A complete family of terminal uranium chalcogenides, [U(E)(N{SiMe3}2)3]- (E = O, S, Se, Te)

Molecular Models of Atomically Dispersed Uranium at MoS2 Surfaces Reveal Cooperative Mechanism of Water Reduction

Single atoms of uranium supported on molybdenum sulfide surfaces (U@MoS2) have been recently demonstrated to facilitate the hydrogen evolution reaction (HER) through electrocatalysis. Theoretical calculations have predicted uranium hydroxide moieties bound to edge-sulfur atoms of MoS2 as a proposed transition state involved in the HER process. However, the isolation of relevant intermediates involved in this process remains a challenge, rendering mechanistic hypotheses unverified. The present work describes the isolation and characterization of a uranium-hydroxide intermediate on molybdenum sulfide surfaces using [(Cp*3Mo3S4)UCp*], a molecular model of a reduced uranium center supported at MoS2. Mechanistic investigations highlight the metalloligand cooperativity with uranium involved in the water activation pathway. The corresponding uranium-oxo analogue, [(Cp*3Mo3S4)Cp*U(═O)], was also accessed from the hydroxide cluster via hydrogen atom transfer and from [(Cp*3Mo3S4)UCp*] through an alternative direct oxygen atom transfer. These results provide an atomistic perspective on the reactivity of low-valent uranium at molybdenum sulfide surfaces toward water, modeling key intermediates associated with the HER of U@MoS2 catalysts.

Thorium(IV)-antimony complexes exhibiting single, double, and triple polar covalent metal-metal bonds

There is continued burgeoning interest in metal-metal multiple bonding to further our understanding of chemical bonding across the periodic table. However, although polar covalent metal-metal multiple bonding is well known for the d and p blocks, it is relatively underdeveloped for actinides. Homometallic examples are found in spectroscopic or fullerene-confined species, and heterometallic variants exhibiting a polar covalent σ bond supplemented by up to two dative π bonds are more prevalent. Hence, securing polar covalent actinide double and triple metal-metal bonds under normal experimental conditions has been a fundamental target. Here we exploit the protonolysis and dehydrocoupling chemistry of the parent dihydrogen-antimonide anion, to report one-, two- and three-fold thorium-antimony bonds, thus introducing polar covalent actinide-metal multiple bonding under normal experimental conditions between some of the heaviest ions in the periodic table with little or no bulky-substituent protection at the antimony centre. This provides fundamental insights into heavy element multiple bonding, in particular the tension between orbital-energy-driven and overlap-driven covalency for the actinides in a relativistic regime.

Synthesis and Characterization of U≡C Triple Bonds in Fullerene Compounds

Despite decades of efforts, the actinide-carbon triple bond has remained an elusive target, defying synthesis in any isolable compound. Herein, we report the successful synthesis of uranium-carbon triple bonds in carbide-bridged bimetallic [U≡C-Ce] units encapsulated inside the fullerene cages of C72 and C78. The molecular structures of UCCe@C2n and the nature of the U≡C triple bond were characterized through X-ray crystallography and various spectroscopic analyses, revealing very short uranium-carbon bonds of 1.921(6) and 1.930(6) Å, with the metals existing in their highest oxidation states of +6 and +4 for uranium and cerium, respectively. Quantum-chemical studies further demonstrate that the C2n cages are crucial for stabilizing the [UVI≡C-CeIV] units through covalent and coordinative interactions. This work offers a new fundamental understanding of the elusive uranium-carbon triple bond and informs the design of complexes with similar bonding motifs, opening up new possibilities for creating distinctive molecular compounds and materials.

Accessing five oxidation states of uranium in a retained ligand framework

Understanding and exploiting the redox properties of uranium is of great importance because uranium has a wide range of possible oxidation states and holds great potential for small molecule activation and catalysis. However, it remains challenging to stabilise both low and high-valent uranium ions in a preserved ligand environment. Herein we report the synthesis and characterisation of a series of uranium(II-VI) complexes supported by a tripodal tris(amido)arene ligand. In addition, one- or two-electron redox transformations could be achieved with these compounds. Moreover, combined experimental and theoretical studies unveiled that the ambiphilic uranium-arene interactions are the key to balance the stabilisation of low and high-valent uranium, with the anchoring arene acting as a δ acceptor or a π donor. Our results reinforce the design strategy to incorporate metal-arene interactions in stabilising multiple oxidation states, and open up new avenues to explore the redox chemistry of uranium.

