73%
Ph
HC
CH3
IIIc
I_
C3H7
Ph
+
N
P
C
H
Ph
C3H7
IIId
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 1 2010

STOICHIOMETRY OF THE REACTION OF DIPHENYLCHLOROPHOSPHINE
103
I1
I1
C19
C15
C15
C13
C12
C12
C13
C16
N1
P1
C11
C1
C17
N1
P1
C11
C14
C1
C8
C7
H1A
C14
C8
H1A
C17
C2
C7
C6
C9
C10
C2
C3
C4
C18
C9
C10
C6
C3
C4
C16
C5
C5
Fig. 1. General view of Шb molecule, the atoms are
represented by heat vibration ellipsoids (p = 50%).
Fig. 2. General view of Шc molecule, the atoms are
represented by heat vibration ellipsoids (p = 50%).
Table 2. Principal bond lengths and bond angles in
compounds IIIa [6], IIIb and IIIc
maximum conjugation should occur in the case of IIIa,
while in IIIb and IIIc it should be less and comparable
(Table 2). The effect of the anion–cation interaction on
the distribution of the bond lengths in this system is
confirmed independently by similarity of the obtained
values for IIIb and IIIc with the related value for di-t-
butyldimethylaminomethylenephosphonium chloride
[1] where the Cl–···C=N interaction is not observed.
Compound
Atoms
IIIa
IIIb
IIIc
Bond lengths, Å
P1–C1
1.807(6)
1.826(6)
1.838(6)
1.289(7)
1.475(7)
1.455(7)
1.839(5)
1.827(5)
1.822(5)
1.291(6)
1.488(6)
1.479(6)
1.838(3)
1.828(3)
1.830(3)
1.286(4)
1.513(4)
1.497(4)
P1–C2
Thus we can conclude that in all studied salts a
formation of tight ion pairs occurs where the strength
of interaction is defined predominately by steric
reasons. Further study of this class of compounds and
quantum-chemical calculations of cation–anion pairs
will make it possible to analyze more completely the
nature of I–···C=N interactions and their role in the
stabilization of the cation.
P1–C8
N1–C1
N1–Alkа
N1–Alk
Bond angles, deg
C2P1C1
103.5(3)
98.8(2)
106.3(3)
121.4(5)
123.2(5)
115.4(5)
127.8(5)
72.8
101.5(2)
103.6(2)
99.9(2)
120.3(4)
122.9(4)
116.8(4)
123.7(4)
49.1
98.7(1)
105.42(1)
102.64(1)
121.2(3)
121.6(3)
117.2(2)
122.8(2)
52.1
C2P1C8
C8P1C1
EXPERIMENTAL
C1N1Alk
C1N1Alk
AlkN1Alk
N1C1P1
The 31Р and 1Н NMR spectra (δ, ppm) were
registered on a Bruker AV-400 instrument with operat-
ing frequencies 161.98 and 400.13 MHz respectively.
The 31Р and 1Н NMR spectra of individual compounds
dissolved in CDCl3 were registered, for the 31Р NMR
spectra of reaction mixtures was used CН2Cl2 as
solvent, external reference 85% Н3РО4. Synthesis of
compounds IIIa–IIIc and the data of X-ray structural
analysis of IIIa have been published earlier [6]. The
N,N-dialkylformamides used (except DMF) were
synthesized along the earlier published procedure [13].
LpP1С1N1 a
Cation···anion contact
I1···C1
I1C1P1
3.526(1)
86.76(3)
3.782(1)
88.96(3)
3.928(1)
88.15(3)
a
Alk refers to the carbon atoms in alkyl substituents, C14, C16 in
IIIb and C14, C17 in IIIc.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 1 2010

104
MORGALYUK et al.
