Novel synthetic approach to thiophosphinates incorporating different N-heterocycles

Article abstract of DOI:10.1080/10426500802060735

Eight new cycloiminylidenamidothiophosphinates incorporating pyridine, pyrimidine, thiazole, and benzothiazole heterocycles were synthesized by phosphorylation of the quaternary iminium salts of the heterocycles by diphenylchlorophosphine followed by in situ sulfurization by elemental sulfur. Crystalline solid products were well characterized by elemental analysis and NMR spectroscopy. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426500802060735

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Phosphorus, Sulfur, and Silicon
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Novel Synthetic Approach to
Thiophosphinates Incorporating
Different N-Heterocycles
Vijaya Kabra a , Sunita Mitharwal a , Arpana Meel a
Suman Tanwar a
a Department of Chemistry , University of
Rajasthan , Jaipur, India
&
Published online: 03 Nov 2008.
To cite this article: Vijaya Kabra , Sunita Mitharwal , Arpana Meel & Suman Tanwar
(2008) Novel Synthetic Approach to Thiophosphinates Incorporating Different N-
Heterocycles, Phosphorus, Sulfur, and Silicon and the Related Elements, 183:12,
3109-3115, DOI: 10.1080/10426500802060735
To link to this article: http://dx.doi.org/10.1080/10426500802060735
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Phosphorus, Sulfur, and Silicon, 183:3109–3115, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500802060735
Novel Synthetic Approach to Thiophosphinates
Incorporating Different N-Heterocycles
Vijaya Kabra, Sunita Mitharwal, Arpana Meel,
and Suman Tanwar
Department of Chemistry, University of Rajasthan, Jaipur, India
Eight new cycloiminylidenamidothiophosphinates incorporating pyridine, pyrimi-
dine, thiazole, and benzothiazole heterocycles were synthesized by phosphorylation
of the quaternary iminium salts of the heterocycles by diphenylchlorophosphine fol-
lowed by in situ sulfurization by elemental sulfur. Crystalline solid products were
well characterized by elemental analysis and NMR spectroscopy.
Keywords Chlorodiphenylphosphine; cycloiminium salts; phosphorylation; thiophos-
phinates
INTRODUCTION
Organothiophosphinates are tetracoordinated phosphorus derivatives
and have a significant place in the literature as ligands for metal com-
plexes, catalysis, ion exchangers and synthons for biaryls.1–6 Anchoring
of phosphinate coupled molecules on titania particles7 has recently at-
tracted interest for their numerous applications such as self assembled
monolayers,8 ceramic membrane9, optical write - read - erase devices10.
A number of methods for the synthesis of the title compounds are
available in the literature.11,12 Recently, we have reported a facile
route for the synthesis of organophosphorus derivatives in which the
phosphorus exists in different coordination states, which include phos-
pholes, organothiophosphates, and organothiophosphonates. Meth-
ods for the latter include phosphorylation of 2-aminocycloiminium
halides with phosphorus trichloride and phenyldichlorophosphine,
Received 6 November 2007; accepted 16 March 2008.
Authors are highly thankful to Department of Chemistry, University of Rajasthan,
Jaipur, for recording a number of NMR spectra and providing all necessary laboratory
facilities.
Address correspondence to Vijaya Kabra, Department of Chemistry, University of
Rajasthan, Jaipur 302004, India. E-mail sgkabra@sancharnet.in
3109

