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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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High-Resolution Photoelectron Imaging of IrB 3 − : Observation of a π-Aromatic B 3 + Ring Coordinated to a Transition Metal
We report a high-resolution photoelectron imaging and theoretical study of the IrB3‾ cluster. Two isomers are observed experimentally with electron affinities (EAs) of 1.3147(8) eV and 1.937(4) eV. Quantum calculations reveal two nearly degenerate isomers competing for the global minimum, both with a B3 ring coordinated with the Ir atom. One of the isomers consists of a B3 ring with a bridge-bonded Ir (Cs, 2A), which has the higher EA; and the second isomer features a tetrahedral structure (C3v, 2A1), which has the lower EA. The neutral tetrahedral structure is predicted to be overwhelmingly more stable than all other isomers. Chemical bonding analyses show that the neutral C3v isomer involves significant covalent Ir–B bonding and weak ionic bonding with charge transfers from B3 to Ir, which can be viewed as an Ir‾(η3-B3+) complex. The current study reports the first example of a boron-to-metal charge transfer complex and provides evidence of a π-aromatic B3+ ring coordinated to a transition metal.
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- PAR ID:
- 10096582
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/anie.201902406
