Trivalent Uranium Complex Research Articles

A Genuine Trivalent Bis‐Acylphosphide (BAP) Complex of Uranium

AbstractThe genuine trivalent uranium complex, K[UIII(mesBAP)4], employing four bidentate bis(2,4,6‐trimethylbenzoyl)phosphide (mesBAP) chelating ligands, is reported and obtained by the reduction of the literature‐known tetravalent analog [UIV(mesBAP)4]. Hence, the bis(acyl)phosphide mesBAP ligand allowed to establish a fully reversible redox couple with uranium in the oxidation states +III and +IV. In both complexes [U(mesBAP)4]0/−, the uranium ions are coordinated to four mesBAP ligands in a square antiprismatic geometry. All new compounds have been characterized by single‐crystal XRD analysis, 1H and 31P NMR, and UV/Vis/NIR electronic absorption spectroscopy, as well as SQUID magnetization and electrochemical measurements, and CW X‐band EPR in the case of the trivalent complex.

Chlorination of Pu and U Metal Using GaCl3.

The oxidative chlorination of the plutonium metal was achieved through a reaction with gallium(III) chloride (GaCl3). In DME (DME = 1,2-dimethoxyethane) as the solvent, substoichiometric (2.8 equiv) amounts of GaCl3 were added, which consumed roughly 60% of the plutonium metal over the course of 10 days. The salt species [PuCl2(dme)3][GaCl4] was isolated as pale-purple crystals, and both solid-state and solution UV-vis-NIR spectroscopies were consistent with the formation of a trivalent plutonium complex. The analogous reaction was performed with uranium metal, generating a dicationic trivalent uranium complex crystallized as the [UCl(dme)3][GaCl4]2 salt. The extraction of [UCl(dme)3][GaCl4]2 in DME at 70 °C followed by crystallization produced [{U(dme)3}2(μ-Cl3)][GaCl4]3, a product arising from the loss of GaCl3. This method of halogenation worked on a small scale for plutonium and uranium, providing a route to cationic Pu3+ and dicationic U3+ complexes using GaCl3 in DME.

Cyaarside (CAs- ) and 1,3-Diarsaallendiide (AsCAs2- ) Ligands Coordinated to Uranium and Generated via Activation of the Arsaethynolate Ligand (OCAs- ).

Reaction of the trivalent uranium complex [((Ad,Me ArO)3 N)U(DME)] with one molar equiv [Na(OCAs)(dioxane)3 ], in the presence of 2.2.2-crypt, yields [Na(2.2.2-crypt)][{((Ad,Me ArO)3 N)UIV (THF)}(μ-O){((Ad,Me ArO)3 N)UIV (CAs)}] (1), the first example of a coordinated η1 -cyaarside ligand (CAs- ). Formation of the terminal CAs- is promoted by the highly reducing, oxophilic UIII precursor [((Ad,Me ArO)3 N)U(DME)] and proceeds through reductive C-O bond cleavage of the bound arsaethynolate anion, OCAs- . If two equiv of OCAs- react with the UIII precursor, the binuclear, μ-oxo-bridged U2 IV/IV complex [Na(2.2.2-crypt)]2 [{((Ad,Me ArO)3 N)UIV }2 (μ-O)(μ-AsCAs)] (2), comprising the hitherto unknown μ:η1 ,η1 -coordinated (AsCAs)2- ligand, is isolated. The mechanistic pathway to 2 involves the decarbonylation of a dimeric intermediate formed in the reaction of 1 with OCAs- . An alternative pathway to complex 2 is by conversion of 1 via addition of one further equiv of OCAs- .

