Syntheses and structures of exo- and endo-cyclopalladated phenylhydrazones

Abstract

The reaction of substituted benzylidenephenylhydrazones with palladium(II) salts has been found to give exo in preference to endo five-membered metallacycles. The endo derivatives can only be obtained if the hydrazone phenyl ring contains chlorine substituents in the ortho or meta positions. The tendency of these hydrazone ligands to give exo derivatives, in contrast to the results found with similar N-benzylideneamines which favour the formation of endo-palladocycles, can be explained by the planarity of the hydrazone ligands, which favours the interaction of the C–H bond of the hydrazone phenyl ring with the palladium. Moreover, the aminic nitrogen atom activates this phenyl ring to electrophilic attack. The crystal structures of two of the metallacycles have been determined.