Highly Selective Synthesis of <i>ctt</i>-1,5,9-Cyclododecatriene from 1,3-Butadiene via Nitrogen-Ligand-Supported Titanium Catalysts: Experimental Optimization and Mechanistic Insights

Facing global energy and environmental challenges, transportation industries are adopting lightweighting as a key strategy to improve energy efficiency. Nylon12 is a crucial material in lightweight applications. However, 1,5,9-cyclododecatriene (1,5,9-CDT) serves as a key intermediate in its synthesis, and the preparation methods of 1,5,9-CDT currently still suffer from low catalytic activity and insufficient conversion, coupled with a lack of mechanistic studies on macrocyclic formation. To address these challenges, this study focuses on the key synthesis technology of 1,5,9-CDT by designing and preparing four novel nitrogen-ligand-supported transition metal catalysts (Cat.1-Cat.4). Using 1,3-butadiene as the monomer, the effects of the catalyst performance and reaction conditions on the oligomerization process were systematically investigated. These results demonstrate that Cat.2, under optimized conditions (toluene as solvent, catalyst content of 0.2 g/L in polymerization solution, polymerization temperature of 50 °C, and <i>n</i>(Al)/<i>n</i>(Ti) ratio of 50 with sesquiethylaluminum chloride as cocatalyst), achieves a 93% yield of <i>ctt</i>-1,5,9-CDT, verified by ¹H (¹³C) NMR, FT-IR, and GC-MS. Density functional theory (DFT) calculations reveal a thermodynamically controlled reaction pathway, confirming the experimental product as the most stable conformation and elucidating the origin of high selectivity. This work provides a green and efficient catalytic system for 1,5,9-CDT synthesis while enriching the theoretical foundation of macrocyclic compound formation mechanisms. The findings exhibit significant potential for industrial-scale applications.