Testing Lipophilic Cyclic(Alkyl)(Amino)Carbene-Based Ruthenium Benzylidene Catalysts in Cross Metathesis of 1-Dodecene at Ultralow Loadings (Below One Part-Per-Million)

A series of ruthenium benzylidene complexes bearing cyclic(alkyl)(amino)carbene (CAAC) ligands were evaluated for the cross-metathesis of 1-dodecene (2) to produce (E/Z)-docos-11-ene (3), a valuable fine chemical for producing of alkenyl succinic anhydride (ASA, 1) for papermaking applications. The studied reaction was found to be highly sensitive to steric hindrance in the CAAC-catalyst ligand sphere, with bulkier groups (introduced to increase the lipophilicity of the catalyst) decreasing catalytic activity. The most optimal catalyst selected (Ru4) combined acceptable solubility in nonpolar solvents with high activity and nearly ideal selectivity achieved without benzoquinone additives. Further optimization of key reaction parameters, including efficient ethylene removal, reaction vessel shape, and portion-wise catalyst addition, allowed the cross-metathesis reaction of 1-dodecene to achieve a turnover number (TON) exceeding two million.