Harnessing <i>o</i> -Carborane to Access the BN-Ketenimine Structure

BN-isosterism provides a powerful concept for constructing BN analogues of classical organic frameworks. Here, we introduce the concept of BN-ketenimines (R₂C═C═NR' vs R₂N═B═NR') and demonstrate that the unique electronic effect of the <i>o</i>-carboranyl group enables the synthesis and single crystal structural characterization of the first compound that predominantly adopts a BN-ketenimine structure in the solid state, namely, (Me₃Si)₂N═B═NCb (Cb = <i>o</i>-carboranyl). DFT calculations reveal that the push-pull effect between the (Me₃Si)₂N and <i>o</i>-carboranyl substituents plays a crucial role in reversing the typical electronic preference of iminoboranes, thereby shifting the equilibrium from (Me₃Si)₂N─B≡N─Cb to (Me₃Si)₂N═B═NCb. Furthermore, this BN-ketenimine serves as a versatile platform for further functionalization, displaying nucleophilic behavior at nitrogen and electrophilic reactivity at boron and readily participating in inorganic-alkyne-based click (^iaclick) reactions.