The X-ray structures of 2- and 3-sulfolene and two halogenated derivatives

The structures of the isomeric 2,5-dihydrothiophene 1,1-dioxide [orthorhombic, a = 11.340(2), b = 7.0887(15), c = 6.2811(13) Å, space group Pnma] and 2,3-dihydrothiophene 1,1-dioxide [orthorhombic, a = 6.3903(13), b = 7.2783(16), c = 11.075(2) Å, space group Pnma] have been determined and show perfectly planar rings with the expected bond lengths and angles. In contrast, the halogenated derivatives 3,3,4,4-tetrachlorotetrahydrothiophene 1,1-dioxide [monoclinic, a = 11.8716(8), b = 6.5579(4), c = 11.4802(8) Å, β = 97.705(17), space group P21/c] and 2,3-dibromotetrahydrothiophene 1,1-dioxide [orthorhombic, a = 5.2502(3), b = 11.3561(6), c = 24.9802(17) Å, space group Pbca] both show twisted conformations. The degree of planarity is compared with that in the structures of comparable 5-membered ring cyclic sulfones and C–H…O hydrogen bonding patterns are discussed for all four structures.Publisher PDFPeer reviewe

APA2[Zn3(HPO4)4(H2O)2], a layered zincophosphate featuring template-to-framework N-H⋯O and "synergic" framework-to-template O-H⋯N hydrogen bonds and C-H⋯O interactions (APA = 2-Amino-1-phenyleneammonium, C6H9N2 +)

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Aerobic synthesis of N-sulfonylamidines mediated by N-heterocyclic carbene copper(I) catalysts

The authors gratefully acknowledge the EPSRC National Mass Spectroscopy Facilities for the HMRS analysis at the University of Swansea.A new catalytic strategy for the one-pot synthesis of N-sulfonylamidines is described. The cationic copper(I) complexes were found to be highly active and efficient under mild conditions in air and in the absence of solvent. A copper acetylide is proposed as key intermediate in this transformation.Publisher PDFPeer reviewe

Aryl Boronic Acid Catalysed Dehydrative Substitution of Benzylic Alcohols for C−O Bond Formation

We thank the University of St Andrews and the EPSRC for the award of a DTA studentship (S.E.-D.). We would also like to thank the EPSRC, University of St Andrews, and CRITICAT Centre for Doctoral Training for financial support [Ph.D. studentships to B.M.H, E.B.M and L.J.D; Grant code: EP/L016419/1]. J.E.T thanks the Leverhulme Trust for the award of an Early Career Fellowship (Grant code: ECF-2014-005).A combination of pentafluorophenylboronic acid and oxalic acid catalyses the dehydrative substitution of benzylic alcohols with a second alcohol to form new C-O bonds. This method has been applied to the intermolecular substitution of benzylic alcohols to form symmetrical ethers, intramolecular cyclisations of diols to form aryl-substituted tetrahydrofuran and tetrahydropyran derivatives, and intermolecular crossed-etherification reactions between two different alcohols. Mechanistic control experiments have identified a potential catalytic intermediate formed between the arylboronic acid and oxalic acid.PostprintPeer reviewe

Formal synthesis of (+)-lactacystin from l-serine

A formal, stereocontrolled synthesis of lactacystin has been completed from t-Bu-O-l-serine, providing the key intermediate 13, also useful for the generation of a range of C-9 analogues

Rate and equilibrium constants for the addition of triazolium salt derived N-heterocyclic carbenes to heteroaromatic aldehydes

