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

Reaction of the trivalent uranium complex [(( ArO) N)U(DME)] with one molar equiv [Na(OCAs)(dioxane) ], in the presence of 2.2.2-crypt, yields [Na(2.2.2-crypt)][{(( ArO) N)U (THF)}(μ-O){(( ArO) N)U (CAs)}] (1), the first example of a coordinated η -cyaarside ligand (CAs ). Formation of the terminal CAs is promoted by the highly reducing, oxophilic U precursor [(( ArO) 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 U precursor, the binuclear, μ-oxo-bridged U complex [Na(2.2.2-crypt)] [{(( ArO) N)U } (μ-O)(μ-AsCAs)] (2), comprising the hitherto unknown μ:η ,η -coordinated (AsCAs) 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 .