New Oxygen Chelated Ruthenium Indenylidene Metathesis Catalysts: Synthesis, Characterization And Reactivity

Olefin metathesis is a transition metal-mediated transformation that rearranges the carbon atoms of the carbon-carbon double bond of olefins. The success of the olefin metathesis reaction, a key reaction in organic, polymer and petro chemistry, can be greatly recognized to its versatility and the development of well-defined catalysts. Therefore, the development of new well-defined, highly active and selective catalysts is very desirable and valuable. Consequently in this thesis, we mainly focus on the modification of propargylic alcohol, which is the key part for the synthesis of catalyst.In the first part, 5-Bromovanillin, a commercialized pharmaceutical intermediate, was used as a starting material. After reduction, methylation, oxidation, and the use of Grignard reagent, the first target propargylic alcohol was obtained successfully. By modification of the indenylidene fragment from t-butyl group to cyclohexyl group, the second target propargylic alcohol was obtained. All the ligands were characterized by 1H NMR and13 C NMR.In the second part, several methods were attempted to synthesize the target compound, and finally a suitable way was found as a standard method to synthesize such kind of oxygen chelated indenylidene ruthenium catalysts. From 31 P NMR analysis, these two catalysts were supposed to be synthesized successfully. Applying an alkoxyl group on the indenylidene fragment could generate the Ru-O chelating bond, resulting in a chelating six-membered ring, which was considered to benefit the rupture of chelation bond during the initiation step. But unfortunately, all the efforts made to purify the target complex failed, finally these two catalysts were obtained as an impure mixture. From our experimental results and the findings of literature, the aldehyde we used were pivalaldehyde and cyclohexanecarbaldehyde, which were aliphatic aldehyde. The conjugation effects between the indenyl and aliphatic substituent are assumed to decrease and the methoxy does not protect the metal carbene from oxidation as compared to the isopropyl group.In the third part, two series of substrates for RCM were synthesized to screen the activity of the catalysts mixture. A commercial available indenylidene catalyst was also used for screening as benchmark. From the screening results, the two catalysts mixture had a very low activity for some substrates and showed a relatively better activity for the DA series than the DE series, which is similar with most of the other catalysts.The exploration on the synthesis and formation mechanism of oxygen chelated indenylidene ruthenium catalyst may lay a foundation for the design of future catalysts.