Concave reagents:: Part 40 -: The copper(II) complex of a concave reagent as a selective catalyst for ester methanolysis

We have shown that the Cu-II complexes of the concave ligand 1 and its model compound 2 are efficient catalysts of ester methanolysis under conditions close to neutrality. Turnover catalysis without product inhibition was demonstrated by the clean first-order release of a greater than stoichiometric amount of product. Compared with background methanolysis, the metal catalysts give greater rate accelerations for methyl acetate methanolysis than for the p-nitrophenyl acetate methanolysis. Analysis of electronic and steric effects on rates of metal-mediated vs metal-free methoxide addition to the esters has provided compelling evidence that transfer of methoxide from the metal to the carbonyl carbon is accompanied by extensive Lewis acid activation of the carbonyl via a four-membered chelate transition state that includes the metal ion. Copyright (C) 2004 John Wiley Sons, Ltd.