Studies on the nonbonded interactions of divalent organic selenium

Abstract

We report here the characteristics of the weak nonbonded interactions formed by a divalent selenium atom; i.e., Se⋯N, Se⋯O, Se⋯F, Se⋯Cl, and Se⋯Br interactions. Seven series of 2-substituted benzeneselenenyl compounds [2-C6H4(SeY)CH2X; X = NRR′, OH, F, Cl, etc.; Y = Cl, Br, CN, etc.], some of which were labeled with an NMR active stable isotope, were synthesized. The intramolecular Se⋯X interactions were characterized by 1H, 15N, 17O, 19F, and 77Se NMR spectroscopy in solution as well as by quantum chemical calculation and natural bond orbital (NBO) analysis. It was found that the strength of the Se⋯X interactions decreases with decreasing the basicity of the X atom, i.e., in the order of X = N, O, F, Cl, Br. The trend demonstrated the importance of the hypervalent nature of selenium for formation of the Se⋯X interactions. Convenient correlations were proposed for estimation of the strength of Se⋯X interaction from the 77Se NMR chemical shift or the nonbonded Se⋯X atomic distance.