Łukasz Gułajski

A green catalyst for green chemistry: Synthesis and application of an olefin metathesis catalyst bearing a quaternary ammonium group

The novel catalyst 8, bearing a polar quaternary ammonium group, is very stable and can be easily prepared from commercially available reagents. Catalyst 8 can be efficiently used for olefin metathesis not only in traditional but also in aqueous media. Various ring closing-, cross- and enyne-metathesis reactions were conducted in water–methanol mixtures in air. The electron withdrawing quaternary ammonium group not only activates the catalyst chemically, but at the same time allows its efficient separation after reaction. Application of 8 leads to organic products of high purity, which exhibit very low ruthenium contamination levels (12–68 ppm) after filtering through a pad of silica gel.

A Highly Active Aqueous Olefin Metathesis Catalyst Bearing a Quaternary Ammonium Group

A polar olefin metathesis catalyst that bears a quaternary ammonium group was prepared from commercially available reagents. The electron-withdrawing quaternary ammonium group not only activates the Ru catalyst electronically but at the same time makes the catalyst more hydrophilic. The catalyst can therefore be efficiently used both in traditional media, such as dichloromethane and toluene, as well as in technical-grade alcohols, alcohol-water mixtures and in neat water. Various metathesis reactions, including ring-closing, cross- and enyne metathesis, were conducted in these solvents in the presence of air. In addition, the Ru catalyst can act as an inisurf (initiator and surfactant) molecule, promoting metathesis under heterogeneous aqueous conditions.

Olefin metathesis in water using acoustic emulsification

The performance of two commercially available olefin metathesis catalysts in water has been studied. Ultrasonication of the water-insoluble substrates and catalysts in water allowed the formation of stable emulsions without added surfactants, while the smooth catalytic metathesis took place in the water-insoluble emulsion droplets. Ring-closing (RCM), enyne and cross metathesis (CM) of a variety of substrates proceed with remarkable efficiency in water using acoustic emulsification.

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.

A simple and practical phase-separation approach to the recycling of a homogeneous metathesis catalyst

The air stable asarone-derived Ru carbene 16, a robust olefin metathesis catalyst, can be easily separated after reaction by deposition on silica gel and reused up to nine times. This procedure provides products of excellent purity with low Ru content.

The Influence of the Anionic Counter-Ion on the Activity of Ammonium Substituted Hoveyda-Type Olefin Metathesis Catalysts in Aqueous Media

Polar olefin metathesis catalysts, bearing an ammonium group are presented. The electron withdrawing ammonium group not only activates the catalysts electronically, but at the same time makes the catalysts more hydrophilic. Catalysts can be therefore efficiently used not only in traditional media, such as methylene chloride and toluene, but also in technical-grade alcohols, alcohol— water mixtures and in neat water. Finally, in this overview the influence of the anionic counter-ion on the activity of ammonium substituted Hoveyda-type olefin metathesis catalysts in aqueous media is presented.