Cooperativity of binuclear Zn(II) complexes of bisimidazolyl ligands in the hydrolysis of bis(2,4-dinitrophenyl) phosphate in aqueous solution

Abstract

Hydrolysis of bis(2,4-dinitrophenyl) phosphate (BDNPP) by Zn(II) with ligands bearing plural bis(imidazol-2-yl) groups was kinetically studied in aqueous solution. The binuclear Zn(II) complex of 1,3-bis(diimidazol-2-ylhydroxymethyl)benzene (2a) was found to be most effective for hydrolysis of BDNPP (1.2 × 10³-fold). ESI-MS study revealed formation of 2a·Zn(II)₂ in MeOH–H₂O, suggesting that the rate acceleration is due to so called double Lewis acid activation. The pH–rate profile showed that the pK_a of the active species is around 7.5. The rate accelerations by the complexes of 2a with other metal ions were 4.3-fold for Ni(II), 7.1-fold for Co(II), and 1.9 × 10²-fold for La(III).