Altered mechanisms of reactions ofphosphate esters bridging a dinuclear metal center
Journal of the American Chemical Society
Kinetic isotope effects in the nucleophile and leaving group were obtained for the reaction of p-nitrophenyl phosphate monoester coordinated to a dinuclear Co(III) complex. The metal complex of the p-nitrophenyl phosphate monoester was found to hydrolyze by a single-step concerted mechanism, with significant nucleophilic participation in the transition state. By contrast, the hydrolysis of uncomplexed p-nitrophenyl phosphate occurs by a very loose transition state with little bond formation to the nucleophile. Previously, the metal complex of the diester methyl-p-nitrophenyl phosphate was found to hydrolyze via a two-step addition−elimination mechanism, in contrast to the concerted hydrolysis mechanism followed by uncomplexed diesters with the p-nitrophenolate leaving group. These results show that coordination to a metal complex can significantly alter the mechanism of phosphoryl transfer.
T. Humphry, M. Forconi, N. H. Williams and A. C. Hengge. “Altered mechanisms of reactions of phosphate esters bridging a dinuclear metal center” J. Am. Chem. Soc., 2004, 126, 11864-11869.