Hemin immobilization in hydrophobic SBA15 as a Recyclable Catalyst for trans-selective Cyclopropanation in Aqueous Media

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 SBA-15 material. The inner core of SBA-15 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 confirmed the successful immobilization of hemin within the hydrophobic pores of functionalized SBA-15. 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 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.