Investigations into Ruthenium Metathesis Catalysts with Six-Membered Chelating NHC Ligands: Relationship between Catalyst Structure and Stereoselectivity.
A series of ruthenium catalysts bearing five-membered chelating NHC architectures that exhibit very highZ-selectivity in a variety of metathesis reactions have recently been reported. It was envisioned that catalysts possessing sixmembered chelates could similarly exhibit highZ-selectivity and address limitations of this methodology. We thus prepared a number of new catalysts and systematically investigated the impact of the NHC and anionic ligand on their stereoselectivity. In standard metathesis assays, only catalysts containing six-membered chelated NHC structures and η2-bound anionic ligands favored theZ-olefin products compared to traditional ruthenium catalysts. In addition, substitution with bulkierN-aryl groups led to improvedZ-selectivity. The effect of ligand structure on stereoselectivity discovered in this study will be useful in the future design of highly active andZ-selective ruthenium catalysts.
Arnold and Mabel Beckman Laboratory of Chemical Synthesis, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States.
Koji
K
Endo
Myles B
MB
Herbert
Robert H
RH
Grubbs