Synthesis and molecular structure of [2,3,4,5-tetrafluoro-6-(p- methoxyphenylamino)phenyl]diphenylphosphine

Article abstract of DOI:10.1134/S1070363208060121

The reaction of (pentafluorophenyl)diphenylphosphine with C-ethoxycarbonyl-(p-methoxyphenyl) nitrile imine was used to synthesize [2,3,4,5-tetrafluoro-6-(p-methoxyphenylamino)phenyl]diphenylphosphine oxide whose reduction with trichlorosilane gave [2,3,4,

Full text of DOI:10.1134/S1070363208060121

ISSN 1070-3632, Russian Journal of General Chemistry, 2008, Vol. 78, No. 6, pp. 1172–1176. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © Yu.G. Trishin, О.V. Gozhina, L.А. Таmm, А.I. Stash, V.E. Zavodnik, V.К. Bel’skii, 2008, published in Zhurnal Obshchei Khimii,
2008, Vol. 78, No. 6, pp. 945–949.
Synthesis and Molecular Structure of [2,3,4,5-Tetrafluoro-6-(p-
methoxyphenylamino)phenyl]diphenylphosphine
Yu. G. Trishina, О. V. Gozhinaa, L. А. Таmma, А.I. Stashb, V. E. Zavodnikb, and V. К. Bel’skiib
aSt.Petersburg State Technological University of Plant Polymers,
ul. Ivana Chernykh 4, St. Petersburg, 198095 Russia
e-mail: trish@YT4470.spb.edu
b Karpov Research Physical and Chemical Institute Russian Federation State Research Center,
ul. Vorontsovo Pole 10, Moscow, 103064 Russia
Received December 24, 2007
Abstract—The reaction of (pentafluorophenyl)diphenylphosphine with C-ethoxycarbonyl- (p-methoxyphenyl)
nitrile imine was used to synthesize [2,3,4,5-tetrafluoro-6-(p-methoxyphenylamino)phenyl]diphenylphosphine
oxide whose reduction with trichlorosilane gave [2,3,4,5-tetrafluoro-6-(p-methoxyphenylamino)phenyl]
diphenylphosphine, the first representative of tertiary ortho-arylamino-substituted arylphosphines. According
to X-ray diffraction data, the principal steric characteristics of the phosphine are close to those known for
triarylphosphines.
DOI: 10.1134/S1070363208060121
One of the new directions of the search for ligands
for metal complex catalysts is associated with the
synthesis of phosphorus- and nitrogen-containing
compounds which have a P–C–C–N frame [1]. These
bidentate ligands containing simultaneously a soft
(phosphorus) and a hard (nitrogen) coordination
centers hold promise for creation on their basis of
unique complexes with platinum, palladium, rhodium
and other metals.
substitution of the fluorine atom in the ortho position
to the phosphonium group, followed by heteroring
close, take place. Therewith, the expelled fluoride
attaches to the phosphorus atom to form fluorinated
phosphorane Ib as a brown oily, gradually hardening
substance. It is stable enough at 20°C in the absence of
air moisture. The 31Р NMR spectrum of compound Ib
shows a typical doublet at δР –96.4 ppm (1JPF 655.0 Hz).
Under the action of water, phosphorane Ib undergoes
facile hydrolysis, releasing hydrogen fluoride and
forming as intermediates first hydroxyphosphorane Ic
and then phosphine oxide Id which contains a hydrazo
group bound with a fluorinated benzene ring. Finally,
the hydrazo group cleaves with liberation of ethyl
cyanoformate and formation the final phosphorus-
containing product, [2,3,4,5-tetrafluoro-6-(p-methoxy-
phenylamino)phenyl]diphenylphosphine oxide (I).
In this work we obtained [2,3,4,5-tetrafluoro-6-(p-
methoxyphenylamino)phenyl]diphenylphosphine oxide
(I) on the basis of our recently discovered reaction of
(pentafluorophenyl)diphenylphosphine with nitrile
imines. Compound I was reduced with trichlorosilane
to synthesize [2,3,4,5-tetrafluoro-6-(p-methoxyphenyl-
amino)phenyl]diphenylphosphine (II), the first
representative of tertiary ortho-arylamino-substituted
arylphosphines.
The formation of ethyl cyanoformate is established
by the presence in the IR spectrum of the reaction
mixture of an absorption band at 2250 cm–1 (νC≡N).
Earlier we mentioned [2] that N–N bond cleavage in
intermediates like Id is, in essence, a new example of
the amino–nitrile rearrangement well known in
hydrazones [3]. Phosphine oxide I is a colorless
crystalline substance stable for a long time on storage
The reaction of (pentafluorophenyl)diphenylphos-
phine with C-ethoxycarbonyl-N-p-methoxyphenyl-
nitrile imine, leading to phosphine oxide I, is a multi-
step process. It is probably begins with the nucleo-
philic attack of the phosphine phosphorus on the nitrile
imine carbenium carbon, which gives rise to a dipolar
ion Ia. Further on intramolecular nucleophilic aromatic
1172

