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.