Crown ether, thia

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... 

Other bridged derivatives are also known, examples being illustrated by the metacyclo-phane derivative (37) (74T2633), the thia crown ether (38) (74AG126) and the isomeric and separable cyclophanes (39) and (40) (74TL799). 

Most of the liquid crystals discussed in this section bear a diaza[18]crown-6 40, a 4,4 -diaminodibenzo[18]crown-6 41, or a thia crown ether 42 in their center (Scheme 23). Substitution in 40 and 41 is conveniently feasible on the nitrogen atoms by formation of a Schiff base or an aza compound (in the case of 41) or by N-alkylation or -acylation (in the case of 41). O-Alkylation and -acylation of 42, which are difficult to obtain, open a path to thia crown centered liquid crystals. 

Scheme 32 Liquid crystalline thia crown ethers 55, 56...

Simple addition of bases resulted in a S- C cleavage in the thia crown ether complex [Ru(Bzo2-18-S-6)]2+ (33a). A vinylthioether thiolate ligand formed and the reaction is rationalized by a base induced H+ abstraction as indicated in Eq. 23. 

The S—C bond-breaking and bond-making reactions take place when [Ru(CO)(Ss)] is treated with S(C2H4Br)2 to give the thia crown ether complex [Ru(CO)(Br)2(Bzo-9-S-3)] (Bzo-9-S-3 = Trithio-benzo[9]crown-6) according to Eq. 27 (98), where DMF = dimethylformamide. 

This reaction is rather different from the reaction between [Fe(CO)(S5)] and S hUBrh, which yielded the target thia crown ether complex [Fe(Bzo2-18-S-6)]Br2 (33b). 

The investigation of thia crown ethers, e.g. trithiacyclononane (64, 9S3 ). wh< complexation properties towards transition metal cations were of interest [61,62], was complicated for a long time by the low yields obtained from the corresponding cyclization reactions [63]. The combined application of the cesium effect and of the high dilution principle [1] in the reaction of 1,2-dichloroethane and the dithiol 63 led to an increase of the yield of 64 from 4.1 % (tetraalkylammonimn methano-late as the base) [64] to 50% [65, 66]. 

Equimolar amounts of dimethylthallium(III) perchlorate and thia-crown-ether were dissolved in CH3CN and the solution was allowed to stand overnight at room temperature. Whiter precipitates obtained after evaporation of solvent under reduced pressure were purified by recrystallization from CH2Cl2-THF(3 l)/n-hexane. Diethylthallium(III) complexes were also prepared by the similar method but the mixture was heated at reflux for 8 hr. Purification was made by recrystallization from CH3CN/(C2H5)2O for 1,10-DTC and 1,4,7-TTC complexes and from CH2CI2-THF(3 l)/n-hexane for MTC,1,7-DTC, and 1,7,13 TTC. Analytical data of the complexes are shown in Table I and relevant NMR data of the complexes measured in CD3CN are shown in Table II. 

Several series of styryl-based dyes incorporating thia-crown ether moieties (e.g., II) have been prepared and smdied as selective optical sensors for heavy metal ions in aqueous solutions. 

A series of cage-annulated thia-crown ethers and cryptands and an adamantylidene-derived hexathioether macrocycle have been prepared the crystal structure of the latter is shown in Figure iP... 

The replacement of the oxygen atoms present in classic Pederson-type crown ethers by S atoms results in the formation of thia-crown hgands. These latter hgands are characterized by a tendency to form complexes with softer ions, including those of the transition, lanthanide, and actinide series. This stands in contrast to what is true for oxygen-based crown ethers, for which a preference for hard cations, such as alkali metal ions, is well established. One of the earliest examples of ISEs based on a thia-crown ether was reported... 

Some thia-crown ethers have been prepared from the reaction between caesium thiolates of appropriate l,w-dithiols and polyethylene glycol dibromides.The synthesis of mono-aza-crown ethers from dialkanolamines [equation (17)] can be performed without the need for a protecting group on... 

Scheme 5.27 Synthesis of thia-crown ethers starting from the reaction of l,2-bis(4-hydroxy- and 4-mercaptophenyl)ethane-l,2-diones with 1,2-DABs...

It has been shown that the crown ether 126a is a sensing and selective material for the construction of the strontium-PVC (polyvinyl chloride) membrane sensor (Zamani et al. 2009). It should also be pointed out that crown 126a-d and thia-crown ethers 126e-h appear prove to be reagents for the selective extraction of alkaline earth over alkali metal ions with 2.7 (Mg Na extraction ratio) for the crown ether 126b, whereas this ratio for the thia-crown ether 126f is 8.0 (Ca rK extraction ratio) (Bakavoli et al. 2010). 

Bakavoli M, Rahimizadeh M, Rezaei-Seiesht E, Esfahani MM, Ziaee P (2010) Synthesis and complexing properties of novel crown ethers and thia-crown ethers incorporating new heterocyclic moieties. Phosphoms, Sulfur, and Sihcon RelatElem 185(10) 2152—2158. doi 10. 1080/10426500903544280... 

Figure 20 Thia crown ether-assisted enzymatic regioselective deacetylation.

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