DFT and TDDFT study on cation-π complexes of diboryne (NHC → B ≡ B←NHC).

In this study, density functional theory calculation on mono-cationic cation-π complexes of diborynes has been made to understand the interaction in cation-π complexes of diboryne. Results suggest that apart from the smaller cations Li and Na, larger cation like K ion could also form complexes with diboryne compounds via cation-π interaction. From the calculated structural and spectroscopic analysis B, C NMR (Nuclear Magnetic Resonance), FTIR (Fourier Transform Infra red) (force constant, value), and UV-vis spectra, it is found that the interaction between the cations and π-electron cloud of the diboryne is purely electrostatic. It is also observed that smaller cation (Li) with high electronegativity interacts more strongly compared to larger cation (K). Calculated interaction energy advocates that the π-electron cloud of the B unit contributes more to the cation-π interaction than the two aromatic phenyl rings of the NHC (N-heterocyclic carbene) substituted with 2,6-diisopropylphenyl group. The aryl substituent at the NHC-ligands undergoes a change in spatial orientation with respect to the size of cations in order to provide suitable space to the cations for effective cation-π interaction. Quantum theory of atoms in molecules study clarifies further the nature and extent of B-B and B-cation interactions.B-NMR, C-NMR, and time dependent density functional theory analysis indicate that cation-π interaction annihilates the B → C (NHC) π-back donation and favours the B≡B bond formation.