Supported Iridium Catalyst for Clean Transfer Hydrogenation of Aldehydes and Ketones using Methanol as Hydrogen Source

Graphical Hydrogen pool : Recyclable Ir/ZnO-catalysed additive-free transfer hydrogenation of aldehydes and ketones using methanol as hydrogen source was achieved at 110 °C, delivering alcohols in up to 98 % yield. The fine cooperation of ZnO and positively charged IrO x enables the complete cleavage of O−H and less reactive C−H bonds of methanol to generate active H for carbonyl hydrogenation. The use of methanol as abundant and low-toxic hydrogen source under mild and clean conditions is promising for the development of safe and sustainable reduction processes, but remains a daunting challenge. This work presents a recyclable ZnO-supported Ir catalyst for the additive-free transfer hydrogenation of aldehydes and ketones using methanol as hydrogen source at 110 °C, delivering alcohols in up to 98 % yield. Mechanistic studies disclose that methanol is first dehydrogenated to formaldehyde and then fully decomposed into active hydrogen species for hydrogenation. The superior performance is related to the high ratio of positively charged IrO x species and their ultrafine dispersion over ZnO. And the delicate cooperation of IrO x and ZnO enhances the catalytic activities for the selective scission of O−H and less reactive C−H bonds in methanol, maintaining a good balance between methanol decomposition and C=O hydrogenation in this green transfer hydrogenation.