Chemists develop new reagent for deelectronization

Chemists from Freiburg succeeded in converting polynuclear changeover metal carbonyls into their homoleptic complex cations using typical inorganic oxidants. In their work, the research team of Malte Sellin, Christian Friedmann and Prof. Dr. Ingo Krossing from the Institute of Inorganic and Analytical Chemistry and Maximilian Mayländer and Sabine Richert from the Institute of Physical Chemistry at the University of Friborg show that the anthracene derivative with a half-step potential of 1.42 Volts with respect to Fc0/+ can be converted into a radical deelectronization salt by a nitrosonium salt . “We have thus pushed the frontiers of basic research in coordination chemistry as well as in organometallic chemistry a little further,” Krossing said. The research group published their findings in the journal Chemical Science.

Deelectronator made from commercial chemicals

In order to gain access to the hitherto almost unknown class of clustered transition metal carbonyl cations, chemists at the University of Friborg sought a way to ionize substrates without triggering unwanted side reactions . During ionization, a neutral molecule loses one or more electrons. As a result, a positively charged molecule, also called a cation, is formed. A so-called harmless deelectronator is an ionizing agent that only accepts electrons from the substrate and otherwise shows no other unwanted reactivity. The only innocent deelectronator known to date, a perfluorinated ammonium cation, requiring a laborious and time-consuming synthesis, the Friborg scientists have developed an alternative produced directly from a commercially available chemical product: the anthracene derivative, with potential half-step of 1.42 volts against Fc0/+, can be converted into a radical deelectronator salt by a nitrosonium salt. “The deelectronizing salt allows us to remove electrons from the system while preserving the composition. It is therefore particularly gentle and creates systems that we have not been able to represent before. In the long run, these could help us produce better catalysts,” Krossing explains.

The perhalogenated anthracene deelectronator is putative

First, the research group attempted to generate the desired transition metal carbonyl cations by reacting trimetallic dodecacarbonyls with a silver salt as an oxidant. Direct reaction of trimetallic dodecacarbonyls with nitrosyl cations also did not produce the expected result. “However, if the nitrosyl cation is reacted in advance with a perhalogenated anthracene derivative, the resulting acene radical cation deelectronizes the trimetallic dodecacarbonyls under a carbon monoxide atmosphere and leads to the desired salts,” says Sellin. “So far, no one has succeeded in converting polynuclear changeover metal carbonyls into their homoleptic complex cations by typical inorganic oxidants. We’ve now shown it’s likely,” Krossing says. Sellin adds: “Surprisingly, structural characterization as well as vibrational and nuclear magnetic resonance spectroscopies of our new cluster indicate three electronically strongly different carbonyl ligands. It surprised us to see such different electronic behavior of virtually the same ligands in a molecule.

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