A representative member of the amino‐imidazolin‐2‐imine ligand class (HAmIm) is studied as a strong monoanionic N , N ′‐chelating ligand in zinc(I) and zinc(II) complexes. The Brønsted‐basic zinc precursors ZnH 2 , ZnEt 2 , and [Zn 2 ( η 5 ‐C 5 Me 5 ) 2 ] undergo in situ deprotonation with HAmIm, accompanied by the formation of only volatile side products (H 2 , C 2 H 6 , C 5 Me 5 H). Under these mild conditions, both Zn(II) complexes [(AmIm)ZnH] 2 and [(AmIm)ZnEt], as well as the more sensitive Zn(I) complexes [( η 5 ‐C 5 Me 5 )Zn 2 (AmIm)] and [Zn 2 (AmIm) 2 ] with a covalent ZnZn bond, are obtained in high purity. In comparison to related β‐diketimine ligands (HNacNac), the amino‐imidazolin‐2‐imine (HAmIm) proves to be more controllable in its reactivity toward zinc precursors.

Late transition metal hydroxides are important intermediates in many catalytic processes. In [Ni,Fe] carbon monoxide dehydrogenase enzymes (CODHs), which catalyze the reversible CO/CO2 interconversion, CO insertion in the Ni-(μ-OH) bond of a Ni/Fe-bridging hydroxide is the proposed C-O bond-forming step during CO oxidation. Here, we report that CO reacts with the dinickel(II) complex LNi2(μ-OH) (L3- is a pyrazolato-centered ligand with two {N3} compartments), finally leading to HLNiII(CO); this is coupled to the formation of CO2 and Ni(CO)4, which is the driving force of the overall reaction. Mechanistic details have been investigated by 13CO labeling experiments and DFT calculations, and the product derivative HLNiII(CNBn) has been crystallographically characterized. The findings demonstrate that a nickel(II)-bound μ-OH can serve as a nucleophile toward CO and promote its oxidation to CO2, which is suggested to proceed via a metal-bridging O-protonated carbonite intermediate, emulating a key step of [Ni,Fe]-CODH reactivity. For CO2 release, in the present system, one of the nickel ions serves as a terminal electron sink and the corresponding ligand {N3} site of L3- as a proton acceptor.

We investigate cross-correlation between 11B quadrupole and 11B-19F dipole-dipole coupling in two BODIPY compounds and one bis(benzoxazol)methanide in partially oriented polystyrene (PS) samples. Especially for the bis(benzoxazol)methanide, the transitions for which the two interactions interfere con- or destructively clearly show distinct linewidths.

Starting from the six-coordinate tetracarbene iron(II) bis(acetonitrile) complexes, a series of structurally characterized iron(II) thiolato complexes [(MTC)FeII(SR)(NCMe)]OTf (R=tBu, Ada) was synthesized based on the equatorial macrocyclic tetracarbene (MTC) ligands 18HL (3,9,14,20-tetraaza-1,6,12,17-tetraazoniapenta-cyclohex-acosane-1(23),4,6(26),10,12(25),15,17(24),21-octaene) and its octamethylated derivative 18MeL. Those thiolato complexes can be viewed as bioinspired organometallic analogues of the iron(II) state of heme enzymes with axial cysteine coordination like cytochrome P450. Depending on the equatorial and axial ligands, the spin states of the complexes can change from low-spin (S=0) to intermediate-spin (S=1), but the strong donation by the MTC prevents the formation of any high-spin species. The electronic structure was analyzed using 57Fe M & ouml;ssbauer spectroscopy and magnetic susceptibility measurements. In addition, both axial ligands - acetonitrile and the thiolate - were found to be labile, leading to scrambling in solution as observed via NMR spectroscopy and ESI-MS. A temperature-dependent equilibrium was found for all complexes due to dissociation of the axial MeCN forming a 5-coordinate species in solution. This 5-coordinate species is significantly preferred for the 18MeL being in line with the higher donating ability of the equatorial ligand and thus the weakening of the axial ligand bonds, in line with cyclic voltammetry data.

