Recycling of homogeneous catalysts generally and of Ru-catalysts used in metathesis chemistry is an important unsolved problem. This study will discuss how polyolefins and polyethylene (PEolig) in particular can be used as supports and/or solvents to recover Ru-catalysts or separate its residues from products. For example, by using a polyethylene-supported catalyst that is soluble hot and insoluble cold, we have shown that it is possible to affect both ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROMP) reactions with separation of products and catalysts or catalyst residues. In these cases, the quantitative insolubility of these catalysts or its residues and the products' solubility allowed the products to be separated at room temperature as solutions from the insoluble catalysts. These polyethylene-bound second-generation Hoveyda-Grubbs catalysts were formed using N-heterocyclic carbene ligands that contained polyethylene oligomers. Based on other work where polyisobutylene-bound (PIB) species that are phase selectively soluble in heptane have been used for catalyst recovery, other still ongoing work is exploring additional strategies where unfunctionalized polyethylene (Polywax) is used as a solvent in place of heptane to recover either PIB- or PEOlig-bound catalysts. Such waxes are low viscosity liquids at ca. 75 �C but separate as solids or gels at room temperature. The results of both of these studies are that products can be prepared with substantially lower Ru contamination. For example, ROMP products have been prepared with 7.48 ppm Ru residues.

Polyolefins as supports and solvents in Ru-catalyzed metathesis chemistry

247th National Meeting (2014)

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