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21.
Pim R. Linnebank Stephan Falcão Ferreira Alexander M. Kluwer Prof. Dr. Joost N. H. Reek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(37):8214-8219
Regioselective catalytic transformations using supramolecular directing groups are increasingly popular as it allows for control over challenging reactions that may otherwise be impossible. In most examples the reactive group and the directing group are close to each other and/or the linker between the directing group is very rigid. Achieving control over the regioselectivity using a remote directing group with a flexible linker is significantly more challenging due to the large conformational freedom of such substrates. Herein, we report the redesign of a supramolecular Rh–bisphosphite hydroformylation catalyst containing a neutral carboxylate receptor (DIM pocket) with a larger distance between the phosphite metal binding moieties and the DIM pocket. For the first time regioselective conversion of internal and terminal alkenes containing a remote carboxylate directing group is demonstrated. For carboxylate substrates that possess an internal double bond at the Δ-9 position regioselectivity is observed. As such, the catalyst was used to hydroformylate natural monounsaturated fatty acids (MUFAs) in a regioselective fashion, forming of an excess of the 10-formyl product (10-formyl/9-formyl product ratio of 2.51), which is the first report of a regioselective hydroformylation reaction of such substrates. 相似文献
22.
Raoul Plessius Vera Deij Prof. Dr. Joost N. H. Reek Prof. Dr. Ir. Jarl Ivar van der Vlugt 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(58):13241-13248
Three Pt4L2L′2 heteroleptic rectangles ( 1 – 3 ), containing ditopic redox-active bis-pyridine functionalized perylene bisimide (PBI) ligands PBI-pyr2 ( L ) are reported. Co-ligand L′ is a dicarboxylate spacer of varying length, leading to modified overall size of the assemblies. 1H NMR spectroscopy reveals a trend in the splitting and upfield chemical shift of the PBI-hydrogens in the rectangles with respect to free PBI, most pronounced with the largest strut length ( 3 ) and least with the smallest strut length ( 1 ). This is attributed to increased rotational freedom of the PBI-pyr 2 ligand over its longitudinal axis (Npy-Npy), due to increased distance between the PBI-surfaces, which is corroborated by VT-NMR measurements and DFT calculations. The intramolecular motion entails desymmetrization of the two PBI-ligands, in line with cyclic voltammetry (CV) data. The first (overall two-electron) reduction event and re-oxidation for 1 display a subtle peak-to-peak splitting of 60 mV, whilst increased splitting of this event is observed for 2 and 3 . The binding of pyrene in 1 is probed to establish proof of concept of host-guest chemistry enabled by the two PBI-motifs. Fitting the binding curve obtained by 1H NMR titration with a 1:1 complex formation model led to a binding constant of 964±55 m −1. Pyrene binding is shown to directly influence the redox-chemistry of 1 , resulting in a cathodic and anodic shift of approximately 46 mV on the first and second reduction event, respectively. 相似文献
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25.
