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 chemoselective C–H bond activation reactions. Using DTC ligands with trimethoxysilyl-terminated tethers, the palladium­(II) units can be attached to the surface of core–shell, silica-coated Fe3O4 nanoparticles. Once tethered, these units form 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.配合物[PdI₂(Me₂dazdt)]可通过以Me₂dazdt（N,N′-二甲基全氢二氮杂环庚烷-2,3-二硫酮）与碘为试剂的100%原子经济性Pd(0)浸出反应，从钯粉中制备得到。该配合物是与（二）膦类配体发生配体交换反应的通用起始原料，可生成反式-[PdI₂(PPh₃)₂]与[PdI₂(dppe)]（其中dppe为1,2-双(二苯基膦基)乙烷）。进一步与二硫代氨基甲酸盐反应，可得到通式为[Pd(DTC)(L)ₙ]⁺的化合物（其中DTC为二硫代氨基甲酸酯；当L为PPh₃时n=2，当L为dppe时n=1），这类化合物对区域选择性与化学选择性C-H键活化反应具有极高的催化活性。采用带有三甲氧基硅基末端连接臂的DTC配体，可将Pd(II)活性单元固载于硅包覆Fe₃O₄核壳纳米颗粒的表面。固载完成后，这些活性单元即可构成基于回收钯的可循环准多相Pd(II)催化体系的催化活性组分，验证了所提出的循环模型策略。本研究为该循环过程的关键环节提供了支撑，包括高效且原子经济的回收工艺、配体取代反应的化学选择性验证、催化活性的实证，以及从回收金属中获取催化活性表面单元并实现固载的可行性。