The effect of substituents on triply bonded boron
antimony molecules: a theoretical approach†
Abstract
Three (M06-2X/Def2-TZVP, B3PW91/Def2-TZVP and B3LYP/LANL2DZ+dp) levels of theory are used to study the effect of substituents on the potential energy surfaces of RBSbR (R = F, OH, H, CH3, SiH3, SiMe(SitBu3)2, SiiPrDis2 and NHC). The theoretical results demonstrate that the triply bonded RB
SbR molecules favor a bent geometry: that is, ∠R–B–Sb ≈ 180° and ∠B–Sb–R ≈ 120°. Regardless of the type of substituents that are attached to the RB
SbR compounds, theoretical evidence strongly indicates that their B
Sb triple bonds have a donor–acceptor nature and are proven to be very weak. Two valence bond models clarify the bonding characters of the B
Sb triple bond. For RB
SbR molecules that feature small substituents, the triple bond is represented as
. For RB
SbR molecules that feature large substituents, the triple bond is represented as
. Most importantly, this theoretical study predicts that only bulkier substituents significantly stabilize the triply bonded RB
SbR molecules, from the kinetic viewpoint.