Reactivity of Pnictaalumenes Towards 1,3-Dipole Molecules.

Alkynes undergo 1,3-dipolar cyclization reactions with organic azides giving 1,2,3-triazoles. Pnictaalumenes RPn═AlR' are the isoelectronic congeners of alkynes, hence a similar reactivity toward 1,3-dipole molecules is expected. Herein, we report the reactions of TerPn═AlCp* (Ter  =  2,6-(2,6-iPrCH)-CH, Cp*  =  [MeC], Pn  =  P, As) toward aryl azides. Instead of the anticipated phosphaaluminatriazole products from a [3+2] cyclization, the formation of four-membered AlNPn ring systems of the general form TerPn(μ-NR)AlCp* was observed. Depending on the steric profile of the azide, different outcomes were observed: a) N insertion into the Pn═Al bond accompanied by twofold N elimination, b) N insertion under preservation of the N motif, or c) mixed N/N products. The bonding situation is complex and best described as Al(III) complexes with NPnN-amino-amide-type ligands. A twofold insertion also occurs with the isovalent electronic diazoalkane MeSi(H)C═N, yielding imine-substituted AlNPn derivatives. In the case of its P-congener, two thermal rearrangements were observed, which first result in a AlNP ring species with a terminal Al─CN unit, followed by a second slower rearrangement to an aluminate cyanido complex with an unusual NNN pincer-type ligand framework. The current study contrasts well-established [3+2] cyclization reactions between alkynes and 1,3-dipoles and provides access to unprecedented ligand motifs.