BN Analogue of Butadiyne: A B─B‐Bonded sp–sp Diboron(2) Species and Its Desymmetrization

In contrast to our earlier contribution on BN analogue of butadiyne featuring a conjugated B≡N─N≡B motif, we report here an alternative and distinct isoelectronic system, Ar*─N≡B─B≡N─Ar* ( 2 ; Ar* = C 6 H 3 ‐2,6‐Trip 2 , Trip = C 6 H 2 ‐2,4,6‐ i Pr 3 ). This B─B‐bonded bis(iminoborane) constitutes an rare example of an sp–sp diboron(2) species. Compound 2 exhibits characteristic mono‐ and double E–H (E = N, O) bond addition across the B≡N units to afford diboron(3) and diborane(4) species, respectively. Notably, mono‐N‐heterocyclic carbene (NHC) coordination induces desymmetrization of the NBBN core, fundamentally altering its electronic structure and reactivity profile. The resulting sp–sp 2 diboron(3) species undergoes a broader range of transformations with DMAB, DABSO, and CO 2 , furnishing novel products through addition, metathesis, and cycloaddition pathways involving selective cleavage of B─B, B≡N, and B═N bonds. Together, these results demonstrate how desymmetrization enables access to distinct reactivity modes within B─B‐bonded bis(iminoborane) frameworks.