Precise control of selective hydrogenation of α,β-unsaturated aldehydes in water mediated by ammonia borane

Hydrogenation of unsaturated biomass in a control manner is highly desirable but challenging, especially under mild conditions. We here report selective hydrogenation of α,β-unsaturated aldehydes (UALs), featuring a precise control of all potential products by adjustment of the role of ammonia borane (AB) in transfer and/or catalytic hydrogenation. The hydrogenation can be readily operated in neat water without using any external H2-source, because AB as the H2-source is favorable in aqueous solution. Impressively, unsaturated alcohols are prepared in 100% conversion by the room-temperature transfer hydrogenation of UALs with AB, while saturated aldehydes are obtained in 100% conversion and > 90% selectivity with high activity (i.e., turnover frequency = 0.98 s−1 for cinnamaldehyde), by the catalytic hydrogenation with H2 released from AB and Pd immobilized on two-dimensional metal organic layer. On the other hand, UALs can be completely converted into the saturated alcohols through a combination of transfer and catalytic hydrogenation in one pot. This strategy can be extended to more than 8 types of UALs, and provides a facile way to fine-control the selective hydrogenation of unsaturated compounds with competing bonds. Precise control of selective hydrogenation of α,β-unsaturated aldehydes (UALs) under environmentally benign conditions is achieved by simply switching the roles of ammonia borane (AB) in transfer and/or catalytic hydrogenation. Unsaturated alcohols are easily prepared by room-temperature transfer hydrogenation of UALs with 100% conversion by AB. Saturated aldehydes are selectively prepared through catalytic hydrogenation by Pd/MOL and in-situ released H2 from AB. UALs are completely hydrogenated to prepare saturated alcohols by transfer hydrogenation along with catalytic hydrogenation using Pd/MOL and AB together. [Display omitted] •A facile strategy is developed to precisely control of selective hydrogenation of α,β-unsaturated aldehydes.•The hydrogenation is controlled by switching the roles of ammonia borane in transfer and/or catalytic hydrogenation.•α,β-Unsaturated aldehydes are converted into three potential products with extremely high conversion and selectivity.•The hydrogenation is carried out in neat water without using additional H2 source.