Heteroaromatic aldehydes are often used preferentially or exclusively in a range of NHC-catalysed processes that proceed through the generation of a reactive diaminoenol or Breslow Intermediate (BI), with the reason for their unique reactivity currently underexplored. This manuscript reports measurement of rate and equilibrium constants for the reaction between N-aryl triazolium NHCs and heteroaromatic aldehydes, providing insight into the effect of the NHC and heteroaromatic aldehyde structure up to formation of the BI. Variation in NHC catalyst and heteroaromatic aldehyde structure markedly affect the observed kinetic parameters of adduct formation, decay to starting materials and onward reaction to BI. In particular, large effects are observed with both 3-halogen (Br, F) and 3-methyl substituted pyridine-2-carboxaldehyde derivatives which substantially favour formation of the tetrahedral intermediate relative to benzaldehyde derivatives. Key observations indicate that increased steric hindrance leads to a reduction in both k2 and k−1 for large (2,6-disubstituted)-N-Ar groups within the triazolium scaffold, and sterically demanding aldehyde substituents in the 3-position, but not in the 6-position of the pyridine-2-carboxaldehyde derivatives. As part of this study, the isolation and characterisation of twenty tetrahedral adducts formed upon addition of N-aryl triazolium derived NHCs into heteroaromatic aldehydes are described. These adducts are key intermediates in NHC-catalysed umpolung addition of heteroaromatic aldehydes and are BI precursors

Physical and photophysical properties of a linear copper(I) complex of a bulky acenapthene-based NHC ligand

CFRM and EZ-C wish to thank the Engineering and Physical Sciences Research Council (EP/M02105X/1 and EP/R035164/1) for financial support. We would like to thank the Engineering and Physical Sciences Research Council and CRITICAT Centre for Doctoral Training for financial support (Ph.D. studentship to B. H.; EP/L016419/1).We report the first example of a charge-neutral linear 2-coordinate copper(I) complex bearing a sterically demanding acenaphthoimidazolylidene-based N-heterocyclic carbene ligand. The identity and geometry of the complex was confirmed by single-crystal XRD (X-Ray Diffraction) analysis. The complex is poorly emissive at room temperature, showing either ligand-centered (LC) emission at around 340 nm when excited at 300 nm or ligand-to-ligand charge-transfer (LLCT) emission at around 540 nm when excited at 420 nm; in chloroform, dual emission is observed upon photoexcitation at 300 nm. Nanosecond emission lifetimes were recorded for these processes. This is the first example of emissive linear copper(I) complexes containing this bulky NHC ligand.PostprintPeer reviewe

Analysis of two [2]catenanes based on electron densities from invariom refinement and results from DFT calculations

The authors are grateful to the Deutsche Forschungsgemeinschaft (DFG) for financial support by project DI 921/6-1.Catenanes are of considerable interest as potential building blocks for molecular machines. The simplest [2]catenanes, Hopf links, consist of two macrocycles that are mechanically interlocked. This unusual architecture cannot be opened without breaking at least one covalent bond. Based on these structural characteristics, unusual properties on Hirshfeld or electrostatic potential surfaces could be expected. For a comparison of their structural and electronic properties, the electron densities (EDs) of two [2]catenanes, coded H22 and H4L7 in the original papers, were examined after application of the invariom formalism, relying on X-ray diffraction data collected earlier. The obtained electron density distributions were subjected to an analysis using the QTAIM formalism to yield bond and atomic properties. Moreover, molecular Hirshfeld surfaces and electrostatic potentials (ESP) were calculated. There are different types of intra- and intermolecular interactions in these two [2]catenanes. In addition to classical N-H···N and C-H···O hydrogen bonds, various types of π···π interactions in H22 and in H4L7 exist. Most of them are verified by local ED concentrations visible on the corresponding Hirshfeld surfaces, except for the parallel π···π interactions in H22, which are either too weak or too diffuse to generate an ED signal on the Hirshfeld surface between the contributing aromatic rings. The electrostatic potentials (ESPs) were calculated and displayed on molecular surfaces. The interaction in the cavity of one macrocycle with the penetrated fragment of the second one was examined and it was found that corresponding to the above-mentioned contacts attractive and repulsive interactions exist. Additionally the ED was examined using results of density functional calculations, including non-covalent interaction index (NCI) and electron localizability indicator (ELI-D) surface analysis, complementing experimental findings.Publisher PDFPeer reviewe

