Seven-Membered Cyclic Diamidoalumanyls of Heavier Alkali Metals: Structures and C–H Activation of Arenes

[Image: see text] Like the previously reported potassium-based system, rubidium and cesium reduction of [{SiN(Dipp)}AlI] ({SiN(Dipp)} = {CH(2)SiMe(2)NDipp}(2)) with the heavier alkali metals [M = Rb and Cs] provides dimeric group 1 alumanyl derivatives, [{SiN(Dipp)}AlM](2). In contrast, similar treatment with sodium results in over-reduction and incorporation of a formal equivalent of [{SiN(Dipp)}Na(2)] into the resultant sodium alumanyl species. The dimeric K, Rb, and Cs compounds display a variable efficacy toward the C–H oxidative addition of arene C–H bonds at elevated temperatures (Cs > Rb > K, 110 °C) to yield (hydrido)(organo)aluminate species. Consistent with the synthetic experimental observations, computational (DFT) assessment of the benzene C–H activation indicates that rate-determining attack of the Al(I) nucleophile within the dimeric species is facilitated by π-engagement of the arene with the electrophilic M(+) cation, which becomes increasingly favorable as group 1 is descended.