A milestone on the way to transition metal catalysis with aluminum

Chemists Philipp Dabringhaus, Julie Willrett and Prof. Dr. Ingo Krossing from the Institute for Inorganic and Analytical Chemistry of the University of Freiburg succeeded in synthesizing the complex of low-valent cationic aluminum + by a metathesis reaction. The team presents their research in the journal Character Chemistry.

“In chemistry, low-valence cationic aluminum compounds are highly sought after due to their potential changeover metal-style ambiphile reactivity. However, many previous attempts to synthesize low-valence cationic aluminum compounds by oxidative or reductive methods have been largely unsuccessful,” Krossing said. Explain. So far, he said, there has been only one example of a low-valence cationic aluminum compound, but it cannot be prepared by rational synthesis. “We now show that there is surprisingly easy access to low-valence aluminum complexes with metathesis after all,” says Krossing. In metathesis, the partial structures are simply exchanged between the reaction partners.

Aluminum as a cheaper alternative to catalysis

The chemists of Friborg prepared the +- salt of the Schnöckel tetramer (AlCp*)4, in which the aluminum is already present in the +1 oxidation state. The (AlCp*)4 reacted with Li and the reaction mixture immediately turned from yellow to red. When the reaction mixture was crystallized, the scientists got the +–salt as dark purple crystals. “X-ray crystallographic, UV spectrometric and computational studies indicate the presence of the dimeric structure both in the solid state and optionally at high concentration and low temperature, but at low focus and room temperature the monomer form. This clearly indicates an ambiphilic reactivity of the cation,” Dabringhaus said. due to its cationic nature, might be able to perform reversible oxidative additions and reductive removals of small molecules,” Krossing explains. “This brings us one step closer to our long-term goal of achieving catalysis – currently done with expensive and rare transition metals – with aluminum. Aluminum is the second most abundant element in the earth’s crust and able to do so in principle, as our work shows. But unfortunately, it will probably be at least another 20 years before our research on this is applied.”

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