Porous polymer monolith supported Suzuki-Miyaura catalysis in microreactors
thesisposted on 2023-05-26, 04:10 authored by Deverell, JA
Miniaturisation of reactions to the sub-millilitre scale, through the use of microreactor technology, has the potential to reduce costs by drastically reducing reaction times, improving yields and selectivities, as well as decreasing the environmental impact by reducing reagent and solvent use. Further improvements can be achieved by utilising heterogeneous and supported catalysts within microreactors in order to increase reaction efficiency, reduce energy requirements, and simplify product purification. This should also enable the integration of microreactors with other existing microfluidic technologies allowing synthesis, purification, analysis, and bio-testing to be performed on a single device in an automated fashion. In this work, novel microreactors were fabricated utilising porous polymer monoliths (PPM's) prepared in situ within microfluidic devices as a support for the immobilisation of palladium complexes. Poly(glycidyl methacrylate-co-ethylene glycol dimethylacrylate) and poly(chloromethylstyrene-co-divinylbenzene) monoliths were prepared by either thermal or UV initiated radical polymerisation in several formats, including capillary, microchip, and column using both glass and polymer substrates. This required the development of new methods for anchoring PPM within polymer substrates with poor transmission in the deep UV region, which is necessary for photografting, thus enabling the use of polymer substrates with greater thermal resistance. The development of polymeric microreactors was pursued as mass production of microfluidic devices with multiple components is considerably easier and more economical compared to other substrates. Additionally, conditions were developed to allow the formation of PPM in columns with an internal diameter (ID) greater than 1 mm without the need for external compression to avoid shrinkage. The preparation of PPM using light emitting diode light sources was investigated with the aim of reducing the cost associated with development of photoinitiated PPM's, enabling greater access to this technique. The PPM's were utilised to immobilise ligands that will bind palladium, 5-hydroxy-1,10- phenanthroline, 5-amino-1,10-phenanthroline, and an N-methylimidazolium salt. In order to demonstrate the feasibility of this technology, the Suzuki-Miyaura coupling of iodobenzene and p-tolylboronic acid was performed under continuous flow in the reactors, which produced quantitative yields with less than 0.01% of the immobilised palladium leached over a 24 h reaction period. This is the first reported used on a polymer microchip for supported Suzuki-Miyaura catalysis and also the first demonstration of non-room temperature supported palladium catalysis within a polymer microreactor. Novel technology was developed to allow easy interfacing with a broad range of microchips and for producing PPM in batch via UV initiation using low intensity light sources.
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