Rational Design of Tridentate NNN Zn(II) Catalysts: Ligand-Assisted Synthesis of Trisubstituted s -Triazines via Dehydrogenative Coupling of Primary Alcohols with Amidines and Biguanides

Abstract s-Triazines are important N-heterocycles used in pharmaceuticals, sensors, and optoelectronic devices, but their synthesis typically relies on prefunctionalized substrates and harsh conditions. In this study, we synthesized a series of well-characterized zinc complexes, confirmed by various spectroscopic methods, which serve as catalysts for the dehydrogenative coupling of alcohols with amidines and biguanides to produce 2,4,6-trisubstituted s-triazines. This eco-friendly catalytic method offers a sustainable route to s-triazines, with H2, H2O, and NH3 as the main small-molecule byproducts and eliminates the need for stoichiometric oxidants. The technique has been successfully tested with 77 substrates, including both aliphatic and aromatic primary alcohols, amidines, and biguanides. Additionally, the synthesis of several functional triazines featuring fluorescent dyes, organic linkers, and bioactive molecules demonstrates the efficiency of our catalytic system. Mechanistic investigations supported by DFT studies suggest that the catalyst functions via a metal–ligand cooperative mechanism, involving reversible aromatic and nonaromatic states of the pyridyl-hydrazone backbone, substrate activation, hydrogen transfer, and stabilization of key intermediates, with the ligand playing a crucial role in bond formation.