Open questions on aromaticity in organometallics

Zhu, Jun

doi:10.1038/s42004-020-00419-5

Cited by 25 publications

(19 citation statements)

References 25 publications

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“…In other words, species can display aromaticity either in the S 0 or T 1 state generally. On the contrary, adaptive aromaticity is a recently proposed concept, which means that species could be aromatic in two states, i.e., both the S 0 and T 1 states. − Besides, benzene with strong π-accepting substituent groups (CHO, COCH 3 , NO, and NO 2 ) was reported to display aromaticity in both S 0 and T 1 states . However, spin density is mainly localized at the substituent in these cases .…”

Section: Introductionmentioning

confidence: 99%

Adaptive Aromaticity in Metallasilapentalynes

2021

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Cyclic molecules with 4n + 2 or 4n electrons are aromatic in the lowest singlet state (S0) or the lowest triplet state (T1) according to Hückel and Baird’s rules. Thus, the design of aromatic species in both the S0 and T1 states (termed as adaptive aromaticity) is particularly challenging. In this work, we demonstrate that metallasilapentalynes show adaptive aromaticity supported by structural, magnetic, and electronic indices, in sharp contrast to metallapentalynes, which exhibit aromaticity in the S0 state only. The sharp difference in aromaticity could be caused by the distinctive excitation pattern. Specifically, the T1 state in metallasilapentalyne is formed by the excitation from the π to σ* molecular orbital, whereas it is excited from π to π* molecular orbital in metallapentalyne. In addition, a series of metallasilapentalynes with adaptive aromaticity are predicted by tuning the ligands. Our findings enrich the family of adaptive aromatics, inviting experimental chemists’ examination.

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Section: Introductionmentioning

confidence: 99%

Adaptive Aromaticity in Metallasilapentalynes

2021

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“…27,45−47 Nevertheless, other interpretations of electron counting would be also acceptable, as electron counting in aromatic organometallics is far from trivial. 48,49 Meanwhile, the Mobius-type π-MO of 3a′ (HOMO − 1) is associated with an antibonding interaction between osmium and adjacent carbons. This interaction becomes weaker in the twisted geometry of 3a, leading to the corresponding π-MO in a lower energy with shorter Os−C bonds (Figure S23, Supporting Information).…”

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confidence: 71%

“…The five occupied π-molecular orbitals (π-MOs) of 3a′ render a ten-center ten-electron (10c-10e) antiaromatic system constituted of three Craig- or Möbius-type (with d xz involved) π-MOs and two Hückel-type (with d yz involved) π-MOs, aligning with the previous result of Hückel–Möbius hybrids . Thus, 3a′ could be a Hückel–Möbius hybrid antiaromatic system. ,− Nevertheless, other interpretations of electron counting would be also acceptable, as electron counting in aromatic organometallics is far from trivial. , Meanwhile, the Möbius-type π-MO of 3a′ (HOMO – 1) is associated with an antibonding interaction between osmium and adjacent carbons. This interaction becomes weaker in the twisted geometry of 3a , leading to the corresponding π-MO in a lower energy with shorter Os–C bonds (Figure S23, Supporting Information).…”

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Releasing Antiaromaticity in Metal-Bridgehead Naphthalene

Tang

Zhao

et al. 2021

J. Am. Chem. Soc.

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As a fundamental chemical property, aromaticity guides the synthesis of novel structures and materials. Replacing the carbon moieties of aromatic hydrocarbons with transition metal fragments is a promising strategy to synthesize intriguing organometallic counterparts with a similar aromaticity to their organic parents. However, since antiaromaticity will endow compound instability, it is a great challenge to obtain an antiaromatic organometallic counterpart based on such transition metal replacement in aromatic hydrocarbons. Here, we report an efficient aromaticity transformation on aromatic naphthalene through the bridgehead replacement of an osmium fragment, leading to the unprecedented synthesis of metal-bridgehead naphthalene featuring a highly twisted structure as confirmed by X-ray crystallography characterization. Such a twisted conformation works together with its phosphonium substituents to release the antiaromaticity in the planar conformation of the metal-bridgehead naphthalene. Our findings prove the bridgehead involvement of transition metals in unexpected aromaticity modifications and open an avenue for novel metal-bridgehead complexes.

