Rapid dissolution of noble metals in organic solvents
Abhijit Nag, Carole A. Morrison, Jason B. Love
ChemSusChem, 2022, DOI:10.1002/cssc.202201285.
Abstract: The dissolution of elemental noble metals (NMs) such as gold, platinum, palladium, and copper in organic solutions is necessary for their recycling but carries a high environmental burden due to the use of strong acids and toxic reagents. Herein, a new approach is presented for the rapid dissolution of elemental NMs in organic solvents using mixtures of triphenylphosphine dichloride or oxalyl chloride and hydrogen peroxide, forming metal chloride salts directly. Almost quantitative dissolution of metallic Au, Pd, and Cu was observed within minutes at room temperature. For Pt, dissolution by hydrogen peroxide was inhibited but achieved, albeit more slowly, using the chlorinating oxidant alone. After leaching, transfer of Pt(IV) and Pd(II) chloride salts from the organic phase into a 6 M HCl aqueous phase facilitated the separation of Pt(IV) by precipitation using a simple diamide ligand. In contrast, the retention of Au(III) chloridometalate in the organic phase allowed its selective separation from Ni and Cu from a leachate solution obtained from electronic CPUs. This new approach has potential application in the hydrometallurgical leaching and purification of NMs from ores, spent catalysts, and electronic- and nano-wastes.
Selective separation of light rare-earth elements by supramolecular encapsulation and precipitation
Nature Communications, 2022, 13, 4497
J. O’Connell-Danes, B. T. Ngwenya, C. A. Morrison, J. B. Love
Abstract: Supramolecular chemical strategies for Rare Earth (RE) element separations are emerging which amplify the small changes in properties across the series to bias selectivity in extraction or precipitation. These advances are important as the REs are crucial to modern technologies yet their extraction, separation, and recycling using conventional techniques remain challenging. We report here a pre-organised triamidoarene platform which, under acidic, biphasic conditions, uniquely and selectively precipitates light RE nitratometalates as supramolecular capsules. The capsules exhibit both intra- and intermolecular hydrogen bonds that dictate selectivity, promote precipitation, and facilitate the straightforward release of the RE and recycling of the receptor. This work provides a self-assembly route to metal separations that exploits size and shape complementarity and has the potential to integrate into conventional processes due to its compatibility with acidic metal feed streams.
Exploring the Redox Properties of Bench-Stable Uranyl(VI) Diamido–Dipyrrin Complexes
Karlotta van Rees, Emma K. Hield, Ambre Carpentier, Laurent Maron, Stephen Sproules, Jason B. Love
Inorg. Chem., 2022, DOI:10.1021/acs.inorgchem.1c03744
The uranyl complexes UO2(OAc)(L) and UO2Cl(L) of the redox-active, acyclic diamido–dipyrrin anion L– are reported and their redox properties explored. Because of the inert nature of the complexes toward hydrolysis and oxidation, synthesis of both the ligands and complexes was conducted under ambient conditions. Voltammetric, electron paramagnetic resonance spectroscopy, and density functional theory studies show that one-electron chemical reduction by the reagent CoCp2 leads to the formation of a dipyrrin radical for both complexes [Cp2Co][UO2(OAc)(L•)] and [Cp2Co][UO2Cl(L•)].
A Johnson Matthey iCASE PhD studentship is available in the groups of Jason Love and Carole Morrison (School of Chemistry, The University of Edinburgh; https://jasonlovegroup.wordpress.com/).
The studentship is fully funded for 48 months and covers tuition fees and an annual stipend (starting at £15,609 per annum) for a candidate satisfying EPSRC criteria: https://www.ukri.org/councils/esrc/career-and-skills-development/funding-for-postgraduate-training/eligibility-for-studentship-funding/#contents-list
Why are some PGM complexes respiratory and dermal sensitisers when others are not? Early screening work proposed that it was Pt halides that were allergenic, but a number of non-halide, non-Pt compounds have since also proved sensitising. Knowing whether a new research compound is likely to be sensitising would significantly change practises at Johnson Matthey. However, workplace safety focuses on epidemiology and toxicology studies, and there is a dearth of modern research on the nature of the sensitising complex and the changes it undergoes under physiological conditions. Although chloroplatinates are assumed to be the culprits, occupational exposure limits (OEL) are not measured based on amount of chloroplatinate; only recently has the Advanced Characterisation group at Johnson Matthey Technology Centre devised a method to quantify the Pt and chloride anionic species in air or wipe samples. The aim of this PhD is to synthesise single PGM compounds to specify which are sensitising (in vitro testing), to identify which components of physiological solutions (e.g. alveolar lining fluid) they interact with (computational chemistry and protein interactions), and to understand the processes that convert them into the biological haptan (EXAFS/XANES, thermodynamic/kinetic modelling).
