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.本研究通过不同氮给体配体（N-donors）对环庚三烯亚基合钯配合物进行亲核进攻，合成了一系列咪唑鎓（imidazolium）与吡啶鎓（pyridinium）取代的η³-环庚三烯基合钯配合物。本文报道了该系列配合物的完整表征结果，以及其形成过程与特殊性质的密度泛函理论（DFT）研究。该目标化合物是首例经晶体学表征的二卤化钯单核烯丙基配合物。环庚三烯基环上的阳离子取代基可与一个溴配体形成强分子内氢键。研究发现，钯-烯丙基键（Pd–allyl bond）具有高度流变特性，即便在低温条件下，金属仍可沿七元环持续迁移。将其中一个溴配体替换为弱配位阴离子（weakly coordinating anion）后，可得到二聚体结构，同时改善了这类配合物较差的溶解性，使其可进一步应用于合成反应中。