Reactivity of Aluminum Complexes of Redox-Active Ligand toward N‑Heterocyclic Carbene and Its Thione

The reaction of dialane (dpp-Bian)­Al–Al­(dpp-Bian) (1) (dpp-Bian is dianion of 1,2-bis­[(2,6-diisopropylphenyl)­imino]-acenaphthene) with 1 mol equiv of 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (iPr₂Im^Me) results in the Al-carbene adduct (dpp-Bian)­(iPr₂Im^Me)­Al–Al­(dpp-Bian) (3). In the course of the reaction of dialane 1 with 2 mol equiv of 1,3-diisopropyl-4,5-dimethylimidazol-2-thione (iPr₂Imt^Me) a half of the thione amount undergoes a cleavage of sulfur–carbon double bond. In the product (dpp-Bian)­(iPr₂Im^Me)­Al­(μ-S)­Al­(iPr₂Imt^Me)­(dpp-Bian) (4) aluminum atoms coordinate carbene as well as thione ligands. Compound 4 is thermally robust: no reduction of CS bond in thione moiety by the dpp-Bian ligands could be observed in toluene for 24 h at 100 °C. Complex {(dpp-Bian)­(iPr₂Im^Me)­Al}₂(μ-S) (5) was isolated from the reaction of dialane 1, iPr₂Im^Me, and iPr₂Imt^Me (1:1:1). The reaction of mononuclear (dpp-Bian)­AlH­(THF) (2) (THF = tetrahydrofuran) affords compound (dpp-Bian)­AlH­(iPr₂Im^Me) (6). Compounds 3–6 were characterized by ¹H NMR and IR spectroscopy; their molecular structures were established by single-crystal X-ray analysis.