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“…Metalla-aromatics of intriguing structures are still emerging in an endless stream. Search for unprecedented and exciting aromatic systems, particularly with transition metals being involved, will continue to drive research in this area, as transition metals can make the impossible formation or transformation possible …”

Section: Summary and Future Prospectsmentioning

confidence: 99%

Metalla-aromatics: Planar, Nonplanar, and Spiro

Zhang

Huang

et al. 2021

Acc. Chem. Res.

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Metrics & MoreArticle Recommendations CONSPECTUS:The concept of aromaticity is one of the most fundamental principles in chemistry. It is generally accepted that planarity is a prerequisite for aromaticity, and typically the more planar the geometry of an aromatic compound is, the stronger aromatic it is. However, it is not always the case, particularly when transition metals are involved in conjugation and electron delocalization of aromatic systems, i.e., metalla-aromatics. Because of the intrinsic nature of transition-metal orbitals, besides planar geometries, the most stable molecular structures of metallaaromatic compounds could take nonplanar and even spiro geometries. In this Account, we outline several unprecedented types of metalla-aromatics developed recently in our research group.Around seven years ago, we found that 1,4-dilithio-1,3-butadienes, dilithio reagents with π-conjugation, could function as noninnocent ligands and react with low-valent transition-metal complexes, generating monocyclic metalla-aromatic compounds. Later on, by taking advantage of the unique behavior of dilithio reagents and the intrinsic nature of different transition metals, we have synthesized a series of metalla-aromatic compounds, of which four types are discussed here, and each of them represents the first of its kind. First, nearly planar aromatic dicupra[10]annulenes, a 10 π-electron aromatic system with two bridging Cu atoms participating in the orbital conjugation and electron delocalization, are synthesized by annulating two dilithio reagents with two Cu(I) complexes.Second, four kinds of spiro metalla-aromatics, featuring planar (with Pd, Pt, or Rh as the spiro atom) geometry with a whole 10π aromatic system, octahedral (tris-spiro metalla-aromatics with V as the spiro atom) geometry with an entire 40π Craig−Mobius aromatic system, tetrahedral (with Mn as the spiro atom) geometry having two independent and perpendicular 6π planar aromatic rings, and tetrahedral (with Mn as the spiro atom) geometry with one planar and one nonplanar 6π aromatic rings, respectively, are generated. In sharp contrast to spiroaromaticity with carbon acting as the spiro atom described in Organic Chemistry, the metal spiro atom herein takes part in orbital conjugation and electron delocalization. Third, nonplanar aromatic butadienyl diiron complexes are realized. Different from planar aromatic systems featuring delocalized πtype overlap, this nonplanar metalla-aromaticity is achieved by the novel σ-type overlap between the two Fe 3d xz orbitals and the butadienyl π orbital, forming a 6π aromatic system. Fourth, dinickelaferrocene, a ferrocene analogue with two aromatic nickeloles, is synthesized from our monocyclic aromatic dilithionickelole and FeBr 2 . The aromaticity of dinickelaferrocene and its nickelole ligands is realized by electron back-donation from the Fe 3d orbital to the π* orbital of nickeloles, which also deepens our understanding of the origin of aromaticity.The search for unprecedented and exciting aromatic systems, particul...

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Open questions on aromaticity in organometallics

Cited by 25 publications

References 25 publications

Adaptive Aromaticity in Metallasilapentalynes

Adaptive Aromaticity in Metallasilapentalynes

Releasing Antiaromaticity in Metal-Bridgehead Naphthalene

Metalla-aromatics: Planar, Nonplanar, and Spiro

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