Characteristics and nature of the intermolecular interactions in boron-bonded complexes with carbene as electron donor: an ab initio, SAPT and QTAIM study

We report geometries, stabilization energies, symmetry adapted perturbation theory (SAPT) and quantum theory of atoms in molecules (QTAIM) analyses of a series of carbene-BX3 complexes, where X = H, OH, NH2, CH3, CN, NC, F, Cl, and Br. The stabilization energies were calculated at HF, B3LYP, MP2, MP4 and CCSD(T)/aug-cc-pVDZ levels of theory using optimized geometries of all the complexes obtained from B3LYP/aug-cc-pVTZ. Quantitatively, all the complexes indicate the presence of B-C-carbene interaction due to the short B-C-carbene distances. Inspection of stabilization energies reveals that the interaction energies increase in the order NH2 > OH > CH3 > F > H > Cl > Br > NC > CN, which is the opposite trend shown in the binding distances. Considering the SAPT results, it is found that electrostatic effects account for about 50% of the overall attraction of the studied complexes. By comparison, the induction components of these interactions represent about 40% of the total attractive forces. Despite falling in a region of charge depletion with a double dagger(2) rho (BCP) > 0, the B-C-carbene bond critical points (BCPs) are characterized by a reasonably large value of the electron density (rho (BCP)) and H-BCP < 0, indicating that the potential energy overcomes the kinetic energy density at BCP and the B-C-carbene bond is a polar covalent bond.