Synthesis and characterization of some novel triphenylarsenic(V) derivatives of monofunctional bidentate 2,2-disubstituted benzothiazoline ligands

Article abstract of DOI:10.1002/hc.20233

A series of triphenylarsenic(V) derivatives Ph₃As(OPr ⁱ)[SC₆H₄N:C(R)CH₂C(O)R′] have been synthesized by the reactions of triphenylarsenic(V)-isoproproxide, Ph ₃As(OPrⁱ)₂

Full text of DOI:10.1002/hc.20233

Heteroatom Chemistry
Volume 18, Number 1, 2007
Synthesis and Characterization of Some Novel
Triphenylarsenic(V) Derivatives
of Monofunctional Bidentate 2,2-Disubstituted
Benzothiazoline Ligands
Pankaj K. Sharma, A. K. Rai, and Yashpal Singh
Department of Chemistry, University of Rajasthan, Jaipur 302 004, India
Received 10 November 2004; revised 2 February 2006
and as precursors for superconducting materials in
ABSTRACT: A series of triphenylarsenic(V) deriva-
MOCVD process [4,5]. The use of organoarsenic in
tives Ph3As(OPri)[SC6H4N:C(R)CH2C(O)Rꢀ] have been
medicines dates from the discovery in 1905 by H.W.
synthesized by the reactions of triphenylarsenic(V)-
Thomas after atoxyl cure hypsoniasis, i.e., sleeping
isoproproxide, Ph3As(OPri)2 with the corresponding
sickness. In 1907, R.E. Rechard and A. Bertheins
2,2-disubstituted benzothiazolines of the type
showed that atoxyl was sodium hydrogen-4-
HNC6H4 SC(R)CH2C(O)Rꢀ (where R = CH3, Rꢀ =
aminophenylarsonate [6]. Recently interest has also
CH3(1); R = CH3, Rꢀ = C6H5(2); R = CH3, Rꢀ = 4-
been renewed in low temperature ionic liquid tech-
CH3C6H4(3); R = CH3, Rꢀ = 4-ClC6H4(4); and R = CF3,
nology using organoarsenic derivatives for electrode-
Rꢀ = C6H5(5)) in equimolar ratio in refluxing ben-
position of actinides of relevance to nuclear fuel pro-
zene solution. Molecular weight measurements of
cessing [7]. In addition to these applications, these
these complexes show their monomeric nature in
compounds also display structural diversity which,
solution. Characterization of these compounds using
for various organoarsenic complexes, has been es-
elemental analyses, molecular weight measurements,
tablished ranging from monomeric complexes [8,9]
and spectral studies (IR as well as NMR (1H and
to structures with infinite polymeric chains [10,11].
13C)) shows the monofunctional bidentate nature
Benzothiazolines constitute an important class
of the ligands and a hexacoordination around the
of multidentate ligands [12]. The use of these Lewis
central arsenic atom in these organoarsenic(V) deriva-
base functionalized ligands can be effective in in-
ꢁ
C
tives.
2007 Wiley Periodicals, Inc. Heteroatom Chem
creasing the coordination number of the group 15
center at the expense of benzothiazoline ring to the
corresponding Schiff base leading to greater stabil-
ity of the compounds. In view of the above and in
continuation of our analogous studies on organoan-
timony(V) derivatives [13], we report herein the syn-
thesis and characterization of triphenylarsenic(V)
derivatives of these ligands.
18:76–80, 2007; Published online in Wiley InterScience
(www.interscience.wiley.com). DOI 10.1002/hc.20233
INTRODUCTION
Compounds containing heavier group 15 elements
have attracted attention over the last decade because
of their applications in heterogeneous catalysis [1–3]
RESULTS AND DISCUSSION
The reactions of Ph3As(OPri)2 with a number of benz-
othiazoline ligands of the type H NC6H4SC(R)CH2-
C(O)Rꢀ in 1:1 molar ratios in refluxing anhydrous
Correspondence to: Yashpal Singh; e-mail: yp singh07@yahoo.
co.in.
Contract grant sponsor: University Grants Commission, India.
c
ꢁ
2007 Wiley Periodicals, Inc.
76