A Comprehensive Study Concerning the Synthesis, Structure, and Reactivity of Terminal Uranium Oxido, Sulfido, and Selenido Metallocenes

Terminal uranium oxido, sulfido, and selenido metallocenes were synthesized, and their reactivity was comprehensively studied. Heating of an equimolar mixture of [η⁵-1,2,4-(Me₃Si)₃C₅H₂]₂UMe₂ (2) and [η⁵-1,2,4-(Me₃Si)₃C₅H₂]₂U(NH-p-tolyl)₂ (3) in the presence of 4-dimethylaminopyridine (dmap) in refluxing toluene forms [η⁵-1,2,4-(Me₃Si)₃C₅H₂]₂U═N(p-tolyl)(dmap) (4), which is a useful precursor for the preparation of the terminal uranium oxido, sulfido, and selenido metallocenes [η⁵-1,2,4-(Me₃Si)₃C₅H₂]₂U═E(dmap) (E = O (5), S (6), Se (7)) employing a cycloaddition-elimination methodology with Ph₂C═E (E = O, S) or (p-MeOPh)₂CSe, respectively. Metallocenes 5-7 are inert toward alkynes, but they act as nucleophiles in the presence of alkylsilyl halides. The oxido and sulfido metallocenes 5 and 6 undergo [2 + 2] cycloadditions with isothiocyanate PhNCS or CS₂, while the selenido derivative 7 does not. The experimental studies are complemented by density functional theory (DFT) computations.

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

We present the synthesis and reactivity of a newly developed, cyclen-based tris-aryloxide ligand precursor, namely cyclen(Me)( t-Bu,t-BuArOH)3, and its coordination chemistry to uranium. The corresponding uranium(iii) complex [UIII((OAr t-Bu,t-Bu)3(Me)cyclen)] (1) was characterized by 1H NMR analysis, CHN elemental analysis and UV/vis/NIR electronic absorption spectroscopy. Since no single-crystals suitable for X-ray diffraction analysis could be obtained from this precursor, 1 was oxidized with methylene chloride or silver fluoride to yield [(cyclen(Me)( t-Bu,t-BuArO)3)UIV(X)] (X = Cl (2), F (3)), which were unambiguously characterized and successfully crystallized to gain insight into the molecular structure by single-crystal X-ray diffraction analysis (SC-XRD). Further, the activation of H2O and N2O by 1 is presented, resulting in the U(iv) complex [(cyclen(Me)( t-Bu,t-BuArO)3)UIV(OH)] (4) and the U(v) complex [(cyclen(Me)( t-Bu,t-BuArO)3)UV(O)] (6). Complexes 2, 3, 4, and 6 were characterized by 1H NMR analysis, CHN elemental analysis, UV/vis/NIR electronic absorption spectroscopy, IR vibrational spectroscopy, and SQUID magnetization measurements as well as cyclic voltammetry. Furthermore, chemical oxidation of 3, 4, and 6 with AgF or AgSbF6 was achieved leading to complexes [(cyclen(Me)( t-Bu,t-BuArO)3)UV(F)2] (5), [(cyclen(Me)( t-Bu,t-BuArO)3)UV(OH)][SbF6] (7), and [(cyclen(Me)( t-Bu,t-BuArO)3)UVI(O)][SbF6] (8). Finally, reduction of 7 with KC8 yielded a U(iv) complex, spectroscopically and magnetochemically identified as K[(cyclen(Me)( t-Bu,t-BuArO)3)UIV(O)].

Actinide-Oxygen Multiple Bonds from Air: Synthesis and Characterization of a Thorium Oxo Supported by Redox-Active Ligands

The first non-uranyl, f-element oxo complex synthesized from dioxygen in dry air is presented in this work. The synthesis was accomplished by treating the redox-active thorium amidophenolate complex, [Th(^dippap)₃][K(15-c-5)₂]₂ (1-ap crown), with dioxygen in dry air, forming a rare terminal thorium oxo, [O═Th(^dippisq)₂(^dippap)][K(15-c-5)₂]₂ (2-oxo). Compound 1-ap crown was regenerated by treating 2-oxo with potassium graphite. X-ray crystallography of 2-oxo revealed a comparatively longer bond length for the thorium-oxygen double bond when compared to other thorium oxos. As such, several thorium-oxygen single bonds were synthesized for comparison, including Th(^dippisq)₂(OSiMe₃)₂(THF) (4-OSiMe₃), Th(OSiMe₃)₄(bipy)₂ (5-OSiMe₃), and [Th(OH)₂ (^dippHap)₄][K(15-c-5)₂]₂ (6-OH). Full spectroscopic and structural characterization of the complexes was performed via ¹H NMR spectroscopy, X-ray crystallography, EPR spectroscopy, and electronic absorption spectroscopy as well as SQUID magnetometry, which all confirmed the electronic structure of these complexes.

Ditelluride, Terminal Tellurido, and Bis(tellurido) Motifs of Titanium

Highly modular and rational syntheses of titanium compounds containing ditelluride, terminal telluride, and bis(telluride) structural motifs are disclosed in this study. Titanate anions bearing two cis and terminal telluride functionalities bound to the same metal center represent a unique example of a group 4 transition metal bis(chalcogenide) ion and are accessed in a simple, single-step procedure from Ti(III) bis(alkyl) complexes in the presence of an outer-sphere reductant and at least 3 equiv of Te⁰ powder. These compounds have been characterized crystallographically and spectroscopically with some preliminary reactivity reported for the anionic Ti(═Te)₂ motif. We also report solution ¹²⁵Te NMR spectral data in addition to theoretical studies addressing the bonding and structure for these titanate bis(tellurido) systems.

