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

Carbocyclic aluminium halides [(ADC)AlX 2 ] 2 (2-X) (X=F, Cl, and I) based on an anionic dicarbene (ADC=PhC{N(Dipp)C} 2 , Dipp = 2,6-iPr 2 C 6 H 3 ) framework are prepared as crystalline solids by dehydrohalogenations of the alane [(ADC)AlH 2 ] 2 (1). KC 8 reduction of 2-I affords the peri-annulated Al(III) compound [(ADC H )AlH] 2 (4) (ADC H= PhC{N(Dipp)C 2 (Dipp H )N}, Dipp H =2-iPr,6-(Me 2 C)C 6 H 3 )) as a colorless crystalline solid in 76 % yield. The formation of 4 suggests intramolecular insertion of the putative bis-aluminylene species [(ADC)Al] 2 (3) into the methine C-H bond of HCMe 2 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.