Olefinations silver® carbonate

In a process developed by Myers et al., aromatic carboxylic acids were directly employed as substrates for Heck olefinations, albeit in the presence of a large excess of silver carbonate [38]. This base both facilitates the decarboxylation step and acts as an oxidant, generating arylpalladium(II) intermediates. In related processes, arylphosphonic [39] and arylboronic acids [40] were used as aryl sources in the presence of an oxidant. 

Ethylene oxide is prepared industrially by the vapor phase oxidation of ethylene over a supported silver catalyst at elevated temperatures.49la c Application of this reaction to higher olefins results in complete oxidation of the olefin to carbon dioxide and water. In general, autoxidations of olefins are notoriously unselective because of the many competing reactions of the intermediate peroxy radicals in these systems. 

The silver-carbon bond in compounds containing a perfluoroalkyl group is considerably more stable than in non-fluorinated compounds. The synthesis can be accomplished by the nucleophilic addition of silver fluoride to fluoro-olefines. A typical example of this reaction is given in equation 9. The complexes are soluble in organic solvents and have been isolated as the 1 1 complexes with acetonitrile [RAg(CH3CN)]23. 

The role of steric interactions on anomalous stereoselectivity in the Wittig reaction has been examined. " DFT calculations combined with a distortion/interaction energy analysis show that the anomalous Z selectivity observed in Wittig reactions of o-substituted benzaldehydes is not caused by phosphorus-heteroatom interactions in the addition transition state but is predominantly steric in nature. The calculations reproduced correctly the stereoselectivity preferences for a wide range of reactant pairs as well as relative reactivities for different substituent types. An efficient synthesis of olefins by the coupling of stabilized, semi-stabilized, and non-stabilized phosphorus ylides with various carbonyl compounds in the presence of silver carbonate has been reported. Wittig olefination of aromatic, heteroaromatic, and aliphatic aldehydes (yields up to 97%) and a ketone (yield 42%) was demonstrated. 

The conversion of acetylenes into olefinic esters by use of addition reactions has been illustrated by the following two examples, (i) 1-Alkenyl boranes, which are readily prepared by the hydroboration of alkynes, are converted into a,fi-unsaturated carboxylic esters in good yield by reaction with carbon monoxide in the presence of palladium chloride and sodium acetate in methanol the process is carried out at atmospheric pressure and occurs with retention of configuration with respect to the alkenyl borane. (ii) Carboxylic acids add to acetylenes in the presence of silver carbonate to provide a novel synthesis of enol esters, which are formed in an 8 2 mixture of isomers. ... 

The olefin complexes of these metals are often readily decomposed in aqueous solution and Cu(I)-olefin complexes are conveniently prepared by reduction of ethanolic solutions of copper(II) halides and the olefin with SO2 [73]. Distribution studies of olefins between carbon tetrachloride and aqueous solutions of silver and copper salts show that the Cu(I)-olefin complexes hav6 considerably higher stability constants than the analogous silver complexes [74]. Evidence for a relatively weak olefin-metal bond in the complexes of both metals comes from infrared and Raman spectra which show that usually the stretching frequency of the co-ordinated C=C is lowered by only 50-60 cm i compared with a lowering of > 120 cm i found for most olefin-platimun complexes. In the acrolein complex [(CHj=CHCHO)CuCflj the C=C stretch is lowered by 90 an [74fl]. 

Olefin Complexes. Silver ion forms complexes with olefins and many aromatic compounds. As a general rule, the stabihty of olefin complexes decreases as alkyl groups are substituted for the hydrogen bonded to the ethylene carbon atoms (19). 

In the 1940s and 1950s, a considerable amount of research was funded to find and develop the chemists impossible dream a process for the direct oxidation of ethylene to EO, without any by-products. Finally, Union Carbide found the silver bullet that did the joE)—a catalyst made of silver oxide. Silver oxide is the only substance found having sufficient activity and selectivity. (Activity relates to the amount of conversion, selectivity relates to the right yield.) Moreover, ethylene is the only olefin affected in this way. The others, propylene, butylene, etc., tend to oxidize completely, forming carbon dioxide and water. But when silver oxide is used as a catalyst with ethylene, the dominant reaction is the formation of EO. Some ethylene still ends up being further oxidized, as much as 25% in some processes, as shown in Figure 10—2. 

