Haptophilicity and Substrate-Directed Reactivity in Diastereoselective Heterogeneous Hydrogenation

Stereoselectivity in heterogeneous hydrogenation of olefins and arenes is typically dictated by the steric properties of the organic substrate, and the inherent steric preference is difficult to alter through the modification of the catalyst or experimental parameters. One strategy to access counter-steric selectivity is to incorporate a stereochemically defined functional group into the substrate that can adsorb to the catalyst surface and "direct" hydrogen addition from the same face. This Perspective provides an overview of heterogeneous directed hydrogenation and elucidates a few design rules about directing group identity, substrate structure, and catalyst composition that lead to diastereoselective reactivity. Monometallic heterogeneous catalysts are capable of diastereoselective directed hydrogenation with only a limited set of substrate scaffolds and directing functional groups. In a given substrate, the complex interplay between directing group conformation, steric bulk, and adsorption strength makes it difficult to predict whether steric or electronic factors will dominate the diastereoselectivity. We then discuss more recent examples of bimetallic catalysts for this reaction and look toward opportunities for bimetallic structures to yield more tunable and general heterogeneous directed hydrogenation catalysts.