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

Rock 'n' Roll cyaarside: Reaction of a strongly reducing oxophilic U^III precursor with arsaethynolate (OCAs⁻) yields dinuclear uranium complexes with an η¹‐bound cyaarside ligand (CAs⁻) and a unique diarsaallendiide (AsCAs²⁻) bridging ligand. Both ligands are new to metal coordination chemistry, and the CAs⁻ ligand currently presents the heaviest analogue of the ubiquitous cyanide.

Abstract

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)U^IV(THF)}(μ‐O){((^Ad,MeArO)₃N)U^IV(CAs)}] (1), the first example of a coordinated η¹‐cyaarside ligand (CAs⁻). Formation of the terminal CAs⁻ is promoted by the highly reducing, oxophilic U^III 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 U^III precursor, the binuclear, μ‐oxo‐bridged U₂^IV/IV complex [Na(2.2.2‐crypt)]₂[{((^Ad,MeArO)₃N)U^IV}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⁻.

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