Plutonium(III) versus uranium(III) and samarium(III) in small molecule activation chemistry

We report the Pu^III complex, [Pu^III(Cp^Me4)₃] (1-Pu), and demonstrate its differences in small molecule reactivity compared to the U^III and Sm^III analogs, [U^III(Cp^Me4)₃] (1-U) and [Sm^III(Cp^Me4)₃] (1-Sm), respectively. 1-Pu reductively cleaves the small molecule (PhS)₂, affording a Pu^III complex, [{Pu^III(Cp^Me4)₂}₂(μ-SPh)₂] (2-Pu), while retaining the Pu^III center and eliminating (Cp^Me4)₂ as a by-product, a fingerprint of a sterically induced reduction (SIR) reaction. Sm is often used as a surrogate for Pu, but the analogous [Sm^III(Cp^Me4)₃], (1-Sm), is unreactive. The (PhS)₂ cleavage by 1-U proceeds solely via a metal-based oxidation (i.e., U^III → U^IV), to form [U^IV(Cp^Me4)₃(SPh)] (3-U). Only 1-U reacts with (PhHN)₂, affording the reductive cleavage product, [U^IV(Cp^Me4)₃(NHPh)] (4-U). The difference in reactivity of 1-Pu compared to complexes 1-Sm and 1-U was unexpected, and since SIR chemistry can enable complexes to participate in otherwise impossible reductive transformation of substrates, this reinforces the importance of studying small molecule reactivity with the transuranic elements.