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

Carbocyclic aluminium halides [(ADC)AlX2](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)AlH2](2) (1). KC8 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-(Me2C)C6H3)) 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 HCMe2 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.