SYNTHESIS AND MOLECULAR STRUCTURE
1173
_
N
+
C
EtOC(O)
F
Et3N
N
OMe Et3N HCl
+
+
EtOC(O)
C
N
F
NH
OMe
Cl
F
F
F
F
F
F
F
_
N
+
+
C
N
OMe
Ph2P
EtOC(O)
+
Ph2P
_
N
C
F
N
OMe
F
EtOC(O)
F
Iа
F
F
F
F
F
F
F
H2O
HO
−HF
Ph2P
N
OMe
Ph2P
N
OMe
C
N
C
N
EtOC(O)
EtOC(O)
Ib
Ic
F
F
F
F
F
F
F
F
O
O
−EtOC(O)CN
Ph
2P
NH
Ph
2P
CH
N
OMe
OMe
N
EtOC(O)
Id
I
in usual conditions. It is readily soluble in chloroform,
acetone, benzene, and tetrahydrofuran, moderately
soluble in diethyl ether, and poorly soluble in hexane.
Phosphine oxide I was reduced into phosphine II
by the action of trichlorosilane in the presence of
triethylamine in benzene under prolong heating (100°
The signal in the 31P NMR spectrum appears at δP C) in
a
sealed ampule. After separation of
32.3 ppm, which is characteristic of triarylphosphine
oxides [4]. The H NMR spectrum shows amino (δ
9.52 ppm), methoxy (δ 3.69 ppm), and aromatic (δ
6.62–7.76 ppm) proton signals. The presence of NH
and P=O groups is proved by IR spectral data (νNH
3175 cm–1, νPO 1242 cm–1).
triethylamine hydrochloride and treatment of the
reaction mixture with aqueous sodium hydroxide,
phosphine II was isolated in 47 % yield as light yellow
crystals. Unlike triphenylphosphine, compound II is
gradually oxidized in air; therefore, it was stored under
argon.
1
F
F
F
F
(SiHCl3)
F
F
F
F
O
Ph
2P
NH
OMe
Ph
2P
NH
OMe
I
II
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 6 2008

