Mechanistic Complexity of Asymmetric Transfer Hydrogenation with Simple Mn–Diamine Catalysts

The catalytic asymmetric
transfer hydrogenation (ATH) of ketones
is a powerful methodology for the practical and efficient installation
of chiral centers. Herein, we describe the synthesis, characterization,
and catalytic application of a series of manganese complexes bearing
simple chiral diamine ligands. We performed an extensive experimental
and computational mechanistic study and present the first detailed
experimental kinetic study of Mn-catalyzed ATH. We demonstrate that
conventional mechanistic approaches toward catalyst optimization fail
and how apparently different precatalysts lead to identical intermediates
and thus catalytic performance. Ultimately, the Mn–N,N complexes
under study enable quantitative ATH of acetophenones to the corresponding
chiral alcohols with 75–87% ee.