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,Me ArO)3 N)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,Me ArO)3 N)UIV (THF)}(μ-O){((Ad,Me ArO)3 N)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,Me ArO)3 N)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 U2 IV/IV complex [Na(2.2.2-crypt)]2 [{((Ad,Me ArO)3 N)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- .