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The facile synthesis of the cationic dinuclear group 10 complexes [M2(PCP)2μ-Cl]+ (M = Ni, Pd, Pt) by transmetallation from a simple Ga precursor is reported (PCP = 2,6-(Ph2P)C6H3). Their use for the catalysed dehydrogenation of Me2NHBH3 shows that Ni has a higher reactivity than Pt, whereas Pd is inactive. [ABSTRACT FROM AUTHOR]

The facile synthesis of the cationic dinuclear group 10 complexes [M2(PCP)2μ-Cl]+ (M = Ni, Pd, Pt) by transmetallation from a simple Ga precursor is reported (PCP = 2,6-(Ph2P)C6H3). Their use for the catalysed dehydrogenation of Me2NHBH3 shows that Ni has a higher reactivity than Pt, whereas Pd is inactive. [ABSTRACT FROM AUTHOR]

A macrocyclic azobenzene with unique thermal stability, demonstrating potential for use in optical data storage material is presented: The Z‐isomer of this novel photoswitch exhibits unparalleled thermal stability, with a thermal half‐life surpassing 120 years at 25 °C. This stability is attributed to the strategic fluorination at two ortho‐ and both para‐positions. Comparative analyses involving its non‐fluorinated counterpart, ortho‐only‐fluorinated variant, and open‐chain analog are performed. Employing NMR and UV–vis spectroscopy, X‐ray diffraction, alongside Arrhenius, Eyring, and DFT calculations, revealed insights into its extraordinary stability. Furthermore, when incorporated into poly(methylmethacrylate), this material showcase efficient switching with visible light in the solid state, emphasizing its potential for optical data storage applications. [ABSTRACT FROM AUTHOR]

The bulky aryl thiol, MSFluindSH (1S), and aryl selenol, MSFluindSeH (1Se), possessing a tetramethyl‐s‐hydrindacen‐4'‐yl‐(Rind)‐based substituent containing two fluorenyl groups in 9 and 9'‐positions, were prepared (MSFluind=dispiro[fluorene‐9,3'‐(1',1',7',7'‐tetramethyl‐s‐hydrindacene‐4'‐yl)‐5',9"‐fluorene]). The reaction of 1S and 1Se with Et2Zn provided a monomeric zinc aryl thiolate, Zn(SMSFluind)2 (2S), and zinc aryl selenolate, Zn(SeMSFluind)2 (2Se), with essentially two‐coordinate zinc atoms. [ABSTRACT FROM AUTHOR]

The title compound, [Zn(C20H18BN2)2] (ZnL2), is an overall uncharged chelate that consists of two units of an NH-deprotonated 10-aza-9-borabenzo[h] quinoline ligand (L) per ZnII center. It was synthesized in two steps by treating the protonated ligand HL with lithium bis(trimethylsilyl)amide and further conversion with diethylzinc. Its asymmetric unit comprises one ZnL fragment; the molecule is completed by application of inversion symmetry at Zn. Due to the fourfold coordination with nitrogen atoms, the zinc(II) ion is located in a distorted tetrahedral environment. Besides the relatively short N--Zn bonds, ZnL2 is characterized by the significant protrusion of the central ion from the plane of the ligand backbone. The crystal structure is consolidated by intra- and intermolecular π-π stacking interactions, while the polarized B--N bond is barely involved in any close atom contacts. [ABSTRACT FROM AUTHOR]

