Donor-free 9,10-dihydro-9,10-dialuminaanthracenes

Despite their promising potential, e.g. , as ditopic, cooperatively binding Lewis acids, 9,10-dihydro-9,10-dialuminaanthracenes (DAA-R 2 ; R: terminal Al-bonded substituent) have remained unexplored for long due to the challenges in synthesizing the ligand-free species. We demonstrate that DAA-Me 2 is accessible via the reaction of 1,2-(Me 3 Sn) 2 C 6 H 4 with AlMe 3 , producing volatile SnMe 4 as the sole byproduct. In non-coordinating solvents and in the solid state, DAA-Me 2 exists as a dimer (DAA-Me 2 ) 2 . Treatment of (DAA-Me 2 ) 2 with 4 equiv. AlBr 3 cleaves the dimer, leads to quantitative Me/Br exchange, and forms the double AlBr 3 adduct DAA-Br 2 ·(AlBr 3 ) 2 . Removal of AlBr 3 with 2,2′-bipyridine gives free DAA-Br 2 , which also dimerizes in the absence of bases to form (DAA-Br 2 ) 2 . (DAA-Me 2 ) 2 and (DAA-Br 2 ) 2 readily react with mono- ( e.g. , pyridine) or ditopic Lewis bases ( e.g. , potassium pyrazolide) to afford trans -diadducts or triptycene-type frameworks. Upon addition of [ n Bu 4 N]Br, DAA-Br 2 ·(AlBr 3 ) 2 undergoes selective cleavage of Al-C bonds to produce the Br − chelate complex of 1,2-(Br 2 Al) 2 C 6 H 4 , a valuable synthon for 1,2-dideprotonated benzenes. Donor-free 9,10-dialuminaanthracenes were prepared and fully characterized with Al-bonded Me or Br substituents. The low steric demand of the Me group ensures high reactivity of the unprotected Al centers: the Al-Br bonds allow late derivatizations.