Facile Oxidation of Ce(III) to Ce(IV) Using Cu(I) Salts

The synthesis, luminescence, and electrochemical properties of the Ce(III) compound, [(C5Me5)2(2,6-iPr2C6H3O)Ce(THF)], 1, were investigated. Based on the electrochemical data, treatment of 1 with CuX (X = Cl, Br, I) results in the formation of the corresponding Ce(IV) complexes, [(C5Me5)2(2,6-iPr2C6H3O)Ce(X)]. Each complex has been characterized using NMR, IR, and UV-vis spectroscopy as well as structurally determined using X-ray crystallography. Additionally, the treatment of [(C5Me5)2(2,6-iPr2C6H3O)Ce(Br)] with AgF results in the formation of the putative [(C5Me5)2(2,6-iPr2C6H3O)Ce(F)]. The electronic structure of these Ce(IV)-X complexes was investigated by bond analyses and the Ce(IV)-F moiety using quantum chemistry NMR calculations.

From a mercury(II) bis(yldiide) complex to actinide yldiides

The bis(yldiide) mercury complex, (L-Hg-L) [L = C(PPh3)P(S)Ph2], is prepared from the corresponding potassium yldiide and used to access the first substituted yldiide actinide complexes [(C5Me5)2An(L)(Cl)] (An = U, Th) via salt metathesis. Compared to previously reported phosphinocarbene complexes, the complexes exhibit long actinide-carbon distances, which can be explained by the strong polarization of the π-electron density toward carbon.

Cooperative dihydrogen activation with unsupported uranium-metal bonds and characterization of a terminal U(iv) hydride

Cooperative chemistry between two or more metal centres can show enhanced reactivity compared to the monometallic fragments. Given the paucity of actinide-metal bonds, especially those with group 13, we targeted uranium(iii)-aluminum(i) and -gallium(i) complexes as we envisioned the low-valent oxidation state of both metals would lead to novel, cooperative reactivity. Herein, we report the molecular structure of [(C5Me5)2(MesO)U-E(C5Me5)], E = Al, Ga, Mes = 2,4,6-Me3C6H2, and their reactivity with dihydrogen. The reaction of H2 with the U(iii)-Al(i) complex affords a trihydroaluminate complex, [(C5Me5)2(MesO)U(μ2-(H)3)-Al(C5Me5)] through a formal three-electron metal-based reduction, with concomitant formation of a terminal U(iv) hydride, [(C5Me5)2(MesO)U(H)]. Noteworthy is that neither U(iii) complexes nor [(C5Me5)Al]4 are capable of reducing dihydrogen on their own. To make the terminal hydride in higher yields, the reaction of [(C5Me5)2(MesO)U(THF)] with half an equivalent of diethylzinc generates [(C5Me5)2(MesO)U(CH2CH3)] or treatment of [(C5Me5)2U(i)(Me)] with KOMes forms [(C5Me5)2(MesO)U(CH3)], which followed by hydrogenation with either complex cleanly affords [(C5Me5)2(MesO)U(H)]. All complexes have been characterized by spectroscopic and structural methods and are rare examples of cooperative chemistry in f element chemistry, dihydrogen activation, and stable, terminal ethyl and hydride compounds with an f element.

Synthesis, Characterization, and Reduction of Thorium Pyridinediimine Complexes

A family of thorium complexes featuring the redox-noninnocent pyridinediimine ligand MesPDIMe was synthesized, including (MesPDIMe)ThCl4 (1-Th), (MesPDIMe)ThCl3(THF) (2-Th), (MesPDIMe)ThCl2(THF)2 (3-Th) and [(MesPDIMe)Th(THF)]2 (5-Th) Full characterization of these species shows that these complexes feature MesPDIMe in four different oxidation states. The electronic structures of these complexes have been explored using 1H NMR and electronic absorption spectroscopies, X-ray crystallography, and SQUID magnetometry where appropriate.

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

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- ^t Bu₂-4-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(μ ₂:κ ²:η ¹-C₃O₃)], which can be further reacted with CO₂ to yield a ketene dicarboxylate complex, [{(C₅Me₅)₂(MesO)U}₂(μ ₂:κ ²:κ ²-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([double bond, length as m-dash]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.

