Silver complexes ether

Hoveyda and coworkers reported that the silver complex generated from AgF2 and an amino acid-based ligand could be used for the asymmetric aldol reaction with silyl enol ethers and a-ketoesters (Table 9.11).23... 

Spot test To 1 drop of the test solution add 1 drop nitric acid (2m), then 1 drop of the reagent. A red-violet precipitate or stain is formed if silver ions are present. Alternatively, the test may be performed on a spot plate, or in a semimicro test tube in the latter case the excess of the reagent is extracted with diethyl ether or amyl alcohol, when violet specks of the silver complex will be visible under the yellow solvent layer. 

The cationic complex of silver and 1,10-phenanthroline (phen) has been found to react with Bromopyrogallol Red to yield an ion-associate which can be extracted into nitrobenzene (e = 3.2T0" at 590 nm) [31,32]. The cationic complex, Ag(phen)2 gives ion-associates also with acid dyes, such as Rose Bengal (formula 4.35) and eosin (formula 4.34) (nitrobenzene) [33]. Extractable ion-associates of cationic silver complex with 1,4,8,11-tetrathiacyclotetradecane (crown ether), and various chromogenic anions [34] should also be mentioned. 

The synthesis of cahx[4]arene dimelamines with different functionalities and their self-assembly with barbituric and cyanuric acid to hydrogen-bonded nanostructures have been published <05OBC3727> Unique ionophores of penta-crown ethers have been prepared by the reaction of l,3,5-triacryloylhexahydro-l,3,5-triazine (TAHTA) with diaza 18-crown-6 followed by Michael addition, and their binding capabilities towards alkali metal cations studied <05SL2257>. New silver complexes of polydentate ligands including a derivative of pyrazol-l-yl-l,3,5-triazine have been reported <05EJ14370>. 

Macrocyclic Thiophens. - Novel macrocyclic Schiff-bases (161), containing thiophen, have been prepared by the non-template condensation of a,co-amino-ethers with thiophen-2,5-dicarbaldehyde. Silver complexes were prepared and crystal structures were determined both for some macrocycles and for a silver complex. In attempts to prepare bridged thia[17]-annulenes, (162) was prepared through the reaction of 2,5-dichloromethyl-thiophen with p-carboxytoluene-a-thiol. Transformation of the carboxyl groups of (162) into bromomethyl, followed by reaction with sodium sulphide,gave (163). The Wittig reaction of 3,4-diformyl-2,5-dimethylthiophen... 

Several silver complexes with crown ethers and cal-rxarenes have been synthesized. In the design of discrete molecules and infinite chains in silver acetylide chemistry, crown ethers function as blocking groups or protective cordons around a polyhedral C2 Ag cage so that the isolation of lower-dimensional supramolecular entities can be achieved. ... 

The anionic nature of 5 results in excellent solubility in ether solvents compared with that of the neutral, silver complex 3. Although we have isolated several silver tellurium eomplexes 3 with different phosphine ligands (PEt3, PEtaPh, PPr"3), the same cannot be said for 5 for which, to date, only the PEt3 derivative has been isolated and characterized via the condensation reaction outlined in Scheme 4. One distinct advantage this route does offer is, however, the possibility of synthesizing ternary and quaternary phase nanoclusters by promoting condensation of different cluster molecules. 

To introduce an epoxy group on the terminal double bond, the other alkene function was protected by bromoetherification to produce the bromo ether, which was desilylated and compound 452 provided. In the final two steps, olefin 453 was epoxidized with m-CPBA and deprotected with a zinc-silver complex to obtain ( )-verrucarol (454) (Scheme 8.13). 

A family of tris(pyrazolyl)borate (Tp) silver complexes (Scheme 1, catalysts 1-7) have been independently developed by Dias and Perez s groups, which proved to be efficient for carbene insertion in sp C-H bonds with diazoacetates [8, 15-24]. For example, in 2004, Dias, Lovely, and coworkers reported early examples of carbene insertion into sp C-H bond of alkanes and ethers by silver with tris (pyrazolyl)borate complex 1 [18,19]. In this reaction, using neat alkane as substrate... 

