Leveraging Diamines to Unlock the Mn-MACHO Catalyst in the Reduction of CO2 to Methanol

The conversion of CO₂ into energy-dense liquid fuels, such as methanol, represents a cornerstone of sustainable chemistry; however, most homogeneous catalytic systems still rely on noble metals or Lewis acid additives. Here, we report the first protocol for amine-assisted CO₂ hydrogenation to methanol using a Mn–MACHO catalyst without any Lewis acid co-catalyst, achieving turnover numbers up to 45.2, the highest reported for Mn systems. A combined computational, microkinetic, and experimental study reveals that diamines dramatically enhance activity compared to monoamines by promoting a highly exergonic double amidation step. This thermodynamic driving force shifts the equilibrium away from formate resting states toward the active catalyst, thereby accelerating methanol formation. The correlation established between amidation free energies (ΔGamidation) and methanol productivity provides a rational design principle for tailoring amine promoters across Ru- and Mn-based MACHO catalysts. These insights advance the development of sustainable, base-metal-catalyzed CO₂ conversion strategies and open opportunities for integrated carbon capture and utilization.