Rapid hydrolysis of phosphate monoesters by zirconium(IV) complexes in neutral solution

Three zirconium(IV) complexes (1-3) with mono- and dinucleating tripodal ligands are reported that promote the hydrolysis of the phosphate monoesters p-nitrophenyl phosphate (NPP) and phenyl phosphate (PP) in neutral solution. At pH 7 up to 10⁴- and 10⁶-fold rate accelerations of the hydrolysis of NPP and PP are observed. A detailed kinetic study has been carried out for NPP. The complexes show Michaelis-Menten behavior, k_cat and 1/K_m values at pH 7.0, 25 °C are 2.7 × 10^-5 s^-1 and 806 M^-1 (1), 1.1 × 10^-4 s ^-1 and 556 M^-1 (2) and 1.1 × 10^-4 s ^-1 and 565 M^-1 (3). Entropies of activation of -92.0 J K^-1 mol^-1 (1), -75.6 J K^-1 mol^-1 (2) and -98.6 J K^-1 mol^-1 (3) are consistent with an associative mechanism.