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A team from the University of Freiburg led by Prof. Dr Ingo Krossing and Dr Antoine Barthélemy is researching chemical processes that could form the basis for new, more sustainable catalyst systems. In a recent study, they demonstrated that a doubly positively charged digallene can activate very strong covalent bonds. The work was highlighted as Pick of the Week in the journal Chemical Science.
Prof. Dr Ingo Krossing, Dr Antoine Barthélemy and their team at the Institute of Inorganic and Analytical Chemistry at the University of Freiburg have investigated the special reactivity of a specific chemical compound, a doubly positively charged digallene. This compound contains two gallium atoms and is particularly reactive due to its doubly positive charge. In their study, the researchers systematically investigate how normally very stable covalent bonds can be activated, i.e. made more reactive, with the help of such a positively charged main group element complex.
The activation and conversion of chemical bonds often involves two steps: oxidative addition, in which an active complex enters a bond, and reductive elimination, which restores the complex while simultaneously forming a new bond. These steps are central to redox catalysis, i.e. systems that have a major effect in small quantities. Until now, industrial processes have mostly used expensive precious metals for this purpose, many of which are extracted under problematic conditions. Although it has been shown in recent years that electron-rich main group species can also add oxidatively to bonds, these complexes are often costly to produce.
The Freiburg team has now shown that a divalent digallene from the main groups can perform this task and activate the strong single bonds H–C, H–N, H–O and C≡C/C=C multiple bonds via oxidative addition. Many of these reactions are being described for the first time for a cationic, subvalent compound of group 13. “The great practical advantage of the system is that The digallene can be produced easily and directly in the reaction solution,” explains Barthélemy.
The high reactivity of digallene is based on two factors: a commercially available electron-rich, bidentate bisphosphane ligand, which increases the reactivity of the cation, and a weakly coordinating aluminate anion, which prevents unwanted interactions. Mechanistic studies show that the activation of multiple bonds proceeds cooperatively via two gallium atoms and also enables the catalytic isomerisation of olefins. In the case of single bonds, an asymmetric conformer of the digallene apparently plays an important role and favours the cooperative mechanism.
“The results are a promising step towards true redox catalysis with main group elements, which would also be very attractive for the chemical industry,” explains Krossing. “They open up prospects for new, easily accessible catalyst systems with high but controllable reactivity, not only within group 13, but also beyond.”
https://uni-freiburg.de/en/alternative-to-precious-metals-cationic-digallene-bre...
The molecular structure of the dicationic digallene examined here. The reactive unit of the molecule ...
Copyright: Antoine Barthélemy / Ingo Krossing
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