Reaction of the trivalent uranium complex [((Ad,MeArO)3N)­U­(DME)] with [Na­(OCP)­(dioxane)2.5] and 2.2.2-crypt yields the μ-oxo-bridged, diuranium complex [Na­(2.2.2-crypt)]­[{((Ad,MeArO)3N)­U­(DME)}­(μ-O)­{((Ad,MeArO)3N)­U­(CP)}] (1). Complex 1 features an asymmetric, dinuclear UIV–O–UIV core structure with a cyaphide (CP–) anion η1-CP bound to one of the U ions, and a κ2-O DME coordinated to the other. The CP– ligand is unprecedented in uranium chemistry and is formed through reductive C–O bond cleavage of the phosphaethynolate anion (OCP–). An analogous reaction was performed starting from the tetravalent uranium halide complex [((Ad,MeArO)3N)­U­(DME)­(Cl)]. This salt metathesis approach with [Na­(OCP)­(dioxane)2.5] results in formation of the mononuclear complex [((Ad,MeArO)3N)­U­(DME)­(OCP)] (2) with an OCP– anion bound to the uranium­(IV) center via the oxygen atom in an η1-OCP fashion.

The utility of the bulky aryloxide ligands 2,6-Ad 2 -4-Me-C 6 H 2 O − ( Ad,Ad,Me ArO − ) and 2,6-Ad 2 -4-t-Bu-C 6 H 2 O − ( Ad,Ad,t-Bu ArO − ; Ad = 1-adamantyl) for stabilizing the Y(II) ion is reported and compared with the results with 2,6-t-Bu 2 -4-Me-C 6 H 2 O − (Ar′O − ). In contrast to the reduction product obtained from reducing Y(OAr′) 3 with potassium graphite, which is only stable in solution for 60 s at room temperature, KC 8 reduction of Y(OAr Ad,Ad,t-Bu ) 3 in THF in the presence of 2.2.2-cryptand (crypt) produces the room-temperature stable, crystallographically characterizable Y(II) aryloxide [K(crypt)]-[Y(OAr Ad,Ad,t-Bu ) 3 ]. The X-band EPR spectrum at 77 K shows an axial pattern with resonances centered at g ⊥ = 1.97 and g ∥ = 2.00 and hyperfine coupling constants of A ⊥ = 156.5 G and A ∥ = 147.8 G and at room temperature shows an isotropic pattern with g iso = 1.98 and A iso = 153.3 G, which is consistent with an S = 1/2 spin system with nuclear spin I = 1/2 for the 89 Y isotope (100% natural abundance).

The reductive disproportionation of nitric oxide (1 atm) is mediated by the bulky UIII aryloxide [UIII(OArAd,Ad,Me)3] (1) (Ad,Ad,MeArO = O-C6H2-2,6-Ad-4-Me) to form the UV terminal oxo species [(Ad,Ad,MeArO)3UV(O)] (2) and N2O, as confirmed by single crystal X-ray diffraction and GC-MS measurements.

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−.