Yue Hu (Norton Group)
2:00pm - 3:00pm
The hydrogenation of C=N bonds has been widely used in industry. Conventional chiral ruthenium hydride complexes were unable to achieve the enantioselective hydrogenation of iminium cations. A planar-chiral ruthenium hydride complex was designed, synthesized and resolved. However, the increased steric hindrance around the ruthenium has slowed the catalysis, leading to an impractical catalyst. Thus, I have developed several rhodium (III) and iridium (III) hydride complexes, among which the rhodium hydride complex, Cp*Rh(2-phenylpyridine)H, turns out to be a very efficient catalyst. Kinetic studies have shown that it transfers the hydride ligand around 106 times faster than the best ruthenium hydride catalyst, CpRu(dppm)H. This rhodium hydride significantly speeds up the ionic hydrogenation of iminium and pyridinium cations from days to minutes, with a broad substrate scope. The unusually fast hydride transfer prompted a quantitative evaluation of this hydride’s properties. Therefore, I have measured the kinetics and thermodynamics of H−, H•, and H+transfers from this rhodium hydride, showing that it is both a good H− donor and a good H• donor, but a poor H+ donor. The unique combination reflects the high energy of the Rh(I) anion [Cp*Rh(2-phenylpyridine)]−. This is the first transition metal hydride complex for which the kinetics and thermodynamics of all three transfers have been studied.