Evidence for ligand- and solvent-induced disproportionation of uranium(IV)

Disproportionation, where a chemical element converts its oxidation state to two different ones, one higher and one lower, underpins the fundamental chemistry of metal ions. The overwhelming majority of uranium disproportionations involve uranium(III) and (V), with a singular example of uranium(IV) to uranium(V/III) disproportionation known, involving a nitride to imido/triflate transformation. Here, we report a conceptually opposite disproportionation of uranium(IV)-imido complexes to uranium(V)-nitride/uranium(III)-amide mixtures. This is facilitated by benzene, but not toluene, since benzene engages in a redox reaction with the uranium(III)-amide product to give uranium(IV)-amide and reduced arene. These disproportionations occur with potassium, rubidium, and cesium counter cations, but not lithium or sodium, reflecting the stability of the corresponding alkali metal-arene by-products. This reveals an exceptional level of ligand- and solvent-control over a key thermodynamic property of uranium, and is complementary to isolobal uranium(V)-oxo disproportionations, suggesting a potentially wider prevalence possibly with broad implications for the chemistry of uranium.

Fragmentation, catenation, and direct functionalisation of white phosphorus by a uranium(IV)-silyl-phosphino-carbene complex

Room temperature reaction of the uranium(iv)-carbene [U{C(SiMe3)(PPh2)}(BIPMTMS)(μ-Cl)Li(TMEDA)(μ-TMEDA)0.5]2 (1, BIPMTMS = C(PPh2NSiMe3)2) with white phosphorus (P4) produces the organo-P5 compound [P5{C(SiMe3)(PPh2)}2][Li(TMEDA)2] (2) and the uranium(iv)-methanediide [U{BIPMTMS}{Cl}{μ-Cl}2{Li(TMEDA)}] (3). This is an unprecedented example of cooperative metal-carbene P4 activation/insertion into a metal-carbon double bond and also an actinide complex reacting with P4 to directly form an organophosphorus species. Conducting the reaction at low temperature permits the isolation of the diuranium(iv) complex [{U(BIPMTMS)([μ-η2:η2-P2]C[SiMe3][PPh2])}2] (4), which then converts to 2 and 3. Thus, surprisingly, in contrast to all other actinide P4 reactivity, although this reaction produces catenation overall it proceeds via P4 cleavage to functionalised P2 units. Hence, this work establishes a proof of concept synthetic cycle for direct fragmentation, catenation, and functionalisation of P4.

Nature of the Arsonium-Ylide Ph3 As=CH2 and a Uranium(IV) Arsonium-Carbene Complex

Treatment of [Ph₃ EMe][I] with [Na{N(SiMe₃ )₂ }] affords the ylides [Ph₃ E=CH₂ ] (E=As, 1As; P, 1P). For 1As this overcomes prior difficulties in the synthesis of this classical arsonium-ylide that have historically impeded its wider study. The structure of 1As has now been determined, 45 years after it was first convincingly isolated, and compared to 1P, confirming the long-proposed hypothesis of increasing pyramidalisation of the ylide-carbon, highlighting the increasing dominance of E⁺ -C^- dipolar resonance form (sp³ -C) over the E=C ene π-bonded form (sp² -C), as group 15 is descended. The uranium(IV)-cyclometallate complex [U{N(CH₂ CH₂ NSiPrⁱ ₃ )₂ (CH₂ CH₂ SiPrⁱ ₂ CH(Me)CH₂ )}] reacts with 1As and 1P by α-proton abstraction to give [U(Tren^TIPS )(CHEPh₃ )] (Tren^TIPS =N(CH₂ CH₂ NSiPrⁱ ₃ )₃ ; E=As, 2As; P, 2P), where 2As is an unprecedented structurally characterised arsonium-carbene complex. The short U-C distances and obtuse U-C-E angles suggest significant U=C double bond character. A shorter U-C distance is found for 2As than 2P, consistent with increased uranium- and reduced pnictonium-stabilisation of the carbene as group 15 is descended, which is supported by quantum chemical calculations.

Construction of heterometallic clusters with multiple uranium-metal bonds by using dianionic nitrogen-phosphorus ligands

Compared with the prevalent metal–metal bond in transition metals, examples of the actinide–metal bond in heterometallic clusters are rare. Herein, a series of heterometallic clusters with multiple uranium–metal bonds has been prepared based on two newly synthesized nitrogen–phosphorus ligands L1 {O[(CH₂)₂NHP(ⁱPr)₂]₂} and L2 {[CH₂O(CH₂)₂NHP(ⁱPr)₂]₂}. Different P–P distances, 6.069 and 4.464 Å, are observed in the corresponding uranium complexes 1 {O[(CH₂)₂NP(ⁱPr)₂]₂UCl₂} and 2 {[CH₂O(CH₂)₂NP(ⁱPr)₂]₂UCl₂}, respectively, and lead to the different coordination modes with transition metals. The reactions of zero-valent group 10 metal compounds with complex 1 generate heterometallic clusters (3-U2Ni2 and 4-U2Pd2) featuring four uranium–metal bonds; whereas reactions with 2 afford one-dimensional metal-chain 5-(UNi)n, bimetallic species 6-UPd, and a tri-platinum bridged diuranium molecular cluster 7-U2Pt3. Complex 5-(UNi)n represents the first infinite chain containing the U–M bond and 7-U2Pt3 is the first species with multiple U–Pt bonds. This study further highlights the important role of ligands in the construction of multiple uranium–metal bonds and may allow the synthesis of novel d–f heterometallic clusters and the investigation of their applications in catalysis and small-molecule activation.

