Beyond Formate Trapping: A Mechanistic Framework for Homogeneous CO₂-to-Methanol Conversion With First-Row Transition Metals

Homogeneous CO₂-to-methanol conversion with first-row transition catalysts is constrained by more than CO₂ activation. The dominant limitations vary with the metal, ligand framework, and reaction medium and may include inefficient H₂ activation, insufficiently persistent or unreactive metal hydrides, slow reduction beyond formate- or CO-derived intermediates, and inhibition by CO, water, methanol, or capture agents. This review assesses Fe, Co, Ni, Mn, and selected Cu catalysts across three reaction classes: direct and capture-assisted CO₂ hydrogenation, H₂-driven reduction of preactivated C₁ substrates, and reactions using stoichiometric hydride donors. Particular attention is given to the experimental basis for proposed intermediates and pathways under the relevant catalytic reaction conditions. Formate is often observed as a resting state, but its abundance and further reactivity depend strongly on the catalyst and medium. Subsequent reduction can be affected by metal-ligand cooperation, secondary-sphere interactions, proton availability, ion pairing, and solvent composition. Reactions involving preactivated substrates or sacrificial hydrides are therefore treated mainly as probes of individual reduction steps, not as direct benchmarks of catalytic performance. Across these systems, catalyst development requires reversible H₂ activation, reactive yet sufficiently persistent hydrides, controlled formate and CO binding, tolerance to products and additives, and compatibility with the CO₂-capture medium.