Abstract
Reversible single-metal two-electron oxidative addition and reductive elimination are common fundamental reactions for transition metals that underpin major catalytic transformations. However, these reactions have never been observed together in the f-block because these metals exhibit irreversible one- or multi-electron oxidation or reduction reactions. Here we report that azobenzene oxidises sterically and electronically unsaturated uranium(III) complexes to afford a uranium(V)-imido complex in a reaction that satisfies all criteria of a single-metal two-electron oxidative addition. Thermolysis of this complex promotes extrusion of azobenzene, where H-/D-isotopic labelling finds no isotopomer cross-over and the non-reactivity of a nitrene-trap suggests that nitrenes are not generated and thus a reductive elimination has occurred. Though not optimally balanced in this case, this work presents evidence that classical d-block redox chemistry can be performed reversibly by f-block metals, and that uranium can thus mimic elementary transition metal reactivity, which may lead to the discovery of new f-block catalysis.
Highlights
Reversible single-metal two-electron oxidative addition and reductive elimination are common fundamental reactions for transition metals that underpin major catalytic transformations
F-block catalysts can be highly active in σ-bond metathesis reactions[22], but despite decades of f-block research there are no examples of any lanthanide or actinide complexes that perform pure, classical oxidative addition and and reductive elimination reactions
We previously reported that reduction of the uranium(IV) triamide complex [U(TsXy)(Cl)(THF)] [1, TsXy = HC(SiMe2NAr)[3], Ar = 3,5-Me2C6H3] with potassium graphite in the presence of toluene afforded the formal diuranium(V) arene inverted sandwich complex [{U(TsXy)}2(μ-η6:η6-C6H5Me)]51, but in hexane solvent the putative uranium(III) complex [U(TsXy)] (2) that is generated by reduction of 1 activates one of the N-aryl bonds of the TsXy ligand to generate the dinuclear imido-aryl-bridged complex [U{HC(SiMe2NAr)2(SiMe2–μ–N)}(μ–η1:η1–Ar)U(TsXy)]51
Summary
Reversible single-metal two-electron oxidative addition and reductive elimination are common fundamental reactions for transition metals that underpin major catalytic transformations. The physicochemical properties of the f-block metals render them generally unable to support classical oxidative addition and reductive elimination reactions because the lanthanides and actinides cannot typically access two electron metalbased redox couples, though irreversible Grignard type reactions (e.g., M0 + RI → RMIII; M = Eu, Yb, Sm, R = Me, Et, Ph)[21], which are oxidative additions overall, are known; their reactivity is instead usually defined by single-electron transfers and σ-bond metathesis chemistries that exploit their highly electropositive and polarising natures. Sterically open and electronically unsaturated uranium (III) triamide complex that supports a reversible two-electron metal-centred U(III)-U(V) redox couple This oxidative additionreductive elimination couple is not well-balanced, but it suggests that the idea that f-block elements can support such reactivity is valid and could form the basis for new catalytic cycles supported
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