Aminophosphine Oxides: A Platform for Diversified Functions

This review summarizes significant contributions reported on aminophosphine oxides (AmPOs), specifically those containing at least one amino group present as amino substituents on α- and β-carbons including direct P-N bond containing molecules. AmPOs have additional 'N' site(s), including highly basic 'P=O' groups, and these features make favor smooth and unexpected behavior. The most striking manifestations of flexibility of AmPOs are that they are exciting ligand systems for the coordination chemistry of actinides, and their involvement in catalytic organic reactions including enantioselective opening of meso-epoxides, addition of silyl enol ethers, allylation with allyltributylstannane, etc. The diverse properties of the AmPOs and their metal complexes demonstrate both the scope and complexity of these systems, depending on the basicity of phosphoryl group, and nature of the substituents on the pentavalent tetracoordinate phosphorus atom and metal. Two components key to understanding the challenges of actinide separations are detailed here, namely, previously described separation methods, and recent investigations into the fundamental coordination chemistry of actinides. Both are aimed at probing the critical features necessary for improved selectivity of separations. This review leads to the conclusion that, although many AmPOs have already been discovered and developed over the past century, many opportunities nevertheless exist for further developments towards new extraction processes and new catalytic materials by fine tuning the electronic and steric properties of substituents on the central phosphorus atom.

Polymeric Materials for the Separation of f-Elements Utilizing Carbamoylmethylphosphine Oxide Chelating Ligands

The ability of carbamoylmethylphosphine oxide (CMPO) ligands to selectively chelate actinides has been shown to be enhanced by preorganizing the ligands on molecular scaffolds. To increase the preorganization, a new polymeric material with a polyoxanorbornene backbone and CMPO ligand pendant groups has been synthesized, and the ability of the material to selectively extract actinides utilizing a biphasic extraction strategy has been tested. In liquid-liquid extractions of f-block metals from acidic aqueous media into an organic solution containing chelating materials, the polymeric material exhibited a significantly higher ability to extract Th⁴⁺ ions than the monomer, with an order of magnitude greater affinity for the polymeric material in most cases. Due to the unique properties of polymeric materials versus small molecules, additional questions arose as to the effect of molecular weight on extraction efficiency. Extraction and separation efficiencies varied for materials of differing molecular weights, with the largest molecular weight polymer extracting near quantitative amounts of thorium ions, and the smaller molecular weight polymers showing separation factors for Th⁴⁺ ions over Ce³⁺, La³⁺, and Eu³⁺ ions ranging from 124 to 328.

Bis(carbamoylmethylphosphine oxide) ligands fixed on the arene core via 1,2,3-triazole linkers: novel effective extractants for palladium, lanthanides and actinides

The extraction of U(vi) and Th(iv) from 3 M HNO₃ solutions with 0.01 M solutions of extractants 1–8 in 1,2-dichloroethane.

CMPO-calix[4]arenes with spacer containing intramolecular hydrogen bonding: effect of local rigidification on solvent extraction toward f-block elements

To understand intramolecular hydrogen bonding in effecting liquid-liquid extraction behavior of CMPO-calixarenes, three CMPO-modified calix[4]arenes (CMPO-CA) 5a-5c with hydrogen-bonded spacer were designed and synthesized. The impact of spacer rotation that is hindered by introduction of intramolecular hydrogen bonding upon extraction of La(3+), Eu(3+), Yb(3+), Th(4+), and UO2(2+) has been examined. The results show that 5b and 5c containing only one hydrogen bond with a less hindered rotation spacer extract La(3+) more efficiently than 5a containing two hydrogen bonds with a more hindered rotation spacer, demonstrating the importance of local rigidification of spacer in the design of extractants in influencing the coordination environment. The large difference in extractability between La(3+) and Yb(3+) (or Eu(3+)) by 5b (or 5c), and the small difference by 5a, suggests intramolecular hydrogen bonding do exert pronounced influence upon selective extraction of light and heavy lanthanides. Log-log plot analysis indicates a 1:1, 2:1 and 1:1 stoichiometry (ligand/metal) for the extracted complex formed between 5b and La(3+), Th(4+), UO2(2+), respectively. Additionally, their corresponding acyclic analogs 7a-7c exhibit negligible extraction toward these metal ions. These results reveal the possibility of selective extraction via tuning local chelating surroundings of CMPO-CA by aid of intramolecular hydrogen bonding.

