@article{59510, abstract = {{The use of organo-catalysis in continuous-flow reactor systems is gaining attention in medicinal chemistry due to its cost-effectiveness and reduced chemical waste. In this study, bioactive curcumin (CUM) derivatives were synthesized in a continuously operated microfluidic reactor (MFR), using piperidine-based polymeric networks as catalysts. Piperidine methacrylate and piperidine acrylate were synthesized and subsequently copolymerized with complementary monomers (MMA or DMAA) and crosslinkers (EGDMA or MBAM) via photopolymerization, yielding different polymeric networks. Initially, batch reactions were optimized for the organo-catalytic Knoevenagel condensation between CUM and 4-nitrobenzaldehyde, under various conditions, in the presence of polymer networks. Conversion was assessed using offline 1H NMR spectroscopy, revealing an increase in conversion with enhanced swelling properties of the polymer networks, which facilitated greater accessibility of catalytic sites. In continuous-flow MFR experiments, optimized polymer gel dots exhibited superior catalytic performance, achieving a conversion of up to 72%, compared to other compositions. This improvement was attributed to the enhanced swelling in the reaction mixture (DMSO/methanol, 7:3 v/v) at 40 °C over 72 h. Furthermore, the MFR system enabled the efficient synthesis of a series of CUM derivatives, demonstrating significantly higher conversion rates than traditional batch reactions. Notably, while batch reactions required 90% catalyst loading in the gel, the MFR system achieved a comparable or superior performance with only 50% catalyst, resulting in a higher turnover number. These findings underscore the advantages of continuous-flow organo-catalysis in enhancing catalytic efficiency and sustainability in organic synthesis.}}, author = {{Killi, Naresh and Rumpke, Katja and Kuckling, Dirk}}, issn = {{2310-2861}}, journal = {{Gels}}, keywords = {{flow chemistry, heterogeneous catalysis, sustainable synthesis, organo-catalysis, polymeric gel dots}}, number = {{4}}, publisher = {{MDPI AG}}, title = {{{Synthesis of Curcumin Derivatives via Knoevenagel Reaction Within a Continuously Driven Microfluidic Reactor Using Polymeric Networks Containing Piperidine as a Catalyst}}}, doi = {{10.3390/gels11040278}}, volume = {{11}}, year = {{2025}}, } @article{63970, abstract = {{Abstract Recent advances in solid-state nuclear magnetic resonance (NMR) spectroscopy, combined with dynamic nuclear polarization (DNP), quantum chemical DFT calculations, and gas-phase NMR spectroscopy investigating the structure and reactivity of heterogeneous catalysts are reviewed. The investigated catalysts range from classical mononuclear catalysts, like immobilized derivates of Wilkinson’s catalysts over binuclear catalysts such as the dirhodium paddlewheel catalyst to catalytic nanoparticles, employing various support materials, such as mesoporous silica gels, coordination polymers, and biomaterials such as cellulose.}}, author = {{Haro Mares, Nadia and Logrado, Millena and Kergassner, Jan and Zhang, Bingyu and Gutmann, Torsten and Buntkowsky, Gerd}}, issn = {{1867-3880}}, journal = {{ChemCatChem}}, keywords = {{solid-state nmr, heterogeneous catalysis, dynamic nuclear polarization, Nanocatalysis, Surface-reactions}}, pages = {{e202401159}}, publisher = {{John Wiley & Sons, Ltd}}, title = {{{Solid-State NMR of Heterogeneous Catalysts}}}, doi = {{10.1002/cctc.202401159}}, year = {{2024}}, } @article{35645, abstract = {{Poly(quinuclidin-3-yl methacrylate-co-divinylbenzene) microparticles having porous as well as nonporous morphology and varying contents of quinuclidine functionality were synthesized by distillation–precipitation polymerization. Further, the synthesized microparticles were explored to catalyze the Baylis–Hillman reaction between 4-nitrobenzaldehyde and acrylonitrile. Porous and nonporous microparticles functionalized with a catalytic moiety with a loading of 70% (labeled as P70 and NP70) were employed to optimize reaction parameters such as water content, solvent, and temperature for the Baylis–Hillman reaction between 4-nitrobenzaldehyde and acrylonitrile. Using