Fluoride's new role: Selective and efficient monoreductions of imides can be achieved with polymethylhydrosiloxane (PMHS) and tetra‐n‐butylammonium fluoride (TBAF) as catalyst (see scheme). The system is characterized by good chemoselectivity, operational simplicity, and functional‐group tolerance; a concise mechanistic proposal was possible from in situ spectroscopic investigations.

Coupled ATR‐FTIR, UV/Vis, and Raman spectroscopy has been introduced for the monitoring of liquid phase hydrogenation reactions under elevated H2 pressure by implementation of spectroscopic immersion probes into a modified autoclave reactor. The setup was successfully tested for the heterogeneously catalyzed hydrogenation of several imine substrates under H2 pressures up to 20 bar. The conversion of the imines could be analyzed by Raman spectroscopy and the product formation was observable by attenuated total reflectance FTIR spectroscopy (ATR‐FTIR), which illustrates the benefits of coupling complementary spectroscopic methods. Separate spectroscopic investigations show that imines intensively interact with the phosphoric acid ester that is used as catalyst modifier, indicated by a shift of the original ν(CN) band of the imine to higher wavenumbers. UV/Vis spectroscopic investigations reveal a distinct shift of the absorption edge to a higher wavelength. Furthermore, the formation of adsorbates on the surface of used Pt/Al2O3 catalysts, resulting mainly from adsorbed imine, was detected by FTIR spectroscopic analysis. The potential of UV/Vis spectroscopy in transmission mode for analyzing the organic components was tested. Due to its high sensitivity at low concentrations this method offers an additional possibility for a quantitative in situ analysis of the reaction progress in real time.

As a new approach for tuning the electronic properties of pyrene derivatives, we converted 1‐bromopyrene into different substituted styrenes using the Mizoroki–Heck reaction. Several 1‐(arylalkenyl)pyrenes have been characterized and their electronic properties studied by absorption and emission spectroscopy. The effect of the electronic ambience on the emission spectra of these compounds is discussed. Amongst the intramolecular influences, such as electron donating or withdrawing groups, other influences in the form of solvatochromatism are considered. Electrochemical oxidation potentials determined by DPV (differential pulse voltammetry) are discussed with regard to substituent effects. The fine structure of the absorbance spectra obtained from photophysical measurements is compared with theoretical calculations performed by time dependent B3LYP DFT (TD‐DFT) methods using the 6‐31G* basis set. In this context, we discuss the calculated potential energy surfaces and geometric structures with regard to the substitution pattern of the pyrenes.

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Different spectroscopic methods were applied in situ as well as ex situ to elucidate the mode of action of the Lewis acids TiCl 4 and trimethylsilyl trifluoromethanesulfonate (TMSOTf) in the formal [3 + 3] cyclization reaction of a 1,3-bis(silyloxy)-1,3-butadiene with fluorinated ketenacetales. Different products were formed depending on the type of Lewis acid employed, which can be explained by their completely different interaction with the ketenacetale. Results of attenuated total reflection infrared (ATR-IR) and UV/vis spectroscopic studies revealed that TMSOTf interacts with only one site of the ketenacetale, forming an ionic species. In contrast, TiCl 4 forms a bischelate complex, which was confirmed by using X-ray crystal structure analysis. Both reaction pathways were studied by simultaneously applying in situ ATR-IR/UV/vis spectroscopy in a specifically developed reaction cell. During cooling and subsequent heating of the reaction mixture, formation and structural changes of different intermediates were observed, in particular in the case of the TMSOTf catalyzed reaction. Although the TiCl 4 mediated reaction proceeds in only one step, the TMSOTf route comprises two reaction steps. In situ spectroscopic results revealed that the applied workup procedure influences product formation and distribution as well.Scheme 1. General reaction scheme.

Neue Aufgabe für Fluorid: Selektive und effiziente Monoreduktionen von Imiden werden durch Verwendung von Polymethylhydrosiloxan (PMHS) und Tetra‐n‐butylammoniumfluorid (TBAF) als Katalysator ermöglicht (siehe Schema). Das System zeichnet sich durch gute Chemoselektivität, einfache Anwendbarkeit und Toleranz gegenüber verschiedenen funktionellen Gruppen aus. In‐situ‐spektroskopische Untersuchungen erlauben einen Vorschlag zum Mechanismus.

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The Mizoroki-Heck coupling of 1-bromopyrene with acrylates provides a convenient access to a variety of 3-pyrenylacrylates in very good yields (up to 93 %). Their photophysical properties combined with solvatochromic effects were studied. In addition, electrochemical oxidation potentials were determined by DPV (differential pulse voltammetry) measurements. The fine structure of the absorbance spectra obtained from photophysical measurements are compared with the results of theoretical calculations performed by time dependent TD-B3LYP methods using the 6-31G* basis set.