Dr. Nicole M. G. Franssen Dr. Bernd Ensing Maruti Hegde Prof. Dr. Theo J. Dingemans Ben Norder Prof. Dr. Stephen J. Picken Gert O. R. Alberda van Ekenstein Dr. Ernst R. H. van Eck Dr. Johannes A. A. W. Elemans Mark Vis Prof. Dr. Joost N. H. Reek Prof. Dr. Bas de Bruin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(35):11577-11589
The self‐assembly of poly(ethylidene acetate) (st‐PEA) into van der Waals‐stabilized liquid‐crystalline (LC) aggregates is reported. The LC behavior of these materials is unexpected, and unusual for flexible sp3‐carbon backbone polymers. Although the dense packing of polar ester functionalities along the carbon backbone of st‐PEA could perhaps be expected to lead directly to rigid‐rod behavior, molecular modeling reveals that individual st‐PEA chains are actually highly flexible and should not reveal rigid‐rod induced LC behavior. Nonetheless, st‐PEA clearly reveals LC behavior, both in solution and in the melt over a broad elevated temperature range. A combined set of experimental measurements, supported by MM/MD studies, suggests that the observed LC behavior is due to self‐aggregation of st‐PEA into higher‐order aggregates. According to MM/MD modeling st‐PEA single helices adopt a flexible helical structure with a preferred trans‐gauche syn‐syn‐anti‐anti orientation. Unexpectedly, similar modeling experiments suggest that three of these helices can self‐assemble into triple‐helical aggregates. Higher‐order assemblies were not observed in the MM/MD simulations, suggesting that the triple helix is the most stable aggregate configuration. DLS data confirmed the aggregation of st‐PEA into higher‐order structures, and suggest the formation of rod‐like particles. The dimensions derived from these light‐scattering experiments correspond with st‐PEA triple‐helix formation. Langmuir–Blodgett surface pressure–area isotherms also point to the formation of rod‐like st‐PEA aggregates with similar dimensions as st‐PEA triple helixes. Upon increasing the st‐PEA concentration, the viscosity of the polymer solution increases strongly, and at concentrations above 20 wt % st‐PEA forms an organogel. STM on this gel reveals the formation of helical aggregates on the graphite surface–solution interface with shapes and dimensions matching st‐PEA triple helices, in good agreement with the structures proposed by molecular modeling. X‐ray diffraction, WAXS, SAXS and solid state NMR spectroscopy studies suggest that st‐PEA triple helices are also present in the solid state, up to temperatures well above the melting point of st‐PEA. Formation of higher‐order aggregates explains the observed LC behavior of st‐PEA, emphasizing the importance of the “tertiary structure” of synthetic polymers on their material properties. 相似文献
26.
Xianwen Lou Sandra M. C. Schoenmakers Joost L. J. van Dongen Miguel Garcia-Iglesias Nicolás M. Casellas Marcos Fernández-Castaño Romera Rint P. Sijbesma E. W. Meijer Anja R. A. Palmans 《Journal of polymer science. Part A, Polymer chemistry》2021,59(12):1151-1161
A comprehensive understanding of the structure, self-assembly mechanism, and dynamics of one-dimensional supramolecular polymers in water is essential for their application as biomaterials. Although a plethora of techniques are available to study the first two properties, there is a paucity in possibilities to study dynamic exchange of monomers between supramolecular polymers in solution. We recently introduced hydrogen/deuterium exchange mass spectrometry (HDX-MS) to characterize the dynamic nature of synthetic supramolecular polymers with only a minimal perturbation of the chemical structure. To further expand the application of this powerful technique some essential experimental aspects have been reaffirmed and the technique has been applied to a diverse library of assemblies. HDX-MS is widely applicable if there are exchangeable hydrogen atoms protected from direct contact with the solvent and if the monomer concentration is sufficiently high to ensure the presence of supramolecular polymers during dilution. In addition, we demonstrate that the kinetic behavior as probed by HDX-MS is influenced by the internal order within the supramolecular polymers and by the self-assembly mechanism. 相似文献
27.
Valentinos Mouarrawis Eduard O. Bobylev Prof. Dr. Bas de Bruin Prof. Dr. Joost N. H. Reek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(32):8390-8397
Confinement of a catalyst can have a significant impact on catalytic performance and can lead to otherwise difficult to achieve catalyst properties. Herein, we report the design and synthesis of a novel caged catalyst system Co−G@Fe8(Zn−L ⋅ 1)6 , which is soluble in both polar and apolar solvents without the necessity of any post-functionalization. This is a rare example of a metal-coordination cage able to bind catalytically active porphyrins that is soluble in solvents spanning a wide variety of polarity. This system was used to investigate the combined effects of the solvent and the cage on the catalytic performance in the cobalt catalyzed cyclopropanation of styrene, which involves radical intermediates. Kinetic studies show that DMF has a protective influence on the catalyst, slowing down deactivation of both [Co(TPP)] and Co−G@Fe8(Zn−L ⋅ 1)6 , leading to higher TONs in this solvent. Moreover, DFT studies on the [Co(TPP)] catalyst show that the rate determining energy barrier of this radical-type transformation is not influenced by the coordination of DMF. As such, the increased TONs obtained experimentally stem from the stabilizing effect of DMF and are not due to an intrinsic higher activity caused by axial ligand binding to the cobalt center ([Co(TPP)(L)]) . Remarkably, encapsulation of Co−G led to a three times more active catalyst than [Co(TPP)] (TOFini) and a substantially increased TON compared to both [Co(TPP)] and free Co−G . The increased local concentration of the substrates in the hydrophobic cage compared to the bulk explains the observed higher catalytic activities. 相似文献
28.
