CO2 and CO/H2 Conversion to Methoxide by a Uranium(IV) Hydride

Here we show that a scaffold combining siloxide ligands and a bridging oxide allows the synthesis and characterization of the stable dinuclear uranium­(IV) hydride complex [K2{[U­(OSi­(OtBu)3)3]2(μ-O)­(μ-H)2}], 2, which displays high reductive reactivity. The dinuclear bis-hydride 2 effects the reductive coupling of acetonitrile by hydride transfer to yield [K2{[U­(OSi­(OtBu)3)3]2(μ-O)­(μ-κ2-NC­(CH3)­NCH2CH3)}], 3. Under ambient conditions, the reaction of 2 with CO affords the oxomethylene2– reduction product [K2{[U­(OSi­(OtBu)3)3]2(μ-CH2O)­(μ-O)}], 4, that can further add H2 to afford the methoxide hydride complex [K2{[U­(OSi­(OtBu)3)3]2(μ-OCH3)­(μ-O)­(μ-H)}], 5, from which methanol is released in water. Complex 2 also effects the direct reduction of CO2 to the methoxide complex 5, which is unprecedented in f element chemistry. From the reaction of 2 with excess CO2, crystals of the bis-formate carbonate complex [K2{[U­(OSi­(OtBu)3)3]2(μ-CO3)­(μ-HCOO)2}], 6, could also be isolated. All the reaction products were characterized by X-ray crystallography and NMR spectroscopy.