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Supermolecular Catalysts
Published in Qingmin Ji, Harald Fuchs, Soft Matters for Catalysts, 2019
Shangbin Jin, Jiang He, Qingmin Ji, Jonathan P. Hill, Katsuhiko Ariga
Various efficient, water-soluble, ruthenium-benzylidene olefin, metathesis catalysts for metathesis of olefins in water have been reported. In some cases for olefin metathesis of hydrophobic substrates in pure water, ultrasonification of surfactants is required to get a homogeneously dispersion state. Astruc et al. reported the catalysis of ring-closing metathesis (RCM), cross metathesis (CM) and enyne metathesis (EYM) of hydrophobic substrates in water and air under ambient or mild conditions using very low catalytic amounts (0.083 mol%) of a dendritic catalysis system [172]. The system is based on a suitably designed dendrimer terminated by 27 tetraethyleneglycol tethers and Grubbs' second-generation olefin-metathesis catalyst (Fig. 3.28). The water-soluble dendrimer allows the decrease in the amount of commercial ruthenium (Ru) catalyst for olefin RCM reactions in water. The aqueous solution of dendrimer can also be recovered and reused at least 10 times without significant decrease of metathesis product yield. The dendrimer plays the protection role as a nanoreactor towards the catalytically active species, in particular the sensitive Ru-methylene intermediate in the metathesis catalytic cycle, and also prevents catalyst decomposition in the presence of an olefin substrate.
New latent metathesis catalysts equipped with exchangeable boronic ester groups on the NHC
Published in Journal of Coordination Chemistry, 2018
Revannath Sutar, Danielle Butilkov, N. Gabriel Lemcoff, Ofer Reany
Latent metathesis catalysts equipped with pinacol boronate were efficiently synthesized and the termini pinacol units were readily exchanged by several 1,2 and 1,3-diols without affecting the metal coordination sites. The latency and the stability of S-chelated ruthenium benzylidene complex allowed the first synthesis of metathesis catalysts loaded with diallyl units which are commonly used substrates in RCM reactions. The G0 catalysts, cis-Ru IIa,c-e, equipped with different diols at the terminal boronic esters demonstrated similar catalytic activities in photo-induced enyne metathesis reaction and thermal RCM reactions of DEDAM. However, their catalytic activities in photo-induced RCM reaction of DEDAM showed different behaviors that may be a result of catalyst deterioration upon prolonged irradiation.