Synthesis and electrochemistry of remotely thioether‐functionalized disilenes

We report the synthesis of p-methylthio-functionalized disilenes with (oligo)phenylene-linkers of different sizes between the thiomethyl group and the Si=Si moiety. 29Si NMR and UV/vis data suggests that the linker-size affects the Si=Si moiety only moderately. Cyclic voltammetry reveals an increasing number of reduction events with the number of phenylene rings, which are therefore clearly associated to the oligo(phenylene) linking unit. The exchange current density of the oxidation and reduction reactions as determined by linear sweep voltammetry with a rotating disc electrode also shows significant differences between the prepared disilenes

Free Radical Chemistry of Phosphasilenes

Understanding the characteristics of radicals formed from silicon-containing heavy analogues of alkenes is of great importance for their application in radical polymerization. Bulky and electronic substituent effects in such compounds as phosphasilenes not only stabilize the Si=P double bond, but also influence the structure and species of the formed radicals. Herein we report our first investigations of radicals derived from phosphasilenes with Mes (2,4,6-trimethylphenyl), Tip (2,4,6-triisopropylphenyl), Dur (2,3,5,6-tetramethylphenyl) and NMe2 (dimethylamino) substituents on the P atom, using muon spin spectroscopy and DFT calculations. Adding muonium (a light isotope of hydrogen) to phosphasilenes reveals that: a) the electron-donor NMe2 and the bulkiest Tip-substituted phosphasilenes form several muoniated radicals with different rotamer conformations; b) bulky Dur-substituted phosphasilene forms two radicals (Si- and P-centred); and c) Mes-substituted phosphasilene mainly forms one species of radical, at the P centre. These significant differences result from intramolecular substituent effects

Chemie freier Radikale von Phosphasilenen

Das Verständnis der Eigenschaften von Radikalen, die ausgehend von Si-haltigen, schweren Analoga von Alkenen gebildet werden, ist wichtig für ihre Anwendung in der radikalischen Polymerisation. Sterische und elektronische Substituenteneffekte in Phosphasilenen stabilisieren nicht nur die Si=P-Doppelbindung, sondern beeinflussen auch die Struktur und Natur der gebildeten Radikale. Wir berichten hier über Untersuchungen an Phosphasilen-abgeleiteten Radikalen mit Mes-, Tip-, Dur- und NMe2-Substituenten am P-Atom mithilfe von Myonenspinspektroskopie und DFT-Rechnungen. Die Addition von Myonium (einem leichten Isotop von Wasserstoff) an Phosphasilene zeigt, dass a) das Elektronendonor-NMe2- und das sperrigste Tip-substituierte Phosphasilen mehrere myonierte Radikale mit unterschiedlichen Rotamer-Konformationen bilden; b) das sperrige Dur-substituierte Phosphasilen zwei Radikale (Si- und P-zentriert) bildet; und c) Mes-substituiertes Phosphasilen hauptsächlich eine Radikalspezies am P-Zentrum bildet. Diese signifikanten Unterschiede rühren von einem intramolekularen Substituenteneffekt her

Ungesättigte Siliziumspecies mit Peripherer Funktionalität - von Mehrfachbindungen zu Silicoid Clustern

Functional groups are a prerequisite for the application of unsaturated heavier main group species, e.g. as building blocks of extended systems. The thesis deals with the introduction and transformation of functionality in the periphery of "classical" multiply bonded species and of unsaturated clusters of silicon (siliconoids). A P-amino functionalized phosphasilene is shown to be a suitable reagent for the electrophilic transfer of the P=Si unit. Depending on the solvent polarity, it reacts with anionic nucleophiles either under substitution of the NMe2 group or in an unprecedented metal-amino exchange. In the context of the doping of Si=Si systems at the molecular scale, disilenes and heteronuclear silicon rings with boron and phosphorus functionalities were prepared from an anionic Si=Si reagent. Disilenes featuring remote sulfur-based anchors (designed for the grafting of Si=Si to gold surfaces) were obtained by a similar route. The reduction of siliconoids affords the first anionic silicon clusters with additional "naked" vertices. With these results, the missing link between silicon-based Zintl anions and neutral unsaturated silicon clusters was established. Proof-of-principle for the high potential for the transfer of the intact unsaturated cluster skeleton was demonstrated by reactions with representative electrophiles of Groups 13, 14 and 15. A broad variety of functionalized siliconoids is now readily accessible.Funktionelle Gruppen sind eine Voraussetzung für die Anwendung ungesättigter schwerer Hauptgruppenspezies, z. B. als Bausteine für erweiterte Systeme. Die Arbeit behandelt die Einführung und Umwandlung von Funktionalität in der Peripherie „klassischer“ mehrfach gebundener Spezies und ungesättigter Cluster des Siliciums (Silicoide). Ein P-Amino funktionalisiertes Phosphasilen erweist sich als geeignetes Reagenz zur elektrophilen Übertragung der P=Si-Einheit. Abhängig von der Lösemittelpolarität reagiert es mit anionischen Nukleophilen entweder unter Substitution der NMe2-Gruppe oder in einem neuartigen Metall-Amino-Austausch. Im Kontext der Dotierung von Si=Si-Systemen auf molekularer Ebene wurden Disilene und heteroatomare Siliciumringe mit Bor- und Phosphorfunktionalitäten aus einem anionischen Si=Si-Reagenz hergestellt. Disilene mit schwefelbasierenden Ankern (konzipiert für das Aufbringen von Si=Si auf Goldoberflächen) wurden auf gleichem Wege erhalten. Die Reduktion von Silicoiden lieferte die ersten anionischen Cluster mit zusätzlichen „nackten“ Gerüstatomen. Mit diesen Ergebnissen wurde das fehlende Bindeglied zwischen siliciumbasierenden Zintl-Anionen und neutralen Siliciumclustern etabliert. Das hohe Potential für den Transfer des intakten, ungesättigten Clustergerüstes wurde durch Reaktionen mit typischen Elektrophilen der Gruppen 13, 14 und 15 grundsätzlich demonstriert. Damit ist jetzt eine breite Vielfalt an funktionalisierten Silicoiden zugänglich

