Twisted and Disconnected Chains: Flexible Linear Tetracuprous Arrays and a Decanuclear CuI Cluster as Blue- and Green/Yellow-Light Emitters

Defined arrays of transition metal ions embedded in tailored polydentate ligand scaffolds allow for a systematic design of their physical properties. Such molecular strings of closed-shell transition metal centers are particularly interesting for Group 11 metal ions in the oxidation state +1 if they undergo metallophilic d10···d10 contact interactions since these clusters are oftentimes efficient photoluminescence (PL) emitters. Copper is particularly attractive as a sustainable earth-abundant coinage metal source and because of the ability of several CuI complexes to serve as powerful thermally activated delayed fluorescence (TADF) emitters in molecular/organic light-emitting devices (OLEDs). Our combined synthetic, crystallographic, photophysical, and computational study describes a straight tetracuprous array possessing a centrally disconnected CuI2···CuI2 chain and a continuous helically bent CuI4 complex. This molecular helix undergoes a facile rearrangement in diethyl ether solution, yielding an unprecedented nanosized CuI10 cluster (2.9 × 2.0 nm) upon crystallization. All three clusters show either bright blue phosphorescence, TADF, or green/yellow multiband phosphorescence with quantum yields between 6.5 and 67%, which is persistent under hydrostatic pressure up to 30 kbar. Temperature-dependent PL investigations in combination with time-dependent density-functional theory (TD-DFT) calculations and void space analyses of the crystal packings complement a comprehensive correlation between the molecular structures and photoluminescence properties.

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.

Hydrogen bonds and dispersion forces serving as molecular locks for tailored Group 11 bis(amidine) complexes

A flexible polydentate bis(amidine) ligand LH2 operates as a molecular lock for various coinage metal fragments and forms the dinuclear complexes [LH2(MCl)2], M = Cu (1), Au (2), the coordination...

Elucidation of Thorium Redox-Active Ligand Complexes: Evidence for a Thorium-Tri(radical) Species

A series of thorium(IV) complexes featuring the redox-active 4,6-di-tert-butyl-N-(2,6-di-isopropylphenyl)-o-iminobenzoquinone (^dippiq) ligand family have been synthesized and characterized. The neutral iminoquinone ligand was used to generate Th(^dippiq)Cl₄(dme)₂ (1-iq) and Th(^dippiq)₂Cl₄ (2-iq), both of which show dative bonds between the thorium(IV) ion and the ligands. One electron reduction of the ligand forms the unique tris(iminosemiquinone) complex, Th(^dippisq)₃Cl (3-isq), which features a radical in each ligand. Further reduction furnishes the amidophenolate species, Th(^dippap)₃]K₂(THF)₂ (4-ap), which has the ligands in their dianionic form. Attempts to sequester the potassium ions with cryptand resulted in the [Th(^dippap)₃K][K(crypt)] (4-ap mono crypt) and [Th(^dippap)₃][K(crypt)]₂ (4-ap crypt) species. A bis(amidophenolate) complex was accessed by incorporating bulky triphenylphosphine oxide (OPPh₃) ligands to generate Th(^dippap)₂(OPPh)₃ (5-ap). Spectroscopic and structural characterization of each derivative established the +4 oxidation state for thorium with redox chemistry occurring at the ligands rather than the thorium ion. The reported 3-isq complex is unprecedented as it is the first tri(radical) thorium complex with the highest reported magnetic moment for a thorium species as characterized by SQUID magnetometry.

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.

Amidinate Supporting Ligands Influence Molecularity in Formation of Uranium Nitrides

Uranium nitride complexes are attractive targets for chemists as molecular models for the bonding, reactivity, and magnetic properties of next-generation nuclear fuels, but these molecules are uncommon and can be difficult to isolate due to their high reactivity. Here, we describe the synthesis of three new multinuclear uranium nitride complexes, [U(BCMA)₂]₂(μ-N)(μ-κ¹:κ¹-BCMA) (7), [(U(BIMA)₂)₂(μ-N)(μ-NⁱPr)(K₂(μ-η³:η³-CH₂CHNⁱPr)]₂ (8), and [U(BIMA)₂]₂(μ-N)(μ-κ¹:κ¹-BIMA) (9) (BCMA = N,N-bis(cyclohexyl)methylamidinate, BIMA = N,N-bis(iso-propyl)methylamidinate), from U(III) and U(IV) amidinate precursors. By varying the amidinate ligand substituents and azide source, we were able to influence the composition and size of these nitride complexes. ¹⁵N isotopic labeling experiments confirmed the bridging nitride moieties in 7-9 were formed via two-electron reduction of azide. The tetra-uranium cluster 8 was isolated in 99% yield via reductive cleavage of the amidinate ligands; this unusual molecule contains nitrogen-based ligands with formal 1-, 2-, and 3- charges. Additionally, chemical oxidation of the U(IV) precursor U(N₃)(BCMA)₃ yielded the cationic U(V) species [U(N₃)(BCMA)₃][OTf]. Magnetic susceptibility measurements confirmed a U(IV) oxidation state for the uranium centers in the three nitride-bridged complexes and provided a comparison of magnetic behavior in the structurally related U(III)-U(IV)-U(V) series U(BCMA)₃, U(N₃)(BCMA)₃, and [U(N₃)(BCMA)₃][OTf]. At 240 K, the magnetic moments in this series decreased with increasing oxidation state, i.e., U(III) > U(IV) > U(V); this trend follows the decreasing number of 5f valence electrons along this series.

