Since
its discovery in the 1950s, and because of its broad functional group
tolerance, and straightforward implantations, olefin metathesis, a
fundamentally different olefination method, has gained acceptance as a powerful
tool for construction of carbon-carbon double bonds. In recent years detailed,
experimental and computational mechanistic studies have resulted in syntheses
of well-defined ruthenium, tungsten, and molybdenum complexes, capable of
selectively generating either Z, or E alkenes. Because of its value, to have
one catalyst to generate both E and Z-olefins via one method, stereoretentive
olefin metathesis has recently gained a lot of attention.

 

 

 Early studies using not very well defines
catalysts showed evidence of retention of stereochemistry at low conversion.
But, as the reaction proceeded towards equilibrium thermodynamic E to Z ratios
were observed.  Large number of olefins
were tried, and it showed that the stereochemistry of reactant olefin can sometimes
influence the stereochemistry of product, despite using the same catalyst. Despite
its higher cost, ruthenium catalysis is particularly interesting, because the catalysts
show high air and moisture tolerance and high functional group compatibility.

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

 

Ruthenium-based
metathesis catalysts have become some of the most useful complexes in total
synthesis of natural products and complex materials. Different Z-selective
ruthenium-based olefin metathesis catalysts have been developed in the past
years. One of these systems uses a ruthenium bearing cathecothiolate ligands, the
ligand through stereoretention to provide z-olefins. Computational studies, and
experimental screening revealed that this catalyst also Kinetically generates
E-olefins. Although the behavior of these ruthenium complexes are mainly
attributed to sterics, the electronic properties of anionic cathecothiolate
ligands, play key roles in kinetics and thermodynamics of the reaction. In the
past year both Hoveyda and Grubbs have published extensive studies on modifying
this catalyst for fast stereoretentive reactions