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 (a), Et (b), Et/Cl (c), i-Bu (d)) afforded, after initial coordination and formation of [AlMe3]2(μ-η1:η1-C12H8N2) (1), a further slow and complex transformation. As a result, the dinuclear and diamagnetic [AlR2]2(μ-η1:η1-C12H8N2)2 (R = Me (2a), Et (2b), Et/Cl (2c), i-Bu (2d)) were formed in parallel to the paramagnetic and monomeric (AlR3)­[η1-C14H13NN­(R)] (3). The diamagnetism of 2 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)] (3c) 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 2c and 3c from the same reaction, a mechanism is proposed involving ligand-assisted homolysis of Al–C bonds.