Ligands with Two Monoanionic N,N-Binding Sites: Synthesis and Coordination Chemistry

Polytopic ligands have become ubiquitous in coordination chemistry because they grant access to a variety of mono- and polynuclear complexes of transition metals as well as rare-earth and main-group elements. Nitrogen-based ditopic ligands, in which two monoanionic N,N-binding sites are framed within one molecule, are of particular importance and are therefore the primary focus of this review. In detail, bis(amidine)s, bis(guanidine)s, bis(β-diimine)s, bis(aminotroponimine)s, bis(pyrrolimine)s, and miscellaneous bis(N,N-chelating) ligands are reviewed. In addition to the general synthetic protocols, the application of these ligands is discussed along with their coordination chemistry, the multifarious binding modes, and the ability of these ligands to bridge two (or more) metal(loids).

Dioxygen reacts with metal-carbon bonds in thorium dialkyls to produce bis(alkoxides)

Exposure of bis-amidinate and -guanidinate supported thorium dialkyl complexes to dioxygen results in facile oxygen atom insertion and formation of the corresponding thorium bis(alkoxide) species. Preliminary mechanistic studies suggest a radical propagation mechanism is operative. All new complexes were fully characterized by 1H and 13C NMR spectroscopy, IR, EA and X-ray crystallography.

Two-electron oxidation of a homoleptic U(iii) guanidinate complex by diphenyldiazomethane

Reaction of the first homoleptic U(iii) guanidinate complex with diphenyldiazomethane results in two-electron oxidation of U(iii) to U(v) and isolation of a U(v) hydrazido complex. Corresponding U(v) imido, U(v) oxo, and U(iv) azido complexes were also synthesized for structural comparison.

Homoleptic U(iii) and U(iv) amidate complexes

Homoleptic U(iv) and U(iii) amidate complexes have been isolated and characterized; these species undergo an unusual and reversible change in coordination number upon reduction/oxidation.

Organoactinides in catalytic transformations: scope, mechanisms and Quo Vadis

The last decade has witnessed brilliant and remarkable advances in the chemistry of the early actinides in stoichiometric and in challenging catalytic processes. This canvas of knowledge allows the design of chemical reactivities reaching a high level of sophistication. This review highlights the latest results obtained since 2008 on those catalytic processes.

Catalytic insertion of E-H bonds (E = C, N, P, S) into heterocumulenes by amido-actinide complexes

We report herein the actinide-mediated insertion of E-H bonds (E = C, N, P, S) into various heterocumulenes including carbodiimides, isocyanates, and isothiocyanates. The precatalysts are prepared by a simple, one-pot procedure using readily available starting materials, and challenging insertions are achieved with excellent selectivity in short reaction times. Spectroscopic data are utilised to propose the active catalytic mechanism and derive thermodynamic activation parameters, which are described in this study. The only example of an actinide-mediated C-H bond insertion into a carbon-heteroatom bond is presented within this study.

Uranium and thorium complexes of the phosphaethynolate ion

New tris-amidinate actinide (Th, U) complexes containing a rare O-bound terminal phosphaethynolate (OCP ^- ) ligand were synthesized and fully characterized. The cyanate (OCN ^- ) and thiocyanate (SCN ^- ) analogs were prepared for comparison and feature a preferential N-coordination to the actinide metals. The Th(amid)₃(OCP) complex reacts with Ni(COD)₂ to yield the heterobimetallic adduct (amid) ₃ Th(μ-η ¹ (O):η ² (C,P)-OCP)Ni(COD) featuring an unprecedented reduced (OCP ^- ) bent fragment bridging the two metals.

Uranium-mediated ring-opening polymerization of ε-caprolactone: a comparative study

This study shows and compares the catalytic activity and the mechanism of the uranium complexes [(Im^DippN)₂U(NMeEt)₂] (3), [(C₅Me₅)₂U(NMe₂)₂] (4) and [(C₅Me₅)₂U(NCMePh)₂] (5) in the ring-opening polymerization of ε-caprolactone, among which the bis(imidazolin-2-iminato) uranium complex3displayed the highest catalytic activity.