Accessing a Highly Reducing Uranium(III) Complex through Cyclometalation.

U(IV) cyclometalated complexes have shown rich reactivity, but their low oxidation state analogues still remain rare. Herein, we report the isolation of [K(2.2.2-cryptand)][U{N(SiMe)}(κ-C,N-CHSiMeNSiMe)], , from the reduction of [U{N(SiMe)}] with KC and 2.2.2-cryptand at room temperature. Cyclic voltammetry studies demonstrate that has a reduction potential similar to that of the previously reported [K(2.2.2-cryptand)][U{N(SiMe)}] (E = -2.6 V versus Fc and E = -2.8 V versus Fc, respectively). Complex , indeed, shows similar reducing abilities upon reactions with 4,4'-bipyridine, 2,2'-bipyridine, and 1-azidoadamantane. Interestingly, was also found to be the first example of a mononuclear U(III) complex that is capable of reducing pyridine. In addition, it is shown that a wide variety of substrates can be inserted into the U-C bond, forming new U(III) metallacycles. These results highlight that cyclometalated U(III) complexes can serve as versatile precursors for a broad range of reactivity and for assembling a variety of novel chemical architectures.