Highly active catalysts for olefin metathesis in water

Abstract

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.

Acid‐Assisted Direct Olefin Metathesis of Unprotected Carbohydrates in Water

“…Installation of the quaternary amino groups was envisaged by late-stagem ethylation of the nonmethylated catalyst structure to allow easier synthesis and purification. [47] Synthesiso fc arbenep recursors matching similar criteria has been reported by Plenio and co-workers, [59] and an analogous strategy was adopted in the present case ( Figure 1). Thus, electrophilic aromatic substitution between 2,6-dimethylaniline and the morpholinium ion of formaldehyde first yielded morpholine-substituted aniline 1.T reatment of 1 with glyoxal provided diimine 2,w hich on reductionw ithl ithium aluminum hydride yielded the corresponding 1,2-diamine 3.S ubsequentr ing closure of this species by using triethylo rthoformate in the presence of ammonium chloride provided imidazolinium chloride 4,s erving as the NHC ligand precursor.…”

“…To address this limitation, several strategies to enable olefin metathesis in aqueous media have been proposed,i ncluding the use of biphasic systems, [32] immobilized catalysts, [33,34] nanoreactors and micellar catalysis, [35][36][37][38][39] artificial metallo-enzymes, [40] as well as modificationso ft he catalysts or the reaction conditions to increase the reactivity. [41][42][43][44][45][46][47][48][49][50] Unfortunately,m any of these systems are either incompatiblew ith water-soluble substrates or have av ery narrow substrate scope. [31,51,52] The olefin metathesis reactionhas nevertheless been applied to carbohydrates to somee xtent, [53] generally by using protected structures in organic solvents.…”

Tube‐In‐Tube Reactor as a Useful Tool for Homo‐ and Heterogeneous Olefin Metathesis under Continuous Flow Mode

“…We decided to test this system by performing both hetero-and homogenous metathesis. The former, which in CF-mode can be even more challenging than the latter, was promoted by catalyst 6, which was synthesized in our laboratory [13] and deposited on commercially available silica gel. Heterogeneous 6-SiO 2 was used in the RCM of 7 in toluene at 80 8C (Table 1 and Figure 3).…”

Click Chemistry in Complex Mixtures: Bioorthogonal Bioconjugation

“…S -allylcysteine can be easily introduced into proteins by a variety of methods, including conjugate addition of allyl thiol to dehydroalanine, direct allylation of cysteine, desulfurization of allyl disulfide, or metabolic incorporation as a methionine surrogate in methionine auxotrophic E. coli (van Hest et al, 2000), or by reassignment of the amber stop codon (Ai et al, 2010). The resulting allyl sulphides (Lin et al, 2008) are effective substrates for cross metathesis using standard (Figure 8E) and new catalysts developed for aqueous-phase applications (Burtscher and Grela, 2009; Skowerski et al, 2012; Tomasek and Schatz, 2013). …”