A MP2(full) and CCSD(T) theoretical investigation on unusual cation–π interaction between OCB [tbnd]BCO and H +, Li +, Na +, Be 2+ or Mg 2+

Abstract

The unusual and strong cation–π interactions are found between cations (H +, Li +, Na +, Be 2+, and Mg 2+) and the electron-deficient B B bond using MP2(full) and CCSD(T) methods at 6-311+G(2df) (6-311++G(2df,2p) for H + complexes) and aug-cc-pVTZ levels, accompanied by the B B bond contraction. A comparison with those between the corresponding cations and HC CH are also carried out. The binding energies follow the order of OCB BCO⋯H + ≈ OCB BCO⋯Be 2+ > OCB BCO⋯Mg 2+ >> OCB BCO⋯Li + > OCB BCO⋯Na + and OCB BCO⋯cations > HC CH⋯cations at four levels. The atoms in molecules (AIM) theory has been applied to convince covalent interaction in the H + complexes and confirm that the electron-deficient B B triple bond can be as the strong π-electron donor in the cation–π interaction. The analyses of natural bond orbital (NBO) and electron density shifts have revealed the nature of the cation–π interaction and explained the origin of B B bond contraction.