Synthesis, Magnetic Properties, and Catalytic Properties of a Nickel(II)-Dependent Biomimetic of Metallohydrolases

A dinickel(II) complex of the ligand 1,3-bis(bis(pyridin-2-ylmethyl)amino)propan-2-ol (HL1) has been prepared and characterized to generate a functional model for nickel(II) phosphoesterase enzymes. The complex, [Ni₂(L1)(μ-OAc)(H₂O)₂](ClO₄)₂·H₂O, was characterized by microanalysis, X-ray crystallography, UV-visible, and IR absorption spectroscopy and solid state magnetic susceptibility measurements. Susceptibility studies show that the complex is antiferromagnetically coupled with the best fit parameters J = −27.4 cm⁻¹, g = 2.29, D = 28.4 cm⁻¹, comparable to corresponding values measured for the analogous dicobalt(II) complex [Co₂(L1)(μ-OAc)](ClO₄)₂·0.5 H₂O (J = −14.9 cm⁻¹ and g = 2.16). Catalytic measurements with the diNi(II) complex using the substrate bis(2,4-dinitrophenyl)phosphate (BDNPP) demonstrated activity toward hydrolysis of the phosphoester substrate with K_m ~10 mM, and k_cat ~0.025 s⁻¹. The combination of structural and catalytic studies suggests that the likely mechanism involves a nucleophilic attack on the substrate by a terminal nucleophilic hydroxido moiety.