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

Correction for ‘Isolation of C1 through C4 derivatives from CO using heteroleptic uranium(iii) metallocene aryloxide complexes’ by Robert J. Ward et al., Chem. Sci., 2023, 14, 2024–2032, https://doi.org/10.1039/D2SC06375A.

Deep eutectic solvents comprising creatine and citric acid and their hydrated mixtures

We report the phase diagram for the binary creatine-citric acid mixture which features a stable and broad eutectic region. Combinations containing 10-60 mol% creatine yield a deep eutectic solvent with a glass transition temperature at 270 K. Addition of up to 70 mol% water to the binary mixture affords retention of the eutectic nature and a handle to vary solvent viscosity and polarity.

Crystal structures of metallocene complexes with uranium–germanium bonds

The first structural examples of complexes with uranium–germanium bonds are presented, namely, bis[3,5-bis(trifluoromethyl)phenyl-2κC 1](hydrido-2κH)(iodido-1κI)bis[1,1(η5)-pentamethylcyclopentadienyl]germaniumuranium(Ge—U), [GeU(C10H15)2(C8H3F6)2HI], and bis[3,5-bis(trifluoromethyl)phenyl-2κC 1](fluorido-1κI)(hydrido-2κH)bis[1,1(η5)-pentamethylcyclopentadienyl]germaniumuranium(Ge—U), [GeU(C10H15)2(C8H3F6)2FH]. The two complexes both have a long U—Ge bond [distances of 3.0428 (7) and 3.0524 (7) Å].

Backbonding in Thorium(IV) and Uranium(IV) Diarsenido Complexes with tBuNC and CO

The coordination of tBuNC and CO with the diarsenido complexes (C₅ Me₅ )₂ An(η² -As₂ Mes₂ ), An=Th, U, has been investigated. For the first time, a comparison between isostructural complexes of Th^IV and U^IV has been possible with CO; density functional calculations indicated an appreciable amount of π backbonding that originates from charge transfer from an actinide-arsenic sigma bond. The calculated CO stretching frequencies in the Th^IV and U^IV diarsenido complexes are consistent with the experimental measurements, both show large shifts to lower frequency. We demonstrate that the π backbonding is crucial to explaining the red shifts of CO frequency upon An^IV complex formation. Interestingly, this interaction essentially correlates to the parallel orientation of π*(C-O) orbitals relative to the An-As bond.

Structural, Spectroscopic, and Computational Analysis of Heterometallic Thorium Phosphinidiide Complexes

To synthesize complexes with thorium-phosphorus multiple-bond character, reactions of (C₅Me₅)₂Th[P(H)Mes]₂ with monovalent alkali-metal bases, MN(SiMe₃)₂, as well as CuMes, have been investigated. The results with MN(SiMe₃)₂ are phosphinidiide complexes of the form {(C₅Me₅)₂Th[μ₂-P(Mes)][μ₂-P(H)Mes]M(L)_n}₂ (M = Na, n = 0; M = K, L = THF, n = 1; M = Rb, L = THF, n = 1; M = Cs, L = Et₂O, n = 1). With CuMes, the product is a Th₂Cu₃P₅ heterometallic structure, {(C₅Me₅)₂Th[(μ₂-P(H)Mes)P(Mes)]Cu}₂Cu[μ₂-P(H)Mes]. All complexes have been characterized using heteronuclear NMR and IR spectroscopy, density functional theory calculations, and their solid-state structure identified by X-ray crystallography. We also report the structure of {(C₅Me₅)₂Th[(μ₂-As(H)Mes)As(Mes)]Cu}₂Cu[μ₂-As(H)Mes] obtained from (C₅Me₅)₂Th[As(H)Mes]₂ with CuMes.