Studio u dubrovačkim kućama prve polovice 15. stoljeća

Drvodjeljski radovi ugovoreni između 1425. i 1435. godine otkrivaju mnoge podatke o unutarnjem prostoru i uređenju dubrovačkih kuća. Izradom fiksnog namještaja određuje se i namjena pojedinih prostorija, među kojima se pojavljuje i studio. Ta riječ može značiti i zasebnu sobu ali i komad pokućstva sastavljen od pisaćeg stola, sjedala i polica za knjige. Po mjestu na kojem se unutar dubrovačkih kuća studio nalazi – na prvom ili na nekom od viših katova, uočena je podudarnost s opisom kuće »savršenog trgovca« Benedikta Kotrulja iz 1458. godine. On i nazivljem razlikuje »zajedničku pisarnicu« (scriptore ili scrittoio comune) »pogodnu za poslove«, koja je na prvom katu, od »male pisarnice« (scriptoreto separato ili studiolo a parte), koja je »u spavaćoj sobi ili blizu nje«, a služi onome »koji uživa u knjizi«

Silicon redistribution, acid site loss and the formation of a core-shell texture upon steaming SAPO-34 and their impact on catalytic performance in the methanol-to-olefins (MTO) reaction

IBM has received funding from the Engineering and Physical Sciences Research Council (EPSRC, Centre for Doctoral Training in Critical Resource Catalysis, EP/I017008/1) and Scotland's Chemistry departments (ScotCHEM). IBM also received a scholarship from the SCI and Santander. Johnson Matthey is thanked for in-kind contributions and hosting IBM in their R&D labs. ABN gratefully acknowledges support from the EPSRC (grants EP/L017008/1 and EP/R023751/1). The research data supporting this publication can be accessed at: https://doi.org/10.17630/09ddc03e-f121-4e79-9b55-674f64d9c8c4 [62].SAPO-34 is a commercially-implemented silicoaluminophosphate catalyst for selective high yield production of ethene and propene from methanol, but high temperature regeneration in the presence of steam leads to its deactivation. A comprehensive investigation of the effect of prolonged hydrothermal treatment on the structure and properties of SAPO 34 explains the changes in its catalytic methanol-to-olefins (MTO) performance. Microcrystalline powdered SAPO-34 (ca. 3 µm crystals, Al17.1P15.6Si3.3O72) and two batches of larger single crystals of SAPO-34 of different Si concentration (20-100 µm; Al17.3P14.7Si4.0O72 and Al17.7P12.3Si5.9O72 ) were steamed (pH2O = 0.95 atm) at 873–1023 K for up to 240 h. The acidity (NH3-TPD), crystallinity (PXRD), framework cation environment (solid-state 27Al, 29Si and 31P MAS NMR) and porosity were followed for all materials; larger crystals were amenable to single crystal X-ray diffraction, FIB-SEM and synchrotron IR microspectroscopy, including operando study during methanol and dimethyl ether conversions. Some level of steaming improved the lifetime of all SAPO-34 materials in MTO catalysis without affecting their olefin selectivity, although more severe conditions led to the formation of core-shell structures, microporosity loss and eventually at 1023 K, recrystallization to a dense phase. All these irreversible changes occurred faster in crystals with higher Si contents. The initial increase in catalytic lifetime results from an activated reduction in acid site density (Eact = 146(18) kJ mol⁻1), a result of redistribution of Si within the SAPO framework without porosity loss. Operando IR with online product analysis during methanol conversion suggests similar reaction pathways in calcined and steamed crystals, but with greatly reduced methoxy group densities in the latter. The gradual development of optically dark crystal cores upon progressive steaming was shown by FIB-SEM to be due to the formation of regions with meso- and macropores, and these were shown by IR mapping to possess low hydroxyl densities.PostprintPostprintPeer reviewe