Monohydrides of the Group 13 Elements M=B, Al and Ga: Axial Bi‐Nucleophilicity and the Propensity to Form Both H−M⋅⋅⋅HX and M−H⋅⋅⋅HX Hydrogen Bonds (X=F, Cl, Br, I, CN, CCH, CP)

Abstract

AbstractEquilibrium dissociation energies De of the hydrogen‐bonded complexes HAl⋅⋅⋅HX and HGa⋅⋅⋅HX (X=F, Cl, Br, I, CN, CCH, and CP) were calculated ab initio at the CCSD(T)‐(F12c)/cc‐pVDZ−F12 level of theory. The gradients of graphs of De versus the electrophilicity EHX of the Lewis acids HX yielded the nucleophilicities NM−X of the Group 13 atoms M in these diatomic molecules. Molecular electrostatic surfaces potentials reveal that H−Al and H−Ga are bi‐nucleophilic and that the H ends of these H−M molecules are more nucleophilic than the M ends for M=Al and Ga, but not when M=boron. Therefore, the complexes M−H⋅⋅⋅HX were investigated using the same approach. It was concluded for M=Al and Ga that, for a given X, the M−H⋅⋅⋅HX complexes were more strongly bound than the corresponding H−M⋅⋅⋅HX complexes for both M=Al and Ga but the reverse order applies for M = boron. The effects of substituting the H atoms in the M−H molecules by F atoms and by methyl groups were investigated to measure the −I and +I inductive effects relative to H, respectively, on the nucleophilicities of the molecules M−H when M is acting as hydrogen‐bond acceptor in complexes H−M⋅⋅⋅H−X.