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.