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, 1H NMR, EPR, Mössbauer, 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 PdIII center bound to a ferrocene core which remains unchanged (FeII) during the oxidative activation. These are the first recognized PdIII complexes acting as enantioselective catalysts.