Spirocyclic phosphazene complexes of arsenic(III): Synthesis and characterization

Article abstract of DOI:10.1080/10426500307773

A new acyclic phosphazene ligand, [HN(PPh₂NPh)₂] (A) has been synthesized and characterized. Spirocyclic phosphazene-glycolate complexes of arsenic(III) with ligand (A) and [HN(PPh₂NSiMe₃)₂] (B), havi

Full text of DOI:10.1080/10426500307773

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Spirocyclic Phosphazene Complexes of Arsenic(III):
Synthesis and Characterization
a
a
Yash Paul & Sushil K. Pandey
a
University of Jammu , Jammu, India
Published online: 27 Oct 2010.
To cite this article: Yash Paul & Sushil K. Pandey (2003) Spirocyclic Phosphazene Complexes of Arsenic(III): Synthesis and
Characterization, Phosphorus, Sulfur, and Silicon and the Related Elements, 178:1, 159-170, DOI: 10.1080/10426500307773
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Phosphorus, Sulfur and Silicon, 2003, Vol. 178:159–170
Copyright �C 2003 Taylor & Francis
1
042-6507/03 $12.00 + .00
DOI: 10.1080/10426500390170318
SPIROCYCLIC PHOSPHAZENE COMPLEXES
OF ARSENIC(III): SYNTHESIS AND
CHARACTERIZATION
Yash Paul and Sushil K. Pandey
University of Jammu, Jammu, India
(Received June 3, 2002; accepted July 27, 2002)
A new acyclic phosphazene ligand, [HN(PPh NPh) ] (A) has been
2
2
synthesized and characterized. Spirocyclic phosphazene-glycolate com-
plexes of arsenic(III) with ligand (A) and [HN(PPh NSiMe ) ]
2
3 2
(
B), having the general formula [N(PPh NPh) AsOGO] and
2
2
[
N(PPh NSiMe ) AsOGO] (where G = CH CH2
�
,
CHMeCH2
�
,
2
3 2
2
CHMeCH CMe
�
,
CH CH CH
�
, or CMe CMe
�
) also have
2
2
2
2
2
2
2
been synthesized by their reaction with chloro dioxarsolanes and
-
arsenanes in anhydrous medium. These moisture sensitive complexes
1
13
31
are characterized by elemental analysis, IR, NMR ( H, C, and P),
and mass spectral data which have been discussed in relation to plau-
sible structure for these arsenic(III) derivatives.
Keywords: Dioxarsenane; dioxarsolane; heterometallacyclophosp-
hazene; metallaphosphazene; phosphazene-glycolate
INTRODUCTION
Arsenic compounds find extensive use in agriculture as herbicides for
weed control, such as MSMA (monosodium methylarsonate), DSMA
(
the disodium salt, Na2MeAsO3), and cacodylic acid. The use of
organoarsenicals in medicine dates from the discovery in 1905 by H. W.
Thomas that “atoxyl” cured experimental trypnosomiasis (e.g., sleep-
ing sickness). A literature survey revealed that much work has been
1� 7
done on arsenic compounds containing As O and As S linkages,
but there is paucity of information on the arsenic derivatives of nitrogen
The authors are thankful to DST, New Delhi for financial assistance. Y. P. is grateful
for JRF. We are also grateful to RRL, Jammu and CDRI, Lucknow for spectral studies.
Address correspondence to Sushil K. Pandey, P. G. Department of Chemistry,
New Campus, University of Jammu, Jammu–180006 (J&K), India. E-mail: kpsushil@
rediffmail.com
1
59

1
60
Y. Paul and S. K. Pandey
containing ligand. However, synthesis of Sb N and Bi N heterocycles
8
,9
has been reported.
In the last five decades, a substantial amount of work has been
1
0� 15
carried out on phosphazene derivatives,
particularly by using
(
NPCl2)3. But the present work is motivated by a recent development
of heterometallacyclophosphazenes in which one of the phosphorus
atoms is substituted by another hetero atom. The phosphazene is
isoelectronic to siloxane moiety that has shown many interesting
aspects in view of their utility as inorganic polymer and ceramics.
Similarly, metallacyclophosphazenes have shown interesting struc-
1
6� 18
tural features and physical properties.
These compounds have
been employed as precursors in inorganic polymer chemistry and also
in generating new materials. In the past, we also have contributed to
this field by synthesizing new heterometallacyclophosphazenes1
9� 22
of
various elements, so it was thought worthwhile to insert arsenic into
the P N ring system. Here, we report on the synthesis of heteromet-
allacyclophosphazene by using acyclic phosphazene ligand (A) and
(
-
B) with arsenic(III)glycolates. We have used chlorodioxarsolanes and
arsenanes as reacting species because they already have been well
characterized and their application as starting materials serve many
purposes. Moreover, it is expected that these phosphazene-arsolane/-
arsenane derivatives may get their applications as precursors for
metal oxides and materials for “high-tech” purposes.
RESULTS AND DISCUSSION
The phenylated acyclic phosphazene ligand (A) was obtained in about
�
6
5–70% yield as pale yellow powder (m.p. 156–159 C) in a two step
synthesis (i and ii). The reaction of chlorodiphenylphosphine with
hexamethyldisilazene in 2:1 molar ratio in toluene formed compound
HN(PPh2)2, which on treatment with phenylazide resulted in the for-
mation of A.

