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

We report the synthesis and characterisation of the naphthyridine-based dippDAMN and dippNDC 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 dippNDC-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 dippNDC 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: dippDAMN forms the LMg2(n-Bu)2·(THF)2 complex cleanly, whereas dippNDC produces paramagnetic species via Mg–C homolysis, triggering radical reactivity which results in ligand butylation and dimerisation. These findings underscore the unique steric and electronic features of dimagnesium complexes supported by rigid, dinucleating naphthyridine ligands, highlighting how seemingly subtle variations in ligand architecture can profoundly influence coordination chemistry and reactivity.