The present work describes the grafting of a polymer-metal chelate (PMC) from mesoporous silica (SBA-15) via the Surface Initiated-Atom Transfer Radical Polymerization (SI-ATRP). SBA-15 was silylated by 2-bromo-2-methyl-N-(3-(trimethoxysilyl)propanamide (BTPAm) to give the surface-anchored ATRP initiator. The monomer, N-(4-(5-(pyridin-2-yl)-1,3,4-oxadiazol-2-yl)phenyl)acrylamide (POPA), was polymerized from the SBA-15 surface via the ATRP approach to give poly(POPA)-g-SBA-15. The grafted chelating polymer ligand (CPL) was treated with an ethanolic solution of PdCl2 to afford the SBA-15 grafted PMC, poly(POPA)-g-SBA-15-Pd(II). The grafted PMC was characterized by FT-IR, CP/MAS 13C NMR, thermo-gravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) analysis. X‐Ray photoelectron spectroscopy (XPS) corroborated that the major palladium species have the (+2) oxidation state. The catalytic activity of the grafted PMC was examined in the Heck reaction between haloarenes and olefins after establishing the optimal reaction conditions. Interestingly, chloroarenes exhibited enhanced activities than bromoarenes. Their activity was comparable to iodoarenes. The excellent recyclability of the catalyst was shown by negligible deactivation over six runs.

The present work describes the grafting of polymer-metal chelates (PMC) from Fe3O4@SBA-15 via the Surface Initiated-Atom Transfer Radical Polymerization (SI-ATRP) method. Fe3O4@SBA-15 were silylated by 2-bromo-2-methyl-N-(3-(trimethoxysilyl)propanamide (BTPAm) to give the surface-anchored ATRP initiator. Acrylamide (AAm) was polymerized from the Fe3O4@SBA-15 surface via the ATRP approach and trans-amidated with ethylenediamine to give poly(N-2-aminoethylacrylamide) grafted magnetic mesoporous silica, Fe3O4@SBA-g-PAE-AAm. The grafted chelating polymer ligand (CPL) was treated with an acetonitrile solution of Cu(OAc)2 to afford the Fe3O4@SBA-g-PAE-AAm-Cu(II). The grafted PMC was characterized by FT-IR, 13C CP/MAS NMR, thermo-gravimetric analysis (TGA), and Brunauer-Emmett-Teller (BET) analysis. The oxidation state of copper (+2) was confirmed using X-ray photoelectron spectroscopy (XPS). The catalytic activity of the grafted PMC was examined in the C-O bond formation via the Ullmann-type O-arylation reaction between haloarenes and phenols after establishing the optimal reaction conditions. The excellent recyclability of the catalyst was shown by small deactivation over seven runs.

Abstract Nuclear magnetic resonance (NMR) is fundamental in the natural sciences, from chemical analysis and structural biology, to medicine and physics. Despite its enormous achievements, one of its most severe limitations is the low sensitivity, which arises from the small population difference of nuclear spin states. Methods such as dissolution dynamic nuclear polarization and parahydrogen induced hyperpolarization can enhance the NMR signal by several orders of magnitude, however, their intrinsic limitations render multidimensional hyperpolarized liquid-state NMR a challenge. Here, we report an instrumental design for 9.4 Tesla liquid-state dynamic nuclear polarization that enabled enhanced high-resolution NMR spectra in one and two-dimensions for small molecules, including drugs and metabolites. Achieved enhancements of up to two orders of magnitude translate to signal acquisition gains up to a factor of 10,000. We show that hyperpolarization can be transferred between nuclei, allowing DNP-enhanced two-dimensional 13C–13C correlation experiments at 13C natural abundance. The enhanced sensitivity opens up perspectives for structural determination of natural products or characterization of drugs, available in small quantities. The results provide a starting point for a broader implementation of DNP in liquid-state NMR.

The catalytic activity of the supported bis(oxime palladacycle) catalyst was evaluated in the acyl Sonogashira reaction. The reaction conditions, such as solvent, base, and palladium content, were screened to achieve the best catalytic performance. Tetrahydrofuran (THF) solvent, triethylamine (Et3N) base, and the reaction temperature of 110 degrees C were found to be ideal for achieving high yields of the desired products. Furthermore, a catalyst loading of only 0.22 mol% palladium was sufficient to achieve good conversion. Broad ranges of aryl acetylenes and benzoyl chlorides were successfully coupled to give the desired acetylenic ketones. The reaction appeared to proceed efficiently using a small amount of catalyst. The magnetic property of the catalyst allowed for easy separation using an external magnet. The catalyst was stable and reused for multiple reaction runs without a significant deactivation. After seven cycles, the catalyst maintained over 90 % of its initial catalytic activity. A bis(oxime palladacycle) anchored on Fe3O4@SBA was evaluated in the acyl Sonogashira reaction. The reaction conditions were optimized by choosing a model reaction. Broad ranges of aryl acetylenes and benzoyl chlorides were coupled to give ynones. The magnetic property of the catalyst allowed for easy separation using a magnet. The catalyst stability was shown by Pd-leaching, recyclability, and hot-filtration experiments. image

