Several highly active, recoverable and recyclable Ru-based metathesis catalysts are presented. The crystal structure of Ru complex 5, bearing a 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene and styrenyl ether ligand is disclosed. The heterocyclic ligand significantly enhances the catalytic activity, and the styrenyl ether allows for the easy recovery of the Ru complex. Catalyst 5 promotes ring-closing metathesis (RCM) and the efficient formation of various trisubstituted olefins at ambient temperature in high yield within 2 h; the catalyst is obtained in >95% yield after silica gel chromatography and can be used directly in subsequent reactions. Tetrasubstituted olefins can also be synthesized by RCM reactions catalyzed by 5. In addition, the synthesis and catalytic activities of two dendritic and recyclable Ru-based complexes are disclosed (32 and 33). Examples involving catalytic ring-closing, ring-opening, and cross metatheses are presented where, unlike monomer 5, dendritic 33 can be readily recovered.

A Ru carbene (8, Scheme ) that contains an internal metal−oxygen chelate is an active metathesis catalyst and is readily obtained by the sequential treatment of Cl2Ru(PPh3)3 with (2-isopropoxyphenyl)diazomethane and PCy3. This Ru-carbene complex offers excellent stability to air and moisture and can be recycled in high yield by silica gel column chromatography. The structures of this and related complexes have been unambiguously established by NMR and single-crystal X-ray diffraction studies.

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Page 4955. Enantioselectivity values for non-UV active compounds 14a and 14b were measured by HPLC/ELSD methods. Subsequent investigations led us to determine that ELSD methods are unreliable in measuring ee values of these compounds. Through reliable alternative analysis methods, we have established that the above reactions proceed in 80 and 82% ee, respectively. The remaining enantioselectivities are correct as initially reported. For additional details, see: Van Veldhuizen, J. J.; Gillingham, D. G.; Garber, S. B.; Kataoka, O.; Hoveyda, A. H.

The discovery and development of a new class of Ru-based catalysts for olefin metathesis is described. These catalysts, particularly those that do not bear a phosphine ligand, have been demonstrated to promote unique levels of reactivity in a variety of olefin metathesis reactions. The design and development of supported and chiral optically pure variants of this class of Ru catalysts for use in enantioselective metathesis are discussed as well. All catalysts are air stable, reusable, and can be employed with unpurified solvents.