Bioinspired Nanoparticle-Assembly Route to a Hybrid Scaffold: Designing a Robust Heterogeneous Catalyst for Asymmetric Dihydroxylation of Olefins

A hierarchical polyamine-silica structure is shown to encase osmate ions resulting in robust and reusable catalysts for asymmetric dihydroxylation of olefins with a high TON (>700). Whilst the polypeptide and related polyamines resembling a proteinaceous matrix in biosilica nanostructures preserve the osmate as the active centre, the surrounding assembly of silica nanoparticles imparts stability and textural properties to the catalyst. This confinement of osmate in the microsphere leads to higher catalytic activity and enantioselectivity for a variety of olefins as the substrate. The hybrid nature of the catalyst not only allows for the usage of various solvent systems, but also provides a means to be integrated with multi-components/functions for tuning the activity, catalysis separation and reusability. Interestingly, the presence of polyamine makes the catalyst retain its activity even in the presence of chelating acids like citrate that are known to diminish enantioselectivity. A bioinspired hybrid design based on the biosilica nanostructure allows chemical transformations with entrapped osmium species enabling superior catalytic activity, stability and reusability in the asymmetric dihydroxylation of olefins.