Formation of Inclusion Organoactinide Complexes with Boron-Containing Macrocycles

Thorium(IV) and Uranium(IV) Thioether and Selenoether Complexes: Synthesis and An-ER2 (E = S, Se) Bonding Comparison

Reactions of the rigid thioether- and selenoether-containing ligand salts [{Li(AE2Ph2)}2] (E = S or Se; AE2Ph2 = 4,5-bis(phenylchalcogenido)-2,7,9,9-tetramethylacridanide) with ThCl4(dme)2 or UCl4 (for E = Se) afforded the actinide chalcogenoether complexes [(AE2Ph2)2ThCl2] (E = S (1), Se (2)), and [(ASe2Ph2)2UCl2] (3). X-ray crystal structures of 1-3 revealed tetravalent actinide cations complexed to two κ3-coordinated AE2Ph2 ligands, with Th-ER2 and U-ER2 distances below the sum of the covalent radii. Complexes 1-3 provide extremely rare examples of thorium-thioether, thorium-selenoether, and uranium-selenoether bonds, and 1 and 2 contain the shortest known Th-SR2 and Th-SeR2 distances. DFT and QTAIM calculations confirm the presence of significant An(IV)-ER2 interactions in 1-3 and provide insight into the extent of covalency in the An-ER2 bonds.

Arene-, Chlorido-, and Imido-Uranium Bis- and Tris(boryloxide) Complexes

We introduce the boryloxide ligand {(HCNDipp)2BO}- (NBODipp, Dipp = 2,6-di-isopropylphenyl) to actinide chemistry. Protonolysis of [U{N(SiMe3)2}3] with 3 equiv of NBODippH produced the uranium(III) tris(boryloxide) complex [U(NBODipp)3] (1). In contrast, treatment of UCl4 with 3 equiv of NBODippK in THF at room temperature or reflux conditions produced only [U(NBODipp)2(Cl)2(THF)2] (2) with 1 equiv of NBODippK remaining unreacted. However, refluxing the mixture of 2 and unreacted NBODippK in toluene instead of THF afforded the target complex [U(NBODipp)3(Cl)(THF)] (3). Two-electron oxidation of 1 with AdN3 (Ad = 1-adamantyl) afforded the uranium(V)-imido complex [U(NBODipp)3(NAd)] (4). The solid-state structure of 1 reveals a uranium-arene bonding motif, and structural, spectroscopic, and DFT calculations all suggest modest uranium-arene δ-back-bonding with approximately equal donation into the arene π4 and π5 δ-symmetry π* molecular orbitals. Complex 4 exhibits a short uranium(V)-imido distance, and computational modeling enabled its electronic structure to be compared to related uranium-imido and uranium-oxo complexes, revealing a substantial 5f-orbital crystal field splitting and extensive mixing of 5f |ml,ms⟩ states and mj projections. Complexes 1-4 have been variously characterized by single-crystal X-ray diffraction, 1H NMR, IR, UV/vis/NIR, and EPR spectroscopies, SQUID magnetometry, elemental analysis, and CONDON, F-shell, DFT, NLMO, and QTAIM crystal field and quantum chemical calculations.

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.

Highly symmetric Ln(iii) boron-containing macrocycles as bright fluorophores for living cell imaging

Boron-assisted highly symmetric rigid Ln macrocycles were designed and synthesized, showing high brightness and promising potential applications in bioimaging.

Uranium(IV) Thio- and Selenoether Complexes: Syntheses, Structures, and Computational Investigation of U-ER2 Interactions

Rigid thioether- and selenoether-containing pincer proligands H[AS₂ Ph 2 ] (1) and H[ASe₂ Ph 2 ] (2) were synthesized, and deprotonation provided the potassium salts [K(AS₂ Ph 2 )(dme)] (3) and [K(ASe₂ Ph 2 )(dme)₂ ] (4). Reaction of two equivalents of 3 or 4 with [UI₄ (dioxane)₂ ] afforded the uranium thioether complex [(AS₂ Ph 2 )₂ UI₂ ] (5) and the first example of a uranium-selenoether complex, [(ASe₂ Ph 2 )₂ UI₂ ] (6). X-ray structures revealed distorted square antiprismatic geometries in which the AE₂ Ph 2 ligands are κ³ -coordinated. The nature of the U-ER₂ bonding in 5 and 6, as well as methyl-free analogues of 5 and 6 and a hypothetical ether analogue, was investigated computationally (including NBO, AIM, and ELF calculations) illustrating increasing covalency from O to S to Se.

Recent developments in highly basic N-heterocyclic iminato ligands in actinide chemistry

In the last decade, major conceptual advances in the chemistry of actinide molecules and materials have been made to demonstrate their distinct reactivity profiles as compared to lanthanide and transition metal compounds, but some difficult questions remain concerning the intriguing stability of low-valent actinide complexes, and the importance of the 5f-orbitals in reactivity and bonding. The imidazolin-2-iminato moiety has been extensively used in ligands for the advancement of actinide chemistry owing to its unique capability of stabilizing the reactive and highly electrophilic metal ions by virtue of its strong electron donation and steric tunability. The current review article describes recent developments in the chemistry of light actinide metal ions (thorium and uranium) bearing these N-heterocyclic iminato moieties as supporting ligands. In addition, the effect of ring expansion of the N-heterocycle on the catalytic aptitude of the organoactinides is also described herein. The synthesis and reactivity of actinide complexes bearing N-heterocyclic iminato ligands are presented, and promising apposite applications are also presented. The current review focuses on addressing the catalytic behavior of actinide complexes with oxygen-containing substrates such as in the Tishchenko reaction, hydroelementation processes, and polymerization reactions. Actinide complexes have also found new catalytic applications, as demonstrated by the potent chemoselective carbonyl hydroboration and tandem proton-transfer esterification (TPTE) reaction, featuring coupling between an aldehyde and alcohol.