Table 3. Principal crystallographic data and refinement
parameters for compounds IIIb and IIIc
3.5 g (0.023 mol) of NaI. The reaction mixture was
stirred at 20оC for 10 h, then it was diluted with 30 ml
of CH2Cl2, after 2 h the precipitate formed was filtered
off and washed with 2×5 ml of CH2Cl2. The combined
filtrate was evaporated in a vacuum, and to the oily
residue 30 ml of benzene was added, the precipitate
was reprecipitated from DMF–benzene and then from
CH2Cl2–benzene. After filtration, washing with 2×5 ml
of benzene, and drying in a vacuum we obtained 3.35 g
(41%) of compound IIIa as light yellow needle
Parameter
Empirical formula
IIIb
IIIc
C17H21INP
397.22
C19H25INP
425.27
Molecular mass
T, K
100
Monoclynic
P21/n
100
Monoclynic
P21/n
Crystal system
Space group
Z
4
4
1
crystals. The 31Р, Н NMR spectra, and the melting
a, Å
8.986(3)
9.430(4)
20.474(9)
101.396(15)
1700.7(13)
1.551
11.0953(13)
14.437(2)
12.750(2)
111.123(5)
1905.1(5)
1.483
point of the compound matched those in the earlier
experiments [6].
b, Å
c, Å
To the filtrate after firsrt precipitation of IIIa was
added 0.8 ml of water and after 2-h stirring it was left
for two day at room temperature. Then the precipitate
was filtered off, washed with 2×5 ml of benzene, dried
in air, and crystallized from CНCl3–i-PrOH mixture.
1.1 g (44%) diphenylphosphinic acid V (white needles)
was obtained, mp 193–195˚C. The 31Р NMR spectrum:
33.1 ppm, singlet (CDCl3). The 1Н NMR spectrum: 7.7
m (2Н, o-Н), 7.42 m (1Н, m-Н), 7.35 m (2Н, p-Н).
β, deg
V, Å3
d
calc, g cm–3
μ, cm–1
19.68
17.62
F(000)
792
856
2θmax, deg
56
58
Total number of reflexes
Number of independent reflexes
Number of reflexes with I >2σ(I)
Number of refined parameters
R1
12421
4078
14974
5043
Along the same procedure were synthesized N,N-
diethyl(diphenylphosphinomethylene)iminium (IIIb)
[6], N,N-diisopropyl(diphenylphosphinomethylene)
iminium (IIIc) [6] and N,N-dipropyl(diphenyl-
phosphinomethylene)iminium (IIId) iodides. The
reaction duration was 48 h in each case. The products
yields are listed in Table 1.
2804
3701
183
203
0.0415
0.1150
1.041
0.0386
0.0817
0.975
WR2
GOF
N,N-Dipropyl(diphenylphosphinomethylene)-
iminium iodide (IIId) (first synthesized). Yield 39%,
Residual electron density,
1.350/–0.945 1.068/–0.913
e Å–3 (dmin/dmax
)
31
yellow needles, mp 94–96°C. The P NMR spectrum:
1
6.2 ppm; The H NMR spectrum: 9.90 s (N=C–H),
7.83 m (4Н, o-Н, Ph), 7.48 m (6H, m,p-Н, Рh), 4.19 s
(Δν1/2 = 27 Hz, 2Н, CН2CН2), 3.52 t (2Н, CН2CН2, Jнн
8.0 Hz), 1.85 q (2Н, CН2CН2, Jнн 8.0 Hz), 1.69 q (2Н,
CН2CН2, Jнн 8.0 Hz), 0.96 t (3Н, CН3, Jнн 7.8 Hz),
0.66 t (3Н, CН3, Jнн 7.8 Hz). Found, % C 53.66; Н
5.93; N 3.29; Р 7.28. C19H25INP. Calculated, %: C
53.66; Н 5.88; N 3.18; Р 7.24. Yield of IIId is given in
Table 1.
X-ray diffraction studies of compounds IIIb and
IIIc were carried out on a SMART APEX II CCD
diffractometer (MoKα-radiation, graphite monochro-
mator, ω-scanning). The structures were solved by the
direct method and refined by the least-squares method
in anisotropic full matrix approximation on F2hkl. The
hydrogen atoms positions were calculated geo-
metrically and refined using rider model. The basic
crystallographic data and parameters of refinements
are listed in Table 3. All calculations were carried out
with the program package SHELXTL PLUS.
