Reversible Complexes for the Recovery of Dioxygen

Abstract

Dioxygen 1s produced 1n tonnage quantities by the distillation of air at cryogenic temperatures. In recent years, alternative technologies have emerged that employ O₂- or N₂-select1ve sorbents or O₂-permselectlve polymer membranes. New transition metal complexes that can bind O₂ reversibly and with high specificity may provide the basis for even better processes for dioxygen recovery. One of the more promising approaches 1s the use of such complexes as O₂ carriers In facilitated transport Immobilized liquid membranes. The performance of the cyclidene lacunar “protected site” dioxygen complexes developed by D. Busch et al. has been evaluated 1n such membranes operating at ca. 0°C. The complexes facilitate the transport of dioxygen and result 1n O₂ permeabilities and O₂/N₂ select1v1t1es that have been related 1n a preliminary manner to the complex concentration, equilibrium O₂ binding, reaction kinetics, and carrier and O₂ dlffuslvltles. While the cyclidene complexes proved to be useful in these experimental studies, for practical membranes new carriers would have to be devised that are much more stable toward oxidative degradation. The synthesis and structure of a new “protectedsite” M reversible cobalt dioxygen complex are described.