title: Dramatic effect of the metal cation in dealkylation reactions of phosphinic esters promoted by complexes of polyether ligands with metal iodides.
abstract: 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 MI(n) (M[n+] = Li(+), Na(+), K(+), Rb(+), Ca(2+), Sr(2+), Ba(2+)) in low polarity solvents (chlorobenzene, 1,2-dichlorobenzene, and toluene) at 60 degrees C. The catalytic effect increases with increasing the Lewis acid character of the cation, in the order Rb(+)< K(+)< Na(+)< Li(+) and Ba(2+)< Sr(2+)< Ca(2+). The results are interpreted in terms of a transition state where the complexed cation (M[n+] subset Lig) assists the departure of the leaving group Ph(2)P(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 >> i-Pr and t-Bu) shows that this reaction can be utilized for the selective dealkylation of these substrates.
authors.affiliation: Centro CNR and Dipartimento di Chimica Organica e Industriale, Via Venezian 21, I-20133 Milano, Italy.
authors.forename: D
authors.initials: D
authors.lastname: Albanese
authors.forename: D
authors.initials: D
authors.lastname: Landini
authors.forename: A
authors.initials: A
authors.lastname: Maia