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

The reaction of dialane (dpp-Bian)Al-Al(dppBian) (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 (iPr(2)Im(Me)) results in the Al-carbene adduct (dpp-Bian)(iPr(2)Im m e)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 (iPr(2)Imt(Me)) a half of the thione amount undergoes a cleavage of sulfur-carbon double bond. In the product (dpp- Bian)(iPr(2)Imt(Me))Al(p-S)Al(iPr(2)Imt(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 degrees C. Complex {(dpp-Bian)(iPr(2)Imt(Me))Al}(2)(mu-S) (5) was isolated from the reaction of dialane 1, iPr(2)Im(Me), and iPr(2)Imt(Me)(1:1:1). The reaction of mononuclear (dpp-Bian)AIH(THF) (2) (THF = tetrahydrofuran) affords compound (dpp-Bian)AlH(iPr(2)Im(Me)) (6). Compounds 3-6 were characterized by H-1 NMR and IR spectroscopy; their molecular structures were established by single-crystal X-ray analysis.