Cyaarside (CAs−) and 1,3‐Diarsaallendiide (AsCAs2−) Ligands Coordinated to Uranium and Generated via Activation of the Arsaethynolate Ligand (OCAs−)

AbstractReaction of the trivalent uranium complex [((Ad,MeArO)3N)U(DME)] with one molar equiv [Na(OCAs)(dioxane)3], in the presence of 2.2.2‐crypt, yields [Na(2.2.2‐crypt)][{((Ad,MeArO)3N)UIV(THF)}(μ‐O){((Ad,MeArO)3N)UIV(CAs)}] (1), the first example of a coordinated η1‐cyaarside ligand (CAs−). Formation of the terminal CAs− is promoted by the highly reducing, oxophilic UIII precursor [((Ad,MeArO)3N)U(DME)] and proceeds through reductive C−O bond cleavage of the bound arsaethynolate anion, OCAs−. If two equiv of OCAs− react with the UIII precursor, the binuclear, μ‐oxo‐bridged U2IV/IV complex [Na(2.2.2‐crypt)]2[{((Ad,MeArO)3N)UIV}2(μ‐O)(μ‐AsCAs)] (2), comprising the hitherto unknown μ:η1,η1‐coordinated (AsCAs)2− ligand, is isolated. The mechanistic pathway to 2 involves the decarbonylation of a dimeric intermediate formed in the reaction of 1 with OCAs−. An alternative pathway to complex 2 is by conversion of 1 via addition of one further equiv of OCAs−.

Formation of a Uranium-Bound η1-Cyaphide (CP–) Ligand via Activation and C–O Bond Cleavage of Phosphaethynolate (OCP–)

Reaction of the trivalent uranium complex [((Ad,MeArO)3N)U(DME)] with [Na(OCP)(dioxane)2.5] and 2.2.2-crypt yields the μ-oxo-bridged, diuranium complex [Na(2.2.2-crypt)][{((Ad,MeArO)3N)U(DME)}(μ-O){((Ad,MeArO)3N)U(CP)}] (1). Complex 1 features an asymmetric, dinuclear UIV–O–UIV core structure with a cyaphide (CP–) anion η1-CP bound to one of the U ions, and a κ2-O DME coordinated to the other. The CP– ligand is unprecedented in uranium chemistry and is formed through reductive C–O bond cleavage of the phosphaethynolate anion (OCP–). An analogous reaction was performed starting from the tetravalent uranium halide complex [((Ad,MeArO)3N)U(DME)(Cl)]. This salt metathesis approach with [Na(OCP)(dioxane)2.5] results in formation of the mononuclear complex [((Ad,MeArO)3N)U(DME)(OCP)] (2) with an OCP– anion bound to the uranium(IV) center via the oxygen atom in an η1-OCP fashion.

Trivalent Uranium Complex in Small Molecules Activation

Uranium, one of typical actinide elements, has strong polarizing property. Using 5f orbitals for bonding with lig- ands, uranium(III) compounds have some unique reactivities including: migratory insertion, σ-bond metathesis and redox activity etc., which provides researchers with good opportunities to obtain organic uranium complexes or materials with unique structures and reactional properties. In the last 20 years, it has been found that trivalent uranium organic complexes exhibit a wide variety of activation towards small molecules. Due to the significant research and potential industrial value, this field has been well developed in recent years. Some research results for small molecules (such as N2, CO, CO2) activation promoted by trivalent uranium complexes were summarized in the paper. Keywords actinide chemistry; trivalent uranium complex; coordination chemistry; activation of N2, CO and CO2

ChemInform Abstract: Advances in Computational Actinide Chemistry in China

AbstractReview: 143 refs.

Performance of Twelve Density Functional Theory Methods in the Characterization of Three Trivalent Uranium Complexes

We report a comparative study on the characterization of three trivalent uranium complexes using 12 density functional theory (DFT) methods, i.e., BP86, PBE, B3LYP, B3PW91, BHandHLYP, PBE0, X3LYP, CAM-B3LYP, TPSS, M06L, M06, and M06-2X, representing (meta-)GGA and hybrid (meta-)GGA levels of treatment of molecular systems. The MP2 method was used in single-point calculations to provide an ab initio view of the electronic structure. Three model systems in the experimental work on the activation of CO2 and CS2 by a trivalent uranium complex (Tp*)(2)U-eta(1)-CH2Ph (Cpd2) were used i.e., (Tp*)(2)U-eta(1)-CH2Ph (Cpd2), (Tp*)(2)U-kappa(2)-O2CCH2Ph (Cpd3), and (Tp*)(2)U-kappa(2)-S2CCH2Ph (Cpd4) (Tp=hydrotris(3,5-dimethylpyrazolyl)borate). The hybrid functionals, B3LYP and B3PW91, displayed good performance in view of both the geometrical and electronic structures. The MP2 method generated consistent results as OFT methods for Cpd2 and Cpd3, while provided an odd picture of the electronic structure of Cpd4 that may be due to its single determinant feature, leading to its capture of an electronic configuration of Cpd4 different from the one with the DFT methods. The use of a quasi-relativistic 5f-in-core ECP (LPP) treatment for U(III) in the thermodynamic calculations was supported by the calculations with a small-core ECP treatment (SPP) for U. Owing to increasing interests in low-valent actinide molecular systems, this work complements previous comparative studies, which mainly focus on high-valent actinide complexes, and provides timely information on the performance of 12 widely used DFT methods in studying low-valent actinide systems. It is expected to contribute to a more sensible selection of DFT methods in the study of low-valent actinide molecular systems.

