In silico studies toward the recognition of fluoride ion by novel bicyclic diborane receptors and tuning through remote substituent effects

Derivatives of 5,6-diborylbicyclo[2.1.1]hexane have been presented as the novel bicyclic diborane receptors for the recognition of fluoride ion. The MP2/ 6-311?G^**//B3LYP/6-311?G^** calculated results suggest for much higher fluoride ion affinity for these studied receptors. Dicyano derivative of 5,6-diborylbicyclo[2.1.1]hexane (7) shows ~25.0 kcal/mol higher fluoride ion affinity than the prototype 1,8-naphthalenediylbis(dimethylborane) (1). Further, it has been shown that the affinity of these receptors can be tuned through remote substituent effect. The molecular electrostatic isopotential surface calculations reveal the change in the value of V_S,max on boron center due to remote substitutions. Quantum theory of atoms in molecule analyses shows that the binding of F^-to the boron centers of the receptor molecules is non-covalent in nature. Incorporation of chromogenic units at the remote positions also influences the affinity of receptors toward analytes. Further, the calculated higher fluoride ion affinities of these receptors in the aqueous medium suggest that they can be promising candidates to function as F^-ion receptors in water medium also. The Cl^-and Br^-ion affinities of these receptors have also been discussed. The designed bicyclo[2.1.1]hexane receptors are synthetically achievable as similar systems have been reported (Wiberg et al. in J Am Chem Soc 83:3998, 1961; Martínez et al. in Tetrahedron Asym 4:2333, 1993).