Synthesis and characterization of a new cyclic phosph(V)azane ligand [(C6H5N)P(O)H]2and its zinc(II) complex

Article abstract of DOI:10.1080/00958972.2011.585642

The new cyclic phosph(V)azane ligand [(C(JH₅N)P(O)H]₂ (2) is obtained from the reaction between PCl₃ and PhNH ₂in toluene followed by controlled hydrolysis of the product in an H₂O-CHCl₃ so

Full text of DOI:10.1080/00958972.2011.585642

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Synthesis and characterization of a
new cyclic phosph(V)azane ligand
[(C6H5N)P(O)H]2 and its zinc(II) complex
Abbas Tarassoli a & Shiva Hojatpanah a
a Department of Chemistry , College of Science, Shahid Chamran
University , Ahvaz , Iran
Published online: 11 Aug 2011.
To cite this article: Abbas Tarassoli & Shiva Hojatpanah (2011) Synthesis and characterization of a
new cyclic phosph(V)azane ligand [(C6H5N)P(O)H]2 and its zinc(II) complex, Journal of Coordination
Chemistry, 64:11, 2028-2033, DOI: 10.1080/00958972.2011.585642
To link to this article: http://dx.doi.org/10.1080/00958972.2011.585642
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Journal of Coordination Chemistry
Vol. 64, No. 11, 10 June 2011, 2028–2033
Synthesis and characterization of a new cyclic
phosph(V)azane ligand [(C6H5N)P(O)H]2
and its zinc(II) complex
ABBAS TARASSOLI* and SHIVA HOJATPANAH
Department of Chemistry, College of Science, Shahid Chamran University, Ahvaz, Iran
(Received 25 January 2011; in final form 25 March 2011)
The new cyclic phosph(V)azane ligand [(C6H5N)P(O)H]2 (2) is obtained from the reaction
between PCl3 and PhNH2 in toluene followed by controlled hydrolysis of the product in an
H2O–CHCl3 solution. Compound 2 is the first example of P(V) dimer [(m-NC6H5)P(H)¼O]2, a
P2N2 ring with two P(O)H moieties. The reaction of 2 with ZnCl2 in a molar ratio of 1 : 1 in
tetrahydrofuran yields the cyclophosph(V)azane complex Cl2Zn[(C6H5N)P(O)H]2 (3) in which
Zn–O bonds form directly between a cyclic phosph(V)azane ligand and Zn(II). The products
have been characterized by infrared, multinuclear (1H, 31P, 13C) NMR, mass spectrometry, and
elemental analysis.
Keywords: Cyclic phosph(V)azane; Zinc complex; 31P Spectroscopy; P2N2-ring
1. Introduction
Compounds containing phosphorus and nitrogen, with direct bonds between these two
elements, have been employed as ligands for many years [1, 2]. Among these
compounds cyclodiphosph(V)azanes as ligands have attracted considerable interest,
since the four-membered P2N2 ring contains active positions in close proximity [3–6].
They bear active sites as hard and soft centers N, O, and P and are reactive to form
various metal complexes [7–10]. The reactions of phosphazanes with molybdenum
carbonyls have been extensively studied and a number of synthetic methods have been
devised to form new inorganic complexes [11–13]. In addition, small heterocycles with
P–N and P–O bonds have biochemical and commercial importance [7, 8].
The coordination behavior of bis(anilino)phosphine oxide [14] with Al, Si, Sn, Ti,
and Pt has already been reported [15–19]. Herein we report the synthesis of the
first example of P(V) dimer [(m-NC6H5)P(H)¼O]2 (2). Some Zn(II) complexes of
cyclodiphosph(V)azane have shown considerable biological and antimicrobial activities
and have potential application in drug delivery systems [20]. This article will focus on
the synthesis and characterization of the new ligand (2) and its coordination chemistry
with ZnCl2.
*Corresponding author. Email: tarassoli@scu.ac.ir
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2011 Taylor & Francis
DOI: 10.1080/00958972.2011.585642