Compared with the prevalent metal–metal bond in transition metals, examples of the actinide–metal bond in heterometallic clusters are rare.

The synthesis and versatile reducing power of low-valent uranium complexes

This synthesis and diverse reactivity of uranium(iii) and uranium(ii) complexes is discussed.

f-Element Half-Sandwich Complexes: A Tetrasilylcyclobutadienyl-Uranium(IV)-Tris(tetrahydroborate) Anion Pianostool Complex

Despite there being numerous examples of f-element compounds supported by cyclopentadienyl, arene, cycloheptatrienyl, and cyclooctatetraenyl ligands (C_5-8 ), cyclobutadienyl (C₄ ) complexes remain exceedingly rare. Here, we report that reaction of [Li₂ {C₄ (SiMe₃ )₄ }(THF)₂ ] (1) with [U(BH₄ )₃ (THF)₂ ] (2) gives the pianostool complex [U{C₄ (SiMe₃ )₄ }(BH₄ )₃ ][Li(THF)₄ ] (3), where use of a borohydride and preformed C₄ -unit circumvents difficulties in product isolation and closing a C₄ -ring at uranium. Complex 3 is an unprecedented example of an f-element half-sandwich cyclobutadienyl complex, and it is only the second example of an actinide-cyclobutadienyl complex, the other being an inverse-sandwich. The U-C distances are short (av. 2.513 Å), reflecting the formal 2- charge of the C₄ -unit, and the SiMe₃ groups are displaced from the C₄ -plane, which we propose maximises U-C₄ orbital overlap. DFT calculations identify two quasi-degenerate U-C₄ π-bonds utilising the ψ₂ and ψ₃ molecular orbitals of the C₄ -unit, but the potential δ-bond using the ψ₄ orbital is vacant.

Small molecule activation by multimetallic uranium complexes supported by siloxide ligands

The synthesis and reactivity of uranium compounds supported by the tris-tert-butoxysiloxide ligand is surveyed. The multiple binding modes of the tert-butoxysiloxide ligand have proven very well suited to stabilize highly reactive homo- and heteropolymetallic complexes of uranium that have shown an unusual high reactivity towards small molecules such as CO2, CS2, chalcogens and azides. Moreover, these ligands have allowed the isolation of dinuclear nitride and oxide bridged complexes of uranium in various oxidation states. The ability of the tris-tert-butoxysiloxide ligands to trap alkali ions in these nitride or oxide complexes leads to unprecedented ligand based and metal based reduction and functionalization of N2, CO, CO2 and H2.

Identification of a uranium-rhodium triple bond in a heterometallic cluster

The chemistry of d-block metal-metal multiple bonds has been extensively investigated in the past 5 decades. However, the synthesis and characterization of species with f-block metal-metal multiple bonds are significantly more challenging and such species remain extremely rare. Here, we report the identification of a uranium-rhodium triple bond in a heterometallic cluster, which was synthesized under routine conditions. The uranium-rhodium triple-bond length of 2.31 Å in this cluster is only 3% longer than the sum of the covalent triple-bond radii of uranium and rhodium (2.24 Å). Computational studies reveal that the nature of this uranium-rhodium triple bond is 1 covalent bond with 2 rhodium-to-uranium dative bonds. This heterometallic cluster represents a species with f-block metal-metal triple bond structurally authenticated by X-ray diffraction. These studies not only demonstrate the authenticity of the uranium-metal triple bond, but also provide a possibility for the synthesis of other f-block metal-metal multiple bonds. We expect that this work may further our understanding of the bonding between uranium and transition metals, which may help to design new d-f heterometallic catalysts with uranium-metal bonds for small-molecule activation and to promote the utilization of abundant depleted uranium resources.

A complete series of uranium(iv) complexes with terminal hydrochalcogenido (EH) and chalcogenido (E) ligands E = O, S, Se, Te

We here report the synthesis and characterization of a complete series of terminal hydrochalcogenido, U-EH, and chalcogenido uranium(iv) complexes, U≡E (with E = O, S, Se, Te), supported by the (^Ad,MeArOH)₃tacn (1,4,7-tris(3-(1-adamantyl)-5-methyl-2-hydroxybenzyl)-1,4,7-triazacyclononane) ligand system. Reaction of H₂E with the trivalent precursor [((^Ad,MeArO)₃tacn)U] (1) yields the corresponding uranium(iv) hydrochalcogenido complexes [((^Ad,MeArO)₃tacn)U(EH)] (2). Subsequent deprotonation of the terminal hydrochalcogenido species with KN(SiMe₃)₂, in the presence of 2.2.2-cryptand, gives access to the uranium(iv) complexes with terminal chalcogenido ligands [K(2.2.2-crypt)][((^Ad,MeArO)₃tacn)U≡E] (3). In order to study the influence of the varying terminal chalogenido ligands on the overall molecular and electronic structure, all complexes were studied by single-crystal X-ray diffractometry, UV/vis/NIR, electronic absorption, and IR vibrational spectroscopy as well as SQUID magnetometry and computational analyses (DFT, MO, NBO).

