Aqueous olefin metathesis still poses a challenge to the synthetic chemist. Water is a metathesis inhibitor and hence, catalysts operating under homogenous, aqueous conditions have been performing with low efficiency and low rates thus far. We have developed novel Ru-based catalyst bearing an N-heterocyclic carbene ligand with two pH-responsive NMe2 groups bonded remotely to the aryl substituents. The complexes were isolated as 4-dimethylaminopyridine (DMAP) 3rd generation Grubbs-type ruthenium complexes. Under acidic aqueous conditions, the catalysts become water-soluble and perform aqueous metathesis at remarkable rates. For example, a rate was accomplished up to 100 times faster than the fastest aqueous ring opening metathesis polymerization (ROMP) reaction known to date. Quantitative ROMP conversions have been accomplished using catalyst loadings as low as 0.1 %. Furthermore, the majority of polymerization reactions follow 1st order kinetics which suggest a good level of molecular weight control. We also investigated the aqueous ring closing metathesis RCM) with these catalysts using various substrates. While extremely fast conversions were recorded within minutes, the catalytic activity for these complexes seized within minutes. Unsurprisingly, higher turnover numbers were accomplished at lower catalyst loadings. We are currently investigating RCM protocols that allow for extended catalyst lifetimes and hence higher conversion rates.

Extremely fast olefin metathesis in aqueous media with 3rd generation Grubbs-type catalysts

255th National Meeting (2018)

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