Grzegorz Szczepaniak

Highly active catalysts for olefin metathesis in water

Preparation of novel, highly water soluble Ru complexes, which contain quaternary ammonium chloride tags is presented. The “on-site” quaternisation method can be used to obtain polar metathesis catalysts in an easy and efficient manner. Application profiles of three representative catalysts are described.

Easily removable olefin metathesis catalysts

A small family of olefin metathesis catalysts bearing a polar quaternary ammonium group is described. The presence of this group allows for efficient separation of ruthenium impurities after the reaction. Application of catalysts 9 and 11 leads to organic products of high purity, which exhibit surprisingly low ruthenium contamination levels (usually below 5 ppm) after a simple and inexpensive purification step.

Towards “cleaner” olefin metathesis: tailoring the NHC ligand of second generation ruthenium catalysts to afford auxiliary traits

The increasing use of olefin metathesis in practical syntheses led to a greater demand for tailored catalysts that offer not only high reactivity and stability in the presence of impurities, but also improved handling characteristics, such as custom solubility profiles, simpler post-reaction workup and easier removal of ruthenium residues from the products. Due to mechanistic considerations, the most appropriate way to create such compounds is to decorate known catalysts with utility related tags placed in nonlabile ligands. This critical review summarizes how the NHC ligand can be modified to confer novel auxiliary traits and examines the practical consequences of these modifications.

High-Performance Isocyanide Scavengers for Use in Low-Waste Purification of Olefin Metathesis Products

Three isocyanides containing a tertiary nitrogen atom were investigated for use as small-molecule ruthenium scavenging agents in the workup of olefin metathesis reactions. The proposed compounds are odorless, easy to obtain, and highly effective in removing metal residues, sometimes bringing the metal content below 0.0015 ppm. The most successful of the tested compounds, II, performs very well, even with challenging polar products. The performance of these scavengers is compared and contrasted with other known techniques, such as silica gel filtration and the use of self-scavenging catalysts. As a result, a new hybrid purification method is devised, which gives better results than using either a self-scavenging catalyst or a scavenger alone. Additionally, isocyanide II is shown to be a deactivating (reaction quenching) agent for olefin metathesis and superior to ethyl vinyl ether.

Highly efficient and time economical purification of olefin metathesis products from metal residues using an isocyanide scavenger

A sustainable protocol of olefin metathesis in non-degassed, undistilled ethyl acetate under air with commercially available self-scavenging ruthenium catalysts is described. Furthermore, a time economical, cost-effective and scalable method of removal of ruthenium residues is presented. Treatment of post-reaction mixtures with an isocyanide scavenger and then with acid followed by a simple filtration is shown to yield OM products with ruthenium contamination below 5 ppm even in highly challenging cases. Finally, a telescope RCM/Suzuki–Miyaura sequence with a rapid and efficient purification protocol for simultaneous removal of Ru and Pd residues from solution is described.