1,4-Dialumination of benzene by sodium and potassium aluminyls

The activation of C( sp 2 ) H bonds of benzene was achieved by sodium and potassium aluminyls. The products were studied by single-crystal X-ray diffraction showing inverse sandwich structures in which 1,4-dialumination had been achieved. The mechanism was studied using density functional theory, identifying Meisenheimer-type intermediates preceding each activation step. Under forcing conditions, the aluminyls [AM{Al(NON)}] 2 ([NON] 2− = [O(SiMe 2 NDipp) 2 ] 2− , Dipp = 2,6- i Pr 2 C 6 H 3 , AM = Na, K) react with benzene to give the 1,4-phenylene di(hydrido)aluminate complexes, AM 2 [1,4-{Al(NON)(H)} 2 (C 6 H 4 )]. Crystal structure analysis of the products shows that the ’Al(NON)(H)’ groups are in the plane of the para -substituted C 6 -ring, with the alkali metals above and below forming an inverse sandwich structure. Density functional theory calculations were performed to analyse the mechanism leading to the di-substituted product. Results identify a viable dimeric pathway and show that each alumination step is preceded by a Meisenheimer-type intermediate leading to the observed trans -dialuminated product.