ChemPhysChem 17, 3112–3119 (2016)

DOI: 10.1002/cphc.201600435

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

MP2/aug’-cc-pVTZ calculations have been carried out to investigate boron as an electron-pair donor in halogen-bonded complexes (CO)2(HB):ClX and (N2)2(HB):ClX, for X = F, Cl, OH, NC, CN, CCH, CH3, and H.  Equilibrium halogen-bonded complexes with boron the electron-pair donor have been found on all of the potential surfaces except for (CO)2(HB):ClCH3 and (N2)2(HB):ClF.  The majority of these complexes are stabilized by traditional halogen bonds, except for (CO)2(HB):ClF, (CO)2(HB):ClCl, (N2)2(HB):ClCl, and (N2)2(HB):ClOH which are stabilized by chlorine-shared halogen bonds.  These complexes have increased binding energies and shorter B-Cl distances.  Charge transfer stabilizes all complexes, and occurs from the B lone pair to the σ* Cl-A orbital of ClX, with A the atom of X directly bonded to Cl.  A second reduced charge transfer interaction occurs in (CO)2(HB):ClX complexes from the Cl lone pair to the π* C≡O orbitals.  EOM-CCSD spin-spin coupling constants 1xJ(B-Cl) across the halogen bonds are also indicative of the changing nature of this bond.  1xJ(B-Cl) values for both series of complexes are positive at long distances, increase as the distance decreases, and then decrease as the halogen bonds change from traditional to chlorine-shared bonds, and begin to approach the values for the covalent bonds in the corresponding ions [(CO)2(HB)-Cl]+ and [(N2)2(HB)-Cl]+.  Changes in 11B chemical shieldings upon complexation correlate with changes in the charges on B.