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 [K-2{[U(OSi((OBu)-Bu-t)(3))(3)](2)(mu-O)(mu-H)(2)}], 2, which displays high reductive reactivity. The dinuclear bis-hydride 2 effects the reductive coupling of acetonitrile by hydride transfer to yield [K-2{[U(OSi((OBu)-Bu-t)(3))(3)](2)(mu-O)(mu-kappa(2)-NC(CH3)NCH2CH3)}], 3. Under ambient conditions, the reaction of 2 with CO affords the oxomethylene(2-) reduction product [K-2{[U(OSi((OBu)-Bu-t)(3))(3)](2)(mu-CH2O)(mu-O)}], 4, that can further add H 2 to afford the methoxide hydride complex [K-2{[U(OSi((OBu)-Bu-t)(3))(3)](2)(mu-OCH3)(mu-O)(mu-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 [K-2{[U(OSi((OBu)-Bu-t)(3))(3)](2)(mu-CO3)(mu-HCOO)(2)}], 6, could also be isolated. All the reaction products were characterized by X-ray crystallography and NMR spectroscopy.