Amines silver complexes

When ethylenediamine comes into contact with silver perchlorate it detonates. This accident is explained by the formation of an amine/silver complex that is unstable. 

Trilialophenols can be converted to poly(dihaloph.enylene oxide)s by a reaction that resembles radical-initiated displacement polymerization. In one procedure, either a copper or silver complex of the phenol is heated to produce a branched product (50). In another procedure, a catalytic quantity of an oxidizing agent and the dry sodium salt in dimethyl sulfoxide produces linear poly(2,6-dichloro-l,4-polyphenylene oxide) (51). The polymer can also be prepared by direct oxidation with a copper—amine catalyst, although branching in the ortho positions is indicated by chlorine analyses (52). 

To minimize the formation of fuhninating silver, these complexes should not be prepared from strongly basic suspensions of silver oxide. Highly explosive fuhninating silver, beheved to consist of either silver nitride or silver imide, may detonate spontaneously when silver oxide is heated with ammonia or when alkaline solutions of a silver—amine complex are stored. Addition of appropriate amounts of HCl to a solution of fuhninating silver renders it harmless. Stable silver complexes are also formed from many ahphatic and aromatic amines, eg, ethylamine, aniline, and pyridine. 

Thermodynamics of complex formation of silver with several ligands such amines,368 hindered pyridine bases,369 nitrogen donor solvents,370 and azoles371 have been carried out. Other studies include the secondary-ion mass spectra of nonvolatile silver complexes,372 the relationship between Lewis acid-base behavior in the gas phase and the aqueous solution,373 or the rates of hydride abstraction from amines via reactions with ground-state Ag+.374... 

Table 6 Some Thermodynamic Data for Silver Complexes of Primary Amines...

Silver(I) complexes can also be obtained when the pyridyl N becomes quatemized, if the aliphatic group contains an amine. Thermodynamic data for silver complexes with ligands of the type C5H5N+(CH2) NH (n = 2-5) are given in Table 16.88,89... 

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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). 

During the reaction silver(0) deposits on the sides of the reaction vessel. The sequence of events leading to the azomethine ylide is unclear. However, evidently single-electron transfer (SET) from the amine to silver takes place either prior or subsequent to fluoride-enabled silyl cleavage. This process is repeated with a second equivalent of silver fluoride resulting in the formation of 38 either in free form or more likely as its silver complex. The scope of the method was expanded to the synthesis of bicylic systems exemplified here by tropinone 42 (Scheme 2.11).19 Pandey has also extended the protocol to the synthesis of tricycloalkanes20 and applied it to a total synthesis of the poisonous frog alkaloid epibatidine.21... 

In general, the relationship between the Kb values for the bases (measured toward the proton) is approximately linearly related to the K values for the formation of the silver complexes when several nitrogen bases (amines) having similar structure are considered. However, for a base such as 4-cyanopyridine, it is found that the silver complex is much more stable than would be predicted from the basicity of the ligand toward H+. The reason for this is that some multiple bonding in the silver complex is possible as shown here ... 

Activation of the acetylene by coordination of the triple bond to the silver cation enables a 5-endo-dig cydization via nucleophilic attack of the amine [14]. Protonation of the resulting vinyl silver complex leads to an iminium ion. Subsequent p-hydride elimination affords metallic silver and a pyrrylium ion which aromatizes by proton loss to the pyrrole. For trimethylsilyl-substituted homopropargylamines (R = SiMes), the resulting pyrrole (R = SiMe3) undergoes protodesilylation to the 1,2-disubstituted pyrrole. 

Amination of benzo[d]isoxazoles 83 proceeds regioselectively under the ONS conditions, thus leading to ort/jo-nitroamines 84 [47] (Scheme 39). The reaction was carried out in a saturated methanohc solution of NH3, with the silver complex Ag (Py)2Mn04 being used as an oxidant. Treatment with PhI(OAc)2 allowed to convert amines 84 into furoxan derivatives. According to the NMR data the reaction product in DMSO solution existed as two isomers 85 and 86 in the ratio of 5 1. 

Distribution measurements show that the silver complex of dr-cyclo-octene is less stable than that of cycloheptene, presumably owing to more ring strain in the latter 129,130). tronr-Cyclooctene is considerably more strained than the cis isomer, and can be separated from it by extraction with 20% aqueous silver nitrate 32), but there are no quantitative measurements of the stability of the silver complex of the tram isomer. The interesting possibility of isomerizing cis to trom-cyclooctene via metal complexes has not yet been achieved. tronr-Cyclooctene has been resolved via its platinum(II) complex with the optically active amine l-phenyl-2-amino-propane (am), 7r-CgH]4PtCl2am. 29). 

As a noble metal, silver becomes one of the most important metals in the life of human beings, which has been used as currency and ornaments by humans for thousands of years. Nowadays, silver and its salts have been widely used in photography, electrical equipment, jewelry, as well as transition metal for catalysis in chemistry. In chemical research, silver complexes were usually thought to be low activity and used as either co-catalysts [1, 2] or Lewis acids [3] for decades. In recent years, a wide range of important organic transformation has been catalyzed by silver complexes, including C-H insertion, amination/amidation, fluorination, hydrosilylation, decarboxylation, and so on [4-12]. 

Scheme 12 Sp C-H bond amination using silver complex 8 as catalyst...

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