Ruthenium Olefin Metathesis Catalysts Bearing Carbohydrate-Based N-Heterocyclic Carbenes

Ru-based olefin metathesis catalysts containing carbohydrate-derived NHCs from glucose and galactose were synthesized and characterized by NMR spectroscopy. 2D-NMR spectroscopy revealed the presence of Ru−C (benzylidene) rotamers at room temperature, and the rate of rotation was measured using magnetization transfer and VT-NMR spectroscopy. The catalysts were found to be effective at ring-opening metathesis polymerization (ROMP), ring-closing metathesis (RCM), cross-metathesis (CM), and asymmetric ring-opening cross-metathesis (AROCM) and showed surprising selectivity in both CM and AROCM

A Tandem Approach to Photoactivated Olefin Metathesis: Combining a Photoacid Generator with an Acid Activated Catalyst

Combining an acid activated precatalyst with a photoacid generator (PAG) in the presence of ultraviolet light resulted in a highly efficient catalyst for olefin metathesis. The tandem system of precatalyst and PAG was capable of both ring closing metathesis (RCM) and ring opening metathesis polymerization (ROMP) in good to excellent conversion. Mechanistic investigations revealed that the catalytically active species is very similar to that of other well-known Ru-based catalysts

Cis-Selective Ring-Opening Metathesis Polymerization with Ruthenium Catalysts

Cis-selective ring-opening metathesis polymerization of several monocyclic alkenes as well as norbornene and oxanorbornene-type monomers using a C–H activated, ruthenium-based metathesis catalyst is reported. The cis content of the isolated polymers depended heavily on the monomer structure and temperature. A cis content as high as 96% could be obtained by lowering the temperature of the polymerization

Application of Diode Laser Molecular Absorption Spectroscopy for Studies of Gas Concentrations in Food Packages

When it comes to absorbing and emitting radiation, molecules show similar properties as atoms do. A signicant dierence though, is that a molecular spectrum consists of notably more absorption lines compared to an atomic spectrum. The additional lines appear due to the fact that molecules can not only exist in electronic, but also in vibrational and rotational energy states. Each gas has uniquely dened absorption lines, which makes it possible to associate a ngerprint to the gas. Molecular spectroscopy enables to scan over these lines to determine the existence of a specic gas. With, for example, the help of Tunable Diode Laser Absorption Spectroscopy (TDLAS), which has been used in this work, and by applying the Beer-Lambert law, also the gas concentration can be obtained. Nevertheless, for a precise calculation of the gas concentration the path length travelled by light needs to be available. This especially can cause diculties when turbid materials are examined, in which the light scatters a lot, and therefore the dimension of the sample does not correspond to the path length of the light anymore. This work includes the examination of food packages lled with modied atmosphere. Diode lasers emitting wavelengths around 760 nm and 2054 nm are used to scan over an absorption line of oxygen and carbon dioxide, respectively. First, it is presented how the carbon dioxide concentration of 75 % in a sealed bread rolls package is obtained. Afterwards TDLAS combined with a technique called Wavelength Modulation Spectroscopy (WMS), which allows to detect low absorption signals, is used to perform a time dependent measurement on a package with ageing milk inside. The carbon dioxide and oxygen concentrations are monitored simultaneously over 5 days. With the relation between the two concentrations it is possible to speculate about biological activity in the milk package. Another important aspect is, that all the measurements are done non-intrusively, which leaves the package intact allowing usage after the measurement.

Protonolysis of a Ruthenium–Carbene Bond and Applications in Olefin Metathesis

The synthesis of a ruthenium complex containing an N-heterocylic carbene (NHC) and a mesoionic carbene (MIC) is described wherein addition of a Brønsted acid results in protonolysis of the Ru–MIC bond to generate an extremely active metathesis catalyst. Mechanistic studies implicated a rate-determining protonation step in the generation of the metathesis-active species. The activity of the NHC/MIC catalyst was found to exceed those of current commercial ruthenium catalysts

Z-Selective Homodimerization of Terminal Olefins with a Ruthenium Metathesis Catalyst

The cross-metathesis of terminal olefins using a novel ruthenium catalyst results in excellent selectivity for the Z-olefin homodimer. The reaction was found to tolerate a large number of functional groups, solvents, and temperatures while maintaining excellent Z-selectivity, even at high reaction conversions

Thermally Stable, Latent Olefin Metathesis Catalysts

Highly thermally stable N-aryl, N-alkyl N-heterocyclic carbene (NHC) ruthenium catalysts were designed and synthesized for latent olefin metathesis. These catalysts showed excellent latent behavior toward metathesis reactions, whereby the complexes were inactive at ambient temperature and initiated at elevated temperatures, a challenging property to achieve with second-generation catalysts. A sterically hindered N-tert-butyl substituent on the NHC ligand of the ruthenium complex was found to induce latent behavior toward cross-metathesis reactions, and exchange of the chloride ligands for iodide ligands was necessary to attain latent behavior during ring-opening metathesis polymerization (ROMP). Iodide-based catalysts showed no reactivity toward ROMP of norbornene-derived monomers at 25 °C and upon heating to 85 °C gave complete conversion of monomer to polymer in less than 2 h. All of the complexes were very stable to air, moisture, and elevated temperatures up to at least 90 °C and exhibited a long catalyst lifetime in solution at elevated temperatures

The capability of satellite borne remote sensors to measure stratospheric trace constituents. Volume 3: Supporting material

Contained in this volume is material of a supportive nature not considered to be of sufficient importance to be included in the other two previous volumes. This material is of two types:(1) information and numerical evaluations used in the development of mission evaluations for stratospheric trace constituent measurement;and (2) various spatial and temporal distributions for those stratospheric trace species having sufficient measurements available to warrant their presentation