Observation of Transition‐Metal–Boron Triple Bonds in IrB2O− and ReB2O

• Published in: Angewandte Chemie Vol. 132; no. 35; pp. 15372 - 15377
• Main Authors: Chen, Teng‐Teng, Cheung, Ling Fung, Chen, Wei‐Jia, Cavanagh, Joseph, Wang, Lai‐Sheng
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 24.08.2020
• Subjects: Boron; borylyne; Carbyne; chemical bonding; Chemical bonds; Chemistry; Chromium; Coordination compounds; Electrons; Metals; Photoelectron spectroscopy; Photoelectrons; Transition metals; triple bonds
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.202006652

Multiple bonds between boron and transition metals are known in many borylene (:BR) complexes via metal dπ→BR back‐donation, despite the electron deficiency of boron. An electron‐precise metal–boron triple bond was first observed in BiB2O− [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 IrB2O− and ReB2O− 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 IrB2O− has a closed‐shell bent structure (Cs, 1A′) with BO− coordinated to an Ir≡B unit, (−OB)Ir≡B, whereas ReB2O− is linear (C∞v, 3Σ−) 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. To bend or not to bend: Photoelectron spectroscopy and ab‐initio calculations show that IrB2O− has a bent (−OB)Ir≡B structure and ReB2O− has a linear structure, [Re≡B−B≡O]−. The latter is the first example of a transition‐metal borylyne complex.