Cobalt(III) Complex Promoted Hydrolysis pf Phosphate Diesters: Change in Rate-Determining Step with Change in Phosphate Diester Reactivity

Article abstract of DOI:10.1021/ja00209a036

The effects of four Co(III) complexes, ²⁺, ²⁺, ²⁺, and ²⁺, on the rate of hydrolysis of bis(p-nitrophenyl) phosphate, p-nitrophenyl phosphate, and bis-(2,4-dinitrophenyl) phosphate have been examined at 50 deg C, under neutral-pH conditions.In neutral water, the cobalt-bound phosphodiester >⁺ is cleaved 1E7 times more rapidly (2.7E-3 s^-1) than the unbound phosphodiester, whereas the corresponding cobalt-bound phosphomonoester > is cleaved only 1E4 times more rapidly than the unbound phosphomonoester.The reactivity patterns for cobalt complex promoted hydrolysis of bis(p-nitrophenyl) phosphate and bis(2,4-dinitrophenyl) phosphate are, respectively, ²⁺ > ²⁺ > ²⁺ and ²⁺ > ²⁺ > ²⁺ > ²⁺.The difference in the reactivity pattern for the hydrolysis of the two phosphodiesters is explained in terms of a change in the rate-determining step with change in the phosphodiester reactivity.The structure of the amine ligand on the cobalt complex has a significant effect on both the rate of binding of the phosphate ester to the cobalt complex and the rate of cleavage of the phosphoester bond.