Synthesis and Characterization of Some Novel Triphenylarsenic(V) Derivatives 77
benzene yielded the corresponding organoarsenic-
(V) derivatives 1–5 represented by the following
equations:
measurements reveal their monomeric nature in the
benzene solution.
(i)
2PriOH + 2Na
−→ 2NaOPri + H2↑
IR SPECTRA
A comparison of the IR spectra of the complexes
1–5 with the IR spectra of corresponding free lig-
ands show the following features: Disappearance of
the broad stretching vibrations, observed at 3225–
3335 cm−1 due to >N H group in the spectra of
the free ligands, suggesting the rearrangement of
the benzothiazoline ring during complexation and
the formation of the C N bond. This rearrangement
of the benzothiazoline ring is also supported by the
appearance of three new bands at 1610–1622 cm−1,
427–435 cm−1, and 373–390 cm−1 due to ν(>C N),
ν(As←N) [14], and ν(As–S) [15] vibrations, respec-
tively. No shift has been observed in the position
(1720–1730 cm−1) of the absorption band due to
>C O group on complexation, indicating that this
group does not participate in bonding. The As–Ph vi-
brations (Y-mode) have been observed in the range
470–495 cm−1 [16].
C6H6
(ii)
2NaOPri + Ph3AsBr2
−→ Ph3As(OPri)2
Reflux
+ 2NaBr↓
(iii) Ph3As(OPri)2
C6H6
−→
Reflux
+ H NC6H4SC(R)CH C(O)Rꢀ
Ph3As(OPri)[SC6H4N:C(R)CH C(O)Rꢀ] +
2
2
PriOH
where R = CH3, Rꢀ = CH3(1); R = CH3, Rꢀ = C6H5(2);
R = CH3, Rꢀ = 4-CH3C6H4(3); R = CH3, Rꢀ = 4-
ClC6H4(4), and R = CF3, Rꢀ = C6H5(5).
The synthetic and analytical data of these deriva-
tives 1–5 are summarized in Table 1. All these reac-
tions are quantitative and quite facile. Their progress
and completion has been checked by estimat-
ing the isopropanol liberated azeotropically dur-
ing the course of the reactions. The products ob-
tained are hygroscopic, light to dark brown col-
ored, viscous compounds, and soluble in common
organic solvents. Ebullioscopic molecular weight
1H NMR SPECTRA
The characteristic signals in the 1H NMR spectra of
these derivatives are summarized in Table 2. The
TABLE 1 Synthetic and Analytical Data and Physical Properties of the Derivatives from 1 to 5
Molecular
Reactants (g) (mmol)
Formula, Color, PriOH(g)
Analysis % Found (Calcd)
Physical State,
and % Yield
Found
(Calcd)
Molecular Weight
Found (Calcd)
Complex
Na Ph3AsBr2 Ligand
As
N
S
OPri
1. R = CH3
Rꢀ = CH3
0.30
(13.05) (6.50)
3.03
1.35
(6.51)
C32H34NO2SAs,
Light brown,
viscous,
0.37
13.05 2.38 5.57
10.24
563
(571.60)
(0.39) (13.11) (2.45) (5.61) (10.34)
83
2. R = CH3
Rꢀ =
0.29
3.00
1.73
C37H36NO2SAs
0.36
11.75 2.18 5.01
9.25
622
(12.87) (6.44)
(6.42)
Dark brown,
viscous,
(0.39) (11.82) (2.21) (5.06) (9.32)
(633.67)
86
3. R = CH3
Rꢀ =
0.31
3.15
1.91
C38H38NO2SAs,
0.37
11.50 2.12 4.88
9.04
635
(13.48) (6.76)
(6.77)
Light brown,
viscous,
85
(0.41) (11.56) (2.16) (4.95) (9.12)
(647.70)
4. R = CH3
Rꢀ =
0.28
2.79
1.82 C37H35ClNO2SAs,
0.34
11.16 2.04 4.74
8.77
659
(12.18) (5.99)
(5.99)
Black,
viscous,
81
(0.36) (11.21) (2.10) (4.80) (8.84)
(668.12)
5. R = CF3
Rꢀ =
0.26
(11.31) (5.62)
2.62
1.82 C37H33F3NO2SAs, 0.31
10.85 1.98 4.57
8.51
680
(687.64)
(5.63)
Dark brown,
(0.34) (10.90) (2.04) (4.66) (8.59)
viscous,
88
Heteroatom Chemistry DOI 10.1002/hc

