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

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 Br-2 and I-2 to gain clues on the formation mechanism of the corresponding s-butadienyl derivatives. We were able to obtain the pure s-butadienyl derivative only in the case of Br-2 reacting with the palladacyclopentadienyl complex bearing the unsubstituted quinoline. However, an equilibrium mixture of the s-butadienyl and a novel zwitterionic species was obtained when the same complex reacts with I-2. Furthermore, we have obtained exclusively an unprecedented zwitterionic complex when I-2 reacts with the palladacyclopentadienyl complex bearing the substituted quinoline and a different ratio of an equilibrium mixture of s-butadienyl and the zwitterionic species when the latter derivative reacts with Br-2. The solid state structures of one s-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.