Isolation of C1 through C4 derivatives from CO using heteroleptic uranium(iii) metallocene aryloxide complexes

Abstract

The conversion of C1 feedstock molecules such as CO into commodity chemicals is a desirable, but challenging, endeavour. When the U(III) complex, [(C₅Me₅)₂U(O-2,6-^tBu₂-4-MeC₆H₂)], is exposed to 1 atm of CO, only coordination is observed by IR spectroscopy as well as X-ray crystallography, unveiling a rare structurally characterized f element carbonyl. However, using [(C₅Me₅)₂(MesO)U (THF)], Mes = 2,4,6-Me₃C₆H₂, reaction with CO forms the bridging ethynediolate species, [{(C₅Me₅)₂(MesO)U}₂(μ₂-OCCO)]. While ethynediolate complexes are known, their reactivity has not been reported in much detail to afford further functionalization. For example, addition of more CO to the ethynediolate complex with heating forms a ketene carboxylate, [{(C₅Me₅)₂(MesO)U}₂(μ₂:κ²:η¹-C₃O₃)], which can be further reacted with CO₂ to yield a ketene dicarboxylate complex, [{(C₅Me₅)₂(MesO)U}₂(μ₂:κ²:κ²-C₄O₅)]. Since the ethynediolate showed reactivity with more CO, we explored its reactivity further. A [2 + 2] cycloaddition is observed with diphenylketene to yield [{(C₅Me₅)₂U}₂(OC(CPh₂)C(O)CO)] with concomitant formation of [(C₅Me₅)₂U(OMes)₂]. Surprisingly, reaction with SO₂ shows rare S–O bond cleavage to yield the unusual [(O₂CC(O)(SO)]²⁻ bridging ligand between two U(IV) centres. All complexes have been characterized using spectroscopic and structural methods, and the reaction of the ethynediolate with CO to form the ketene carboxylate has been investigated computationally as well as the reaction with SO₂.