Metal as Source of Chirality in Octahedral Complexes with Tripodal Tetradentate Ligands

The
challenging control of the absolute configuration of chiral-at-metal
complexes is efficiently achieved using the tripodal tetradentate
ligand L. The optical resolution of rac-[RhCl2(κ4C,N,N′,P–L)] mediated by (S)-α-phenylglycine
provides access to enantiopure complexes of general formula [Rh­(κ4C,N,N′,P–L)­A­(Solv)]­[SbF6]n that enantioselectively catalyze the Diels–Alder
reaction between methacrolein and HCp with enantiomeric ratio of up
to >99/1. The nature of the active species, the origin of the enantioselectivity
and mechanistic details are disclosed by means of NMR spectroscopy
and DFT studies.