Factors affecting the coordination mode of an amidato group on aluminum will be presented. The reaction of N-tert-butylalkylacetamide ((BuNHCR)-Bu-t(=O)) with 1.1 molar equiv of Me3Al in refluxing hexane affords a pentacoordinated, dimeric compound {Me2Al[eta(2)-(BuNC)-Bu-t(R)(mu(2)-O)]}(2) (3, R = p-Bu-t-C6H4; 4, R = 2,6-F,F-C6H3; 5, R = Me; 6, R = CF3; 7, R = p-F3C-C6H4). However, in the presence of 2.2 molar equiv of Me3Al, N-tert-butyl-4-tert-butylbenzamide ((BuNHC)-Bu-t(p-Bu-t-C6H4)(=O)) in refluxing hexane gives {Me2Al[eta(2)-(BuNC)-Bu-t(p-Bu-t-C6H4)(mu(2)-O)]AlMe3}, 8. In contrast, the reaction of R'NHCR"(=O) with 1 molar equiv of R3Al at room temperature produces tetracoordinated, dimeric, eight-membered ring aluminum compounds {R2Al[mu,eta(2)-R'NC(R")O]}(2) (9, R = Me, R' = 2,6-Pr-i, /Pr-C6H3, R" = Ph; 10, R = Me, R' = Bu-i, R" = Ph; 11, R = Et, R' = Bn, R" = Ph; 12, R = Me, R' = Ph, R" = CF3; 13, R = Me, R' = Bn, R" = CF3). On the other hand, 4'-chlorobenzanilide ((P-Cl-C6H4)-NHCPh(=O)) reacts with R3Al to produce trimeric, twelve-membered ring aluminum compounds {R2Al[mu,eta(2)-(p-Cl-C6H4)NC(Ph)O]}(3) (14, R = Me; 15, R = Et). Furthermore, the reaction of 2'-methoxybenzanilide with 1 molar equiv of Me3Al in hexane yields a dinuclear aluminum complex [Me2Al(o-OMe-Ph)NC(Ph)(O)AlMe3], 16.