Reaction of chlorodiphenylphosphine with sodium
iodide. To 3.5 g (0.023 mol) of NaI was added 4.1 ml
(5 g, 0.023 mol) of chlorodiphenylphosphine I and
then 10 ml of dioxane. The mixture was stirred under
inert gas flow at 20оC for 4 days. The NaCl precipitate
was filtered off, washed with 2×5 ml of CH2Cl2, and
the filtrate was evaporated in a vacuum. 6.7 g of Ph2PI
(VI) (92%), 93% purity was obtained and used further
N,N-Dimethyl(diphenylphosphinomethylene)-
iminium (IIIa) [6] and diphenylphosphinic iodide
(IV). To 7 ml of DMF (II) (6.58 g, 0.09 mol) at
stirring under inert gas atmosphere was added 4.1 ml
(5 g, 0.023 mol) of chlorodiphenylphosphine (I) and
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STOICHIOMETRY OF THE REACTION OF DIPHENYLCHLOROPHOSPHINE
105
without distillation. The 31Р NMR spectrum (CH2Cl2):
solidified completely at rubbing, the solid was
recrystallized from hexane–CНCl3 and hexane–
dichloroethane mixtures. Triphenylphosphine oxide
(VIII), 5.17 g (81%), was isolated, mp 155–157°C
[12]. The 31Р NMR spectrum: 29.5 ppm, singlet [11].
40.3 ppm, singlet [10].
Reaction of iododiphenylphosphine with DMF.
To 7 ml of DMF II (6.58 g, 0.09 mol) at stirring under
inert gas atmosphere was added 4.1 ml (5 g,
0.023 mol) of iododiphenylphosphine VI. The reaction
mixture was stirred at 20°C for 10 h, then it was
diluted with 30 ml of CH2Cl2 and after 2 h the
precipitate was filtered off and washed with 2×5 ml of
CH2Cl2. The combined filtrate was evaporated in a
vacuum, to the oily residue was added 30 ml of
benzene and the precipitate was reprecipitated from
DMF–benzene and then from CH2Cl2–benzene. After
filtration, washing with 2×5 ml of benzene, and drying
in a vacuum, 3.59 g (42%) of compound IIIa was
1
The Н NMR spectrum: 7.65 m (4H, o-Н); 7.52 m
(2Н; m-Н); 7.43 m (4Н; p-Н).
By similar scheme with the use of Рh3P were
synthesized N,N-diethyl(diphenylphosphinomethyl-
ene)iminium (IIIb), N,N-diisopropyl(diphenylphos-
phinomethylene)iminium (IIIc), and N,N-dipropyl-
(diphenylphosphinomethylene)iminium (IIId) iodides.
Yields of these products are listed in Table 1.
REFERENCES
1
obtained as light-yellow needle crystals. The 31Р, Н
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Khim., 1992, vol. 62, no. 12, p. 2670.
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NMR spectra and the melting point of the obtained
IIIa were the same as in preceding experiments [6].
Synthesis of N,N-dimethyl(diphenylphosphino-
methylene)iminium iodide in the presence of tri-
phenylphosphine. To 7 ml of DMF II (6.58 g,
0.09 mol) at stirring under inert gas atmosphere was
added 4.1 ml (5 g, 0.023 mol) chlorodi-phenyl-
phosphine I, 6 g (0.023 mol) of Рh3P VII and 3.5 g
(0.023 mol) of NaI. The reaction mixture was stirred at
20°C for 10 h, then diluted with 30 ml of CH2Cl2, after
2 h the precipitate was filtered off and washed with
2×5 ml of CH2Cl2. The combined filtrate was
evaporated in a vacuum and to the oily residue was
added 30 ml of benzene. The precipitate was
reprecipitated from DMF–benzene and then from
CH2Cl2–benzene mixtures. After filtration, washing
with 2×5 ml of benzene, and drying in a vacuum 5.88 g
(72%) of compound IIIa was obtained as light-yellow
needle crystals, mp 140–141°C (decomp.) The 31Р and
1Н NMR spectra and the melting point are the same as
those obtained in the preceding experiments [6]
performed without triphenylphosphine.
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1967, p. 285.
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The filtrate after first precipitation of IIIa was
evaporated to dryness. To the oily residue was added
20 ml of anhydrous diethyl ether. The oil obtained
13. Schmidt, O., Z. Phys. Chem., 1907, vol. 58, p. 513.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 1 2010