optimal conditions, the catalytic efficiency of porous and nonporous microparticles at different feed compositions was determined. Porous microparticles containing 70% of quinuclidine (P70) displayed 100% conversion within 16 h at 50 °C, while nonporous microparticles containing 70% of quinuclidine (NP70) displayed a relatively less catalytic conversion, which is attributed to their lower surface area. Furthermore, the catalytic activity of porous microparticles containing 70% of quinuclidine (P70) for the Baylis–Hillman reaction involving a variety of aryl aldehyde derivatives was determined, where the microparticles displayed impressive catalytic efficiency. In addition, the reusability of the microparticles functionalized with a catalytic moiety was evaluated for five cycles of catalytic reaction.}}, author = {{Kumar, Amit and Kuckling, Dirk and Nebhani, Leena}}, issn = {{2637-6105}}, journal = {{ACS Applied Polymer Materials}}, keywords = {{distillation−precipitation polymerization, porous microparticles, heterogeneous catalysis Baylis−Hillman reaction, reusable catalyst}}, number = {{12}}, pages = {{8996--9005}}, publisher = {{American Chemical Society (ACS)}}, title = {{{Quinuclidine-Immobilized Porous Polymeric Microparticles as a Compelling Catalyst for the Baylis–Hillman Reaction}}}, doi = {{10.1021/acsapm.2c01330}}, volume = {{4}}, year = {{2022}}, } @article{63960, abstract = {{Recent advances in solid-state nuclear magnetic resonance (NMR) spectroscopy and dynamic nuclear polarization (DNP) of nanostructured materials are reviewed. A first group of materials is based on crystalline nanocellulose (CNC) or microcrystalline cellulose (MCC), which are used as carrier materials for dye molecules, catalysts or in combination with heterocyclic molecules as ion conducting membranes. These materials have widespread applications in sensorics, optics, catalysis or fuel cell research. A second group are metal oxides such as V-Mo-W oxides, which are of enormous importance in the manufacturing process of basic chemicals. The third group are catalytically active nanocrystalline metal nanoparticles, coated with protectants or embedded in polymers. The last group includes of lead-free perovskite materials, which are employed as environmentally benign substitution materials for conventional lead-based electronics materials. These materials are discussed in terms of their application and physico-chemical characterization by solid-state NMR techniques, combined with gas-phase NMR and quantum-chemical modelling on the density functional theory (DFT) level. The application of multinuclear 1H, 2H, 13C, 15N and 23Na solid state NMR techniques under static or MAS conditions for the characterization of these materials, their surfaces and processes on their surfaces is discussed. Moreover, the analytic power of the combination of these techniques with DNP for the identification of low-concentrated carbon and nitrogen containing surface species in natural abundance is reviewed. Finally, approaches for sensitivity enhancement by DNP of quadrupolar nuclei such as 17O and 51V are presented that enable the identification of catalytic sites in metal oxide catalysts.}}, author = {{Gutmann, Torsten and Groszewicz, Pedro B. and Buntkowsky, Gerd}}, journal = {{Annual Reports on NMR Spectroscopy}}, keywords = {{solid-state nmr, heterogeneous catalysis, dynamic nuclear polarization, Ferroelectrics, Nanocatalysis, Surface reactions}}, pages = {{1–82}}, title = {{{Solid-state NMR of nanocrystals}}}, doi = {{10.1016/bs.arnmr.2018.12.001}}, volume = {{97}}, year = {{2019}}, } @article{63956, abstract = {{The synthesis of novel robust and stable iridium-based immobilized catalysts on silica-polymer hybrid materials (Si-PB-Ir) is described. These catalysts are characterized by a combination of 1D P-31 CP-MAS and 2D P-31-H-1 HETCOR and J-resolved multinuclear solid state NMR experiments. Different binding situations such as singly and multiply coordinated phosphines are identified. Density functional theory (DFT) calculations are performed to corroborate the interpretation of the experimental NMR data, in order to propose a structural model of the heterogenized catalysts. Finally, the catalytic activity of the Si-PB-Ir catalysts is investigated for the hydrogenation of styrene employing para-enriched hydrogen gas.