Catalytic hydrogenation of tetrasubstituted olefins provides opportunity to access elusive 1,2-contigious stereocenters. However, these moieties commonly exhibit low reactivity and selectivity in homogeneous catalytic systems due to steric crowding between ligand scaffolds and substrate. We previously demonstrated that bimetallic Pd3Cu nanoparticles are capable of haptophilic control in diastereoselective hydrogenation of tri-substituted olefins, where an ancillary directing group on the substrate binds to the surface for subsequent facially selective hydride delivery. To expand the scope of this reaction, our current work focuses on using bimetallic platinum nanoparticles as more powerful hydrogenation catalysts. Initial optimization of catalyst synthesis strategies provided access to a PtNi2/SiO2 species with excellent batch to batch reproducibility. We postulate that this reproducibility arises from the formation of an ordered PtNi intermetallic phase and investigate the presence of this phase using synchrotron X-ray diffraction and X-ray absorption spectroscopy. We then test the optimized catalyst on a variety of sterically encumbered cyclopentenols and compare the hydrogenated product distribution of our catalyst to monometallic Pt catalyst and commercially available [Ir(cod)(py)(PCy3)]PF6. We find that the PtNi2 catalyst is not only chemoselective for olefin reduction in the presence of other reducible functionality present on the substrate but exhibits significant minimization of substrate isomerization and dehydration while achieving diastereoselectivities as high as 99:1.

Haptophilic control in diastereoselective hydrogenation of tetra-substituted olefins using bimetallic Pt-Ni nanoparticles

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