Substituent Effects on Boron–Bismuth Triple Bond: A New Target for Synthesis

The substituent effects on the potential energy surfaces of RBBiR (R = F, OH, H, CH3, SiH3, Tbt, Ar*, SiMe­(SitBu3)2, and SiiPrDis2) are determined using density functional theories (M06-2X/Def2-TZVP, B3PW91/Def2-TZVP, and B3LYP/LANL2DZ+dp). The theoretical results show that all of the triply bonded RBBiR molecules prefer to adopt a bent geometry (i.e., ∠RBBi ≈ 180° and ∠BBiR ≈ 90°), which agrees well with the valence-electron bonding model. It is also demonstrated that the smaller groups, such as R = H, F, OH, CH3, and SiH3, neither kinetically nor thermodynamically stabilize the triply bonded RBBiR compounds, except for H3SiBBiSiH3. However, triply bonded R′BBiR′ molecules that feature bulkier substituents (R′ = SiiPrDis2, SiMe­(SitBu3)2, Tbt, and Ar*) are predicted to have a thermodynamic and kinetic global minimum. This theoretical study finds that both the steric and the electronic effects of bulkier substituent groups play a significant role in forming triply bonded RBBiR species that are experimentally obtainable and isolable in a stable form.