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A method to explore head‐to‐head ϕ back‐bonding from uranium f‐orbitals into allyl π* orbitals has been pursued. Anionic allyl groups were coordinated to uranium with tethered anilide ligands, then the products were investigated by using NMR spectroscopy, single‐crystal XRD, and theoretical methods. The (allyl)silylanilide ligand, N‐((dimethyl)prop‐2‐enylsilyl)‐2,6‐diisopropylaniline (LH), was used as either the fully protonated, singly deprotonated, or doubly deprotonated form, thereby highlighting the stability and versatility of the silylanilide motif. A free, neutral allyl group was observed in UI2(L1)2 (1), which was synthesized by using the mono‐deprotonated ligand [K][N‐((dimethyl)prop‐2‐enyl)silyl)‐2,6‐diisopropylanilide] (L1). The desired homoleptic sandwich complex U[L2]2 (2) was prepared from all three ligand precursors, but the most consistent results came from using the dipotassium salt of the doubly deprotonated ligand [K]2[N‐((dimethyl)propenidesilyl)‐2,6‐diisopropylanilide] (L2). This allyl‐based sandwich complex was studied by using theoretical techniques with supporting experimental spectroscopy to investigate the potential for phi (ϕ) back‐bonding. The bonding between UIV and the allyl fragments is best described as ligand‐to‐metal electron donation from a two carbon fragment‐localized electron density into empty f‐orbitals. [ABSTRACT FROM AUTHOR]

Two new aqueous UIV complexes were synthesized by the interaction between the tetravalent uranium cation and the (1,4,7,10‐Tetraazacyclododecane‐1,4,7,10‐tetra(methylene phosphonic acid) (DOTP) macrocyclic ligand. Two distinct homonuclear complexes were identified; the first was characterized by X‐ray crystallography as a unique "out‐of‐cage", [U(DOTPH6)2] complex, in which the UIV cation is octa‐coordinated to 4 phosphonic arms from each ligand in a square anti‐prism geometry, with a C4 symmetry. The second is the "in‐cage" [U(DOTPH4)] complex, in which the tetravalent cation is located between the macrocycle O4 and N4 planes. With the help of UV‐Vis absorption, 1H/31P NMR, ATR‐IR, and MALDI‐TOFMS analytical techniques, the chemical interchange between both species is presented. It is shown that the one‐way transition is governed by the formation of a multiple number of soluble oligomeric species consisting of varied stoichiometric ratios of both characterized homonuclear complexes. [ABSTRACT FROM AUTHOR]

The synthesis, electronic structure, and reactivity of a uranium metallacyclopropene were comprehensively studied. Addition of diphenylacetylene (PhC≡CPh) to the uranium phosphinidene metallocene [η5‐1,2,4‐(Me3C)3C5H2]2U=P‐2,4,6‐tBu3C6H2 (1) yields the stable uranium metallacyclopropene, [η5‐1,2,4‐(Me3C)3C5H2]2U[η2‐C2Ph2] (2). Based on density functional theory (DFT) results the 5f orbital contributions to the bonding within the metallacyclopropene U‐(η2‐C=C) moiety increases significantly compared to the related ThIV compound [η5‐1,2,4‐(Me3C)3C5H2]2Th[η2‐C2Ph2], which also results in more covalent bonds between the [η5‐1,2,4‐(Me3C)3C5H2]2U2+ and [η2‐C2Ph2]2− fragments. Although the thorium and uranium complexes are structurally closely related, different reaction patterns are therefore observed. For example, 2 reacts as a masked synthon for the low‐valent uranium(II) metallocene [η5‐1,2,4‐(Me3C)3C5H2]2UII when reacted with Ph2E2 (E=S, Se), alkynes and a variety of hetero‐unsaturated molecules such as imines, ketazine, bipy, nitriles, organic azides, and azo derivatives. In contrast, five‐membered metallaheterocycles are accessible when 2 is treated with isothiocyanate, aldehydes, and ketones. [ABSTRACT FROM AUTHOR]

