Anion-Induced Intramolecular Cyclization of Urea-Based Receptors: Entrapment of Cyclic [SO₄(H₂O)₄^2–]_<i>n</i> Cluster and Encapsulation of Anions with Varied Dimensionality

Two unsymmetrical dipodal monourea anion receptors BPU-1 and BPU-2 with varying π-acidic terminal electron-withdrawing substituents (–NO2 and –CF3) can interact with anions of varied geometries (spherical, trigonal planar, and tetrahedral). Receptors are designed with an arm having a flexible urea unit, and the other arm contains a semirigid fluorophoric benzimidazole unit. BPU-1 could entrap cyclic sulfate water cluster, [SO4(H2O)42–]n, resulting in R44(8) and R44(12) arrangements in the solid state. Anion-sensing behavior of both receptors has been investigated in the aqueous medium, where BPU-1 could selectively sense SO42–/HSO4– among other biologically relevant anions. Anion-induced intramolecular cyclization of both receptors in the presence of F–/HO– to yield benzimidazo[1,2-c]quinazolin-6-ones has also been investigated in detail

Probing the Potential of Hitherto Unexplored Base-Stabilized Borylenes in Dinitrogen Binding

Computational investigations were carried out to probe the potential of several dicoordinate, singly base-stabilized borylenes of the form [L→BR] (L=neutral Lewis base) in dinitrogen binding. The calculated reaction free energies and activation barriers associated with the formation of mono- and diborylene-N2 adducts suggest the presence of thermally surmountable kinetic barriers towards their possible isolation. Our results show that the exergonicity of dinitrogen activation and fixation is linearly dependent on the natural charge at the boron center, which can be tuned to design novel boron-based compounds with potential applications to small-molecule activation. EDA-NOCV analysis reveals strong binding of dinitrogen to these base-stabilized borylenes