The Study Of Metathesis For Tuning Olefin Distribution And New Catalysts

α-Olefins are important materials for modern petrochemical and fine chemical industry, anda large amount of products. Ethylene oligomerization catalyzed by transition metal complexesis an advanced process to produce linearα-olefins. However, the products distribute accordingto Flory-Schultz rule and about half of theα-olefins are unpopularity on market. Therefore, aα-olefins factory can not operate unless theseα-olefins can be utilized fully. Shell higherolefins process (SHOP) is nowadays the most advanced and the ripest process. It consists ofethylene oligomerization to produceα-olefins, isomerization of double bond inα-olefinswhich are unpopularity on market and cross metathesis in order to change theseα-olefins touseful products. This is an accepted method to bring production and sale into balance.However, the low efficiency of the metathesis catalysts and high energy consumption ofSHOP are the insufficiencies. This process must operate in large scale for economicconsiderations. Thereby, the work to enhance catalysts performance and increace selectivityof the useful olefins has specific industry background and important scientific significance forα-olefins industry of our country.The key of theme cast about for the more effective catalysts of metathesis reaction. By far,Grubbs-type ruthenium carbene complexes have become the best metathesis catalysts andfound the most extensive applications. However, the Grubbs catalysts are deficient in thermalsensitivity and tolerance toward the functional group with strong coordination. Therefore, it isthe emphasis to enhance the thermal stability and improve their tolerance of rutheniumcarbene complexes in olefin metathesis at present.In this dissertation, synthesis of benzylidene[1,3-bis(2,6-dimethylphenyl)-4,5-dihydroimidazol-2-ylidene]dichloro(triphenylphosphine)ruthenium (41) has been improved. Ifn-hexane is used as solvent, complex 41 is obtained with high yield and purity without furthercomplicated purification. The catalytic performance of complex 41 has been investigated.Complex 41 proves to be an excellent catalyst for cross metathesis (CM) reaction of 1-butenewith isomerized octadecene. The optimal reaction conditions have been found. If n_c18:n_c4=1:3, sub./cat.=1000, 70℃, 1h, 1-octadecen/octadecene=5.4%, the total conversion is93.6%, the selectivity of C₈⁼～C₁₂⁼ (monomers of synthesizing lubricants) reaches 22.3%, theselectivity of C₁₃⁼～C₁₇⁼ (materials for synthesizing detergents) is 24.2%; if n_c18:n_c4=1:3,sub./cat.=1000, 60℃, 6h, the total conversion is 85.6%, the selectivity of C₁₃⁼～C₁₇⁼ reaches 39.8ï¼…, the selectivity of C₈^-～C₁₂^- is 14.4ï¼…. In other words, the selectivity of C₈⁼～C₁₂⁼ andC₁₃⁼～C₁₇⁼ can be regulated by varying the reaction conditions.If the mixed solvent of n-hexane and THF (V_hexane/V_THF=10:1) is used, benzylidene-bis[1,3-bis(2,6-dimethylphenyl)-4,5-dihydroimidazol-2-ylidene]dichlororuthenium (42) canbe synthesized by facile one-step reaction of benzylidenebis(triphenylphosphine)dichlororuthenium (4) with excess N-heterocyclic carbene (NHC) ligand 1,3-bis(2,6-dimethylphenyl)-4,5-dihydroimidazol-2-ylidene (H₂IMe) (40). Compared with the three-step synthesis methoddescribed by Grubbs, this method features simpler manipulations and higher yield. It isconfirmed by X-ray crystallographic analysis that the coordination geometry of complex 42 isdistorted square pyramid, and the coordination between ruthenium and benzylidene ligand isstrengthened. As the success of the ring-closing metathesis (RCM) reactions of diethyldiallylmalonate (49) and diallylmalononitrile (50) catalyzed by complex 42, the better thermalstability and cyano group tolerance of complex 42 is proved.Stability of the ruthenium benzylidene complexes can be enhanced by introducing thechelating ligands. New ruthenium benzylidene complexes benzylidene[1,3-bis(2,6-dimethylphenyl)-4,5-dihydroimidazol-2-ylidene] [k²(O,P)-diphenylphosphinoacetato] monochlororuthenium (46), benzylidene[1,3-bis(2,6-dimethylphenyl)-4,5-dihydroimidazol-2-ylidene][k²(O,P)-3-(diphenylphosphino)propionato]monochlororuthenium (47), benzylidene[1,3-bis(2,6-dimethylphenyl)-4,5-dihydroimidazol-2-ylidene] [k²(O,P)-2-(diphenylphosphino)benzonato]monochlororuthenium (48) featured five-membered, flexible six-membered and rigidsix-membered chelating rings respectively are prepared by reactions of complex 41 withcorresponding sodium phosphino-carboxylates. It is confirmed by X-ray crystallographicanalysis that the coordination geometries of complexes 46 and 47 are distorted squarepyramids with phosphino-carboxylate ligands chelating to ruthenium, and the coordinationbetween ruthenium and benzylidene ligands are strengthened. The chelate property of thephosphino-carboxylate ligands can inhibit the decomposition of the catalytically activeintermediate. RCM reactions of 49 and 50 are chosen to evaluate the catalytic performance ofthe complexes 46-48 because they are informative and simple to manipulate. The resultsindicated that ruthenium benzylidene complexes 46 and 48 possess significant thermalstability and cyano group tolerance.According to the dissociative mechanism of metathesis reaction, the initiation rate andcyano group tolerance of the catalyst can be enhanced by increasing the dissociative rate of itsligand. Six ruthenium benzylidene complexes (60-65) containing pyridine derivative ligandsare prepared and three of them are new. Benzylidene[1,3-bis(2,6-dimethylphenyl)-4,5-dihydroimidazol-2-ylidene]dichloro(2-methylpyridine)ruthenium (62), benzylidene[1,3-bis(2,6-dimethylphenyl)-4,5-dihydroimidazol-2-ylidene] dichloro(2,4-dimethylpyridine)ruthen ium (63) introduce ortho substituted pyridine as dissociating ligand to weaken Ru-N bondand accelerate dissociation of pyridine derivative ligand through steric hindrance. It isconfirmed by ¹H NMR,¹³C NMR and X-ray crystallographic analysis that complexes 60-63are monopyridine complexes and show distorted square pyramid geometries; complexes 64and 65 are bispyridine complexes and show pseudo-octahedral geometries, where twopyridine ligands are in cis arrangement and trans to the NHC and the benzylidene ligandrespectively, the bond length between ruthenium and pyridine ligand trans to the benzylideneligand is 16 pm longer than the bond length between ruthenium and pyridine ligand trans tothe NHC ligand. It can be deduced through tandem mass spectroscopy that the labilities of thepyridine derivative ligands in ruthenium benzylidene complexes accord to the following order:62＞61＞60＞65＞41. Based on studies of RCM reaction of 50 and CM reaction ofacrylonitrile with 1-octene or 1-decene catalyzed by pyridine derivative-coordinatedruthenium benzylidene complexes, it can be concluded that ruthenium benzylidene complexwith the more labile dissociating ligand exhibits the higher initial activity and better catalyticperformance. 2-Methylpyridine-coordinated ruthenium benzylidene complex 62 shows thehighest catalytic activity. TOF=960 h^-1 is achieved during RCM reaction of 50, TOF=4 h^-1is obtained during the CM reaction of acrylonitrile with 1-decene.