Thioether silver

Many other cyclic and noncyclic organic carriers with remarkable ion selectivities have been used successfiilly as active hosts of various liquid membrane electrodes. These include the 14-crown-4-ether for lithium (30) 16-crown-5 derivatives for sodium bis-benzo-18-crown-6 ether for cesium the ionophore ETH 1001 [(R,R)-AA -bisd l-ethoxycarbonyl)undecyl-A,yVl-4,5-tctramcthyl-3,6-dioxaoctancdiamide] for calcium the natural macrocyclics nonactin and monensin for ammonia and sodium (31), respectively the ionophore ETH 1117 for magnesium calixarene derivatives for sodium (32) and macrocyclic thioethers for mercury and silver (33). 

In 2007, Fernandez et al. demonstrated that transition-metal complexes with heterobidentate S/C ligands based on imidazopyridin-3-ylidene and thioether functionalities could be readily prepared from the corresponding azolium salts by reaction with Ag20 and transmetalation of the resulting silver carbenes with appropriate metal sources. The cationic Pd(allyl)(carbene-S) complexes have proven to be active catalysts in the test reaction, reaching enantioselectivities of... 

The chemistry of silver(I) with crown thioethers has developed in the last years,1094,1095 but now numerous examples with a great variety of ligands have been reported. The first homoleptic silver compounds have been described with 1,4,7-trithiacyclononane ([9]aneS3), [Ag([9]aneS3)2]OTf (168), which is octahedral and shows a reversible oxidation assigned to the Ag1/Ag11 couple,1096,1097 and the trimeric species [Ag3([9]aneS3)3]3+ (169).1097 The complexes... 

Macrocyclic thioethers which contain a carborane backbone have also been prepared and the silver(I) complexes obtained. The reaction of AgN03 with the sulfur-containing macrocyclic ligand... 

Coordination studies of acyclic thioether ligands to silver(I) centers has also been studied. Poly(alkylthio)aromatic systems have been used to form supramolecular silver(I) compounds. With the ligand 2,3,5,6-tetrakis(isopropylthio)benzoquinone the compound has a linear chain structure in which silver(I) has a tetrahedral coordination.1156 A similar structure has the compound with the hexakis(methylthio)benzene,1157 but with the hexakis(tolylthio)benzene the silver... 

Villamo, O., Barboiu, C., Barboiu, M., Yau-Chun-Wan, W. and Hovnanian, N. (2002) Hybrid organic-inorganic membranes containing a fixed thioether complexing agent for the facilitated transport of silver ions. Journal of Membrane Science, 204, 97-110. 

Investigations by Vermeer and co-workers have shown that 3-substituted allenyl methyl thioethers 309 can be prepared by regioselective addition of an alkyl silver species to the terminal C=C bond of enyne sulfides 308 (Scheme 8.83) [172], Remarkably, this method can also be applied to the preparation of several allenyl-phosphines starting from the corresponding phosphorus-substituted alkynes. 

Alternatively, a-(dialkylsulfonium)alkyl iron complexes can be prepared from a-haloalkyl iron complexes by silver- or thallium-promoted nucleophilic substitution with thioethers [474],... 

The general trend is similar for the four hosts, although some discrepancy appears along these data. In spite of some systematic errors arising from the extraction method, it must be underlined for example the discrepancy of data for Ag. The silver(I) cation is much better extracted by the thioether-substituted host 12g probably because Ag can interact not only with the phosphorylated binding sites of the cavitand, but also with the thioether functionality of the lower rim. Furthermore, it must be pointed out that the Hpophihcity of the host can interfere in the extraction process. For both al-kahne and alkaline-earth picrate salts, the extractability increases with the... 

The equivalence of sulfur and oxygen in this ring system carries over to NSAIDs as well. Preparation of the sulfur analogue of isoxepac (6-4) starts with the alkylation of thiophenol (27-1) with benzyl chloride (26-1). Cyclization of the intermediate thioether (27-2) then affords the homothioxanthone (27-3). The carboxyl side chain is then extended by means of the Amdt-Eistert homologation reaction. The acid is thus hrst converted to its acid chloride by means of thionyl chloride. Reaction with excess diazomethane leads to the diazoketone (27-4). Treatment of that intermediate with silver benzoate and triethylamine leads the ketone to rearrange to an acetic acid. There is thus obtained tiopinac (27-5) [28]. 

Dialkyl and diaryl thioethers generally react with silver(I) salts to form 1 1 complexes.309,310 Few data are available for these adducts however, on the basis of formation constants they appear to have relatively high stability (Table 44).311,312... 

Table 44 Formation Constants for some 1 1 Silver(I) Thioether Complexes...

With bidentate thioethers such as RS(CH2) SR (n = 2-5), c s-R SHC=CHSR and o-C6H4(SMe)2, silver(I) forms 1 2 chelate complexes involving tetrahedral Ag1. The stabilities in aqueous solution of some of these complexes in which R = CH2CH2OH have been measured.312... 

Recently the structures of silver(I) complexes with cyclo-(glycyl-L-histidyl), cyclo-(L-methionyl-L-histidyl) and cyclo-(L-histidyl-L-histidyl) were examined using 7H and 13CNMR spectroscopy. The NMR measurements suggested that the silver ion was bound to the sulfur atom of the thioether and to the nitrogen atom of imidazole groups in these cyclic peptides, but not to their amide groups.417... 

Caution. Silver trifluoromethanesulfonate is an irritant. Propanenitrile, thioethers, and all organic solvents used are toxic. Contact with the liquids and vapors should be avoided. Appropriate precautions must be taken, and an efficient hood must be used. 

Again, the precise roles of coordination-compound chemical sensitizers, in most cases, are not understood. In fact, their effects may have little to do with their own coordination chemistry. Many simple salts of gold and other noble metals are effective sensitizers. They also may be added to solutions during silver halide precipitation to produce doped emulsions that have special properties. A variety of compounds that can act as ligands to metal ions are also effective alone as chemical sensitizers, the result of complicated oxidation-reduction, ion replacement and adsorption reactions on the silver halide grain surface. These include polyamines, phosphines and thioether- or thiol-containing compounds. The chemistry of these materials with the silver halide surface is discussed in the reference literature. 

A list of more common silver complexing agents includes thiosulfates, thiocyanates, sulfites, cyanides, ammonia and other amines, thiols, thiourea, thioacids, thioethers and alkali halides. Most are not practical as fixing agents because they fail to satisfy all the above criteria. Many find use as silver halide stabilizers (Section 59.2.1.8). These include thiocyanate, thiourea and other thioorganic compounds. These and other complexing agents such as cyclic imides, phosphines and arsines find use in silver halide diffusion transfer processes (Section 59.2.1.6). 

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