Exchange metathesis

Using a similar protocol, Loupy and coworkers have reported the synthesis of chiral ionic liquids based on (ll ,2S)-(-)-ephedrinium salts under microwave irradiation conditions (Scheme 4.21a) [75]. Importantly, the authors were also able to demonstrate that the desired hexafluorophosphate salts could be prepared in a one-pot protocol by in situ anion-exchange metathesis (Scheme 4.21b). The synthesis and transformation of so-called task-specific ionic liquids is discussed in more detail in Section 7.4. 

The reactivity of organoxenonium salts [RXe]Y towards anions X is determined by the nucleophilicity of the latter and nature of solvent. When X is a weakly nucleophilic anion, anion exchange (metathesis) occurs in polar solvents forming the corresponding [RXe]X salts in high yields (eqs 11,12). 

Homogeneous, single-component catalysts such as, e.g., W(=CCMe3)(OCMe3)3 or W(=CMe)(OCMe2CF3)3, cannot only be used for exchange metathesis of alkynes but also for ROMP of cycloalkynes, ADMET of a,to-diynes, and RCM of a,co-diynes [751]. 

Metathesis of alkenes is essentially a class of reactions where an interchange of C atoms between pairs of double bonds takes place. A few representative examples are shown by the reactions listed in Fig. 7.10. The industrial use of metathesis reactions so far has been limited mainly to exchange metathesis (Fig. 7.10, top, backward reaction) as in the SHOP process, and ring-open metathesis polymerization (ROMP). As already mentioned (Section 7.5), Vas-tenamer is a polymer made by Hulls by ROMP from cyclooctene. Similarly, the polymer from norborene by ROMP is manufactured by CdF Chemie and is sold by the trade name of Norsorex . 

Acid-base, precipitation and complexation reactions are all examples of exchange (metathesis) reactions in which ions in solution exchange partners , for example ... 

Subsequent ion exchange metathesis of these lithium salts with trityl chloride affords the desired... 

Suggest a mechanism and a hard and soft Lewis acids and bases (HSAB) rationale for the following ligand exchange (metathesis) reaction ... 

Exchange (metathesis) reaction a reaction between compounds that, when written as a molecular equation, appears to involve the exchange of parts between the two reactants. (43)... 

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