Radical Cleavage of Al–C Bonds Promoted by Phenazine: From Noninnocent Ligand to Radical Abstractor

The reaction of phenazine with standard aluminum alkyls AlR₃ (R = Me (<b>a</b>), Et (<b>b</b>), Et/Cl (<b>c</b>), <i>i</i>-Bu (<b>d</b>)) afforded, after initial coordination and formation of [AlMe₃]₂(μ-η¹:η¹-C₁₂H₈N₂) (<b>1</b>), a further slow and complex transformation. As a result, the dinuclear and diamagnetic [AlR₂]₂(μ-η¹:η¹-C₁₂H₈N₂)₂ (R = Me (<b>2a</b>), Et (<b>2b</b>), Et/Cl (<b>2c</b>), <i>i</i>-Bu (<b>2d</b>)) were formed in parallel to the paramagnetic and monomeric (AlR₃)­[η¹-C₁₄H₁₃NN­(R)] (<b>3</b>). The diamagnetism of <b>2</b> is obtained via dimerization and implementation of an efficient intramolecular antiferromagnetic coupling. In the case of the reaction with Et₂AlCl, the corresponding (AlEtCl₂)­[η¹-C₁₄H₁₃NN­(Et)] (<b>3c</b>) was isolated and fully characterized. In all the other cases, only compelling ESR evidence was obtained for the formation of isostructural species. On the basis of the isolation of both <b>2c</b> and <b>3c</b> from the same reaction, a mechanism is proposed involving ligand-assisted homolysis of Al–C bonds