The archetypal uranyl fragment (UO22+) exists exclusively as the trans isomer, which makes a cis-uranyl complex an intriguing synthetic target. While the cis-uranyl fragment has yet to be isolated, there have been several attempts made toward its synthesis. For instance, several attempted preparations of cis-Cp’2UO2 have resulted in either ligand oxidation and precipitation of UO2, or formation of U(IV) oxide clusters. Intriguingly, however, the cis-uranyl isomer has been studied by DFT. These results suggest that a cis-uranyl complex, while higher in energy than the trans isomer, represents a local minimum on the energy landscape. Herein, we will present our attempts to prepare a cis-uranyl complex by ligation of macrocyclic ligands to the uranyl fragment. In particular, we explored the reactivity of [UO2Cl2(THF)2]2 with tmtaa (dibenzotetramethylaza[14]annulene), a 14-membered macrocycle. We rationalized that the tmtaa ligand would be unable to accommodate the trans-UO22+ fragment within its small ring cavity, thereby forcing a trans to cis isomerization. The characterization and reactivity of the resulting complexes will also be discussed.

Synthetic investigations towards a cis-uranyl complex

251st National Meeting (2016)

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