Homogeneous hydrogenation has become a mature science. Initially, the focus was very much on the development of asymmetric hydrogenation catalysts. These days many chiral ligands are available, some of which quite affordable. The focus has now shifted towards selective hydrogenation of one functional group in the presence of another one.<br/>As part of our investigation of the conversion of bioethanol into butadiene, we developed an interest in the selective reduction of alpha,beta-unsaturated aldehydes to the allylic alcohols. The problem here is that most efficient ruthenium catalysts are activated by base, which can lead to serious side-reactions of the substrate aldehyde. We have solved this problem with the use of Ru-MACHO-BH as base-free transfer hydrogenation catalyst; this catalyst functions both with <i>i</i>-PrOH as well as with EtOH as reductant. Another low-cost solution, surprisingly does not come from a low-cost metal like iron, but rather from a catalyst made from ruthenium and a cheap NNS pincer ligand. This catalyst is highly active and selective for the hydrogenation of a,b-unsaturated aldehydes and ketones. In addition, we have found that this is the first catalyst that is capable of selectively reducing alpha,beta-unsaturated esters to the allylic aldehydes.<br/>In the second part of the lecture the asymmetric hydrogenation (AH) of pyridine derivative will be discussed. Although these days good methods exist for the asymmetric hydrogenation of 2-substituted pyridine derivatives, no good methods exist for the AH of 3-substituted pyridine derivatives. Using deuterium labeling studies we have been able to unravel the mechanism of this reaction. High enantioselectivity can be obtained in this reaction, but only at relatively low conversions.

New developments in homogeneous hydrogenation

254th National Meeting (2017)

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