Stereodivergent Anion Binding Catalysis with Molecular Motors

A photoresponsive chiral catalyst based on an oligotriazole-functionalized unidirectional molecular motor has been developed for stereodivergent anion binding catalysis. The motor function controls the helical chirality of supramolecular assemblies with chloride anions, which by means of chirality transfer enables the enantioselective addition of a silyl ketene acetal nucleophile to oxocarbenium cations. Reversal of stereoselectivity (up to 142 % Δee) was achieved through rotation of the motor core induced by photochemical and thermal isomerization steps

Photoswitchable catalysis based on the isomerisation of double bonds

Photoswitchable catalysis is a young but rapidly evolving field that offers great potential for non-invasive dynamic control of both activity and selectivity in catalysis. Within this context, the E/Z photoisomerisation of double bonds in molecular switches and motors is one of the most popular tools to control the catalytic activity essentially due to its reversible nature, the large concomitant geometrical changes, and the high tunability of such photochromic entities. This Feature Article summarises the key developments accomplished over the past years through the incorporation of photoswitchable double bonds into the structure of catalytically competent molecules and shows some perspectives on the remaining challenges and possibilities arising from this, yet still somehow immature, exciting area of research

Regiodivergent and Stereoselective Hydrosilylation of 1,3‐Disubstituted Allenes

Methods for the highly stereoselective and regiodivergent hydrosilylation of 1,3‐disubstituted allenes have been developed. The synthesis of E allylsilanes is accomplished with palladium NHC catalysts, and trisubstituted Z alkenylsilanes are accessed with nickel NHC catalysts. Unsymmetrically substituted allenes are well tolerated with nickel catalysis and afford Z alkenylsilanes. Evidence for a plausible mechanism was obtained through an isotopic double‐labeling crossover study.Silane haben die Wahl: Die Hydrosilylierung von 1,3‐disubstituierten Allenen, die sonst äußerst schwierige Substrate für regioselektive Additionen sind, kann jetzt mit ausgezeichneter Regio‐ und Stereoselektivität durchgeführt werden. Durch den Wechsel von Metallkatalysator und Ligand werden entweder trisubstituierte Z‐Alkenylsilane oder trans‐Allylsilane erhalten.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/112220/1/ange_201503521_sm_miscellaneous_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/112220/2/9216_ftp.pd

Higher acenes by on‐surfacedehydrogenation : from heptacene to undecacene

A unified approach to the synthesis of the series of higher acenes up to previously unreported undecacene has been developed through the on‐surface dehydrogenation of partially saturated precursors. These molecules could be converted into the parent acenes by both atomic manipulation with the tip of a scanning tunneling and atomic force microscope (STM/AFM) as well as by on‐surface annealing. The structure of the generated acenes has been visualized by high‐resolution non‐contact AFM imaging and the evolution of the transport gap with the increase of the number of fused benzene rings has been determined on the basis of scanning tunneling spectroscopy (STS) measurements

Regiodivergent and Stereoselective Hydrosilylation of 1,3‐Disubstituted Allenes

Methods for the highly stereoselective and regiodivergent hydrosilylation of 1,3‐disubstituted allenes have been developed. The synthesis of E allylsilanes is accomplished with palladium NHC catalysts, and trisubstituted Z alkenylsilanes are accessed with nickel NHC catalysts. Unsymmetrically substituted allenes are well tolerated with nickel catalysis and afford Z alkenylsilanes. Evidence for a plausible mechanism was obtained through an isotopic double‐labeling crossover study.Silanes with a choice: The hydrosilylation of 1,3‐disubstituted allenes, which have presented a notorious challenge for regioselective additions, can now be accomplished with outstanding levels of regio‐ and stereocontrol. By altering the metal catalyst and ligand structure, access to trisubstituted Z alkenylsilanes or trans allylsilanes is provided in a simple catalytic operation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/112189/1/anie_201503521_sm_miscellaneous_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/112189/2/9088_ftp.pd

The Buchwald-Hartwig Amination After 25 Years

The Pd-catalyzed coupling of aryl (pseudo)halides and amines is one of the most powerful approaches for the formation of C(sp(2))-N bonds. The pioneering reports from Migita and subsequently Buchwald and Hartwig on the coupling of aminostannanes and aryl bromides rapidly evolved into general and practical tin-free protocols with broad substrate scope, which led to the establishment of what is now known as the Buchwald-Hartwig amination. This Minireview summarizes the evolution of this cross-coupling reaction over the course of the past 25 years and illustrates some of the most recent applications of this well-established methodology

