Hemin Immobilization in Hydrophobic SBA15 as a Recyclable Enzyme Mimetic Catalyst for Trans‐Selective Cyclopropanation in Aqueous Media

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Abstract
Metal‐porphyrin‐based biocatalysts are gaining popularity in sustainable chemical synthesis. Heme‐based enzymes like myoglobins, cytochrome P450s are known for their regio‐ and stereo‐selective cyclopropanation reactions in aqueous media. However, their practical application is challenged by complex, multistep synthesis procedures and inherent structural instability. To address these limitations, we developed a stable, enzyme‐mimicking heterogeneous catalyst using porous SBA15 material. The inner core of SBA15 was functionalized with an alkyl chain and protoporphyrin IX iron (III) (hemin), resulting in alkyl‐SBA15‐amideHemin. Characterization through TEM, UV–vis and FT‐IR spectroscopy, CHN analysis etc., confirmed the successful immobilization of hemin within the hydrophobic pores of functionalized SBA15. The catalytic performance of alkyl‐SBA15‐amideHemin was evaluated in the cyclopropanation reaction of styrene with ethyl diazoacetate (EDA), achieving a turnover number (TON) of 144—nearly double that of free hemin (TON 75). The catalyst exhibited high trans diastereoselectivity (∼70%) for 2‐(cyclopropyl benzene) esters in aqueous media, outperforming other known heterogeneous catalysts. Its catalytic activity and selectivity were maintained over four recycling cycles, highlighting its stability and reusability. Steady‐state emission studies, as well as the kinetics of the iron‐carbene complex, provided insights into the catalytic mechanism. These findings suggest that immobilized hemin within a hydrophobic environment serves as a robust and selective catalyst for chemical transformations in aqueous media.
Funding Information
  • Department of Atomic Energy, Government of India (RTI4003)
  • Tata Institute of Fundamental Research (RTI4003)

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