From recovered palladium to molecular and nanoscale catalysts

[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 regio- and chemo-selective C-H bond activation reactions. Using DTC ligands with trimethoxysily-terminated tethers, the palladium(II) units can be attached to the surface of core-shell, silica-coated 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