Advances in computational actinide chemistry in China

Abstract The advances in computational actinide chemistry made in China are reviewed. Several areas relevant to chemistry of actinides in gas, liquid, and solid phases have been explored. However, we limit the scope to selected contributions in the chemistry of molecular actinide systems in gas and liquid phases. These studies may be classified into two categories: treatment of relativistic effects, which cover the development of two- and four-component Hamiltonians and the optimization of relativistic pseudopotentials, and the applications of theoretical methods in actinide chemistry. The applications include (1) the electronic structures of actinocene, noble gas complexes, An-C multiple bonding compounds, uranyl and its isoelectronic species, fluorides and oxides, molecular systems with metal-metal bonding in their isolated forms (U2, Pu2) and in fullerene (U2@C60), and the excited states of actinide complexes; (2) chemical reactions, including oxidation, hydrolysis of UF6, ligand exchange, reactivities of thorium oxo and sulfido metallocenes, CO2/CS2 functionalization promoted by trivalent uranium complex; and (3) migration of actinides in the environment. A future outlook is discussed.

Trivalent Uranium Complex As a Catalyst to Promote the Functionalization of Carbon Dioxide and Carbon Disulfide: A Computational Mechanistic Study.

We report our recent DFT mechanistic study on the functionalization of CO2 and CS2 promoted by a trivalent uranium complex (Tp*)2UCH2Ph. In the calculations, the uranium atom is described by a quasi-relativistic 5f-in-core ECP basis set (LPP) developed for the trivalent uranium cation, which was qualified by the calculations with a quasi-relativistic small core ECP basis set (SPP) for uranium. According to our calculations, the functionalization proceeds in a stepwise manner, and the CO2 or CS2 does not interact with the central uranium atom to form a stable complex prior to the reaction due to the steric hindrance from the bulky ligands but directly cleaves the U-C (benzyl) bond by forming a C-C covalent bond. The released coordination site of uranium is concomitantly occupied by one chalcogen atom of the incoming molecule and gives an intermediate with the uranium atom interacting with the functionalized CO2 or CS2 in an η(1) fasion. This step is followed by a reorientation of the (dithio)carboxylate side chain of the newly formed PhCH2CE2(-) (E = O, S) ligand to give the corresponding product. Energetically, the first step is characterized as the rate-determining step with a barrier of 9.5 (CO2) or 25.0 (CS2) kcal/mol, and during the reaction, the chalcogen atoms are reduced, while the methylene of the benzyl group is oxidized. Comparison of the results from SPP and LPP calculations indicates that our calculations qualify the use of an LPP treatment of the uranium atom toward a reasonable description of the model systems in the present study.

Insight into the Reaction Mechanisms of (MeC5H4)3U with Isoelectronic Heteroallenes CS2, COS, PhN3, and PhNCO by DFT Studies: A Unique Pathway that Involves Bimetallic Complexes

The mechanisms of the reduction of four isoelectronic heteroallenes (CS(2), COS, PhN(3), and PhNCO) by trivalent uranium complex (MeC(5)H(4))(3)U were determined by using DFT methods. The experimental formation of either the bimetallic CS(2) and the PhNCO uranium(IV) adducts or the bimetallic sulfide complex (COS) and the monometallic uranium(V) phenylimide complex (PhN(3)) were rationalized. The formation of the products was explained by a unique reaction mechanism with a uranium(IV)-bridged heteroallene intermediate.

