Evidence of Al II Radical Addition to Benzene

Electrophilic Al species have long dominated the aluminum reactivity towards arenes. Recently, nucleophilic low-valent Al aluminyl anions have showcased oxidative additions towards arenes C-C and/or C-H bonds. Herein, we communicate compelling evidence of an Al radical addition reaction to the benzene ring. The electron reduction of a ligand stabilized precursor with KC 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 Al radical intermediate, whose stability is a consequence of a rigid scaffold in combination with strong steric protection.