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(OCH-Bu-2,4,6)}(μ-η:η-N)], , allows us to generate, for the first time, a uranium complex presenting a rare triply reduced N moiety ((μ-η:η-N)). Importantly, the bound dinitrogen can be further reduced, affording the UN cubane cluster, , and the UN edge-shared cubane cluster, , thus showing that (N) 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 UN providing the first example of a molecular nitride of any metal formed from a complete cleavage of three N molecules.