The structure of and bonding in two base-free t e r m i n a l a c t i n i d e i m i d o m e t a l l o c e n e s , [ η 5 -1 , 2 , 4 -(Me 3 C) 3 C 5 H 2 ] 2 An�N(p-tolyl) (An = U (1), Th (1′)) are compared and connected to their individual reactivity. While structurally rather similar, the U(IV) derivative 1 is slightly more sterically crowded. Furthermore, density functional theory (DFT) studies imply that the 5f orbital contribution to the bonding within the individual actinide imido An�N(p-tolyl) moieties is significantly larger for 1 than for 1′, which makes the bonds between the [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 U 2+ and [(p-tolyl)N] 2− fragments more covalent. Therefore, steric and electronic factors impact the reactivity of these imido complexes. For example, complex 1 is inert toward internal alkynes, but it readily forms Lewis base adducts [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 U�N(p-tolyl)(L) (L = OPMe 3 (6), dmap (9), PhCN (14), and 2,6-Me 2 PhNC (17)) with Me 3 PO, 4-dimethylaminopyridine (dmap), nitrile, PhCN, or isonitrile 2,6-Me 2 PhNC. It may also react as a nucleophile or undergo a [2 + 2] cycloaddition with CS 2 , isothiocyanates, thioketones, ketones, lactides, and acyl nitriles, forming the four-or five-membered metallaheteroacycles, terminal sulfido, or oxido complexes, and cyanide amidate complexes, respectively. In contrast, after the addition of aldehyde p-tolylCHO, the tetranuclear complex [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 4 [OCH(p-tolyl)CH(p-tolyl)O] 2 U 4 O 4 (10) is isolated. However, while 1 is unreactive toward dicyclohexylcarbodiimide (DCC), an equilibrium exists in benzene solution between N,N′-diisopropylcarbodiimide (DIC), 1, and the four-membered metallaheterocycle [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 U[N(p-tolyl)C(�N i Pr)N( i Pr)] (12). Furthermore, 1 may also engage in single-and two-electron transfer processes. It is singly oxidized by Ph 3 CN 3 , CuI, Ph 2 S 2 , and Ph 2 Se 2 , yielding the uranium(V) imido complexes [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 U�N(p-tolyl)(X) (X = N 3 (20), I (22), PhS (23), and PhSe (24)), or is doubly oxidized by organic azides (RN 3 ) and 9-diazofluorene, forming the uranium(VI) bis-imido metallocenes [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 U�N(p-tolyl)(=NR) (R = p-tolyl (18), mesityl (19)) and [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 U=N(p-tolyl)[=NN=(9-C 13 H 8 )] (21), respectively.