Synthesis silver ions

A third type of metal sulfide nanoparticle stabilized by GSH is Ag2S. Ag2S nanoparticle synthesis is challenging particularly in aqueous media due to the tendency to form bulk material rather than discrete nanoparticles. Mehra et al. have developed a standard synthesis for efficient production of this material. In this synthesis, silver ions are reacted with GSH to form a Ag(I)-(GSH) complex (where n is undetermined) and after sufficient reaction time, the inorganic sulfide is added to the solution in stoichiometric amounts to... 

Since a few protective groups cannot satisfy all these criteria for elaborate substrates, a large number of mutually complementary protective groups are needed and, indeed, are becoming available. In early syntheses the chemist chose a standard derivative known to be stable to the subsequent reactions. In a synthesis of callistephin chloride the phenolic —OH group in 1 was selectively protected as an acetate. In the presence of silver ion the aliphatic hydroxyl group in 2 displaced... 

An analogous regioselective effect of silver ions on an addition reaction of arene-diazonium ions was found by Ignasiak et al. (1975) with cyanide salts. Potassium cyanide yields diazocyanides (Ar— N2 — C = N see Sec. 6.6), i.e., C-coupling products, but with silver cyanide - albeit in low yield (7-9%) - diazoisocyanides (Ar—N2 — N = C) are formed (a better synthesis of diazoisocyanides is described in Sec. 6.4). 

Trost, B.M., Godleski, S.A., Genet, J.P. (1978) A Total Synthesis of Racemic and Optically Active Ibogamine. Utilization and Mechanism of a New Silver Ion Assisted Palladium Catalyzed Cyclization. Journal of the American Chemical Society, 100, 3930-3931. 

Scheme 10.14 gives some other examples of Wolff rearrangement reactions. Entries 1 and 2 are reactions carried out under the classical silver ion catalysis conditions. Entry 3 is an example of a thermolysis. Entries 4 to 7 are ring contractions done under photolytic conditions. Entry 8, done using a silver catalyst, was a step in the synthesis of macbecin, an antitumor antibiotic. Entry 9, a step in the synthesis of a drug candidate, illustrates direct formation of an amide by trapping the ketene intermediate with an amine. 

Adsorption of Ag on the surface of PdO is also an interesting option offered by colloidal oxide synthesis. Silver is a well-known promoter for the improvement of catalytic properties, primarily selectivity, in various reactions such as hydrogenation of polyunsaturated compounds." The more stable oxidation state of silver is -F1 Aquo soluble precursors are silver nitrate (halide precursors are aU insoluble), and some organics such as acetate or oxalate with limited solubility may also be used." Ag" " is a d ° ion and can easily form linear AgL2 type complexes according to crystal field theory. Nevertheless, even for a concentrated solution of AgNOs, Ag+ does not form aquo complexes." Although a solvation sphere surrounds the cation, no metal-water chemical bonds have been observed. 

The synthesis of an optically active semibullvalene has been realized for the first time Sequential reaction of methylcyclooctatetraene with one equivalent each of bromine and (—)-e/Kfo-bomyltriazolinedione gave a mixture of Diels-Alder adducts which when debrominated afforded 362. Photocyclization to bishomocubane 363 allowed for chromatographic separation of the two diastereomers. Silver ion-... 

SCHEME 2. Hydroperoxide synthesis via silver ion promoted bromide substitution and oxidation with H2O2... 

Aromatic fiuorination by the silver ion-promoted decomposition of aryl-diazo sulfides is similar to the Balz-Schiemann process. It provides efficient utilization of stoichiometric levels of fluoride ion, but has yet to be used for heterocyclic synthesis (91JOC4993). 

Indolizidine has been made in 68% yield by the action of silver ions on JV-chloroazacyclononane in dioxane.231 Pyrrolizidine and quinolizi-dine have been prepared similarly but in much poorer yields. Also, 1-methyl-5-hydroxyazacyclononane gave a trans-iustd quaternary salt (172) when heated with either perchloric, hydriodic, or picric acid in ethanol.232 However, it is more usual to apply this reaction in the reverse direction for synthesis of medium ring compounds. 

Silver ion catalysis has also been used with allenic oximes to generate cyclic nitrones, which are trapped by 1,2-dipolarophiles (equation 142).270 This reaction was used in a synthesis of pyrrolizidine alkaloids.270 5... 

An extension of this reaction leading to a general synthesis of N-substituted (3-lactams involves the addition of a primary amine to a freshly prepared solution of cyclopropanone, conversion of the resulting carbinol amine to the N-chloro derivative, and then decomposition of this intermediate with silver ion in acetonitrile. 87a> The method permits one to prepare N-substituted (3-lactams of great variety (Table 14), including those constructed from amino acid esters. 87b The use of valine ethyl ester (123) as a nitrogen source leading to 124 is illustrated. 

A silver ion-mediated desulfurization of thiocarbonyl compounds 163 or 164 followed by condensation with benzohydroxamic acid in the presence of excess triethylamine affords, respectively, dioxazole derivatives 165 or 166 (Scheme 25) <2002H(57)143>. Other reports concern the synthesis of l,4-(oxa/thia)-2-azoles 170-173 from unusual four-atom components such as the sulfur diimides 167, the thietan sulfimide 168, and the carbimidoyl chloride 169 <1996CHEC-II(4)530>. 

An interesting variation on this theme has been reported by Lehn and coworkers. In 1986, they reported the synthesis of macrocycle 33, which consists of a zinc porphyrin bearing two linked cyclic binding subunits [87]. It was later found that addition of silver triflate to a solution of 33 in methanol resulted in the incorporation of a silver ion in each of the binding subunits [88], Thus, the complex may be represented as Ag+-P-Ag+. The porphyrin fluorescence of the silver complex was quenched, and transient absorption studies demonstrated that the porphyrin singlet state was quenched with a rate constant of 5.0 x 109 s 1 to yield a charge separated state Ag°-P+-Ag+. Some quenching of the porphyrin triplet... 

Silver salts are also common activators in numerous Suzuki coupling reactions. The earliest example could probably be found in the Kishi s palytoxin synthesis. Silver oxide as well as thallium hydroxide provided dramatic rate enhancements in the couplings of vinylboronic acids (Scheme 10.41).69 Both thallium and silver ions are most probably abstracting halide in palladium intermediates, but silver is clearly the most efficient. Moreover, with the right counterion, the silver salt also acts as a mild base and activator. 

The synthesis of chloro(2,2 6, 2"-terpyridine)platinum(ll) was first reported by Morgan and Burstall in 1934.4 Better yields for this compound can be obtained by the method of Intille,s which is given below. The (2,2 6, 2"-terpyri-dine)thiolato compounds were reported in 1974,1 and a general synthetic procedure for these complexes was recently described.3 In this method silver ions are introduced during an intermediate step. Since silver is known to bind... 

The remarkable affinity of the silver ion for hahdes can be conveniently applied to accelerate the chiral palladium-catalyzed Heck reaction and other reactions. Enantioselectivity of these reactions is generally increased by addition of silver salts, and hence silver(I) compounds in combination with chiral ligands hold much promise as chiral Lewis acid catalysts for asymmetric synthesis. Employing the BINAP-silver(I) complex (8) as a chiral catalyst, the enantioselective aldol addition of tributyltin enolates (9) to aldehydes (10) has been developed." This catalyst is also effective in the promotion of enantioselective allylation, Mannich, ene, and hetero Diels-Alder reactions. 

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