Synthesis, characterization and reactivity of an imidazolin-2-iminato aluminium dihydride

Abstract

The reaction of bis(2,6-diisopropylphenyl)imidazolin-2-imine (LH, 1) with Me₃N·AlH₃ furnishes {μ-LAlH₂}₂ (2). The marked tendency of 2 to release its hydride substituents is ascribed to the strong electron-donor character of the imidazolin-2-iminato ligand. This is supported by its reactivity study and DFT calculations. In fact, compound 2 was further converted with Me₃SiOTf, Me₂S·BH₃, Me₂S·BBr₃, and BX₃ (with X = Cl, Br, and I) into {μ-LAl(H)OTf}₂ (3), {μ-LAl(BH₄)₂}₂ (4), and {μ-LAlX₂}₂ (5, X = Br; 6, X = Cl; 7, X = I), respectively. For all new aluminium complexes the formulation as dimers was evidenced by high resolution mass spectrometry, as well as single-crystal X-ray diffraction analysis. A prominent structural motif of these compounds is the square-planar four-membered Al₂N₂ ring with two bridging bulky imidazolin-2-imino moieties.