Synthesis and Application of Planar Chiral NHC/Rh Complexes Bearing CoC 4 Ph 4 Group.

Sandwich compound-based planar chiral N -heterocyclic carbene (NHC) ligands having a bulky η 5 -cyclopentadienyl-cobalt-η 4 -tetraphenylcyclobutadiene core were developed, and their donor strengths were evaluated by determining the Tolman electronic parameter (TEP) of the Rh dicarbonyl complex. The TEP was high at 2048 cm -1 , as expected for an NHC ligand. The utility of the carbenes as chiral ligands was examined in the Rh-catalyzed asymmetric ring-opening reaction of oxabenzonorbornadienes with benzylamine, and the corresponding products were obtained with moderate enantioselectivities (up to 66% ee).