Activation of Carbon Dioxide at Uranium Complexes

In our efforts to activate small molecules of industrial and biological relevance, we have turned our attention to coordinatively unsaturated, highly reactive, low- and high-valent uranium coordination complexes.  For instance, the hexadentate tris(aryloxide) triaza­cyclo­nonane chelating ligand, (^t-BuArO)₃tacn^3–, and its sterically more demanding and protective neo­pentyl and adamantyl derivatives have provided access to reactive coordination compounds of uranium, [((^RArO)₃tacn)U] (R = t-Bu, Neo, Ad), in oxidation states III, IV, V, and VI and custom-tailored ligand environments.  These complexes display a pronounced selectivity and reactivity towards carbon dioxide and related heteroallene molecules, such as COS and CS₂. 

Here, reactions are presented that result in CO₂ coordination, activation, stoichiometric and catalytic “disproportionation” to CO and CO₃^2–, insertion, and functionalization via multiple bond metathesis.  Most recently, we also could show that oxalates form under optimized conditions.

It is shown that charge-separated complexes of uranium are particularly reactive species that often lead to unprecedented chemistry.