Rhenium(I)-Based Heteroleptic Pentagonal Toroid-Shaped Metallocavitands: Self-Assembly and Molecular Recognition Studies

Abstract

A family of neutral, heteroleptic, dinuclear M 2 LL′type pentagonal toroid-shaped metallomacrocycles (1−8) were synthesized using flexible ditopic N donors (L n = L 1 −L 2 ), rigid bischelating ligands (H 2 −L′ = H 2 −E), and Re 2 (CO) 10 in a one-pot solvothermal self-assembly approach. The ligands and the metallomacrocycles were characterized using ATR-IR, electrospray ionization mass spectrometry, nuclear magnetic resonance, ultraviolet−visible, and emission spectroscopy methods. The molecular structures of 1, 2, 4, 6, and 7 were confirmed by an X-ray diffraction study and are similar to those of calix[5]arene. The cyclic inner cavities of the metallomacrocycles accommodate toluene/mesitylene/acetone/chlorobenzene as guest molecules that are stabilized by cumulative C−H•••π and π•••π interactions with the cyclic framework of metallomacrocycle. The photophysical properties of the ligands and the metallomacrocycles were studied. The host−guest recognition properties of metallocavitands 1, 2, 7, and 8 as a model host with phenol and nitrobenzene derivatives as guest molecules were studied by emission spectroscopy methods.

Rhenium–Pyrazolyl-Based Figure-Eight- and Z-Shaped Metallocycles: Self-Assembly, Solid-State Structures, Dynamic Properties in Solution, and Competitive Ligand-Induced Supramolecular Transformations into Rhenium-Pyridyl/-Benzimidazolyl/-Phosphine-Based Metallocycles/Acyclic Complexes

“…The design and synthesis of metallocycles such as cages, helicates, and simple-to-complex topological architectures via coordination-driven self-assembly have been gaining significant attention owing to their potential applications in materials and medicinal fields. − Further, new aesthetically appealing molecular architectures including intricate topological metallocyclic architectures such as metallo-links (a series of interlocked metallocyclic rings where at least one ring has to be broken to separate them) and metallo-knots similar to those found in nature can be prepared using the self-assembly. − Among various topologies, “figure-eight” architecture is one of the elegant self-assembled structures, which is found in natural systems such as Lissoclinamide 7, the recombinant structure of circular DNA and marine alkaloid. , However, very few examples of “figure-eight”-shaped metallocycles are known until now. − The design and synthesis of “figure-eight”-shaped metallocycles and other metallocyclic architectures using various metal precursors and organic building units are important in the development of the field, which might yield molecules having various potential applications in the near future. Among the few metal ion-based coordination-driven approaches, the fac -[Re(CO) 3 ] core-based self-assembly method is one of the methods to construct neutral homoleptic and heteroleptic metallocycles, which have potential applications in the field of host–guest encapsulation, catalysis, selective reactivity, sensing, and as bioactive agents. − Although a considerable number of synthetic principles for the preparation of various sizes and shapes of fac -[Re(CO) 3 ] core-based metallocycles are currently available, synthetic approaches for preparing “figure-eight” topology, complex-knot, and complex-link-shaped metallocycles are scarce. In addition to the metal core, the nature of the ligand is crucial to obtaining com...…”