Structural Dependence of Catenand Effect: Thermodynamic and Kinetic Modulation of Catenane Coordination Properties via Ring-size and Exocyclic Substituent Variation

Although effects from ligand interlocking on coordination geometry and ligand exchange rate have been identified almost 40 years ago, relationship between structural features that characterize the ligand interlocking and the resulting coordination features remains unexplored, and hence exploitation of metal complexes supported by mechanically interlocked ligands is greatly hampered. In this work, structures, thermodynamics, kinetics and chemical reactivities of a series of Cu(I) catenane complexes of varying size of the interlocked macrocycles and exocyclic substituents are systematically compared and analyzed. In addition to the distortion of the coordination geometry and enhancement of interactions in the secondary sphere, reducing the size of the interlocked rings and increasing the steric hindrance of the exocyclic substituents are both found to suppress the opening of the Cu(I) coordination sphere, thus leading to a slower ligand exchange rate in both associative and dissociative exchange, which in turn affects chemical reactivity of the metal in which a substantial opening of the primary sphere is required. These detail understandings of the relationship between structures of the catenane ligand and the coordination properties and chemical reactivity thus form the basis of rational design of new metal complexes featuring the unique properties from mechanical bond for diverse applications.