CARBOXYESTER HYDROLYSIS PROMOTED BY NEW Z INC(II) MACROCYCLIC TETRAAMINE COMPLEXES WITH A PHENOL PENDANT

Three new macrocyclic tetraamine ligands (L-1, L-2, L-3) bearing subst ituted phenol pendant were synthesized and charaterized by elementary analysis, IR, and H-1 NMR. By ph titration at 25+/-0.1 degrees C, I = 0.1 mol/L KNO3, studies of protonation of L-3 and complexation of Zn(I I) with L-3 have been carried out and revealed that the pendant phenol deprotonates with relative low pK(a) values of 8.3 and 8.5 for these two cases, respectively. It is due to the formation of hydrogen bond b etween phenol and proton combining on the nitrogen atoms of macrocycle , and the coordination between phenol and Zn(II) metal ion. The Zn(II) -bound phenol is shown to be a reactive nucleophile and catalyzes 4-ni trophenyl acetate (NA) hydrolysis. A kinetic study of NA hydrolysis by these three ligands' Zn(II) complexes in 10% (volume ratio) CH3CN at 25 degrees C, I = 0.1 mol/L NaClO4, and pH 8.63(20 mmol/L Tris buffer) , has established a second-order rate constant k(c)/(mol/L)(-1) s(-1)] of 3.48X10(-2), 1.52X10(-2), 2.85X10(-2), respectively.