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  • Title: Di- and trinuclear Zn2+ complexes of calix[4]arene based ligands as catalysts of acyl and phosphoryl transfer reactions.
    Author: Cacciapaglia R, Casnati A, Mandolini L, Reinhoudt DN, Salvio R, Sartori A, Ungaro R.
    Journal: J Org Chem; 2005 Jan 21; 70(2):624-30. PubMed ID: 15651810.
    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.
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