78 Sharma, Rai, and Singh
TABLE 2 1H NMR Spectral Data (δ ppm) of the Derivatives 1–5
Schiff Base Moiety
Isopropoxy Moiety
Complex
R
Rꢀ
CH2
NC6H4S
OCH
CH3
1.04 (d)
1.09 (d)
Phenyl (Ph-Sb) Moiety
7.74–8.04(m)
1.
2.
R = CH3
Rꢀ = CH3
R = CH3
2.19(s)
1.82(s)
2.83(s) 7.13–7.70(m) 3.72(sept)
2.55(s) 7.20–7.78(m) 2.75(s) 7.20–7.78(m) 3.67(sept)
2.62(s) 6.97–7.70(m) 2.61(s) 6.97–7.70(m) 3.70(sept)
2.40(s) 6.91–7.64(m) 2.43(s) 6.91–7.64(m) 3.71(sept)
7.82–8.08(m)
Rꢀ =
3.
4.
5.
R = CH3
1.03 (d)
0.96 (d)
1.02 (d)
7.78–8.12(m)
7.68–8.03(m)
7.82–8.11(m)
aRꢀ =
R = CH3
Rꢀ =
R = CF3
–
7.26–7.78(m) 2.49(s) 7.26–7.78(m) 3.70(sept)
Rꢀ =
(s) = singlet; (d) = doublet; t = triplet; (m) = multiplet; (sept) = septet.
aA singlet for –CH3 protons has been observed at δ 2.40 ppm.
broad signal observed at δ 4.53–6.46 ppm, due to
the NH group resonance in the spectra of benzoth-
iazolines, is found to be absent in the correspond-
ing triphenylarsenic(V) derivatives indicating the de-
protonation of NH proton and rearrangement of the
benzothiazoline ring during the complex formation.
A sharp singlet observed at δ 2.43–2.83 ppm has been
assigned to CH2 protons. The absence of CH as well
as C OH signals and the presence of CH2 signal
in the spectra of both ligands and their correspond-
ing complexes indicate the absence of enolization of
>C O group in these ligands, i.e., these ligands do
not behave as bifunctional moieties in these deriva-
tives, as reported by earlier workers in the case of
Al [17], Ga and In [18]. Different R and Rꢀ protons
have been observed at their expected positions with
small downfield shifts as compared to their positions
in corresponding free ligands. Phenyl (directly at-
tached to As) protons appear as a complex pattern
in the range δ 7.68–8.12 ppm.
ticipation of this group in bonding with rearrange-
ment of the benzothiazoline ring on complexation
followed by the formation of As←N and As–S bonds.
The signals for various R, Rꢀ, and CH2 carbons show
a small shift in comparison to their positions in free
ligands.
The presence of the CH2 signal instead of the
CH signal indicates that enolization does not take
place in these ligands. Appearance of >C O signal
at δ 195.93–198.57 in the spectra of ligand also rules
out the possibility of the enolization in these ligands.
This resonance signal does not show any shift in its
position indicating that oxygen is not coordinated to
the central atom. The presence of >CH(OPri) and
CH3(OPri) resonances at
δ 79.30–81.12 and
δ 19.67–25.94 ppm, respectively, indicates the mono-
functional behavior of these ligands. It is clear from
the above facts that, in contrast to the earlier [17,18],
these ligands behave as monofunctional bidentate
moiety in these derivatives. The phenyl carbons ap-
pear in the region δ 128.25–155.85 ppm.
On the basis of these results, the plausible
structure (Fig. 1) may be proposed for these
13
C NMR SPECTRA
Some useful information about the complexation be-
havior of benzothiazolines with central As atom and
the geometry of these derivatives have been obtained
from 13C NMR spectral data summarized in Table 3.
The signal observed for >C N group carbon at
δ 161.39–165.74 ppm in the spectra of free benzoth-
iazolines (present as C N) have been observed at
δ 165.18–167.26 ppm in the spectra of these deriva-
tives. This small downfield shifting (∼2–4 ppm) in
the position of >C N group signal suggests the par-
FIGURE 1 Proposed structure of the derivatives 1–5.
Heteroatom Chemistry DOI 10.1002/hc

