Showing papers on "Lewis acids and bases published in 1983"

Electron‐Rich Half‐Sandwich Complexes—Metal Bases par excellence

Abstract: Electron-rich, half-sandwich complexes of the type CnRnML2 or CnRnMLL′ are built up of an aromatic five- or six-membered ring, a d8-metal, and either a pair of two-electron donors or an equivalent chelating ligand. Such complexes behave like Lewis bases and react with a wide variety of electrophiles, El or ElX, to form products with a new metal-element bond. According to their reactivity they are comparable to the Vaska-type compounds. Certain of the products obtained after addition of the electrophile undergo interesting subsequent reactions in which, for example, metal complexes containing molecules that are unstable in the free state, such as CS, CSe, CH2S, CH2Se, CH2Te, CH3CHS, CH3CHSe, CH2CS, CH2CSe, and CH2CTe are formed. Moreover, cycloadditions as well as reactions with coordinatively unsaturated transition-metal compounds which result in formation of heterometal binuclear complexes demonstrate that the metal bases CnRnML2 and CnRnMLL′ are valuable synthetic building blocks. Furthermore, very recent investigations have indicated links between metal basicity and the problem of CH activation.

Direct hydrogenation of carboxylic acids to alcohol and esters

Abstract: This invention provides an improved process for direct hydrogenation of a carboxylic acid to its corresponding alcohol with synthesis gas in the presence of a homogeneous catalyst comprising a ruthenium compound and a Lewis Acid metal halide.

Asymmetric Diels-Alder reaction: applications of chiral dienophiles

Abstract: On etudie les reactions de Diels-Alder d'une hydroxycetone vinylique avec divers dienophiles en presence d'acides de Lewis

Process for the preparation of aromatic carbonates

Abstract: An improved process for the preparation of aromatic carbonates selected from aliphatic aromatic carbonates and diaromatic carbonates comprising reacting at least one phenolic compound with at least one dialiphatic carbonate or at least one aliphatic aromatic carbonate in the presence of a catalytic amount of a catalyst comprised of (i) at least one Lewis acid, and (ii) at least one protic acid.

Method for modifying rubbers

Abstract: A method for modifying a rubber having an unsaturated carbon bond which comprises reacting the rubber with an organic compound represented by the general formula ##STR1## wherein --R represents a hydrocarbon group, and --X is --H, --CN or ##STR2## in which --Y represents an organic atomic grouping, in the presence of a Lewis acid to introduce an ester group. Optionally, the ester group introduced is converted into a carboxyl group by chemically treating the reaction product.

Scope and limitations of aliphatic friedel-crafts alkylations. lewis acid catalyzed addition reactions of alkyl chlorides to carbon-carbon double bonds

Abstract: Lewis acid catalyzed addition reactions of alkyl halides 1 with unsaturated hydrocarbons 2 have been studied. 1:l addition products 3 are formed if the addends 1 dissociate faster than the corresponding products 3; otherwise, polymerization of 2 takes place. For reaction conditions under which 1 and 3 exist mainly undissociated, solvolysis constants of model compounds can be used to predict the outcome of any such addition reactions if systems with considerable steric hindrance are excluded.

Baeyer-Villiger Oxidation with Me3SiOOSiMe3 under Assistance of SnCl4 or BF3·OEt2

Abstract: Treatment of ketones with bis(trimethylsilyl) peroxide and Lewis acid such as SnCl4 or BF3·OEt2 in dichloromcthane at room temperature affords esters in fair to excellent yields. Jasmine lactone is synthesized from 2-[(Z)-2-pentenyl]cyclopentanone by means of Me3SiOOSiMe3–BF3·OEt2 system without any protection of the carbon-carbon double bond. The oxidation of enol acetates of ketones to α-hydroxy (or α-acetoxy) ketones with Me3SiOOSiMe3–FeCl3 system is also disclosed.

