Cyaarside (CAs-) and 1,3-Diarsaallendiide (AsCAs2-) Ligands Coordinated to Uranium and Generated via Activation of the Arsaethynolate Ligand (OCAs-).

Reaction of the trivalent uranium complex [((Ad,MeArO)3N)-U(DME)] with one molar equivalent [Na(OCAs)(dioxane)3], in the presence of 2.2.2-crypt, yields [Na(2.2.2-crypt)]-[{((Ad,MeArO)3N)-UIV(THF)}-(μ-O)-{((Ad,MeArO)3N)-UIV(CAs)}] (1), which is the arsenic containing analogue of the previously reported, μ-oxo-bridged di-uranium cyaphide complex. The structural characterization of complex 1 reveals the first example of a coordinated η1-cyaarside ligand (CAs-). The terminal CAs- anionic ligand formation is promoted by the highly reducing, oxo-philic uranium(III) precursor [((Ad,MeArO)3N)-U(DME)] and proceeds through reductive C-O bond cleavage of the bound arsaethynolate anion, OCAs-. If two equivalents of OCAs- are allowed to react with the uranium(III) precursor, the binuclear, µ-oxo-bridged diuran-ium(IV/IV) complex [Na(2.2.2-crypt)]2-[{((Ad,MeArO)3N)-UIV}2-(μ-O)(μ-AsCAs)] (2), comprising the hitherto unknown μ:η1,η1-coordinated (AsCAs)2- ligand, is isolated. The mechanistic pathway en route to the metalla-arsa-allene complex forma-tion likely is the decarbonylation of a dimeric inter-mediate formed in the reaction of 1 with OCAs-. An alternative path-way to complex 2 is the conver-sion of complex 1 to 2 by addition of one further equivalent of OCAs-. The mechanistic proposals are corroborated by DFT calculations.