Unprecedented pairs of uranium (<scp>iv</scp>/<scp>v</scp>) hydroxido and (<scp>iv</scp>/<scp>v</scp>/<scp>vi</scp>) oxido complexes supported by a seven-coordinate cyclen-anchored tris-aryloxide ligand

Löffler, Sascha T.; Hümmer, Julian; Scheurer, Andreas; Heinemann, Frank W.; Meyer, Karsten

doi:10.1039/d2sc02736d

Cited by 6 publications

(8 citation statements)

References 77 publications

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“…Table of this review suggests that a simple halide exchange from chloride ( U E L (Cl) = −0.266 V) to fluoride ( U E L (F) = −0.526 V), with an otherwise unchanged cyclen chelator environment, should shift the complex’s U V/IV oxidation 260 mV more negative, thus, rendering the fluorido complex the stronger reductant with an expected U V/IV oxidation at −0.40 V. Indeed, UV/vis spectroscopic control of a reaction between TCNQ and [(( t Bu, t Bu ArO) 3 (Me)cyclen)U(F)] did confirm the chemical reduction to TCNQ – (see Scheme and SI, Figure S12). Electrochemical analysis of the respective fluoride complex then indeed revealed an experimental U V/IV oxidation at −0.40 V, which is in perfect agreement to the prediction by U E L parameters (prediction of −0.40 V).…”

Section: Reactivity Predictions With U E L Parameterssupporting

confidence: 78%

“…The Meyer group had recently synthesized a U IV complex [(( tBu,tBu ArO) 3 (Me)cyclen)U(Cl)] (with ( tBu,tBu ArO) 3 (Me)cyclen = 1,4,7-tris(3,5-di-tert-butyl-2hydroxybenzylate)-1-methyl-1,4,7,10-tetraazacyclododecane), for which the experimental U V/IV oxidation potential of −0.14 V was measured. 110 With an experimentally determined TCNQ/TCNQ − reduction potential of −0.30 V in THF (SI, Figure S10), [(( tBu,tBu ArO) 3 (Me)cyclen)U(Cl)] should not be able to reduce TCNQ. This test reaction is straightforwardly monitored by UV/vis electronic absorption spectroscopy, due to characteristic and well-separated absorption features of TCNQ and TCNQ − .…”

Section: Reactivity Predictions With U E L Parametersmentioning

confidence: 99%

“…In order to exemplarily benchmark the new U E L parameters for the prediction of reactivity tied to a U V/IV couple, the one-electron reduction of TCNQ (tetracyanochinodimethane) to TCNQ – was investigated. The Meyer group had recently synthesized a U IV complex [(( t Bu, t Bu ArO) 3 (Me)cyclen)U(Cl)] (with ( t Bu, t Bu ArO) 3 (Me)cyclen = 1,4,7-tris(3,5-di- tert -butyl-2-hydroxybenzylate)-1-methyl-1,4,7,10-tetraazacyclododecane), for which the experimental U V/IV oxidation potential of −0.14 V was measured . With an experimentally determined TCNQ/TCNQ – reduction potential of −0.30 V in THF (SI, Figure S10), [(( t Bu, t Bu ArO) 3 (Me)cyclen)U(Cl)] should not be able to reduce TCNQ.…”

Section: Reactivity Predictions With U E L Parametersmentioning

confidence: 99%

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Nonaqueous Electrochemistry of Uranium Complexes: A Guide to Structure–Reactivity Tuning

2023

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Uranium complexes can be stabilized in a wide range of oxidation states, ranging from U II to U VI and a very recent example of a U I complex. This review provides a comprehensive summary of electrochemistry data reported on uranium complexes in nonaqueous electrolyte, to serve as a clear point of reference for newly synthesized compounds, and to evaluate how different ligand environments influence experimentally observed electrochemical redox potentials. Data for over 200 uranium compounds are reported, together with a detailed discussion of trends observed across larger series of complexes in response to ligand field variations. In analogy to the traditional Lever parameter, we utilized the data to derive a new uranium-specific set of ligand field parameters U E L (L) that more accurately represent metal−ligand bonding situations than previously existing transition metal derived parameters. Exemplarily, we demonstrate U E L (L) parameters to be useful for the prediction of structure−reactivity correlations in order to activate specific substrate targets.

