Chelation and Hydrolysis of Orthophosphate Coordinated to Cobalt(III). Reactions of [Co(en)₂(O₂PO₂)] Under Alkaline Conditions

Abstract

Ring opening and closing under alkaline conditions of the four-membered orthophosphate chelate [Co(en)₂(O₂PO₂)] has been followed by both visible absorption and ³¹P n.m.r. spectroscopy. The former reaction follows the rate law ^khyd = k₂+k_l[OH^-] with k₂ = 2.2 × 10^-5 s^-1 and k₁ = (1.63 ± 0.04)×10^-2 mol^-1 dm³ s^-1, and ring closure the rate law k_ch = k_-2 + k^-1 with k_-2 = 6×10^-4 s^-1 for cis -[Co(en)₂(OH)(OPO₃H)1 and k_-1 = 7.5×10^-5 s^-1 for cis-[Co(en)₂(OH)(OPO₃)]^-, all at 25°C and I = 1.0 mol dm^-3 (NaNO₃).trans- Monodentate species adopt higher concentrations than cis-monodentate species at equilibrium under all alkaline conditions.