Cyclic phosph(V)azane ligand
2029
2. Experimental
2.1. Materials and instrumentation
All experiments requiring inert atmosphere were carried out under nitrogen using
standard Schlenk techniques. The solvents were purified and dried as indicated:
Tetrahydrofuran (THF) was treated with KOH and freshly distilled twice from sodium
before use. Aniline was distilled from P4O10. Toluene was distilled over sodium after
refluxing for 7 h. Phosphorus trichloride was used as purchased from Merck Co. The
bis(anilino)phosphine oxide (C6H5NH)2P(O)H (1) was prepared by previously reported
procedures [14, 19].
NMR spectra were recorded on a Bruker Avance 400 MHz at ambient temperature.
1H (400.13 MHz) and 13C NMR (100.62 MHz) were recorded using (CD3)2SO as a
solvent with TMS as an external standard.
The 31P spectra (161.97 MHz) were referenced to external 85% H3PO4. Infrared (IR)
spectra were measured on a Bomen FT–IR spectrophotometer. FAB (þ) mass spectra
were recorded using a JEOL SX – 102A instrument. Elemental analysis (C, H, N) was
performed by the microanalytical service of N.I.O.C Research Institute of Petroleum
Industry. The zinc content for 3 was determined by flame atomic absorption
spectrometry. The chloride content for 3 was measured by potentiometric titration
(argentometry).
2.2. Preparation of [(C6H5N)P(O)H]2 (2)
To pure aniline (26 mL) in dry toluene (50 mL) at 0ꢀC, phosphorus trichloride (5 mL,
0.057 mmol) in dry toluene (10 mL) was added dropwise with stirring,. Then, the
temperature was slowly raised to 25ꢀC and after 2 h, chloroform (3 mL) and H2O (1 mL)
mixture was slowly added and refluxed at 90ꢀC for 2 h. The PhNH3þClꢁ was filtered off
immediately from the hot solution by a sintered glass filter. The solvent was removed in
vacuum from the filtrate and the resulting white solid was washed with cold toluene and
THF. After drying under vacuum for 24 h pure [(C6H5N)P(O)H]2 (2) was obtained,
yield 80%, m.p. 155–157ꢀC (dec). Anal. Calcd for C12H12N2P2O2 (%): C, 51.81;
H, 4.34; N, 10.07. Found (%): C, 51.75; H, 4.56; N, 9.94. IR (KBr): 2361(P–H),
1
1280(C–N), 1180(P¼O), 872(P–N), 1568–1393(C¼C); H NMR (25ꢀC, (CD3)2SO,
ppm): 7.03–6.48(m, 10H, ph), 6.62(d, 2H, PH); 31P NMR (25ꢀC, (CD3)2SO, ppm): 18.82
1
13
(d, JPH ¼ 639.7 Hz); C{1H}NMR (25ꢀC, (CD3)2SO, ppm): 118.6(CP), 122.5(Cm),
129.9(C0), 140.0(Ci); Ms: m/z 278, 261, 202, 122, 94, 91, 79, 63, 61, 60.
2.3. Synthesis of Cl2Zn[(C6H5N)P(O)H]2 (3)
ZnCl2 (0.048 g, 0.359 mmol) was dissolved in dry THF (8 mL) and added dropwise to
[(C6H5N)P(O)H]2 (2) (0.1 g, 0.359 mmol) in dry THF (25 mL) under N2 at 25ꢀC in the
absence of light. The mixture was stirred for 24 h, filtered, and the solvent removed
under vacuum. The resulting pale-yellow precipitate was washed with THF and dried
under vacuum for 24 h to obtain pure Cl2Zn[(C6H5N)P(O)H]2 (3), yield 64%, m.p.
110–112ꢀC (dec). Anal. Calcd for C12H12N2P2O2Cl2Zn (%): C, 34.77; H, 2.89; N, 6.75;
Cl, 17.11; Zn 15.78. Found (%): C, 34.64; H, 2.78; N, 6.68; Cl, 17.21; Zn, 15.72.

2030
A. Tarassoli and S. Hojatpanah
IR(KBr): 2376(P–H), 1259(C–N), 1151(P¼O), 867(P–N), 1583 and 1496(C¼C),
1
553(Zn–O). H NMR (25ꢀC, (CD3)2SO, ppm): 6.63–7.11(m, 10H, ph), 6.71(d, 2H,
31
1
PH); P NMR (25ꢀC, (CD3)2SO, ppm): 19.02(d, JPH ¼ 641.3 Hz); 13C{1H}NMR
(25ꢀC, (CD3)2SO, ppm): 116.0 (CP), 118.3(Cm), 129.4(C0), 146.0(Ci).
3. Results and discussion
The principal starting material for these investigations, (C6H5NH)2P(O)H (1) is
prepared in good yield by the reaction between of PCl3 with PhNH2 in a molar ratio of
1 : 5 through reaction (1).
PCl3 þ 5PhNH2 þ H2O ! ðC6H5NHÞ2PðOÞH þ 3C6H5NH3Cl:
Compound 2 is produced in a condensation reaction of 1 by elimination of two
ð1Þ
aniline molecules as shown in reaction (2) (scheme 1).
90ꢀC
2½ðC6H5NHÞ2PðOÞHꢂ ꢁꢁ! ½ðC6H5NÞPðOÞHꢂ2 þ 2PhNH2:
ð2Þ
Compound 2 is a very stable solid with a P2N2 ring, which is the first example of P(V)
dimer [(m-NC6H5)P(H)¼O]2, and it has the potential to act as a precursor for obtaining
new phosphorus–nitrogen macrocycles and complexes. A compound of composition
[(m-NC6H5)P(H)¼O]2 has been mentioned by Wright et al. [21] as a minor contaminant
in a reaction, however, its isolation and characterization was not accomplished. It
should be noted that 2 is also the first P2N2 ring with two P(O)H moieties instead of one
P(O)H moiety reported by Kumara Swamy et al. [22]. Compound 2 was reacted with
ZnCl2 in 1 : 1 molar ratio in dry THF at 25ꢀC and the new complex
Cl2Zn[(C6H5N)P(O)H]2 (3) is obtained as pale-yellow powder in 64% yield through
reaction (3) (scheme 2).
ZnCl2 þ ½ðC6H5NÞPðOÞHꢂ2 ! Cl2Zn½ðC6H5NÞPðOÞHꢂ2:
ð3Þ
The coordination occurs through oxygens of the ligand. Similar situation is seen in
the reaction of 1 with organotin halides [17, 19]. All manipulations were carried out in
an inert atmosphere. The new products, 2 and 3, were characterized by IR, mass, and
(1H, 31P, 13C) NMR spectroscopy as well as elemental analysis. All attempts to grow
single crystals of these new compounds suitable for X-ray crystallography were
unsuccessful.
O
H
P
O
H
HN
NH
P
N
N
P
O
H
(1)
(2)
Scheme 1. The formula of bis(aniline)phosphine oxide (1) and new cyclic phosphazane ligand (2).

