Dinitrogen cleavage provides an attractive but poorly studied route to the assembly of multimetallic nitride clusters. Here, we show that the monoelectron reduction of the dinitrogen complex [{U(OC6H2-Bu-3(t)-2,4,6)(3)}(2)(mu-eta(2):eta(2)-N-2)], 1, allows us to generate, for the first time, a uranium complex presenting a rare triply reduced N-2 moiety ((mu-eta(2):eta(2)-N-2)(center dot 3-)). Importantly, the bound dinitrogen can be further reduced, affording the U4N4 cubane cluster, 3, and the U6N6 edge-shared cubane cluster, 4, thus showing that (N-2)(center dot 3-) can be an intermediate in nitride formation. The tetranitride cluster showed high reactivity with electrophiles, yielding ammonia quantitatively upon acid addition and promoting CO cleavage to yield quantitative conversion of nitride into cyanide. These results show that dinitrogen reduction provides a versatile route for the assembly of large highly reactive nitride clusters, with U6N6 providing the first example of a molecular nitride of any metal formed from a complete cleavage of three N-2 molecules.