Mn(III) complex supported on Fe₃O₄ nanoparticles: magnetically separable nanocatalyst for selective oxidation of thiols to disulfides

Abstract

A manganese(III) complex, [Mn(phox)₂(CH₃OH)₂]ClO₄ (phox = 2-(2′-hydroxyphenyl)oxazoline), was immobilized on silica-coated magnetic Fe₃O₄ nanoparticles through the amino propyl linkage using a grafting process in dichloromethane. The resulting Fe₃O₄@SiO₂–NH₂@Mn(III) nanoparticles are used as efficient and recyclable catalysts for selective oxidation of thiols to disulfides using urea-hydrogen peroxide as the oxidant. The nanocatalyst was recycled several times. Leaching and recycling experiments revealed that the nanocatalyst can be recovered, recycled, and reused more than five times, without the loss of catalytic activity and magnetic properties. The recycling of the nanocatalyst in six consecutive runs afforded a total turnover number of more than 10,000. The heterogeneous Fe₃O₄@SiO₂–NH₂@Mn(III) nanoparticle shows more selectivity for the formation of disulfides in comparison with the homogeneous manganese complex.

Keywords:

• Mn(III) complex
• Fe₃O₄ nanoparticle
• Magnetically separable nanocatalyst
• Thiol oxidation
• Disulfides

Acknowledgments

We acknowledge the Research Council of Sharif University of Technology for the research funding of this project. Omid Zandi and Meghdad Hosseini are kindly acknowledged for the SEM analysis.