Synthesis And Characterization Of New Ruthenium Carbene Complexes For Olefin Metathesis

a-olefins are important materials of petrochemicals and fine chemicals. There are great demands of α-olefins in the world, but only a few countries master the production technique. In the last decades, our group have obtained many patents with respect to olefins. Linear a-olefins were synthesized via ethylene oligomerization catalyzed by transition metal complexes, in which α-olefms accorded to Flory-Schultz distribution. It is important how to utilize >C₁8⁼α-olefins with low economic value.The olefin metathesis has received much attenation for solving the utilization of long-chain a-olefins. Supported by the grant from the China National Petroleum Corporation (CNPC), we have developed many new ruthenium carbene complexes as catalysts for olefin metathesis. The results are as follows:1. Eighteen different Ligands were synthesized and reacted with corresponding metal compounds to give twelve N-heterocyclic carbene (NHC)-coordinated ruthenium alkylidenes. These compounds were characterized by IR ¹H NMR ¹3C NMR ³1P NMR and MS. The new N-heterocyclic carbene (NHC)-coordinated mthenium alkylidene obtained are:[1,3-bis (2,6-dimethylphenyl)4,5-dihydroimidazol -2-ylidene] (PPh₃)(Cl)₂Ru=CHPh 43; [1,3-bis(2,6-dimethylphenyl)-imidazol-2-ylidene](PPh₃)(Cl)₂Ru=CHPh 44; [1,3-bis(2,6-iisoprophenyl)4,5-dihydroimidazol -2-ylidene](PPh₃)(Cl)₂Ru=CHPh 55; [l,3-bis(2,6-diisoprophenyl)-imidazol-2-ylidene](PPh₃)(Cl)₂Ru=CHPh56;[l,3-bis(2,6-dimethylphenyl) -4,5-dihydroimidazol-2-ylidene](C₅H₅N)₂(Cl)₂Ru=CHPh57; [l,3-bis(2,6-dimethylphenyl) -4,5-dihydroimidazol-2-ylidene](PPh₃)(I)₂Ru=CHPh61; [l,3-bis(2,6-dimethylphenyl)-4,5-dihydroimidazol-2-ylidene](C₅H₅N)(I)₂Ru=CHPh62.2. Different carbene ruthenium complexes used as catalysts for the metathesis of 1 -hexene. The results showed that [l,3-bis(2,6-dimethylphenyl)4,5-dihydroimidazol-2-ylidene] (PPh₃)(Cl)₂Ru=CHPh was the best one with the catalytic activity up to 142.8 h^-1 convension frequency and 85.7% conversion with the catalyst loading of 0.1 mol% at 70℃ for 6h in the absence of any solvent.3. We also undertook the kinetics study of ruthenium complexes (PPh₃)₂Cl₂Ru=CHPh 38 utilizing the self-metathesis of 1-hexene as the basis reaction. The results indicated thatconversion of 1-hexene obeyed first order reaction model and activation energy was 64.8 KJ/mol. Mechanistic studies indicated that the dissociation mechanistic were major pathway.4. We found that significant olefin isomerization occurs for 1-hexene metathesis reaction with the ruthenium complex in an autoclave. The isomerization products were adjusted by reaction conditions. It open up a new pathway to solve the problem in olefm products installation and sale.5. Further expansion of the substrate scope was made for cross metathesis of various functionalized olefins with the iV-heterocyclic carbene ruthenium as catalyst. The following results were obtained:(1) The phosphine-free carbene ruthenium complex 57 can efficiently catalyze the cross metathesis of functionalized olefins. For example, the yield of cross metathesis of acrylonitrile with allylbenzene by 57 is 71%.(2) The poor results with ruthenium carbene catalysts for cross-metathesis of various functionalized olefins predominately origninate from the strong coordination of functional groups to the ruthenium center leading to the deactivation of the catalyst. The formation of a cyano-substituted alkylidene during the metathesis of acrylonitrile also results in the deactivation of the carbene ruthenium.(3) There exists a sequence in CM of acrylonitrile with different functionalized olefins: carboxylic acid>ester> alcohol > aldehyde.(4) The coordination solvents have great negative effect on the reaction. The existence of a Lewis acid such as Ti(Oz-Pr)4 can effectively improve the reaction rate and the yield. The CM of acrylonitrile with functional olefins, such as acrylonitrile with 4-buten-l-ol, can be performed in 92%.