Destruction of chemical warfare agent simulants by air and moisture stable metal NHC complexes

The cooperative effect of both NHC and metal centre has been found to destroy chemical warfare agent (CWA) simulants. Choice of both the metal and NHC is key to these transformations as simple, monodentate N-heterocyclic carbenes in combination with silver or vanadium can promote stoichiometric destruction, whilst bidentate, aryloxide-tethered NHC complexes of silver and alkali metals promote breakdown under mild heating. Iron–NHC complexes generated in situ are competent catalysts for the destruction of each of the three targetted CWA simulants

Controlling uranyl oxo group interactions to group 14 elements using polypyrrolic Schiff-base macrocyclic ligands

Heterodinuclear uranyl/group 14 complexes of the aryl- and anthracenyl-linked Schiff-base macrocyclic ligands LMe and LA were synthesised by reaction of UO2(H2L) with M{N(SiMe3)2}2 (M = Ge, Sn, Pb). For complexes of the anthracenyl-linked ligand (LA) the group 14 metal sits out of the N4-donor plane by up to 0.7 Å resulting in relatively short M⋯OUO distances which decrease down the group; however, the solid state structures and IR spectroscopic analyses suggest little interaction occurs between the oxo and group 14 metal. In contrast, the smaller aryl-linked ligand (LMe) enforces greater interaction between the metals; only the PbII complex was cleanly accessible although this complex was relatively unstable in the presence of HN(SiMe3)2 and some organic oxidants. In this case, the equatorial coordination of pyridine-N-oxide causes a 0.08 Å elongation of the endo UO bond and a clear interaction of the uranyl ion with the Pb(II) cation in the second donor compartment

Uranyl to Uranium(IV) Conversion through Manipulation of Axial and Equatorial Ligands

The controlled manipulation of the axial oxo and equatorial halide ligands in the uranyl dipyrrin complex, UO2Cl(L), allows the uranyl reduction potential to be shifted by 1.53 V into the range accessible to naturally occurring reductants that are present during uranium remediation and storage processes. Abstraction of the equatorial halide ligand to form the uranyl cation causes a 780 mV positive shift in the UV/UIV reduction potential. Borane functionalization of the axial oxo groups causes the spontaneous homolysis of the equatorial U–Cl bond and a further 750 mV shift of this potential. The combined effect of chloride loss and borane coordination to the oxo groups allows reduction of UVI to UIV by H2 or other very mild reductants such as Cp*2Fe. The reduction with H2 is accompanied by a B–C bond cleavage process in the oxo-coordinated borane

Uranium(III) coordination chemistry and oxidation in a flexible small-cavity macrocycle

U(III) complexes of the conformationally flexible, small-cavity macrocycle trans-calix[2]benzene[2]pyrrolide (L)2–, [U(L)X] (X = O-2,6-tBu2C6H3, N(SiMe3)2), have been synthesized from [U(L)BH4] and structurally characterized. These complexes show binding of the U(III) center in the bis(arene) pocket of the macrocycle, which flexes to accommodate the increase in the steric bulk of X, resulting in long U–X bonds to the ancillary ligands. Oxidation to the cationic U(IV) complex [U(L)X][B(C6F5)4] (X = BH4) results in ligand rearrangement to bind the smaller, harder cation in the bis(pyrrolide) pocket, in a conformation that has not been previously observed for (L)2–, with X located between the two ligand arene rings

Metal-Metal Bonding in Uranium-Group 10 Complexes

Heterobimetallic complexes containing short uranium–group 10 metal bonds have been prepared from monometallic IU^IV(OAr^P-κ²<i>O</i>,<i>P</i>)₃ (<b>2</b>) {[Ar^PO]⁻ = 2-<i>tert</i>-butyl-4-methyl-6-(diphenylphosphino)­phenolate}. The U–M bond in IU^IV(μ-OAr^P-1κ¹<i>O</i>,2κ¹<i>P</i>)₃M⁰, M = Ni (<b>3–Ni</b>), Pd (<b>3–Pd</b>), and Pt (<b>3–Pt</b>), has been investigated by experimental and DFT computational methods. Comparisons of <b>3–Ni</b> with two further U–Ni complexes XU^IV(μ-OAr^P-1κ¹<i>O</i>,2κ¹<i>P</i>)₃Ni⁰, X = Me₃SiO (<b>4</b>) and F (<b>5</b>), was also possible via iodide substitution. All complexes were characterized by variable-temperature NMR spectroscopy, electrochemistry, and single crystal X-ray diffraction. The U–M bonds are significantly shorter than any other crystallographically characterized d–f-block bimetallic, even though the ligand flexes to allow a variable U–M separation. Excellent agreement is found between the experimental and computed structures for <b>3–Ni</b> and <b>3–Pd</b>. Natural population analysis and natural localized molecular orbital (NLMO) compositions indicate that U employs both 5f and 6d orbitals in covalent bonding to a significant extent. Quantum theory of atoms-in-molecules analysis reveals U–M bond critical point properties typical of metallic bonding and a larger delocalization index (bond order) for the less polar U–Ni bond than U–Pd. Electrochemical studies agree with the computational analyses and the X-ray structural data for the U–X adducts <b>3–Ni</b>, <b>4</b>, and <b>5</b>. The data show a trend in uranium–metal bond strength that decreases from <b>3–Ni</b> down to <b>3–Pt</b> and suggest that exchanging the iodide for a fluoride strengthens the metal–metal bond. Despite short U–TM (transition metal) distances, four other computational approaches also suggest low U–TM bond orders, reflecting highly transition metal localized valence NLMOs. These are more so for <b>3–Pd</b> than <b>3–Ni</b>, consistent with slightly larger U–TM bond orders in the latter. Computational studies of the model systems (PH₃)₃MU­(OH)₃I (M = Ni, Pd) reveal longer and weaker unsupported U–TM bonds vs <b>3</b>

Thorium Mono- and Bis(imido) Complexes Made by Reprotonation of cyclo-Metalated Amides

International audienceMolecules containing actinide–nitrogen multiple bonds are of current interest as simple models for new actinide nitride nuclear fuels, and for their potential for the catalytic activation of inert hydrocarbon C–H bonds. Complexes with up to three uranium–nitrogen double bonds are now being widely studied, yet those with one thorium–nitrogen double bond are rare, and those with two are unknown. A new, simple mono(imido) thorium complex and the first bis(imido) thorium complex, K[Th(═NAr)N″3] and K2[Th(═NAr)2N″2], are readily made from insertion reactions (Ar = aryl, N″ = N(SiMe3)2) into the Th–C bond of the cyclometalated thorium amides [ThN″2(N(SiMe3)(SiMe2CH2))] and K[ThN″(N(SiMe3)(SiMe2CH2))2]. X-ray and computational structural analyses show a “transition-metal-like” cis-bis(imido) geometry and polarized Th═N bonds with twice the Wiberg bond order of the formally single Th–N bond in the same molecule