Chelating ligand precursors for the preparation of olefin metathesis
catalysts are disclosed. The resulting catalysts are air stable monomeric
species capable of promoting various metathesis reactions efficiently,
which can be recovered from the reaction mixture and reused. Internal
olefin compounds, specifically beta-substituted styrenes, are used as
ligand precursors. Compared to terminal olefin compounds such as
unsubstituted styrenes, the beta-substituted styrenes are easier and less
costly to prepare, and more stable since they are less prone to
spontaneous polymerization. Methods of preparing chelating-carbene
metathesis catalysts without the use of CuCl are disclosed. This
eliminates the need for CuCl by replacing it with organic acids, mineral
acids, mild oxidants or even water, resulting in high yields of
Hoveyda-type metathesis catalysts. The invention provides an efficient
method for preparing chelating-carbene metathesis catalysts by reacting a
suitable ruthenium complex in high concentrations of the ligand
precursors followed by crystallization from an organic solvent.