Synthesis and Reactivities of Organopalladium Complexes as Models for Active Species in Catalytic Reactions

Abstract

Various neutral and cationic monoorganopalladium complexes have been prepared as models of active species involved in palladium-catalyzed catalytic processes. Removal of a halide ligand from monoalkyl- and arylpalladium halide complexes by treatment with a silver salt afforded cationic monoorganopalladium complexes coordinated with a solvent molecule at the vacant site of the cationic palladium center. Generation of the vacant site has been found to be a dominant factor in enhancing the reactivities of organopalladium complexes toward β-hydrogen elimination from alkylpalladium complexes as well as CO and olefin insertions into palladium-carbon bond. Further addition of the silver salt was found to accelerate the CO insertion rate by removing a phosphine ligand from the palladium complexes. Cationic solvent-coordinated Pd (II) complexes also proved to be suitable model compounds for studying the mechanism of nucleophilic attack on coordinated CO. Utility of the concept of the reactivity enhancement by creation of a vacant cationic center at palladium has been demonstrated in catalytic double carbonylation of aryl and allyl halides with a secondary amine to give α-keto amides.