Observation of Transition-Metal-Boron Triple Bonds in IrB O and ReB O.

Multiple bonds between boron and transition metals are known in many borylene (:BR) complexes via metal d →BR back-donation, despite the electron deficiency of boron. An electron-precise metal-boron triple bond was first observed in BiB 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 O and ReB 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 O has a closed-shell bent structure (C , A') with BO coordinated to an Ir≡B unit, ( OB)Ir≡B, whereas ReB O is linear (C , 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.