New Ruthenium Indenylidene Olefin Metathesis Catalysts:Synthesis,Characterization And Reactivity

Olefin metathesis is a kind of reaction in which carbon-carbon double bonds redistribute between two olefins in the presence of metal carbene complex,and then reform the carbon skeleton.The breaking and recombination of carbon-carbon bonds are the basis of organic synthesis.Therefore,olefin metathesis has already become an important and effective catalytic reaction and its application exhibits a revolutionary progress in polymer science and modern organic synthesis.In order to further broaden the scope of its application in scientific research and industry,it is still important to design and synthesize new catalysts with better activity and stability.In this dissertation,three parts of work were done.With the experimental outcomes,it is hoped to furtherly guide the design and synthesis of novel catalysts and their applications in oleochemical industry.In the first part,four novel ligands with different structures were prepared,and none of them have been reported to date.Among these four novel ligands,two of them were aimed to get the new catalysts with six-membered chelating ring,and the other two were aimed to get the new catalysts with five-membered chelating ring.Moreover,cyclopentyl group was introduced into some ligands,which was never been involved in the ruthenium indenylidene catalysts.Finally,these four novel ligands were obtained,and their structures were confirmed by ¹H and ¹³C NMR spectrum.Moreover,we used the aforementioned ligands to synthesize new oxygen chelated ruthenium indenylidene catalysts and tested their activity.However,the novel ligand containing cyclopentyl group,which was supposed to form six-membered chelating ring,didn’t show any new peaks on ³¹P NMR spectrum after reaction with RuCl₂（PPh₃）₃.Meanwhile,to the novel ligand containing cyclopentyl group,aiming to generate five-membered chelating ring,an expected single peak emerged on ³¹P NMR spectrum.This result implied that the catalyst with five-membered chelating ring was much easier to be synthesized than that with six-membered chelating ring,which was attributed to its better stability.Besides,the other two catalysts containing isopropyl group also demonstrated the expected single peak on ³¹P NMR spectrum,respectively.Thereby,it is assumed that the desired catalysts were generated when compared with references.But when we tried to purify the target compound by column chromatography,decomposition happened.Although many methods had been used,we failed to isolate the pure catalysts.This may be due to the substitution of methoxy group to isopropoxy group,which was supposed to improve the catalytic activity.Furthermore,the decomposition during column chromatography indicated that,isopropoxy group with a bigger steric hindrance can protect the metal center better than methoxy group,and then improve the stability of catalyst to some extent.Although we didn’t isolate the pure catalysts at last,the mixture still showed activity in the ring-closing metathesis of substrates.Thirdly,we investigated the application of ruthenium indenylidene catalysts in oleochemical industry.Eleven ruthenium catalysts were chosen and four different conditions were set to test the activity of self-metathesis of methyl oleate.The results showed that,the second generation catalysts with N-heterocyclic carbene ligand exhibited high conversions in these four conditions,as they possess good stability as well as good reactivity.Therefore,if there is no strict requirement of conversion when it comes to application,we can consider these two reaction conditions:one is at40℃,using toluene as solvent,the concentration of methyl oleate is 0.1 M,and the quantity of catalyst is 0.5 mol%;the other condition is at 80℃,without solvent,and the quantity of catalyst is 0.1 mol%.The former one doesn’t need high temperature,then save the energy;the latter one doesn’t need solvent and uses less catalysts,then it will be more environment-friendly.