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 equiv [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), the first example of a coordinated η1‐cyaarside ligand (CAs−). Formation of the terminal CAs− is promoted by the highly reducing, oxophilic UIII precursor [((Ad,MeArO)3N)U(DME)] and proceeds through reductive C−O bond cleavage of the bound arsaethynolate anion, OCAs−. If two equiv of OCAs− react with the UIII precursor, the binuclear, μ‐oxo‐bridged U2IV/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 to 2 involves the decarbonylation of a dimeric intermediate formed in the reaction of 1 with OCAs−. An alternative pathway to complex 2 is by conversion of 1 via addition of one further equiv of OCAs−. As statt N: Eine stark reduzierende oxophile UIII‐Vorstufe reagiert mit Arsaethinolat (OCAs−) zu zweikernigen Urankomplexen mit neuartigem η1‐gebundenem Cyaarsid‐Ligand (CAs−) und beispiellosem Diarsaallendiid(AsCAs2−)‐Brückenligand. Der CAs−‐Ligand ist das schwerste bisher bekannte Cyanid‐Analogon.