Recently, a new class of ligands based on the quinoline scaffold has achieved groundbreaking advancements in the field of catalysis. A research team, through molecular design and optimization, developed transition-metal complexes centered around 2,2'-biquinoline derivatives, successfully scaling up production to kilogram levels. These ligands are synthesized via a tandem process combining the azahetero-Diels-Alder reaction with oxidative aromatization, using readily available starting materials under mild reaction conditions. Notably, the gram-scale synthesis consistently delivers yields ranging from 58% to 73%.

In terms of catalytic performance, this ligand demonstrates significant advantages when paired with transition metals such as ruthenium and iridium to form half-sandwich complexes. For instance, in the oxidation of alcohols to produce adipaldehyde, the catalyst loading can be reduced to just 1/5 of that used in conventional processes under ambient temperature and pressure with air as the oxidant. As a result, the yield of the desired product increases to 92%, representing a threefold improvement in efficiency compared to the original system. At the heart of this enhanced performance lies the ligand's ability to modulate the reactivity of the metal center via steric shielding, while its long alkyl chain structure also improves the catalyst's dispersibility in polar solvents, thereby accelerating the reaction rate.

Currently, this technology has been collaboratively advanced toward industrialization with several chemical companies, achieving an annual production capacity of 60 tons of adipaldehyde and generating approximately 5 million yuan in additional annual revenue. The associated ligands have also demonstrated exceptional performance in the aminobenzyl alcohol cyclization-oxidation-addition reaction for synthesizing quinoline derivatives, with kilogram-scale scale-up experiments confirming their process stability—and paving the way for a new, eco-friendly approach to synthesizing pharmaceutical intermediates.