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Mesoporous heterogeneous santa barbara amorphous (SBA)‐15‐supported cobalt complex, as a novel nanocatalyst containing N–O chelating Schiff‐base ligand was successfully synthesized by the reaction of SBA‐15 and Cobalt(II)‐Schiff‐base complex. The Co(II)‐Schiff base complex also was prepared for the first time, by the reaction of pyridoxal 5′‐phosphate or PLP (biological active form of vitamin B6), 3‐(aminopropyl)‐triethoxysilane in methanol that complexation with CoCl2. The subsequent grafting of entitled complex to SBA‐15 afforded Co(II)‐PLP‐Schiff base/SBA‐15 mesoporous catalyst. Characterization of the product was carried out with powder X‐ray diffraction, Brunauer–Emmett–Teller nitrogen adsorption–desorption, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, atomic absorption spectroscopy, and inductively coupled plasma, Fourier‐transform infrared spectroscopy. The results revealed the retention of the textural properties and hexagonally uniform structures of SBA‐15 during the grafting procedure. This nanocatalyst was applied successfully for one‐pot synthesis of various benzothiazole heterocycles under green conditions. This catalyst is an active, reusable, and stable nanomaterial with no leaching of metal ions to the reaction medium. It was used for the synthesis of desired benzothiazole heterocycles by the cyclo‐condensation of aryl‐aldehydes with 2‐aminothiophenol with good to excellent yields and under green conditions.

In this work, three speculative mechanisms of the reaction between triphenylphosphine and dimethyl acetylendicarboxylate in the presence of 3‐chloropentane‐2,4‐dione were energetically and thermodynamically developed using quantum mechanical calculations and were profoundly compared with stopped‐flow and UV spectrophotometry approaches. The third speculative mechanism that led to the five‐membered ring structure was experimentally and theoretically favorable. The five‐membered ring structure of product was characterized by X‐ray crystallographic data. Also, steps 1 and 2 of the third mechanism were determined as fast and rate‐determining steps, respectively. The experimental kinetic evidence of the formation and decay of intermediate in steps 1 and 2 (fast and rate‐determining steps, respectively) was compatible with theoretical data. Experimental kinetic data were recognized for overall reaction along with activation parameters for fast and rate‐determining steps of the reaction. Theoretical kinetic data (k and Ea) and activation parameters (ΔG≠, ΔS,≠ and ΔH≠) were calculated for each step and overall reactions.

The reaction between triphenyl or trialkyl phosphite and acetylenic esters in the