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Issue 22, 2018
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Metathesis in water conducted by tailor-made encapsulated Grubbs’ catalyst

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Abstract

Metathesis in water represents a current challenge in green chemistry, since hydrophobic catalysts are non-soluble in this medium. Although this issue has been addressed by modification of the hydrophobic ligand structure, alternative methods for conducting metathesis in water are of interest, such as catalyst encapsulation. In this contribution we report successful encapsulation of the Grubbs’ second-generation catalyst in alginate hydrogels, representing a renewable resource, to perform ring-closing metathesis (RCM) in water. We initially investigated the influence of different solvents on the reaction rate and confirmed that water is a preferred solvent. A comparison of non-encapsulated and encapsulated catalyst in calcium alginate revealed that the reaction rate for non-encapsulated catalyst was notably higher, which can be explained by “on water” conditions in this case. Inside the beads the encapsulated catalyst remained heterogeneous, thus allowing to switch the catalysis mode between “in/on water” through encapsulation. To overcome diffusion limitation and enhance reaction rate, we prepared a tailor-made bead material by introducing hydrophobic octyl-grafted alginate amide. Using such a hydrogel, diffusion limitation was positively influenced by hydrophobisation of the matrix, resulting in up to quadrupled reaction rates compared to calcium alginate as a standard encapsulation material. In terms of recycling, this encapsulated catalyst revealed promising performance, retaining 80% of its activity after ten runs. This is the first reported application of hydrophobised alginate derivatives in catalysed organic synthesis, achieving excellent encapsulation efficiency, no measurable leaching and yields of up to 87%.

Graphical abstract: Metathesis in water conducted by tailor-made encapsulated Grubbs’ catalyst

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Publication details

The article was received on 12 Jul 2018, accepted on 16 Oct 2018 and first published on 16 Oct 2018


Article type: Paper
DOI: 10.1039/C8GC02164C
Citation: Green Chem., 2018,20, 5179-5187
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    Metathesis in water conducted by tailor-made encapsulated Grubbs’ catalyst

    J. Pauly, H. Gröger and A. V. Patel, Green Chem., 2018, 20, 5179
    DOI: 10.1039/C8GC02164C

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