All‐Inorganic sp‐Chain Ligands: Isoelectronic B/N Analogues of E. O. Fischer's Alkynylcarbynes

Borylation of a tungsten‐bound N2 ligand and halide abstraction provides access to a cationic complex with an unprecedented linear NNBR ligand. This complex undergoes [3+2] cycloaddition with azides, and an unexpected chain‐extension reaction with an iminoborane, leading to a complex with a five‐atom B/N chain. These two [NNBR]‐containing complexes, inorganic analogues of E. O. Fischer's alkynylcarbynes, are very rare examples of molecules containing all‐inorganic chains of sp‐hybridized atoms.