Paramagnetic Palladacycles with PdIII Centers Are Highly Active Catalysts for Asymmetric Aza-Claisen Rearrangements

A combination of spectroscopic and electrochemical methods-XANES, EXAFS, X-ray, H-1 NMR, EPR, Mossbauer, and cyclic voltammetry-demonstrate that the most efficient Pd catalysts for the asymmetric rearrangement of allylic trifluoroacetimidates unexpectedly possess in the activated oxidized form a Pd-III center bound to a ferrocene core which remains unchanged (Fe-II) during the oxidative activation. These are the first recognized Pd-III complexes acting as enantioselective catalysts.