Sangeeta Obrai

The chemistry of pyridinethiols and related ligands, Part 9. Synthesis, spectroscopy and crystal structure of sulphur bridged dimeric [{η3-(O-μ-S)-1-oxopyridine-2-thione}(triphenylphosp hine)silver(I)]

Reaction of 1-hydroxypyridine-2-thione (HpyOS) in CHCl3 with Ag2CO3 suspended in CHCl3 under magnetic stirring followed by addition of PPh3 yields a product of stoichiometry: Ag(pyOS)(PPh3). The compound adopts a dimeric structure [Ag(pyOS)(PPh3)]2 (1) where each Ag atom acquires a distorted tetrahedral geometry by co-ordinating to one oxygen, two sulphur and one phosphorus atoms. The Ag2S2 core forms a parallelogram [Ag—S 2.507(1), 2.822(1)Å] with Ag—S—Ag and S—Ag—S angles of 74.8(1) and 105.2(1)°, respectively.

5-Methyl-5-aryldipyrromethanes: synthesis, crystal structure and anion binding studies

The eco-friendly and selective syntheses of 5-methyl-5-aryldipyrromethanes (1–4) in which aryl is FC6H4 1, ClC6H5 2, CH3OC6H5 3 and CH3C6H5 4, have been reported in the presence of citric acid (weak organic acid) and characterised by IR, 1H NMR, 13C NMR and mass spectroscopy. The structures of 2–4 have been confirmed by X-ray crystallography. Anion binding studies of 1–4 with different anions (e.g. F− , Cl− , CH3COO− , and ) have been carried out by 1H NMR titrations and binding constants have been evaluated using EQNMR program, revealing that they bind fluoride selectively compared with other anions with 1:1 stoichiometry in CDCl3. The binding affinities of these compounds are influenced by the nature of the substituent on the meso-carbon atom.

Highly regioselective nucleophilic/cycloaddition reactions of N-arylamino 1,3-diazabuta-1,3-dienes with α-nitrosostyrenes: synthesis of functionalised imidazoles and imidazole oxides

The α-nitrosostyrenes 2, generated in situ from α-halogeno oximes, underwent regioselective cycloadditon/nucleophilic reactions with N-arylamino 1,3-diazabuta-1,3-dienes 1 leading to a mixture of imidazoles and cyclic nitrones shown to have structures 3 and 4, respectively, by X-ray crystallographic analysis. The structure 4 for cyclic nitrones was also supported by their 1,3-dipolar cycloaddition with dimethyl acetylenedicarboxylate (DMAD). The thermolysis of nitrones 4 gives imidazoles 3 via oxadiazine intermediates 6.