239 research outputs found
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. IronâNHC 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 Ă
resulting in relatively short MâŻOUO 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 Ă
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 UâCl 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 BâC 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)2â, [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 UâX 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)2â, with X located between the two ligand arene rings
Metal-Metal Bonding in Uranium-Group 10 Complexes
Heterobimetallic
complexes containing short uraniumâgroup
10 metal bonds have been prepared from monometallic IU<sup>IV</sup>(OAr<sup>P</sup>-Îș<sup>2</sup><i>O</i>,<i>P</i>)<sub>3</sub> (<b>2</b>) {[Ar<sup>P</sup>O]<sup>â</sup> = 2-<i>tert</i>-butyl-4-methyl-6-(diphenylphosphino)Âphenolate}.
The UâM bond in IU<sup>IV</sup>(ÎŒ-OAr<sup>P</sup>-1Îș<sup>1</sup><i>O</i>,2Îș<sup>1</sup><i>P</i>)<sub>3</sub>M<sup>0</sup>, M = Ni (<b>3âNi</b>), Pd (<b>3âPd</b>), and Pt (<b>3âPt</b>), has been
investigated by experimental and DFT computational methods. Comparisons
of <b>3âNi</b> with two further UâNi complexes
XU<sup>IV</sup>(ÎŒ-OAr<sup>P</sup>-1Îș<sup>1</sup><i>O</i>,2Îș<sup>1</sup><i>P</i>)<sub>3</sub>Ni<sup>0</sup>, X = Me<sub>3</sub>SiO (<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 UâM bonds are significantly
shorter than any other crystallographically characterized dâf-block
bimetallic, even though the ligand flexes to allow a variable UâM
separation. Excellent agreement is found between the experimental
and computed structures for <b>3âNi</b> and <b>3âPd</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 UâM bond critical point properties typical
of metallic bonding and a larger delocalization index (bond order)
for the less polar UâNi bond than UâPd. Electrochemical
studies agree with the computational analyses and the X-ray structural
data for the UâX adducts <b>3âNi</b>, <b>4</b>, and <b>5</b>. The data show a trend in uraniumâmetal
bond strength that decreases from <b>3âNi</b> down to <b>3âPt</b> and suggest that exchanging the iodide for a fluoride
strengthens the metalâmetal bond. Despite short UâTM
(transition metal) distances, four other computational approaches
also suggest low UâTM bond orders, reflecting highly transition
metal localized valence NLMOs. These are more so for <b>3âPd</b> than <b>3âNi</b>, consistent with slightly larger UâTM
bond orders in the latter. Computational studies of the model systems
(PH<sub>3</sub>)<sub>3</sub>MUÂ(OH)<sub>3</sub>I (M = Ni, Pd) reveal
longer and weaker unsupported UâTM bonds vs <b>3</b>
Thorium Mono- and Bis(imido) Complexes Made by Reprotonation of cyclo-Metalated Amides
International audienceMolecules containing actinideânitrogen 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 CâH bonds. Complexes with up to three uraniumânitrogen double bonds are now being widely studied, yet those with one thoriumânitrogen 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(âNAr)Nâł3] and K2[Th(âNAr)2Nâł2], are readily made from insertion reactions (Ar = aryl, Nâł = N(SiMe3)2) into the ThâC bond of the cyclometalated thorium amides [ThNâł2(N(SiMe3)(SiMe2CH2))] and K[ThNâł(N(SiMe3)(SiMe2CH2))2]. X-ray and computational structural analyses show a âtransition-metal-likeâ cis-bis(imido) geometry and polarized ThâN bonds with twice the Wiberg bond order of the formally single ThâN bond in the same molecule
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