Fixation and sequestration of carbon dioxide by copper(II) complexes

Abstract

The fixation of carbon dioxide ( $$\hbox {CO}_{2})$$ is an important global challenge. A significant increase of the atmospheric $$\hbox {CO}_{2}$$ due to the industrial emissions and a steady increase in combustion of fossil fuels is a widespread environmental concern. This article is a short literature review on the recent developments in the field of $$\hbox {CO}_{2}$$ activation and fixation by bioinspired copper(II) catalysts. In our laboratory, copper(II) complexes of bidentate ligands have been reported as catalysts for the fixation of $$\hbox {CO}_{2}$$ . The molecular structure of one of the complexes has shown unusual trigonal bipyramid geometry ( $$\tau $$ , 0.936) by the coordination of two ligand units and a water molecule. All the complexes exhibited a well-defined Cu(II)/Cu(I) redox potentials around 0.352 to 0.401 V in acetonitrile. The rhombic EPR spectra of the complexes indicate the existence of a geometrical equilibrium between trigonal bipyramidal and square pyramidal at 70 K. The d-d transitions around 750–800 and 930–955 nm further supports five coordination geometry in solution. These copper(II) complexes have successfully fixed atmospheric $$\hbox {CO}_{2}$$ as $$\hbox {CO}_{3}^{2-}$$ by using $$\hbox {Et}_{3}\hbox {N}$$ as sacrificial reducing agent and afforded [ $$\hbox {Cu(L)CO}_{3}$$ ( $$\hbox {H}_{2}\hbox {O}$$ )]. The $$\hbox {CO}_{3}^{2-}$$ bound complex has shown a distorted square pyramidal geometry ( $$\tau $$ , 0.369) around copper(II) center via the coordination of only one ligand unit, a carbonate, and water molecules. The catalysts are active enough to fix $$\hbox {CO}_{2}$$ for eight repeating cycles without any change in the efficiency. The fixation of $$\hbox {CO}_{2}$$ possibly proceeds via the formation of Cu(I)-species. This is supported by X-ray structure, which reveals distorted tetrahedral geometry by the coordination of two units of ligand. SYNOPSIS The fixation of carbon dioxide ( $$\hbox {CO}_{2})$$ is an important global challenge. This review summarizes the recent developments in $$\hbox {CO}_{2}$$ fixation by bioinspired Cu(II) catalysts.