Manganese-Catalyzed Formate Synthesis via Coupled Methanol Dehydrogenation and Bicarbonate Reduction

The formate salt represents an indispensable chemical found in a plethora of applications. A base-metal-catalyzed formate synthesis employing the simultaneous dehydrogenation of methanol and reduction of bicarbonate protocol is demonstrated in this paper. The reaction is catalyzed by a pincer Mn complex (Mn-1) bearing a PN^HP ligand (PN^HP = bis(2-(diphenylphosphino)ethyl)amine). The reaction proceeds via consecutive catalytic steps: a) the dehydrogenation of methanol, b) the reduction of bicarbonate to formate with the H₂ generated from methanol dehydrogenation, and c) the formation of formate salt from the formaldehyde (dehydrogenated methanol) in the presence of a base (with/without a catalyst). A maximum TON of up to 2630 was achieved for the formation of potassium formate from the reaction of potassium bicarbonate and methanol in the presence of KOH. A ¹³C labeling experiment demonstrated that formate formation primarily originated from methanol (76%), while bicarbonate contributed 24%. In addition to stoichiometric mechanistic investigations, we have also carried out a detailed computational study, which sheds light on the plausible mechanistic pathway. The developed methodology employs renewable raw materials─methanol and bicarbonates─and also produces hydrogen as a valuable byproduct. However, low methanol conversion (3.3% for the highest TON) and inefficient reduction of bicarbonate highlight the need for the development of a more efficient catalytic system.