Silver(I) and copper(I) complexes with ferrocenyl ligands bearing imidazole or pyridyl substituents

The reactions between five ferrocenyl derivatives containing both a Cdouble bond; length as m-dashO and at least an imidazole or pyridine nitrogen atom and AgPF6, AgOTf, or [Cu(NCCH3)4]PF6 precursors were studied. The ligand {[bis(2-pyridyl)amino]carbonyl}ferrocene (L3), derived from (2-pyridyl)amine, favored tetrahedral coordination of Ag+ (with two ligands) and of Cu+ (with two acetonitrile ligands left from the precursor). In all the other ligands, both metal centers coordinated linearly to two ligands, preferring the imidazole or pyridinic nitrogen to other nitrogen atoms (amine) or oxygen donors. When the counter anions were triflate, the crystal structure showed a dimerization of the complex, with the ferrocenyl moieties occupying cis positions, by means of a weak Ag⋯Ag interaction. This was shown experimentally in the crystal structure of complex [Ag(L1)2]OTf (L1 = ferrocenyl imidazole) and in the presence of peaks corresponding to {Ag2(L2)3(OTf)}+ and {Ag2(L2)4(OTf)}+ in the mass spectra of [Ag(L2)2]OTf (L2 = ferrocenyl benzimidazole). In all complexes containing PF6, there was no evidence for dimerization. Indeed, in the crystal structure of [Ag(L2)2]PF6, the ferrocenyl moieties occupy trans positions and the metal centers are far from each other. DFT calculations showed that the energy of the cis and trans conformers is practically the same and the balance of crystal packing forces leads to dimerization when triflate is present.