All-photochemical rotation of molecular motors with a phosphorus stereoelement

Unidirectional molecular rotation based on alternating photochemical and thermal isomerizations of overcrowded alkenes is well established, but rotary cycles based purely on photochemical isomerizations are rare. Herein we report three new second-generation molecular motors featuring a phosphorus center in the lower half, which engenders a unique element of axial chirality. These motors exhibit unusual behavior, in that all four diastereomeric states can interconvert solely photochemically. Kinetic analysis and modeling reveal that the behavior of the new motors is consistent with all-photochemical unidirectional rotation. Furthermore, X-ray crystal structures of all four diastereomeric states of two of these new motors were obtained, which constitute the first achievements of crystallographic characterization of the full 360° rotational cycle of overcrowded-alkene-based molecular motors. Finally, the axial phosphorus stereoelement in the phosphine motor can be thermally inverted, and this epimerization enables a “shortcut” of the traditional rotational cycle of these compounds

Electronic decoupling of polyacenes from the underlying metal substrate by sp ³ carbon atoms

We report on the effect of sp3 hybridized carbon atoms in acene derivatives adsorbed on metal surfaces, namely decoupling the molecules from the supporting substrates. In particular, we have used a Ag(100) substrate and hydrogenated heptacene molecules, in which the longest conjugated segment determining its frontier molecular orbitals amounts to five consecutive rings. The non-planarity that the sp3 atoms impose on the carbon backbone results in electronically decoupled molecules, as demonstrated by the presence of charging resonances in dI/dV tunneling spectra and the associated double tunneling barriers, or in the Kondo peak that is due to a net spin S=1/2 of the molecule as its LUMO becomes singly charged. The spatially dependent appearance of the charging resonances as peaks or dips in the differential conductance spectra is further understood in terms of the tunneling barrier variation upon molecular charging, as well as of the different orbitals involved in the tunneling process

On-surface synthesis of heptacene on Ag(001) from brominated and non-brominated tetrahydroheptacene precursors

Achieving the Ag(001)-supported synthesis of heptacene from two related reactants reveals the effect of the presence of Br atoms on the reaction process. The properties of reactants, intermediates and end-products are further characterized by scanning tunneling microscopy and spectroscopy.Fil: Colazzo, Luciano. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Mohammed, Mohammed S. G.. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Dorel, Ruth. Barcelona Institute of Science and Technology; EspañaFil: Nita, Pawel. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; EspañaFil: García Fernández, Carlos. Donostia International Physics Center; EspañaFil: Abufager, Paula Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Lorente Palacios, Nicolas. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Echavarren, Antonio M.. Barcelona Institute of Science and Technology; España. Universitat Rovira I Virgili; EspañaFil: De Oteyza, Dimas G.. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; España. Ikerbasque; Españ

Hyperoxemia and excess oxygen use in early acute respiratory distress syndrome : Insights from the LUNG SAFE study

Publisher Copyright: © 2020 The Author(s). Copyright: Copyright 2020 Elsevier B.V., All rights reserved.Background: Concerns exist regarding the prevalence and impact of unnecessary oxygen use in patients with acute respiratory distress syndrome (ARDS). We examined this issue in patients with ARDS enrolled in the Large observational study to UNderstand the Global impact of Severe Acute respiratory FailurE (LUNG SAFE) study. Methods: In this secondary analysis of the LUNG SAFE study, we wished to determine the prevalence and the outcomes associated with hyperoxemia on day 1, sustained hyperoxemia, and excessive oxygen use in patients with early ARDS. Patients who fulfilled criteria of ARDS on day 1 and day 2 of acute hypoxemic respiratory failure were categorized based on the presence of hyperoxemia (PaO2 > 100 mmHg) on day 1, sustained (i.e., present on day 1 and day 2) hyperoxemia, or excessive oxygen use (FIO2 ≥ 0.60 during hyperoxemia). Results: Of 2005 patients that met the inclusion criteria, 131 (6.5%) were hypoxemic (PaO2 < 55 mmHg), 607 (30%) had hyperoxemia on day 1, and 250 (12%) had sustained hyperoxemia. Excess FIO2 use occurred in 400 (66%) out of 607 patients with hyperoxemia. Excess FIO2 use decreased from day 1 to day 2 of ARDS, with most hyperoxemic patients on day 2 receiving relatively low FIO2. Multivariate analyses found no independent relationship between day 1 hyperoxemia, sustained hyperoxemia, or excess FIO2 use and adverse clinical outcomes. Mortality was 42% in patients with excess FIO2 use, compared to 39% in a propensity-matched sample of normoxemic (PaO2 55-100 mmHg) patients (P = 0.47). Conclusions: Hyperoxemia and excess oxygen use are both prevalent in early ARDS but are most often non-sustained. No relationship was found between hyperoxemia or excessive oxygen use and patient outcome in this cohort. Trial registration: LUNG-SAFE is registered with ClinicalTrials.gov, NCT02010073publishersversionPeer reviewe