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Section: Reactivity Predictions With U E L Parameterssupporting

confidence: 78%

Section: Reactivity Predictions With U E L Parametersmentioning

confidence: 99%

Section: Reactivity Predictions With U E L Parametersmentioning

confidence: 99%

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Nonaqueous Electrochemistry of Uranium Complexes: A Guide to Structure–Reactivity Tuning

2023

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“…Tetravalent 1‐U features redox couples that are markedly similar to those reported for pentavalent imido (U 6+/5+ =−0.42 V) [11a] and organouranium imido/ketimido complexes (U 5+/4+ =−1.21 V to −1.84 V; U 6+/5+ =+0.36 V to −0.34 V) [2c] which are stabilized significantly by covalent MLMB interactions. The readily accessible U 6+/5+ couple in 1‐U represents a highly‐stabilized hexavalent state comparable to those of higher‐valent, higher‐coordinate, and MLMB complexes (−0.23 V to −1.51 V) [11b–d] . Relative to similar complexes with monoanionic donors, including U(NCyTMS) 4 (−0.37 V) and U[N(TMS) 2 ] 4 (+0.49 V), the U 5+/4+ couple in 1‐U is cathodically shifted by ~−1.2 V and −2.1 V, respectively, though solvent and electrolyte differences complicate direct comparisons [10,12] .…”

Section: Resultsmentioning

confidence: 93%

Divergent Stabilities of Tetravalent Cerium, Uranium, and Neptunium Imidophosphorane Complexes**

et al. 2023

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The study of the redox chemistry of mid‐actinides (U−Pu) has historically relied on cerium as a model, due to the accessibility of trivalent and tetravalent oxidation states for these ions. Recently, dramatic shifts of lanthanide 4+/3+ non‐aqueous redox couples have been established within a homoleptic imidophosphorane ligand framework. Herein we extend the chemistry of the imidophosphorane ligand (NPC=[N=PtBu(pyrr)2]−; pyrr=pyrrolidinyl) to tetrahomoleptic NPC complexes of neptunium and cerium (1‐M, 2‐M, M=Np, Ce) and present comparative structural, electrochemical, and theoretical studies of these complexes. Large cathodic shifts in the M4+/3+ (M=Ce, U, Np) couples underpin the stabilization of higher metal oxidation states owing to the strongly donating nature of the NPC ligands, providing access to the U5+/4+, U6+/5+, and to an unprecedented, well‐behaved Np5+/4+ redox couple. The differences in the chemical redox properties of the U vs. Ce and Np complexes are rationalized based on their redox potentials, degree of structural rearrangement upon reduction/oxidation, relative molecular orbital energies, and orbital composition analyses employing density functional theory.

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“…Cyclen-derived chelates are known as excellent hosts for the study of U and Ce oxidation states in aqueous ,, and nonaqueous solutions. ,, DOTAM is expected to provide a comparable framework for such equivalent redox transitions for its chelated cations, but with different energetics and stability of the transition products due to its similar cyclen backbone and relatively soft metal–amide O-donor bonds. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to characterize the U IV/III DOTAM and Ce IV/III DOTAM redox couples as well as that induced for each of their amide-arm hydrolysis products.…”

Section: X-ray Crystallographymentioning

confidence: 99%

Macrocyclic Ligand Coordinating Amide-Arm Hydrolysis Reaction Activation in Aqueous Solutions: Tetravalent Uranium Does It Better

Dovrat,

Pevzner,

Maimon

et al. 2023

Inorg. Chem.

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Chelation of lanthanide and actinide cations within a suitable macrocyclic ligand often results in a rigid, kinetically inert, and thermodynamically stable complex. A benchmark for such cation− ligand suitability are cyclen-derived macrocyclic ligands, frequently used as large cation hosts for various applications. Herein, a comprehensive study of the 1,4,7,10-tetrakis(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane ligand (DOTAM) chelates of U IV and Ce III and their properties in aqueous solutions is presented. By employing multiple analysis techniques, including X-ray crystallography, UV−vis absorbance, 1 H NMR, UPLC-MS, cyclic voltammetry, and differential pulse voltammetry, the study has revealed that the two aqueous complexes undergo a spontaneous, gradual, and stepwise hydrolysis of each of the coordinated amides toward carboxylates. The coordination of U IV in the studied reaction has been shown to significantly enhance the reaction rate, leading to an acceleration of up to 6 orders of magnitude compared to the natural process of simple aqueous amides at room temperature. An attempt to describe the unusual chelated metal cation amide-activation feature, based on the relatively lower rigidity of the complex structure, is presented. Additionally, the electrochemical properties of the complex series are discussed in detail, along with the limitations of the analytical methods employed.

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Unprecedented pairs of uranium (iv/v) hydroxido and (iv/v/vi) oxido complexes supported by a seven-coordinate cyclen-anchored tris-aryloxide ligand

Abstract: We present the synthesis and reactivity of a newly developed, cyclen-based tris-aryloxide ligand, namely cyclen(Me)(t-Bu,t-BuArOH)3, and its coordination chemistry to uranium. The corresponding uranium(III) complex [UIII((OArt-Bu,t-Bu)3(Me)cyclen)] (1) was characterized by...

Cited by 6 publications

References 77 publications

Nonaqueous Electrochemistry of Uranium Complexes: A Guide to Structure–Reactivity Tuning

Nonaqueous Electrochemistry of Uranium Complexes: A Guide to Structure–Reactivity Tuning

Divergent Stabilities of Tetravalent Cerium, Uranium, and Neptunium Imidophosphorane Complexes**

Macrocyclic Ligand Coordinating Amide-Arm Hydrolysis Reaction Activation in Aqueous Solutions: Tetravalent Uranium Does It Better

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