The Impact of Ligand Structure and Reaction Temperature on Ethenolysis of Fatty Acid Methyl Esters Catalyzed by Spirocyclic Alkyl Amino Carbene Ru Complexes

Spirocyclic alkyl amino carbene (SCAAC) Ru complexes demonstrate outstanding activity and selectivity in ethenolysis of methyl oleate (MO) or fatty acid methyl esters (FAMEs), and 5,6-dimethoxyindane derivative was the most active catalyst to date. For the further catalyst design, we proposed modifying the spirocyclic fragment by fusion of saturated carbo- or heterocycle, linked to the 5,6-positions of indane or 6,7- positions of tetralin. Another suggested way of the modification of SCAAC complex was the insertion of chromane fragment to the carbene ligand. Using an alternative approach to SCAAC ligand precursors, based on hydroformylation of indenes, dihydronaphthalenes and their analogs, new SCAAC complexes were synthesized, their cis-configuration was confirmed by XRD. Comparative study of new and known selected complexes in ethenolysis of FAMEs (84 wt% MO) revealed that each of SCAAC catalysts has a temperature optimum of activity. At 60 °C 0.5 ppm of the complex containing 1,2,3,4,5,6,7,8-octahydroanthracene spirocyclic fragment provided 56 % conversion of FAMEs with TON=1.1⋅10 ; 0.25 ppm of this complex in ethenolysis of high-purity MO demonstrated the TON ~2⋅10 , leading among the catalysts under study. In ethenolysis of FAMEs chromane derivative showed TON of 4-6⋅10 and unprecedented temperature-independent 99.7-99.9 % selectivity at 15-60 °C.