The Lewis Acidity of the BO Triple Bond in Methyl(oxo)­borane

Abstract

The interaction of methyl(oxo)borane, CH3BO, with typical Lewis bases (nitrogen based and N‐heterocyclic carbenes) was investigated using density functional theory (B97‐D, TPSS‐D3), double hybrid density functionals (PWPB95‐D3, B2PLYP‐D3) in conjunction with empirical dispersion corrections, and coupled cluster theory involving singles, doubles, and a perturbative estimate of triple excitations [CCSD(T)]. A polarized quadruple‐zeta basis set was used throughout. The interaction energies computed with the double‐hybrid methods agree very well with CCSD(T). Compared to typical boron Lewis acids, the interaction energies are much smaller for methyl(oxo)borane, indicating that the BO triple bond results in significantly reduced Lewis acidity. An analysis of the mechanical bond strengths in CH3BO and its complexes indicates that the relaxed BO force constants (compliance constants) and the stretching vibrations decrease with increasing strengths of the dative interactions.

Additive Covalent Radii for Single-, Double-, and Triple-Bonded Molecules and Tetrahedrally Bonded Crystals: A Summary

“…The r 3 would predict an R of 126 pm. Bettinger et al report for MeBO calculated and experimental B–O bond lengths of 121.3 and 120.1 pm, respectively. Further examples at 120–123 pm are quoted by Brand et al In the series B–X, Al–X, the Ga–X, X = F, Cl, Br have bond lengths comparable with the Σ r 3 .…”