Access to a peri-Annulated Aluminium Compound via C-H Bond Activation by a Cyclic Bis-Aluminylene.

Carbocyclic aluminium halides [(ADC)AlX] (2-X) (X=F, Cl, and I) based on an anionic dicarbene (ADC=PhC{N(Dipp)C}, Dipp = 2,6-iPrCH) framework are prepared as crystalline solids by dehydrohalogenations of the alane [(ADC)AlH] (1). KC reduction of 2-I affords the peri-annulated Al(III) compound [(ADC)AlH] (4) (ADCPhC{N(Dipp)C(Dipp)N}, Dipp=2-iPr,6-(MeC)CH)) as a colorless crystalline solid in 76 % yield. The formation of 4 suggests intramolecular insertion of the putative bis-aluminylene species [(ADC)Al] (3) into the methine C-H bond of HCMe group. Calculations predict singlet ground state for 3, while the conversion of 3 into 4 is thermodynamically favored by 61 kcal/mol. Compounds 2-F, 2-Cl, 2-I, and 4 have been characterized by NMR spectroscopy and their solid-state molecular structures have been established by single crystal X-ray diffraction.