Oxidation of uranium(iv) mixed imido-amido complexes with PhEEPh and to generate uranium(vi) bis(imido) dichalcogenolates, U(NR)2(EPh)2(L)2

This work provides new routes for the conversion of U(iv) into U(vi) bis(imido) complexes and offers new information on the manner in which the U(vi) compounds form. Many compounds from the series described by the general formula U(NR)₂(EPh)₂(L)₂ (R = 2,6-diisopropylphenyl, tert-butyl; E = S, Se, Te; L = py, EPh) were synthesized via oxidation of an in situ generated U(iv) amido-imido species with Ph₂E₂. This synthetic sequence provides a general route into bis(imido) U(vi) chalcogenolate complexes, circumventing the need to perform problematic salt metathesis reactions on U(vi) iodides. Investigation into the speciation of the U(iv) complexes that form prior to oxidation found a significant dependence on the identity of the ancillary ligands, with ^tBu₂bpy forming the isolable imido-(bis)amido complex, U(NDipp)(NHDipp)₂(^tBu₂bpy)₂. Together, these data are consistent with the view that the bis(imido) U(vi) motif - much like the uranyl ion, UO₂²⁺- is a thermodynamic sink into which simple ligand frameworks are unable to prevent uranium from falling when in the presence of a suitable retinue of imido proligands.

Multiple Bonds in Uranium-Transition Metal Complexes

Novel heterobimetallic complexes featuring a uranium atom paired with a first-row transition metal have been computationally predicted and analyzed using density functional theory and multireference wave function based methods. The synthetically inspired metalloligands U{(ⁱPr₂PCH₂NAr)₃tacn} (1) and U(ⁱPr₂PCH₂NPh)₃ (2) are explored in this study. We report the presence of multiple bonds between uranium and chromium, uranium and manganese, and uranium and iron. The calculations predict a 5-fold bonding between uranium and manganese in the UMn(ⁱPr₂PCH₂NPh)₃ complex, which is unprecedented in the literature.

Facile N-functionalization and strong magnetic communication in a diuranium(v) bis-nitride complex

Uranium nitride complexes are of high interest because of their ability to effect dinitrogen reduction and functionalization and to promote magnetic communication, but studies of their properties and reactivity remain rare. Here we have prepared in 73% yield the diuranium(v) bis-nitride complex [K2{[U(OSi(O t Bu)3)3]2(μ-N)2}], 4, from the thermal decomposition of the nitride-, azide-bridged diuranium(iv) complex [K2{[U(OSi(O t Bu)3)3]2(μ-N)(μ-N3)}], 3. The bis-nitride 4 reacts in ambient conditions with 1 equiv. of CS2 and 1 equiv. of CO2 resulting in N-C bond formation to afford the diuranium(v) complexes [K2{[U(OSi(O t Bu)3)3]2(μ-N)(μ-S)(μ-NCS)}], 5 and [K2{[U(OSi(O t Bu)3)3]2(μ-N)(μ-O)(μ-NCO)}], 6, respectively. Both nitrides in 4 react with CO resulting in oxidative addition of CO to one nitride and CO cleavage by the second nitride to afford the diuranium(iv) complex [K2{[U(OSi(O t Bu)3)3]2(μ-CN)(μ-O)(μ-NCO)}], 7. Complex 4 also effects the remarkable oxidative cleavage of H2 in mild conditions to afford the bis-imido bridged diuranium(iv) complex [K2{[U(OSi(O t Bu)3)3]2(μ-NH)2}], 8 that can be further protonated to afford ammonia in 73% yield. Complex 8 provides a good model for hydrogen cleavage by metal nitrides in the Haber-Bosch process. The measured magnetic data show an unusually strong antiferromagnetic coupling between uranium(v) ions in the complexes 4 and 6 with Neel temperatures of 77 K and 60 K respectively, demonstrating that nitrides are attractives linkers for promoting magnetic communication in uranium complexes.

A sulphur and uranium fiesta! Synthesis, structure, and characterization of neutral terminal uranium(vi) monosulphide, uranium(vi) η2-disulphide, and uranium(iv) phosphine sulphide complexes

Three new uranium species, (C₅Me₅)₂U(N-2,6-ⁱPr₂-C₆H₃)(S), (C₅Me₅)₂U(N-2,6-ⁱPr₂-C₆H₃)(η²-S₂), and (C₅Me₅)₂U(N-2,6-ⁱPr₂-C₆H₃)(SPMe₃) have been prepared.

