Facile Access to Chelating CAArC‐Phosphine (CAArCPhos) Palladium Complexes

In this article, we present a synthetic route to 4‐(diphenyl‐phosphino) isoindolium salts based on a new protecting group strategy. Key to success is the use of hemi‐aminal methyl ether precursors, which serve as base‐stable iminium salt equivalents that enable halogen‐metal exchange and subsequent functionalization. After removal of the protecting group, the catalytically active palladium(II) complexes are formed of phosphine isoindolium salts by a CMD‐like metalation process, producing the first examples of chelating cyclic amino(aryl) carbene complexes. Calculations on the mechanism support an acetate‐assisted intramolecular palladation of the cyclic amino(aryl) carbene‐phosphine (CAArCPhos) ligand enabled by the phosphine directing group through a six‐membered transition state.