Synthesis And Catalytic Applications Of New Z-selective Ruthenium Carbene Complexes For Olefin Metathesis

Olefin metathesis is a simple,fast and efficient method for constructing complex molecules by carbon-carbon bond remodeling.With the rapid development of biology,medicine and organic synthesis,more and more cis-olefins are needed.So the design of catalysts with high Z-selectivity and activity has become a very challenging and hot topic in the field of olefin metathesis.At present,the latest research results of Z-selective catalysts are a kind of ruthenium carbene catalysts with 1,2-benzenedithiol chelated.This kind of catalyst has very high Z-selectivity and activity,which is a new direction for future research.Generally,there are two factors affecting the activity and selectivity of these Z-selective catalysts:first,the steric hindrance of ligands greatly affects the selectivity of catalysts;second,the electronegativity of ligands,which has a great impact on the stability and activity of the catalysts.In this thesis,several new ruthenium catalysts were designed and synthesized,and the stability,activity and selectivity of these catalysts were studied.Firstly,in order to study the effect of ligand steric hindrance on the catalyst,a ruthenium carbene catalyst containing a 1,2-dicarbadodecaborane(12)-1,2-dithiolate ligand was synthesized and the structure was determined by single crystal X-ray diffraction.This catalyst can catalyze ring opening metathesis polymerization(ROMP)reaction and ring opening cross metathesis(ROCM)reactions in high Z/E(98:2)ratio and yields(73%-93%);Cross metathesis(CM)reactions of terminal alkenes with(Z)-but-2-ene-1,4-diol to give high Z/E ratios(91:9-98:2).DFT calculation was also performed in order to understand the process of forming Z-olefin products and the decomposition process of catalysts.A Z-selective olefin metathesis ruthenium carbene catalyst containing a naphthalene-1,8-dithiol ligand was synthesized,and the structure was determined by single crystal X-ray diffraction.The effects of this ligand on the stability,activity and selectivity of the catalyst were studied.The new ruthenium carbene catalyst could catalyze cross-metathesis reactions of terminal alkenes with(Z)-but-2-ene-1,4-diol to give highly Z-selective products.In order to further investigate the effect of nitrogen heterocyclic carbene(NHC)on the stability and activity of the catalyst,a series of ruthenium carbene catalysts containing 2-mercaptophenol were synthesized and their struc tures were determined by single crystal X-ray diffraction.The ruthenium carbene catalyst ca n catalyze the ROMP and CM reactions with high Z-selectivity.When Al C l₃ was added into the CM reactions,the yields(51%-88%)were significantly improved and highly selective for E-olefin products(E/Z ratios,79:21-96:4).Subsequently,in order to study the ligand electronegativity effect on the activity and stability of the catalyst,a ruthenium carbene catalyst chelated with a3-cyclobutene-1,2-dione-3,4-dimercapto ligand was synthesized and its molecular structure was determined by single crystal X-ray diffraction.In this thesis,the stability,activity and selectivity of the catalyst were studied.Compared with the previously reported catalysts,the catalyst has better stability and does not need nitrogen protection in the reaction process.Catalytic studies indicated that the Ru catalyst promotes high yield and Z/E ratio in ROMP,ROCM and CM reactions.DFT calculations showed that the new catalyst has high stability and is not easy to decompose in air.Finally,in order to further study the ligand electronegativity effect on the stability and activity of the catalyst,a new ruthenium carbene catalyst with4,5-dimercapto-1,3-dithiol-2-one ligand was synthesized,and the structure of the catalyst was determined by NMR and HRMS.The stability and activity of the catalyst were studied.The stability of the catalyst is poor due to the instability of the ligand itself.However,the ROMP reactions of norbornene and 1,5-cyclooctadiene still showed high Z-selectivity.These studies provide important experimental methods and theoretical basis for the design and development of new Z-selective ruthenium carbene catalyst for olefin metathesis.