From Recovered Palladium to Molecular and Nanoscale Catalysts

Abstract

PdI2(Me2dazdt)] is obtained from palladium powder via a 100% atom economical Pd(0) leaching reaction using Me2dazdt (N,N'-dimethyl-perhydrodiazepine-2,3-dithione) and iodine. This complex is a versatile starting point for ligand exchange reactions with (di)phosphines, yielding trans-[PdI2(PPh3)2] and [PdI2(dppe)] (dppe = 1,2-bis(diphenylphosphino)ethane). Further reaction with dithiocarbamates provides compounds of the form [Pd(DTC)(L)n]+ (DTC = dithiocarbamate; L = PPh3, n = 2; L = dppe, n = 1), which are highly active catalysts for regioand chemo-selective C-H bond activation reactions. Using DTC ligands with trimethoxysilyterminated tethers, the palladium(II) units can be attached to the surface of core-shell, silicacoated Fe3O4 nanoparticles. Once tethered, these units formed the catalytically-active component of a recyclable, quasi-heterogeneous, Pd(II)-based catalytic system based on recovered palladium, illustrating the proposed circular model strategy. These investigations contribute to key steps in this process, such as efficient, atom-economical recovery, chemoselectivity of ligand substitution reactions, demonstration of catalytic activity and the potential for immobilization of catalytic surface units derived from recovered metal.

Homogeneous Gold Catalysis Using Complexes Recovered from Waste Electronic Equipment

“…Direct application of compounds 1a and 2a would enable their valorization and thus create a new end-of-life application for gold-containing waste that is currently sent to landfill as well as provide additional economic incentive for the implementation of Deplano’s recovery process (Scheme a). The present study seeks to achieve exactly this by demonstrating that the recovery products [AuI 2 (Me 2 dazdt)]­I 3 ( 1a ) and [AuBr 2 (Me 2 dazdt)]­IBr 2 ( 2a ) can be used as effective homogeneous catalysts for a range of catalytic reactions, hence connecting an existing mild and effective recovery process with a major application of this metal (Scheme b). − Inspired by the implementation of circular economy models, we have recently illustrated this approach in our own study through the use of palladium complexes recovered from spent three-way catalytic converters (TWCs) in catalysis. − The complex [Pd­(Me 2 dazdt) 2 ]­I 6 is obtained as the palladium recovery product from spent TWCs through the action of solvometallurgical leaching using Me 2 dazdt·2I 2 . This molecular recovery product was subsequently used as a precursor for a nanostructured Pd-TiO 2 photocatalyst used to produce hydrogen through the photoreforming of alcohols .…”

From Waste to Green Applications: The Use of Recovered Gold and Palladium in Catalysis

“…Despite the efficacy of the process for recovering palladium, the poor atom-economy of Lawesson's reagent used in the synthesis of Me 2 dazdt, as well as the lack of commercial availability of the dithiooxamide reagent, hinders the industrial viability of this process. As a result, the same group has explored, with expert research groups in the field, direct valorisation of the recovery product, both as a homo-and heterogeneous catalyst [105][106][107]. Finding a direct use for the palladium recovery product [Pd(Me 2 dazdt) 2 ]I 6 in this way helps improve the economic viability of the process and provides synthetic chemists with catalysts derived from a secondary source of palladium.…”

“…Similar recovery yields were obtained as for Me 2 dazdt•2I 2 (albeit under slightly more forcing conditions), which represents a considerable reduction in material consumption. In addition, [PdI 2 (Me 2 dazdt)] could be further functionalised through ligand exchange with phosphines to yield additional catalytically useful products, while recovering the Me 2 dazdt ligand (Figure 13) [107].…”

“…consumption. In addition, [PdI2(Me2dazdt)] could be further functionalised through ligand exchange with phosphines to yield additional catalytically useful products, while recovering the Me2dazdt ligand (Figure 13) [107]. To date, these examples of palladium catalysts have been recovered either from acidic leach solutions, or directly from the solid waste using non-acidic oxidative dissolution.…”

From Electronic Waste to Suzuki−Miyaura Cross‐Coupling Reaction in Water: Direct Valuation of Recycled Palladium in Catalysis

“…[21] The trash-to-resource approach has been proposed on model three-way catalysts prepared at the laboratory using Pd only: [22] Leaching of metallic Pd using organic reagents enables the formation of a Pd(II) complex, [22] which can be either decomposed into nanoparticles to obtain a heterogeneous catalyst, [23] or subject of ligand exchange to obtain molecular catalysts. [24,25] Harvesting Pd dispersed in the environment appears as an appealing complementary solution, thanks to phytoextraction, [26] considering the possible use of 'green' Pd recovered from plants directly into catalysed reactions. [27,28] But latter proof of concept was based on rhizofiltration of a synthetic solution containing solely Pd, [27] and levels of Pd accumulation in plants after phytoextraction from soil are below that required for active Pd-catalysts.…”