Evidence of AlII Radical Addition to Benzene

Electrophilic AlIII species have long dominated the aluminum reactivity towards arenes. Recently, nucleophilic low‐valent AlI aluminyl anions have showcased oxidative additions towards arenes C−C and/or C−H bonds. Herein, we communicate compelling evidence of an AlII radical addition reaction to the benzene ring. The electron reduction of a ligand stabilized precursor with KC8 in benzene furnishes a double addition to the benzene ring instead of a C−H bond activation, producing the corresponding cyclohexa‐1,3(orl,4)‐dienes as Birch‐type reduction product. X‐ray crystallographic analysis, EPR spectroscopy, and DFT results suggest this reactivity proceeds through a stable AlII radical intermediate, whose stability is a consequence of a rigid scaffold in combination with strong steric protection. The electron reduction of diamido‐naphthyl aluminum iodide in benzene produces dialuminyl substituted Birch‐type reduction product. Time dependent EPR experiments in combination with DFT calculations suggest a reaction mechanism where stable AlII radical intermediates play a crucial role for the reaction outcome. The aluminum radical stability is a consequence of a rigid supporting ligand with silyl protective substituents.