Kinetic analysis of carboxy ester hydrolysis by a dinuclear Zn(II) complex

Abstract A dinuclear Zn(II) complex with hexaaza macrocyclic ligand bearing two 2-hydroxypropyl pendants, 3,6,9,16,19,22-hexaaza-6,19-bis(2-hydroxypropyl)-tricyclo [22,2,2,2 11,14 ]triaconta-11,13,24,26,27,29-hexane (L) was synthesized and studied as a catalyst of the cleavage of 4-nitrophenyl acetate (NA). X-ray diffraction analysis of [Zn 2 LCl 2 ]Cl 2  · 6H 2 O revealed that Zn(II) adopts a trigonal-bipyramidal geometry. The complexation constants of L with Zn(II) have been determined at 298 K by means of potentiometric titration. [Zn 2 H −2 L] 2+ is the dominant species in aqueous solution around pH 8. The Zn 2 L-promoted hydrolysis of NA showed a second-order rate constant of 0.33 M −1  s −1 at pH 9.0, and the main promoter species are concluded to be the deprotonated species [Zn 2 H −2 L] 2+ .