Crystal structure of [Th3(Cp*)3(O)(OH)3]2Cl2(N3)6: a discrete mol-ecular capsule built from multinuclear organothorium cluster cations

An unusually large and structurally complex charge-neutral polynuclear cluster, hexa-μ2-azido-di-μ3-chlorido-hexa-μ2-hydroxido-di-μ3-oxido-hexa-kis-(penta-methyl-cyclo-penta-dien-yl)hexa-thorium-diethyl ether-tetra-hydro-furan (1/0.56/1.44), [Th3(C10H15)6Cl3(N3)6(OH)6O2]·0.56C4H10O·1.44C4H8O or [Th3(Cp*)3(O)(OH)3]2Cl2(N3)6·0.56C4H10O·1.44C4H8O (Cp* = [penta-methyl-cyclo-penta-dien-yl])-, has been crystallized as a mixed tetra-hydro-furan/diethyl ether solvate and structurally characterized. The mol-ecule contains a number of unusual features, the most notable being a finite yet exceptionally long cyclic metal-azido chain. These rare features are the consequence of both sterically protecting Cp* ligands and highly bridging oxide and hydroxide ligands in the same system and illustrate the inter-esting new possibilities that can arise from combining organometallic and solvothermal f-block element chemistry.

Two-Electron Reduction of a U(VI) Complex with Al(C5Me5)

The reduction of U(VI) to U(IV) is rare, especially in one step, and not observed electrochemically as a one-wave, two-electron couple. Here, we demonstrate that reduction of the uranium(VI) bis(imido) complex, (C₅Me₅)₂U[═N(4-OⁱPrC₆H₄)]₂, is readily accomplished with Al(C₅Me₅), forming the bridging uranium(IV)/aluminum(III) imido complex (C₅Me₅)₂U[μ₂-N(4-OⁱPrC₆H₄)]₂Al(C₅Me₅). The structure and bonding of the bridging imido complex is examined with electrochemical measurements in tandem with density functional theory calculations.

Divergent uranium- versus phosphorus-based reduction of Me3SiN3 with steric modification of phosphido ligands

We describe an example of a two-electron metal- and ligand-based reduction of Me₃SiN₃ using uranium(iv) complexes with varying steric properties. Reaction of (C₅Me₅)₂U(CH₃)[P(SiMe₃)(Ph)] with Me₃SiN₃ produces the imidophosphorane complex, (C₅Me₅)₂U(CH₃)[N Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> P(SiMe₃)₂(Ph)] through oxidation of phosphorus. However, a similar reaction with a more sterically encumbering phosphido ligand, (C₅Me₅)₂U(CH₃)[P(SiMe₃)(Mes)] forms the U(iv) complex, (C₅Me₅)₂U[κ²-(N,N)–N(SiMe₃)P(Mes)N(SiMe₃)]. In probing the mechanism of this reaction, a U(vi) bis(imido) complex, (C₅Me₅)₂U(NSiMe₃){N[P(SiMe₃)(Mes)]} was isolated. DFT calculations show an intramolecular reductive cycloaddition reaction leads to the formation of the U(iv) bis(amido)phosphane from the U(vi) bis(imido) complex. This is a rare example of the isolation of a reaction intermediate in f element chemistry.

We describe an example of a two-electron metal- and ligand-based reduction of Me₃SiN₃ using uranium(iv) complexes with varying steric properties. With uranium-based reduction, a U(vi) intermediate is isolated.

Hydration of α-UO3 following storage under controlled conditions of temperature and relative humidity

Experimental measurements and theoretical evaluation of changes in chemical speciation of α-UO₃ using XRD, EXAFS, TGA, and DFT calculations.

Synthesis and Utility of Neptunium(III) Hydrocarbyl Complex

To extend organoactinide chemistry beyond uranium, reported here is the first structurally characterized transuranic hydrocarbyl complex, Np[η⁴ -Me₂ NC(H)C₆ H₅ ]₃ (1), from reaction of NpCl₄ (DME)₂ with four equivalents of K[Me₂ NC(H)C₆ H₅ ]. Unlike the U^III species, the neptunium analogue can be used to access other Np^III complexes. The reaction of 1 with three equivalents of HE₂ C(2,6-Mes₂ -C₆ H₃ ) (E=O, S) yields [(2,6-Mes₂ -C₆ H₃ )CE₂ ]₃ Np(THF)₂ , maintaining the trivalent oxidation state.

Structure and properties of [(4,6-tBu2C6H2O)2Se]2An(THF)2, An = U, Np, and their reaction with p-benzoquinone

The synthesis and characterization of U(iv) and Np(iv) selenium bis(phenolate) complexes are reported. The reaction of two equivalents of the U(iv) complex with p-benzoquinone results in the formation of a U(v)-U(v) species with a bridging reduced quinone. This represents a rare example of high-valent uranium chemistry as well as a rare example of a neptunium aryloxide complex.