Liquid crystalline polymer networks (LCN) with azobenzene monomers bend reversibly under UV‐light irradiation, combining photomechanical and photothermal effects. However, the harmful nature of UV‐light limits their use in biology and soft robotics. Although visible light‐absorbing tetra‐ortho‐fluoro‐substituted azobenzenes exist, liquid crystalline monomers have never been prepared. Previously, such azobenzenes were added as photoactive additives (up to 10%) to otherwise passive liquid crystalline polymer networks. In this work, a molecular design of a liquid crystalline, polymerizable azobenzene switchable by visible light is presented. The monomer assembles in a highly fluid nematic phase, but polymerizes in a layered smectic C phase. The films are produced solely from the monomer without additional liquid crystalline components and are actuated with visible light. Bending experiments in air and under water differentiate photomechanical and photothermal effects. Remarkably, a 60 µm splay aligned film maintains its deformation for hours, slowly reverting over days. Monomer liquid crystallinity is characterized using differential scanning calorimetry (DSC), wide‐angle X‐ray scattering (WAXS), and polarized optical microscopy (POM); polymer films are analyzed using WAXS and DSC on a homogeneously aligned film. The synthetic procedure is high yielding and polymer film fabrication is scalable, which enables the use of safe and efficient photomechanical LCNs in soft robotics, engineering and biology. [ABSTRACT FROM AUTHOR]

The isoelectronic relationship of 1,2-azaborinine (B=N structural motif) and benzene (C=C) is well documented. Upon deprotonation of the former, the anionic 1,2-azaboratabenzene is obtained, which is isosteric with pyridine (C=N) and has a similar capability as an aromatic N-donor. We present the complexation of boron and aluminum precursors with a κ2-N,O-donating 8-hydroxy-BN-naphthalene ligand (H2(BQ), 1). Six chelate complexes with 1:1 and 2:1 stoichiometries were isolated and characterized by X-ray diffraction analysis and NMR spectroscopy. Comparing the isosteric dimethylaluminum complexes of H2(BQ) and an 8-hydroxyquinoline (HQ', 2) as a reference allowed us to quantify the influence of a formal substitution of carbon by boron on the structure and the electronic properties: While the structural parameters of the ligands were similar, the electropositive boron atom affected the electron density distributions within the complexes substantially. As the consequence, the Al–N bond was significantly shortened, and the aluminum atom showed a different coordination geometry than in the quinoline analog. Moreover, strong hypsochromic shifts of both the absorption and the emission were observed. The results highlight that the differences between CN and BN polyaromatic complexes are more distinct than between equally charged BN and CC congeners. [ABSTRACT FROM AUTHOR]

Sila‐ibuprofen is a new potential nonsteroidal anti‐inflammatory drug which deviates from its parent ibuprofen in terms of the electrostatic potential around the carbon/silicon‐switched C/Si—H group. Therefore, sila‐ibuprofen is more water soluble and has a lower melting enthalpy. However, its binding and inhibition properties of cyclooxygenases appear to be very similar to regular ibuprofen. Therefore, in this study, intermolecular interactions and interaction densities of both ibuprofen and sila‐ibuprofen in their biologically active forms, i.e. deprotonated and as the pure S‐enantiomers are investigated. Quantum‐crystallographically refined salts with argininium and 1‐phenylethan‐1‐amoninium (PEA) counter‐cations as crystalline models of the interactions with the guanidine functional group of arginine inside cyclooxygenases are presented. The similarities and differences between the polarization of ibuprofen and sila‐ibuprofen in the crystal, enzyme, solvent and isolated environments are discussed based on quantum‐chemical calculations. For the explicit crystal and enzyme environments, specifically, molecular dynamics simulations starting from the crystal models were combined with QM/MM calculations. [ABSTRACT FROM AUTHOR]

Abstract: Ru(NNS)(PPh3)Cl2 (NNS=2‐(methylthio)‐N‐(pyridin‐2‐yl‐methyl)ethan‐1‐amine) was employed in the hydrogenation of α,β‐unsaturated esters, reaching selectivities for the allylic alcohol up to 95% in the hydrogenation of iso‐butylcinnamate. In addition, several ester substrates were hydrogenated with catalyst loadings as low as 0.05 mol%. Surprisingly, selectivity of the hydrogenation of the C=O vs the C=C bonds strongly depends on the solvent. [ABSTRACT FROM AUTHOR]