Homosalate (HMS) is an organic UV filter used in sunscreens and personal care products. Despite its widespread use and detection in environmental matrices, little is known regarding its exposure in humans. HMS is used as a mixture of cis- and trans-isomers, and we recently revealed major differences in human toxicokinetics, indicating the need to consider these isomers separately in exposure and risk assessments. In the course of these previous investigations of human HMS toxicokinetics, we identified two trans-HMS-specific and one cis-HMS-specific biomarker candidates. However, the latter lacks sensitivity due to only low amounts excreted in urine, prompting the search for another cis-HMS-specific biomarker. Our toxicokinetic investigations revealed a total of five isomers of HMS carboxylic acid metabolites (HMS-CA). Of these, only one was specifically formed from cis-HMS (HMS-CA 5), but its full identity in terms of constitution and configuration had, so far, not been elucidated. Here, we describe the synthesis of three HMS-CA isomers, of which the isomer (1R,3S,5S)/(1S,3R,5R)-3-((2-hydroxybenzoyl)oxy)-1,5-dimethylcyclohexane-1-carboxylic acid turned out to be HMS-CA 5. Taken together with two previously synthesized HMS-CA isomers, we were able to identify the constitution and configuration of all five HMS-CA isomers observed in human metabolism. We integrated the newly identified cis-HMS-specific metabolite HMS-CA 5 into our previously published human biomonitoring LC-MS/MS method. Intra- and interday precisions had coefficients of variation below 2% and 5%, respectively, and the mean relative recovery was 96%. The limit of quantification in urine was 0.02 μg L-1, enabling the quantification of HMS-CA 5 in urine samples for at least 96 h after sunscreen application. The extended method thus enables the sensitive and separate monitoring of cis- and trans-HMS in future human biomonitoring studies for exposure and risk assessment.

We present the synthesis and characterization of a new Cu(I) complex supported on SBA-15 as a catalyst for preparing anilines from the reaction of aryl halides with sodium azide. The SBA-15 support was modified by treating it sequentially with (3-aminopropyl) triethoxysilane (APTES), cyanuric chloride, and 2-aminothiazole (AT). The modified mesoporous silica, SBA-15@BAT, was then treated with a CuI solution in acetonitrile to give SBA-15@BAT-Cu(I). The catalyst underwent thorough characterization using conventional methods. X-Ray photoelectron spectroscopy (XPS) analysis corroborated the presence of copper in the +1 oxidation state in the catalyst. The supported Cu(I) complex sufficiently catalyzed the amination reaction of iodo-, bromo-, and chloroarenes with NaN3. The catalyst was centrifuged, washed, and applied in the subsequent run. We investigated the effects of various reaction components and parameters to determine the optimal conditions for the reaction. The heterogeneous catalyst exhibited noticeable stability and was reused over seven runs with slight deactivation. Supporting and characterization of a new Cu(I) catalyst catalyst based on 2-aminothiazole-Cu(I) on SBA-15. Optimization of the reaction conditions for the supported catalyst in the amination of haloarens with sodium azide. Preparation of a wide range of anilines from chloro-, bromo-, and iodoarens. image

Most stable isotopes have a nuclear spin >1/2, but the quadrupole interaction poses challenge on their detection by nuclear magnetic resonance (NMR). On the other hand, the quadrupole interaction is a rich source of structural information that may be exploited for solution NMR in the form of residual quadrupolar couplings (RQCs) of weakly oriented samples. While 2H RQCs are now well established for structure verification and enantiomeric discrimination of organic molecules, we will in this article highlight some recent work on RQCs of other nuclei (especially 7Li and 11B).

The present work describes the grafting of a polymer-metal chelate (PMC) from Fe3O4@SiO2 core-shells via the Surface Initiated-Atom Transfer Radical Polymerization (SI-ATRP). The magnetic core-shells were silylated by 2-bromo-2-methyl-N-(3-(trimethoxysilyl)propanamide (BTPAm) to give the surface-anchored ATRP initiator. Acrylamide was polymerized from the Fe3O4@SiO2 surface via the ATRP approach. The grafted magnetic nanoparticles were trans-amidated with ethylenediamine to give poly(N-2-aminoethylacrylamide) grafted magnetic core-shells, Fe3O4@SiO2-g-PAE-AAm. The grafted chelating polymer ligand (CPL) was treated with an acetonitrile solution of CuI to afford the Fe3O4@SiO2-g-PAE-AAm-Cu(I). The grafted PMC was characterized by FT-IR, CP/MAS C-13 NMR, and thermo-gravimetric analysis (TGA). The grafted PMC catalyzed the N-C bond formation via the Ullmann-type N-arylation reaction of haloarenes and anilines under optimal reaction conditions. Mono N-arylation product was obtained as the major product with excellent selectivity. The excellent recyclability of the catalyst was shown by negligible deactivation over six runs.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Shedding light on the structure and solvation state of lithium compounds in aligned solution: The residual quadrupolar coupling of 7Li in a range of lithium complexes due to the interaction of the electric field gradient (shown in its graphical tensor form) with the alignment in a stretched polymer gel has been investigated using NMR spectroscopy. The preferred orientation of the molecules in the anisotropic environment is illustrated in the background. More information can be found in the Research Article by M. John and co-workers (DOI: 10.1002/chem.202203995).

