A route to magnetically separable nanocatalysts: Combined experimental and theoretical investigation of alkyl substituent role in ligand backbone towards epoxidation ability

Abstract

We have prepared two chiral Schiff base ligands, H2L1 and H2L2, and one achiral Schiff base ligand, H2L3, by treating 2,6‐diformyl‐4‐methylphenol separately with (R)‐1,2‐diaminopropane, (R)‐1,2‐diaminocyclohexane and 1,1′‐dimethylethylenediamine, in ethanolic medium, respectively. The complexes MnL1ClO4 (1), MnL2ClO4 (2), MnL3ClO4 (3), FeL1ClO4 (4), FeL2ClO4 (5) and FeL3ClO4 (6) have been obtained by reacting the ligands H2L1, H2L2 and H2L3 with manganese(III) perchlorate or iron(III) perchlorate in methanol. Circular dichroism studies suggest that ligands H2L1 and H2L2 and their corresponding complexes have asymmetric character. Complexes 1–6 have been used as homogeneous catalysts for epoxidation of alkenes. Manganese systems have been found to be much better than iron counterparts for alkene epoxidation, with 3 as the best catalyst among manganese systems and 6 as the best among iron systems. The order of their experimental catalytic efficiency has also been rationalized by theoretical calculations. We have observed higher enantiomeric excess product with catalysts 1 and 4, so they were attached to surface‐modified magnetic nanoparticles to obtain two new magnetically separable nanocatalysts, Fe3O4@dopa@MnL1 and Fe3O4@dopa@FeL4. They have been characterized and their alkene epoxidation ability has been investigated. These catalysts can be easily recovered by magnetic separation and recycled several times without significant loss of catalytic activity. Hence our study focuses on the synthesis of a magnetically recoverable asymmetric nanocatalyst that finds applications in epoxidation of alkenes and at the same time can be recycled and reused.

Oxidation of Organic Functionalities by PhI(OAc)2 Catalysed by Magnetically Separable Fe3O4@dopa‐Supported Mn(III) Complexes: Combined Experimental and Theoretical Approach

“…Our group had previously found that Fe(III) halogen salen complexes (built from 1,2‐diaminopropane) in conjunction with PhIO as terminal oxidant rendered the opposite efficiency for the oxidation of alkenes, that is, those catalysts with chlorine substituents were the least effective and the efficiency raised with the increase in the halogen size ,. However, apart from the change in the metal, the reactants here used show two decisive differences with respect to those in our previous work:the bridge in the salen ligand (coming from 2,2‐dimethyl‐1,3‐propandiamine) and the oxidizing agent.…”

“…The preparation of magnetically separable nanoparticles is displayed in Scheme .Synthesis and characterization of magnetic nanoparticles Fe 3 O 4 and Fe 3 O 4 @dopa has been executed following earlier reported methods ,. Preparation of Fe 3 O 4 @dopa@MnL 1 Cl has been carried out by adding 1 g of complex 1 , i. e., MnL 1 Cl a dispersed acetonitrile solution of amine‐functionalized nano‐Fe 3 O 4 (Fe 3 O 4 @dopa, 500 mg) followed by stirring of the mixture for 14 h at room temperature.…”

“…Magnetically separable nanocatalysts (MSNs) can be considered a bridge between homogeneous and heterogeneous catalysts. Magnetic stimulation provides unique characteristics such as eco‐friendly nature, ease of recyclability and simple operation of the catalyst . In addition, MSNs provides excellent surface‐to‐volume ratio which significantly amplifies the proximity between reactants and catalyst.…”

Excellent alkene epoxidation catalytic activity of macrocyclic‐based complex of dioxo‐Mo(VI) on supermagnetic separable nanocatalyst

“…[15][16][17][18] A main idea for supporting of metal complexes is to anchor the metal complexes onto large-surface-area inorganic materials such as zeolites and metal oxides. [16,[19][20][21][22][23][24][25] Nowadays, magnetite nanoparticles are of particular interest because of their unique properties including high surface area, low toxicity, ability to be separated and biocompatibility. [16,[26][27][28][29][30] Magnetic separation renders the recycling of catalysts from solution using external magnetic fields much easier than filtration and centrifugation.…”

Manganese Ferrite Nanoparticles Modified by Mo(VI) Complex: Highly Efficient Catalyst for Sulfides and Olefins Oxidation Under Solvent‐less Condition

“…Supporting the metal complexes onto nanomaterials such as metal oxides is a widely strategy to overcome these limitations. Magnetite nanoparticles, in particular spinel ferrites‐ such as MnFe 2 O 4 nanoparticle are largely employed for this purpose due to their high saturation magnetization, high mechanical hardness and chemical stability …”