Processes for the conversion of CO₂ to valuable chemicals are highly desired as a result of the increasing CO₂ levels in the atmosphere and the subsequent elevating global temperature. However, CO₂ is thermodynamically and kinetically inert to transformation and, therefore, many efforts were made in the last few decades. Reformation/hydrogenation of CO₂ is widely used as a means to access valuable products such as acetic acids, CH₄, CH₃OH, and CO. The electrochemical reduction of CO₂ using hetero- and homogeneous catalysts recently attracted much attention. In particular, molecular CO₂ reduction catalysts were widely studied using transition-metal complexes modified with various ligands to understand the relationship between various catalytic properties and the coordination spheres above the metal centers. Concurrently, the coupling of CO₂ with various electrophiles under homogeneous conditions is also considered an important approach for recycling CO₂ as a renewable C-1 substrate in the chemical industry. This review summarizes some recent advances in the conversion of CO₂ into valuable chemicals with particular focus on the metal-catalyzed reductive conversion and functionalization of CO₂.

Latent catalysts can be tuned to function smartly by assigning a sensing threshold using the displacement approach for targeted analytes. Three cyano-bridged bimetallic complexes were synthesized as “smart” latent catalysts through the supramolecular assembly of different metallic donors [Fe^II(CN)₆]⁴⁻, [Fe^II(tBubpy)(CN)₄]²⁻, and Fe^II(tBubpy)₂(CN)₂ with a metallic acceptor [Cu^II(dien)]²⁺. The investigation of both their thermodynamic and kinetic properties on binding with toxic pollutants provided insight into their smart off–on catalytic capabilities, enabling us to establish a threshold-controlled catalytic system for the degradation of pollutants such as cyanide and oxalate. With these smart latent catalysts, a new catalyst displacement assay (CDA) was demonstrated and applied in a real wastewater treatment process to degrade cyanide pollutants in both domestic (level I, untreated) and industrial wastewater samples collected in Hong Kong, China. The smart system was adjusted to be able to initiate the catalytic oxidation of cyanide at a threshold concentration of 20 μM (the World Health Organization’s suggested maximum allowable level for cyanide in wastewater) to the less harmful cyanate under ambient conditions.

A multifunctional device that can monitor the level of pollutants, magnify weak signals, and subsequently degrade pollutants is highly desirable. A new Ru(ii)–Fe(iii) complex—[Ru^II(^tBubpy)(CN)₄]₂–[Fe^III(H₂O)₃Cl]₂·8H₂O (1,^tBubpy = 4,4′-di-tert-butyl-2,2′-bipyridine)—was synthesized and characterized.