Structure and Dynamics of Imidazolium- and Pyridinium-Substituted η3-Cycloheptatrienide-Pd Complexes

A range of imidazolium- and pyridinium-substituted η3-cycloheptatrienide-Pd complexes was synthesized by nucleophilic attack of different N-donors on cycloheptatrienylidene-Pd complexes. Their full characterization is reported along with DFT studies of their formation and special properties. The target compounds represent the first crystallographically characterized monomeric allyl complexes of a Pd dihalide. The cationic substituents on the cycloheptatrienide ring form strong intramolecular H-bonds to one bromide ligand. The Pd–allyl bond was found to be highly fluxional, showing a continuous migration of the metal along the seven-membered ring even at low temperatures. The exchange of one bromide for a weakly coordinating anion yields dimeric structures and improves the poor solubility of these complexes, allowing their further synthetic utilization.