Strain-dependent enantioselectivity in mechanochemically coupled catalytic hydrogenation
The ultimate realization of top-down atomic manipulation is to push or pull molecules in a way that changes their function, such as catalysis. The forces in a stretched polymer distort molecular conformation in ways that couple to reactivity, but the use of this type of polymer mechanochemistry to bias the outcome of a reaction has been limited to stoichiometric reactions. Here we demonstrate that the selectivity of a catalytic site can be manipulated by straining a polymer support to which the catalyst is covalently bound. The enantiomeric ratio of the products of the hydrogenation of a series of 2-acetamidoacrylates by a bisphosphine rhodium catalyst increases with macroscopic strain, reaching up to twice its initial value when the support is compressed by 73% in a single dimension. Reactivity reverts upon relaxing support. Control experiments, structure–activity studies using strained macrocycles, and computations support mechanochemical coupling as the dominant cause of the improved selectivity and suggest that larger effects are possible with advances controlling the molecular topology of the supporting network. (Figure presented.).