Estimating moisture changes in concrete using GPR velocity analysis: potential and limitations

Chloride-induced corrosion of steel rebars is a key problem for the durability and safety of reinforced concrete buildings such as bridges. Penetrating rainwater transports the chlorides into exposed parts of these buildings. Hence, the characterization of moisture conditions and their tempospatial variability is a fundamental part of an on-site practical investigation. Ground-penetrating radar (GPR) is a common tool for efficient non-destructive imaging of small-scale structural defects in concrete. When evaluating constant-offset GPR data, the analysis of diffraction hyperbolas yields quantitative information on GPR velocity, and thereby on the water content of the medium. However, when performing a thorough velocity analysis to estimate moisture content, precise information on time zero is a key problem. In this study, a GPR monitoring experiment has been performed under laboratory-like conditions across a reinforced concrete specimen. We show the results of a typical processing flow providing a highly-resolved structural image. Furthermore, we develop and apply a migration-based velocity and time-zero analysis and calculate changes in moisture content. We compare our results to independent measurements of concrete moisture to evaluate the potential and limitations of GPR for estimating tempo-spatial changes in concrete moisture content.Geo.XDFGposte

Diverse reactivity of an electrophilic phosphasilene towards anionic nucleophiles: Substitution or metal-amino exchange

WOS: 000383473600074PubMed: 27509901The reaction of MesLi (Mes=2,4,6-trimethylphenyl) with the electrophilic phosphasilene R-2(NMe2)Si-RSi=PNMe2 (2, R=Tip=2,4,6-triisopropylphenyl) cleanly affords R-2(NMe2)Si-RSi=PMes and thus provides the first example of a substitution reaction at an unperturbed Si=P bond. In toluene, the reaction of 2 with lithium disilenide, R2Si=Si(R)Li (1), apparently proceeds via an initial nucleophilic substitution step as well (as suggested by DFT calculations), but affords a saturated bicyclo[1.1.0]butane analogue as the final product, which was further characterized as its Fe(CO)(4) complex. In contrast, in 1,2-dimethoxyethane the reaction of 1 with 2 results in an unprecedented metal-amino exchange reaction.Deutsche Forschungsgemeinschaft (DFG) [SCHE906/4-1]; Alfried Krupp von Bohlen und Halbach-Foundation; COST Action [CM1302]Funding by the Deutsche Forschungsgemeinschaft (DFG SCHE906/4-1), the Alfried Krupp von Bohlen und Halbach-Foundation, and COST Action CM1302 (Smart Inorganic Polymers) is gratefully acknowledged. We thank the reviewers for their helpful comments

Site-selective functionalization of Si6R6 siliconoids

The recent progress in the synthesis of partially substituted neutral silicon clusters (siliconoids) revealed unique structures and electronic anisotropies that are reminiscent of bulk and nano surfaces of silicon. Here, we report the selective 2-lithiation of the global minimum Si6R6 siliconoid at a different vertex than in the previously reported isomeric 4-lithiated derivative (R = 2,4,6-iPr3C6H2). In order to enable an intuitive distinction of the vertices of the global minimum Si6R6 scaffold (which can be considered the silicon analogue of benzene in terms of thermodynamic stability), we introduce a novel nomenclature in analogy to the ortho–meta–para nomenclature of disubstituted benzenes. By treatment of the 2-lithiated Si6 cluster with Me3SiCl, SiCl4 H3B·SMe2, (Me2N)2PCl as well as with carboxylic acid chlorides RCOCl (R = tBu, Ph) various 2-functionalized Si6 clusters were obtained and characterized in solution and – in most cases – the solid state. The structural and spectroscopic effect of the position of the newly introduced functional group is discussed by comparison to the corresponding 4-functionalized derivatives

Modern Interdisciplinary and Interhospital Acute Stroke Therapy—What Patients Think About It and What They Really Understand

BackgroundAccess to reperfusion therapies in patients with large vessel occluding acute ischemic stroke demands process reorganization and optimization. Neurovascular networks are being built up to provide 24/7 endovascular stroke therapy service. In times of an increasingly complex stroke rescue chain little is known about patients’ and their relatives’ treatment awareness.MethodsAll patients, who received any kind of acute reperfusion treatment between January and August 2017 in the university hospital Aachen, and their proxies, were included in the survey. Patients were either primarily or secondarily transferred.ResultsFor all questions regarding stroke treatment patients and their caregivers provided concurring answers. 40% of both patients and caregivers did not understand the treatment that was performed. Finally, patients who perceived on their own that stroke detection was delayed had significantly longer onset to door times than patients who did not have this impression.ConclusionsThis study showed that patients’ and proxies’ answers correlated significantly. In case of patients’ unavailability extrapolation of treatment satisfaction from answers by proxies might be permitted. High percentages of patients and caregivers do not understand relevant information, possibly due to limits of communication in an emergency setting or deficits in communication during the hospital stay. More emphasis should be laid on providing further information during the hospital stay