Divergent Organomagnesium Reactivity of Rigid, Dinucleating Naphthyridine Ligands: Backbone Changes with Big Impact.

We report the synthesis and characterization of two naphthyridine-based ligands bearing pendant secondary amine and amide donors, respectively. We additionally report their deprotonation chemistry and reactivity with dialkylmagnesium and Grignard reagents. The Grignard reactions yield structurally distinct MgCl·(THF) complexes, with the amide-based complex exhibiting reduced steric strain from the ligand around the MgCl core. Comparison of the steric profiles of the MgCl·(THF) complexes reveals that this reduced steric strain stems from the difference in binding modes of the ligands, which in the amide case points the bulk of sterically demanding substituents away from the MgCl core. Reactivity of the ligands with Mg-(-Bu) shows divergent outcomes: the secondary amine-based ligand forms the Mg(-Bu)·(THF) complex cleanly, whereas the amide-based ligand produces paramagnetic species via Mg-C homolysis, triggering radical reactivity that results in ligand butylation and dimerization. These findings underscore the unique steric and electronic features of dimagnesium complexes supported by rigid, dinucleating naphthyridine ligands, highlighting how variations in ligand architecture can profoundly influence coordination chemistry and reactivity.