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

Abstract

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 LMg₂Cl₂·(THF)_n complexes, with the amide-based complex exhibiting reduced steric strain from the ligand around the Mg₂Cl₂ core. Comparison of the steric profiles of the LMg₂Cl₂·(THF)_n 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 Mg₂Cl₂ core. Reactivity of the ligands with Mg(n-Bu)₂ shows divergent outcomes: the secondary amine-based ligand forms the LMg₂(n-Bu)₂·(THF)₂ 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.