title: Di- and trinuclear Zn2+ complexes of calix[4]arene based ligands as catalysts of acyl and phosphoryl transfer reactions.
abstract: The calix[4]arene scaffold, blocked in the cone conformation by proper alkylation of the lower rim hydroxyls, was used as a convenient molecular platform for the design of bi- and trimetallic Zn2+ catalysts. The catalytic activity of the Zn2+ complexes of calix[4]arenes decorated at the 1,2-, 1,3-, and 1,2,3-positions of the upper rim with 2,6-bis[(dimethylamino)methyl]pyridine units were investigated in the cleavage of ester 6 and of the RNA model compound HPNP. High rate enhancements, up to 4 orders of magnitude, were observed in a number of catalyst-substrate combinations. Interestingly the order of catalytic efficiency among regioisomeric dinuclear complexes in the cleavage of ester 6 is 1,2-vicinal >> 1,3-distal, but it is reversed in the reaction of HPNP. The higher efficiency of trinuclear compared to dinuclear complexes provides an indication of the cooperation of three Zn2+ ions in the catalytic mechanism.
authors.affiliation: Dipartimento di Chimica and IMC-CNR Sezione Meccanismi di Reazione, Università di Roma La Sapienza, Box 34-Roma 62, 00185 Roma, Italy.
authors.forename: Roberta
authors.initials: R
authors.lastname: Cacciapaglia
authors.forename: Alessandro
authors.initials: A
authors.lastname: Casnati
authors.forename: Luigi
authors.initials: L
authors.lastname: Mandolini
authors.forename: David N
authors.initials: DN
authors.lastname: Reinhoudt
authors.forename: Riccardo
authors.initials: R
authors.lastname: Salvio
authors.forename: Andrea
authors.initials: A
authors.lastname: Sartori
authors.forename: Rocco
authors.initials: R
authors.lastname: Ungaro