Cyclic phosph(V)azane ligand
2031
O
H
Cl
Cl
P
Zn
PhN
NPh
P
O
H
(3)
Scheme 2. The formula of cyclophosph(V)azane zinc complex.
3.1. IR spectra
IR spectra indicate that 2 shows strong bands at 2361, 1259, 1185, and in the region of
1568–1393 cmꢁ1, assigned to P–H, C–N, P¼O, and C¼C vibrations, respectively. The
IR spectrum also showed the absence of N–H bands of ligand which usually appear at
3334 cmꢁ1. IR spectrum for 3 shows that the P¼O stretching shifted by almost 34 cmꢁ1
to lower frequency upon coordination, as a result of decrease in the P¼O bond order.
The appearance of a new band at 553 cmꢁ1, assigned to Zn–O bonds [20], supports the
bonding of zinc to oxygen.
3.2. 1H NMR spectra
The 1H NMR spectrum of 2 exhibited phenyl-protons at ꢀ 6.48–7.03 ppm and P–H as a
doublet at ꢀ 6.62 ppm with 1JPH ¼ 640.1 Hz. The 1H NMR of 3 showed phenyl and P–H
resonances with the appropriate relative intensities at ꢀ 6.63–7.11 ppm as a multiplet and
ꢀ 6.71 ppm as a doublet.
3.3. 31P NMR spectra
The presence of P(O)H rather than the P(OH) in 2 is readily deduced from the
proton-coupled 31P NMR spectrum [14]. One signal occurs as a doublet at
1
ꢀ 18.82 ppm with JPH ¼ 639.7 Hz in the 31P NMR spectrum of 2, which is in the
1
region associated with P(V) oxide species. The relatively large JPH coupling
constant (639.7 Hz) is also consistent with that of a directly bonded hydrogen. In
the 31P NMR spectrum of 3 only one signal is seen at ꢀ 19.52 ppm with
1JPH ¼ 641.3 Hz.
3.4. 13C NMR spectra
The 13C{1H}NMR of 2 showed characteristic bands at 118.6(CP), 122.5(Cm),
129.9(C0), and 140.0(Ci) ppm. Also, 13C{1H}NMR spectrum of 3 exhibited four char-
acteristic signals in the aromatic region at 116.0(CP), 118.3(Cm), 129.4(C0), and
146.0(Ci) ppm.

2032
A. Tarassoli and S. Hojatpanah
3.5. The mass spectra data
The mass spectrum of 2 showed a strong parent peak at m/z 278 attributable to the
molecular ion, along with a series of less intense peaks at m/z 60 [N–PH–N], 61 [N–
P¼O], 63 [NH–P–OH], 79 [HPNHPH], 91 [C6H5–N], 94 [H2P2N2H2], 122 [OP2N2O],
202 [Mþ–C6H5], 261 [Mþ–OH], and 278 [Mꢃþ]. The mass spectrum of 3 exhibited a low
intensity peak at m/z 414 assigned to the molecular ion of C12H12N2P2O2Cl2Zn and a
relatively intense mass line at m/z 278 [(C6H5N)P(O)H]2. Characteristic mass envelopes
of phenylamido-containing phosphorus species in a similar manner to 2 are also seen
for 3, consistent with the presence of 2 in the complex.
4. Conclusions
This article has described the synthesis and spectral characterization of the first example
of a P2N2 ring with two P(O)H moieties, [(m-NC6H5)P(H)¼O]2. The product was
obtained cleanly and used as a ligand to react with zinc dichloride to afford the desired
phosph(V)azane complex. The new ligand and its zinc complex have been fully
characterized by IR, multinuclear (1H, 31P, 13C) NMR, mass spectrometry, and
elemental analysis.
Acknowledgment
The authors wish to thank Shahid Chamran University Research Council for financial
support of this project (Grant 1389).
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