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 PNHP ligand (PNHP = 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.