Portal de Periódicos da CAPES

The hydrolysis of 4-nitrophenylphosphate promoted by [(N)4Co(OH/H)(OH/H)]+/2+/3+ species ((N)4=abap, tren); use of 31P NMR to uncover mechanistic complexity

2003; Elsevier BV; Volume: 342; Linguagem: Inglês

10.1016/s0020-1693(02)01170-2

1873-3255

Rachel L. Fanshawe, Allan G. Blackman, Charles R. Clark,

Chemical Synthesis and Characterization

Rate studies of the reaction of [(N)4Co(OH/H)(OH/H)]+/2+/3+ species ((N)4=abap (5- and 6-isomers), tren) with sodium 4-nitrophenylphosphate (Na2NPP) in aqueous solution (15, 25 or 40 °C, I=0.50 M, NaClO4) have been carried out using UV–Vis spectrophotometry and 31P NMR spectroscopy. Under weakly acidic conditions (pH ca. 5, excess Co(III) reagent) anation is faster than hydrolysis, and the first formed [(N)4Co(OH2)(NPP/H)]1+/2+ complex reacts largely with [(N)4Co(OH2)OH]2+ to produce a host of dimeric Co(III) products plus 4-nitrophenol. Under less acidic conditions (pH 6) rates of anation approach those of hydrolysis, and 4-nitrophenol production increasingly occurs via the intramolecular reaction of [(N)4Co(OH)NPP]. For [Co]T=0.040 M (abap system) this pathway account for 4% of the observed products at pH 5, 47% at pH 7 and 96% at pH 9. Rate laws for the processes are described. Under no pH condition does the pseudo first-order rate constant (or apparent pseudo first-order rate constant) determined from spectrophotometry directly relate to that for intramolecular hydrolysis in [(N)4Co(OH)NPP]. The X-ray crystal structure of 6-[(abap)Co(O2PO2)]·6H2O is reported, and confirms the presence of chelated phosphate in this species.