Reduction of CO2 and CS2 with Uranium(III) Metallocene Aryloxides

The reactivity of two metallocene aryloxide U­(III) complexes, [(C5Me5)2U­(O–Ar)], Ar = 4-tBuC6H4, 1; Ar = 2,6-tBu2-4-CH3C6H2 (BHT), 3, with CO2 and CS2 has been investigated. The reaction of 1 with CO2 produces a bridging oxo complex, [{(C5Me5)2(4-tBuC6H4–O)­U}2(μ2-O)], 4, while 3 with CO2 results in reductive disproportionation to form the bridging carbonate species, [{(C5Me5)2(BHT)­U}2(μ2-κ2:η1-CO3)], 5. The difference in reactivity can be attributed to the steric properties of the ligand because the reaction of 3 with an oxo-delivering agent yields a U­(V) terminal oxo complex, [(C5Me5)2(BHT)­UO], 6. Reduction of CS2 to form a bridging (CS2)2– ligand, [{(C5Me5)2(tBuC6H4–O)­U}2(μ2-CS2)], 7, is observed with 1, while the reaction of 3 with CS2 also produces a bridging (CS2)2– reduced ligand complex, followed by C–H bond activation of a methyl group from one (C5Me5)1– ring, [(C5Me5)2(BHT)­U­{μ2-C­(H)­S2}­U­(C5Me4CH2)­(C5Me5)­(BHT)], 8. All compounds are characterized by NMR and IR spectroscopy, and their solid-state structures are determined by X-ray crystallography.