Dynamic Configuration on a Chiral-at-Rhodium Catalyst Featuring a Flexible Tetradentate Ligand

The unique dynamic configuration of an enantioselective chiral-at-metal catalyst based on Rh(III) and a non-chiral tetradentate ligand is described and resolved. At room temperature, the catalyst undergoes a dynamic configuration process leading to the formation of two interconvertible metal-stereoisomers, remarkably without racemization. Density functional theory (DFT) calculations indicate that this metal-isomerization proceeds via a concerted transition state, which features a trigonal bipyramidal geometry stabilized by the tetradentate ligand. Furthermore, the resolved enantiopure complex shows high catalytic enantioinduction in the Friedel-Crafts reaction, achieving enantiomeric ratios as high as 99 : 1. The first chiral-at-metal catalyst with a dynamic configuration has been successfully synthesized and subsequently resolved. Both experimental and DFT studies show that the stereogenic rhodium center preserves its chiral information. Furthermore, the resolved complex provides enantiomeric ratios of up to 99 : 1 in the catalytic Friedel-Crafts alkylation of indoles. These findings highlight its immense potential in asymmetric catalysis.image