Radical cleavage of Al-C bonds promoted by phenazine: From noninnocent ligand to radical abstractor

Abstract

The reaction of phenazine with standard aluminum alkyls AlR 3 (R = Me (a), Et (b), Et/Cl (c), i-Bu (d)) afforded, after initial coordination and formation of [AlMe 3] 2(μ-η 1: η 1-C 12H 8N 2) (1), a further slow and complex transformation. As a result, the dinuclear and diamagnetic [AlR 2] 2(μ-η 1:η 1-C 12H 8N 2) 2 (R = Me (2a), Et (2b), Et/Cl (2c), i-Bu (2d)) were formed in parallel to the paramagnetic and monomeric (AlR 3)[η 1-C 14H 13NN(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 Et 2AlCl, the corresponding (AlEtCl 2) [η 1-C 14H 13NN(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. © 2012 American Chemical Society.