Inhibition of the Decomposition Pathways of Ruthenium Olefin Metathesis Catalysts: Development of Highly Efficient Catalysts for Ethenolysis

Ruthenium-based Hoveyda-type olefin metathesis catalysts
bearing
novel rigid spirocyclic alkyl amino carbenes (CAACs) have been developed.
They are characterized by exceptional stability toward decomposition
through β-elimination and bimolecular pathways, thus enabling
unprecedented efficiency in the cross-metathesis of seed oil-derived
fatty acid esters with ethylene (ethenolysis). Catalyst loading as
low as 100 ppb was applied to the ethenolysis of the model substrate
methyl oleate, leading to a remarkable turnover number (TON) of 2.6
million, significantly higher than previously reported (TON 340 000
at 1 ppm and 744 000 at 0.5 ppm catalyst loading). Ethenolysis
of methyl esters derived from high oleic sunflower oil and rapeseed
oil, readily available on an industrial scale, inexpensive, and renewable
feedstocks, was for the first time effectively carried out with 0.5
ppm catalyst loading with TON as high as 964 000.