A diuranium carbide cluster stabilized inside a C80 fullerene cage

Unsupported non-bridged uranium-carbon double bonds have long been sought after in actinide chemistry as fundamental synthetic targets in the study of actinide-ligand multiple bonding. Here we report that, utilizing Ih(7)-C80 fullerenes as nanocontainers, a diuranium carbide cluster, U=C=U, has been encapsulated and stabilized in the form of UCU@Ih(7)-C80. This endohedral fullerene was prepared utilizing the Krätschmer-Huffman arc discharge method, and was then co-crystallized with nickel(II) octaethylporphyrin (NiII-OEP) to produce UCU@Ih(7)-C80·[NiII-OEP] as single crystals. X-ray diffraction analysis reveals a cage-stabilized, carbide-bridged, bent UCU cluster with unexpectedly short uranium-carbon distances (2.03 Å) indicative of covalent U=C double-bond character. The quantum-chemical results suggest that both U atoms in the UCU unit have formal oxidation state of +5. The structural features of UCU@Ih(7)-C80 and the covalent nature of the U(f1)=C double bonds were further affirmed through various spectroscopic and theoretical analyses.

A Very Short Uranium(IV)-Rhodium(I) Bond with Net Double-Dative Bonding Character

Reaction of [U{C(SiMe3 )(PPh2 )}(BIPM)(μ-Cl)Li(TMEDA)(μ-TMEDA)0.5 ]2 (BIPM=C(PPh2 NSiMe3 )2 ; TMEDA=Me2 NCH2 CH2 NMe2 ) with [Rh(μ-Cl)(COD)]2 (COD=cyclooctadiene) affords the heterotrimetallic UIV -RhI2 complex [U(Cl)2 {C(PPh2 NSiMe3 )(PPh[C6 H4 ]NSiMe3 )}{Rh(COD)}{Rh(CH(SiMe3 )(PPh2 )}]. This complex has a very short uranium-rhodium distance, the shortest uranium-rhodium bond on record and the shortest actinide-transition metal bond in terms of formal shortness ratio. Quantum-chemical calculations reveal a remarkable RhI→→ UIV net double dative bond interaction, involving RhI 4dz2 - and 4dxy/xz -type donation into vacant UIV 5f orbitals, resulting in a Wiberg/Nalewajski-Mrozek U-Rh bond order of 1.30/1.44, respectively. Despite being, formally, purely dative, the uranium-rhodium bonding interaction is the most substantial actinide-metal multiple bond yet prepared under conventional experimental conditions, as confirmed by structural, magnetic, and computational analyses.

Silyl-Phosphino-Carbene Complexes of Uranium(IV)

Unprecedented silyl-phosphino-carbene complexes of uranium(IV) are presented, where before all covalent actinide-carbon double bonds were stabilised by phosphorus(V) substituents or restricted to matrix isolation experiments. Conversion of [U(BIPMTMS )(Cl)(μ-Cl)2 Li(THF)2 ] (1, BIPMTMS =C(PPh2 NSiMe3 )2 ) into [U(BIPMTMS )(Cl){CH(Ph)(SiMe3 )}] (2), and addition of [Li{CH(SiMe3 )(PPh2 )}(THF)]/Me2 NCH2 CH2 NMe2 (TMEDA) gave [U{C(SiMe3 )(PPh2 )}(BIPMTMS )(μ-Cl)Li(TMEDA)(μ-TMEDA)0.5 ]2 (3) by α-hydrogen abstraction. Addition of 2,2,2-cryptand or two equivalents of 4-N,N-dimethylaminopyridine (DMAP) to 3 gave [U{C(SiMe3 )(PPh2 )}(BIPMTMS )(Cl)][Li(2,2,2-cryptand)] (4) or [U{C(SiMe3 )(PPh2 )}(BIPMTMS )(DMAP)2 ] (5). The characterisation data for 3-5 suggest that whilst there is evidence for 3-centre P-C-U π-bonding character, the U=C double bond component is dominant in each case. These U=C bonds are the closest to a true uranium alkylidene yet outside of matrix isolation experiments.

Reduction of Carbonyl Groups by Uranium(III) and Formation of a Stable Amide Radical Anion

Methyl benzoate, N,N-dimethylbenzamide, and benzophenone were reduced by U^III [N(SiMe₃ )₂ ]₃ resulting in uranium(IV) products. Reduction of benzophenone lead to U^IV [OC⋅Ph₂ )][N(SiMe₃ )₂ ]₃ , (1.1) which forms the dinuclear complex, [N(SiMe₃ )₂ ]₃ U^IV (OCPhPh-CPh₂ O)U^IV [N(SiMe₃ )₂ ]₃ (1.2), through coupling of the ketyl radical species upon crystallization. Reaction of N,N-dimethylbenzamide with U^III [N(SiMe₃ )₂ ]₃ resulted in U^IV [OC⋅(Ph)(NMe₂ )][N(SiMe₃ )₂ ]₃ (2), a uranium(IV) compound and the first example of a charge-separated amide radical. In the case of methyl benzoate, the reduction resulted in U^IV (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 U^V (=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)₂ K][UO[N(SiMe₃ )₂ ]₃ ] (5). The results expand the reduction capabilities of U^III complexes and demonstrate a strategy for isolating novel metal-stabilized radicals.

