Revealing Germylene Compounds to Attain Superbasicity with Sigma Donor Substituents: A Density Functional Theory Study

摘要

Compounds of GeII are shown for the first time to function as superbases. Two B(N=PiPr_3)_2 groups attached to a germanium(II) center show a gas-phase proton affinity of 296.2 kcalmol~(-1), which is close to the range of a hyperbase as revealed by B3LYP-D3/6-31G(2d,p) level of theory. These DFT calculations showed better agreement of geometrical parameters for the reported stable germylene compound 1 than previously reported calculations. A systematic study with different substitutions of Ge~(II) revealed that such a system can achieve basicity close to a hyperbase. The stabilities of these superbases were examined with dimerization energy and singlet-triplet state energy difference (ΔE_(S-T)). Furthermore, the calculated gas-phase proton affinity values also show good correlation with the most negative valued point (V_(min)) in electron-rich regions from the molecular electrostatic potential. The high PA values of compounds were also supported by ionization potential, electron affinity, absolute electronegativity, and absolute hardness calculations. The energetics for the reaction with BH_3 and AlMe_3 further suggest that the lone pair of Ge~(II) can act as a Lewis base and display higher donor-acceptor bond strengths.