Characteristic Reactivity of Highly Lewis-Acidic Aryl-Substituted Diborane(4) toward Multiple Bonds

Abstract

This account focuses on the synthesis and reactivity of the diborane(4) compounds, pinB-BMes₂ and B₂(o-tol)₄ (pin = pinacolato, Mes = 2,4,6-Me₃C₆H₂, o-tol = 2-MeC₆H₄), which have been recently reported by the author’s group. Both compounds exhibit higher Lewis acidity than the most common diborane(4) B₂pin₂, which is due to the overlapping vacant p-orbitals of the two boron atoms. As a result, pinB-BMes₂ and B₂(o-tol)₄ exhibit a peculiar reactivity toward multiple bond compounds and small molecules such as CO, isocyanides, alkynes, nitriles, pyridine, and H₂. DFT calculations revealed that the combination of the high electrophilicity of these diborane(4)s, which facilitates the complexation of weak nucleophiles, and the reactive B-B bonding electrons should be responsible for the observed unique reactivity.