Tandem Catalysis: The Sequential Mediation of Olefin Metathesis, Hydrogenation, and Hydrogen Transfer with Single-Component Ru Complexes

Organometallic catalysts are traditionally designed and optimized to mediate a single reaction. However, the increasing demand for expedient and efficient synthetic processes requires the development of organometallic reagents that are capable of catalyzing multiple, mechanistically distinct reactions directly or by simple modification. While the Ru complex (PCy_3)_2Cl_2Ru= CHPh (1) has found extensive use in olefin metathesis, it was also recently shown to be an effective precatalyst for mediating radical additions and hydrogenation reactions. We recently demonstrated all three reactions could be performed in tandem to afford well-defined block copolymers. Herein, we report that complex 1, or its more active derivative 2, is also useful in mediating a variety of other catalytic hydrogenation reactions that include regiospecific ketone and olefin reductions, transfer hydrogenations of ketones, and dehydrogenative oxidations of alcohols. In addition, we demonstrate a variety of "one-pot" tandem metathesis-hydrogenation procedures for the rapid construction of small molecules, including (R)-(-)-Muscone.