Uranium(iii) and thorium(iv) alkyl complexes as potential starting materials

The synthesis and characterisation of a rare U(iii) alkyl complex, U[η⁴-Me₂NC(H)C₆H₅]₃, using the dimethylbenzylamine (DMBA) ligand has been accomplished. While attempting to prepare the U(iv) compound, reduction to the U(iii) complex occurred. In the analogous Th(iv) system, C-H bond activation of a methyl group of one dimethylamine was observed yielding Th[η⁴-Me₂NC(H)C₆H₅]₂[η⁵-(CH₂)MeNC(H)C₆H₅] with a dianionic DMBA ligand. The utility of these complexes as starting materials has been analyzed using a bulky dithiocarboxylate ligand to yield tetravalent actinide species.

Four-electron reduction chemistry using a uranium(iii) phosphido complex

The first uranium(iii) phosphido complex is reported.

Synthesis and fluorescence spectroscopy of tris(pyrenyl)pnictogen compounds

A homologous series of tris(pyrenyl)pnictogen compounds has been prepared and studied, revealing the dramatic impact of pnictogen choice on fluorescence quantum yield and photophysical properties.

Copper(i) clusters with bulky dithiocarboxylate, thiolate, and selenolate ligands

Dithiocarboxylate, thiolate, and selenolate ligands based on the terphenyl moiety produce tetra-, tri-, di-, and mononuclear copper(i) complexes.

Insertion of tBuNC into thorium–phosphorus and thorium–arsenic bonds: phosphaazaallene and arsaazaallene moieties in f element chemistry

The reactivity of thorium–phosphido and thorium–arsenido bonds was probed using tert-butyl isocyanide, ^tBuNC.

Dithio- and Diselenophosphinate Thorium(IV) and Uranium(IV) Complexes: Molecular and Electronic Structures, Spectroscopy, and Transmetalation Reactivity

We report a comparison of the molecular and electronic structures of dithio- and diselenophosphinate, (E2PR2)(1-) (E = S, Se; R = (i)Pr, (t)Bu), with thorium(IV) and uranium(IV) complexes. For the thorium dithiophosphinate complexes, reaction of ThCl4(DME)2 with 4 equiv of KS2PR2 (R = (i)Pr, (t)Bu) produced the homoleptic complexes, Th(S2P(i)Pr2)4 (1S-Th-(i)Pr) and Th(S2P(t)Bu2)4 (2S-Th-(t)Bu). The diselenophosphinate complexes were synthesized in a similar manner using KSe2PR2 to produce Th(Se2P(i)Pr2)4 (1Se-Th-(i)Pr) and Th(Se2P(t)Bu2)4 (2Se-Th-(t)Bu). U(S2P(i)Pr2)4, 1S-U-(i)Pr, could be made directly from UCl4 and 4 equiv of KS2P(i)Pr2. With (Se2P(i)Pr2)(1-), using UCl4 and 3 or 4 equiv of KSe2P(i)Pr2 yielded the monochloride product U(Se2P(i)Pr2)3Cl (3Se-U(iPr)-Cl), but using UI4(1,4-dioxane)2 produced the homoleptic U(Se2P(i)Pr2)4 (1Se-U-(i)Pr). Similarly, the reaction of UCl4 with 4 equiv of KS2P(t)Bu2 yielded U(S2P(t)Bu2)4 (2S-U-(t)Bu), whereas the reaction with KSe2P(t)Bu2 resulted in the formation of U(Se2P(t)Bu2)3Cl (4Se-U(tBu)-Cl). Using UI4(1,4-dioxane)2 and 4 equiv of KSe2P(t)Bu2 with UCl4 in acetonitrile yielded U(Se2P(t)Bu2)4 (2Se-U-(t)Bu). Transmetalation reactions were investigated with complex 2Se-U-(t)Bu and various CuX (X = Br, I) salts to yield U(Se2P(t)Bu2)3X (6Se-U(tBu)-Br and 7Se-U(tBu)-I) and 0.25 equiv of [Cu(Se2P(t)Bu2)]4 (8Se-Cu-(t)Bu). Additionally, 2Se-U-(t)Bu underwent transmetalation reactions with Hg2F2 and ZnCl2 to yield U(Se2P(t)Bu2)3F (6) and U(Se2P(t)Bu2)3Cl (4Se-U(tBu)-Cl), respectively. The molecular structures were analyzed using (1)H, (13)C, (31)P, and (77)Se NMR and IR spectroscopy and structurally characterized using X-ray crystallography. Using the QTAIM approach, the electronic structure of all homoleptic complexes was probed, showing slightly more covalent bonding character in actinide-selenium bonds over actinide-sulfur bonds.

