Inherent in the Intergovernmental Panel on Climate Change’s goal of limiting global temperature increases to 1.5 °C above the pre−industrial average, is the concept of Negative CO2 Emissions. This implies that the well−recognized requirement to cut greenhouse gas emissions will have to be complemented by the active capture, storage and utilization of CO2. On the latter point, CO2 can be reduced to yield a range of value−added products, thereby providing an economic and environmental impetus to this activity. Amongst the possible products are fuels (e.g., methanol and methane), commodity chemicals (e.g., formaldehyde, polymers) and chemical precursors (e.g., syngas and C1 or C2 building block compounds).

The principal barrier to the practical realization of this vision relates to the intrinsic thermal stability of the CO2 molecule. Several different chemical, thermochemical and biochemical processes have been designed to overcome this energy barrier: where powered by renewable energy, electrolytic and photolytic reduction processes can also offer the possibility of efficient and, in principle, emission−free CO2 conversion. Indeed, the term ‘solar fuels’ has emerged to describe the use of abundant solar radiation to affect the reduction of CO2 (coupled with H2O oxidation), with the harvested energy stored in the bonds of the reduction products.

A series of rhenium tricarbonyl compounds based on the so−called Lehn catalyst, have been amongst the most studied homogeneous CO2 reduction photocatalysts since the initial report of their catalytic ability in 1983. In this DCU research collaboration, we report the syntheses and characterization of three novel rhenium−NHC tricarbonyl compounds.