A systematic study of naphthyridine-derived ligands for well-defined silver(I) dimers

Dinuclear silver(I) complexes have recently gained attention for potential applications in visible light photochemistry. Our group has demonstrated that strong visible light absorption can occur in silver(I) dimers featuring redox-active naphthyridine diimine (NDI) ligands, resulting from a combination of close silver-silver interactions and low-lying ligand π* orbitals. A shortcoming of this previous work is that the sliver-NDI complexes displayed fluxional behavior due to rapid ligand exchange in solution; the ability to produce silver(I) dimers with targeted properties that maintain well-defined structures in solution remains an unmet challenge. Here, we describe the synthesis and characterization of a series of silver(I) dimers with naphthyridine-derived ligands, in which the ligand scaffold is systematically varied in order to determine structure/property relationships. We find that truncation of the NDI framework into an asymmetric "L-shaped" design results in a family of ligands that reliably produce structurally analogous silver(I) dimers. Ligands that maintain the π-conjugation of the iminopyridine motif consistently give silver(I) dimers with visible light absorption due to metal-metal to ligand charge transfer (MMLCT) transitions, and introduction of anionic (X-type) sites further increases stability in solution.