Harnessing o‑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 o-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 = o-carboranyl). DFT calculations reveal that
the push–pull effect between the (Me3Si)2N and o-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.