Flexible bidentate aluminum Lewis acids for host–guest complex formation†

Abstract

This study investigates the design, synthesis, and reactivity of bidentate aluminum Lewis acids supported by amido and cyclopentadienyl donor sets within a flexible 1,4-disubstituted phenylene framework. The reactivity of these complexes with nitrogen-based ditopic donors was systematically explored, revealing their capacity to form host–guest assemblies. Reactions with equimolar pyrazine or quinoxaline yielded 1 : 1 colored adducts, highlighting the potential of these two systems as colorimetric sensors for ditopic nitrogen donors. The reaction with 4,4′-bipyridine, which features a longer N⋯N distance, resulted in a dimeric 2 : 2 adduct. In contrast, sterically demanding nitrogen donors such as 2,3,5,6-tetramethylpyrazine or phenazine showed no reactivity with these bidentate Lewis acids. The results reveal not only the robust Lewis acidic nature of the aluminum centers but also the pivotal role of ligand flexibility in facilitating diverse molecular interactions.