ReB₆^–: A Metallaboron Analog of Metallabenzenes

Abstract

Metallabenzenes are a class of molecules in which a CH unit in benzene is replaced by a functionalized transition-metal atom. While all-boron analogues of aromatic and antiaromatic hydrocarbons are well-known, there have not been any metallaboron analogs. We have produced and investigated two metal-doped boron clusters, ReB6 – and AlB6 –, using high-resolution photoelectron imaging and quantum chemical calculations. Vibrationally resolved photoelectron spectra have been obtained and compared with the theoretical results. The ReB6 – cluster is found to be perfectly planar with a B-centered hexagonal structure (C 2v , 1A1), while AlB6 – is known to have a similar structure, but with a slightly out-of-plane distortion (C s , 1A′). Chemical bonding analyses show that the closed-shell ReB6 – is doubly σ- and π-aromatic, while AlB6 – is known to be σ-aromatic and π-antiaromatic. The out-of-plane distortion in AlB6 – is due to antiaromaticity, akin to the out-of-plane distortion of the prototypical antiaromatic cyclooctatetraene. The π-bonding in ReB6 – is compared with that in both benzene and rhenabenzene [(CO)4ReC5H5], and remarkable similarities are found. Hence, ReB6 – can be viewed as the first metallaboron analog of metallabenzenes and it may be viable for syntheses with suitable ligands.

MnB6–: An Open-Shell Metallaboron Analog of 3d Metallabenzenes

“…The structures and relative energies of other low-lying isomers within 1 eV of the global minimum are given in Figure S1. The ground state of MnB 6 – consists of a B-centered six-membered ring with Mn being on the periphery, similar to the structure of ReB 6 – . While ReB 6 – is closed shell, MnB 6 – is found to have a high spin state ( 5 A 2 ) with an electron configuration of 1a 1 2 1b 2 2 2a 1 2 2b 2 2 1b 1 2 3a 1 2 1a 2 2 3b 2 2 4a 1 2 4b 2 2 - 5a 1 2 6a 1 1 7a 1 1 2b 1 1 5b 2 1 .…”

“…We report an investigation of a 3d transition-metal metallaboron cluster, MnB 6 – , produced by laser vaporization of a mixed Mn/B target. The selection of Mn was inspired by the recent synthesis of manganacycles and the ReB 6 – metallaboron analog of 5d metallabenezenes . High-resolution photoelectron imaging (PEI) in conjunction with computational chemistry has shown that MnB 6 – has a planar structure with the Mn atom on the periphery of the cluster, similar to that of ReB 6 – .…”

Observation of “Outlaw” Dual Aromaticity in Unexpectedly Stable Open-Shell Metal Clusters Caused by Near-Degenerate Molecular Orbital Coupling

“…Various aromaticity criteria have been proposed theoretically since aromaticity is not a directly measurable quantity. Herein, different criteria demonstrated as effective in probing aromaticity of metal clusters, [27][28][29][30][31][32][33][34][35][36] including magnetic [nucleus-independent chemical shift (NICS) and magnetic susceptibility anisotropy Δχ] and electronic [multicenter indices (MCI) and localized orbital locator (LOL)] indices were calculated to examine their aromaticity in both the T 0 and S 1 states. The explanations about other criteria that are not indicated here are listed in Supporting Information Note 1.…”

Structural transformations in boron clusters induced by metal doping

“…According to high-resolution photoelectron imaging and quantum chemical calculations, it is also the GM of B 6 Re − and B 6 Mn − . 91,92 The study on B 6 Al − reported a detailed AdNDP analysis, which shows four peripheral B–B bonds and two B–Al bonds as 2c-2e σ-bonds and three 7c-2e σ- and two 7c-2e π-bonds. 89 The preference for the hexagonal arrangement with a B in the center and the dopant at the periphery is maintained even in the experimentally observed B 6 Ta − .…”