The Study of the Asymmetric Transfer Hydrogenation of Imines by RuTsDPEN Catalyst – Theoretical and Practical Aspects

Nowadays asymmetric hydrogenation of imines has an important role from the practical point of view. For its hydrogenation are reported two different methods using gaseous hydrogen or phase transfer hydrogenation. The transfer hydrogenation is from the practical point of view very useful method which uses organic sources of hydrogen, e.g. propane-2-ol, formic acid.

Our work was focused on studies of imines by the transfer hydrogenation using HCOOH/base as a hydrogen donor catalyzed by RuCl-(p-cymene)-TsDPEN. Density functional theory computational methods were used to investigate the increasingly popular ionic mechanistic concept for the theoretical investigation of the reaction. Applying the ionic mechanism, the reaction preferentially affords the (R)-amine product, which is in agreement with the experimental observations. Calculated transition state structures for the hydrogenation of protonated 1-methyl-3,4-dihydroisoquinoline are discussed together with their preceding and following energy minima. Finally, to compare the proposed mechanism of imines hydrogenation with hydrogenation of ketones, transition state geometries for the asymmetric transfer hydrogenation of acetophenone are proposed, which take the “standard” six-membered cyclic form.

Furthermore, series of kinetic experiment and spectral analysis allowed us to get experimental data to clarify the practical aspects of the reaction under study.

Acknowledgement

The work was supported by the Grant Agency of the Czech Republic (Grant 104/09/1497)