The reaction of diphenyldiazomethane with [((t-BuArO)(3)tacn)U-III] (1) results in an eta(2)-bound diphenyldiazomethane uranium complex. This complex exhibits unusual electronic properties as a charge-separated species with a radical anionic open-shell ligand, [((t-BuArO)(3)tacn)U-IV(eta(2)-NNCPh2)] (2). Treating Ph2CN2 with a uranium complex that contains a sterically more demanding adamantane functionalized ligand, [(((ArO)-Ar-Ad)(3)tacn)U-III] (3) results in an unprecedented C-H activation and nitrogen insertion to produce a five-membered heterocyclic indazole complex, [(((ArO)-Ar-Ad)(3)tacn)U-IV(eta(2)-3-phen(Ind))] (5). X-ray crystallography and spectroscopic characterization of these two compounds show that the [((t-BuArO)(3)tacn)U-IV(eta(2)-NNCPh2)] compound is a U(IV) complex with a radical anionic ligand, whereas [(((ArO)-Ar-Ad)(3)tacn)U-IV(eta(2)-3-phen(Ind))] is a U(IV) f(2) species with a closed-shell ligand.