The silver complexes containing chiral ligands are scarcely investigated as chiral catalyst. Recently, cationic silver(I)-BINAP complex has been shown to be an effective catalyst in the asymmetric Mukaiyama aldol reaction (316). A similar system derived from AgC104 and BINAP showed high enantioselectivity in asymmetric amination of silyl enol ethers (317). 

The successful use of the silver complex formed from an iso-leucine-derived phosphine (L2 in Scheme 11.4) as catalyst for the multicomponent Mannich reaction of silyl enol ethers 10 with in situ formed aliphatic imines allowed its application in the enantioselective synthesis of the alkaloid sedamine (56% yield, 98% ee) [17]. Also cyclic and acyclic alkenyl trichloroacetates (10, Z = EtOCO) can be used in the reaction with ethyl glyoxylate and diverse aniline derivatives 11 catalyzed by... 

Evaporate to dryness and examine only an aliquot of the ether extract. To the rest, prior to evaporation, add a few drops of 50 per cent silver nitrate solution, dropwise, with shaking. Shake well and allow the precipitate to settle, then filter through a Whataian No. 541 filter paper washing well with ether. Dry in a desiccator and examine by infrared spectrophotometry and the nujol emulsion technique. Also, suspend an aliquot of the precipitate in chloroform, acidify with a little hydrochloric acid, shake and carry out nuclear magnetic resonance spectroscopic examination of the chloroform extract. This should suffice for the identification of the thioacid. The dark colour of the silver complex is probably due to the presence of silver sulphide. 

If required, the free acid, usually thioglycollic, or thiol can be obtained in a purer state by acidifying the silver complex with hydrochloric acid and extracting the liberated acid and thiol with diethyl ether. The infrared and nuclear magnetic resonance examinations can then be repeated on the thioacid or thiol itself. 

One approach to achieve this slower reaction is to complex the silver ion with an appropriate reagent such that the rate of silver-polymer formation should be retarded, and consequently its desired unimolecular decomposition will be more controlled. The crown ethers are species capable of such complexation. The rate of appearance of silver metal is an inverse function of the stability of the silver-crown ether complex. 

The conversion of primary alcohols and aldehydes into carboxylic acids is generally possible with all strong oxidants. Silver(II) oxide in THF/water is particularly useful as a neutral oxidant (E.J. Corey, 1968 A). The direct conversion of primary alcohols into carboxylic esters is achieved with MnOj in the presence of hydrogen cyanide and alcohols (E.J. Corey, 1968 A,D). The remarkably smooth oxidation of ethers to esters by ruthenium tetroxide has been employed quite often (D.G. Lee, 1973). Dibutyl ether affords butyl butanoate, and tetra-hydrofuran yields butyrolactone almost quantitatively. More complex educts also give acceptable yields (M.E. Wolff, 1963). 

Silver fluoborate, reaction with ethyl bromide in ether, 46, 114 Silver nitrate, complexing with phenyl-acetylene, 46, 40 Silver oxide, 46, 83 Silver thiocyanate, 45, 71 Sodium amide, in alkylation of ethyl phenylacetate w ith (2-bromo-ethyl)benzene, 47, 72 in condensation of 2,4-pentanedione and 1 bromobutane to give 2,4-nonanedione, 47, 92 Sodium 2 ammobenzenesulfinate, from reduction of 2 mtrobenzenesul-finic acid, 47, 5... 

Silver(I) complexes with oxygen donor ligands have been prepared with three different types of ligands /3-diketonates, carboxylates, and crown ethers. 

Thia-crown ethers incorporating propan-2-one units and dimeric silver(I) compounds as (176) and other polymeric species have been prepared.1132,1133 Other substituents can be diisopropyl idene groups which form complexes of the type [AgL(PPh3)]OTf (177),1134 pyridazine,1133 phthalazine1136 ligands or even organometallic compounds as ferrocene in (178).1137... 

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