The utility of the 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinato ligand, (hpp)(-), in uranium chemistry has been probed by synthesizing metallocene complexes and studying their reactivity, (C5Me5)(2)UMe2 reacts with 1 equiv of Hhpp to form (C5Me5)(2)(hpp)UMe, 1, which does not react further with Hhpp. (C5Me5)(2)UCl2 reacts with Khpp to form (C5Me5)(2)(hpp)UCl, 2, which similarly does not react with additional Khpp. Complex 2 reacts with NaN3 to form the azide complex, (C5Me5)(2)(hpp)UN3, 3. The trivalent uranium (hpp)(-) metallocene complex, (C5Me5)(2)(hpp)U, 4, can be synthesized by the reaction Of [(C5Me5)(2)U][BPh4] with Khpp and from 2 with KC8. Complex 4 can be oxidized with Ph3P=Se to produce the tetravalent product, [(C5Me5)(2)(hpp)U](2)(mu-Se), 5. The reaction of 4 with Me3SiN3 provides the pentavalent uranium complex, (C5Me5)(2)(hpp)U(=NSiMe3), 6