development based on low-valent uranium complexes
In our efforts to activate small molecules of industrial and biological importance, we have turned our attention to coordinatively unsaturated, reactive uranium coordination complexes. For example, the chelating triazacyclononane (tacn), single N, and arene-anchored tris(aryloxide) ligands, (ArO)3tacn3–, (ArO)3N3–, and (ArO)3mes3– have provided access to reactive coordination compounds of uranium in oxidation states II, III, IV, V, and VI with tailorable steric and electronic profiles. These complexes display a pronounced selectivity and reactivity in reactions with carbon dioxide, related small heteroallene molecules (COS and CS2), and H2O.
Recently, the stoichiometric and catalytic “disproportionation” of CO2 to CO and CO32– via reductive cleavage of CO2 was accomplished. In analogy, we were able to isolate an entire series of chalcogenide mixed-carbonate complexes by reacting bridged chalcogenide complexes U‒E‒U (E = S, Se, Te) with CO2, CS2, and COS.
With respect to fundamental understanding of actinide chemistry, the molecular and electronic structure of a new oxidation state in U coordination chemistry, namely U(II), with a 5f 4 quintet ground state was stabilized by a mesitylene anchored tris(aryloxide) ligand. In K(crypt)[((Ad,MeArO)3mes)U], the U(II) center is supported by d backbonding, a general motive of the (ArO)3mes3– ligand.
In analogy to the CO2 reduction, a rare U(IV) hydroxo complex, [((Ad,MeArO)3mes)U(OH)], with a terminal OH functionality was synthesized by selective reduction of H2O with the U(III) complex [((Ad,MeArO)3mes)U]. Mechanistic studies were performed to understand this fundamental reaction, establishing the basis of catalytic H2O reduction for H2 evolution. Comprehensive electrochemical studies revealed that the U(III) complex can be regenerated in a catalytic cycle combining chemical and electrochemical reaction steps to produce H2 from water.
Most recent projects comprise the development of air and water stable U(IV) complexes for catalysis, the utilization of U(III) species with monodentate ligands for N2, N2O and NO activation, and finally the immobilization of catalysts on electrode surfaces.
For details on the research interest please see:
D. P. Halter, F.W. Heinemann, J. Bachmann, and K. Meyer
“Uranium-Mediated Electrocatalytic H2 Production from Water”
Nature 2016, 530, 317–321.
A.-C. Schmidt, A.V. Nizovtsev, A. Scheurer, F.W. Heinemann and K. Meyer
“Uranium-Mediated Reductive Conversion of CO2 to CO and Carbonate in a Single-Vessel Closed Synthetic Cycle” Chem. Comm. 2012, 48, 8634–8636.
S.M. Franke, F.W. Heinemann and K. Meyer
“Reactivity of Uranium(IV) Bridged Chalcogenido Complexes UIV-E-UIV (E = S, Se) with Elemental Sulfur and Selenium: Synthesis of Polychalcogenido-Bridged Uranium Complexes”
Chem. Sci. 2014, 5, 942–950.
O.P. Lam, S.M. Franke, F.W. Heinemann and K. Meyer
“Reactivity of U-E-U (E = S, Se) Towards CO2, CS2, and COS: New Mixed-carbonate Complexes of the Types U-CO2E-U (E = S, Se), U-CS2E-U (E = O, Se) and U-COSSe-U”
J. Am. Chem. Soc. 2012, 134, 16877–16881.
H.S. La Pierre, H. Kameo, D.P. Halter, F.W. Heinemann and K. Meyer
“Coordination and Redox Isomerization in the Reduction of a Uranium(III) Monoarene Complex”
Angew. Chem. Int. Ed. 2014, 53, 7154–7157.
H.S. La Pierre, A. Scheurer, F.W. Heinemann, W. Hieringer and K. Meyer
“Synthesis and Characterization of a Uranium(II) Monoarene Complex Supported by d Backbonding”
Angew. Chem. Int. Ed. 2014, 53, 7158–7162.
D.P. Halter, H.S. La Pierre, F.W. Heinemann and K. Meyer
“Uranium (IV) Halide (F–, Cl–, Br–, and I–) Monoarene Complexes”
Inorg. Chem. 2014, 53, 8418–8424.
S.M. Franke, M.W. Rosenzweig, F.W. Heinemann and K. Meyer
“Reactivity of Uranium(III) with H2E (E = S, Se, Te): Synthesis of a Series of Mononuclear and Dinuclear Uranium(IV) Hydrochalcogenido Complexes”
Chem. Sci. 2015, 6, 275–282.