Anionic polymerization of conjugated dienes in the presence of hindered triaryl boron or aluminum derivatives

Abstract: A process for the anionic polymerization of a conjugated 1,3-diene in a polar solvent consists of contacting the 1,3-diene with an organo alkali or alkaline earth metal initiator and a sterically hindered Lewis acid, allowing the 1,3-diene to polymerize in the polar solvent and terminating the polymerization reaction. Preferably the Lewis acid is a substituted triaryl derivative of a Group III element, especially boron. However in certain cases (e.g. where the aryl derivative itself is large) the Lewis acid may be an unsubstituted triaryl derivative of a Group III element. Suitable Lewis acids include trimesityl boron and tri (2,6-dimethylphenyl) boron. In preferred embodiments of the present process the 1,3-diene is butadiene, the polar solvent is tetrahydrofuran and the initiator is a difunctional initiator, especially an electron transfer reagent. The main advantages of the present process are that polymers with enhanced 1,4-content, a narrow molecular weight distribution and, in the case of telechelic polymers, with an enhanced difunctional specificity are obtained.

Synthesis of electron-deficient oxetanes. 3-Azidooxetane, 3-nitrooxetane, and 3,3-dinitrooxetane

Abstract: L'azido-3 oxetanne (A) est obtenu par reaction de l'azoture de sodium avec le tosylate d'oxetannol-3; le nitro-3 oxetanne est obtenu par reduction de A puis oxydation par l'acide m-chloroperbenzoique; il est ensuite transforme en dinitro-3,3 oxetanne (B) par oxydation et nitration par le tetranitromethane. Polymerisations de A et B

Polymerization of conjugated dienes

Abstract: The invention relates to a catalyst system comprising (a) a compound of a rare earth element and, as cocatalyst, a second component (b) comprising an organomagnesium compound. In the polymerization of a conjugated diene this catalyst gives a polymer having a very high content of trans 1,4 isomer. A third component (c) which is a Lewis acid alters the reaction to give a polymer having a very high content of cis 1,4 isomer. If desired reaction can be initiated using components (a) and (b) alone and component (c) then added at the desired conversion to produce a block polymer having a block of high trans content followed by a block of high cis content.

Homogeneous nickel‐catalyzed olefin hydrocyanation

Abstract: Publisher Summary This chapter discusses homogeneous nickel-catalyzed olefin hydrocyanation. It describes the chemistry behind the du Pont adiponitrile process from a mechanistic viewpoint. The hydrocyanation process can be broken down into two major steps. In the first step, hydrogen cyanide (HCN) is added to butadiene in the presence of NiL4 catalyst to give 3-pentenenitrile (3PN) and 2-methyl-3-butenenitrile (2M3BN). In the second step, a Lewis acid promoter is added to the NiL4 (L = a phosphorus ligand) catalyst to effect the double bond isomerization of 3PN to 4-pentenenitrile (4PN) concurrently with the selective addition of HCN to 4PN. By-products in the second step include 2-methylglutaronitrile (MGN), ethylsuccinonitrile (ESN), and 2-pentenenitrile (2PN) arising, respectively, from Markovnikov addition to 4PN, direct addition of HCN to 3PN, and isomerization of 3PN to its conjugated isomer that is not hydrocyanated. The three different types of reactor system include (1) semibatch, (2) pulse, and (3) continuous. The semibatch reactor is the simplest. All reagents except the HCN are placed in a thermostated vessel (usually glass).

Selective .gamma.-substitution of .alpha.,.beta.-unsaturated esters via .alpha.-trimethylsilyl .beta.,.gamma.-unsaturated esters

Abstract: Preparation d'un certain nombre d'esters du type methyl-3 trimethylsilyl-2 butene-3oate d'ethyle et etude de leurs reactions avec divers electrophiles (aldehydes, cetones, acetals, chlorures d'acyle etc.) en presence d'acides de Lewis (TiCl 4 et triflate de trimethylsilyle)

Metallorganische Lewis-Säuren, XIV [1]. Ethylen-verbrückte Mangan- und Rheniumcarbonyle; Tieftemperatur-Röntgenstrukturanalyse von (OC)5ReCH2CH2Re(CO)5 / Organometallic Lewis Acids, XIV [1]. Ethylene Bridged Manganese and Rhenium Carbonyls; Low Temperature X-Ray Structure of (OC)5ReCH2CH2Re(CO)5

