Mechanistic studies of the reaction of bis(2,4,6-tripyridyl 1,3,5-triazine)iron(II) with triazines

Bis(2,4,6-tripyridyl 1,3,5-triazine) iron(II), FedTPTZ_ 2_ 2 reacts with 3-(2-pyridyl)-5,6-bis(4-phenyl-sulfonicacid)- 1,2,4-triazine (PDTS) and 3-(4-(4-phenylsulfonicacid)2- pyridyl)-5,6-bis(4-phenylsulfonic-acid)-1,2,4-triazine (PPDTS) to giveFe(PDTS)(3)(4-) and Fe(PPDTS)(3)(7-) respectively. Both of these substitution reactions are fast and their kinetics weremonitored by stopped-flowspectrophotometry in acetate buffers in the pH range of 3.6-5.6 at 25-45 degrees C. Both reactions are first order in Fe(TPTZ)(2)(2+) and triazine, and pH has negligible effect on the rate. The kinetic data suggest that these reactions occur in an associative path and a mechanism is proposed considering both protonated and unprotonated forms of PDTS and PPDTS are very similar in reactivity. The kinetic and activation parameters have been evaluated.