A Free Aluminylene with Diverse σ-Donating and Doubly σ/π-Accepting Ligand Features for Transition Metals

Aluminium based ligands have garnered tremendous interest in the past decades due to the fundamental significance of the structural and electronic properties as well as their applications in synthetic chemistry. We report herein the synthesis, characterization, and coordination chemistry of a free N-aluminylene, namely a carbazolylaluminylene 2b. This species is prepared via a reduction reaction of the corresponding carbazolyl aluminium diiodide and is stable under an inert atmosphere. The coordination behavior of 2b towards transition metal centers (Mn, W, Cr) is shown to afford a series of novel aluminylene complexes with diverse coordination modes. We demonstrate that the Al center in 2b can behave as: 1. a σ-donating and doubly π-accepting ligand; 2. a σ-donating, σ-accepting and π-accepting ligand; and 3. σ-donating and doubly σ-accepting ligand. Additionally, we show ligand exchange at the aluminylene center providing access to the modulation of electronic properties of transition metals without changing the coordinated atoms. Further investigations of 2b with IDippCuCl (IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) showcase an unprecedented one-step aluminylene-alumanyl transformation leading to the facile synthesis of a rare terminal Cu-alumanyl complex. The electronic structures of such complexes and the mechanism of the unusual aluminylene-alumanyl transformation are investigated through density functional theory (DFT) calculations.