Title: Synthesis of chiral-at-metal rhodium complexes from achiral tripodal tetradentate ligands

Abstract

Over some 60 years of asymmetric catalysis, the source of catalyst chirality has mainly been based on chiral organic molecules with stereogenic carbon atoms or chiral molecules exhibiting atropisomerism. However, there is a virtually unexplored option in the design of enantioselective catalysts, where the metal cation of the catalyst is a stereogenic center. In these cases, the metal center can be surrounded by any achiral ligand as long as they lead to metal complexes with the stereogenic metal, commonly called chiral-at-metal complexes. However, few examples of enantioselective catalysts with exclusive metal-centered chirality exhibit a stable configuration. This work describes the completely diastereoselective synthesis of the chiral complexes [RhCl2(κ4-L)] (1) and [Rh(κ4-L)(NCMe)2][SbF6] (2) containing a new tripodal tetradentate ligand. The resolution of the racemic mixture of 2 has been achieved through kinetic resolution using enantiopure (S)-2-(4-isopropyl-4,5-dihydrooxazol-2-yl)phenol as a chiral auxiliary. The results of catalytic tests on the 1,3-dipolar cycloaddition reaction proving that the chirality is efficiently transferred from the metal to the substrate.