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.