N-Tris[(2-aminoethyl)-2-(diphenylphosphoryl) acetamide)] — novel CMPO tripodand: synthesis, extraction studies and luminescent properties of lanthanide complexes

A ligand system containing three carbamoylmethylphosphine oxide (CMPO) moieties attached to a tripodal platform with a central nitrogen atom has been synthesized for metal complexation and extraction from neutral and nitric acid solutions. Liquid-liquid extractions performed for Ln(III), both from neutral and acidic media, show excellent extraction properties which exceeded those for the known mono- and di-CMPO derivatives as well as the related tripodands. A considerable enhancement of the DLn values was observed in the presence of IL ([bmim][Tf2N]) in the organic phase towards lanthanide ions from 3M HNO3 solutions. The protonation of the central amine nitrogen atom of the ligand 1 in the acidic media provides also the effective extraction of the perrhenate anionic complexes. The europium complexes formed by mono- and tris-CMPO ligands in the solid state, as well as Eu(III) and Tb(III) complexes generated in solutions, possess intensive luminescence at 300K

Perfluorinated phenols as extraction agents for Cs+ and Sr2+

The extraction efficiency of some perfluorinated phenols for the removal of Cs+ and Sr2+ from aqueous solutions is reported. The perfluorinated phenols C6F5OH and 2,3,5,6-C6F4HOH have been shown to extract 90Sr2+ or Cs+ from aqueous solutions into a 100:1 mixture of toluene and pyridine in reasonable efficiencies, using radio-tracer and ICP-OES techniques. Additionally uranium, 59Fe3+ {as a model for Pu(IV)} and Eu3+ {as a model for Am(III)} were investigated, with only iron not being successfully extracted.

Synergistic effect of dicarbollide anions in liquid-liquid extraction: a molecular dynamics study at the octanol-water interface

We report a molecular dynamics study of chlorinated cobalt bis(dicarbollide) anions [(B(9)C(2)H(8)Cl(3))(2)Co](-)"CCD(-)" in octanol and at the octanol-water interface, with the main aim to understand why these hydrophobic species act as strong synergists in assisted liquid-liquid cation extraction. Neat octanol is quite heterogeneous and is found to display dual solvation properties, allowing to well solubilize CCD(-), Cs(+) salts in the form of diluted pairs or oligomers, without displaying aggregation. At the aqueous interface, octanol behaves as an amphiphile, forming either monolayers or bilayers, depending on the initial state and confinement conditions. In biphasic octanol-water systems, CCD(-) anions are found to mainly partition to the organic phase, thus attracting Cs(+) or even more hydrophilic counterions like Eu(3+) into that phase. The remaining CCD(-) anions adsorb at the interface, but are less surface active than at the chloroform interface. Finally, we compare the interfacial behavior of the Eu(BTP)(3)(3+) complex in the absence and in the presence of CCD(-) anions and extractant molecules. It is found that when the CCD(-)'s are concentrated enough, the complex is extracted to the octanol phase. Otherwise, it is trapped at the interface, attracted by water. These results are compared to those obtained with chloroform as organic phase and discussed in the context of synergistic effect of CCD(-) in liquid-liquid extraction, pointing to the importance of dual solvation properties of octanol and of the hydrophobic character of CCD(-) for synergistic extraction of cations.

Multicoordinate ligands for actinide/lanthanide separations

In nuclear waste treatment processes there is a need for improved ligands for the separation of actinides (An(III)) and lanthanides (Ln(III)). Several research groups are involved in the design and synthesis of new An(III) ligands and in the confinement of these and existing An(III) ligands onto molecular platforms giving multicoordinate ligands. The preorganization of ligands considerably improves the An(III) extraction properties, which are largely dependent on the solubility and rigidity of the platform. This tutorial review summarizes the most important An(III) ligands with emphasis on the preorganization strategy using (macrocyclic) platforms.