A halide-free pyridinium-substituted η3-cycloheptatrienide–Pd complex

We report the synthesis and characterization of a novel 4-(dimethylamino)pyridinium-substituted η3-cycloheptatrienide–Pd complex which is free of halide ligands. Diacetonitrile{η3-[4-(dimethylamino)pyridinium-1-yl]cycloheptatrienido}palladium(II) bis(tetrafluoroborate), [Pd(C2H3N)2(C14H16N2)](BF4)2, was prepared by the exchange of two bromide ligands for noncoordinating anions, which results in the empty coordination sites being occupied by acetonitrile ligands. As described previously, exchange of only one bromide leads to a dimeric complex, di-μ-bromido-bis({η3-[4-(dimethylamino)pyridinium-1-yl]cycloheptatrienido}palladium(II)) bis(tetrafluoroborate) acetonitrile disolvate, [Pd2Br2(C14H16N2)2](BF4)2·2CH3CN, with bridging bromide ligands, and the crystal structure of this compound is also reported here. The structures of the cycloheptatrienide ligands of both complexes are analogous to the dibromide derivative, showing the allyl bond in the β-position with respect to the pyridinium substituent. This indicates that, unlike a previous interpretation, the main reason for the formation of the β-isomer cannot be internal hydrogen bonding between the cationic substituents and bromide ligands.