Metal Ion Catalysis in Nucleophilic Substitution Reactions Promoted by Complexes of Polyether Ligands with Alkali Metal Salts

Article abstract of DOI:10.1021/jo00123a036

Metal ion effects have been revealed on nucleophilic substitution reactions of n-octyl sulfonates 1-3 promoted by complexes of polyether ligands (PEGs, crown ethers, cryptands) with alkali metal salts MY (M = Li, Na, K; Y = I, Br) in low polarity solvents (chlorobenzene, o-dichlorobenzene, toluene) at 60 deg C.Rate constants increase, in the order K(+) < Na(+) < Li(+), with the complexes of crown ethers 5 and 6 and PEG 4, whereas they are independent of the cation in the case of cryptates of 7.In the series of sulfonic esters 1-3 these effects progressively diminish with increasing nucleofugality of the leaving group.These results are interpreted on the basis of a transition state where the complexed cation (Li<*>M(+)) assists the departure of the leaving group ("electrophilic catalysis").