Dr. Joost Steverlynck Dr. Ruzal Sitdikov Prof. Dr. Magnus Rueping 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(46):11751-11772
In the field of medicinal chemistry, the precise installation of a trideuteromethyl group is gaining ever-increasing attention. Site-selective incorporation of the deuterated “magic methyl” group can provide profound pharmacological benefits and can be considered an important tool for drug optimization and development. This review provides a structured overview, according to trideuteromethylation reagent, of currently established methods for site-selective trideuteromethylation of carbon atoms. In addition to CD3, the selective introduction of CD2H and CDH2 groups is also considered. For all methods, the corresponding mechanism and scope are discussed whenever reported. As such, this review can be a starting point for synthetic chemists to further advance trideuteromethylation methodologies. At the same time, this review aims to be a guide for medicinal chemists, offering them the available C−CD3 formation strategies for the preparation of new or modified drugs. 相似文献
29.
Didjay F. Bruggeman Tijmen M. A. Bakker Dr. Simon Mathew Prof. Dr. Joost N. H. Reek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(1):218-221
This work reports a dye-sensitized photoelectrochemical cell (DSPEC) that couples redox-mediated light-driven oxidative organic transformations to reductive hydrogen (H2) formation. The DSPEC photoanode consists of a mesoporous anatase TiO2 film on FTO (fluorine-doped tin oxide), sensitized with the thienopyrroledione-based dye AP11 , while H2 was formed at a FTO-Pt cathode. Irradiation of the dye-sensitized photoanode transforms 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) to the oxidized TEMPO (TEMPO+), which acts as a chemical oxidant for the conversion of benzyl alcohol. The TEMPO0/+ couple, previously used as redox mediator in DSSC, mediates efficient electron transfer from the organic substrate to the photo-oxidized dye. A DSPEC photoreactor was designed that allows in situ monitoring the reaction progress by infrared spectroscopy and gas chromatography. Sustained light-driven oxidation of benzyl alcohol to benzaldehyde within the DSPEC photoreactor, using of TEMPO as mediator, demonstrated the efficiency of the device, with a photocurrent of 0.4 mA cm−2, approaching quantitative Faradaic efficiency and exhibiting excellent device stability. 相似文献
30.
Xianwen Lou Christianus M. A. Leenders Arthur H. A. M. van Onzen Ralf A. A. Bovee Joost L. J. van Dongen Jef A. J. M. Vekemans E. W. Meijer 《Journal of the American Society for Mass Spectrometry》2014,25(2):297-300
Tetrahydrofuran (THF) is one of the most frequently used solvents in the MALDI TOF MS analysis of synthetic compounds. However, it should be used with caution because a trace amount of 4-hydroxybutanal (HBA) might be generated and accumulated in THF during storage. Since only a tiny amount of analytes is required in MALDI MS measurements, a trace amount of HBA might have a significant effect on the MS results. It was found that HBA will quickly react with primary and secondary amino compounds, leading to false results about the sample composition with an extra series of ions with additional mass of 70 Da in between. The formation of HBA can be inhibited by butylated hydroxytoluene (BHT) antioxidant. Therefore, when THF is required as the solvent for sample preparation, it is strongly recommended to use a BHT-stabilized one, at least for the analysis of compounds with amino groups. Figure
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