Lewis Acidic Salts Research Articles

ChemInform Abstract: Recent Advances in Metallo/Organo‐Catalyzed Immortal Ring‐Opening Polymerization of Cyclic Carbonates.

AbstractReview: ca. 50 refs.

Recent advances in metallo/organo-catalyzed immortal ring-opening polymerization of cyclic carbonates

The ring-opening polymerization of cyclic carbonate monomers derived from biomass feedstocks constitutes an attractive way to prepare polycarbonates that are potentially useful as high-tech materials or commodity “bioplastics”. This process can be catalyzed by inherently different systems ranging from simple basic organocatalysts, simple Lewis acidic metallic salts such as triflates, or more sophisticated discrete metallo-organic complexes derived from oxophilic metals (zinc, yttrium). In this perspective, the most recent achievements in this chemistry are reviewed. The quite different performances within reach of those catalytic systems, which are assessed in terms of intrinsic reactivity, robustness and regioselectivity towards dissymmetric monomers, are highlighted.

From bifunctional to trifunctional (tricomponent nucleophile-transition metal-lewis acid) catalysis: the catalytic, enantioselective α-fluorination of acid chlorides.

We report in full detail our studies on the catalytic, asymmetric α-fluorination of acid chlorides, a practical method that produces an array of α-fluorocarboxylic acid derivatives in which improved yield and virtually complete enantioselectivity are controlled through electrophilic fluorination of a ketene enolate intermediate. We discovered, for the first time, that a third catalyst, a Lewis acidic lithium salt, could be introduced into a dually activated system to amplify yields of aliphatic products, primarily through activation of the fluorinating agent. Through our mechanistic studies (based on kinetic data, isotopic labeling, spectroscopic measurements, and theoretical calculations) we were able to utilize our understanding of this "trifunctional" reaction to optimize the conditions and obtain new products in good yield and excellent enantioselectivity.

Kinetic resolution of terminal epoxides with phenols promoted by heterometallic Co–Al and Co–Ga salen complexes

The binuclear chiral (salen) Co complexes bearing Lewis acid salt (Al and Ga) and 4-nitrobenzene sulfonic acid (NBS) catalyze the enantioselective ring opening of terminal epoxides with phenol derivatives. The easily prepared complexes exhibited very high catalytic reactivity and enantioselectivity for the asymmetric ring opening of terminal epoxides with phenol and consequently provide enantiomerically enriched corresponding α-aryloxy alcohols (up to >99% ee). The two unit of salen complexes combined by Lewis acid exhibited co-operative catalysis during the ring opening reaction.

Activation of Lewis acid catalysts in the presence of an organic salt containing a non-coordinating anion: its origin and application potential

In the presence of a soluble organic salt containing non-coordinating anion (e.g., [bmim][SbF(6)] or [NR(4)][SbF(6)]), the catalytic activity of Lewis acid (MX(n)) was dramatically enhanced due to the anion exchange between the Lewis acid and organic salt.

Metal catalyzed rearrangement of a 2,2′-bipyridine Schiff-base ligand to a quaterpyridine-type complex

A Co(II) quaterpyridine-type complex has been prepared via a one-pot transformation of a 2,2'-bipyridine Schiff-base ligand in the presence of a Lewis acidic metal salt.

A Simple Homemade Reaction Station for use in Parallel Solution-Phase Synthesis. Optimization of a Regioselective One-Step Deprotective o-formylation Reaction Mediated by the Vilsmeier-Haack Reagent POCl3⋅DMF

We report herein the fabrication of a simple and price-affordable portable reaction station for use in parallel solution-phase synthesis. This homemade device uses currently available laboratory components and equipment. Specifically designed to fit standard magnetic hotplates/stirrers, it can simultaneously hold up to 24 heated and magnetically stirred glass reactors of both 10 and 50 mL capacities. Glass reactors are connected by flexible 16-gauge metal needles to a central gas manifold equipped with an inlet/outlet for vacuum and inert gases. Reaction temperatures can be optimally varied from -78 ( composite function)C to 150 degrees C. Using a statistical screening DOE method, this parallel array reactor station has been successfully operated to optimize the one-step deprotective O-formylation of a sterically hindered bis-O-tert-butyldiphenylsilyl (O-TBDPS) aromatic diol. The latter transformation was mediated by the Vilsmeier-Haack reagent POCl3.DMF using a range of Lewis acid and metal salt promoters, including their binary combinations.

