Synthesis and structural characterization of palladium pincer complexes: Sustainable synthesis of benzothiazoles

An efficient Pd(II)N<^>N<^>S pincer type catalysts-promoted sustainable construction of pharmaceutically important benzothiazole derivatives from primary alcohols and 2-aminothiophenol via acceptorless dehydrogenative coupling (ADC) method has been described. The newly synthesized ligand L-2 and the Pd(II) complexes in addition to L-1 and L-3 were characterized by analytical and Fourier transform infrared spectroscopy (FT-IR), UV-visible (UV-vis), and nuclear magnetic resonance (NMR) spectral techniques. Further, the ORTEP views of the complexes 2 and 3 were established by a single crystal XRD study, which evidenced the coordination of the thiosemicarbazone ligands and disclose the square-planar geometry around the Pd(II) ion. The present homogeneous catalytic system involves synthesizing a range of benzothiazoles via C-S and C-N bond formation with excellent yields up to 93%. The described methodology employs a sustainable, highly abundant, and inexpensive alcohol as starting material using 1 mol% catalyst loading, and water and hydrogen gas are the only by-products. Furthermore, a plausible mechanism involving in situ aldehyde formation via dehydrogenation of primary alcohols has been proposed. A large-scale synthesis of 2-(4-methoxyphenyl)benzo[d]thiazole illustrates the synthetic utility of the present catalytic protocol.

Automated summary

An efficient method for the sustainable construction of pharmaceutically important benzothiazole derivatives from primary alcohols and 2-aminothiophenol using Pd(II)N<^>N<^>S pincer type catalysts has been described. The catalytic system allows for the synthesis of benzothiazoles via C-S and C-N bond formation with excellent yields. The use of an abundant and inexpensive alcohol as the starting material, along with the minimal production of water and hydrogen gas as by-products, demonstrates the sustainability of this methodology.