Water-soluble protic Mn(I)-NHC complex for reversible CO2 hydrogenation and formic acid dehydrogenation in aqueous medium

The excessive consumption of carbon-based fossil fuels generates greenhouse gases, primarily CO₂, one of the largest contributors to global climate change. However, capturing CO₂ and transforming it into value-added chemicals has garnered significant attention recently leading to greener and more efficient energy conversion processes. Among various strategies for CO₂ utilization, catalytic conversion of CO₂ to formic acid (FA) or formate salts using H₂ gas is one of the important sustainable synthetic methods because they act as crucial LOHCs.¹ The generated H₂ gas from FA offers an environmentally benign alternate green energy source to fossil-fuels. There are several reports of homogeneous transition metal catalysts for reversible CO₂ hydrogenation and FA dehydrogenation, mostly in organic solvents.² Few water soluble Ir³ and Ru⁴ based catalysts are known for reversible hydrogen storage and release in aqueous medium, but no water soluble 3d metal catalyst has been developed for the same purpose. Towards our continuous effort to design efficient bifunctional catalysts, we have developed a water-soluble Mn(I)-NHC catalyst featuring a hydrophilic arm associated with a protic pyridyl -NH/=N motif. The catalyst showed excellent activity for reversible CO₂ hydrogenation and dehydrogenation of FA in aqueous medium. Detail mechanistic investigations were performed to demonstrate the crucial role of the PRU in bifunctional activation of H₂ for hydrogenation and in FA dehydrogenation.