Development of a method for the preparation of ruthenium indenylidene-ether olefin metathesis catalysts

The reactions between several derivatives of 1-(3,5-dimethoxyphenyl)-prop-2-yn-1-ol and different ruthenium starting materials [i.e., RuCl₂(PPh₃)₃ and RuCl₂(p-cymene)(L), where L is tricyclohexylphosphine di-t-butylmethylphosphine, dicyclohexylphenylphosphine, triisobutylphosphine, triisopropylphosphine, or tri-n-propylphosphine] are described. Several of these reactions allow for the easy, in-situ and atom-economic preparation of olefin metathesis catalysts. Organic precursor 1-(3,5-dimethoxyphenyl)-1-phenyl-prop-2-yn-1-ol led to the formation of active ruthenium indenylidene-ether complexes, while 1-(3,5-dimethoxyphenyl)-prop-2-yn-1-ol and 1-(3,5-dimethoxyphenyl)-1-methyl-prop-2-yn-1-ol did not. It was also found that a bulky and strong σ-donor phosphine ligand was required to impart good catalytic activity to the new ruthenium complexes.

Solvent Effects in Alternating ADMET Polymerization

Alternating AB copolymers were synthesized by exploiting the selectivity of the metathesis reaction between α,ω-dienes and α,ω-diacrylates. Unlike standard acyclic diene metathesis (ADMET) polymerizations, the copolymerization of dienes and diacrylates does not require high vacuum conditions. This work utilizes this unique characteristic to explore the effect of various solvents on ADMET polymerization. We found significant variation in the efficacy of the solvents we screened, with CH₂Cl₂ yielding the highest molecular weight polymer. Additionally, the performance of Grubbs second generation catalyst was compared with Hoveyda-Grubbs second generation catalyst in different solvents, revealing a stark difference in the molecular weight of the resulting polymers in CH₂Cl₂ but a relatively minor difference in the final molecular weight from polymerizations in acetic acid.

Improved ruthenium catalysts for Z-selective olefin metathesis

Several new C-H-activated ruthenium catalysts for Z-selective olefin metathesis have been synthesized. Both the carboxylate ligand and the aryl group of the N-heterocyclic carbene have been altered and the resulting catalysts evaluated using a range of metathesis reactions. Substitution of bidentate with monodentate X-type ligands led to a severe attenuation of metathesis activity and selectivity, while minor differences were observed between bidentate ligands within the same family (e.g., carboxylates). The use of nitrato-type ligands in place of carboxylates afforded a significant improvement in metathesis activity and selectivity. With these catalysts, turnover numbers approaching 1000 were possible for a variety of cross-metathesis reactions, including the synthesis of industrially relevant products.

Toward a simulation approach for alkene ring-closing metathesis: scope and limitations of a model for RCM

A published model for revealing solvent effects on the ring-closing metathesis (RCM) reaction of diethyl diallylmalonate 7 has been evaluated over a wider range of conditions, to assess its suitability for new applications. Unfortunately, the model is too flexible and the published rate constants do not agree with experimental studies in the literature. However, by fixing the values of important rate constants and restricting the concentration ranges studied, useful conclusions can be drawn about the relative rates of RCM of different substrates, precatalyst concentration can be simulated accurately and the effect of precatalyst loading can be anticipated. Progress has also been made toward applying the model to precatalyst evaluation, but further modifications to the model are necessary to achieve much broader aims.