Reactions of Amides with Organoaluminum Compounds: Factors Affecting the Coordination Mode of Aluminum Amidates

Factors affecting the coordination mode of an amidato group on aluminum will be presented. The reaction of
N-tert-butylalkylacetamide (tBuNHCR(O)) with 1.1 molar equiv of Me3Al in refluxing hexane affords a
pentacoordinated, dimeric compound {Me2Al[η2-tBuNC(R)(μ2-O)]}2 (3, R = p-tBu-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 (tBuNHC(p-tBu-C6H4)(O)) in refluxing hexane gives {Me2Al[η2-tBuNC(p-tBu-C6H4)(μ2-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[μ,η2-R‘NC(R‘ ‘)O]}2 (9, R = Me, R‘ =
2,6-iPr, iPr-C6H3, R‘ ‘ = Ph; 10, R = Me, R‘ = iBu, 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[μ,η2-(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.