The applicant will require a strong background in chemistry, either through a good chemistry degree or related fields. Because of the multidisciplinary nature of this research, experience in metal coordination chemistry, biochemistry, and computational modelling would be advantageous.
In the first instance, informal enquiries (accompanied by a CV) should be directed to: Prof. Jason Love and Prof. Carole Morrison, School of Chemistry, University of Edinburgh. Email: email@example.com; firstname.lastname@example.org
A PhD studentship as part of the NERC E4-DTP is available: “New approaches to copper production: arsenic capture and solventless extraction.”
For informal enquiries please contact Prof. Jason Love (email@example.com), Prof. Carole Morrison (firstname.lastname@example.org) or Prof. Bryne Ngwenya (email@example.com).
The deadline for applications is Thu Jan 06 2022 at 12:00.
Tuneable separation of gold by selective
precipitation using a simple and recyclable diamide
Luke M. M. Kinsman, Bryne T. Ngwenya, Carole A. Morrison & Jason B. Love
Nature Communications, 2021, DOI:10.1038/s41467-021-26563-7
ABSTRACT The efficient separation of metals from ores and secondary sources such as electronic waste is necessary to realising circularity in metal supply. Precipitation processes are increasingly popular and are reliant on designing and understanding chemical recognition to achieve selectivity. Here we show that a simple tertiary diamide precipitates gold selectively from aqueous acidic solutions, including from aqua regia solutions of electronic waste. The X-ray crystal structure of the precipitate displays an infinite chain of diamide cations interleaved with tetrachloridoaurate. Gold is released from the precipitate on contact with water, enabling ligand recycling. The diamide is highly selective, with its addition to 29 metals in 2 M HCl resulting in 70% gold uptake and minimal removal of other metals. At 6 M HCl, complete collection of gold, iron, tin, and platinum occurs, demonstrating that adaptable selective metal precipitation is controlled by just one variable. This discovery could be exploited in metal refining and recycling processes due to its tuneable selectivity under different leaching conditions, the avoidance of organic solvents inherent to biphasic extraction, and the straightforward recycling of the precipitant.
C-H Borylation Catalysis of Heteroaromatics by a Rhenium Boryl Polyhydride
Liam J. Donnelly, Teresa Faber, Carole A. Morrison, Gary S. Nichol, Stephen P. Thomas and Jason B. Love
ACS Catalysis, 2021, accepted
ABSTRACT: Transition metal complexes bearing metal-boron bonds are of particular relevance to catalytic C-H borylation reactions, with iridium polyboryl and polyhydrido-boryl complexes the current benchmark catalysts for these transformations. Herein, we demonstrate that polyhydride boryl phosphine rhenium complexes are accessible and catalyze the C-H borylation of heteroaromatic substrates. Reaction of [K(DME)(18-c-6)][ReH4(Bpin)(η2-HBpin)(κ2-H2Bpin)] 1 with 1,3-bis(diphenylphosphino)propane (dppp) produced [K(18-c-6)][ReH4(η2-HBpin)(dppp)] 2 through substitution of two equivalents of HBpin, and protonation of 2 formed the neutral complex [ReH6(Bpin)(dppp)] 3. Combined X-ray crystallographic and DFT studies show that 2 is best described as a s-borane complex, whereas 3 is a boryl complex. Significantly, the boryl complex 3 acted as a catalyst for the C(sp2)-H borylation of a variety of heteroarenes (14 examples including furan, thiophene, pyrrole and indole derivatives) and displayed similar reactivity to the iridium analogues.
Simple Amides and Amines for the Synergistic Recovery of Rhodium from Hydrochloric Acid by Solvent Extraction
Andrew Carrick, Euan Doidge, Alexander Bouch, Gary Nichol, Jane Patrick, Emma Schofield, Carole Morrison, Jason Love
Chem. Eur. J., 2021, DOI:10.1002/chem.202100630
A synergistic combination of a simple primary amine (LA) and a simple primary amide (L1) is shown to extract rhodium from hydrochloric acid. A range of experimental and computational techniques are used to elucidate the structures of two different complexes in the organic phase; the ion-pair [HLA]3[RhCl6] and the amide complex [HLA]2[RhCl5(L1)]. In the latter complex, the amide is tautomerized to its enol form and coordinated through the nitrogen atom.