1174
TRISHIN et al.
Table 1. Bond lengths in the molecule of diphenyl(2,3,4,5-
tetrafluoro-6-p-methoxyphenylaminophenyl)phosphine II
Тable 2. Valence angles in the molecule of diphenyl
(2,3,4,5-tetrafluoro-6-p-methoxyphenylaminophenyl)phos-
phine II
Bond
P–C19
d, Å
Bond
d, Å
Angle
ω, deg
Angle
ω, deg
C19PC13
C19PC1
C13PC1
C10OC25
C2NC7
C6C1C2
C6C1P
104.70(9)
105.63(9)
100.80(9)
117.8(2)
C8C7N
C9C8C7
C10C9C8
C9C10O
C9C10C11
OC10C11
C10C11C12
C7C12C11
C14C13C18
C14C13P
123.45(19)
121.0(2)
120.5(2)
116.04(19)
119.2(2)
124.7(2)
119.9(2)
121.5(2)
118.5(2)
125.50(16)
115.97(18)
120.3(2)
120.9(3)
119.4(3)
120.8(3)
120.0(3)
117.6(2)
123.86(17)
118.07(17)
121.5(2)
120.2(3)
119.4(2)
120.5(3)
120.8(2)
1.821(2)
C7–C8
1.385(3)
P–C13
P–C1
1.835(2)
1.839(2)
1.349(2)
1.340(2)
1.332(2)
1.348(2)
1.377(3)
1.411(3)
1.392(3)
1.427(3)
1.383(3)
1.414(3)
1.390(3)
1.364(3)
1.380(3)
1.372(3)
1.372(3)
C8–C9
1.380(3)
1.370(3)
1.378(3)
1.382(3)
1.383(3)
1.392(3)
1.384(3)
1.369(4)
1.362(4)
1.391(4)
1.377(3)
1.388(3)
1.382(3)
1.369(4)
1.367(4)
1.385(4)
C9–C10
C10–C11
C11–C12
C13–C14
C13–C18
C14–C15
C15–C16
C16–C17
C17–C18
C19–C20
C19–C24
C20–C21
C21–C22
C22–C23
C23–C24
F1–C3
F2–C4
F3–C5
F4–C6
O–C10
O–C25
N–C2
N–C7
C1–C6
C1–C2
C2–C3
C3–C4
C4–C5
C5–C6
C7–C12
121.75(19)
117.67(18)
124.31(14)
117.65(15)
119.43(19)
118.1(2)
C2C1P
C3C2N
C3C2C1
NC2C1
F1C3C4
F1C3C2
C4C3C2
F2C4C3
F2C4C5
C3C4C5
F3C5C6
F3C5C4
C6C5C4
F4C6C5
F4C6C1
C5C6C1
C12C7C8
C12C7N
122.41(19)
117.9(2)
C18C13P
C13C14C15
C16C15C14
C17C16C15
C16C17C18
C13C18C17
C20C19C24
C20C19P
119.6(2)
122.46(19)
120.7(2)
119.5(2)
119.85(19)
121.4(2)
120.08(19)
118.5(2)
C24C19P
The 31P NMR spectrum phosphine I contains a
signal at δP –27.1 ppm, which is typical for triaryl-
phosphines [4]. In 1H NMR spectrum, the proton signal
of the amino group is shifted upfield (δ 6.44 ppm) from
that of starting compound I, implying absence of the
intramolecular NH…OP hydrogen bond inherent in
phosphine oxide I. We previously found such bond in
C19C20C21
C22C21C20
C21C22C23
C22C23C24
C23C24C19
116.90(18)
119.69(17)
123.39(18)
117.9(2)
118.60(19)
F2
C4
F1
a structurally similar [2,3,4,5-tetrafluoro-6-(phenyl-
amino)phenyl]phosphine oxide [2].
F3
F4
C3
C2
C5
C6
C9
C8
The molecular structure of phosphine II was
studied by X-ray diffraction (Figs. 1 and 2; Tables 1
and 2) to find that its principal geometric parameters
correspond to those in known triarylphosphines [5].
Thus, the Р–С bond lengths with an unsubstituted
benzene ring are 1.821 Ǻ (Р–С19) and 1.835 Ǻ (Р–С13),
and with fluorinated, 1.839 Ǻ (Р–С1). The bond angles
at the pyramidal phosphorus atom are 100.8–105.6о.
The torsion angles between the rings are as follows,
deg: С1–С6 and С7–С12 67.9; С1–С6 and С13–С18 92.6;
С1–С6 and С19–С24 63.0; and С13–С18 and С19–С24
63.3.
C7
O
C25
C10
C1
C12 C11
C20
P
C19
C13
C18
C21
C22
C14
C24
C17
C15
C16
C23
Fig. 1. Molecular structure of diphenyl(2,3,4,5-tetrafluoro-
6-p-methoxyphenylaminophenyl)phosphine II.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 6 2008

