The use of chiral (salen)TiCl2 complexes to induce the asymmetric addition of trimethylsilyl cyanide
to aldehydes has been investigated. The complexes are catalytically active at substrate-to-catalyst ratios as
high as 1000:1, and the optimal catalyst (2e) which is derived from (R,R)-1,2-diaminocyclohexane and 3,5-di-tert-butyl-2-hydroxybenzaldehyde produces trimethylsilyl ethers of cyanohydrins with up to 90% enantiomeric
excess at ambient temperature. Water plays a key role in these reactions since under strictly anhydrous conditions
much lower enantiomeric excesses are produced. The role of water has been shown to be to generate dimeric
complexes of the form [(salen)Ti(μ-O)]2 (4) which are the real catalyst precursors. A structure for one of these
complexes (4a derived from (R,R)-1,2-diaminocyclohexane and 2-hydroxybenzaldehyde) has been determined
by X-ray crystallography. The dimeric complexes are more active than the dichloride precursors, and at substrate-to-catalyst ratios between 100 and 1000:1 give cyanohydrin trimethylsilyl ethers with up to 92% enantiomeric
excess in less than 1 h at ambient temperature.
Keywords: Asymmetric catalysis / Cyanohydrins / Titanium / AldehydesTitanium complexes 1 derived from chiral salen ligands are highly active precatalysts for the asymmetric addition of trimethylsilyl cyanide to aldehydes and ketones. Based on spectroscopic studies and the identification of adducts between complexes 1 and carbonyl compounds or trimethylsilyl Scheme 1 [a]
Keywords: Asymmetric catalysis / Cyanohydrins / Titanium / AldehydesTitanium complexes 1 derived from chiral salen ligands are highly active precatalysts for the asymmetric addition of trimethylsilyl cyanide to aldehydes and ketones. Based on spectroscopic studies and the identification of adducts between complexes 1 and carbonyl compounds or trimethylsilyl
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Geotechnical data are increasingly utilized to aid investigations of coastal erosion and the development of coastal morphological models; however, measurement techniques are still challenged by environmental conditions and accessibility in coastal areas, and particularly, by nearshore conditions. These challenges are exacerbated for Arctic coastal environments. This article reviews existing and emerging data collection methods in the context of geotechnical investigations of Arctic coastal erosion and nearshore change. Specifically, the use of cone penetration testing (CPT), which can provide key data for the mapping of soil and ice layers as well as for the assessment of slope and block failures, and the use of free-fall penetrometers (FFPs) for rapid mapping of seabed surface conditions, are discussed. Because of limitations in the spatial coverage and number of available in situ point measurements by penetrometers, data fusion with geophysical and remotely sensed data is considered. Offshore and nearshore, the combination of acoustic surveying with geotechnical testing can optimize large-scale seabed characterization, while onshore most recent developments in satellite-based and unmanned-aerial-vehicle-based data collection offer new opportunities to enhance spatial coverage and collect information on bathymetry and topography, amongst others. Emphasis is given to easily deployable and rugged techniques and strategies that can offer near-term opportunities to fill current gaps in data availability. This review suggests that data fusion of geotechnical in situ testing, using CPT to provide soil information at deeper depths and even in the presence of ice and using FFPs to offer rapid and large-coverage geotechnical testing of surface sediments (i.e., in the upper tens of centimeters to meters of sediment depth), combined with acoustic seabed surveying and emerging remote sensing tools, has the potential to provide essential data to improve the prediction of Arctic coastal erosion, particularly where climate-driven changes in soil conditions may bias the use of historic observations of erosion for future prediction.
This exploratory study evaluates the following moderation scheme against global warming: deploying nanoparticles in the atmosphere in order to scatter a tiny amount of sunlight (1% or 2W/m2) up to space. Such a strategy could be a last-resort method to counteract unbearable effects of global warming. For particles made of a wide range of known materials, the scattering ability is defined to quantify how efficient the particle is at scattering sunlight. This scattering ability is a function of the particle radius and index of refraction, and is calculated by an in-house numerical code solving the Mie scattering equations. The code is validated against scattering calculations for SO2 particles published by Schwartz[1]. Our calculations show that an optimum particle size exists, which would minimize the amounts to be deployed in the atmosphere. Also, we evaluate the deployment of biodegradable nanoparticles, which would counteract global warming and minimize dangers related to their redeposition.
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