The first metal-olefin complex was reported in 1827 by Zeise, but, until a few years ago, only palladium(II), platinum(Il), copper(I), silver(I), and mercury(II) were known to form such complexes (67, 188) and the nature of the bonding was not satisfactorily explained until 1951. However, recent work has shown that complexes of unsaturated hydrocarbons with metals of the vanadium, chromium, manganese, iron, and cobalt subgroups can be prepared when the metals are stabilized in a low-valent state by ligands such as carbon monoxide and the cyclopentadienyl anion. The wide variety of hydrocarbons which form complexes includes olefins, conjugated and nonconjugated polyolefins, cyclic polyolefins, and acetylenes. 

Complexes of Olefines and. Silver Ion.—Much work has been done on the interaction of the silver ion, Ag+, with unsaturated and aromatic hydrocarbons. (Mercuric ion and some other metal ions also react with carbon-carbon double bonde.) The structure proposed by Win-gtein and Lucas11 is probably essentially correct. Let us consider a silver ion and ethylene. The system is an electron-deficient one there are 12 valence electrons and 13 valence orbitals (including one orbital for the silver ion). We may write three structures for the complex ... 

A method of considerable industrial importance for the large-scale preparation of ethylene oxide is direct oxidation of ethylene at elevated temperatures over a suitably prepared metallic silver catalyst. Although the reaction may be written aa indicated in Eq. (09), in actual practice only about half the ethylene is converted into ethylene oxide, the remainder being oxidized further to carbon dioxide and water. In spite of this seeming disadvantage, catalytic oxidation appears at present to bo economically competitive with chlorohydrin formation aa a means for the commercial production of ethylene oxide.MM Unfortunately, other olefins, such as propylene and mo-butylene for example, apparently give only carbon dioxide and water under the usual oxidation conditions,1310 so that until now the patent hu balance ethylene oxide has been the only representative accessible by tins route. 

Concurrently with the work on carbon dioxide and hydrogen sulfide at General Electric, Steigelmann and Hughes [27] and others at Standard Oil were developing facilitated transport membranes for olefin separations. The principal target was the separation of ethylene/ethane and propylene/propane mixtures. Both separations are performed on a massive scale by distillation, but the relative volatilities of the olefins and paraffins are so small that large columns with up to 200 trays are required. In the facilitated transport process, concentrated aqueous silver salt solutions, held in microporous cellulose acetate flat sheets or hollow fibers, were used as the carrier. 

With the chemical activation process, the precursor is oxidized by silver ion. An electrochemical process using a carbon-carbon pair of electrodes, has been shown to promote the formation of the ylid which is reacted with electron-poor olefins 452... 

A paper dating from 1976 investigated the reaction of olefins or alcohols with cationic copper and silver complexes of carbon monoxide 49 The remarkable outcome of these kinetic measurements is that there is no difference between the catalytic behavior of Cu(CO) + and Ag(CO)2 +. 

Compounds containing carbon-carbon double bonds m y also act as Lewis bases. The rather high solubilities of the inorganic Lewis acids, boron trifluoride, aluminum bromide, and silver perchlorate, in benzene derivatives and in olefinic compounds suggest acid-base interactions. Addition compounds formed from silver perchlorate and a number of such hydrocarbons have been isolated it has been shown that the silver ion is not bonded to any single carbon atom but sits astride the two -electron dumbbells as shown in Figure 5-1. Thus, such adducts are... 

The hydroxy-binaphthyl functionalised saturated imidazolium salt is readily available from 1-amino-I -hydroxy-binaphthyl in a reaction with a ( oc-protected mesitylamine aldehyde [86] (see Figure 4.24). The resulting Schiff base is reduced to the diamine by Na(OAc)3BH. Subsequent deprotection and ring closure reaction with triethyl orthoformate yields the corresponding hydroxy-binaphthyl functionalised saturated imidazolium salt. Reaction with silver(I) carbonate and subsequent carbene transfer to the ruthenium(II) precursor yields the asymmetric olefin metathesis precatalyst. 

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