The addition of bromine and iodine to palladacyclopentadienyl complexes bearing bidentate heteroditopic P−N spectator ligands derived from differently substituted quinolinic frames. The unexpected evolution of the reaction

Abstract

We have synthesized two palladacyclopentadienyl derivatives bearing bidentate ligands heteroditopic 8-(diphenylphosphino)quinoline or 8-(diphenylphosphino)-2-methylquinoline. We have reacted the palladacyclopentadienyl complexes with Br₂ and I₂ to gain clues on the formation mechanism of the corresponding σ-butadienyl derivatives. We were able to obtain the pure σ-butadienyl derivative only in the case of Br₂ reacting with the palladacyclopentadienyl complex bearing the unsubstituted quinoline. However, an equilibrium mixture of the σ-butadienyl and a novel zwitterionic species was obtained when the same complex reacts with I₂. Furthermore, we have obtained exclusively an unprecedented zwitterionic complex when I₂ reacts with the palladacyclopentadienyl complex bearing the substituted quinoline and a different ratio of an equilibrium mixture of σ-butadienyl and the zwitterionic species when the latter derivative reacts with Br₂. The solid state structures of one σ-butadienyl complex and of the two novel zwitterionic derivatives were determined and an interpretation of the observed reactivity based on kinetic data and a computational study has been suggested.