Straightforward and efficient oxidation of tris(aryloxide) and tris(amide) uranium(III) complexes using copper(I) halide reagents

Reaction of the trivalent uranium complex U(O-2,6-tBu2C6H3)3(THF) (4) with copper(I) iodide affords the corresponding uranium(IV) mixed iodide–aryloxide complex (I)U(O-2,6-tBu2C6H3)3(THF) (5). The oxidative functionalization protocol can also be extended to the synthesis of (Cl)U[N(SiMe3)2]3 (7) from the reaction of the tris(amide) uranium(III) complex U[N(SiMe3)2]3 (6) with copper(I) chloride. These represent the first examples of Cu-based oxidative functionalization of simple trivalent uranium coordination complexes supported by non-metallocene ligand frameworks. With several advantages over existing oxidation methods for uranium tris(aryloxide) and tris(amide) complexes, this Cu-based procedure promises to be a useful and versatile synthetic protocol for uranium chemistry. The X-ray crystal structure of (I)U(O-2,6-tBu2C6H3)3(THF) (5) is also reported and represents a rare example of a structurally characterized 5-coordinate uranium aryloxide complex. In the solid-state, complex 5 adopts a distorted square pyramidal geometry about the uranium atom, with the iodide ligand occupying the axial position and the THF and three 2,6-di-tert-butylphenoxide ligands occupying the sites of the square pyramid base.

Uncovering alternate reaction pathways to access uranium(IV) mixed-ligand aryloxide–chloride and alkoxide–chloride metallocene complexes: Synthesis and molecular structures of (C 5Me 5) 2U(O-2,6- iPr 2C 6H 3)(Cl) and (C 5Me 5) 2U(O– tBu)(Cl)

Reaction of the trivalent uranium complex (C 5Me 5) 2U(O-2,6- i Pr 2C 6H 3)(THF) ( 1) with copper(I) chloride affords the corresponding tetravalent mixed-ligand aryloxide–chloride complex (C 5Me 5) 2U(O-2,6- i Pr 2C 6H 3)(Cl) ( 2). The oxidative functionalization protocol cannot be extended to the synthesis of (C 5Me 5) 2U(O– t Bu)(Cl) ( 3) since the corresponding trivalent precursor is not stable. Salt metathesis between (C 5Me 5) 2UCl 2 and KO t Bu is the method of choice for the preparation of the tetravalent alkoxide–chloride derivative (C 5Me 5) 2U(O– t Bu)(Cl) ( 3). The X-ray crystal structures of (C 5Me 5) 2U(O-2,6- i Pr 2C 6H 3)(Cl) ( 2) and (C 5Me 5) 2U(O– t Bu)(Cl) ( 3) are reported and represent the first structurally characterized uranium(IV) metallocene aryloxide–chloride and alkoxide–chloride complexes, respectively. Both complexes adopt a pseudo-tetrahedral geometry, with a chloride and aryloxide/alkoxide ligand occupying the plane bisecting the metallocene unit.

ChemInform Abstract: Reaction of Saturated Ketones with a Trivalent Uranium Complex. Isolation and Characterization of the Alcoholate and Enolate Products.

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Amide from dinitrogen by in situ cleavage and partial hydrogenation promoted by a transient zero-valent thorium synthon.

Amide from dinitrogen by in situ cleavage and partial hydrogenation promoted by a transient zero-valent thorium synthon.

Dinuclear Trivalent and Mixed-Valence Uranium [(−CH2−)5]4-calix[4]tetrapyrrole Complexes with Short Intermetallic Distances

A dinuclear trivalent uranium complex (1) and a mixed-valence U(III)/U(IV) complex (2) have been prepared by using the [(−CH2-)5]4-calix[4]tetrapyrrole tetraanion. Both compounds display unusually ...

Reaction of saturated ketones with a trivalent uranium complex. Isolation and characterization of the alcoholate and enolate products

The uranium (III) complex Cp 3U(THF) (CpηC 5H 5, THF = tetrahydrofuran) reacted with saturaed ketones RCOCH 2R′ to give equimolar mixtures of the compounds Cp 3UOCHR(CH 2R′) and Cp 3UOCR(′).