Bidentate ligands in self-assembly: Synthesis, structure and applications

Self-assembly is the organization of molecular units into ordered structures using non-covalent interactions like hydrogen bonding, Van der Waals forces, π-π stacking, capillarity, entropy, and others. The most widely reported interactions in self-assembly are hydrogen bonding and π-π stacking interactions. Self-assembly can be employed in the synthesis of bidentate ligands and their complexes using the hydrogen bond interaction of monodentate ligands. These self-assembled bidentate ligands and their metal complexes have found applications in hydrogenation, hydroformylation, hydrocyanation, and hydration reactions with excellent yields and good catalytic properties. In two of the reports, complexes derived from self-assembled bidentate ligands had catalytic activities better than t-Bu-XANTPHOS (22) and BIPHEPHOS (23), special ligands, used for catalyzing the hydroformylation of alkenes. In addition to the self-assembly of bidentate ligands from monodentate ligands, bidentate ligands have also been used as linkers, spacers, inter-lockers, and ligands in the construction of supramolecular complexes. In this work, (i) the structure and application of self-assembly in the synthesis of bidentate ligands, (ii) the structure and application of these self-assembled bidentate ligands and their metal complexes in catalysis and (iii) the structure and application of bidentate ligands in the construction of molecular knots, catenanes, molecular rotors, and other supramolecules were studied. While catenanes and rotaxanes consist of two or more molecular components interlocked, molecular knots are a single entwined macrocycle. Structural features like steric restriction, surface cavity, surface area, porosity, and flexibility of the molecules determined their applications as catalysts.