The catalytic activity of the zinc(11) complexes of calix[4]arenes decorated with 1,5,9-triazacyclododecane ligands at the 1,2-, 1,3-, and 1,2,3-positions of the upper rim was investigated in the basic methanolysis (pH 10.4) of aryl acetates functionalised at the meta- and para-positions with a carboxylate anchoring group. Michaelis-Menten kinetics and turnover catalysis were observed. High rate accelerations, up to more than 10(4)-fold at 0.2 mM catalyst, were recorded in the most favourable catalyst-substrate combinations. The order of catalytic efficiency of regioisomeric bimetallic complexes is 1,2-vicinal >> 1,3-distal, resulting from a significant degree of synergism between metal ions in the former, and a complete lack in the latter. The moderately higher efficiency of the trimetallic compared with the 1,2-vicinal bimetallic catalyst provides an indication of a possible cooperation of three zinc(11) ions in the catalysis. (c) 2006 Elsevier B.V. All rights reserved.
Di- and trinuclear arrangements of zinc(II)-1,5,9-triazacyclododecane units on the calix[4]arene scaffold: Efficiency and substrate selectivity in the catalysis of ester cleavage / Roberta, Cacciapaglia; Alessandro, Casnati; Mandolini, Luigi; David N., Reinhoudt; Salvio, Riccardo; Andrea, Sartori; Rocco, Ungaro. - In: INORGANICA CHIMICA ACTA. - ISSN 0020-1693. - STAMPA. - 360:3(2007), pp. 981-986. [10.1016/j.ica.2006.07.024]
Di- and trinuclear arrangements of zinc(II)-1,5,9-triazacyclododecane units on the calix[4]arene scaffold: Efficiency and substrate selectivity in the catalysis of ester cleavage
MANDOLINI, Luigi;SALVIO, RICCARDO;
2007
Abstract
The catalytic activity of the zinc(11) complexes of calix[4]arenes decorated with 1,5,9-triazacyclododecane ligands at the 1,2-, 1,3-, and 1,2,3-positions of the upper rim was investigated in the basic methanolysis (pH 10.4) of aryl acetates functionalised at the meta- and para-positions with a carboxylate anchoring group. Michaelis-Menten kinetics and turnover catalysis were observed. High rate accelerations, up to more than 10(4)-fold at 0.2 mM catalyst, were recorded in the most favourable catalyst-substrate combinations. The order of catalytic efficiency of regioisomeric bimetallic complexes is 1,2-vicinal >> 1,3-distal, resulting from a significant degree of synergism between metal ions in the former, and a complete lack in the latter. The moderately higher efficiency of the trimetallic compared with the 1,2-vicinal bimetallic catalyst provides an indication of a possible cooperation of three zinc(11) ions in the catalysis. (c) 2006 Elsevier B.V. All rights reserved.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
