Metathesis under Biphasic Conditions Using Monolithic-Supported Ionic Liquids

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Polymeric monolithic supports shall be prepared either via ring-opening metathesis polymerization (ROMP) or via electron beam (EB) triggered free radical polymerization. The resulting porous monolithic structures shall serve as support materials for Ionic liquids (ILs) in which a series of novel metathesis catalysts bearing ionic moieties shall be dissolved. Metathesis reactions shall be run under biphasic conditions using a second organic phase immiscible with the IL. For these purposes, novel persistent, IL-soluble Schrock and Grubbs-Hoveyda-type catalysts with pendant ionic groups are to be synthesized. The monoliths shall be subject to in situ surface functionalization using ionic monomers based on quaternary ammonium, imidazolium and phosphonium salts as well as with 2-propoxystyryl ethers. In the case of ROMP-derived monoliths, this is to be accomplished by the use of the corresponding norborn-2-ene or cyclooctene derivatives. In the case of EB-triggered free radical polymerization-derived monoliths, acrylates containing quaternary ammonium, imidazolium and phosphonium salts as well as 2-propoxystyryl ethers are to be surface-grafted via post-synthesis, EB-triggered free radical polymerization. Alternatively, a ROMP-based protocol using the above-mentioned norborn-2-ene or cyclooctene derivatives shall be applied. The thus prepared surface-functionalized monoliths shall then be treated with appropriate amounts of ionic liquids (ILs) based on a similar structural motif as used for surface grafting (i.e. for the corresponding quaternaized N- and P-based monomers). Special care shall be devoted to compatibility issues, which are mainly related to both the nature of the grafted molecules and the ILs and to the grafting density as well as of the degree of polymerization of the graft polymers based on the quaternary ammonium, imidazolium and phosphonium salts, respectively. In all cases, the final functionalized monoliths shall be characterized by micro- and mesopores. Apart from ionic interactions between the graft polymers and the ILs, these pores allow for retaining the ionic liquids (ILs) at the surface by capillary forces. In addition, sufficient interconnected pores in the μm-range shall be present and guarantee for a fast flow-through. An optimization in terms of grafting density, chain length of the graft polymers, nature of the functional monomer and IL as well as optimum layer thickness of the IL shall be carried out, thus offering optimum catalytic performance while resulting in a minimum leaching. The ultimate goal is the realization of novel ionic metathesis catalysts, their immobilization within monolith-supported ILs, and the use of the thus prepared supported catalysts in continuous metathesis reactions including ring-closing metathesis (RCM), ring-opening cross metathesis (ROC), cross-metathesis and ene-yne cross metathesis reactions under biphasic conditions. The thus created immobilized systems shall provide further insight into the reactivity of both Schrock- and Grubbs-Hoveyda-type catalysts in metathesis reactions within ILs. Even more important, the supported catalysts to be developed here shall help to solve the problems of support-regeneration and recharging, metal contamination of products and catalyst longevity.