The first stable base‐free terminal uranium phosphinidene metallocene is presented; and its structure and reactivity have been studied in detail and compared to that of the corresponding thorium derivative. Salt metathesis reaction of the methyl iodide uranium metallocene Cp"'2U(I)Me (2, Cp"'=η5‐1,2,4‐(Me3C)3C5H2) with Mes*PHK (Mes*=2,4,6‐(Me3C)3C6H2) in THF yields the base‐free terminal uranium phosphinidene metallocene, Cp"'2U=PMes* (3). In addition, density functional theory (DFT) studies suggest substantial 5f orbital contributions to the bonding within the uranium phosphinidene [U]=PAr moiety, which results in a more covalent bonding between the [Cp"'2U]2+ and [Mes*P]2− fragments than that for the related thorium derivative. This difference in bonding besides steric reasons causes different reactivity patterns for both molecules. Therefore, the uranium derivative 3 may act as a Cp"'2U(II) synthon releasing the phosphinidene moiety (Mes*P:) when treated with alkynes or a variety of hetero‐unsaturated molecules such as imines, thiazoles, ketazines, bipy, organic azides, diazene derivatives, ketones, and carbodiimides. [ABSTRACT FROM AUTHOR]

While carbene complexes of uranium have been known for over a decade, there are no reported examples of complexes between an actinide and a „heavy carbene." Herein, we report the syntheses and structures of the first uranium‐heavy tetrylene complexes: (CpSiMe3)3U‐Si[PhC(NR)2]R' (R=tBu, R'=NMe21; R=iPr, R'=PhC(NiPr)22). Complex 1 features a kinetically robust uranium‐silicon bonding interaction, while the uranium‐silicon bond in 2 is easily disrupted thermally or by competing ligands in solution. Calculations reveal polarized σ bonds, but depending on the substituents at silicon a substantial π‐bonding interaction is also present. The complexes possess relatively high bond orders which suggests primarily covalent bonding between uranium and silicon. These results comprise a new frontier in actinide‐heavy main‐group bonding. [ABSTRACT FROM AUTHOR]

The preparation and structural characterization of a series of lanthanide and uranium(IV) phthalocyanine halide complexes were achieved by reaction of the corresponding metal halide with Li2Pc. A preliminary survey of their reactivity includes ring reduction of Li(THF)4[PcUCl3] with KC8 leading to the first structurally characterized Pc4− actinide complex, hydrolysis of PcDyCl(DMSO) to PcDyOH(H2O)3 and preparation of a unique trimeric triangular Li(PcDy)3(OH)4(H2O) cluster. [ABSTRACT FROM AUTHOR]

Enrichment of UVI is an urgent project for nuclear energy development. Herein, magnetic graphitic carbon nitride nanosheets were successfully prepared by in situ anchoring of pyrrhotite (Fe7S8) on the graphitic carbon nitride nanosheet (CNNS), which were used for capturing UVI. The structural characterizations of Fe7S8/CNNS‐1 indicated that the CNNS could prevent the aggregation of Fe7S8 and the saturation magnetization was 4.69 emu g−1, which meant that it was easy to separate the adsorbent from the solution. Adsorption experiments were performed to investigate the sorption properties. The results disclosed that the sorption data conformed to the Langmuir isotherm model with the maximum adsorption capacity of 572.78 mg g−1 at 298 K. The results of X‐ray photoelectron spectroscopy (XPS) demonstrated that the main adsorption mechanism are as follows: UVI is adsorbed on the surface of Fe7S8/CNNS‐1 through surface complexation initially, then it was reduced to insoluble UIV. Thereby, this work provided an efficient and easy to handle sorbent material for extraction of UVI. Collecting U from seawater: A new magnetic Fe7S8/carbon nitride nanosheets (CNNS) nanocomposite was prepared for efficient immobilization of uranium. The CNNS can effectively prevent the agglomeration of Fe7S8 nanoparticles and expose more active sites for extraction of uranium. The mechanism of interaction between the composite and UVI is mainly surface complexation and chemical reduction (see scheme). [ABSTRACT FROM AUTHOR]

