Platinum assisted cyclization of S-methyl 3-acyl-2-methyldithio-carbazates under mild conditions. Crystal structure of [Pt_2(μ-SMe)-(terpy)_2][ClO_4]_3

摘要

The reaction of the newly synthesized aqua complex [Pt(terpy)(OH)_2][BF_4]_2 with S-methyl 3-acyl-2-methyldithio-carbazates under a variety of experimental conditions have been studied. Using a 2:1 metal to ligand ratio in methanol, a platinum assisted cyclization was observed. The reaction products were #DELTA#~2-1, 3,4-oxadiazoling-5-thione derivatives and the binuclear tricationic complex [Pt_2(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 #DELTA#~2-1, 3,4-oxadiazoline-5-thiones under mild conditions. In the presence of an excess of a non-co-ordinating acid (HClO_4,CH_3SO_3H or CF_3SO_3H) the cyclization is completely quenched and comlexes 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.