Scrutinizing Ligand Pre-reduction: Unlocking Pathways to Mono-, Homo-, and Heterobimetallic Naphthyridine Diimine Complexes

Abstract

The redox-active naphthyridine diimine (NDI) framework serves as a versatile scaffold for synthesising monometallic as well as homo- and heterobimetallic complexes, owing to its electronic flexibility and rigid geometry. This comprehensive study investigates the influence of ligand pre-reduction on the reactivity and structural outcomes of NDI with alkali and alkaline earth metals. Systematic analyses reveal that the nature and extent of NDI reduction critically determine the resulting metalation pathways. Pre-reduction with sodium favors the formation of homobimetallic complexes, while lithium enables access to heterobimetallic architectures, and magnesium yields monometallic species. The use of pre-reduced NDI intermediates allows for salt metathesis reactions with group 13 halides, giving rise to well-defined Al–Al, Al–Li, Ga, and Ga–Li complexes. Structural and spectroscopic data, provide insight into oxidation states and electronic delocalization within the NDI framework. A metrical model is introduced to classify NDI redox states based on characteristic bond lengths. These results highlight the synthetic utility of pre-reduction strategies for tailoring the electronic and structural diversity of NDI-based complexes across a broad range of metals.