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.
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.
The recycling of metals such as gold and copper from discarded end-of-life electronic waste (e-waste or WEEE) is an important aspect to the development of environmentally benign manufacturing processes that exhibit circularity in materials flow. Global e-waste production is increasing at a 3-5 % rate, so it is concerning that only 30 % is recycled using regulated processes. We present here a new hydrometallurgical route for the technically feasible recycling of copper and gold from waste printed circuit boards (WPCBs) of mobile phones. This process comprises the liberation of the metallic fractions from downsized WPCBs, a two-stage acid leaching process to provide a bulk separation of copper and gold from the other metals present, and subsequent purification of the copper and gold-containing solutions by solvent extraction using highly selective phenolic oxime and amide extractants, respectively. Complete dissolution of the base metals was seen using 3 M nitric acid at 30 °C and the selective separation of copper from this leach liquor was achieved by solvent extraction using ACORGA M5640 dissolved in kerosene. The residues from base-metal leaching were treated with a mixture of 3 M sulfuric acid and 3 M sodium bromide at 70 °C, resulting in greater than 95 % gold dissolution. The selective separation of gold from this precious metal leachate was achieved by solvent extraction using 0.1 M primary amide extractant dissolved in toluene. This process delivers complete copper and gold recycling from WPCBs under relatively benign laboratory conditions and represents a proof of concept for liberating valuable and critical metals back into active service from end-of-life electronic devices.
A new constrained-cavity [1+1] Schiff-base dipyrrin macrocycle comprising an N4 donor-pocket has been synthesised by spontaneous oxidation and in-situ crystallisation. Access to Fe(II) and Zn(II) complexes is achieved by salt elimination reactions of the lithium salt. All compounds have been characterised by NMR and UV-vis spectroscopy, X-ray crystallography, and DFT analysis.
Abstract: Titanium dioxide (TiO2) is one of the most promising photocatalytic materials, but its practical applications are always limited since it could be only excited in the UV and has low photocatalytic efficiency due to its wide band gap and fast recombination rate. To overcome these problems, transition metals have been used as dopants to improve the photocatalytic performance of titanium dioxide. However, doping by hydrothermal, sol-gel or other synthetic pathways in the catalyst synthesis in previous investigations which are difficult to scale-up for mass production. Herein, ilmenite (FeTiO3), the most abundant titanium mineral was used as the raw material to produce iron-doped titanium oxide nanorods by an economic acid treatment approach. Compared with commercial titanium oxide nanomaterials, the photocatalytic performance for Rhodamine B (RHB) degradation of as-prepared materials were significantly improved and could be activated by visible light irradiation. The results from characterization also shows the band gap and recombination rate are modified by the iron dopant. This work provides a possible method which can significantly reduce the cost for producing iron doped TiO2 in high yield for photocatalytic application
Profs. Jason Love, Carole Morrison, and Bryne Ngwenya with PhD student Luke Kinsman and UG students Rosa Crevecoeur and Amrita Singh-Morgan have won the 2020 Anders Gustav Ekeberg Prize for their paper on tantalum recycling https://www.mdpi.com/2075-4701/10/3/346.
The rhenium complex, [K(DME)(18-c-6)][ReH4(Bpin)(h2-HBpin)(k2-H2Bpin)] 1, comprising hydride and boron ligands only, has been synthesized by exhaustive deoxygenation of the commercially available perrhenate anion (ReO4−) with pinacol borane (HBpin). The structure of 1 was analysed by X-ray crystallography, NMR spectroscopy, and DFT calculations. While no hydrides were located in the X-ray crystal structure, it revealed a trigonal arrangement of pinacol boron ligands. Variable-temperature NMR spectroscopy supported the presence of seven hydride ligands but further insight was hindered by the fluxionality of both hydride and boron ligands at low temperature. Further evaluation of the structure by Ab Initio Random Structure Searching (AIRSS) identified the presence of hydride, boryl, s-borane, and dihydroborate ligands. This complex, either isolated or prepared in situ, is a catalyst for the 1,4-hydroboration of N-heteroaromatic substrates under simple operating procedures. It also acts as a reagent for the stoichiometric C-H borylation of toluene, displaying high meta regioselectivity in the borylated products. Reaction of 1 with 9-BBN resulted in HBpin substitution to form the new anionic tetra(dihydroborate) complex [K(DME)(18-c-6)][Re(k2-H-9-BBN)4] 4 for which the hydride positions were clearly identified by X-ray crystallography. The method used to generate these isolable yet reactive boron-hydride complexes is direct and straightforward and has potential utility for the exploitation of other metal oxo compounds in operationally simple catalytic reactions.