A New Perspective on Borane Chemistry: The Nucleophilicity of the B−H Bonding Pair Electrons

An unknown side of boron chemistry: Similar to the nucleophilicity of boron compounds such as boryl anions and borylenes, the B−H bonding pair electrons in borane complexes also show nucleophilic properties that have led to the discovery of new chemical reactions.

Abstract

A number of recently discovered nucleophilic boron compounds, such as boryl anions and borylenes, are breaking the rules regarding boron and boron‐containing compounds and their reputation as Lewis acids/electrophiles. In a similar fashion, the B−H bonding pair electrons in boranes also show nucleophilicity which is ascribed to the lower electronegativity of boron relative to that of hydrogen. However, this nucleophilicity of the B−H bond has received far less attention. Explorations of the nucleophilicity of the B−H bonding pair electrons have led to the formation of B−H−B bonded units and B−H⋅⋅⋅H−Y dihydrogen bonds, based on which new chemistry has been uncovered, including the elucidation of the mechanism of formation of aminodiborane (ADB), the diammoniate of diborane (DADB), and lithium or sodium salts of octahydrotriborates (B₃H₈⁻), as well as the development of more convenient and straightforward synthetic routes to these reagents. Moreover, the recognition of the nucleophilic properties of the B−H bonding pair electrons will also help to more deeply understand the different mechanisms operating in hydroboration reactions.

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