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.

Treatment of a suspension of phenazine and CrCl2(THF)2 in toluene with 4 equiv of triethylaluminum (Scheme ) affords the pentanuclear, heterobimetallic, and divalent [AlEt2(THF)(μ3-η1:η1-C12H8N2)(μ-κ1-AlEt2Cl)]2(μ-Cr) (1). In this species the two nitrogen atoms of each phenazine ligand are connected to three metals. A similar reaction with thiophenazine afforded trimetallic [(η1:η1-C12H8NS)(μ-κ1-AlEt2Cl)]2(μ-Cr) (2), where the sulfur atoms remained uncoordinated. When the preparation of 1 was carried out in the presence of excess Et3Al, the reaction took a different pathway, affording [AlEt2]2(μ-η1:η1-η6:η6-C12H8N2Cr)2 (3). The aluminate residues hold two parallel and eclipsed phenazine molecules, forming a rigid cage where the two chromium atoms are encapsulated. The ambiguity about the metal oxidation state has been solved by DFT calculations, revealing the formal oxidation state of chromium as being better described as monovalent.

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