Di-Palladium Complexes are Active Catalysts for Mono-N-Protected Amino Acid Accelerated Enantioselective C-H Functionalization

The role of mono-protected amino acid (MPAA) ligands in accelerating enantioselective cyclopalladation and palladium catalyzed C-H func-tionalization was investigated using kinetic, spectroscopic, and computational methods. Single crystal X-ray diffraction and NMR spectroscopy demonstrate that MPAA ligands bind catalytically competent di-palladium complexes as bridging carboxylates. The catalytic relevance of the observed di-palladium species was evaluated by kinetic analysis. The kinetic method of continuous variation demonstrated that a complex contain-ing a single MPAA-bridged di-palladium core (Pd2(MPAA)1) is an active catalyst for the reactions studied. The experimental studies are con-sistent with density functional theory calculations that indicate enantioinduction can be achieved by a single MPAA ligand bridging a di-palladium catalyst through secondary sphere hydrogen-bonding interactions that lower the barrier to C-H activation of the major enantiomer.