Amaranthus L. leaves are consumed as vegetables and are a rich source of secondary plant metabolites. The phenolic profiles of the three analyzed genotypes by LC-Q-TOF-MS/MS and HPLC-DAD were characterized by high amounts of hydroxycinnamic glucaric and -isocitric acids. 'Gartenfuchsschwanz' (A. hybridus L.) and 'Red Callaloo' (A. tricolor L.) had similar profiles. 'Gemüse-Amaranth' (A. tricolor L.) had a high amount of caffeoylglucaric acid 4, which was isolated, and afterward identified by NMR. Its antioxidant activity, measured by TEAC, DPPH, and TPC, was similar to 5-caffeoylquinic acid, common in many plant species. The antioxidant activity of Amaranthus L. can be explained rather by their different phenolic- and ascorbic acid concentrations than by their species. Household cooking reduces antioxidant activity due to oxidation processes while leaching into cooking water could be neglected. Amaranthus L. baked into a wheat-dough-matrix showed lower phenolic concentrations, presumably due to the formation of phenol-protein-bounds and thermal degradation.

The study of composition, aggregation, or solvation of reactive molecules in solution is of fundamental interest for the classification of reaction mechanisms or the estimation of reactivities. In the past, methodologies have already been presented to make organolithium compounds accessible to a DOSY-NMR-based molecular weight determination. However, complexes with heavy atoms, such as transition metals, were excluded from this because of their elevated van der Waals density. In this publication, we show that our heavy-atom correction based on the external calibration curve data is also suitable for addressing such complexes.

A new NMR method for structural verification and 11B resonance assignment in (car)borane clusters is presented, based on the measurement of 11B residual quadrupolar couplings (RQCs) in a stretched polystyrene (PS) gel. The method was applied to ortho-carborane (B10C2H12), a derivative thereof with reduced symmetry, meta-carborane and decaborane (B10H14).

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

A new NMR method for the structure elucidation of lithium compounds under solution-like conditions is presented. It is based on the measurement of Li-7 residual quadrupolar couplings (RQCs) in a stretched polystyrene (PS) gel, and comparison to RQCs predicted from crystal or DFT-derived model structures in combination with alignment tensors derived from one-bond H-1,C-13 residual dipolar couplings (RDCs). The method was applied to five lithium model complexes containing monoanionic, bidentate bis(benzoxazole-2-yl)methanide, bis(benzothiazole-2-yl)methanide and bis(pyridyl)methanide ligands, of which two are first introduced in this work. In agreement with the crystalline state, four complexes are monomeric with Li coordinated fourfold by two additional THF molecules, whereas in one complex bulky tBu groups only provide space for one additional THF molecule.

Two mononuclear ruthenium(II) complexes based on dianionic {N-4} ligands and with axial pyridines have been prepared and characterized crystallographically (1) or by 2D NMR spectroscopy using residual dipolar couplings (2). The {N-4} ligands provide a constrained equatorial coordination with one large N-Ru-N angle, and additional non-coordinating N atoms in case of 2. Their redox properties have been investigated (spectro)electrochemically, and their potential to serve as water oxidation catalysts has been probed using cerium ammonium nitrate (CAN) at pH 1.0. Complex 1 undergoes rapid degradation, likely via ligand oxidation, whereas 2 is more rugged and exhibits 80 % efficiency in the Ce-IV-driven water oxidation, with a high initial turnover frequency (TOFi) of 3.07x10(-2) s(-1) (at 100 equiv. CAN). The initial rate of O-2 evolution exhibits 1(st) order dependence on catalyst concentration, suggesting a water nucleophilic attack mechanism. Repeated addition of CAN and control experiments show that high ionic strength conditions (both NO3- and Ce-III) significantly decrease the TOF.