The use of monodentate phosphorus ligands, such as phosphonites, phosphites and phosphoramidites, in the rhodium-catalysed asymmetric hydrogenation of a range of mostly alkene type substrates was reported for the first time in 2000. Not only are these ligands cheap and easy to prepare in one or two steps, their use has also created new opportunities, such as their robotic parallel synthesis and the use of complexes containing two different monodentate ligands, which tremendously increases the available diversity. This review covers the period between 2006 and 2016. Many new ligands have been made during this time; not only new variants on the three ligand types that were earlier reported, but also monodentate phosphines and secondary phosphine oxides. These were mostly tested on the usual N-acetyl-dehydroamino acids, itaconic esters and enamide type substrates. Other more novel substrates were N-formyl-dehydroamino acids, all the variants of the beta-dehydroamino acid family, enol esters, 2-methylidene-1,2,3,4-tetrahydro-β-carbolines, alkenes containing phosphonate or thioether substituents, several substituted acrylic acids as well as substituted cinnamic acids. The mechanism of the rhodium-catalysed hydrogenation with phosphites, phosphonites, phosphoramidites as well as phosphepines has been reported. A common theme in these mechanisms is the formation of a dimeric bimetallic complex after subjecting the [RhL2(cod)]X or [RhL2(nbd)]X (X = BF4,PF6, SbF6) complexes to hydrogen. Since these hydrogenations are usually carried out in non-polar solvents, the formation of the expected RhL2(Solvent)2 complexes does not occur after the removal of the diene and instead each rhodium atom in these dimeric complexes coordinates not only to two monodentate ligands, but also in η6 fashion to an aromatic ring of one of the ligands that is bound to the other rhodium atom. These complexes can react with the substrate to form the substrate complex that is hydrogenated. Other studies also found that it is possible to form rhodium hydride complexes first, which react with the substrate to form product. There is one well-described industrial application on large scale in which a substituted 2-isopropyl-cinnamic acid is hydrogenated using a rhodium complex with a mixture of 2 eq. of 3,3'-dimethyl-PipPhos and 1 eq. of triphenylphosphine. The addition of the non-chiral triarylphosphine not only accelerated the reaction 50-fold, also the enantioselectivity was much improved. The product was used as a building block for AliskirenTM, a blood-pressure lowering agent. [ABSTRACT FROM AUTHOR]

The Trost ligand, (1 S,2 S)-1,2-diaminocyclohexane- N, N′-bis(2′-diphenylphosphinobenzoyl) ( L), is reported for the first time as a ligand for the asymmetric hydrogenation (AH) of ketones. Ligand ( S, S)- L was screened in the presence of several metal salts and was found to form active catalysts if combined with ruthenium sources in the presence of hydrogen and a base. Reaction optimization was performed by screening different Ru sources, solvents, and bases. Under the optimized conditions, the complex formed by the combination of ( S, S)- L with RuCl3(H2O) x in the presence of Na2CO3 was able to promote the AH of several ketones at room temperature in good yields with up to 96 % ee. The reaction kinetics measured under the optimized conditions revealed the presence of a long induction period, during which the initially formed Ru species was transformed into the catalytically active complex by reaction with hydrogen. Remarkably, a ketone that is a precursor of the antiemetic drug aprepitant was hydrogenated in excellent yield with a good ee value. [ABSTRACT FROM AUTHOR]

The selective hydrogenation of the carbonyl functionality of α,β-unsaturated aldehydes and ketones is catalysed by ruthenium dichloride complexes bearing a tridentate NNS ligand as well as triphenylphosphine. The tridentate ligand backbone is flexible, as evidenced by the equilibrium observed in solution between the cis- and trans-isomers of the dichloride precatalysts, as well as crystal structures of several of these complexes. The complexes are activated by base in the presence of hydrogen and readily hydrogenate carbonyl functionalities under mild conditions. Despite the activation by base, side reactions are negligible, even for aldehyde substrates, because of the low amount of base. Thus, the corresponding allylic alcohols can be isolated in very good yields on a 10-25 mmol scale. Turnover numbers up to 200 000 were achieved. [ABSTRACT FROM AUTHOR]