Crystalline Diuranium Phosphinidiide and μ-Phosphido Complexes with Symmetric and Asymmetric UPU Cores

Reaction of [U(TrenTIPS )(PH2 )] (1, TrenTIPS =N(CH2 CH2 NSiPri3 )3 ) with C6 H5 CH2 K and [U(TrenTIPS )(THF)][BPh4 ] (2) afforded a rare diuranium parent phosphinidiide complex [{U(TrenTIPS )}2 (μ-PH)] (3). Treatment of 3 with C6 H5 CH2 K and two equivalents of benzo-15-crown-5 ether (B15C5) gave the diuranium μ-phosphido complex [{U(TrenTIPS )}2 (μ-P)][K(B15C5)2 ] (4). Alternatively, reaction of [U(TrenTIPS )(PH)][Na(12C4)2 ] (5, 12C4=12-crown-4 ether) with [U{N(CH2 CH2 NSiMe2 But )2 CH2 CH2 NSi(Me)(CH2 )(But )}] (6) produced the diuranium μ-phosphido complex [{U(TrenTIPS )}(μ-P){U(TrenDMBS )}][Na(12C4)2 ] [7, TrenDMBS =N(CH2 CH2 NSiMe2 But )3 ]. Compounds 4 and 7 are unprecedented examples of uranium phosphido complexes outside of matrix isolation studies, and they rapidly decompose in solution underscoring the paucity of uranium phosphido complexes. Interestingly, 4 and 7 feature symmetric and asymmetric UPU cores, respectively, reflecting their differing steric profiles.

Metathesis of a UV imido complex: a route to a terminal UV sulfide

The metathesis reaction of a U^V imido complex supported by sterically demanding tris(tert-butoxy)siloxide ligands with CS₂ afforded a terminal U^V thiocarbonate but metathesis with H₂S afforded the first example of a terminal U^V sulfide.

Herein, we report the synthesis and characterisation of the first terminal uranium(v) sulfide and a related U^V trithiocarbonate complex supported by sterically demanding tris(tert-butoxy)siloxide ligands. The reaction of the potassium-bound U^V imido complex, [U(NAd){OSi(OtBu)₃}₄K] (4), with CS₂ led to the isolation of perthiodicarbonate [K(18c6)]₂[C₂S₆] (6), with concomitant formation of the U^IV complex, [U{OSi(OtBu)₃}₄], and S Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CNAd. In contrast, the reaction of the U^V imido complex, [K(2.2.2-cryptand)][U(NAd){OSi(OtBu)₃}₄] (5), with one or two equivalents of CS₂ afforded the trithiocarbonate complex, [K(2.2.2-cryptand)][U(CS₃){OSi(OtBu)₃}₄] (7), which was isolated in 57% yield, with concomitant elimination of the admantyl thiocyanate product, SCNAd. Complex 7 is likely formed by fast nucleophilic addition of a U^V terminal sulfide intermediate, resulting from the slow metathesis reaction of the imido complex with CS₂, to a second CS₂ molecule. The addition of a solution of H₂S in thf (1.3 eq.) to 4 afforded the first isolable U^V terminal sulfide complex, [K(2.2.2-cryptand)][US{OSi(OtBu)₃}₄] (8), in 41% yield. Based on DFT calculations, triple-bond character with a strong covalent interaction is suggested for the U–S bond in complex 7.

Assessing crystal field and magnetic interactions in diuranium-μ-chalcogenide triamidoamine complexes with UIV-E-UIV cores (E = S, Se, Te): implications for determining the presence or absence of actinide-actinide magnetic exchange

We report the synthesis and characterisation of a family of diuranium(iv)-μ-chalcogenide complexes including a detailed examination of their electronic structures and magnetic behaviours. Treatment of [U(Tren^TIPS)] [1, Tren^TIPS = N(CH₂CH₂NSiPrⁱ₃)₃] with Ph₃PS, selenium or tellurium affords the diuranium(iv)-sulfide, selenide, and telluride complexes [{U(Tren^TIPS)}₂(μ-E)] (E = S, 2; Se, 5; Te, 6). Complex 2 is also formed by treatment of [U(Tren^TIPS){OP(NMe₂)₃}] (3) with Ph₃PS, whereas treatment of 3 with elemental sulfur gives the diuranium(iv)-persulfido complex [{U(Tren^TIPS)}₂(μ-η²:η²-S₂)] (4). Complexes 2-6 have been variously characterised by single crystal X-ray diffraction, NMR, IR, and optical spectroscopies, room temperature Evans and variable temperature SQUID magnetometry, elemental analyses, and complete active space self consistent field spin orbit calculations. The combined characterisation data present a self-consistent picture of the electronic structure and magnetism of 2, 5, and 6, leading to the conclusion that single-ion crystal field effects, and not diuranium magnetic coupling, are responsible for features in their variable-temperature magnetisation data. The presence of magnetic coupling is often implied and sometimes quantified by such data, and so this study highlights the importance of evaluating other factors, such as crystal field effects, that can produce similar magnetic observables, and to thus avoid misassignments of such phenomena.