Formation of a Bridging Phosphinidene Thorium Complex

The synthesis and structural determination of the first thorium phosphinidene complex are reported. The reaction of 2 equiv of (C5Me5)2Th(CH3)2 with H2P(2,4,6-(i)Pr3C6H2) at 95 °C produces [(C5Me5)2Th]2(μ2-P[(2,6-CH2CHCH3)2-4-(i)PrC6H2] as well as 4 equiv of methane, 2 equiv from deprotonation of the phosphine and 2 equiv from C-H bond activation of one methyl group of each of the isopropyl groups at the 2- and 6-positions. Transition state calculations indicate that the steps in the mechanism are P-H, C-H, C-H, and then P-H bond activation to form the phosphinidene.

Stabilization of MIV = Ti, Zr, Hf, Ce, and Th using a selenium bis(phenolate) ligand

We report M(iv) M = Ti, Zr, Hf, Ce, and Th, complexes of a selenium bis(phenolate) ligand, 2,2'-selenobis(4,6-di-tert-butylphenol), (H(2)(Ar)OSeO), 1. Reaction of Ti(NEt(2))(4) with two equivalents of affords Ti((Ar)OSeO)(2), 2. Salt metathesis of ZrCl(4) and HfCl(4) with two equivalents of Na(2)(Ar)OSeO produces Zr((Ar)OSeO)(2)(THF), 3, and Hf((Ar)OSeO)(2)(THF), 4, respectively. Protonolysis of ThCl[N(SiMe(3))(2)](3) with two equivalents of yields Th((Ar)OSeO)(2)(THF)(2), 5. Salt metathesis of Ce(OTf)(3) and two equivalents of Na(2)(Ar)OSeO produces [Na(THF)(3)][Ce((Ar)OSeO)(2)], which was oxidized in situ using 0.5 equivalents of I(2) to yield the diamagnetic Ce(iv) product, Ce((Ar)OSeO)(2)(THF)(2), 6. Addition of 2,2'-bipyridyl to forms Ce((Ar)OSeO)(2)(bipy), 6a. Each diamagnetic complex was characterized using (1)H, (13)C, and (77)Se NMR and IR spectroscopy and the structures of 2-6a were established with X-ray crystallography. Electrochemical measurements using cyclic voltammetry on complexes 2, 5, and 6a re also reported.

Di- and Trinuclear Mixed-Valence Copper Amidinate Complexes from Reduction of Iodine

Molecular examples of mixed-valence copper complexes through chemical oxidation are rare but invoked in the mechanism of substrate activation, especially oxygen, in copper-containing enzymes. To examine the cooperative chemistry between two metals in close proximity to each other we began studying the reactivity of a dinuclear Cu(I) amidinate complex. The reaction of [(2,6-Me2C6H3N)2C(H)]2Cu2, 1, with I2 in tetrahydrofuran (THF), CH3CN, and toluene affords three new mixed-valence copper complexes [(2,6-Me2C6H3N)2C(H)]2Cu2(μ2-I3)(THF)2, 2, [(2,6-Me2C6H3N)2C(H)]2Cu2(μ2-I) (NCMe)2, 3, and [(2,6-Me2C6H3N)2C(H)]3Cu3(μ3-I)2, 4, respectively. The first two compounds were characterized by UV-vis and electron paramagnetic resonance spectroscopies, and their molecular structure was determined by X-ray crystallography. Both di- and trinuclear mixed-valence intermediates were characterized for the reaction of compound 1 to compound 4, and the molecular structure of 4 was determined by X-ray crystallography. The electronic structure of each of these complexes was also investigated using density functional theory.