Overview of research in critical and precious metal recovery using biosorption, application to real-life wastes and uses of the metal-loaded materials.

A series of copper­(I) complexes bearing electron-deficient β-diketiminate ligands have been prepared. The study includes [{{ArNC­(CR3)}2CH}­Cu­(η2-toluene)n] (Ar = Mes, R = F, n = 0.5, [1 2 ·tol]; Ar = C6F5, R = Me, n = 1, [2·tol]; Ar = 2,6-Cl2C6H3, R = H, n = 0.5, [3 2 ·tol]). Reactions of [1–3 n ·tol] with boranes, alanes, a zinc hydride, a magnesium hydride, and a calcium hydride generate the corresponding σ complexes ([1–3·B], [3·B′], [3·Al], [3·Al′], [1–3·Zn], [1·Mg], and [1·Ca]). These species all form reversibly, being in equilibrium with the arene solvates in solution. With the exception of the calcium complex, the complexes have all been characterized by single-crystal X-ray diffraction studies. In solution, the σ-hydride of the aluminum, zinc, magnesium, and calcium derivatives resonates between −0.12 and −1.77 ppm (C6D6 or toluene-d 8, 193–298 K). For the σ-borane complexes, the hydrides are observed as a single resonance between 2 and 3.5 ppm (C6D6, 298 K) and bridging and terminal hydrides rapidly exchange on the NMR time scale even at 193 K. Quantification of the solution dynamics by van’t Hoff analysis yields expectedly small values of ΔH° and negative values of ΔS° consistent with weak binding and a reversible process that does not involve aggregation of the copper species. The donor–acceptor complexes can be rationalized in terms of the Dewar–Chatt–Duncanson model. Density functional theory calculations show that the donation of σ-M–H (or E–H) electrons into the 4s-based orbital (LUMO or LUMO+1) of the copper fragment is accompanied by weak back-donation from a d xz -based orbital (HOMO or HOMO–1) into the σ*-M–H (or E–H) orbital.

A series of heterobimetallic complexes containing three-center, two-electron Au-H-Cu bonds have been prepared from addition of a parent gold hydride to a bent d copper(I) fragment. These highly unusual heterobimetallic complexes represent a missing link in the widely investigated series of neutral and cationic coinage metal hydride complexes containing Cu-H-Cu and M-H-M moieties (M=Cu, Ag). The well-defined heterobimetallic hydride complexes act as precatalysts for the conversion of CO into HCO Bpin with HBpin as the reductant. The selectivity of the heterobimetallic complexes for the catalytic production of a formate equivalent surpasses that of the parent monomeric Group 11 complexes.

The preparation and structural characterisation of three new heterobimetallic hydride complexes containing 3-centre,2-electron W-H-Cu bonds is reported. These complexes have been characterised by single crystal X-ray crystallography and multinuclear NMR spectroscopy. The bonding in these complexes has been analysed by DFT calculations.

As eries of heterobimetallic complexes containing three-center,two-electron Au À H À Cu bonds have been prepared from addition of ap arent gold hydride to ab ent d 10 copper(I) fragment. These highly unusual heterobimetallic complexes represent am issing link in the widely investigated series of neutral and cationic coinage metal hydride complexes containing Cu À H À Cu and M À H À M + moieties (M = Cu, Ag). The well-defined heterobimetallic hydride complexes act as precatalysts for the conversion of CO 2 into HCO 2 Bpin with HBpin as the reductant. The selectivity of the heterobimetallic complexes for the catalytic production of aformate equivalent surpasses that of the parent monomeric Group 11 complexes.

Review: 217 refs.