3110
V. Kabra et al.
respectively, followed by in situ nucleophilic substitution and
sulfurization.13−18
Extending this work, we now present the synthesis of novel
organothiophosphinates by an analogous synthetic strategy using
diphenylchlorophosphine as a phosphorylating agent. These thiophos-
phinates can be used as ligands for complexes as well as potential
pesticides.
RESULTS AND DISCUSSION
The starting materials, N-alkylcycloiminium halides (3), were synthe-
sized by treating 2-amino-N-heterocycles (1) and appropriately sub-
stituted alkyl halides (2) in THF at room temperature.13–15 The syn-
thesized N-alkylcycloiminium halides13–15 (3) were further allowed to
react with chlorodiphenylphosphine (1 equivalent) in a methylene chlo-
ride/toluene mix (2:1) in the presence of two and a half equivalents
of triethylamine at 0–5◦C. The resulted diphenylphosphines (4) were
subjected to sulfurizaton using one equivalent of elemental sulfur at
ambient temperature and furnished the corresponding diphenylthio-
phosphinates (5) (Scheme 1).
All synthesized thiophosphinates were obtained as white to creamy
yellow crystalline solids, stable under a nitrogen atmosphere. All the
products have been well characterized by elemental analysis, 31P, and
1H NMR spectroscopy.
Characterization
31P NMR. The reactions were monitored by 31P NMR spectroscopy of
the reaction mixture. The solids (5a–h) show 31P NMR signal between
49.19-80.87 ppm which were in good agreement with their tetra coor-
dinated pentavalent nature19 (Table I).
1H NMR. The structures of cycloiminylidenamidothiophosphinates
(5a–h) are confirmed by 1H NMR studies (Table I). In the 1H NMR all
NCH3 (5a–d) and NCH2 (5e–h) protons absorbed as a singlet between
3.62–5.42 ppm. Three protons of OCH3 (5g) were found at 3.69 ppm
while three protons of OCH2CH3 (5h) and two protons of OCH2 (5h)
were found to absorb at 1.25 ppm and 4.22 ppm as triplet and quartet,
respectively.
All aromatic and heterocyclic protons were found to absorb in their
characteristic range at 6–9 ppm with expected multiplicities (Table I).

Thiophosphinates Incorporating Different N-Heterocycles
3111
SCHEME 1
EXPERIMENTAL
All glassware used was washed with alkali followed by dilute acid
then water and acetone sequentially and were dried in an elec-
tric oven for 4–6 h at a high temperature until just before use.
Standard syringe techniques were used for the addition of chem-
icals. All solvents and reagents were freshly dried. Fine chem-
icals like 2-aminopyridine, 2-aminobenzothiazole, 2-aminothiazole,

3112

3113

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V. Kabra et al.
2-aminopyrimidine were procured from Aldrich and Merck and used
without further purification. All the synthetic procedures were carried
out in an inert atmosphere of nitrogen and due to the highly hygroscopic
nature of the synthesized products. Elemental analyses were performed
on Heraens Carlo Erba 1108 analyzer. 31P NMR spectra were recorded
on Jeol AL 300 at 121.50
1
MHz using 85% H3PO4 as an external standard. H NMR spectra
were recorded in CDCl3 on Jeol AL300 at 300.4 MHz using TMS as a in-
ternal reference. Melting points were determined by standard capillary
method on Electric Tempo Instrument and are uncorrected.
General Procedure for the Synthesis of
N-alkyl-2-iminodiphenyl-thiophosphinate (5a–h)
Starting material N-alkyl cycloiminium halides (13 mmol) were stirred
in minimum amount of 2:1 mix of dichloromethane (40 mL)/ toluene (20
mL). To this suspension one equivalent of chlorodiphenylphosphine (13
mmol) in the presence of two and a half equivalents of triethylamine
(32.5 mmol) were added at 0–5◦C. This reaction mixture was then al-
lowed to come to room temperature. After 2 h of continuous stirring, one
equivalent of elemental sulfur (13 mmol) was added at ambient tem-
perature. After 48 h of stirring the solution was filtered; the solvent
removed in vacuo; and the residue extracted with dried diethylether.
Extraction was left in refrigerator whereupon a solid was separated
out, which was dried under vacuum and recrystallized with hexane.
CONCLUSION
Eight diphenylthiophosphinates incorporating different N-cycloimines
have been successfully synthesized and characterized. These novel
organophosphorus molecules could be potential ligands for metal com-
plexes and due to the presence of different heterocycle rings should be
potentially bioactive molecules. Now, we are pursuing further research
to find out the application of these phosphinates as ligands of transition
metals, as well as their pesticidal properties.
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