Synthesis and characterization of Pd(II) tetradentate Schiff base complex as an efficient catalyst for the oxidative coupling of thiols to disulfides using tert-BuOOH

Conversion of thiols to the corresponding disulfides under mild reaction conditions plays crucial roles in organic synthetic chemistry and biochemistry. On the other hand, disulfides have many industrial applications and are important reagent in organic synthesis [1]. Although, various reagents for the preparation of disulfides from thiols have been reported, however, these procedures have some drawbacks such as low yields, long reaction times and harsh reaction conditions. To improve mentioned problems, various catalytic methods have been developed for the oxidative coupling of thiols to their corresponding disulfides. In this regard, the Schiff base transition metel complexes are attractive catalysts due to their easy synthesis and their thermal and chemical stability [2].In this work, the tetradentate Schiff base ligand was prepared according to published method [2] and metallated with PdCl2 by the standard procedure of refluxing ethanolic solutions of Schiff base ligand and metal salt in 1:1 molar ratio to obtain complex 1. The prepared complex 1 was characterized by FT-IR, UV-vis and 1HNMR spectroscopic techniques and elemental analysis (CHN). The synthesized complex 1 successfully applied as a new homogeneous catalyst for oxidative coupling of thiols with tert-BuOOH (TBHP) at room temperature (Fig. 1). In order to elucidate the role of the palladium complex as catalyst, the reaction was carried out in the absence of the Pd(II) complex, and a trace amount of the product was obtained. Good yields of the products, mild reaction conditions and no by-products can be mentioned as advantages of this method for the preparation of disulfides.