Abstract: Abstract The tetrafluoroborato complexes (OC)5MFBF3 (M = Mn, Re) which are obtained by methyl abstraction from (OC)5MCH3 using Ph3CBF4 react with ethylene or propene at room temperature and 1 bar to give [(OC)5M(alkene)]+ BF4-. By nucleophilic addition of the carbonylmetalates [M(CO)s] -(M = Mn, Re) to the coordinated alkene in these cationic complexes [(OC)5M(alkene)]+ the alkene bridged complexes (OC)5MCH2CH(R)M(CO)5 (M = Mn, Re; R = H, Me) are formed. Also the mixed-metal complex (OC)5MnCH2CH2Re(CO)5 has been isolated. According to an X-ray structure at low temperature (OC)5ReCH2CH2Re(CO)5 can be considered as a dimetal substituted ethane with a carbon-carbon distance of 152 pm.

Process for preparing an oligomer of a diisocyanate

Abstract: The invention is directed to a process for preparing an oligomer of a diisocyanate, optionally in an inert solvent, in the presence of a suitable catalyst, followed by deactivation of the catalyst. The invention is characterized in that a diisocyanate according to formula I of the formula sheet, where R 1 represents an alkyl group with one or more C atoms, a substituted or unsubstituted phenyl group or a group according to formula II of the formula sheet, where R 1 ' and R 1 " represent alkyl groups with one or more C atoms, and where R 2 . R 3 and R 4 are the same or different and are chosen from the group consisting of: - alkyl groups with one or more C atoms - alkoxy groups with one or more C atoms - H, is allowed to react at a temperature of between 10°C and 100°C in the presence of a metal salt of a C 2-20 carboxylic acid and/or of a C 2 -C 20 alkanol in an amount of between 50 and 1000.10 -6 mole/kg of polyisocyanate until the conversion desired has been reached, followed by deactivation of the reaction by addition of a deactivating agent from the group formed by inorganic acids, Lewis acids, and carboxylic acid halides in an amount at least stoichiometrically equivalent to the amount of catalyst.

The platinum complex catalyzed reductive N-carbonylation of nitroarenes to the carbamates.

Abstract: The platium catalyst combined with triphenylphosphine, tin(IV) chloride, and triethylamine showed high activity for the reductive N-carbonylation of nitroarene in ethanol at 180 °C under carbon monoxide of 60 kg cm−2. From nitrobenzene, ethyl phenylcarbamate was obtained in 83% yield. Iron(III) chloride, aluminum chloride and titanium(IV) chloride could be used as Lewis acids in place of tin(IV) chloride. Various nitroarenes were transformed into corresponding carbamate in moderate to excellent yields with the platinum catalyst.

The production of ethyl acetate from ethylene and acetic acid using clay catalysts

Abstract: A B S T R A C T: Wyoming bentonite, exchanged with cations of high charge density, is an efficient and selective catalyst for the production of ethyl acetate, in a single step, from ethylene and acetic acid. The reaction occurs in the interlamellar space of the clay where it is proposed that strong Br6nsted acid sites on the clay coupled with highly polarized intercalated reactants produce a reaction which is otherwise difficult to carry out. Montmorillonites have both Br6nsted and Lewis acid sites and when exchanged with cations having a high charge density produce highly-active catalysts for proton-catalysed reactions. Intercalated organic molecules are mobile and can be highly polarized when situated in the space between the charged clay layers. These exchanged montmorillonites have been successfully used as catalysts, e.g. for the dehydration of alcohols to di-alkyl ethers (Ballantine et al., 198 l a), the condensation of primary amines to secondary amines (Ballantine et al., 1981b) and the esterification of organic acids by alkenes (Ballantine et al., 198 lc); all these are thought to be interlamellar reactions. The present study is also concerned with esterification, and examines the catalytic activity of different ion-exchanged Wyoming bentonites in the reaction of ethylene and acetic acid to yield ethyl acetate. This difficult reaction (equation l) requires catalysts with strong Br6nsted activity:

Synthesis of (±)-trixagol by an electrophilic cyclization of an allylsilane

Abstract: 1,5-Dienes containing an allylsilane are cyclized by Lewis acids to methylenecyclohexanes. The trimethylsilyl group exerts a strong activating and directing influence on the regioselectivity of thi...