}}, author = {{Gutmann, Torsten and Alkhagani, S. and Rothermel, N. and Limbach, H. H. and Breitzke, H. and Buntkowsky, G.}}, issn = {{0942-9352}}, journal = {{Zeitschrift Fur Physikalische Chemie-International Journal of Research in Physical Chemistry & Chemical Physics}}, keywords = {{Chemistry, dynamic nuclear-polarization, solid-state nmr, DFT, heterogeneous catalysis, hydrido complexes, hydrogenation, immobilized catalyst, inorganic hybrid, iridium, materials, mesoporous, molecular-orbital methods, PHIP, phosphine complexes, reusable catalysts, silica, solid-state-NMR, wilkinsons catalyst}}, number = {{3}}, pages = {{653–669}}, title = {{{P-31-Solid-State NMR Characterization and Catalytic Hydrogenation Tests of Novel heterogenized Iridium-Catalysts}}}, doi = {{10.1515/zpch-2016-0837}}, volume = {{231}}, year = {{2017}}, } @article{64047, abstract = {{A novel strategy for the immobilization of Wilkinson’s catalyst on silica nanoparticles is presented, employing pyridyl linkers as anchoring groups. The coordination binding of the catalyst to the pyridyl linker via ligand exchange of the trans-phosphine group is verified by 1 D and 2 D solid-state NMR spectroscopy. Catalytic activities are monitored by GC employing the hydrogenation of styrene as model reaction, and the leaching properties as well as the robustness of the catalyst are investigated. The resulting immobilized catalyst shows high catalytic activity, which is within a factor of three comparable to the homogeneous catalyst, and excellent stability in leaching tests. Finally, it is efficient to produce hyperpolarization in solution by employing parahydrogen-enriched hydrogen gas for hydrogenation.}}, author = {{Srour, Mohamad and Hadjiali, Sara and Sauer, Grit and Brunnengräber, Kai and Breitzke, Hergen and Xu, Yeping and Weidler, Heiko and Limbach, Hans-Heinrich and Gutmann, Torsten and Buntkowsky, Gerd}}, journal = {{ChemCatChem}}, keywords = {{heterogeneous catalysis, hydrogenation, immobilization, phosphane ligands, rhodium}}, number = {{21}}, pages = {{3409–3416}}, title = {{{Synthesis and Solid-State NMR Characterization of a Robust, Pyridyl-Based Immobilized Wilkinson’s Type Catalyst with High Catalytic Performance}}}, doi = {{10.1002/cctc.201600882}}, volume = {{8}}, year = {{2016}}, } @article{63963, abstract = {{A novel heterogeneous dirhodium catalyst has been synthesized. This stable catalyst is constructed from dirhodium acetate dimer (Rh2(OAc)4) units, which are covalently linked to amine- and carboxyl-bifunctionalized mesoporous silica (SBA-15NH2COOH). It shows good efficiency in catalyzing the cyclopropanation reaction of styrene and ethyl diazoacetate (EDA) forming cis- and trans-1-ethoxycarbonyl-2-phenylcyclopropane. To characterize the structure of this catalyst and to confirm the successful immobilization, heteronuclear solid-state NMR experiments have been performed. The high application potential of dynamic nuclear polarization (DNP) NMR for the analysis of binding sites in this novel catalyst is demonstrated. Signal-enhanced 13C CP MAS and 15N CP MAS techniques have been employed to detect different carboxyl and amine binding sites in natural abundance on a fast time scale. The interpretation of the experimental chemical shift values for different binding sites has been corroborated by quantum chemical calculations on dirhodium model complexes.}}, author = {{Gutmann, Torsten and Liu, Jiquan and Rothermel, Niels and Xu, Yeping and Jaumann, Eva and Werner, Mayke and Breitzke, Hergen and Sigurdsson, Snorri T. and Buntkowsky, Gerd}}, journal = {{Chemistry A European Journal}}, keywords = {{heterogeneous catalysis, immobilized catalyst, dynamic nuclear polarization, hyperpolarization, NMR spectroscopy}}, number = {{9}}, pages = {{3798–3805}}, publisher = {{WILEY-VCH Verlag}}, title = {{{Natural Abundance 15N NMR by Dynamic Nuclear Polarization: Fast Analysis of Binding Sites of a Novel Amine-Carboxyl-Linked Immobilized Dirhodium Catalyst}}}, doi = {{10.1002/chem.201405043}}, volume = {{21}}, year = {{2015}}, }