Silver salts systems

The transient existence of the silylenium ion has been considered in other reactions of chlorosilanes in the presence of Lewis acids. Guyot (147) successfully used the silyl chloride-silver salt system for initiation of the cationic polymerization of vinyl ethers [Eq. (35)]. Gel permeation... 

Heat-processed photographic systems have been described that utilize silver behenate, silver laurate, and silver stearate. These silver salts are coated on paper in the presence of organic reducing agents (78,79). 

Cyclization of bromostilbenes 6 to dibenz[/ ,/]oxepins 7 can be achieved by irradiation in excellent yield.102 103 Under solvolytic conditions (60% NaOH, EtOH), the yield is greatly reduced. When a silver salt (AgOAc) is used, however, complete conversion to the tricyclic system is accomplished.102 Tribenz[/>,catalyzed cyclization of biphenyl-2-yl 2 -chlorosulfonylphenyl ether in 44% yield.260... 

As no simple copper-perrhenate salts previously existed to serve as a model for structural relationships to [Cu2(pzc)2(H20)2Re04], our attention turned to the syntheses of the isoelectronic silver-perrhenate systems. Shortly after an analysis of the structure above, a synthesis of the new pyrazine-pillared (=pyz) AgRe04(pyz) solid was found [30], and is shown in Fig. 17.3 alongside the re-... 

Several modified reaction conditions have been developed. One involves addition of silver salts, which activate the halide toward displacement.134 Use of sodium bicarbonate or sodium carbonate in the presence of a phase transfer catalyst permits Reactions involving especially mild conditions to be used for many systems.135 Tetraalkylammonium salts... 

The ligand group can be introduced either on the meso or on the /5-pyrrole position of the porphyrin ring, but the synthesis of the meso-functionalized derivatives is easier and has been more widely exploited. Balch (50-53) reported that the insertion of trivalent ions such as Fe(III) (32) and Mn(III) (33) into octaethyl porphyrins functionalized at one meso position with a hydroxy group (oxophlorins) leads to the formation of a dimeric head-to-tail complex in solution (Fig. 11a) (50,51). An X-ray crystal structure was obtained for the analogous In(III) complex (34), and this confirmed the head-to-tail geometry that the authors inferred for the other dimers in solution (53) (Fig. lib). The dimers are stable in chloroform but open on addition of protic acids or pyridine (52). The Fe(III) octaethyloxophlorin dimer (52) is easily oxidized by silver salts. The one-electron oxidation is more favorable than for the corresponding monomer or p-oxo dimer, presumably because of the close interaction of the 7r-systems in the self-assembled dimer. 

Not only has the prostanoid [2.2.1] skeleton yielded to the onslaught, but seven other bicyclic peroxide systems have also been obtained. Particularly versatile have been the singlet oxygen-diimide and silver salt routes which have provided higher [n.2.2] systems (n = 2-4), and [n.2.1] systems (n = 3-5) respectively the [3.3.2] skeleton, unique in its lack of both 5- and 6-membered peroxide rings, was afforded via peroxymercuration. 

This powerful but relatively insensitive explosive decomposes violently at 202° C, and gives lead and silver salts which are highly impact sensitive [1], Though not endothermic (AH°f —103.3 kJ/mol), as a bis-nitramine it has a rather high heat of decomposition (3.91 kJ/g) which it is calculated would attain an adiabatic decomposition temperature over 2250°C, with a 60-fold pressure increase in a closed system [2],... 

Other anomeric-oxygen exchange reactions have been recently investigated quite extensively. Closely related to the Koenigs-Knorr method is the introduction offluorine as the leaving group (Scheme 1, path B) (6,9-13). Because of the difference in halophilicity of this element as compared with bromine and chlorine, additional promoter systems besides silver salts were found useful as activators for glycosylation reactions (14-16). However,... 

In 2007, Dickson et al. found that it is possible to stain fixed cells with fluorescent silver clusters instead of silver nanoparticles by tuning the staining conditions [57]. The new approach consists of staining fixed cells with a low concentrated silver nitrate solution 20-100 mM, within 20 h at ambient conditions, and reducing the silver by photoactivation, with the result of small silver clusters that present a broad emission band between 500 and 700 nm (Fig. 8a-d). The discovery that fluorescent silver clusters can be generated by photoactivation of cells fed with silver salt, opens up new paths for the application of silver clusters in biological systems. 

A number of modified reaction conditions have been developed. One involves addition of silver salts, which activate the halide toward displacement.94 Use of sodium bicarbonate or sodium carbonate in the presence of a phase-transfer catalyst permits especially mild conditions to be used for many systems.95 Tetraalkylammonium salts often accelerate reaction.96 Solid-phase catalysts in which the palladium is complexed by polymer-bound phosphine groups have also been developed.97 Aryl chlorides are not very reactive under normal Heck reaction conditions, but reaction can be achieved by inclusion of triphenylphosphonium salts with Pd(OAc)2 or PdCl2 as the catalyst.98... 

In addition to water, a variety of organic liquids, including amines, carboxylic acids, and hydrocarbons, have been used as solvents in the study of the homogeneous reactions of hydrogen with metal salts. In general, there is more uncertainty about the nature of the species present in such systems than in aqueous solution and, correspondingly, it is usually more difficult to elucidate the reaction mechanisms in detail. The most extensive solvent effect studies have been made on cupric, cuprous, and silver salts. A number of the more important results are considered below. 

Research in this area was developed further by Li et at. using 1,3-dienes 64 for the gold-catalyzed annulation of phenols and naphtols [58, 59]. These generated various dihydrobenzofuran derivatives. The best yields were achieved when the catalytic system included enough AuCl3 and silver salt to remove halogen atoms and deliver cationic gold. 

Since the discovery in 1964 that the antibiotic valinomydn exhibited alkali cation specificity in rat liver mitochondria, a new area of research has developed, based not only on biological systems but also on model systems such as crown ethers.484 The ability of neutral compounds to form lipid-soluble alkali and alkaline earth complexes was observed in 1951. The structure of the corresponding ligand, the anion of the antibiotic nigericin (78), was characterized as its silver salt in 1968.488 486 Silver was used as a heavy atom crystaUographically, since the Ag+ cation had a radius between that of Na+ and K+, which were the two alkali cations with which nigericin was most active. 

In a photothermographic system disclosed by Itek Corporation, the light-sensitive element is a silver halide and the image-forming material is the silver salt of EDTA or a related compound.200... 

Cyclization of 8-allenylamines is successful also. Synthesis of 2-alkenylpiperidines can be effected with mercury(II) or silver salts, with silver salts giving higher yields (equation 141 and Table 35).268a The significant asymmetric induction found in the cyclization of a chiral allene (78% ee, entry 2) suggests that the low stereoselectivity observed in the synthesis of the 2,6-disubstituted system (entry 3)269 may be a result of starting with a diastereomeric mixture. Aminopalladation/methoxycarbonylation has been effected in moderate yield also (entry 4). 

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