Silver complexes crown ethers

Silver(I) complexes with oxygen donor ligands have been prepared with three different types of ligands /3-diketonates, carboxylates, and crown ethers. 

Thia-crown ethers incorporating propan-2-one units and dimeric silver(I) compounds as (176) and other polymeric species have been prepared.1132,1133 Other substituents can be diisopropyl idene groups which form complexes of the type [AgL(PPh3)]OTf (177),1134 pyridazine,1133 phthalazine1136 ligands or even organometallic compounds as ferrocene in (178).1137... 

The cyanide ion is an ambident nucleophile and isocyanides may be side products. If the preparation of isocyanides is desired, they can be made the main products by the use of silver or copper(I) cyanide1577 (p. 368). Vinylic bromides can be converted to vinylic cyanides with CuCN,1578 with KCN, a crown ether, and a Pd(0) complex,1579 with KCN and a Ni(0) catalyst,15 1 or with K4Ni2(CN)6.1581 Tertiary halides can be converted to the corresponding nitriles by treatment with trimethylsilyl cyanide in the presence of catalytic amounts of SnCl4 RjCCl + Me3SiCN — R3CCN.1582... 

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. 

We have prepared a variety of new Schiff base bis crown ether ligands (98-100) that contain alkali and transition metal coordinating sites via the condensation of two or three equivalents of 4-formyl-benzo-15-crown-5 with an appropriate di- or triamine (Scheme 18). Homometallic copper(I), silver(I), and heteropolymetallic copper(I)-sodium, silver-(I)-sodium, and potassium complexes have been isolated. The singlecrystal X-ray structure of the [Cu(57)K](PF6)2 complex (100) is shown... 

Crown ether 4 has been shown to be a source of unusual dinuclear silver(l) complexes <2002ICA(332)18>. In the crystal, the silver ions interact with the crown ether ligand at both the hard donor ethereal oxygens and soft benzene ring carbon atoms via intermolecular cation-Tt-interaction in -fashion, as depicted in Figure 6. The dimeric structure is further stabilized by the occurrence of intermolecular Tt-Tt-intcractions between facing benzo groups. 

The most important classes of oxygen donor ligands for complexation of silver(I) are /3-diketonates, carboxylates, crown ethers, and calixarenes. 

Several silver(I) complexes with crown ethers and calixarenes have been synthesized. In the design of discrete molecules and infinite chains in silver acetylide chemistry, crown ethers function as blocking groups or protective cordons around a polyhedral C2 Ag cage so that the isolation of lower-dimensional supramolecular entities can be achieved. " ... 

The cationic complex of silver and 1,10-phenanthroline (phen) has been found to react with Bromopyrogallol Red to yield an ion-associate which can be extracted into nitrobenzene (e = 3.2T0" at 590 nm) [31,32]. The cationic complex, Ag(phen)2 gives ion-associates also with acid dyes, such as Rose Bengal (formula 4.35) and eosin (formula 4.34) (nitrobenzene) [33]. Extractable ion-associates of cationic silver complex with 1,4,8,11-tetrathiacyclotetradecane (crown ether), and various chromogenic anions [34] should also be mentioned. 

The synthesis of cahx[4]arene dimelamines with different functionalities and their self-assembly with barbituric and cyanuric acid to hydrogen-bonded nanostructures have been published <05OBC3727> Unique ionophores of penta-crown ethers have been prepared by the reaction of l,3,5-triacryloylhexahydro-l,3,5-triazine (TAHTA) with diaza 18-crown-6 followed by Michael addition, and their binding capabilities towards alkali metal cations studied <05SL2257>. New silver complexes of polydentate ligands including a derivative of pyrazol-l-yl-l,3,5-triazine have been reported <05EJ14370>. 

Monserrat et al. have discussed the properties of surfactant aza-crown ethers complexed with silver. Photoinduced electron transfer from a surfactant Ru complex was found to lead to the formation of zerovalent silver stabilized by the microenvironment of the vesicles and again the electron-transfer reaction was extraordinarily rapid, competing efficiently with other pathways for the deactivation of the excited singlet state. 

Asfari, Z. Vicens, J. Silver ion complexation by a calix[4]arene bis(crown ether). Ambivalence towards ether 26. and polyhapto coordinations. Supramol. Chem. 1999, 11. 

Another ultrasonic absorption study of the rates of complexation-decom-plexation of 15-crown-5 and 18-crown-6 complexes for a series of bivalent cations in aqueous solution shows that non-spherically co-ordinated Hg + (similarly to the previously studied - Ag+) reacts faster with the crown ethers than spherically co-ordinated metal ions, which gives additional evidence for water loss as the rate-determining step. The more rigid crown ethers have to undergo considerable conformational strain to accommodate themselves to the linear geometry of silver(i) and mercury(ii), so the rigidity of the ligand is especially important for the rate of complexation with these metal ions. ... 

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