Triel tris(aminoaryl)aluminum, gallium, and indium complexes and their homocoupling reactions mediated by NiBr2

Abstract

Here, we present the synthesis, spectroscopic characterization, structural analysis, and studies on the bonding situation of group 13 tris(o-aminoaryl) complexes, [M(C6H4(o-NMe2))3] (1–3) and [M(C10H6(o-NMe2))3] (4–6) where M = Al, Ga, In. X-ray and DFT structural parameters, in conjunction with the inspection of the molecular electrostatic potential (MEP) of related triaryl, MAr3, models where Ar = C6H4, C10H6, suggest for 1–6 the presence of two partially polar covalent intramolecular M–N triel bonds. Interestingly, indium complexes 3 and 6 bind a third nitrogen atom with a Van der Waals type interaction. Stoichiometrical reactions of 1–3 with NiBr2 at 25 °C afforded the homocoupling product bi-o-dimethylaminophenyl (7) in up to 73 % isolated yield with 1 and 3 as the nucleophile. While 4–6 performed poorly under the same reaction conditions or at 100 °C providing either traces or at most 13 % of bi-o-dimethylaminonaphtyl (8) with 4 according to GC–MS. Hypothetical DFT bimetallic species [BrNi(μ-Br)M{C6H4(o-NMe2)}3] and [Ni(Br)2M{C10H6(o-NMe2}3] where M = Al (9, 12), Ga (10, 13), In (11, 14) are proposed reaction intermediates implied in the transmetalation/reductive elimination process that affords diaromatic amines 7 and 8.