The effect of substituents on triply bonded boron[triple bond, length as m-dash]antimony molecules: a theoretical approach.

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 RB[triple bond, length as m-dash]SbR (R = F, OH, H, CH3, SiH3, SiMe(SitBu3)2, SiiPrDis2 and NHC). The theoretical results demonstrate that the triply bonded RB[triple bond, length as m-dash]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[triple bond, length as m-dash]SbR compounds, theoretical evidence strongly indicates that their B[triple bond, length as m-dash]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[triple bond, length as m-dash]Sb triple bond. For RB[triple bond, length as m-dash]SbR molecules that feature small substituents, the triple bond is represented as . For RB[triple bond, length as m-dash]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[triple bond, length as m-dash]SbR molecules, from the kinetic viewpoint.