Atomic-thick two-dimensional Janus interphase catalyst with an interfacial ionic liquid bridge for quasi-homogeneous Pickering interfacial catalysis

Atomic-thick 2D Janus catalyst with an interfacial ionic liquid bridge were developed. • The catalyst positions catalytic site at oil–water interface by the formation of stable emulsion. • IL acts as a compatible   bridge, creating quasi-homogeneous interfacial microenvironments. • Unprecedented activity was obtained as a result of “quasi-homogeneous interfacial catalysis”. • The catalyst could be easy recovered for efficient reuse via simple centrifugation. Pickering emulsions are of considerable interest in the chemical industry because they provide large oil–water interfacial areas for interfacial catalysis. However, solid emulsifiers located at oil–water interface often impede the mass transfer across the interface, thereby limiting the reactivity of biphasic reactions. Here we report a quasi-homogeneous Pickering interfacial catalysis strategy to overcome this diffusion barrier by employing an ultrathin amphiphilic Janus film as the solid emulsifier and introducing a compatible ionic liquid (IL) as a multifunctional   interfacial   bridge. Hydrophobic chiral neat Ti IV salen complexes (Ti(salen)) were thus selectively grafted onto one side of single-layer porous graphene oxide (PGO) through an imidazolium-based IL linker, enabling asymmetric oxidation of sulfides with H 2 O 2 in water. The atomic-thick GO film precisely positions Ti(salen) catalytic sites at oil–water interface, while the hydrophilic IL moieties located on the hydrophobic catalytic side act as molecular bridge between the oil and aqueous phases owing to their unique compatibility. This engineered interfacial microenvironment allows the water-soluble oxidant to directly access the hydrophobic substrate at the catalytic interface without a significant diffusion barrier. As a consequence, asymmetric sulfoxidation in water proceeds in a quasi-homogeneous manner, affording a broad range of chiral sulfoxides in excellent yields (93–98%) and enantioselectivities (92–99% ee), surpassing the performance of most reported Pickering interfacial catalysts. Moreover, the quasi-homogeneous Pickering interfacial catalysis strategy also delivers efficient asymmetric sulfa-Michael addition in water when chiral Fe Ⅲ –salen complexes are used as catalytic sites. Download: Download high-res image (179KB) Download: Download full-size image