A sterically congested NHC-AlMe(3) Lewis adduct (NHC = 1,3-di-tert-butylimidazol-2-ylidene) was found to either isomerize to an "abnormal" NHC-AlMe(3) species or to be involved in the deprotonation of AlMe(3) to form the corresponding imidazolium species along with an AlMe(3)-stabilized methylene aluminium anion.