SYNTHESIS AND MOLECULAR STRUCTURE
1175
EXPERIMENTAL
The IR spectra were recorded on an IKS-29
1
spectrophotometer (KBr). The Н NMR spectra of
compounds I and II were obtained on a Bruker AC-
2
200 spectrometer (200.1 МHz) operated in the H
internal stabilization mode. The 31Р spectra were
measured on the same device at 81.4 MHz, solvent
CDCl3, reference 85 % Н3РО4.
c
0
b
The X-ray structural analysis of crystals of [2,3,4,5-
tetrafluoro-6-(p-methoxyphenylamino)phenyl]diphenyl-
phosphine (II) was performed on a CAD-4 diffrac-
tometer (MoKa radiation, W/2Q scanning). Crystals are
monoclinic: С24H16F4NOP; а 9.256(2), b 21.169(4), c
11.060(2) Ǻ, b 94.00(3)°, V 2161.8 (7) Ǻ; space group
P21/n, Z 4, dcalc 1.399 g/cm3. The structure was solved
by the direct method; R 0.0204 and RW 0.0875 [4122
reflections with I > 2σ(I)]. The bond lengths and bond
angles are given in Tables 1 and 2. The atomic
coordinates and equivalent isotropic thermal factors
are available in the Cambridge Structural Database
(registration number CCDC 668615).
a
[2,3,4,5-Tetrafluoro-6-(phenylamino)phenyl]phos-
phine oxide (I). A solution of 2.7 g of (pentafluo-
rophenyl)diphenyl phosphine, 2.0 g of ethyl chloro(p-
methoxyphenylhydrazono)acetate, and 3 ml of triethyl-
amine in 40 ml of absolute benzene was left to stand
for 24 h under argon. Triethylamine hydrochloride (95 %)
precipitated and was filtered off and washed with
benzene. The filtrate was evaporated at reduced
pressure. The brown oily was fluorinated phosphorane
Fig. 2. Crystal cell of diphenyl(2,3,4,5-tetrafluoro-6-p-
methoxyphenylaminophenyl)phosphine II.
off and treated with 30 ml of 30% aqueous sodium
hydroxide. The organic layer was separated and dried
over sodium sulfate. Benzene was removed at reduced
pressure. Petroleum ether (40–70°C), 10 ml, was added
to the residue. The precipitate was recrystallized from
a benzene–hexane mixture (1 : 3). Yield 0.5 g (47.0 %),
1
Ib, according to 31Р NMR data (δР –96.4 ppm, JPF
655.0 Hz). It was dissolved in 10 ml of absolute
diethyl ether. The solution was decanted from a little
undissolved residue, diluted with 0.2 ml of water, and
left to stand for 24 h at 20°C. Ether was then removed
at atmospheric pressure, and the residue was
recrystallized from ethanol. Yield 2.2 g (60.9 %), mp
110–112°С. IR spectrum, ν, cm–1 : 3175 (NH), 1242
1
slightly yellowish crystals, mp 79–80°C. Н NMR
spectrum (СDСl3, δ, ppm): 3.75 s (3Н, ОСН3), 6.62–
7.76 m (14Н, Ar), 6.44 (1Н, NH). 31Р NMR spectrum
(СDCl3): δР –27.1 ppm. Found, % : С 65.75; Н 3.78; N
3.19; Р 6.95. C25H18F4NOP. Calculated, % : С 65.94; Н
3.98; N 3.08; Р 6.80.
1
(Р=О). Н NMR spectrum (СDСl3), δ, ppm): 3.69 s
ACKNOWLEDGMENTS
(3Н, ОСН3), 6.62–7.76 m (14Н, Ar), 9.52 s (1Н, NH).
31Р NMR spectrum (СDCl3): δР 32.3 ppm. Found, % :
С 63.87; Н 3.67; N 2.72; Р 6.69. C25H18F4NO2P.
Calculated, % : С 63.70; Н 3.85; N 2.97; Р 6.57.
The work was financially supported by the Russian
Foundation for Basic Research (project no. 07-03-
00544).
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ampoule at 100ºC for 10 h. After cooling, the
precipitate of triethylamine hydrochloride was filtered
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