B–Hb⋯π interaction in heteroaromatics and anionic arenes: a DFT study

Abstract

This study presents a quantitative estimation of the B–H_b⋯π interaction of diborane with heteroarenes (pyrrole, furan, oxazole, isoxazole, thiophene, thiazole, and isothiazole) and anionic arenes (cyclopentadienyl anion and pentazolate ion). The DFT-D3 method at the B3LYP-D3/6-311++G(d,p) level of theory was exclusively used for geometry optimization and scrutinizing the stability of the complexes. The results indicated the formation of weakly stable complexes with heterocycles and pentazolate ion (ΔE < 6.0 kcal mol⁻¹). The complex formed between diborane and the cyclopentadienyl anion is very stable (ΔE > 12.0 kcal mol⁻¹) with dispersive interaction playing a secondary role. The stability of the complexes suggested from MP2 calculation and other DFT (ωB97X-D and M06-2X) methods is consistent with the results obtained from the DFT-D3 method. The process of complexation is enthalpy driven, except for the complex between diborane and the cyclopentadienyl ion. The spontaneity of the process is mainly governed by the entropy factor. The plot of NCI was used to visualize the non-covalent interaction regions. NBO analysis was also performed to estimate the strength of the donor-acceptor interaction. The asymmetric and symmetric stretching of the B–H_b⋯π vibrational modes and ¹H NMR shift in the free diborane and that in the complexes were also analysed.