Synthesis and Characterization of Some Novel Triphenylarsenic(V) Derivatives 79
TABLE 3 13C NMR Spectral Data (δ, ppm) of the Derivatives 1–5
Schiff Base Moiety
CH2 NC6H4S
Isopropoxy Moiety
Complex
R
Rꢀ
>C O >C N OCH
CH3
Phenyl (Ph-Sb) Moiety
1. R = CH3
Rꢀ = CH3
24.38 19.64 42.25 152.34,136.76, 195.93 165.18 79.67
25.94
154.17 (i)
135.26 (o)
128.97 (m)
128.43 (p)
155.85 (i)
133.75 (o)
134.70,131.18,
127.43, 122.16
2. R = CH3
Rꢀ =
26.64 135.20 40.32 151.78, 135.19, 197.85 166.79 79.30
19.67
25.16
25.40
24.16
133.09
133.50,130.68,
130.26
129.65
127.13,122.85
128.78 (m)
128.29 (p)
154.76 (i)
3. R = CH3
aRꢀ =
26.10 132.78 41.86 151.98,135,77, 198.15 166.40 80.35
131.98
130.29
129.35
143.14,130.87,
127.64,122.88
133.40 (o)
128.72 (m)
128.25 (p)
154.73 (i)
4. R = CH3
Rꢀ =
26.53 135.18 40.82 154.09,135.23, 198.57 165.78 81.12
133.04
128.51
129.93
133.15,130.64,
127.34,122.13
136.75 (o)
129.04 (m)
128.43 (p)
155.27 (i)
5. R = CF3
Rꢀ =
108.12 134.13 40.26 152.69,135.18, 197.35 167.26 79.96
132.25
128.87
130.92
133.03,130.54,
127.35,122.86
136.37 (o)
128.98 (m)
130.29 (p)
a13C signal for –CH3 group has been observed at δ 27.64 ppm.
triphenylarsenic(V) derivatives in which central ar-
senic atom adopts an octahedral geometry.
MHz NMR spectrometer, using TMS as an internal
and external reference, respectively.
EXPERIMENTAL
Synthesis of 1
Moisture was carefully excluded throughout the ex-
perimental manipulations. All the chemicals used
were of reagent grade. Solvents (E. Merck) were care-
fully dried by standard methods before use. The ben-
zothiazoline ligands were prepared [12] by equimo-
lar condensation reactions of 2-aminothiophenol
with corresponding ꢀ-diketones in refluxing benzene
solution and were purified by distillation under vac-
uum before use. Ph3AsBr2 was prepared by the liter-
ature method [19]. Triphenylarsenic(V) isopropox-
ide was prepared by the reaction of Ph3AsBr2 with
sodium isopropoxide [20]. Arsenic was estimated
iodometrically [21]. Nitrogen and sulfur were esti-
mated by Kjeldahl’s and Messenger’s methods, re-
spectively [21]. Isopropanol and isopropoxide were
estimated by the chromate oxidimetric method [22].
Molecular weight measurements were carried
out by ebullioscopic method in the benzene solu-
tion using a Beckmann’s thermometer. The IR spec-
tra were recorded on a Nicolet DX FTIR spectropho-
tometer in the range 4000–200 cm−1 on a CsI cell.
1H and 13C NMR spectra were recorded in DMSO-
d6 solution on a JEOL-FX-90Q or Brucker DPX-300
A weighed amount of sodium metal (0.30 g, 13.05
mmol) was added to ∼20 mL of anhydrous iso-
propanol, and the mixture was stirred for ∼1 h. A
benzene solution of Ph3AsBr2 (3.03 g, 6.50 mmol)
was added to it, and the reaction mixture was re-
fluxed for about 4 h. The NaBr thus precipitated was
filtered off, and the excess solvent from the filtrate
was removed under the reduced pressure to give vis-
cous triphenylarsenic (V) isopropoxide. A benzene
solution of the ligand HNC6H4SC(CH3)CH2C(CH3)
(1.35 g, 6.51 mmol) was added in the above
Ph3As(OPri)2, and the mixture was refluxed for ∼5 h
under a fractionating column. The progress as well
as the completion of the reaction was checked by es-
timating the liberated isopropanol in the azeotrope.
After the completion of the reaction, the excess sol-
vent was distilled off and traces of solvent were re-
moved under reduced pressure to give a viscous
product. This product was purified by dissolving it
in a small amount of anhydrous benzene and then
adding into it well-dried petroleum ether (40–60◦C)
until the compound began to separate. This solution
was kept overnight at –10◦C. After decanting off
Heteroatom Chemistry DOI 10.1002/hc

80 Sharma, Rai, and Singh
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the solvent, the compound was dried under vacuum
(yield 83%, (3.72g)).
Similar procedure was adopted for the synthesis
of all other complexes. Their synthesis and analytical
data are summarized in Table 1.
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Heteroatom Chemistry DOI 10.1002/hc