Multi-electron reduction of sulfur and carbon disulfide using binuclear uranium(iii) borohydride complexes

The first use of a dinuclear UIII/UIII complex in the activation of small molecules is reported. The octadentate Schiff-base pyrrole, anthracene-hinged 'Pacman' ligand LA combines two strongly reducing UIII centres and three borohydride ligands in [M(THF)4][{U(BH4)}2(μ-BH4)(LA)(THF)2] 1-M, (M = Li, Na, K). The two borohydride ligands bound to uranium outside the macrocyclic cleft are readily substituted by aryloxide ligands, resulting in a single, weakly-bound, encapsulated endo group 1 metal borohydride bridging the two UIII centres in [{U(OAr)}2(μ-MBH4)(LA)(THF)2] 2-M (OAr = OC6H2t Bu3-2,4,6, M = Na, K). X-ray crystallographic analysis shows that, for 2-K, in addition to the endo-BH4 ligand the potassium counter-cation is also incorporated into the cleft through η5-interactions with the pyrrolides instead of extraneous donor solvent. As such, 2-K has a significantly higher solubility in non-polar solvents and a wider U-U separation compared to the 'ate' complex 1. The cooperative reducing capability of the two UIII centres now enforced by the large and relatively flexible macrocycle is compared for the two complexes, recognising that the borohydrides can provide additional reducing capability, and that the aryloxide-capped 2-K is constrained to reactions within the cleft. The reaction between 1-Na and S8 affords an insoluble, presumably polymeric paramagnetic complex with bridging uranium sulfides, while that with CS2 results in oxidation of each UIII to the notably high UV oxidation state, forming the unusual trithiocarbonate (CS3)2- as a ligand in [{U(CS3)}2(μ-κ2:κ2-CS3)(LA)] (4). The reaction between 2-K and S8 results in quantitative substitution of the endo-KBH4 by a bridging persulfido (S2)2- group and oxidation of each UIII to UIV, yielding [{U(OAr)}2(μ-κ2:κ2-S2)(LA)] (5). The reaction of 2-K with CS2 affords a thermally unstable adduct which is tentatively assigned as containing a carbon disulfido (CS2)2- ligand bridging the two U centres (6a), but only the mono-bridged sulfido (S)2- complex [{U(OAr)}2(μ-S)(LA)] (6) is isolated. The persulfido complex (5) can also be synthesised from the mono-bridged sulfido complex (6) by the addition of another equivalent of sulfur.

The inverse-trans-influence in tetravalent lanthanide and actinide bis(carbene) complexes

Across the periodic table the trans-influence operates, whereby tightly bonded ligands selectively lengthen mutually trans metal-ligand bonds. Conversely, in high oxidation state actinide complexes the inverse-trans-influence operates, where normally cis strongly donating ligands instead reside trans and actually reinforce each other. However, because the inverse-trans-influence is restricted to high-valent actinyls and a few uranium(V/VI) complexes, it has had limited scope in an area with few unifying rules. Here we report tetravalent cerium, uranium and thorium bis(carbene) complexes with trans C=M=C cores where experimental and theoretical data suggest the presence of an inverse-trans-influence. Studies of hypothetical praseodymium(IV) and terbium(IV) analogues suggest the inverse-trans-influence may extend to these ions but it also diminishes significantly as the 4f orbitals are populated. This work suggests that the inverse-trans-influence may occur beyond high oxidation state 5f metals and hence could encompass mid-range oxidation state actinides and lanthanides. Thus, the inverse-trans-influence might be a more general f-block principle.

Thorium copper phosphides: more diverse metal–phosphorus and phosphorus–phosphorus interactions than U analogues

Three new thorium phosphides synthesized through CuI-mediated solid-state reactions exhibit more diverse ion–ion interactions than those in U pnictides.

Thorium-phosphorus triamidoamine complexes containing Th-P single- and multiple-bond interactions

Despite the burgeoning field of uranium-ligand multiple bonds, analogous complexes involving other actinides remain scarce. For thorium, under ambient conditions only a few multiple bonds to carbon, nitrogen, oxygen, sulfur, selenium and tellurium are reported, and no multiple bonds to phosphorus are known, reflecting a general paucity of synthetic methodologies and also problems associated with stabilising these linkages at the large thorium ion. Here we report structurally authenticated examples of a parent thorium(IV)-phosphanide (Th-PH₂), a terminal thorium(IV)-phosphinidene (Th=PH), a parent dithorium(IV)-phosphinidiide (Th-P(H)-Th) and a discrete actinide-phosphido complex under ambient conditions (Th=P=Th). Although thorium is traditionally considered to have dominant 6d-orbital contributions to its bonding, contrasting to majority 5f-orbital character for uranium, computational analyses suggests that the bonding of thorium can be more nuanced, in terms of 5f- versus 6d-orbital composition and also significant involvement of the 7s-orbital and how this affects the balance of 5f- versus 6d-orbital bonding character.