The one-electron cleavage of benzylic bromides at palladium and palladized cathodes: Benzyl radicals generation and immobilization onto solid interfaces

Benzyl bromide 1 and 4-nitrobenzyl bromide 2 are reduced at solid electrodes in propylene carbonate (PC) and dimethylformamide (DMF) containing tetraalkylammonium salts. Palladium electrodes and these covered with layers of Cu–Pd, Ag–Pd, Au–Pd, and Ni–Pd were especially found to favour the one-electron scission of the C–Br bond. Under these conditions, 1 and 2 are reduced in two separated steps assigned to the transient formation of a free radical capable to couple or to add onto the cathodic material. The formation of benzyl radical allows the in situ addition onto unsaturated organic systems (mono- and di-benzylations). The formation of benzylic radical was confirmed by ESR technique (trapping the paramagnetic intermediate with nitrones). Lastly, preliminary experiments were achieved in order to test the grafting feasibility of benzyl radicals onto cathodic interfaces.