Christophe Vichard, T. Kaden
Sep 26, 2002
Citations
0
Influential Citations
48
Citations
Journal
Inorganica Chimica Acta
Abstract
Abstract The kinetics and mechanism of the hydrolysis of bis(4-nitrophenyl)phosphate and (4-nitrophenyl)phenylphosphonate were studied in the presence of the dinuclear Ni 2+ , Cu 2+ , and Zn 2+ complexes of 1,1-[(1H-pyrazole-3,5-diyl)bis(methylene)]bis(octahydro-1H-1,4,7-triazonine) (LH). Whereas the dinuclear Cu 2+ complex does not promote the hydrolysis of these substrates, the dinuclear complexes of Zn 2+ and Ni 2+ are good catalysts for it. It has been shown by kinetical and 31 P NMR studies that the monohydroxo complex [M 2 (LH −2 )] 2+ binds the substrate to give an intermediate species, in which an intramolecular attack of the coordinated OH − onto the substrate takes place. Phosphate monoester or phenylphosphonate which are the products of the hydrolysis remain coordinated to the dinuclear complex, and, thus inhibit the further reaction. From the Michaelis–Menten type reactivity which we have observed at high substrate concentrations, K M and k cat values were obtained. The values of K M are very similar to each other as well as for the two substrates as for the two metal ions. In contrast, k cat values are distinctly different, the phosphonate ester being more reactive than the phosphate diester by a factor of 3–4. The major effect is however, due to the metal ion, the dinuclear Ni 2+ complex being 50–60 times more reactive than the Zn 2+ complex.