The role of the aromatic ligand in the asymmetric transfer hydrogenation of the CN bond on Noyori's chiral Ru catalysts

Only four types of dimeric precursors [RuCl2(η6-arene)]2 for the synthesis of Noyori's half sandwich diamine catalysts [RuCl(TsDPEN)(η6-arene)] are commercially available, yet so far no study has tried to systematically evaluate how these systems perform during the asymmetric transfer hydrogenation of various 3,4-dihydroisoquinolines (i.e., the typical substrates for Noyori asymmetric transfer hydrogenation benchmarking). Experiments combined with molecular modeling allowed us to assess their properties and formulate a hypothesis clarifying the difference in enantioselectivity of these systems.