Platinum assisted cyclization of S-methyl 3-acyl-2-methyldithiocarbazates under mild conditions. Crystal structure of [Pt2(µ-SMe)(terpy)2][ClO4]3†

Abstract

The reaction of the newly synthesized aqua complex [Pt(terpy)(OH₂)][BF₄]₂ with S-methyl 3-acyl-2-methyldithiocarbazates under a variety of experimental conditions has been studied. Using a 2∶1 metal to ligand ratio in methanol, a platinum assisted cyclization was observed. The reaction products were Δ²-1,3,4-oxadiazoline-5-thione derivatives and the binuclear tricationic complex [Pt₂(µ-SMe)(terpy)₂]³⁺ whose molecular structure has been determined by X-ray crystallography. This platinum assisted transformation is proposed as a new synthetic route to Δ²-1,3,4-oxadiazoline-5-thiones under mild conditions. In the presence of an excess of a non-co-ordinating acid (HClO₄, CH₃SO₃H or CF₃SO₃H) the cyclization is completely quenched and complexes with co-ordinated S-methyl 3-acyl-2-methyldithiocarbazates have been isolated. A general mechanism which accounts for the observed transformations is proposed on the basis of ¹H NMR and UV/Vis evidence.