Synthesis and reactivity of a new type of crown ether thiosemicarbazone

Palladacycles are very versatile compounds and they are known for a good number of ligands. Their main applications are as catalysts, sensors or as antitumor agents. In the particular case of the thiosemicarbazone ligands, these react with palladium salts to give very robust cyclometallated compounds, which present great air and thermal stability; the ligands themselves show a high biological activity. Moreover, when the corresponding thiosemicarbazone is functionalized with a crown-ether moiety, the resulting palladacycle behaves as a new type of sensor.

Once palladated the thiosemicarbazone ligand behaves as tridentate, thus occupying all but one of the coordination positions in the square planar environment of the palladium atom. If the ligand is forced to react in the thione fashion with respect to the sulfur atom, the resulting palladacycle is a mononuclear species with the fourth coordination position readily accessible for further modifications.

In this communication we present the synthesis of [3,4-(C₈H₁₆O₅) C₆H₃C(H)=NN(Me)C(=S)NH₂] (1) and its reactivity towards Li₂PdCl₄ to obtain the mononuclear cyclometallated compound [Pd{3,4-(C₈H₁₆O₅)C₆H₃C(H)=NN(Me)C(=S)NH₂}(Cl)] (1Pd). The characterization of both compounds was carried out using IR and ¹H NMR spectroscopy.