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1. [La(η ^x -B _x )La] ⁻ ( x = 7–9): a new class of inverse sandwich complexes

   https://doi.org/10.1039/c8sc05443f  

   Chen, Teng-Teng; Li, Wan-Lu; Li, Jun; Wang, Lai-Sheng (February 2019, Chemical Science)

   Despite the importance of bulk lanthanide borides, nanoclusters of lanthanide and boron have rarely been investigated. Here we show that lanthanide–boron binary clusters, La 2 B x − , can form a new class of inverse-sandwich complexes, [Ln(η x -B x )Ln] − ( x = 7–9). Joint experimental and theoretical studies reveal that the monocyclic B x rings in the inverse sandwiches display similar bonding, consisting of three delocalized σ and three delocalized π bonds. Such monocyclic boron rings do not exist for bare boron clusters, but they are stabilized by the sandwiching lanthanide atoms. An electron counting rule is proposed to predict the sizes of the B x ring that can form stable inverse sandwiches. A unique (d-p)δ bond is found to play important roles in the stability of all three inverse-sandwich complexes. 

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

   https://doi.org/10.1002/anie.202006652  

   Chen, Teng‐Teng; Cheung, Ling Fung; Chen, Wei‐Jia; Cavanagh, Joseph; Wang, Lai‐Sheng (June 2020, Angewandte Chemie International Edition)

   Abstract 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 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 (C_s,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. 

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3. An Atomistic Picture of Boron Oxide Catalysts for Oxidative Dehydrogenation Revealed by Ultrahigh Field ¹¹ B– ¹⁷ O Solid-State NMR Spectroscopy

   https://doi.org/10.1021/jacs.2c08237  

   Dorn, Rick W.; Mark, Lesli O.; Hung, Ivan; Cendejas, Melissa C.; Xu, Yijue; Gor’kov, Peter L.; Mao, Wenping; Ibrahim, Faysal; Gan, Zhehong; Hermans, Ive; et al (October 2022, Journal of the American Chemical Society)

   Boron oxide/hydroxide supported on oxidized activated carbon (B/OAC) was shown to be an inexpensive catalyst for the oxidative dehydrogenation (ODH) of propane that offers activity and selectivity comparable to boron nitride. Here, we obtain an atomistic picture of the boron oxide/hydroxide layer in B/OAC by using 35.2 T 11B and 17O solid-state NMR experiments. NMR spectra measured at 35.2 T resolve the boron and oxygen sites due to narrowing of the central-transition powder patterns. A 35.2 T 2D 11B{17O} dipolar heteronuclear correlation NMR spectrum revealed the structural connectivity between boron and oxygen atoms. The approach outlined here should be generally applicable to determine atomistic structures of heterogeneous catalysts containing quadrupolar nuclei. 

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4. Solid-state ¹¹ B NMR studies of coinage metal complexes containing a phosphine substituted diboraanthracene ligand

   https://doi.org/10.1039/d1dt02981a  

   Huynh, Winn; Taylor, Jordan W.; Harman, W. Hill; Conley, Matthew P. (October 2021, Dalton Transactions)

   Transition metal interactions with Lewis acids (M → Z linkages) are fundamentally interesting and practically important. The most common Z-type ligands contain boron, which contains an NMR active 11 B nucleus. We measured solid-state 11 B{ 1 H} NMR spectra of copper, silver, and gold complexes containing a phosphine substituted 9,10-diboraanthracene ligand (B 2 P 2 ) that contain planar boron centers and weak M → BR 3 linkages ([(B 2 P 2 )M][BAr F 4 ] (M = Cu (1), Ag (2), Au (3)) characterized by large quadrupolar coupling ( C Q ) values (4.4–4.7 MHz) and large span ( Ω ) values (93–139 ppm). However, the solid-state 11 B{ 1 H} NMR spectrum of K[Au(B 2 P 2 )] − (4), which contains tetrahedral borons, is narrow and characterized by small C Q and Ω values. DFT analysis of 1–4 shows that C Q and Ω are expected to be large for planar boron environments and small for tetrahedral boron, and that the presence of a M → BR 3 linkage relates to the reduction in C Q and 11 B NMR shielding properties. Thus solid-state 11 B NMR spectroscopy contains valuable information about M → BR 3 linkages in complexes containing the B 2 P 2 ligand. 

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5. Transition-metal-like bonding behaviors of a boron atom in a boron-cluster boronyl complex [(η ⁷ -B ₇ )-B-BO] ⁻

   https://doi.org/10.1039/D1SC00534K  

   Tian, Wen-Juan; Chen, Wei-Jia; Yan, Miao; Li, Rui; Wei, Zhi-Hong; Chen, Teng-Teng; Chen, Qiang; Zhai, Hua-Jin; Li, Si-Dian; Wang, Lai-Sheng (June 2021, Chemical Science)

   Boron displays many unusual structural and bonding properties due to its electron deficiency. Here we show that a boron atom in a boron monoxide cluster (B 9 O − ) exhibits transition-metal-like properties. Temperature-dependent photoelectron spectroscopy provided evidence of the existence of two isomers for B 9 O − : the main isomer has an adiabatic detachment energy (ADE) of 4.19 eV and a higher energy isomer with an ADE of 3.59 eV. The global minimum of B 9 O − is found surprisingly to be an umbrella-like structure ( C 6v , 1 A 1 ) and its simulated spectrum agrees well with that of the main isomer observed. A low-lying isomer ( C s , 1 A′) consisting of a BO unit bonded to a disk-like B 8 cluster agrees well with the 3.59 eV ADE species. The unexpected umbrella-like global minimum of B 9 O − can be viewed as a central boron atom coordinated by a η 7 -B 7 ligand on one side and a BO ligand on the other side, [(η 7 -B 7 )-B-BO] − . The central B atom is found to share its valence electrons with the B 7 unit to fulfill double aromaticity, similar to that in half-sandwich [(η 7 -B 7 )-Zn-CO] − or [(η 7 -B 7 )-Fe(CO) 3 ] − transition-metal complexes. The ability of boron to form a half-sandwich complex with an aromatic ligand, a prototypical property of transition metals, brings out new metallomimetic properties of boron. 

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