The cycloauration of pyridine-2-thiocarboxamide ligands

Reactions of H[AuCl4] with N-substituted 2-pyridine thiocarboxamide ligands 2-(C5H4N)C(S)NHR (R = p-C6H4Me, CH2Ph, Me, p-C6H4OMe) gave cycloaurated derivatives {(C5H4N)C(S)NR}AuCl2, with the ligand bonded as the thiol tautomer through the deprotonated SH group and the pyridine N atom to give a five-membered metallacyclic ring. The X-ray structure determination of the R = CH2Ph derivative shows a square–planar gold(III) complex that dimerises in the solid state by weak Au···S intermolecular interactions. In contrast, in the reaction of H[AuCl4] with 2-(C5H4N)C(S)NHR where R = 2-pyridyl, the ligand was oxidised to give a 1,2,4-thiadiazolo[2,3-a]pyridinium heterocyclic ring that was crystallographically characterised.

Graphical abstract2-Pyridine thiocarboxamides 2-(C5H5N)C(S)NHR (R = p-C6H4Me, CH2Ph, Me, p-C6H4OMe) undergo direct cycloauration with H[AuCl4]; the deprotonated ligand coordinates via the pyridyl nitrogen and sulphur atom. The ligand with R = 2-pyridyl reacted differently; instead of cycloauration, the ligand was oxidised to give a heterocyclic 1,2,4-thiadiazolo[2,3-a]pyridinium ring.Figure optionsDownload full-size imageDownload as PowerPoint slide