Arene C−H Activation at Aluminium(I): meta Selectivity Driven by the Electronics of S N Ar Chemistry

Abstract The reactivity of the electron‐rich anionic Al I aluminyl compound K 2 [(NON)Al] 2 (NON=4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐ tert ‐butyl‐9,9‐dimethylxanthene) towards mono‐ and disubstituted arenes is reported. C−H activation chemistry with n ‐butylbenzene gives exclusively the product of activation at the arene meta position. Mechanistically, this transformation proceeds in a single step via a concerted Meisenheimer‐type transition state. Selectivity is therefore based on similar electronic factors to classical S N Ar chemistry, which implies the destabilisation of transition states featuring electron‐donating groups in either ortho or para positions. In the cases of toluene and the three isomers of xylene, benzylic C−H activation is also possible, with the product(s) formed reflecting the feasibility (or otherwise) of competing arene C−H activation at a site which is neither ortho nor para to a methyl substituent.