Kinetics and mechanism of carboxyester hydrolysis using Zn(II) complexes with functionalized phenanthroline complexes

Zinc(II) complexes of six new functionalized phenanthrolines have been exam ined as catalysts for the hydrolysis of 4-nitrophenyl acetate (NA). The new ligands form a 1:1 zinc complex in the pH range 6.5-9.0. In the kinetic st udies using the zinc complexes in 10% (v/v) CH3CN at 298 K, I = 0.10 mol dm (-3) KNO3 and pH 6.8-9.0, it was shown than an axial OH- serves as a good n ucleophile that effectively catalyzes NA hydrolysis. The hydrolysis rate fo llows the law v = (k(plus)[complex] + k(OH)[OH- ] + k(o)[NA]. The second-or der rate constants of ZnLH-1 are 0.934, 0.420, 0.360, 0.307, 0.257 and 0.14 3 mol(-1) dm(3) s(-1) for L-1, L-2, L-3, L-4, L-5 and L-6, respectively, ob viously larger than the corresponding value of 0.047 mol(-1) dm(3) s(-1) fo r the N-methylcyclen-Zn(II)-OH- complex catalyst. (C) 2001 Elsevier Science B.V. All rights reserved.