Crown ethers reactions with metal halides

By far the most frequently used method is the deprotonation with potassium tert-butoxide, which gives the potassium salts in nearly quantitative yields. The method seems to be usable for any bis(chalcogenophosphinyl and -phosphoryl)imide and has been employed for a broad diversity of derivatives, regardless of the nature of the chalcogen.2,26,30,33,36-38,49,89,91,99 If the salts are needed for further use in reactions with metal halides to form complexes, the potassium salt can be used in situ, without isolation, e.g., with zinc(II) chloride or palladium and platinum chloro complexes.41,43 Potassium metal in THF also forms the salt K[SPh2PNPPh2S] in 82% yield, 38 but the method is not practical for preparative purposes. Potassium-crown ether complexes, [K(18-crown-6)][Q1Ph2PNPPh2Q1] with Q1 = O,92 Q1 = S,93 and Q1 = Se,98 have been prepared by direct complexation of the potassium salt with the macrocyclic ligand. 

Substitution reactions of cyanide with secondary alkyl halides are often accompanied by the formation of elimination products in variable amounts (Cook et al., 1974). The same holds for reactions of metal acetate complexes of crown ethers (Liotta et al., 1974). 

In general, the reaction is run with an excess of the metal halide. The use of metal salts that have a high lattice energy require the addition of a crown ether. 

Similar arguments are also valid for the successful preparation of hydridophosphinemetalates (shown in Figure 5) from the reaction of transition metal halide complexes with KH and suitable crown ether reagents <1998JA13138>. These materials are quite interesting for their reactivity as strong nucleophiles and reductants. 

In 1967, Pedersen described the preparation and properties of crown ethers,3 which are macrocyclic polyethers capable of sequestering metal cations. These catalysts can enhance the solubility and reactivity of salts in nonpolar solvents. For example, 18-crown-6, i.e., yxo-anhydro-hexaethylene glycol, forms a host-guest complex with potassium cation (K+) (Equation (1)). This association enables ionic potassium fluoride (KF) to dissociate in nonpolar benzene. And since the nucleophilic F counterions are not complexed,4 the yield of the Finkelstein reaction,5 i.e., halide-halide exchange, is increased 6... 

Alkylthiocyanates have been prepared in higji yield by reaction of alkali metal thiocyanates with various primary and secondary alkyl halides under phase transfer conditions. Quaternary alkylammonium salts [12—14], crown ethers [15], cryptates [16], and tertiary amines [14] have all proved effective phase transfer catalysts for this reaction (Eq. 13.7 and Table 13.4). The mechanism of the thiocyanate displacement is probably similar to that of the cyanide displacement reaction (see Sect. 7.2). 

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