Design and development of chiral N-heterocyclic carbenes for ruthenium-based asymmetric olefin metathesis

Chapter 1. A brief assessment of asymmetric olefin metathesis and comparison of the achiral Mo- and Ru-based catalysts for olefin metathesis demonstrate a need for an efficient air-stable chiral catalyst. A survey of reactions carried out with metal catalysts bearing a monodentate N-heterocyclic carbene is provided, followed by initial attempts to develop a chiral monodentate N-heterocyclic carbene for Ru-based asymmetric olefin metathesis.; Chapter 2. A preliminary study discloses the synthesis, structure and reactivity of an enantiomerically pure Ru catalyst bearing a bidentate N-heterocyclic carbene containing a chiral binaphthyl moiety. The chiral Ru complex is stereogenic at the metal center, air-stable, and recyclable. Under catalytic conditions the enantiomerically pure Ru complex efficiently promotes asymmetric ring-opening metathesis/cross metathesis of strained olefins to give products in high enantioselectivity and yield. The chiral Ru catalysts can be recovered and reused without significant loss of activity.; Chapter 3. Design, synthesis, and reactivity of enantiomerically pure Ru catalysts that are steric and electronic modifications of the chiral Ru catalyst discussed in Chapter 2 are disclosed. These studies provide insight to the differences in activity, the mechanism, and induction of enantioselectivity. Modifications of the chiral Ru catalyst lead to an increase in reactivity by over two orders of magnitude relative to the previous chiral Ru catalyst. Some of the newly developed chiral Ru catalysts expand the scope of asymmetric olefin metathesis by promoting asymmetric ring-opening metathesis/cross metathesis and asymmetric ring-closing metathesis reactions that cannot be effected by the first generation chiral Ru catalyst.; Chapter 4. Using the knowledge gained from the data discussed in Chapter 3, the design, synthesis, and reactivity of an enantiomerically pure Ru catalyst bearing a bidentate N-heterocyclic carbene containing a chiral biphenyl moiety is disclosed. The newly developed Ru catalysts deliver a slight increase in activity and enantioselectivity in selected metathesis reactions that were unavailable from previously discussed catalysts. A brief review on chiral bidentate N-heterocyclic carbenes in metal catalyzed reactions is provided.