Observation of Transition‐Metal–Boron Triple Bonds in IrB 2 O − and ReB 2 O −

Multiple bonds between boron and transition metals are known in many borylene (:BR) complexes via metal d π →BR back‐donation, despite the electron deficiency of boron. An electron‐precise metal–boron triple bond was first observed in BiB 2 O − [Bi≡B−B≡O] − in which both boron atoms can be viewed as sp‐hybridized and the [B−BO] − fragment is isoelectronic to a carbyne (CR). To search for the first electron‐precise transition‐metal‐boron triple‐bond species, we have produced IrB 2 O − and ReB 2 O − and investigated them by photoelectron spectroscopy and quantum‐chemical calculations. The results allow to elucidate the structures and bonding in the two clusters. We find IrB 2 O − has a closed‐shell bent structure ( C s , 1 A ′) with BO − coordinated to an Ir≡B unit, ( − OB)Ir≡B, whereas ReB 2 O − is linear ( C ∞v , 3 Σ − ) with an electron‐precise Re≡B triple bond, [Re≡B−B≡O] − . The results suggest the intriguing possibility of synthesizing compounds with electron‐precise M≡B triple bonds analogous to classical carbyne systems.