Synthesis And Characterization Of Hoveyda-type Olefin Metathesis Catalysts Bearing Six-membered Chelating Ring

Study on olefin metathesis reaction and exploitation of relevant catalysts have made great achievement,and catalytic mechanism also have had intimate knowledge till now.However,some issues still remain in this area.For example,how the chelated ring size in Hoveyda type catalysts influence catalysts'activity and stability,and how the electron density and steric hindrance around X atom in Ru-X bond influence catalysts'property in detail,etc.In this paper,we aimed at the questions mentioned above,modified existing catalysts,and synthesized many kinds of new catalysts bearing six-membered chelating ring.After researching on their catalytic properties,not only were these questions expatiated,but several valuable olefin metathesis catalysts were obtained.The following aspects have been included.1)Based on Hoveyda 1^st and 2^nd generation catalysts C5 and C6,and catalyst C34 bearing CAAC ligand and five-membered O-chelating ring,several catalysts bearing six-membered O-chelating ring were synthesized?Fig.1-31?.Their initiation rate on catalyzing RCM reaction of DEDAM were increased dramatically compared with corresponding existing catalysts.2)When the ligating atom in six-membered chelating ring was changed to nitrogen or sulfur atom,catalysts'activity decreased and stability increased because of the stronger Ru-N or Ru-S bond compared to Ru-O bond.The conjugated effect of phenyl and electron-withdrawing group?EWG?will reduce electron density on heteroatom,and catalysts'activity will be consequently increased in different level.Notablely,in some case EWG displayed disadvantageous electron-deficient character.3)The steric hindrance on ligating heteroatom exert a tremendous influence on catalysts'properties.In general,with the increasing of steric hindrance,catalysts's initiation rate and catalytic activity increase,while catalytic efficiency and stability decrease.4)Spectator ligands with different electronic and steric effect,including phosphineligand?PCy3?,cyclicdiaminocarbene?NHC?and cyclic?alkyl??amino?carbene?CAAC?,have big influence on catalysts'initiation rate,catalytic efficiency and especially selectivity.Normally,initiation rate order was NHC>PCy₃>CAAC,catalytic efficiency order was NHC?CAAC>PCy₃,and terminal olefin selectivity order was CAAC>PCy₃>NHC.5)C54 with chelating methoxy group displayed higher conversion on the reaction of ethenolysis of methyl oleate than C34.Based on high selectivity of terminal olefin,conversion can reach to 90%from 65%.C45 with chelating dimethylamino group was an excellent latent cataltst,which can be activated at high temperature or acidic condition.C43 with chelating isopropylthioethyl group have good activity on the RCM reaction of steric olefin substrate.