Metathesis reactions chelated alkylidene catalysts

In the past few years the groups of Schrock at MIT and Hoveyda at Boston College introduced a new type of Mo-alkylidene MonoAryloxide Pyrrolide (MAP) complexes as highly reactive and enantioselective olefin metathesis catalysts [56,57]. These stereogenic-at-metal complexes supported by non-chelating ligands turned out to be fascinating catalysts forZ-selective olefin metathesis reactions with the level of Z-selectivities that was completely out of reach before. 

In 2014, two independent reports from Poland disclosed the preparation of ruthenium-alkylidene complexes chelated via a phenoxide anion [29)7 After activation with hydrogen chloride or other suitable acidic additives, these stable catalyst precursors became efficient promoters for various CM, RCM, and enyne metathesis reactions, including butenolysis. It is noteworthy that they were soluble in neat dicyclopentadiene, thereby enabling their use as latent catalysts for the ROMP of this highly reactive monomer. 

Earlier this year, the Grubbs group reported the preparation of the Ru-based catalyst with a chelating iV-heterocyclic carbene (NHC) ligand that catalyzes highly Z-selective olefin metathesis (Fig. 31) [69, 70]. This catalytic system provided similar levels of efficiency and selectivity to the W-alkylidene complexes for homocoupling reactions. The reason for the Z-selectivity is not clear at this point. Extension of the substrate scope of this catalytic system is expected. 

---