Monoalkylaluminium Complexes Stabilized by a Rigid Dianionic Diimine Ligand: Synthesis, Solid State Structure, and Dynamic Solution Behaviour of (dpp‐BIAN)AlR (R = Me, Et, iBu)

Abstract

Abstract(dpp‐BIAN)Na2 (dpp‐BIAN = 1,2‐bis[(2,6‐di‐iso‐propylphenyl)imino]acenaphthene) reacts with two equivalents of R2AlCl in Et2O to give the monoalkylaluminium complexes (dpp‐BIAN)AlR(Et2O) (R = Me, 1; Et, 2; iBu, 3). Compounds 1‐3 have been characterized by elemental analysis, IR and 1H NMR spectroscopy. Single crystal X‐ray diffraction has been used to determine the molecular structures of 1 and 2. Both structures show the aluminium atom tetrahedrally coordinated by the two N atoms of the dianionic dpp‐BIAN ligand, the alkyl group, and a diethyl ether molecule. Temperature dependent 1H NMR spectroscopic measurements of 2 in THF‐d8 revealed a dynamic process caused by positional exchange between the ethyl group and the ether molecule relative to the metallacycle, which slows down with decreasing temperature. In the case of the methyl derivative 1, the corresponding process is fast at ambient as well as at low temperatures, whereas in the case of the isobutyl derivative 3 the larger size of the alkyl group prevents such a positional ligand exchange already at room temperature.