Methyl benzoate, N,N-dimethylbenzamide, and benzophenone were reduced by UIII[N(SiMe3)2]3 resulting in uranium(IV) products. Reduction of benzophenone lead to UIV[OC·Ph2)][N(SiMe3)2]3, (1.1) which forms the dinuclear complex, [N(SiMe3)2]3UIV(OCPhPh-CPh2O)UIV[N(SiMe3)2]3 (1.2), through coupling of the ketyl radical species upon crystallization. Reaction of N,N-dimethylbenzamide with UIII[N(SiMe3)2]3 resulted in UIV[OC·(Ph)(NMe2)][N(SiMe3)2]3 (2), a uranium(IV) compound and the first example of a chargeseparated amide radical. In the case of methyl benzoate, the reduction resulted in UIV(OMe)[N(SiMe3)2]3 (3) and benzaldehyde as the reduced organic fragment. Compound 2 showed the ability to act as a uranium(III) synthon in its reactivity with trimethylsilyl azide, a reaction that yielded UV(= NSiMe3)[N(SiMe3)2]3. Additionally, 2 was reduced with potassium graphite resulting in [U(μ-O)[O=C(NMe2)(Ph)] [N(SiMe3)2]2]2 (4), a dinuclear uranium compound bridged by oxo ligands. Reduction of 2 in the presence of 15-crown-5 afforded isolation of the mono-oxo compound, [(15-crown- 5)2K][UO[N(SiMe3)2]3] (5). The results expand the reduction capabilities of UIII complexes and demonstrate a strategy for isolating novel metal-stabilized radicals. [ABSTRACT FROM AUTHOR]

Organic azides that contain naphthyl functional groups were used to prepare uranium(V) imido complexes UV[=NC(2-naph)Ph2][N(SiMe3)2]3 ( 2), UV[=NC(2-naph)3][N(SiMe3)2]3 ( 3), and UV[=N(2-naph)][N(SiMe3)2]3 ( 4), and their properties were compared with UV[=NCPh3][N(SiMe3)2]3 ( 1). The electronic structures of these compounds were investigated by solution electrochemistry studies, which revealed accessible UV/VI, UIV/V, and naphthalene0/naphthalene−1 couples. The uranium(V) naphthylimido complexes were reduced by potassium graphite to yield their uranium(IV) congeners K[UIV[=NC(2-naph)Ph2][N(SiMe3)2]3] ( 2-K), K[UIV[=NC(2-naph)3][N(SiMe3)2]3] ( 3-K), and K[UIV[=N(2-naph)][N(SiMe3)2]3] ( 4-K). The electronic structure of the dianionic compounds were investigated by DFT calculations, and this revealed that the second reduction was ligand-based, which opens the possibility of accomplishing multi-electron redox chemistry by using a tailored multiply-bonded ligand. [ABSTRACT FROM AUTHOR]

The specific molecular interactions responsible for uranium toxicity are not yet understood. The uranyl binding sites in high-affinity target proteins have not been identified yet and the involvement of phosphoamino acids is still an important question. Short cyclic peptide sequences, with three glutamic acids and one phosphoamino acid, are used as simple models to mimic metal binding sites in phosphoproteins and to help understand the mechanisms involved in uranium toxicity. A combination of peptide design and synthesis, analytical chemistry, extended X-ray absorption fine structure (EXAFS) spectroscopy, and DFT calculations demonstrates the involvement of the phosphate group in the uranyl coordination sphere together with the three carboxylates of the glutamate moieties. The affinity constants measured with a reliable analytical competitive approach at physiological pH are significantly enhanced owing to the presence of the phosphorous moiety. These findings corroborate the importance of phosphoamino acids in uranyl binding in proteins and the relevance of considering phosphoproteins as potential uranyl targets in vivo. [ABSTRACT FROM AUTHOR]

