Enantioselective Olefin Metathesis with Cyclometalated Ruthenium Complexes

The
success of enantioselective olefin metathesis relies on the design
of enantioenriched alkylidene complexes capable of transferring stereochemical
information from the catalyst structure to the reactants. Cyclometalation
of the NHC ligand has proven to be a successful strategy to incorporate
stereogenic atoms into the catalyst structure. Enantioenriched complexes
incorporating this design element catalyze highly Z- and enantioselective asymmetric ring opening/cross metathesis (AROCM)
of norbornenes and cyclobutenes, and the difference in ring strain
between these two substrates leads to different propagating species
in the catalytic cycle. Asymmetric ring closing metathesis (ARCM)
of a challenging class of prochiral trienes has also been achieved.
The extent of reversibility and effect of reaction setup was also
explored. Finally, promising levels of enantioselectivity in an unprecedented Z-selective asymmetric cross metathesis (ACM) of a prochiral
1,4-diene was demonstrated.