Recent developments on methanol as liquid organic hydrogen carrier in transfer hydrogenation reactions

Abstract Transition metal-catalyzed hydrogen transfer reactions have been widely exploited using alcohols, acids, etc. as hydrogen donors. The widespread use of such hydrogen donors in transfer hydrogenation reactions validate these methods as practical alternates to direct hydrogenation reactions requiring toxic, flammable molecular hydrogen that often require high-pressure conditions. Surprisingly, methanol, with its high H/C ratio and availability from renewable feedstock is overlooked compared to other sacrificial hydrogen donors and it can act as an ideal candidate in transfer hydrogenation/acceptorless dehydrogenation reactions. However, dehydrogenation of methanol is a high-energy process, and it requires a catalyst that can surpass high-energy transition states to produce hydrogen. In this review, we summarize the efforts that have been put forth by chemists to develop various catalytic systems over the last three decades for efficient dehydrogenation of methanol as well as use of methanol as liquid organic hydrogen carrier (LOHC) for the transfer hydrogenation of various substrates such as alkynes, alkenes, ketones, aldehydes etc.