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

## TL;DR

A new method uses diamines with a manganese-based catalyst to convert CO2 into methanol efficiently without needing noble metals or Lewis acids.

## Contribution

The first protocol for CO2 hydrogenation to methanol using Mn–MACHO without Lewis acid co-catalysts, achieving high turnover numbers.

## Key findings

- Diamines enhance catalytic activity by promoting a double amidation step, shifting equilibrium toward methanol formation.
- A correlation between amidation free energy and methanol productivity enables rational design of amine promoters.
- The Mn–MACHO system achieves turnover numbers up to 45.2, the highest reported for Mn-based systems.

## Abstract

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 (ΔG
amidation) 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.

CO2 hydrogenation to methanol using a Mn–MACHO catalyst was achieved without Lewis acid promoters, delivering TONs up to 45.2. Diamines, by driving a highly exergonic double amidation reaction, divert formate resting states toward the active catalyst. The correlation between ΔG
amidation and methanol productivity enables the rational design of the amine for novel Ru and Mn‐MACHO catalysis.