Binding enabled catalytic activation of SO2 by copper koneramine complexes under ambient conditions

Abstract

Reported is an unprecedented, simple and sustainable strategy to catalytically convert SO₂ gas into sulfate dianions under ambient conditions utilizing ferrocene (SO₂ + 2Fc + aerial O₂ → Fc₂SO₄) and aerial oxygen, whereby ferrocenium sulfate was formed without any unwanted byproducts. The frequent urban haze and increase in respiratory health issues connected to the atmospheric SO₂ concentration attracted interest in the sequestration and valorization of SO₂. Even though a number of methods have been reported in the past decade for the stoichiometric sequestration and activation of SO₂, effective catalytic activation of SO₂ through homogeneous catalysis has not been realized before. The copper(II) koneramine complex [Cu(L-H)Cl₂] was designed to have exclusive basic sites for SO₂ binding, which complemented efficient electron transfer from ferrocene to SO₂ that underwent S-oxygenation to yield sulfate dianions. In this proof of concept study, SO₂ binding coupled electron transfer (SOCET) from ferrocene was established with the assistance of control experiments, electronic absorption spectroscopy, cyclic voltammetry and electrospray ionization mass spectrometry.