Phosphazene Complexes of Arsenic(III)
161
This bis-phenylated acyclic ligand (A) has shown the characteristic
pattern in the IR spectrum. The bands for �P N have been found in
�
1
� 1
1
the region 1228–1176 cm and �NH at 3345 cm . The H NMR has
given a chemical shift as two multiplet in the region � 6.6–7.9 ppm, the
multiplet in high field region (� 6.7–7.0 ppm) may be attributed to 20H
of phenyl groups attached to the phosphorus while the multiplet toward
low field region (� 7.0–7.9 ppm) has been assigned to the 10H of phenyl
groups attached to the nitrogen. The 3 P NMR has shown chemical shift
as singlet at � 7.1 ppm, which indicates the equivalence of phosphorus
nuclei in the molecule. The mass spectrum of ligand (A) has revealed
1
+
+
the presence of molar (M ) ion at m/z 566 (20%) [M-H ], suggesting the
monomeric nature of ligand. Another ligand, bis-silylated acyclic phosp-
hazene (B), also used here for complexation, was prepared as described
2
3� 24
in the literature.
Various chlorodioxarsolanes and -dioxarsenanes, OGOAsCl, have re-
acted with ligand (A) and (B) in toluene in equimolar ratio which re-
sulted spirocyclic phosphazene-arsolane/-arsenane complexes.

1
62

163

1
64
Y. Paul and S. K. Pandey
These compounds obtained almost in quantitative yield, soluble in
common organic solvents, and appear to be susceptible to moisture but
can be kept unchanged for a long time under a dry and nitrogen atmo-
sphere. The derivatives of ligand (A) are yellow viscous while the deriva-
tives of ligand (B) are light yellow semi-solids. They were obtained as
sufficiently pure for spectral and other studies. The synthetic and ana-
lytical data are given in Table I.
The mass spectra of few represented compounds such as (7) and (8)
+
have shown molar ion (M ) peak at m/z 706 (14%) beside the usual frag-
mentation pattern that occurs for phosphazene complexes. The peak
+
for M -OGOAs fragement was found at m/z 149, 11% in complex (7)
and 41% in complex (8). The base peak for both cases was occurring
for phenyl group at m/z 77 (100%). The characteristic absorptions for
�
1
�
P N bonds were found in the region 1290–1100 cm in the IR spectra
of these complexes which are in accordance with the symmetric nature
�
1
of �P N P system. Further, disappearance of �N-H (3345 cm ) and
appearance of �As-N in the region 520–490 cm is suggestive of forma-
tion of bond between arsenic and nitrogen. The �C O and �As O occurs
in the region 1040–1020 cm and 700–590 cm , but �C O found with
slight shift. All the relevant IR data are given in the Table II. H NMR
�
1
�
1
� 1
1
chemical shift of these complexes were recorded in CDCl3. The signal
for NH proton in the region � 4.5–5.0 ppm have not been observed in
all these compound. The phenyl protons for PPh2 and NPh in the
complexes with ligand (A) are found in the region � 6.7–7.0 ppm and
�
7.2–8.1 ppm respectively, as two multiplet, while in the complexes with
ligand (B), the protons for PPh2 found as one multiplet in the region
6.9–8.0 ppm. The chemical shift for NPh and NSiMe3 have been
�
1
observed in the H NMR spectra of these compounds. However, it was
observed earlier that in some cases the SiMe3 has been substituted.9,25
Various protons of glycol moiety have appeared in their usual pattern
but with a slight chemical shift toward the downfield, which is indicative
1
3
of complexation. The C NMR spectra have shown the characteristic
chemical shift with slight downfield shift compared to the phosphazene
ligands, dioxarsolanes, and dioxarsenanes. In the cases of ligand (A)
derivatives, signals for phenyl carbons were observed as multiplets in
the range � 127–138 ppm and the carbons of trimethylsilyl were found
in the region � 8.0–8.5 ppm. The derivatives of ligand (B) have shown
three multiplet for phenyl carbons, the signal for NPh appearing as
one multiplet in the region � 115–125 ppm and for PPh2 two multiplet
in the region � 127–132 ppm. The other carbons of glycoxy moiety were
present in their characteristic range (Table III). In 31P NMR, one singlet
was found in the complexes of both ligand (A) and (B) with a downfield

