Planar Cationic Imine Radical Iodide Charge Transfer Complexes: Key Intermediates for Iodine-(co)catalyzed Homogenous Asymmetric Hydrogenation of N-Arylimines

19 September 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


The mechanism of why both reactivity and enantioselectivity remarkably improves by adding an iodide and an acid in Ir-catalyzed asymmetric hydrogenation of N-arylimines is a decades’ mystery. And the excellent efficiency of iodine as a sole soft Lewis acid catalyst in the transfer hydrogenation of N-arylimines is also unclear at the molecular level. Via a systematic analysis of experimental data in reported small molecular iodine imine complexes and iodine-poly(Schiff base)s complexes, as well as iodine catalysis involved N-arylimines, planar cationic imine radical iodide charge transfer complexes were proposed as more reactive intermediates, in comparison with the twisted N-arylimines. Via the active species, a hydride transfer that occurs first in the outer-sphere mechanism was demonstrated to be more probable. The new understanding is insightful for the rational design of iodine catalysis and iodine additive for asymmetric catalysis.


iodine additive
iodine catalysis
transfer hydrogenation
hydride transfer first mechanism


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