Ruthenium-Catalysed Olefin Metathesis in Environmentally Friendly Solvents: 2-Methyltetrahydrofuran Revisited

Application profiles of a set of popular second-generation ruthenium catalysts were experimentally investigated in an environmentally friendly solvent, 2-methyltetrahydrofuran (2-MeTHF), and compared with the activity of the same catalysts in toluene, a popular solvent used in industrial olefin metathesis. It was found that a catalyst containing a 2-isopropoxy-5-nitrobenzylidene moiety and a symmetrical N-heterocyclic (NHC) ligand with 2,6-diisopropylphenyl substituents (SIPr) exhibits the highest catalytic activity in 2-MeTHF also at a lower temperature (30 °C). Ab initio studies showed that initiation rates of Ru catalysts bearing NHC ligands in 2-MeTHF can be correlated with partial charges and bond lengths between selected crucial atoms in the studied ruthenium complexes. The results demonstrate that aromatic or chlorinated solvents, typically used in metathesis reactions, can be successfully replaced in many cases by 2-MeTHF.