Applications of boroxide ligands in supporting small molecule activation by U(iii) and U(iv) complexes

The boroxide ligand [OBAr2]- (Ar = Mes, Trip) is shown to be able to support both UIII and UIV centres for the first time. The synthesis and structures of homoleptic and heteroleptic UIII and UIV complexes are reported. The UX3 complex with larger substituents, [U(OBTrip2)3]2, exhibits greater thermal stability compared to less encumbered [U(OBMes2)3]2 but reacts with a smaller range of the small molecules tested to date. Initial studies on their capacity to participate in small molecule chemistry show that dark purple [U(OBMes2)3]2 binds and/or reductively activates a variety of small molecules such as pyridine-oxide, triphenylphosphineoxide, sulfur, and dicyclohexylcarbodiimide. While [U(OBMes2)3]2 shows no reaction with CO or CO2, [U(OBTrip2)3]2 is oxidised by both, in the former case forming [U(OBTrip2)4], and in the latter case forming a small quantity of the structurally characterised μ-carbonate product [(μ-CO3){U(OBTrip2)3}2].

Catalytic regeneration of a Th-H bond from a Th-O bond through a mild and chemoselective carbonyl hydroboration

Here we present an unprecedented chemoselective hydroboration for aldehydes and ketones catalysed by actinides. The reaction features a very low catalyst loading (0.1-0.004 mol%) and quantitative product formation in less than 15 minutes, at room temperature. Thermodynamic and kinetic studies including stoichiometric and labeling studies with deuterated pinacolborane allow us to propose a plausible mechanism for this remarkable catalytic regeneration of a Th-H bond via carbonyl hydroboration.

Exploring the catalytic activity of Lewis-acidic uranyl complexes in the nucleophilic acyl substitution of acid anhydrides

Uranyl(vi) ion is a strongly hard Lewis-acid and plays a catalytic role in the nucleophilic acyl substitution of acid anhydrides.

Atom-efficient regioselective 1,2-dearomatization of functionalized pyridines by an earth-abundant organolanthanide catalyst

Developing earth-abundant, non-platinum metal catalysts for high-value chemical transformations is a critical challenge to contemporary chemical synthesis. Dearomatization of pyridine derivatives is an important transformation to access a wide range of valuable nitrogenous natural products, pharmaceuticals and materials. Here, we report an efficient 1,2-regioselective organolanthanide-catalysed pyridine dearomatization process using pinacolborane, which is compatible with a broad range of pyridines and functional groups and employs equimolar reagent stoichiometry. Regarding the mechanism, derivation of the rate law from NMR spectroscopic and kinetic measurements suggests first order in catalyst concentration, fractional order in pyridine concentration and inverse first order in pinacolborane concentration, with C=N insertion into the La-H bond as turnover-determining. An energetic span analysis affords a more detailed understanding of experimental activity trends and the unusual kinetic behaviour, and proposes the catalyst 'resting' state and potential deactivation pathways.

Synthesis, characterization, and reactivity of a novel thallium arylspiroboronate ester

Addition of 3,5-di-tert-butylcatechol (butcat) to solutions of H3B·SMe2 gave the novel diboron species B2(butcat)3 (2) in moderate to high yields. Compound 2 reacts with Tl(acac) to give butcatB(acac) (4) and Tl(Bbutcat2) (5). Attempts to abstract the chlorides from [(dppb)Rh(µ-Cl)]2 (where dppb = 1,4-bis(diphenylphosphino)buthane) using 5 led to the unusual dimer [(dppb)Rh(µ-Cl)2(µ-Tl)Rh(dppb)][Bbutcat2] (6), which contains an unsymmetrical Rh–Tl–Rh bridge.Key words: arylspiroboronate ester, non-coordinating anion, rhodium, thallium.

Unique σ-Bond Metathesis of Silylalkynes Promoted by an ansa-Dimethylsilyl and Oxo-Bridged Uranium Metallocene

The tetrachloride salt of uranium reacts with 1 equiv of the lithium ligand Li2[(C5Me4)2SiMe2] in DME to form the complex [eta5-(C5Me4)2SiMe2]UCl2.2LiCl.2DME (1), which undergoes a rapid hydrolysis in toluene to yield the dimeric bridged monochloride, monooxide complex [{[eta5-(C5Me4)2SiMe2]UCl}2(mu-O)(mu-Cl)*Li*1/2DME]2 (2). Metathesis of 2 with BuLi in DME gives the mono-bridged dibutyl complex {[eta5-(C5Me4)2SiMe2]UBu}2(mu-O) (3). Complex 2 was characterized by solid-state X-ray analysis. Complex 3 was found to be an active catalyst for the disproportionation metathesis of TMSCCH (TMS = SiMe3) and the cross-metathesis of TMSCCH or TMSCCTMS with various terminal alkynes. The metathesis of TMSCCH gives TMSCCTMS and HCCH, whereas the cross-metathesis of TMSCCH or TMSCCTMS with terminal alkynes (RCCH) yields TMSCCTMS, TMSCCR, and HCCH. In addition, TMSCCCH3 also was found to react with tBuCCH, yielding TMSCCBut and CH3CCH. A plausible mechanism for the catalytic process is presented.

Self-repairing polymers: poly(dioxaborolane)s containing trigonal planar boron

The molecular weight of poly(dioxaborolane)s can be controlled during the polymerization reaction or through post-polymerization processing in such a manner that hydrolytic damage to these materials may be repaired, thereby regenerating the polymer.