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EXPLORING URANYL-OXO ACTIVATION VIA IMIDO SUBSTITUENTS AND EXPANDING THE LIBRARY OF URANIUM MULTIPLE IMIDO COMPLEXES
Uranium imido complexes are highly sought after for their analogous nature to the uranyl moiety. Because of the highly reactive characteristics of uranium imido bonds compared to uranyl oxygen bonds these complexes have been used to investigate chemistry that can be used to activate the uranyl moiety. The activation of the trans-oxo groups of the uranyl moiety would open the door for the recycling of spent nuclear waste, diverting these chemicals from long term storage to a second life beyond nuclear fission. A suitable analog to the uranyl moiety has been discovered with the uranium bis(imido) family of complexes, these complexes can participate in chemistry that is similar if not, exactly the same as uranyl complexes. Studies with the uranium bis(imido) complex have been used to probe uranyl reactivity because the analogous nature of the two moieties. With that a uranium(IV) cis-bis(imido) complex was synthesized demonstrating how electron donation to the metal center can disrupt the Inverse Trans Influence (ITI) can as a result activate the trans-ligands on uranium. This complex is the first reported U(IV) bis(imido) with trans imido groups and achieved this geometry without large steric ligands to facilitate the cis- geometry. Computational analysis of this complex shows the stable nature of the geometry and how the fundamental electronics of this complex are the leading factor in the resultant geometry. When reactivity of the cis-bis(imido) was explored via protonation experiments a unique U(V) complex was isolated.
Additional protonation reactivity was explored using UO2(tBubpy)(NTSA)2 with a variety of anilines to synthesize uranyl imido complexes. These experiments showed that the electronic environment—not the steric profile—of the anilines has a much greater effect on the stability of the resulting uranyl imido. The resulting uranyl imido complexes demonstrate the analogous nature of uranyl and uranium imido chemistry.
Activation of the trans-imido groups on uranium bis(imido) complexes has also been shown with the synthesis of the uranium tris- and tetrakis(imido) complexes. These later complexes have shown that increased electron donation to the uranium metal center weakens and elongates the imido bonds, exposing these compounds to reactivity previously unavailable to uranium compounds with fewer multiply bound groups.
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