The reaction between [UO2F2] and an excess of Me3SiN3 in acetonitrile solution results in fluoride-azide exchange and the uranium(VI) dioxodiazide adduct [UO2(N3)2⋅CH3CN] was isolated in quantitative yield. The subsequent reaction of [UO2(N3)2⋅CH3CN] with 2,2′-bipyridine (bipy) resulted in the formation of the azido-bridged binuclear complex [(bipy)2(UO2)2(N3)4]. The triazido anion [(bipy)UO2(N3)3]− was obtained by the reaction of [UO2(N3)2⋅CH3CN] with stoichiometric amounts of bipy and the ionic azide [PPh4][N3]. The reaction of [UO2(N3)2] with two equivalents of the [PPh4][N3] resulted in the formation of the mononuclear tetraazido anion [UO2(N3)4]2− as well as the azido-bridged binuclear anion [(UO2)2(N3)8]4−. The novel uranium oxoazides were characterized by their vibrational spectra and in the case of [(bipy)2(UO2)2(N3)4]⋅CH3CN, [PPh4][(bipy)UO2(N3)3], [PPh4]2[UO2(N3)4], [PPh4]2[UO2(N3)4]⋅2CH3CN, and [PPh4]4[(UO2)2(N3)8]⋅4CH3CN by their X-ray crystal structures. [ABSTRACT FROM AUTHOR]

Uranium(IV)-carbene-imido complexes [U(BIPMTMS)(NCPh3)(κ2- N, N′-BIPY)] ( 2; BIPMTMS=C(PPh2NSiMe3)2; BIPY=2,2-bipyridine) and [U(BIPMTMS)(NCPh3)(DMAP)2] ( 3; DMAP=4-dimethylamino-pyridine) that contain unprecedented, discrete R2C=U=NR′ units are reported. These complexes complete the family of E=U=E (E=CR2, NR, O) metalla-allenes with feasible first-row hetero-element combinations. Intriguingly, 2 and 3 contain cis- and trans-C=U=N units, respectively, representing rare examples of controllable cis/ trans isomerisation in f-block chemistry. This work reveals a clear-cut example of the trans influence in a mid-valent uranium system, and thus a strong preference for the cis isomer, which is computed in a co-ligand-free truncated model-to isolate the electronic trans influence from steric contributions-to be more stable than the trans isomer by approximately 12 kJ mol−1 with an isomerisation barrier of approximately 14 kJ mol−1. [ABSTRACT FROM AUTHOR]

After more than 50 years, the synthesis and electronic structure of the first and only reported 'U0 complex' [U(bipy)4] ( 1) has been reinvestigated. Additionally, its one-electron reduced product [Na(THF)6][U(bipy)4] ( 2) has been newly discovered. High resolution crystallographic analyses combined with magnetic and computational data show that 1 and its derivative 2 are best described as highly reduced species containing mid-to-high-valent uranium ligated by redox non-innocent ligands. [ABSTRACT FROM AUTHOR]

Uranium-based compounds have been put forward as ideal candidates for the design of single-molecule magnets (SMMs) with improved properties, but to date, only two examples of exchange-coupled 3d-5f SMM containing uranium have been reported and both are based on the MnII ion. Here we have synthesized the first examples of exchange-coupled uranium SMMs based on FeII and NiII. The SMM behavior of these complexes containing a quasi linear {MOUOM} core arises from intramolecular FeU and NiU exchange interactions combined with the high Ising anisotropy of the uranyl(V) moiety. The measured values of the relaxation barrier (53.9±0.9 K in the UFe2 complex and of 27.4±0.5 K in the UNi2 complex) show clearly the dependency on the spin value of the transition metal, providing important new information for the future design of improved uranium-based SMMs. [ABSTRACT FROM AUTHOR]

