Sc-Cr Metal complexes open benzene ring

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Discussion Overview

The discussion centers around the ability of scandium-chromium (Sc-Cr) metal complexes to interact with and potentially open the benzene ring, a topic relevant to inorganic chemistry and the study of chemical bonding. Participants explore the implications of these interactions for various applications, including the degradation of polyaromatic compounds.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that benzene's aromaticity makes it difficult to convert into linear products under mild conditions, referencing past work involving aluminum complexes and enzymes that can open the benzene ring.
  • A participant highlights a new study where a scandium complex is used to form an inverted sandwich complex with benzene, suggesting this arrangement allows benzene to carry extra electrons.
  • Another participant expresses interest in the applications of scandium, mentioning its role as a strengthener in aluminum and its limited availability due to few production sources.
  • One participant speculates whether Sc-Cr complexes could be effective in degrading polyaromatic compounds like PCBs and biphenyls.
  • A later reply questions the ability of polyaromatic compounds to emulate the coordination seen in the benzene ring with the Sc/Sc active site as illustrated in the referenced article.

Areas of Agreement / Disagreement

Participants express interest in the topic and share various insights, but there is no consensus on the effectiveness of Sc-Cr complexes for degrading polyaromatic compounds or the coordination capabilities of these complexes with different aromatic structures.

Contextual Notes

Some participants reference specific studies and applications of scandium, but there are limitations regarding the assumptions made about the behavior of polyaromatic compounds and the conditions under which these metal complexes operate.

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https://cen.acs.org/physical-chemis...3/web/2025/07?sc=250723_sc_eng_fb_cen_boosted

Benzene’s aromaticity makes it a tough nut to crack, and there are very few ways to convert it into linear products under mild conditions, says Jiaxiang Chu of the University of Chinese Academy of Sciences, who led the experimental aspects of the work.

Back in 2019, for example, a team led by Simon Aldridge at the University of Oxford made an aluminum complex that inserts itself into benzene, priming it for a reaction with a tin reagent that breaks open the ring. In addition, certain enzymes can pry open the benzene ring in catechol.

The team behind the new study instead drew inspiration from the kinds of metal complexes that can break the strong bonds in dinitrogen or carbon monoxide. First they made a scandium complex containing a pincer-like ligand that stabilizes a range of metal oxidation states. Then they mixed the complex with potassium graphite (KC8), which is a strong reducing agent, and benzene at room temperature. This formed an inverted sandwich complex in which each of benzene’s faces binds to a scandium complex. In this arrangement, the benzene carries four extra electrons in its antibonding orbitals.

“Scandium is always good for a surprise because it’s one of the smallest, highest-charged metal cations,” says Sjoerd Harder of Friedrich Alexander University Erlangen-Nuremberg, an organometallic chemist who uses main-group metal complexes to activate strong bonds. Harder was not involved in the new work. “It can do stuff that other metals can’t do.”
 
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It is always interesting to see Scandium getting applied.

We inorganic chemists sometimes forget that the first row doesn't start at titanium!
 
I havent perused the article, but their illustrations suggest that the benzene ring coordinates axially to the Sc/Sc active site. I am not sure how well polyaromatics can emulate this.