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.