A tetravalent uranium compound with a radical azobenzene ligand, namely, [{(SiMe2NPh)3-tacn}UIV(η2-N2Ph2.)] ( 2), was obtained by one-electron reduction of azobenzene by the trivalent uranium compound [UIII{(SiMe2NPh)3-tacn}] ( 1). Compound 2 was characterized by single-crystal X-ray diffraction and 1H NMR, IR, and UV/Vis/NIR spectroscopy. The magnetic properties of 2 and precursor 1 were studied by static magnetization and ac susceptibility measurements, which for the former revealed single-molecule magnet behaviour for the first time in a mononuclear UIV compound, whereas trivalent uranium compound 1 does not exhibit slow relaxation of the magnetization at low temperatures. A first approximation to the magnetic behaviour of these compounds was attempted by combining an effective electrostatic model with a phenomenological approach using the full single-ion Hamiltonian. [ABSTRACT FROM AUTHOR]

The ex-situ qualitative study of the kinetic formation of the poly-oxo cluster U38, has been investigated after the solvothermal reaction. The resulting products have been characterized by means of powder XRD and scanning electron microscopy (SEM) for the solid phase and UV/Vis, X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and NMR spectroscopies for the supernatant liquid phase. The analysis of the different synthesis batches, stopped at different reaction times, revealed the formation of spherical crystallites of UO2 from t=3 h, after the formation of unknown solid phases at an early stage. The crystallization of U38 occurred from t=4 h at the expense of UO2, and is completed after t=8 h. Starting from pure uranium(IV) species in solution ( t=0-1 h), oxidation reactions are observed with a UIV/UVI ratio of 70:30 for t=1-3 h. Then, the ratio is inversed with a UIV/UVI ratio of 25/75, when the precipitation of UO2 occurs. Thorough SEM observations of the U38 crystallites showed that the UO2 aggregates are embedded within. This may indicate that UO2 acts as reservoir of uranium(IV), for the formation of U38, stabilized by benzoate and THF ligands. During the early stages of the U38 crystallization, a transient crystallized phase appeared at t=4 h. Its crystal structure revealed a new dodecanuclear moiety (U12), based on the inner hexanuclear core of {U6O8} type, decorated by three additional pairs of dinuclear U2 units. The U12 motif is stabilized by benzoate, oxalates, and glycolate ligands. [ABSTRACT FROM AUTHOR]

Keywords: bonding; covalency; selenoether; thioether; uranium EN bonding covalency selenoether thioether uranium 1 1 1 01/06/22 20220103 NES 220103 B Uranium - selenoether linkages b have been accessed for the first time, enabling the study of U-SeR SB 2 sb versus U-SR SB 2 sb and U-OR SB 2 sb bonding. Bonding, covalency, selenoether, thioether, uranium The shape of the uranium selenoether complex resembles a butterfly, and the cover art depicts a metamorphosis from the protio-ligand (caterpillar), to the potassium salt of the ligand (chrysalis), to the uranium complex (butterfly). [Extracted from the article]

Two new arene inverted-sandwich complexes of uranium supported by siloxide ancillary ligands [K{U(OSi(O tBu)3)3}2(μ-η6:η6-C7H8)] ( 3) and [K2{U(OSi(O tBu)3)3}2(μ-η6:η6-C7H8)] ( 4) were synthesized by the reduction of the parent arene-bridged complex [{U(OSi(O tBu)3)3}2(μ-η6:η6-C7H8)] ( 2) with stoichiometric amounts of KC8 yielding a rare family of inverted-sandwich complexes in three states of charge. The structural data and computational studies of the electronic structure are in agreement with the presence of high-valent uranium centers bridged by a reduced tetra-anionic toluene with the best formulation being UV-(arene4−)-UV, KUIV-(arene4−)-UV, and K2UIV-(arene4−)-UIV for complexes 2, 3, and 4 respectively. The potassium cations in complexes 3 and 4 are coordinated to the siloxide ligands both in the solid state and in solution. The addition of KOTf (OTf=triflate) to the neutral compound 2 promotes its disproportionation to yield complexes 3 and 4 (depending on the stoichiometry) and the UIV mononuclear complex [U(OSi(O tBu)3)3(OTf)(thf)2] ( 5). This unprecedented reactivity demonstrates the key role of potassium for the stability of these complexes. [ABSTRACT FROM AUTHOR]