Reversible Two-Electron Redox Reactions Involving Tetralithio/Dilithio Palladole, Platinacycle, and Dicupra[10]annulene

The reaction chemistry of metalla-aromatics is fundamentally interesting. In this work, we find that tetralithio spiroaromatic palladole and platinacycle complexes 1 undergo selective two-electron oxidation with 1,2-dibromoethane as a mild oxidant, affording their corresponding dilithio spiro metallacyclopentadienes 3. These dilithio spiro complexes 3 can be reductively transformed to their corresponding tetralithio spiroaromatic complexes 1 with metallic lithium. When treated with an appropriate amount of oxidants, both 1 and 3 can generate 1,4-dihydropentalene derivatives 5 via a mechanism involving reductive elimination and silyl migration, as supported by density functional theory calculation. Similarly, tetralithio aromatic dicupra[10]­annulene 2 can also undergo the reversible two-electron redox reaction mentioned above. These results improve our understanding of the reactivity of metalla-aromatic compounds.