Asymmetric Synthesis of Acyclic Amines Through Zr‐ and Hf‐Catalyzed Enantioselective Alkylzinc Reagents to Imines

AbstractReadily available chiral amino acid‐based ligands are used in metal‐catalyzed additions of alkylzinc reagents to various aromatic and aliphatic imines; the desired amine products are formed efficiently and in high levels of optical purity. In cases where the more Lewis acidic Zr salts afford lower efficiency, Hf‐based catalysts deliver significantly higher yields with similar enantioselectivities. Critical structural features of the N‐activating groups as well as the optimal chiral ligands are discussed. A mechanistic working model is presented to rationalize the existing data and to serve as a predictive tool.

Enantioselective Diels-Alder reactions catalyzed by hydrogen bonding.

Like molecules of life (e.g., proteins and DNA), many pharmaceutical drugs are also asymmetric (chiral); they are not superimposable on their mirror images. One mirror image form (enantiomer) of a drug can have desirable activity, the other not. Consequently, the development of methods for the selective synthesis of one enantiomer is of great scientific and economic importance. We report here that a simple, commercially available chiral alcohol, alpha,alpha,alpha',alpha'-tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL), catalyzes the all-carbon Diels-Alder reactions of aminosiloxydienes and substituted acroleins to afford the products in good yields and high enantioselectivities (up to 92% enantiomeric excess). It is remarkable that the reactions are promoted by hydrogen bonding, the ubiquitous "glue" that helps to keep water molecules together and holds up the 3D structures of proteins. Hydrogen bond catalysis is little used in chemical synthesis, wherein most reactions are promoted by complexes of Lewis acidic metal salts coordinated to chiral ligands. As it does for enzymes, hydrogen bonding not only organizes TADDOL into a well defined conformation, but, functioning as a Brønsted acid catalyst, it also activates the dienophile toward reaction with the diene. The gross structure of the TADDOL has been found to have a profound influence on both the rate and the enantioselectivity of the cycloadditions. These structure-function effects are rationalized by evaluating the conformation adopted by the TADDOLs in the crystal state. It is suggested that pi,pi-stacking plays an central role in the overall catalytic cycle, in particular, the enantioselective step.

The Influence of Lewis Acid/Base Chemistry on the Removal of Gallium by Volatility from Weapons-Grade Plutonium Dissolved in Molten Chlorides

It has been proposed that GaCl3 can be removed by direct volatilization from a Pu-Ga alloy that is dissolved in a molten chloride salt. Although pure GaCl3 is quite volatile (boiling point: 201°C), the behavior of GaCl3 dissolved in chloride salts is quite different because of solution effects and is critically dependent upon the composition of the solvent salt (i.e., its Lewis acid/base character). In this technical note, the behavior of gallium in prototypical Lewis acid and Lewis base salts is contrasted. It is found that gallium volatility is suppressed in basic melts and promoted in acidic melts. These results have an important influence on the potential for simple gallium removal in molten salt systems.

Titanium(IV) chloride and quaternary ammonium salt promoted Baylis-Hillman reaction.

The Baylis-Hillman reaction of aldehydes with alpha,beta-unsaturated ketones can be drastically affected by the reaction temperature and Lewis bases. When the reaction was carried out at -78 degrees C using catalytic amounts of quaternary ammonium salts (R4N+X-, X = Cl, Br, I) as Lewis bases, in the presence of titanium(IV) chloride, the chlorinated aldol adduct 1 was obtained as the major product. Quaternary ammonium bromides and iodides (R4N+X-, X = Br, I) have higher catalytic activity than corresponding chlorides (R4N+Cl-). Quaternary ammonium fluorides (R4N+F-) do not have activity at all. The amounts of Lewis acid and quaternary ammonium salts used affect the reaction rate and product. A plausible reaction mechanism is proposed. If the reaction was carried out at room temperature (about 20 degrees C) in the presence of titanium(IV) chloride and quaternary ammonium salts (R4N+X-, X = Cl, Br, I), the elimination product 3, derived from 1, was formed as the major product.

Raman spectra and isomerism of some chlorophenylphosphoranes (C6H5)nPCl5 — n (1 ≤ n ≤ 3) and their lewis acid salts

AbstractSyntheses of stable and metastable isomers for each of the chlorophenylphosphoranes, PhPCl4, Ph2PCl3 and Ph3PCl2, together with some Lewis acid salts are described. Comparison of Raman spectra of the salts with one set of isomers suggests an ionic formulation [PhnPCl] [Cl−] (1 ≤ n ≤ 3); correlation with spectra of Sb and As analogues of known structure suggest pseudo‐trigonal bipyramidal (Ψtbp) structures for the other isomers. Thermodynamically stable isomers are ionic Ph3PCl+Cl−, Ψtbp Ph2PCl3 and Ψtbp PhPCl4. Vibrational Raman assignments for the skeletal modes are given for each of the isomers and some of their Lewis acid salts. Frequency shifts arising from non‐bonded interactions in the ionic species are compared with those in the methyl‐substituted analogues.

