Silver complexes amino

Other transition metals have received much less attention. Complexes of palladium and 2-amino-phenyl-containing formazans have been reported.397 Mercury complexes of tridentate formazans have been studied.398 Silver complexes of tridentate benzothiazolyl-containing formazans have also been studied.399 Recently, alkali and alkaline earth metals have been the subject of many studies. Formazans such as 228 and 229 as well as the macrocyclic 204 have received considerable attention as metal-specific analytical reagents.400-41 1... 

For amino- and cyano-pyridines, it has been found that coordination to silver primarily occurred through the pyridyl N atom.82,83 IR spectral evidence has been used to show that this was not the case for substituted 2-amino-85 or 2-cyano-pyridines, however. Some cyano stretching frequencies for silver complexes are collected in Table IS.86,87... 

When side chains containing alkenic groups were introduced, it was found that the stability was generally higher than in amino adds having fully saturated side chains. Interaction of the silver ion with the alkene was proposed to account for this increase in stability. 00 Thermodynamic data for the formation of some silver(I) amino acid complexes are collected in Table 54.398 04,411... 

Table 54 Thermodynamic Data for the Formation of some Silver(I) Amino Add Complexes...

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... 

The use of Lewis acid drastically changes the regioselectivity. The highly enantioselective and O-selective nitroso aldol reactions of tin enolates with nitrosobenzene have been developed with the use of (i )-BINAP-silver complexes as catalysts. AgOTf and AgCICL complexes are optimal in the O-selective nitroso aldol reaction in both asymmetric induction (up to 97% ee) and regioselection (0/N= > 99/1), affording amino-oxy ketone. The product can be transformed to a-hydroxy ketone without any loss of enantioselectivity (Equation (71)).224... 

Figure 3.56 The silver complex of an N-boc protected imidazolium derivatised a-amino acid.

Lithium(l) NHC adducts are extremely rare, but some examples have been isolated as stable crystalline solids when a ftmctional group is involved for their stabilization, the amino group, for instance. Since these showed to be effective in transmetallation processes, they represent an interesting alternative to the expensive silver complexes. As an example, Arnold reported the synthesis of covalently tethered lanthanide carbene complexes (214) using adduct (213) as source ofNHC (equation 39). Using (213) and the same methodology, unusual cerium complexes (215) and (216) were isolated and characterized (equation 40). ... 

In a recent study the acid dissociation constants of substituted l-amino-4-aryl-2(li/)-pyrimidinethiones of the type 1 and stability constants of their silver complexes have been measured pH-potentiometrically in a 75% (v/v) mixture of dioxane/water11. The influence of the substituents R1 and R2 on pKa and lgf n values has been discussed11. 

Previous studies have reported silver staining with other amino acids. Heukeshoven and Dernick reported silver staining of the homopolymers of glycine, serine, proline and aspartic acid (4 ) while Nielsen and Brown reported the formation of colored silver complexes with aspartate, and tyrosine (45,). Staining of these homopolymers was not observed in the study of Merril and Pratt (32,), and prior metal binding studies failed to demonstrate metal interactions with the side-chain hydroxyl groups of serine, threonine or tyrosine... 

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... 

The bicyclic compound (14) formed by the reaction of phosphorus trichloride with an amino-diketone <84JA1164> has been shown to be planar, which has been interpreted as evidence for the delocalized dipolar canonical structure (15) rather than the neutral form (14). It forms a silver complex with trigonal bipyramidal stereochemistry at phosphorus <91JA1071>. 

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). 

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