Abstract Cationic dialkylaluminum and m-terphenylalkylaluminum compounds catalyze the intramolecular hydroamination of primary and secondary aminopentenes. The reaction rates are strongly dependent on the substrate and the catalyst substituents. The bulky species [Dipp∗AlEt][CHB 11H 5I 6] (Dipp∗ = 2,6-Dipp 2C 6H 3–, Dipp = 2,6- iPr 2C 6H 3–), 4, was the most active catalyst. Although the neutral species DcpAlEt 2 (Dcp = 2,6-(2,6-Cl 2C 6H 3) 2C 6H 3–), 7, and Dipp∗AlEt 2, 8, showed some catalytic activity, they were more than 25 times less reactive than their cationic counterparts [DcpAlEt][CHB 11H 5Cl 6], 3, and 4. The cyclization of secondary benzylaminopentenes with [Et 2Al][CHB 11H 5I 6], 1, was strongly dependent on the substitution of the C-2 olefinic carbon.