Ring Transformation Mediated by Lewis Acids and Oxidizing Agents. Synthesis of 2-Methoxy-1H-imidazole from 5-Aminopyrimidin-4(3H)-one.

Treatment of 5-aminopyrimidln-4(3H)-one (1) with Lewis acidic metal salts such as zinc chloride, zinc bromide, zinc iodide, aluminum chloride, aluminum bromide, nickel chloride, copper(I) chloride, or copper(I) iodide in the presence of oxidizing agents such as ceric ammonium nitrate, ammonium persulfate, or phenyliodine(III) diacetate in methanol gave 2-methoxy-1H-imidazole (2).

Studies of titanium(IV) chloride in a strongly Lewis acidic molten salt: electrochemistry and titanium NMR and electronic spectroscopy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStudies of titanium(IV) chloride in a strongly Lewis acidic molten salt: electrochemistry and titanium NMR and electronic spectroscopyR. T. Carlin, Robert A. Osteryoung, J. S. Wilkes, and J. RovangCite this: Inorg. Chem. 1990, 29, 16, 3003–3009Publication Date (Print):August 1, 1990Publication History Published online1 May 2002Published inissue 1 August 1990https://doi.org/10.1021/ic00341a030RIGHTS & PERMISSIONSArticle Views467Altmetric-Citations70LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (877 KB) Get e-Alerts Get e-Alerts

Equilibria between Me xSiCl 4- x, x = 3, 2, 1, 0 and alkyl carboxylate esters

At 150°C equilibria are established between chlorosilanes and alkyl esters according to the equation: Me x SiCl 4- x + RCOOR′ → Me xSi(O 1 2 ) y (OOCR) z-y Cl 4- x-y-z + yRCOCl + zR′Cl When x = 3, y = 0, z = 0.56, when x = 1, y = 0.26, z = 098 When x = 1, y = z = 0.56; when x = 0, y = z = 0.53 Lewis acid salts such as ZnCl 2 or FeCl 3 are effective catalysts for the reactions leading to mixtures of these compounds.

How Mixed Catalysts Differ'

Catalysts from combinations of Lewis-acid salts, or from a Lewis-acid salt and a Bronsted acid, have been used in crosslink finishing of cotton textiles for many years. Whereas the effect on formaldehyde release was not a major factor in the early use of these catalysts, this effect presently influences the selection of the integral components of the mixture as well as the component ratio within the mixture. Interactions of physical property variables with formaldehyde release are given for mixtures of magnesium chloride and zinc nitrate with organic acids and with other salts, and for aluminum sulfate and selected alum salts. When proton donors are added to catalysts possessing considerable Bronsted activity, antagonism can occur. When proton donors are added in correct proportion to catalysts exhibiting little Bronsted activity, improvements can be realized in appearance-related properties while low formalde hyde release is maintained. Both pH of the crosslinking bath and of the fabric during cure influence property modification.

Refractive index of molten Lewis acid salt hydrates: mixtures of chromium(III) nitrate nonahydrate + calcium nitrate tetrahydrate

Refractive index of molten Lewis acid salt hydrates: mixtures of chromium(III) nitrate nonahydrate + calcium nitrate tetrahydrate

Catalyzed Orientation Reversals in Diels–Alder Reactions

Lewis acid catalysts cause an orientation reversal in the Diels–Alder additions of 2,6-di-methyl-1,4-quinone (1) and toluquinone (12) to 1-substituted 1,3-butadienes and to 1,2- and 1,3-dialkyl dienes. These results are explained by the preferential formation of one reactive quinone–Lewis acid salt.

Strong Lewis Acid Salts as Catalysts in Mild-Cure Finishing Treatments for Wrinkle Resistance

Lewis acid salts have been investigated in place of mineral acids as catalysts for wrinkle resistance treatments of cotton fabric with dimethylol methyl carbamate under mild-cure finishing conditions. Salts that are strong Lewis acids, such as aluminum chloride, aluminum nitrate, aluminum sulfate, and stannic chloride, produced finishes essentially equivalent to those of mineral acid catalysis when curing was conducted at 100°C. With curing at 60°C, however, the mineral acids are much more effective catalysts. Zinc chloride, zinc nitrate, and magnesium chloride, the catalysts widely used in con ventional pad-dry-cure finishing treatments, are weaker Lewis acids and are not suitable for mild-cure finishing.