Synthesis And Property Study Of Large Steric Hindrance NHC-Ru Complexes

Olefin metathesis reaction is a unique carbon skeleton rearrangement reaction between unsaturated carbon-carbon double bonds or three bonds under the participation of carbene metal complexes.Because of its mild reaction conditions and high yield,it is widely used in organic synthesis and polymer chemistry.In recent years,ruthenium olefin metathesis catalysts have been widely applied in industry due to its unique catalytic activity.Three Ru complexes with high steric hindrance were designed and synthesized,and their stability and catalytic activity were studied IPentHCl{1,3-bis[2,6-bis?1-ethylpropyl?phenyl]imidazolium chloride}was prepared from 1,3-dimethyl-2-nitrobenzene by oxidation and hydrogenated reduction.The results were characterized by ¹H NMR.The IPr*HCl[1,3-bis?2,6-dibenzhydryl-4-methylphenyl?imidazolium chloride]was prepared with methyl aniline and two benzyl alcohol as raw materials.The results were characterized by ¹H NMR.The first generation Grubbs catalyst was prepared from RuCl₃ as raw material for preparing new large steric hindrance Ru complexes.The results were characterized by ¹H NMR and ³¹P NMR.Using IPrHCl[1,3-bis?2,6-diisopropylphenyl?-imidazolidinium chloride],IPentHCl and IPr*HCl as raw materials,three new Hoveyda-Grubbs second generation type NHC-ruthenium complexes 70,72 and 74 were synthesized via deproton reaction and olefin metathesis reaction.The structures were fully characterized by ¹H NMR,¹³C NMR,HRMS?high resolution mass spectrometry?and X-ray single crystal.The crystal and molecular structure of NHC-ruthenium catalyst 74 were confirmed by X-ray single crystal diffraction analysis,and the length of Ru=CH bond was 1.837?.Compound 74 belongs to monoclinic system,P21/n space group,cell parameter:a=1.37210 nm,b=2.57255 nm,c=1.89935 nm,?=90°,?=108.3309°,?=90°,V=6364.10?³.Using density functional theory,the structure of NHC-ruthenium catalyst 72 was simulated and calculated by Gaussian 09 software,and the length of Ru=C bond was 2.002?,the energy of Ru=C bond was 1.97 eV.The UV-Vis spectra of NHC-ruthenium complexes show that the stability of the complex increases with the increasing of NHC ligand resistance.By comparing the catalytic activity of complexes 67,70,72 and 74,the activity of catalyst 70 and catalyst 72 is similar to that of catalyst 66,and the catalytic activity of catalyst74 is lower than that of catalyst 67.