Osmium(II) CNN Pincer Complexes as Efficient Catalysts for both Asymmetric Transfer and H2 Hydrogenation of Ketones

we have described the isolation of the first CNN pincer osmium complexes [OsX(CNN)P2] to display high catalytic activity and productivity in the reduction of ketones by either TH or HY (TOFand TON up to 106 h1 and 105, respectively). A high enantioselectivity (up to 98% ee) is possible in both reactions with a remarkably low catalyst loading (0.005–0.002 mol%). To the best of our knowledge, this is the first example of an osmium complex that catalyzes the asymmetric HY of ketones. Evidence for an Os-OR vs. Os-H equilibrium suggests that both these species are involved in the catalytic pathways.