Magnetic carbon-coated cobalt nanoparticles as a versatile platform for polymer-design, scavenging and catalysis

The application of magnetic nanobeads as semi-heterogeneous supports has gained considerable attention over the last century, allowing a facile recovery and sustainable recyclability of the immobilized reagents, scavengers, or catalysts. The first chapter of this thesis compares the influence of different monomers for the synthesis of microporous organic polymers and their resulting capability to encapsulate palladium nanoparticles (Figure 42). Starting with toluene-based polymers, the impact of the external cross-linker FDA was investigated. The highest surface area was achieved for polymer 4a-γ with 2.5 equivalents of the crosslinker. Incorporating palladium nanoparticles further demonstrated the beneficial effect of the high cross-linker content by means of the highest catalytic activity for the Pd-catalyst 5a-γ. Thus, high turnover frequencies of up to 3000 h-1 were achieved for the hydrogenation of alkenes, alkynes, and nitro arenes, whereby the magnetic core of the nanobeads ensured an easy and fast recyclability for at least six consecutive runs. Introducing hydroxyl groups into the MOP via 2,2′-biphenol as monomer reduced the metal leaching from the catalyst (5d) to a minimum, while maintaining a high catalytic activity and recyclability in the hydrogenation reaction. In the second chapter, a palladium-based nanocatalyst is described for the use in the Suzuki-Miyaura coupling with focus on mild reaction conditions with low temperatures up to 50 °C. An immobilized Nheterocyclic carbene palladium(II) complex enabled the efficient coupling of aryl iodides as well as aryl bromides with boronic acids for up to six cycles (Figure 43). The linking of this complex to polystyrenefunctionalized Co/C nanobeads facilitated the recycling protocol by simple magnetic decantation combined with an overall low metal leaching. Thus, palladium(II) NHC-functionalized catalyst Pd(II)@PS-NHC@Co/C 22 was considered to be worthwhile for further investigation in its application towards genetically-tagged small molecule libraries. Currently conducted in the working group of Dr. Brunschweiger at the TU Dortmund. The third chapter describes the immobilization of chiral copper(II)-aza-bis(oxazoline) complexes onto polystyrene-functionalized magnetic Co/C nanobeads via two common linking strategies. As model reaction, the asymmetric copper-catalyzed cyclopropanation of styrene 33 was chosen, revealing a distinct advantage of the directly linked catalyst 30c with a high ligand loading (Scheme 25). Low ligand loadings and the grafting to azide-functionalized nanoparticles 52 via ‘click-chemistry’ showed a decreased enantioselectivity and lack of recyclability. Applying catalyst 30c, six consecutive cyclopropanation cycles were performed with up to 63% yield of 35 and 76% ee for trans-35. The final chapter investigates MOPs immobilized on Co/C nanobeads as recyclable high capacity adsorbents for toxic heavy metal ions with special attention to lead and mercury. Again, different monomers were utilized for the synthesis of a broad variety of nanomaterials. Comparing these in the competitive extraction of mercury, lead, copper, and chromium ions revealed a high adsorption potential for all of these metal ions using 2,2’-biphenol@Co/C 71h as polymer (Figure 44). Further, this nanoscavenger showed an excellent selectivity towards mercury ions with an outstanding adsorption capacity up to 810 mg Hg2+ per gram of nanoparticles. The facile recycling procedure enabled an efficient decontamination of water polluted with lead, chromium, and copper ions with the aid of an external magnet for up to nine cycles. Adjusting the applied amount of nanoscavenger allowed either the selective extraction of mercury ions or the purification of the water from all metal ions