Multi-Functionality of Methanol in Sustainable Catalysis: Beyond Methanol Economy

Methanol is a fundamental feedstock and is widely used in the chemical and petroleum industries. It can serve as a C1 source to make a variety of C–C and C–N bond formation and dehydrogenative coupling products, which have important applications in natural products and drug discovery. A high hydrogen content (12.5 wt%) of methanol makes it an effective H2 donor for the transfer hydrogenation of various reducible functional groups. A plethora of various transition metal-based dehydrogenative processes have been developed using methanol. Notably, recent review articles focused on the C1 aspect of methanol. However, a more updated review that examines the challenges and applications of methanol as both a C1-source and H2-source in organic transformations contributing to the concept of the methanol economy has not been presented yet. This Review summarizes the transition metal-based (homogeneous, heterogeneous, and photo-) catalyst system for C-, N-, and O-methylation of ketones, alcohols, amides, nitriles, heterocyclic compounds, sulfones, amines, amides, sulfonamides and direct N-methylation of nitro compounds under borrowing hydrogen strategy and N-formylation of amines using methanol under acceptorless dehydrogenation coupling using methanol as a C1 source. It also covers insights into reaction mechanisms and the role of carefully selected ligands in the metal catalysis for methanol activation and incorporation of -CD3, methylation of drug molecules. Moreover, it describes transfer hydrogenation of various functional groups such as aldehydes, ketones, alkynes, and nitro with methanol as an H2 donor in detail.