Phosphazene Complexes of Arsenic(III)
165
shift in the range � 7–12 ppm and � 9–10 ppm. The singlet was ob-
served in the region � 14.4–18.9 ppm and � 20.8 to � 21.0 ppm for the
complexes with ligand (A) and (B) respectively. The occurrence of one
3
1
singlet with downfield shift in P NMR compare to ligands, (A = �
7
.1 ppm and B = � 11.1 ppm), showing the equivalence of phosphorus
1 31
nuclei in the molecule and the formation of As N bond. The H, P,
and 13C NMR data of all the compounds are summarized in Table III
respectively.
Since, we could not get the crystals in order to get them analyzed
by x-ray, so we relied on the basis of the above observations and a
comparison of relevant data from literature to propose a plausible ge-
ometry for these complexes. These acyclic phosphazene ligands be-
haved in bidentate manner in most of the cases.1
7� 23
Analogus cy-
clophosphazene antimony(III) complex also has shown a bidentate
mode of bonding by two terminal nitrogen atoms with antimony as
determined by single crystal x-ray diffraction analysis (Sb N bond
2
5
lengths are 202.7 pm and 203.2 pm). As(III) is not a strong Lewis
acid, therefore it may presumed that the anisobidentate mode of bond-
ing exists in these complexes with one sigma bond (Sb N) and a very
weak electrostatic attraction to the second nitrogen atom. Consider-
ing the above details, a distorted 9-trigonal bipyramidal geometry
around arsenic (lone pair of electron at equatorial position) may be
suggested.
EXPERIMENTAL
These heterometallacyclophosphazenes of As(III) are extremely sus-
ceptible to moisture. Therefore, stringent precautions have been taken
to maintain anhydrous conditions during the syntheses of these

1
66

167

1
68
Y. Paul and S. K. Pandey
complexes as well as ligands. All the syntheses and subsequent manipu-
lations were conducted under an inert atmosphere and anhydrous con-
ditions using standard Schelenk techniques, solvents were dried prior
to use and were kept under nitrogen atmosphere. The bis-silylated phos-
2
4
26� 27
phazene ligand (B), arsolanes and arsenanes
were synthesized
by using literature methods. Phenyl azide was prepared by diazotiza-
2
8
tion reaction as described in the literature. The glycols, triethylamine
were supplied commercially, but distilled prior to use. The percentage
of arsenic in the complexes was determined by iodometric titration.2
IR spectra were recorded in KBr mulls on Perkin Elemer-377 spec-
9
�
1
1
13
trophotometer in the range 4000–400 cm . The H and C NMR were
31
recorded on a Jeol FX90 Q MHz using TMS as external reference, P-
NMR were done on BurkerDRX 300(120 MHz) using 85% H3PO4 as
external reference. The mass spectrophotometer analysis (EI) was car-
ried out on ESQUIRE-3000 (BRUKER-DALTONICS) using LC-MS n
technique.
Synthesis of [HN(PPh NPh) ]
2
2
To a toluene solution of 3.42 g (21.1 mmol) of hexamethyldisilazene,
HN(SiMe3)2 was added drop wise a toluene solution of Ph2PCl 9.33 g
(
8
42.3 mmol) under nitrogen atmosphere. The contents were stirred at
0 C for 3 h and the thus formed trimethylsilylchloride (Me3SiCl), was
�
distilled off under reduced pressure. After removal of trimethylsilylchlo-
ride, 5.03 g (42.3 mmol) of phenyl azide (PhN3) was added drop wise at
�
6
0 C which resulted in the evolution of nitrogen gas. The contents were
refluxed till the evolution of nitrogen gas (about 2 h). Finally, the sol-
vent was removed under vacuo, when a pale-yellow solid was obtained.
Washing with n-hexane can further purify this. Yield 7.2 g (65%), m.p.
�
� 1
1
1
9
56–159 C. IR (KBr, cm ): 3345 m, 3050 m, 1600 s, 1580 vs, 1485 vs,
430 s, 1315 vs, 1280 vs, 1260 vs, 1220 vs, 1170 s, 1040 s, 1020 s, 990 s,
1
35 s, 750 vs, 720 vs, 695 vs, 595 s, 545 s, 520 vs and 500 s. H NMR
(
CDCl3, ppm): � 7.9–6.6, m, Ph (30H) and � 5.0–4.5,s br., NH (1H).
P NMR (CDCl3, ppm): � 7.1, s.
3
1
Synthesis of Complexes of Arsenic(III),
N(PPh NR) AsOGO] (R = Ph/ SiMe3)
[
2
2
Chloro dioxarsolanes/arsenanes, OGOAsCl, in toluene was added drop-
wise to a toluene solution of phenylated (A) or bis-silylated (B) phos-
phazene ligand, [HN(PPh2NR)2]; R = Ph(A) and SiMe3(B), in an
equimolar (1:1) ratio containing a stoichiometric amount of triethy-
lamine at room temperature. An immediate reaction takes place which

Phosphazene Complexes of Arsenic(III)
169
is indicated by the formation of white precipitates of triethylaminehy-
drochloride, Et3N�HCl, and the contents were also turned to yellow. The
reaction mixture was continuously stirred at moderate temperature
�
(
about 60 C) for 2–4 h for the sake of completion. Using an alkoxy fun-
nel triethylaminehydrochloride was filtered. The solvent was removed
under vacuo, which yielded the products quantitatively. The complexes
were yellow viscous products incase of ligand (A) while light yellow
semi-solid for ligand (B).
This methodology was applied to synthesize all the complexes using
stoichiometric weights except for a slight difference in stirring time.
The relevant synthetic and analytical data for all the complexes are
given in Table I.
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[
[
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