Boron as an Electron-Pair Donor for B⋅⋅⋅Cl Halogen Bonds

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Supramolecular Chemistry

Background:

• Halogen bonding is a significant non-covalent interaction involving a Lewis acid and a Lewis base.
• The role of boron as an electron-pair donor in halogen-bonded complexes is not fully understood.
• Investigating diverse substituents on the halogen donor can elucidate the nature of these interactions.

Purpose of the Study:

• To computationally investigate boron as an electron-pair donor in halogen-bonded complexes.
• To characterize the nature of halogen bonds formed, including traditional and chlorine-shared types.
• To analyze charge transfer and spectroscopic properties (spin-spin coupling, NMR shielding) within these complexes.

Main Methods:

• Utilized MP2/aug'-cc-pVTZ calculations to model halogen-bonded complexes of (CO)2(HB):ClX and (N2)2(HB):ClX.
• Employed Equation-of-Motion Coupled Cluster Singles and Doubles (EOM-CCSD) for spin-spin coupling constants.
• Analyzed charge transfer pathways and 11B chemical shielding changes upon complexation.

Main Results:

• Equilibrium halogen-bonded complexes were identified, with boron acting as the electron-pair donor.
• Identified both traditional and novel chlorine-shared halogen bonds, the latter showing increased binding energies and shorter B-Cl distances.
• Charge transfer from the boron lone pair to the Cl-A σ* orbital stabilizes all complexes; a secondary interaction exists in (CO)2(HB):ClX complexes.

Conclusions:

• Boron can effectively act as an electron-pair donor in various halogen-bonded complexes.
• The discovery of chlorine-shared halogen bonds expands the known types of halogen bonding interactions.
• Spectroscopic data (J(B-Cl) and 11B NMR) provide valuable insights into the electronic structure and bonding characteristics of these complexes.