Metal ion electrophilic catalysis has been revealed in dealkylation reactions of phosphinic esters 1-4 promoted by complexes of polyether ligands 5-7 with metal iodides MIn (Mn+ = Li+, Na+, K+, Rb+, Ca2+, Sr2+, Ba2+) in low polarity solvents (chlorobenzene, l,e-dichlorobenzene, and toluene) at 60 degreesC. The catalytic effect increases with increasing the Lewis acid character of the cation, in the order Rb+ < K+ < Na+ < Li+ and Ba2+ < Sr2+ < Ca2+. The results are interpreted in terms of a transition state where the complexed cation (Mn+ subset of Lig) assists the departure of the leaving group Ph2P(O)O- and, at the same time, favors the attack at carbon of the nucleophile I- ("push-pull" mechanism). The rate sequence found for 1-4 (Me > Et much greater than i-Pr and t-Bu) shows that this reaction can be utilized for the selective dealkylation of these substrates.
|Titolo:||Dramatic effect of the metal cation in dealkylation reactions of phosphinic esters promoted by complexes of polyether ligands with metal iodides|
ALBANESE, DOMENICO (Primo)
LANDINI, DARIO (Secondo)
|Settore Scientifico Disciplinare:||Settore CHIM/06 - Chimica Organica|
|Data di pubblicazione:||2001|
|Digital Object Identifier (DOI):||10.1021/jo0056388|
|Appare nelle tipologie:||01 - Articolo su periodico|